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31. sigma Ori GTC+INT spectroscopy
ID:
ivo://CDS.VizieR/J/A+A/629/A114
Title:
sigma Ori GTC+INT spectroscopy
Short Name:
J/A+A/629/A114
Date:
21 Oct 2021
Publisher:
CDS
Description:
Only a few open clusters are as important for the study of stellar and substellar objects, and their formation and evolution, as the young sigma Orionis cluster. However, a complete spectroscopic characterisation of its whole stellar population is still missing. We filled most of that gap with a large spectroscopic and astrometric survey of targets towards sigma Orionis. Eventually, it will be one of the open clusters with the lowest proportion of interlopers and the largest of confirmed cluster members with known uncontrovertible youth features. We acquired 317 low-resolution optical spectra with IDS at the 2.5m Isaac Newton Telescope and OSIRIS at the 10.4m Gran Telescopio Canarias. On them, we measured equivalent widths of LiI, H{alpha}, and other key lines, and determined spectral types. We complemented the information with Gaia DR2 astrometric data and other features of youth (mid-infrared excess, X-ray emission) compiled with Virtual Observatory tools and from the literature. Of the 168 observed targets, we determined for the first time spectral types of 39 stars and equivalent widths of LiI and H{alpha} of 34 and 12 stars, respectively. We identified 11 close ({rho}<~3-arcsec) binaries resolved by Gaia, of which three are new, 14 strong accretors, of which four are new and another four have H{alpha} emission shifted by over 120km/s, two juvenile star candidates in the sparse population of the Ori OB1b association, and one spectroscopic binary candidate. Remarkably, we found 51 cluster non-members, 35 of which were previously considered as sigma Orionis members and taken into account in high-impact works on, e.g., disc frequency and initial mass function.
32. Spectroscopic transit depths of LHS 3844b
ID:
ivo://CDS.VizieR/J/AJ/160/188
Title:
Spectroscopic transit depths of LHS 3844b
Short Name:
J/AJ/160/188
Date:
21 Oct 2021
Publisher:
CDS
Description:
Atmospheric studies of spectroscopically accessible terrestrial exoplanets lay the groundwork for comparative planetology between these worlds and the solar system terrestrial planets. LHS3844b is a highly irradiated terrestrial exoplanet (R=1.303{+/-}0.022R{Earth}) orbiting a mid-M dwarf 15parsecs away. Work based on near-infrared Spitzer phase curves ruled out atmospheres with surface pressures >~10bars on this planet. We present 13 transit observations of LHS3844b taken with the Magellan Clay telescope and the LDSS3C multi-object spectrograph covering 620-1020nm. We analyze each of the 13 data sets individually using a Gaussian process regression, and present both white and spectroscopic light curves. In the combined white light curve we achieve an rms precision of 65ppm when binning to 10minutes. The mean white light-curve value of (Rp/Rs)^2^ is 0.4170{+/-}0.0046%. To construct the transmission spectrum, we split the white light curves into 20 spectrophotometric bands, each spanning 20nm, and compute the mean values of (Rp/Rs)^2^ in each band. We compare the transmission spectrum to two sets of atmospheric models. We disfavor a clear, solar composition atmosphere ({mu}=2.34) with surface pressures >~0.1bar to 5.2{sigma} confidence. We disfavor a clear, H2O steam atmosphere ({mu}=18) with surface pressures >~0.1bar to low confidence (2.9{sigma}). Our observed transmission spectrum favors a flat line. For solar composition atmospheres with surface pressures >~1bar we rule out clouds with cloud-top pressures of 0.1bar (5.3{sigma}), but we cannot address high-altitude clouds at lower pressures. Our results add further evidence that LHS3844b is devoid of an atmosphere.
