On the Ga II and Ga III resonance lines and the implication for chemical stratification in HGMN stars

• The gallium abundance in HgMn stars has been reported to be different for analyses conducted from spectral lines in the optical versus those from the ultraviolet. We pursue this ultraviolet-optical discrepancy from a line-blending perspective by investigating the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) spectrum of the sharp-lined HgMn binary star chi Lup. Its gallium abundance is derived to be log N-Ga = 4.5 (log N-H = 12) based on nonresonance Ga II lines, and we are able to demonstrate the line-blending problems associated with the abundances determined from the resonance lines of Ga II lambda 1414 and Ga III lambda 1495. The HST STIS spectrum for chi Lup is also compared with a co-added International Ultraviolet Explorer (IUE) spectrum to further illustrate the importance of accounting for the line blending in quantitative abundance analyses. We have compared an IUE co-added spectrum of mu Lep with an LTE-based synthetic spectrum and managed to fit both Ga II lambda 1414 and Ga III lambda 1495 with an abundance of log N-Ga = 7.3. However, the fitting of these lines requires a dramatic change in the radiative damping constants, which may indicate a breakdown in our LTE modeling or the need to include other atmospheric effects.

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

stars : abundances

stars : chemically peculiar

ultraviolet : stars

line : profiles

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