The EC 14026 stars - XI. Feige 48: a link in its class

Koen, C.; O'Donoghue, D.; Pollacco, D.; Nitta, A.

doi:10.1046/j.1365-8711.1998.01983.x

Cited by 36 publications

(38 citation statements)

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“…2). The periods of HS0702+6043 are very similar to those of Feige 48 (340-380 s, Koen et al 1998) and HS2201+2610 (350 s, Østensen et al 2001a). This star therefore fits well into that relation.…”

Section: Discussionsupporting

confidence: 57%

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HS0702+6043 – A new large amplitude sdB variable at the cool end of the instability region

Schuh¹,

Deetjen²,

Edelmann³

et al. 2002

A&A

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Abstract. We report on time series photometry of hot sdB stars from the Hamburg Schmidt survey carried out at the Calar Alto 1.23 m and 2.2 m telescopes. Among 14 spectroscopically selected candidates we detected oscillations in the sdB star HS0702+6043 with a period of 363 s and an amplitude of 29 mmag which is among the largest amplitude observed in sdBV stars. A second period of 382 s with a significantly smaller amplitude (3.8 mmag) might be present. Our NLTE model atmosphere analysis of the time-averaged optical spectra, obtained at the Calar Alto 3.5 m telescope, indicates that HS0702+6043 has T eff = 28 400 K and log g = 5.35. This places the star at the cool end of the theoretical sdBV instability strip (EC 14026 stars). Among the other thirteen sdB stars we confirmed the variablity of the previously discovered sdBV HS0815+4243 and identified twelve stars to be stable, for which we give upper limits for light variations.

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Section: Discussionsupporting

confidence: 57%

“…2). The atmospheric parameters of HS0702+6043 are very similar to the parameters of the pulsating sdB stars Feige 48 and HS 2201+2610 (Heber et al 2000b;Koen et al 1998;Østensen et al 2001a), which allows a comparison of the pulsation periods in relation to the spectroscopic parameters (see Sect. 5).…”

Section: Spectroscopymentioning

confidence: 93%

HS0702+6043 – A new large amplitude sdB variable at the cool end of the instability region

Schuh¹,

Deetjen²,

Edelmann³

et al. 2002

A&A

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“…This places Feige 48 close to the red edge of the EC 14026 instability region in the log g − T eff plane. A standard Fourier analysis of our high signal-to-noise ratio Canada-France-Hawaii Telescope (CFHT) light curves reveals the presence of nine distinct harmonic oscillations with periods in the range 343−383 s, a significant improvement over previous reported observations that recovered only five periods (Koen et al 1998, MNRAS, 300, 1105Reed et al 2004, MNRAS, 348, 1164. Out of these nine periods, only four turn out to be independent modes having different k and/or indices suitable for detailed asteroseismology.…”

Section: Introductionmentioning

confidence: 65%

“…Koen et al (1998) were the first to report on short period nonradial oscillations in that star, revealing a relatively simple spectrum of 5 periods found in the range 344−379 s (see also Reed et al 2004), i.e., somewhat longer than in most of the other known EC 14026 stars. Estimated surface parameters from quantitative spectroscopy provided by these authors indicate that Feige 48 is among the coolest known rapid sdB pulsators, which places it close to the red edge of the instability domain .…”

Section: Introductionmentioning

confidence: 90%

Structural parameters of the hot pulsating B subdwarf Feige 48 from asteroseismology

