Multisite campaign on the open cluster M67 – I. Observations and photometric reductions

Abstract

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.

A search for solar-like oscillations in K giants in the globular cluster M 4

“…CCD non-linearity was considered, and in the case of the La Silla data it was corrected using the technique described by Stello et al (2006b). The other cameras did not provide the same option for a correction and were assumed to be linear.…”

“…6.2). Therefore, following the approach of Stello et al (2006b), we subtracted lowfrequency peaks down to S /N > 4. We specify below whether we used the raw or the cleaned spectra (see Sect.…”

“…However, based on their multi-site campaign using 4-m class telescopes they made no clear detection. Recently, another campaign was carried out on the same cluster (Stello et al 2006b, this time concentrating on stars on the lower part of the giant branch, where larger oscillation amplitudes are expected.…”

The Gaia spectrophotometric standard stars survey: II. Instrumental effects of six ground‐based observing campaigns

“…The second method we tested is described by Stello et al (2006) and is a variation on the literature methods described above. It requires the acquisition of at least two spectroscopic flat fields, one reaching the saturation level and the other covering a fainter intensity range.…”

“…2.1, but taking into account that lamp drifts in spectra can show also colour variations. Afterwards, we applied the method as described in the original paper by Stello et al (2006), by computing the intensity ratio of exposure pairs, normalized by their respective t exp , (2006) method for NTT, using data obtained on the 26 and 2008 November 27, with 1×1 and 2×2 binning, respectively, with the ESO grism #3. The dashed line is for the 2×2 binning while the solid line is for the 1×1 binning.…”