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141. LAMOST DR5 White dwarf-main sequence binaries
ID:
ivo://CDS.VizieR/J/MNRAS/477/4641
Title:
LAMOST DR5 White dwarf-main sequence binaries
Short Name:
J/MNRAS/477/4641
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the data release (DR) 5 catalogue of white dwarf-main sequence (WDMS) binaries from the Large sky Area Multi-Object fibre Spectroscopic Telescope (LAMOST). The catalogue contains 876 WDMS binaries, of which 757 are additions to our previous LAMOST DR1 sample and 357 are systems that have not been published before. We also describe a LAMOST-dedicated survey that aims at obtaining spectra of photometrically selected WDMS binaries from the Sloan Digital Sky Survey (SDSS) that are expected to contain cool white dwarfs and/or early-type M dwarf companions. This is a population under-represented in previous SDSS WDMS binary catalogues. We determine the stellar parameters (white dwarf effective temperatures, surface gravities and masses, and M dwarf spectral types) of the LAMOST DR5 WDMS binaries and make use of the parameter distributions to analyse the properties of the sample. We find that, despite our efforts, systems containing cool white dwarfs remain under-represented. Moreover, we make use of LAMOST DR5 and SDSS DR14 (when available) spectra to measure the NaI {lambda}{lambda} 8183.27, 8194.81 absorption doublet and/or H{alpha} emission radial velocities of our systems. This allows identifying 128 binaries displaying significant radial velocity variations, 76 of which are new. Finally, we cross-match our catalogue with the Catalina Surveys and identify 57 systems displaying light-curve variations. These include 16 eclipsing systems, two of which are new, and nine binaries that are new eclipsing candidates. We calculate periodograms from the photometric data and measure (estimate) the orbital periods of 30 (15) WDMS binaries.
142. L and T dwarfs from UKIDSS LAS
ID:
ivo://CDS.VizieR/J/MNRAS/449/3651
Title:
L and T dwarfs from UKIDSS LAS
Short Name:
J/MNRAS/449/3651
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the spectroscopic analysis of a large sample of late-M, L, and T dwarfs from the United Kingdom Deep Infrared Sky Survey. Using the YJHK photometry from the Large Area Survey and the red-optical photometry from the Sloan Digital Sky Survey we selected a sample of 262 brown dwarf candidates and we have followed-up 196 of them using the echelle spectrograph X-shooter on the Very Large Telescope. The large wavelength coverage (0.30-2.48um) and moderate resolution (R~5000-9000) of X-shooter allowed us to identify peculiar objects including 22 blue L dwarfs, 2 blue T dwarfs, and 2 low-gravity M dwarfs. Using a spectral indices-based technique, we identified 27 unresolved binary candidates, for which we have determined the spectral type of the potential components via spectral deconvolution. The spectra allowed us to measure the equivalent width of the prominent absorption features and to compare them to atmospheric models. Cross-correlating the spectra with a radial velocity standard, we measured the radial velocity of our targets, and we determined the distribution of the sample, which is centred at -1.7+/-1.2km/s with a dispersion of 31.5km/s. Using our results, we estimated the space density of field brown dwarfs and compared it with the results of numerical simulations. Depending on the binary fraction, we found that there are (0.85+/-0.55)x10^-3^ to (1.00+/-0.64)x10^-3^ objects per cubic parsec in the L4-L6.5 range, (0.73+/-0.47)x10^-3^ to (0.85+/-0.55)x10^-3^ objects per cubic parsec in the L7-T0.5 range, and (0.74+/-0.48)x10^-3^ to (0.88+/-0.56)x10^-3^ objects per cubic parsec in the T1-T4.5 range. We notice that there seems to be an excess of objects in the L-T transition with respect to the late-T dwarfs, a discrepancy that could be explained assuming a higher binary fraction than expected for the L-T transition, or that objects in the high-mass end and low-mass end of this regime form in different environments, i.e. following different initial mass functions.
143. L and T dwarfs in 2MASS/SDSS
ID:
ivo://CDS.VizieR/J/ApJ/676/1281
Title:
L and T dwarfs in 2MASS/SDSS
Short Name:
J/ApJ/676/1281
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report new L and T dwarfs found in a cross-match of the SDSS Data Release 1 and 2MASS. Our simultaneous search of the two databases effectively allows us to relax the criteria for object detection in either survey and to explore the combined databases to a greater completeness level. We find two new T dwarfs in addition to the 13 already known in the SDSS DR1 footprint. We also identify 22 new candidate and bona fide L dwarfs, including a new young L2 dwarf and a peculiar potentially metal-poor L2 dwarf with unusually blue near-IR colors. These discoveries underscore the utility of simultaneous database cross-correlation in searching for rare objects.
