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Optical and X-Ray Studies of Chromospherically Active Stars: FR Cancri, HD 95559, and LO Pegasi
We present a multiwavelength study of three chromospherically activestars, namely, FR Cnc (BD +16°1753), HD 95559, and LO Peg (BD+22°4409), including newly obtained optical photometry andlow-resolution optical spectroscopy for FR Cnc, as well as archival IRand X-ray observations. The BVR photometry carried out from 2001 to 2004has found significant photometric variability to be present in all threestars. For FR Cnc, a photometric period of 0.8267+/-0.0004 days has beenestablished. The strong variation in the phase and amplitude of the FRCnc light curves when folded on this period implies the presence ofevolving and migrating spots or spot groups on its surface. Twoindependent spots with migration periods of 0.97 and 0.93 yr,respectively, are inferred. The photometry of HD 95559 suggests theformation of a spot (group) during the interval of our observations. Weinfer the existence of two independent spots or groups in thephotosphere of LO Peg, one of which has a migration period of 1.12 yr.The optical spectroscopy of FR Cnc carried out during 2002-2003 revealsthe presence of strong and variable Ca II H and K, Hβ, and Hαemission features indicative of a high level of chromospheric activity.The value of 5.3 for the ratio of the excess emission in Hα toHβ, EHα/EHβ, suggests that thechromospheric emission may arise from an extended off-limb region. Wehave searched for the presence of color excesses in the near-IR JHKbands of these stars using Two Micron All Sky Survey data, but none ofthem appear to have any significant color excess. We have also analyzedarchival X-ray observations of HD 95559 and LO Peg carried out with theROSAT observatory. The best-fit models to their X-ray spectra imply thepresence of two coronal plasma components of differing temperatures andwith subsolar metal abundances. The inferred emission measures andtemperatures of these systems are similar to those found for otheractive dwarf stars. The kinematics of FR Cnc suggest that it is a veryyoung (35-55 Myr) main-sequence star and a possible member of the IC2391 supercluster. LO Peg also has young disk-type kinematics and hasbeen previously suggested to be a member of the 100 Myr old LocalAssociation (Pleiades moving group). The kinematics of HD 95559 indicateit is a possible member of the 600 Myr old Hyades supercluster.
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