We conducted a search for narrowband radio signals over four observing sessions in 2020–2023 with
the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the
telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of
∼11,860 stars and planetary systems in the ∼9 arcminute beam of the telescope. All detections were
either automatically rejected or visually inspected and confirmed to be of anthropogenic nature. In
this work, we also quantified the end-to-end efficiency of radio SETI pipelines with a signal injection
and recovery analysis. The UCLA SETI pipeline recovers 94.0% of the injected signals over the usable
frequency range of the receiver and 98.7% of the injections when regions of dense RFI are excluded. In
another pipeline that uses incoherent sums of 51 consecutive spectra, the recovery rate is ∼15 times
smaller at ∼6%. The pipeline efficiency affects SETI search volume calculations as well as calculations
of upper bounds on the number of transmitting civilizations. We developed an improved Drake Figure
of Merit for SETI search volume calculations that includes the pipeline efficiency and frequency drift
rate coverage. Based on our observations, we found that there is a high probability (94.0–98.7%) that
fewer than ∼0.014% of stars earlier than M8 within 100 pc host a transmitter that is detectable in
our search (EIRP > 1012 W). Finally, we showed that the UCLA SETI pipeline natively detects the
signals detected with AI techniques by Ma et al. (2023).
This document presents the target selection process for the first year of the Breakthrough Listen search for intelligent life using the Green Bank Telescope, Parkes Telescope, and Automated Planet Finder. The targets include: 1) The 60 nearest stars within 5.1 parsecs to search for faint signals; 2) 1649 stars spanning stellar types from the Hipparcos catalog; 3) 123 nearby galaxies representing different morphological types to search billions of stars simultaneously; and 4) several classes of exotic objects like white dwarfs and neutron stars. The telescopes will observe 1,000,000 stars and galaxies at radio and optical wavelengths between 350 MHz to 100 GHz and 374-950nm, respectively, to search for technological signals.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
A Simultaneous dual-site technosignature search using international LOFAR sta...Sérgio Sacani
The Search for Extraterrestrial Intelligence (SETI) aims to find evidence of technosignatures, which
can point towards the possible existence of technologically advanced extraterrestrial life. Radio signals
similar to those engineered on Earth may be transmitted by other civilizations, motivating technosignature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band
has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at
110 − 190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations
took place simultaneously with two international stations (non-interferometric) of the Low Frequency
Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrow-band transmissions in the barycentric frame of reference, with equivalent isotropic radiated power of 1017 W, for
0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effectiveness of using multi-site simultaneous observations for rejecting anthropogenic signals in the search for
technosignatures.
Artigo que descreve a descoberta do exoplaneta Kepler-432b, um exoplaneta mais massivo que Júpiter que orbita uma estrela gigante vermelha bem próximo e numa órbita extremamente alongada.
Imaging the Milky Way with Millihertz Gravitational WavesSérgio Sacani
Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from
long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our
own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been
added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been
extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which
radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave
detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and
provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be
used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational
waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify
interesting multimessenger sources through cross-matching, and for educational and outreach purposes.
An excess of_dusty_starbusts_related_to_the_spiderweb_galaxySérgio Sacani
Artigo que descreve as últimas observações do APEX revelando como se dá a formação de estrelas e a construção do Aglomerado de Galáxias da Teia de Aranha.
An excess of dusty starbursts related to the Spiderweb galaxyGOASA
This document summarizes a study that used the LABOCA instrument on the APEX telescope to observe a field around the high-redshift radio galaxy MRC1138-262 at z=2.16. 16 submillimeter galaxies (SMGs) were detected in the field, with fluxes between 3-11 mJy, indicating a density up to 4 times higher than blank field surveys. Photometric redshifts using Herschel, Spitzer, and VLT data show that at least 8 of the SMGs have z~2.2 and are part of the protocluster associated with MRC1138-262. This corresponds to a star formation rate density 1500 times higher than blank fields at this redshift, concentrated
The nustar extragalactic_survey_a_first_sensitive_lookSérgio Sacani
The document summarizes the first ten sources detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) as part of its extragalactic survey. NuSTAR provides the first sensitive census of the cosmic X-ray background source population at energies above 10 keV. The ten sources have a broad range of redshifts and luminosities, with a median redshift of 0.7 and luminosity of 3×10^44 erg/s. Based on broad-band spectroscopy and SED analysis, the dominant population is quasars with luminosities above 10^44 erg/s, of which around 50% are obscured. However, none are Compton thick and the fraction of Compton thick quasars is constrained to
This document presents the target selection process for the first year of the Breakthrough Listen search for intelligent life using the Green Bank Telescope, Parkes Telescope, and Automated Planet Finder. The targets include: 1) The 60 nearest stars within 5.1 parsecs to search for faint signals; 2) 1649 stars spanning stellar types from the Hipparcos catalog; 3) 123 nearby galaxies representing different morphological types to search billions of stars simultaneously; and 4) several classes of exotic objects like white dwarfs and neutron stars. The telescopes will observe 1,000,000 stars and galaxies at radio and optical wavelengths between 350 MHz to 100 GHz and 374-950nm, respectively, to search for technological signals.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
A Simultaneous dual-site technosignature search using international LOFAR sta...Sérgio Sacani
The Search for Extraterrestrial Intelligence (SETI) aims to find evidence of technosignatures, which
can point towards the possible existence of technologically advanced extraterrestrial life. Radio signals
similar to those engineered on Earth may be transmitted by other civilizations, motivating technosignature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band
has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at
110 − 190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations
took place simultaneously with two international stations (non-interferometric) of the Low Frequency
Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrow-band transmissions in the barycentric frame of reference, with equivalent isotropic radiated power of 1017 W, for
0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effectiveness of using multi-site simultaneous observations for rejecting anthropogenic signals in the search for
technosignatures.
Artigo que descreve a descoberta do exoplaneta Kepler-432b, um exoplaneta mais massivo que Júpiter que orbita uma estrela gigante vermelha bem próximo e numa órbita extremamente alongada.
Imaging the Milky Way with Millihertz Gravitational WavesSérgio Sacani
Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from
long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our
own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been
added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been
extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which
radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave
detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and
provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be
used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational
waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify
interesting multimessenger sources through cross-matching, and for educational and outreach purposes.
An excess of_dusty_starbusts_related_to_the_spiderweb_galaxySérgio Sacani
Artigo que descreve as últimas observações do APEX revelando como se dá a formação de estrelas e a construção do Aglomerado de Galáxias da Teia de Aranha.
An excess of dusty starbursts related to the Spiderweb galaxyGOASA
This document summarizes a study that used the LABOCA instrument on the APEX telescope to observe a field around the high-redshift radio galaxy MRC1138-262 at z=2.16. 16 submillimeter galaxies (SMGs) were detected in the field, with fluxes between 3-11 mJy, indicating a density up to 4 times higher than blank field surveys. Photometric redshifts using Herschel, Spitzer, and VLT data show that at least 8 of the SMGs have z~2.2 and are part of the protocluster associated with MRC1138-262. This corresponds to a star formation rate density 1500 times higher than blank fields at this redshift, concentrated
The nustar extragalactic_survey_a_first_sensitive_lookSérgio Sacani
The document summarizes the first ten sources detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) as part of its extragalactic survey. NuSTAR provides the first sensitive census of the cosmic X-ray background source population at energies above 10 keV. The ten sources have a broad range of redshifts and luminosities, with a median redshift of 0.7 and luminosity of 3×10^44 erg/s. Based on broad-band spectroscopy and SED analysis, the dominant population is quasars with luminosities above 10^44 erg/s, of which around 50% are obscured. However, none are Compton thick and the fraction of Compton thick quasars is constrained to
Simulation of the Earth’s radio-leakage from mobile towers as seen from selec...Sérgio Sacani
Mobile communication towers represent a relatively new but growing contributor to the total radio leakage associated with
planet Earth. We investigate the overall power contribution of mobile communication towers to the Earth’s radio leakage budget,
as seen from a selection of different nearby stellar systems. We created a model of this leakage using publicly available data of
mobile tower locations. The model grids the surface of the planet into small, computationally manageable regions, assuming
a simple integrated transmission pattern for the mobile antennas. In this model, these mobile tower regions rise and set as the
Earth rotates. In this way, a dynamic power spectrum of the Earth was determined, summed over all cellular frequency bands.
We calculated this dynamic power spectrum from three different viewing points - HD 95735, Barnard’s star, and Alpha Centauri
A. Our preliminary results demonstrate that the peak power leaking into space from mobile towers is ∼ 4GW. This is associated
with LTE mobile tower technology emanating from the East Coast of China as viewed from HD 95735. We demonstrate that
the mobile tower leakage is periodic, direction dependent, and could not currently be detected by a nearby civilisation located
within 10 light years of the Earth, using instrumentation with a sensitivity similar to the Green Bank Telescope (GBT). We plan
to extend our model to include more powerful 5G mobile systems, radar installations, ground based up-links (including the Deep
Space Network), and various types of satellite services, including low-Earth orbit constellations such as Starlink and OneWeb.
Two warm Neptunes transiting HIP 9618 revealed by TESS and CheopsSérgio Sacani
This document summarizes the discovery of two warm Neptunes transiting the bright star HIP 9618, as revealed by TESS and CHEOPS observations. TESS observed two transits of one planet (HIP 9618 b), separated by an 11.8 day gap, and one transit of a second planet (HIP 9618 c). Follow-up photometry and reanalysis of the TESS data determined the true period of HIP 9618 b to be 20.77291 days. CHEOPS then performed targeted photometry to determine the true 52.56349 day period of HIP 9618 c. High-resolution spectroscopy found HIP 9618 b has a mass of 10.0 ± 3.
Chandra deep observation_of_xdcpj004402033_a_massive_galaxy_cluster_at_z_1_5Sérgio Sacani
Artigo apresenta os resultados obtidos pelo Chandra ao medir com precisão a massa do mais massivo aglomerado de galáxias do universo distante, o Aglomerado Gioiello.
Hubble Asteroid Hunter III. Physical properties of newly found asteroidsSérgio Sacani
Context. Determining the size distribution of asteroids is key to understanding the collisional history and evolution of the inner Solar System. Aims. We aim to improve our knowledge of the size distribution of small asteroids in the main belt by determining the parallaxes of newly detected asteroids in the Hubble Space Telescope (HST) archive and subsequently their absolute magnitudes and sizes. Methods. Asteroids appear as curved trails in HST images because of the parallax induced by the fast orbital motion of the spacecraft. Taking into account the trajectory of this latter, the parallax effect can be computed to obtain the distance to the asteroids by fitting simulated trajectories to the observed trails. Using distance, we can obtain the absolute magnitude of an object and an estimation of its size assuming an albedo value, along with some boundaries for its orbital parameters. Results. In this work, we analyse a set of 632 serendipitously imaged asteroids found in the ESA HST archive. Images were captured with the ACS/WFC and WFC3/UVIS instruments. A machine learning algorithm (trained with the results of a citizen science project) was used to detect objects in these images as part of a previous study. Our raw data consist of 1031 asteroid trails from unknown objects, not matching any entries in the Minor Planet Center (MPC) database using their coordinates and imaging time. We also found 670 trails from known objects (objects featuring matching entries in the MPC). After an accuracy assessment and filtering process, our analysed HST asteroid set consists of 454 unknown objects and 178 known objects. We obtain a sample dominated by potential main belt objects featuring absolute magnitudes (H) mostly between 15 and 22 mag. The absolute magnitude cumulative distribution logN(H > H0) ∝ αlog(H0) confirms the previously reported slope change for 15 < H < 18, from α ≈ 0.56 to α ≈ 0.26, maintained in our case down to absolute magnitudes of around H ≈ 20, and therefore expanding the previous result by approximately two magnitudes. Conclusions. HST archival observations can be used as an asteroid survey because the telescope pointings are statistically randomly oriented in the sky and cover long periods of time. They allow us to expand the current best samples of astronomical objects at no extra cost in regard to telescope time.
