<Catalog Name>
iraspsc | Point Source Catalog, Version 2.0
<Description>
The Infrared Astronomical Satellite (IRAS) surveyed 96% of the sky from
January 1983 through November 1983. The IRAS survey was conducted in four
wavelength bands centered at 12, 25, 60 and 100 microns. IRAS spent
approximately two-thirds of its 300 day mission performing an unbiased
survey of the sky. The IRAS survey led to the 1984 release of the IRAS
Point Source Catalog (PSC), which contains some 250,000 sources. The PSC,
along with other aspects of the IRAS mission, are explained in detail in
the Explanatory Supplement to the IRAS Catalogs and Atlases (1988).
The IRAS sky survey was designed to produce an extremely reliable catalog.
IRAS scanned the sky repeatedly by multiple detectors, and over half of the
sky was covered by more than twelve (12) individual detector scans per
wavelength band. The PSC was produced by detecting sources in each of the
individual detector scans, and then by applying a series of stringent
confirmation criteria to establish the reliability of the sources. The
process led to a reliability of the PSC which exceeds 99.997% over most of
the sky, excluding cirrus sources. However, the PSC reliability attainment
was at the cost of not reaching the full sensitivity attainable with the
IRAS data. The IRAS Faint Source Catalog (FSC) reaches about a magnitude
(2.5 times) fainter than the PSC by relaxing the reliability requirements
and gives improved flux densities for weaker PSC sources. Thus the FSC
should be consulted for sources that are below a few Jy.
A number of flags discussed below have values in each of the wavelength
bands. For compactness, these values are encoded into a single base-16
(Hex) digit (values 0-F). The four bits of that hex digit correspond to
the four wavelength bands with bit 0 (the Least Significant Bit) for 12
micron, bit 1 for 25 micron, bit 2 for 60 micron and bit 3 for 100 micron.
The presence of a flag in a band is denoted by setting its bit to 1. Thus
a source with a particular flag, for example, CONFUSE, set at 12 and 25
microns, would have CONFUSE=0011=3(Hex); while another source confused in
25, 60 and 100 microns would have CONFUSE=1110=E(Hex). A flag encoded in
this manner will be referred to as "hex-encoded by band."
<Contact>
Tom Chester, IPAC; tchester@ipac.caltech.edu
<Filename>
iraspsc.dsc
<Origin>
ADC CD-ROM Vol. 1, No. 1
(DATE) NOV-84
<Revised>
1988
<Columns>
77
<Rows>
245,889
<Time Period>
JAN-83 to NOV-83
<General>
1. COLUMN <pscname>
The IRAS Source Name is derived from its position by combining the hours,
minutes and tenths of minutes of right ascension and its sign, degrees and
minutes of declination. In obtaining the minutes of right ascension and
the declination for a source name, the positions are truncated. The
letters 'A,' 'B,' 'C,' etc., are appended to names of sources so close
together that they otherwise would have identical names. Names are
assigned uniquely both to catalog sources and to reject file sources.
Catalog sources receive letters first. The reference to the Point Source
Catalog (PSC) source is IRAS 12345-6789. The reference to the Point Source
Reject File source is IRAS R12345-6789.
Example (pscname) (char11): '12288+2811'
2. COLUMNS <ra> <dec> <cra> <cdec> <ra1950> <dec1950> <cra1950> <cdec1950>
<glat> <glon> <elat> <elon> <rah> <ram> <ras> <decsign> <decd>
<decm> <decs>
rah, ram, ras, decsign, decd, decm, decs, ra1950, dec1950, cra1950, and
cdec1950 are all given for the equinox 1950.0 and for the epoch 1983.5, while
ra, dec, cra, and cdec are for the equinox 2000.0 and the epoch 1983.5.
ra, dec, ra1950, and dec1950 are in decimal degrees. cra, cdec, cra1950, and
cdec1950 are in sexigesimal notation. rah, ram, ras, decsign, decd, decm,
and decs are the original equinox 1950.0, epoch 1983.5 sexigesimal coordinates
taken directly from the Point Source Catalogue. Both galactic and ecliptic
coordinates (glat, glon, elat, and elon) are in decimal degrees.
