Lithium in LP 944−20★

Pavlenko, Ya. V.; Jones, H. R. A.; Martín, E. L.; Guenther, E. W.; Kenworthy, Matthew A.; Osorio, M. R. Zapatero

doi:10.1111/j.1365-2966.2007.12182.x

Cited by 32 publications

(41 citation statements)

References 81 publications

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“…Higher signal-to-noise and resolution spectroscopic observations could be used to study such interesting subpopulations e.g. by searching for the presence of lithium to directly assess age and mass (Pavlenko et al 2007) and the use of higher resolution cross correlation techniques to measure radial velocities and space motions, yielding important kinematic information.…”

Section: Discussionmentioning

confidence: 99%

Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors

Zhang

Pokorny

Jones

et al. 2009

A&A

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Aims. We try to identify ultra-cool dwarfs from the seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7) with SDSS i-z and r-z colors. We also obtain proper motion data from SDSS, 2MASS, and UKIDSS and improve spectral typing from SDSS and 2MASS photometric colors. Methods. We selected ultra-cool dwarf candidates from the SDSS DR7 with new photometric selection criteria, which are based on a parameterization study of known L and T dwarfs. The objects are then cross-identified with the Two Micron All Sky Survey and the Fourth Data Release of the UKIRT Infrared Deep Sky Survey (UKIDSS DR4). We derive proper motion constraints by combining SDSS, 2MASS, and UKIDSS positional information. In this way we are able to assess, to some extent, the credence of our sample using a multi epoch approach, which complements spectroscopic confirmation. Some of the proper motions are affected by short baselines, but, as a general tool, this method offers great potential to confirm faint L dwarfs as UKIDSS coverage increases. In addition we derive updated color-spectral type relations for L and T dwarfs with SDSS and 2MASS magnitudes. Results. We present 59 new nearby M and L dwarfs selected from the imaging catalog of the SDSS DR7, including proper motions and spectral types calculated from the updated color-spectral type relations. and obtain proper motions from SDSS, 2MASS, and UKIDSS for all of our objects.

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Section: Discussionmentioning

confidence: 99%

Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors

Zhang

Pokorny

Jones

et al. 2009

A&A

Self Cite

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“…Full spectral energy distribution of SDSS1256 from the optical all the way to the mid-infrared. Overplotted in red is the synthetic spectra from the atmosphere models of Allard et al (2001) generated with the DUST546 code of Pavlenko et al (2007a), which produces a satisfactory fit.…”

Section: Comparison With Theoretical Modelsmentioning

confidence: 99%

“…Our observed absorption is weaker than the two most depleted abundances, suggesting that our tentative detection is . Overplotted in red is the synthetic spectrum from the NextGen atmosphere models of Baraffe et al (1998) generated with the DUST546 code of Pavlenko et al (2007a), which provides the best fit to the data (a low-resolution version is shown for plotting purposes). The synthetic spectra, convolved by the instrument profile, have been generated for a metallicity of [M/H] = −2.0, gravity of log g = 5.0, Li abundance of log N(Li) = −1.0.…”

Section: Comparison With Theoretical Modelsmentioning

confidence: 99%

“…Then, we increased the absorption of CaH bands by factor of two, likely related to the well-known enhancement of calcium and other alpha-elements in the atmospheres of metal-poor dwarfs (Magain 1987). Moreover, we added some phenomenological dust opacity in the modelling of theoretical spectra, following the scheme of Pavlenko et al (2007a). The wavelength-independent dust opacity of a total optical depth of τ = 0.3 is located in a cloud-like layer at τ ross = 0.001, i.e above the photosphere of the dwarf.…”

Section: Comparison With Theoretical Modelsmentioning

confidence: 99%

“…To validate the possible presence of Li I in the spectrum of SDSS1256 and infer its atmospheric composition, we generated grids of synthetic spectra following the procedure outlined in Pavlenko et al (2007a). We started with the NextGen model atmospheres of Allard et al (2001) at solar metallicity.…”

Section: Comparison With Theoretical Modelsmentioning

confidence: 99%

See 2 more Smart Citations

A search for lithium in metal-poor L dwarfs

Lodieu

Burgasser

Pavlenko

et al. 2015

A&A

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Aims. The aim of the project is to search for lithium in absorption at 6707.8 Å to constrain the nature and mass of the brightest low-metallicity L-type dwarfs (referred to as L subdwarfs) identified in large-scale surveys. Methods. We obtained low-to intermediate-resolution (R ∼ 2500-9000) optical (∼560-770 nm) spectra of two mid-L subdwarfs, SDSS J125637.13−022452.4 (SDSS1256; sdL3.5) and 2MASS J162620.14+392519.5 (2MASS1626; sdL4) with spectrographs on the European Southern Observatory Very Large Telescope and the Gran Telescopio de Canarias. Results. We report the presence of a feature at the nominal position of the lithium absorption doublet at 6707.8 Å in the spectrum of SDSS1256, with an equivalent width of 66 ± 27 Å at 2.4σ, which we identify as arising from a CaH molecular transition based on atmosphere models. We do not see any feature at the position of the lithium feature in the spectrum of 2MASS1626. The existence of overlapping molecular absorption sets a confusion detection limit of [Li/H] = −3 for equivalently typed L subdwarfs. We provided improved radial velocity measurements of −126±10 km s −1 and −239±12 km s −1 for SDSS1256 and 2MASS1626, respectively, as well as revised Galactic orbits. We implemented adjusting factors for the CaH molecule in combination with the NextGen atmosphere models to fit the optical spectrum of SDSS1256 in the 6200-7300 Å range. We also estimate the expected Li abundance from interstellar accretion ([Li/H] = −5), place limits on circumstellar accretion (10 9 g/yr), and discuss the prospects of Li searches in cooler L and T subdwarfs.

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Theoretical modelling of optical and IR spectra of brown dwarfs and ultracool dwarfs

Pavlenko¹

2005

Astron Nachr

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Abstract. The current state of theoretical modelling of the spectra of cool dwarfs and ultracool objects are discussed. Fits of synthetical spectral energy distributions (SEDs) in the optical and IR spectral regions to observed spectra show problems of theoretical modelling. Problems of interpretation of observed spectra are more obvious for the case of L and T dwarfs. Still even for late-M dwarfs the situation is far from being perfect. Some examples of the fine analysis of the spectra of ultracool dwarfs are presented.

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Lithium in LP 944−20★

Cited by 32 publications

References 81 publications

Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors

Ultra-cool dwarfs: new discoveries, proper motions, and improved spectral typing from SDSS and 2MASS photometric colors

A search for lithium in metal-poor L dwarfs

Theoretical modelling of optical and IR spectra of brown dwarfs and ultracool dwarfs

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