IRAS Explanatory Supplement
XII. Errata and Revisions as of 1987
A. Version 2.0 of the Point Source Catalog
Table of Contents | Index | Previous Section | Next Section
- The Flux Overestimation Correction
- Additional Flux Density Changes
- New and Deleted Sources
- Revised Completeness Estimates for Version 2.0
- Associations
- Source Names
- Revised Positional Uncertainties for Bright Sources
- Correction of Point Source Neighbor Counts
- Spurious 25 µm Only Sources
- Working Survey Data Base and Ancillary File
The most important difference between the first and second versions of the IRAS Point Source Catalog (hereafter denoted PSC-1 and PSC-2) is the application of a statistical correction to reduce the overestimation of the flux densities of sources near the detection threshold (see Section XI.J for a discussion of the effect); changes of as much as a factor of two were made for some weak sources.
A number of other, less significant changes were also made. Flux densities for almost all sources changed by a few percent due to refined calculations of certain calibration factors; a few sources changed by as much as 10%. Corrections to errors in some calibration and confused source processing algorithms resulted in the loss of 6 sources from and the addition of 56 new objects for a revised total of 245,889 individual sources in PSC-2. Table XII.A.5 lists 12 sources which were omitted from both PSC-1 and PSC-2 due to a software error, but which are of sufficient quality to be noted for completeness. A number of new catalogs were added to the list used for associations. Finally, a number of minor errors in calculations of some of the quantities associated with point sources, e.g. the number of neighboring sources, were corrected.
As described in
Chapter V,
sources were extracted from individual
detector streams by means of a zero-sum filter followed by a template
fit to the data. Only if the detection exceeded thresholds in
its signal to noise ratio (SNR) and in its correlation with the
template of a "perfect" point source was the detection
accepted for subsequent processing. A source was accepted into
the catalog if it had enough valid detections to confirm its existence
on time scales of seconds, hours and weeks. However, a failing
of this strategy (as described in more detail in
Section XI.J)
is that the flux density of weak sources is overestimated, since
the combination of weak source and positive-going noise (Gaussian
excursions or spikes due to radiation hits) resulted in a "valid"
detection, while the combination of a weak source and negative-going
noise (Gaussian excursions) forced the detection below the acceptable
thresholds. Thus, for weak sources, the detections used to form
the average flux density.
A.1 The Flux Overestimation Correction
Table XII.A.1
Status as March 1987
PRODUCT DESCRIPTION MEDIUM VERSION DATE
Explanatory Supplement Detailed description of hardware, data processing, and products Book 1.0 Nov. 1984
Revisions, New Chap XII, Index Book 2.0 Jun. 1987
Point Source Catalog (PSC-1) 245,839 point sources Tape, Microfiche 1.0 Nov. 1984
Tape 1.1 Jan. 1986
(PSC-1) 245,889 point sources Tape 2.0 Nov. 1986
(PSC-2). Updates described Book in this Chapter 2.0 Jun. 1987
Ancillary File More detailed information on point sources Tape 2.0 Nov. 1984
2.1 Jan. 1986
3.0 Nov. 1986
Working Survey Data Base More detailed information on point sources Tape 2.0 Nov. 1984
3.0 Feb. 1986
4.0 (PSC-2) Nov. 1986
High Source Density Bins Bins processed by high source density processor for Catalog Tape 1.0 Nov. 1984
Point Source Reject File 372,774 rejected point sources Tape available at IRAS data centers only
Reject File More detailed information on rejected point sources
Ancillary File
Reject File
Working Survey Data Base
LRS Spectra Catalog Spectra of 5,425 catalog point sources (8-22 µm). See XII.C Tape, Hard Copy 1.0 Nov.1984
