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iantresman
2009-Oct-18, 03:25 PM
Anyone know where the RR comes from? A catalog? Person's name? Elsewhere?

Romanus
2009-Oct-18, 03:55 PM
It was discovered by Jacob Railroad.

;)

Kidding, of course.

Any combination of upper-case letters refers only to the order in which a variable star was discovered. For the first few variable stars discovered in a given constellation, you have simple single letters (e.g., P Cygni). Once you run through the alphabet, you start with it again, but *this* time using A, and then the following combination of letters afterward (e.g., AH Scorpii). The process is repeated for all 26 letters over and over, until finally you reach ZZ, and in fact there is a well-known variable white dwarf named ZZ Ceti. After that, you just use "V" for variable, and a number afterward (e.g. V838 Monoceratis).

Perikles
2009-Oct-18, 03:56 PM
Anyone know where the RR comes from? A catalog? Person's name? Elsewhere?Johannes Bayer, beg. 17th century, used Greek or Roman letters for stars. Later, Argelander designated capital R for variable stars, and double letters were needed to cope with the quantities. RR Lyrae is the prototype star for the category.

grant hutchison
2009-Oct-18, 05:08 PM
Bayer used the Greek alphabet, then the lower case Roman alphabet, then upper case Roman letters to designate stars. Even with the largest constellations, he got no further than upper case Q.
Hence Argelander's choice of R as his designator for the first identified variable in a constellation. The sequence then runs from R to Z, then RR to RZ, SS to SZ, TT to TZ, and so down to ZZ. Then we start our double letters at the beginning of the alphabet: AA to AZ, BB to BZ and finally end up with QZ. The second letter is never taken from a higher alphabetical position than the first letter, and for some reason the letter J is always omitted, so there are a total of 334 letter-based designations in this system (334 = the sum of all positive integers less than or equal to 25, plus the nine single-letter designators from R to Z). The V-prefix system therefore starts with V335: the 335th designated variable in the constellation.

P Cygni is therefore actually an old Bayer designation, which has turned out to be variable; there is no P in Argelander's sequence. Stars with existing Bayer letters which turn out to be variables in this way simply take a V prefix as their variable designator: "V P Cyg", in this instance.

Grant Hutchison

AndreasJ
2009-Oct-19, 12:38 PM
for some reason the letter J is always omitted
It's because in older German typography, capital 'I' and 'J' were not consistently distinguished.

grant hutchison
2009-Oct-19, 12:40 PM
It's because in older German typography, capital 'I' and 'J' were not consistently distinguished.Ah, that makes sense. Thanks. :)

Grant Hutchison