Continuous absorption by He2(+) and H2(+) in cool white dwarfs

Details Continuous absorption by He2(+) and H2(+) in cool white dwarfs Continuous absorption by He2(+) and H2(+) in cool white dwarfs

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994apj...430..360s&link_type=abstract

The Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 430, no. 1, p. 360-370

Astronomy and Astrophysics

Astrophysics

44

Absorptivity, Continuous Radiation, Cool Stars, Cross Sections, Molecular Excitation, Molecular Ions, Photodissociation, White Dwarf Stars, Electron Transitions, Helium, Hydrogen, Quantum Mechanics, Rotational States, Vibrational States

Scientific paper

Photodissociation cross sections and absorption coefficents of the He2(+) molecular ions for transitions from the Chi (2)Epsilon(+) ground state to the vibrational continuum of the A (2)Epsilon(+) excited state have been determined for photon wavelengths lambda between 50 nm and 20 microns and for temperatures T between 4200 and 50,400 K and between 3150 and 25,200 K, respctivley. The cross sections are obtained through a fully quantum-mechanical method, and it is shown that inclusion of the high-lying rotational states is important for determination of the correct long-wavelengthh cross section amplitude and the peak wavelength. Free-free absorption coefficients are also obtained using the semiclassical method of Bates. The detection possibility of He2(+) and H2(+) in cool white dwarfs is dicussed and shown to be insignificant. An effectively temperature independent cutoff in the He2(+) photodissociation cross section in the EUV at approximately 60 nm appears to be the only possible observable feature. It is suggested that He2(+) may be responsible for an observed UV flux deficiency in some cool DB stars as well as in the DZ stars WD 0552 - 041 and WD 1334 + 039. We further suggest that the star WD 0752 - 676 currently assumed to be helium-rich may actually have a hydrogen-dominated atmosphere.

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