Issue |
A&A
Volume 433, Number 1, April I 2005
|
|
---|---|---|
Page(s) | 117 - 125 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20041748 | |
Published online | 14 March 2005 |
L- and M-band imaging observations of the Galactic Center region*,**
1
I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany e-mail: viehmann@ph1.uni-koeln.de
2
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
Received:
28
July
2004
Accepted:
16
November
2004
In this paper we present near-infrared H-, K-, L- and M-band photometry
of the Galactic Center from images obtained at the ESO VLT in May and August
2002, using the NAOS/CONICA (H and K) and the ISAAC (L and M)
instruments.
The large field of view (70´´ 70´´) of the ISAAC instrument and
the large number of sources identified (
data for a total of 541 sources)
allows us to investigate their colors, infrared excesses and the extended dust
emission.
Our new L-band magnitude calibration reveals an important offset to the
traditionally used “standard” calibrations, which we attribute to the use of
the variable star IRS 7 as a flux calibrator.
Together with new results on the extinction towards the Galactic Center
[CITE], our magnitude calibration results in stellar
color properties expected from standard stars and removes any necessity to
modify the K-band extinction.
The large number of sources for which we have obtained
colors allows us to
measure the M-band extinction to AM = (0.056 ± 0.006)AV, i.e.
, a considerably higher value than what has so far been assumed.
color data has not been investigated previously, due to lack of useful
M-band data. We find that this color is a useful diagnostic tool for the
preliminary identification of stellar types, since hot and cool stars show a
fairly clear
color separation, with average
colors of 0.46 ± 0.17
for emission-line stars and -0.05 ± 0.27 for cool red giants/AGB stars.
This is especially important if visual colors are not available, as in the
Galactic Center.
For one of the most prominent dust embedded sources, IRS 3, we find extended L- and M-band continuum emission with a characteristic bow-shock shape. An
explanation for this unusual appearance is that IRS 3 consists of a massive,
hot, young mass-losing star surrounded by an optically thick, extended dust
shell, which is pushed northwest by wind from the direction of the IRS 16
cluster and Sgr A*.
Key words: Galaxy center / infrared: stars / techniques: photometric / stars: imaging
© ESO, 2005
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