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

Pavlenko, Ya. V.

doi:10.1002/asna.200510458

Cited by 3 publications

(2 citation statements)

References 52 publications

(52 reference statements)

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“…EWs and pEWs of the Li i resonance doublet differ significantly (see Zapatero Osorio et al 2002; Pavlenko 2005). The computed EW of the Li i feature at 670.8 nm for the DUSTY model atmosphere 2000/4.5/0 and log N (Li) = 0.0 is 0.54 and 0.58 Å for turbulent velocities of 2 and 3 km s −1 , respectively.…”

Section: Results Based On Standard Spectral Modellingmentioning

confidence: 99%

Lithium in LP 944−20★

Pavlenko

Jones

Martín

et al. 2007

Monthly Notices of the Royal Astronomical Society

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We present a new estimate of the lithium abundance in the atmosphere of the brown dwarf LP 944−20. Our analysis is based on a self‐consistent analysis of low‐, intermediate‐ and high‐resolution optical and near‐infrared spectra. We obtain log N(Li) = 3.25 ± 0.25 using fits of our synthetic spectra to the Li i resonance line doublet profiles observed with Very Large Telescope/Ultraviolet–Visual Echelle Spectrograph (VLT/UVES) and Anglo‐Australian Telescope/Segmented Pupil/Image Reformatting Array of Lenslets (AAT/SPIRAL). This lithium abundance is over two orders of magnitude larger than previous estimates in the literature. In order to obtain good fits of the resonance lines of K i and Rb i and better fits to the TiO molecular absorption around the Li i resonance line, we invoke a semi‐empirical model atmosphere with the dusty clouds located above the photosphere. The lithium abundance, however, is not changed by the effects of the dusty clouds. We discuss the implications of our estimate of the lithium abundance in LP 944−20 for the understanding of the properties of this benchmark brown dwarf.

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Section: Results Based On Standard Spectral Modellingmentioning

confidence: 99%

Lithium in LP 944−20★

Pavlenko

Jones

Martín

et al. 2007

Monthly Notices of the Royal Astronomical Society

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“…Synthetic spectra of Setup2 for a T eff = 3000 K and log(g) = 4.0 displaying the Li i with varied abundances from log( ) = 1.3 to 3.7. Tinney (1998), Joergens & Guenther (2001), and Pavlenko (2005), based on intermediate-resolution spectra by Kenyon et al (2005) and , and based on low-resolution spectra by Zapatero Osorio et al (2002).…”

Section: Introductionmentioning

confidence: 99%

Lithium abundances of very low mass members of Chamaeleon I

Johnas¹,

Guenther

Joergens

et al. 2007

A&A

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Aims. We present the first study of the lithium abundances of very low mass objects in Chamaeleon I close to the hydrogen burning mass limit based on atmospheric models and high-resolution spectroscopic observations. The studied objects, Cha Hα 2, 3, 4, 5, 6 and 8, are very young brown dwarf candidates and very low mass stars on the verge of lithium depletion. Methods. For this analysis, we have computed a new "GAIA-cond" class model grid over effective temperatures from 2600 K to 3100 K, surface gravities from log(g) = 3.5 to 5.5, and lithium abundances from log = 0.0 to 3.7, for two different line profile setups introduced in previous work. Calculated synthetic spectra are compared with high-resolution UVES / VLT echelle spectra of the objects. Results. We find good descriptions of the lithium resonance doublet lines at 6708 Å and of the surrounding pseudo-continuum and determine a consistent set of lithium abundances (log( ) = 1.55). However, the derived lithium abundances are lower than the meteoritic one (log( ) = 3.31) and that of higher mass stars in Cha I (log( ) = 3.1/3.4 for LTE-/non-LTE-calculations). By modeling the TiO-line, we demonstrate that veiling does not make the lithium lines appear weaker. We can also rule out that the results are spoiled by the presence of spots. Conclusions. A possible explanation for these results would be that the objects are either more massive, or much older, than previously thought, so that the lithium depletion has already started. Although the uncertainties of the masses and ages are large, they are not large enough as to explain the observed lithium depletion. Therefore, the most likely explanation is either a lack of understanding of the details of the formation of the lithium line, or a lack of understanding of the internal structure of the very young low-mass objects.

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Correlations between laboratory line lists for FeH, CrH, and NiH and M-star spectra collected with ESPaDOnS and SPIRou

Crozet,

Morin,

Ross

et al. 2023

A&A

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Context. Molecular bands of metal oxides and hydrides dominate the optical and near-infrared spectra of M dwarfs. High-resolution spectra of these bands have immense potential for determining many properties of these stars, such as effective temperature, surface gravity, elemental abundances, radial velocity, or surface magnetic fields. Techniques are being developed to do this but remain limited by the current availability and accuracy of molecular data and spectral line lists. Aims. This paper reports metal monohydride line lists selected from near-infrared and visible laboratory data to show that specific bands in several electronic transitions can be used to identify CrH, NiH, and FeH in M stars and to determine radial velocities from Doppler shifts. The possibility of measuring magnetic fields is also investigated for FeH and CrH. Methods. We used systematic cross-correlation analysis between unpolarised spectra from a selection of M stars and state-specific laboratory line lists. These lists were generated from a combination of existing data and new laboratory laser-excitation spectra recorded at Doppler-limited resolution, in zero-field conditions or in magnetic fields up to 0.6 tesla. Results. We show that transitions at visible wavelengths in FeH and NiH, usually neglected in the analysis of the spectra of M-type stars, do in fact contribute to the spectra, and we demonstrate the influence of magnetic sensitivity on selected transitions in CrH and FeH. Conclusions. Although the new line lists focus on transitions recorded at temperatures significantly lower than those of stellar objects, they remain pertinent because they cover some band-head regions of high spectral density. FeH bands can provide a useful supplement to atomic lines for the analysis of high-resolution optical and near-infrared spectra of M dwarfs. We demonstrate the influence of a magnetic field on CrH signatures around 862 nm.

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

Cited by 3 publications

References 52 publications

Lithium in LP 944−20★

Lithium in LP 944−20★

Lithium abundances of very low mass members of Chamaeleon I

Correlations between laboratory line lists for FeH, CrH, and NiH and M-star spectra collected with ESPaDOnS and SPIRou

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