Page 8 - 83 basic knowledge of astronomy

5 Designations of Astronomical Radio Sources

There are many designation systems for naming radio sources. Examples
are given in the following. As a result, radio sources are often identified by
several different names.

• IAU 1974 system of designation (‘IAU name’, see, e.g., Explanatory
Supplement to American Astronomical Almanac)

– identifies a radio source by a six, seven, or eight-digit number,
such as 0134+329, which tells us that the right ascension of the
h
◦
m
source is 01 34 , and its declination is +32. 9 (usually in the
B1950 equinox system).
– sometimes source types or catalog acronyms are added, e.g., pul-
sars are called ‘PSR0950+08’, and sources from the Parkes Sky
Survey as ‘PKS1322-42’.

• 3C-name, 4C-name

– identifies an extragalactic radio source by a serial number in the
Third Cambridge Catalog, and by declination in the Fourth Cam-
bridge Survey Catalog.
– examples are 3C84, 3C273, 3C345, 4C39.25, etc.

• W-name

– is based on Westerhout’s (1958) catalog of HII regions.

– examples are W49 N, W3(OH), W51 M, etc.

6 Designations of Frequency Bands

The basic unit of radio frequency is Hz (Hertz: cycle per second). In order
to describe high frequency, typically used in radio astronomical observations
or communications, we frequently use the following secondary units: kHz
3
9
6
(kilohertz: 10 Hz), MHz (megahertz: 10 Hz), GHz (gigahertz: 10 Hz),
and THz (terahertz: 10 12 Hz).
Radio frequency bands used in astronomical observations, as well as in
communications, are designated by one or a few alphabetic characters. Two
systems of designations are shown in Figure 7.
In radio astronomy, IEEE STD-521-1976 designations have been used.
Examples are:

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