Triple star in Eridanus
Keid is an inconspicuous 4th magnitude star in Eridanus, but it is a very interesting one. At a distance of about 16 light years, it is one of the closest star systems to us.
The brightest star of the trio is yellow-orange, an example of a type K dwarf star. It is somewhat smaller in diameter than our Sun and only 40% as luminous.
The second-brightest star is a white dwarf, only about 1.3% as bright as our Sun, and its diameter is only about 50% larger than that of the planet Earth!
The third star of the group is a red dwarf, and although it is dimmer than the white dwaf it is larger in diameter. The white and red dwarfs orbit each other at an aveage distance of about 35 astronomical units (for comparison, Neptune is 30 astronomical units from the Sun) and one orbit takes about 250 years (Nepture's orbital period is 164 years). Even as they orbit each other, the red and white dwarfs together circle the orange star over a period of more than 7000 years.
This is a fascinating star system, one worth taking a look at through a telescope on a winter night.
| Magnitudes | 4.4, 9.7, 11.2 |
| Separation | 83", 9" |
| Distance (light yrs) | 16.4 |
| Right Ascension | 4:15.2 |
| Declination | -7 40 |
| Field of View | 20' x 15' |
Image details: A combination of several 5-second exposures in luminance, red, green, and blue, taken with an SBIG STF-8300M imager and a Meade 14” LX850 telescope at f/6.
February 2019