136 research outputs found
Pre-discovery observations of CoRoT-1b and CoRoT-2b with the BEST survey
The BEST wide-angle telescope installed at the Observatoire de Haute-Provence
and operated in remote control from Berlin by the Institut fuer
Planetenforschung, DLR, has observed the CoRoT target fields prior to the
mission. The resulting archive of stellar photometric lightcurves is used to
search for deep transit events announced during CoRoT's alarm-mode to aid in
fast photometric confirmation of these events. The "initial run" field of CoRoT
(IRa01) has been observed with BEST in November and December 2006 for 12
nights. The first "long run" field (LRc01) was observed from June to September
2005 for 35 nights. After standard CCD data reduction, aperture photometry has
been performed using the ISIS image subtraction method. About 30,000
lightcurves were obtained in each field. Transits of the first detected planets
by the CoRoT mission, CoRoT-1b and CoRoT-2b, were found in archived data of the
BEST survey and their lightcurves are presented here. Such detections provide
useful information at the early stage of the organization of follow-up
observations of satellite alarm-mode planet candidates. In addition, no period
change was found over ~4 years between the first BEST observation and last
available transit observations.Comment: AJ, accepte
Periodic variable stars in CoRoT field LRa02 observed with BEST II
The Berlin Exoplanet Search Telescope II (BEST II) is a small wide
field-of-view photometric survey telescope system located at the Observatorio
Cerro Armazones, Chile. The high duty cycle combined with excellent observing
conditions and millimagnitude photometric precision makes this instrument
suitable for ground based support observations for the CoRoT space mission.
Photometric data of the CoRoT LRa02 target field collected between November
2008 and March 2009 were analysed for stellar variability. The presented
results will help in the future analysis of the CoRoT data, particularly in
additional science programs related to variable stars. BEST II observes
selected CoRoT target fields ahead of the space mission. The photometric data
acquired are searched for stellar variability, periodic variable stars are
identified with time series analysis of the obtained stellar light curves. We
obtained the light curves of 104335 stars in the CoRoT LRa02 field over 41
nights. Variability was detected in light curves of 3726 stars of which 350
showed a regular period. These stars are, with the exception of 5 previously
known variable stars, new discoveries.Comment: The figures with light curves can be find in the A&A journal as
online onl
Characterization of CoRoT target fields with BEST: Identification of periodic variable stars in the IR01 field
We report on observations of the CoRoT IR01 field with the Berlin Exoplanet
Search Telescope (BEST). BEST is a small aperture telescope with a wide field
of view (FOV). It is dedicated to search for variable stars within the target
fields of the CoRoT space mission to aid in minimizing false-alarm rates and
identify potential targets for additional science. CoRoT's observational
programm started in February 2007 with the "initial run" field (IR01) observed
for about two months. BEST observed this field for 12 nights spread over three
months in winter 2006. From the total of 30426 stars observed in the IR01 field
3769 were marked as suspected variable stars and 54 from them showed clear
periodicity. From these 19 periodic stars are within the part of the CoRoT FOV
covered in our data set
The evaporation of planetary atmosphere
In recent years the focus of exoplanet research has shifted from the mere
detection to detailed characterization. Precise measurements of the masses and
radii of transiting planets have shown that some low-mass planets have extended
atmospheres while others are bare rocks. Hybrid atmospheres consisting of a
mixture of Hydrogen and large amount of heavy elements have also been detected.
A key factor in explaining this diversity of planetary atmospheres is the
erosion by the X-ray and EUV-radiation (XUV) from the host-star. The
evaporation through XUV-radiation has already been measured for a few
exoplanets.The apparent weakness of the CaIIHK and the MgIIhk emission cores
has been interpreted as evidence for the evaporation of planetary atmospheres.
The interpretation is that the evaporating material from the planet forms a
thick torus which absorbs the C,IIHK and the MgIIhk lines from the host star.
