Based on photometric observations by TESS, we present the discovery of a Venussized planet transiting LHS 475, an M3 dwarf located 12.5 pc from the Sun. The mass
of the star is 0.274 ± 0.015 M. The planet, originally reported as TOI 910.01, has an
orbital period of 2.0291025 ± 0.0000020 days and an estimated radius of 0.955 ± 0.053
R⊕. We confirm the validity and source of the transit signal with MEarth ground-based
follow-up photometry of five individual transits. We present radial velocity data from
CHIRON that rule out massive companions. In accordance with the observed massradius distribution of exoplanets as well as planet formation theory, we expect this
Venus-sized companion to be terrestrial, with an estimated RV semi-amplitude close to
1.0 m/s. LHS 475 b is likely too hot to be habitable but is a suitable candidate for
emission and transmission spectroscopy.
Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-...Sérgio Sacani
The main scientific goal of TESS is to find planets smaller than Neptune around stars bright enough to allow further characterization studies. Given
our current instrumentation and detection biases, M dwarfs are prime targets to search for small planets that are in (or nearby) the habitable zone
of their host star. Here we use photometric observations and CARMENES radial velocity measurements to validate a pair of transiting planet
candidates found by TESS. The data was fitted simultaneously using a Bayesian MCMC procedure taking into account the stellar variability
present in the photometric and spectroscopic time series. We confirm the planetary origin of the two transiting candidates orbiting around TOI-
2095 (TIC 235678745). The star is a nearby M dwarf (d = 41:90 0:03 pc, Te = 3759 87 K, V = 12:6 mag) with a stellar mass and radius
of M? = 0:44 0:02 M and R? = 0:44 0:02 R, respectively. The planetary system is composed of two transiting planets: TOI-2095b with an
orbital period of Pb = 17:66484 (7 105) days and TOI-2095c with Pc = 28:17232 (14 105) days. Both planets have similar sizes with
Rb = 1:250:07 R and Rc = 1:330:08 R for planet b and c, respectively.We put upper limits on the masses of these objects with Mb < 4:1 M
for the inner and Mc < 7:4 M for the outer planet (95% confidence level). These two planets present equilibrium temperatures in the range of 300
- 350 K and are close to the inner edge of the habitable zone of their star.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
Refined parameters of the HD 22946 planetary system and the true orbital peri...Sérgio Sacani
Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period
planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared
to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star
around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital
period of the outermost planet d was unknown until now.
Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d
and to refine the orbital and planetary properties of the system, especially the radii of the planets.
Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS.
We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and
then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky
Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in
order to obtain final planetary and system parameters.
Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d
to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and
2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ
upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO
radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host
star.
Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission
spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar
confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and
internal structure.
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
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.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Two warm Neptunes transiting HIP 9618 revealed by TESS and CheopsSérgio Sacani
HIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright (G = 9.0 mag) solar analogue. TESS photometry revealed the
star to have two candidate planets with radii of 3.9 ± 0.044 R⊕ (HIP 9618 b) and 3.343 ± 0.039 R⊕ (HIP 9618 c). While the
20.77291 d period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-d gap
in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of
period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d.
High-resolution spectroscopy with HARPS-N, SOPHIE, and CAFE revealed a mass of 10.0 ± 3.1M⊕ for HIP 9618 b, which,
according to our interior structure models, corresponds to a 6.8 ± 1.4 per cent gas fraction. HIP 9618 c appears to have a lower
mass than HIP 9618 b, with a 3-sigma upper limit of <18M⊕. Follow-up and archival RV measurements also reveal a clear
long-term trend which, when combined with imaging and astrometric information, reveal a low-mass companion (0.08+0.12
−0.05M)
orbiting at 26.0+19.0 −11.0 au. This detection makes HIP 9618 one of only five bright (K < 8 mag) transiting multiplanet systems known
to host a planet with P > 50 d, opening the door for the atmospheric characterization of warm (Teq < 750 K) sub-Neptunes.
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.
Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-...Sérgio Sacani
The main scientific goal of TESS is to find planets smaller than Neptune around stars bright enough to allow further characterization studies. Given
our current instrumentation and detection biases, M dwarfs are prime targets to search for small planets that are in (or nearby) the habitable zone
of their host star. Here we use photometric observations and CARMENES radial velocity measurements to validate a pair of transiting planet
candidates found by TESS. The data was fitted simultaneously using a Bayesian MCMC procedure taking into account the stellar variability
present in the photometric and spectroscopic time series. We confirm the planetary origin of the two transiting candidates orbiting around TOI-
2095 (TIC 235678745). The star is a nearby M dwarf (d = 41:90 0:03 pc, Te = 3759 87 K, V = 12:6 mag) with a stellar mass and radius
of M? = 0:44 0:02 M and R? = 0:44 0:02 R, respectively. The planetary system is composed of two transiting planets: TOI-2095b with an
orbital period of Pb = 17:66484 (7 105) days and TOI-2095c with Pc = 28:17232 (14 105) days. Both planets have similar sizes with
Rb = 1:250:07 R and Rc = 1:330:08 R for planet b and c, respectively.We put upper limits on the masses of these objects with Mb < 4:1 M
for the inner and Mc < 7:4 M for the outer planet (95% confidence level). These two planets present equilibrium temperatures in the range of 300
- 350 K and are close to the inner edge of the habitable zone of their star.
A nearby yoiung_m_dwarf_with_wide_possibly_planetary_m_ass_companionSérgio Sacani
O objeto de massa planetária J2126, anteriormente pensado como sendo um planeta solitário, orbita sua estrela mãe na maior órbita já descoberta até agora no universo, de acordo com uma equipe de astrônomos liderada pelo Dr. Niall Deacon, da Universidade de Hertfordshire, no Reino Unido.
O J2126, cujo nome completo é 2MASS J21265040-8140293, tem cerca de 13 vezes a massa de Júpiter.
Sua órbita é de aproximadamente 6900 Unidades Astronômicas de distância da sua estrela, a TYC 9486-927-1, uma estrela ativa, de rotação rápida e classificada como sendo do tipo Anã-M.
Essa é uma órbita 6900 vezes maior que a distância da Terra ao Sol, ou seja, aproximadamente 1 trilhão de quilômetros. Nessa sua órbita, o planeta leva 900000 anos para completar uma volta ao redor da sua estrela.
Refined parameters of the HD 22946 planetary system and the true orbital peri...Sérgio Sacani
Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period
planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared
to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star
around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital
period of the outermost planet d was unknown until now.
Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d
and to refine the orbital and planetary properties of the system, especially the radii of the planets.
Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS.
We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and
then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky
Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in
order to obtain final planetary and system parameters.
Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d
to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and
2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ
upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO
radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host
star.
Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission
spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar
confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and
internal structure.
The atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
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.
Detection of solar_like_oscillations_in_relies_of_the_milk_way_asteroseismolo...Sérgio Sacani
Asteroseismic constraints on K giants make it possible to infer radii, masses and ages of tens
of thousands of field stars. Tests against independent estimates of these properties are however
scarce, especially in the metal-poor regime. Here, we report the detection of solar-like
oscillations in 8 stars belonging to the red-giant branch and red-horizontal branch of the globular
cluster M4. The detections were made in photometric observations from the K2 Mission
during its Campaign 2. Making use of independent constraints on the distance, we estimate
masses of the 8 stars by utilising different combinations of seismic and non-seismic inputs.
When introducing a correction to the Δν scaling relation as suggested by stellar models, for
RGB stars we find excellent agreement with the expected masses from isochrone fitting, and
with a distance modulus derived using independent methods. The offset with respect to independent
masses is lower, or comparable with, the uncertainties on the average RGB mass
(4 − 10%, depending on the combination of constraints used). Our results lend confidence to
asteroseismic masses in the metal poor regime. We note that a larger sample will be needed
to allow more stringent tests to be made of systematic uncertainties in all the observables
(both seismic and non-seismic), and to explore the properties of RHB stars, and of different
populations in the cluster.