Zodiacal History Time-ordered data at 0.5 degree resolution Tape 1.0 Nov. 1987
2.0 May 1986
All Sky Maps All sky images at 0.5 degree resolution Tape 1.0 Nov.1984
Sky Brightness images (HCON 3) 16° × 16°
2' ResolutionB/W, Color Negatives 1.0 Nov.1984
(Sept-Nov)a
B/W Negatives 2.0 May 1986
(Dec.1985)a
Tapes 2.0 May 1986
(Mar.1986)a
Sky Brightness Images (HCON 1) 16° × 16° field
2' ResolutionB/W Negatives 1.0 Aug.1985
(Feb-Apr)a
Tapes 1.0 Aug 1985
(May 1985)a
Sky Brightness Images (HCON 2) 16° × 16° field
2' ResolutionB/W Negatives 1.0 June 1986
(Apr 1986)a
Tapes 1.0 June 1986
Sky Brightness 16° × 16° field B/W Negatives
Images (Overlays)1.0 Nov. 1984
Galactic Plane Images (HCON 3) 2° × 15° field
2' resolutionB/W Negatives, Tapes 1.0 Jan. 1985
2.0 July 1986
Galactic Plane Images (HCON 1) 2° × 15° field
2' resolutionB/W Negatives, Tapes 1.0 Oct. 1985
Galactic Plane Images (HCON 2) 2° × 15° field
2' resolutionB/W Negatives, Tapes 1.0 Jul.1986
Cataloged Galaxies and Quasars 11,444 point sources associated with cataloged galaxies and quasars Book 1.0 Feb.1985
Pointed Observations 13,853 images with 0.25'-1.0 resolution, each covering ~ 1 square degree Tapes 1.0 Oct.1985
Pointed Observations User's Guide b Description of AO's, data reduction, and released grids Book 1.0 Nov.1985
Serendipitous Survey Explanatory Supplement c Description of Catalog Book 1.0 Dec.1986
Serendipitous Survey Catalog 43,866 point sources derived from the Additional Observations Tape, micro-fiche 1.0 Dec.1986
Small Scale Structure Catalog Explanatory Supplement Description of Catalog Book 1.0 Dec. 1985
Mar. 1987
Small Scale Structure Catalog 16,740 sources with sizes < 8' Tape, Microfiche 1.0 Dec. 1985
Book Mar. 1987
CPC Explanatory Supplement Detailed description of CPC hardware, data, processing, and products Book 1.0 Aug. 1985
CPC data Chopped photometric channel image data 3 tapes 1.0 Jan. 1986
IRAS Asteroid and Comet Survey IRAS and derived data on known asteroids Tape 1.0 Oct. 1986
IRAS Asteroid and Comet Survey Explanatory Supplement Description of Catalog and Summary Information Book 1.0 Oct. 1986
The most direct way of measuring the overestimation is to
compare the brightness of sources in PSC-1 with the values obtained
from the more sensitive pointed mode of the satellite
(Young
et al. 1985). Observations made in the pointed mode were three
to five times more sensitive than the scans making up the survey
so that the sources detected in the pointed mode would not suffer
from threshold effects at the same flux level. The Serendipitous
Source Catalog
(Kleinmann et al. 1987, hereafter denoted as the
SSC) is the catalog of sources extracted from selected pointed
mode observations and was used as a "truth table" to
determine the magnitude of the magnitude of the flux overestimation
effect and to help develop a correction for it.
Figures XII.A.1a-4a
show the ratio of SSC to PSC-1 flux densities for the four bands
as a function of SSC flux density; the presence of an overestimate
in the PSC-1 values below about 2 Jy is obvious.
 |
|
Figure XII.A.1 Ratio of SSC to PSC-1 (a) or PSC-2 (b) 12 µm flux
densities vs. SSC flux density before (a) and after (b) the correction
of the overestimation effect. larger largest |
A simple model for the overestimation described in Section XI.J leads to an algorithm for the correction of the effect. Consider a detector stream with an intrinsic Gaussian noise level (X) and a source with an intrinsic brightness of n(X). The zeroth moment of the Gaussian distribution above the threshold of m(x) for a source with true flux n(X) gives the probability of detection (Eqn. XI.J.1) and the first moment above m(X) gives the observed flux (Eqn. XI.J.2). These moments were used to relate the flux correction factor to the observed fraction of possible sightings for a given source.
