The importance of binary stars

Stars are mostly found in binary and multiple systems, as at least 50% of all solar-like stars have companions - a fraction that goes up to 100% for the most massive stars. Moreover, a large fraction of them will interact in some way or another over the course of their lives. Such interactions can, and often will, alter the structure and evolution of both components in the system. This will, in turn, lead to the production of exotic objects whose existence cannot be explained by standard single star evolution models, including gravitational wave progenitors, blue stragglers, symbiotic and barium stars, novae, and supernovae. More generally, binary stars prove crucial in many aspects, ranging from cultural ones, to constraining models of stellar evolution, star formation, and even, possibly, of gravity itself. They also provide a quasi-model independent way to determine stellar masses, radii, and luminosities. We here provide a brief summary of the importance of binary stars.
http://arxiv.org/abs/2411.18470

Identification of a turnover in the initial mass function of a young stellar cluster down to 0.5 Jupiter masses

Identification of a turnover in the initial mass function of a young stellar cluster down to 0.5 MJ

A successful theory of star formation should predict the number of objects as a function of their mass produced through star-forming events. Previous studies in star-forming regions and the solar neighborhood identify a mass function increasing from the hydrogen-burning limit down to about 10 Jupiter masses (MJ). Theory predicts a limit to the fragmentation process, providing a natural turnover in the mass function down to the opacity limit of turbulent fragmentation thought to be 2-10 MJ. Programs to date have not been sensitive enough to probe the hypothesized opacity limit of fragmentation. Here we present the first identification of a turnover in the initial mass function below 12 MJ within NGC 2024, a young star-forming region. With JWST/NIRCam deep exposures across 0.7-5 {\mu}m, we identified several free floating objects down to ~ 3 MJ with sensitivity to 0.5 MJ. We present evidence for a double power law model increasing from about 60 MJ to roughly 12 MJ, consistent with previous studies, followed by a decrease down to 0.5 MJ. Our results support the predictions of star and brown dwarf formation theory, identifying the theoretical turnover in the mass function and suggest the fundamental limit of turbulent fragmentation near 3 MJ.
http://arxiv.org/abs/2409.04624

The JWST/NIRISS Deep Spectroscopic Survey for Young Brown Dwarfs and Free-Floating Planets

The discovery and characterization of free-floating planetary-mass objects (FFPMOs) is fundamental to our understanding of star and planet formation. Here we report results from an extremely deep spectroscopic survey of the young star cluster NGC1333 using NIRISS WFSS on the James Webb Space Telescope. The survey is photometrically complete to K~21, and includes useful spectra for objects as faint as K~20.5. The observations cover 19 known brown dwarfs, for most of which we confirm spectral types using NIRISS spectra. We discover six new candidates with L-dwarf spectral types that are plausible planetary-mass members of NGC1333, with estimated masses between 5-15 MJup. One, at ~5 MJup, shows clear infrared excess emission and is a good candidate to be the lowest mass object known to have a disk. We do not find any objects later than mid-L spectral type (M less than 4 MJup). The paucity of Jupiter-mass objects, despite the surveys unprecedented sensitivity, suggests that our observations reach the lowest mass objects formed like stars in NGC1333. Our findings put the fraction of FFPMOs in NGC1333 at ~10% of the number of cluster members, significantly more than expected from the typical log-normal stellar mass function. We also search for wide binaries in our images and report a young brown dwarf with a planetary-mass companion.
http://arxiv.org/abs/2408.12639