Two warm Neptunes transiting HIP 9618 revealed by TESS and CheopsSérgio Sacani
HIP 9618 (HD 12572, TOI-1471, TIC 306263608) is a bright (G = 9.0 mag) solar analogue. TESS photometry revealed the
star to have two candidate planets with radii of 3.9 ± 0.044 R⊕ (HIP 9618 b) and 3.343 ± 0.039 R⊕ (HIP 9618 c). While the
20.77291 d period of HIP 9618 b was measured unambiguously, HIP 9618 c showed only two transits separated by a 680-d gap
in the time series, leaving many possibilities for the period. To solve this issue, CHEOPS performed targeted photometry of
period aliases to attempt to recover the true period of planet c, and successfully determined the true period to be 52.56349 d.
High-resolution spectroscopy with HARPS-N, SOPHIE, and CAFE revealed a mass of 10.0 ± 3.1M⊕ for HIP 9618 b, which,
according to our interior structure models, corresponds to a 6.8 ± 1.4 per cent gas fraction. HIP 9618 c appears to have a lower
mass than HIP 9618 b, with a 3-sigma upper limit of <18M⊕. Follow-up and archival RV measurements also reveal a clear
long-term trend which, when combined with imaging and astrometric information, reveal a low-mass companion (0.08+0.12
−0.05M)
orbiting at 26.0+19.0 −11.0 au. This detection makes HIP 9618 one of only five bright (K < 8 mag) transiting multiplanet systems known
to host a planet with P > 50 d, opening the door for the atmospheric characterization of warm (Teq < 750 K) sub-Neptunes.
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.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-...Sérgio Sacani
We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby
spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in
the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs
and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data
reach 3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances,
structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations
(age ∼12 Gyr, [M/H] −1.5) and have sizes (rh ∼ 110–3000 pc) and luminosities (MV ∼ −7 to −12 mag) largely
consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered
beyond the Local Group. We also use archival H I data to place limits on the gas content of our discoveries. Deep
imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity
function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
Photoevaporation is a potential explanation for several features within exoplanet demographics. Atmospheric escape
observed in young Neptune-sized exoplanets can provide insight into and characterize which mechanisms drive this
evolution and at what times they dominate. AU Mic b is one such exoplanet, slightly larger than Neptune (4.19 R⊕).
It closely orbits a 23 Myr pre-main-sequence M dwarf with an orbital period of 8.46 days. We obtained two visits of
AU Mic b at Lyα with Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph. One flare within the
first HST visit is characterized and removed from our search for a planetary transit. We present a nondetection in our
first visit, followed by the detection of escaping neutral hydrogen ahead of the planet in our second visit. The outflow
absorbed ∼30% of the star’s Lyα blue wing 2.5 hr before the planet’s white-light transit. We estimate that the
highest-velocity escaping material has a column density of 1013.96 cm−2 and is moving 61.26 km s−1 away from the
host star. AU Mic b’s large high-energy irradiation could photoionize its escaping neutral hydrogen in 44 minutes,
rendering it temporarily unobservable. Our time-variable Lyα transit ahead of AU Mic b could also be explained by
an intermediate stellar wind strength from AU Mic that shapes the escaping material into a leading tail. Future Lyα
observations of this system will confirm and characterize the unique variable nature of its Lyα transit, which,
combined with modeling, will tune the importance of stellar wind and photoionization.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
An Earth-sized exoplanet with a Mercury-like compositionSérgio Sacani
Earth, Venus, Mars and some extrasolar terrestrial planets1
have a mass and radius that is consistent with a mass fraction
of about 30% metallic core and 70% silicate mantle2
. At the
inner frontier of the Solar System, Mercury has a completely
different composition, with a mass fraction of about 70%
metallic core and 30% silicate mantle3
. Several formation or
evolution scenarios are proposed to explain this metal-rich
composition, such as a giant impact4, mantle evaporation5
or the depletion of silicate at the inner edge of the protoplanetary
disk6. These scenarios are still strongly debated.
Here, we report the discovery of a multiple transiting planetary
system (K2-229) in which the inner planet has a radius
of 1.165 ± 0.066 Earth radii and a mass of 2.59 ± 0.43 Earth
masses. This Earth-sized planet thus has a core-mass fraction
that is compatible with that of Mercury, although it was
expected to be similar to that of Earth based on host-star
chemistry7
. This larger Mercury analogue either formed with
a very peculiar composition or has evolved, for example, by
losing part of its mantle. Further characterization of Mercurylike
exoplanets such as K2-229 b will help to put the detailed
in situ observations of Mercury (with MESSENGER and
BepiColombo8) into the global context of the formation and
evolution of solar and extrasolar terrestrial planets.
The Possible Tidal Demise of Kepler’s First Planetary SystemSérgio Sacani
We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet
(1.1RJ, 5.9MJ) orbiting an evolved host star (2.9Re, 1.5Me). Using transit timing measurements from Kepler,
Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate = -
+ P 131 22
20 ms yr−1
, corresponding to an infall timescale P P » 2.5 Myr. We consider other explanations for the
data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed
period derivative implies a tidal quality factor
¢ = ´ -
+ Q 2.50 10 0.62
0.85 4, in good agreement with theoretical
predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire
inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for
the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new
benchmark for understanding tidal physics at the end of the planetary life cycle
Discovery of rotational modulations in the planetary mass companion 2m1207b i...Sérgio Sacani
Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties
of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution.
Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We
present here, for the first time, time-resolved high-precision photometric measurements of a planetarymass
companion, 2M1207b. We observed the binary system with HST/WFC3 in two bands and with
two spacecraft roll angles. Using point spread function-based photometry, we reach a nearly photonnoise
limited accuracy for both the primary and the secondary. While the primary is consistent with
a flat light curve, the secondary shows modulations that are clearly detected in the combined light
curve as well as in di↵erent subsets of the data. The amplitudes are 1.36% in the F125W and 0.78%
in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period
of 10.7+1.2
−0.6 hours and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b
is very similar to a field brown dwarf that has identical spectral type but di↵erent J-H color. Importantly,
our study also measures, for the first time, the rotation period for a directly imaged extra-solar
planetary-mass companion.
A Spatially Resolved Analysis of Star Formation Burstiness by Comparing UV an...Sérgio Sacani
The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields
(UVCANDELS) program provides Hubble Space Telescope (HST)/UVIS F275W imaging for four CANDELS
fields. We combine this UV imaging with existing HST/near-IR grism spectroscopy from 3D-HST+AGHAST to
directly compare the resolved rest-frame UV and Hα emission for a sample of 979 galaxies at 0.7 < z < 1.5,
spanning a range in stellar mass of 108−11.5 Me. Using a stacking analysis, we perform a resolved comparison
between homogenized maps of rest-UV and Hα to compute the average UV-to-Hα luminosity ratio (an indicator of
burstiness in star formation) as a function of galactocentric radius. We find that galaxies below stellar mass of
∼109.5 Me, at all radii, have a UV-to-Hα ratio higher than the equilibrium value expected from constant star
formation, indicating a significant contribution from bursty star formation. Even for galaxies with stellar mass
109.5 Me, the UV-to-Hα ratio is elevated toward their outskirts (R/Reff > 1.5), suggesting that bursty star
formation is likely prevalent in the outskirts of even the most massive galaxies, but is likely overshadowed by their
brighter cores. Furthermore, we present the UV-to-Hα ratio as a function of galaxy surface brightness, a proxy for
stellar mass surface density, and find that regions below ∼107.5 Me kpc−2 are consistent with bursty star formation,
regardless of their galaxy stellar mass, potentially suggesting that local star formation is independent of global
galaxy properties at the smallest scales. Last, we find galaxies at z > 1.1 to have bursty star formation, regardless of
radius or surface brightness.
