Transcript Search for radio emission in extrasolar planets detected by COROT

Search for radio emission in
extrasolar planets detected
by COROT
Accepted AP
observational requirements, feasability,
expectations
Walter Gonzalez, Francisco Jablonski,
Felipe Madsen and
Eder Martioli
Instituto Nacional de Pesquisas Espaciais
São José dos Campos, SP - Brazil
Introduction
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Jupiter shows non-thermal emission in
the kHz to GHz frequency range (e.g.,
Carr et al. 1983)
Below 40 MHz  cyclotron emission
Higher frequencies  synchrotron
emission
Average power radiated is above the
Giga-Watt level
Predictions for the power emitted by
extrasolar planets in Bastian et al.
(2000) and Zarka et al. (2001)
The star-planet connection
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Many planets very close (<< 1 AU) to
their primaries
Magnetic / tidal interaction
Energy input into the planet's
magnetosphere orders of magnitude
larger than in Jupiter
Mass > MJup  B > BJup
Power emitted likely to be much stronger
than in Jupiter (Farrel et al. 2003)
Radio-optical connection
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In Jupiter, radio emission is enhanced by
orders of magnitude after Coronal Mass
Ejection (CME) events in the Sun
CME events produce global intensity
variations in the Sun with fractional r.m.s
~10-4
CME events can be detected in COROT
photometry!
~Real-time monitoring with COROT could be
useful to early warn radio campaigns to
observe enhanced Jupiter-like emission
Alternatively, off-line analysis of
simultaneous radio and optical observations
likely to show time-correlated events
Possible observational
scenario
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A planet is found in the sismo field
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New planets are found among the
brightest targets in the exo field
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Unlikely, but very good, since objects tend to
be close to us
Large number, but at relatively larger
distances
COROT observes a star already known to
bear a planet
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Very good (eg. HD46375)
Impulsive event detection
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Bayesian approach suitable, like in Aigrain
and Favata (2002) and Defaÿ et al. (2001)
 Photon (Poisson) noise + RON
 Two-rate (1, 2) model for flares, similar
to the method of Gregory and Loredo
(1992), for m=2
 2 > 1 included as prior information
 Model comparison to select best timewindow
 Segment analysis to set up baseline of
"zero activity"
 More elaborate models should include
information available on the shape of
events
Observational requirements
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Light curves of stars showing planet
transits
 Interesting stuff not transits
themselves, but impulsive events
signaling CME
The brighter (closer) the stars, the better
Close to real-time access to data (say, in
~24 h) would be great since it could be used
to trigger radio observations
 Offline analysis of simultaneous COROT
and radio data ok too
Feasability
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Scaling laws predict that among the
known exoplanets, 18 should deliver more
than 10 mJy at f<100 Mhz
GMRT observations carried out in March
2005
 55 Cnc, 70 Vir, upsilon And, tau Boo
No radio emission detected
 Sensitivity (2 s) of 3 mJy at 150 Mhz, 1 h
exp. time
Simultaneous optical observations at LNA,
Brazil
 Bad weather, but some results
 Difficult observations
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Expectations
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Expectation from a scientific point of view
is of a fundamental contribution to
magnetospheric studies, for the first time
gathering data in environment quite
different from that in the solar system.
Increasing levels of scientific cooperation
among groups at INPE and abroad
Attracting more people to exoplanetary
research
Resources
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Quite good computing infrastructure,
including access to the supercomputer used
by INPE for weather forecasting
Experience with GMRT data acquisition and
reduction
Experience with time-series analysis
Summary
The sensitivity level of existing meter-wavelength
radiotelescopes (better than 10 mJy in the region 10100 MHz) is such that nonthermal emission from
extrasolar planets could be detected with integration
times less than one hour. With LOFAR this limit will be
at least a factor of ten better. This means that a large
number of transit-discovered planets in COROT fields
could be monitored for impulsive events that lead
enhanced radio- emission.
References
Aigrain, S., and Favata, F. 2002, A&A, 395, 625
Bastian, T., Dulk, G.A., and Leblanc, Y. 2000, ApJ, 545, 1058
Carr, T.D., M.D. Desch, and J. K. Alexander, Phenomenology of
magnetospheric radio emissions, in Physics of the Jovian
Magnetosphere, edited by A.J. Dessler, Chapter 7, pp. 226-284,
Cambridge University Press, New York, 1983.
Defaÿ, C., Deleuil, M., and Barge, P. 2001, A&A, 365, 330
Farrel, W.M., Desch, M.D., Lazio, T.J., Bastian, T. and Zarka, P.
2003, ASP Conf. Ser. 294: Scientific Frontiers in Research on
Extrasolar Planets, ed. D. Deming and S. Seager (San Francisco:
ASP), 151
Gregory, P.C., and Loredo, T.J. 1992, ApJ, 398, 146
Zarka, P. Treumann, R.A., Ryabov, B.P. and Ryabov, V.B. 2001,
Ap&SS, 277, 293