Star of the week.....

[Orstio]

OK, we'll see how long my schedule will allow this.  I'll try to post a new star each week.  Here's this week's:

Gamma Andromeda



AKA: Almach
Visual Magnitude: 2.12; spectrum K2 II or K3
Position:  RA 2h 0.8 m; Dec +42^o 06'.

This is a beautiful double star, one of the finest within range of a small telescope.  According to T.W. Webb it was probably discovered by J.T. Mayer in 1788 (R.H. Allen gives the date as 1778) but the first recorded measurements appear to be those of F.G.W. Struve in 1830.  The brighter star is golden-yellow or slightly orange, and the companion (mag 5.08) appears a definite greenish-blue.  The color contrast is unusually fine, and often seems more striking with the eyepiece very slightly displaced from the position of sharpest focus.  There has been no definite change in separation or angle in the pair in the last 130 years.  In 1962 the measurement made at Lowell was: 10" in PA 63^o.

In 1842, Struve discovered that the companion is itself a close double.  It is a binary with a period of 61 years according to computations by P. Muller (1957).  The star was at periastron in 1891 and again in 1952; the greatest separation of the components is about 0.55" and was last reached in 1982.  The apparent orbit is a much-elongated ellipse extending toward PA 110^o; the semi-major axis is 0.3" and the eccentricity is 0.93.  Both of the stars are late B or early A type; the individual magnitudes are 5.5 and 6.3.

The brightest member of this close pair is itself a spectroscopic binary with a period of 2.67 days and two identical spectra (about B9) visible.  Gamma Andromedae is thus a quadruple star system.  The luminosity of the K-star is about 650 times that of our sun; the B-C-D system totals about 50 times the light of the sun.  The actual separation of the A-B pair may be about 800 AU, and the B-C separation averages about 30 AU.

The distance from us is approximately 260 light years; the annual proper motion is 0.07"; the radial velocity is about 7 miles per second in approach.  The total absolute magnitude is about -2.4.

[Qazaq2001]

Orstio,
Excellent idea, keep up the good work. It reminds me of reading entries out of Burnham's Celestial Handbook, which I have copies of, all three volumes. Best, Qazaq8)

[Orstio]

Burnham's Celestial Handbook is my main resource for this.  I also have all three volumes.  Thought I'd start with some of the more exciting objects that can be seen with a small telescope, post some pics, and fill in the links as I find them.

[greenleaf1]

Great idea - thanks Orstio!

[Orstio]

Sirius
Visual Magnitude: -1.46
Position: RA: 6h 45min, 8.821sec   DEC: -16° 42' 56.85'' ±0.06 arcsec

proper motion: RA: -0.0385 arcsec/a   DEC: -1.205 arcsec/a s
radial velocity 8 km/s in approach

[img]http://www.maths.soton.ac.uk/relativity/GRExplorer/NS/sirius.jpg" align="right]
Sirius is 9 times brighter than a standard first magnitude star.  T.W. Webb stated that Sirius had been observed at noon with an aperture of one-half inch.  In color, the star is a brilliant white with a definite tinge of blue, but in its rapid scintillation it often seems to flicker with all the colors of the rainbow.

Sirius is an A1 type main sequence star about 23 times the luminosity of the Sun, 1.8 times the diameter, and 2.35 times the mass.  The star has a yearly proper motion of 1.324" in PA 204^o; in the last 2000 years it has changed position by 44' or about 1.5 times the apparent size of the moon.

At a distance of 8.7 light years, Sirius is the 5th nearest star known.  It is a member of a group of moving stars often called the Ursa Major Stream.  This widely-dispersed stream shows nearly the same motion as the Ursa Major cluster.

Sirius actually has 6 suspected components: The central star Sirius A appears to be orbited by 4 bodies including Sirius B, which also has a suspected (but not yet confirmed) satellite (Sirius C).

Sirius B has a mass that is nearly equal to that of the Sun.  The luminosity, however, is less than 1/400th of our Sun, with a magnitude of 8.5, making it one of the first white dwarf stars ever discovered.  Sirius D has a magnitude of 14. The E and F components are suspected planets or brown dwarves, but are also not yet confirmed.

 

[greenleaf1]

I'm probably missing something obvious, but why is SIruis so bright?

[Orstio]

In addition to being over twice the mass, it also has a surface temperature about 1.5 times that of our Sun.  So it's got a lot of fuel, and burning hot.

PLC probably knows more about the processes involved.

[greenleaf1]

Makes sense, thanks!

[skyjim]

And Sirius is really close at less than 9 LY.

[Orstio]

[img]http://www.solstation.com/stars/barnards.gif" align="right]



Right Ascension:  17h 58m
Declination:          4^o41'
Distance:               5.97 ly
Visual Magnitude: 9.56
Spectral Type:       M3.8V


This is a faint red dwarf star famous for having the greatest known apparent motion of any known star.  It was discovered by E. Barnard in 1916 through a comparison of plates made in 1894 and 1916.  The annual motion of the star is 10.49” in a direction almost due north (PA 356^o).  Its position changes in the sky by 1^o every 351 years.

The actual luminosity of Barnard's Star is about 1/2500 that of our sun.  J.C. Duncan found the mass to be about 16% that of the sun, and the diameter to be about 140,000 miles.

At a distance of less than 6 light years, it is the second closest known star to our solar system, with only the Alpha Centauri triple system being closer.  The large apparent motion is thus a result of the nearness of the star combined with an unusually high space velocity of about 103 miles per second.  The radial velocity is quite large also, amounting to about 87 miles per second in approach.  It will reach it's closest point to us around the year 10,800 at about 3.8 light years.

Astronomers  have long sought to find perturbations ("wobbles") in this star's motion that could be due to planet-sized companions. During the  late 1960s, Peter  van de Kamp (1901-1995) announced the detection of two planets,  whose estimated masses were  fine-tuned in 1982 to be about 0.7  and 0.5 of Jupiter's mass with orbital  periods of 12 and 20 years,  respectively, based on astrometric positions  obtained from 1938  to 1981 (van  de Kamp, 1982). Until his death in 1995, Van de Kamp devoted  most of his  life (at the Sproul Observatory of Swarthmore College)  to analyzing over 2,000  plates of Barnard's Star that he and his  students had taken from 1938 through  1981. Neither planet was  ever verified, and more recent observations with the  Hubble Space  Telescope have failed to yield supporting evidence for a large  Jupiter  or brown dwarf sized object (Schroeder  et al, 2000). In 1995, George  G. Gatewood (director of the University of Pittsburgh's Allegheny  Observatory) suggested  that, while brown dwarfs exceeding Jupiter's  mass by more than 10 times could  not exist around Barnard's Star,  planets having a mass smaller than Jupiter's  may possibly be present.

[RedWhiteArcher]

Oh so thats is what this Branard's Star is where you can buy lotsa robots and sell them back in Sol

[Remcook]

very cool animation orstio!

[Orstio]

Thanks for pointing out the typo RWA.

You can thank the people here for the animated gif.  It is very well done;  it illustrates the movement perfectly.

[RedWhiteArcher]

Err I think I had a typo 'cause thats how I always read it.
Barnard's Star is should be.

[Remcook]

very nice site! thanks