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Post Info TOPIC: PG 1159-035
Blobrana


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RE: PG 1159-035
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Title: Iron abundance in the prototype PG1159 star, GW Vir pulsator PG1159-035, and related objects
Authors: Klaus Werner, Thomas Rauch, Jeff W. Kruk, Robert L. Kurucz

We performed an iron abundance determination of the hot, hydrogen deficient post-AGB star PG1159-035, which is the prototype of the PG1159 spectral class and the GW Vir pulsators, and of two related objects (PG1520+525, PG1144+005), based on the first detection of Fe VIII lines in stellar photospheres. In another PG1159 star, PG1424+535, we detect Fe VII lines. In all four stars, each within Teff = 110,000 - 150,000 K, we find a solar iron abundance. This result agrees with our recent abundance analysis of the hottest PG1159 stars (Teff = 150,000 - 200,000 K) that exhibit Fe X lines. On the whole, we find that the PG1159 stars are not significantly iron deficient, in contrast to previous notions.

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Blobrana


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Title: The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035
Authors: J. E. S. Costa, S. O. Kepler
(Version v2)

PG 1159-035, a pre-white dwarf with T=140000 K, is the prototype of the PG1159 spectroscopic class and of the DOV pulsating class. Changes in the star cause variations in its oscillation periods. The measurement of the temporal changes in the oscillation periods, dP/dt, allows us to directly estimate the magnitude of stellar evolutionary changes, such as the cooling rate and the envelope contraction rate, providing a way to test and to refine the current evolutionary models for pre-white dwarf pulsating stars.
We measured 27 pulsation modes period changes. The periods are varying with rates between 1 and 100 ms/yr, a nd several of them can be directly measured with a standard uncertainty below 10%. Particularly, for the 516.0 s mode (the highest in amplitude) the dP/dt can be not only directly measured with a standard uncertainty of 2%, but the second order period change, d(dP/dt)/dt, is significant as well. By using the (O-C) method we refined the dP/dt and estimated the d(dP/dt)/dt for six other pulsation periods. As a first application, we calculated the change in the PG~1559-035 rotation period, dP_rot/dt = -2.13*10^{-6} s/s; the envelope contraction rate dR/dt = -2.2*10^{-13} solar radius/s; and the cooling rate dT/dt = -1.42*10^{-3} K/s.

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Blobrana


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Title: Asteroseismological measurements on PG 1159-035, the prototype of the GW Vir variable stars
Authors: A. H. Córsico, L. G. Althaus, S. O. Kepler, J. E. S. Costa, M. M. Miller Bertolami

An asteroseismological study of PG 1159-035, the prototype of the GW Vir variable stars, has been performed on the basis of detailed and full PG1159 evolutionary models presented by Miller Bertolami & Althaus (2006). We carried out extensive computations of adiabatic g-mode pulsation periods on PG1159 evolutionary models with stellar masses spanning the range 0.530 to 0.741 Mo. We derive a stellar mass in the range 0.56-0.59 Mo from the period-spacing data alone. We also find, on the basis of a period-fit procedure, a seismic model representative of PG 1159-035 that reproduces the observed period pattern with an average of the period differences of 0.64-1.03 s, consistent with the expected model uncertainties. The results of the period-fit analysis carried out in this work suggest that the surface gravity of PG 1159-035 would be 1 sigma larger than the spectroscopically inferred gravity. For our best-fit model of PG 1159-035, all of the pulsation modes are characterised by positive rates of period changes, at odds with the measurements by Costa & Kepler (2007).

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Blobrana


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GW Virginis
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PG 1159-035 is the prototypical PG 1159 star after which the class of PG 1159 stars were named. It was discovered in the Palomar-Green survey of ultraviolet-excess stellar objects and, like the other PG 1159 stars, is in transition between being the central star of a planetary nebula and being a white dwarf

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GW Virginis
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Right ascension 12h 01m 46.1s, Declination -03° 45 39
Spectral type: DO

-- Edited by Blobrana at 15:03, 2008-01-12

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Blobrana


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Posts: 131433
Date:
PG 1159-035
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Title: The pulsation modes of the pre-white dwarf PG 1159-035
Authors: J. E. S. Costa, S. O. Kepler, D. E. Winget, M. S. O'Brien, S. D. Kawaler, A. F. M. Costa, O. Giovannini, A. Kanaan, A. S. Mukadam, F. Mullally, A. Nitta, J. L. Provençal, H. Shipman, M. A. Wood, T. J. Ahrens, A. Grauer, M. Kilic, P. A. Bradley, K. Sekiguchi, R. Crowe, X. J. Jiang, D. Sullivan, T. Sullivan, R. Rosen, J. C. Clemens, R. Janulis, D. O'Donoghue, W. Ogloza, A. Baran, R. Silvotti, S. Marinoni, , G. Vauclair, N. Dolez, M. Chevreton, S. Dreizler, S. Schuh, J. Deetjen, T. Nagel, J.-E. Solheim, J. M. Gonzalez Perez, A. Ulla, Martin Barstow, M. Burleigh, S. Good, T.S. Metcalfe, S.-L. Kim, H. Lee, A. Sergeev, M.C. Akan, Ö. Çakirli, M. Paparo, G. Viraghalmy, B. N. Ashoka, G. Handler, Özlem Hürkal, F. Johannessen, S. J. Kleinman, R. Kalytis, J. Krzesinski, et al (18 additional authors not shown)

PG 1159-035, a pre-white dwarf with T_eff=140,000 K, is the prototype of both two classes: the PG1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. In this work, we used all available WET photometric data from 1983, 1985, 1989, 1993 and 2002 to identify the pulsation periods and identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M = 0.59 ± 0.02 solar masses for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at r_c = 0.83 ± 0.05 stellar radius. From the multiplet splitting, we calculated the rotational period P_rot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for l=1 modes and less than 50% for l=2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.

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