FUSE Observations of EC14026 Stars

Chayer, P.; Fontaine, G.; Fontaine, Mathieu; Lamontagne, R.; Wesemaël, F.; Dupuis, J.; Heber, U.; Napiwotzki, R.; Moehler, S.

doi:10.1023/b:astr.0000044344.92680.b8

Cited by 36 publications

(50 citation statements)

References 9 publications

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“…The T eff and log g of V361 Hya stars, between 28 400−35 700 K and 5.25−6.11 dex, place them in an area of the HR diagram where they coexist with non-variable sdBs. A possible explanation for this co-existence comes from mass loss, which is thought to play an important role in emptying the iron reserve (Chayer et al 2004). …”

Section: Introductionmentioning

confidence: 99%

PG 1657+416: a new fast pulsating sdB star

Oreiro

Hernández

Østensen

et al. 2006

A&A

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Context. Since the discovery in 1997 of stellar oscillations in some B-type hot subdwarfs (sdBs), much effort is being made both observationally and theoretically to characterize this new group of pulsating objects. Aims. To increase the number of members of such pulsators and to perform a theoretical analysis of new pulsating stars. Methods. The Nordic Optical Telescope was used to measure the brightness as function of time for a list of selected sdBs. Pulsator candidates were selected by deriving the effective temperatures and gravities of sdB stars from various spectroscopic surveys, and picking targets in the instability region. Pulsational properties were investigated by Fourier analysis. For the theoretical analysis, the predicted frequencies of sdB structural models in the T eff − log g region of interest were computed. Results. From our list of candidates we detected one, PG 1657+416, as a new oscillating star. Follow-up photometry revealed at least four frequencies in the range 6.9−7.9 mHz, whose amplitudes vary from one data set to another. The theoretical comparison indicates that the observed periods are well reproduced by structural models whose physical parameters are in good agreement with the effective temperature and gravity estimates from a spectral energy distribution fit, which also shows that the sdB has a G5 main sequence companion with T eff ∼ 5500 K.

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Section: Introductionmentioning

confidence: 99%

PG 1657+416: a new fast pulsating sdB star

Oreiro

Hernández

Østensen

et al. 2006

A&A

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“…The inclusion of both diffusion processes is therefore not only important to explain the low atmospheric helium abundances, but also to create the driving region for the pulsations. Since the pulsation regions are by no means pure, inefficient stellar winds have been proposed to destroy the diffusive balance in the driving region [27].…”

Section: Hot Subdwarf B Starsmentioning

confidence: 99%

Asteroseismic Constraints on the Models of Hot B Subdwarfs: Convective Helium-Burning Cores

2017

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Abstract.Asteroseismology of non-radial pulsations in Hot B Subdwarfs (sdB stars) offers a unique view into the interior of core-helium-burning stars. Ground-based and space-borne high precision light curves allow for the analysis of pressure and gravity mode pulsations to probe the structure of sdB stars deep into the convective core. As such asteroseismological analysis provides an excellent opportunity to test our understanding of stellar evolution. In light of the newest constraints from asteroseismology of sdB and red clump stars, standard approaches of convective mixing in 1D stellar evolution models are called into question. The problem lies in the current treatment of overshooting and the entrainment at the convective boundary. Unfortunately no consistent algorithm of convective mixing exists to solve the problem, introducing uncertainties to the estimates of stellar ages. Three dimensional simulations of stellar convection show the natural development of an overshooting region and a boundary layer. In search for a consistent prescription of convection in one dimensional stellar evolution models, guidance from three dimensional simulations and asteroseismological results is indispensable. Hot Subdwarf B starsSubdwarf B (sdB) stars are a class of hot (T eff = 20, 000−40, 000 K) and compact (log g = 5.0−6.2) stars with very thin hydrogen envelopes (M H < 0.01 M ) [1,2]. They form the so-called extreme horizontal branch (EHB) in the Hertzsprung-Russell diagram, where most of them quietly burn helium in their cores for ∼10 8 years. A violent process stripped them of most of their hydrogen envelope before they underwent the helium flash near the tip of the red giant branch (RGB). As a consequence they will not climb up the asymptotic giant branch (AGB) once their core helium is exhausted, but rather evolve directly to become white dwarfs.Although some sdB stars appear to be single and others occur in wide binaries, surveys have concluded that the majority are in close binaries with white dwarf or lowmass main sequence companions [3][4][5]. A small fraction of the latter exhibit eclipses, offering insight into the orbital parameters and masses of the systems. These HW Virginis stars, named after the discovery system, play a crucial role in determining the mass distribution of sdB stars. The median mass of sdB stars estimated from these binaries is 0.469 M [6].The formation scenarios for sdB stars have to explain their existence in both single and binary systems as well as introduce a process by which the hydrogen envelope of the progenitor stars can be lost. Common envelope ejection (CE) or stable Roche lobe overflow (RLOF) during binary evolution result in systems with close and wide e-mail: jtschindler@email.arizona.edu separations, respectively, [7]. Population synthesis models can well explain the occurrence of binary systems and the mass distribution of the primary and secondary components [8]. To explain the existence of single sdB stars, extreme mass loss on the RGB [9-11] as well as white dwarf mergers...

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“…Appreciable (to 2 dex) excesses of lead, germanium, and zirconium have been measured for normal sdB stars using UV spectra [222,223]. In the case of sdB stars enriched in heavy elements, the excesses for Zr, Ge, Sr, Y, and Pb measured using several lines in the visible were 4 dex [224,225].…”

Section: Hot Subdwarfs In the Uvmentioning

confidence: 99%

Scientific problems addressed by the Spektr-UV space project (world space Observatory—Ultraviolet)

et al. 2016

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Abstract-The article presents a review of scientific problems and methods of ultraviolet astronomy, focusing on perspective scientific problems (directions) whose solution requires UV space observatories. These include reionization and the history of star formation in the Universe, searches for dark baryonic matter, physical and chemical processes in the interstellar medium and protoplanetary disks, the physics of accretion and outflows in astrophysical objects, from Active Galactic Nuclei to close binary stars, stellar activity (for both low-mass and high-mass stars), and processes occurring in the atmospheres of both planets in the solar system and exoplanets. Technological progress in UV astronomy achieved in recent years is also considered. The well advanced, international, Russian-led Spektr-UV (World Space Observatory-Ultraviolet) project is described in more detail. This project is directed at creating a major space observatory operational in the ultraviolet (115-310 nm). This observatory will provide an effective, and possibly the only, powerful means of observing in this spectral range over the next ten years, and will be an powerful tool for resolving many topical scientific problems.

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FUSE Observations of EC14026 Stars

Cited by 36 publications

References 9 publications

PG 1657+416: a new fast pulsating sdB star

PG 1657+416: a new fast pulsating sdB star

Asteroseismic Constraints on the Models of Hot B Subdwarfs: Convective Helium-Burning Cores

Scientific problems addressed by the Spektr-UV space project (world space Observatory—Ultraviolet)

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