SNR1994 (E0): Green 1994 Catalog of Galactic Supernova Remnants (19950128)
FILES:
snr1994.e0 (182 remnants)
snr1994.ls (position-list for locating supernova remnants)
CONTENTS: Catalog of Galactic Supernova Remnants, D.A. Green, 1994
DATASET: This file comes in HyperSky dataset E-17, version 19950128. Availability on HyperSky CD-ROM: Vol. 2 (1995)
DESCRIPTION: This datafile contains 182 Galactic Supernova Remnants (SNRs) known as of 1994, in the catalog of D.A. Green of MRAO (Mullard Radio Astronomy Observatory), Cavendish Laboratory, Cambridge, England. The catalog is an updated version of the catalogs of Galactic SNRs presented in detail in Green (1984, MN, 209, 449; 1988, ApSS, 148, 3) and in summary form in Green (1991, PASP, 103, 209). Because serious selection effects apply to the identification of Galactic SNRs (see Green 1991), great care must be taken if the catalog data are used in statistical studies.
There are many objects that have been identified as SNRs and are listed in the catalog, although they have been barely resolved in the available observations, or are faint, and have not been well separated from confusing background or nearby thermal emission, and their identification as SNRs, or at least their parameters, remain uncertain.
Omitted from the catalog are a number of possible SNRs for which further observations are required to confirm their nature. Such cases are identified and discussed in the documentation that accompanies the catalog. It should also be noted that some radio loops in the Galactic plane may be parts of very large, old SNRs, but have not been included in the catalog.
The HyperSky file is based on a copy of the catalog available directly from the author at Cambridge, at the following Internet WWW (World-Wide-Web) address: http://www.phy.cam.ac.uk/www/research/ra/SNRs/snrs.intro.html The catalog is also available from the Stellar Data Centre (CDS), Strasbourg, France, as catalog VII/163.
DATA: The HyperSky datafile contains the following data from the catalog:
POSITION: The catalog B1950 Right Ascension and Declination, precessed to equinox 2000.
The accuracy of the position values depends on the remnant size. For small remnants they are to the nearest few seconds of time and the nearest arc minute for RA and DEC respectively. For larger remnants they are rounded to coarser values. They are in every case sufficient to specify a point within the boundaries of the remnant. All coordinates are deduced from radio maps rather than X-ray or optical observations. Cataloged SNRs range from +73 to -63 degrees 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 SNR above a desired 1GHz 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 SNR flux strengths. For the HyperSky catalog, the brightest SNR (S1 = 2720 Jy) is arbitrarily assigned the magnitude m1 = 1.0. Given this, any other SNR 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 (2720 / S2);
In this system, the faintest catalog SNR (0.5 Jy) has a magnitude of 10.3. The following table summarizes the relation between magnitude and SNR strength for catalog extremes and intermediate magnitudes:
Magnitude SNR 1GHz Strength, Jy (+ examples)
----------|-------------------------------------------
1.0 2720 (strongest SNR: Cas A = G111.7-2.1)
2.0 1040 (Crab nebula = G184.6-5.8)
3.2 350 (Lupus Loop = G330.0+15.0)
4.1 160
5.0 69
6.0 27
7.0 11
8.0 4.4
9.1 1.6
10.0 0.7
10.3 0.5 (weakest SNR)
With the above table, you can set HyperSky's limiting magnitude (for emission sources) to mask out catalog SNRs below a desired flux strength. Except for this use, the derived SNR magnitudes have NO significance. It should be emphasized again that the magnitudes are NOT provided in the catalog; only the SNR flux strengths are fundamental catalog values.
IDENTIFICATION: The SNR catalog designation is composed of the prefix "G", followed by the concatenation of galactic latitude and longitude, both in degrees, accurate to 0.1 degree.
COMMENTS: The comment lines following the identification contain the following information, where available, for each SNR:
* A line starting with "=", giving up to 3 alternate SNR names.
* A line giving the angular size of the SNR in arc minutes. This size is usually taken from the highest resolution radio map available, although for some barely resolved sources that are thought to be SNRs the only available size is that from Gaussian models after deconvolution with the observed beam size.
The boundary of most remnants approximates reasonably well to a circle or an ellipse. A single value is quoted for the angular size of the more nearly circular remnants, which is the diameter of a circle with an area equal to that of the remnant. But for elongated remnants two values are quoted, these being the major and minor axes of the remnant boundary modelled as an ellipse. In a few cases an ellipse is not a satisfactory description of the boundary of the object, although an angular size is still quoted for information.
For "filled-center" remnants the size quoted is for the largest extent of the observed radio emission, not, as at times has been used, the half-width of the centrally brightened peak.
* A line describing the SNR radio structure type, which can be one of:
"filled center"
"shell"
"composite/combination"
"uncertain"
The term "uncertain" applies to several cases where an object is conventionally regarded as an SNR even though its nature is poorly known or not well understood. A question mark is appended where there is some uncertainty regarding any of the other descriptions.
* A line giving the SNR flux density at 1 GHz. Measurement units are janskys (Jy, originally flux units). One jansky equals 1E-26 watt per square meter per hertz. The given flux is not a measured value, but that deduced from the observed radio frequency spectrum of the SNR. The 1 GHz frequency is chosen since flux density measurements at frequencies above and below this value are usually available.
* A line giving the spectral index of the SNR's integrated radio emission. This is either a value that is quoted in the literature, or one deduced from the available integrated flux densities of the remnant. For several SNRs a simple spectral model is not adequate to describe the radio emission because there is evidence that the spectral index varies across the face of the remnant or that he integrated spectrum is curved, and in these cases the spectral index is given as "varies". In a few cases, where the remnant is highly confused with thermal emission, the spectral index is given as `?' since no value can be deduced with any confidence.
POSITION-LIST: The position-list snr1994.ls, if loaded, will enable you to locate any catalog SNR using either of two sublists:
* A list using galactic-coordinate based names, ordered by galactic longitude.
* A list of alternate SNR names, in alphanumeric order.
Remember that this is only a position-list; it does not actually display an object at the position you select. The object you select will appear at the position only if you have also loaded snr1994.e0, or some other HyperSky catalog file which contains the object.
REFERENCES
Proc. IAU Colloq. 145, "Supernovae and Supernovae Remnants", held May 22-29 1993, in Xian, China, Eds. McCray, R., and Wang, Z., Camb. Univ.