This document summarizes an analysis of high resolution infrared spectra from the Cassiopeia A supernova remnant taken by the Spitzer Space Telescope. The analysis finds:
1) The reverse shock of the remnant is spherical to within 7%, though offset from the geometric center by 810 km/s.
2) Nucleosynthetic layers of Si and O show velocities differing by up to 500 km/s in some directions, indicating separation during the supernova.
3) Small-scale corrugated velocity structures seen in the ejecta likely formed during the supernova rather than by later instabilities at the remnant's reverse shock.
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
1. Chandra observations of the galaxy NGC 3351 revealed X-ray emission from its circumnuclear star-forming ring that is composed of numerous point-like sources embedded in diffuse hot gas.
2. The morphology of the X-ray emission is similar to but not identical with UV and H-alpha hot spots in the ring, which can be understood if star formation occurs through intermittent starbursts around the ring with different emissions tracing later evolutionary stages.
3. X-ray emission also extends beyond the ring, which is interpreted as outflowing gas from the ring into the disk and halo of NGC 3351, providing evidence for confined outflow near the plane but less restricted outflow perpendicular to
The tumbling rotational state of 1I/‘OumuamuaSérgio Sacani
The discovery1
of 1I/2017 U1 (1I/‘Oumuamua) has provided
the first glimpse of a planetesimal born in another planetary
system. This interloper exhibits a variable colour within a
range that is broadly consistent with local small bodies, such
as the P- and D-type asteroids, Jupiter Trojans and dynamically
excited Kuiper belt objects2–7
. 1I/‘Oumuamua appears
unusually elongated in shape, with an axial ratio exceeding
5:1 (refs 1,4,5,8). Rotation period estimates are inconsistent
and varied, with reported values between 6.9 and 8.3 h
(refs 4–6,9). Here, we analyse all the available optical photometry
data reported to date. No single rotation period can explain
the exhibited brightness variations. Rather, 1I/‘Oumuamua
appears to be in an excited rotational state undergoing nonprincipal
axis rotation, or tumbling. A satisfactory solution
has apparent lightcurve frequencies of 0.135 and 0.126 h−1
and
implies a longest-to-shortest axis ratio of ≳5:1, although the
available data are insufficient to uniquely constrain the true
frequencies and shape. Assuming a body that responds to
non-principal axis rotation in a similar manner to Solar System
asteroids and comets, the timescale to damp 1I/‘Oumuamua’s
tumbling is at least one billion years. 1I/‘Oumuamua was
probably set tumbling within its parent planetary system and
will remain tumbling well after it has left ours.
This document summarizes a study that identified 195 compact elliptical galaxies across different environments using data from optical and ultraviolet sky surveys. The researchers constructed the sample by selecting galaxies that were outliers from the universal color-magnitude relation and had small sizes and high stellar velocity dispersions based on spectral modeling. They found that 7 of the galaxies were isolated, not belonging to any known galaxy groups. For these isolated galaxies, the researchers identified possible host galaxies located up to 3.3 Mpc away. The stellar populations of the isolated compact elliptical galaxies were found to be similar to those in galaxy groups and clusters, suggesting a common formation mechanism.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
The auroral footprint of enceladus on saturn nature09928Sérgio Sacani
The document reports the detection of magnetic-field-aligned ion and electron beams downstream of Enceladus, indicating electrodynamic coupling between Enceladus and Saturn similar to Io and Jupiter. Auroral ultraviolet emission was observed in Saturn's ionosphere at the footprint location of Enceladus, varying in intensity more than can be explained by changes in magnetospheric parameters alone and likely indicating variable plume activity on Enceladus. The footprint latitude matches predictions based on Saturn's magnetic field model. Flickering of the electron beams between different energy levels was also observed and may be related to standing Alfven waves driven by Enceladus.
A higher efficiency_of_converting_gas_to_stars_push_galaxies_at_z_1_6_well_ab...Sérgio Sacani
Galáxias formando estrelas em taxas extremas a nove bilhões de anos atrás eram mais eficientes do que a média das galáxias atuais, descobriram os pesquisadores.
A maioria das estrelas acredita-se localizam-se na sequência principal onde quanto maior a massa da galáxia, mais eficiente ela é na formação de novas estrelas. Contudo, de vez em quando uma galáxia apresentará uma explosão de novas estrelas que brilham mais do que o resto. Uma colisão entre duas grandes galáxias é normalmente a causa dessas fases de explosões de formação de estrelas, onde o gás frio que reside nas grandes nuvens moleculares torna-se o combustível para sustentar essas altas taxas de formação de estrelas.
A questão que os astrônomos têm feito é se essas explosões de estrelas no início o universo foram o resultado de se ter um suprimento de gás abundante, ou se as galáxias convertiam o gás de maneira mais eficiente.
Um novo estudo, publicado no Astrophysical Journal Letters de 15 de Outubro, liderado por John Silverman, do Kavli Institute for Physics and Mathematics of the Universe, estudou o conteúdo do gás monóxido de carbono (CO) em sete galáxias de explosão de estrelas muito distantes, quando o universo tinha apenas 4 bilhões de anos de vida. Isso foi possível devido a capacidade do Atacama Large Millimiter/Submillimiter Array (ALMA), localizado no platô no topo da montanha no Chile, que trabalha para detectar as ondas eletromagnéticas no comprimento de onda milimétrico (importante para se estudar o gás molecular) e um nível de sensibilidade que só agora começa a ser explorado pelos astrônomos.
Os pesquisadores descobriram que a quantidade de gás CO emitido já tinha diminuído, mesmo apesar da galáxia continuar a formar estrelas em altas taxas. Essas observações são similares àquelas registradas para as galáxias de explosões de estrelas próximas da Terra atualmente, mas a quantidade da depleção de gás não foi tão rápida quanto se esperava. Isso levou os pesquisadores a concluírem que poderia haver um contínuo aumento na eficiência, dependendo em de quanto acima da taxa de se formar estrelas ela está da sequência principal.
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
1. Chandra observations of the galaxy NGC 3351 revealed X-ray emission from its circumnuclear star-forming ring that is composed of numerous point-like sources embedded in diffuse hot gas.
2. The morphology of the X-ray emission is similar to but not identical with UV and H-alpha hot spots in the ring, which can be understood if star formation occurs through intermittent starbursts around the ring with different emissions tracing later evolutionary stages.
3. X-ray emission also extends beyond the ring, which is interpreted as outflowing gas from the ring into the disk and halo of NGC 3351, providing evidence for confined outflow near the plane but less restricted outflow perpendicular to
The tumbling rotational state of 1I/‘OumuamuaSérgio Sacani
The discovery1
of 1I/2017 U1 (1I/‘Oumuamua) has provided
the first glimpse of a planetesimal born in another planetary
system. This interloper exhibits a variable colour within a
range that is broadly consistent with local small bodies, such
as the P- and D-type asteroids, Jupiter Trojans and dynamically
excited Kuiper belt objects2–7
. 1I/‘Oumuamua appears
unusually elongated in shape, with an axial ratio exceeding
5:1 (refs 1,4,5,8). Rotation period estimates are inconsistent
and varied, with reported values between 6.9 and 8.3 h
(refs 4–6,9). Here, we analyse all the available optical photometry
data reported to date. No single rotation period can explain
the exhibited brightness variations. Rather, 1I/‘Oumuamua
appears to be in an excited rotational state undergoing nonprincipal
axis rotation, or tumbling. A satisfactory solution
has apparent lightcurve frequencies of 0.135 and 0.126 h−1
and
implies a longest-to-shortest axis ratio of ≳5:1, although the
available data are insufficient to uniquely constrain the true
frequencies and shape. Assuming a body that responds to
non-principal axis rotation in a similar manner to Solar System
asteroids and comets, the timescale to damp 1I/‘Oumuamua’s
tumbling is at least one billion years. 1I/‘Oumuamua was
probably set tumbling within its parent planetary system and
will remain tumbling well after it has left ours.
This document summarizes a study that identified 195 compact elliptical galaxies across different environments using data from optical and ultraviolet sky surveys. The researchers constructed the sample by selecting galaxies that were outliers from the universal color-magnitude relation and had small sizes and high stellar velocity dispersions based on spectral modeling. They found that 7 of the galaxies were isolated, not belonging to any known galaxy groups. For these isolated galaxies, the researchers identified possible host galaxies located up to 3.3 Mpc away. The stellar populations of the isolated compact elliptical galaxies were found to be similar to those in galaxy groups and clusters, suggesting a common formation mechanism.
This document summarizes observations of the debris disk around the subgiant star κ CrB using Herschel and Keck. Herschel spatially resolved images of the debris disk, the first such images of a disk around a subgiant star. Keck radial velocity monitoring provided evidence for a second planetary companion around κ CrB. Keck adaptive optics imaging placed an upper limit on the mass of this companion. Modeling of the Herschel images showed the dust is broadly distributed but could not distinguish between a single wide belt or two narrow belts. The observations are consistent with dynamical depletion or collisional erosion clearing the inner regions of the disk.
This document summarizes the results of a deep near-infrared survey of the Carina Nebula complex using the HAWK-I instrument on the VLT. The survey imaged an area of 0.36 square degrees down to magnitudes of J=23, H=22, and Ks=21, detecting over 600,000 infrared sources. Color-magnitude diagrams of the sources were analyzed to determine properties of the low-mass stellar population such as ages and masses. The survey found that about 3200 sources have masses above 1 solar mass, consistent with expectations from the initial mass function. It also found that about half of the young stars in Carina are in a widely distributed, non-clustered configuration. Six
The auroral footprint of enceladus on saturn nature09928Sérgio Sacani
The document reports the detection of magnetic-field-aligned ion and electron beams downstream of Enceladus, indicating electrodynamic coupling between Enceladus and Saturn similar to Io and Jupiter. Auroral ultraviolet emission was observed in Saturn's ionosphere at the footprint location of Enceladus, varying in intensity more than can be explained by changes in magnetospheric parameters alone and likely indicating variable plume activity on Enceladus. The footprint latitude matches predictions based on Saturn's magnetic field model. Flickering of the electron beams between different energy levels was also observed and may be related to standing Alfven waves driven by Enceladus.
