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TEXAS - Texas Survey of Radio Sources at 365 MHz |
HEASARC Archive |
Overview
This catalog is from the Texas Survey of discrete radio sources between -35.5 degrees and +71.5 degrees declination (B1950), which was carried out at a frequency of 365 MHz (82 cm wavelength) with the Texas Interferometer during the period from 1974 to 1983. The Survey lists accurate positions with internal errors of about an arcsecond, flux densities (which for strong point sources have internal errors of about 1% and total errors of about 5%), simple structure models and indications of spectrum and variability for 66841 sources. Results of comparisons with other data show that the Survey is 90% complete at 0.4 Jy and 80% complete at 0.25 Jy, is nearly free from spurious sources, and has a lobeshift incidence which is reasonably described by quality flags associated with each source.The University of Texas Radio Astronomy Observatory (UTRAO) carried out, with the Texas Interferometer, this 365 MHz survey of the sky, which was intended to be complete to a flux density level of 0.25 Jy, to provide positions with an accuracy of about 1 arcsec in both coordinates, to give accurate flux densities and indication of source variability, and to give rough structure models for each source. The observations began in 1974 and were completed in 1983. A preliminary version of one declination strip was published (Douglas et al., Publ. Dept. Astron. Univ. Texas, No. 17, Oct. 1980), and a number of intermediate versions of the survey were privately circulated for various purposes, pending completion of the final analysis and adjustment of the data.
Catalog Bibcode
1996AJ....111.1945DReferences
The Texas survey of radio sources covering -35.5{deg} < {delta} < 71.5{deg}
at 365MHz
Douglas J.N., Bash F.N., Bozyan F.A., Torrence G.W., Wolfe C.
<Astron. J. 111, 1945 (1996)>
=1996AJ....111.1945D
Provenance
This database was created by the HEASARC in February 2001, based on CDS/ADC catalog VIII/42.Parameters
Strip
A code letter corresponding to the declination strip from which the
particular entry was taken. The survey observations were carried out in ten
overlapping declination strips. Each strip was surveyed for four observing
cycles, at two or three frequencies. The catalog was originally decomposed
into 10 tables, (3a to 3j), on the AAS CD-Rom accompanying the published
version of this catalog, corresponding to the 10 declination strips, and the
code letters A to J correspond to these:
Strip Range of Declination
A -26 [-35.7,-18.7]
B -12 [-18.6,-06.4]
C -01 [-06.3,+03.9]
D +09 [+04.0,+13.5]
E +18 [+13.6,+22.6]
F +27 [+22.7,+31.6]
G +36 [+31.7,+40.6]
H +45 [+40.7,+49.9]
I +55 [+50.0,+59.8]
J +65 [+59.9,+71.5]
Simple_Flag
This is a flag that is set to 'Y' if simpler model(s) exist
for a source. 14964 of the 66841 sources in this catalog have one or more
simpler models available: these 14964 simpler models are not listed in this
catalog but appeared in a separate tabulation, which can be examined at
https://cdsarc.cds.unistra.fr/ftp/cats/VIII/42/simpler.dat.gz.
Name
The Texas Catalog designation in the form recommended in the
Dictionary of Nomenclature of Celestial Objects maintained at the CDS
(http://vizier.u-strasbg.fr/cgi-bin/Dic). The name is constructed from the
hours and minutes of right ascension, the sign of declination, and truncated
tenths of degrees of declination: hhmmsddd. Suffixes 'A', 'B', etc., are also
used in cases where close sources would otherwise have duplicate names, e.g.,
'TXS 0001-234A' and 'TXS 0001-234B'. Because of a final position system
adjustment, the source name may not agree with the position now listed in the
table, but should be used regardless.
Xpvr_Flag
This flag is left blank if the fringe visibility of the adopted
structure model is within the first minimum on all three subbeams. Such a
model is in the Principal Value Region (PVR) of the catalog authors'
structure-fitting algorithm. If the fringe visibility of the adopted
structure model is near or beyond the first minimum in one or more subbeams,
the value of this flag is set to the number of such subbeams, and thus may be
1, 2, or 3. Such models are called XPVR models, and although they are often
perfectly accurate, they are more subject to structure lobeshift than are the
PVR models.
