Query : 2006A&A...459..885J

2006A&A...459..885J - Astronomy and Astrophysics, volume 459, 885-899 (2006/12-1)

Stellar archaeology: the evolving spectrum of FG Sagittae.


Abstract (from CDS):

Over an interval of 120 years, the extraordinary object FG Sge has been transformed from a hot post-AGB star to a very luminous cool supergiant. Theoretically, this evolution has been associated with the reignition of a helium-shell during the post-AGB stage. A series of studies of the chemical composition of the photosphere have suggested that this evolution has been associated with a dramatic increase of approximately 3dex in the abundances of s-process elements between about 1960 and 1995. The problem with this apparent change is that it occurred at a time when the surface convection zone, which is governed by the star's effective temperature, could not have developed sufficiently to dredge processed material from the stellar interior to the surface. We have reviewed the chemical evolution of FG Sge by means of modelling the time-varying spectrum under a range of assumptions. By comparing these models with published observational data, a self-consistent picture has emerged. In particular we find that surface hydrogen has been depleted during the interval in question. In contrast, the s-process abundances have generally maintained a steady enhancement of around 1-2dex, although some modest changes may have occurred since 1950. This implies that FG Sge has not just completed dredging up freshly-produced s-process isotopes. However, there remains a contradiction between the observed hydrogen-depletion, the age of the associated planetary nebula, and current evolutionary models for a pre-white dwarf suffering a late thermal pulse.

Abstract Copyright:

Journal keyword(s): stars: fundamental parameters - stars: abundances - stars: evolution - stars: individual: FG Sge

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 * alf Per V* 03 24 19.3700924 +49 51 40.245455 2.64 2.27 1.79     F5Ib 820 1
2 V* V4334 Sgr CV* 17 52 32.69352 -17 41 08.0160           F2Ia 355 0
3 PN A66 58 PN 19 18 20.476 +01 46 59.62           [WC4] 304 0
4 Hen 1-5 pA* 20 11 56.0595568008 +20 20 04.420944132 11.41 10.66 9.45     G8/K0Iae 498 0
5 * alf Cyg sg* 20 41 25.91514 +45 16 49.2197 1.11 1.34 1.25 1.14 1.04 A2Ia 734 0

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