A higher efficiency_of_converting_gas_to_stars_push_galaxies_at_z_1_6_well_ab...Sérgio Sacani
Galáxias formando estrelas em taxas extremas a nove bilhões de anos atrás eram mais eficientes do que a média das galáxias atuais, descobriram os pesquisadores.
A maioria das estrelas acredita-se localizam-se na sequência principal onde quanto maior a massa da galáxia, mais eficiente ela é na formação de novas estrelas. Contudo, de vez em quando uma galáxia apresentará uma explosão de novas estrelas que brilham mais do que o resto. Uma colisão entre duas grandes galáxias é normalmente a causa dessas fases de explosões de formação de estrelas, onde o gás frio que reside nas grandes nuvens moleculares torna-se o combustível para sustentar essas altas taxas de formação de estrelas.
A questão que os astrônomos têm feito é se essas explosões de estrelas no início o universo foram o resultado de se ter um suprimento de gás abundante, ou se as galáxias convertiam o gás de maneira mais eficiente.
Um novo estudo, publicado no Astrophysical Journal Letters de 15 de Outubro, liderado por John Silverman, do Kavli Institute for Physics and Mathematics of the Universe, estudou o conteúdo do gás monóxido de carbono (CO) em sete galáxias de explosão de estrelas muito distantes, quando o universo tinha apenas 4 bilhões de anos de vida. Isso foi possível devido a capacidade do Atacama Large Millimiter/Submillimiter Array (ALMA), localizado no platô no topo da montanha no Chile, que trabalha para detectar as ondas eletromagnéticas no comprimento de onda milimétrico (importante para se estudar o gás molecular) e um nível de sensibilidade que só agora começa a ser explorado pelos astrônomos.
Os pesquisadores descobriram que a quantidade de gás CO emitido já tinha diminuído, mesmo apesar da galáxia continuar a formar estrelas em altas taxas. Essas observações são similares àquelas registradas para as galáxias de explosões de estrelas próximas da Terra atualmente, mas a quantidade da depleção de gás não foi tão rápida quanto se esperava. Isso levou os pesquisadores a concluírem que poderia haver um contínuo aumento na eficiência, dependendo em de quanto acima da taxa de se formar estrelas ela está da sequência principal.
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U...Sérgio Sacani
During the formation and evolution of the Solar System, significant
numbers of cometary and asteroidal bodies were
ejected into interstellar space1,2. It is reasonable to expect that
the same happened for planetary systems other than our own.
Detection of such interstellar objects would allow us to probe
the planetesimal formation processes around other stars, possibly
together with the effects of long-term exposure to the
interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known
interstellar object, discovered by the Pan-STARRS1 telescope
in October 2017 (ref. 3). The discovery epoch photometry
implies a highly elongated body with radii of ~ 200 × 20 m
when a comet-like geometric albedo of 0.04 is assumed. The
observable interstellar object population is expected to be
dominated by comet-like bodies in agreement with our spectra,
yet the reported inactivity of 'Oumuamua implies a lack
of surface ice. Here, we report spectroscopic characterization
of ‘Oumuamua, finding it to be variable with time but similar
to organically rich surfaces found in the outer Solar System.
We show that this is consistent with predictions of an insulating
mantle produced by long-term cosmic ray exposure4.
An internal icy composition cannot therefore be ruled out by
the lack of activity, even though ‘Oumuamua passed within
0.25 au of the Sun.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
Discovery of xray_emission_from_young_suns_in_the_small_magellaniccloudSérgio Sacani
1) The document reports on the discovery of extended X-ray emission from the young star cluster NGC 602a in the Small Magellanic Cloud based on Chandra X-ray Observatory observations.
2) X-ray emission was detected from the cluster core, which has the highest stellar density, and from a surrounding dusty ridge.
3) The X-ray emission from the cluster core is suggested to originate from an ensemble of low- and solar-mass pre-main-sequence stars, while the emission from the dusty ridge is attributed to embedded young stellar objects known from infrared studies.
This document summarizes a study of the Corona Australis star-forming region using data from the Herschel space telescope. Key findings include:
1) Herschel maps reveal many cluster members, including some embedded very low-mass objects, several protostars (some extended), and substantial emission from the surrounding cloud.
2) Striking structures are seen, such as bright filaments around the IRS 5 protostar complex and a bubble-shaped rim associated with the Class I object IRS 2.
3) Disks around Class II objects show a wide range of properties, from massive primordial disks to disks with substantial dust depletion or evidence of inside-out evolution. This indicates a diversity of disk evolution
The document is a collection of images from NASA's Solar and Heliospheric Observatory (SOHO) spacecraft, along with brief captions describing each image. The images show various phenomena on the sun's surface and atmosphere such as solar prominences, the corona, coronal mass ejections, sunspots, and oscillations within the sun's interior. They demonstrate what the sun looks like in different wavelengths of light beyond the visible spectrum.
Probing Extreme Physics With Compact ObjctsSérgio Sacani
This document discusses compact objects like white dwarfs, neutron stars, and black holes, which exist under extreme conditions of density, temperature, gravity, and magnetism. It summarizes key findings and areas of ongoing research regarding these objects. In particular, it highlights how studying the cooling of neutron stars can help constrain their interior physics, and how quantum electrodynamics effects in strong magnetic fields can be probed by observing the spectra and polarization of neutron star atmospheres.
The article discusses observations from multiple space-based observatories that tracked a sun-diving comet, C/2011 N3 (SOHO), as it passed through the Sun's corona and disintegrated. The observatories captured details of the comet's flight path, emissions, and disintegration over time. Studying how comets interact with and break apart in the corona can provide insights into comet composition and the early solar system.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
This document summarizes observations of the exoplanet HD 189733b taken with Chandra and XMM-Newton telescopes. The observations detected X-ray emissions from both the planet-hosting star HD 189733A and its companion star HD 189733B. A transit of HD 189733b in front of its star was detected in soft X-rays, with a transit depth of 6-8% compared to 2.41% in the optical. This is interpreted as evidence for an extended atmosphere around the planet that is opaque to X-rays but transparent at optical wavelengths. The magnetic activity of the companion star HD 189733B was also found to be inconsistent with the activity of the planet-hosting star, possibly due to
Uma espetacular colisão de galáxias foi descoberta além da Via Láctea. O sistema mais próximo já descoberto, a identificação foi anunciada por uma equipe de astrônomos liderada pelo Professor Quentin Parker da Universidade de Hong Kong e pelo Professor Albert Zijlstra na Universidade de Manchester.
A galáxia está a 30 milhões de anos-luz de distância, o que significa que ela é relativamente próxima. Ela foi chamada de Roda de Kathryn, em homenagem à sua semelhança com o famoso fogo de artifício e também em homenagem à esposa do coautor do trabalho.
Esses sistemas são muito raros e nascem da colisão entre duas galáxias de tamanhos similares. As ondas de choque geradas na colisão comprimem o reservatório de gás em cada galáxia e disparam a formação de novas estrelas. Isso cria um espetacular anel de intensa emissão, e ilumina o sistema, do mesmo modo que a Roda Catherine ilumina a noite num show de fogos de artifício.
As galáxias crescem através de colisões, mas é raro registrar esse processo acontecendo, e é extremamente raro ver o anel da colisão em progresso. Pouco mais de 20 sistemas com anéis completos são conhecidos.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
The close circumstellar environment of betelgeuseSérgio Sacani
This document summarizes observations of the red supergiant star Betelgeuse and its circumstellar environment using the VLT/VISIR instrument. Diffraction-limited images were obtained in 6 filters between 7.76-12.81 μm and 2 filters between 17.65-19.50 μm. The images reveal a bright, extended, and complex circumstellar envelope at all wavelengths, pointing to the presence of oxygen-rich dust like silicates. A partial circular shell is observed between 0.5-1.0" from the star, which may correspond to the inner radius of the dust envelope. Several knots and filamentary structures are also identified within the nebula.
The operational environment and rotational acceleration of asteroid (101955) ...Sérgio Sacani
During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation,
Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed
Bennu’s immediate environment, photometric properties, and rotation state. Discovery of
a dusty environment, a natural satellite, or unexpected asteroid characteristics would have
had consequences for the mission’s safety and observation strategy. Here we show that
spacecraft observations during this period were highly sensitive to satellites (sub-meter
scale) but reveal none, although later navigational images indicate that further investigation is
needed. We constrain average dust production in September 2018 from Bennu’s surface
to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric
phase function validates measurements from the pre-encounter astronomical campaign.
We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6
degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with
evolutionary implications.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
This paper analyzes Spitzer observations of the Eagle Nebula to study the energetics and evolution of dust. The observations show a shell of emission within the nebula at mid-IR wavelengths that is distinct from the morphology at longer wavelengths. Spectral energy distributions are measured across the nebula and modeled to constrain dust properties and heating sources. Two possible interpretations are proposed for the nature of the mid-IR shell: 1) dust processing in shocks driven by stellar winds, or 2) emission from a hot plasma where dust is collisionally heated. The goal is to better understand dust evolution in massive star forming regions.
The document summarizes the discovery of transient bright features detected in Titan's northern sea, Ligeia Mare, by the Cassini spacecraft's radar instrument in July 2013. These features were not seen in previous or subsequent observations. The author analyzes potential explanations and argues that the features were likely ephemeral phenomena caused by surface waves, bubbles, or suspended solids. This suggests dynamic processes are starting in Titan's northern lakes and seas as summer approaches in the northern hemisphere.
1. Scientists used stellar occultation to measure the size of the dwarf planet Eris more accurately. They found it has a radius of 1,163 km, smaller than previous estimates, though not definitively smaller than Pluto due to uncertainties in Pluto's size.
2. Surprisingly, Eris' surface was found to be very bright, which could indicate a collapsed or localized atmosphere had recently condensed onto the surface from sublimated ices as Eris moves closer to the Sun in its orbit.
3. The discovery of Eris and other large Kuiper Belt objects has challenged definitions of planets and our understanding of the outer solar system, showing Pluto is not unique and sparking debate about what constitutes
Olivine in an_unexpected_location_on_vesta_surfaceSérgio Sacani
The document reports on the discovery of olivine on the surface of the asteroid Vesta in unexpected locations, based on data from the Dawn spacecraft's VIR instrument. Specifically:
- Olivine was found in the northern hemisphere of Vesta, rather than the southern basins where mantle rocks were expected based on previous models.
