Other
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...8e..63p&link_type=abstract
Solar and Stellar Activity Cycles, 26th meeting of the IAU, Joint Discussion 8, 17-18 August 2006, Prague, Czech Republic, JD08,
Other
Scientific paper
We will discuss some aspects relevant to the detection of coronal activity cycles in late-type stars. The effects of the activity solar cycle manifest themselves in many bands, and most notably in the X-ray band. Since strong X-ray emission and other forms of activity are very evident in active late-type stars, one would expect detection of analogous X-ray cycles on these stars. However this is not the case. So to which extent can we apply the Solar-stellar connection in the coronal context? Certainly the Sun fits in the general late-type-stars "trend" of activity vs. rotation, age, temperature, flux etc.; on the other side extreme stellar activity shows "saturation" in rapidly rotating stars and the above "trend" may change significantly or break for very active stars, suggesting the action of a mechanism different from the solar-type dynamo. In this context, proving the presence of coronal solar-like cycles and determining their characteristics, hopefully for a large stellar sample, would provide fundamental tests. Detecting stellar coronal cycles is difficult, given the limited availability of present day X-ray telescopes for this purpose. Also, since X-ray observations aimed at cycle determinations cover time intervals much shorter than cycles themselves, and separated by years, it is hard to disentangle the mix of short term variability and cycles. Nonetheless there is some evidence of long term variability in some samples and in relatively old solar-mass stars (but not in young solar-mass stars neither in M stars). Some projects dedicated to find X-ray cycles using present day telescopes (e.g. those driven by Schmitt and by Favata) have started yielding results. A possibly more fruitful approach to detecting X-ray cycles is devising a relatively small X-ray satellite entirely dedicated to a long observing program to monitor active stars, like SADE (recently proposed by P. Martens and collaborators). One of the important goals of this research would be tracing the evolutionary path of the cyclic activity and of dynamo physics by measuring the activity of solar analogs in different stages of their life-cycles and for different stellar masses.
et. al.
Micela Giuseppina
Peres Giovanni
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