uvbyβphotometry of early type open cluster and field stars

Abstract

Context. The β Cephei stars and slowly pulsating B (SPB) stars are massive main sequence variables. The strength of their pulsational driving strongly depends on the opacity of iron-group elements. As many of those stars naturally occur in young open clusters, whose metallicities can be determined in several fundamental ways, it is logical to study the incidence of pulsation in several young open clusters. Aims. To provide the foundation for such an investigation, Strömgren-Crawford uvbyβ photometry of open cluster target stars was carried out to determine effective temperatures, luminosities, and therefore cluster memberships. Methods. In the course of three observing runs, uvbyβ photometry for 168 target stars was acquired and transformed into the standard system by measurements of 117 standard stars. The list of target stars also included some known cluster and field β Cephei stars, as well as β Cephei and SPB candidates that are targets of the asteroseismic part of the Kepler satellite mission. Results. The uvbyβ photometric results are presented. The data are shown to be on the standard system, and the properties of the target stars are discussed: 140 of these are indeed OB stars, a total of 101 targets lie within the β Cephei and/or SPB star instability strips, and each investigated cluster contains such potential pulsators. Conclusions. These measurements will be taken advantage of in a number of subsequent publications.

New slowly pulsating B stars in the field of the young open cluster NGC 2244 discovered by the MOST photometric satellite★

“…The considerably lower reddening of GSC 00154−00785 is understandable given its position in the outer parts of the region of NGC 2244. With V magnitudes of 10.93 and 11.30 respectively (Handler 2011), we obtain distances of 980 ± 400 and 800 ± 350 pc for GSC 00154−00785 and GSC 00154−01871, respectively.…”

“…For both stars Strömgren uvby β photometry is available (Handler 2011). Applying the calibrations by Napiwotzki, Schönberner & Wenske (1993) to the data provide the atmospheric parameters which are listed in Table 2.…”

“…Fig. 6 is a dereddened colour–magnitude diagram (CMD) containing stars from the samples of Heiser (1977), Perez et al (1989), Kaltcheva, Olsen & Clausen (1999), Hensberge, Pavlovski & Verschueren (2000) and Handler (2011). These have a membership probability >85 per cent [cross‐checked against Marschall, van Altena & Chiu (1982); Kharchenko et al (2005); Baumgardt, Dettbarn & Wielen (2000); Chen et al (2007)].…”

Newβ Cephei stars in the young open cluster NGC 637

“…The Strömgren uvbyβ photometry by Handler (2011) can be used to derive T eff and M V , thus log L of the individual stars, but also their reddenings and distance moduli. The routines by Napiwotzki et al (1993) were employed to this end.…”

“…One has been classified as a β Cephei star, and the other was said to be an ellipsoidal variable. New standard uvbyβ photometry (Handler 2011) puts all seven bright stars into the β Cephei instability strip (Fig. 1).…”