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.
(A 2MASS Survey image of EZ Aquarii from the NASA
Star and Exoplanet Database may become available.)

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). The high proper motion of 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.

AC-B Multiple Star System

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.)

---------------------------------------------- [Guide] -- [Larger] ----------------------------------------------

Orbital
Distance
(a=AUs) Orbital
Period
(P=years) Orbital
Eccentricity
(e) Orbital
Inclination
(i=degrees) Mass
Estimate
(Solar)
Diameter
(Solar)
Density
(Earths) Surface
Gravity
(Earths)
Metallicity
(Solar)
AC-B Mass Center 0.0 ... ... ... ... ... ... ... ...
EZ Aquarii B 0.43 2.25 0.437 112.4 ~0.1 0.08-0.35 ... ... ...
Inner H.Z. Edge B? 0.022 0.010 0 112.4 ... ... ... ... ...
Outer H.Z. Edge B? 0.054 0.040 0 112.4 ... ... ... ... ...
AC Mass Center 0.79 2.25 0.437 112.4 ... ... ... ... ...
EZ Aquarii A 0.053 0.01 0 112.4? ~0.1 0.08-0.35 ... ... ...
Inner H.Z. Edge A? 0.022 0.010 0 112.4? ... ... ... ... ...
Outer H.Z. Edge A? 0.054 0.040 0 112.4? ... ... ... ... ...
EZ Aquarii C 0.077 0.01 0 112.4? ~0.1 0.08-0.35 ... ... ...
Inner H.Z. Edge C? 0.022 0.010 0 112.4? ... ... ... ... ...
Outer H.Z. Edge C? 0.054 0.040 0 112.4? ... ... ... ... ...

	Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass Estimate (Solar)	Diameter (Solar)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
AC-B Mass Center	0.0	...	...	...	...	...	...	...	...
EZ Aquarii B	0.43	2.25	0.437	112.4	~0.1	0.08-0.35	...	...	...
Inner H.Z. Edge B?	0.022	0.010	0	112.4	...	...	...	...	...
Outer H.Z. Edge B?	0.054	0.040	0	112.4	...	...	...	...	...
AC Mass Center	0.79	2.25	0.437	112.4	...	...	...	...	...
EZ Aquarii A	0.053	0.01	0	112.4?	~0.1	0.08-0.35	...	...	...
Inner H.Z. Edge A?	0.022	0.010	0	112.4?	...	...	...	...	...
Outer H.Z. Edge A?	0.054	0.040	0	112.4?	...	...	...	...	...
EZ Aquarii C	0.077	0.01	0	112.4?	~0.1	0.08-0.35	...	...	...
Inner H.Z. Edge C?	0.022	0.010	0	112.4?	...	...	...	...	...
Outer H.Z. Edge C?	0.054	0.040	0	112.4?	...	...	...	...	...

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 (0.1187 Solar-mass according to Torres et al, 2010), about eight to 35 percent of its diameter, and only 8.7-12/100,000th of its luminosity. 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, G 156-31, 2MASS J22383372-1517573 A, and WDS J22385-1519 A.

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. Some alternative names and useful catalogue numbers for this star are: L 789-6 B, Gl 866 B, 2MASS J22383372-1517573 B, and WDS J22385-1519 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. It is also known as Gl 866 C (RECONS' list of the 100 Nearest Star Systems).

Jeffrey L. Linsky, JILA, STScI, NASA

Larger image.

Like Gliese 752 B, EZ Aquarii A, B, and C
are so small, with less than 20 percent of
Sol's mass, that it can transport core heat
only through convection, unlike larger larger
red dwarf stars like Gliese 752 A (more).

Habitable Zone for Star A, B, or C

With a spectral type of M5.5, Proxima Centauri can be used as a rough proxy for either Stars A or B (M4.9-5.5 and M5.5 or later, respectively). Accounting for infrared radiation, the distance from Proxima where an Earth-type planet could have liquid water on its surface is around 0.022 to 0.054 AU (Endl and Kürster, 2008; and Endl et al, 2003, in pdf) -- much closer than Mercury's orbital distance of about 0.4 AU from Sol -- with a corresponding orbital period of 3.6 to 13.8 days (Endl and Kürster, 2008), while the NASA Star and Exoplanet Database has calculated a slightly farther out habitable zone between 0.033 and 0.064 AUs around Proxima. In any case, the rotation of such a planet would probably be tidally locked so that one side would be in perpetual daylight and the other in darkness.

Hunt for Substellar Companions

A 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.

------------------------------------- [Guide] -- [Full Near Star Map] -------------------------------------

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 / Gl 832	M1.5 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 for Star A and Star B, the NASA Star and Exoplanet Database for Star A and B, and 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.