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Start Over Subject brown dwarfs Validation Level 2
21. New substellar discoveries from Kepler and K2
ID:
ivo://CDS.VizieR/J/AJ/158/38
Title:
New substellar discoveries from Kepler and K2
Short Name:
J/AJ/158/38
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the discoveries of a brown dwarf (BD) and a low-mass star from the Kepler and K2 missions. The newly discovered BD is EPIC 212036875b and the low-mass star is KOI-607b. EPIC 212036875b has a mass of M_b_=52.3+/-1.9 M_J_, a radius of R_b_=0.874+/-0.017 R_J_, and orbits its host star in P=5.169885+/-0.000027 days. Its host star is a late F-type star with M_*_=1.288+/-0.065 M_{sun}_, R_*_= 1.498+/-0.025 R_{sun}_, and T_eff_=6238+/-60 K. KOI-607b has a mass of M_b_=95.1+/-3.4 M_J_, a radius of R_b_=1.089+/-0.089 R_J_, and an orbital period of P=5.89399148+/-0.00000060 days. The primary star in the KOI-607 system is a G dwarf with M_*_=0.993+/-0.052 M_{sun}_, R_*_= 0.915+/-0.031 R_{sun}_, and T_eff_=5418+/-87 K. We also revisit a BD, CWW 89Ab, that was previously published by Nowak et al. 2017AJ....153..131N (under the designation EPIC 219388192b). CWW 89Ab is one of two known transiting BDs associated with a star cluster, which illustrates the need for more BDs with accurate masses, radii, and reliable age determinations to test theoretical models. We find that the newly discovered BD, EPIC 212036875b, falls in the middle of the so-called BD desert, indicating that EPIC 212036875b is either a particularly rare object, or the BD desert may not be so dry after all.
22. New young stars and brown dwarfs in Upper Sco
ID:
ivo://CDS.VizieR/J/AJ/156/76
Title:
New young stars and brown dwarfs in Upper Sco
Short Name:
J/AJ/156/76
Date:
21 Oct 2021
Publisher:
CDS
Description:
To improve the census of the Upper Sco association (~11 Myr, ~145 pc), we have identified candidate members using parallaxes, proper motions, and color-magnitude diagrams from several wide-field imaging surveys and have obtained optical and infrared spectra of several hundred candidates to measure their spectral types and assess their membership. We also have performed spectroscopy on a smaller sample of previously known or suspected members to refine their spectral types and evidence of membership. We have classified 530 targets as members of Upper Sco, 377 of which lack previous spectroscopy. Our new compilation of all known members of the association contains 1631 objects. Although the census of Upper Sco has expanded significantly over the last decade, there remain hundreds of candidates that lack spectroscopy. The precise parallaxes and proper motions from the second data release of Gaia should extend down to substellar masses in Upper Sco, which will greatly facilitate the identification of the undiscovered members.
23. NIR spectra of 2 extreme T-type subdwarfs
ID:
ivo://CDS.VizieR/J/ApJ/898/77
Title:
NIR spectra of 2 extreme T-type subdwarfs
Short Name:
J/ApJ/898/77
Date:
21 Mar 2022 08:47:02
Publisher:
CDS
Description:
We present the discoveries of WISEAJ041451.67-585456.7 and WISEAJ181006.18-101000.5, two low-temperature (1200-1400K), high proper motion T-type subdwarfs. Both objects were discovered via their high proper motion (>0.5yr^-1^); WISEA J181006.18-101000.5 as part of the NEOWISE proper motion survey and WISEA J041451.67-585456.7 as part of the citizen science project Backyard Worlds; Planet 9. We have confirmed both as brown dwarfs with follow-up near-infrared spectroscopy. Their spectra and near-infrared colors are unique among known brown dwarfs, with some colors consistent with L-type brown dwarfs and other colors resembling those of the latest-type T dwarfs. While no forward model consistently reproduces the features seen in their near-infrared spectra, the closest matches suggest very low metallicities ([Fe/H]<=-1), making these objects likely the first examples of extreme subdwarfs of the T spectral class (esdT). WISEAJ041451.67-585456.7 and WISEA J181006.18-101000.5 are found to be part of a small population of objects that occupy the "substellar transition zone", and have the lowest masses and effective temperatures of all objects in this group.