Example (ra) (real): 187.214
Example (dec) (real): 28.1997
Example (cra) (char8): '12 28 51.4'
example (cdec) (char9): '+28 11 59'
Example (ra1950) (real): 123.4669
Example (dec1950) (real): 30.6539
Example (cra1950) (char8): '053652.3'
example (cdec1950) (char9): '+303915.5'
Example (glat) (real): 85.4745
Example (glon) (real): 201.654
Example (elat) (real): 28.5266
Example (elon) (real): 174.351
Example (rah) (int): 23
Example (ram) (int): 56
Example (ras) (real): 45.8
Example (decsign) (char1): -
Example (decd) (int): 16
Example (decm) (int): 28
Example (decs) (int): 47
3. COLUMNS <fnu_12> <fnu_25> <fnu_60> <fnu_100>
Each of the four wavelength bands has a noncolor-corrected flux density
in Jansky units (1 Jy = 10**-26 Wm**-2 Hz**-1). The quality of each of
these flux densities is designated by the Flux Density Qualities, fqual.
For a description of the fquals, see below.)
The flux densities are calculated based upon the assumption that there is
an intrinsic source energy distribution such that the flux density fnu is
proportional to nu**-1. Corrections to other spectral shapes can be made
by consulting Section VI, "Flux Reconstruction and Calibration," subsection
C, of the Main Supplement.
Example (fnu_12) (real): 0.256
Example (fnu_25) (real): 0.25
Example (fnu_60) (real): 0.4832
Example (fnu_100) (real): 1
4. COLUMNS <fqual_12> <fqual_25> <fqual_60> <fqual_100>
A flux density measurement may be either of high quality (fqual = 3), of
moderate quality (fqual = 2), or of an upper limit (fqual = 1). There is
an fqual flag for each of the wavelength bands.
Example (fqual_12) (int): 1
Example (fqual_25) (int): 1
Example (fqual_60) (int): 3
Example (fqual_100) (int): 1
5. COLUMNS <major> <minor> <posang>
The uncertainty in the position of a source primarily depends upon a
source's brightness in the various wavelength bands and in the number of
sightings of a source. A final positional uncertainty is expressed as an
ellipse whose semi-major (major) and semi-minor (minor) axes are the 1
sigma errors given in seconds of arc (i.e., arc-seconds). The orientation
(posang) of the ellipse on the sky is expressed in terms of the angle
between the major axis of the ellipse and the local equatorial meridian.
The posang is expressed in degrees East of North.
Example (major) (int): 79
Example (minor) (int): 18
Example (posang) (int): 117
6. COLUMNS <relunc_12> <relunc_25> <relunc_60> <relunc_100>
Each flux density measurement (except for an upper limit) has an
associated uncertainty expressed as a 1-sigma value in units of 100 x
(delta) fnu / fnu.
Example (relunc_12) (int): 0
Example (relunc_25) (int): 0
Example (relunc_60) (int): 12
Example (relunc_100) (int): 0
7. COLUMNS <cirr1> <cirr2> <cirr3>
The infrared cirrus affects a large portion of the entire sky at 60 and 100
microns. Cirrus can seriously hamper efforts to extract point sources from
the data. Additionally, cirrus can also produce structure on a point
source scale that can masquerade as true point source.
The cirr1 flag gives the number of 100 micron-only sources in the
extraction data base within a radius of 30' from the source. The flag is a
good discriminant that warns a user that cirrus which contains structure on
a point source scale is present in a given region. Values above 2 signify
probable contamination.
The cirr2 flag gives the cirrus indication on a larger scale than the
cirr1 flag and compares a "cirrus flux" with the source flux at 100
micron. Values larger than ~4-5 indicate the presence of considerable
structure in the 100 micron emission on a 1/2 degree scale. A value of 0
indicates that no 1/2 degree data was available for the source in
question.
The cirr3 flag is the total surface brightness of the sky surrounding the
source in a 1/2 degree beam at 100 micron, clipped to exclude values
greater than 254 MJy sr**-1. Values of the cirr3 flag greater than 30 MJy
sr**-1 indicate emission from dust with an appreciable column level. A
value of -1 means that no data were available.