- The olivine occurs in large patches hundreds of meters across mixed with howardite regolith, unlike in meteorites where it is a minor component of diogenites.
- The amount and distribution of olivine-rich material suggests a complex evolutionary history for Vesta and is not consistent with previous ideas of olivine occurrence being associated with diogenites
The magnetic field of the irregular galaxy ngc 4214Sérgio Sacani
This document summarizes a study of the magnetic field in the irregular galaxy NGC 4214 using radio continuum polarization data from the Very Large Array. The researchers find that the global radio spectrum shows signs of free-free absorption and synchrotron losses. They estimate the magnetic field strength is 30 ± 9.5 μG in the center and 10 ± 3 μG at the edges. They do not detect significant polarization on scales greater than 200 pc and place an upper limit of 8 μG on any uniform field in the galaxy.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U...Sérgio Sacani
During the formation and evolution of the Solar System, significant
numbers of cometary and asteroidal bodies were
ejected into interstellar space1,2. It is reasonable to expect that
the same happened for planetary systems other than our own.
Detection of such interstellar objects would allow us to probe
the planetesimal formation processes around other stars, possibly
together with the effects of long-term exposure to the
interstellar medium. 1I/2017 U1 ‘Oumuamua is the first known
interstellar object, discovered by the Pan-STARRS1 telescope
in October 2017 (ref. 3). The discovery epoch photometry
implies a highly elongated body with radii of ~ 200 × 20 m
when a comet-like geometric albedo of 0.04 is assumed. The
observable interstellar object population is expected to be
dominated by comet-like bodies in agreement with our spectra,
yet the reported inactivity of 'Oumuamua implies a lack
of surface ice. Here, we report spectroscopic characterization
of ‘Oumuamua, finding it to be variable with time but similar
to organically rich surfaces found in the outer Solar System.
We show that this is consistent with predictions of an insulating
mantle produced by long-term cosmic ray exposure4.
An internal icy composition cannot therefore be ruled out by
the lack of activity, even though ‘Oumuamua passed within
0.25 au of the Sun.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
Discovery of xray_emission_from_young_suns_in_the_small_magellaniccloudSérgio Sacani
1) The document reports on the discovery of extended X-ray emission from the young star cluster NGC 602a in the Small Magellanic Cloud based on Chandra X-ray Observatory observations.
2) X-ray emission was detected from the cluster core, which has the highest stellar density, and from a surrounding dusty ridge.
3) The X-ray emission from the cluster core is suggested to originate from an ensemble of low- and solar-mass pre-main-sequence stars, while the emission from the dusty ridge is attributed to embedded young stellar objects known from infrared studies.
This document summarizes a study of the Corona Australis star-forming region using data from the Herschel space telescope. Key findings include:
1) Herschel maps reveal many cluster members, including some embedded very low-mass objects, several protostars (some extended), and substantial emission from the surrounding cloud.
2) Striking structures are seen, such as bright filaments around the IRS 5 protostar complex and a bubble-shaped rim associated with the Class I object IRS 2.
3) Disks around Class II objects show a wide range of properties, from massive primordial disks to disks with substantial dust depletion or evidence of inside-out evolution. This indicates a diversity of disk evolution
The document is a collection of images from NASA's Solar and Heliospheric Observatory (SOHO) spacecraft, along with brief captions describing each image. The images show various phenomena on the sun's surface and atmosphere such as solar prominences, the corona, coronal mass ejections, sunspots, and oscillations within the sun's interior. They demonstrate what the sun looks like in different wavelengths of light beyond the visible spectrum.
Probing Extreme Physics With Compact ObjctsSérgio Sacani
This document discusses compact objects like white dwarfs, neutron stars, and black holes, which exist under extreme conditions of density, temperature, gravity, and magnetism. It summarizes key findings and areas of ongoing research regarding these objects. In particular, it highlights how studying the cooling of neutron stars can help constrain their interior physics, and how quantum electrodynamics effects in strong magnetic fields can be probed by observing the spectra and polarization of neutron star atmospheres.
The article discusses observations from multiple space-based observatories that tracked a sun-diving comet, C/2011 N3 (SOHO), as it passed through the Sun's corona and disintegrated. The observatories captured details of the comet's flight path, emissions, and disintegration over time. Studying how comets interact with and break apart in the corona can provide insights into comet composition and the early solar system.
“A ring system detected around the Centaur (10199) Chariklo”GOASA
- The Centaur object (10199) Chariklo was observed to occult a star, revealing the presence of two narrow rings around the object.
- The rings have widths of about 7 km and 3 km, and orbital radii of 391 km and 405 km from the center of Chariklo.
- Evidence supports the rings being composed of water ice and their geometry explaining the dimming and changing spectrum of Chariklo observed between 1997 and 2008. The discovery of rings around a minor planet is a first for the Solar System.
This document summarizes observations of the exoplanet HD 189733b taken with Chandra and XMM-Newton telescopes. The observations detected X-ray emissions from both the planet-hosting star HD 189733A and its companion star HD 189733B. A transit of HD 189733b in front of its star was detected in soft X-rays, with a transit depth of 6-8% compared to 2.41% in the optical. This is interpreted as evidence for an extended atmosphere around the planet that is opaque to X-rays but transparent at optical wavelengths. The magnetic activity of the companion star HD 189733B was also found to be inconsistent with the activity of the planet-hosting star, possibly due to
Uma espetacular colisão de galáxias foi descoberta além da Via Láctea. O sistema mais próximo já descoberto, a identificação foi anunciada por uma equipe de astrônomos liderada pelo Professor Quentin Parker da Universidade de Hong Kong e pelo Professor Albert Zijlstra na Universidade de Manchester.
A galáxia está a 30 milhões de anos-luz de distância, o que significa que ela é relativamente próxima. Ela foi chamada de Roda de Kathryn, em homenagem à sua semelhança com o famoso fogo de artifício e também em homenagem à esposa do coautor do trabalho.
Esses sistemas são muito raros e nascem da colisão entre duas galáxias de tamanhos similares. As ondas de choque geradas na colisão comprimem o reservatório de gás em cada galáxia e disparam a formação de novas estrelas. Isso cria um espetacular anel de intensa emissão, e ilumina o sistema, do mesmo modo que a Roda Catherine ilumina a noite num show de fogos de artifício.
As galáxias crescem através de colisões, mas é raro registrar esse processo acontecendo, e é extremamente raro ver o anel da colisão em progresso. Pouco mais de 20 sistemas com anéis completos são conhecidos.
Stellar-like objects with effective temperatures of 2700K and below are referred to as
20 "ultracool dwarfs"1. This heterogeneous group includes both extremely low-mass stars
21 and brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion),
22 and represents about 15% of the stellar-like objects in the vicinity of the Sun2. Based on
23 the small masses and sizes of their protoplanetary disks3,4, core-accretion theory for
24 ultracool dwarfs predicts a large, but heretofore undetected, population of close-in
25 terrestrial planets5, ranging from metal-rich Mercury-sized planets6 to more hospitable
26 volatile-rich Earth-sized planets7. Here we report the discovery of three short-period
27 Earth-sized planets transiting an ultracool dwarf star 12 parsecs away. The inner two
28 planets receive four and two times the irradiation of Earth, respectively, placing them
29 close to the inner edge of the habitable zone of the star8. Eleven orbits remain possible
30 for the third planet based on our data, the most likely resulting in an irradiation
31 significantly smaller than Earth's. The infrared brightness of the host star combined
32 with its Jupiter-like size offer the possibility of constraining the composition and
33 thoroughly characterizing the atmospheric properties of the components of this nearby
34 planetary system, notably to detect potential biosignatures.
The close circumstellar environment of betelgeuseSérgio Sacani
This document summarizes observations of the red supergiant star Betelgeuse and its circumstellar environment using the VLT/VISIR instrument. Diffraction-limited images were obtained in 6 filters between 7.76-12.81 μm and 2 filters between 17.65-19.50 μm. The images reveal a bright, extended, and complex circumstellar envelope at all wavelengths, pointing to the presence of oxygen-rich dust like silicates. A partial circular shell is observed between 0.5-1.0" from the star, which may correspond to the inner radius of the dust envelope. Several knots and filamentary structures are also identified within the nebula.
The operational environment and rotational acceleration of asteroid (101955) ...Sérgio Sacani
During its approach to asteroid (101955) Bennu, NASA’s Origins, Spectral Interpretation,
Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft surveyed
Bennu’s immediate environment, photometric properties, and rotation state. Discovery of
a dusty environment, a natural satellite, or unexpected asteroid characteristics would have
had consequences for the mission’s safety and observation strategy. Here we show that
spacecraft observations during this period were highly sensitive to satellites (sub-meter
scale) but reveal none, although later navigational images indicate that further investigation is
needed. We constrain average dust production in September 2018 from Bennu’s surface
to an upper limit of 150 g s–1 averaged over 34 min. Bennu’s disk-integrated photometric
phase function validates measurements from the pre-encounter astronomical campaign.
We demonstrate that Bennu’s rotation rate is accelerating continuously at 3.63 ± 0.52 × 10–6
degrees day–2, likely due to the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect, with
evolutionary implications.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
This paper analyzes Spitzer observations of the Eagle Nebula to study the energetics and evolution of dust. The observations show a shell of emission within the nebula at mid-IR wavelengths that is distinct from the morphology at longer wavelengths. Spectral energy distributions are measured across the nebula and modeled to constrain dust properties and heating sources. Two possible interpretations are proposed for the nature of the mid-IR shell: 1) dust processing in shocks driven by stellar winds, or 2) emission from a hot plasma where dust is collisionally heated. The goal is to better understand dust evolution in massive star forming regions.
The document summarizes the discovery of transient bright features detected in Titan's northern sea, Ligeia Mare, by the Cassini spacecraft's radar instrument in July 2013. These features were not seen in previous or subsequent observations. The author analyzes potential explanations and argues that the features were likely ephemeral phenomena caused by surface waves, bubbles, or suspended solids. This suggests dynamic processes are starting in Titan's northern lakes and seas as summer approaches in the northern hemisphere.
