Asteroseismological measurements on PG 1159-035, the prototype of the GW Virginis variable stars

Córsico, A. H.; Althaus, Leandro Gabriel; Kepler, S. O.; Costa, Jose Eduardo da Silveira; Bertolami, M. M. Miller

doi:10.1051/0004-6361:20078646

Cited by 46 publications

(53 citation statements)

References 30 publications

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“…About half of the modes show increasing periods and half show decreasing ones. Two of the modes that are identified as trapped modes in the best-fit model of Córsico et al (2008) show decreasing periods, as expected. The dominant mode at 516 s shows a regularly increasing period.…”

Section: The Rate Of Change Of the Pulsation Frequencies Predicted Bysupporting

confidence: 78%

The period and amplitude changes in the coolest GW Virginis variable star (PG 1159-type) PG 0122+200

Vauclair

Solheim

et al. 2011

A&A

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Context. The PG 1159 pre-white dwarf stars experiment a rapidly cooling phase with a time scale of a few 10 6 years. Theoretical models predict that the neutrinos produced in their core should play a dominant role in the cooling, mainly at the cool end of the PG 1159 sequence. Measuring the evolutionary time scale of the coolest PG 1159 stars could offer a unique opportunity to empirically constrain the neutrino emission rate. Aims. A subgroup of the PG 1159 stars are nonradial pulsators, the GW Vir type of variable stars. They exhibit g-mode pulsations with periods of a few hundred seconds. As the stars cool, the pulsation frequencies evolve according to the change in their internal structure. It was anticipated that the measurement of their rate of change would directly determine the evolution time scale and so constrain the neutrino emission rates. As PG 0122+200 (BB Psc) defines the red edge of the GW Vir instability strip, it is a good candidate for such a measurement. Methods. The pulsations of PG 0122+200 have been observed during 22 years from 1986 to 2008, through the fast photometry technique. We used those data to measure the rate of change of its frequencies and amplitudes. Results. Among the 24 identified = 1 modes, the frequency and amplitude variations have been obtained for the seven largest amplitude ones. We find changes of their frequency of much larger amplitudes and shorter time scales than the one predicted by theoretical models that assume that the cooling dominates the frequency variations. In the case of the largest amplitude mode at 2497 μHz (400 s), its variations are best fitted by a combination of two terms: one long term with a time scale of 5.4 × 10 4 years, which is significantly shorter than the predicted evolutionary time scale of 8 × 10 6 years; and one additional periodic term with a period of either 261 or 211 days. Some other mechanism(s) than the cooling must be responsible for such variations. We suggest that the resonant coupling induced within triplets by the star rotation could be such a mechanism. As a consequence, no useful constraints on the neutrino emission rate can presently be derived as long as the dominant mechanism is not properly understood. Conclusions. The temporal variations in the pulsation frequencies observed in PG 0122+200 cannot be simply attributed to the cooling of the star, regardless of the contribution of the neutrino losses. Our results suggest that the resonant coupling induced by the rotation plays a dominant role which must be further investigated.

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Section: The Rate Of Change Of the Pulsation Frequencies Predicted Bysupporting

confidence: 78%

The period and amplitude changes in the coolest GW Virginis variable star (PG 1159-type) PG 0122+200

Vauclair

Solheim

et al. 2011

A&A

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“…Also, the rates of period changes measured by are 10 times larger than those predicted by the asteroseismological model. We stress that the PG 1159 evolutionary models employed in the series of asteroseismological studies of Córsico et al (2007aCórsico et al ( , 2007bCórsico et al ( , 2008Córsico et al ( , 2009b are characterized by thick He-rich outer …”

Section: The Rate Of Period Change Of Pg 1159−035mentioning

confidence: 90%

“…We also note that the asymptotic period spacing overestimates the stellar mass of the studied PG 1159 stars, as expected on the grounds that these stars (except RX J2117.1+3412) are not in the asymptotic limit of g-mode pulsations, and then the asymptotic theory is not completely valid in such cases. The main conclusion of the series of studies by Córsico et al (2007bCórsico et al ( , 2008Córsico et al ( , 2009b) is that for most well-observed pulsating PG 1159 stars (PG 0122+200, PG 1159−035, PG 2131+066, and PG 1707+427) it is possible to find a stellar model (the asteroseismological model) with M * near the spectroscopic determinations to a high internal accuracy. The next step is an assessment of the question if the asteroseismological models can provide more accurate masses for these objects.…”

