The experience of BEST. Heike Rauer and the BEST Team Institut für Planetenforschung Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) and Zentrum für Astronomie und Astrophysik Technische Universität Berlin +. The experience of BEST. Berlin Exoplanet Search Telescope System.
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Heike Rauer and the BEST Team
Institut für Planetenforschung
Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR)
Zentrum für Astronomie und Astrophysik
Technische Universität Berlin
Berlin Exoplanet Search Telescope System
Goals of BEST: - support for CoRoT
- detect large planets
- variable stars, additional science
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
Since end 2004 Observatoire de Haute Provence (OHP), France
TEST at TLS
Instituto de Astronomía - Universidad Católica del Norte (UCN) in Antofagasta, Chile
Astronomisches Institut- Ruhr-Universität Bochum (RUB), Germany.
Telescope BRC - 250
Aperture 25 cm
Focal ratio f/5.0
Instrument FLI IMG-1680 CCD
Size 4096 x 4096 pixels
Pixel size 9 µm
Pixel scale 1.5 arcsec/pixel
Field of view 1.7° x 1.7°
Precision < 1% V=15-16
smaller FoV for BEST II is compensated by less stars influenced by crowding
Need: High duty cycle, full coverage of planetary orbits by observations of sufficient quality.
BEST experience: duty cycle is the major limiting factor from central Europe (not a surprise ). Next:
place BEST II at OCA, Chile
start building a network (NEST)
participate to ASTEP
For example: a star moves across a hot pixel during the night due to imperfect guiding of the telescope….
Correction of atmosphere (extinction, seeing, scintillation, …)
- Airmass correction is critical (no filter, large FOV)
restriction in airmass, depending on site and target field
adapt reduction method, e.g. work on sub-fields
implement filter if possible
- Effect of seeing variations on crowding
Accurate photometry (aperture/image subtraction/PSF fitting, crowding)
- Crowding can be a major problem
improve photometric method (image subtraction ok)
match the pixel scale of h/w
B.E.S.T. Candidate 3
BEST Magnitude of host star 12.1
Depth [%] 2.5
Duration [h] 3.0
Orbital period [d] 423.10/n
Number of detections 2
depth [%] 1.0
duration [h] 4.5
orbital period [d] > 10 ?
semi mayor axis[AU] ?
number of detections 1
target field No. 8
host star M dwarf
V magnitude 14.73
BEST 18.3‘ x 18.3‘
The photometric data reduction algorithm needs to be adopted.
* 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 photometric accuracy
Comparison of both methods for the COROT field photometric accuracy
Data from 4 nights in spring 2005 obtained at OHP (COROT winter field)
Karoff et al. 2005
a reduction routine able to deal with very crowded target fields is important
Performance of BEST I at OHP after evaluation of its first regular observing season at OHP in summer 2005.
BEST at OHP: Variable stars in the CoRoT center field regular observing season at OHP in summer 2005.
37 nights/142 hours observations from OHP in summer 2005.
Karoff et al. 2006
Location of the variables in the center field regular observing season at OHP in summer 2005.
See Karoff et al. 2006
Eclipsing binaries in Hipparcos data
Eclipsing binaries in BEST observations
Söderhjelm & Dischler 2005
Karoff et al. 2006
The BEST survey is complete only up to 10 – 20% for
periods > 1 day.
But: we have indications that the detection algorithm for periodic variables is not perfect…