J/AJ/134/2099 Variability of point sources in infrared (Robitaille+, 2007)
Infrared point-source variability between the Spitzer and Midcourse Space
Experiment surveys of the Galactic midplane.
Robitaille T.P., Cohen M., Whitney B.A., Meade M., Babler B.,
Indebetouw R., Churchwell E.
<Astron. J., 134, 2099-2112 (2007)>
=2007AJ....134.2099R 2007AJ....134.2099R (SIMBAD/NED BibCode)
ADC_Keywords: Surveys ; Infrared sources ; Stars, variable ;
Photometry, infrared
Keywords: infrared: stars - stars: variables: other - surveys
Abstract:
We present a list of 552 sources with suspected variability, based on
a comparison of mid-infrared photometry from the GLIMPSE I and
Midcourse Space Experiment (MSX) surveys, which were carried out
nearly a decade apart. We were careful to address issues such as the
difference in resolution and sensitivity between the two surveys, as
well as the differences in the spectral responses of the instruments.
We selected only sources where the IRAC 8.0um and MSX 8.28um fluxes
differ by more than a factor of 2, in order to minimize contamination
from sources where the difference in fluxes at 8um is due to a strong
10um silicate feature. We present a subset of 40 sources for which
additional evidence suggests variability, using 2MASS and MIPSGAL
data. Based on a comparison with the variability flags in the IRAS and
MSX point-source catalogs we estimate that at least a quarter of the
552 sources and at least half of the 40 sources in the subset are
truly variable. In addition, we tentatively confirm the variability of
one source using multiepoch IRAS LRS spectra. We suggest that most of
the sources in our list are likely to be asymptotic giant branch
stars.
Description:
In order to search for point-source variability, we made use of the
following data:
* The MSX survey of the Galactic plane (Price et al.,
2001AJ....121.2819P 2001AJ....121.2819P, Cat. V/114), which was carried out between 1996
and 1997 and consisted of imaging in four bands: A (8.28um),
C (12.13um), D (14.65um), and E (21.3um).
* The Two Micron All Sky Survey (2MASS; Skrutskie et al., 2006, Cat.
VII/233), which was carried out between 1997 and 2001. The
observations consist of imaging in three bands: J (1.25um),
H (1.65um), and Ks (2.15um).
* The GLIMPSE I survey of the Galactic midplane (Benjamin et al.,
2003PASP..115..953B 2003PASP..115..953B, see Cat. II/293), which was carried out in
2004 at 3.6, 4.5, 5.8, and 8.0um using the IRAC instrument on
board Spitzer.
* The MIPSGAL survey of the same region as GLIMPSE I, carried out in
2005 and 2006 at 24, 70, and 160um using the MIPS instrument on board
Spitzer. We make use only of the data taken at 24um.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 150 552 The sample of 552 sources with apparent
variability at 8 microns
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See also:
V/114 : MSX6C Infrared Point Source Catalog (Egan+ 2003)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 17 A17 --- MSX MSX source name (GLLL.llll+BB.bbbb)
19- 25 A7 --- --- [SSTGLMC]
27- 43 A17 --- SSTGLMC GLIMPSE source name (GLLL.llll+BB.bbbb)
45- 53 F9.5 deg RAdeg Right Ascension in decimal degrees (J2000)
55- 63 F9.5 deg DEdeg Declination in decimal degrees (J2000)
65- 70 F6.1 mJy FJ ? 2MASS J band flux density (1)
72- 77 F6.1 mJy FH ? 2MASS H band flux density (1)
79- 84 F6.1 mJy FKs ? 2MASS Ks band flux density (1)
86- 90 F5.1 mJy F3.6 ? Spitzer/IRAC 3.6 micron band flux density (1)
92- 96 F5.1 mJy F4.5 ? Spitzer/IRAC 4.5 micron band flux density (1)
98-103 F6.1 mJy F5.8 Spitzer/IRAC 5.8 micron band flux density (1)
105-110 F6.1 mJy F8.0 Spitzer/IRAC 8.0 micron band flux density (1)
112-117 F6.1 mJy F8.3 MSX 8.28 micron band flux density (1)
119-124 F6.1 mJy F12 ? MSX 12.13 micron band flux density (1)
126-131 F6.1 mJy F15 ? MSX 14.65 micron band flux density (1)
133-138 F6.1 mJy F21 ? MSX 21.3 micron band flux density (1)
140-145 F6.1 mJy F24 ? Spitzer/MIPS 24 micron band flux density (1)
147 I1 --- Mvar [0/4] Sum of MSX point source catalog
variability flags in all bands (2)
149-150 I2 % Ivar ? IRAS variability likelihood
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Note (1): The uncertainties are not shown for clarity. However, these are
bright sources at mid-IR wavelengths in the Spitzer data, and
therefore the uncertainties are very low in IRAC and MIPS 24 microns.
In fact, the main source of uncertainty at IRAC and MIPS 24 microns
wavelengths are likely to be the calibration uncertainties. For MSX
data, one of the requirements used in Section 3.3 was the uncertainty
at 8.28 microns should be less than 10%. For the JHK and MSX errors we
refer the reader to the original catalogs. The IRAC 8 micron flux
calculated from the smoothed mosaics is not shown, but for sources to
be in this list we required the original IRAC 8 micron flux to agree
with our calculated IRAC 8 micron flux from smoothed mosaics by less
than 20%. Finally, we note that this table does not show all fluxes
present in the original MSX Catalog (i.e. fluxes have been removed
when a source was not seen, or seen with a very low signal-to-noise,
in the images).
Note (2): Each variability flag is set to 1 when the variation of the
measurements over the mission exceeds the 3σ limit.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Patricia Vannier [CDS] 07-Feb-2010