Life, the Universe, andSETI in a NutshellSérgio Sacani
Todate,no
SETI
observing
program
hassucceededindetectinganyunambiguousevidenceofan
extraterrestrial
technology.Regrettably,
this
paper
willtherefore
not
dazzleyou
with
the
analysisof
the
contentsofanyinterstellarmessages.However,asis
appropriate
foraplenarypresentation,
this
paper
doesprovidean
update
on
the
state
of
SETI
programsworldwide.Itdiscusses
the
various flavors ofobservational
SETI
projectscurrentlyon
the
air,plansforfutureinstrumentation,recent
attempts
toproactively
plan
forsuccess,
andthe
prospectsforfuture
public/private
partnershipstofundtheseefforts.
Thepaper
concludes
with
some
tentative
responsesto
the What
ifeverybodyislistening,
and
nobodyis
transmitting?
query.
VaTEST III: Validation of 8 Potential Super-Earths from TESS DataSérgio Sacani
NASA’s all-sky survey mission, the Transiting Exoplanet Survey Satellite (TESS) is specifically designed to detect transiting exoplanets
orbiting bright stars. TESS has already identified about 400 transiting exoplanets, as well as approximately 6000 candidates awaiting
validation. In this work, we present the outcomes of the project Validation of Transiting Exoplanets using Statistical Tools (VaTEST), an
ongoing endeavor dedicated to validating and characterizing new exoplanets using statistical validation tools. We have validated eight
potential super-Earths using a combination of ground-based telescope data, high-resolution imaging, and the statistical validation tool
known as TRICERATOPS. These validated planets bear the designations: TOI-238b (1.61+0.09
–0.10 R⊕), TOI-771b (1.42+0.11
–0.09 R⊕), TOI-871b
(1.66+0.11
–0.11 R⊕), TOI-1467b (1.83+0.16
–0.15 R⊕), TOI-1739b (1.69+0.10
–0.08 R⊕), TOI-2068b (1.82+0.16
–0.15 R⊕), TOI-4559b (1.42+0.13
–0.11 R⊕), and TOI5799b (1.62+0.19
–0.13 R⊕). We also studied the synthetic transmission spectra of all eight validated planets in the HST and JWST band-pass
using PLATON and PandExo. Among all these validated planets, six of them fall within the region known as ’keystone planets,’ which makes
them particularly interesting for study. Based on the location of TOI-771b and TOI-4559b below the radius valley we characterized them
as likely super-Earths, though radial velocity mass measurements for these planets will provide more details about their characterization.
It is noteworthy that planets within the size range investigated herein are absent from our own solar system, making their study crucial
for gaining insights into the evolutionary stages between Earth and Neptune.
First light of VLT/HiRISE: High-resolution spectroscopy of young giant exopla...Sérgio Sacani
A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of
their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation
and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed
to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using
optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT),
which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The
goal of HiRISE is to enable the characterization of known companions in the H band, at a spectral resolution of the order of R = λ/∆λ = 100 000,
in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three
major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance
of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we
detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak
value of ∼3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to
illustrate its potential.
A population of_fast_radio_bursts_ar_cosmological_distancesSérgio Sacani
1) Four fast radio bursts (FRBs) lasting only a few milliseconds were detected in a radio survey of the high Galactic latitude sky.
2) The bursts' properties indicate they are of celestial rather than terrestrial origin and likely originate from cosmological distances of 0.5 to 3 billion light years.
3) No coincident x-ray or gamma-ray signals were found associated with the bursts. Characterizing the population of FRBs could help determine the baryonic content of the universe.
Detection of an atmosphere around the super earth 55 cancri eSérgio Sacani
We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near
infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent
star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness
of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length
and a very high scanning speed. We use our specialized pipeline to take into account systematics
introduced by these observational parameters when coupled with the geometrical distortions of the
instrument. We measure the transit depth per wavelength channel with an average relative uncertainty
of 22 ppm per visit and nd modulations that depart from a straight line model with a 6 condence
level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably
hydrogen-rich. Our fully Bayesian spectral retrieval code, T -REx, has identied HCN to be the
most likely molecular candidate able to explain the features at 1.42 and 1.54 m. While additional
spectroscopic observations in a broader wavelength range in the infrared will be needed to conrm
the HCN detection, we discuss here the implications of such result. Our chemical model, developed
with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a
high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic
than previously thought.
A candidate super-Earth planet orbiting near the snow line of Barnard’s starSérgio Sacani
This document summarizes the discovery of a candidate super-Earth planet orbiting Barnard's star. Analysis of over 20 years of radial velocity measurements revealed a periodic signal of 233 days, attributed to a planet with a minimum mass of 3.2 Earth masses in a near-circular orbit near the star's snow line. Long-term monitoring also detected a possible second signal with a period over 6,000 days, which could be from a more distant planet or stellar magnetic activity cycle. Independent photometric and spectroscopic monitoring ruled out stellar activity as the cause of the 233-day signal. This candidate planet has one of the lowest minimum masses detected around an M dwarf star.
The JWST Discovery of the Triply-imaged Type Ia “Supernova H0pe” and Observat...Sérgio Sacani
A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared
Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–
2 kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational
lensing by G165. These data can yield a value for Hubble’s constant using time delays from this
multiply-imaged SN Ia that we call “SN H0pe.” Over the entire field we identified 21 image multiplicities,
confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new
lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014M⊙. The photometry uncovered
a galaxy overdensity at Arc 2’s redshift. NIRSpec confirmed six member galaxies, four of which
surround Arc 2 with relative velocity ≲900 km s−1 and projected physical extent ≲33 kpc. Arc 2
dominates the stellar mass ((5.0±0.1)×1011M⊙), which is a factor of ten higher than other members
of this compact galaxy group. These other group members have specific star formation rates (sSFR)
arXiv:2309.07326v1 [astro-ph.GA] 13 Sep 2023
2 Frye, Pascale, Pierel et al.
of 2–260 Gyr−1 derived from the Hα-line flux corrected for stellar absorption, dust extinction, and slit
losses. Another group centered on the dusty star forming galaxy Arc 1 is at z = 2.24. The total SFR
for the Arc 1 group (≳400M⊙ yr−1) translates to a supernova rate of ∼1 SNe yr−1, suggesting that
regular monitoring of this cluster may yield additional SNe.
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
An infrared transient from a star engulfing a planetSérgio Sacani
Planets with short orbital periods (roughly under 10 days) are common around stars like the Sun1,2. Stars expand as they evolve and thus we expect their close planetary companions to be engulfed, possibly powering luminous mass ejections from the host star3–5. However, this phase has never been directly observed. Here we report observations of ZTF SLRN-2020, a short-lived optical outburst in the Galactic disk accompanied by bright and long-lived infrared emission. The resulting light curve and spectra share striking similarities with those of red novae6,7—a class of eruptions now confirmed8 to arise from mergers of binary stars. Its exceptionally low optical luminosity (approximately 1035 erg s−1) and radiated energy (approximately 6.5 × 1041 erg) point to the engulfment of a planet of fewer than roughly ten Jupiter masses by its Sun-like host star. We estimate the Galactic rate of such subluminous red novae to be roughly between 0.1 and several per year. Future Galactic plane surveys should routinely identify these, showing the demographics of planetary engulfment and the ultimate fate of planets in the inner Solar System.
A Deep and Wide Twilight Survey for Asteroids Interior to Earth and VenusSérgio Sacani
This document describes a survey to discover asteroids interior to Earth's and Venus' orbits using the Dark Energy Camera on the Blanco 4m telescope in Chile. The survey has discovered three new asteroids so far, including two rare Atira asteroids completely interior to Earth and one Apollo asteroid crossing Earth's orbit. Two discoveries are estimated to be over 1 km in diameter. The survey has covered 624 square degrees near and interior to Venus' orbit, detecting about 15% of all known Atira asteroids. The survey aims to better understand asteroid populations in the inner solar system to improve models of near-Earth object populations and impact risks.
AT 2022aedm and a New Class of Luminous, Fast-cooling Transients in Elliptica...Sérgio Sacani
This document reports the discovery and follow-up observations of a remarkable fast-evolving optical transient called AT 2022aedm. Key points:
- AT 2022aedm was discovered by the ATLAS survey and reached an extremely luminous peak magnitude of Mg ≈ -22 mag.
- It exhibited an unusually fast rise time of 9 days and faded by 2 magnitudes in the following 15 days.
- Most surprisingly, its host galaxy was found to be a massive elliptical galaxy with negligible star formation.
- Extensive follow-up observations including spectroscopy found it shared properties with two other similar transients in passive galaxies, suggesting a new class of "luminous fast coolers." However
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
A dynamically packed_planetary _system_around_gj667_c_with_three_superearths_...Sérgio Sacani
This document summarizes the discovery of six potentially habitable super-Earth planets orbiting the red dwarf star GJ 667C. Analyzing new Doppler measurements from HARPS and previous data from other spectrographs, the authors detect six planetary candidates with orbital periods of 7, 28, 92, 62, 39, and 260 days. They validate the signals against stellar activity and find the system could be dynamically stable. Three or four of the planets may be located within the star's habitable zone where liquid water could exist, making this one of the first exoplanetary systems discovered with multiple Earth-sized planets in the habitable zone of an M-dwarf star.
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
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Simulation of the Earth’s radio-leakage from mobile towers as seen from selec...Sérgio Sacani
Mobile communication towers represent a relatively new but growing contributor to the total radio leakage associated with
planet Earth. We investigate the overall power contribution of mobile communication towers to the Earth’s radio leakage budget,
as seen from a selection of different nearby stellar systems. We created a model of this leakage using publicly available data of
mobile tower locations. The model grids the surface of the planet into small, computationally manageable regions, assuming
a simple integrated transmission pattern for the mobile antennas. In this model, these mobile tower regions rise and set as the
Earth rotates. In this way, a dynamic power spectrum of the Earth was determined, summed over all cellular frequency bands.
We calculated this dynamic power spectrum from three different viewing points - HD 95735, Barnard’s star, and Alpha Centauri
A. Our preliminary results demonstrate that the peak power leaking into space from mobile towers is ∼ 4GW. This is associated
with LTE mobile tower technology emanating from the East Coast of China as viewed from HD 95735. We demonstrate that
the mobile tower leakage is periodic, direction dependent, and could not currently be detected by a nearby civilisation located
within 10 light years of the Earth, using instrumentation with a sensitivity similar to the Green Bank Telescope (GBT). We plan
to extend our model to include more powerful 5G mobile systems, radar installations, ground based up-links (including the Deep
Space Network), and various types of satellite services, including low-Earth orbit constellations such as Starlink and OneWeb.
Two warm Neptunes transiting HIP 9618 revealed by TESS and CheopsSérgio Sacani
This document summarizes the discovery of two warm Neptunes transiting the bright star HIP 9618, as revealed by TESS and CHEOPS observations. TESS observed two transits of one planet (HIP 9618 b), separated by an 11.8 day gap, and one transit of a second planet (HIP 9618 c). Follow-up photometry and reanalysis of the TESS data determined the true period of HIP 9618 b to be 20.77291 days. CHEOPS then performed targeted photometry to determine the true 52.56349 day period of HIP 9618 c. High-resolution spectroscopy found HIP 9618 b has a mass of 10.0 ± 3.
Chandra deep observation_of_xdcpj004402033_a_massive_galaxy_cluster_at_z_1_5Sérgio Sacani
Artigo apresenta os resultados obtidos pelo Chandra ao medir com precisão a massa do mais massivo aglomerado de galáxias do universo distante, o Aglomerado Gioiello.