The algorithm was implemented in the following manner. The Working Survey Data Base (WSDB) contains the number, N, of all accepted detections. If the total number of possible detections is denoted by M, then the ratio N/M is an estimate of the probability of detection, denoted by p, which can be used in Equation XI.J.1 to estimate the quantity n - m. This value can be used with Equation XI.J.3 to derive the ratio n'/n which is an estimate of the amount by which the true brightness of the source was overestimated in PSC-1.
For each source fainter than a certain, band-dependent level (2 Jy at 12, 25 and 60 µm and 3 Jy at 100 µm), the number of accepted detections, N, was determined from the WSDB. At the same time the total number of possible detections, M, was determined from a detailed calculation of the satellite's pointing history over the entire mission. If the source passed within the central portion of a working detector then a possible sighting was recorded. The central portion of the detector was defined by a distance in from the edge of the detector and was considered a free parameter, denoted by (X)Z, in each band; the value of this parameter affected the number of possible detections for a given source. The resultant value of N/M was used along with an estimate of the cutoff threshold, m, in that band to derive the correction factor as described above.
 |
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Figure XII.A.2 Ratio of SSC to PSC-1 (a) or PSC-2 (b) 25 µm flux
densities vs. SSC flux density before (a) and after (b) the correction
of the overestimation effect. larger largest |
The SSC data represented in Figure XII.A.1a-4a were assumed to give the true brightness for faint sources and were used to adjust the parameters (X)Z and m on a band by band basis to make the curves as flat as possible. The algorithm was applied only to those sources which were neither confused nor located in regions of high source density in a given band. Approximately 100,000 sources were adjusted in at least one wavelength. Values of (X)Z and m and the maximum derived correction factors are given in Table XII.A.2.
Table XII.A.2
Wavelength
(µm)m (X)Z
(')Max. Correction
12 4 0.2 1.72
25 2 0.1 3.00
60 3 0.7 2.01
100 3 1.0 2.38
 |
|
Figure XII.A.3 Ratio of SSC to PSC-1 (a) or PSC-2 (b) 60 µm flux
densities vs. SSC flux density before (a) and after (b) the correction
of the overestimation effect. larger largest |
The photometric uncertainty associated with each flux was also adjusted slightly by examining how uncertainties in the pointing of the telescope could affect the number of possible sightings. Variations in the N/M ratio were propagated through Eqn. XI.J.1 and XI.J.3 and the resulting uncertainty added in quadrature to the uncertainty already given in the catalog.
The above formalism obviously ignores many complications such as differing sensitivities among the detectors within a band and non-Gaussian noise sources like radiation hits and cirrus which could increase a source's flux on some occasions, but not others. Detections could have fallen below thresholds for any number of reasons including sightings by a detector of poor sensitivity or passage over the edge of a detector rather than over its center. A sighting could have been rejected for failing to exceed either the SNR or template thresholds. All of these effects were ignored in the above algorithm. As a result, although the corrections are quite good in a statistical sense, they may be considerably in error in any individual case.
 |
|
Figure XII.A.4 Ratio of SSC to PSC-1 (a) or PSC-2 (b) 100 µm flux
densities vs. SSC flux density before (a) and after (b) the correction
of the overestimation effect. larger largest |
Figure XII.A.5 shows the effect of the flux overestimation on the photometry for weak sources in PSC-1 and the effectiveness of the correction applied in the generation of PSC-2. The figure plots the 12/25 µm color of stars as a function of their 12 µm brightness. In Figure XII.A.5a the flux density ratio comes from PSC-1 and the 12 µm brightness from the SSC. Above about 2 Jy a distinct populationof stars with colors characteristic of hot (>3000 K) photospheres is apparent, but below 2 Jy the population of stars with photospheric colors disappears and all stars appear to have a 25 µm excess. This astrophysically puzzling result can be understood terms of the 25 µm flux being systematically overestimated for faint stars. The corrected colors from PSC-2 (Fig. XII.A.5.b) reveals a distinct population of stars with normal photospheres at faint levels.
