A photometric study of chemically peculiar stars with the STEREO satellites - I. Magnetic chemically peculiar stars★

Abstract

About 10 per cent of upper main‐sequence stars are characterized by the presence of chemical peculiarities, often found together with a structured magnetic field. The atmospheres of most of those chemically peculiar stars present surface spots, leading to photometric variability caused by rotational modulation. The study of the light curves of those stars therefore permits a precise measurement of their rotational period, which is important to study stellar evolution and to plan further detailed observations. We analysed the light curves of 1028 chemically peculiar stars obtained with the STEREO spacecraft. We present here the results obtained for the 337 magnetic chemically peculiar stars in our sample. Thanks to the cadence and stability of the photometry, STEREO data are perfectly suitable to study variability signals with a periodicity typical of magnetic chemically peculiar stars. Using a matched filter algorithm and then two different period searching algorithms, we compiled a list of 82 magnetic chemically peculiar stars for which we measured a reliable rotational period; for 48 of them, this is the first measurement of their rotational period. The remaining 255 stars are likely to be constant, although we cannot exclude the presence of long‐period variability. In some cases, the presence of blending or systematic effects prevented us from detecting any reliable variability and in those cases we classified the star as constant. For each star we classified as variable, we determined temperature, luminosity, mass and fractional age, but the limited statistics, biased towards the shorter periods, prevented us from finding any evolutionary trend of the rotational period. For a few stars, the comparison between their projected rotational velocity and equatorial velocity let us believe that their real rotational period might be longer than that found here and previously obtained. For the 82 stars identified as variable, we give all necessary information needed to plan further phase‐dependent observations.

A search for photometric variability in magnetic chemically peculiar stars using ASAS-3 data

“…RM09 list only five bona fide candidates for eclipsing Ap stars from which one, AO Velorum, has been confirmed (González et al 2006). In their photometric study of Ap stars with the STEREO satellites, Wraight et al (2012) did not identify any eclipsing binaries or ellipsoidal variables among their sample of 337 stars. However, some of them show distinct double-waved light curves.…”

“…Considerable effort has been devoted to the study of the photometric variability of the magnetic Ap stars by photometric investigations or by mining available sky survey data (Manfroid & Mathys 1986;Paunzen & Maitzen 1998;Paunzen et al 2011;Wraight et al 2012). The present paper investigates the photometric variability of Ap stars using the publicly available observations from the third phase of the All Sky Automated Survey (ASAS-3, Pojmański 2002) and aims at finding previously unidentified ACV variables.…”

Differential Rotation in Sun-like Stars from Surface Variability and Asteroseismology

“…The measured variability is not necessarily of magnetic origin, but could arise from, for example, chemical surface inhomogeneities in chemically peculiar hot stars. Chemical spots can produce photometric variability that traces the stellar rotation (Wraight et al 2012, Paunzen et al 2013). The short periods measured for the early spectral types (see Fig.…”

“…Aerts et al 2010, Chapter 2. ), or local changes of surface opacities in hot stars (Wraight et al 2012). These types of variability are however only prevalent in hot stars that do not have surface convection zones.…”

The Hvar survey for roAp stars

“…Unfortunately, for only six objects Strömgren, Geneva, or UBV photometry is available therein. We therefore proceeded like Wraight et al (2011) the ASCC catalogue (Kharchenko 2001), providing TYCHO-2 transformed B, V photometry as well as 2MASS data (Cutri et al 2003). Furthermore, the TASS survey (Droege et al 2006) was queried for V, I photometry.…”