Hubble Asteroid Hunter III. Physical properties of newly found asteroidsSérgio Sacani
Context. Determining the size distribution of asteroids is key to understanding the collisional history and evolution of the inner Solar System. Aims. We aim to improve our knowledge of the size distribution of small asteroids in the main belt by determining the parallaxes of newly detected asteroids in the Hubble Space Telescope (HST) archive and subsequently their absolute magnitudes and sizes. Methods. Asteroids appear as curved trails in HST images because of the parallax induced by the fast orbital motion of the spacecraft. Taking into account the trajectory of this latter, the parallax effect can be computed to obtain the distance to the asteroids by fitting simulated trajectories to the observed trails. Using distance, we can obtain the absolute magnitude of an object and an estimation of its size assuming an albedo value, along with some boundaries for its orbital parameters. Results. In this work, we analyse a set of 632 serendipitously imaged asteroids found in the ESA HST archive. Images were captured with the ACS/WFC and WFC3/UVIS instruments. A machine learning algorithm (trained with the results of a citizen science project) was used to detect objects in these images as part of a previous study. Our raw data consist of 1031 asteroid trails from unknown objects, not matching any entries in the Minor Planet Center (MPC) database using their coordinates and imaging time. We also found 670 trails from known objects (objects featuring matching entries in the MPC). After an accuracy assessment and filtering process, our analysed HST asteroid set consists of 454 unknown objects and 178 known objects. We obtain a sample dominated by potential main belt objects featuring absolute magnitudes (H) mostly between 15 and 22 mag. The absolute magnitude cumulative distribution logN(H > H0) ∝ αlog(H0) confirms the previously reported slope change for 15 < H < 18, from α ≈ 0.56 to α ≈ 0.26, maintained in our case down to absolute magnitudes of around H ≈ 20, and therefore expanding the previous result by approximately two magnitudes. Conclusions. HST archival observations can be used as an asteroid survey because the telescope pointings are statistically randomly oriented in the sky and cover long periods of time. They allow us to expand the current best samples of astronomical objects at no extra cost in regard to telescope time.
Life, the Universe, andSETI in a NutshellSérgio Sacani
Todate,no
SETI
observing
program
hassucceededindetectinganyunambiguousevidenceofan
extraterrestrial
technology.Regrettably,
this
paper
willtherefore
not
dazzleyou
with
the
analysisof
the
contentsofanyinterstellarmessages.However,asis
appropriate
foraplenarypresentation,
this
paper
doesprovidean
update
on
the
state
of
SETI
programsworldwide.Itdiscusses
the
various flavors ofobservational
SETI
projectscurrentlyon
the
air,plansforfutureinstrumentation,recent
attempts
toproactively
plan
forsuccess,
andthe
prospectsforfuture
public/private
partnershipstofundtheseefforts.
Thepaper
concludes
with
some
tentative
responsesto
the What
ifeverybodyislistening,
and
nobodyis
transmitting?
query.
VaTEST III: Validation of 8 Potential Super-Earths from TESS DataSérgio Sacani
NASA’s all-sky survey mission, the Transiting Exoplanet Survey Satellite (TESS) is specifically designed to detect transiting exoplanets
orbiting bright stars. TESS has already identified about 400 transiting exoplanets, as well as approximately 6000 candidates awaiting
validation. In this work, we present the outcomes of the project Validation of Transiting Exoplanets using Statistical Tools (VaTEST), an
ongoing endeavor dedicated to validating and characterizing new exoplanets using statistical validation tools. We have validated eight
potential super-Earths using a combination of ground-based telescope data, high-resolution imaging, and the statistical validation tool
known as TRICERATOPS. These validated planets bear the designations: TOI-238b (1.61+0.09
–0.10 R⊕), TOI-771b (1.42+0.11
–0.09 R⊕), TOI-871b
(1.66+0.11
–0.11 R⊕), TOI-1467b (1.83+0.16
–0.15 R⊕), TOI-1739b (1.69+0.10
–0.08 R⊕), TOI-2068b (1.82+0.16
–0.15 R⊕), TOI-4559b (1.42+0.13
–0.11 R⊕), and TOI5799b (1.62+0.19
–0.13 R⊕). We also studied the synthetic transmission spectra of all eight validated planets in the HST and JWST band-pass
using PLATON and PandExo. Among all these validated planets, six of them fall within the region known as ’keystone planets,’ which makes
them particularly interesting for study. Based on the location of TOI-771b and TOI-4559b below the radius valley we characterized them
as likely super-Earths, though radial velocity mass measurements for these planets will provide more details about their characterization.
It is noteworthy that planets within the size range investigated herein are absent from our own solar system, making their study crucial
for gaining insights into the evolutionary stages between Earth and Neptune.
First light of VLT/HiRISE: High-resolution spectroscopy of young giant exopla...Sérgio Sacani
A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of
their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation
and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed
to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using
optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT),
which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The
goal of HiRISE is to enable the characterization of known companions in the H band, at a spectral resolution of the order of R = λ/∆λ = 100 000,
in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three
major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance
of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we
detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak
value of ∼3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to
illustrate its potential.
A population of_fast_radio_bursts_ar_cosmological_distancesSérgio Sacani
1) Four fast radio bursts (FRBs) lasting only a few milliseconds were detected in a radio survey of the high Galactic latitude sky.
2) The bursts' properties indicate they are of celestial rather than terrestrial origin and likely originate from cosmological distances of 0.5 to 3 billion light years.
3) No coincident x-ray or gamma-ray signals were found associated with the bursts. Characterizing the population of FRBs could help determine the baryonic content of the universe.
Detection of an atmosphere around the super earth 55 cancri eSérgio Sacani
We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near
infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent
star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness
of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length
and a very high scanning speed. We use our specialized pipeline to take into account systematics
introduced by these observational parameters when coupled with the geometrical distortions of the
instrument. We measure the transit depth per wavelength channel with an average relative uncertainty
of 22 ppm per visit and nd modulations that depart from a straight line model with a 6 condence
level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably
hydrogen-rich. Our fully Bayesian spectral retrieval code, T -REx, has identied HCN to be the
most likely molecular candidate able to explain the features at 1.42 and 1.54 m. While additional
spectroscopic observations in a broader wavelength range in the infrared will be needed to conrm
the HCN detection, we discuss here the implications of such result. Our chemical model, developed
with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a
high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic
than previously thought.
A candidate super-Earth planet orbiting near the snow line of Barnard’s starSérgio Sacani
This document summarizes the discovery of a candidate super-Earth planet orbiting Barnard's star. Analysis of over 20 years of radial velocity measurements revealed a periodic signal of 233 days, attributed to a planet with a minimum mass of 3.2 Earth masses in a near-circular orbit near the star's snow line. Long-term monitoring also detected a possible second signal with a period over 6,000 days, which could be from a more distant planet or stellar magnetic activity cycle. Independent photometric and spectroscopic monitoring ruled out stellar activity as the cause of the 233-day signal. This candidate planet has one of the lowest minimum masses detected around an M dwarf star.
The JWST Discovery of the Triply-imaged Type Ia “Supernova H0pe” and Observat...Sérgio Sacani
A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared
Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–
2 kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational
lensing by G165. These data can yield a value for Hubble’s constant using time delays from this
multiply-imaged SN Ia that we call “SN H0pe.” Over the entire field we identified 21 image multiplicities,
confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new
lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014M⊙. The photometry uncovered
a galaxy overdensity at Arc 2’s redshift. NIRSpec confirmed six member galaxies, four of which
surround Arc 2 with relative velocity ≲900 km s−1 and projected physical extent ≲33 kpc. Arc 2
dominates the stellar mass ((5.0±0.1)×1011M⊙), which is a factor of ten higher than other members
of this compact galaxy group. These other group members have specific star formation rates (sSFR)
arXiv:2309.07326v1 [astro-ph.GA] 13 Sep 2023
2 Frye, Pascale, Pierel et al.
of 2–260 Gyr−1 derived from the Hα-line flux corrected for stellar absorption, dust extinction, and slit
losses. Another group centered on the dusty star forming galaxy Arc 1 is at z = 2.24. The total SFR
for the Arc 1 group (≳400M⊙ yr−1) translates to a supernova rate of ∼1 SNe yr−1, suggesting that
regular monitoring of this cluster may yield additional SNe.
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
An infrared transient from a star engulfing a planetSérgio Sacani
Planets with short orbital periods (roughly under 10 days) are common around stars like the Sun1,2. Stars expand as they evolve and thus we expect their close planetary companions to be engulfed, possibly powering luminous mass ejections from the host star3–5. However, this phase has never been directly observed. Here we report observations of ZTF SLRN-2020, a short-lived optical outburst in the Galactic disk accompanied by bright and long-lived infrared emission. The resulting light curve and spectra share striking similarities with those of red novae6,7—a class of eruptions now confirmed8 to arise from mergers of binary stars. Its exceptionally low optical luminosity (approximately 1035 erg s−1) and radiated energy (approximately 6.5 × 1041 erg) point to the engulfment of a planet of fewer than roughly ten Jupiter masses by its Sun-like host star. We estimate the Galactic rate of such subluminous red novae to be roughly between 0.1 and several per year. Future Galactic plane surveys should routinely identify these, showing the demographics of planetary engulfment and the ultimate fate of planets in the inner Solar System.
A Deep and Wide Twilight Survey for Asteroids Interior to Earth and VenusSérgio Sacani
This document describes a survey to discover asteroids interior to Earth's and Venus' orbits using the Dark Energy Camera on the Blanco 4m telescope in Chile. The survey has discovered three new asteroids so far, including two rare Atira asteroids completely interior to Earth and one Apollo asteroid crossing Earth's orbit. Two discoveries are estimated to be over 1 km in diameter. The survey has covered 624 square degrees near and interior to Venus' orbit, detecting about 15% of all known Atira asteroids. The survey aims to better understand asteroid populations in the inner solar system to improve models of near-Earth object populations and impact risks.
AT 2022aedm and a New Class of Luminous, Fast-cooling Transients in Elliptica...Sérgio Sacani
This document reports the discovery and follow-up observations of a remarkable fast-evolving optical transient called AT 2022aedm. Key points:
- AT 2022aedm was discovered by the ATLAS survey and reached an extremely luminous peak magnitude of Mg ≈ -22 mag.
- It exhibited an unusually fast rise time of 9 days and faded by 2 magnitudes in the following 15 days.
- Most surprisingly, its host galaxy was found to be a massive elliptical galaxy with negligible star formation.
- Extensive follow-up observations including spectroscopy found it shared properties with two other similar transients in passive galaxies, suggesting a new class of "luminous fast coolers." However
We present the 2020 version of the Siena Galaxy Atlas (SGA-2020), a multiwavelength optical and infrared
imaging atlas of 383,620 nearby galaxies. The SGA-2020 uses optical grz imaging over ≈20,000 deg2 from the
Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9 and infrared imaging in
four bands (spanning 3.4–22 μm) from the 6 year unWISE coadds; it is more than 95% complete for galaxies larger
than R(26) ≈ 25″ and r < 18 measured at the 26 mag arcsec−2 isophote in the r band. The atlas delivers precise
coordinates, multiwavelength mosaics, azimuthally averaged optical surface-brightness profiles, model images and
photometry, and additional ancillary metadata for the full sample. Coupled with existing and forthcoming optical
spectroscopy from the DESI, the SGA-2020 will facilitate new detailed studies of the star formation and mass
assembly histories of nearby galaxies; enable precise measurements of the local velocity field via the Tully–Fisher
and fundamental plane relations; serve as a reference sample of lasting legacy value for time-domain and
multimessenger astronomical events; and more.
A dynamically packed_planetary _system_around_gj667_c_with_three_superearths_...Sérgio Sacani
This document summarizes the discovery of six potentially habitable super-Earth planets orbiting the red dwarf star GJ 667C. Analyzing new Doppler measurements from HARPS and previous data from other spectrographs, the authors detect six planetary candidates with orbital periods of 7, 28, 92, 62, 39, and 260 days. They validate the signals against stellar activity and find the system could be dynamically stable. Three or four of the planets may be located within the star's habitable zone where liquid water could exist, making this one of the first exoplanetary systems discovered with multiple Earth-sized planets in the habitable zone of an M-dwarf star.
Similar to A Search for Technosignatures Around 11,680 Stars with the Green Bank Telescope at 1.15–1.73 GHz (20)
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
Describing and Interpreting an Immersive Learning Case with the Immersion Cub...Leonel Morgado
Current descriptions of immersive learning cases are often difficult or impossible to compare. This is due to a myriad of different options on what details to include, which aspects are relevant, and on the descriptive approaches employed. Also, these aspects often combine very specific details with more general guidelines or indicate intents and rationales without clarifying their implementation. In this paper we provide a method to describe immersive learning cases that is structured to enable comparisons, yet flexible enough to allow researchers and practitioners to decide which aspects to include. This method leverages a taxonomy that classifies educational aspects at three levels (uses, practices, and strategies) and then utilizes two frameworks, the Immersive Learning Brain and the Immersion Cube, to enable a structured description and interpretation of immersive learning cases. The method is then demonstrated on a published immersive learning case on training for wind turbine maintenance using virtual reality. Applying the method results in a structured artifact, the Immersive Learning Case Sheet, that tags the case with its proximal uses, practices, and strategies, and refines the free text case description to ensure that matching details are included. This contribution is thus a case description method in support of future comparative research of immersive learning cases. We then discuss how the resulting description and interpretation can be leveraged to change immersion learning cases, by enriching them (considering low-effort changes or additions) or innovating (exploring more challenging avenues of transformation). The method holds significant promise to support better-grounded research in immersive learning.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
Current Ms word generated power point presentation covers major details about the micronuclei test. It's significance and assays to conduct it. It is used to detect the micronuclei formation inside the cells of nearly every multicellular organism. It's formation takes place during chromosomal sepration at metaphase.