The pristine nature of SMSS 1605−1443 revealed by ESPRESSOSérgio Sacani
SMSS J160540.18−144323.1 is the carbon-enhanced metal-poor (CEMP) star with the lowest iron abundance ever measured, [Fe/H] =
−6.2, which was first reported with the SkyMapper telescope. The carbon abundance is A(C) ≈ 6.1 in the low-C band, as the majority of the stars
in this metallicity range. Yet, constraining the isotopic ratio of key species, such as carbon, sheds light on the properties and origin of these elusive
stars.
Aims. We performed high-resolution observations of SMSS 1605−1443 with the ESPRESSO spectrograph to look for variations in the radial
velocity (vrad) with time. These data have been combined with older MIKE and UVES archival observations to enlarge the temporal baseline. The
12C/
13C isotopic ratio is also studied to explore the possibility of mass transfer from a binary companion.
Methods. A cross-correlation function against a natural template was applied to detect vrad variability and a spectral synthesis technique was used
to derive 12C/
13C in the stellar atmosphere.
Results. We confirm previous indications of binarity in SMSS 1605−1443 and measured a lower limit 12C/
13C > 60 at more than a 3σ confidence
level, proving that this system is chemically unmixed and that no mass transfer from the unseen companion has happened so far. Thus, we confirm
the CEMP-no nature of SMSS 1605−1443 and show that the pristine chemical composition of the cloud from which it formed is currently imprinted
in its stellar atmosphere free of contamination.
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.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
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.
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AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-...Sérgio Sacani
We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby
spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in
the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs
and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data
reach 3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances,
structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations
(age ∼12 Gyr, [M/H] −1.5) and have sizes (rh ∼ 110–3000 pc) and luminosities (MV ∼ −7 to −12 mag) largely
consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered
beyond the Local Group. We also use archival H I data to place limits on the gas content of our discoveries. Deep
imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity
function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come
The Variable Detection of Atmospheric Escape around the Young, Hot Neptune AU...Sérgio Sacani
Photoevaporation is a potential explanation for several features within exoplanet demographics. Atmospheric escape
observed in young Neptune-sized exoplanets can provide insight into and characterize which mechanisms drive this
evolution and at what times they dominate. AU Mic b is one such exoplanet, slightly larger than Neptune (4.19 R⊕).
It closely orbits a 23 Myr pre-main-sequence M dwarf with an orbital period of 8.46 days. We obtained two visits of
AU Mic b at Lyα with Hubble Space Telescope (HST)/Space Telescope Imaging Spectrograph. One flare within the
first HST visit is characterized and removed from our search for a planetary transit. We present a nondetection in our
first visit, followed by the detection of escaping neutral hydrogen ahead of the planet in our second visit. The outflow
absorbed ∼30% of the star’s Lyα blue wing 2.5 hr before the planet’s white-light transit. We estimate that the
highest-velocity escaping material has a column density of 1013.96 cm−2 and is moving 61.26 km s−1 away from the
host star. AU Mic b’s large high-energy irradiation could photoionize its escaping neutral hydrogen in 44 minutes,
rendering it temporarily unobservable. Our time-variable Lyα transit ahead of AU Mic b could also be explained by
an intermediate stellar wind strength from AU Mic that shapes the escaping material into a leading tail. Future Lyα
observations of this system will confirm and characterize the unique variable nature of its Lyα transit, which,
combined with modeling, will tune the importance of stellar wind and photoionization.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
An Earth-sized exoplanet with a Mercury-like compositionSérgio Sacani
Earth, Venus, Mars and some extrasolar terrestrial planets1
have a mass and radius that is consistent with a mass fraction
of about 30% metallic core and 70% silicate mantle2
. At the
inner frontier of the Solar System, Mercury has a completely
different composition, with a mass fraction of about 70%
metallic core and 30% silicate mantle3
. Several formation or
evolution scenarios are proposed to explain this metal-rich
composition, such as a giant impact4, mantle evaporation5
or the depletion of silicate at the inner edge of the protoplanetary
disk6. These scenarios are still strongly debated.
Here, we report the discovery of a multiple transiting planetary
system (K2-229) in which the inner planet has a radius
of 1.165 ± 0.066 Earth radii and a mass of 2.59 ± 0.43 Earth
masses. This Earth-sized planet thus has a core-mass fraction
that is compatible with that of Mercury, although it was
expected to be similar to that of Earth based on host-star
chemistry7
. This larger Mercury analogue either formed with
a very peculiar composition or has evolved, for example, by
losing part of its mantle. Further characterization of Mercurylike
exoplanets such as K2-229 b will help to put the detailed
in situ observations of Mercury (with MESSENGER and
BepiColombo8) into the global context of the formation and
evolution of solar and extrasolar terrestrial planets.
The Possible Tidal Demise of Kepler’s First Planetary SystemSérgio Sacani
We present evidence of tidally-driven inspiral in the Kepler-1658 (KOI-4) system, which consists of a giant planet
(1.1RJ, 5.9MJ) orbiting an evolved host star (2.9Re, 1.5Me). Using transit timing measurements from Kepler,
Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate = -
+ P 131 22
20 ms yr−1
, corresponding to an infall timescale P P » 2.5 Myr. We consider other explanations for the
data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed
period derivative implies a tidal quality factor
¢ = ´ -
+ Q 2.50 10 0.62
0.85 4, in good agreement with theoretical
predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire
inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for
the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new
benchmark for understanding tidal physics at the end of the planetary life cycle
Discovery of rotational modulations in the planetary mass companion 2m1207b i...Sérgio Sacani
Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties
of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution.
Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We
present here, for the first time, time-resolved high-precision photometric measurements of a planetarymass
companion, 2M1207b. We observed the binary system with HST/WFC3 in two bands and with
two spacecraft roll angles. Using point spread function-based photometry, we reach a nearly photonnoise
limited accuracy for both the primary and the secondary. While the primary is consistent with
a flat light curve, the secondary shows modulations that are clearly detected in the combined light
curve as well as in di↵erent subsets of the data. The amplitudes are 1.36% in the F125W and 0.78%
in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period
of 10.7+1.2
−0.6 hours and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b
is very similar to a field brown dwarf that has identical spectral type but di↵erent J-H color. Importantly,
our study also measures, for the first time, the rotation period for a directly imaged extra-solar
planetary-mass companion.
A Spatially Resolved Analysis of Star Formation Burstiness by Comparing UV an...Sérgio Sacani
The UltraViolet imaging of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey Fields
(UVCANDELS) program provides Hubble Space Telescope (HST)/UVIS F275W imaging for four CANDELS
fields. We combine this UV imaging with existing HST/near-IR grism spectroscopy from 3D-HST+AGHAST to
directly compare the resolved rest-frame UV and Hα emission for a sample of 979 galaxies at 0.7 < z < 1.5,
spanning a range in stellar mass of 108−11.5 Me. Using a stacking analysis, we perform a resolved comparison
between homogenized maps of rest-UV and Hα to compute the average UV-to-Hα luminosity ratio (an indicator of
burstiness in star formation) as a function of galactocentric radius. We find that galaxies below stellar mass of
∼109.5 Me, at all radii, have a UV-to-Hα ratio higher than the equilibrium value expected from constant star
formation, indicating a significant contribution from bursty star formation. Even for galaxies with stellar mass
109.5 Me, the UV-to-Hα ratio is elevated toward their outskirts (R/Reff > 1.5), suggesting that bursty star
formation is likely prevalent in the outskirts of even the most massive galaxies, but is likely overshadowed by their
brighter cores. Furthermore, we present the UV-to-Hα ratio as a function of galaxy surface brightness, a proxy for
stellar mass surface density, and find that regions below ∼107.5 Me kpc−2 are consistent with bursty star formation,
regardless of their galaxy stellar mass, potentially suggesting that local star formation is independent of global
galaxy properties at the smallest scales. Last, we find galaxies at z > 1.1 to have bursty star formation, regardless of
radius or surface brightness.
