MOLONGLO (E0): Molonglo 408 MHz Radio Source Catalog; 1990 (19950119)
FILE: molonglo.e0 (12,141 sources)
CONTENTS: Molonglo 408 MHz Radio Source Reference Catalog, of 2 May 1990
DATASET: This file comes in HyperSky dataset E-15, version 19950119. Availability on HyperSky CD-ROM: Vol. 2 (1995)
DESCRIPTION: This datafile contains the 12,141 radio sources in the Molonglo Radio Telescope 408 MHz Reference Catalog, version of 2 May 1990. Each discrete source has a flux density of > = 0.7 Jy. The survey covers 7.85 sr of the sky defined by +18.5 (deg) > = dec(1950) > = -85.0 (deg), mod(b) > = 3 (deg). A few sources beyond the declination limits are also included.
The catalog contains celestial coordinates with standard error typically between 3 and 10 arcsec, and 408-MHz flux densities with standard errors typically lying between 4 and 10 per cent. The overall source density is 1500/sr, corresponding to 0.001 per beam area. There are 7347 sources of listed flux density > = 1.00 Jy, at which level the catalog is substantially complete. The reliability is believed to be better than 99.9 per cent.
The HyperSky file is based on the version of the catalog available through the U.S. National Space Sciences Data Center (NSSDC) as Astronomical Data Center (ADC) catalog #8016.
DATA: The HyperSky datafile contains the following data from the catalog:
POSITION: Right Ascension and Declination are based on the catalog J2000 positions, as provided in the catalog. Catalog positions were provided to an accuracy of 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, you can display only those sources above a desired flux 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 flux strengths. For the HyperSky catalog, the brightest source (S1 = 2740.0 Jy) 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)
or in this case:
m2 = 1.0 + 2.5 * log10 (2740.0 / S2)
In this system, the faintest catalog source (0.67 Jy) has a magnitude of 10.0. The following table summarizes the relation between magnitude and source strength for catalog extremes and intermediate magnitudes:
Magnitude Source Strength (example)
----------|--------------------------------------------------
1.0 2740.0 (brightest source: B1322-427 = Cen A)
2.8 519.0 (B1228+126)
3.6 259.0 (B0320-373)
4.0 169.5 (B1648+050)
5.1 61.3 (B1717-009)
6.0 27.5
7.0 10.8
8.0 4.3
9.0 1.75
10.0 0.67 (faintest source)
With the above table, you 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 Molonglo catalog; only the flux strengths are fundamental catalog values.
IDENTIFICATION: The catalog designation is composed of the prefix "B" (indicating equinox B1950), followed by the right ascension in hours and minutes and the declination in degrees and tenths of a degree. See the above table for examples.
COMMENTS: The comment lines following the identification contain the following information, where available, for each radio source:
* A line giving the source flux strength at 408 MHz. Measurement units are Janskys (Jy, originally flux units). One jansky equals 1E-26 watt per square meter per hertz.
* One line (or rarely more) giving a brief description of the source extent, based on morphology flags int the catalog. The description will be one of the following:
"point source"
"small-scale structure"
"extended source"
"complex extended source"
"multiple sources within 8'"
"weak nearby sources"
Most catalog sources are identified as point sources.
* A line starting with "err=", giving the standard Declination error in arcsec, as a rough indication of the overall error. A standard error in RA is also provided in the catalog, but omitted in the HyperSky display.
REFERENCE
The original MRC was published in Mon. Not. R. astr. Soc., Vol 194,
pp 693-704 and Microfiches MN 194/1.