A Search for Technosignatures Around 11,680 Stars with the Green Bank Telescope at 1.15–1.73 GHz
1. Draft version August 8, 2023
Typeset using L
A
TEX default style in AASTeX631
A Search for Technosignatures Around 11,680 Stars with the Green Bank Telescope at 1.15–1.73 GHz
Jean-Luc Margot,1, 2
Megan G. Li,1
Pavlo Pinchuk,3
Nathan Myhrvold,4
Lea E. Alcantara,5
Megan T. Andrakin,2
Jeth Arunseangroj,2
Damien S. Baclet,6
Madison H. Belk,7
Zerxes R. Bhadha,8
Nicholas W. Brandis,9
Robert E. Carey,7
Harrison P. Cassar,10
Sai S. Chava,2
Calvin Chen,6
James Chen,7
Kellen T. Cheng,7
Alessia Cimbri,2
Benjamin Cloutier,6
Jordan A. Combitsis,9
Kelly L. Couvrette,11
Brandon P. Coy,1
Kyle W. Davis,2
Antoine F. Delcayre,2
Michelle R. Du,7
Sarah E. Feil,1
Danning Fu,2
Travis J. Gilmore,1
Emery Grahill-Bland,12
Laura M. Iglesias,1
Zoe Juneau,2
Anthony G. Karapetian,10
George Karfakis,7
Christopher T. Lambert,1
Eric A. Lazbin,7
Jian H. Li,13
Zhuofu (Chester) Li,2
Darren J. Lu,10
Detao Ma,7
Vedant Mathur,9
Mary H. Minasyan,2
Mark T. Nasielski,9
Janice T. Nguyen,2
Lorraine M. Nicholson,2
Divij Ohri,10
Atharva U. Padhye,7
Supreethi V. Penmetcha,13
Yugantar Prakash,6
Xinyi (Cindy) Qi,2
Vedant Sahu,2
Joshua A. Scally,2
Zefyr Scott,7
Trevor J. Seddon,2
Lara-Lynn V. Shohet,2
Anchal Sinha,9
Anthony E. Sinigiani,14
Jiuxu Song,9
Spencer M. Stice,9
Andria Uplisashvili,2
Krishna Vanga,7
Amaury G. Vazquez,2
George Vetushko,15
Valeria Villa,1
Maria Vincent,1
Ian J. Waasdorp,2
Ian B. Wagaman,2
Amanda Wang,10
Jade C. Wight,1
Ella Wong,2
Natsuko Yamaguchi,2
Zijin Zhang,1
Junyang Zhao,7
and
Ryan S. Lynch16
1Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA 90095, USA
2Department of Physics and Astronomy, University of California, Los Angeles, CA 90095, USA
3National Renewable Energy Laboratory, Golden, CO 80401, USA
4Intellectual Ventures, 3150 139th Ave SE, Bellevue, WA 98005, USA
5UCLA Samueli School of Engineering, University of California, Los Angeles, CA 90095, USA
6Department of Mathematics, University of California, Los Angeles, CA 90095, USA
7Department of Electrical Engineering, University of California, Los Angeles, CA 90095, USA
8Department of Public Affairs, University of California, Los Angeles, CA 90095, USA
9Department of Electrical and Computer Engineering, University of California, Los Angeles, CA 90095, USA
10Department of Computer Science, University of California, Los Angeles, CA 90095, USA
11Department of Materials Engineering, University of California, Los Angeles, CA 90095, USA
12UCLA College of Letters and Science, University of California, Los Angeles, CA 90095, USA
13Department of Mechanical Engineering, University of California, Los Angeles, CA 90095, USA
14Department of Aerospace Engineering, University of California, Los Angeles, CA 90095, USA
15Department of Neuroscience, University of California, Los Angeles, CA 90095, USA
16Green Bank Observatory, P.O. Box 2, Green Bank, WV 24494, USA
ABSTRACT
We conducted a search for narrowband radio signals over four observing sessions in 2020–2023 with
the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the
telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of
∼11,860 stars and planetary systems in the ∼9 arcminute beam of the telescope. All detections were
either automatically rejected or visually inspected and confirmed to be of anthropogenic nature. In
this work, we also quantified the end-to-end efficiency of radio SETI pipelines with a signal injection
and recovery analysis. The UCLA SETI pipeline recovers 94.0% of the injected signals over the usable
frequency range of the receiver and 98.7% of the injections when regions of dense RFI are excluded. In
another pipeline that uses incoherent sums of 51 consecutive spectra, the recovery rate is ∼15 times
smaller at ∼6%. The pipeline efficiency affects SETI search volume calculations as well as calculations
of upper bounds on the number of transmitting civilizations. We developed an improved Drake Figure
of Merit for SETI search volume calculations that includes the pipeline efficiency and frequency drift
rate coverage. Based on our observations, we found that there is a high probability (94.0–98.7%) that
fewer than ∼0.014% of stars earlier than M8 within 100 pc host a transmitter that is detectable in
our search (EIRP > 1012
W). Finally, we showed that the UCLA SETI pipeline natively detects the
signals detected with AI techniques by Ma et al. (2023).
Corresponding author: Jean-Luc Margot
jlm@epss.ucla.edu
arXiv:2308.02712v1
[astro-ph.IM]
4
Aug
2023
2. 2 Margot et al.
Keywords: Search for extraterrestrial intelligence - technosignatures - astrobiology — exoplanets -
radio astronomy - Milky Way Galaxy
1. INTRODUCTION
In the 1982 decadal report, the Astronomy Survey Committee of the National Research Council (NRC) recommended
the approval and funding of “An astronomical Search for Extraterrestrial Intelligence (SETI), supported at a modest
level, undertaken as a long-term effort rather than as a short-term project, and open to the participation of the general
scientific community” (National Research Council 1982). The Committee noted:
It is hard to imagine a more exciting astronomical discovery or one that would have greater impact on
human perceptions than the detection of extraterrestrial intelligence. After reviewing the arguments for
and against SETI, the Committee has concluded that the time is ripe for initiating a modest program
that might include a survey in the microwave region of the electromagnetic spectrum while maintaining an
openness to support of other innovative studies as they are proposed.
In a subsequent report on the search for life’s origins, the NRC stated: “Two parallel avenues of research should
be pursued in attempts to detect life beyond the solar system: searches for evidence of biological modification of an
extrasolar planet and searches for evidence of extraterrestrial technology” (National Research Council 1990). The
report’s recommendations included the “commencement of a systematic ground-based search through the low end of
the microwave window for evidence of signals from an extraterrestrial technology”.
The detection of extraterrestrial life forms is expected to usher profound developments in a wide range of scientific
and cultural disciplines. These potential benefits provide compelling incentives to invest in multi-faceted searches for
biological indicators (biosignatures) and technological indicators (technosignatures) of extraterrestrial life. Searches
for biosignatures and technosignatures are highly complementary. In particular, the latter can “expand the search for
life in the universe from primitive to complex life and from the solar neighborhood to the entire Galaxy” (Margot
et al. 2019). In the Milky Way Galaxy alone, the ratio of search volumes with current and near-future technology is
Vtechno/Vbio ≳ 106
. In terms of the number of accessible targets, the ratio is Ntechno/Nbio ≳ 109
.
Although some types of Solar System biosignatures (e.g., a fossil or sample organism) may offer compelling inter-
pretations, the proposed exoplanet biosignatures are expected to yield inconclusive interpretations for some time (e.g.,
Fujii et al. 2018). Abiogenic interpretations may remain difficult to rule out (e.g., Rein et al. 2014), as evidenced by
biosignature claims for planets that are a million times closer than the nearest exoplanet (methane on Mars, phosphine
on Venus). In many cases, the spectroscopic observations may be consistent with but not diagnostic of the presence
of life (e.g., Catling et al. 2018; Meadows et al. 2022). In contrast, the search for technosignatures provides an op-
portunity to obtain robust detections with unambiguous interpretations. An example of such a technosignature is a
narrowband (say, <10 Hz at gigahertz frequencies) signal from an emitter located beyond the Solar System. Detection
of a signal with these characteristics would provide sufficient evidence for the existence of another civilization because
natural settings cannot generate such signals. In order to confine the signal bandwidth within 10 Hz at L band, the
velocity dispersion and Doppler broadening of the species participating in the emission must remain below 2 m/s. Such
coherence in velocity would have to be maintained over the physical scales of the emission sites. Fluid astrophysical
settings cannot produce such conditions because the thermal velocity of species is much larger, even in the coldest
environments. Even astrophysical masers cannot maintain this degree of coherence: the narrowest reported OH (1612
MHz) maser line width is 550 Hz (Cohen et al. 1987; Qiao et al. 2020), roughly two orders of magnitude wider than
the proposed narrowband radio technosignatures.
Here, we describe a search for narrowband radio technosignatures around ∼11,860 stars and their planetary systems.
2. OBSERVATIONS
We observed ∼11,680 stars and their planetary systems in 62 distinct directions aligned with TESS Objects of
Interest (TOIs). The characteristics of our primary targets are listed in Appendix A. To compute the number of stars
captured by the 8.4 arcmin beamwidth of the telescope at 1.42 GHz, we followed Wlodarczyk-Sroka et al. (2020) and
performed cone searches with the GAIA catalog (Gaia Collaboration 2023). We found 11,680 known stars, of which
8091 have measured positive parallaxes. By simple inversion of these parallaxes, we find median and mean distance
estimates for these sources of 5385 ly and 18,173 ly, respectively.
3. A Search for Technosignatures Around TESS exoplanets with the GBT 3
We observed these stars and their planetary systems with the GBT during 2-hour sessions on 2020 April 22, 2021
April 28, 2022 May 22, and 2023 May 13. The observing cadence consisted of two scans of 150 s each per source,
with sources arranged in pairs resulting in an A-B-A-B sequence for sources A and B. Angular separations between
sources always exceed several telescope beamwidths. These ON-OFF-ON-OFF (or OFF-ON-OFF-ON) sequences are
particularly useful in the detection of radio frequency interference (RFI) (Section 3.4).
We recorded both linear polarizations of the L-band receiver with the VEGAS backend in its baseband recording
mode (Anish Roshi et al. 2012). We sampled 800 MHz of bandwidth between 1.1 and 1.9 GHz. We sampled complex
(in-phase and quadrature) voltages with 8-bit quantization, but preserved only 2-bit samples after requantization with
an optimal four-level sampler, which yields a quantization efficiency ηQ of 0.8825 (Kogan 1998).
3. METHODS
Our data processing techniques are generally similar to those used by Margot et al. (2018), Pinchuk et al. (2019),
and Margot et al. (2021). Here, we give a brief overview and refer the reader to these other works for additional details.
3.1. Bandpass Correction
The VEGAS instrument splits the 800 MHz recorded bandwidth into 256 coarse channels of 3.125 MHz each. In
the process of doing so, it applies a bandpass filter to each coarse channel. This filter reduces the amplitude of the
baseline near both edges of the spectra. We restored an approximately flat baseline by dividing each spectrum by a
model of the bandpass filter response. This model was obtained by fitting a 16-degree Chebyshev polynomial to the
median bandpass response of 28 scans in the 1664.0625–1667.1875 MHz frequency range, which is generally devoid of
interference because it falls in the middle of the radio astronomy protected band (1660.6–1670.0 MHz) for the hydroxyl
radical. We enforced an even response by setting the odd coefficients of the polynomial to zero.
