Issue |
A&A
Volume 418, Number 1, April IV 2004
|
|
---|---|---|
Page(s) | L13 - L16 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20040105 | |
Published online | 02 April 2004 |
Letter to the Editor
High-amplitude, long-term X-ray variability in the solar-type star HD 81809: The beginning of an X-ray activity cycle?
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
Corresponding author: F. Favata, Fabio.Favata@rssd.esa.int
Received:
4
February
2004
Accepted:
4
March
2004
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 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
© ESO, 2004
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