Nature of The System
At −0.27v visual magnitude, Alpha Centauri appears to the naked eye as a single star and is fainter than Sirius and Canopus. The next brightest star in the night sky is Arcturus. When considered among the individual brightest stars in the sky (excluding the Sun), Alpha Centauri A is the fourth brightest at −0.01 magnitude, being only fractionally fainter than Arcturus at −0.04v magnitude. Alpha Centauri B at 1.33v magnitude is twenty-first in brightness.
Alpha Centauri A is the principal member, or primary, of the binary system, being slightly larger and more luminous than the Sun. It is a solar-like main sequence star with a similar yellowish color, whose stellar classification is spectral type G2 V. From the determined mutual orbital parameters, Alpha Centauri A is about 10% more massive than the Sun, with a radius about 23% larger. The projected rotational velocity ( v·sin i ) of this star is 2.7 ± 0.7 km·s−1, resulting in an estimated rotational period of 22 days, which gives it a slightly faster rotational period than the Sun's 25 days.
Alpha Centauri B is the companion star, or secondary, of the binary system, and is slightly smaller and less luminous than the Sun. This main sequence star is of spectral type K1 V, making it more an orange color than the primary star. Alpha Centauri B is about 90% the mass of the Sun and 14% smaller in radius. The projected rotational velocity ( v·sin i ) is 1.1 ± 0.8 km·s−1, resulting in an estimated rotational period of 41 days. (An earlier, 1995 estimate gave a similar rotation period of 36.8 days.) Although it has a lower luminosity than component A, star B emits more energy in the X-ray band. The light curve of B varies on a short time scale and there has been at least one observed flare.
Alpha Centauri C, also known as Proxima Centauri, is of spectral class M5 Ve or M5 VIe, suggesting this is either a small main sequence star (Type V) or sub-dwarf (VI) with emission lines, whose B–V color index is +1.90. Its mass is about 0.123 M☉, or 129 Jupiter masses.
Together, the bright visible components of the binary star system are called Alpha Centauri AB (α Cen AB). This "AB" designation denotes the apparent gravitational centre of the main binary system relative to other companion star(s) in any multiple star system. "AB-C" refers to the orbit of Proxima around the central binary, being the distance between the centre of gravity and the outlying companion. Some older references use the confusing and now discontinued designation of A×B. Since the distance between the Sun and Alpha Centauri AB does not differ significantly from either star, gravitationally this binary system is considered as if it were one object.
Asteroseismic studies, chromospheric activity, and stellar rotation (gyrochronology), are all consistent with the α Cen system being similar in age to, or slightly older than, the Sun, with typical ages quoted between 4.5 and 7 billion years (Gyr). Asteroseismic analyses that incorporate the tight observational constraints on the stellar parameters for α Cen A and/or B have yielded age estimates of 4.85 ± 0.5 Gyr, 5.0 ± 0.5 Gyr, 5.2-7.1 Gyr, 6.4 Gyr, 6.52 ± 0.3 Gyr. Age estimates for stars A and B based on chromospheric activity (Calcium H & K emission) yield 4.4-6.5 Gyr, while gyrochronology yields 5.0 ± 0.3 Gyr.
Read more about this topic: Alpha Centauri
Famous quotes containing the words nature of, nature and/or system:
“The so-called consumer society and the politics of corporate capitalism have created a second nature of man which ties him libidinally and aggressively to the commodity form. The need for possessing, consuming, handling and constantly renewing the gadgets, devices, instruments, engines, offered to and imposed upon the people, for using these wares even at the danger of one’s own destruction, has become a “biological” need.”
—Herbert Marcuse (1898–1979)
“For Nature is the noblest engineer, yet uses a grinding economy, working up all that is wasted to-day into to-morrow’s creation;Mnot a superfluous grain of sand, for all the ostentation she makes of expense and public works.”
—Ralph Waldo Emerson (1803–1882)
“The human body is not a thing or substance, given, but a continuous creation. The human body is an energy system ... which is never a complete structure; never static; is in perpetual inner self-construction and self-destruction; we destroy in order to make it new.”
—Norman O. Brown (b. 1913)