5 research outputs found
A Lucky Imaging search for stellar sources near 74 transit hosts
Many transiting planet host stars lack high resolution imaging and thus close
stellar sources can be missed. Those unknown stars potentially bias the
derivation of the planetary and stellar parameters from the transit light
curve, no matter if they are bound or not. In addition, bound stellar
companions interact gravitationally with the exoplanet host star, the disk and
the planets and can thus influence the formation and evolution of the planetary
system strongly. We extended our high-resolution Lucky Imaging survey for close
stellar sources by 74 transiting planet host stars. 39 of these stars lack
previous high-resolution imaging, 23 are follow up observations of companions
or companion candidates, and the remaining stars have been observed by others
with AO imaging though in different bands. We determine the separation of all
new and known companion candidates and estimate the flux ratio in the observed
bands. All observations were carried out with the Lucky Imaging camera AstraLux
Norte at the Calar Alto 2.2 m telescope in i' and z' passbands. We find new
stellar sources within 1 arcsec to HAT-P-27, HAT-P-28, HAT-P-35, WASP-76, and
WASP-103, and between 1 and 4 arcsec to HAT-P-29 and WASP-56.Comment: 6 pages, 1 figure, accepted for publication in Astronomy &
Astrophysic
A Lucky Imaging search for stellar companions to transiting planet host stars
The presence of stellar companions around planet hosting stars influences the
architecture of their planetary systems. To find and characterise these
companions and determine their orbits is thus an important consideration to
understand planet formation and evolution. For transiting systems even unbound
field stars are of interest if they are within the photometric aperture of the
light curve measurement. Then they contribute a constant flux offset to the
transit light curve and bias the derivation of the stellar and planetary
parameters if their existence is unknown. Close stellar sources are, however,
easily overlooked by common planet surveys due to their limited spatial
resolution. We therefore performed high angular resolution imaging of 49
transiting exoplanet hosts to identify unresolved binaries, characterize their
spectral type, and determine their separation. The observations were carried
out with the Calar Alto 2.2m telescope using the Lucky Imaging camera AstraLux
Norte. All targets were imaged in i' and z' passbands. We found new companion
candidates to WASP-14 and WASP-58, and we re-observed the stellar companion
candidates to CoRoT-2, CoRoT-3, CoRoT-11, HAT-P-7, HAT-P-8, HAT-P-41, KIC
10905746, TrES-2, TrES-4, and WASP-2. We deduce from the stellar density around
all sources that two companion candidates out of the targets with the first
position measurement (CoRoT-11, HAT-P-41, KIC 10905746, WASP-14 and WASP-58)
are probably unbound. In addition, we re-analyse the influence of the sources
close to WASP-14 and WASP-58 on the planetary parameters given in the
literature and find no significant changes
Stellar companions to exoplanet host stars: A Lucky Imaging survey of transiting exoplanet systems
About half of all nearby stars are part of a binary or multiple star system, yet little is known about how multiplicity affects the formation and subsequent evolution of planetary systems. For instance, stellar companions may promote the inward migration of massive planets into very short orbits or cause misalignment between the planetary orbit and the stellar spin axis depending on the properties of the system. Moreover, the ignorance about the presence of a close stellar companion to a transiting exoplanet host star may introduce biases in the derivation of planetary parameters.
In this thesis, I present the results of our Lucky Imaging search for stellar companions around more than 100 transiting exoplanet host stars. Besides characterizing the companion candidates, I calculate the probability that the companion candidates are gravitationally bound using two different statistic approaches, and I look for a correlation between binarity and hot Jupiters with aligned/misaligned orbits. I calculate the effect of unresolved stellar companions on the deduced planetary parameters, in particular the correction for the radii for two planets.
Additionally, I present photometric and spectroscopic observations of the young binary HD102077 for which I determine the orbital parameters, the spectral type of the two components, the space motion, age, and moving group membership
The young binary HD 102077: Orbit, spectral type, kinematics, and moving group membership
The K-type binary star HD 102077 was proposed as a candidate member of the TW
Hydrae Association (TWA) which is a young (5-15 Myr) moving group in close
proximity (~50 pc) to the solar system. The aim of this work is to verify this
hypothesis by different means. We first combine diffraction-limited
observations from the ESO NTT 3.5m telescope in SDSS-i' and -z' passbands and
ESO 3.6m telescope in H-band with literature data to obtain a new, amended
orbit fit, estimate the spectral types of both components, and reanalyse the
Hipparcos parallax and proper motion taking the orbital motion into account.
Moreover, we use two high-resolution spectra of HD 102077 obtained with the
fibre-fed optical echelle spectrograph FEROS at the MPG/ESO 2.2m telescope to
determine the radial velocity and the lithium equivalent width of the system.
The trajectory of HD 102077 is well constrained and we derive a total system
mass of M and a semi-major axis of AU. From the i'-z' colours we infer an integrated spectral type of K2V,
and individual spectral types of K0 +/- 1 and K5 +/- 1. The radial velocity
corrected for the orbital motion of the system is km/s. Even
though the parallax determination from the Hipparcos data is not influenced by
the orbital motion, the proper motion changes to mas/yr and mas/yr. With
the resultant space motion, the probability of HD 102077 being a member of TWA
is less than 1%. Furthermore, the lithium equivalent width of m\AA
is consistent with an age between 30 Myr and 120 Myr and thus older than
the predicted age of TWA. In conclusion, HD 102077's age, galactic space
motion, and position do not fit TWA or any other young moving group