144. L and T dwarf stars
ID:
ivo://CDS.VizieR/J/other/ARA+A/43.195
Title:
L and T dwarf stars
Short Name:
J/other/ARA+A/43
Date:
21 Oct 2021
Publisher:
CDS
Description:
The establishment of new spectral classes cooler than type M has had a brief, yet already rich, history. Prototypes of the new "L dwarf" and "T dwarf" classes were first found in the late 1980s to mid-1990s, with a flood of new discoveries occurring in the late 1990s with the advent of deep, large-area, digital sky surveys. Over four hundred and fifty L and T dwarfs are now catalogued. This review concentrates on the spectroscopic properties of these objects, beginning with the establishment of classification schemes rooted in the MK Process. The resulting grid of spectral types is then used as a tool to ferret out the underlying physics. The temperature ranges covered by these spectral types, the complex chemical processes responsible for the shape of their emergent spectra, their nature as either true stars or brown dwarfs, and their number density in the Galaxy are discussed. Two promising avenues for future research are also explored: the extension of the classification system to three dimensions to account for gravity- and metallicity-dependent features, and the capability of newer large-area surveys to uncover brown dwarfs cooler than those now recognized.
145. LASSO; Robo-AO observation of 444 young stars
ID:
ivo://CDS.VizieR/J/AJ/162/102
Title:
LASSO; Robo-AO observation of 444 young stars
Short Name:
J/AJ/162/102
Date:
14 Mar 2022 06:43:15
Publisher:
CDS
Description:
We present results from the Large Adaptive optics Survey for Substellar Objects, where the goal is to directly image new substellar companions (<70M_Jup_) at wide orbital separations (>~50au) around young (<~300Myr), nearby (<100pc), low-mass (~0.1-0.8 M{odot}) stars. We report on 427 young stars imaged in the visible (i') and near-infrared (J or H ) simultaneously with Robo-AO on the Kitt Peak 2.1m telescope and later the Maunakea University of Hawaii 2.2m telescope. To undertake the observations, we commissioned a new infrared camera for Robo-AO that uses a low-noise high-speed SAPHIRA avalanche photodiode detector. We detected 121 companion candidates around 111 stars, of which 62 companions are physically associated based on Gaia DR2 parallaxes and proper motions, another 45 require follow-up observations to confirm physical association, and 14 are background objects. The companion separations range from 2 to 1101 au and reach contrast ratios of 7.7 mag in the near-infrared compared to the primary. The majority of confirmed and pending candidates are stellar companions, with ~5 being potentially substellar and requiring follow-up observations for confirmation. We also detected a 43{+/-}9 M_Jup_ and an 81{+/-}5M_Jup_ companion that were previously reported. We found 34 of our targets have acceleration measurements detected using Hipparcos-Gaia proper motions. Of those, 58_-14_^+12^% of the 12 stars with imaged companion candidates have significant accelerations ({chi}^2^>11.8), while only 23_-6_^+11^% of the remaining 22 stars with no detected companion have significant accelerations. The significance of the acceleration decreases with increasing companion separation. These young accelerating low-mass stars with companions will eventually yield dynamical masses with future orbit monitoring.
146. Late-Type Extension to MoVeRS (LaTE-MoVeRS)
ID:
ivo://CDS.VizieR/J/AJ/153/92
Title:
Late-Type Extension to MoVeRS (LaTE-MoVeRS)
Short Name:
J/AJ/153/92
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the Late-Type Extension to the Motion Verified Red Stars (LaTE-MoVeRS) catalog, containing 46,463 photometric late-type (>M5) dwarfs within the Sloan Digital Sky Survey (SDSS) footprint. Proper motions were computed for objects combining astrometry from the SDSS Data Release 12 (DR12), the Two-micron All-Sky Survey (2MASS) Point Source Catalog, and the Wide-field Infrared Survey Explorer (WISE) AllWISE data sets. LaTE-MoVeRS objects were required to have significant proper motion . Using the LaTE-MoVeRS sample and Gaia Data Release 1, we estimate Gaia will be ~64% complete for very low-mass objects (>M5) in comparison to the combined SDSS+2MASS+WISE data set (i<21.3). We computed photometric distances and estimated stellar effective temperatures for the LaTE-MoVeRS catalog. The majority of the dwarfs in the sample have distances <150pc and T<3000K. Thirteen objects that have not been previously identified as nearby eff objects were identified within LaTE-MoVeRS with estimated photometric distances within 25pc. We also identified one new object that has not been previously identified with a large amount of excess mid-infrared flux (2MASS J11151597+1937266). This object appears to be an L2{gamma} at ~50pc showing spectroscopic signs of a flaring event (e.g., strong hydrogen Balmer emission lines). This object does not exhibit kinematics similar to any known kinematic association. The LaTE-MoVeRS catalog is available through SDSS CasJobs and VizieR.