24. OSIRIS K-band spectroscopy of {kappa} Andromedae b
ID:
ivo://CDS.VizieR/J/AJ/160/207
Title:
OSIRIS K-band spectroscopy of {kappa} Andromedae b
Short Name:
J/AJ/160/207
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present moderate-resolution (R~4000) K-band spectra of the "super- Jupiter," {kappa}-Andromedae-b. The data were taken with the OSIRIS integral field spectrograph at Keck Observatory. The spectra reveal resolved molecular lines from H2O and CO, and are compared to a custom PHOENIX atmosphere model grid appropriate for young planetary-mass objects. We fit the data using a Markov chain Monte Carlo forward-modeling method. Using a combination of our moderate-resolution spectrum and low-resolution, broadband data from the literature, we derive an effective temperature of Teff=1950-2150K, a surface gravity of logg=3.5--4.5, and a metallicity of [M/H]=-0.2--0.0. These values are consistent with previous estimates from atmospheric modeling and the currently favored young age of the system (<50Myr). We derive a C/O ratio of 0.70_-0.24_^+0.09^ for the source, broadly consistent with the solar C/O ratio. This, coupled with the slightly subsolar metallicity, implies a composition consistent with that of the host star, and is suggestive of formation by a rapid process. The subsolar metallicity of {kappa}-Andromedae-b is also consistent with predictions of formation via gravitational instability. Further constraints on formation of the companion will require measurement of the C/O ratio of {kappa}-Andromedae-A. We also measure the radial velocity of {kappa}-Andromedae-b for the first time, with a value of -1.4{+/-}0.9km/s relative to the host star. We find that the derived radial velocity is consistent with the estimated high eccentricity of {kappa}-Andromedae-b.
25. Parallaxes of late-T and Y dwarfs
ID:
ivo://CDS.VizieR/J/ApJS/240/19
Title:
Parallaxes of late-T and Y dwarfs
Short Name:
J/ApJS/240/19
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present preliminary trigonometric parallaxes of 184 late-T and Y dwarfs using observations from Spitzer (143), the U.S. Naval Observatory (18), the New Technology Telescope (14), and the United Kingdom Infrared Telescope (9). To complete the 20pc census of >=T6 dwarfs, we combine these measurements with previously published trigonometric parallaxes for an additional 44 objects and spectrophotometric distance estimates for another 7. For these 235 objects, we estimate temperatures, sift into five 150K wide T_eff_ bins covering the range 300-1050K, determine the completeness limit for each, and compute space densities. To anchor the high-mass end of the brown dwarf mass spectrum, we compile a list of early- to mid-L dwarfs within 20pc. We run simulations using various functional forms of the mass function passed through two different sets of evolutionary code to compute predicted distributions in T_eff_. The best fit of these predictions to our L, T, and Y observations is a simple power-law model with {alpha}~0.6 (where dN/dM{propto}M^-{alpha}^), meaning that the slope of the field substellar mass function is in rough agreement with that found for brown dwarfs in nearby star-forming regions and young clusters. Furthermore, we find that published versions of the log-normal form do not predict the steady rise seen in the space densities from 1050 to 350K. We also find that the low-mass cutoff to formation, if one exists, is lower than ~5M_Jup_, which corroborates findings in young, nearby moving groups and implies that extremely low-mass objects have been forming over the lifetime of the Milky Way.
26. Photometry of 38708 stars in W3 complex with HST
ID:
ivo://CDS.VizieR/J/AJ/161/138
Title:
Photometry of 38708 stars in W3 complex with HST
Short Name:
J/AJ/161/138
Date:
11 Mar 2022
Publisher:
CDS
Description:
We have used archival infrared images obtained with the Wide Field Camera 3 on board the Hubble Space Telescope to constrain the initial mass function of low-mass stars and brown dwarfs in the W3 star-forming region. The images cover 438arcmin^2^, which encompasses the entire complex, and were taken in the filters F110W, F139M, and F160W. We have estimated extinctions for individual sources in these data from their colors and have dereddened their photometry accordingly. By comparing an area of the images that contains the richest concentration of previously identified W3 members to an area that has few members and is dominated by background stars, we have estimated the luminosity function for members of W3 with masses of 0.03-0.4M{sun}. That luminosity function closely resembles data in typical nearby star-forming regions that have much smaller stellar populations than W3 ( ~500 versus several thousand objects). Thus, we do not find evidence of significant variations in the initial mass function of low-mass stars and brown dwarfs with star-forming conditions, which is consistent with recent studies of other distant massive star-forming regions.
27. Planetary-mass brown dwarfs in the Taurus SFR
ID:
ivo://CDS.VizieR/J/AJ/154/134
Title:
Planetary-mass brown dwarfs in the Taurus SFR
Short Name:
J/AJ/154/134
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the initial results from a survey for planetary-mass brown dwarfs in the Taurus star-forming region. We have identified brown dwarf candidates in Taurus using proper motions and photometry from several ground- and space- based facilities. Through spectroscopy of some of the more promising candidates, we have found 18 new members of Taurus. They have spectral types ranging from mid-M to early-L, and they include the four faintest known members in extinction-corrected K_s_, which should have masses as low as ~4-5 M_Jup_ according to evolutionary models. Two of the coolest new members (M9.25, M9.5) have mid-IR excesses that indicate the presence of disks. Two fainter objects with types of M9-L2 and M9-L3 also have red mid-IR colors relative to photospheres at =<L0, but since the photospheric colors are poorly defined at >L0, it is unclear whether they have excesses from disks. We also have obtained spectra of candidate members of the IC 348 and NGC 1333 clusters in Perseus that were identified by Luhman et al. Eight candidates are found to be probable members, three of which are among the faintest and least-massive known members of the clusters (~5 M_Jup_).
