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

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

Berlin Exoplanet Search Telescope Specifications: Telescope Schmidt-Cassegrain Aperture 20 cm Focal ratio f/2.7 Instrument AP-10 CCD Size 2048 x 2048 pixels Pixel size 14 µm Pixel scale 5.5 arcsec/pixel Field of view 3.1° x 3.1° 2001 - 2004 Thüringer Landessternwarte Tautenburg (TLS), Germany From end 2004 Observatoire de Haute Provence (OHP), France

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

The OHP phase in 2005 Target fields: COROT anticenter (winter) and center (summer) fields (+ TLS fields) Statistics: anticenter: 15 + … nights center: 37 nights reduction and analysis ongoing Data base: data from COROT fields to be included in ExoDat Main limitation: Duty cycle (~40%) and crowding

Coverage of the center field 37 nights 142 hours

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.

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

SExtractor used in less crowded fields TLS

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

First result COROT center field from OHP in total 37 nights (142 hours) around 30000 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!

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 0.286- 117 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)

~0.07 mag

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.

Summery: Status of BEST observations at OHP Observations of anticenter field ongoing Statistics so far: anticenter: 15 + … nights center: 37 nights reduction and analysis ongoing 77 new variable stars have been identified with periods between 0.286-117 days In general 10 – 20% of the stars are variable Search for transit like signals ongoing Lightcurves will be made available through ExoDat

If your are interested to know about the variable stars found in the COROT target fields by BEST contact: heike.rauer@dlr.de