1. Scientists used stellar occultation to measure the size of the dwarf planet Eris more accurately. They found it has a radius of 1,163 km, smaller than previous estimates, though not definitively smaller than Pluto due to uncertainties in Pluto's size.
2. Surprisingly, Eris' surface was found to be very bright, which could indicate a collapsed or localized atmosphere had recently condensed onto the surface from sublimated ices as Eris moves closer to the Sun in its orbit.
3. The discovery of Eris and other large Kuiper Belt objects has challenged definitions of planets and our understanding of the outer solar system, showing Pluto is not unique and sparking debate about what constitutes
Olivine in an_unexpected_location_on_vesta_surfaceSérgio Sacani
The document reports on the discovery of olivine on the surface of the asteroid Vesta in unexpected locations, based on data from the Dawn spacecraft's VIR instrument. Specifically:
- Olivine was found in the northern hemisphere of Vesta, rather than the southern basins where mantle rocks were expected based on previous models.
- The olivine occurs in large patches hundreds of meters across mixed with howardite regolith, unlike in meteorites where it is a minor component of diogenites.
- The amount and distribution of olivine-rich material suggests a complex evolutionary history for Vesta and is not consistent with previous ideas of olivine occurrence being associated with diogenites
The magnetic field of the irregular galaxy ngc 4214Sérgio Sacani
This document summarizes a study of the magnetic field in the irregular galaxy NGC 4214 using radio continuum polarization data from the Very Large Array. The researchers find that the global radio spectrum shows signs of free-free absorption and synchrotron losses. They estimate the magnetic field strength is 30 ± 9.5 μG in the center and 10 ± 3 μG at the edges. They do not detect significant polarization on scales greater than 200 pc and place an upper limit of 8 μG on any uniform field in the galaxy.
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
This document summarizes the results of a 180 ks Chandra-LETGS observation of Mrk 509 as part of a larger multi-wavelength campaign. The observation detected several absorption features in the X-ray spectrum originating from an ionized absorber, including ions with three distinct ionization degrees. The lowest ionized component is slightly redshifted and not in pressure equilibrium with the others, likely belonging to the host galaxy's interstellar medium. The other two components are outflowing at velocities of around -200 and -455 km/s. Simultaneous HST-COS observations detected 13 UV kinematic components, and at least three can be associated with the X-ray components, providing evidence that the UV and X-
The document presents evidence for azimuthal variations in cosmic ray ion acceleration at the blast wave of the supernova remnant SN 1006. Using radio, X-ray, and optical observations, the researchers find that the ratio of radii between the blast wave and contact discontinuity varies azimuthally, being smallest in the brightest synchrotron emission regions, indicating more efficient cosmic ray acceleration. They interpret this as evidence that the injection rate, magnetic field strength, and turbulence level - which influence cosmic ray acceleration - all vary azimuthally and are highest in the brightest regions.
This paper presents a study of the extended X-ray emission in the Seyfert galaxy NGC 4151 using deep Chandra observations. Key findings include:
1) Emission line maps show strong OVII, OVIII, and NeIX line emission extending along the northeast-southwest direction, consistent with an ionization cone.
2) Spectral analysis finds the extended emission is well described by photoionized plasma models, supporting a dominant role for nuclear photoionization.
3) Faint extended emission is also seen perpendicular to the ionization cone, indicating some leakage of nuclear ionizing radiation through warm absorbers rather than being blocked by an obscuring torus.
This document summarizes a study using deep Chandra observations of the Seyfert 1 galaxy NGC 4151. The observations allow examination of emission line morphology in the inner 150 pc region with high spatial resolution. The maps show structures correlated with the radio outflow and optical emission. There is evidence for jet-gas cloud interactions, including regions with elevated NeIX/OVII ratios and X-ray emission exceeding expectations from nuclear photoionization alone, suggesting collisional ionization. Constraints are also placed on the spatial distribution of iron Kα emission, finding less than 5% originates beyond 150 pc, in disagreement with a prior claim of 65% from larger regions.
The ALMA observations of the Fomalhaut debris disk resolve the ring of parent bodies that produce the dust. The parent body ring has a sharp inner edge at 135 AU and outer edge at 151 AU, giving it a width of 16 AU. The ring has a vertical scale height corresponding to an opening angle of 1 degree. The observations are consistent with the ring being confined by shepherd planets. The dust in the ring has a total mass of 0.017 Earth masses, requiring the parent body population to be at least 1.7 Earth masses.
The document summarizes the first observations of the magnetic Kelvin-Helmholtz instability in the solar corona using high-resolution imaging from NASA's Solar Dynamics Observatory. The instability was detected on the northern flank of a fast coronal mass ejection, appearing as substructures or waves against the darker coronal background. Analysis found the observed phase speed of the waves to be about half the speed of the ejecta front, validating theories of the non-linear dynamics of this instability in magnetized plasma environments. The findings provide new insights into fundamental plasma processes in the solar atmosphere and solar-terrestrial system.
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.
This document summarizes follow-up observations of galaxies selected from WISE as being hyperluminous. The authors observed 14 galaxies at 350-850 μm with SHARC-II and 18 galaxies at 1.1 mm with Bolocam, detecting 9 and 5 galaxies respectively. They also observed 25 targets at 3.6 and 4.5 μm with Spitzer and obtained optical spectra for 12 targets. By combining these data with WISE observations, they constructed mid-IR to millimeter spectral energy distributions that showed hotter dust temperatures than galaxy templates, estimated to be 60-120 K. These galaxies have infrared luminosities over 10^13 solar luminosities and represent an extreme population of luminous, hot dust-ob
The most luminous_galaxies_discovered_by_wiseSérgio Sacani
This document presents a sample of 20 extremely luminous galaxies discovered by the Wide-field Infrared Survey Explorer (WISE). Five of these galaxies have infrared luminosities exceeding 1014 solar luminosities, the highest infrared luminosity threshold yet observed. They were selected using criteria requiring weak or no detection in the first two WISE bands but strong detections in the third and fourth bands. Spectral energy distribution modeling suggests their high luminosities are powered by obscured active galactic nuclei with hot dust temperatures around 450 Kelvin. The existence of such luminous galaxies at redshifts above 3 provides constraints on the early growth of supermassive black holes through rapid accretion.
The first hyper_luminous_infrared_galaxy_discovered_by_wiseSérgio Sacani
This document summarizes the discovery of WISE J181417.29+341224.9 (WISE 1814+3412), the first hyper-luminous infrared galaxy (LIR > 1013 L⊙) discovered by the Wide-field Infrared Survey Explorer (WISE). Follow-up images of WISE 1814+3412 revealed four nearby sources - a QSO, two Lyman Break Galaxies at z = 2.45, and an M dwarf star. The brighter LBG dominates the bolometric emission and has a star formation rate of ~300M⊙ yr−1, accounting for <10% of the bolometric luminosity. An obscured AGN combined with starburst and
The first hyper_luminous_infrared_galaxy_discovered_by_wiseSérgio Sacani
This document summarizes the discovery of WISE J181417.29+341224.9 (WISE 1814+3412), the first hyper-luminous infrared galaxy (LIR > 1013 L⊙) discovered by the Wide-field Infrared Survey Explorer (WISE). Follow-up images of WISE 1814+3412 revealed four nearby sources - a QSO, two Lyman Break Galaxies at z=2.45, and an M dwarf star. The brighter LBG dominates the bolometric emission of WISE 1814+3412 and has a star formation rate of ~300M⊙ yr−1, accounting for <10% of the total luminosity. An obscured
Spirals and clumps in V960 Mon: signs of planet formation via gravitational i...Sérgio Sacani
The formation of giant planets has traditionally been divided into two pathways: core accretion and gravitational instability. However, in recent years, gravitational instability has become less favored, primarily due
to the scarcity of observations of fragmented protoplanetary disks around young stars and low occurrence rate
of massive planets on very wide orbits. In this study, we present a SPHERE/IRDIS polarized light observation
of the young outbursting object V960 Mon. The image reveals a vast structure of intricately shaped scattered
light with several spiral arms. This finding motivated a re-analysis of archival ALMA 1.3 mm data acquired
just two years after the onset of the outburst of V960 Mon. In these data, we discover several clumps of continuum emission aligned along a spiral arm that coincides with the scattered light structure. We interpret the
localized emission as fragments formed from a spiral arm under gravitational collapse. Estimating the mass of
solids within these clumps to be of several Earth masses, we suggest this observation to be the first evidence of
gravitational instability occurring on planetary scales. This study discusses the significance of this finding for
planet formation and its potential connection with the outbursting state of V960 Mon.
Identification of the central compact object in the young supernova remnant 1...Sérgio Sacani
Oxygen-rich young supernova remnants1
are valuable objects
for probing the outcome of nucleosynthetic processes in massive
stars, as well as the physics of supernova explosions.
Observed within a few thousand years after the supernova
explosion2
, these systems contain fast-moving oxygen-rich and
hydrogen-poor filaments visible at optical wavelengths: fragments
of the progenitor’s interior expelled at a few thousand
kilometres per second during the supernova explosion. Here
we report the identification of the compact object in the supernova
remnant 1E 0102.2–7219 in reprocessed Chandra X-ray
Observatory data, enabled by the discovery of a ring-shaped
structure visible primarily in optical recombination lines of
Ne i and O i. The optical ring has a radius of (2.10 ± 0.35)″≡
(0.63 ± 0.11) pc, and is expanding at a velocity of 90 . 5 30
+40 − km s−1
.
It surrounds an X-ray point source with an intrinsic X-ray luminosity
Li
(1.2–2.0 keV) = (1.4 ± 0.2) × 1033 erg s−1
. The energy
distribution of the source indicates that this object is an isolated
neutron star: a central compact object akin to those
present in the Cas A3–5
and Pup A6 supernova remnants, and
the first of its kind to be identified outside of our Galaxy.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
1. VFTS 682 is a very massive star located 29 pc in projection from the young massive cluster R136 in the Tarantula Nebula of the LMC.
2. Spectral modeling finds it has an unusually high luminosity of log(L/L) = 6.5, corresponding to a present-day mass of ~150 solar masses.
3. Its isolation and mass pose the question of whether it formed in situ, which would profoundly impact theories of massive star formation, or if it was ejected from R136, making it the most massive runaway star known.