Strong constraints on the gravitational law from Gaia DR3 wide binaries

We test Milgromian dynamics (MOND) using wide binary stars (WBs) with separations of 2−30 kAU. Locally, the WB orbital velocity in MOND should exceed the Newtonian prediction by ≈20% at asymptotically large separations given the Galactic external field effect (EFE). We investigate this with a detailed statistical analysis of \emph{Gaia} DR3 data on 8611 WBs within 250 pc of the Sun. Orbits are integrated in a rigorously calculated gravitational field that directly includes the EFE. We also allow line of sight contamination and undetected close binary companions to the stars in each WB. We interpolate between the Newtonian and Milgromian predictions using the parameter αgrav, with 0 indicating Newtonian gravity and 1 indicating MOND. Directly comparing the best Newtonian and Milgromian models reveals that Newtonian dynamics is preferred at 19σ confidence. Using a complementary Markov Chain Monte Carlo analysis, we find that αgrav=−0.021+0.065−0.045, which is fully consistent with Newtonian gravity but excludes MOND at 16σ confidence. This is in line with the similar result of Pittordis and Sutherland using a somewhat different sample selection and less thoroughly explored population model. We show that although our best-fitting model does not fully reproduce the observations, an overwhelmingly strong preference for Newtonian gravity remains in a considerable range of variations to our analysis. Adapting the MOND interpolating function to explain this result would cause tension with rotation curve constraints. We discuss the broader implications of our results in light of other works, concluding that MOND must be substantially modified on small scales to account for local WBs.
http://arxiv.org/abs/2311.03436

Robust Evidence for the Breakdown of Standard Gravity at Low Acceleration from Statistically Pure Binaries Free of Hidden Companions

It is found that Gaia DR3 binary stars selected with stringent requirements on astrometric measurements and radial velocities naturally satisfy Newtonian dynamics without hidden close companions when projected separation s>2 kau, showing that pure binaries can be selected. It is then found that pure binaries selected with the same criteria show a systematic deviation from the Newtonian expectation when s<2 kau. When both proper motions and parallaxes are required to have precision better than 0.003 and radial velocities better than 0.2, I obtain 1558 statistically pure binaries within a 'clean' G-band absolute magnitude range. From this sample, I obtain an observed to Newtonian predicted kinematic acceleration ratio of γg=gobs/gpred=1.43+0.23−0.19 for acceleration <10−10 m s−2, in excellent agreement with a recent finding 1.43±0.06 for a much larger general sample with the amount of hidden close companions self-calibrated. I also investigate the radial profile of stacked sky-projected relative velocities without a deprojection to the 3D space. The observed profile matches the Newtonian predicted profile for s<2 kau without any free parameters but shows a clear deviation at a larger separation with a significance of 4.6σ. The projected velocity boost factor for s>8 kau is measured to be γvp=1.18±0.06 matching γg−−√. Finally, for a small sample of 23 binaries with exceptionally precise radial velocities (precision <0.0043) the directly measured relative velocities in the 3D space also show a boost at larger separations. These results robustly confirm the recently reported gravitational anomaly at low acceleration for a general sample.
http://arxiv.org/abs/2309.10404

Discovery of the elusive carbonic acid (HOCOOH) in space

After a quarter century since the detection of the last interstellar carboxylic acid, acetic acid (CH3COOH), we report the discovery of a new one, the cis-trans form of carbonic acid (HOCOOH), toward the Galactic Center molecular cloud G+0.693-0.027. HOCOOH stands as the first interstellar molecule containing three oxygen atoms and also the third carboxylic acid detected so far in the interstellar medium. Albeit the limited available laboratory measurements (up to 65 GHz), we have also identified several pairs of unblended lines directly in the astronomical data (between 75-120 GHz), which allowed us to slightly improve the set of spectroscopic constants. We derive a column density for cis-trans HOCOOH of N = (6.4 ± 0.4) × 1012 cm−2, which yields an abundance with respect to molecular H2 of 4.7 × 10−11. Meanwhile, the extremely low dipole moment (about fifteen times lower) of the lower-energy conformer, cis-cis HOCOOH, precludes its detection. We obtain an upper limit to its abundance with respect to H2 of ≤ 1.2 ×10−9, which suggests that cis-cis HOCOOH might be fairly abundant in interstellar space, although it is nearly undetectable by radio astronomical observations. We derive a cis-cis/cis-trans ratio ≤ 25, consistent with the smaller energy difference between both conformers compared with the relative stability of trans- and cis-formic acid (HCOOH). Finally, we compare the abundance of these acids in different astronomical environments, further suggesting a relationship between the chemical content found in the interstellar medium and the chemical composition of the minor bodies of the Solar System, which could be inherited during the star formation process.
http://arxiv.org/abs/2307.08644

Breakdown of the Newton-Einstein Standard Gravity at Low Acceleration in Internal Dynamics of Wide Binary Stars

