Ultracool dwarfs identified using spectra in LAMOST DR7

Abstract

In this work, we identify 734 ultracool dwarfs with a spectral type of M6 or later, including one L0. Of this sample, 625 were studied spectroscopically for the first time. All of these ultracool dwarfs are within 360~pc, with a \textit{Gaia} G magnitude brighter than ~19.2 mag. By studying the spectra and checking their stellar parameters (Teff, logg, and [FeH] derived with the LAMOST pipeline, we found their cool red nature and their metallicity to be consistent with the nature of Galactic thin-disk objects. Furthermore, 77 of them show lithium absorption lines at 6708A, further indicating their young ages and substellar nature. Kinematics obtained through LAMOST radial velocities, along with the proper motion and parallax data from Gaia EDR3, also suggest that the majority of our targets are thin-disk objects. Kinematic ages were estimated through the relationship between the velocity dispersion and the average age for a certain population. Moreover, we identified 35 binaries, with 6 of them reported as binaries for the first time.

13 pages, 11 figures, published in A&A, Volume 660. A38 (2022)

References in corpus (12)

• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• Stellar SEDs from 0.3-2.5 Microns: Tracing the Stellar Locus and Searching for Color Outliers in SDSS and 2MASS
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
• SpeX Spectroscopy of Unresolved Very Low Mass Binaries. II. Identification of Fourteen Candidate Binaries with Late-M/Early-L and T Dwarf Components
• Activity indicators and stellar parameters of the Kepler targets. An application of the ROTFIT pipeline to LAMOST-Kepler stellar spectra
• Space Velocities of L- and T-type Dwarfs
• Kinematics of the local disk from the RAVE survey and the Gaia first data release
• 591 high velocity stars in the Galactic halo selected from LAMOST DR7 and Gaia DR2
• Effective Temperatures of Low-Mass Stars from High-Resolution H-band Spectroscopy
• A homogeneous sample of 34 000 M7-M9.5 dwarfs brighter than $J$=17.5 with accurate spectral types