EZ Aquarii 3

NASA -- larger image

EZ Aquarii ABC may all be dim red dwarf stars, like
Gliese 623 A (M2.5V) and B (M5.8Ve) at lower right.
(See a Digitized Sky Survey field image around
EZ Aquarii at the Nearby Stars Database.)

System Summary

This triple star system is located only about 11.1 light-years (ly) from our Sun, Sol, in the eastern part (22:38:33.9-15:18:02:C~, ICRS 2000.0) of Constellation Aquarius, the Water Bearer -- west of Skat (Delta Aquarii). EZ Aquarii may have been discovered by Willem Jacob Luyten (1899-1994), who found the proper motions of over 520,000 stars despite the loss of sight in one eye since 1925 by building an automated photographic plate scanner and measuring machine. All three stars appear to be M-type red dwarfs near the hydrogen burning mass limit -- at least 75 Jupiter masses -- with an aggregate mass of about 34 percent of Sol's (Woitas et al, 2000; or Defosse et al, 1999). At least one of the three stars is a flare star, but all three are too faint to be seen with the naked eye.

Arnold O. Benz, Institute of Astronomy, ETH Zurich

High resolution and jumbo images (Benz et al, 1998).

EZ Aquarii ABC may all be flare stars, like UV Ceti
shown flaring at left. UV Ceti is an extreme example of
a flare star that can boost its brightness by five times
in less than a minute, then fall somewhat slower back
down to normal luminosity within two or three minutes
before flaring suddenly again after several hours.

EZ Aquarii A (or Aa)

This cool and dim, main sequence red dwarf is of spectral and luminosity type M5.0-5.5 (Ve). It is a variable star with only about a tenth of Sol's mass, about eight to 35 percent of its diameter, and only 8.7-12/100,000th of its luminosity. As a result, the distance from the star where an Earth-type planet would be comfortable with liquid water is only about 0.009 AU, , but such an orbit would likely be disrupted by the proximity of Star A. Some alternative names and useful catalogue numbers for this star are: EZ Aqr, Gl 866 A, LHS 68, LP 820-64, LPM 837, LTT 9122, LFT 1729, L 789-6 A, and G 156-31.

According to the new Sixth Catalog of Orbits of Visual Binary Stars, Stars A and B have an "average" separation, or semi-major axis, of about 1.22 times the Earth-Sun distance (AU) in an eccentric orbit (e= 0.437), a period of about 2.25 years, and an inclination from the perspective of an observer on Earth of about 112.4° (Woitas et al, 2000). In addition, Star A is a spectroscopic binary (whose companion has been designated as star "C") with an orbit period of only 3.8 days (Defosse et al, 1999). (See an animation of the orbits of Stars A, B, and C and their potentially habitable zones, with a table of basic orbital and physical characteristics.)

EZ Aquarii B

This probable M-type red dwarf has a luminosity of only 34/1,000,000th of Sol's and about a tenth of its mass. As a result, the distance from star B where an Earth-type planet would be comfortable with liquid water is less than 0.006 AU. Some alternative names and useful catalogue numbers for this star are: L 789-6 B and Gl 866 B.

EZ Aquarii C (or Ab?)

Like the other two stars, EZ Aquarii C is a probable M-type red dwarf that is close to the hydrogen-burning mass limit and so may have less than a tenth of Sol's mass. As a result, the distance from star C where an Earth-type planet would be comfortable with liquid water is less than 0.006 AU, but such an orbit would likely be disrupted by the proximity of Star A. It is also known as Gl 866 C (RECONS) list of the 100 Nearest Star Systems).

Hunt for Substellar Companions

A recent search for faint companions using the Hubble Space Telescope found no supporting evidence for a large Jupiter or brown dwarf sized object (Schroeder et al, 2000).

Closest Neighbors

The following star systems are located within 10 ly of EZ Aquarii 3.

Star System	Spectra & Luminosity	Distance (light-years)
Lacaille 9352	M1.5-3 Ve	4.1
Lacaille 8760	K7-M2 Ve	4.2
Gliese 876 / Ross 780	M3.5 V	4.3
Epsilon Indi	K3-5 Ve	4.8
G 158-27	M5.5 V	6.7
Cincinnati	M2-4 V	7.2
YZ Ceti	M4.5 Ve	7.5
Luyten 726-8	M5.6 Ve	7.7
Tau Ceti	G8 Vp	8.8
L 722-22 AB	M4 V M4 V	8.9
Van Maanen's Star	DF-G/VII	9.0
Hip 103039	?	9.2
Ross 154	M3.5-6 Ve	9.5
CD-49 13515	M1 V	7.3

Other Information

Up-to-date technical summaries on this star can be found at: the Astronomiches Rechen-Institut at Heidelberg's ARICNS, the Nearby Stars Database, and the Research Consortium on Nearby Stars (RECONS) list of the 100 Nearest Star Systems. Additional information may be available at Roger Wilcox's Internet Stellar Database.

Aquarius was "Latinized" by the Romans from Ganymede in Greek mythology, who was "cup-bearer to the gods." For more information on stars and other objects in Constellation Aquarius and an illustration, go to Christine Kronberg's Aquarius. For another illustration, see David Haworth's Aquarius.

For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.