The pristine nature of SMSS 1605−1443 revealed by ESPRESSOSérgio Sacani
SMSS J160540.18−144323.1 is the carbon-enhanced metal-poor (CEMP) star with the lowest iron abundance ever measured, [Fe/H] =
−6.2, which was first reported with the SkyMapper telescope. The carbon abundance is A(C) ≈ 6.1 in the low-C band, as the majority of the stars
in this metallicity range. Yet, constraining the isotopic ratio of key species, such as carbon, sheds light on the properties and origin of these elusive
stars.
Aims. We performed high-resolution observations of SMSS 1605−1443 with the ESPRESSO spectrograph to look for variations in the radial
velocity (vrad) with time. These data have been combined with older MIKE and UVES archival observations to enlarge the temporal baseline. The
12C/
13C isotopic ratio is also studied to explore the possibility of mass transfer from a binary companion.
Methods. A cross-correlation function against a natural template was applied to detect vrad variability and a spectral synthesis technique was used
to derive 12C/
13C in the stellar atmosphere.
Results. We confirm previous indications of binarity in SMSS 1605−1443 and measured a lower limit 12C/
13C > 60 at more than a 3σ confidence
level, proving that this system is chemically unmixed and that no mass transfer from the unseen companion has happened so far. Thus, we confirm
the CEMP-no nature of SMSS 1605−1443 and show that the pristine chemical composition of the cloud from which it formed is currently imprinted
in its stellar atmosphere free of contamination.
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.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
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.
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.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Efficient spin-up of Earth System Models usingsequence accelerationSérgio Sacani
Marine and terrestrial biogeochemical models are key components of the Earth System Models (ESMs) used toproject future environmental changes. However, their slow adjustment time also hinders effective use of ESMsbecause of the enormous computational resources required to integrate them to a pre-industrial equilibrium. Here,a solution to this "spin-up" problem based on "sequence acceleration", is shown to accelerate equilibration of state-of-the-art marine biogeochemical models by over an order of magnitude. The technique can be applied in a "blackbox" fashion to existing models. Even under the challenging spin-up protocols used for Intergovernmental Panelon Climate Change (IPCC) simulations, this algorithm is 5 times faster. Preliminary results suggest that terrestrialmodels can be similarly accelerated, enabling a quantification of major parametric uncertainties in ESMs, improvedestimates of metrics such as climate sensitivity, and higher model resolution than currently feasible.
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
This presentation explores a brief idea about the structural and functional attributes of nucleotides, the structure and function of genetic materials along with the impact of UV rays and pH upon them.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Comparative structure of adrenal gland in vertebrates
LHS 475 b: A Venus-sized Planet Orbiting a Nearby M Dwarf
1. Draft version April 5, 2023
Typeset using L
A
TEX preprint style in AASTeX631
LHS 475 b: A Venus-sized Planet Orbiting a Nearby M Dwarf
Kristo Ment ,1 David Charbonneau ,1 Jonathan Irwin,1 Jennifer G. Winters ,1, 2
Emily Pass ,1 Avi Shporer ,3 Zahra Essack ,3, 4 Veselin B. Kostov ,5, 6
Michelle Kunimoto ,3 Alan Levine ,3 Sara Seager ,3, 7, 8 Roland Vanderspek ,3 and
Joshua N. Winn 9
1
Center for Astrophysics | Harvard & Smithsonian, 60 Garden Street, Cambridge, MA 02138, USA
2
Williams College, 880 Main Street, Williamstown, MA 01267, USA
3
Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of
Technology, Cambridge, MA 02139, USA
4
Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA
02139, USA
5
NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
6
SETI Institute, 189 Bernardo Ave, Suite 200, Mountain View, CA 94043, USA
7
Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA
02139, USA
8
Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
9
Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
(Received April 5, 2023)
Submitted to AJ
ABSTRACT
Based on photometric observations by TESS, we present the discovery of a Venus-
sized planet transiting LHS 475, an M3 dwarf located 12.5 pc from the Sun. The mass
of the star is 0.274 ± 0.015 M . The planet, originally reported as TOI 910.01, has an
orbital period of 2.0291025 ± 0.0000020 days and an estimated radius of 0.955 ± 0.053
R⊕. We confirm the validity and source of the transit signal with MEarth ground-based
follow-up photometry of five individual transits. We present radial velocity data from
CHIRON that rule out massive companions. In accordance with the observed mass-
radius distribution of exoplanets as well as planet formation theory, we expect this
Venus-sized companion to be terrestrial, with an estimated RV semi-amplitude close to
1.0 m/s. LHS 475 b is likely too hot to be habitable but is a suitable candidate for
emission and transmission spectroscopy.
1. INTRODUCTION
The Transiting Exoplanet Survey Satellite (TESS; Ricker et al. 2015) was launched in 2018 and
has already yielded a plethora of planet discoveries. At the time of this writing, there are 326
Corresponding author: Kristo Ment
kristo.ment@cfa.harvard.edu
arXiv:2304.01920v1
[astro-ph.EP]
4
Apr
2023
2. 2
confirmed TESS planets as well as thousands of TESS Objects of Interest (TOIs) still awaiting
validation. Of particular interest are planets transiting nearby red dwarfs due to the relatively larger
size of the planet compared to the star. This leads to a larger transit depth, facilitating planet
detection. It also increases the feasibility for detailed atmospheric characterization of the planet via
transit spectroscopy, which is among the goals of the recently launched James Webb Space Telescope
(JWST). Only a handful of stars with masses below 0.3 M located within 15 pc of the Sun are
known to host transiting planets: GJ 1132 (Berta-Thompson et al. 2015), GJ 1214 (Charbonneau
et al. 2009), LHS 1140 (Dittmann et al. 2017; Ment et al. 2019), LHS 3844 (Vanderspek et al. 2019),
LTT 1445A (Winters et al. 2019; Winters et al. 2022), TOI 540 (Ment et al. 2021), and TRAPPIST-1
(Gillon et al. 2016, 2017).
Follow-up observations of TOIs, typically by ground-based observatories, are essential for multiple
reasons. Firstly, they provide an independent validation of the transiting planet, ruling out in-
strument systematics as the cause of the transit-like signal. Secondly, the sky-projected size of each
individual TESS pixel is large (2100
×2100
) and typically contains many background light sources in ad-
dition to the intended target. Subsequently, follow-up observations are crucial to exclude background
stars (including unresolved eclipsing binaries) as potential sources of the transit signal. Thirdly,
ground-based photometric observations are a relatively cost-effective way to increase the total num-
ber of observed transits, leading to more precise estimates for modeled system parameters as well as
refined ephemerides, which are often essential for planning additional follow-up observations. Finally,
spectroscopic follow-up observations can yield estimates for the planet’s mass, a crucial parameter
that cannot be determined from transit photometry.
The vast majority of confirmed transiting planets have estimated radii larger than that of the
Earth. Only six sub-Earth-sized planets are currently known to orbit stars within a distance of 15
pc from the Sun, including GJ 367 b (Lam et al. 2021), L 98-59 b (Kostov et al. 2019), TOI 540 b
(Ment et al. 2021), and TRAPPIST-1 d, e, and h (Gillon et al. 2016, 2017; Agol et al. 2021). Unlike
planets substantially larger than Earth, sub-Earth-sized planets are likely too small to hold on to a
substantial volatile envelope, and therefore they are highly likely to be terrestrial in nature with a
mostly rocky interior composition. The existence of a population of terrestrial planets distinct from
larger sub-Neptunes and water worlds is evidenced by the bimodal radius distribution of planets
(Owen & Wu 2013; Fulton et al. 2017). The gap between the two populations occurs at planet radii
of 1.6-2.0 R⊕ for Sun-like stars (Fulton & Petigura 2018) and moves down to 1.5 R⊕ for M dwarfs
(Cloutier & Menou 2020), with planets below these radii mainly expected to have terrestrial bulk
compositions (Weiss & Marcy 2014; Dressing et al. 2015; Rogers 2015). Therefore, we expect a sub-
Earth-sized planet to be terrestrial with a high degree of confidence even in the absence of a mass
estimate from radial velocity or transit timing variation data.
