ACDS V10.0 - Mon Apr 22 18:12:10 CEST 2019
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Detailed Description of VIII/62 :
The Westerbork Northern Sky Survey (Leiden, 1998)
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Note : this is the description file of the original catalog.
This HTML page corresponds well to the original description, but some minor
changes in the format may have been introduced in the FITS output
files in order to allow for arithmetic operations on quantities
such as coordinates and times. h:m:s and d:m:s units are normally
converted into degrees, and YYYY-MM-DD into julian days.
Similarly, some slight changes may have been introduced in the
units; the value given in the HTML files supersedes the value indicated in the ReadMe
file for this catalogue.
VIII/62 The Westerbork Northern Sky Survey (Leiden, 1998)
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Westerbork Northern Sky Survey (WENSS)
de Bruyn G., Miley G., Rengelink R., Tang Y., Bremer M., Rottgering H.,
Raimond R., Bremer M., Fullagar D.
<WENSS Collaboration NFRA/ASTRON and Leiden Observatory (1998)>
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ADC_Keywords: Radio sources ; Surveys
Description:
The Westerbork Northern Sky Survey (WENSS) is a low-frequency radio
survey that covers the whole sky north of 30° at a wavelength of
92cm (330MHz) to a limiting flux density of approximately 18 mJy
(5{sigma}). This survey has a resolution of 54"x54" cosec(delta) and a
positional accuracy for strong sources of 1.5".
The WENSS project is a collaboration between the Netherlands
Foundation for Research in Astronomy (NFRA/ASTRON) and the
Leiden Observatory.
Introduction to the WENSS:
The Westerbork Northern Sky Survey (WENSS) is a radio survey made with
the WSRT at wavelengths 92 and 49 cm. At 92 cm the entire sky above
declination 30° is covered. The other wavelength regime does
not cover the whole sky, but only 30-50 percent, due to the amount of
telescope time that is needed to do this. Using a synthesis array like
the WSRT means that we get a better resolution than single dish
observations, but also has the disadvantage of a smaller field of
view, unless we find a way of dealing with wide field imaging. The
solution for this problem is mosaicing. Instead of making one
observation of a large field we make a lot of snapshots of different
fields and bind them together with the help of special build software.
A typical mosaic contains 80 pointing centres. Each pointing centre is
sampled during 20 seconds and then the telescope moves to another
centre. This takes about 10 seconds. After 40 minutes all fields are
scanned and the procedure starts again. This means that in a 12 hour
observation each field is scanned 18 times. To move grating rings of
the map 6 different baseline settings are used, so 1 mosaic data block
involves 72 hours of observational data. Each pointing centre is
located at half half-power maximum beamwidth in order to get a smooth
sampling grid of the data. The noise background is uniform up to 5
percent. At 92 cm (declination 30°) a mosaic block is about 10
by 14° large.
The final product that the WENSS survey produces contain 6x6°
frames taken from the mosaic blocks. They are centered on the new POSS
plate positions (5° grid). The limiting flux density will be about
15 mJy (5 sigma) at both wavelengths. As a result the final catalogue
will consist of 300,000 sources at 92 cm and 60,000 at 49 cm. The
positional accuracy will be superior to all other all sky surveys (5"
for the faint sources to better than 1" for the stronger sources). A
large number of sources will have sufficient accurate positions to
allow optical identification using a digitized version of the Palomar
Sky Survey made with the APM at Cambridge. Final maps will be made at
different resolutions in order to make accurate spectral index
measurements. At each wavelength we will make high, medium and low
resolution maps (1', 2.5' and 4' resolution at 92 cm and 0.5', 1' and
2.5' resolution at 49 cm). Maps will be made with all Stokes
parameters (I, Q, U and V). This means that source information will be
available both on spectral type and polarization characteristics. This
is important for using the catalogue as a database for finding sources
based on well known selection criteria, such as steep spectra for high
redshift radio galaxies.