3.2. Doppler Dechirping
Over the 150 s duration of our scans, narrowband signals from fixed-frequency transmitters are well approximated
at the receiver by linear frequency modulated (FM) “chirp” signals, where the rate of change in frequency is dictated
by the orbital and rotational motions of both the emitter and the receiver. The linear FM waveform is characterized
by a signal of the form
s(t) = A cos(2π(f0t + Kt2
/2)), 0 ≤ t ≤ τ, (1)
where A is the signal amplitude, f0 is the frequency at t = 0, K is the rate of change of frequency, and τ is the duration
of a scan. In complex exponential notation,
s(t) = A exp (j2π(f0t + Kt2
/2)) = A exp (jθ(t)), 0 ≤ t ≤ τ. (2)
The instantaneous frequency is the time derivative of the phase, i.e.,
f(t) =
1
2π
dθ(t)
dt
= f0 + Kt. (3)
The frequency increases linearly as f(t) = f0 + Kt, with a total frequency excursion equal to Kτ. An audible signal
with this time-frequency behavior would sound like a chirp, hence the name commonly attributed to the waveform.
Doppler dechirping consists of compensating for a signal’s drift in time-frequency space to facilitate integration of the
signal power over the scan duration. In SETI searches, the drift rate is not known a priori. We used a tree algorithm
of complexity O(N log N) (Taylor 1974; Siemion et al. 2013) to integrate the signal power at 1023 trial drift rates
over the range ±8.86 Hz s−1
with a drift rate resolution of ∆ ˙
f = 0.0173 Hz s−1
. This approximate technique, known
as incoherent dechirping, does not recover 100% of the signal power. Margot et al. (2021) quantified this signal loss
with a dechirping efficiency factor ηD (0 ≤ ηD ≤ 1) for a variety of settings, including searches that utilize incoherent
summing of power spectra prior to signal detection. In this and previous UCLA SETI work, we do not use incoherent
averaging (i.e., NINC SUMS = 1) and the dechirping efficiency ranges between 60% and 100% with an average ηD ≃ 72%
over the ±8.86 Hz s−1
drift rate range. For searches with NINC SUMS = 51 over a ±4 Hz s−1
drift rate range (e.g.,
Price et al. 2020; Gajjar et al. 2021) the dechirping efficiency ranges between 4% and 100% with an average ηD ≃ 16%.
Importantly, the nominal performance of the tree algorithm for such searches is maintained in only a fairly narrow
range of drift rates up to ±0.15 Hz s−1
, and the efficiency drops precipitously at larger drift rates due to Doppler
smearing of the signal (Margot et al. 2021, Figure 7).
4. 4 Margot et al.
The received frequency fr of a monochromatic transmission at frequency ft experiences a time rate of change that
depends on the line of sight acceleration v̇ between transmitter and receiver. To first order,
˙
fr
ft
=
v̇
c
, (4)
where an overdot denotes a time derivative and c is the speed of light. Our selection of a range of trial drift rates with
maximum value ˙
fr,max = ±8.86 Hz s−1
corresponds to a fractional drift rate of ±6.24 nHz at ft = 1.42 GHz (maximum
accelerations v̇max of 1.87 ms−2
). It is an appropriate choice because it accommodates line-of-sight accelerations due
to the spins and orbits of most exoplanets. It can handle accelerations due the orbits of ∼73% of confirmed exoplanets
with known semi-major axes and orbital periods, ∼93% of confirmed exoplanets with semi-major axes greater than 0.05
au, and 100% of confirmed exoplanets with semi-major axes greater than 0.1 au (NASA Exoplanet Archive 2019). It
can also handle accelerations due to the spins of Earth-size planets at arbitrary periods (above the rotational breakup
period) and Jupiter-size planets with spin periods greater than 11.5 h. Transmitters located on exotic platforms that
somehow exceed these limits could escape detection by our pipeline if the transmitted waveforms were not compensated
to account for the platform’s acceleration (Figure 1).
0 1000 2000 3000 4000
Frequency drift for signal at rest frequency of 1.42 GHz (Hz)
0
30
60
90
120
150
Scan
duration
(s)
Earth's spin
Mercury's orbit
Io's orbit
Jupiter's spin
Beta Pictoris b's spin
Project Cyclops (1.4 Hz/s)
Breakthrough Listen (2 Hz/s)
Breakthrough Listen (4 Hz/s)
UCLA SETI (8.9 Hz/s)
Figure 1. Expected frequency drifts from monochromatic (ft = 1.42 GHz) transmitters experiencing spin and orbital acceler-
ations in various settings. The solid lines represent the maximum drift rates corresponding to Project Cyclops, BL, and UCLA
SETI searches. This figure is adapted from Sheikh et al. (2019) and reduces the drift rates sampled by BL by a factor of ∼7 to
correct an error in the original figure.
3.3. Signal Detection
At each frequency bin, our algorithm selects the trial drift rate that yields the greatest integrated signal power and
determines whether the prominence of the signal (Margot et al. 2021) exceeds 10 times the standard deviation of the
noise. The properties of signals that exceed the threshold are stored in a structured query language (SQL) database.
In practice, the algorithm proceeds in order of decreasing prominence in each coarse channel.
3.4. Doppler and Direction-of-origin Filters
Signals with ˙
fr = 0 are marked as anthropogenic RFI because they imply zero line-of-sight acceleration between
transmitter and receiver. Signals that are detected in more than one direction on the sky are also marked as RFI
because a signal emitted beyond the Solar System can appear in only one telescope beam. Finally, sources that are
detected in only one of the two scans are also marked as intermittent RFI.
The direction-of-origin filter, also known as a directional filter or sky localization filter, can be run efficiently by
retrieving the signal properties from our SQL database. A more stringent filter can be obtained by running the machine
learning algorithm of Pinchuk & Margot (2022).
5. A Search for Technosignatures Around TESS exoplanets with the GBT 5
3.5. Visual Inspection of Remaining Signals
Signals that remain after the line-of-sight distance and acceleration elimination process are marked as candidate
technosignatures. All such candidates that fall outside of permanent RFI bands (Pinchuk et al. 2019) are visually
inspected.
3.6. Sensitivity
The flux from a transmitter with Equivalent Isotropic Radiated Power (EIRP) at distance r is S = EIRP/(4πr2
).
The S/N of a narrowband radio link has been computed by, e.g., Friis (1946); Kraus (1986); Enriquez et al. (2017);
Margot et al. (2018). It reads
S/N =
S
SEFD
r
npolτ
∆f
, (5)
where S is the observed flux, SEFD is the system equivalent flux density, a common measure of telescope and receiver
performance, npol is the number of polarizations summed incoherently, τ is the integration time, and ∆f is the channel
receiver bandwidth (i.e., frequency resolution).
In a more rigorous formulation, the S/N includes the quantization efficiency ηQ due to imperfect digitization of the
voltage signals and the dechirping efficiency ηD due to imperfect integration of the signal power (Margot et al. 2021):
S/N = ηQηD
S
SEFD
r
npolτ
∆f
. (6)
Quantization efficiency approaches unity with 8-bit sampling and is ηQ = 88.25% for an optimal two-bit sampler
(Kogan 1998). Dechirping efficiency with an O(N log N) algorithm depends on the frequency drift rate and ranges
between 60% and 100% for the data acquisition and processing choices in this and previous UCLA SETI work, and
between 4% and 100% for a BL-like process with NINC SUMS = 51 and ˙
fr within ±4 Hz s−1
. It is possible to improve
the dechirping efficiency if one is willing to use a costly O(N2
) incoherent dechirping algorithm. For signals of interest
with known frequency drift rates, UCLA SETI has the capability to apply a coherent dechirping algorithm to the raw
voltage data, in which case ηD ≃ 1.
For the UCLA SETI program at the GBT, we have ηQ = 0.8825, SEFD = 10 Jy, npol = 2, τ = 150 s, and ∆f ≃
3 Hz. Our usual detection threshold is set at S/N=10, such that signals with flux Sdet = 11.3 × 10−26
W/m2
are
detectable. With these parameters, an Arecibo Planetary Radar (EIRP=2.2 × 1013
W) is detectable at 415 ly and a
thousand Arecibos can be detected at 13,123 ly. Conversely, transmitters located 1000 ly away are detectable with 5.8
Arecibos and transmitters located at the galactic center are detectable with 4130 Arecibos.
3.7. Signal Injection and Recovery Analysis
To quantify the end-to-end efficiency of the UCLA SETI pipeline, we injected 10,000 artificial chirp signals in raw
voltage data from our 2021 search, processed the data as we normally do, and quantified the number of injected signals
that were recovered by the pipeline.
We used Equation (2) to inject the artificial signals in complex voltage data sampled with 8 bit quantization, and
we adjusted the signal amplitudes to achieve a S/N upon recovery of approximately 20. The starting frequencies of
the signals were drawn randomly from a uniform distribution in the range 1.15–1.73 GHz, with the exclusion of the
1.20–1.34 GHz range that is blocked by a notch filter at the GBT. The drift rates were drawn randomly from a uniform
distribution in the range ±8.86 Hz s−1
(Figure 2).
We used the exact same data files (raw voltage data files injected with 10,000 artificial signals) to estimate the
end-to-end efficiency of a process that imitates the Breakthrough Listen (BL) pipeline. Specifically, we computed
power spectra with the FFTW library (Frigo & Johnson 2005) and a transform length of 220
, yielding a frequency
resolution ∆f = 2.98 Hz that approximates the finest frequency resolutions (2.79 Hz, 2.84 Hz, 2.93 Hz) of BL spectra
(Lebofsky et al. 2019, Table 4). We applied a bandpass correction appropriate for the BL data acquisition backend.
We then summed 51 consecutive power spectra incoherently, yielding a time resolution of 17.11 s, to approximate the
51-fold incoherent summing and time resolutions (17.40 s, 17.98 s, 18.25 s) of the High Spectral Resolution (HSR)
BL spectra (Lebofsky et al. 2019, Table 4). Finally, we ran BL’s version of the Doppler dechirping tree algorithm, as
implemented in turboSETI (Enriquez et al. 2017), with a maximum drift rate of ±8.88 Hz s−1
and minimum S/N of
10, to identify signals and quantify the number of injected signals that were recovered (turboSETI -M 8.881784197
-s 10).
6. 6 Margot et al.
1.2 1.3 1.4 1.5 1.6 1.7
Frequency (GHz)
0
20
40
60
80
100
Count
Injected signals
7.5 5.0 2.5 0.0 2.5 5.0 7.5
Drift rate (Hz/s)
0
20
40
60
80
100
Count
Injected signals
Figure 2. Distributions of starting frequencies (Left) and drift rates (Right) of 10,000 artificial, linear FM “chirp” signals
injected in voltage data. Frequencies corresponding to a notch filter at the GBT (1.2 – 1.3412 GHz) are excluded.
A signal was deemed to be recovered if two conditions were jointly met: (1) the recovered frequency was within
±6 Hz of the injected frequency, and (2) the recovered drift rate was within ±0.05 Hz s−1
of the injected drift rate.
These tolerances were designed to accommodate slight mismatches of up to two bins in the frequency dimension and
the frequency drift rate dimension. The probability of an accidental match is less than 1 in a billion. Because of
differences in algorithm implementation, the drift rate bins were 0.0173 Hz s−1
for UCLA SETI and 0.0249 Hz s−1
for
turboSETI.
3.8. Native Detections of Machine Learning Candidates by the UCLA SETI Pipeline
Ma et al. (2023) used a β-convolutional variational autoencoder and random forest analysis to identify 8 promising
signals not previously identified by the BL pipeline. They named these candidates MLc1 to MLc8, in reference to the
machine learning (ML) process used in their analysis. We were interested in finding out whether these signals could
be natively detected by the UCLA SETI pipeline, without any ML assistance. We downloaded the BL HSR power
spectra of the MLc candidates and corresponding OFF scans, applied a bandpass correction (Section 3.1) appropriate
for the BL data acquisition backend, and ran the resulting spectra through the UCLA SETI pipeline. We used only
the first four of six scans of each pair of sources to mimic the A-B-A-B sequence used in UCLA SETI observations.
