Issue |
A&A
Volume 409, Number 3, October III 2003
|
|
---|---|---|
Page(s) | 1017 - 1030 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20031161 | |
Published online | 17 November 2003 |
Magnetic activity of six young solar analogues II. Surface Differential Rotation from long-term photometry
1
Catania Astrophysical Observatory, INAF, Via S. Sofia 78, 95123 Catania, Italy
2
Dept. of Astronomy and Astrophysics, Villanova University, Villanova 19085, PA, USA e-mail: edward.guinan@villanova.edu
Corresponding author: S. Messina, sme@ct.astro.it
Received:
16
May
2003
Accepted:
18
July
2003
The present paper is the second of a series dedicated to the study of the magnetic
activity in a selected sample of young solar analogues. The sample includes five single G0-G5V stars with ages between
130 Myr and 700 Myr: EK Dra, π1 UMa, HN Peg, k1 Cet and BE Cet. In this study we also
include the Pleiades-age (
130 Myr) K0V star DX Leo. Our analysis
is based on high precision photometric observations carried out as part
of The Sun in Time project, aimed at a multiwavelength study of stars
with solar-like global properties, but with different ages and thus at
different stages of evolution.
In the first paper of this series we presented the photometric observations
and determined the existence of starspot cycles
and their correlation with the global stellar properties.
In the present paper we investigate the surface differential rotation (SDR).
The periodogram analysis of the photometric data time series has allowed us to determine
the rotational periods and
to derive the following results: i) all the selected stars show variations of the
rotational period. Such variations are
definitely periodic and in phase with the starspot cycle for BE Cet and DX Leo.
They are likely periodic and in phase also for π1 UMa, EK
Dra and HN Peg, but still need confirmation. By analogy with the solar butterfly diagram,
the rotational period variations are interpretable in terms of surface differential rotation, that
is, they are attributable to the existence of active latitude belts migrating
during the activity cycle on a differentially rotating star; ii)
BE Cet, π1 UMa and EK Dra show a solar-like
pattern of SDR, that is the rotational period steadily decreases along the
activity cycle, jumping back to higher values at the beginning of the next
cycle; on the contrary, DX Leo, k1 Cet and HN Peg show an antisolar pattern;
iii)
the amplitude of the rotational period variations shows a power law dependence on
the rotational period similar to that found in previous studies.
Contrary to theoretical predictions, the cycle length is not correlated to the
Dynamo number, it is indeed positively correlated to the SDR amplitude. More
precisely, stars tend to concentrate along three different branches with the
cycle length increasing with increasing
/Ω.
Moreover, we found that the SDR amplitude changes from cycle to cycle, which
is reminiscent of a wave of excess rotation propagating in latitude;
iiii) the apparently different solar and antisolar behaviours are probably
due to different inclinations of the stellar rotation axis under which the star is seen.
The long-term photometry of the
young single star LQ Hya, although not included in the initial project, is also used in the
present analysis to enlarge the
investigated sample. We determined for LQ Hya three different starspot cycles and an
antisolar pattern of SDR.
Key words: stars: activity / stars: late-type / stars: magnetic fields / stars: rotation / stars: starspots
© ESO, 2003
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