Gravity Indicators in the Near‐Infrared Spectra of Brown Dwarfs

Gorlova, Nadya; Meyer, Michael; Rieke, G. H.; Liebert, James

doi:10.1086/376730

Cited by 149 publications

(200 citation statements)

References 98 publications

(129 reference statements)

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“…Gorlova et al 2003;McGovern et al 2004;Kirkpatrick et al 2006 2007). We measured the equivalent widths (EW) of the gravity sensitive Na I doublet at 1.138µm and the K I doublets at 1.169, 1.177µm and 1.243, 1.253µm with associated errors as described in Bonnefoy et al (2014), with the psuedocontinuum wavelength regions reported therein.…”

Section: Surface Gravity and Chromospheric Activitymentioning

confidence: 99%

Characterization of close visual binaries from the AstraLux Large M Dwarf Survey

Bergfors¹,

Brandner²,

Bonnefoy³

et al. 2015

Mon. Not. R. Astron. Soc.

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We present VLT/SINFONI J, H + K spectra of seven close visual pairs in M dwarf binary/triple systems, discovered or observed by the AstraLux M dwarf survey. We determine the spectral types to within ±1.0 subclasses from comparison to template spectra and the strength of K-band water absorption, and derive effective temperatures. The results are compared to optical spectral types of the unresolved binary/multiple systems, and we confirm that our photometric method to derive spectral types in the AstraLux M dwarf survey is accurate. We look for signs of youth such as chromospheric activity and low surface gravity, and find an age in the range 0.25 − 1 Gyr for the GJ 852 system. Strong Li absorption is detected in optical spectra of the triple system J024902 obtained with FEROS at the ESO-MPG 2.2 m telescope. The equivalent width of the absorption suggests an age consistent with the β Pic moving group. However, further observations are needed to establish group membership. Ongoing orbital monitoring will provide dynamical masses and thus calibration of evolutionary models for low mass stars.

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Section: Surface Gravity and Chromospheric Activitymentioning

confidence: 99%

Characterization of close visual binaries from the AstraLux Large M Dwarf Survey

Bergfors¹,

Brandner²,

Bonnefoy³

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Spectroscopic surface gravity estimates have been used to identify giants and young brown dwarfs among samples of ultracool candidates (Martín et al 1996;Luhman et al 1998;Gorlova et al 2003;Martín & Zapatero Osorio 2003;McGovern et al 2004;Allers et al 2006). Atomic gravity-sensitive features present in our spectra include the KI resonance doublet at 766.5 nm and 766.9 nm, and the NaI subordinate doublet at 818.3 nm and 819.9 nm.…”

Section: Surface Gravitymentioning

confidence: 99%

Spectroscopic characterization of 78 DENIS ultracool dwarf candidates in the solar neighborhood and the Upper Scorpii OB association

Martín¹,

Phan-Bao²,

Bessell³

et al. 2010

A&A

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Aims. We search for new ultracool dwarfs and report here our observations of 78 ultracool dwarf candidates that have been photometrically selected using the DENIS survey point source catalogue. We analyze low-resolution optical spectroscopic observations to estimate spectral types of all candidates. Methods. We derive spectral types for each object using measurements of the PC3 spectral index as defined in Martín et al. They range from M6 to L3. The Hα emission and NaI subordinate doublet (818.3 nm and 819.9 nm) equivalent widths are measured in the spectra to identify young stellar objects. Spectroscopic indices of TiO, VO, CrH, and FeH molecular features are also reported. Results. A rule-of-thumb criterion for selecting young very low-mass objects using the NaI doublet equivalent width is given. It is used to confirm seven new members of the Upper Sco OB association and two new members of the R Cr-A star-forming region. Four of our field objects are also classified as very young, but are not members of any known nearby young association. The frequency of lower-gravity young objects in our field ultracool sample is 8.5%. Our results provide the first spectroscopic classification for 42 ultracool dwarfs in the solar vicinity with spectrophotometric distances in the range 17 pc to 65 pc (3 of them being new L dwarfs within 20 pc).

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“…It has been shown that source ages can be measured using gravity sensitive alkali metal absorption lines in the optical or near-infrared (Martin, Rebolo, & Zapatero-Osorio 1996;Steele & Jameson 1995;Gorlova et al 2003;Allers et al 2007, hereafter A07;Riddick, Roche, & Lucas 2007;Luhman et al 2007;Close et al 2007). This technique can differentiate 1 Myr objects from 5 Myr objects, and 5-10 Myr objects from field dwarfs, since very young substellar objects rapidly contract to smaller radii.…”

Section: Introductionmentioning

confidence: 99%

Towards precise ages and masses of Free Floating Planetary Mass Brown Dwarfs

Canty¹,

Lucas²,

Roche³

et al. 2013

Monthly Notices of the Royal Astronomical Society

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Measurement of the substellar initial mass function (IMF) in very young clusters is hampered by the possibility of the age spread of cluster members. This is particularly serious for candidate planetary mass objects (PMOs), which have a very similar location to older and more massive brown dwarfs on the Hertzsprung-Russell Diagram (HRD). This degeneracy can be lifted by the measurement of gravity sensitive spectral features. To this end we have obtained medium resolution (R≈5000) Near-infrared Integral Field Spectrometer (NIFS) K band spectra of a sample of late M-/early L-type dwarfs. The sample comprises old field dwarfs and very young brown dwarfs in the Taurus association and in the σ Orionis cluster. We demonstrate a positive correlation between the strengths of the 2.21 µm NaI doublet and the objects' ages. We demonstrate a further correlation between these objects' ages and the shape of their K band spectra. We have quantified this correlation in the form of a new index, the H 2 (K) index. This index appears to be more gravity-sensitive than the NaI doublet and has the advantage that it can be computed for spectra where gravity-sensitive spectral lines are unresolved, while it is also more sensitive to surface gravity at very young ages (<10 Myr) than the triangular H band peak. Both correlations differentiate young objects from field dwarfs, while the H 2 (K) index can distinguish, at least statistically, populations of ∼1 Myr objects from populations of ∼10 Myr objects. We applied the H 2 (K) index to NIFS data for one Orion nebula cluster (ONC) PMO and to previously published low resolution spectra for several other ONC PMOs where the 2.21 µm NaI doublet was unresolved and concluded that the average age of the PMOs is ∼1 Myr.

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Gravity Indicators in the Near‐Infrared Spectra of Brown Dwarfs

Cited by 149 publications

References 98 publications

Characterization of close visual binaries from the AstraLux Large M Dwarf Survey

Characterization of close visual binaries from the AstraLux Large M Dwarf Survey

Spectroscopic characterization of 78 DENIS ultracool dwarf candidates in the solar neighborhood and the Upper Scorpii OB association

Towards precise ages and masses of Free Floating Planetary Mass Brown Dwarfs

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