High-amplitude, long-term X-ray variability in the solar-type star HD 81809: the beginning of an X-ray activity cycle?
نویسندگان
چکیده
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.
منابع مشابه
Forty Years of X-Ray Binaries
In 2012 it was forty years ago that the discovery of the first X-ray binary Centaurus X-3 became known. That same year it was discovered that apart from the High-Mass X-ray Binaries (HMXBs) there are also Low-Mass X-ray Binaries (LMXBs), and that Cygnus X-1 is most probably a black hole. By 1975 also the new class of Be/X-ray binaries was discovered. After this it took 28 years before ESAs INTE...
متن کاملA systematic analysis of X-ray variability of dM stars
We have systematically analyzed X-ray variability of dM stars. Our data base is the sample of all dM stars listed in the CNS3 (Gliese & Jahreiss 1991) catalog which have been observed with the ROSAT PSPC. Our data sample includes 86 pointed observations of 55 distinct stars or multiple systems. A large fraction of stars shows significant variations, regardless of their quiescent flux. Variabili...
متن کاملThe Effect of Long-Term X-Ray Exposure on Human Lymphocyte
The aim of the paper is to investigate effects of long term x-ray exposure on the human lymphocyte, reactive lymphocyte parameters and morphology of lymphocytes in x-ray technicians at Kirkuk hospitals. The study included 54 apparently healthy male x-ray technicians were matched with another 54 apparently healthy control to show any alteration in the lymphocytes, reactive lymphocytes and morpho...
متن کاملar X iv : a st ro - p h / 98 12 27 0 v 1 1 4 D ec 1 99 8 The Active Corona of HD 35850 ( F 8 V )
We present Extreme Ultraviolet Explorer spectroscopy and photometry of the nearby F8 V star HD 35850 (HR 1817). The EUVE short-wavelength 75–175 Å and medium-wavelength 160–365 Å spectra reveal 28 emission lines from Fe IX and Fe XV to Fe XXIV. The Fe XXI λλ102, 129 ratio yields an upper limit for the coronal electron density, log ne < 11.6 cm −3. The EUVE SW spectrum shows a small but clearly ...
متن کاملThe Be / X - ray transient 4 U 0115 + 63 / V 635 Cassiopeiae III . Quasi - cyclic variability ⋆
Context. 4U 0115+63 is one of the most active and best studied Be/X-ray transients. Previous studies of 4U 0115+63 have led to the suggestion that 4U 0115+63 undergoes relatively fast quasi-cyclic activity. However, due to the lack of good coverage of the observations, the variability time scales are uncertain. Aims. Our objective is to investigate the long-term behaviour of 4U 0115+63/V635 Cas...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
دوره شماره
صفحات -
تاریخ انتشار 2004