33. Spitzer follow up of 95 brown dwarfs
ID:
ivo://CDS.VizieR/J/ApJ/899/123
Title:
Spitzer follow up of 95 brown dwarfs
Short Name:
J/ApJ/899/123
Date:
14 Mar 2022 07:05:10
Publisher:
CDS
Description:
We present Spitzer follow-up imaging of 95 candidate extremely cold brown dwarfs discovered by the Backyard Worlds: Planet 9 citizen science project, which uses visually perceived motion in multiepoch Wide-field Infrared Survey Explorer (WISE) images to identify previously unrecognized substellar neighbors to the Sun. We measure Spitzer [3.6]-[4.5] color to phototype our brown dwarf candidates, with an emphasis on pinpointing the coldest and closest Y dwarfs within our sample. The combination of WISE and Spitzer astrometry provides quantitative confirmation of the transverse motion of 75 of our discoveries. Nine of our motion-confirmed objects have best-fit linear motions larger than 1"/yr; our fastest-moving discovery is WISEAJ155349.96+693355.2 ({mu}~2.15/yr), a possible T-type subdwarf. We also report a newly discovered wide-separation (~400au) T8 comoving companion to the white dwarf LSPMJ0055+5948 (the fourth such system to be found), plus a candidate late T companion to the white dwarf LSRJ0002+6357 at 5.5 projected separation (~8700au if associated). Among our motion-confirmed targets, five have Spitzer colors most consistent with spectral type Y. Four of these five have exceptionally red Spitzer colors suggesting types of Y1 or later, adding considerably to the small sample of known objects in this especially valuable low-temperature regime. Our Y dwarf candidates begin bridging the gap between the bulk of the Y dwarf population and the coldest known brown dwarf.
34. Spitzer observations of Y and T dwarfs
ID:
ivo://CDS.VizieR/J/ApJ/867/109
Title:
Spitzer observations of Y and T dwarfs
Short Name:
J/ApJ/867/109
Date:
21 Oct 2021
Publisher:
CDS
Description:
Y dwarfs provide a unique opportunity to study free-floating objects with masses <30M_Jup_ and atmospheric temperatures approaching those of known Jupiter-like exoplanets. Obtaining distances to these objects is an essential step toward characterizing their absolute physical properties. Using Spitzer's Infrared Array Camera (IRAC) [4.5] images taken over baselines of ~2-7yrs, we measure astrometric distances for 22 late-T and early Y dwarfs, including updated parallaxes for 18 objects and new parallax measurements for 4 objects. These parallaxes will make it possible to explore the physical parameter space occupied by the coldest brown dwarfs. We also present the discovery of six new late-T dwarfs, updated spectra of two T dwarfs, and the reclassification of a new Y dwarf, WISE J033605.04-014351.0, based on Keck/NIRSPEC J-band spectroscopy. Assuming that effective temperatures are inversely proportional to absolute magnitude, we examine trends in the evolution of the spectral energy distributions of brown dwarfs with decreasing effective temperature. Surprisingly, the Y dwarf class encompasses a large range in absolute magnitude in the near- to mid-infrared photometric bandpasses, demonstrating a larger range of effective temperatures than previously assumed. This sample will be ideal for obtaining mid-infrared spectra with the James Webb Space Telescope because their known distances will make it easier to measure absolute physical properties.
35. Spitzer variability detections of 79 brown dwarfs
ID:
ivo://CDS.VizieR/J/AJ/160/38
Title:
Spitzer variability detections of 79 brown dwarfs
Short Name:
J/AJ/160/38
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present Spitzer Space Telescope variability monitoring observations of three low-gravity L dwarfs with previous detections of variability in the near-IR: 2MASSJ0045+16, 2MASSJ0501-00, and 2MASSJ1425-36. We detect significant periodic variability in two of our targets, 2MASS J0045+16 and 2MASS J0501-00. We do not detect variability in 2MASS J1425-36. Combining our new rotation periods with rotational velocities, we calculate inclination angles of 22{deg}{+/-}1{deg}, 60_-8_^+13^{deg}, and 52_-13_^+19^{deg} for 2MASSJ0045+16, 2MASSJ0501-00, and 2MASSJ1425-36, respectively. Our three new objects are consistent with the tentative relations between inclination, amplitude, and color anomaly previously reported. Objects with the highest variability amplitudes are inclined equator on, while the maximum observed amplitude decreases as the inclination angle decreases. We also find a correlation between the inclination angle and (J-K)_2MASS_ color anomaly for the sample of objects with measured inclinations. Compiling the entire sample of brown dwarfs with Spitzer variability detections, we find no enhancement in amplitude for young, early-L dwarfs compared to the field dwarf population. We find a possible enhancement in amplitude of low-gravity late-L dwarfs at 4.5{mu}m. We do not find a correlation between amplitude ratio and spectral type for field dwarfs or for the young population. Finally, we compile the rotation periods of a large sample of brown dwarfs with ages 1Myr-1Gyr and compare the rotation rates predicted by evolutionary models assuming angular momentum conservation. We find that the rotation rates of the current sample of brown dwarfs fall within the expected range set by evolutionary models and breakup limits.