In this contribution a new way how to prove, or disprove this hypothesis by
observations is proposed. It is furthermore shown that there are enough bright
targets are already known that can be observed, and more will be found with the
PLATO mission.Comment: 8 page with 3 figure
Ground-based photometry of space-based transit detections: Photometric follow-up of the CoRoT mission
The motivation, techniques and performance of the ground-based photometric
follow-up of transit detections by the CoRoT space mission are presented. Its
principal raison d'\^{e}tre arises from the much higher spatial resolution of
common ground-based telescopes in comparison to CoRoT's cameras. This allows
the identification of many transit candidates as arising from eclipsing
binaries that are contaminating CoRoT's lightcurves, even in low-amplitude
transit events that cannot be detected with ground-based obervations. For the
ground observations, 'on'-'off' photometry is now largely employed, in which
only a short timeseries during a transit and a section outside a transit is
observed and compared photometrically. CoRoT planet candidates' transits are
being observed by a dedicated team with access to telescopes with sizes ranging
from 0.2 to 2 m. As an example, the process that led to the rejection of
contaminating eclipsing binaries near the host star of the Super-Earth planet
CoRoT-7b is shown. Experiences and techniques from this work may also be useful
for other transit-detection experiments, when the discovery instrument obtains
data with a relatively low angular resolution.Comment: Accepted for the A&A special issue on CoRo
Improved Variable Star Search in Large Photometric Data Sets -- New Variables in CoRoT Field LRa02 Detected by BEST II
The CoRoT field LRa02 has been observed with the Berlin Exoplanet Search
Telescope II (BEST II) during the southern summer 2007/2008. A first analysis
of stellar variability led to the publication of 345 newly discovered variable
stars. Now, a deeper analysis of this data set was used to optimize the
variability search procedure. Several methods and parameters have been tested
in order to improve the selection process compared to the widely used J index
for variability ranking. This paper describes an empirical approach to treat
systematic trends in photometric data based upon the analysis of variance
statistics that can significantly decrease the rate of false detections.
Finally, the process of reanalysis and method improvement has virtually
doubled the number of variable stars compared to the first analysis by Kabath
et al. A supplementary catalog of 272 previously unknown periodic variables
plus 52 stars with suspected variability is presented. Improved ephemerides are
given for 19 known variables in the field. In addition, the BEST II results are
compared with CoRoT data and its automatic variability classification.Comment: 16 pages, 15 figures; figure set, machine-readable and VO tables
available in the electronic edition of the Astronomical Journa
Regaining the FORS: optical ground-based transmission spectroscopy of the exoplanet WASP-19b with VLT+FORS2
In the past few years, the study of exoplanets has evolved from being pure
discovery, then being more exploratory in nature and finally becoming very
quantitative. In particular, transmission spectroscopy now allows the study of
exoplanetary atmospheres. Such studies rely heavily on space-based or large
ground-based facilities, because one needs to perform time-resolved, high
signal-to-noise spectroscopy. The very recent exchange of the prisms of the
FORS2 atmospheric diffraction corrector on ESO's Very Large Telescope should
allow us to reach higher data quality than was ever possible before. With
FORS2, we have obtained the first optical ground-based transmission spectrum of
WASP-19b, with 20 nm resolution in the 550--830 nm range. For this planet, the
data set represents the highest resolution transmission spectrum obtained to
date. We detect large deviations from planetary atmospheric models in the
transmission spectrum redwards of 790 nm, indicating either additional sources
of opacity not included in the current atmospheric models for WASP-19b or
additional, unexplored sources of systematics. Nonetheless, this work shows the
new potential of FORS2 for studying the atmospheres of exoplanets in greater
detail than has been possible so far.Comment: 7 pages, 9 figures, 3 tables. Accepted for publication in A&
A Variable Star Census in a Perseus Field
The Berlin Exoplanet Search Telescope is a small-aperture, wide-field
telescope dedicated to time-series photometric observations. During an initial
commissioning phase at the Thueringer Landessternwarte Tautenburg, Germany, and
subsequent operations at the Observatoire de Haute-Provence, France, a 3.1
{\deg} x 3.1 {\deg} circumpolar field close to the galactic plane centered at
({\alpha}, {\delta}) = (02h 39m 23s, +52{\deg} 01' 46") (J 2000.0) was observed
between 2001 August and 2006 December during 52 nights. From the 32129 stars
observed, a subsample of 145 stars with clear stellar variability was detected
out of which 125 are newly identified variable objects. For five bright
objects, the system parameters were derived by modeling the light curve.Comment: 8 pages, 5 figures, 3 table
- …