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Multisite campaign on the open cluster M67 – I. Observations and photometric reductions
Stello, D.,Arentoft, T.,Bedding, T. R.,Bouzid, M. Y.,Bruntt, H.,Csubry, Z.,Dall, T. H.,Dind, Z. E.,Frandsen, S.,Gilliland, R. L.,Jacob, A. P.,Jensen, H. R.,Kang, Y. B.,Kim, S.-L.,Kiss, L. L.,Kjeldsen, Blackwell Publishing Ltd 2006 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.373 No.3
<P>ABSTRACT</P><P>We report on an ambitious multisite campaign aimed at detecting stellar variability, particularly solar-like oscillations, in the red giant stars in the open cluster M67 (NGC 2682). During the six-week observing run, which comprised 164 telescope nights, we used nine 0.6-m to 2.1-m class telescopes located around the world to obtain uninterrupted time series photometry. We outline here the data acquisition and reduction, with emphasis on the optimization of the signal-to-noise ratio of the low-amplitude (50–500 μmag) solar-like oscillations. This includes a new and efficient method for obtaining the linearity profile of the CCD response at ultrahigh precision (∼10 parts per million). The noise in the final time series is 0.50 mmag per minute integration for the best site, while the noise in the Fourier spectrum of all sites combined is 20 μmag. In addition to the red giant stars, this data set proves to be very valuable for studying high-amplitude variable stars such as eclipsing binaries, W UMa systems and δ Scuti stars.</P>
Multisite campaign on the open cluster M67 – III. δ Scuti pulsations in the blue stragglers
Bruntt, H.,Stello, D.,Suá,rez, J. C.,Arentoft, T.,Bedding, T. R.,Bouzid, M. Y.,Csubry, Z.,Dall, T. H.,Dind, Z. E.,Frandsen, S.,Gilliland, R. L.,Jacob, A. P.,Jensen, H. R.,Kang, Y. B.,Kim, S.-L. Blackwell Publishing Ltd 2007 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.378 No.4
<P>ABSTRACT</P><P>We have made an asteroseismic analysis of the variable blue stragglers in the open cluster M67. The data set consists of photometric time-series from eight sites using nine 0.6–2.1 m telescopes with a time-baseline of 43 d. In two stars, EW Cnc and EX Cnc, we detect the highest number of frequencies (41 and 26) detected in δ Scuti stars belonging to a stellar cluster, and EW Cnc has the second highest number of frequencies detected in any δ Scuti star. We have computed a grid of pulsation models that take the effects of rotation into account. The distribution of observed and theoretical frequencies shows that in a wide frequency range a significant fraction of the radial and non-radial low-degree modes are excited to detectable amplitudes. Despite the large number of observed frequencies we cannot constrain the fundamental parameters of the stars. To make progress we need to identify the degrees of some of the modes from either multicolour photometry or spectroscopy.</P>