|
Description
This table contains the Cosmic Background Explorer (COBE) Diffuse Infrared Background Experiment (DIRBE) Point Source Catalog, an all-sky catalog containing infrared photometry in 10 bands from 1.25 microns to 240 microns for 11,788 of the brightest near and mid-infrared point sources in the sky. Since DIRBE had excellent temporal coverage (100-1900 independent measurements per object during the 10 month cryogenic mission in 1989 to 1990), the catalog also contains information about variability at each wavelength, including amplitudes of variation observed during the mission. Since the DIRBE spatial resolution is relatively poor (0.7 degrees), the authors carefully investigated the question of confusion, and flagged sources with infrared-bright companions within the DIRBE beam. In addition, they filtered the DIRBE light curves for data points affected by companions outside of the main DIRBE beam but within the `sky' portion of the scan. At high Galactic latitudes (|b| > 5 degrees), the catalog contains essentially all of the unconfused sources with flux densities greater than 90, 60, 60, 50, 90, and 165 Jy at 1.25, 2.2, 3.5, 4.9, 12, and 25 microns, respectively, corresponding to magnitude limits of approximately 3.1, 2.6, 1.7, 1.3, -1.3, and -3.5. At longer wavelengths and in the Galactic Plane, the completeness is less certain because of the large DIRBE beam and possible contributions from extended emission. For each source, for comparison, the names of the sources in other catalogs, their spectral types, variability types, IRAS and 2MASS photometry, SIMBAD spectral types and published variability types, and whether or not the sources are known OH/IR stars are also included. Unlike the IRAS and 2MASS Catalogs, the DIRBE Point Source Catalog was not constructed by searching the DIRBE database with a point source template and extracting sources based on S/N and confirmation criteria. The DIRBE Catalog was constructed using a target sample list obtained from other infrared catalogs. Since DIRBE is much less sensitive per scan than IRAS or 2MASS, essentially all of the point sources with high S/N light curves in the DIRBE database are already contained in IRAS, 2MASS, and/or MSX. Thus, for simplicity, the authors used these previous catalogs to select a sample for the DIRBE Point Source Catalog. Their initial sample included a total of 21,335 sources; the final catalog contains 11,788 sources. The initial sample was selected from the IRAS Point Source Catalog (1988), the 2MASS Point Source Catalog (Cutri 2003), and/or the MSX Point Source Catalog Version 1.2 (Egan et al. 1999, A&A, 349, 236) that satisfied at least one of the following criteria: (a) 2MASS J magnitude <= 4.51 (F<sub>1.25</sub> >= 25 Jy), (b) 2MASS K magnitude <= 3.81 (F<sub>2.2</sub> >= 20 Jy), (c) IRAS or MSX F<sub>12</sub> >= 15 Jy, or (d) IRAS or MSX F<sub>25</sub> >= 27.5 Jy. The 1.25 and 2.2 micron limits are equal to the average 1-sigma sensitivity per scan in the raw DIRBE light curves of Smith et al. (2002, AJ, 123, 948), while the 12 and 25 micron limits are 0.5 times the average noise levels per scan in that study. These low limits were selected in order to avoid missing variable stars that may have been faint during the 2MASS, IRAS, or MSX mission and to improve the completeness at 3.5 and 4.9 micron. Since the filtering process improves the average per measurement uncertainty, a sensitive selection criterion is warranted to include as many sources as possible. There were 7872 sources with 2MASS J <= 4.51, 20,492 sources with 2MASS K <= 3.81, 4969 sources with IRAS F12 >= 15 Jy, 40 sources in the MSX IRAS Gaps survey with MSX F12 >= 15 Jy, 2753 sources with IRAS F25 >= 27.5 Jy, and 18 sources in the MSX IRAS Gaps survey with MSX F25 >= 27.5 Jy. Thus, the initial list is dominated by stars selected by the 2MASS criteria. These lists were merged together to make a single target list, containing 21,335 sources. To merge the 2MASS and IRAS/MSX lists, the authors used a 60 arcsecond matching radius. If more than one 2MASS source was within 60 arcseconds of the IRAS position, they assumed that the brightest K band source was the match. Note that the authors did not include sources in their input list based on their 60 and/or 100 micron IRAS flux densities, as extended emission from cirrus becomes more significant at these wavelengths. This means that the DIRBE Point Source Catalog is biased against very cold objects, such as galaxies and molecular clouds. Since the authors only used the point source catalogs of 2MASS, IRAS, and MSX for source selection, their sample is also biased against extended objects. Note also that they are only targeting sources bright enough to detect their possible variability in the DIRBE database (i.e., sources that may be detected in a single DIRBE scan at at least one DIRBE wavelength). By co-adding the full light curves, it may be possible to detect fainter objects in the DIRBE database, but without variability information and with a higher likelihood of confusion. The COBE DIRBE Point Source Catalog as presented here contains the time-averaged DIRBE flux densities F<sub>nu</sub> in the 10 DIRBE bands for all 11,785 sources in the initial list that had a flux at minimum in the weekly averaged light curve in any of the six shortest DIRBE wavelengths greater than 3 times the average noise per data point, plus three additional sources (see Section 6 of the reference paper). These flux densities were calculated after filtering the light curves. The name of the object in the catalog from which it was originally selected from is also given (IRAS/MSX and/or 2MASS). This table was created by the HEASARC in April 2012 based on <a href="https://cdsarc.cds.unistra.fr/ftp/cats/J/ApJS/154/673">CDS Catalog J/ApJS/154/673</a> files table1.dat, table4.dat and table8.dat, and contains the DIRBE data for 11,788 of the brightest near- and mid-infrared point sources in the sky together with supporting data from 2MASS, IRAS, MSX and other catalogs. This is a service provided by NASA HEASARC .
|
