Ground-based observations of the β Cephei CoRoT main target HD 180 642: abundance analysis and mode identification

Abstract

The known β Cephei star HD 180 642 was observed by the CoRoT satellite in 2007. From the very high-precision light curve, its pulsation frequency spectrum could be derived for the first time (Degroote and collaborators). In this paper, we obtain additional constraints for forthcoming asteroseismic modeling of the target. Our results are based on both extensive ground-based multicolour photometry and high-resolution spectroscopy. We determine T eff = 24 500 ± 1000 K and log g = 3.45 ± 0.15 dex from spectroscopy. The derived chemical abundances are consistent with those for B stars in the solar neighbourhood, except for a mild nitrogen excess. A metallicity Z = 0.0099 ± 0.0016 is obtained. Three modes are detected in photometry. The degree is unambiguously identified for two of them: = 0 and = 3 for the frequencies 5.48694 d −1 and 0.30818 d −1 , respectively. The radial mode is non-linear and highly dominant with an amplitude in the U-filter about 15 times larger than the strongest of the other modes. For the third frequency of 7.36673 d −1 found in photometry, two possibilities remain: = 0 or 3. In the radial velocities, the dominant radial mode presents a so-called stillstand but no clear evidence of the existence of shocks is observed. Four low-amplitude modes are found in spectroscopy and one of them, with frequency 8.4079 d −1 , is identified as ( , m) = (3, 2). Based on this mode identification, we finally deduce an equatorial rotational velocity of 38 ± 15 km s −1 .

Evidence for nonlinear resonant mode coupling in the $\mathsf{\beta}$ Cephei star HD 180642 (V1449 Aquilae) from CoRoT photometry

“…An extensive ground-based observing campaign has been organised with that goal and is discussed in Briquet et al (2009). As indicated in Fig.…”

“…Additional time series of multicolour photometry and high-resolution spectroscopy of the star are the subject of a twin paper (Briquet et al 2009). …”

Ground‐based follow‐up in relation to Kepler asteroseismic investigation

“…For these targets, the identification of the mode parameters associated with the frequencies observed by Kepler requires groundbased multi-colour and spectral time-series analysis (e.g. Briquet et al 2009;Uytterhoeven et al 2008;Poretti et al 2009). Information on the degree ℓ of the modes can be derived from the amplitudes and phases in the different photometric passbands (e.g.…”

Is macroturbulent broadening in OB Supergiants related to pulsations?

“…Regarding point (3) above, this project will require an important amount of observational time (as it is usual in asteroseismic studies, e.g. Aerts et al 2004;Handler et al 2006;Uytterhoeven et al 2008;Briquet et al 2009;Poretti et al 2009). Although we have already obtained time-series spectra during several observing campaigns (using FIES, SES, and HERMES spectrographs, attached to the NOT, STELLA and MERCATOR telescopes, respectively), the amount and time span of the collected spectra are still not enough for a proper seismic study.…”