CHI CYGNI: THE EPITOME OF THE WORD VARIABLE.
Photo Credit: Sylvestre Lacour. CLICK photo for full size and see below for all related links and a video.
This particular star is a new favorite of mine as I have watched it through the last half-year or so. In the constellation Cygnus lies the Mira type variable star, Chi Cygni. This is a star that has burned through its fuel in the core and is now pulsating as it swells then contracts over the course of 408 days or 13.4 months on average which places the peak brightness about 6 weeks later every year. With that vacillation comes great changes in the stars brightness. Its apparent magnitude has been documented from 3.3 to an extremely dim 14.2 which means to the naked eye, it literally appears and disappears over the course of its cycle. The star ranges in size from about 300 million miles in diameter to a massive 480 million miles which is large enough to engulf our solar system out to the asteroid belt.
So what’s a Mira type variable star? In short it’s a pulsating red giant star that has a cycle of 80 to 1000 days and display great changes in brightness through said cycle. They have masses similar to our Sun (Give or take) but because of their great size they exhibit a weak gravitational influence at their outer layers and thus lose a lot of material through stellar wind. This material loss creates shell of material that surrounds the star.
NAME: Chi Cygni, HD187796 or SAO68943.
WHAT IS IT?: Mira type variable star (Long Period Variable) with an average fluctuation of 408 days or 13.4 months.
HOW BIG IS IT?: Similar to the Sun but much larger.
HOW FAR AWAY IS IT?: Approximately 345 light years distant.
APPARENT MAGNITUDE?: Extreme observational recordings have been from 3.3 to 14.2 which is a massive change in brightness. Peak for 2013 was around late-May and low will be around November-ish.
WHERE IS IT? (General): Constellation Cygnus the Swan, the Northern Cross and within the Summer Triangle of Deneb, Vega & Altair.
WHERE IS IT? (Exact RA/DEC J2000): RA 19h 50m 33.92s / DEC +32° 54′ 50.61″.
Observatoire de Paris: http://lesia.obspm.fr/?lang=fr
Sylvestre Lacour IAU member page: http://www.iau.org/administration/membership/individual/13140/
AAVSO page on variable stars: http://www.aavso.org/types-variables
Jim Kaler stars page: http://stars.astro.illinois.edu/sow/sowlist.html