Issue |
A&A
Volume 379, Number 2, November IV 2001
|
|
---|---|---|
Page(s) | 436 - 452 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20011325 | |
Published online | 15 November 2001 |
ESO imaging survey*
Pre-FLAMES survey: Observations of selected stellar fields
1
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
2
Dipartimento di Astronomia, Universitá di Padova, Vicolo dell'Osservatorio 5, 35122 Padova, Italy
3
Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy
4
Universidade Estadual de Feira de Santana, Campus Universitário, Feira de Santana, BA, Brazil
5
Observatório Nacional, Rua Gen. José Cristino 77, Rio de Janerio, R.J., Brasil
6
Max-Planck Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85748 Garching b. München, Germany
Corresponding author: Y. Momany, ymomany@eso.org
Received:
30
July
2001
Accepted:
18
September
2001
This paper presents the first set of fully calibrated images
and associated stellar catalogs of the Pre-FLAMES survey being carried
out by the ESO Imaging Survey (EIS) project. The primary goal of this
survey is to provide the ESO community with data sets from which
suitable target lists can be extracted for follow-up observations with
the new VLT facility FLAMES (Fiber Large Array Multi Element
Spectrograph). For this purpose, 160 stellar fields have been selected
for observations in B, V and I using the Wide
Field Imager (WFI) at the MPG/ESO 2.2 m telescope at La Silla. Out of
those, over 100 fields have already been observed. The list of selected
fields includes open clusters, globular clusters, regions in the
Galaxy bulge, dwarf spheroidal galaxies in the vicinity of the Milky
Way, contiguous regions of SMC and LMC and few nearby clusters of
galaxies. The present paper discusses the results obtained for a small
subset of these data, which include four open clusters (M 67, NGC 2477,
NGC 2506 and Berkeley 20) and two regions of the SMC. These data have
been used to assess the observing strategy adopted, a combination of
short- and long-exposures, and to define suitable reduction techniques
and procedures for the preparation of input catalogs for FLAMES. In
order to minimize light losses due to misplacements of FLAMES fibers,
the astrometric calibration of crowded stellar fields is a critical
issue. The impact of different swarping techniques and different
reference catalogs on the astrometric calibration of the images is
evaluated and compared to those of other authors. From this
comparison, one finds that both USNO 2.0 and the recently released GSC 2.2
yield comparable results with the positional differences having a rms
of about 0.15 arcsec, well within the requirements (0.2 arcsec)
specified by the FLAMES science team. The internal accuracy of the
astrometry is estimated to be ≲0.1 arcsec, primarily limited by
the reference catalog used. The major difference between these
catalogs is the systematic variation of the positional residuals as a
function of the apparent magnitude of the objects, with the GSC 2.2
yielding by far the best results. The astrometric calibration of the
images presented here is based on the USNO 2.0 catalog because not all
fields considered are covered by the current release of the GSC 2.2.
Future EIS calibrations will be done using the GSC 2.2 catalog. The
extraction and photometric measurements of stellar sources are carried
out using a PSF fitting technique. Comparison with results available
in the literature shows that the photometric measurements are in good
agreement, apart from possible zero-point offsets, with the magnitude
differences having a scatter of ~0.06 mag at
mag. This
demonstrates that the data allow for the selection of robust targets
down to the expected spectroscopic limit of FLAMES. The combination of
catalogs extracted from the short and long-exposures allows one to
produce color-magnitude diagrams (CMD) spanning ~13 mag in V
and reaching a limiting magnitude of
. These data have
also been combined with data from the Two Micron All Sky Survey
(2MASS) survey allowing for a
better color-based object classification and target selection. The
Pre-Flames (PF) survey data meet the requirements of FLAMES, and
provide a good starting point for detailed studies of the examined
systems.
The images and catalogs presented here are publicly available and can be
requested from the URL address "http://www.eso.org/eis" .
Key words: techniques: image processing / astronomical data bases: miscellaneous
© ESO, 2001
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