As a result of this correction algorithm, the machine readable version of PSC-2 includes five new fields: MHCON, the number of possible hours confirmed sightings a source could have had and the four band dependent correction factors that were applied to the PSC-1 flux densities to produce the PSC-2 fluxes. These quantities are given only for those sources for which a flux overestimation correction was made. It should be noted that the value of MHCON for any given source could be uncertain by one or two sightings.
The format of the Catalog tape has been revised to incorporate these new quantities. Table XII.A.3 lists the changes to the original format (Table X.B.1).
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Figure XII.A.5 Ratio of 12 µm to 25 µm flux densities from the
PSC-1 (a) or PSC-2 (b) vs.12 µm flux density from the SSC before
(a) and after (b) the correction of the overestimation effect. larger largest |
Flux densities for all sources in the PSC-2 were adjusted by
a few percent to make them consistent with the final calibration
described in Chapter VI. The differences
arose because PSC-1 used
a preliminary version of the all-sky intensity maps to correct
for the non-linearities of the feedback resistor
(Section VI.A.5).
Also, as a result of this change, minimum upper limit fluxes are
now exactly 0.25, 0.25, 0.40, and 1.0 Jy, instead of varying by
a few percent from these values.
In two areas of the sky, from 0° to 29° ecliptic
longitude at -90° to 67° latitude and at 60° to 65°
latitude, flux densities reported in PSC-1 were factors
of 1.076, 1.099, 1.013, and 0.967 too high at 12, 25, 60 and 100
um, respectively. Approximately 1% of all sources were affected
by this error which has been corrected in PSC-2.
A number of effects changed the total number of point sources
present in PSC-2. First, six sources present in PSC-l were deleted
from PSC-2 because the small flux changes mentioned above pushed
the fluxes for these sources below a threshold used by the high
source density processor. Second, fiftysix sources were added
to PSC-2 because the very near neighbor window was set incorrectly
in parts of the production of PSC-l. Thus. the total number of
sources in PSC-2 is 245,889. The names of the changed sources
are given in
Table XII.A.4.
Finally, a software error, discovered after the release of
PSC-2, led to the exclusion of a small number of sources from
both PSC-1 and PSC-2. Examination of the Working Survey Data Base
(WSDB) led to the discovery of sources with similar fluxes located
within ± 30" in-scan and ± 90"
cross-scan of one another.
In each case only a single hours confirmed sighting was reported
for each object. Evidently, the weeks confirmation software failed
to confirm and merge these objects into a single source which
would then have appeared in the catalog.
A procedure was developed for finding these objects systematically
in the WSDB. First, the WSDB was searched for all sources with
only one hours confirmed sighting, located above an absolute galactic
latitude of 10° and above an ecliptic latitude of -80°
(to avoid the Large Magellanic Cloud). Second, sources detected
only at 25 µm or only at 100 µm were eliminated to avoid
contamination
by asteroids or cirrus. This sample was examined for objects
having companions within ± 30" in-scan and ± 90"
cross-scan. Those objects with nearby companions and meeting the
final catalog selection criteria
(Sections V.H.2 and
V.H.7) were
taking as real objects. A final position was derived by simply
averaging the position from each sighting; final flux densities
were computed by averaging the logarithms of the flux densities
without using any weights.
