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

Abstract

Context. The (magnetic) chemically peculiar (CP) stars of the upper main sequence are well-suited laboratories for investigating the influence of magnetic fields on the stellar surface because they produce abundance inhomogeneities (spots), which results in photometric variability that is explained in terms of the oblique rotator model. CP stars exhibiting this phenomenon are normally classified as α 2 Canum Venaticorum (ACV) variables. It is important to increase the sample of known rotational periods among CP stars by discovering new ACV variables. An increased sample size will contribute to the understanding of the CP stars' evolution in time. Aims. We aim at discovering new ACV variables in the public data of the third phase of the All Sky Automated Survey (ASAS-3). Furthermore, by analysis of the available photometric data, we intend to derive rotational periods of the stars. Methods. The ASAS-3 data were cross-correlated with the Catalogue of Ap, HgMn, and Am stars in order to analyse the light curves of bona fide CP and related stars. The light curves were downloaded and cleaned of outliers and data points with a flag indicating bad quality. Promising candidates showing a larger scatter than observed for constant stars in the corresponding magnitude range were searched for periodic signals using a standard Fourier technique. Objects exhibiting periodic signals well above the noise level were considered and visually inspected, whereas borderline cases were rejected. Results. In total, we found 323 variables, from which 246 are reported here for the first time, and 77 were probably wrongly classified before. The observed variability pattern of most stars is in accordance with an ACV classification. For some cases, it is difficult to distinguish between the light curves of double-waved ACVs and the variability induced by orbital motion (ellipsoidal variables/eclipsing variables), especially for objects exhibiting very small amplitudes and/or significant scatter in their light curves. Thus, some eclipsing or rotating ellipsoidal variables might be present. However, we are confident that the given periods are the correct ones. There seems to be a possible weak correlation between the rotational period and colour, in the sense that cooler magnetic CP stars rotate more slowly. However, this correlation seems to disappear when correcting for the interstellar reddening. Conclusions. The next steps have to include a compilation of all available rotational periods from the literature and a detailed investigation of the astrophysical parameters of these stars. This includes a determination of the individual masses, luminosities, ages, and inclination angles. However, this information cannot be straightforwardly determined from photometric data alone.

Doppler imaging of chemical spots on magnetic Ap/Bp stars

“…It should also be noted that this fourspot configuration is more structured than the typical chemical abundance distributions found for magnetic Ap/Bp stars: for the majority of stars single or double-spot distributions are prevalent resulting in a single or double-wave photometric variability (e.g. Bernhard et al 2015).…”

Magnetic OB[A] Stars with TESS: probing their Evolutionary and Rotational properties (MOBSTER) – I. First-light observations of known magnetic B and A stars

“…Frinchaboy & Majewski 2008). Bernhard et al (2015) measured a photometric period of 3.7367±0.0003 d and attributed it to component A, although both visual components were within the aperture of ASAS-3. We report this period in Table 1, since we find a similar period in the TESS observations (3.759±0.002 d).…”

Tidally trapped pulsations in a close binary star system discovered by TESS

“…Four decades later, ref. 16 reported photometric variability with a period of 0.79037(1) d and a peak-to-peak amplitude of 0.08 mag found in ASAS-3 data (ref. 17 ).…”

“…1 shows a section of the initial light curve (the full light curve would be too compressed at this scale to see the details) where the variations already reported by ref. 16 are obvious. However, the light curve shows minima of alternating depth whereas the maxima do not alternate.…”

“…23 ) and less reminiscent of a rotational variable as implied by ref. 16 . The differing minima arise, in part, from differential gravity darkening near the L1 and L2 points of the tidally distorted star.…”