WTS-1 b

The end of the twentieth century saw a revolution in our knowledge
of planetary systems. The detection of the first extrasolar planet
in 1992 marked the beginning of a modern era and changed our idea
of planets and planetary systems. The discoveries continue rapidly
and reveal an extraordinary diversity of planetary systems and
physical properties of the exoplanets, raising new questions in the
field of planetary science. So far, more than 800 extrasolar
planets have been detected, spanning a wide range of masses from a
few Earth masses to a few tens of Jupiter masses. This Ph.D. Thesis
is devoted to the confirmation via radial velocity follow-up of the
candidate planets detected by the WFCAM Transit Survey (WTS), which
is an on-going photometric monitoring campaign using the Wide Field
Camera on the United Kingdom Infrared Telescope at Mauna Kea
(Hawaii, USA). The WTS and the present work were supported by the
RoPACS (Rocky Planets Around Cool Stars) group, a Marie Curie
Initial Training Network funded by the Seventh Framework Programme
of the European Commission. Since the WTS was primarily designed to
find planets transiting M-dwarf stars, the observations are
obtained in the J-band (1.25 micron). This wavelength is near to
the peak of the spectral energy distribution of a typical M-dwarf.
Simulations show that operating in the J-band reduces the effects
of stellar variability, which became important at optical
wavelengths in cool stars. The J-band light curves that show a
periodic drop and pass all the selection criteria, progress to the
candidate confirmation phase. After a transit depth consistency
check performed with i'-band observations, intermediate resolution
spectra enable to rule out false-positive eclipsing binaries
scenarios. Finally, high-resolution spectroscopic follow-up is
performed to confirm, by the radial velocity method, the planetary
nature of the stellar companion detected by the WTS. The spectra
employed in this phase were observed with the High Resolution
Spectrograph (HRS) housed in the basement of the 9.2-m Hobby-Eberly
Telescope (HET) in Texas, USA. The pipeline for the reduction and
analysis of the HET spectra has been created. Debug, optimization
and test of the whole procedure were performed observing several
target stars with different apparent magnitude and spectral type.
These observations allowed to estimate the precision on the
velocity measures for different targets. Errorbars of 10 m/s are
expected for solar type stars of magnitude up to mV=10 and SNR of
the observed spectra >150. Spectra with a SNR of 30 can be
measured for faint (mV=14) M stars, leading to a final radial
velocity uncertainty of about 60 m/s. Furthermore, a technical
problem occurring under given instrumental configurations could be
identified and fixed, removing a possible source of systematic from
any later observation. Finally, the zero-point offset with respect
to the HARPS data was computed allowing the comparison of the HET
measures with those related to any other instruments involved in
radial velocity follow-up. The radial velocities computed from the
HET high-resolution spectra allowed to confirm the detection of the
first two extrasolar planet performed by the WTS. WTS1 b is a 4 MJ
planet orbiting in 3.35 days a late F-star with possibly slightly
sub-solar metallicity. With a radius of 1.49 RJ, it is the third
largest planet of the known extrasolar planets in the mass range
3-5 MJ. Its unusual large radius can not be explained within the
standard evolution models, even considering the strong radiation
that the planet receives from the parent star. Ohmic heating could
be a possible mechanism able to bring energy in the deeper layers
of WTS1 b and hence explaining its radius anomaly. WTS2 b is
instead a 1 MJ planet orbiting an early K-star in about 1 day only.
The measure of its secondary eclipses in the Ks-band will allow to
study a highly irradiated planet around a cool star, cooler than
many of the currently known very hot-Jupiters host star. This will
provide an insight to the effect of the stellar spectrum on the
composition and structure of hot-Jupiter atmospheres. Beyond the
RoPACS program, the pipeline has been employed in the radial
velocity follow-up of the white dwarf NLTT 5306, confirming the
presence of a brown dwarf companion of 56 MJ orbiting its host star
in 102 minutes, the shortest period ever observed in such systems.
The discoveries of WTS1 b and WTS2 b demonstrate the capability of
WTS to find planets, even if it operates in a back-up mode during
dead time on a queue-schedule telescope and despite of the somewhat
randomised observing strategy. Moreover, the two new discovered
planets are hot-Jupiters orbiting an F-star and a K-star. Both are
hotter than an M-dwarf, the main target sample of the WTS. As
described in Kovacs et al. (2012, MNRAS submitted), no planets
around M-dwarf stars monitored by the WTS (mV