Forty-three objects were selected by this procedure. Examination
of the raw data led to the elimination of seven of these 43 as
being due to either cirrus or confused objects. Finally, to avoid
any problems of source reliability or flux overestimation only
sources with a flux density greater than 1 Jy in at least one
band were selected for inclusion in
Table XII.A.5. The format
of the table is similar to that of the printed version of the
catalog, as described in Section X.B.2.
It should be emphasized
that these sources appear only in the table and are not included
in the printed or machine readable versions of either PSC-1 or
PSC-2.
The completeness of PSC-2 was investigated in two different
ways. First, PSC-2 was internally checked through analysis of
the differential source counts. Second, PSC-2 was externally checked
against the SSC which is complete to significantly fainter flux
densities than PSC-2. Results from both methods corroborate the
general statements made in
Chapter VIII that the survey (PSC-1
or PSC-2) is complete, in unconfused regions of the sky, to 0.4,
0.5, 0.6 and 1.0 Jy at 12, 25, 60, and 100 µm.
PSC-1 and PSC-1 differ in the flux density level associated
with a given completeness level.
Figures XII.A.6a,b show the differential
log N/log S curves for 12 and 60 µm for PSC-1 and PSC-2 at high
Galactic latitudes covered with two sets of hours confirming scans.
Because of the correction for flux overestimation,
the peak of the curves is broader in PSC-2 than in PSC-1. The
shapes of the curves implies that PSC-2 has more weak sources
than PSC-1, but that those sources are very incompletely represented
e.g., ~10% completeness at 0.3 Jy at 12µm. At the same time, PSC-2
does not achieve a 90% completeness level until slightly higher
flux density than PSC-1.
Tables XII.6a,b summarize the flux densities at which a given
completeness is reached derived from the source counts in PSC-1
and PSC-2. Values are given for regions with both two or three
sets of hours confirming scans (2 or 3 HCONs). To the extent that
the flux overestimation algorithm was successful, the table for
PSC-2 reflects the true completeness of the IRAS survey as a function
of flux density. Note that while it is quite accurate to derive
the completeness from the logN/logS curves below completeness
levels of about 50%, it is difficult to derive accurate estimates
above that level. Thus the flux density values at completeness
levels of 90% and 95% are indicated in the tables as uncertain.
Table XII.A.3
(see Table X.B.1)
Byte Name Description Units Format
139 MHCON Possible number of HCONs --- I*2
141 FCOR Flux Correction Factors
Applied (x 1000)
(1 value per band) --- 4I*4
149 SPARE 3 Spare bytes --- 3A*1
A.2 Additional Flux Density Changes
A.3 New and Deleted Sources
Table XII.A.4
New Sources
01241-7332 05265-6840 08220-4404 18373-0918
04531-6708 05299-6830 08573-4718 19514+4306
04532-6710 05303-6951 09040-7402 21097+4953
04534-6657 05305-6952 09101-5100 21099+4954
05044-7012 05341-6632 09179-7034 21314+5805
05046-7014 05371-6944 09215-7028 21329+5126
05122-6829 05374-6946 09437-6034 21345+5706
05150-6629 05375-6650 10075-5747 21445+5653
05150-6631 05392-6847 10075-5824 21446+5655
05207-6636 05393-6930 10182-5742 21478+5649
05236-6702 05448-6720 12376-6122 22126+6905
05239-6939 05486-7001 13191-6245 22299+6440
05242-6940 08003-5012 18092+4419 22510+7138
05264-6730 08005-5013 18285-0830 22512+7140
Deleted Sources
