CCD photometric search for peculiar stars in open clusters

Abstract

Context. We continue our survey of magnetic chemically peculiar (CP2) stars in galactic open clusters to shed more light on their origin and evolution. Aims. To study the group of CP2 stars, it is essential to find these objects in different galactic environments and at a wide range of evolutionary stages. The knowledge of open cluster ages and metallicities can help for finding a correlation between these parameters and the (non-)presence of peculiarities, which has to be taken into account in stellar evolution models. Methods. The intermediate band ∆a photometric system samples the depth of the 5200 Å flux depression by comparing the flux at the centre with the adjacent regions with bandwidths of 110 Å to 230 Å. It is capable of detecting magnetic CP2 and CP4 stars with high efficiency, but also the groups of (metal-weak) λ Bootis and classical Be/shell stars can be successfully investigated. In addition, it allows the age, reddening, and distance modulus to be determined with appropriate accuracy by fitting isochrones. Results. From the 1677 observed members of the eight open clusters, one Ae and twenty-five CP2 stars were identified. Furthermore nineteen deviating stars are designated as questionable for several reasons. The estimated age, reddening, and distance for the programme clusters were compared with published values of the literature and discussed in this context. Conclusions. The current paper shows that CP2 stars are continuously present in very young (7 Myr) to intermediate age (500 Myr) open clusters at distances greater than 2 kpc from the Sun.

Towards a photometric metallicity scale for open clusters

“…Netopil et al 2007), which is dedicated to the detection of chemically peculiar (CP) stars. So far, about 80 open clusters have been covered.…”

“…APASS photometry, to recalibrate the Δa photometry by Netopil et al (2007), in order to obtain at least V and (B − V) for the fainter stars. The complete available data set of the APASS survey cannot be safely used for the reason described previously.…”

A search for peculiar stars in the open cluster Hogg 16

“…The basic CCD reductions (bias subtraction and flatfield correction) and point-spread-function fitting were carried out with standard IRAF V2.16 routines. The method of calculating the normality line (the reference a index of apparently normal type stars), deriving the errors, and the calibration of our (g 1 − y), and y measurements is identical to that of previous works (see e.g., Netopil et al 2005Netopil et al , 2007Paunzen et al 2006b) and we refer to them for more details.…”

“…Paunzen et al (2005c) have shown that up to 95 % of mCP stars can be detected by ∆a. Most objects display positive ∆a values up to 60 mmag, though extreme values of the order of 100 mmag are also found (Netopil et al 2007). The class of λ Bootis stars (see e.g.…”

“…Although variability or binarity might interfere the results, the photometric system can be considered as an efficient pre-selection tool in particular for mCP stars. The system was not only applied to Galactic field stars, open clusters (Netopil et al 2007) and globular clusters , but also to clusters in the Large Magellanic Cloud (Paunzen et al 2006a), where photometric mCP star detections are also confirmed by spectroscopy (Paunzen et al 2011).…”