VLT/X-shooter observations and the chemical composition of cool white dwarfs

Abstract

We present a model atmosphere analysis of cool hydrogen-rich white dwarfs observed at the Very Large Telescope (VLT) with the X-shooter spectrograph. The intermediate-dispersion and high signal-to-noise ratio of the spectra allowed us to conduct a detailed analysis of hydrogen and heavy element line profiles. In particular, we tested various prescriptions for hydrogen Balmer line broadening parameters and determined the effective temperature and surface gravity of each star. Three objects (NLTT 1675, 6390 and 11393) show the presence of heavy elements (Mg, Al, Ca, or Fe). Our abundance analysis revealed a relatively high iron to calcium ratio in NLTT 1675 and NLTT 6390. We also present an analysis of spectropolarimetric data obtained at the VLT using the focal reducer and low dispersion spectrograph (FORS) and we established strict upper limits on the magnetic field strengths in three of the DAZ white dwarfs and determined the longitudinal magnetic field strength in the DAZ NLTT 10480. The class of DAZ white dwarfs comprises objects that are possibly accreting material from their immediate circumstellar environment and the present study contributes in establishing class properties.

Accepted for publication in Astronomy and Astrophysics

References in corpus (5)

• X-shooter, the new wide band intermediate resolution spectrograph at the ESO Very Large Telescope
• Found: The missing blue opacity in atmosphere models of cool hydrogen white dwarfs
• Spectropolarimetric Survey of Hydrogen-rich White Dwarf Stars
• The accretion-diffusion scenario for metals in cool white dwarfs
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