Eta Cassiopeiae 2

Eta Cassiopeiae A

The main sequence yellow-orange primary (G3 V) may have about 90 to 110 percent of Sol's mass (RECONS; Allende Prieto and Lambert, 1999; and Daniel M. Popper, 1980), almost the same diameter -- 98 to 101 percent (Johnson and Wright, 1983, page 647; and Daniel M. Popper, 1980; or Petr Harmanec, 1988), and 1.2 times its luminosity. It is about 63 to 68 percent as enriched as Sol in elements heavier than hydrogen (metallicity), based on its abundance of iron (Cayrel de Strobel et al, 1991, page 5).

According to a 1969 article by Kaj Aage Gunnar Strand (1907-2000; obit), Star A and B are separated by an "average" distance of 71 times the Earth-Sun distance (AU) (of a semi-major axis) in an eccentric orbit (e= 0.497) of about 480 years, so that the two stars get as close as 36 AU and as far away as 107 AU. (See an animation of the orbits of Stars A and B and their potentially habitable zones, with a table of basic orbital and physical characteristics.) However, Achird is no longer thought to have a spectroscopic binary with a nine-day orbital period (Morbey and Griffin, 1987; and Helmut Abt, 1987). Some useful catalogue numbers for this star are: Eta Cas, 24 Cas, HR 219, Gl 34 A, Hip 3821, HD 4614, BD+57 150, SAO 21732, LHS 123, LTT 10287, LFT 74, Wolf 24, Struve 60, and ADS 671 A.

Eta Cassiopeiae B

This cooler and dimmer, main sequence orange-red dwarf star (K7 V) may have 56 to 60 percent) of Sol's mass (RECONS; and Daniel M. Popper, 1980), 66 percent of its diameter (Johnson and Wright, 1983, page 647), and around three percent of its luminosity. Radial velocity variations have been detected (Andrei A. Tokovinin, 1992). Useful catalogue numbers for this star include: Gl 34 B, LHS 122, and ADS 671 B.

© Torben Krogh & Mogens Winther,

(Amtsgymnasiet and EUC Syd Gallery,
student photo used with permission)


Eta Cassiopeiae B ia a orange-red
dwarf star, like Epsilon Eridani at
left center of meteor

Hunt for Substellar Companions

An attempt to find large planets from December 1986 to February 1987 failed to detect large periodic variations in radial velocities (McMillan and Smith, 1987; more discussion at Hatzes et al, 2004).

The distance from Eta Cassiopeiae A where an Earth-type planet would be "comfortable" with liquid water is centered around 1.13 AU -- just a little farther than Earth's orbital distance in the Solar System. At that distance from the star, such a planet would have an orbital period of about 1.15 years. For Star B, the liquid water zone would be centered around 0.18 AU, where the orbital period would be 37 days. Astronomers are hoping to use NASA's Terrestrial Planet Finder (TPF) and the ESA's Darwin planned groups of observatories to search for a rocky inner planet in the so-called "habitable zone" (HZ) around Star A. As currently planned, the TPF will include two complementary observatory groups: a visible-light coronagraph to launch around 2014; and a "formation-flying" infrared interferometer to launch before 2020, while Darwin will launch a flotilla of three mid-infrared telescopes and a fourth communications hub beginning in 2015.