samedi 6 septembre 2008

Lupus 4

The constellation may refer to the ancient king of Arcadia, King Lycaon (a word which is related to both 'wolf' and 'light').
King Lycaon, who ruled Arcadia with his fifty sons, was said to continue the practice of human sacrifice when other parts of Greece had abolished it as barbaric.
One variation of the story has King Lycaon offering Zeus the sacrifice of a young boy, which angered Zeus so much he promptly changed Lycaon into a wolf and struck his house down with lightning, killing all his fifty sons.
In another version Zeus one day visited Arcadia disguised as a simple traveller. Lycaon and his sons offered him soup made not only from the meat of goats and sheep, but also of his own son Nyctimus. Zeus overthrew the table in disgust and killed all the king's sons with lightning bolts (restoring the life of Nyctimus in the process).
While it may seem ludicrous to memorialise this barbaric King of Arcadia, even prior to the Greeks the constellation seems to have represented a sacrificial animal of some sort.
The asterism is not very obvious, and in fact the constellation itself is fairly difficult to separate from its closest neighbour Centaurus.
Lupus is narrowly squeezed between Centaurus and Hydra to the west, Scorpius and Norma to the east. Although small, since it lies in the Milky Way it is packed with interesting items, especially double stars.

The Bayer stars are generally third and fourth magnitude. To locate Lupus, one might first begin with the arms of Centaurus (if need be, one can review this constellation from the Archives). Starting at theta Centauri starhop to phi Centauri then eta and finally kappa Centauri.
In the same field to the south is beta Lupi, which at 2.7 magnitude is slightly brighter than kappa Centauri (3.1). Now drop down to the southwest some five degrees and you'll find alpha Lupi.
Alpha Lupi (a beta Cephei variable) is the brightest star of the constellation at 2.3 magnitude. There is some dispute over its distance; some authorities put it at 430 light years, while others at around 620. From the absolute magnitude of -4.4, it would have a distance of 710 light years.

Double stars in Lupus:
Gamma Lupi is a very close binary with a nearly edge-on orbit whose period is 147 years. Currently the companion is at the greatest distance: PA 274º, separation 0.68".
Epsilon Lupi is also a close binary: 3.4, 5.5; 247º, 0.6".
Eta Lupi is a pleasant fixed binary with slight colour contrast: 3.4, 7.8; 20º, 15".
Kappa1 and kappa2 form a wide fixed binary: 3.9, 5.7; 144º, 27".
Mu Lupi is a multiple system. AB: 5.1, 5.2; 142 degrees, 1.2". The third component is much easier: PA 130º, 24".
Xi1 and xi2 Lupi are a fixed pair. This double is the most attractive binary in Lupus: 5.3, 5.8; 49º, 10.4".

Variable stars in Lupus:
Lupus has three beta Cephei variables among its Bayer stars.
Beta Cephei variables are pulsating variables (prototypes are beta Cephei and beta Canis Majoris). These are massive and very luminous stars which rapidly rotate. The range of magnitude change is very small.
Alpha Lupi: 2.29-2.34; period 6h14m.
Delta Lupi: 3.2-3.24; period 3h58m.
Tau1 Lupi: 4.54-4.58; period 4h15m.

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