Effect of the variation of electric-dipole moments on the shape of pressure-broadened atomic spectral lines

Allard, N. F.; Royer, A.; Kielkopf, John F.; Feautrier, N.

doi:10.1103/physreva.60.1021

Cited by 110 publications

(167 citation statements)

References 36 publications

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“…The new calculations for the broadening of the Lyman α line, and in particular the quasi-molecular satellites at 1400 and 1600 Å, use the unified theory as described in Allard & Kielkopf (1982) and Allard et al (1999). The program code for the profiles, however, has been completely rewritten with improved numerical algorithms to overcome problems with numerical noise and artifacts, caused by the very large dynamical range of ten or more orders of magnitude between the line core absorption and the far wing in very broad lines.…”

Section: Atmospheric Parametersmentioning

confidence: 99%

The frequency of planetary debris around young white dwarfs

Koester

Gänsicke

Farihi

2014

A&A

442

531

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Context. Heavy metals in the atmospheres of white dwarfs are thought in many cases to be accreted from a circumstellar debris disk, which was formed by the tidal disruption of a rocky planetary body within the Roche radius of the star. The abundance analysis of photospheric elements and conclusions about the chemical composition of the accreted matter are a new and promising method of studying the composition of extrasolar planetary systems. However, ground-based searches for metal-polluted white dwarfs that rely primarily on the detection of the Ca ii K line become insensitive at T eff > 15 000 K because this ionization state depopulates.Aims. We present the results of the first unbiased survey for metal pollution among hydrogen-atmosphere (DA type) white dwarfs with cooling ages in the range 20-200 Myr and 17 000 K < T eff < 27 000 K. Methods. The sample was observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope in the far ultraviolet range between 1130 and 1435 Å. The atmospheric parameters were obtained using these spectra and optical observations from the literature. Element abundances were determined using theoretical models, which include the effects of element stratification due to gravitational settling and radiative levitation. Results. We find 48 of the 85 DA white dwarfs studied, or 56% show traces of heavy elements. In 25 stars (showing only Si and occasionally C), the elements can be explained by radiative levitation alone, although we argue that accretion has very likely occurred recently. The remaining 23 white dwarfs (27%), however, must be currently accreting. Together with previous studies from the ground and adopting bulk Earth abundances for the debris, accretion rates range from a few 10 5 g s −1 to a few 10 8 g s −1 , with no evident trend in cooling age from ≈40 Myr to ≈2 Gyr. Only a single, modest case of metal pollution (Ṁ < 10 6 g s −1 ) is found among ten white dwarfs with T eff > 23 000 K, in excellent agreement with the absence of infrared excess from dust around these warmer stars. The median, main sequence progenitor of our sample corresponds to an A-type star of ≈2 M , and we find 13 of 23 white dwarfs descending from main sequence 2-3 M , late B-and A-type stars to be currently accreting. Only one of 14 targets with M wd > 0.8 M is found to be currently accreting, which suggests a large fraction of these stars result from double-degenerate mergers, and the merger disks do not commonly reform large planetesimals or otherwise pollute the remnant. We reconfirm our previous finding that two 625 Myr Hyades white dwarfs are currently accreting rocky planetary debris. Conclusions. At least 27% of all white dwarfs with cooling ages 20-200 Myr are accreting planetary debris, but that fraction could be as high as ≈50%. At T eff > 23 000 K, the luminosity of white dwarfs is probably sufficient to vaporize circumstellar dust grains, so no stars with strong metal-pollution are found. Planetesimal disruption events should occur in this cooling age and temper...

