Variable Be Stars in h and χ Persei

Waelkens, Christoffel; Lampens, P.; Cuypers, J.; Denoyelle, J.; Heynderickx, D.; Rufener, F.; Smeyers, Paul

doi:10.1017/s0252921100116690

Cited by 26 publications

(39 citation statements)

References 3 publications

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“…As almost all observations of SPB stars have been undertaken in the Geneva photometric system (e.g. Waelkens & Rufener 1985; Waelkens 1991; North & Paltani 1994; Waelkens et al 1998; De Cat & Aerts, in preparation) the focus of subsequent sections is placed almost wholly on the presentation and analysis of the data in the Geneva UB 1 BB 2 V 1 VG passbands. However, the amplitude and phase data of all photometric systems considered have been made available for download from the World Wide Web, at http://www.star.ucl.ac.uk/∼rhdt/download/…”

Section: Methodsmentioning

confidence: 99%

Photometric modelling of slowly pulsating B stars

Townsend

2002

Monthly Notices of the Royal Astronomical Society

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A B S T R A C TThe photometric characteristics of slowly pulsating B stars are investigated using a numerical approach. Stability calculations are performed for a set of stellar models representative of the mid-B type, using a non-radial non-adiabatic pulsation code. The results from these calculations are used to synthesize photometry, in several common systems, for unstable modes of harmonic degrees ' ¼ 1. . .4. Focusing on the Geneva system for illustrative purposes, a variety of techniques are employed to analyse and visualize the synthetic data, including the use of multicolour-amplitudes and amplitude -phase diagnostic diagrams. One outstanding aspect of the analysis is the discovery, for the ' ¼ 2. . .4 modes, of 'inter-term cancellation' (ITC) -the process of destructive interference between the flux variations originating from surface temperature perturbations and those arising from radius perturbations.The ITC can be severe enough that a mode may be excited to a significant amplitude, and yet exhibit levels of photometric variability that fall below typical observational detection thresholds. Furthermore, it can affect not only the light variations in a given photometric passband, but also the variations of the bolometric flux. However, the cancellation is dependent on wavelength, and will not occur to the same degree in more than one passband. Therefore, simultaneous observation in a multitude of passbands represents the best approach to ensuring that no modes are overlooked during searches for variability in B-type stars.A consequence of ITC is that ratios between the variability amplitude, in differing passbands, become very sensitive towards mode-to-mode changes in the pulsation. This increased sensitivity will tend to complicate any attempts at identifying the harmonic degrees of the modes responsible for observed variability. However, the cancellation also introduces significant phase differences between the light variations in each passband, especially for the ' ¼ 3 and ' ¼ 4 modes. On the grounds that correspondingly large phase differences are not seen in observational data, it is argued that the variability seen in slowly pulsating B stars can tentatively be attributed to ' ¼ 1 and ' ¼ 2 modes.

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Section: Methodsmentioning

confidence: 99%

Photometric modelling of slowly pulsating B stars

Townsend

2002

Monthly Notices of the Royal Astronomical Society

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“…We searched for frequencies using the PDM method (Stellingwerf 1978) and pre‐whitened the data for the orbital frequency and eight other low‐frequency signals (<0.2 d −1 ) using a spline fit to the bin means (see e.g. Waelkens & Rufener 1983). This resulted in a residual light curve without the binary and satellite signature.…”

Section: Variations On Other Time‐scalesmentioning

confidence: 99%

CoRoT photometry and high-resolution spectroscopy of the interacting eclipsing binary AU Monocerotis

Desmet¹,

Frémat²,

Baudin³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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Analyses of very accurate CoRoT space photometry, past Johnson V photoelectric photometry and high-resolution echelle spectra led to the determination of improved and consistent fundamental stellar properties of both components of AU Monocerotis. We derived new, accurate ephemerides for both the orbital motion (with a period of 11. d 113) and the long-term, overall brightness variation (with a period of 416. d 9) of this strongly interacting Be + G semi-detached binary. It is shown that this long-term variation must be due to attenuation of the total light by some variable circumbinary material. We derived the binary mass ratio M G /M B = 0.17 ± 0.03 based on the assumption that the G-type secondary fills its Roche lobe and rotates synchronously. Using this value of the mass ratio as well as the radial velocities of the G-star, we obtained a consistent light curve model and improved estimates of the stellar masses, radii, luminosities and effective temperatures. We demonstrate that the observed lines of the B-type primary may not be of photospheric origin. We also discover rapid and periodic light changes visible in the high-quality residual CoRoT light curves. AU Mon is put into perspective by a comparison with known binaries exhibiting long-term cyclic light changes.Based on photometry collected by the CoRoT space mission as well as spectroscopy obtained with the FEROS spectrograph attached to the 2.2-m telescope at European Southern Observatory (ESO), La Silla, Chile, under the ESO Large Programme LP178.D-0361, and with the SOPHIE spectrograph of the Observatoire de Haute-Provence (France). The CoRoT space mission was developed and is operated by the French space agency CNES, with the participation of ESA's RSSD

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“…The slowly pulsating B (SPB) stars are a homogeneous class of mid‐B‐type, main‐sequence objects that exhibit multiperiodic light and line‐profile variations over time‐scales on the order of 1–5 d. Waelkens (1991) was the first to classify these stars as a distinct group of early‐type non‐radial pulsators, by combining under the same aegis the photometric variables discovered by Waelkens & Rufener (1985) and the 53 Per spectroscopic variables first observed by Smith (1977). The theoretical pulsation characteristics of these objects have since been studied extensively, resulting in a canonical picture (see, e.g., Pamyatnykh 1999, and references therein) of high‐order g‐mode pulsation, driven by the same iron‐group κ mechanism responsible for the instability of the β Cep pulsators (Dziembowski & Pamyatnykh 1993).…”

Section: Introductionmentioning

confidence: 99%

Influence of the Coriolis force on the instability of slowly pulsating B stars

Townsend

2005

Monthly Notices of the Royal Astronomical Society

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This paper explores the effect of rotation on the κ‐mechanism instability of slowly pulsating B stars. A new non‐adiabatic code, which adopts the so‐called traditional approximation to treat the Coriolis force, is used to investigate the influence exerted by rotation over the stability of stellar models covering the mass range 2.5 M⊙≤M*≤ 13.0 M⊙. The principal finding is that, for all modes considered apart from the prograde sectoral (PS) class, rotation shifts the κ‐mechanism instability toward higher luminosities and effective temperatures; these shifts are accompanied by broadenings in the extent of instability strips. Such behaviour is traced to the shortening of mode periods under the action of the Coriolis force. Instability strips associated with PS modes behave rather differently, being shifted to marginally lower luminosities and effective temperatures under the influence of rotation. The implications of these results are discussed in the context of the observational scarcity of pulsation in B‐type stars having significant rotation; various scenarios are explored to explain the apparent dichotomy between theory and observations. Furthermore, the possible significance of the findings to Be stars is briefly examined.

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Variable Be Stars in h and χ Persei

Cited by 26 publications

References 3 publications

Photometric modelling of slowly pulsating B stars

Photometric modelling of slowly pulsating B stars

CoRoT photometry and high-resolution spectroscopy of the interacting eclipsing binary AU Monocerotis

Influence of the Coriolis force on the instability of slowly pulsating B stars

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