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Register a new userA Study of the Coronal Plasma in RS CVn binary systems
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XMM-Newton has been performing comprehensive studies of X-ray bright RS CVn binaries in its Calibration and Guaranteed Time programs. We present results from ongoing investigations in the context of a systematic study of coronal emission from RS CVns. We concentrate in this paper on coronal abundances and investigate the abundance pattern in RS CVn binaries as a function of activity and average temperature. A transition from an Inverse First Ionization Potential (FIP) effect towards an absence of a clear trend is found in intermediately active RS CVn systems. This scheme corresponds well into the long-term evolution from an IFIP to a FIP effect found in solar analogs. We further study variations in the elemental abundances during a large flare.
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XMM-Newton has been performing comprehensive studies of X-ray luminous RS CVn binary systems in its calibration and guaranteed time programs. We present results from ongoing investigations in the context of a systematic study of coronal emission from RS CVns. We concentrate here on coronal abundances and investigate the abundance pattern in RS CVn binaries as a function of activity and average temperature. We find a transition from an Inverse First Ionization Potential (FIP) effect towards an absence of a clear trend (no FIP) in intermediately active RS CVn systems. This scheme fits well into the long-term evolution from an IFIP to a FIP effect found in solar analogs. We further study variations in the elemental abundances during a large flare.
We present our new photometry of DV Psc obtained in 2010 and 2011, and new spectroscopic observation on Feb. 14, 2012. During our observations, three flare-like events might be detected firstly in one period on DV Psc. The flare rate of DV Psc is about 0.017 flares per hour. Using Wilson-Devinney program, we derived the preliminary starspot parameters. Moreover, the magnetic cycle is 9.26(+/-0.78) year analyzed by variabilities of Max.I - Max.II.
BVR photometric and quasi-simultaneous optical spectroscopic observations of the star HD 81032 have been carried out during the years 2000 - 2004. A photometric period of $18.802 pm 0.07$ d has been detected for this star. A large group of spots with a migration period of $7.43 pm 0.07$ years is inferred from the first three years of the data. H$alpha$ and Ca II H and K emissions from the star indicate high chromospheric activity. The available photometry in the BVRIJHK bands is consistent with spectral type of K0 IV previously found for this star. We have also examined the spectral energy distribution of HD 81032 for the presence of an infrared colour excess using the 2MASS JHK and IRAS photometry, but found no significant excess in any band abovethe normal values expected for a star with this spectral type. We have also analyzed the X-ray emission properties of this star using data obtained by the ROSAT X-ray observatory during its All-Sky Survey phase. An X-ray flare of about 12 hours duration was detected during the two days of X-ray coverage obtained for this star. Its X-ray spectrum, while only containing 345 counts, is inconsistent with a single-temperature component solar-abundance coronal plasma model, but implies either the presence of two or more plasma components, non-solar abundances, or a combination of both of these properties. All of the above properties of HD 81032 suggest that it is a newly identified, evolved RS CVn binary.
Using the high-precision photometry from the Kepler space telescope, thousands of stars with stellar and planetary companions have been observed. The characterization of stars with companions is not always straightforward and can be contaminated by systematic and stellar influences on the light curves. Here, through a detailed analysis of starspots and eclipses, we identify KOI-1003 as a new, active RS CVn star---the first identified with data from Kepler. The Kepler light curve of this close binary system exhibits the systems primary transit, secondary eclipse, and starspot evolution of two persistent active longitudes. The near equality of the systems orbital and rotation periods indicates the orbit and primary stars rotation are nearly synchronized ($P_mathrm{orb} = 8.360613pm0.000003$ days; $P_mathrm{rot} sim 8.23$ days). By assuming the secondary star is on the main sequence, we suggest the system consists of a $1.45^{+0.11}_{-0.19} M_odot$ subgiant primary and a $0.59^{+0.03}_{-0.04} M_odot$ main-sequence companion. Our work gives a distance of $4400 pm 600$ pc and an age of $t = 3.0^{-0.5}_{+2.0}$ Gyr, parameters which are discrepant with previous studies that included the star as a member of the open cluster NGC 6791.
We present an analysis of seven flares detected from five RS CVn-type binaries (UZ Lib, sigma Gem, lambda And, V711 Tau and EI Eri) observed with XMM-Newton observatory. The quiescent state X-ray luminosities in the energy band of 0.3-10.0 keV of these stars were found to be 10^{30.7-30.9} erg/s. The exponential decay time in all the sample of flares range from ~ 1 to 8 hrs. The luminosity at peak of the flares in the energy band of 0.3-10.0 keV were found to be in the range of 10^{30.8} - 10^{31.8} erg/s. The great sensitivity of the XMM-EPIC instruments allowed us to perform time resolved spectral analysis during the flares and also in the subsquent quiescent phases. The derived metal abundances of coronal plasma were found to vary during the flares observed from sigma Gem, V771 Tau and EI Eri. In these flares elemental abundances found to be enhanced by factors of ~ 1.3-1.5 to the quiescent states. In most of the flares, the peak temperature was found to be more than 100 MK whereas emission measure increased by factors of 1.5 - 5.5. Significant sustained heating was present in the majority of flares. The loop lengths (L) derived for flaring structure were found to be of the order of 10^{10 -11} cm and are smaller than the stellar radii (R*) i.e. L/R* lesssim 1. The flare from sigma Gem showed a high and variable absorption column density during the flare.
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