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Start Over Subject dwarf stars Publisher CDS
251. New close binary systems from the SDSS DR5
ID:
ivo://CDS.VizieR/J/AJ/134/741
Title:
New close binary systems from the SDSS DR5
Short Name:
J/AJ/134/741
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the latest catalog of more than 1200 spectroscopically selected close binary systems observed with the Sloan Digital Sky Survey through Data Release Five. We use the catalog to search for magnetic white dwarfs in cataclysmic variable progenitor systems. Given that approximately 25% of cataclysmic variables contain a magnetic white dwarf, and that our large sample of close binary systems should contain many progenitors of cataclysmic variables, it is quite surprising that we find only two potential magnetic white dwarfs in this sample.
252. New L and T dwarfs from the SDSS
ID:
ivo://CDS.VizieR/J/AJ/131/2722
Title:
New L and T dwarfs from the SDSS
Short Name:
J/AJ/131/2722
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present near-infrared observations of 71 newly discovered L and T dwarfs, selected from imaging data of the Sloan Digital Sky Survey (SDSS) using the i-dropout technique. Sixty-five of these dwarfs have been classified spectroscopically according to the near-infrared L dwarf classification scheme of Geballe et al. (2002ApJ...564..466G) and the unified T dwarf classification scheme of Burgasser et al. (2006, Cat. <J/ApJ/637/1067>). The spectral types of these dwarfs range from L3 to T7 and include the latest types yet found in the SDSS. Six of the newly identified dwarfs are classified as early to mid-L dwarfs according to their photometric near-infrared colors, and two others are classified photometrically as M dwarfs. We also present new near-infrared spectra for five previously published SDSS L and T dwarfs, and one L dwarf and one T dwarf discovered by Burgasser et al. (2006, Cat. <J/ApJ/637/1067>) from the Two Micron All Sky Survey. The new SDSS sample includes 27 T dwarfs and 30 dwarfs with spectral types spanning the complex L-T transition (L7-T3).
253. New nearby M, L, and T dwarfs
ID:
ivo://CDS.VizieR/J/PASP/125/809
Title:
New nearby M, L, and T dwarfs
Short Name:
J/PASP/125/809
Date:
21 Oct 2021
Publisher:
CDS
Description:
In our effort to complete the census of low-mass stars and brown dwarfs in the immediate solar neighborhood, we present spectra, photometry, proper motions, and distance estimates for 42 low-mass star and brown dwarf candidates discovered by the Wide-field Infrared Survey Explorer (WISE). We also present additional follow-up information on 12 candidates selected using WISE data but previously published elsewhere. The new discoveries include 15 M dwarfs, 17 L dwarfs, five T dwarfs, and five objects of other types. Among these discoveries is a newly identified "unusually red L dwarf" (WISE J223527.07+451140.9), four peculiar L dwarfs whose spectra are most readily explained as unresolved L+T binary systems, and a T9 dwarf (WISE J124309.61+844547.8). We also show that the recently discovered red L dwarf WISEP J004701.06+680352.1 may be a low-gravity object and hence young and potentially low-mass (<25M_Jup_).
254. New reduction of UVES data for 35 M dwarfs
ID:
ivo://CDS.VizieR/J/AJ/158/251
Title:
New reduction of UVES data for 35 M dwarfs
Short Name:
J/AJ/158/251
Date:
21 Oct 2021
Publisher:
CDS
Description:
The UVES (Ultraviolet and Visible Spectrometer) M Dwarf Planet Search program surveyed 40 M dwarfs and 1 M giant from 2000 through 2007 March. Two of the M dwarfs were double-lined spectroscopic binaries. The 38 single-lined M dwarfs in this survey are among the nearest and brightest M dwarfs. Starting with the reduced 1D spectra provided by the UVES team, we reanalyzed the UVES velocities of Proxima Cen as part of the "Pale Red Dot" program. The velocity rms decreased from 3.6 to 2.3 m/s. Motivated by this result, we have harvested all of the raw data from the UVES M Dwarf Planet Search from the European Southern Observatory (ESO) archives and have written custom packages to generate 1D spectra from the raw data, and velocities from the 1D spectra. The median improvement in the velocity rms from the new analysis is 1.8 m/s. Six of the 38 M dwarfs from the original study had a velocity rms<4 m/s. In the reanalysis presented here, 22 of these stars have a velocity rms<4 m/s. We improve the upper limits on possible planets orbiting these stars by a factor of typically two to three. For many of these M dwarfs, these observations represent the first epoch of high-precision velocity measurements.
