LO Peg: surface differential rotation, flares, and spot-topographic evolution

Abstract

Using the wealth of ∼24 yr multiband data, we present an in-depth study of the starspot cycles, surface differential rotations (SDR), optical flares, evolution of star-spot distributions, and coronal activities on the surface of young, single, main-sequence, ultrafast rotator (UFR) LO Peg. From the long-term V -band photometry, we derive rotational period of LO Peg to be 0.4231 ± 0.0001 d. Using the seasonal variations on the rotational period, the SDR pattern is investigated, and shows a solar-like pattern of SDR. A cyclic pattern with period of ∼2.7 yr appears to be present in rotational period variation. During the observations, 20 optical flares are detected with a flare frequency of ∼1 flare per two days and with flare energy of ∼10 31−34 erg. The surface coverage of cool spots is found to be in the range of ∼9-26 per cent. It appears that the high-and low-latitude spots are interchanging their positions. Quasi-simultaneous observations in X-ray, UV, and optical photometric bands show a signature of an excess of X-ray and UV activities in spotted regions.

Coronae of an active fast rotator FR Cnc

“…LO Peg, BO Mic, AB Dor etc. ; Karmakar et al 2016;García-Alvarez et al 2008) whereas its X-ray luminosity is less than the other fast rotating (period \1 d) active dwarf binaries (see Catalogue of Chromospherically Active Binaries; Eker et al 2008). If we compare our results with evolved active stars, we found that FR Cnc is less active with respect to them.…”

Magnetic activities on active solar-type stars

“…Doppler images of LO Peg provided evidence of high polar activities (Piluso et al 2008 and references therein). Several photometric, polarimetric, and X-ray studies also carried out by Dal & Tas ¸(2003), Pandey et al (2005), Csorvási (2006), Tas ¸(2011), Karmakar et al (2016), andSavanov et al (2016).…”

“…Using the Gaia Data Release 2 (DR2), Gaia Collaboration (2018) derived parallax of this star to be 3.41±0.02 mas which corresponds to a distance of 290.7 pc by Bailer-Jones et al (2018). LO Peg is an active, single, young, main-sequence, K5-8 type UFR with a rotational period of 0.4231±0.0001 day (Karmakar et al 2016). LO Peg has been extensively studied in last two decades.…”

“…Figure 1: Optical light curves of selected four objects. Normalized source flux of KIC 6791060 (top panel) was obtained from first Kepler mission, second panel shows the V band light curve of LO Peg.The details of observations of V band data are given inKarmakar et al (2016). The normalized flux for K2-33 (third panel) and EPIC 211901114 (fourth panel) were obtained from K2 mission.…”

Four years of starspot evolution on an active F-type ultra-fast rotator KIC 6791060

“…Dark spots move across the stellar disk due to the stellar rotation and thus modulate the total brightness with the rotational period of the star. In order to determine locations of spots on the stellar surface, we have performed inversion of the phased light curves into stellar images using the light curve inversion code (iPH; see Savanov & Strassmeier 2008;Karmakar et al 2016;Savanov et al 2016). The model assumes that, due to the low spatial resolution, the local intensity of the stellar surface always has a contribution from the photosphere (I P ) and from cool spots (I S ) weighted by the fraction of the surface covered by spots, i.e., the spot filling factor f by the following relation:…”