Section: Asteroseismological Inferences On Gw Vir Starsmentioning

confidence: 98%

Evolutionary and pulsational properties of white dwarf stars

Althaus

Córsico

Isern

et al. 2010

Astron Astrophys Rev

379

372

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White dwarf stars are the final evolutionary stage of the vast majority of stars, including our Sun. Since the coolest white dwarfs are very old objects, the present population of white dwarfs contains a wealth of information on the evolution of stars from birth to death, and on the star formation rate throughout the history of our Galaxy. Thus, the study of white dwarfs has potential applications to different fields of astrophysics. In particular, white dwarfs can be used as independent reliable cosmic clocks, and can also provide valuable information about the fundamental parameters of a wide variety of stellar populations, like our Galaxy and open and globular clusters. In addition, the high densities and temperatures characterizing white dwarfs allow to use these stars as cosmic laboratories for studying physical processes under extreme conditions that cannot be achieved in terrestrial laboratories. Last but not least, since many white dwarf stars undergo pulsational instabilities, the study of their properties constitutes a powerful tool for applications beyond stellar astrophysics. In particular, white dwarfs can be used to constrain fundamental properties of elementary particles such as axions and neutrinos, and to study problems related to the variation of fundamental constants.These potential applications of white dwarfs have led to a renewed interest in the calculation of very detailed evolutionary and pulsational models for these stars. In this work, we review the essentials of the physics of white dwarf stars. We enumerate the reasons that make these stars excellent chronometers and we describe why white dwarfs provide tools for a wide variety of applications. Special emphasis is placed on the physical processes that lead to the formation of white dwarfs as well as on the different energy sources and processes responsible for chemical abundance changes that occur along their evolution. Moreover, in the course of their lives, white dwarfs cross different pulsational instability strips. The existence of these instability strips provides astronomers with an unique opportunity to peer into their internal structure that would otherwise remain hidden from observers. We will show that this allows to measure with unprecedented precision the stellar masses and to infer their envelope thicknesses, to probe the core chemical stratification, and to detect rotation rates and magnetic fields. Consequently, in this work, we also review the pulsational properties of white dwarfs and the most recent applications of white dwarf asteroseismology.

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“…For DBVs, an estimate of the rate of period change has been obtained for PG 1351+489 (Π = 2.0 ± 0.9 × 10 −13 s/s, Redaelli et al 2011), in line with the theoretical expectations (Π ∼ 10 −13 −10 −14 s/s; Winget et al 2004;Córsico & Althaus 2004). In the case of pulsating hot WD and pre-WD stars, also called GW Vir or pulsating PG1159 stars (He-, C-, and O-rich atmosphere), theoretical models predict rates of period change in the range 10 −11 −10 −12 s/s (Kawaler & Bradley 1994;Córsico & Althaus 2006;Córsico et al 2008). For the high effective temperatures characterizing the GW Vir instability strip, gravitational A73, page 2 of 13 contraction is still significant, to such a degree that its influence onΠ can overcome the effects of cooling.…”

Section: Introductionmentioning

confidence: 99%

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

Calcaferro

Córsico

Althaus

2017

A&A

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Context. An increasing number of low-mass (M /M 0.45) and extremely low-mass (ELM, M /M 0.18−0.20) white-dwarf stars are being discovered in the field of the Milky Way. Some of these stars exhibit long-period g-mode pulsations, and are called ELMV variable stars. Also, some low-mass pre-white dwarf stars show short-period p-mode (and likely radial-mode) photometric variations, and are designated as pre-ELMV variable stars. The existence of these new classes of pulsating white dwarfs and pre-white dwarfs opens the prospect of exploring the binary formation channels of these low-mass white dwarfs through asteroseismology. Aims. We aim to present a theoretical assessment of the expected temporal rates of change of periods (Π) for such stars, based on fully evolutionary low-mass He-core white dwarf and pre-white dwarf models. Methods. Our analysis is based on a large set of adiabatic periods of radial and nonradial pulsation modes computed on a suite of low-mass He-core white dwarf and pre-white dwarf models with masses ranging from 0.1554 to 0.4352 M , which were derived by computing the non-conservative evolution of a binary system consisting of an initially 1 M ZAMS star and a 1.4 M neutron star companion. Results. We computed the secular rates of period change of radial ( = 0) and nonradial ( = 1, 2) g and p modes for stellar models representative of ELMV and pre-ELMV stars, as well as for stellar objects that are evolving just before the occurrence of CNO flashes at the early cooling branches. We find that the theoretically expected magnitude ofΠ of g modes for pre-ELMVs is by far larger than for ELMVs. In turn,Π of g modes for models evolving before the occurrence of CNO flashes are larger than the maximum values of the rates of period change predicted for pre-ELMV stars. Regarding p and radial modes, we find that the larger absolute values ofΠ correspond to pre-ELMV models. Conclusions. We conclude that any eventual measurement of a rate of period change for a given pulsating low-mass pre-white dwarf or white dwarf star could shed light about its evolutionary status. Also, in view of the systematic difficulties in the spectroscopic classification of stars of the ELM Survey, an eventual measurement ofΠ could help to confirm that a given pulsating star is an authentic low-mass white dwarf and not a star from another stellar population.

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Asteroseismological measurements on PG 1159-035, the prototype of the GW Virginis variable stars

Cited by 46 publications

References 30 publications

The period and amplitude changes in the coolest GW Virginis variable star (PG 1159-type) PG 0122+200

The period and amplitude changes in the coolest GW Virginis variable star (PG 1159-type) PG 0122+200

Evolutionary and pulsational properties of white dwarf stars

Pulsating low-mass white dwarfs in the frame of new evolutionary sequences

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