A gravitational anomaly is found at weak gravitational acceleration gN<10−9 m s−2 from analyses of the dynamics of wide binary stars selected from the Gaia DR3 database that have accurate distances, proper motions, and reliably inferred stellar masses. Implicit high-order multiplicities are required and the multiplicity fraction is calibrated so that binary internal motions agree statistically with Newtonian dynamics at a high enough acceleration of 10−8 m s−2. The observed sky-projected motions and separation are deprojected to the three-dimensional relative velocity v and separation r through a Monte Carlo method, and a statistical relation between the Newtonian acceleration gN≡GM/r2 (where M is the total mass of the binary system) and a kinematic acceleration g≡v2/r is compared with the corresponding relation predicted by Newtonian dynamics. The empirical acceleration relation at less than 10^−9 m s−2 systematically deviates from the Newtonian expectation. A gravitational anomaly parameter δobs−newt between the observed acceleration at gN and the Newtonian prediction is measured to be: δobs−newt=0.034±0.007 and 0.109±0.013 at gN≈10−8.91 and 10−10.15 m s−2, from the main sample of 26,615 wide binaries within 200 pc. These two deviations in the same direction represent a 10σ significance. The deviation represents a direct evidence for the breakdown of standard gravity at weak acceleration. At gN=10−10.15 m s−2, the observed to Newton predicted acceleration ratio is gobs/gpred=102√δobs−newt=1.43±0.06. This systematic deviation agrees with the boost factor that the AQUAL theory predicts for kinematic accelerations in circular orbits under the Galactic external field.
http://arxiv.org/abs/2305.04613

G 68-34: A Double-Lined M-Dwarf Eclipsing Binary in a Hierarchical Triple System

Using high-resolution spectra from the Tillinghast Reflector Echelle Spectrograph (TRES) and photometry from sector 56 of the Transiting Exoplanet Survey Satellite (TESS), we report that the nearby M dwarf G 68-34 is a double-lined eclipsing binary. The pair is spin-orbit synchronized with a period of 0.655 days. The light curve shows significant spot modulation with a larger photometric amplitude than that of the grazing eclipses. We perform a joint fit to the spectroscopic and photometric data, obtaining masses of 0.3280±0.0034M⊙ and 0.3207±0.0036M⊙ and radii of 0.345±0.014R⊙ and 0.342±0.014R⊙ after marginalizing over unknowns in the starspot distribution. This system adds to the small but growing population of fully convective M dwarfs with precisely measured masses and radii that can be used to test models of stellar structure. The pair also has a white dwarf primary at 9" separation, with the system known to be older than 5 Gyr from the white-dwarf cooling age. The binarity of G 68-34 confirms our hypothesis from Pass et al. (2022): in that work, we noted that G 68-34 was both rapidly rotating and old, highly unusual given our understanding of the spindown of M dwarfs, and that a close binary companion may be responsible.
http://arxiv.org/abs/2304.02466

Direct Discovery of the Inner Exoplanet in the HD206893 System

Long term precise radial velocity (RV) monitoring of the nearby star HD206893, as well as anomalies in the system proper motion, have suggested the presence of an additional, inner companion in the system. Here we describe the results of a multi-epoch search for the companion responsible for this RV drift and proper motion anomaly using the VLTI/GRAVITY instrument. Utilizing information from ongoing precision RV measurements with the HARPS spectrograph, as well as Gaia host star astrometry, we report a high significance detection of the companion HD206893c over three epochs, with clear evidence for Keplerian orbital motion. Our astrometry with ∼50-100 μarcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7+1.2−1.0 MJup and an orbital separation of 3.53+0.08−0.06 au for HD206893c. Our fits to the orbits of both companions in the system utilize both Gaia astrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore derive an age of 155±15 Myr. We find that theoretical atmospheric/evolutionary models incorporating deuterium burning for HD206893c, parameterized by cloudy atmospheres provide a good simultaneous fit to the luminosity of both HD206893B and c. In addition to utilizing long-term RV information, this effort is an early example of a direct imaging discovery of a bona fide exoplanet that was guided in part with Gaia astrometry. Utilizing Gaia astrometry is expected to be one of the primary techniques going forward to identify and characterize additional directly imaged planets. Lastly, this discovery is another example of the power of optical interferometry to directly detect and characterize extrasolar planets where they form at ice-line orbital separations of 2-4\,au.
http://arxiv.org/abs/2208.04867

