The Molecular Line Opacity of MgH in Cool Stellar Atmospheres

Weck, Philippe F.; Schweitzer, A.; Stancil, P. C.; Hauschildt, P. H.; Kirby, K.

doi:10.1086/344722

Cited by 58 publications

(43 citation statements)

References 26 publications

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“…In the case of the Q 1 and Q 2 lines of MgH, this leads to f v j ,v j = f v v /2 at the large j limit, whereas the similar formulae (3) and (4) of Weck et al (2003) …”

Section: Recalculation Of the Hönl-london Factorsmentioning

confidence: 92%

“…As different values can be found in the literature for the oscillator strengths of the lines under interest (Kurucz's values are reported in Table 1; Weck et al 2003, derive twice smaller values), we have found necessary to recalculate the Hönl-London factors of these lines. This calculation is based on the most recent basic reference works in this field by Larsson (1983) and Whiting & Nicholls (1974).…”

Section: Recalculation Of the Hönl-london Factorsmentioning

confidence: 97%

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Collisional influence on the differential Hanle effect method applied to the second solar spectrum of the A$^\mathsf{{2}}\Pi$–X$^\mathsf{{2}}\Sigma^{+}$ (0, 0) band of MgH

Bommier¹,

Degl’Innocenti

Feautrier³

et al. 2006

A&A

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Methods. This analysis is performed as follows: a) the Hanle effect Γ H parameter is derived by applying the differential Hanle effect method between the two extreme pairs of lines. Assuming no depolarizing collisions, a magnetic field strength follows, which is found to be 9.2 Gauss, in agreement with previous observations of the same kind; b) this Γ H parameter is entered in a code solving the NLTE polarized radiative transfer equations, and the other depolarizing parameter, namely the depolarizing collision rate, is then derived by adjusting the computed polarization to the observed one. Thus an average value of the rate per colliding hydrogen atom α (2) = 1.20 × 10 −9 cm 3 s −1 is obtained for the upper levels of the 12 lines (standard deviation 0.21 × 10 −9 cm 3 s −1 ). The corresponding model-dependent depolarizing rate is D (2) = (4.2 ± 0.7) × 10 7 s −1 at h = 200 km; c) this depolarizing rate is now introduced in the conversion of the Γ H parameter in terms of magnetic field strength: an average turbulent field strength of 29 ± 12 Gauss is derived as the final value, at height h = 200 ± 80 km where the polarization is formed. The Hönl-London factors of the lines under interest have been recalculated, leading to detect an error of a factor 2 in the recent literature. Results. The derived value B = 29 ± 12 Gauss at h = 200 ± 80 km is in fairly good agreement with the previous determinations based on the interpretation of the Sr i 4607 Å limb polarization, which has led to fields in the range 35−60 Gauss. Conclusions. Given the error bars, it seems unnecessary to put forward different formation regions for the Sr i and MgH lines.

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“…In the case of the Q 1 and Q 2 lines of MgH, this leads to f v j ,v j = f v v /2 at the large j limit, whereas the similar formulae (3) and (4) of Weck et al (2003) …”

Section: Recalculation Of the Hönl-london Factorsmentioning

confidence: 92%

Section: Recalculation Of the Hönl-london Factorsmentioning

confidence: 97%

Collisional influence on the differential Hanle effect method applied to the second solar spectrum of the A$^\mathsf{{2}}\Pi$–X$^\mathsf{{2}}\Sigma^{+}$ (0, 0) band of MgH

Bommier¹,

Degl’Innocenti

Feautrier³

et al. 2006

A&A

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“…Convective energy transport and velocities are calculated using mixing length theory with a mixing length of 2.0 pressure scale heights, and overshoot is treated as an exponential velocity field with a scale height based on the RHD simulations of Ludwig et al (2002Ludwig et al ( , 2006 and Freytag et al (2010Freytag et al ( , 2012; an additional advective mixing term due to gravity waves is included as described in Freytag et al (2010). All relevant molecular absorbers are treated with line-by-line opacities in direct opacity sampling as in Allard et al (2003b); regarding this, the molecular line lists have been updated as follows: watervapor (BT2, Barber et al 2006), CIA of H 2 (Borysow 2002), and FeH (Plez 1998;Weck et al 2003;Dulick et al 2003). Nonequilibrium chemistry for CO, CH 4 , CO 2 , N 2 , and NH 3 is treated with height-dependent diffusion also based on the RHD simulation results of Freytag et al (2010).…”

Section: Spectral Synthesismentioning

confidence: 99%

New constraints on the formation and settling of dust in the atmospheres of young M and L dwarfs