Here we present the discovery and subsequent ground-based validation observations of LHS 475 b,
a Venus-sized planet orbiting a nearby M dwarf. Section 2 describes the properties of the host star.
Section 3 summarizes various data sets used in this study. We describe our modeling procedure in
Section 4 and present results in Section 5. Finally, Section 6 summarizes the article and offers a brief
discussion.
2. STELLAR PARAMETERS OF LHS 475
LHS 475 (also known as 2MASS J19205439-8233170 and L 22-69) is a main-sequence red dwarf
belonging to the M3 spectral class (Hawley et al. 1996). Based on the trigonometric parallax of
3. 3
π = 80.113±0.021 mas from Gaia Data Release 3 (Gaia Collaboration et al. 2016, 2022), we calculate
a distance of 12.482 ± 0.003 pc. Gaia DR3 determined its proper motion to be µα = 342.30 ± 0.03
mas yr−1
and µδ = −1230.30 ± 0.02 mas yr−1
.
There are no additional light sources listed within 10” in either the 2MASS catalog or the TESS
Input Catalog (TIC). Leveraging the high proper motion of the target, we used archival images from
the Two Micron All-Sky Survey (2MASS; Skrutskie et al. 2006) as well as the Digitized Sky Survery
(DSS) to rule out the presence of any distant background stars at the location of LHS 475 at the
time of the observations presented in this paper (years 2019-2021). The 2MASS images were taken
in year 2000 while the DSS images are from years 1976-1999. While there are no visible sources
in the 2MASS J, H, and K images, the bluer DSS images do reveal an additional light source at
a sky-projected distance of 7” from LHS 475 at the time of the observations. We later identified
this background source within the Gaia DR3 catalog with an ID of 6347643496607834880. It has a
BP − RP color of 1.05 mag, in contrast to the BP − RP = 2.73 mag estimate for LHS 475. It is
6.7 magnitudes fainter than LHS 475 in the Gaia bandpass, and based on the color difference, we
estimate a difference close to 8 magnitudes in the TESS and MEarth bandpasses. As a result, this
object would be too faint to produce the planetary transits described within this work. We further
investigate the presence of other nearby bright objects in Section 3.4.
We adopt a K-band apparent brightness of K = 7.686 ± 0.042 mag from 2MASS, yielding an
absolute brightness of MK = 7.205 ± 0.042 mag. We also adopt J and H-band fluxes from 2MASS
and V RI-photometry from Jao et al. (2011). Using the mass-luminosity relation for main-sequence
M dwarfs in Benedict et al. (2016), we estimate a stellar mass of M = 0.274 ± 0.015 M . We use
two independent radius-mass relations to estimate the stellar radius: we obtain R = 0.281 ± 0.013
R from optical interferometry of single stars (Boyajian et al. 2012) and R = 0.291 ± 0.014 R from
eclipsing binary measurements (Bayless & Orosz 2006). We combine the two and adopt a weighted
average of R = 0.286 ± 0.010 R as the final radius. We check for consistency with the mass-radius
relation for M dwarfs by Mann et al. (2015) which yields R = 0.287 ± 0.026 R .
We employ bolometric corrections (BC) to determine the luminosity of LHS 475. We use Table
5 of Pecaut & Mamajek (2013) to interpolate between the V − K color and BCV , obtaining a
V -band correction value of BCV = −2.35 mag and a bolometric luminosity of L = 0.00907 L .
Next, we apply the third-order polynomial fit between V − J and BCV in Mann et al. (2015, and
subsequent erratum) to derive BCV = −2.25 and L = 0.00829 L . Finally, the relationship between
BCK and I − K in Leggett et al. (2001) produces BCK = 2.70 and L = 0.00870 L . We adopt
as the stellar luminosity the average of the three estimates; therefore, L = 0.00869 ± 0.00039 L .
The uncertainty in L was taken from the unbiased sample variance of the individual estimates. We
then proceed to use the Stefan-Boltzmann law to determine the effective stellar surface temperature,
obtaining Teff = 3295 ± 68 K. This result was based on the solar values of Mbol, = 4.7554 mag and
Teff, = 5772 K published by Mamajek (2012).
LHS 475 appears to be a magnetically quiet star. The CHIRON spectra (described in Section 3.3)
do not show evidence of rotational broadening, and Hα is in absorption. LHS 475 has a previously
determined photometric rotation period of Prot = 79.3 days (Newton et al. 2018), consistent with its
relative inactivity. It also flares relatively infrequently; specifically, the star has an estimated flare
rate of ln R31,5 = −11.90 ± 0.79 where R31,5 is the number of flares per day with total energy above
3.16 × 1031
ergs in the TESS bandpass (Medina et al. 2020).
4. 4
While M dwarfs do slowly spin down as they evolve, accurately determining their age is known
to be a difficult endeavor. For the slowest-rotating mid-to-late M dwarfs (Prot > 70 days), galactic
kinematics suggests a mean age of 5+4
−2 Gyr (Newton et al. 2016). More recently, Medina et al. (2022)
used galactic kinematics to derive a mean age of 5.6±2.7 Gyr for mid-to-late M dwarfs with rotation
periods between 10-90 days while such stars with Prot > 90 days would have an estimated age of
12.9 ± 3.5 Gyr. Ultimately, we are unable to ascertain the age of LHS 475, but it is unlikely to be
less than a few billion years old.
3. DATA
3.1. TESS
The Transiting Exoplanet Survey Satellite (TESS) gathered photometric measurements of LHS 475
during its Prime Mission (observation sectors 12 and 13) as well as its first Extended Mission (sectors
27 and 39). These observations span a Barycentric Julian Date (BJD) range of 2458625.0-2459389.7
between May 2019 and June 2021. The target was included in the TESS Input Catalog (TIC) with a
TIC ID of 369327947 as well as the original TESS Candidate Target List (CTL; Stassun et al. 2018).
LHS 475 was also included in TESS Guest Investigator Programs G011180 (PI: Courtney Dressing)
and G011231 (PI: Jennifer Winters). The observations were made with a two-minute cadence during
the Prime Mission and a 20-second cadence within the Extended Mission. We utilize photometric
data reduced by the NASA Ames Science Processing Operations Center (SPOC) pipeline (Jenkins
et al. 2016). Specifically, we adopt the Pre-search Data Conditioning Simple Aperture Photometry
(PDCSAP; Smith et al. 2012; Stumpe et al. 2012, 2014) two-minute cadence version of the light curve
which has been cotrended and corrected for instrument systematics as well as crowding: unresolved
light from other sources that fall within the same TESS CCD pixel. We exclude 6 measurements
that were marked through the SPOC Data Quality Flags to correspond to impulsive outliers (cadence
quality flag bit 10). We also manually exclude a section of the data at the end of sector 27 spanning
the BJD range 2459059.5-2459060.2 (comprising 0.68% of the total number of data points) due to a
strong negative trend in the observed flux that is indicative of spacecraft systematics. The remaining
data set contains a total of 73,604 individual measurements.