Direct imaging discovery of a super-Jovian around the young Sun-like star AF Leporis

Expanding the sample of directly imaged companions to nearby, young stars that are amenable to detailed astrometric and spectroscopic studies is critical for the continued development and validation of theories of their evolution and atmospheric processes. The recent release of the {\it Gaia} astrometric catalogue allows us to efficiently search for these elusive companions by targeting those stars that exhibit the astrometric reflex motion induced by an orbiting companion. The nearby (27 pc), young (24 Myr) star AF Leporis (AF Lep) was targeted because of its astrometric acceleration, consistent with a wide-orbit planetary companion detectable with high-contrast imaging. We used the SPHERE instrument on the VLT to search for faint substellar companions in the immediate vicinity of AF Lep. We used observations of a nearby star interleaved with those of AF Lep to efficiently subtract the residual point spread function. This provided sensitivity to faint planetary-mass companions within 1 arcsec (∼30 au) of the star. We detected the companion AF Lep b at a separation of 339 mas (9 au), within the inner edge of its unresolved debris disk. The measured K-band contrast and the age of the star yield a model-dependent mass of 4 and 6 MJup, consistent with the mass derived from an orbital fit of 4.3+2.9−1.2 MJup. The near-infrared SED of the planet is consistent with an object at the L--T spectral type transition, but under-luminous with respect to field-gravity objects. AF Lep b joins a growing number of substellar companions imaged around stars in the young β Pic moving group. With a mass of between 3 and 7 MJup, it occupies a gap in this isochronal sequence between the hotter, more massive companions like PZ~Tel~B and β~Pic~b, and the cooler 51~Eri~b, which is sufficiently cool for methane to form within its photosphere.
http://arxiv.org/abs/2302.06332

A red giant orbiting a black hole

We report spectroscopic and photometric follow-up of a dormant black hole (BH) candidate from Gaia DR3. We show that the system, which we call Gaia BH2, contains a ∼1M⊙ red giant and a dark companion with mass M2=8.9±0.3M⊙ that is very likely a BH. The orbital period, Porb=1277 days, is much longer than that of any previously studied BH binary. Our radial velocity (RV) follow-up over a 6-month period spans most of the orbit's dynamic range in RV and is in excellent agreement with predictions of the Gaia solution. UV imaging and high-resolution optical spectra rule out all plausible luminous companions that could explain the orbit. The star is a bright (G=12.3), slightly metal-poor ([Fe/H]=−0.22) low-luminosity giant (Teff=4600K; R=7.9R⊙; log[g/(cms−2)]=2.6). The binary's orbit is moderately eccentric (e=0.52). The giant is strongly enhanced in α−elements, with [α/Fe]=+0.26, but the system's Galactocentric orbit is typical of the thin disk. We obtained X-ray and radio nondetections of the source near periastron, which support BH accretion models in which the net accretion rate at the horizon is much lower than the Bondi-Hoyle-Lyttleton rate. At a distance of 1.16 kpc, Gaia BH2 is the second-nearest known BH, after Gaia BH1. Its orbit -- like that of Gaia BH1 -- seems too wide to have formed through common envelope evolution. Gaia BH1 and BH2 have orbital periods at opposite edges of the Gaia DR3 sensitivity curve, perhaps hinting at a bimodal intrinsic period distribution for wide BH binaries. Dormant BH binaries like Gaia BH1 and Gaia BH2 likely significantly outnumber their close, X-ray bright cousins, but their formation pathways remain uncertain.
http://arxiv.org/abs/2302.07880

An Ice Age JWST inventory of dense molecular cloud ices

Icy grain mantles are the main reservoir of the volatile elements that link chemical processes in dark, interstellar clouds with the formation of planets and composition of their atmospheres. The initial ice composition is set in the cold, dense parts of molecular clouds, prior to the onset of star formation. With the exquisite sensitivity of JWST, this critical stage of ice evolution is now accessible for detailed study. Here we show the first results of the Early Release Science program "Ice Age" that reveal the rich composition of these dense cloud ices. Weak ices, including, 13CO2, OCN−, 13CO, OCS, and COMs functional groups are now detected along two pre-stellar lines of sight. The 12CO2 ice profile indicates modest growth of the icy grains. Column densities of the major and minor ice species indicate that ices contribute between 2 and 19% of the bulk budgets of the key C, O, N, and S elements. Our results suggest that the formation of simple and complex molecules could begin early in a water-ice rich environment.
http://arxiv.org/abs/2301.09140

