EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 418/1 Article
Free access article

Issue A&A
Volume 418, Number 1, April IV 2004
Page(s) L13 - L16
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20040105



A&A 418, L13-L16 (2004)
DOI: 10.1051/0004-6361:20040105

Letter

High-amplitude, long-term X-ray variability in the solar-type star HD 81809: The beginning of an X-ray activity cycle?

F. Favata1, G. Micela2, S. L. Baliunas3, J. H. M. M. Schmitt4, M. Güdel5, F. R. Harnden Jr.6, S. Sciortino2 and R. A. Stern7

1  Astrophysics Division - Research and Science Support Dept. of ESA, Postbus 299, 2200 AG Noordwijk, The Netherlands
2  INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
3  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 15, Cambridge, MA 02138, USA
4  Universität Hamburg, Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany
5  Paul Scherrer Institut, Würenlingen and Villigen, 5235 Switzerland
6  Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambdridge 02138 MA, USA
7  Lockheed Martin Advanced Technology Ctr., USA

(Received 4 February 2004 / Accepted 4 March 2004)

Abstract
We present the initial results from our XMM-Newton program aimed at searching for X-ray activity cycles in solar-type stars. HD 81809 is a G2-type star (somewhat more evolved than the Sun, and with a less massive companion) with a pronounced 8.2 yr chromospheric cycle, as evident from from the Mt. Wilson program data. We present here the results from the initial 2.5 years of XMM-Newton observations, showing that large amplitude (a factor of  $\simeq$ 10) modulation is present in the X-ray luminosity, with a clearly defined maximum in mid 2002 and a steady decrease since then. The maximum of the chromospheric cycle took place in 2001; if the observed X-ray variability is the initial part of an X-ray cycle, this could imply a phase shift between chromospheric and coronal activity, although the current descent into chromospheric cycle minimum is well reflected into the star's X-ray luminosity. The observations presented here provide clear evidence for the presence of large amplitude X-ray variability coherent with the activity cycle in the chromosphere in a star other than the Sun.


Key words: stars: X-rays

Offprint request: F. Favata, Fabio.Favata@rssd.esa.int

SIMBAD Objects



© ESO 2004


What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.