Manjavacas

Bonnefoy

Schlieder

et al. 2014

A&A

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Context. Gravity modifies the spectral features of young brown dwarfs (BDs). A proper characterization of these objects is crucial for the identification of the least massive and latest-type objects in star-forming regions, and to explain the origin(s) of the peculiar spectrophotometric properties of young directly imaged extrasolar planets and BD companions. Aims. We obtained medium-resolution (R ∼ 1500−1700) near-infrared (1.1−2.5 µm) spectra of seven young M9.5-L3 dwarfs classified at optical wavelengths. We aim to empirically confirm the low surface gravity of the objects in the near-infrared. We also test whether self-consistent atmospheric models correctly represent the formation and the settling of dust clouds in the atmosphere of young late-M and L dwarfs. Methods. We used the Infrared Spectrometer And Array Camera (ISAAC) at the Very Large Telescope (VLT) to obtain the spectra of the targets. We compared the spectra to those of mature and young BDs, and to young late-type companions to nearby stars with known ages to identify and study gravity-sensitive features. We computed spectral indices weakly sensitive to the surface gravity to derive near-infrared spectral types. Finally, we found the best fit between each spectrum and synthetic spectra from the BT-Settl 2010 and 2013 atmospheric models. Using the best fit, we derived the atmospheric parameters of the objects and identified which spectral characteristics the models do not reproduce. Results. We confirmed that our objects are young BDs and we found near-infrared spectral types in agreement with the ones determined at optical wavelengths. The spectrum of the L2γ dwarf 2MASSJ232252.99-615127.5 reproduces the spectrum of the planetary mass companion 1RXS J160929.1-210524b well. The BT-Settl models fit the spectra and the 1−5 µm spectral energy distribution of the L0-L3 dwarfs for temperatures between 1600−2000 K. But the models fail to reproduce the shape of the H band and the near-infrared slope of some of our targets. This fact, and the best-fit solutions found with super-solar metallicity, are indicative of a lack of dust, in particular at high altitude, in the cloud models. Conclusions. The modeling of the vertical mixing and of the grain growth will be revised in the next version of the BT-Settl models. These revisions may suppress the remaining non-reproducibilities. Our spectra provide additional templates for the characterization of the numerous young L-type companions that will be detected in the coming years by planet imaging instruments such as VLT/SPHERE, Gemini/GPI, Subaru/SCexAO, and LBTI/LMIRCam.

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“…Both have very similar properties. This is followed by x 2.3, where we discuss the metal hydrides TiH ( Burrows et al 2005), CrH ( Burrows et al 2002), FeH (Dulick et al 2003), MgH (Skory et al 2003;Weck et al 2003a), and CaH (Leininger & Jeung 1995;Weck et al 2003b), which all have similar properties.…”

Section: Introductionmentioning

confidence: 99%

Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres

Sharp

Burrows

2007

ASTROPHYS J SUPPL S

346

375

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We present a comprehensive description of the theory and practice of opacity calculations from the infrared to the ultraviolet needed to generate models of the atmospheres of brown dwarfs and extrasolar giant planets. Methods for using existing line lists and spectroscopic databases in disparate formats are presented, and plots of the resulting absorptive opacities versus wavelength for the most important molecules and atoms at representative temperature/ pressure points are provided. Electronic, rovibrational, bound-free, bound-bound, free-free, and collision-induced transitions and monochromatic opacities are derived, discussed, and analyzed. The species addressed include the alkali metals, iron, heavy metal oxides, metal hydrides, H 2 , H 2 O, CH 4 , CO, NH 3 , H 2 S, PH 3 , and representative grains. Once monochromatic absorption cross sections for all constituents have been derived, chemical abundances have to be obtained before the resulting product can be summed to obtain total opacities. Hence, we include a review of the thermochemistry, techniques, and databases needed to derive equilibrium abundances and provide some sample results.

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The Molecular Line Opacity of MgH in Cool Stellar Atmospheres

Cited by 58 publications

References 26 publications

Collisional influence on the differential Hanle effect method applied to the second solar spectrum of the A$^\mathsf{{2}}\Pi$–X$^\mathsf{{2}}\Sigma^{+}$ (0, 0) band of MgH

Collisional influence on the differential Hanle effect method applied to the second solar spectrum of the A$^\mathsf{{2}}\Pi$–X$^\mathsf{{2}}\Sigma^{+}$ (0, 0) band of MgH

New constraints on the formation and settling of dust in the atmospheres of young M and L dwarfs

Atomic and Molecular Opacities for Brown Dwarf and Giant Planet Atmospheres

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