[quote="Joe Stieber"][quote="Ann"]
And thank you, Joe Stieber, for identifying the stars for me. I was unable to do so myself, although I wondered about the bright blue star that you identified as Alpheratz, Alpha Andromedae, the top left star in the Great Square of Pegasus.[/quote]
You're welcome Ann!
I suppose you were wondering why a star in Andromeda is the corner of the Great Square of Pegasus? That common corner pre-dates the official IAU boundries circa 1930. You couldn't have a star in two constellations at the same time, so it ended up in Andromeda, but it still marks the corner of the stick figure of the Great Square (which is just an asterism anyway). A simialr situation exists with Alnath, or Beta Tauri, the northen horn tip of Taurus which also marks the southern corner of Auriga's pentagonal stick figure.[/quote][quote=" http://stars.astro.illinois.edu/sow/alpheratz.html"]
<<ALPHERATZ (Alpha Andromedae). Andromeda runs like a string of pearls to the northeast of the Great Square of Pegasus. Since its three principal stars have almost the same brightness, Beyer simply lettered them Alpha, Beta, and Gamma in order, Alpha and Beta tied for the lead in apparent magnitude. Mid-second magnitude (2.06) Apheratz, the Alpha star, connects Andromeda (the Lady) with Pegasus, the Flying Horse that carried Perseus to Andromeda's rescue. As such, Alpheratz is also the northeastern star of the Great Square of Pegasus. The name has a confused origin possibly transferred from another star, and is commonly taken to mean "the horse's shoulder" or "naval," showing that the star originally belonged more to Pegasus, though now it is formally within the boundaries of Andromeda. As a linking star, Alpheratz is one of two that carries two Greek letter names, and is also Delta Pegasi, though the name is no longer used. (The other star is Elnath, Beta Tauri, which links Taurus to Auriga and is also called Gamma Aurigae.) If you draw a line through Alpheratz and Algenib, Gamma Pegasi to the south, it will pass just to the east of the vernal equinox in Pisces. Alpheratz, at the cool end of the B star range (B8 subgiant) , is still hot, with a temperature of about 13,000 Kelvin. At a distance of 97 light years, we calculate a total luminosity, including the star's ultraviolet radiation, of about 200 times that of the Sun. Alpheratz stands out in a couple of ways. It is a "spectroscopic binary," a close double that can be investigated only through the examination of its spectrum, the pair orbiting each other every 96.7 days. The much dimmer companion seems to be about a tenth the brightness of the principal star. [b][color=#0000FF]The bright member of the pair, the one that makes the impression on the human eye, is also chemically peculiar, and is the brightest member of the odd class of "mercury-manganese" stars. Compared to our standard, the Sun, and to the vast majority of other stars, the atmosphere of these stars have vast enrichments of these elements, mercury overabundant by a factor of tens of thousands. Other elements such as gallium and europium are hugely enriched as well, while some others are depressed. We believe we are seeing a separation of elements as a result of the inward pull of gravity and the outward pressure of radiation that act differently on different elements.[/color][/b]>>[/quote][quote=" http://stars.astro.illinois.edu/sow/elnath.html"]
<<[ELNATH (Alnath, or Beta Tauri)] is one of the sky's rare linking stars. Formally now in Taurus, the star is also a part of the classic outline of Auriga and is simultaneously Gamma Aurigae (though it ranks number two in Auriga as well, after Capella). (The other linking star, Alpheratz or Alpha Andromedae, is also Delta Pegasi.) "Gamma Aurigae" is never used, however.
Elnath is a hot (13,600 Kelvin) class B giant star. From its distance of 130 light years, we find a luminosity (corrected for the ultraviolet radiation from the hot surface) almost 700 times that of the Sun. Like so many stars of its class, Elnath is "chemically peculiar" and appears to be a "mercury-manganese" star, the manganese abundance 25 times normal, the calcium and magnesium abundance reduced and only an eighth solar. These peculiarities are caused by the combined action of gravity and radiation, which make the atoms of some elements drift downward and out of sight and others rise. [b][color=#0000FF]The best bright example, is, by rather amazing coincidence, the other "linking star," Alpheratz![/color][/b]>> [/quote]