Star of the week.....

[Orstio]

R Leonis

Position:  RA: 9h 47min 33.5sec  DEC: +11° 25' 44''
Proper Motion: RA: 0.002 arcsec/a  DEC: -0.042 arcsec/a
Radial Velocity: 13 km/s in recession
Spectral Class:  M8IIIe
Variable Period: 309.95 days
Magnitude at Maximum: 4.4
Magnitude at Minimum: 11.3

R Leonis is one of the brightest of the long long-period variable stars.A pulsating Red Giant of Mira class, R Leonis sometimes rises above 5th magnitude, and declines to less than 11th magnitude.  The star is noted for the peculiar intensity of its red light, best described as a rosy scarlet with often a seeming touch of purple.  

This is a late M-type giant, the spectrum varying from M7e to about M9 in the course of the cycle.  From an estimated distance of 600 light years, the luminosity of the star at maximum would appear to be in the range of 200-260 times that of the Sun;  the absolute magnitude is -1 at peak brightness.

There is a very good animation illustrating how a Mira-class variable works here if you have the patience to wait for a 4 MB gif to load. (Just a warning:  It is only a few frames, even though it is such a big file.  If you have a narrow-band connection, it is not worth the download time.)

[RedWhiteArcher]

Listen to Orstio, its not worth it even on broadband since their connection sucks too.

[Orstio]

Position: Right Ascension: 19h 58m 21.9s   Declination: 35^o12'09"
Magnitude: 8.8
Distance:  5600 light years
 
Cygnus  X-1 was discovered as an X-ray source in 1965.  This binary system, distant of 2.5 kiloparsecs, consists of the O9.7 Iab type blue supergiant HDE 226868 and  a compact object orbiting around with a period of 5.6 days, estimated to have a diameter of only about 9 miles. The mass of the unseen companion, significantly larger then 5 solar  masses suggests that it is a black hole. Focused wind accretion from a primary star being  extremely close to filling the Roche lobe drives the powerful source of the  X-ray radiation. Cygnus  X-1 is one of the brightest X-ray sources in the sky.
 
Studies of the system in 1973 established the existence of a strongly heated stream of gas passing from the B-star to the unseen component; the X-ray energy originates in this tremendously hot stream as it falls into the black hole.
 
The star lies slightly less than 0.5^o ENE from Eta Cygni; it may be located easily in small telescopes.

[Orstio]

http://webs.wichita.edu/lapo/binocs/arcturus.jpg 
 
Magnitude: -0.06
Spectrum:  K2 III
Postion: RA: 14h 15min 39.7 sec  Dec: +19^o 10' 57
 
Arcturus is located at a distance of about 37 light years.  Its diameter is roughly 25 times the diameter of the Sun.  The luminosity is about 115 times that of our Sun, and the absolute magnitude is -0.3.  The heat we receive from the star has been measured to be equal to that of a single candle at a distance of 5 miles.   The proper motion of Arcturus has been bringing it closer to us, and it is now almost at its minimum distance.  It still shows an approach radial velocity of about 3 miles/second, which will gradually diminish to zero several thousand years from now.  After that it will begin to recede, and will disappear from naked-eye view approximately 500,000 years from now.

[Sarah90]

um...that image kinda sat on about 19 lines of script?...(Probably due to my ineptitude...)...

[Remcook]

sarah: probably not. or I'm losing it too.

[Astronuc]

Position: Right Ascension: 19h 58m 21.9s   Declination: 35^o12'09"
Magnitude: 8.8
Distance:  5600 light years
 
Cygnus  X-1 was discovered as an X-ray source in 1965.  This binary system, distant of 2.5 kiloparsecs, consists of the O9.7 Iab type blue supergiant HDE 226868 and  a compact object orbiting around with a period of 5.6 days, estimated to have a diameter of only about 9 miles. The mass of the unseen companion, significantly larger then 5 solar  masses suggests that it is a black hole. Focused wind accretion from a primary star being  extremely close to filling the Roche lobe drives the powerful source of the  X-ray radiation. Cygnus  X-1 is one of the brightest X-ray sources in the sky.
 
. . .

  A nice article on Cygnus X-1 and HDE 226868
 
http://en.wikipedia.org/wiki/Cygnus_X-1
 
HDE 226868 is a supergiant star with a spectral class of O9.7 Iab, which is not quite a B-type star.  It has a surface temperature of about 30,000 K.

[Astronuc]

Postion:  Right ascension  20h 41m 25.9s   Declination  +45? 16' 49"
Spectral type: A2 Ia
Apparent magnitude: (V) 1.25
 

Deneb (Alpha Cygni) is the brightest star in the constellation Cygnus and one of the vertices of the Summer Triangle.  It is the 19th brightest star in the night sky, with an apparent magnitude of 1.25.  A white supergiant, Deneb is also one of the most luminous stars known.  It is, or has been, known by a number of other traditional names, including Arided and Aridif, but today these are almost entirely forgotten.

  http://en.wikipedia.org/wiki/Deneb
 

Deneb's absolute magnitude is about -8.5, placing it among the most luminous stars known.
 
Estimates for Deneb's luminosity range from about 60,000 times the brightness of our Sun (if Deneb is 1600 light-years away) to 250,000 times the Sun's brightness (if 3,200 light-years away).
 
Based on its temperature and luminosity and also on direct measurements of its tiny angular diameter (a mere 0.002 second of arc), Deneb appears to have a diameter about 200 to 300 times that of the Sun.  It is one of the largest stars known and the most powerful class A star identified.
 
Deneb's mass is estimated at 20 to 25 solar masses
 
Deneb's solar wind causes it to lose mass at a rate of 0.8 millionth of a solar mass per year, a hundred thousand times the flow rate from the Sun.

http://www.astro.uiuc.edu/~kaler/sow/deneb.html
 
http://www.heavens-above.com/hipentry.asp?hip=102098

[Astronuc]

A piece of trivia about Arcturus -
 

Arcturus, the leading star of Bootes, the herdsman, is in the west tonight. The bright yellow-orange star moves across our line of sight faster than almost any other star. Even so, it is so distant that it takes centuries for the changing position to become obvious.
 
. . . .
 
From the northern hemisphere, the bright star with the greatest proper motion is yellow-orange Arcturus, which is visible in the west tonight. In fact, Arcturus is one of the stars that Edmund Halley used to make his discovery. He saw that the star had a slightly different position in his time from those recorded in ancient times -- a sign that the star was moving as it followed its own path through the galaxy.

http://stardate.org/radio/program.php?f=detail&id=2008-07-26
 
 

[alokmohan]

Nice   to   be  back.