SPOC initially detected a transit-like signal in phase-folded sector 12 data and the TESS team
dubbed the planet candidate TESS Object of Interest (TOI) 910.01. The accompanying Data Vali-
dation Report (DVR; Twicken et al. 2018; Li et al. 2019) cited a candidate period of 2.029 days, a
transit depth close to 1100 parts per million (ppm), and a transit signal-to-noise ratio (SNR) of 12.0
based on 12 transits from sector 12. The detected signal passed preliminary validation tests and had
a very low bootstrap false alarm probability, favoring the hypothesis that TOI 910.01 indeed repre-
sents a planet. An updated DVR from SPOC based on all four observation sectors later updated the
orbital period to P = 2.029088 ± 0.000006 days, the transit depth to 978 ± 73 ppm, and the SNR to
19.3 based on a total of 45 transits. We note that despite the availability of 20-second cadence data
from the Extended Mission, SPOC only performs a transit search in the 2-minute cadence version of
those data. Either cadence is much shorter than the fitted transit duration of 41.6 minutes.
Since the estimated rotation period of LHS 475 (Prot = 79.3 days) is substantially longer than
the duration of a single TESS sector, we do not attempt to include an explicit model for the quasi-
periodic flux variation caused by stellar rotation. Instead, we de-trend the light curve using a sliding
median with a fixed width of 12 hours. This approach has the benefit of smoothing out any long-
5. 5
Figure 1. TESS photometry of LHS 475 in Sectors 12, 13, 27, and 39. The black line represents the fitted
baseline as described in Section 3.1.
term variations while not affecting the light curve on short timescales (e.g. the estimated duration
of a transit). We provide a plot of the TESS light curve as well as the fitted baseline within each
observation sector in Figure 1. All the TESS data used in this paper can be found in MAST:
10.17909/bmdh-kd60.
3.2. MEarth
We obtained follow-up observations for five individual transits of LHS 475 b with the ground-based
MEarth-South telescope array (Nutzman & Charbonneau 2008; Berta et al. 2012; Irwin et al. 2015).
The MEarth-South array consisted of eight robotically controlled 40-centimeter telescopes at the
Cerro Tololo Inter-American Observatory in Chile. Each telescope was equipped with a CCD camera
that is sensitive to red optical and near-infrared light. The observations took place in August and
September of 2019; the corresponding Barycentric Julian Date (BJD) range is 2458717.5-2458727.8.
A total of 7 individual telescopes were used concurrently to monitor the star during transit events,
and a separate light curve was produced for each telescope as a result of the data reduction process.
We perform aperture photometry with fixed aperture radii of 12, 17, 24, and 34 pixels (at a scale
of 0.8400
per pixel) and verify that the transit signal persists regardless of the choice of aperture. We
also generate light curves for every detected light source within 2.50
of LHS 475 and verify that the
6. 6
transit signal is not present in any of them. We adopt an aperture radius of 12 pixels (or 10.0800
) for
the remainder of the analysis.
The MEarth light curves need to be detrended to account for atmospheric effects and telescope
systematics. We begin by estimating a full transit duration of Tfull = 40.0 minutes based on the
TESS data. For each observed transit, we fit a baseline to the MEarth light curve, including all
points within 2Tfull of the transit midpoint t0 while excluding the transit window itself; that is, we
include every observation timestamp t such that
0.5 ≤
t − t0
Tfull
≤ 2
In order to best describe the behavior of each transit’s baseline, we utilize several competing models.
Specifically, we fit each baseline with a constant, linear, and quadratic function. We adopt the model
with the lowest value for the Bayesian information criterion (BIC) which accounts for the number of
model parameters. We display the detrended transit light curves in Figure 2. The baselines for the
first two of the five transits were fit with a linear function while the remaining three were detrended
using a quadratic function.
LHS 475 was monitored as part of the MEarth survey from October 2016 until August 2018. Over
that time, the star accumulated 12,836 photometric observations. However, LHS 475 b was not
detected by the MEarth team due to the small transit depth induced by the planet (approx. 1 ppt)
and the relatively low cadence of observations. While the planet remained undetected, this data
set enabled the critical photometric determination of the stellar rotation period of 79.317 days by
Newton et al. (2018).
3.3. CHIRON
We utilized the CHIRON spectrograph (Tokovinin et al. 2013) mounted on the 1.5-meter SMARTS
telescope at the Cerro Tololo Inter-American Observatory (CTIO) to gather 7 reconnaissance spectra
of LHS 475. Four of these spectra were obtained as part of the volume-complete spectroscopic
survey of nearby mid-to-late M dwarfs by Winters et al. (2021). We carried out the observations
between August 2018 and June 2021. We produced radial velocities (RVs) from each of the spectra
according to the reduction methods described in detail in Pass et al. (2023, submitted). The reduction
process involves performing a cross-correlation between the CHIRON spectra and a set of rotationally
broadened templates of inactive stars over wavelength ranges in the regime of 6400-7850 Å. We provide
a list of relative RVs in Table 1 and display the entire RV time series in Figure 3. Note that the
quoted RVs do not include a derived systemic RV of −10.3 ± 0.5 km/s, where the RV uncertainty is
dominated by the cross-correlation process. We also adopt a noise floor of 20 m/s based on instrument
instability for mid-to-late M dwarfs (Pass et al. 2023, submitted).
The RV time series does not show any evidence of an overall trend, which would point to the
existence of a massive companion. The RMS of the RVs is 22.1 m/s, very close to the quoted
individual RV uncertainties. In addition, we are able to rule out companions more massive than 0.20
Jupiter masses at the orbital period of the planet with 99.73% (3σ) confidence. We obtained this
value by fitting an RV model with the orbital period, eccentricity, and time of mid-transit fixed to
the values given in Table 2 and calculating the required RV semi-amplitude such that the χ2
values
of the fits, each with NRV − 1 degrees of freedom, have associated p-values below 0.0027.
7. 7
Figure 2. MEarth-South follow-up photometry of five individual transits of LHS 475. The Barycentric
Julian Date values (BJD) within the plots denote the times of transit midpoints. The vertical dashed lines
encompass the full transit duration. The solid line depicts the best-fit model for all MEarth data; it is
identical to the model in the middle panel of Figure 5 and is further described in Section 5.2.
8. 8
Figure 3. Relative radial velocities of LHS 475 from CHIRON. The estimated systemic velocity is −10.3±0.5
km/s.
Table 1. CHIRON relative RVs of
LHS 475
BJD (TDB) RV Uncertainty
(m/s) (m/s)
2458332.6635 -26 20
2458650.7860 41 26
2458701.7103 -4 20
2458707.6332 2 20
2458718.6361 8 20
2458724.5771 28 27
2459367.7897 -18 20
The spectra show Hα in absorption. Medina et al. (2020) obtained an Hα equivalent width of
0.26 ± 0.09 Å using a subset of these spectra.
9. 9
0.0 0.2 0.4 0.6 0.8 1.0 1.2
angular separation (arcsec)
0
1
2
3
4
5
6
7
m
562 nm
832 nm
LHS0475
1"
832 nm
Figure 4. Speckle imaging sensitivity curves of LHS 475 utilizing the 562 nm (blue line) and 832 nm (red
line) bandpasses. No nearby light sources are detected.
3.4. Zorro
We performed speckle imaging observations of LHS 475 with the Zorro dual-channel imager on
the 8.1-meter Gemini South telescope in Chile (program number GS-2019A-Q-302, PI: Winters).
The star was observed on 18 July 2019 in the 562 nm and 832 nm bandpasses. The images are
diffraction-limited with an estimated FWHM of 0.0200
. We provide the detection sensitivity curve
and the auto-correlation function of the imaging data in Figure 4. No nearby light sources (within
1.200
, corresponding to 15 AU) are detected in either band down to an estimated contrast ∆m of 4.88
mag (562 nm) or 5.87 mag (832 nm) at 0.500
from the star.