Direct Imaging and Astrometric Discovery of a Superjovian Planet Orbiting an Accelerating Star

We detect a superjovian extrasolar planet around the dusty A star HIP 99770 using precision astrometry from the Gaia and Hipparcos satellites and direct imaging using the Subaru Coronagraphic Extreme Adaptive Optics Project. HIP 99770 b is the first exoplanet ever discovered jointly through direct imaging and astrometry and the first discovery leveraging on μ-arcsecond precision Gaia astrometry. HIP 99770 b is in a low-eccentricity orbit ∼16.9 au from the primary, receiving about as much light as Jupiter does from the Sun. The planet induces an astrometric acceleration on the host star; its directly-measured companion-to-primary mass ratio is similar to that of many radial-velocity detected planets and some of the first imaged exoplanets, including HR 8799 cde. The planet's spectrum reveals an atmosphere resembling a slightly less cloudy and likely older analogue of these first imaging discoveries, enabling a new, critical probe of how gas giant planets evolve with time. HIP 99770 b's discovery is a direct proof-of-concept for a fundamentally new strategy for finding imageable planets: selecting targets based on dynamical evidence from indirect methods like astrometry instead of conducting blind searches. This combined approach prefigures the campaigns that could one day directly detect and characterize an extrasolar Earth-like planet.
http://arxiv.org/abs/2212.00034

A Sun-like star orbiting a black hole

We report discovery of a bright, nearby (G=13.8; d=480 pc) Sun-like star orbiting a dark object. We identified the system as a black hole candidate via its astrometric orbital solution from the Gaia mission. Radial velocity monitoring validated and refined the Gaia solution, and spectroscopy ruled out significant light contributions from another star. Joint modeling of radial velocities and astrometry constrains the companion mass to M2=9.8±0.2M⊙. The spectroscopic orbit alone sets a minimum companion mass of M2>5M⊙; if the companion were a 5M⊙ star, it would be 500 times more luminous than the entire system. These constraints are insensitive to the assumed mass of the luminous star, which appears as a slowly-rotating G dwarf (Teff=5850 K, logg=4.5, M=0.93M⊙), with near-solar metallicity ([Fe/H] = -0.2) and an unremarkable abundance pattern. We find no plausible astrophysical scenario that can explain the orbit and does not involve a black hole. The orbital period, Porb=185.6 days, is longer than that of any known stellar-mass black hole binary, and the eccentricity is modest, e=0.45. The system's Galactic orbit is typical of thin-disk stars, suggesting that it formed in the Milky Way disk with at most a weak natal kick. Explaining the system's formation with standard binary evolutionary models is challenging: it is difficult for the luminous star to survive a common envelope event under standard assumptions, and difficult for it to end up in a wide orbit afterward. Formation models involving triples or dynamical assembly in an open cluster may be more promising. This is the nearest known black hole by a factor of 3, and its discovery suggests the existence of a sizable population of dormant black holes in binaries. Future Gaia releases will likely facilitate the discovery of dozens more.
http://arxiv.org/abs/2209.06833

New Coronae and Stellar Associations Revealed by a Clustering Analysis of the Solar Neighborhood

We present the results of a density-based clustering analysis of the 6-dimensional XYZ Galactic positions and UVW space velocities of nearby (≤ 200 pc) Gaia EDR3 stars with radial velocities using HDBSCAN, in opposition to previous studies that only included positions and tangential velocities. Among the 241 recovered clusters, we identify more than 50 known associations, 32 new candidate stellar streams aged 100 Myr-3 Gyr, 9 extensions of known Theia groups uncovered by Kounkel & Covey (2019), and 8 newly recognized coronae around nearby open clusters. Three confirmed exoplanet-hosting stars and three more TESS transiting exoplanet candidates are part of the new groups discovered here, including TOI-1807 and TOI-2076 from Hedges et al. (2021) that were suspected to belong to a yet unidentified moving group. The new groups presented here were not previously recognized because of their older ages, low spatial density, and projection effects that spread out the tangential velocities of their nearby co-moving members. Several newly identified structures reach distances within 60 pc of the Sun, providing new grounds for the identification of isolated planetary-mass objects. The nearest member of the newly recognized corona of Volans-Carina is V419 Hya, a known young debris disk star at a distance of 22 pc. This study outlines the importance of further characterization of young associations in the immediate Solar neighborhood, which will provide new laboratories for the precise age calibration of nearby stars, exoplanets and substellar objects. http://arxiv.org/abs/2206.04567

