Calcium and magnesium in the helium white dwarf GD 401

Journal Article · Sat Nov 15 00:00:00 EST 1980 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/158455· OSTI ID:6791109

Cottrell, P L; Greenstein, J L

A calcium abundance (Ca/Heapprox.6--9 x 10/sup -9/) has been derived for the DB degenerate object GD 401 using spectrum synthesis techniques and observational data acquired with the SIT spectrograph. From these data we have also derived upper limits for the Mg/He and Fe/He ratios of approx.1 x 10/sup -8/ and approx.6 x 10/sup -9/, respectively. The errors on these abundances are relatively high (factors of approx.5--10), since we used a cooler model (T/sub e/=8800 K; cf. 9500 K, Greenstein) and abundances of the electron donors (C, N, O, H) which are uncertain because of the lack of observable features. However, two conclusions can be made from this analysis: (1) calcium is deficient relative to the Sun, contrary to the estimates of Liebert et al., and (2) the Mg/Ca ratio limit is much smaller than the solar value, in contrast to the results of the two other well-studied metal-line white dwarfs (Ross 640, van Maanen 2). The second result for GD 401 is at variance with recent diffusion theories for white dwarfs, which generally predict light-to-heavy element ratios larger than the Sun. If more detailed model atmospheres confirm these results, GD 401 may reflect abundance ratios from recently accreted interstellar material which has noncosmic abundances.

• Research Organization: Palomar Observatory, California Institute of Technology
• OSTI ID: 6791109
• Journal Information: Astrophys. J.; (United States), Vol. 241:4
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CALCIUM
WHITE DWARF STARS
MAGNESIUM
CHEMICAL COMPOSITION
ABUNDANCE
DATA ANALYSIS
ENERGY SPECTRA
HELIUM
IRON
STELLAR ATMOSPHERES
ALKALINE EARTH METALS
ATMOSPHERES
DWARF STARS
ELEMENTS
FLUIDS
GASES
METALS
NONMETALS
RARE GASES
SPECTRA
STARS
TRANSITION ELEMENTS
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources