Doppler imaging of stellar surface structure

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.

Activity on a Li-rich giant: DI Psc revisited

“…This result should be regarded as a preliminary one, since unexpected rearrangements in spot configuration (e.g., emerging new flux) can disturb seriously the pure differential rotation pattern, thus yielding false observation. We note, however, that antisolar-type differential rotation was reported also for DP CVn, which is another Li-rich K-giant, the twin of DI Psc (Kővári et al 2013). High Li-abundance might be related to strong meridional circulation (i.e., extra mixing), which, on the other hand, can eventuate antisolar-type differential rotation (cf.…”

“…Moreover, the role of rotation and magnetic activity in these processes is also unclear. Surface Li-abundance and the position of DI Psc on the HRD was determined in our recent Doppler imaging study (Kővári et al 2013). In this paper we aim to investigate the time evolution of the surface by Doppler imaging, as well as the Li-distribution on the surface.…”

Time-series Doppler images and surface differential rotation of the effectively single, rapidly rotating K-giant KU Pegasi

“…Such observations (e.g. Korhonen et al 2007;Weber 2007;Kővári et al 2013Kővári et al , 2015 as well as theoretical considerations (Kitchatinov & Rüdiger 2004;Küker & Rüdiger 2012) imply that stellar surface rotation could probably be more complex for evolved stars than for main sequence stars like the Sun. Differential rotation (DR) for main sequence and pre-main sequence stars is found to decrease with effective temperature (Barnes et al 2005;Reinhold et al 2013) just as was predicted from mean-field models (Küker 2015).…”

Lithium enrichment on the single active K1-giant DI Piscium

“…In our recent paper (Kővári et al 2013, hereafter Paper I), we investigated the possible connections between rapid rotation, enchanced stellar activity, and elevated Li abundance on DI Psc (HD 217352) and DP CVn (HD 109703), two fast-rotating A&A 571, A74 (2014) Li-rich K1 giants identified by the Vienna-KPNO Doppler imaging candidate survey . We concluded, in accordance with Fekel & Balachandran (1993), that these stars with unusually high Li-abundance (A DI Psc (Li) = 2.20, A DP CVn (Li) = 2.28) had just left their first dredge-up.…”