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tracer
2004-Mar-06, 10:54 PM
In the movie Contact, near the beginning, Dr. Arroway points up at the constellation of Cassiopeia and says:

Cassiopeia A gives off a whole lot of radio signals, I actually listen to it a lot. It's a remnant of a supernova.
Is there really a pulsar or nebula in Cassiopeia called "Cassiopeia A"? I hadn't heard of the put-an-A-on-the-end-of-the-nominative-constellation-name convention for naming visible objects or radio sources before.

ToSeek
2004-Mar-06, 11:54 PM
Yes, and it's very pretty. (http://chandra.harvard.edu/photo/2002/0237/)

I'm not sure of the origin of the name, but there are other, similar ones, like Sagittarius A.

milli360
2004-Mar-07, 12:59 AM
The astronomy picture of the day (http://antwrp.gsfc.nasa.gov/apod/ap000103.html) for January 3, 2000.

tracer
2004-Mar-07, 02:01 AM
Yes, and it's very pretty. (http://chandra.harvard.edu/photo/2002/0237/)
Or, at least, its false-color X-ray image is very pretty. ;)


I'm not sure of the origin of the name, but there are other, similar ones, like Sagittarius A.
Hmmm ... Since Sagittarius A is the most likely candidate for the black hole theorized to be at the center of the Milky Way, and since that pretty picture of Cassiopeia A was taken by the Chandra orbiting observatory, my guess would be that the "A" nomenclature comes from X-ray astronomy. Perhaps it means the first X-ray source discovered in the constellation. Or the strongest X-ray source in the constellation.

Andromeda321
2004-Mar-07, 09:43 PM
My turn for a question: is Cassiopeia A also the supernova observed around the time of Copernicus? Because I heard that one was in Cassiopeia.

tracer
2004-Mar-08, 01:45 AM
No -- but, apparently, the supernova that created Cassiopeia A may have been sighted by www.seds.org/~spider/spider/Vars/casA.html+%22Cassiopeia+A%22&hl=en&ie=UTF-8]Flamsteed (http://216.239.53.104/search?q=cache:zXABuxkdPeQJ:[url) in 1680[/url].

Maksutov
2004-Mar-08, 03:25 AM
Yes, and it's very pretty. (http://chandra.harvard.edu/photo/2002/0237/)
Or, at least, its false-color X-ray image is very pretty. ;)


I'm not sure of the origin of the name, but there are other, similar ones, like Sagittarius A.
Hmmm ... Since Sagittarius A is the most likely candidate for the black hole theorized to be at the center of the Milky Way, and since that pretty picture of Cassiopeia A was taken by the Chandra orbiting observatory, my guess would be that the "A" nomenclature comes from X-ray astronomy. Perhaps it means the first X-ray source discovered in the constellation. Or the strongest X-ray source in the constellation.

>>>
from the Astronomy Chapter for The Manual of Scientific Style, McGraw-Hill 2002

Radio Sources

The earliest radio sources discovered were designated by the name of the constellation in which they are located, followed by a capital letter indicating the order of discovery within that constellation.
Cygnus A the first radio source discovered in the constellation Cygnus
>>>

That would make Sagittarius A the first radio source discovered in the constellation Sagittarius.

AGN Fuel
2004-Mar-08, 06:06 AM
Hmmm ... Since Sagittarius A is the most likely candidate for the black hole theorized to be at the center of the Milky Way, and since that pretty picture of Cassiopeia A was taken by the Chandra orbiting observatory, my guess would be that the "A" nomenclature comes from X-ray astronomy. Perhaps it means the first X-ray source discovered in the constellation. Or the strongest X-ray source in the constellation.

>>>
from the Astronomy Chapter for The Manual of Scientific Style, McGraw-Hill 2002

Radio Sources

The earliest radio sources discovered were designated by the name of the constellation in which they are located, followed by a capital letter indicating the order of discovery within that constellation.
Cygnus A the first radio source discovered in the constellation Cygnus
>>>

That would make Sagittarius A the first radio source discovered in the constellation Sagittarius.

