15 Sagittae

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**15 Sagittae AB**
Observation data Epoch J2000.0
Constellation (pronunciation)	Sagitta
Right ascension	20^h 04^m 06.22^s
Declination	+17° 04′ 12.6″
Apparent magnitude (V)	+5.8
Characteristics
Spectral type	G1V \ L4.5V
U-B color index	?
B-V color index	?
Variable type	yes
Astrometry
Radial velocity (R_v)	+4.8 km/s
Proper motion (μ)	RA: -394.07 mas/yr Dec.: -406.42 mas/yr
Parallax (π)	56.60 ± 0.64, 0.63, 154 mas
Distance	57.7 ly (17.69 pc)
Absolute magnitude (M_V)	4.56
Visual binary orbit
Companion	15 Sagittae B
Period (P)	100 yr
Semimajor axis (a)	0.79"
Eccentricity (e)	0.3
Inclination (i)	51°
Longitude of the node (Ω)	?°
Periastron epoch (T)	?
Details
Mass	1 \ 0.06 M_☉
Radius	1.1 \ 0.14 R_☉
Luminosity	1.3 L_☉
Temperature	5940 \ ~72 K
Metallicity	?
Rotation	?
Age	1000 - 3000 million years
Other designations
BD+16°4121, HD 190406, Gl 779, HR 7672, HIP 98819, LFT 1517, LHS 3515, LTT 15872, SAO 105635, Wolf 866

15 Sagittae (also known as HD 190406; 15 Sge for short) is a binary star system approximetally 57 light-years away in the constellation Sagitta. The primary star, 15 Sge A, is a yellow dwarf star similar to the Sun. Its mass, radius, and luminosity don't differ greatly from the Sun.

The secondary star is 15 Sge B. Discovered on January 7, 2002, this brown dwarf was imaged by a team of astronomers led by Michael Liu and Geoff Marcy. Based on theoretical models of the cooling of very low mass objects, 15 Sge B is estimated to have between 55 and 78 times Jupiter's mass. As a result, astronomers believe that it may be too massive to have formed like a planet from the circumstellar disk of gas and dust that enveloped 15 Sge when it was less than a hundred million years old. Rather, it may have developed from a fragment of the molecular cloud that was condensing into 15 Sge itself at an earlier stage of stellar formation.

15 Sge B orbits 15 Sge A at a separation of 0.79" or about 14 AU (between the orbital distance of Saturn and Uranus in the Solar System). Given a minimum mass of 48 times that of Jupiter derived from the radial velocity data alone, possible orbits have been generated with semi-major axes of seven to 28 AU and periods of around 50 to 150 years. One good fit would be an orbit with a semi-major axis of 21 AU, a period of 100 years, a low eccentricity, and an inclination of 51° from the perspective of an observer on Earth.

There was a METI message sent to 15 Sagittae. It was transmitted from Eurasia's largest radar — 70-meter Eupatoria Planetary Radar. The message was named Cosmic Call 1, it was sent on June 30, 1999, and it will arrive at 15 Sagittae in February 2057. ^[1]