This document presents an analysis of metallicity gradients in the Milky Way disk as observed by the SEGUE survey. The key findings are:
1) The radial metallicity gradient (change in [Fe/H] with Galactic radius R) becomes flatter at heights above the plane (|Z|) greater than 1 kpc.
2) The median metallicity at large |Z| is consistent with outer disk open clusters, which also exhibit a flat radial gradient of [Fe/H] ∼ -0.5.
3) A flat metallicity gradient at high |Z| has implications for models of thick disk formation, as different formation scenarios predict different metallicity patterns in the thick disk.
Mapping the complex_kinematics_of_l_lobjects_in_the_orion_nebulaSérgio Sacani
This document presents a study of the kinematics of two LL Orionis-type objects (LL objects) in the Orion nebula, LL 1 and LL 2, and their associated Herbig-Haro jets HH 888 and HH 505. The authors combine long-slit spectroscopic observations of the objects with proper motion measurements to construct 3D velocity maps. The maps reveal:
1) Low velocities (10-20 km/s) in the stellar bowshocks of LL 1 and LL 2, with LL 1 showing symmetric motions and LL 2 showing asymmetric motions following nebula gradients.
2) Jet knot velocities over 200 km/s near the stars declining to under 100 km/s farther out in HH 8
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
Similar to Nucleosynthetic layers in_the_shocked_ejecta_of_cassiopeia_a (20)
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
1. Nucleosynthetic Layers in the Shocked Ejecta of Cassiopeia A
Karl Isensee1 , Greg Olmschenk1 , Lawrence Rudnick1 , Tracey DeLaney2 , Jeonghee Rho3 ,
J.D. Smith4 , William T. Reach5 , Takashi Kozasa6 , and Haley Gomez7
arXiv:1208.4034v1 [astro-ph.SR] 20 Aug 2012
ABSTRACT
We present a 3-dimensional analysis of the supernova remnant Cassiopeia A
using high resolution spectra from the Spitzer Space Telescope. We observe su-
pernova ejecta both immediately before and during the shock-ejecta interaction.
We determine that the reverse shock of the remnant is spherical to within 7%,
although the center of this sphere is offset from the geometric center of the rem-
nant by 810 km s−1 . We determine that the velocity width of the nucleosynthetic
layers is ∼1000 km s−1 over 4000 square arcsecond regions, although the velocity
width of a layer along any individual line of sight is <250 km s−1 . Si and O, which
come from different nucleosynthetic layers in the progenitor star, are observed to
be coincident in velocity space in some directions, but segregated by up to ∼500
km s−1 in other directions. We compare these observations of the nucleosynthetic
layers to predictions from supernova explosion models in an attempt to constrain
such models. Finally, we observe small-scale, corrugated velocity structures that
are likely caused during the supernova explosion itself, rather than hundreds of
years later by dynamical instabilities at the remnant’s reverse shock.
1
Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, MN 55455;
isensee@astro.umn.edu, olmsc019@umn.edu, larry@astro.umn.edu
2
Department of Physics and Engineering, West Virginia Wesleyan College, 59 College Avenue, Buckhan-
non, WV 26201; delaney t@wvwc.edu
3
SETI Institute and SOFIA Science Center, NASA Ames Research Center, MS 211-1, Moffett Field, CA
94035; jrho@sofia.usra.edu
4
Ritter Astrophysical Observatory, University of Toledo, Toledo, OH 43606 ; jd.smith@utoledo.edu
5
Stratospheric Observatory for Infrared Astronomy, Universities Space Research Association, MS 232-11,
NASA Ames Research Center, Moffett Field, CA 94035; wreach@sofia.usra.edu
6
Department of Cosmosciences, Graduate School of Science, Hokkaido University, Sapporo 060-0810,
Japan; kozasa@mail.sci.hokudai.ac.jp
7
School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF24 3AA,
UK; haley.gomez@astro.cf.ac.uk
2. –2–
Subject headings: ISM: Infrared – ISM: Supernova Remnants – ISM: Xray –
Supernovae: General – Supernova Remnants: Cassiopeia A
1. Introduction
The supernova remnant Cassiopeia A (Cas A) is a unique astrophysical laboratory due
to its young age (∼340 years - Thorstensen et al. 2001; Fesen et al. 2006) and small distance
(only 3.4 kpc - Reed et al. 1995). The remnant is just entering its Sedov-Taylor phase,
so emission from both forward and reverse shocks can be detected (Hughes et al. 2000).
Emission at most wavelengths, including most of the infrared, is dominated by a ∼120′′
radius “Bright Ring”. The Bright Ring is formed when supernova ejecta encounter Cas A’s
reverse shock and are shocked, heated, and collisionally ionized. It consists of undiluted
ejecta rich in O, Si, S, Ne, Ar, Ca, and Fe (Chevalier & Kirshner 1978; Douvian et al. 1999;
Hughes et al. 2000; Willingale et al. 2003; Hwang & Laming 2003; Laming & Hwang 2003;
Morse et al. 2004; Ennis et al. 2006).
Studies of optical light echoes from the the explosion near peak light have led to the
observation of weak hydrogen lines, indicating a supernova Type IIb origin for Cas A
(Krause et al. 2008). Cas A’s progenitor was therefore a red supergiant that had lost
most, but not all, of its hydrogen envelope. X-ray studies indicate a total ejecta mass of
∼2M⊙ (Willingale et al. 2003). If one adds to this the mass of the central compact object
(Chakrabarty et al. 2001), Cas A’s progenitor had a total mass of at least 4M⊙ immediately
before the supernova explosion. The estimated oxygen mass indicates a main sequence mass
of ∼15-25M⊙ (Young et al. 2006; Vink et al. 1996).
Although Cas A’s appearance is dominated by recently shocked ejecta, it also con-
tains emission that is not the result of collisional ionization at the reverse shock, but pho-
toionization by UV and X-ray emission from the shocked ejecta (Hamilton & Sarazin 1984;
Hamilton & Fesen 1998; Smith et al. 2009). This material is seen toward the central region
of the remnant at low radio frequencies (Kassim et al. 1995) and in the infrared (Rho et al.
2008; Smith et al. 2009; DeLaney et al. 2010; Isensee et al. 2010), and was demonstrated to
be at lower densities and ionization state than recently shocked material on the Bright Ring
through a combination of Doppler analysis and line ratio measurements (Smith et al. 2009).
These ejecta are often referred to as “unshocked ejecta” since they have yet to encounter the
remnant’s reverse shock. That is not an accurate label, since Cas A’s forward shock and a
reverse shock interacted with the ejecta during the supernova explosion itself.
3. –3–
1.1. Previous 3D Maps
3D Maps of Cas A have been made in the optical, infrared, and X-ray. Doppler re-
constructions in the optical used S and O emission lines (Lawrence et al. 1995; Reed et al.
1995) and showed that ejecta on the Bright Ring lie on a roughly spherical shell but are
not uniformly distributed on that shell - most of the ejecta lie nearly in the plane of the
sky. They also observe that the center of the sphere is offset from the geometrical center
of the spherical shell by ∼0.36pc along our line of sight. This indicates that the ejecta are
not traveling at the same velocity in all directions, which is consistent with previous results
which indicated an asymmetric expansion for the ejecta (e.g. Braun 1987; Willingale et al.
2002). These 3D reconstructions give us a selective snapshot of ejecta because only material
that has recently encountered the remnant’s reverse shock will emit strongly in the optical.
DeLaney et al. (2010) created a 3D infrared and X-ray map of Cas A from a Spitzer
Space Telescope spectral cube1 . Isensee et al. (2010) used a similar IR data set, but at
higher spectral resolution, to make a 3D map of ejecta in the center of the remnant. The
advantage of these IR maps lies in the fact that much of the ejecta in the IR will be detectable
both before and after they interact with the reverse shock. Both studies found a similar
distribution of ejecta to that seen in the optical where the center of expansion is offset from
the geometrical center of the remnant both in projection and along the line of sight. These
works were able to study the relationship of several nucleosynthetic layers and are discussed
in the next section.
1.2. Separation of Nucleosynthetic Layers
Si and O emission are observed to be co-located in most regions (e.g. Ennis et al. 2006)
in both the X-ray and infrared. This indicates that the two layers have very similar velocities
(less than 80 km s−1 difference). However, evidence of layer differentiation is found in some
directions in the X-ray (e.g. Hughes et al. 2000), the optical (Fesen et al. 2006), and the
IR (e.g. DeLaney et al. 2010; Isensee et al. 2010), which was likely caused by the different
layers of the star being ejected at different velocities in those directions, thus encountering
the remnant’s reverse shock at different times.
It should be emphasized that we can only observe mixing or separation in velocity space.
We can easily detect any velocity gradients in the supernova explosion since we can detect
Doppler velocities of <100 km s−1 in the IR, while typical observed velocities and velocities
1
Movies showing this 3D structure are available at http://chandra.harvard.edu/photo/2009/casa2/animations.html
4. –4–
predicted by models are an order of magnitude larger (e.g. Hammer et al. 2010). However,
we cannot detect any initial spatial separation of the nucleosynthetic layers - simulations
predict that the relevant nucleosynthetic layers will be < 1011 cm thick prior to the explosion
(e.g. Joggerst et al. 2009), but the typical ejecta clump size of <1′′ corresponds to ∼ 1016
cm at Cas A’s distance. Therefore, we cannot differentiate between a situation where two
nucleosynthetic layers were separated during the supernova explosion but ejected at the
same velocity, and one where the two layers were completely mixed during the explosion
and ejected at the same velocity. But, if we observe two layers that are currently separated
in velocity space, we know that they were separated during the supernova explosion itself
because, to the best of our knowledge, there is no mechanism that will impart different
velocities to spatially overlapping elements.
1.3. Geometrical Asymmetries
Supernova explosion models predict substantial asymmetries due to effects such as rota-
tion as well as instabilities (e.g. Blondin et al. 2003; Burrows et al. 2007; Hammer et al.
2010). Observations of both supernovae and supernova remnants have confirmed this picture.
Spectropolarimetric observations of unresolved supernovae have shown that all observed core
collapse supernovae contain intrinsic polarization, indicating that there is a departure from
spherical symmetry (Wheeler et al. 2005). Although an axis-symmetric geometry, proba-
bly induced by jets, can be used to explain some features in some core collapse super-
novae, significant departures from axial symmetry are needed to explain most observations
(Wang & Wheeler 2008).
