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Issue A&A
Volume 411, Number 3, December I 2003
Page(s) 489 - 502
Section Stellar atmospheres
DOI http://dx.doi.org/10.1051/0004-6361:20031377



A&A 411, 489-502 (2003)
DOI: 10.1051/0004-6361:20031377

Rotational modulation of the photospheric and chromospheric activity in the young, single K2-dwarf PW And

J. López-Santiago1, D. Montes1, M. J. Fernández-Figueroa1 and L. W. Ramsey2

1  Departamento de Astrofísica, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
2  The Pennsylvania State University, Department of Astronomy and Astrophysics, 525 Davey Laboratory, University Park, PA 16802, USA

(Received 20 February 2003 / Accepted 11 August 2003)

Abstract
High resolution echelle spectra of PW And (HD 1405) have been taken during eight observing runs from 1999 to 2002. The detailed analysis of the spectra allow us to determine its spectral type (K2V), mean heliocentric radial velocity ( $V_{\rm hel} = -11.15$ km s $^{\rm -1}$) rotational velocity ( $v\sin{i} = 22.6$ km s $^{\rm -1}$), and equivalent width of the lithium line $\lambda 6707.8~{\rm\AA}$ ( EW(Li I) = 273 mÅ). The kinematic (Galactic Velocity ( U, V, W)) confirms its membership in the Local Association moving group, in agreement with the age (30 to 80 Myrs) inferred from the color magnitude diagram and the lithium equivalent width. Photospheric activity (presence of cool spots that disturb the profiles of the photospheric lines) has been detected as changes in the bisectors of the cross correlation function (CCF) resulting of cross-correlate the spectra of PW And with the spectrum of a non-active star of similar spectral type. These variations of the CCF bisectors are related to the variations in the measured radial velocities and are modulated with a period similar to the photometric period of the star. At the same time, chromospheric activity has been analyzed, using the spectral subtraction technique and simultaneous spectroscopic observations of the H $\alpha$, H $\beta$, Na I D 1 and D 2, He I D 3, Mg I b triplet, Ca II H&K, and Ca II infrared triplet lines. A flare was observed during the last observing run of 2001, showing an enhancement in the observed chromospheric lines. A less powerful flare was observed on 2002 August 23. The variations of the chromospheric activity indicators seem to be related to the photospheric activity. A correlation between radial velocity, changes in the CCF bisectors and equivalent width of different chromospheric lines is observed with a different behaviour between epochs 1999, 2001 and 2002.


Key words: stars: activity -- stars: chromospheres -- stars: starspots -- stars: late-type -- stars: flare -- stars: rotation

Offprint request: J. López-Santiago, jls@astrax.fis.ucm.es

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© ESO 2003


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