OGLE-TR-123

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**OGLE-TR-123**
Observation data Epoch J2000.0 (ICRS)
Constellation (pronunciation)	Carina
Right ascension	11^h 06^m 51.19^s^[1]
Declination	-61° 11′ 10.1″^[1]
Characteristics
Spectral type	F (primary)/M (b)^[2]
Apparent magnitude (infrared, I band)	15.40 (system)^[1]
Variable type	Eclipsing binary
Astrometry
Distance	5000 ± 1000 ly (1600 ± 400 pc)^[2]
Binary orbit
Period (P)	1.804^[2] days
Eccentricity (e)	0^[2]
Semi-major axis	0.031 ± 0.002 AU^[2]
Inclination (i)	86–90° ^[2]
Details
Mass	1.3 (primary)^[2] / 0.085 (b)^[2] M_☉
Radius	1.55 (primary)^[2] / 0.13 (b)^[2] R_☉
Temperature	6,700 ± 300 (primary)^[2] K

OGLE-TR-123 is a binary stellar system containing one of the smallest main-sequence stars whose radius has been measured. It was discovered when the Optical Gravitational Lensing Experiment (OGLE) survey observed the smaller star eclipsing the larger primary. The orbital period is approximately 1.80 days.^[2]

The smaller star, OGLE-TR-123b, is estimated to have a radius around 0.13 solar radii, and a mass of around 0.085 solar masses, or approximately 90 times Jupiter's. OGLE-TR-123b's mass is close to the lowest possible mass, estimated to be around 0.07 or 0.08 solar masses, for a hydrogen-fusing star.^[3] OGLE-TR-123b is the second star with mass less than 0.1 solar mass whose radius has been directly measured; the first such star was the similar OGLE-TR-122b.^[2]

[edit] References

^ ^a ^b ^c The Optical Gravitational Lensing Experiment. Additional Planetary and Low-Luminosity Object Transits from the OGLE 2001 and 2002 Observational Campaigns, A. Udalski, G. Pietrzynski, M. Szymanski, M. Kubiak, K. Zebrun, I. Soszynski, O. Szewczyk, and L. Wyrzykowski, Acta Astronomica 53 (June 2003), pp. 133–149.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m Radius and mass of a transiting M dwarf near the hydrogen-burning limit. OGLE-TR-123, F. Pont, C. Moutou, F. Bouchy, R. Behrend, M. Mayor, S. Udry, D. Queloz, N. Santos, and C. Melo, Astronomy and Astrophysics 447, #3 (March 1, 2006), pp. 1035–1039. doi:10.1051/0004-6361:20053692 . Bibcode: 2006A&A...447.1035P.
^ Theory of Low-Mass Stars and Substellar Objects, Gilles Chabrier and Isabelle Baraffe, Annual Review of Astronomy and Astrophysics 38 (2000), pp. 337–377.