28. Properties of massive giant planets & brown dwarfs
ID:
ivo://CDS.VizieR/J/AJ/156/149
Title:
Properties of massive giant planets & brown dwarfs
Short Name:
J/AJ/156/149
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present thermodynamic material and transport properties for the extreme conditions prevalent in the interiors of massive giant planets and brown dwarfs. They are obtained from extensive ab initio simulations of hydrogen-helium mixtures along the isentropes of three representative objects. In particular, we determine the heat capacities, the thermal expansion coefficient, the isothermal compressibility, and the sound velocity. Important transport properties such as the electrical and thermal conductivity, opacity, and shear viscosity are also calculated. Further results for associated quantities, including magnetic and thermal diffusivity, kinematic shear viscosity, as well as the static Love number k_2_ and the equidistance, are presented. In comparison to Jupiter-mass planets, the behavior inside massive giant planets and brown dwarfs is stronger dominated by degenerate matter. We discuss the implications on possible dynamics and magnetic fields of those massive objects. The consistent data set compiled here may serve as a starting point to obtain material and transport properties for other substellar H-He objects with masses above one Jovian mass and finally may be used as input for dynamo simulations.
29. PS1 proper-motion survey for brown dwarfs. I. Taurus
ID:
ivo://CDS.VizieR/J/ApJ/858/41
Title:
PS1 proper-motion survey for brown dwarfs. I. Taurus
Short Name:
J/ApJ/858/41
Date:
21 Oct 2021
Publisher:
CDS
Description:
We are conducting a proper-motion survey for young brown dwarfs in the Taurus-Auriga molecular cloud based on the Pan-STARRS1 3{pi} Survey. Our search uses multi-band photometry and astrometry to select candidates, and is wider (370deg^2^) and deeper (down to ~3M_Jup_) than previous searches. We present here our search methods and spectroscopic follow-up of our high-priority candidates. Since extinction complicates spectral classification, we have developed a new approach using low-resolution (R~100) near-infrared spectra to quantify reddening-free spectral types, extinctions, and gravity classifications for mid-M to late-L ultracool dwarfs (<=100-3M_Jup_ in Taurus). We have discovered 25 low-gravity (VL-G) and the first 11 intermediate-gravity (INT-G) substellar (M6-L1) members of Taurus, constituting the largest single increase of Taurus brown dwarfs to date. We have also discovered 1 new Pleiades member and 13 new members of the Perseus OB2 association, including a candidate very wide separation (58kau) binary. We homogeneously reclassify the spectral types and extinctions of all previously known Taurus brown dwarfs. Altogether our discoveries have thus far increased the substellar census in Taurus by ~40% and added three more L-type members (<~5-10M_Jup_). Most notably, our discoveries reveal an older (>10Myr) low-mass population in Taurus, in accord with recent studies of the higher-mass stellar members. The mass function appears to differ between the younger and older Taurus populations, possibly due to incompleteness of the older stellar members or different star formation processes.
30. RVs of the late-T dwarf GL 758 B host star
ID:
ivo://CDS.VizieR/J/AJ/155/159
Title:
RVs of the late-T dwarf GL 758 B host star
Short Name:
J/AJ/155/159
Date:
21 Oct 2021
Publisher:
CDS
Description:
Gl 758 B is a late-T dwarf orbiting a metal-rich Sun-like star at a projected separation of {rho}~1.6" (25 au). We present four epochs of astrometry of this system with NIRC2 at Keck Observatory spanning 2010 to 2017 together with 630 radial velocities (RVs) of the host star acquired over the past two decades from McDonald Observatory, Keck Observatory, and the Automated Planet Finder at Lick Observatory. The RVs reveal that Gl 758 is accelerating with an evolving rate that varies between 2 and 5 m/s/yr, consistent with the expected influence of the imaged companion Gl 758 B. A joint fit of the RVs and astrometry yields a dynamical mass of 42_-7_^+19^ M_Jup_ for the companion with a robust lower limit of 30.5 M_Jup_ at the 4-{sigma} level. Gl 758 B is on an eccentric orbit (e=0.26-0.67 at 95% confidence) with a semimajor axis of a=21.1_-1.3_^+2.7^ au and an orbital period of P=96_-9_^+21^ yr, which takes it within ~9 au from its host star at periastron passage. Substellar evolutionary models generally underpredict the mass of Gl 758 B for nominal ages of 1-6 Gyr that have previously been adopted for the host star. This discrepancy can be reconciled if the system is older - which is consistent with activity indicators and recent isochrone fitting of the host star - or alternatively if the models are systematically overluminous by ~0.1-0.2 dex. Gl 758 B is currently the lowest-mass directly imaged companion inducing a measured acceleration on its host star. In the future, bridging RVs and high-contrast imaging with the next generation of extremely large telescopes and space-based facilities will open the door to the first dynamical mass measurements of imaged exoplanets.