255. New SpeX Observations of M7-L6 Dwarfs
ID:
ivo://CDS.VizieR/J/ApJ/794/143
Title:
New SpeX Observations of M7-L6 Dwarfs
Short Name:
J/ApJ/794/143
Date:
21 Oct 2021
Publisher:
CDS
Description:
Multiplicity is a key statistic for understanding the formation of very low mass (VLM) stars and brown dwarfs. Currently, the separation distribution of VLM binaries remains poorly constrained at small separations (<=1 AU), leading to uncertainty in the overall binary fraction. We approach this problem by searching for late-M/early-L plus T dwarf spectral binaries whose combined light spectra exhibit distinct peculiarities, allowing for separation-independent identification. We define a set of spectral indices designed to identify these systems, and we use a spectral template fitting method to confirm and characterize spectral binary candidates from a library of 815 spectra from the SpeX Prism Spectral Libraries. We present 11 new binary candidates, confirm 3 previously reported candidates, and rule out 2 previously identified candidates, all with primary and secondary spectral types in the range M7-L7 and T1-T8, respectively. We find that subdwarfs and blue L dwarfs are the primary contaminants in our sample and propose a method for segregating these sources. If confirmed by follow-up observations, these systems may add to the growing list of tight separation binaries, whose orbital properties may yield further insight into brown dwarf formation scenarios.
256. New T dwarfs identified in Pan-STARRS 1
ID:
ivo://CDS.VizieR/J/AJ/142/77
Title:
New T dwarfs identified in Pan-STARRS 1
Short Name:
J/AJ/142/77
Date:
21 Oct 2021
Publisher:
CDS
Description:
A complete well-defined sample of ultracool dwarfs is one of the key science programs of the Pan-STARRS 1 optical survey telescope (PS1). Here we combine PS1 commissioning data with the Two Micron All Sky Survey (2MASS) to conduct a proper motion search (0.1-2.0"/yr) for nearby T dwarfs, using optical+near-IR colors to select objects for spectroscopic follow-up. The addition of sensitive far-red optical imaging from PS1 enables discovery of nearby ultracool dwarfs that cannot be identified from 2MASS data alone. We have searched 3700deg^2^ of PS1 y-band (0.95-1.03um) data to y~19.5mag (AB) and J~16.5mag (Vega) and discovered four previously unknown bright T dwarfs. Three of the objects (with spectral types T1.5, T2, and T3.5) have photometric distances within 25pc and were missed by previous 2MASS searches due to more restrictive color selection criteria. The fourth object (spectral type T4.5) is more distant than 25pc and is only a single-band detection in 2MASS. We also examine the potential for completing the census of nearby ultracool objects with the PS1 3{PI} survey.
257. New very low-mass members in Taurus
ID:
ivo://CDS.VizieR/J/A+A/446/485
Title:
New very low-mass members in Taurus
Short Name:
J/A+A/446/485
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have performed a large scale optical survey of the Taurus cloud, covering a total area of 28deg^2^, and encompassing the densest parts of the cloud as well as their surroundings, down to a mass detection limit of 15 Jupiter masses. We present the optical spectroscopic follow-up observations of 97 photometrically selected potential new low-mass Taurus members, of which 27 are strong late-M spectral type SpType<M4V candidates. We derive spectral types, visual absorption and luminosity class estimates and discuss our criteria to assess Taurus membership. These observations reveal 5 new VLM Taurus members and 12 new brown dwarfs. Combining our observations with previously published results, we derive an updated substellar to stellar ratio in Taurus of Rss=0.23+/-0.05. This ratio now appears consistent with the value previously derived in the Trapezium cluster under similar assumptions of 0.26+/-0.04. We find indications that the relative numbers of brown dwarfs with respect to stars is decreased by a factor 2 in the central regions of the aggregates with respect to the more distributed population. Our findings are best explained in the context of the embryo-ejection model where brown dwarfs originate from dynamical interactions in small N unstable multiple systems.