IR 3D maps of supernova ejecta in Cas A have found major asymmetries, both on global
scales (DeLaney et al. 2010) and for smaller subsets of ejecta in the the entire supernova
remnant (Isensee et al. 2010). These asymmetries are not immediately apparent in the
visual appearance alone because the highly spherical reverse shock creates a large selection
effect in that we can only observe ejecta near the shock at most wavelengths.
In this paper, we present an analysis of high spectral resolution Spitzer mappings of
the ejecta on the Bright Ring of Cas A. This data set is an extension of that used by
Isensee et al. (2010), and it contains regions with both recently shocked and interior ejecta.
In §2 we present the observations and discuss the methods used in our analysis. We describe
those results in §3 and discuss the physical implications in §4.
5. –5–
2. Observations and Analysis
The Spitzer Infrared Spectrograph (IRS) was used on August 30, 2007 to create spectral
maps of select relatively bright regions in Cas A whose locations are shown and labeled in
Figure 1. High-resolution spectra (R∼600 for all wavelengths) were taken from 20-35µm
using the Long High (LH) module in all regions and from 10-35µm using both the Long
High and Short High (SH) modules in the Southwest region. The FWHM of unresolved
spectral features in these observations is about 0.06µm at 35µm and about 0.02µm at 13µm.
The LH data were taken using a 61 second exposure at each position while the SH data
were taken using a 31 second exposure at each position. The pixel scale of the observations
is ∼1.25′′ and ∼2.5′′ for the SH and LH modules respectively. The background, which was
taken from 3 separate 61 second observations adjacent to the remnant, was subtracted and
3D cubes were created using the S19 version of the IRS pipeline and the CUBISM software
package (Smith et al. 2007). The uncertainties in flux for each line of sight were calculated
from the IRS pipeline using standard error propagation of the BCD level errors.
The undersampling of the IRS modules limits our uncertainties. This is a systematic
error that exists in the wavelength calibration data themselves, and is worst at the short-
wavelength end of both the SH and LH modules. Our obtainable wavelength accuracy is
limited to roughly 1/2 of a spectral bin, or about 100 km s−1 . The relative wavelengths for a
given line can be measured with higher accuracy from position to position or within multiple
Doppler components in a given position.
2.1. Spectra
Cas A’s infrared spectrum is dominated by bright emission lines as shown in Figure 2.
The LH observations contain lines from [O IV] at 25.9µm, [S III] at 33.48µm, and [Si II] at
34.81µm. We tentatively identify the line near 23µm as the 22.9µm [Fe III] line. The lines
observed in the LH module typically have peak fluxes from 100-10,000 MJy sr−1 , with an
rms noise of ∼20 MJy sr−1 . The SH observation contains lines from Ne, S, and Fe. Typical
peak fluxes are ∼300 MJy sr−1 .
2.2. Doppler Deconvolution
We performed a Doppler deconvolution of the spectral lines for each line of sight from
each ion separately using a spectral CLEAN algorithm (Ding et al. 1999). We determined
the uncertainties in Doppler velocity for each Doppler component by applying the spectral
6. –6–
CLEAN to synthetic line data with a realistic range of signal to noise ratios, and using line
free data in order to model the noise. For both procedures, we use identical techniques to
those described in Isensee et al. (2010).
Using synthetic data, the uncertainty in velocity for a single, isolated Doppler component
was determined to be <25 km s−1 , however, we could not differentiate two components from
one another along the same line of sight that were within 65 km s−1 of one another. Therefore,
uncertainties in the absolute velocities are limited by the systematic errors in the calibration
of ∼100 km s−1 rather than random uncertainties.
As in previous studies (e.g. Reed et al. 1995; DeLaney et al. 2010; Isensee et al. 2010),
we assume that the ejecta have been freely expanding at a constant velocity in order to
determine their spatial coordinate perpendicular to the plane of the sky. DeLaney et al.
(2010) demonstrate that this is a good assumption for IR emission by showing that nearly all
ejecta plotted on a Velocity vs. Radius plot fall on a semi-circle. We make a similar Velocity
vs. Radius plot in Figure 3 from our data set and find that ejecta in these regions fall on a
semi-circle that is consistent with that found by DeLaney et al. (2010). The assumption of
constant velocity is still valid despite the fact that the ejecta were likely decelerated during
the supernova explosion itself. The subsequent behavior after the explosion is essentially
identical to free expansion at a reduced velocity because any deceleration happened near
t=0, z=0 where z is the spatial coordinate perpendicular to the plane of the sky.
3. Results
3.1. 3D Maps
We plot the Doppler components from both the 25.89µm [O IV] and the 34.81µm [Si II]
lines in Figures 4, 5, and 6 for the Southwest, Northeast, and Southeast regions respectively.
We converted our velocity coordinates to spatial coordinates using the conversion factor
between the two determined by DeLaney et al. (2010). This conversion factor is more ap-
propriate than one calculated from our own data since it uses data from the entire remnant
rather than a few select regions. The flux from each component is displayed by varying the
transparency; the brightest 3D pixel (or ”voxel”) for a given ionic line is 80% opaque, while
the opacity of all other voxels is linearly scaled downwards as a function of the intensity of
the Doppler component. We have not plotted very weak ejecta with total fluxes less than
15% that of the brightest velocity component. The other strong line, the 33.48µm [S III]
line, is from the same nucleosynthetic layer as Si and traces out nearly identical structures
to the 34.81µm [Si II] line. Therefore, we do not show it here. The low density of the interior
7. –7–
ejecta (∼100 cm−3 , Smith et al. 2009) implies that self-absorption within the ejecta will be
minimal along the line of sight. We note that we are likely only observing the densest ejecta
material, whether it is shocked or interior ejecta, since the emissivity should scale roughly
as the density squared in both cases.
The ejecta in the SW region form a distinct shell-like structure. The O and Si ejecta
all lie along the same shell, although they fill different parts of the shell. Averaging over
the entire SW region, there are an averge of only 1.3 Doppler components per line of sight,
indicating that the thickness of the shell is ≤250 km s−1 along any given line of sight. The
brightest ejecta in the NE region also forms part of a shell, but there are substantially more
dim ejecta inside of the shell than in the SW. O and Si lie both on the shell and inside of the
shell, although it appears that some of the O and Si is systematically separated in velocity
space (see § 3.6). The SE region consists of an irregularly shaped region of both Si and O
emission in addition to a region dominated by O emission in the western most part of the
region.
3.2. Iron
We observe [Fe II] with the SH module at 17.9µm in the SW. We plot the Doppler
components from this line with Si and O emission as shown in Figure 7. The SH data were
binned 2 by 2 pixels to increase the signal to noise ratio. It is clear that the Fe lies on the
Si+O shell described in the previous section.
We confirm that the 25.9µm line is the 25.89µm [O IV] and not the 25.98µm [Fe II] line
by comparing the Doppler structure of the 25.9µm to that of the 34.81µm [Si II] line for
several lines of sight in the SE, SW, and NE. As an example, we display the results for one
line of sight with strong 17.9µm Fe emission in Figure 8. We show the Doppler structure
for the 25.9µm line under the assumption that it is all [O IV] and all [Fe II]. We obtain an
excellent match under the assumption of [O IV], but a poor match under the assumption of
[Fe II] even along this line of sight where we see relatively strong Fe at other wavelengths.
We find no evidence for Fe at 25.9µm for 10 other lines of sight, confirming the results of
Isensee et al. (2010). Therefore, we assume for the remainder of this paper that the 25.9µm
line is entirely due to [O IV] emission.
8. –8–
3.3. Comparison to X-ray Emission
We compared the locations of the IR ejecta to X-ray ejecta detected in the 2004 Chandra
observations of Cas A (see Hwang et al. 2004). The spectral resolution of the X-ray images
is not sufficient to accurately determine the Doppler velocity for most lines. Therefore, we
show the 3D location of the X-ray ejecta as planes perpendicular to the plane of the sky in
Figure 9. These planes represent the forward edge of the X-ray ejecta as seen in Figure 1.
We know that the X-ray material has been recently shocked since the ejecta will only be at
the appropriate ionization states and temperatures if it has recently encountered the reverse
shock - the ejecta will ionize up to states that are difficult to observe in the X-ray within
∼100 years (Mazzotta et al. 1998).
Most of the bright IR ejecta are immediately interior to the leading edge of the X-ray
material. Since it takes some time for a plasma to up ionize to ions visible in the X-ray, this
is consistent with the picture that the brightest IR ejecta have been recently shocked.
3.4. Geometric Structure of Ejecta
We observe that the ejecta plotted in the previous section appear to have a distinct
shell-like geometry in the Southwest and Northeast regions. We attempt to characterize the
shape of this shell with an ellipsoid by fitting bright emission with a total flux at least 15%
that of the brightest Doppler components from all 3 regions.
We determined the best-fit ellipsoid characterized by 8 components - the 3 spatial co-
ordinates for the center of the ellipsoid, the 3 axes lengths, and 2 rotation angles. We
minimized the intensity weighted RMS residuals in the 3D space by iteratively stepping
through all plausible combinations of parameters. We show our best fit ellipsoid in Figure
10. The lengths of the axes in the plane of the sky are 103′′ and 98.3′′, and the length of
the axis perpendicular to the plane of the sky is 97.2′′ . The ellipsoid is a sphere to within
7%. The average residual from the best fit ellipsoid is 270 km s−1 , which is roughly 5% of
the total velocity for ejecta on the ellipsoid. The center of this sphere is offset from the
geometric center of the ejecta by 810 km s−1 along our line of sight. This offset can also be
seen in the Velocity vs. Radius plot shown in Figure 3.
9. –9–
3.5. Corrugation
Although the brightest ejecta lie near a spherical surface, the ejecta appear to be cor-
rugated about that surface. In fact, the residuals from our best fit surface are dominated
by systematic ∼250 km s−1 corrugations about the surface rather than random small-scale
fluctuations. This is most clearly seen in the Southwest region, as shown in Figure 11. We
find that the average wavelength of the corrugation is ∼24′′ and the amplitude is ∼8′′ about
the best fit surface. We further address the issue of corrugation in the next sections by
looking at radial plot of the net intensity of the ejecta.
