38 research outputs found
On the potential of transit surveys in star clusters: Impact of correlated noise and radial velocity follow-up
We present an extension of the formalism recently proposed by Pepper & Gaudi
to evaluate the yield of transit surveys in homogeneous stellar systems,
incorporating the impact of correlated noise on transit time-scales on the
detectability of transits, and simultaneously incorporating the magnitude
limits imposed by the need for radial velocity follow-up of transit candidates.
New expressions are derived for the different contributions to the noise budget
on transit time-scales and the least-squares detection statistic for box-shaped
transits, and their behaviour as a function of stellar mass is re-examined.
Correlated noise that is constant with apparent stellar magnitude implies a
steep decrease in detection probability at the high mass end which, when
considered jointly with the radial velocity requirements, can severely limit
the potential of otherwise promising surveys in star clusters. However, we find
that small-aperture, wide field surveys may detect hot Neptunes whose radial
velocity signal can be measured with present-day instrumentation in very nearby
(<100 pc) clusters.Comment: 14 pages, 2 figures, accepted for publication in MNRA
The Cepheid period-luminosity zero-point from radial velocities and Hipparcos proper motions
A value for the zero-point (ρ) of the Cepheid period-luminosity relation, = 2.81 log P + ρ, is deduced by comparing the value of the Oort constant, A, derived from radial velocities with that derived from Hipparcos proper motions. We find in this way that ρ =−1.47 ± 0.13, in excellent agreement with the value derived from Hipparcos trigonometrical parallaxes, ρ = −1.43 ± 0.10, by Feast & Catchpole in a recent pape
The "missing link": a 4-day period transiting exoplanet around OGLE-TR-111
We report the discovery of a transiting hot Jupiter around OGLE-TR-111, from
our radial velocity follow-up of OGLE transiting candidates in Carina. The
planet has a mass of 0.53 +- 0.11 M_J and a radius of 1.0 +0.13-0.06 R_J. Three
transiting exoplanets have already been found among OGLE candidates, all with
periods near 1.5 days. The planet presented here, with P=4.0 days, is the first
exoplanet detected by transits with the characteristics of a "normal" hot
Jupiter, as found in abundance by radial velocity surveys The radius of
OGLE-TR-111b and the scarcity of hot Jupiters detected among OGLE transit
candidates tend to indicate that the case of HD209458b, with a radius of 1.4
R_J, is exceptional, with most hot Jupiters being smaller.Comment: 4 pages, 4 figures, to be published in A&A Letter
Star-Planet Interactions
Much effort has been invested in recent years, both observationally and
theoretically, to understand the interacting processes taking place in
planetary systems consisting of a hot Jupiter orbiting its star within 10
stellar radii. Several independent studies have converged on the same scenario:
that a short-period planet can induce activity on the photosphere and upper
atmosphere of its host star. The growing body of evidence for such magnetic
star-planet interactions includes a diverse array of photometric, spectroscopic
and spectropolarimetric studies. The nature of which is modeled to be strongly
affected by both the stellar and planetary magnetic fields, possibly
influencing the magnetic activity of both bodies, as well as affecting
irradiation and non-thermal and dynamical processes. Tidal interactions are
responsible for the circularization of the planet orbit, for the
synchronization of the planet rotation with the orbital period, and may also
synchronize the outer convective envelope of the star with the planet. Studying
such star-planet interactions (SPI) aids our understanding of the formation,
migration and evolution of hot Jupiters.Comment: 8 pages, proceedings of Cool Stars 15, St. Andrews, July 2008, to be
published in the Conference Proceedings Series of the American Institute of
Physics - "Star-planet interactions" splinter session summar
ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD189733
Among the 160 known exoplanets, mainly detected in large radial-velocity
surveys, only 8 have a characterization of their actual mass and radius thanks
to the two complementary methods of detection: radial velocities and
photometric transit. We started in March 2004 an exoplanet-search programme
biased toward high-metallicity stars which are more frequently host extra-solar
planets. This survey aims to detect close-in giant planets, which are most
likely to transit their host star. For this programme, high-precision radial
velocities are measured with the ELODIE fiber-fed spectrograph on the 1.93-m
telescope, and high-precision photometry is obtained with the CCD Camera on the
1.20-m telescope, both at the Haute-Provence Observatory. We report here the
discovery of a new transiting hot Jupiter orbiting the star HD189733. The
planetary nature of this object is confirmed by the observation of both the
spectroscopic and photometric transits. The exoplanet HD189733b, with an
orbital period of 2.219 days, has one of the shortest orbital periods detected
by radial velocities, and presents the largest photometric depth in the light
curve (~ 3%) observed to date. We estimate for the planet a mass of 1.15 +-
0.04 Mjup and a radius of 1.26 +- 0.03 RJup. Considering that HD189733 has the
same visual magnitude as the well known exoplanet host star HD209458, further
ground-based and space-based follow-up observations are very promising and will
permit a characterization of the atmosphere and exosphere of this giant
exoplanet.Comment: 5 pages, submitted to Astronomy & Astrophysic