Model_Flag
This flag describes the goodness of the model fit. Parameters
for each entry in this catalog were calculated from 32 independent
interferometer baselines, subject to the model listed, which was itself
chosen to minimize residuals. If the residuals to the fit are consistent with
the system errors, including both noise- and flux-dependent terms, this flag
is assigned the value of '+'. For cases where the residuals are inconsistent
with the expected errors, it is assigned the value of 'C' for Caution, for a
marginal inconsistency, or 'W' for Warning, for a serious inconsistency.
When the residuals are such that the model is clearly incorrect, it is set
to 'N' for No model, although the least bad model has been used for the
entry. Many sources with flag values of 'N' are, in fact, well-modeled,
based on comparison to other work. In such cases, the large residuals are
often the results of nearby sources or of interference which happened to
increase the rms residuals greatly, while affecting the mean tabulated
model quantities by much smaller amounts. But of course, many 'N' models
are truly bad, and a few are attached to entries which do not represent
sources at all, but which are spurious responses.
Environ_Flag
This flag is an estimate of the influence of the environment
for a listed source. It is set to '+' if the sky surrounding the source
(as represented in the Texas Survey itself) contains no other source which
will contribute significantly to the fringe amplitudes at the position of
the particular source. The contributions of other sources were calculated,
and if their flux at the source position was sufficient to contribute
significantly to the residuals in one or more subbeams, this flag was set to
'C' (Caution) or 'W' (Warning) if the contribution of the other source(s)
were expected to dominate the residuals. Occasionally, the interfering
sources have a higher calculated flux density at the source position than
the catalog source itself, in which case the flag is set to 'X'. Some
sources with flag values of 'X' survived to the final Texas Survey Catalog,
when other tests suggested that the sources were indeed real.
Lobe_Flag
This lobeshift flag is an estimate of the reliability that the
correct lobe was chosen. Each tentative source model was used to reduce the
data on a grid of possible lobeshifted positions, and the best-fitting
position was chosen.In many cases, this position was the only decent fit to
the data, and in such cases the flag is set to '+'. If another lobe position
is possible, the flag is set to 'C' (Caution), and if it produces only a
slightly worse fit to the data than the most probable position, it is set
to 'W' (Warning). In the event that the second most likely position is
the only remaining lobe position that is at all likely, its offset from
the best position is given in the parameters lobe2_offset_ra and
lobe2_offset_dec.
Low_Vis_Flag
This is the low-visibility flag,indicating the number of
subbeams on which the source model has fringe visibilities less then 0.2.
Possible values are blank (for 0, presumably), 1, and 2: it is impossible
for all three subbeams of those models attempted to have visibilities less
than 0.2. Sources that are fit by models with essentially no flux on one
or two subbeams may be questionable.
RA
The Right Ascension of the centroid of the listed structure model for
the radio source, in the selected equinox. This was given to a precision of
0.001 seconds of time and in B1950 equatorial coordinates in the original
catalog tables.
RA_Error
The error in the Right Ascension, in seconds of time. This is
the standard deviation of the fitted RA, based on the observed residuals
to the fitted model, or based on propagated noise, whichever is larger.
It is thus purely an internal error, and does not reflect the error in
adjustment of the survey position system to the position calibrators
(typically 0.2" total), nor does it include estimates of other types
of excess error, such as residual systematic error or the centroid
variance found when comparing to catalogs made at other frequencies.
Dec
The Declination of the centroid of the listed structure model for
the radio source, in the selected equinox. This was given to a precision of
0.01 arcseconds and in B1950 equatorial coordinates in the original catalog
tables.
Dec_Error
The error in the Declination, in arcseconds. This is the
standard deviation of the fitted Declination, based on the observed residuals
to the fitted model, or based on propagated noise, whichever is larger.
It is thus purely an internal error, and does not reflect the error in
adjustment of the survey position system to the position calibrators
(typically 0.2" total), nor does it include estimates of other types
of excess error, such as residual systematic error or the centroid
variance found when comparing to catalogs made at other frequencies.
