1998A&A...334..618D


Query : 1998A&A...334..618D

1998A&A...334..618D - Astronomy and Astrophysics, volume 334, 618-632 (1998/6-2)

Spectral analyses of PG1159 star: constraints on the GW Virginis pulsations from HST observations.

DREIZLER S. and HEBER U.

Abstract (from CDS):

We present the results of a quantitative analysis of UV and optical spectra of nine PG1159 stars, very hot hydrogen-deficient [pre-] white dwarfs, by means of line blanketed NLTE model atmospheres. Four programme stars constitute the GWVir variables, a class of non-radial g-mode pulsators. Precise effective temperatures, carbon, nitrogen and oxygen abundances and spectroscopic masses are used to constrain the GWVir pulsations. The blue edge of the instability strip is at 140000K (PG1159-035). PG0122+200 sets the red edge at 80000K, but is also one of the coolest PG1159 stars known, suggesting that the pulsations are stopped when the transformation of a PG1159 star into a hot white dwarf occurs by gravitational settling of the metals. Four non-variables are found to lie inside the GW Vir instability strip indicating that an additional parameter determines whether a PG1159 star pulsates. Abundances of C and O in the pulsating stars appear to be higher than in the non-variables in agreement with the theoretical prediction that the pulsations are driven by cyclic ionization of C and O. The outstanding discovery of our investigation, however, is a strong correlation between the nitrogen abundance and pulsations. All GWVir stars are nitrogen rich, whereas no nitrogen can be detected in the non-variables except in PG1144+005. We conjecture that this correlation provides a key for the understanding of the driving mechanism. Comparing their position in the Teff-logg diagram to new evolutionary models we conclude that most programme stars are post-AGB stars of rather low mass (0.5 ... 0.65 M) which have lost their entire hydrogen-rich envelope and part of their helium-rich envelope whereas we confirm HS0704+6153 to be an AGB manque star. The high nitrogen abundance in four stars is a tracer of mixing processes which have led to ingestion and burning of hydrogen during the final helium shell flash.

Abstract Copyright:

Journal keyword(s): stars: abundances - stars: atmospheres - stars: evolution - stars: oscillations - stars: AGB and post-AGB - stars: white dwarfs

Simbad objects: 24

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Number of rows : 24
N Identifier Otype ICRS (J2000)
RA
ICRS (J2000)
DEC
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
#notes
1 NGC 246 PN 00 47 03.3420341616 -11 52 18.971126076 10.15 11.52 11.76 12.18   PG1159 466 0
2 RX J0122.9-7521 WD* 01 22 53.4122561952 -75 21 14.724358308     15.4     PG1159 40 0
3 PG 0122+200 WD* 01 25 22.5121704552 +20 17 56.963079924   16.2   16.9   DOZ.7 107 0
4 GD 1088 ** 01 32 39.347 -19 21 40.38   15.51 15.77 15.77   PG1159 45 0
5 M 76 PN 01 42 19.6557728208 +51 34 31.534970052     17.48   17.69 DOZ 366 2
6 HS 0444+0453 WD* 04 47 04.5045887496 +04 58 41.340500616   15.9   16.1   DQZO.5 23 0
7 HS 0704+6153 WD* 07 09 32.4965901360 +61 48 19.458822312   17.3   17.1   PG1159 36 0
8 WRAY 17-1 PN 07 14 49.4240697984 -46 57 39.199063500   13.8 13.00     PG1159 78 0
9 PN A66 21 PN 07 29 02.7096654192 +13 14 48.587555184   15.67 15.99     DOZ 186 0
10 PN Lo 4 PN 10 05 45.7880109408 -44 21 33.523482384           sdO 131 1
11 PG 1144+005 WD* 11 46 35.2284791112 +00 12 33.539992056   14.59 14.9     PG1159 84 0
12 PG 1151-029 WD* 11 54 15.0623712576 -03 12 05.135581440   16.07       DOZ1 30 0
13 V* GW Vir WD* 12 01 45.9731868264 -03 45 40.628670300   14.87 15.04     DOQZ1 475 0
14 PG 1424+535 WD* 14 25 55.4615842224 +53 15 25.138507140   15.86       PG1159 71 0
15 PG 1501+664 WD* 15 02 09.6299323152 +66 12 19.148868324   16.07 16.37     DZQ1 153 0
16 HS 1517+7403 WD* 15 16 46.4260387056 +73 52 06.953282400   16.4   16.9   DO 39 0
17 PG 1520+525 PN 15 21 46.5635130432 +52 22 03.867341340   15.56 16.6     PG1159 107 1
18 PG 1707+427 WD* 17 08 47.6869215528 +42 41 00.558430656   16.18       PG1159 112 0
19 PN K 1-16 PN 18 21 52.1086837968 +64 21 53.406292104   14.44 14.96 15.26   PG1159 242 0
20 SH 2-68 PN 18 24 58.4294414904 +00 51 36.021249072   16.0 16.5     DAOZ.6 126 1
21 MWP 1 PN 21 17 08.2817782392 +34 12 27.415995372     12.33     PG1159 179 0
22 V* IR Peg WD* 21 34 08.2124719240 +06 50 57.662044329   16.15       PG1159 115 0
23 V* V409 And WD* 23 27 15.9353097240 +40 01 23.429781408   14.1 15.41     DO 73 0
24 PN Jn 1 PN 23 35 53.3214838680 +30 28 06.336745212   15.52 15.62     DOZ 102 0

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2022.05.24-08:31:45

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