N-bearing complex organics toward high-mass protostars: Constant ratios pointing to formation in similar pre-stellar conditions across a large mass range

No statistical study of COMs toward a large sample of high-mass protostars with ALMA has been carried out so far. We aim to study six N-bearing species: CH3CN, HNCO, NH2CHO, C2H5CN, C2H3CN and CH3NH2 in a large sample of high-mass protostars. From the ALMAGAL survey, 37 of the most line-rich hot molecular cores are selected. Next, we fit their spectra and find column densities and excitation temperatures of the above N-bearing species, in addition to CH3OH. We (tentatively) detect CH3NH2 in ∼32 of the sources. We find three groups of species when comparing their excitation temperatures: hot (NH2CHO; Tex > 250 K), warm (C2H3CN, HN13CO and CH133CN; 100 K < Tex < 250 K) and cold species (CH3OH and CH3NH2; Tex < 100 K). This temperature segregation reflects the trend seen in their sublimation temperatures and validates the idea of onion-like structure of COMs around protostars. Moreover, the molecules studied here show constant column density ratios across low- and high-mass protostars with scatter less than a factor ∼3 around the mean. The constant column density ratios point to a common formation environment of COMs or their precursors, most likely in the pre-stellar ices. The scatter around the mean of the ratios, although small, varies depending on the species considered. This spread can either have a physical origin (source structure, line or dust optical depth) or a chemical one. Formamide is most prone to the physical effects as it is tracing the closest regions to the protostars, whereas such effects are small for other species. Assuming that all molecules form in the pre-stellar ices, the scatter variations could be explained by differences in lifetimes or physical conditions of the pre-stellar clouds. If the pre-stellar lifetimes are the main factor, they should be similar for low- and high-mass protostars.
http://arxiv.org/abs/2208.11128

CORINOS I: JWST/MIRI Spectroscopy and Imaging of a Class 0 protostar IRAS 15398-3359

The origin of complex organic molecules (COMs) in young Class 0 protostars has been one of the major questions in astrochemistry and star formation. While COMs are thought to form on icy dust grains via gas-grain chemistry, observational constraints on their formation pathways have been limited to gas-phase detection. Sensitive mid-infrared spectroscopy with JWST enables unprecedented investigation of COM formation by measuring their ice absorption features. We present an overview of JWST/MIRI MRS spectroscopy and imaging of a young Class 0 protostar, IRAS 15398-3359, and identify several major solid-state absorption features in the 4.9-28 μm wavelength range. These can be attributed to common ice species, such as H2O, CH3OH, NH3, and CH4, and may have contributions from more complex organic species, such as C2H5OH and CH3CHO. The MRS spectra show many weaker emission lines at 6-8 μm, which are due to warm CO gas and water vapor, possibly from a young embedded disk previously unseen. Finally, we detect emission lines from [Fe II], [Ne II], [S I], and H2, tracing a bipolar jet and outflow cavities. MIRI imaging serendipitously covers the south-western (blue-shifted) outflow lobe of IRAS 15398-3359, showing four shell-like structures similar to the outflows traced by molecular emission at sub-mm wavelengths. This overview analysis highlights the vast potential of JWST/MIRI observations and previews scientific discoveries in the coming years.
http://arxiv.org/abs/2208.10673