04526-6951 13046-6222 20250+4316 21503+5105
04538-6952 15574-0052
Table XII.A.5
Name Gal Coord Flux Density in Janskys
(Not Color-Corrected) N C Association MAG
HHMMT DDMM (s) (") 1 b NH 12µm 25µm 60µm 100µm C P S I A Name & Type
00125-0723 33.5 10 98-68 2 .25L .44L 1.46 4.62 0 1 10 M+04-28-050 999
11434+2042 26.3 50 234+74 2 .25L .46: 3.19: 6.45 1 2 10 U07772 103
12337+2616 47.4 51 230+86 2 .52: .53 4.50 23.31 0 1 7 6 9 D0 20951 1
21492+3716 13.4 1 88-12 2 .36: .25L .48 2.95 15 4 1 2 3746 K0 67
22261+8025 9.1 59 117+20 2 1.01 .28L .40L 1.63L 7 1 13 52130 K0 77
22308+4105 50.3 26 97-14 2 2.05 .54 .40L 6.60L 3 2 13 MKN 914 999
22324+4024 28.4 35 97-15 2 4.43 18.49 29.10 64.39 12 2 27 X2232+408 4
22325+4054 32.0 25 97-15 2 .25L .26L 1.08 7.01 8 1 4 1 32 DG 187 999
22326+4031 37.8 9 97-15 2 .41L .25L 1.10 7.33L 9 1 23
22376+2426 36.8 3 89-29 2 .29L .25L 1.05 2.68 0
23019+3405 57.7 32 99-23 2 .25L .25L 1.45 2.50 0
23132+2449 14.4 12 97-33 2 .25L .25L .48 1.35 4 3 9 U12460 155
A.4 Revised Completeness Estimates for PSC-2
 |
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Figure XII.A.6 a) The differential sources counts versus 12 µm
flux density for PSC-1 (dashed line) and PSC-2 (solid line). b) The differential source counts versus 60 µm
flux density for PSC-1 (dashed line) and PSC-2 (solid line). larger largest |
The second way to evaluate the completeness of the survey
is to use the SSC, which, as discussed above, reaches three to
five times fainter than the survey. A comparison was made of
all SSC sources at Galactic latitudes (X) > 30° and
(X)
As a check on the consistency of these two approaches and
on the agreement of the results in the 2 and 3 HCON sky areas,
all the above numbers can be converted to an estimate of the completeness
of a single HCON and plotted on the same graph. To do so, recall
from Chapter VII that in terms of the single HCON completeness
C (= 1 - p), the completeness of the PSC in the 2 HCON is
C2 and in the 3 HCON sky is C2(3 - 2C).
Figures XII.A.7a,b show the single HCON completeness at 12
and 60 µm. There is good agreement between the logN/logS
and the SSC vs PSC-2 results. In addition, the numbers from the 2
HCON sky and the 3 HCON sky are also consistent. However, the
12 µm results are significantly different from the results shown
in
Figure VIII.D.1 derived from sources in the minisurvey. Because
those sources were in the 7 HCON sky, they suffered tremendously
from the effects of flux overestimation. This results in a shift
of the minisurvey completeness curves to erroneously higher flux
densities.
Table XII.A.8 summarizes the Catalog completeness at
12 and 60 µm as derived from the curves shown in
Figure XII.A.6a,b.
Table XII.A.6a
Flux Density (Jy)
Completeness 2 HCON sky 3 HCON sky
(%) 12 µm 60µm 12 µm 60
µm
95 [.42]* [.59] [.38] [.52]
90 [.40] [.56] [.36] [.50]
50 .33 .47 .32 .44
10 .29 .40 .29 .39
5 .28 .37 .28 .38
* Numbers in brackets are uncertain
Table XII.A.6b
Flux Density (Jy)
Completeness 2 HCON sky 3 HCON sky
(%) 12 µm 60µm 12 µm 60
µm
95 [.47]* [.60] [.46] [.60]
90 [.44] [.59] [.44] [.57]
50 .35 .48 .30 .45
10 .24 .38 .23 .33
5 .22 .34 .22 .30
* Numbers in brackets are uncertain
-50° (to avoid the Magellanic Clouds).
The SSC sources were divided into stars [fv(12µm)
> fv(25µm) and fv(12µm)
> fv(60µm)] and galaxies
[fv(12µm) < fv(60µm)], in
order to isolate the 12 and 60 µm bands as much as possible. A search
radius of 120" was used to find counterparts in PSC-2.