4. MODELING
We utilize the exoplanet package (Foreman-Mackey et al. 2021; Foreman-Mackey et al. 2021) in
Python for transit modeling purposes. exoplanet employs the modeling framework of the PyMC
Python library (Salvatier et al. 2016) and uses Theano (Theano Development Team 2016) for compu-
10. 10
tationally efficient Markov Chain Monte Carlo sampling. Limb-darkened transit signals are computed
analytically by the open-source starry package (Luger et al. 2019).
We adopt an identical light curve and transit model for TESS and MEarth data sets, constraining
the modeled parameters with various prior probability distributions. Specifically, the stellar mass
and radius are constrained with Gaussian priors; in each case, the location and width of the prior
matches the estimated value from Section 2. Gaussian priors are also included for the orbital period
P and time of mid-transit t0, although the posterior distributions for either parameter constrain
these values much more tightly. We impose a uniform prior on the planet-to-star radius ratio with
a domain of r/R ∈ [0, 0.1]. Conditioned on the value of r/R, the prior distribution for the impact
parameter b is distributed uniformly between 0 and 1 + r/R. We also include a loose Gaussian prior
centered at a value of 1 on the baseline relative flux of the light curve.
We opt for a quadratic limb darkening model for the stellar surface. The limb darkening coefficients
(u1, u2) are taken from Table 15 of Claret (2018) based on the spherical PHOENIX-COND model
(Husser et al. 2013). Specifically, we adopt u1 = 0.1529 and u2 = 0.4604 which correspond to a surface
gravity of log g = 5.0 and a surface temperature of 3300 K. The metallicity is implicitly assumed
to be equal to the Solar value. While these coefficients were computed for the TESS bandpass, the
MEarth spectral response is sufficiently similar to the one employed by TESS such that we have
not found meaningful differences in the estimated limb darkening coefficients in previous works (e.g.
Ment et al. 2021).
The eccentricity e was fixed to a value of 0 as planets orbiting this close to their stars are expected
to be tidally circularized. In order to estimate the tidal circularization timescale τe, we utilize a
simplified equation that Rasio et al. (1996) adopted based on the work by Goldreich & Soter (1966):
1
τe
≡ −
1
e
de
dt
≈
63
4Q
r
GM
a3
M
m
r
a
5
where Q is the specific dissipation parameter, m and r are the planet’s mass and radius, M is the
stellar mass, and a is the semi-major axis. Assuming an Earth-mass planet and Q 500 (an upper
limit based on terrestrial Solar System planets and satellites), we find τe 9 Myr, much less than
the probable age of the system. Thus, we expect the orbit to be close to circular.
We perform separate model optimization and sampling runs for three different data sets: (1) TESS
photometry, (2) MEarth photometry, and (3) a combined set of TESS and MEarth data. The initial
optimization is carried out by PyMC3 using a limited memory Broyden-Fletcher-Goldfarb-Shanno
(BFGS) algorithm and it returns a local maximum a posteriori (MAP) estimate. We then draw
1000 samples from the posterior, starting at the MAP point, after tuning for 500 iterations before
sampling. We utilize multiprocess sampling with 2 chains, resulting in a total of 2000 drawn samples.
We then adopt the mean and standard deviation from the marginal distributions of each variable.
We present the results of the modeling in the following section.
5. RESULTS
5.1. TESS only
Fitting the model with the four sectors of TESS data alone yields a tightly constrained ephemeris
with an orbital period of P = 2.0291019 ± 0.0000025 days and a transit mid-point BJD of t0 =
2, 458, 626.20451 ± 0.00045. The orbital period is roughly 2σ away from the SPOC estimate quoted
11. 11
Figure 5. Phase-folded photometry of LHS 475 highlighting the 3-hour window surrounding the planetary
transits. Solid lines depict a best-fit model using the maximum a posteriori (MAP) estimates of the orbital
period P and planet radius R. We produce separate subplots for TESS data (top panel), MEarth data
(middle panel), and the combined TESS MEarth data set (bottom panel).
in Section 3.1. Apart from differences in modeling and sampling, this discrepancy could be affected
by the data selection process: the SPOC analysis excluded chunks of data at the beginning and end
of each sector due to spurious flux trendlines caused by instrumental systematics. We successfully
de-trended most of these regions. We obtain a fitted planetary radius of r = 0.955±0.056 R⊕ and an
impact parameter of b = 0.731 ± 0.035. We plot a phase-folded version of our best-fit model utilizing
TESS data in the top panel of Figure 5.
5.2. MEarth only
Repeating the modeling and sampling process with the MEarth data set (consisting of follow-up
light curves of five individual transits), we estimate an orbital period of P = 2.02894 ± 0.00015 days
and a transit mid-point BJD of t0 = 2, 458, 626.2104 ± 0.0065. These values are consistent within 1σ
with the TESS-based results in the previous section. We calculate a planet radius of r = 0.990±0.070
R⊕; however, the best-fit maximum a posteriori (MAP) estimate is 0.95R⊕. Both of these values are
12. 12
consistent with TESS data. The fitted impact parameter from MEarth data is b = 0.753 ± 0.064.
The phase-folded model based on the MAP estimate is displayed in the middle panel of Figure 5.
5.3. Combined TESS MEarth
Noting that the calculated parameter values yielded by the two data sets are remarkably consistent,
we optimize the model again for the combined TESS MEarth light curves in order to produce final
estimates for the model parameters. This produces an orbital period of P = 2.0291025 ± 0.0000020
days and a transit mid-point BJD of t0 = 2, 458, 626.20421 ± 0.00029. We find a planetary radius of
r = 0.955 ± 0.053 R⊕ and an impact parameter of b = 0.705 ± 0.037, corresponding to an inclination
angle of i = 87.44 ± 0.27 degrees. These values are consistent with previous estimates, with the
uncertainties in the transit ephemeris largely set by the TESS light curve due to the substantially
larger number of observed transits and a longer time baseline within that data set. The best-fit
combined model is displayed in the bottom panel of Figure 5. We adopt the values from the combined
analysis as final estimates for LHS 475 b. The values for the system parameters are summarized in
Table 2.
6. DISCUSSION AND CONCLUSION
LHS 475 b is a Venus-sized planet orbiting a nearby magnetically quiet M dwarf. Its host star has
an estimated luminosity equal to 0.9% of the Solar value and it is located at a distance of 12.5 pc
from the Sun. We determine an orbital period of P = 2.0291025 ± 0.0000020 days (corresponding
to an a/R-ratio of 15.77 ± 0.77) which is short enough for the planet to be tidally locked with a
high degree of confidence1
. Thus, the planet is likely to have an uneven surface temperature, with
the exact temperature profile dependent on the composition and dynamics of the planetary surface
and atmosphere. However, we can make a first-order estimate by assuming that the planet absorbs
all incoming stellar radiation hitting its cross-section and produces black body radiation uniformly
from its entire surface according to the Stefan-Boltzmann law. The estimated incident bolometric
flux at the planet’s orbit is S = 20.8 ± 1.1 S⊕. Balancing the input and output energy fluxes yields
an estimated equilibrium temperature of Teq = 587 ± 18 K for a zero-albedo surface, Teq = 537 ± 16
K for an Earth-like Bond albedo (AB = 0.3), and Teq = 407 ± 12 K for a Venusian Bond albedo
(AB = 0.77). All of these values are too high for the planet to be habitable in the traditional sense.
Furthermore, if the absorbed incident radiation is emitted from the dayside only (as would be the
case with tidal locking and zero heat redistribution), the dayside temperatures would be 19% higher
than the values quoted above.