Example (cirr1) (int): 1
Example (cirr2) (int): 3
Example (cirr3) (int): 11
8. COLUMNS <confuse> <hsdflag> <pnearh> <pnearw>
A great deal of care went into trying to untangle instances of confusion
between neighboring sources. The confuse flag is set in a given band if
any instance of confusion is present in that band. Thus the confuse flag
is set if two (2) or more sightings of the source in a given wavelength
band has confusion status bits set indicating confusion in the
seconds-confirmation or in the band-merging processes. In parts of the sky
where the sources density is low, confusion processing is sometimes able to
separate sources that are very close together. The band-merging process
attempts to identify point sources that, for one reason or another, can be
confused with neighboring point sources in one or more bands. In either
case, the confuse flag is hex-encoded by band (see "Description" above for
details).
Regions of high source density receive special processing in order to
improve the reliability of the quoted sources. Each of these regions is
band-dependent. If a particular band of a given source goes through high
source density processing, the hsdflag flag sets the appropriate bit.
The hsdflag flag is hex-encoded by wavelength band (see "Description" above
for details).
The pnearh flag and the pnearw flag serve as other indicators of
possible confusion. The pnearh flag indicates the number of
hours-confirmed point sources located within a 4.5' cross-scan and 6'
in-scan (half-widths) window centered on the source. The pnearw flag
indicates the number of weeks-confirmed point sources located within a 4.5'
cross-scan and 6' in-scan (half-widths) window centered on the source.
Both flags give values larger than 9 as 9.
Example (confuse) (char1): '0'
Example (hsdflag) (char1): '0'
Example (pnearh) (int): 1
Example (pnearw) (int): 5
9. COLUMNS <nid> <idtype>
Much of the utility of the PSC comes from its association of infrared
objects with sources known to exist because of other astronomical catalogs.
Thus a large number of catalogs have been searched for positional matches.
The nid flag identifies the total number of matches found. Each match
results in a 64-character description which is placed in a separate
association file in order to conform to the FITS catalog format.
The idtype flag ranges from 1 to 15. When an association is found, the
idtype flag identifies the type of association as follows:
ASSOCIATION BIT ID
in extragalactic catalogs only (bit 0)
in stellar catalogs only (bit 1)
in catalogs with other types of objects (bit 2)
in catalogs with mixed types (bit 3)
Example (nid) (int): 0
Example (idtype) (int) (1 to 15): 0
10. COLUMNS <cc_12> <cc_25> <cc_60> <cc_100>
The heart of the point source detection processor is the comparison of the
data for candidate sources selected by the squarewave filter with the
profile, or template, expected for an ideal point source. The point source
correlation coefficient can have values between 87% and 100%. These are
encoded as alphabetic characters with A = 100, B = 99, . . . , N = 87.
There is one value per wavelength band. The quoted value for a band is for
the highest correlation coefficient seen for that source on any sighting.
Example (cc_12) (int): 0
Example (cc_25) (int): 0
Example (cc_60) (int): 96
Example (cc_100) (int): 94
11. COLUMNS <rat_12_25> <rat_25_60> <rat_60_100>
<err_12_25> <err_25_60> <err_60_100>
It is often the case that the parameter of interest for an infrared source
is not so much the absolute fluxes in the four bands but rather the ratios
of the fluxes in adjacent bands. This parameter is often directly related
to the temperature of the source. To aid in the process of identifying
sources with specific temperatures, computed fields have been added to the
database which are simply the flux ratios. Percent uncertainties are attached
to each "color" unless the flux ratio is an upper limit -- in which case, err
is set to "-1" -- or the flux ratio is a lower limit -- in which case, err is
set to "-2".
Example (RAT_12_25) (real): 0.440
Example (RAT_25_60) (real): 0.123
Example (RAT_60_100) (real): 0.533
Example (ERR_12_25) (real): -1.
Example (ERR_25_60) (real): -2.
Example (ERR_60_100) (real): 6.2
12. COLUMN <disc>
The disc flag indicates whether any one of the fluxes in a given
wavelength band disagrees with other fluxes in that same band. The flag is
hex-encoded by wavelength band (see "Description" above for details).
Example (disc) (char1): '0'
13. COLUMN <nhcon> <mhcon>
The nhcon flag indicates the number of hours-confirmed sightings, while
mhcon is the number of possible sightings. The WSDB gives a measurement
for each HCON.
