FR Cnc revisited: photometry, polarimetry and spectroscopy★

Abstract

This paper is part of a multiwavelength study aimed at using complementary photometric, polarimetric and spectroscopic data to achieve an understanding of the activity process in late‐type stars. Here, we present the study of FR Cnc, a young, active and spotted star. We performed analysis of All Sky Automated Survey 3 (ASAS‐3) data for the years 2002–08 and amended the value of the rotational period to be 0.826518 d. The amplitude of photometric variations decreased abruptly in the year 2005, while the mean brightness remained the same, which was interpreted as a quick redistribution of spots. BVRC and IC broad‐band photometric calibration was performed for 166 stars in FR Cnc vicinity. The photometry at Terskol Observatory shows two brightening episodes, one of which occurred at the same phase as the flare of 2006 November 23. Polarimetric BVR observations indicate the probable presence of a supplementary source of polarization. We monitored FR Cnc spectroscopically during the years 2004–08. We concluded that the radial velocity changes cannot be explained by the binary nature of FR Cnc. We determined the spectral type of FR Cnc as K7V. Calculated galactic space‐velocity components (U, V, W) indicate that FR Cnc belongs to the young disc population and might also belong to the IC 2391 moving group. Based on Li iλ6707.8 measurement, we estimated the age of FR Cnc to be between 10 and 120 Myr. Doppler tomography was applied to create a starspot image of FR Cnc. We optimized the goodness of fit to the deconvolved profiles for axial inclination, equivalent width and v sin i, finding v sin i=46.2 km s−1 and i= 55°. We also generated a synthetic V‐band light curve based on Doppler imaging that makes simultaneous use of spectroscopic and photometric data. This synthetic light curve displays the same morphology and amplitude as the observed one. The starspot distribution of FR Cnc is also of interest since it is one of the latest spectral types to have been imaged. No polar spot was detected on FR Cnc.

Broad-band linear polarization in late-type active dwarfs

“…This type of behaviour is similar to that which has also been observed in some other active stars (e.g. Huovelin et al 1985;Huovelin & Saar 1988;Yudin & Evans 2002;Alekseev 2003;Rostopchina et al 2007;Golovin et al 2012;Patel et al 2013). The observed polarizations in these active dwarfs are also compa-rable to that of another class of active stars, namely RS CVn binaries (see Liu & Tan 1987, Scaltriti et al 1993).…”

“…Evidence for a connection between linear polarization and magnetic activity indicators is lacking because on one hand the variation, as well as the mean degree of polarization of late-type dwarfs are very small, and on the other hand sizes of samples studied are small. Therefore, we have observed a sample of 50 active late type dwarfs and supplemented it with another sample of 18 active dwarfs, those are available in the literature (Huovelin et al 1985;Alekseev 2000Alekseev , 2003Golovin et al 2012;Patel et al 2013). The criteria of selection of stars in the sample were (i) the V -band magnitude range of 6.0 − 13.0 mag, and (ii) the (B − V ) colour range of 0.5 − 1.5 mag.…”

Coronae of an active fast rotator FR Cnc

“…The X-ray light curve was folded with a period of 0.826518 days and at JD = 2452635.72669 as given Golovin et al (2012). The phase bin of the folded light curve was 0.05.…”

“…A few flaring events were also caught in the past in the optical band. Golovin et al (2012Golovin et al ( , 2007 detected a strong flare in B, V, R, and I filters, where peak flare flux in B band was found to be $ 37 times more than the quiescent flux. Later in 2010, Kozhevnikova et al (2018) reported one flare with flare duration of 32.5 minutes.…”

Coronae of an active fast rotator FR Cnc

“…This indicates that the X-ray light curve is variable with confidence limit of 99%. The X-ray light curve was folded with a period of 0.826518 days and at JD = 2452635.72669 as given Golovin et al (2012). The phase bin of the folded light curve was 0.05.…”