4. RESULTS
4.1. Candidate Technosignatures
We detected 37.1 million narrowband signals with the data from our 2020–2023 observations. Almost all (99.74%) of
these signals were rejected automatically by the UCLA SETI pipeline as RFI, which left approximately 200,000 signals
warranting further consideration. Tens of thousands of these signals are being inspected by thousands of volunteers
on the website http://arewealone.earth as part of a citizen science collaboration (Li & Margot 2023). Almost all
(99.75%) of the remaining signals were detected in regions of dense RFI. We visually inspected all ∼500 candidate
technosignatures that were detected outside of dense RFI regions and determined that they were all anthropogenic.
It is remarkable that, in over 77 million narrowband signal detections obtained during an 8-year period (Table 1),
not a single signal has merited follow-up observations. There have been plenty of instances where promising signals
were only marginally detected in the corresponding OFF scans. We eliminate such signals from consideration.
4.2. Signal Injection and Recovery Analysis
The UCLA SETI pipeline recovered 9400 signals out of 10,000 injections, yielding an end-to-end pipeline efficiency
for narrowband chirp signals of 94%. When regions of dense RFI were excluded, the UCLA SETI pipeline recovered
6716 signals out of 6807 injections, for an improved recovery rate of 98.7% (Figure 3). The distributions of recovered
S/N and drift rates match those of the injected population (Figure 4). Signals that were not recovered are usually
found near the bandpass edges, where the bandpass response and correction may be less than ideal, or intersect other
signals in time-frequency space.
A process designed to imitate the BL pipeline recovered a much smaller fraction of the injections. Specifically, only
570 signals out of 10,000 injections were recovered, with S/N and drift rate distributions that do not match the injected
7. A Search for Technosignatures Around TESS exoplanets with the GBT 7
Data Set Fields Targets Stars Signals Hit Rate Density DFM MDFM
(primary) (in beam) (millions) (sig kHz−1
hr−1
) (GHz m3
W−3/2
) (Hz2
m3
W−3/2
)
UCLA 2016 Kepler 14 11,658 5.22 10.2 6.74e+31 3.95e+32
UCLA 2017 Kepler+ 12 6,924 8.52 16.2 6.35e+31 3.72e+32
UCLA 2018–19 Gal. plane 30 25,293 27.0 24.6 1.44e+32 8.47e+32
UCLA 2020–23 TESS 62 11,680 37.1 16.4 2.99e+32 1.75e+33
Total 2016–23 118 55,555 77.8 18.0 5.74e+32 3.37e+33
Table 1. UCLA SETI search characteristics, showing observation fields, number of primary targets, number of stars observed
in the beam of the telescope, number of narrowband signals detected with S/N>10, hit rate density (number of detections per
unit bandwidth per unit on-source time), Drake Figure of Merit (DFM), and modified DFM (Section 5.1). Properties of all
2016–2019 detections are available online (Margot et al. 2020a,c,b).
population and illuminate the reasons for the poor performance (Figure 5). Almost all (99.1%) signals recovered by the
BL-like process have drift rates within ±1 Hz s−1
. Injections with larger drift rates are rarely recovered. This result
is entirely consistent with the theoretical expectation of low dechirping efficiency for high drift rate signals observed
in incoherently summed power spectra. In this situation, the signal power gets smeared across multiple frequency
resolution cells because of Doppler drift during the longer integration times. For BL incoherent sums of 51 spectra
at ∼3 Hz resolution, which extend the integration times from ∼0.3 s to ∼17 s, drift rates that exceed ±0.15 Hz s−1
experience Doppler smearing. The dechirping efficiency falls rapidly, reaching 16% for drift rates of 1 Hz s−1
(Margot
et al. 2021), making recovery of signals at larger drift rates challenging. The diminishing performance as a function
of drift rate is evident when plotting the S/N of signals recovered by the BL-like process as a function of drift rate
(Figure 6).
Detailed signal counts are listed in Table 2. These counts provide reasonable estimates of the end-to-end pipeline
efficiency of radio SETI pipelines. The efficiency of a BL-like process is ∼5.7% for drift rates within ±8.88 Hz s−1
.
Because injected signals have uniformly distributed drift rates and because all recovered signals have drift rates within
the ±4 Hz s−1
range used by Price et al. (2020) and Gajjar et al. (2021), we can estimate the end-to-end pipeline
efficiency of their searches at 5.7%×8.88/4 = 12.7%. Likewise, we find 5.7%×8.88/2 = 25.3% for the work of Enriquez
et al. (2017), who sampled drift rates within ±2 Hz s−1
.
Number of hits Number of hits Candidate Actual Pipeline
prior to injection after injection matches matches efficiency
UCLA SETI pipeline 329,591 338,238 9634 9400 94.0%
BL-like process 7512 8226 714 570 5.7%
Table 2. Efficiency of radio SETI pipelines quantified by the recovery rates of 10,000 artificial signal injections. In the UCLA
SETI pipeline, a hit is defined as a narrowband signal detection with S/N ≥ 10. In the BL pipeline, a hit has the additional
requirement of a minimum distance (∼ kHz) from previously recorded hits. The factor of ∼50 difference in number of hits
between UCLA and BL for the same data set and drift rate range has been previously documented and is understood primarily
as the result of differences in dechirping efficiency and definition of a hit (Margot et al. 2021). Because injected signals may
replace one or more previously detected signals, the number of candidate matches after injection is not simply the difference in
number of hits prior to and after injection. Actual matches are defined as having both a recovered frequency within ±6 Hz of
the injected frequency and a drift rate within ±0.05 Hz s−1
of the injected drift rate. Although turboSETI in its debug mode
can be coerced to reveal additional hits beyond its nominal hits, the number of actual matches in debug mode remains low at
670 recoveries out of 10,000 injections.
4.3. Native Detections of Machine Learning Candidates by the UCLA SETI Pipeline
The UCLA SETI pipeline successfully detected MLc3, MLc4, MLc5, MLc7, and MLc8 without invoking our own
ML algorithms (Pinchuk & Margot 2022). We did not attempt to detect MLc1, MLc2, and MLc6 because the drift
rates reported by Ma et al. (2023) for these signals (1.11 Hz s−1
, 0.44 Hz s−1
, 0.18 Hz s−1
) exceed the nominal range
of the O(N log N) tree algorithm given the incoherent summing of 51 consecutive spectra in BL HSR data products.
8. 8 Margot et al.
1.2 1.3 1.4 1.5 1.6 1.7
Frequency (GHz)
0
5
10
15
20
25
30
35
Count
GPS/GLONASS
Injected signals
Recovered signals
Figure 3. Distribution of injected signals and signals recovered by the UCLA SETI pipeline as a function of frequency. Blue
bands indicated the operating bands of GPS and GLONASS satellites, where recovery rates are markedly lower. Frequencies
corresponding to a notch filter at the GBT (1.2 – 1.3412 GHz) are excluded.
10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0
Signal to noise ratio
100
101
102
Count
Recovered signals
7.5 5.0 2.5 0.0 2.5 5.0 7.5
Drift rate (Hz/s)
0
10
20
30
40
50
60
70
Count
Recovered signals
Figure 4. Distributions of recovered S/N (Left) and drift rates (Right) for the UCLA SETI pipeline.
10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0
Signal to noise ratio
100
101
102
Count
Recovered signals
7.5 5.0 2.5 0.0 2.5 5.0 7.5
Drift rate (Hz/s)
0
10
20
30
40
50
60
70
Count
Recovered signals
Figure 5. Distributions of recovered S/N (Left) and drift rates (Right) for a process that imitates the BL pipeline, i.e.,
incoherent averaging of the spectra with NINC SUMS = 51 followed by signal detection with turboSETI.
9. A Search for Technosignatures Around TESS exoplanets with the GBT 9
1.00 0.75 0.50 0.25 0.00 0.25 0.50 0.75 1.00
Drift rate (Hz/s)
7.5
10.0
12.5
15.0
17.5
20.0
22.5
25.0
27.5
Signal
to
noise
ratio
Recovered signals
Figure 6. Distribution of recovered S/N as a function of drift rate (0–1 Hz s−1
only) for a process that imitates the BL pipeline.
Only the central region within ±0.15 Hz s−1
(blue lines) is free of Doppler smearing. The recovered S/N values are lower than
the injected values because of Doppler smearing that worsens at larger drift rates, as quantified by smaller dechirping efficiencies
at larger drift rates. Dechirping calculations for a BL-like process had predicted a drop in S/N to about ∼62% of nominal for
df/dt = 0.25 Hz/s, ∼31% for df/dt = 0.5 Hz/s, and ∼16% for df/dt = 1 Hz/s (Margot et al. 2021), which is roughly consistent
with what is observed.
Based on the characteristics and appearance of the signals, we predict that if the raw voltage data had been preserved,
we could have recovered MLc1, MLc2, and MLc6 by processing the data without incoherent summing.
The characteristics of the signals detected by the UCLA SETI pipeline generally match those of the ML detections
well (Table 4.3). The magnitudes of the drift rates match, but the signs differ, which we attribute to an error in Ma
et al. (2023)’s report because our values are consistent with the signal slopes in their supplemental figures.
ID Target Band FreqMa FreqUCLA Offset MJDMa MJDUCLA DRMa DRUCLA S/NMa S/NUCLA
(HIP) (Hz) (Hz) (Hz) (days) (days) (Hz s−1
) (Hz s−1
)
MLc1 13402 1,188,539,231 N/A N/A 57541.68902 57541.6890 +1.11 N/A 6.53 N/A
MLc2 118212 1,347,862,244 N/A N/A 57752.78580 57752.9095 -0.44 N/A 16.38 N/A
MLc3 62207 1,351,625,410 1,351,623,638 -1772 57543.08647 57543.1000 -0.05 +0.049 57.52 80.31
MLc4 54677 1,372,987,594 1,372,984,455 -3139 57517.08789 57517.1017 -0.11 +0.11 30.20 41.71
MLc5 54677 1,376,988,694 1,376,984,409 -4285 57517.09628 57517.1017 -0.11 +0.108 44.58 63.50
MLc6 56802 1,435,940,307 N/A N/A 57522.13197 57522.1527 -0.18 N/A 39.61 N/A
MLc7 13402 1,487,482,046 1,487,476,704 -5342 57544.51645 57544.5977 +0.10 -0.069 129.16 113.14
MLc8 62207 1,724,972,561 1,724,970,630 -1931 57543.10165 57543.1000 -0.126 +0.138 34.09 19.85
Table 3. Characteristics of the top eight signals of interest identified by Ma et al. (2023)’s ML model and corresponding
detections by the UCLA SETI pipeline. MLc1, MLc2, and MLc6 have frequency drift rates beyond the nominal range of the
O(N log N) tree algorithm and we did not attempt to detect them. Columns 3, 6, 8, and 10 with subscripts “Ma” indicate the
band frequency, start epoch, frequency drift rate, and S/N as reported by Ma et al. (2023). Columns 4, 5, 7, 9, and 11 with
subscripts “UCLA” are corresponding UCLA SETI results. Ma et al. (2023) did not report the frequencies of the signals but
rather the center frequencies of the bands in which the signals were identified. We report the actual frequencies of the signals at
the beginning of each scan (column 4) and the frequency offsets (column 5) from the band centers. The modified Julian dates
(MJDs) reported by Ma et al. (2023) are erroneous except for the first one. We provided the correct values (column 7). We
found frequency drift rates (DR) (column 9) that are opposite in sign to those reported by Ma et al. (2023) – our values are
consistent with the signal slopes in their supplemental figures. S/N values differ because of algorithmic differences in outlier
rejection when computing the standard deviation of the noise.
MLc3 was detected by the UCLA SETI pipeline but correctly identified automatically as RFI because the same
signal is detected in the OFF scan at S/N∼12 (Figure 7, Left).
10. 10 Margot et al.
MLc4 was detected by the UCLA SETI pipeline and identified as a candidate warranting visual inspection. Visual
inspection clearly reveals the presence of the signal in the OFF scan (Figure 7, Center), indicating that this candidate
is RFI.
MLc5 was detected by the UCLA SETI pipeline and identified as a candidate warranting visual inspection. Detection
of the signal in the OFF scan is less compelling (Figure 7, Right), but the similarity in signal morphology with MLc4
indicates that this candidate is RFI. The frequency spacing between MLc4 and MLc5 is almost exactly 4 MHz, which
suggests a common interferer.
MLc7 was detected by the UCLA SETI pipeline but correctly identified automatically as RFI because the same
signal is detected in the OFF scan.