However, hot effective surface temperatures make the planet more amenable to characterization
via emission and transmission spectroscopy during its transits. Adopting the Kempton et al. (2018)
framework for a zero-albedo model with full day-night heat redistribution, we obtain a transmission
spectroscopic metric (TSM) value of 27.7 (assuming the appropriate scale factor of 0.19). TSM is
proportional to the expected transmission spectroscopy S/N. This quoted value places LHS 475 b
among a group of other nearby small planets that are promising targets for transit spectroscopy,
such as TRAPPIST-1 c (estimated TSM of 24.1; Gillon et al. 2017; Agol et al. 2021) and LHS 1140
c (TSM = 25.4; Ment et al. 2019). We note that transmission spectroscopy observations of LHS
1
We use Eq. 3 of Pierrehumbert Hammond (2019), based on the results of Goldreich Soter (1966), to estimate a
tidal locking timescale of 290 years for LHS 475 b.
13. 13
Table 2. System parameters for LHS 475
Parameter Values for LHS 475 Sourcea
Stellar parameters
Right ascension (J2000) 19h 20min 54.38s (1)
Declination (J2000) -82◦
33’ 16.17” (1)
Proper motion (mas yr−1
)
µα = 342.30 ± 0.03
(1)
µδ = −1230.30 ± 0.02
Apparent brightness (mag)
V = 12.69 ± 0.03 (2)
R = 11.51 ± 0.03 (2)
I = 10.00 ± 0.03 (2)
J = 8.555 ± 0.030 (3)
H = 8.004 ± 0.038 (3)
K = 7.686 ± 0.042 (3)
Distance (pc) 12.482 ± 0.003 (1)
Mass (M ) 0.274 ± 0.015 (4)
Radius (R ) 0.286 ± 0.010 (4)
Luminosity (L ) 0.00869 ± 0.00039 (4)
Effective temperature (K) 3295 ± 68 (4)
Rotational period (days) 79.317 (5)
Parameter Values for LHS 475 b
Modeled transit parameters
Orbital period P (days) 2.0291025 ± 0.0000020
Eccentricity e 0 (fixed)
Time of mid-transit t0 (BJD) 2458626.20421 ± 0.00029
Impact parameter b 0.705 ± 0.037
Planet-to-star radius ratio r/R 0.03124 ± 0.00065
a/R ratio 15.77 ± 0.77
Derived planetary parameters
Radius r (R⊕) 0.955 ± 0.053
Semi-major axis a (AU) 0.02042 ± 0.00036
Inclination i (deg) 87.44 ± 0.27
Bolometric incident flux S (S⊕) 20.8 ± 1.1
Equilibrium temperatureb Teq (K) 587 ± 18
a(1) Gaia DR3, (2) Jao et al. (2011), (3) 2MASS, (4) This work, (5) Newton
et al. (2018).
bThe equilibrium temperature assumes a Bond albedo of 0. For an albedo
of A, the reported temperature has to be multiplied by (1 − A)1/4
.
475 b were recently conducted with the James Webb Space Telescope during two planetary transits
(Lustig-Yaeger et al. 2023, under review). We can similarly calculate the emission spectroscopic
metric (ESM) and find that ESM = 5.2 for LHS 475 b, comparable to LHS 1445A b (ESM = 5.7;
Winters et al. 2019; Winters et al. 2022).
14. 14
Due to its tidal locking, LHS 475 b is also a feasible target for photometric thermal emission
measurements with JWST during a secondary eclipse. Such observations can quantify the amount
of heat redistibution between the dayside and the nightside, which can be used to constrain the
presence of an optically thick planetary atmosphere. Among the known terrestrial planets orbiting
nearby stars, LHS 3844 b is the only planet where a thick atmosphere has been ruled out (Kreidberg
et al. 2019; Diamond-Lowe et al. 2020). The surface insolation of LHS 475 b is lower than that of
LHS 3844 b, making the former more likely to retain an atmosphere. If an atmosphere were to be
found on LHS 475 b, it would place an important constraint on atmospheric escape in terrestrial
planets. Furthermore, we note that LHS 475 b has a very similar radius and surface insolation to
TOI 540 b (Ment et al. 2021); however, the latter is orbiting an M dwarf that is still within the
magnetically active phase of its evolution. Consequently, a comparative study of the two planets’
atmospheres could yield an important before-and-after test for atmospheric escape.
Our best estimate for the radius of LHS 475 b is r = 0.955 ± 0.053 R⊕. A similar value can
be independently derived from either TESS photometry (see Section 5.1) or MEarth photometry
(Section 5.2) alone with remarkable consistency, demonstrating the power of targeted ground-based
follow-up observations to confirm the validity of TESS planet candidates. Unfortunately, the existing
radial velocity data of LHS 475 does not have the necessary precision to calculate the mass of the
planet. As explained in Section 1, planets of this size are highly likely to be terrestrial. Given that
the planet is close in size to Earth, it is not unreasonable to suppose that it might also have a similar
interior composition. Adopting a simple two-layer composition model with an Earth-like core mass
fraction (CMF) of 0.33, we invert the empirical radius-mass relation by Zeng et al. (2016) and derive
a planetary mass of 0.84 M⊕.2
Subsequently, we estimate that the radial velocity signal induced by
LHS 475 b will have a semi-amplitude of 1.0 m/s. This level of precision is achievable with current
state-of-the-art RV instruments but would likely require a substantial amount of observation time.
2
Adopting a Venusian CMF of 0.31 yields a similar mass estimate of 0.83 M⊕.
15. 15
The MEarth team acknowledges funding from the David and Lucile Packard Fellowship for Science
and Engineering (awarded to DC). This material is based on work supported by the National Science
Foundation under grants AST-0807690, AST-1109468, AST-1004488 (Alan T. Waterman Award)
and AST-1616624. This publication was made possible through the support of a grant from the John
Templeton Foundation. The opinions expressed in this publication are those of the authors and do
not necessarily reflect the views of the John Templeton Foundation. This material is based upon work
supported by the National Aeronautics and Space Administration under Grant No. 80NSSC18K0476
issued through the XRP Program. Funding for the TESS mission is provided by NASA’s Science
Mission Directorate. We acknowledge the use of public TESS data from pipelines at the TESS Science
Office and at the TESS Science Processing Operations Center. This paper includes data collected by
the TESS mission that are publicly available from the Mikulski Archive for Space Telescopes (MAST).
This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.
cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, https:
//www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by
national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
This publication makes use of data products from the Two Micron All Sky Survey, which is a joint
project of the University of Massachusetts and the Infrared Processing and Analysis Center/California
Institute of Technology, funded by the National Aeronautics and Space Administration and the
National Science Foundation. Some of the observations in the paper made use of the High-Resolution
Imaging instrument Zorro. Zorro was funded by the NASA Exoplanet Exploration Program and built
at the NASA Ames Research Center by Steve B. Howell, Nic Scott, Elliott P. Horch, and Emmett
Quigley. Zorro was mounted on the Gemini South telescope of the international Gemini Observatory,
a program of NSF’s NOIRLab, which is managed by the Association of Universities for Research in
Astronomy (AURA) under a cooperative agreement with the National Science Foundation on behalf
of the Gemini partnership: the National Science Foundation (United States), National Research
Council (Canada), Agencia Nacional de Investigación y Desarrollo (Chile), Ministerio de Ciencia,
Tecnologı́a e Innovación (Argentina), Ministério da Ciência, Tecnologia, Inovações e Comunicações
(Brazil), and Korea Astronomy and Space Science Institute (Republic of Korea). We thank the
RECONS team (http://www.recons.org/) for CHIRON support. We thank the Cerro Tololo Inter-
American Observatory (CTIO) TelOps team for MEarth support. This research made use of exoplanet
(Foreman-Mackey et al. 2021; Foreman-Mackey et al. 2021) and its dependencies (Agol et al. 2020;
Kumar et al. 2019; Astropy Collaboration et al. 2013, 2018; Luger et al. 2019; Salvatier et al. 2016;
Theano Development Team 2016).
Facilities: MEarth, TESS, CTIO:1.5m (CHIRON), Gemini:South (Zorro)
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