Charpinet

Fontaine

Brassard

et al. 2005

A&A

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We present observations followed by a thorough analysis of the rapidly pulsating subdwarf B star (or EC 14026 star) Feige 48. This work is part of a long term multifaceted effort to exploit the strong asteroseismological potential of sdB pulsators which involves high sensitivity photometric observations, accurate spectroscopic measurements, and the development of appropriate modelling tools dedicated to the interpretation of the seismic data. Our model atmosphere analysis of the time averaged optical spectrum of Feige 48 obtained at the new Multiple Mirror Telescope (MMT) leads to estimates of T eff = 29 580 ± 370 K and log g = 5.480 ± 0.046 (with log N(He)/N(H) = −2.95 ± 0.08), in excellent agreement with previous spectroscopic measurements of its atmospheric parameters. This places Feige 48 close to the red edge of the EC 14026 instability region in the log g − T eff plane. A standard Fourier analysis of our high signal-to-noise ratio Canada-France-Hawaii Telescope (CFHT) light curves reveals the presence of nine distinct harmonic oscillations with periods in the range 343−383 s, a significant improvement over previous reported observations that recovered only five periods (Koen et al. 1998, MNRAS, 300, 1105Reed et al. 2004, MNRAS, 348, 1164. Out of these nine periods, only four turn out to be independent modes having different k and/or indices suitable for detailed asteroseismology. The remaining periods can be interpreted as rotationally split components of modes with the same (k, ) values, but different m indices that bear the signature of the rotation of the star. On the basis of the four independent periods, we have carried out a detailed asteroseismic analysis of Feige 48 using the well-known forward method. Our analysis leads objectively to the identification of the (k, ) indices of the four independent periods identified in the star, and to the determination of its structural parameters. The periods correspond to low-order modes with adjacent values of k and with = 0, 1, and 2. They define a band of unstable modes, in agreement with nonadiabatic pulsation theory. Furthermore, the average dispersion between the observed periods and the periods of the corresponding theoretical modes of the optimal model is only ∼0.005%, quite close to the actual accuracy of the observations. We emphasise that radiative levitation is a key ingredient in the determination of accurate pulsation periods for sdB stars, and that standard models with uniform metallicity fail to reproduce the observed periods in Feige 48 because they do not incorporate this key piece of constitutive physics. On the basis of our combined spectroscopic and asteroseismic analysis, the inferred global structural parameters of Feige 48 are T eff = 29 580±370 K, log g = 5.4365±0.0060, log M env /M * = −2.97±0.09, M * = 0.460±0.008 M (i.e., close to the canonical mass of extreme horizontal branch stars), R/R = 0.2147±0.0034, and L/L = 31.62±2.58. Combined with detailed model atmosphere calculations, we estimate, in addition, that this star has ...

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“…Our sample includes the short-period pulsators Feige 48 (Koen et al 1998), KPD 2109+440 (Billères et al 1998), PG 1219+534 (O'Donoghue et al 1999 and HE 0230−4323 as well as the long-period pulsators PG 1627+017 (Green et al 2003), LB 1516 , JL 82 (Koen 2009), PHL 44 (Kilkenny et al 2007), PHL 457 (Blanchette et al 2008), PG 1716+426 (Green et al 2003) and PG 0101+039 (Randall et al 2005). Consistent with the results of Heber et al (2000), O'Toole & Heber (2006) and Blanchette et al (2008) no differences have been found in the metal abundance patterns of these stars with respect to the rest of the sample.…”

Section: Abundance Patterns Of Sdb Sub-populationsmentioning

confidence: 99%

Hot subdwarf stars in close-up view

Geier

2013

A&A

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Context. Hot subdwarf B stars (sdBs) are considered to be core helium-burning stars with very thin hydrogen envelopes situated on or near the extreme horizontal branch. The formation of sdBs is still unclear as well as the chemical composition of their atmospheres. The observed helium depletion is attributed to atmospheric diffusion. Metal abundances have been determined for about a dozen sdBs only resulting in puzzling patterns with enrichment of heavy metals and depletion of lighter ones. Aims. We present a detailed metal abundance analysis of 106 sdBs. Methods. From high resolution spectra we measured elemental abundances of up to 24 different ions per star. A semi-automatic analysis pipeline was developed to calculate and fit LTE models to a standard set of spectral lines. Results. A general trend of enrichment was found with increasing temperature for most of the heavier elements. The lighter elements like carbon, oxygen, and nitrogen are depleted and less affected by temperature. Although there is considerable scatter from star to star, the general abundance patterns in most sdBs are similar. State-of-the-art diffusion models predict such patterns and are in qualitative agreement with our results. However, the highest enrichments measured cannot be explained with these models. Peculiar line shapes of the strongest metal lines in some stars indicate vertical stratification to be present in the atmospheres. Such effects are not accounted for in current diffusion models and may be responsible for some of the yet unexplained abundance anomalies.

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The EC 14026 stars - XI. Feige 48: a link in its class

Cited by 36 publications

References 0 publications

HS0702+6043 – A new large amplitude sdB variable at the cool end of the instability region

HS0702+6043 – A new large amplitude sdB variable at the cool end of the instability region

Structural parameters of the hot pulsating B subdwarf Feige 48 from asteroseismology

Hot subdwarf stars in close-up view

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