File Summary:
FileName Lrecl Records Explanations
× 80 . This file
× ReadMe 80 . This file
× main.dat 114 211234 WENSS main catalogue (28 to 76°)
× polar.dat 114 18186 WENSS polar catalogue (sources above 72°)
See also:
http://www.strw.leidenuniv.nl/wenss/ : the WENSS Home Page
ftp://vliet.strw.leidenuniv.nl/pub/wenss/HIGHRES/ : maps in FITS format
J/A+AS/124/259 : The Westerbork Northern Sky Survey I. (Rengelink+ 1997)
Byte-by-byte Description of file: main.dat polar.dat
Bytes Format Units Label Explanations
1- 2 A2 --- --- [WN] Survey name
3- 15 A13 --- Name *Designation of the source
16 A1 --- f_Name *[abmp] Several objects share the same name
18- 19 I2 h RA1950h Right Ascension B1950 (hours)
21- 22 I2 min RA1950m Right Ascension B1950 (minutes)
24- 28 F5.2 s RA1950s Right Ascension B1950 (seconds)
30 A1 --- DE1950- Declination B1950 (sign)
31- 32 I2 deg DE1950d Declination B1950 (degrees)
34- 35 I2 arcmin DE1950m Declination B1950 (minutes)
37- 40 F4.1 arcsec DE1950s Declination B1950 (seconds)
43- 44 I2 h RAh Right Ascension J2000 (hours)
46- 47 I2 min RAm Right Ascension J2000 (minutes)
49- 53 F5.2 s RAs Right Ascension J2000 (seconds)
55 A1 --- DE- Declination J2000 (sign)
56- 57 I2 deg DEd Declination J2000 (degrees)
59- 60 I2 arcmin DEm Declination J2000 (minutes)
62- 65 F4.1 arcsec DEs Declination J2000 (seconds)
68 A1 --- flg1 *[SMEC] source type flag
70 A1 --- flg2 *[*] problems in fitting the source
73- 78 I6 mJy Speak *Peak flux density at 330MHz in mJy/beam
80- 86 I7 mJy Sint *Integrated flux density 330MHz in mJy
88- 91 I4 arcsec MajAxis *Major axis
93- 95 I3 arcsec MinAxis *Minor axis
97- 99 I3 deg PA *Position angle (North to East)
101-104 F4.1 mJy Nse Local rms-noise level in mJy/beam
106-114 A9 --- Frame Frame from which the source was obtained
Note on Name, f_Name:
The name has a format 'Bhhmm.m+ddmmA', where 'B' indicates a name based
on B1950 coordinates, followed by the truncated position to 0.1min in
right ascension and 1 arcmin in declination, followed by a letter
A,B,C,D for components of the multi-component sources.
There are 748 names which are assigned to more than one source; these
names are flagged "a", "b", "m" or "p" in the f_Name column:
a,b when the same name exists in the same file (there are two
identical names in main.dat or polar.dat)
m,p when the same name exists in the other file (there are two
identical names, one in main.dat, and the other one in polar.dat)
Note on flg1: this flag indicates the source type as:
S = Single component source
M = Multicomponent source
C = Component of a multicomponent source
E = Extended source (more than four components)
Note on flg2: warning flag indicating problems in fitting the source.
Source parameters were then obtained using 'aperture' integration.
Note on Speak, Sint:
The frequency is 325MHz in the main part, and 352MHz in the polar part.
Note on MajAxis, MinAxis, PA: sources that are probably resolved.
Non-null numbers indicate that the flux density ratio Sint/Speak
exceeds a signal-to-noise dependent threshold. This threshold is the
flux ratio Sint/Speak that is exceeded by less than 5% of the
unresolved sources. These parameters have not been deconvolved.
Project Team:
Project scientists: A.G. de Bruyn, G.K. Miley
Project manager: E. Raimond
Research assistants: M.A.R. Bremer (Leiden), Y. Tang (Dwingeloo)
Software design/coding (NEWSTAR): W.N. Brouw
Software design/coding (Catalogue building / user interfaces): M.A.R. Bremer
WSRT on-line assistance: R. Braun, H. van Someren-Greve
Dwingeloo off-line processing: G. van Diepen, J.E. Noordam
Several AIO's / OIO's (Ph.D. students) will work with the catalogue,
each with their own sources of interest (e.g. milli-second pulsars,
high redshift galaxies, GHZ peakers).
Data Rights/Acknowledgements:
Anyone using data from the WENSS database in publications is asked to
acknowledge this. Comments or questions about the survey can be
addressed to any of the people mentioned below or to the general
wenss.people@strw.leidenuniv.nl account at Leiden.
History:
* 10-Feb-2000: Prepared at ADC.
* 21-Oct-2003: 19 sources from main.dat had a blank embedded in the
name, just following the "WNB" in the Name column; this blank
was removed at CDS.
* 14-May-2004: the column f_Name was installed to distinguish the
sources sharing an identical name.
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(End) Gail L. Schneider [SSDOO/ADC], Francois Ochsenbein [CDS] 10-Feb-2000