A survey for pulsating subdwarf B stars with the Nordic Optical Telescope

Østensen, R. H.; Oreiro, R.; Solheim, J. E.; Heber, U.; Silvotti, R.; González-Pérez, J. M.; Ulla, A.; Hernández, F. Pérez; Rodríguez‐López, C.; Telting, J. H.

doi:10.1051/0004-6361/200913480

Cited by 65 publications

(34 citation statements)

References 111 publications

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“…This fraction is not complete, because only papers containing larger samples of sdO/B stars A50, page 4 of 11 have been taken into account (Heber et al 1984;Bixler et al 1991;Saffer et al 1994Saffer et al , 1997Maxted et al 2001;Edelmann et al 2003;Lisker et al 2005;Ströer et al 2007;Hirsch 2009;Østensen et al 2010a;Nemeth et al 2012;Geier et al 2013Geier et al , 2015bKupfer et al 2015;Luo et al 2016;Kepler et al 2016).…”

Section: Spectroscopic Parameters and Radial Velocitiesmentioning

confidence: 99%

The population of hot subdwarf stars studied withGaia

Geier

Østensen

Németh

et al. 2017

A&A

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138

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In preparation for the upcoming all-sky data releases of the Gaia mission we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The catalog contains 5613 unique sources and provides multiband photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colors, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques we removed outliers and misclassified objects. By matching this catalog with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalog of hot subdwarf stars based on Gaia data.

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Section: Spectroscopic Parameters and Radial Velocitiesmentioning

confidence: 99%

The population of hot subdwarf stars studied withGaia

Geier

Østensen

Németh

et al. 2017

A&A

Self Cite

138

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“…Indeed, the instability strip predicted by the so-called Montréal "second-generation" models (Charpinet et al 1996(Charpinet et al , 1997 matches that observed almost perfectly. Interestingly, fewer than 10% of sdB stars within the instability strip appear to show pulsations at a measurable level (Billères et al 2002;Østensen et al 2010). The most convincing explanation so far brought forward for this phenomenon is the perturbation of the levitating iron reservoir within the stellar envelope by weak winds (Fontaine et al 2006), but this remains to be modelled in detail.…”

Section: Introductionmentioning

confidence: 99%

Pulsating hot O subdwarfs inωCentauri: mapping a unique instability strip on the extreme horizontal branch

Randall¹,

Calamida

Fontaine

et al. 2016

A&A

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We present the results of an extensive survey for rapid pulsators among Extreme Horizontal Branch (EHB) stars in ω Cen. The observations performed consist of nearly 100 hours of time-series photometry for several off-centre fields of the cluster, as well as low-resolution spectroscopy for a partially overlapping sample. We obtained photometry for some 300 EHB stars, for around half of which we are able to recover light curves of sufficient quality to either detect or place meaningful non-detection limits for rapid pulsations. Based on the spectroscopy, we derive reliable values of log g, T eff and log N(He)/N(H) for 38 targets, as well as good estimates of the effective temperature for another nine targets, whose spectra are slightly polluted by a close neighbour in the image. The survey uncovered a total of five rapid variables with multi-periodic oscillations between 85 and 125 s. Spectroscopically, they form a homogeneous group of hydrogen-rich subdwarf O stars clustered between 48,000 and 54,000 K. For each of the variables we are able to measure between two and three significant pulsations believed to constitute independent harmonic oscillations. However, the interpretation of the Fourier spectra is not straightforward due to significant fine structure attributed to strong amplitude variations. In addition to the rapid variables, we found an EHB star with an apparently periodic luminosity variation of ∼2700 s, which we tentatively suggest may be caused by ellipsoidal variations in a close binary. Using the overlapping photometry and spectroscopy sample we are able to map an empirical ω Cen instability strip in log g − T eff space. This can be directly compared to the pulsation driving predicted from the Montréal "second-generation" models regularly used to interpret the pulsations in hot B subdwarfs. Extending the parameter range of these models to higher temperatures, we find that the region where p-mode excitation occurs is in fact bifurcated, and the well-known instability strip between 29,000-36,000 K where the rapid subdwarf B pulsators are found is complemented by a second one above 50,000 K in the models. While significant challenges remain at the quantitative level, we believe that the same κ-mechanism that drives the pulsations in hot B subdwarfs is also responsible for the excitation of the rapid oscillations observed in the ω Cen variables. Intriguingly, the ω Cen variables appear to form a unique class. No direct counterparts have so far been found either in the Galactic field, nor in other globular clusters, despite dedicated searches. Conversely, our survey revealed no ω Cen representatives of the rapidly pulsating hot B subdwarfs found among the field population, though their presence cannot be excluded from the limited sample.

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“…1 (dotted error bars). Assuming that, like for the sdBV r variables [18] just one out of 10 sdOs within the instability region pulsates, our null results are not yet indicative of systematic differences between the field and globular cluster sdO populations. In Cen we monitored several hundred EHB 04006-p. 3 stars in order to find just four pulsators, so it may simply be a matter of continuing the search for sdO pulsators in the Galactic field.…”

Section: Differences Between the Ehb Instability Strip In X Cen And Tmentioning

confidence: 59%

A survey of hot subdwarf pulsators inωCen

Randal¹,

Calamida

Fontaine

et al. 2013

EPJ Web of Conferences

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Abstract.We recently discovered an apparently new class of pulsating Extreme Horizontal Branch (EHB) star in Cen. Tightly clustered around ∼50,000 K, these H-rich sdO stars exhibit rapid, multi-periodic oscillations on a timescale of 100 s. While four such objects have been detected in Cen, no counterparts have yet been found among the field population. Conversely, the rapid sdB pulsators around 31,000 K that are well-studied in the Galactic field have yet to be found in a globular cluster. We discuss the implications of this and also report the discovery of a fifth EHB pulsator in Cen.

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A survey for pulsating subdwarf B stars with the Nordic Optical Telescope

Cited by 65 publications

References 111 publications

The population of hot subdwarf stars studied withGaia

The population of hot subdwarf stars studied withGaia

Pulsating hot O subdwarfs inωCentauri: mapping a unique instability strip on the extreme horizontal branch

A survey of hot subdwarf pulsators inωCen

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