Spots, plages, and flares onλAndromedae and II Pegasi

Abstract

Aims. We present the results of a contemporaneous photometric and spectroscopic monitoring of two RS CVn binaries, namely λ And and II Peg. The aim of this work is to investigate the behavior of surface inhomogeneities in the atmospheres of the active components of these systems that have nearly the same temperatures but different gravities. Methods. The light curves and the modulation of the surface temperature, as recovered from line-depth ratios (LDRs), were used to map the photospheric spots, while the Hα emission was used as an indicator of chromospheric inhomogeneities. The spot temperatures and sizes were derived from a spot model applied to the contemporaneous light and temperature curves. Results. We find larger and cooler spots on II Peg (T sp 3600 K) than on λ And (T sp 3900 K); this could be the result of both the difference in gravity and the higher activity level of the former. Moreover, we find a clear anti-correlation between the Hα emission and the photospheric diagnostics (temperature and light curves). We have detected a modulation in the intensity of the He i D 3 line with the star rotation, suggesting surface features also in the upper chromosphere of these stars. A rough reconstruction of the 3D structure of their atmospheres was also performed by applying a spot/plage model to the light and temperature curves and to the Hα flux modulation. In addition, a strong flare affecting the Hα, the He i D 3 , and the cores of Na i D 1,2 lines has been observed on II Peg.Conclusions. The spot/plage configuration has been reconstructed in the visible component of λ And and II Peg, which have nearly the same temperature but very different gravities and rotation periods. A close spatial association of photospheric and chromospheric active regions, at the time of our observations, was found in both stars. Larger and cooler spots were found on II Peg, the system with the active component of higher gravity and a higher activity level. The area ratio of plages to spots seems to decrease when the spots get bigger. Moreover, with both this and literature data, a correlation between the temperature difference ∆T = T ph − T sp and the surface gravity is also suggested.

REM near-IR and optical photometric monitoring of pre-main sequence stars in Orion

“…As seen in Table 5, for the three stars with fairly long rotation periods (#10, #14, and #17) ΔT is in the range 1000-1300 K, i.e. smaller than sunspot umbrae but slightly larger than values of 400-900 K found for the giant and sub-giant components of RS CVn binaries adopting a similar approach (Frasca et al 2005(Frasca et al , 2008. Conversely, the spotted area (8-10% of the star surface) is smaller, on average, than that found by Frasca et al (2005Frasca et al ( , 2008 for RS CVn stars (A rel = 11-18%).…”

The young active star SAO 51891 (V383 Lacertae)

“…This fair coherence confirms the hypothesis of cool spots as the primary cause of the observed variations. The temperature varies between 5162 K and 5249 K, with a full amplitude of about 90 K, which is intermediate between the values of ≈40 K found in moderately active stars (Biazzo et al 2007b) and ≈130 K found in highly active stars (Catalano et al 2002;Frasca et al 2005Frasca et al , 2008a.…”

“…Our main aim is the determination of the spot temperature and filling factor and to infer the distribution of chromospheric ARs of SAO 51891. The general scope is the comparison of the results obtained for very young stars, such as SAO 51891, with those found for MS and RS CVn stars (see, e.g., Frasca et al 2005Frasca et al , 2008aBiazzo et al 2007b). …”

“…The structure of a magnetic flux tube breaking into the stellar atmosphere is traced by the configuration of active regions (ARs) at different levels, like photospheric spots and chromospheric plages. Therefore, an accurate determination of spot temperatures and sizes such as that derived from the monitoring of line-depth ratios (LDRs) along a complete rotation period (Catalano et al 2002;Frasca et al 2005) and the associated variability of hydrogen, helium, and calcium lines (Frasca et al 2000(Frasca et al , 2008aBiazzo et al 2006Biazzo et al , 2007b can provide crucial information on the magnetic field topology in young stars to be compared with the results for older main sequence (MS) and giant stars.…”

TheGaia-ESO Survey: Dynamical analysis of the L1688 region in Ophiuchus

“…One of the main aims of the young cluster observations is to study their kinematics and dynamical evolution through the measurement of accurate radial velocities . The high-quality of GIRAFFE and UVES spectra also allows us to study their metallicities and elemental abundances, rotational velocities, chromospheric activity, and accretion rates (e.g., Spina et al 2014;Frasca et al 2015). So far, the dynamical properties of several young clusters have already been observed and analyzed.…”