147. Late-type targets in Taurus, Cha I, and Upper Sco
ID:
ivo://CDS.VizieR/J/ApJ/788/40
Title:
Late-type targets in Taurus, Cha I, and Upper Sco
Short Name:
J/ApJ/788/40
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have used WFPC2 on board the Hubble Space Telescope to obtain images of 47 members of the Taurus and Chamaeleon I star-forming regions that have spectral types of M6-L0 (M~0.01-0.1 M_{sun}_). An additional late-type member of Taurus, FU Tau (M7.25+M9.25), was also observed with adaptive optics at Keck Observatory. In these images, we have identified promising candidate companions to 2MASS J04414489+2301513 ({rho}=0.105"/15 AU), 2MASS J04221332+1934392 ({rho}=0.05"/7 AU), and ISO 217 ({rho}=0.03"/5 AU). We reported the first candidate in a previous study, showing that it has a similar proper motion as the primary in images from WFPC2 and Gemini adaptive optics. We have collected an additional epoch of data with Gemini that further supports that result. By combining our survey with previous high-resolution imaging in Taurus, Chamaeleon I, and Upper Sco ({tau}~10 Myr), we measure binary fractions of 14/93=0.15_-0.03_^+0.05^ for M4-M6 (M~0.1-0.3 M_{sun}_) and 4/108=0.04_-0.01_^+0.03^ for >M6 (M<~0.1 M_{sun}_) at separations of >10 AU. Given the youth and low density of these regions, the lower binary fraction at later types is probably primordial rather than due to dynamical interactions among association members. The widest low-mass binaries (>100 AU) also appear to be more common in Taurus and Chamaeleon I than in the field, which suggests that the widest low-mass binaries are disrupted by dynamical interactions at >10 Myr, or that field brown dwarfs have been born predominantly in denser clusters where wide systems are disrupted or inhibited from forming.
148. LCES HIRES/Keck radial velocity Exoplanet Survey
ID:
ivo://CDS.VizieR/J/AJ/153/208
Title:
LCES HIRES/Keck radial velocity Exoplanet Survey
Short Name:
J/AJ/153/208
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe a 20 year survey carried out by the Lick-Carnegie Exoplanet Survey Team (LCES), using precision radial velocities from HIRES on the Keck I telescope to find and characterize extrasolar planetary systems orbiting nearby F, G, K, and M dwarf stars. We provide here 60949 precision radial velocities for 1624 stars contained in that survey. We tabulate a list of 357 significant periodic signals that are of constant period and phase, and not coincident in period and/or phase with stellar activity indices. These signals are thus strongly suggestive of barycentric reflex motion of the star induced by one or more candidate exoplanets in Keplerian motion about the host star. Of these signals, 225 have already been published as planet claims, 60 are classified as significant unpublished planet candidates that await photometric follow-up to rule out activity-related causes, and 54 are also unpublished, but are classified as "significant" signals that require confirmation by additional data before rising to classification as planet candidates. Of particular interest is our detection of a candidate planet with Msin(i)=3.8M_{Earth}_, and P=9.9 days orbiting Lalande 21185, the fourth-closest main-sequence star to the Sun. For each of our exoplanetary candidate signals, we provide the period and semi-amplitude of the Keplerian orbital fit, and a likelihood ratio estimate of its statistical significance. We also tabulate 18 Keplerian-like signals that we classify as likely arising from stellar activity.
149. LHS faint proper-motion stars
ID:
ivo://CDS.VizieR/J/PASP/117/676
Title:
LHS faint proper-motion stars
Short Name:
J/PASP/117/676
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present low-resolution spectroscopic observations of faint proper-motion stars from the LHS Catalogue, concentrating on stars with m_r_>16.5 and {mu}>0.5"/yr. The present paper includes observations and spectral classifications for 294 M dwarfs, M subdwarfs (sdM), and extreme M subdwarfs (esdM). We also identify white dwarfs among the faintest LHS stars. We have cross-referenced this sample against the Two Micron All Sky Survey (2MASS) sources, and list data for the detected objects. We discuss stars of individual interest, as well as the characteristics of the overall sample. As expected, a significant number of the stars in this proper-motion-selected sample are halo subdwarfs, including an esdM dwarf, LHS 3481, that is likely to lie within 20pc of the Sun. None of the subdwarfs show H{alpha} emission.
150. Li abundances and velocities in F and G stars
ID:
ivo://CDS.VizieR/J/A+A/409/251
Title:
Li abundances and velocities in F and G stars
Short Name:
J/A+A/409/251
Date:
21 Oct 2021
Publisher:
CDS
Description:
Lithium abundances have been determined in 127 F and G Pop I stars based on new measurements of the equivalent width of the {lambda}6707{AA} Li I line from their high resolution CCD spectra. Distances and absolute magnitudes of these stars have been obtained from the Hipparcos Catalogue (<I/239>) and their masses and ages derived, enabling us to investigate the behaviour of lithium as a function of these parameters. Based on their location on the HR diagram superposed on theoretical evolutionary tracks, the sample of the stars has been chosen to ensure that they have more or less completed their Li depletion on the main sequence.

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