VIII/62 The Westerbork Northern Sky Survey (Leiden, 1998)
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)>
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 (5σ). 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¢ `fop 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
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 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.
(End) Gail L. Schneider [SSDOO/ADC], Francois Ochsenbein [CDS] 10-Feb-2000
|The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line|