A scaled-up planetary system around a supernova progenitor

Virtually all known exoplanets reside around stars with M<2.3 M⊙; to clarify if the dearth of planets around more massive stars is real, we launched the direct-imaging B-star Exoplanet Abundance STudy (BEAST) survey targeting B stars (M>2.4 M⊙) in the young (5-20 Myr) Scorpius-Centaurus association (Sco-Cen). Here we present the case of a massive (M∼9 M⊙) BEAST target, μ2 Sco. Based on kinematic information, we found that μ2 Sco is a member of a small group which we label Eastern Lower Scorpius, refining in turn the precision on stellar parameters. Around this star we identified a robustly detected substellar companion (14.4±0.8MJ) at a projected separation of 290±10 au, and a probable second object (18.5±1.5MJ) at 21±1 au. The planet-to-star mass ratios of these objects are similar to that of Jupiter to the Sun, and their irradiation is similar to those of Jupiter and Mercury, respectively. The two companions of μ2 Sco are naturally added to the giant planet b Cen b recently discovered by BEAST; although slightly more massive than the deuterium burning limit, their properties resemble those of giant planets around less massive stars and they are better reproduced by a formation under a planet-like, rather than a star-like scenario. Irrespective of the (needed) confirmation of the inner companion, μ2 Sco is the first star that would end its life as a supernova that hosts such a system. The tentative high frequency of BEAST discoveries shows that giant planets or small-mass brown dwarfs can form around B stars. When putting this finding in the context of core accretion and gravitational instability, we conclude that the current modeling of both mechanisms is not able to produce this kind of companion. BEAST will pave the way for the first time to an extension of these models to intermediate and massive stars. (abridged)
http://arxiv.org/abs/2205.02279

Ice Age : Chemo-dynamical modeling of Cha-MMS1 to predict new solid-phase species for detection with JWST

Chemical models and experiments indicate that interstellar dust grains and their ice mantles play an important role in the production of complex organic molecules (COMs). To date, the most complex solid-phase molecule detected with certainty in the ISM is methanol, but the James Webb Space Telescope (JWST) may be able to identify still larger organic species. In this study, we use a coupled chemo-dynamical model to predict new candidate species for JWST detection toward the young star-forming core Cha-MMS1, combining the gas-grain chemical kinetic code MAGICKAL with a 1-D radiative hydrodynamics simulation using Athena++. With this model, the relative abundances of the main ice constituents with respect to water toward the core center match well with typical observational values, providing a firm basis to explore the ice chemistry. Six oxygen-bearing COMs (ethanol, dimethyl ether, acetaldehyde, methyl formate, methoxy methanol, and acetic acid), as well as formic acid, show abundances as high as, or exceeding, 0.01% with respect to water ice. Based on the modeled ice composition, the infrared spectrum is synthesized to diagnose the detectability of the new ice species. The contribution of COMs to IR absorption bands is minor compared to the main ice constituents, and the identification of COM ice toward the core center of Cha-MMS1 with the JWST NIRCAM/Wide Field Slitless Spectroscopy (2.4-5.0 micron) may be unlikely. However, MIRI observations (5-28 micron) toward COM-rich environments where solid-phase COM abundances exceed 1% with respect to the water ice column density might reveal the distinctive ice features of COMs.
http://arxiv.org/abs/2206.04269

Ice features of low-luminosity protostars in near-infrared spectra of AKARI/IRC

We present near-infrared spectra of three low-luminosity protostars and one background star in the Perseus molecular cloud, acquired using the Infrared Camera (IRC) onboard the \textit{AKARI} space telescope. For the comparison with different star-forming environments, we also present spectra of the massive protostar AFGL 7009S, where the protostellar envelope is heated significantly, and the low-mass protostar RNO 91, which is suspected to be undergoing an episodic burst. We detected ice absorption features of \ch{H2O}, \ch{CO2}, and \ch{CO} at all spectra around the wavelengths of 3.05, 4.27, and 4.67 μm, respectively. At least two low-luminosity protostars, we also detected the \ch{XCN} ice feature at 4.62 μm. The presence of the crystalline \ch{H2O} ice and \ch{XCN} ice components indicates that the low-luminosity protostars experienced a hot phase via accretion bursts during the past mass accretion process. We compared the ice abundances of low-luminosity protostars with those of the embedded low-mass protostars and the dense molecular clouds and cores, suggesting that their ice abundances reflect the strength of prior bursts and the timescale after the last burst.
http://arxiv.org/abs/2207.05178