Hot Jupiters and Hot Spots: The Short- and Long-term Chromospheric Activity on Stars with Giant Planets

Astrophysics, abstract
astro-ph/0411655

From: Evgenya Shkolnik [view email]

Date: Wed, 24 Nov 2004 00:35:25 GMT   (155kb)

We monitored the chromospheric activity in the Ca II H & K lines of 13
solar-type stars (including the Sun); 8 of them over three years at the CFHT
and 5 in a single run at the VLT. Ten 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 & K intensity levels. Four stars display short-term (days)
cyclical activity. For two, HD 73256 and kappa^1 Ceti, 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 kappa^1 Ceti. For the other two,
HD 179949 and upsilon 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. Also, a suggestive
correlation exists between this activity and the M_p sin(i) of the star’s hot
jupiter. Because of their small separation (<= 0.1 AU), many of the hot
jupiters lie within the Alfv\’en 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, tau 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.

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