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Section: Atmospheric Parametersmentioning

confidence: 99%

The frequency of planetary debris around young white dwarfs

Koester

Gänsicke

Farihi

2014

A&A

442

531

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“…Gray lines show the best-fit white dwarf plus hot spot model described in x 4. Ly , and Ly , using the line profile data from Allard et al (1994Allard et al ( , 1998Allard et al ( , 2004. Schmidt et al (1981) detected several Zeeman components of the white dwarf photospheric Balmer absorption lines in optical spectropolarimetry obtained during a low state.…”

Section: White Dwarf Propertiesmentioning

confidence: 99%

FUSEandHSTSTIS Far‐Ultraviolet Observations of AM Herculis in an Extended Low State

Gänsicke

Long

Barstow

et al. 2006

ApJ

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We have obtained FUSE and HST STIS time-resolved spectroscopy of the Polar AM Herculis during a deep low state. The spectra are entirely dominated by the emission of the white dwarf. Both the far-ultraviolet ( FUV ) flux and the spectral shape vary substantially over the orbital period, with maximum flux occurring at the same phase as during the high state. The variations are due to the presence of a hot spot on the white dwarf, which we model quantitatively. The white dwarf parameters can be determined from a spectral fit to the faint-phase data, when the hot spot is self-eclipsed. Adopting the distance of 79 þ8 À6 pc determined by Thorstensen, we find an effective temperature of 19;800 AE 700 K and a mass of M WD ¼ 0:78 þ 0:12 À 0:17 M . The hot spot has a lower temperature than during the high state, $34,000-40,000 K, but covers a similar area, $10% of the white dwarf surface. Low-state FUSE and STIS spectra taken during four different epochs in [2002][2003] show no variation of the FUV flux level or spectral shape, implying that the white dwarf temperature and the hot spot temperature, size, and location do not depend on the amount of time the system has spent in the low state. Possible explanations are ongoing accretion at a low level or deep heating; both alternatives have some weaknesses, which we discuss. No photospheric metal absorption lines are detected in the FUSE and STIS spectra, suggesting that the average metal abundances in the white dwarf atmosphere are lower than $10 À3 times their solar values.

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“…Ab initio calculations of the potentials of K-H 2 for different orientations of the molecule have been reported in Santra & Kirby (2005) and Allard et al (2007c), neglecting the spin-orbit coupling (SO). In a previous paper (Allard et al 1999), we derived a classical path expression for a pressure-broadened atomic spectral line shape that allows for an electric dipole moment that is dependent on the position of perturbers, which is not included in the more usual approximation of Anderson & Talman (1956) and Baranger (1958a,b). This treatment has improved the comparison of synthetic spectra of brown dwarfs with observations (Allard et al 2003(Allard et al , 2007a.…”

Section: Introductionmentioning

confidence: 99%

K–H₂line shapes for the spectra of cool brown dwarfs

Allard

Spiegelman

Kielkopf

2016

A&A

Self Cite

112

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Observations of cooler and cooler brown dwarfs show that the contribution from broadening at many bars pressure is becoming important. The opacity in the red optical to near-IR region under these conditions is dominated by the extremely pressure-broadened wings of the alkali resonance lines, in particular, the K I resonance doublet at 0.77 µm. Collisions with H 2 are preponderant in brown dwarf atmospheres at an effective temperature of about 1000 K; the H 2 perturber densities reach several 10 19 even in Jupiter-mass planets and exceed 10 20 for super-Jupiters and older Y dwarfs. As a consequence, it appears that when the far wing absorption due to alkali atoms in a dense H 2 atmosphere is significant, accurate pressure broadened profiles that are valid at high densities of H 2 should be incorporated into spectral models.

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Effect of the variation of electric-dipole moments on the shape of pressure-broadened atomic spectral lines

Cited by 110 publications

References 36 publications

The frequency of planetary debris around young white dwarfs

The frequency of planetary debris around young white dwarfs

FUSEandHSTSTIS Far‐Ultraviolet Observations of AM Herculis in an Extended Low State

K–H₂line shapes for the spectra of cool brown dwarfs

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Effect of the variation of electric-dipole moments on the shape of pressure-broadened atomic spectral lines

Cited by 110 publications

References 36 publications

The frequency of planetary debris around young white dwarfs

The frequency of planetary debris around young white dwarfs

FUSEandHSTSTIS Far‐Ultraviolet Observations of AM Herculis in an Extended Low State

K–H2line shapes for the spectra of cool brown dwarfs

Contact Info

Product

Resources

About

K–H₂line shapes for the spectra of cool brown dwarfs