Long term photometric monitoring with the Mercator telescope

Context. The detection of pulsational frequencies in stellar photometry is required as input for asteroseismological modelling. The second short run (SRa02) of the CoRoT mission has provided photometric data of unprecedented quality and time-coverage for a number of O-type stars. Aims. We analyse the CoRoT data corresponding to three hot O-type stars, describing the properties of their light curves and search for pulsational frequencies, which we then compare to theoretical model predictions. Methods. We determine the amplitude spectrum of the data, using the Lomb-Scargle and a multifrequency HMM-like technique. Frequencies are extracted by prewhitening, and their significance is evaluated under the assumption that the light curve is dominated by red noise. We search for harmonics, linear combinations, and regular spacings among these frequencies. We use simulations with the same time sampling as the data as a powerful tool to judge the significance of our results. From the theoretical point of view, we use the MAD non-adiabatic pulsation code to determine the expected frequencies of excited modes. Results. A substantial number of frequencies is listed, but none can be convincingly identified as being connected to pulsations. The amplitude spectrum is dominated by red noise. Theoretical modelling shows that all three O-type stars can have excited modes, but the relation between the theoretical frequencies and the observed spectrum is not obvious. Conclusions. The dominant red noise component in the hot O-type stars studied here clearly points to a different origin than the pulsations seen in cooler O stars. The physical cause of this red noise is unclear, but we speculate on the possibility of sub-surface convection, granulation, or stellar wind inhomogeneities being responsible.

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“…Telting et al 2006;De Cat et al 2007;Pigulski & Pojmański 2008). These are all late Otype stars and therefore close to the three-star group.…”

Section: Pulsations and Red Noisementioning

confidence: 67%

Variability in the CoRoT photometry of three hot O-type stars

Blomme

Mahy

Catala

et al. 2011

A&A

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105

121

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“…They are known as β Cep/SPB hybrids (e.g. De Cat et al 2007;Pigulski & Pojmanski 2008;Handler 2009;Balona et al 2011;Degroote et al 2012b;Pápics et al 2012). …”

Section: Oscillation Spectra Of Early-type Starsmentioning

confidence: 99%

Seismic models of O and B stars with Kurucz’s opacity data

Cugier

2014

A&A

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Aims. We investigated seismic models of O and B stars calculated with the new Kurucz opacities implemented in the Opacity Project (OP) and Rogers & Iglesias OPAL opacity tables (OPAL). Methods. We studied the problem using Dziembowski's computer codes for linear, nonadiabatic, and nonradial oscillations. We considered seismic models of main sequence (MS) stars for different chemical compositions of elements in the mass-range 9 ≤ M ≤ 70 M . Results. The new opacity bump at lg T ≈ 5.06 that occurs in Kurucz's data influences evolutionary tracks mainly for M ≥ 30 M and markedly changes the driving zone for pulsations of stars in the whole mass range studied. We obtained no unstable oscillation modes for models corresponding to the abundance parameter Z ≤ 0.013 and only unstable low-frequency g-modes for 0.013 < Z ≤ 0.021. Conclusions. The opacity bump at lg T ≈ 5.3 should be significantly larger than the opacity bump at lg T ≈ 5.06 to drive pulsations of B stars in low-degree p-modes. Models with an increased OPAL (or OP) opacity bump at lg T ≈ 5.3 by a factor of about 1.7 have sufficiently large driving zones to excite modes in the β Cephei frequency-domain for 0.003 ≤ Z ≤ 0.021. These values of Z are in a good agreement with those derived spectroscopically for stars in the Galaxy and Magellanic Clouds.

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“…Here we report on the results of a long-term monitoring of γ Dor stars, while De Cat et al (2007) discussed the results for a sample of variable OB stars.…”

Section: The Instrument and The Observationsmentioning

confidence: 99%

Long-term photometric monitoring with the Mercator telescope

Cuypers¹,

Aerts

Cat³

et al. 2009

A&A

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Context. γ Dor stars are excellent targets for asteroseismology since the gravity modes present in these stars probe the deep stellar interiors. Mode identification will improve the knowledge of these stars considerably. Aims. A selected group of γ Dor stars and some candidates were observed with the Mercator telescope to find and/or confirm the periodicities in the light variations and to derive reliable amplitude ratios in different pass bands. Methods. A frequency analysis was performed on all new data obtained in the Geneva photometric system. In order to have more reliable and accurate frequencies, the new data were combined with similar data from the literature and with Hipparcos observations. A set of frequencies that minimized the residuals in a harmonic fit was searched for while allowing means and amplitudes to vary from one observation set to another. Results. Frequencies and amplitudes in the photometric passbands of the Geneva system are given for 21 γ Dor stars. We report the discovery of HD 74504 as a newly found γ Dor star. Conclusions. Our study provides the first extensive multicolour database for the understanding of gravity modes in F-type stars.

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Long term photometric monitoring with the Mercator telescope

Cited by 61 publications

References 71 publications

Variability in the CoRoT photometry of three hot O-type stars

Variability in the CoRoT photometry of three hot O-type stars

Seismic models of O and B stars with Kurucz’s opacity data

Long-term photometric monitoring with the Mercator telescope

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