1. First results from BEST at OHP
Heike Rauer, Anders Erikson, Christoffer Karoff, Ruth Titz, Holger Voss, Tino Wiese and the BEST team
Institute of Planetary Research, DLR
Berlin, Germany

2. Purpose Ground-based support for COROT Discover Jupiter-sized planets
catalog of bright variable stars in the target fields
Discover Jupiter-sized planets
increase statistics of close-in extrasolar gas giants

3. Berlin Exoplanet Search Telescope
Specifications:
Telescope Schmidt-Cassegrain
Aperture 20 cm
Focal ratio f/2.7
Instrument AP-10 CCD
Size x 2048 pixels
Pixel size 14 µm
Pixel scale 5.5 arcsec/pixel
Field of view 3.1° x 3.1°
Thüringer Landessternwarte
Tautenburg (TLS), Germany
From end Observatoire de Haute Provence (OHP), France

4. BEST at OHP remote data acquisition with minor local support
data reduction in Berlin
gradually improved degree of automatic control
regular operation since spring 2005

5. The OHP phase in 2005
Target fields: COROT anticenter (winter) and center (summer) fields (+ TLS fields)
Statistics:
anticenter: 15 + … nights
center: nights
reduction and analysis ongoing
Data base: data from COROT fields to be included in ExoDat
Main limitation: Duty cycle (~40%) and crowding

6. Coverage of the center field
37 nights
142 hours

7. Crowded target fields lead to further reduction of the photometric accuracy
diluted signals
- neighboring stars are resolved
- but a neighbor contributes flux within the PSF or photometric aperture
b) unresolved stars
- neighboring stars are not resolved
c) a combination of a) and b)
- due to varying seeing the resolution of stars changes over the night
 a transit signal is weakend
 noise is added if the neighbor is variable
The photometric data reduction algorithm needs to be adopted.

8. We had to include a new method: Comparison of Photometric methods
Source-Extractor, SExtractor (Bertin & Arnouts 1996)
Performs different kinds of aperture photometry
Multi Object Multi Frame photometry, MOMF (Kjeldsen & Frandsen 1992)
Combination of aperture and PSF photometry
Image Subtraction, ISIS (Alard 2000)
Subtraction of a convolved reference frame from all frames. 
implementation of parallel approach in data pipeline (SExtractor, ISIS)
Karoff et al. 2005

9. SExtractor used in less crowded fields
TLS

10. Comparison of both methods for the COROT field
Data from 4 nights in spring 2005 obtained at OHP (COROT winter field)
SExtractor
ISIS
 a reduction routine able to deal with very crowded target fields is important

11. First result COROT center field from OHP
in total 37 nights (142 hours)
around detected stars
reduction and analysis ongoing
~4800 stars with 1%
~1000 stars with 0.5%
Individual frames with high noise level (>1 sigma) on all stars excluded.
rms over all 37 nights!

12. Variable stars in the center field
11 variable stars are known in the field from catalogs
77 new variable stars have been identified with periods between days
in total 0.5 % of stars in the field are variables with <13.6 mag for a period could be determined
about 10 – 20 % of all detected stars are variable (period tbd)

14. ~0.07 mag

15. Location of the variables in the center field
~4800 stars with < 1%
~1000 stars with < 0.5%
rms over all 37 nights!
Variable stars are detected over the whole magnitude range.

16. Summery: Status of BEST observations at OHP
Observations of anticenter field ongoing
Statistics so far:
anticenter: 15 + … nights
center: nights
reduction and analysis ongoing
77 new variable stars have been identified with periods
between days
In general 10 – 20% of the stars are variable
Search for transit like signals ongoing
Lightcurves will be made available through ExoDat

17. If your are interested to know about the variable stars found in the COROT target fields by BEST contact: