Procyon 2

MOST, CSA





Procyon is the
brightest star
in Canis Minor,
the Little Dog
(more).

Alpha Canis Minoris A has a close companion star B that is separated "on average" by only about 16 times the distance from the Earth to the Sun -- 14.9 astronomical units (AUs) of an orbital semi-major axis -- which is roughly the distance between Uranus and our Sun. Alpha Minoris B, the companion star, is a white dwarf, stellar remnant and is so dim that it cannot be perceived with the naked eye. After analyzing irregularities in the proper motion of Procyon which were first detected in 1840, Arthur Julius Georg Friedrich von Auswers (1838-1915) deduced the presence of this faint but massive companion and published a computed period of 40 years in 1861. However, Procyon B was not detected visually until 1896 by John Martin Schaeberle (1853-1924) with the 36-inch refractor at Lick Observatory. There is a third optical companion C.

---------------------------------------------- [Guide] -- [Larger] ----------------------------------------------

	Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass (Solar)	Diameter (Solar)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
AB Mass Center	0.0	...	...	...	...	...	...	...	...
Procyon A	4.3	40.8	0.407	31.1	1.50	1.4-2.3	...	...	1.4
Inner H.Z. Edge?	2.0	2.28	0	31.1	...	...	...	...	...
Outer H.Z. Edge?	4.0	6.54	0	31.1	...	...	...	...	...
Procyon B	10.7	40.8	0.407	31.1	0.60	0.02	...	...	1.4

Procyon A

Alpha Canis Minoris A, the Little Dog Star, is the eighth brightest star in the night sky as well as the brightest star in its constellation. Unlike Sol, it is a white-yellow main sequence dwarf star of spectral and luminosity type F5 IV-V (Mosser et al, 2008). This relatively large star has about 1.5 times Sol's mass (Girard et al, 2000) and about 1.4 to 2.3 times its diameter (0.00510 to 0.00550", according to the Yale Bright Star Catalogue, 1991 5th Revised Edition notes entry for HR 2943; but while a diameter of 1.96 has been derived using a power law formula for the NASA Star Exoplanet Database from Kenneth R. Lang, 1980), more recent seismology data is consistent with an evolutionary model that assumes 2.04 of Sol's diameter (Leccia et al, 2007). Compared to Sol, moreover, Procyon A is hotter and about 7.5 times brighter. Procyon radiates somewhat more in ultraviolet wavelengths than Sol, and, not surprisingly, the European Space Agency has used ultraviolet spectral flux distribution data to determine stellar effective temperatures and surface gravities, including those of Procyon.

USAF AMOS, Maui, Hawaii



Procyon at a resolution of 0.2
arc-seconds (larger image).

Procyon A appears to be a relatively young star with only around 1.8 billion years (Leccia et al, 2007; Kenneth Croswell, 2005; and Eggenburger et al, 2005). However, being so much bigger and hotter Sol, the star will exhaust its core hydrogen within even the 4.6 billion years of Sol's current age and turn into a red giant before puffing away its outer layers to reveal a remnant core as a white dwarf. Indeed, Procyon A is unusually bright for its spectral type and so may be becoming a subgiant star that is beginning to evolve off the main sequence, as it begins to fuse the increasing amounts of helium "ash" mixed with hydrogen at its core. Analysis of "soft x-ray" emissions from Silicon ions indicate that Procyon's coronae is cooler than Sol's (Liang and Zhao, 2008).

NASA Observatorium




See a discussion of
the "main sequence"
as part of stellar
evolution and death.

Many astronomers believe that the star has entered the last phase of its life and is becoming dimmer. As a result of studies conducted on the oscillation of our Sun, Sol, Procyon A should be oscillating in a certain pattern. When the Canadian Space Agency's MOST satellite monitored Procyon A for 32 consecutive days from January to February 2004 and in 2005, no oscillations were detected although the aging star should have vibrated and oscillated at a greater amplitude than Sol. As a result, models based on observations of Sol, for measuring stellar (p-mode) oscillations due to "turbulent convection" of its outer layers are being reexamined (UBC press release; and Guenther et al, 2007). In 2008, its oscillations were measured and found to have "a plateau of excess power ... [that] is broader than has been seen for other stars", and there is also "a slow variation in the radial velocity of Procyon ... [which] are remarkably similar to those seen in the Sun, and we interpret them as being due to rotational modulation from active regions on the stellar surface ... [with] a period of about 10 days" (Arentoft et al, 2008).

The star is rich in elements heavier than hydrogen ("metals rich"), as it has about 1.4 times the iron abundance of Sol, and dust has been detected in the system (Kuchner and Brown, 2000 -- in postscript). It was probably enriched by its companion star, which was once bigger and hotter than Procyon A and so evolved and "burnt out" even faster. Procyon B manufactured lots of heavier elements which it puffed out into space and onto Procyon A before becoming a white dwarf.

H. Bond (STSci), R. Ciardullo (PSU), WFPC2, HST, NASA
(Procyon B is a white dwarf, a remnant stellar core, which enriched Procyon A with elements
heavier than hydrogen when it cast off its outer gas layers, like planetary nebula NGC 2440)