And by extension, because the first X-Ray source discovered in a given constellation will tend to be the 'brightest' one (because of the relative insensitivity of the early X-Ray detectors such as Uhuru), typically the 'A' nomenclature will also reflect the most intense X-Ray source as well.

tracer
2004-Mar-09, 12:22 AM
So ... does that mean the "Cassiopeia A" moniker was applied after it was discovered as a radio source, or does it mean that the name was applied after it was discovered as an X-Ray source? Does the first X-ray source in a constellation also get the "A" appelation, separate and distinct from the first radio source?

AGN Fuel
2004-Mar-09, 02:08 AM
So ... does that mean the "Cassiopeia A" moniker was applied after it was discovered as a radio source, or does it mean that the name was applied after it was discovered as an X-Ray source? Does the first X-ray source in a constellation also get the "A" appelation, separate and distinct from the first radio source?

No, I'm sorry Tracer - my previous post was very ambiguous. I was trying to refer to the point that the processes that form the intense radio source can also produce bright X-Ray sources, such as was the case with the Cas A image by Chandra that was discussed earlier.

The 'A' nomenclature refers to the radio source. X-Ray sources are usually given an 'X' rating! (such as Scorpius X-1, Cygnus X-1 etc)

The Bad Astronomer
2004-Mar-09, 02:13 AM
It was Cas A when it was discovered as a radio source. It was found to be an X-ray source much later.

X-rays sources have a similar system; in Cygnus, the first source found was called Cygnus X-1.

I think Cas A was found as a radio source before it was found optically. There isn't much there optically; there is way too much dust between us and it.

tracer
2004-Mar-09, 03:31 AM
So, then, radio sources in Cygnus would be called "Cygnus A", "Cygnus B", "Cygnus C", etc., in order of their discovery, right?

That means that "Cygnus X" would be a radio source, but "Cygnus X-1" would be an X-ray source. :D

AGN Fuel
2004-Mar-09, 05:08 AM
So, then, radio sources in Cygnus would be called "Cygnus A", "Cygnus B", "Cygnus C", etc., in order of their discovery, right?

That means that "Cygnus X" would be a radio source, but "Cygnus X-1" would be an X-ray source. :D

Hypothetically, I suppose, although I am not aware of any that go down that far!! Current convention, especially for discrete, point source signals, is to name the object after the RA/Dec co-ordinates, so that a new radio source identified as a pulsar might be named (for example) PSR0615-2230.

tracer
2004-Mar-09, 03:59 PM
They only specify the RA/Dec coordinates down to the minute and arcminute? No seconds, arcseconds, or epoch?

AGN Fuel
2004-Mar-10, 12:02 AM
They only specify the RA/Dec coordinates down to the minute and arcminute? No seconds, arcseconds, or epoch?

The naming conventions have changed as the technology has improved. While giving an alpha suffix was appropriate when your radio telescope was barely able to pick up the local Rock'n'Roll station, it quickly becomes unwieldy if your VLBA survey has identified 1000 radio sources in a given constellation for example!

These days, sources are more often than not simply identified by their catalogue reference (e.g. MSH11-54 is a radio source associated with an SNR from the Mills, Slee & Hill catalogue, etc). Similarly, and in respect to your question above, the Chandra X-Ray sources will be given a detailed identifier such as, for example, 174513.1-285624 (this is an X-Ray source near the galactic centre).

You would then go to the relevant catalogue to get further info on the object in question, e.g.

http://www.atnf.csiro.au/research/pulsar/psrcat/
http://cdsweb.u-strasbg.fr/viz-bin/VizieR?-source=J/AJ/126/539
http://heasarc.gsfc.nasa.gov/docs/corp/data.html

etc, etc. There are heaps of them. Naming is not as simple as it used to be. :(