3.6. Separation of Nucleosynthetic Layers
We plot the the brightest [Si II] and [O IV] ejecta, which come from different nucle-
osynthetic layers, for the Southwest and Northeast in Figures 4 and 5. There is clearly some
separation between these layers in some directions. We show a closeup of one such region in
Figure 13, where the layers are separated by a few hundred km s−1 (corresponding to ∼5′′ or
∼0.1 pc). The location of this region is shown in Figure 10.
In the SE, we observe a clump of O rich ejecta with almost no corresponding Si emission.
We address this interesting region in more depth in §4.2.
We further examine and quantify the separation between layers by plotting the intensity
of the emission as a function of three-dimensional radius for all intensities of ejecta for both
O and Si in the Southwest. Since Doppler velocity and spatial coordinates are equivalent and
we want to determine the velocity separation between nucleosynthetic layers, we converted
all our spatial coordinates into velocity units in order to determine the 3 dimensional velocity
from the center of expansion found in §3.3. This was accomplished by using the arcseconds
to km s−1 ratio determined by DeLaney et al. (2010). We then plotted the line flux as a
function of 3D velocity by binning the emission in 200 km s−1 increments.
Because we expect the behavior of the layers to vary as a function of direction, we
created plots for many different lines of sight. For each plot we only plotted emission from a
solid angle π/12 steradians wide. Our initial beam was centered π/8 radians above the plane
of the sky and is wide enough to include the entire width of the region, and then incremented
by π/12 radians downward for subsequent lines of sight.
We show the flux vs. 3D velocity plots for the Southwest in Figure 14. The average
radial distance of the O with respect to Si varies significantly between locations. Along some
lines of sight, they overlap to within one 2′′ bin. In different lines of sight, the O peak is at
10. – 10 –
a velocity up to ∼500 km s−1 greater than the Si. And along yet other lines of sight, the Si
and O peak at roughly the same velocity, but much of the O still is at larger radii than the
Si.
Furthermore, the peak velocity of both the Si and O changes as a function of direction
from ∼4400 km s−1 to ∼5200 km s−1 . This is consistent with corrugation in the velocities
of the ejecta along different directions.
The velocity width averaged over the solid angle of the Si and O ejecta in the previous
section are physical widths, and not just instrumental effects. We find that, to first order,
the FWHMs are all ∼1000 km s−1 for both Si and O. The velocity uncertainty in our bins
is roughly 130 km s−1 (since we have an uncertainty of roughly 65 km s−1 in each direction)
and the bins are 200 km s−1 wide.
We note that the velocity width of the peaks is much larger than the velocity width for
any given line of sight determined in §3.1. The velocity widths of the peaks is dominated
by averaging the 3D velocities over the entire solid angle and is not necessarily indicative of
the velocity spread over any single line of sight.
3.7. Faint Ejecta
Although we dealt mostly with bright ejecta that are found to lie on a distinct spherical
structure in the previous sections, there are weaker ejecta which lie interior to this bright
shell, especially in the NE region. On average, these ejecta are ∼10% as bright as the ejecta
on the shock. We plot these ejecta along with the bright material in Figure 12. We note
that nearly all the dim ejecta lie interior to the bright ejecta.
4. Discussion
4.1. Supernova Explosion Physics
The nature of core-collapse supernova explosions is a major area of research. The
assumed structure of the star before the supernova explosion is similar for many different
models. As a massive star fuses different elements during hydrostatic burning, it should
produce denser and denser concentric nucleosynthesis layers, forming the classic “onion-skin”
model of the star.
However, between models, there is substantial variation in the relevant physics be-
11. – 11 –
hind the supernova explosion itself. Most groups propose neutrino-driven shocks as the
main mechanism causing the explosion, but some utilize diffusive, magnetic buoyancy, or
neutrino-bubble instabilities (Janka et al. 2007). Other groups propose jet driven explo-
sions, where the explosion is dominated by MHD driven jets formed in rapidly rotating stars
(e.g. Burrows et al. 2007).
3D maps of different nucleosynthetic layers in Cas A provide a unique opportunity to
test and constrain the various models. Our observations focus on the layers that were initially
near the core of the star, where the supernova explosion begins - the Fe/Ni core, the Si/S
layer immediately above the core, and the O/Ne layer above the Si/S. We can observe the
post-explosion geometry and velocity profile of the different layers. Some models predict that
Si and O will be ejected at nearly the same velocity (e.g. Kifonidis et al. 2006), while others
predict that they will be ejected at velocities that differ by ≥500 km s−1 (e.g. Joggerst et al.
2009).
Along many lines of sight, our results are consistent with the models of Kifonidis et al.
(2006) and the 25M⊙ models of Joggerst et al. (2009) - we see little difference between the
peak velocities of O and Si. However, along other lines of sight, we find that the O and
Si peaks are offset by hundreds of km s−1 which is inconsistent with above models, but is
consistent with the results of the 15M⊙ models of Joggerst et al. (2009). However, even
though this 15M⊙ model produces a reasonable separation between O and Si, it predicts
that the velocity width of O will be nearly twice that of Si, while we observe that both layers
have roughly the same width along all lines of sight. Furthermore, the model predicts overall
velocities of <2000 km s−1 , which is only half of what we observe. Put together, available
models can reproduce most of the various behaviors that we observe, but no single model,
so far, can reproduce observed velocity structure of the nucleosynthetic layers of the Cas A
supernova explosion.
4.2. The Southeast
Ennis et al. (2006) found a Neon “crescent” of ejecta in the Southeast and Northeast of
Cas A where Neon was seen in the IR, but little Si was detected in the IR or X-ray. Our
Southeast region overlaps slightly with the Neon crescent. Most of the IR emission in this
region consists of overlapping Si and O immediately behind the X-ray ejecta. However, in
the Neon crescent, we see only O emission that is more than an order of magnitude stronger
than Si emission as shown in Figure 9. This is consistent with Ennis et al. (2006) and
Smith et al. (2009) since Neon and O come from the same nucleosynthetic layer. The most
likely explanation for this Neon/O crescent is that the Neon and O are currently encountering
12. – 12 –
the reverse shock and therefore becoming brighter as they are compressed, while the Si has
yet to encounter the reverse shock. This is consistent with the picture that there is no IR
emission from the Si because the densest Si clumps have not yet been radiatively shocked,
and there is no observable X-ray emission because the Si ejecta have not been non-radiatively
shocked.
4.3. Geometry
We observe that the center of expansion is offset from the center of the remnant by ∼810
km/s along our line of sight. This is consistent with previous results from 3D reconstructions
in the optical (Reed et al. 1995) and the IR (DeLaney et al. 2010; Isensee et al. 2010). There
are three major possible sources for the cause of this offset - asymmetries in the circumstellar
environment, movement by the progenitor star, and the supernova explosion itself.
Reed et al. (1995) speculated that this offset was due to asymmetries in the pre-supernova
circumstellar environment. Isensee et al. (2010), using one patch toward the center of the
remnant, argue that this cannot be the case since the ejecta interior to the reverse shock
show the same velocity asymmetry, despite the fact that they are unaffected by the circum-
stellar material. The interior ejecta are expanding into a bubble that has been cleared of
any circumstellar material by the shocks associated with the supernova explosion. Since our
new results, which span the Bright Ring, are consistent with those of Isensee et al. (2010),
the velocity offset is not specific to the central regions of Cas A, but applies to the entire
remnant.
In principle, the velocity offset could be caused by progenitor motion, but the observed
810 km s−1 offset is much too large a velocity for a star. Neutron stars may have velocities
>500 km s−1 (e.g. Satterfield et al. 2011), but such large velocities are the result of “kicks”
during the supernova explosion, which are caused by asymmetries in the supernova explosion
itself or a binary companion (e.g. Shklovskii 1969; Chatterjee et al. 2005).
Therefore, the observed offset it most likely caused by asymmetries in the supernova
itself. A likely culprit is asymmetries formed in the first ∼100 milliseconds as seen in the
models of Burrows et al. (2007) and the SASI models of Blondin et al. (2003). Both of
these instabilities allow the initially spherically symmetric forward shock to become highly
asymmetric in just a few crossing times. These instabilities arise due to the response of the
post shock pressure to changes in the shock radius. If the pressure in one region becomes
slightly higher than the surroundings, it will push the shock outward. The preshock pressure
drops with increasing radius, which leads to smaller pressures behind the forward shock due
13. – 13 –
to the outward shock displacement. If the postshock pressure radial profile is steeper than
the preshock pressure profile, a standing acoustic wave is produced by the positive feedback
loop. Ejecta can “slosh” between the standing shocks, resulting in substantial asymmetries
(Blondin et al. 2003). Presumably, the ejecta will maintain this asymmetry as they expand
outward, resulting in a low-order asymmetry that is not necessarily centered on the location
of the progenitor star. Note that although the shock may initially be asymmetric, it will
gradually become spherical over time (e.g. Bisnovatyi-Kogan & Blinnikov 1982), producing
the nearly spherical surface that we observe today.
4.4. Faint Ejecta
The faint ejecta seen interior to the bright ejecta on the nearly spherical shell are likely
ejecta that have yet to encounter the reverse shock. We expect to observe both [Si II] and
[O IV] even if they are not yet shocked because they will be photoionized by energetic UV and
X-ray photons from the reverse shock. Such ejecta were previously detected in the center of
the remnant and interior to the reverse shock by DeLaney et al. (2010), Smith et al. (2009),
and Isensee et al. (2010). The brightness of the ejecta appears to be roughly an order of
magnitude less than that of nearby material which has been shocked. This is consistent with
what is expected from a strong shock - a compression factor of about 4 is expected for a
classic, strong, non-radiative shock, which would cause a rise in emissivity of a factor of 16.
We note that the interior ejecta in the center of the remnant (see Figure 1) discussed
extensively in Isensee et al. (2010) are much brighter than the interior ejecta in all the
regions near the reverse shock. The most obvious explanation for this is that the central
ejecta are at a higher density. This difference in density is probably caused by geometric
effects - the central material from the remnant is traveling at about half the velocity of the
material currently encountering the reverse shock in the plane of the sky (DeLaney et al.