258. NIR Imaging of R136 in 30 Dor
ID:
ivo://CDS.VizieR/J/ApJ/466/254
Title:
NIR Imaging of R136 in 30 Dor
Short Name:
J/ApJ/466/254
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report 0.15" resolution near-infrared (NIR) imaging of R136, the central region of 30 Doradus in the Large Magellanic Cloud. Our 12.8"x12.8" images were recorded with the MPE camera SHARP II at the 3.6m ESO telescope, using the adaptive optics system COME ON+. The high spatial resolution and sensitivity (20th magnitude in K) of our observations allow our H- and K-band images to be compared and combined with recent Hubble Space Telescope (HST) WFPC2 data of R136. We fit theoretical models with variable foreground extinction to the observed magnitudes of ~1000 stars (roughly half of which were detected in HST and NIR bands) and derive the stellar population in this starburst region. We find no red giants or supergiants; however, we detect ~110 extremely red sources which are probably young, pre-main-sequence low- or intermediate-mass stars. We obtained narrow-band images to identify known and new Wolf-Rayet stars by their He II (2.189um) and BrGamma (2.166um) emission lines. The presence of W-R stars and absence of red supergiants narrow the cluster age to 3-5Myr, while the derived ratio of W-R to O stars of 0.05 in the central region favors an age of ~3.5Myr, with a relatively short starburst duration. For the O stars, the core radius is found to be 0.1pc and appears to decrease with increasing stellar mass. The slope of the mass function is Gamma=-1.6 on average, but it steepens with increasing distance from the cluster center from Gamma=-1.3 in the inner 0.4pc to Gamma=-2.2 outside 0.8pc for stars more massive than 12 Msun. The radial variation of the mass function reveals strong mass segregation that is probably due to the cluster's dynamical evolution.
259. NIR spectral of M-T dwarfs
ID:
ivo://CDS.VizieR/J/A+A/503/639
Title:
NIR spectral of M-T dwarfs
Short Name:
J/A+A/503/639
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present complete near-infrared (0.85-2.45um), low-resolution (R~100) spectra of a sample of 54 disk M-, L-, and T-dwarfs with reliable optical or near infrared spectral-type classification from the literature. The observations were obtained with a prism-based optical element, the Amici device, which provides a complete spectrum of the source on the detector. Our observations indicate that low-resolution near-infrared spectroscopy can be used to determine the spectral classification of late-type field dwarfs in a fast but accurate way. We derive a set of near-infrared spectral indices that are useful to the classification of field dwarfs not seriously affected by reddening. Finally, we show that the comparison of Amici spectra with model atmospheres allows us to obtain a reliable estimate of the dwarf effective temperatures
260. NIR spectroscopy of new L and T dwarf candidates
ID:
ivo://CDS.VizieR/J/AJ/154/112
Title:
NIR spectroscopy of new L and T dwarf candidates
Short Name:
J/AJ/154/112
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the final results from a targeted search for brown dwarfs with unusual near-infrared colors. From a positional cross-match of the Sloan Digital Sky Survey (SDSS), 2-Micron All-Sky Survey (2MASS), and Wide-Field Infrared Survey Explorer (WISE) catalogs, we have identified 144 candidate peculiar L and T dwarfs. Spectroscopy confirms that 20 of the objects are peculiar or are candidate binaries. Of the 420 objects in our full sample 9 are young (<~200Myr; 2.1%) and another 8 (1.9%) are unusually red, with no signatures of youth. With a spectroscopic J-K_s_ color of 2.58+/-0.11mag, one of the new objects, the L6 dwarf 2MASS J03530419+0418193, is among the reddest field dwarfs currently known and is one of the reddest objects with no signatures of youth known to date. We have also discovered another potentially very-low-gravity object, the L1 dwarf 2MASS J00133470+1109403, and independently identified the young L7 dwarf 2MASS J00440332+0228112, which was first reported by Schneider and collaborators. Our results confirm that signatures of low gravity are no longer discernible in low to moderate resolution spectra of objects older than ~200Myr. The 1.9% of unusually red L dwarfs that do not show other signatures of youth could be slightly older, up to ~400Myr. In this case a red J-K_s_ color may be more diagnostic of moderate youth than individual spectral features. However, its is also possible that these objects are relatively metal-rich, and thus have enhanced atmospheric dust content.

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