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Title:
Hot Jupiters and Hot Spots: The Short- and Long-Term Chromospheric Activity on Stars with Giant Planets
Authors:
Shkolnik, E.; Walker, G. A. H.; Bohlender, D. A.; Gu, P.-G.; Kürster, M.
Affiliation:
AA(Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada; , ), AB(Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada; , ), AC(Herzberg Institute for Astrophysics, National Research Council of Canada, Victoria, BC V9E 2E7, Canada; ), AD(Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 11529, Taiwan; ), AE(Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany; )
Publication:
The Astrophysical Journal, Volume 622, Issue 2, pp. 1075-1090. (ApJ Homepage)
Publication Date:
04/2005
Origin:
UCP
ApJ Keywords:
Stars: Planetary Systems, Radiation Mechanisms: Nonthermal, Stars: Activity, Stars: Chromospheres, Stars: Late-Type
DOI:
10.1086/428037
Bibliographic Code:
2005ApJ...622.1075S

Abstract

We monitored the chromospheric activity in the Ca II H and K lines of 13 solar-type stars (including the Sun): 8 of them over 3 years at the Canada-France-Hawaii Telescope (CFHT) and 5 in a single run at the Very Large Telescope (VLT). A total of 10 of the 13 targets have close planetary companions. All of the stars observed at the CFHT show long-term (months to years) changes in H and K intensity levels. Four stars display short-term (days) cyclical activity. For two, HD 73256 and κ1 Cet, the activity is likely associated with an active region rotating with the star; however, the flaring in excess of the rotational modulation may be associated with a hot Jupiter. A planetary companion remains a possibility for κ1 Cet. For the other two, HD 179949 and υ And, the cyclic variation is synchronized to the hot Jupiter's orbit. For both stars this synchronicity with the orbit is clearly seen in two out of three epochs. The effect is only marginal in the third epoch at which the seasonal level of chromospheric activity had changed for both stars. Short-term chromospheric activity appears weakly dependent on the mean K line reversal intensities for the sample of 13 stars. In addition, a suggestive correlation exists between this activity and the Mpsini of the star's hot Jupiter. Because of their small separation (<=0.1 AU), many of the hot Jupiters lie within the Alfvén radius of their host stars, which allows a direct magnetic interaction with the stellar surface. We discuss the conditions under which a planet's magnetic field might induce activity on the stellar surface and why no such effect was seen for the prime candidate, τ Boo. This work opens up the possibility of characterizing planet-star interactions, with implications for extrasolar planet magnetic fields and the energy contribution to stellar atmospheres.

Based on observations collected at the Canada-France-Hawaii Telescope operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique of France, and the University of Hawaii, as well as data from the European Southern Observatory's Very Large Telescope, Chile (programme ESO 73.C-0694).

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