The first Doppler images of the eclipsing binary SZ Piscium

TL;DR

This paper presents the first Doppler images of the active eclipsing binary SZ Psc, revealing complex starspot activity on the K subgiant component and detecting a third stellar companion.

Contribution

First Doppler imaging of SZ Psc, including detection of a third component and detailed starspot surface maps of the K subgiant.

Findings

Detected a third component with ~0.9 solar masses and ~1283-day period.

Revealed complex starspot distributions, including high-latitude and low-latitude spots.

No large, stable polar cap observed on the K subgiant.

Abstract

We present the first Doppler images of the active eclipsing binary system SZ Psc, based on the high-resolution spectral data sets obtained in 2004 November and 2006 September--December. The least-squares deconvolution technique was applied to derive high signal-to-noise profiles from the observed spectra of SZ Psc. Absorption features contributed by a third component of the system were detected in the LSD profiles at all observed phases. We estimated the mass and period of the third component to be about $0.9 M_{\odot}$ and $1283 \pm 10$ d, respectively. After removing the contribution of the third body from the LSD profiles, we derived the surface maps of SZ Psc. The resulting Doppler images indicate significant starspot activities on the surface of the K subgiant component. The distributions of starspots are more complex than that revealed by previous photometric studies. The cooler K component exhibited pronounced high-latitude spots as well as numerous low- and intermediate-latitude spot groups during the entire observing seasons, but did not show any large, stable polar cap, different from many other active RS CVn-type binaries.