WBE4850 (E0): 4850 MHz Northern Sky Survey, Sep 1990 (19941112)
FILE: wbe4850.e0 (53522 sources)
CONTENTS: NRAO 140-foot (43m) 4.85 GHz Northern Sky Survey, -3 <= Dec <= +76
DATASET: This file comes in HyperSky dataset E-7, version 19941112. Availability on HyperSky CD-ROM: Vol. 2 (1995)
DESCRIPTION: This datafile contains the 4850 MHz (4.85 GHz or 6cm) Northern Sky Survey, distribution version of 4 September 1990, by R.L. White, R.H. Becker and A.L. Edwards, as discussed in 1991 Ap.J.Supp., 75, 1. The survey was done with the NRAO 140-ft (43 m) radio telescope, and contains 53522 discrete sources. The sources range in strength from 13 to 59740 mJy (milli-Janskys), and cover a declination range of from -3.3 to +75.9 (equinox 2000).
Higher radio frequencies such as 4850 MHz are typically dominated by emissions from thermal sources, and correlate well with astronomical sources where star formation is taking place.
DATA: The HyperSky datafiles contain the following data from the catalog:
POSITION: Right Ascension and Declination are based on the catalog 1950 positions, precessed to equinox 2000. Catalog positions were provided to an accuracy of 0.1 second in Right Ascension and 1" in declination.
MAG: No magnitudes or equivalents were provided in the catalog. A set of artificial magnitudes is provided, however, in the HyperSky catalog strictly to allow use of HyperSky's limiting-magnitude controls. In this way, users can display only those sources above a desired threshold. The artificial magnitude system is based on the relation (from Pogson) used to define visual magnitudes:
m1 - m2 = 2.5 * log10(S1/S2)
where { m1, m2 } are magnitudes, and { S1, S2 } are source strengths. For the HyperSky catalog, the brightest source (S1 = 59740 mJy) is arbitrarily assigned the magnitude m1 = 1.0. Given this, any other source S2 can have its relative magnitude, m2, derived using the relation:
m2 = m1 + 2.5 * log10 (S1/S2);
In this system, the faintest catalog source (13 mJy) has a magnitude of 10.2. The following table summarizes the relation between magnitude and source strength for catalog extremes and intermediate magnitudes:
Magnitude Source Strength (mJy)
----------|----------------------
1.0 59740 (brightest catalog source)
2.0 23659
3.0 9712
4.0 3605
5.0 1542
6.0 621
7.0 254
8.0 97
9.0 39
10.0 16
10.2 13 (faintest catalog source)
With the above table, a user can set HyperSky's limiting magnitude (for emission sources) to mask out catalog sources below a desired strength. Except for this use, the derived source magnitudes have NO significance. It should be emphasized again that the magnitudes are NOT provided in the original catalog; only the source strengths are fundamental catalog values.
IDENTIFICATION: The derived source name, constructed from the equinox 1950 RA, Dec HHMM+DDMM with A or B added at end if needed to make the name unique.
COMMENTS: The comment line contains the following information:
* The 4850 MHz (6cm) flux strength in mJy (milli-Janskys). An asterisk follows if the source is extended at 4850 MHz.