<i>Far Ultraviolet Spectroscopic Explorer</i>Observation of the Ultramassive White Dwarf PG 1658+441

Dupuis, J.; Chayer, P.; Vennes, S.; Allard, N. F.; Hébrard, G.

doi:10.1086/378719

Cited by 20 publications

(23 citation statements)

References 28 publications

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“…We anticipate that the magnitude of the discrepancies will be similar for the variable-dipole calculations. This explains the discrepancy between theoretical and observed quasi-molecular satellites in spectra of massive white dwarfs (Dupuis et al 2003).…”

Section: Synthetic Spectra and Conclusionmentioning

confidence: 88%

New study of the quasi-molecular Lyman-γ satellites due to H-H⁺ collisions

Allard¹,

Noselidze

Kruk

2009

A&A

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Context. Quasi-molecular line satellites in the red wings of Lyman series of atomic hydrogen have been identified in the spectra of hydrogen-rich white dwarfs. These features are produced by radiative collisions. Aims. Structures observed about 995 Å in the Lyman-γ wing of hot white dwarfs have been shown to be caused by quasi-molecular absorption of H + 2 molecules. Methods. Improvements to previous theoretical calculations of the Lyman-γ line profiles can be achieved by using a unified theory that takes into account the dependence of the dipole moments on internuclear distance during the collision. Results. For the first time, we have computed the transition dipole moments. We measure a significant increase in the region of the formation of the satellites, which alters the general shape of the profile. Conclusions. A large increase in the strength of the two main satellites at 992 and 996 Å leads to a deeper broad absorption in the synthetic spectra, which should improve the comparison with observation as previous predicted Lyman-γ satellites were too weak.

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Section: Synthetic Spectra and Conclusionmentioning

confidence: 88%

New study of the quasi-molecular Lyman-γ satellites due to H-H⁺ collisions

Allard¹,

Noselidze

Kruk

2009

A&A

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“…Clearly present is the 1076 8 component of the H þ 2 Ly line; however, the 1058 8 component, which is of noticeable strength in T WD ' 20;000 K DA white dwarfs ( Koester et al 1998;Hébrard & Moos 2003), is not detected. The absence of this feature is intriguing, as Dupuis et al (2003) also noticed a much weaker 1058 8 H þ 2 absorption in the magnetic (B ¼ 2:3 MG) white dwarf PG 1658+441. They argued that the disagreement in the case of the massive ( log g ¼ 9:32) white dwarf PG 1658+441 might be due to the lack of appropriate line profile data for highdensity plasma.…”

Section: Average Spectramentioning

confidence: 97%

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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“…The standard procedure of fitting the Balmer lines for T eff and log g can only be applied to MWDs with fields below a few MG and even in these cases the results have to be treated with some caution (e.g. Ferrario et al 1998;Dupuis et al 2003). For higher field strengths, mass estimates are derived from the combination of effective temperatures, parallaxes, and a mass-radius relation.…”

Section: Mass Distribution Of Isolated Magnetic White Dwarfsmentioning

confidence: 99%

Magnetic White Dwarfs

2015

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In this paper we review the current status of research on the observational and theoretical characteristics of isolated and binary magnetic white dwarfs (MWDs). Magnetic fields of isolated MWDs are observed to lie in the range 10^3-10^9G. While the upper limit cutoff appears to be real, the lower limit is more difficult to investigate. The incidence of magnetism below a few 10^3G still needs to be established by sensitive spectropolarimetric surveys conducted on 8m class telescopes. Highly magnetic WDs tend to exhibit a complex and non-dipolar field structure with some objects showing the presence of higher order multipoles. There is no evidence that fields of highly magnetic WDs decay over time, which is consistent with the estimated Ohmic decay times scales of ~10^11 yrs. MWDs, as a class, also appear to be more massive than their weakly or non-magnetic counterparts. MWDs are also found in binary systems where they accrete matter from a low-mass donor star. These binaries, called magnetic Cataclysmic Variables (MCVs) and comprise about 20-25\% of all known CVs. Zeeman and cyclotron spectroscopy of MCVs have revealed the presence of fields in the range $\sim 7-230$\,MG. Complex field geometries have been inferred in the high field MCVs (the polars) whilst magnetic field strength and structure in the lower field group (intermediate polars, IPs) are much harder to establish. The origin of fields in MWDs is still being debated. While the fossil field hypothesis remains an attractive possibility, field generation within the common envelope of a binary system has been gaining momentum, since it would explain the absence of MWDs paired with non-degenerate companions and also the lack of relatively wide pre-MCVs.Comment: 73 pages, 22 figures, 2 large tables. Invited review chapter on Magnetic White Dwarfs to appear in Space Science Reviews, Springe

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Far Ultraviolet Spectroscopic ExplorerObservation of the Ultramassive White Dwarf PG 1658+441

Cited by 20 publications

References 28 publications

New study of the quasi-molecular Lyman-γ satellites due to H-H⁺ collisions

New study of the quasi-molecular Lyman-γ satellites due to H-H⁺ collisions

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

Magnetic White Dwarfs

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Far Ultraviolet Spectroscopic ExplorerObservation of the Ultramassive White Dwarf PG 1658+441

Cited by 20 publications

References 28 publications

New study of the quasi-molecular Lyman-γ satellites due to H-H+ collisions

New study of the quasi-molecular Lyman-γ satellites due to H-H+ collisions

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

Magnetic White Dwarfs

Contact Info

Product

Resources

About

New study of the quasi-molecular Lyman-γ satellites due to H-H⁺ collisions

New study of the quasi-molecular Lyman-γ satellites due to H-H⁺ collisions