Tables XII.A.7a,b summarize the
completeness derived from the percentage of SSC sources that were found in
PSC-2 for both the 2 and 3 HCON sky at 12 and 60 µm. Given in
the table are the number of actual objects in PSC-2 (denoted N')
compared with the possible number of objects (denoted M') found
in the more complete SSC.
Table XII.A.7a
Flux density (Jy) 2 HCON sky 3 HCON sky
N' M' Completeness N' M' Completeness
0.50-0.55 6 6 1.00 16 16 1.00
0.45-0.50 4 5 .80 18 18 1.00
0.40-0.45 13 15 .87 17 17 1.00
0.35-0.40 7 11 .64 15 15 1.00
0.30-0.35 8 17 .47 15 23 .65
0.25-0.30 6 24 .25 24 39 .62
0.20-0.25 3 26 .12 4 50 .08
 |
|
Figure XII.A.7 a) The single HCON completeness versus 12 µm flux
density. A smooth solid line has been drawn through the data.
The other solid line is from the 2 HCON SSC results, the dashed
line from the 3 HCON SSC results, the solid points from the 2
HCON logN/logS results, and the open points from the 3 HCON
logN/logS results. Uncertain points are in parentheses. larger largest |
 |
|
b) The single HCON completeness versus 60 µm flux
density. The smooth solid line has been drawn through the data.
The other solid line is from the 2 HCON SSC results, the dashed
line from the 3 HCON SSC results, the solid points from the 2
HCON logN/logS results, and the open points from the 3 HCON
logN/logS results. Uncertain points are in parentheses. larger largest |
The PSC-2 contains associations with sources in four additional
catalogs not used in the preparation of PSC-1: the IRAS Small
Structure Catalog, the IRAS Serendipitous Survey Catalog, the
OSU catalog of radio sources and the Michigan Spectral Catalog.
Parameters for these new catalogs are given in revised versions
of
Tables V.H.1 and
X.B.4. These catalogs were added at the end
of the queue for the printing priority in the printed version
of the PSC. However, in the printed version of PSC-2, an asterisk
in the column giving the number of associations (NID) denotes
an association of a PSC-2 source with an object in the Serendipitous
Survey Catalog.
There was an error in associating PSC-1 sources with stars
in the Gliese catalog since the proper motion in right ascension
was erroneously taken as seconds of arc per year instead of seconds
of time per year. Remedying this error resulted in the addition
of 37 associations in PSC-2 and the deletion of five associations
originally presented in PSC-1. The changed associations are given
in
Table XII.A.9.
The ESO/Uppsala Catalog, catalog 14, was previously given
a "multiple" classification instead of "other".
This has been corrected in PSC-2.
Source names were derived from the equatorial position by
taking the hours, minutes and tenths of minutes (truncated, not
rounded) of right ascension as well as the sign, degrees, and minutes
of declination. For example a source at (X) = 12h 32m 15.5s and
(X) = -15° 20' 15" has the name 12222-1520. Separate sources
which would have been given the same name based on the above scheme
were distinguished from one another by appending letters of the
alphabet to their
name. It should be noted that since sources were named before
the decision to retain them in the catalog was made, it is possible
that not all of the sources with names distinguished only by a
letter will be present in the Catalog, e.g. 12222-1520B might
be in the catalog, but not 1222-1520A.
As described in the
Section VII.C.1.b, an additional 3"
was supposed to be added in quadrature to the in-scan uncertainty
of sources that were both faint and had the minimum possible (1")
in-scan uncertainty. That correction was inadvertently applied
in PSC-1 to all sources, faint and bright, with the minimum uncertainty.
PSC-2 corrects this problem and has 84,287 sources with this
increased uncertainty, as opposed to 144,403 sources in PSC-1.
The minimum uncertainty ellipse is now 3" × 5", as
opposed to 3" × 7".