Example (nhcon) (int): 2
Example (mhcon) (int): 3
14. COLUMNS <lrschar> <nlrs>
The low resolution spectrometer obtain 8 - 22 micron spectra of bright 12
and 25 micron sources. All of the LRS spectra are available in tape and
printed forms (Astronomy and Astrophysics Supplement, 65:607, 1986). The
nlrs flag gives the number of statistically meaningful spectra available
for a source. The lrschar flag gives a short characterization of the
nature of a spectrum. The first digit characterizes the overall shape of
the spectrum (main class) and the second digit gives quantitative information
on the dominant feature in the spectrum (subclass). For translation of the
character code, please see the text, section IX.D.
Example (lrschar) (char2): '22'
Example (nlrs) (int): 3
15. COLUMNS <ses1_12> <ses1_25> <ses1_60> <ses1_100> <ses2_12> <ses2_25>
<ses2_60> <ses2_100>
There are two types of small extended source counts, ses1 and ses2. Both
flags warn of the presence of structures larger than point sources. Thus
these two flags cast doubt on whether a reported source is truly point-like
or only part of a larger complex. There is a ses1 flag and a ses2 flag for
each wavelength band.
The ses1_12, ses1_25, ses1_60, and ses1_100 flags are the number of
seconds-confirmed, small extended source detections in a given band found
within a window centered on the source. The size of the window is 6'
in-scan by 4.5' cross=scan (half-widths). Values of any of the ses1s
greater than 1 should caution the reader that significant extended
structure may exist in the region and that the source in question may be a
point source-like piece of a complex field.
The ses2_12, ses2_25, ses2_60, and ses2_100 flags are the number of
weeks-confirmed, small extended sources in a given band located within a 6'
in-scan by 4.5' cross-scan (half-width) centered on the source. Values of
ses2s greater than 0 mean that the point source flux measurement should be
treated with caution as the source in question may, in fact, be extended.
The flux quoted in the catalog of small extended sources may provide a
better value for the source.
Example (ses1_12) (int): 6
Example (ses1_25) (int): 6
Example (ses1_60) (int): 8
Example (ses1_100) (int): 7
Example (ses2_12) (int): 7
Example (ses2_25) (int): 0
Example (ses2_60) (int): 1
Example (ses2_100) (int): 0
16. COLUMNS <tsnr_12> <tsnr_25> <tsnr_60> <tsnr_100>
The signal-to-noise ratio given for an individual hours-confirmed sighting
is the highest value of the detections comprising that sighting. The
values quoted in the catalog are ten (10) times the minimum of the
signal-to-noise ratios for the various sightings (HCONs) of the source. A
tsnr value is given for each of the wavelength bands that contain a high or
moderate quality measurement and for each band with a limit derived from a
nonseconds-confirmed detection. (NOTE: tsnr values greater than 30,000
are given as 30,000.)
Example (tsnr_12) (int): 230
Example (tsnr_25) (int): 58
Example (tsnr_60) (int): 424
Example (tsnr_100) (int): 62
17. COLUMN <var>
The var flag gives the percent variability (0 - 99) that a source is
variable based on an analysis of the 12 and 25 micron flux densities and on
their uncertainties. A value of "-1" indicates that the source has not
been examined for variability.
Example (var) (int) (-1 to 99): -1
18. COLUMNS <fcor_12> <fcor_25> <fcor_60> <fcor_100>
The most important difference between the first and second versions of the
IRAS Point Source Catalog (PSC-2 is the version used here) is the
application of a statistical correction to reduce the overestimation of the
flux densities of sources near the detection threshold; changes of as
much as a factor of two were made for some weak sources. The quantity listed
is actually the correction factor multiplied by 1000 to avoid very small
numbers.
Example (fcor_12) (int): 30
Example (fcor_25 (int): 500
Example (fcor_60) (int): 63
Example (fcor_100) (int): 1567
19. COLUMN <cntr>
The cntr flag is a sequential counter into the IPAC on-line data base.
The first record is 1 and the offset corresponds to the same ordering as in
the published catalog.
Example (cntr) (int): 91494
<References>
Beichman, C.A., Neugebauer, G., Habin, H.J., Clegg, P.E., and Chester, T.J.,
Infrared Astronomical Satellite (IRAS) Catalogs and Atlases Explanatory
Supplement, (1988).
<Additional information>