2012A&A...546A...1A


Query : 2012A&A...546A...1A

2012A&A...546A...1A - Astronomy and Astrophysics, volume 546A, 1-1 (2012/10-1)

Chandra grating spectroscopy of three hot white dwarfs.

ADAMCZAK J., WERNER K., RAUCH T., SCHUH S., DRAKE J.J. and KRUK J.W.

Abstract (from CDS):

High-resolution soft X-ray spectroscopic observations of single hot white dwarfs are scarce. With the Chandra Low-Energy Transmission Grating, we have observed two white dwarfs, one is of spectral type DA (LB1919) and the other is a non-DA of spectral type PG1159 (PG1520+525). The spectra of both stars are analyzed, together with an archival Chandra spectrum of another DA white dwarf (GD246). The soft X-ray spectra of the two DA white dwarfs are investigated in order to study the effect of gravitational settling and radiative levitation of metals in their photospheres. LB1919 is of interest because it has a significantly lower metallicity than DAs with otherwise similar atmospheric parameters. GD246 is the only white dwarf known that shows identifiable individual iron lines in the soft X-ray range. For the PG1159 star, a precise effective temperature determination is performed in order to confine the position of the blue edge of the GW Vir instability region in the HRD. The Chandra spectra are analyzed with chemically homogeneous as well as stratified NLTE model atmospheres that assume equilibrium between gravitational settling and radiative acceleration of chemical elements. Archival EUV and UV spectra obtained with EUVE, FUSE, and HST are utilized to support the analysis. No metals could be identified in LB1919. All observations are compatible with a pure hydrogen atmosphere. This is in stark contrast to the vast majority of hot DA white dwarfs that exhibit light and heavy metals and to the stratified models that predict significant metal abundances in the atmosphere. For GD246 we find that neither stratified nor homogeneous models can fit the Chandra spectrum. The Chandra spectrum of PG1520+525 constrains the effective temperature to Teff=150000±10000K. Therefore, this nonpulsating star together with the pulsating prototype of the GWVir class (PG1159-035) defines the location of the blue edge of the GWVir instability region. The result is in accordance with predictions from nonadiabatic stellar pulsation models. Such models are therefore reliable tools to investigate the interior structure of GW Vir variables. Our soft X-ray study reveals that the understanding of metal abundances in hot DA white dwarf atmospheres is still incomplete. On the other hand, model atmospheres of hydrogen-deficient PG1159-type stars are reliable and reproduce well the observed spectra from soft X-ray to optical wavelengths.

Abstract Copyright:

Journal keyword(s): white dwarfs - stars: abundances - stars: atmospheres - stars: individual: LB1919 - stars: individual: GD246 - stars: individual: PG1520+525

Simbad objects: 20

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Number of rows : 20
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
#notes
1 KPD 0005+5106 WD* 00 08 18.1706793307 +51 23 16.594540226 11.80 13.04 13.32 13.53   DOZ1 118 0
2 NGC 246 PN 00 47 03.3420803259 -11 52 18.975106178 10.15 11.52 11.76 12.18   PG1159 459 0
3 PG 0122+200 WD* 01 25 22.5118179721 +20 17 56.963251283   16.2   16.9   DOZ.7 104 0
4 BD+52 913 WD* 05 05 30.6182785658 +52 49 51.920797126 10.25 11.44 11.69 11.93 12.108 DA.8 1013 0
5 * alf CMa B WD* 06 45 09.3021501316 -16 43 00.716804119   8.41 8.44     DA1.9 506 1
6 PN Lo 4 PN 10 05 45.7878014012 -44 21 33.523563573           sdO 128 1
7 LB 1919 WD* 10 59 16.4297883065 +51 24 43.120746122   15.5 16.8     DA.7 52 0
8 V* GW Vir WD* 12 01 45.9728868857 -03 45 40.627851273   14.87 15.04     DOQZ1 471 0
9 HZ 43A WD* 13 16 21.8529879473 +29 05 55.413524767   12.52 12.66     DAwk 458 0
10 PG 1342+444 WD* 13 44 26.8499261682 +44 08 33.300369384   16.15       DA.7 47 0
11 HE 1429-1209 WD* 14 32 20.7451839082 -12 22 48.257597104   15.7 16.15 16.27   PG1159 22 0
12 PG 1501+664 WD* 15 02 09.6296551839 +66 12 19.146114550   16.07 16.37     DZQ1 151 0
13 PG 1520+525 PN 15 21 46.5638122905 +52 22 03.868713843   15.56 16.6     PG1159 103 1
14 PG 1707+427 WD* 17 08 47.6869967260 +42 41 00.558830272   16.18       PG1159 110 0
15 PN A66 43 PN 17 53 32.2767918769 +10 37 24.211581466   14.53 14.71     O7fk 127 0
16 PN K 1-16 PN 18 21 52.1081781582 +64 21 53.413814961   14.44 14.96 15.26   PG1159 237 0
17 MWP 1 PN 21 17 08.2817539788 +34 12 27.415871206     12.33     PG1159 175 0
18 V* IR Peg WD* 21 34 08.2124719240 +06 50 57.662044329   16.15       PG1159 113 0
19 GD 246 WD* 23 12 21.6156138550 +10 47 04.257261526 11.578 12.772 13.090 13.238 13.418 DA.9 206 0
20 V* V409 And WD* 23 27 15.9352164958 +40 01 23.428438900   14.1 15.41     DO 71 0

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2021.09.24-23:03:55

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