LII
The Galactic Longitude of the radio source.
BII
The Galactic Latitude of the radio source.
Low_Flux_Flag
This low-flux flag is set to 'X' if the source flux density
is less than 0.15 Jy (925 sources), and is left blank otherwise (65916
sources).
Flux_82_cm
The total 365 MHz (82 cm) flux density, in milliJanskies (mJy),
of the source, given the listed model. A fitted spectral slope over the
operating frequency range (335 - 380 MHz) has been removed. Note that the
value of this flux will be a serious overestimate if a large 'D' or 'AD' model
is erroneously used for a point source, and will be a serious underestimate if
the reverse is true.
Flux_82_cm_Error
The internal standard deviation error in the
total 365 MHz (82 cm) flux density, in mJy, given the observed residuals,
or the propagated noise, whichever is greater.
SNR_Flag
This is a Signal-to-Noise (SNR) flag that is set to 'Y' if
4 <= SNR < 5 (2475 sources) and to 'Z' if 5 <= SNR < 7 (8480 sources), and
is left blank if SNR >=7 (55886 sources). All sources with SNR < 4 were
discarded from this final catalog.
Spectral_Index
The source spectral index, gam, defined in the sense:
log flux ~ gam * log nu, where nu is the frequency. Since the Texas Survey
was carried out in at least two of the three frequencies of 335, 365, and
380 MHz, estimation of the flux density at the standard frequency of 365
MHz involved fitting a spectral index to the data. A number of sources have
blanks in this field; they represent instances where the spectral index
could not be determined or, in the case of sources from the TS6 strip, are
sources whose spectral index error is greater than 0.8. For the Survey as
a whole, useful spectral indications are given for 24558 of the 66841
sources.
Spectral_Index_Error
The error in the spectral index, being the standard
deviation of the fit based on observed residuals. Since the Texas Survey
was carried out in at least two of the three frequencies of 335, 365, and
380 MHz, estimation of the flux density at the standard frequency of 365
MHz involved fitting a spectral index to the data. Naturally, the error in
the spectral index is high, given the small frequency range involved, but a
useful indication of the spectrum is afforded in many cases. When this
error is greater than 0.9, this field has been left blank, and the value
of the spectral index (if present) should be treated with suspicion.
If both the spectral index and spectral index error fields are left blank,
this means that the spectral index could not be determined or, in the case
of the 343 sources from the TS6 strip, that the source has a spectral index
error that is greater than 0.8. For the Survey as a whole, useful spectral
indications are given for 24558 of the 66841 sources.
Flux_Chi2_Res
This is a variability indicator, being the sum of the
squared standardized residuals to the flux density of the modeled source
on each of the four observing cycles. It has a Chi-Squared distribution with
2 degrees of freedom (2 were lost by fitting flux and spectrum). Values of
this parameter > 5.99 would be expected for 5% of non-variable sources,
> 9.21 for 1% of non-variable sources, and > 13.82 for 0.1% of non-variable
sources. Since a spectral slope has been removed, a variable source may also
show up by virtue of having a very odd spectral index, notice (see the
var_flag parameter description).
Flux_Chi2_Res_Susp
This is a flag that is set to 'X' rather than left blank,
if the value of the flux_chi2_res parameter is suspect (if the value of the
model_flag parameter is not '+', or fewer than 6 baselines are present in any
one observing cycle, or the normalized Chi-Squared residual for any one
observing cycle was greater than twice the number of baselines present). If
this flag is set to 'X', any variability indication in the var_flag parameter
should be treated with due caution.
Var_Flag
This is a source variability flag, based both on the value of
the flux_chi2_res parameter and on the values of the spectral index and its
error. (Since a spectral slope has been removed, a variable source may
show up by virtue of having a very odd spectral index). This flag is set to 'Y'
if the flux_chi2_res value is greater than 9.21 (the 1% level), or if the
spectral index gam is less than -1.5 - 2 * sigma(gam) or greater than
0.5 + 2 * sigma(gam), otherwise it is left blank. For the Survey as a whole,
49144 sources have variability parameters which are not suspect: 904 of these
are marked as possibly variable (at the 1% level), and 17697 sources have
supspect variability parameters, and 432 of these are marked as possibly
variable.
