Spurious 'active longitudes' in parametric models of heavily spotted eclipsing binaries

Abstract

In this paper, the size distributions of starspots extrapolated from the case of the Sun are modelled on the eclipsing binary SV Cam to synthesize images of stellar photospheres with high spot filling factors. These spot distributions pepper the primary's surface with spots, many of which are below the resolution capabilities of eclipse‐mapping and Doppler‐imaging techniques. The light curves resulting from these modelled distributions are used to determine the limitations of image reconstruction from photometric data. Surface brightness distributions reconstructed from these light curves show distinctive spots on the primary star at its quadrature points. It is concluded that two‐spot modelling or chi‐squared minimization techniques are more susceptible to spurious structures being generated by systematic errors, arising from incorrect assumptions about photospheric surface brightness, than simple Fourier analysis of the light curves.

Starspots, cycles, and magnetic fields

“…Timing methods (measuring drifts in P rot from photometry or Ca II HK) give lower limits to DR. There is also the general worry that P rot derived from photometry/HK can be difficult to interpret properly when the star is highly spotted Eaton et al (1996);Jeffers (2005). Doppler imaging methods can give better DR values, but are subject to extrapolation uncertainties when features are only visible in a limited range of latitudes, and systematics in latitude placement.…”

A compact flare eclipsed in the corona of SV Camelopardalis

“…The Hα and Ca IR triplet profiles are filled in due to chromospheric activity in the secondary star (Montes et al 1995;Pojmanski 1998;Kjurkchieva et al 2002). Recently, Jeffers (2005) found large polar spots in the photosphere of the primary star using Doppler imaging techniques, as well as the presence of smaller spots on the rest of the stellar surface (as is typical of active stars). The outline of this paper is as follows: Sect.…”

Photometric study of the short-period RS Canum Venaticorum binary RT Andromedae

“…Thus, for RT And, there is clear evidence of active longitudes near the quadratures. According to Jeffers (2005), heavily spotted stellar surface can possibly cause spurious active-longitude detections at the quadrature points of the eclipsing binaries. The presence of active longitudes near the quadrature points of RT And could indicate that the surface is peppered with many spots whose sizes are below the resolving capabilities of the present diagnostic techniques for studying starspots.…”