J/ApJ/523/248 Variable stars in the Galactic center (Ott+, 1999)
Variable and embedded stars in the Galactic center.
Ott T., Eckart A., Genzel R.
<Astrophys. J. 523, 248 (1999)>
=1999ApJ...523..248O 1999ApJ...523..248O
ADC_Keywords: Binaries, eclipsing ; Stars, variable ; Polarization ;
Photometry, infrared
Keywords: binaries: eclipsing - Galaxy: center - polarization -
stars: variables: other (long-period variables)
Abstract:
We report results of a time series analysis of high-resolution K-band
imaging, photometry, and polarimetry of stars in the Galactic center
cluster covering 7 consecutive years. In our statistical sample with
mK<13, about half of the stars show indication of variability
consistent with most of them being long-period variable, asymptotic
giant branch stars. Some long-period variables already proposed in the
literature are confirmed. They are identified with asymptotic giant
branch stars. For the first time we show that the bright He I source
IRS 16SW is a short-period variable with a period of ∼9.72 days. It is
most likely an eclipsing binary with a lower mass limit of
≥100M☉. This confirms previous modeling of characteristics of
the near-infrared spectra, which also indicated that IRS 16SW is a
massive, young hot star. We also present the results of a polarization
survey covering the central parsec of the Galaxy. Stars whose
polarization vectors differ from the overall polarization, which is
parallel to the Galactic plane, are mostly situated in the
"minispiral", a region of high thermal flux density at centimeter
radio wavelengths. Some of these sources appear extended in the
high-resolution images and have featureless red spectra. We interpret
these objects as young stars that may have just recently been formed
and are still embedded in a dust shell.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 57 41 Polarization of individual sources
table2.dat 51 218 Photometry of sources brighter than mK=13
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name Object name
15- 18 F4.2 % p Degree of polarization
20- 22 I3 deg q Position angle of polarization vector
24- 27 F4.2 % e_p rms uncertainty on p (1)
29- 30 I2 deg e_q rms uncertainty on q (1)
32- 36 F5.2 mag Kmag K magnitude
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Note (1): The standard errors of e_p=1.9% for the degree of polarization
and e_q=18° for the position angle are the mean of standard
deviations of all 27 sources that were contained in more than one
pointing. These values have been adopted for sources that could only
be measured in a single mosaic pointing as a save upper value.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- [OEG99] Sequential number
5- 18 A14 --- Name Object name
20- 24 F5.2 arcsec oRA Offset in right ascension (1)
26- 31 F6.2 arcsec oDE Offset in declination (1)
33- 37 F5.2 mag Kmag K magnitude
39- 42 F4.2 mag e_Kmag rms uncertainty on Kmag
44- 50 F7.2 --- Chi2 Χ2 value (2)
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Note (1): The offset is given relative to IRS 7 in arcseconds and is
positive for north and east. Typical residual errors on the distances
are ±0.1" (1σ).
Note (2): Χ2 value is a reliable measure of variability of the sources.
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History: From ApJ electronic version
(End) James Marcout, Patricia Bauer [CDS] 08-Nov-1999