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Where do X-ray sources get their
names? |
You've probably seen some very strange names for
X-ray sources. You
may have wondered "how DO they come up with those names?" Well, X-ray
sources get their names from the constellations, from famous catalogs, from the
satellites
that discovered them and their coordinates in
Right Ascension and
Declination
(like longitude and latitude), other coordinate systems and the year
they were discovered, just to name a few.
In the early days of X-ray
astronomy, new
objects were named after the constellation they were in. Objects like
Cygnus X-1, LMC X-4, and Cen X-3 have this form. After it became obvious that
there were going to be more than 20 or 30 X-ray sources, this naming
convention was abandoned. Unfortunately, a single convention has never been
agreed upon. Following are some examples of X-ray source names and where they
came from.
Sco X-1 |
The first cosmic X-ray source ever discovered (after the
Sun). It's in the constellation Scorpius. Each new X-ray source in a
constellation gets an X-#. There is a Cygnus X-1, Cygnus X-2, and a
Cygnus X-3. The Large Magellanic Cloud also has several sources with
names of this form, they're called LMC X-1, LMC X-2, LMC X-3, and
LMC X-4. |
U Gem |
This is another source that's named after its constellation. Usually,
names of this form use a letter of the alphabet to order the
stars in a
constellation by
optical
brightness. However, this only applies to stars
up through the letter Q. Names of this form that start after Q are
*variable stars*. U Gem is a Cataclysmic Variable in the constellation
Gemini.
Tell me more about this strange
naming convention |
Many of the X-ray sources have names that come from a combination of a
catalog abbreviation and the Right Ascension (RA) and Declination (Dec) of
the object. Those funny things that look like backward phone numbers
(0748-676) really list the location of the object. The above example source
is at an RA of 07 hours, 48 minutes and a Dec of -67.6 degrees. Here are
some other examples of this form of naming X-ray sources:
4U 0115+63 |
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4th Uhuru catalog - one of the earliest X-ray satellites
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3S 1820-30 |
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SAS-3 discovery - another early X-ray satellite
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EXO 0748-676 |
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EXOSAT discovery
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PKS 2155-304 |
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Parkes catalog
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H 2252-035 |
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HEAO-1 A2 satellite survey
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A 1916-05 |
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Ariel catalog
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2A 1822-371 |
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2nd Ariel catalog
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GS 2000+25 |
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Ginga satellite discovery
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G 21.5-0.9 |
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Lowell Proper Motion Surveys of optical stars
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MSH 15-52 |
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Mills, Slee & Hill (1958) catalog of
radio
sources
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PSR 1855-09 |
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PSR=Pulsar (normally radio
pulsars)
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X 1608-52 |
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X-ray source (general)
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GX 301-2 |
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This name describes the Galactic coordinates of this X-ray
source. In this coordinate system, the center of our
Galaxy is
defined as 0,0. To find this source, you would go 301 degrees around
the
plane of the Galaxy (as seen from Earth) and then 2 degrees below the
plane. If the source was called GX 4+1, you would go 4 degrees around
the plane and 1 degree above the plane. GX 4+1 is very close to the
center of our Galaxy (as seen from Earth). |
Many objects get their names from a reference number in a catalog. Although
these catalogs are often ordered by RA and Dec, one can't tell from the
reference number where the object is in the sky. Some objects of this form
are:
HD 93162 |
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Henry Draper Catalog (1919-1925)
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SS 433 |
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The Stephenson & Sanduleak catalog
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M 15 |
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Messier catalog of non-stellar objects
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NGC 6624 |
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New General Catalog of Nebulae and Clusters of Stars
(published 1888 by Dreyer)
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IC 443 |
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Index Catalogue (published 1895 by Dreyer)
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Mrk 297 |
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Appears in B. E. Markarian's
ultraviolet catalog of galaxies. Sometimes listed as Mkn instead
of Mrk.
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Abell 2256 |
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George Abell's catalog of
clusters of galaxies
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3C 273 |
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The 3rd Cambridge catalogue
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CTB 109 |
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Cal Tech radio observation reports (catalog B)
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AC 211 |
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Auriere and Cordoni catalog of stars in M15
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W 44 |
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Westerhout (1958) catalog of radio sources
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HZ 43 |
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Humason & Zwicky (1946)
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RCW 103 |
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Rodgers, Campbell & Whiteoak catalog of HII regions
(1960)
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MCG 6-30-15
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Morphological Catalogue of Galaxies (a compilation of information for
approximately 34,000 galaxies found and examined on the Palomar
Observatory Sky Survey (POSS)). The numbers correspond to the zone of
the POSS.
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I Zw 18 |
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First Zwicky Catalogue of Clusters of Galaxies. The Zwicky clusters
were identified by F. Zwicky in 560 POSS fields. They are rich
clusters, each having at least 50 members within 3
magnitudes
of the brightest member. There are II Zw and III Zw sources, as
well.
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SN 1987a |
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This is an object that was in the news in 1987. The SN means that it is
a supernova. 1987 is the year it appeared and the letter "a"
denotes that that it was the first supernova found in that year. Can you
guess
which supernova of 1993 was named SN 1993j? Did you know the Chinese
have records of the supernova, SN 1006? When there are more supernovae
than letters of the alphabet, they add a letter: SN 1995aa, SN 1995ab,
etc. The last supernova discovered in 1995 was given the name SN
1995bd!
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Tycho |
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Another supernova (observed by
Tycho
Brahe in 1572). Can you guess who discovered the
Kepler
supernova? |
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