2010). If the ejecta are expanding homologously and were initially ejected at approximately
the same density, the material in the place of the sky would be at a density one quarter
that of the interior ejecta since the shocked ejecta are at twice the radius. Therefore, we
would expect the emissivity of the central ejecta to be roughly 16 times that of material in
the plane of the sky that is interior to the reverse shock since the emissivity of the ejecta
varies as the square of the density. This is roughly what we observe - interior material in
these regions have an average brightness of ∼300 MJy sr−1 , while material in the center of
the remnant have brightnesses around 4000 MJy sr−1 (Isensee et al. 2010).
14. – 14 –
4.5. Corrugation
Corrugation - that is, ripples in the geometric structure of the ejecta - has been previous
observed in several supernova remnants, including SN1006 (e.g. Winkler & Long 1997) and
the Cygnus Loop (e.g. Raymond 2003). There are several possible explanations for this
corrugation. If the shock is radiative, the ripples could be caused by the thermal instability
(e.g. Berschinger 1986) or the thin shell instability (Vishniac 1983). The thermal instability
is especially relevant for high speed (>150 km s−1 ), high temperature (T>105 K) shocks
where the sound speed crossing time greatly exceeds the cooling time. This “instability”
is actually an overstability that results from the high radiative cooling rate. The thin shell
instability is another overstability. In this scenario, the ram pressure and thermal pressure
are misaligned, causing ripples in the initially smooth distribution of ejecta.
Another possibility is that the ripples are caused by inhomogeneities in the ejecta en-
countering the shock. This inhomogeneity could be caused by Rayleigh-Taylor filaments
created at the contact discontinuity between the ejecta and the ISM as the remnant enters
its Sedov-Taylor phase (Wang & Chevalier 2001). While this is a likely explanation for the
corrugation observed in SN1006 (Long et al. 2003), it is not likely in Cas A since the ISM
has already been swept away by the forward shock by time the ejecta encounter the reverse
shock.
A final explanation is that the corrugation is caused by density variations in the ejecta
itself (e.g. Raymond 2003). In this model, dense ejecta encountering the reverse shock would
be slowed less than less dense clumps of ejecta. Raymond (2003) argues that this instability
is the most likely cause for the corrugation in the Cygnus Loop, where the density variations
may have been caused by ISM turbulence.
Regardless of the mechanism, there is also a question of where the corrugation occurs.
The observed ejecta have encountered several shocks - the forward shock during the supernova
explosion itself, a reverse shock during the supernova, and most recently, a larger scale reverse
shock in the supernova remnant (Isensee et al. 2010). Which shock encounter creates the
observed corrugation?
Most studies expect corrugation at the second, larger forward or reverse shocks associ-
ated with the remnant. However, we conclude that the most likely location for the corruga-
tion is during one of the two shocks that the ejecta encounter during the supernova explosion
itself. Previous studies find little evidence for deceleration of IR ejecta after the explosion,
including recently shocked ejecta (DeLaney et al. 2010). Our data are also inconsistent with
recent deceleration of the ejecta. If the ejecta were suddenly decelerated, the ejecta would
be closer to the plane of they sky in our models due to the reduction in Doppler velocity,
15. – 15 –
forming a flattened surface. However, we do not observe this pattern in the shocked ejecta
- we still see a nearly perfect sphere. In other words, if the corrugation were being caused
at the reverse shock, the ejecta would need to be decelerated by at least several hundred
kilometers per second in order to create the observed corrugation since being shocked. This
effect would be easily visible with our Doppler reconstruction of the global geometry, but
is not observed. Thus, the corrugation must occur during the supernova explosion itself,
perhaps at the initial forward or explosion reverse shock.
5. Conclusions
We create a 3D model of shocked ejecta of Cas A in select regions at unprecedented
spectral resolution using IR ionic lines. We confirm previous studies that indicate that the
remnant is offset by ∼800 km s−1 along our line of sight. We find evidence for velocity
separation between the O and Si layers along some, but not all, lines of sight. We measure
the velocity width of these layers roughly 250 km s−1 thick for a single line of sight, although
the ejecta are often in bands that are ∼1000 km s−1 thick averaged over several nearby lines
of sight due to corrugation. We find evidence for corrugation in some regions of the rem-
nant, and speculate that the corrugation was caused during the explosion itself rather than
hundreds of years later. We use our observations of Si and O velocities to begin constraining
models of supernova explosions, and to motivate future models to explore velocity profiles
as a function of azimuth.
We look forward to potential similar data sets from instruments such as the Herschel
Space Observatory and the Stratospheric Observatory for Infrared Astronomy (SOFIA).
Both these observatories will have the ability to create spectral cubes of Cas A at much
higher spectral resolution. The current instruments on both observatories do not have the
necessary instantaneous bandwidth to observe the 10,000 km s−1 velocity range of ejecta in
Cas A, but future spectrographs will have scanning modes that will allow observations of
ejecta at many different velocities.
This work is based on observations made with the Spitzer Space Telescope, which is
operated by the Jet Propulsion Laboratory, California Institute of Technology under NASA
contract 1407. This work was supported in part by NASA/SAO Award No. AR5-6008X and
NASA/JPL through award 1265552 to the University of Minnesota.
K. I. would like to thank Alexander Heger for valuable insight into the physics of su-
pernova explosions.
16. – 16 –
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A
20. – 20 –
Fig. 1.— 34.81µm [Si II] Spitzer IRS map (left) and X-ray Si Chandra map (right) of Cas A. Both
maps have been continuum subtracted. The regions of high resolution data discussed in this text
are indicated by the boxes. The planes shown in Figure 9 are indicated by the straight lines in the
X-ray image.
Fig. 2.— Typical spectra from the SH and LH Spitzer IRS module of emission in Cas A. The
small bump near 23µm may be from the 22.9µm [Fe III] line.
21. – 21 –
Fig. 3.— Velocity vs radius plot for Si (filled squares) and O (open triangle). Our assumption
of no deceleration is good since all the ejecta lie nearly on the same semi-circle. Note that the
semi-circle is offset from 0 velocity by 810 km s−1 as indicated by the solid horizontal line.
22. – 22 –
Fig. 4.— 3D plot of the the 25.9µm [O IV] line (blue) and 34.8µm [Si II] line (green) in the
Southwest of the remnant as viewed from three different angles. The angles were chosen to best
highlight the 3D structure of the ejecta. The units on the axes are arcseconds from the center of
expansion of the remnant.
23. – 23 –
Fig. 5.— 3D plot of the the 25.9µm [O IV] line (blue) and 34.8µm [Si II] line (green) in the
Northeast of the remnant as viewed from two different angles. The angles were chosen to best
highlight the 3D structure of the ejecta. The units on the axes are arcseconds from the center of
expansion of the remnant.
24. – 24 –
Fig. 6.— 3D plot of the the 25.9µm [O IV] line (blue) and 34.8µm [Si II] line (green) in the
Southeast of the remnant as viewed from two different angles. The angles were chosen to best
highlight the 3D structure of the ejecta. The units on the axes are arcseconds from the center of
expansion of the remnant.
25. – 25 –
Fig. 7.— 3D plot of the the 25.9µm [O IV] line (blue), the 34.8µm [Si II] line (green), and the
17.9µm [Fe II] line (purple) in the Southwest of the remnant as viewed from three different angles.
The velocity axis has been stretched by a factor of approximately 1.8 in order to better highlight
the Doppler structure of the region. The Fe emission lies on the same shell as the O and Si emission.
Fig. 8.— Velocity plot for the [Si II] line (dashed) over-plotted with the 25.9µm line (solid) shifted
under the assumption that it is either all [O IV] (left) or [Fe II] (right). The lines have been
normalized such that the integrated flux is equal for both lines. The velocity structure matches
very well for the assumption that the 25.9µm line is all O, but matches very poorly under the
assumption that it is composed of Fe.
26. – 26 –
Fig. 9.— 3D plot of the the 25.9µm [O IV] line (blue) and 34.8µm [Si II] line (green) in the
Northeast (left) and Southeast (right) of the remnant along with planes of X-ray emission. The
RA and Dec of the X-ray planes were extracted from the lines on the Chandra images in Figure 1.
The IR ejecta are just behind the front edge of the X-ray shock in the Northeast. The same is true
in the Southeast, and we see a substantial amount of Oxygen dominated material where our field
of view overlaps with the Ne-crescent detected by Ennis et al. (2006). This is not surprising given
that Ne and O come from the same nucleosynthetic layer.
27. – 27 –
Fig. 10.— 3D plot of ejecta from all regions and the best fit ellipsoid. The units of the axes are
km s−1 . The ellipsoid is has an eccentricity of 1.07. The zoomed in region in Figure 13 is indicated.
28. – 28 –
Fig. 11.— 3D plot of the 25.9µm [O IV] line in the Southwest of the remnant. The units of the
axes are km s−1 . Two ellipsoids with radii 250 km s−1 greater than and less than the best fit
ellipsoid are also plotted. Although the shell in this region is only ∼200 km s−1 thick along any
single line of sight, the overall velocity of the components systematically varies by ∼250 km s−1
both above and below the best fit ellipsoid.
29. – 29 –
Fig. 12.— 3D plot of all ejecta in the Northeast region with at least 10% the flux of the brightest
Doppler component (left) and all ejecta with at least 25% the flux of the brightest Doppler com-
ponent (right) . The units on the axes are arcseconds from the center of expansion of the remnant.
The dimmer ejecta lie interior to the bright shell formed by the brightest ejecta, indicating that it
may not yet have encountered the reverse shock.
30. – 30 –
Fig. 13.— 3D plot of the the 25.9µm [O IV] line (blue) and 34.8µm [Si II] line (green) in a select
region of the Northeast whose location is indicated in Figure 10. The units of the axes are km s−1 .
The red arrow points to the center of the remnant. We detect clear separation between the O and
Si layers along this line of sight.
31. – 31 –
Fig. 14.— Flux vs radius plot for the Southwest region. The O (dashed) and Si (solid) distributions
overlap along some lines of sight, but are offset by up to ∼500 km s−1 along others. The peak
velocity of the O line and the Si line also vary from about 4400 km s−1 to 5200 km s−1 depending
on the line of sight. This is a clear signature of corrugation. The full-width-half-max of the
distributions is ∼1000 km s−1 along all lines of sight.