MLc8 was detected by the UCLA SETI pipeline and identified as a candidate warranting visual inspection. The
signal is detected in the OFF scan and therefore labeled as RFI.
In summary, none of the MLc signals detected in our work warrant further examination.
0
50
100
150
200
250
Scan 1 - MLc3 - 102
0
50
100
150
200
250
Scan 1 - OFF3
300 200 100 0 100 200 300
0
50
100
150
200
250
Scan 2 - MLc3
0
50
100
150
200
250
Scan 1 - MLc4 - 165
0
50
100
150
200
250
Scan 1 - OFF4
300 200 100 0 100 200 300
0
50
100
150
200
250
Scan 2 - MLc4
0
50
100
150
200
250
Scan 1 - MLc5 - 925
0
50
100
150
200
250
Scan 1 - OFF4
300 200 100 0 100 200 300
0
50
100
150
200
250
Scan 2 - MLc5
Figure 7. (Left) Dynamic spectra showing the ON-OFF-ON scans corresponding to MLc3 as detected by the UCLA SETI
pipeline. The detection of the signal in the OFF scan indicates that the signal can be immediately identified as RFI. (Center)
Same data for MLc4, which was identified by the UCLA SETI pipeline as a candidate worthy of visual inspection. (Right) Same
data for MLc5, which was identified by the UCLA SETI pipeline as a candidate worthy of visual inspection.
5. DISCUSSION
5.1. Figures of Merit
The Drake Figure of Merit (Drake 1984) provides an estimate of the search volume of a SETI program that captures
almost all essential elements: frequency coverage, sky coverage, and sensitivity. It is defined as
DFM =
B Ω
S
3/2
det
, (7)
where B is the total bandwidth examined, Ω is the fractional area of the sky covered, and Sdet is the minimum flux
required for a detection. Typical units are GHz m3
W−3/2
(e.g., Horowitz & Sagan 1993).
For transmitters of a given EIRP, the S
−3/2
det factor is proportional to the total volume that can be examined by
a search with minimum detectable flux Sdet(∝ EIRP/4πr2
max). The fraction of this volume that is actually sampled
by the search is proportional to the fraction Ω of a 4π solid angle. Multiple observations of the same patch of sky
with similar observing parameters can easily be accounted for by rewriting Ω =
P
i Ωi, where the index i represents
individual beam pointings. The fraction of the entire radio spectrum that is captured by the search is proportional to
the bandwidth B.
In its original form, the DFM misses two essential elements. First, it assumes that pipelines are perfect with end-
to-end pipeline efficiencies of 100%, whereas the efficiency of different programs can vary by more than an order of
11. A Search for Technosignatures Around TESS exoplanets with the GBT 11
magnitude. Second, it ignores the frequency drift rate coverage, i.e., range of line-of-sight accelerations sampled in a
search, whereas this range is an obvious indicator of the thoroughness of the search. We propose a modified DFM to
address these limitations:
MDFM = ηP
v̇max
c
B Ω
S
3/2
det
, (8)
where ηP is the end-to-end pipeline efficiency for the detection of signals of interest and v̇max/c is the maximum
fractional frequency drift rate (with respect to the center of the band) considered in the search (Equation 4). We
express the latter in nHz and show MDFM values in units of Hz2
m3
W−3/2
. We chose a metric that is linear
in the range of frequency drift rates examined because we cannot predict the locations, sizes, or spins of preferred
transmitter platforms. In the absence of reliable information, a uniform prior distribution for the frequency drift rate
seems reasonable. One could design the distribution to accommodate the majority of exoplanet settings, with an upper
limit of 26 nHz that accommodates 95% of confirmed exoplanets with known semi-major axes and orbital periods.
Values of the DFM and MDFM metrics for the UCLA SETI search are compared to those of select surveys in Table 4
and Figure 8. We have assumed ηP = 100% for the surveys of Horowitz & Sagan (1993) and Harp et al. (2016) and
the estimates of Section 4.2 for the surveys of Enriquez et al. (2017), Price et al. (2020), and UCLA SETI. The drift
rate coverage of Horowitz & Sagan (1993) is unlike those of modern surveys. It is large but samples only three distinct
values (local standard of rest, galactic barycenter, and cosmic microwave background rest frame). We have assumed
a fractional drift rate of 1 nHz as a compromise, which is the same value that Harp et al. (2016) used. We found that
the MDFM of the UCLA SETI search falls in between the survey of 692 stars of Enriquez et al. (2017) and the survey
of 1327 stars of Price et al. (2020).
Horowitz & Sagan 1993 Harp et al. 2016 Enriquez et al. 2017 Price et al. 2020 UCLA SETI
Freq. coverage B (GHz) 4e-4 variablea
0.660 variableb
0.439
Sky fraction Ω 0.7 1.17e-3c
2.88e-4 5.03e-4 4.91e-5
Sensitivity S (W/m2
) 1700e-26d
260e-26e
17.7e-26f
variableg
11.3e-26h
Pipeline efficiency ηP 100% 100% 25.3% 12.7% 94.0%
Drift rate coverage (nHz) 1 1 1.33 2.66 6.24
DFM (GHz m3
W−3/2
) 1.23e+31 1.70e+32 2.56e+33 2.59e+34 5.74e+32
MDFM (Hz2
m3
W−3/2
) 1.23e+31 1.70e+32 8.63e+32 1.21e+34 3.37e+33
Table 4. Search volume characteristics of select surveys. The Drake Figure of Merit (DFM) does not account for pipeline efficiency
nor frequency drift rate coverage, but the Modified Drake Figure of Merit (MDFM) does.
aWe used 8 GHz for 65 stars, 2.04 GHz for 1959 stars, 0.337 GHz for 2822 stars, and 0.268 GHz for 7459 stars (Harp et al. 2016).
b We used 0.66 GHz for GBT L band, 0.94 GHz for GBT S band, 0.85 GHz for Parkes 10 cm (Price et al. 2020).
c Based on 3’ × 6’ synthesized beam. The solid angle appears to have been overestimated by a factor of 4 in Enriquez et al. (2017).
dFor S/N=30 in 20 s (Horowitz & Sagan 1993).
eFor S/N=6.5 in 93 s (Harp et al. 2016). We used a system temperature of 108 K, which is the average across all four bands.
fFor S/N=25 in 300 s (Enriquez et al. 2017).
gFor S/N=10 in 300 s (Price et al. 2020). We used 7.1e-26 for the GBT and 24.0e-26 for Parkes.
hFor S/N=10 in 150 s. This values takes the quantization efficiency ηQ = 0.8825 into account.
Another possible disadvantage of the DFM is that it assumes a uniform distribution of transmitters on the sky,
whereas transmitters may be preferentially located near stars, which are not uniformly distributed. At ∼1% of the
galactic scale, the assumption of spatial uniformity holds reasonably well. For instance, the Gaia catalog of nearby
(100 pc) stars is expected to be volume-complete for all stars of spectral type earlier than M8 and shows a roughly
12. 12 Margot et al.
Horowitz & Sagan 1993 Harp et al. 2016 Enriquez et al. 2017 Price et al. 2020 UCLA SETI
1031
1032
1033
1034
Drake
Figure
of
Merit
(DFM)
Horowitz & Sagan 1993 Harp et al. 2016 Enriquez et al. 2017 Price et al. 2020 UCLA SETI
1031
1032
1033
1034
Modified
Drake
Figure
of
Merit
(DFM)
Figure 8. Search volume characteristics of select surveys. The Drake Figure of Merit (DFM, Left) does not account for
pipeline efficiency nor frequency drift rate coverage, but the Modified Drake Figure of Merit (MDFM, Right) does.
uniform spatial distribution of the 331,312 objects (Gaia Collaboration et al. 2021). At larger distances, the assumption
breaks down, especially for directions in and out of the plane of the galactic disk. Drake (1984) had anticipated this
problem by considering distances < 1 kpc.
As our galactic models and star catalogs improve, we can refine the MDFM by replacing the physical volume covered
by a search with the actual number of stars sampled by each beam pointing, assuming again that transmitters may
be preferentially located near stars. Let us consider the number of stars in an elemental volume of sky
dN∗(r, θ, ϕ) = ρ∗(r, θ, ϕ)r2
sin θdθdϕdr, (9)
where ρ∗ is a stellar density (number of stars per unit volume), and (r, θ, ϕ) describe spherical coordinates in a frame
centered at the solar system barycenter. The figure of merit for transmitters of a fiducial EIRP can then be written
MDFM|EIRP = ηP
v̇max
c
B
X
i
N∗,i (10)
where the number of stars in each pointing i is extracted from a catalog query that includes distance and angular
bounds or computed from a galactic or extragalactic model
N∗,i =
Z rmax
o
dr
ZZ
Ωi
ρ∗(r, θ, ϕ)r2
sin θdθdϕ, (11)
with rmax =
p
EIRP/(4πSdet) and Ωi is the full width half max (FWHM) solid angle of the telescope beam. Note that
the quantization and dechirping efficiencies are properly taken into account via Sdet and, therefore, rmax. Duplicate
pointings and duplicate stars are allowed in these expressions to account for the fact that repeated observations are
valuable.
5.2. Existence Limits
We can write a formalism to calculate upper bounds on the number of transmitters that are detectable in a SETI
survey. Our calculation presupposes that transmitters are preferentially located near stars.
First, we write the total number of stars surveyed for transmitters of a fiducial EIRP
Nobs|EIRP =
X
i
N∗,i, (12)
where the number of stars is calculated as in Section 5.1. However, in this expression, duplicate stars are disallowed
in the summation to avoid double-counting of stars that are observed either in duplicate pointings or in separate
pointings.
Second, we write the total number of stars in the relevant search volume
Ntot =
Z rmax
o
dr
ZZ
sky
ρ∗(r, θ, ϕ)r2
sin θdθdϕ, (13)
13. A Search for Technosignatures Around TESS exoplanets with the GBT 13
where the double integral is over the entire sky.
Third, we acknowledge the fact that SETI pipelines are not 100% efficient. Even if we covered the entire sky in our
search, the UCLA SETI pipeline would have at most a 94.0–98.7% chance of detecting a narrowband technosignature.
If transmission frequencies are uniformly distributed in the range 1.15–1.73 GHz, the probability is closer to 94.0%.
If the transmission frequencies happen to fall among radio astronomy protected bands or regions where RFI is less
dense, the probability is closer to 98.7%.
For this survey at the fiducial EIRP of 0.058 Arecibos (1.27 × 1012
W) corresponding to detectability up to 100 pc,
we find Nobs|EIRP = 47 and Ntot = 331,312. Therefore, we can infer with high probability (94.0–98.7%) that there
are fewer than 1 star in 7,050 stars (∼0.014%) within 100 pc that host a transmitter detectable in this survey. A
detectable transmitter has the following sufficient characteristics: (1) it emits in the frequency range 1.15–1.73 GHz
(excluding the range 1.20–1.34 GHz), (2) it has a line-of-sight acceleration with respect to the GBT that results in
a frequency drift rate within ±8.86 Hz s−1
, and (3) it emits a fixed-frequency or chirp waveform with bandwidth <
3 Hz, EIRP > 1.27 × 1012
W, and 100% duty cycle. Characteristics (1) and (2) are necessary for detection, but
characteristics (3) are not. For instance, we could detect more complex or broader waveforms (e.g., pulsed waveforms,
non-chirp waveforms, waveforms with > 3 Hz bandwidth) provided that the integrated power exceeded our detection
threshold. We could also detect an intermittent transmitter provided that we observed at a favorable time.
5.3. Revisions to Published Estimates
Previous works (e.g., Enriquez et al. 2017; Price et al. 2020) ignored the dechirping efficiency and provided estimates
of SETI search volumes or upper limits on the number of transmitters in the Galaxy under the assumption that the
end-to-end efficiency of their pipeline was 100%. Our results show that the efficiency of a BL-like process is closer
to 5.7% for drift rates within ±8.88 Hz s−1
, 12.7% for drift rates within ±4 Hz s−1
, and 25.3% for drift rates within
±2 Hz s−1
, suggesting that the published estimates of search volumes and number of transmitters in these works need
revisions.