36. (Sub)Stellar companions of exoplanet hosts
ID:
ivo://CDS.VizieR/J/other/FrASS/8.624907
Title:
(Sub)Stellar companions of exoplanet hosts
Short Name:
J/other/FrASS/8.
Date:
22 Feb 2022
Publisher:
CDS
Description:
We present the latest results of an ongoing multiplicity survey of exoplanet hosts, which was initiated at the Astrophysical Institute and University Observatory Jena, using data from the second data release of the ESA-Gaia mission. In this study the multiplicity of 289 targets was investigated, all located within a distance of about 500pc from the Sun. In total, 41 binary, and five hierarchical triple star systems with exoplanets were detected in the course of this project, yielding a multiplicity rate of the exoplanet hosts of about 16%. A total of 61 companions (47 stars, a white dwarf, and 13 brown dwarfs) were detected around the targets, whose equidistance and common proper motion with the exoplanet hosts were proven with their precise Gaia DR2 astrometry, which also agrees with the gravitational stability of most of these systems. The detected companions exhibit masses from about 0.016 up to 1.66M_{sun}_ and projected separations in the range between about 52 and 9555au.
37. TBOSS Survey. II. ALMA continuum observations
ID:
ivo://CDS.VizieR/J/AJ/155/54
Title:
TBOSS Survey. II. ALMA continuum observations
Short Name:
J/AJ/155/54
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report 885 {mu}m ALMA continuum flux densities for 24 Taurus members spanning the stellar/substellar boundary with spectral types from M4 to M7.75. Of the 24 systems, 22 are detected at levels ranging from 1.0 to 55.7 mJy. The two nondetections are transition disks, though other transition disks in the sample are detected. Converting ALMA continuum measurements to masses using standard scaling laws and radiative transfer modeling yields dust mass estimates ranging from ~0.3 to 20 M_{Earth}_. The dust mass shows a declining trend with central object mass when combined with results from submillimeter surveys of more massive Taurus members. The substellar disks appear as part of a continuous sequence and not a distinct population. Compared to older Upper Sco members with similar masses across the substellar limit, the Taurus disks are brighter and more massive. Both Taurus and Upper Sco populations are consistent with an approximately linear relationship in M_dust_ to M_star_, although derived power-law slopes depend strongly upon choices of stellar evolutionary model and dust temperature relation. The median disk around early-M stars in Taurus contains a comparable amount of mass in small solids as the average amount of heavy elements in Kepler planetary systems on short-period orbits around M-dwarf stars, with an order of magnitude spread in disk dust mass about the median value. Assuming a gas-to-dust ratio of 100:1, only a small number of low-mass stars and brown dwarfs have a total disk mass amenable to giant planet formation, consistent with the low frequency of giant planets orbiting M dwarfs.
38. The first 300 stars observed by the GPIES
ID:
ivo://CDS.VizieR/J/AJ/158/13
Title:
The first 300 stars observed by the GPIES
Short Name:
J/AJ/158/13
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a statistical analysis of the first 300 stars observed by the Gemini Planet Imager Exoplanet Survey. This subsample includes six detected planets and three brown dwarfs; from these detections and our contrast curves we infer the underlying distributions of substellar companions with respect to their mass, semimajor axis, and host stellar mass. We uncover a strong correlation between planet occurrence rate and host star mass, with stars M_*_>1.5 M_{sun}_ more likely to host planets with masses between 2 and 13 M_Jup_ and semimajor axes of 3-100 au at 99.92% confidence. We fit a double power-law model in planet mass (m) and semimajor axis (a) for planet populations around high-mass stars (M_*_>1.5 M_{sun}_) of the form d^2^N/(dm da){prop.to}m^{alpha}^{alpha}^{beta}^, finding {alpha}=-2.4+/-0.8 and {beta}=-2.0+/-0.5, and an integrated occurrence rate of 9_-4_^+5^% between 5-13 M_Jup_ and 10-100 au. A significantly lower occurrence rate is obtained for brown dwarfs around all stars, with 0.8_-0.5_^+0.8^% of stars hosting a brown dwarf companion between 13-80 M_Jup_ and 10-100 au. Brown dwarfs also appear to be distributed differently in mass and semimajor axis compared to giant planets; whereas giant planets follow a bottom-heavy mass distribution and favor smaller semimajor axes, brown dwarfs exhibit just the opposite behaviors. Comparing to studies of short-period giant planets from the radial velocity method, our results are consistent with a peak in occurrence of giant planets between ~1 and 10 au. We discuss how these trends, including the preference of giant planets for high-mass host stars, point to formation of giant planets by core/pebble accretion, and formation of brown dwarfs by gravitational instability.