Comp_Separation
The double component separation, in integer arcseconds,
for sources fit using a symmetric Double model (model_type = 'D') or an
Asymmetric Double model (model_type = 'AD').
Comp_Separation_Error
The error in the double component separation, in
integer arcseconds, for sources fit using a symmetric Double model (model_type
= 'D') or an Asymmetric Double model (model_type = 'AD').
Model_Type
The structure model adopted to fit the source: 'P' if a point
source model was adopted, 'D' if a symmetric Double model was adopted, and
'AD' if an Asymmetric Double model was adopted.
Asymmetry
The asymmetry parameter q for sources fit using an Asymmetric
Double model (model_type = 'AD'), in %.
Asymmetry_Error
The error in the asymmetry parameter q for sources fit
using an Asymmetric Double model (model_type = 'AD'), in %.
Position_Angle
The Position Angle of the double components, in degrees and
increasing eastwards from North, for sources fit using a symmetric Double
model (model_type = 'D'), or an Asymmetric Double model (model_type = 'AD').
Position_Angle_Error
The error in the Position Angle of the double
components, in degrees, for sources fit using a symmetric Double model
(model_type = 'D'), or an Asymmetric Double model (model_type = 'AD').
RA_Overlap_Flag
The Right Ascension overlap zone flag. The Survey was
reduced in ten declination strips, in which regions near the edges overlapped
with adjacent strips, and each declination strip was reduced in RA segments,
with intersegment boundaries also having overlap. Only one version of such
overlap sources was chosen for inclusion in the catalog, and the
ra_overlap_flag is set to 'Y' to denote a source is in such an RA overlap
region, and is left blank otherwise.
Dec_Overlap_Flag
The Declination overlap zone flag. The Survey was
reduced in ten declination strips, in which regions near the edges overlapped
with adjacent strips, and each declination strip was reduced in RA segments,
with intersegment boundaries also having overlap. Only one version of such
overlap sources was chosen for inclusion in the catalog, and the
dec_overlap_flag is set to 'Y' to denote a source is in such a Dec overlap
region, and is left blank otherwise.
Lobe2_Offset_RA
The offset of the second most likely lobe in RA from the
actual lobe choice, in multiples of the lobe interval lambda (defined in the
published paper), for those cases where the lobe selection routines found that
the second most likely lobe choice, although inferior to the most probable
choice, was nonetheless far better than any of the other possibilities.
Lobe2_Offset_Dec
The offset of the second most likely lobe in Dec from the
actual lobe choice, in multiples of the lobe interval lambda (defined in the
published paper), for those cases where the lobe selection routines found that
the second most likely lobe choice, although inferior to the most probable
choice, was nonetheless far better than any of the other possibilities.
RA_Overlap_Zone
The particular Right Ascension overlap zone, with
possible values from A to E, or blank if the source is not in an RA
overlap zone.
Dec_Overlap_Zone
The particular Declination overlap zone, with
possible values from A to K, or blank if the source is not in a Dec
overlap zone.
Source_Strip
The observation strip and segment from which the source was
taken. For example, looking at the entry for the source 'TXS 0000+178',
the quoted value for source_strip of 181 means that the source came from the
+18 degee observation strip, RA segment 1 (although since it is RA overlap
zone A, this source might have come from RA segment 5). Furthermore, some
sources in the +18 degree observation strip came from an entirely different
reduction from the rest of the Survey (although using the same observational
data and the same position and flux system): these are designated with
source_strip = TS6, for Version 6 of the Texas Survey (the main Survey
reduction was Version 7).
Contact Person
Questions regarding the TEXAS database table can be addressed to the HEASARC Help Desk.Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:35:47 EDT
- HEASARC Director: Dr. Andy Ptak
- NASA Official: Dr. Andy Ptak
- Web Curator: J.D. Myers
- Last Modified: 16-Sep-2024