Specifically, we suggest that the statement of Enriquez et al. (2017) that “fewer than ∼0.1% of the stellar systems
within 50 pc possess these types of transmitters” ought to be rephrased as “there is a 25.3% probability that fewer than
∼0.1% of the stellar systems within 50 pc possess the types of transmitters detectable in this search, which sampled
frequency drift rates up to ±2 Hz s−1
.”
6. CONCLUSIONS
Our observations of ∼11,680 stars and planetary systems with the GBT resulted in ∼37 million narrowband detec-
tions, none of which warranted reobservation.
A signal injection and recovery analysis of 10,000 chirp signals with randomly selected frequencies and drift rates
revealed that the UCLA SETI pipeline recovers 94.0% of the injection and 98.7% of the injections outside of regions of
dense RFI. Because the artificial signals were injected in raw voltage data, these percentages represent good estimates
of the end-to-end pipeline efficiency for chirp signals.
A process that simulates the BL pipeline recovers a much smaller fraction of injections (5.7%), which we attribute
largely to Doppler smearing of the signal that results from incoherent summing of 51 consecutive spectra. The
characteristics of the recovered signals match the dechirping efficiency predictions of Margot et al. (2021) and confirm
that the dechirping efficiency is an important factor that affects sensitivity, figure-of-merit, and transmitter prevalence
calculations.
On the basis of our results and a Gaia survey of nearby (100 pc) stars that is expected to be volume-complete for
spectral types earlier than M8, we can state that there is a high probability (94.0–98.7%) that fewer than ∼0.014% of
such stars within 100 pc host a transmitter that is detectable in our search. Provided that the frequency and frequency
drift rate fall within our search bounds, a sufficient condition for detection is the emission of a fixed-frequency or chirp
waveform with bandwidth < 3 Hz, EIRP > 1.27 × 1012
W (0.058 Arecibos), and 100% duty cycle.
We showed that the UCLA SETI pipeline can detect signals that had escaped the BL pipeline and were identified
with AI techniques by Ma et al. (2023). In addition, we found that the detections were due to RFI, either because
our pipeline correctly and automatically identified them as RFI, or because our usual visual inspection process showed
them to be RFI.
We developed an improved Drake Figure of Merit for SETI search volume calculations that includes the pipeline
efficiency and frequency drift rate coverage of a search. With this search volume metric, the UCLA SETI search to
date falls in between the survey of 692 stars of Enriquez et al. (2017) and the survey of 1327 stars of Price et al. (2020).
14. 14 Margot et al.
UCLA SETI observations were designed, obtained, and analyzed by ∼130 undergraduate and ∼20 graduate students
who have taken the annual SETI course since its first offering in 2016. The SETI course helps develop skills in
astronomy, computer science, signal processing, statistical analysis, and telecommunications. Additional information
about the course is available at https://seti.ucla.edu. UCLA SETI data are used in a citizen science collaboration
called “Are we alone in the universe?”, which can be found at http://arewealone.earth.
Funding for UCLA SETI was provided by The Queens Road Foundation, Robert Meadow and Carrie Menkel-Meadow,
Larry Lesyna, Michael W. Thacher and Rhonda L. Rundle, Janet Marott, and other donors (https://seti.ucla.edu). We
are grateful to the BL team for stimulating discussions about search modes and data processing. We thank the Tsay
Family, Smadar Gilboa, Marek Grzeskowiak, and Max Kopelevich for providing an excellent computing environment
in the Jim and Barbara Tsay Computer Study Lab at UCLA. We are grateful to Paul Demorest, John Ford, Ron
Maddalena, Toney Minter, Karen O’Neil, and James Jackson for enabling the GBT observations. We are grateful
to Norma A. Contreras, Nicholas M. Liskij, Anthony V. Lopilato, Samuel R. Mason, Maxwell K. Muller, Samantha
Niemoeller, Lou Baya Ould Rouis, Taylor L. Scott, Nathanael Smith, and Nadine M. Tabucol for assistance with
the data analysis. The Green Bank Observatory is a facility of the National Science Foundation operated under
cooperative agreement by Associated Universities, Inc. This paper includes data collected by the TESS mission.
Funding for the TESS mission is provided by the NASA’s Science Mission Directorate. This work has made use of
data from the European Space Agency (ESA) mission Gaia, processed by the Gaia Data Processing and Analysis
Consortium (DPAC). This research has made use of the NASA Exoplanet Archive, which is operated by the California
Institute of Technology, under contract with NASA under the Exoplanet Exploration Program.
Facilities: Green Bank Telescope, Exoplanet Archive
15. A Search for Technosignatures Around TESS exoplanets with the GBT 15
APPENDIX
A. SOURCES
TOI Disp. Rp Period Insolation Rs Distance RA Dec
(R⊕) (days) (Earth flux) (R⊙) (pc) (hh:mm:ss) (dd:mm:ss)
469.01 CP 3.55 13.63 60.16 1.01 68.19 06:12:13.88 -14:38:57.54
479.01 KP 12.68 2.78 615.47 1.02 194.55 06:04:21.53 -16:57:55.4
488.01 CP 1.12 1.20 58.26 0.35 27.36 08:02:22.47 03:20:13.79
536.01 KP 15.40 9.24 180.87 1.30 844.06 06:30:52.9 00:13:36.82
546.01 KP 13.44 9.20 203.95 1.12 726.41 06:48:46.71 -00:40:22.03
561.01 CP 2.74 10.78 73.35 0.84 85.80 09:52:44.44 06:12:57.97
562.01 CP 1.22 3.93 14.71 0.36 9.44 09:36:01.79 -21:39:54.23
571.01 KP 12.92 4.64 469.05 1.41 405.24 09:01:22.65 06:05:49.5
652.01 CP 2.11 3.98 464.96 1.03 45.68 09:56:29.64 -24:05:57.07
969.01 CP 3.65 1.82 167.63 0.82 77.26 07:40:32.8 02:05:54.92
1235.01 CP 1.89 3.44 134.67 0.63 39.63 10:08:52.38 69:16:35.83
1243.01 PC 4.49 4.66 8.59 0.49 43.19 09:02:55.83 71:38:11.1
1718.01 PC 4.40 5.59 219.06 0.94 52.30 07:28:04.33 30:19:18.24
1726.01 CP 2.24 7.11 145.57 0.90 22.40 07:49:55.05 27:21:47.28
1730.01 PC 2.76 6.23 114.27 0.53 35.69 07:11:27.8 48:19:40.56
1732.01 PC 2.55 4.12 38.33 0.63 74.76 07:27:12.35 53:02:42.97
1766.01 KP 16.72 2.70 1704.57 1.61 210.25 09:54:34.35 40:23:16.6
1774.01 CP 2.74 16.71 73.76 1.09 53.97 09:52:38.86 35:06:39.63
1775.01 PC 8.70 10.24 55.44 0.84 149.23 10:00:27.62 39:27:27.9
1776.01 PC 1.40 2.80 560.33 0.95 44.65 10:59:06.55 40:59:01.39
1779.01 KP 9.93 1.88 21.19 0.31 33.93 09:51:04.45 35:58:06.8
1789.01 CP 16.86 3.21 3000.05 2.26 229.07 09:30:58.42 26:32:23.98
1797.01 CP 2.99 3.65 283.72 1.05 82.34 10:51:06.41 25:38:27.83
1799.01 PC 1.63 7.09 163.47 0.96 62.13 11:08:55.9 34:18:10.85
1800.01 KP 12.42 4.12 459.54 1.26 277.28 11:25:05.98 41:01:40.87
1801.01 PC 1.99 10.64 10.73 0.55 30.68 11:42:18.14 23:01:37.32
1802.01 PC 2.51 16.80 5.92 0.58 60.69 10:57:01.28 24:52:56.42
1803.01 PC 4.22 12.89 18.34 0.69 119.24 11:52:11.07 35:10:18.48
1806.01 PC 2.84 15.15 2.15 0.40 55.52 11:04:28.36 30:27:30.87
1821.01 KP 2.43 9.49 41.92 0.77 21.56 11:14:33.04 25:42:38.15
1822.01 APC 14.57 9.61 192.62 1.71 312.52 11:11:06.68 39:31:36.02
1898.01 PC 9.17 45.52 8.34 1.61 79.67 09:38:13.27 23:32:48.29
Table 5. Characteristics of primary sources observed in 2020–2021. Columns show the TESS Object of Interest (TOI); the
TESS Follow-up Observing Program Working Group disposition as of 2023 March 29 (Disp.), where PC is a planet candidate,
CP is a confirmed planet, KP is a Kepler planet, and APC is an ambiguous planet candidate; the planet radius Rp in Earth
radii; the orbital period in days; the insolation in Earth flux units; the radius of the host star Rs in solar radii; the distance in
parsecs; and the right ascension and declination of the source.
16. 16 Margot et al.
TOI Disp. Rp Period Insolation Rs Distance RA Dec
(R⊕) (days) (Earth flux) (R⊙) (pc) (hh:mm:ss) (dd:mm:ss)
1683.01 PC 2.64 3.06 163.06 0.70 51.19 04:23:55.12 27:49:20.53
1685.01 CP 1.32 0.67 204.71 0.46 37.62 04:34:22.55 43:02:13.34
1693.01 CP 1.42 1.77 57.02 0.46 30.79 06:01:14 34:46:23.13
1696.01 CP 3.17 2.50 13.81 0.28 64.92 04:21:07.36 48:49:11.39
1713.01 PC 4.65 0.56 3415.83 0.95 138.37 06:42:04.94 39:50:34.45
1730.01 PC 2.76 6.23 114.27 0.53 35.69 07:11:27.8 48:19:40.56
3772.01 PC 7.32 4.17 201.89 0.87 309.14 05:44:10.44 36:04:50.35
3795.01 PC 6.47 2.83 462.81 1.01 439.84 06:34:55.79 49:40:35.67
3800.01 PC 5.74 1.67 3970.53 1.40 598.89 06:53:06.26 39:07:56.2
4596.01 PC 2.72 4.12 186.21 0.98 93.49 06:34:49.88 27:23:16.86
4604.01 KP 1.56 2.23 476.88 0.92 90.06 05:05:47.03 21:32:53.52
4610.01 PC 1.56 3.11 114.27 0.69 47.91 05:16:10.38 30:35:06.26
5087.01 KP 3.38 17.31 10.89 0.77 59.25 04:29:39.09 22:52:57.24
5129.01 PC 3.64 7.41 57.53 1.19 201.91 06:38:48.67 29:05:21.56
1459.01 PC 2.49 9.16 66.15 0.82 101.36 01:17:26.83 26:44:45.42
1468.01 CP 2.01 15.53 2.14 0.37 24.74 01:06:36.93 19:13:29.71
1471.01 PC 3.92 20.77 37.34 0.97 67.55 02:03:37.2 21:16:52.78
4511.01 PC 3.09 20.90 42.72 1.00 121.83 03:17:13.27 15:30:06.22
4524.01 CP 1.69 0.93 876.25 1.11 63.68 03:16:42.75 15:39:22.88
4548.01 PC 5.37 4.60 84.87 1.59 165.59 02:25:21.87 25:31:50.44
4607.01 PC 3.08 5.51 262.94 1.31 180.02 01:55:37.25 24:07:05.35
4637.01 PC 2.81 14.35 38.49 0.86 112.15 02:13:03.56 19:24:09.6
4639.01 PC 2.88 3.99 502.42 1.03 205.74 01:49:15.49 21:42:12.57
4649.01 PC 2.75 15.08 68.57 1.01 148.25 01:59:49.57 16:20:48.1
5076.01 PC 3.13 23.44 13.56 0.85 82.86 03:22:02.5 17:14:21.15
5084.01 PC 1.16 5.83 37.73 0.75 21.36 03:03:49.09 20:06:38.12
5319.01 PC 3.75 4.08 38.79 0.48 61.17 02:20:51.25 23:31:13.59
5343.01 PC 2.50 12.84 39.96 0.69 120.86 03:12:06.25 24:32:00.82
5358.01 PC 2.92 2.66 148.44 0.80 138.71 03:36:44.14 28:33:00.97
5553.01 PC 1.55 1.76 439.12 0.81 103.35 02:52:00.52 15:03:20.39
Table 6. Characteristics of primary sources observed in 2022–2023. Columns as in Table 5.
17. A Search for Technosignatures Around TESS exoplanets with the GBT 17
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