Volume 532, August 2011
|Number of page(s)||8|
|Section||Stellar structure and evolution|
|Published online||12 July 2011|
The cool magnetic DAZ white dwarf NLTT 10480⋆
Astronomický ústav, Akademie věd České republiky, Fričova 298, 251 65 Ondřejov, Czech Republic
e-mail: email@example.com; firstname.lastname@example.org
Received: 14 April 2011
Accepted: 1 June 2011
We have identified a new cool magnetic white dwarf in the New Luyten Two-Tenths (NLTT) catalogue. The high proper-motion star NLTT 10480 (μ = 0.5″ yr-1) shows weak Zeeman-split lines of calcium as well as characteristic Hα and β Zeeman triplets. Using VLT X-shooter spectra, we measured a surface-averaged magnetic field BS ~ 0.5 MG. The relative intensity of the π and σ components of the calcium and hydrogen lines imply a high inclination (i ≳ 60°). The optical-to-infrared V − J colour index and the Ca I/Ca II ionization balance indicate a temperature between 4900 and 5200 K, while the Balmer line profiles favour a higher temperature of 5400 K. The discrepancy is potentially resolved by increasing the metallicity to 0.03 × solar, hence increasing the electron pressure. However, the measured calcium abundance and abundance upper limits for other elements (Na, Al, Si, and Fe) imply a low photospheric metallicity ≲ 10-4 solar. Assuming diffusion steady-state, a calcium accretion rate of log Ṁ(g s-1) = 5.6 ± 0.3 is required to sustain a calcium abundance of log n(Ca)/n(H) = −10.30 ± 0.30 in the white dwarf atmosphere. We examine the implications of this discovery for the incidence of planetary debris and weak magnetic fields in cool white dwarf stars.
Key words: white dwarfs / stars: individual: NLTT 10480 / stars: atmospheres / stars: abundances
© ESO, 2011
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.