Long-Term Cyclic Variability of YZ CMi in the Context of Solar and Stellar Physics

Abstract

Manifestations of activity on the YZ CMi (M4.5Ve) flare star which has a rotation period of 2.77 days and belongs to a group of activity-saturated stars, are considered from long-term photometric data together with photographic measurements from 1926 to 2009. Long-term changes in yearly mean brightness of the star are found on a time scale of 27.5 years with an amplitude of 0.2 − 0.3 m that indicate variations in development of surface inhomogeneities and a large degree of surface spottedness in the maximum activity. Spots are distributed unevenly over the surface, their concentration is higher at certain longitudes spaced by intervals equal to 0.6 phases of the rotation period. The recovery of active longitude (a possible "flip-flop" effect) occurs over a period of about 6 years. We note differences in activity of this star from typical for the Sun and solar-like stars, which are associated with its dynamic characteristics P cyc and P rot and its inner structure.

The CARMENES search for exoplanets around M dwarfs

“…We took into account the longterm photometric variability of YZ CMi in the blue optical by re-running the SED fitting at the brightness maximum and minimum. For that, we were very conservative and used the largest reported variability amplitude of 0.3 mag in the B band (Bondar & Katsova 2018), over a scale of decades, to recompute extreme values of bolometric luminosity. We approximately extrapolated such amplitudes to 0.2 mag in the red optical, 0.1 mag in the near infrared, and 0.05 mag in the mid infrared, as observed in multiband photometric monitoring of very active M dwarfs (e.g., Caballero et al 2006).…”

New Observational Constraints on the Winds of M Dwarf Stars

“…This impression is particuarly acute for the M dwarfs, with GJ 15AB and YZ CMi having winds over an order of magnitude stronger than all the other M stars. It is worth noting that EV Lac has a reported short activity cycle of P cyc ≈ 5 yr (Mavridis & Avgoloupis 1986), while the similarly active YZ CMi, with a much stronger wind, has a much longer activity cycle of P cyc = 27.5 yr (Bondar & Katsova 2018).…”

Исследования Космического Магнетизма В Крымской Астрофизической Обсерватории I. Магнитное Поле В Межзвездной Среде И Вторичные Эффекты Звездного Магнетизма

“…В 1992-2004 годы на 1.25-метровом телескопе АЗТ-11 в КрАО с помощью пятикального фотометра-поляриметра в UBVRI -полосах выполнялась программа фотометрических наблюдений, результаты которой были использованы для оценки цикличности активности ряда звезд: V833 Tau, DT Vir, V1396 Cyg, PZ Mon, YZ CMi и др. (Алексеев, Бондарь, 1997, 1998Алексеев, 2001;Alekseev, Bondar', 2006;Бондарь, 2015;Bondar, Katsova, 2018). В настоящее время изучение фотосферной активности звезд выполняется на основании анализа комплексных кривых блеска, построенных по измерениям в фотографических архивах, данным автоматизированных телескопов и широкоугольных камер (Алексеев и Кожевникова, 2017;Bondar, 2019).…”

“…На рис. 9 приведены наибо-лее полные кривые блеска и основные циклы активности у двух активных карликов -V833 Tau (Бондарь, 2015;Bondar' et al, 2019) и YZ CMi (Bondar, Katsova, 2018).…”