39. Upper Scorpius spectroscopy and photometry
ID:
ivo://CDS.VizieR/J/AJ/160/44
Title:
Upper Scorpius spectroscopy and photometry
Short Name:
J/AJ/160/44
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have refined the census of stars and brown dwarfs in the Upper Sco association (~10Myr, ~145pc) by (1) updating the selection of candidate members from our previous survey to include the high-precision astrometry from the second data release of Gaia, (2) obtaining spectra of a few hundred candidate members to measure their spectral types and verify their youth, and (3) assessing the membership (largely with Gaia astrometry) of 2020 stars toward Upper Sco that show evidence of youth in this work and previous studies. We arrive at a catalog of 1761 objects that are adopted as members of Upper Sco. The distribution of spectral types among the adopted members is similar to those in other nearby star-forming regions, indicating a similar initial mass function. In previous studies, we have compiled mid-infrared photometry from the Wide-field Infrared Survey Explorer and the Spitzer Space Telescope for members of Upper Sco and used those data to identify the stars that show evidence of circumstellar disks; we present the same analysis for our new catalog of members. As in earlier work, we find that the fraction of members with disks increases with lower stellar masses, ranging from <~10% for >1M{sun} to ~22% for 0.01-0.3M{sun}. Finally, we have estimated the relative ages of Upper Sco and other young associations using their sequences of low-mass stars in M_G_RP__ versus G_BP_-G_RP_. This comparison indicates that Upper Sco is a factor of two younger than the {beta}Pic association (21-24Myr) according to both nonmagnetic and magnetic evolutionary models.
40. Very low-mass binaries with Gaia DR2 data
ID:
ivo://CDS.VizieR/J/ApJ/889/176
Title:
Very low-mass binaries with Gaia DR2 data
Short Name:
J/ApJ/889/176
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report the discovery of WISE 2150-7520AB (W2150AB): a widely separated (~341au) very low-mass L1+T8 co-moving system. The system consists of the previously known L1 primary 2MASS J21501592-7520367 and a newly discovered T8 secondary found at position 21:50:18.99-75:20:54.6 (MJD=57947) using Wide-field Infrared Survey Explorer data via the Backyard Worlds: Planet 9 citizen science project. We present Spitzer ch1 and ch2 photometry (ch1-ch2=1.41+/-0.04mag) of the secondary and Folded-port InfraRed Echellette prism spectra of both components. The sources show no peculiar spectral or photometric signatures, indicating that each component is likely field age. Using all observed data and the Gaia DR2 parallax of 41.3593+/-0.2799mas for W2150A we deduce fundamental parameters of log(L_bol_/L_{sun}_)=-3.69+/-0.01, Teff=2118+/-62K, and an estimated mass=72+/-12M_Jup_ for the L1 and log(L_bol_/L_{sun}_)=-5.64+/-0.02, Teff=719+/-61K, and an estimated mass=34+/-22M_Jup_ for the T8. At a physical separation of ~341au this system has E_bin_=10^41^erg, making it the lowest binding energy system of any pair with M_tot_<0.1M_{sun}_ not associated with a young cluster. It is equivalent in estimated mass ratio, E_bin_, and physical separation to the ~2Myr M7.25+M8.25 binary brown dwarf 2MASS J11011926-7732383AB (2M1101AB) found in the Chameleon star-forming region. W2150AB is the widest companion system yet observed in the field where the primary is an L dwarf or later.