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Detection of circumstellar disks around nearby young brown dwarf candidates

N. Phan-Bao, M. S. Bessell, E. L. Martín

Abstract

It is important to detect and study circumstellar disks around late-M and brown dwarfs of nearby young associations to understand how these very low-mass objects form and how rocky planets form around them. The detection of new very low-mass members of nearby young associations will also significantly improve our current understanding of young associations. We searched for new young very low-mass members with circumstellar disks in a sample of 3928 candidates. We constructed spectral energy distributions of all candidates using observational photometric data from DENIS, 2MASS, and WISE and trigonometric parallaxes from Gaia to detect infrared excess emission that indicates the presence of circumstellar disks. We then followed up spectroscopic observations of candidates to search for lithium to confirm their youth. The H_alpha emission line was used to detect accretion. We detected 23 among the 3928 candidates with circumstellar disks: Ten objects are new, and 13 were previously reported in the literature. Our mass estimates also indicate that 21 are brown dwarf candidates and 2 are very low-mass stars. DENIS J0534552-104808 has a Gaia distance of 238 pc and might be the first brown dwarf candidate member of a foreground population in front of the Orion D cloud. This foreground population is probably associated with the supergiant kappa Ori. Based on our spectroscopic observations, we detected lithium in 11 candidates. We also identified seven accretors and one potential accretor. The intense long-lived accretion detected in DENIS-P J0500245-333042, a 20 Myr old brown dwarf candidate may be additional evidence to favor the formation of rocky planets around very low-mass objects.

Detection of circumstellar disks around nearby young brown dwarf candidates

Abstract

It is important to detect and study circumstellar disks around late-M and brown dwarfs of nearby young associations to understand how these very low-mass objects form and how rocky planets form around them. The detection of new very low-mass members of nearby young associations will also significantly improve our current understanding of young associations. We searched for new young very low-mass members with circumstellar disks in a sample of 3928 candidates. We constructed spectral energy distributions of all candidates using observational photometric data from DENIS, 2MASS, and WISE and trigonometric parallaxes from Gaia to detect infrared excess emission that indicates the presence of circumstellar disks. We then followed up spectroscopic observations of candidates to search for lithium to confirm their youth. The H_alpha emission line was used to detect accretion. We detected 23 among the 3928 candidates with circumstellar disks: Ten objects are new, and 13 were previously reported in the literature. Our mass estimates also indicate that 21 are brown dwarf candidates and 2 are very low-mass stars. DENIS J0534552-104808 has a Gaia distance of 238 pc and might be the first brown dwarf candidate member of a foreground population in front of the Orion D cloud. This foreground population is probably associated with the supergiant kappa Ori. Based on our spectroscopic observations, we detected lithium in 11 candidates. We also identified seven accretors and one potential accretor. The intense long-lived accretion detected in DENIS-P J0500245-333042, a 20 Myr old brown dwarf candidate may be additional evidence to favor the formation of rocky planets around very low-mass objects.
Paper Structure (7 sections, 8 figures, 5 tables)

This paper contains 7 sections, 8 figures, 5 tables.

Table of Contents

  1. Introduction
  2. Sample
  3. Results and discussion
  4. Determination of age, mass, and membership in young associations
  5. Spectroscopic follow-up observations
  6. Conclusion
  7. SED of late-M dwarfs

Figures (8)

  • Figure 1: 2MASS $J$-band absolute magnitude vs. $I-J$ color diagram for 23 candidates with available Gaia parallaxes. The DENIS $I$-band and 2MASS $J$-band photometric data are listed in Table \ref{['nearir']}. Isochrones and mass tracks from the BT-Settl CIFIST 2011-2015 models baraffe15 are plotted. The hatched blue area indicates the region in which lithium is not completely depleted and can be detected in the stellar atmosphere.
  • Figure 1: continued.
  • Figure 2: R3000 spectra of 11 IR excess candidates. Our spectral types adopted from spectral indices VOa, TiO5, and PC3 (see Table \ref{['spt']}) are also shown.
  • Figure 3: R3000 spectra of 11 candidates. The region of the Li I line is indicated. The R600R INT spectrum of DENIS0524$-$0437 is shown. The low-resolution spectrum of WT 460 (M5.5) without a lithium detection pb17 is also shown for comparison.
  • Figure 4: R7000 spectra of six candidates (see Table \ref{['acc']}). The region of the Li I line is indicated. The spectra of DENIS0103-5351 (M5.5) and SCR 0838-5855 (M6.0) without a lithium detection pb17 are also plotted for comparison.
  • ...and 3 more figures