In PSC-1 the counts of hours and weeks confirmed neighbors,
denoted PNEARH and PNEARW, of a given source are in error for
objects near which a forced weeks confirmation took place
(Section
V.H.3). This problem has been fixed for PSC-2.
The following three sources have been found to be spurious
on the basis of examination of co-added detector data, but were
left in the catalog since no general rule could be used to delete
them. They are: 05570-6722, 08291-6146, and 18021+6556. The first
and third sources were produced by noise and radiation hits; the
second resulted just from noise.
The version of the WSDB corresponding to PSC-2 is 4.0 (Nov.
1986) and differs from 3.0 only in the revised number of sources
in the catalog described above (56 additions, 6 deletions). Version
3.0 (Feb. 1986) corrected a calibration error in the flux densities
of individual HCON sightings. Version 2.0 was the first publicly
released version of the WSDB.
Two errors were remedied in Version 3.0 of the Ancillary
file. First, the "fault" byte in HSDDROC (see
Table
X.B.7c) was incorrect for a small number of sources due to the
incorrect very near neighbor window. This is now corrected. Second,
the first publicly released version of the Ancillary File (version
2.0) contained associations with the weeks-confirmed file for
the Small Scale Structure Catalog: only about half of these weeks-confirmed
sources survived to the final SSS catalog. The hex coding of the
bands in which an extended source was detected
was calculated incorrectly. These problems have been fixed in
version 3.0 of the Ancillary File.
Listings of point sources that failed the catalog selection
criteria, e.g., confusion or insufficient number of HCONs, were
not publicly released, but are available from the IRAS data center
in Pasadena.
Table XII.A.8
Completeness 2 HCON sky 3 HCON sky
(%) 12 µm 60 µm 12 µm 60 µm
95 .46 .65 .41 .58
90 .45 .64 .38 .56
75 .41 .59 .34 .51
50 .35 .52 .29 .45
25 .29 .45 .25 .38
10 .25 .38 .23 .32
5 .23 .34 .22 .30
A.5 Associations
Table XII.A.9
Newly Associated Sources
00027-3737 01365-1812 06562-44l3 16451-4737
00156+4344 01416-1611 08053+6952 16564+4726
00176-6509 01504-2240 11027+4347 17023-0459
00235-773l 02085-5103 13275+l038 20017+2312
00295+6657 02334+0639 13432+1508 20542-4419
00348-2502 03168-6245 13469-2151 21141-3904
00461+5732 03172-6241 14006-4634 21598-5700
00589+7124 03180-4315 14260-6227 22070-0452
01051+5439 05100-4502 14359-6031 23029-3607
23110+5653
Sources No Longer Associated
07483+8023 08355-3958 16267+1831 19145+0505
21362-2732
The following minor changes exist in the associations with
all catalogs for sources in the area bounded by ecliptic longitude
260° - 280° and ecliptic latitude -60° to 60°.
The truncation error mentioned in
Supplement XI.K.10
has been fixed. One new association with the catalog of Suspected
Variables, catalog 16, was made exactly at the maximum 90"
radius allowed (source 18237-2417). The latest version (1984)
of the SAO catalog was used in the generation of PSC-2; six new
associations were made and eight old associations were lost. These
sources are given in
Table XII.A.10. All 14 of these associations
were at the maximum radius allowed.
Table XII.A.1O
Newly Associated Sources
17167-3229 17370-3843 18311-1734 18402-7755
17326-3324 17510-3726
Sources No Longer Associated
16516-6705 17337-0220 17458-0937 17555+3324
17236-2125 17394+2611 17519-3035 17557+3351
A.6 Source Names
A.7 Revised Positional Uncertainties for Bright Sources
A.8 Correction of Point Source Neighbor Counts
A.9. Spurious 25 µm Only Sources
A.10 Working Survey Data Base, Ancillary File and Reject Files
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