Doppler imaging of stellar surface structure

XXIV. The lithium-rich single K-giants DP Canum Venaticorum and DI Piscium^{⋆,⋆⋆,⋆⋆⋆}

¹ Konkoly Observatory of the Hungarian Academy of Sciences, Konkoly Thege út 15–17, 1121, Budapest, Hungary
e-mail: kovari@konkoly.hu
² Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 København Ø, Denmark
³ Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5–7, 1350 København Ø, Denmark
⁴ Leibniz Institute for Astrophysics (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
⁵ Institute of Astronomy of the Russian Academy of Sciences, Pyatnitskaya 48, 119017 Moscow, Russia

Received: 14 August 2012
Accepted: 23 December 2012

Abstract

Aims. We present the first Doppler imaging study of the two rapidly rotating, single K-giants DP CVn and DI Psc in order to study the surface spot configuration and to pinpoint their stellar evolutionary status.

Methods. Optical spectroscopy and photometry were used to determine the fundamental astrophysical properties. Doppler imaging was applied to recover the surface temperature distribution for both stars, while photometric light-curve inversions were carried out for studying the long-term changes of the surface activity of DP CVn. Surface differential rotation of DP CVn was estimated from cross-correlating the available subsequent Doppler reconstructions separated by roughly one rotation period.

Results. Both stars appear to have higher than normal lithium abundance, LTE log n of 2.28 (DP CVn) and 2.20 (DI Psc), and are supposed to be located at the end of the first Li dredge-up on the RGB. Photometric observations reveal rotational modulation with a period of 14.010 d (DP CVn) and 18.066 d (DI Psc). Doppler reconstructions from the available mapping lines well agree in the revealed spot patterns, recovering rather low latitude spots for both stars with temperature contrasts of ΔT ≈ 600−800 K below the unspotted photospheric background. Spots at higher latitudes are also found but either with less contrast (DP CVn) or with smaller extent (DI Psc). A preliminary antisolar-type differential rotation with α = −0.035 is found for DP CVn from cross-correlating the subsequent Doppler images. Long-term photometric analysis supports the existence of active longitudes, as well as the differential rotation.