36 Ophiuchi 3?

AB Binary Star System

Based on an average parallax (0.1675") incorporating Hipparcos data, Stars A and B are separated "on average" by about 88 AUs (of a semi-major axis) in an extremely eccentric orbit (e= 0.922) that swings between seven and 169 AUs. The orbit takes around 570 years to complete, and its best fit inclination is around 99.6 degrees from the line of sight of Earth (Irwin et al, 1996 -- Orbit 4; and Peter Brosche, 1960).

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	Orbital Distance (a=AUs)	Orbital Period (P=years)	Orbital Eccentricity (e)	Orbital Inclination (i=degrees)	Mass (Solar)	Diameter (Solar)	Density (Earths)	Surface Gravity (Earths)	Metallicity (Solar)
AB Mass Center	0.0	...	...	...	...	...	...	...	...
36 Ophiuchi A	43.9	569	0.922	99.6	0.85	0.81	...	...	0.50-0.98
Inner H.Z. A Edge?	~0.5	0.36	0	99.6	...	...	...	...	...
Outer H.Z. A Edge?	~0.9	0.68	0	99.6	...	...	...	...	...
36 Ophiuchi B	43.9	569	0.922	99.6	0.85	0.81	...	...	1.23-2.46
Inner H.Z. B Edge?	~0.5	0.36	0	99.6	...	...	...	...	...
Outer H.Z. B Edge?	~0.9	0.68	0	99.6	...	...	...	...	...

36 Ophiuchi A

A main sequence orange-red dwarf (K0-1.5 Ve), the primary has only around 85 percent of Sol's mass (RECONS estimate), 81 percent of its diameter (Johnson and Wright, 1983, page 689), 28 percent of its luminosity, and 50 to 98 percent of Sol's abundance of elements heavier than hydrogen (metallicity), based on its abundance of iron (Cayrel de Strobel et al, 1991, page 301). Although the SIMBAD Astronomical Database has identified Star A as a pre-main sequence star, astronomers who have made a special study of this stars have identified it as a "chromospherically active" spectral K (orange-red), main-sequence dwarf star (Irwin et al, 1996). Based on chromospheric activity and rotational period, the star may be relatively youthful, somewhere around 1.0 to 1.8 billion years old (Mamajek and Hillenbrand, 2008, Table 13). Some useful star catalogue numbers include: 36 Oph A, HR 6402, Gl 663 A, Hip 84405, HD 155886, CD-26 12026 A, CP(D)-26 5858 A, SAO 185198, LPM 632, LFT 1330, LTT 6871, LHS 437, ADS 10417 A, 2MASS J17152095-2636064 A, and SHJ 243.

Habitable Zone around Star A

With a spectral type of K2, Epsilon Eridani can be used as a rough proxy for 36 Ophiuchi A (K0-1.5). The distance from Epsilon Eridani where an Earth-type rocky planet may have liquid water on its surface has been estimated to be between 0.47 and 0.91 AU (Jones and Sleep, 2003) -- between the orbital distances of Mercury and Earth in the Solar System. In that distance range from the star, such a planet would have an orbital period shorter an Earth year. According to alternative calculations performed for the NASA Star and Exoplanet Database, the inner edge of Epsilon Eridani's habitable zone could be slightly farther out from the star at around 0.507 AUs from the star, while the outer edge lies even farther out at around 1.005 AUs. Given the apparent youth of this star system, however, it is likely that only primitive, single-celled organisms like bacteria that can survive heavy meteorite or cometary bombardment would be likely to survive on any Earth-type planet that has cooled sufficiently to allow carbon-based lifeforms to develop.

36 Ophiuchi B

A main sequence orange-red dwarf (K1-2 Ve), star B has only about 85 percent of Sol's mass (RECONS estimate), 81 percent of its diameter (Johnson and Wright, 1983, page 689), 27 percent of its luminosity, and 1.2 to 2.5 times Sol's abundance of elements heavier than hydrogen (metallicity), based on its abundance of iron (Cayrel de Strobel et al, 1991, page 301), but the difference between Stars A and B are probably not real given their likely birth from the same nebula. Likewise, they should be roughly the same age. Some useful star catalogue numbers include: 36 Oph B, HR 6401, Gl 663 B, CD-26 12026 B, CP(D)-26 5858 B, HD 155885, SAO 185199, LFT 1331, LTT 6872, LHS 438, and ADS 10417 B.

Habitable Zone around Star B

With a spectral type of K2, Epsilon Eridani can be used as a rough proxy for 36 Ophiuchi B (K1-2). The distance from Epsilon Eridani where an Earth-type rocky planet may have liquid water on its surface has been estimated to be between 0.47 and 0.91 AU (Jones and Sleep, 2003) -- between the orbital distances of Mercury and Earth in the Solar System. In that distance range from the star, such a planet would have an orbital period shorter an Earth year. According to alternative calculations performed for the NASA Star and Exoplanet Database, the inner edge of Epsilon Eridani's habitable zone could be slightly farther out from the star at around 0.507 AUs from the star, while the outer edge lies even farther out at around 1.005 AUs. Given the apparent youth of this star system, however, it is likely that only primitive, single-celled organisms like bacteria that can survive heavy meteorite or cometary bombardment would be likely to survive on any Earth-type planet that has cooled sufficiently to allow carbon-based lifeforms to develop.

36 Ophiuchi Bb? and Other Planets

Past measurements of radial-velocity variations appeared to indicate that star B has a substellar companion of about eight times the mass of Jupiter in an orbit of about 30 to 100 years to complete. However, the highly elliptical orbit of the binary pair which brings stars A and B as close together as 6.8 AUs makes the orbit of such a superplanet improbable, as the maximum stable orbit implies an "average" orbital distance of about 1.5 AUs (of a semi-major axis) and a period about two years for an object with no more than two Jupiter-masses. Hence, the velocity variations are likely due to the high chromospheric activity of stars A and B (Irwin et al, 1996). A subsequent study ruled out the presence of planets larger than four Jupiter-masses within 5.2 AUs of either star (Wittenmyer et al, 2006).

36 Ophiuchi C

A main sequence orange-red dwarf (K5-6 Ve), Star C has only about 71 percent of Sol's mass (RECONS estimate), 72 percent of its diameter (Johnson and Wright, 1983, page 689), 8.7 percent percent of its luminosity, and 46 to 100 percent of Sol's abundance of elements heavier than hydrogen (metallicity), based on its abundance of iron (Cayrel de Strobel et al, 1991, page 301). The star orbits the AB pair from around 4,370 to 5,390 AUs away. It is a RS CVn type variable star designated V2215 Oph, according to the SIMBAD Astronomical Database. Some useful star catalogue numbers include: Gl 663 C, Gl 664, Hip 84478, HD 156026, CD-26 12036, CP(D)-26 5863, SAO 185213, LPM 634, LFT 1332, LTT 6874, and LHS 439.

Habitable Zone around Star C

The distance from Star C where an Earth-type rocky planet may have liquid water on its surface is probably between 0.4 and 0.5 AU -- between the orbital distances of Mercury and Venus in the Solar System. At that distance range from Star C, such a planet would have an orbital period of less than 154 days, less than half an Earth year.

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