Epoch J2000 Equinox J2000
|Right ascension||05h 55m 32.6868s|
|Declination||−57° 17′ 26.064″|
|Apparent magnitude (V)||9.98 / 10.76|
|Spectral type||G0V|
|Radial velocity (Rv)||23.419±0.74 km/s|
|Proper motion (μ)|| RA: 3.858 mas/yr |
Dec.: −39.713 mas/yr
|Parallax (π)||5.16 ± 0.36 mas|
|Distance||630 ± 40 ly |
(190 ± 10 pc)
|Position (relative to A)|
|Epoch of observation||1998|
|Angular distance||2.50″ |
|Position angle||254° |
|479 AU |
|Semi-major axis (a)||0.0817±0.0019 au|
|Argument of periastron (ω)|
|Surface gravity (log g)||4.18±0.21 cgs|
|Metallicity [Fe/H]||−0.24±0.16 dex|
|Rotational velocity (v sin i)||7.60±0.28 km/s|
|Surface gravity (log g)||5.50+0.03|
EBLM J0555-57 is a triple star system approximately 600 light-years from Earth. EBLM J0555-57Ab, the smallest star in the system, orbits its primary star with a period of 7.8 days, and at the time of discovery, was the smallest known star with a mass sufficient to enable the fusion of hydrogen in its core.
EBLM J0555-57, also known as CD−57 1311, is a triple star system in the constellation Pictor, which contains a visual binary system consisting of two sun-like stars separated by 2.5": EBLM J0555-57Aa, a magnitude 9.98 spectral type F8 star, and EBLM J0555-57B, a magnitude 10.76 star. No orbital motion has been detected but they have almost identical radial velocities and are assumed to be gravitationally bound.
Component A of the system is itself an eclipsing binary (EBLM J0555-57Ab orbiting EBLM J0555-57Aa). Eclipses, also known as transits in the context of planetary searches, have been detected in the near infrared, with brightness drops of 0.05% during the eclipse. The shape and duration of the transits allow the radii of the two stars to be determined. A full solution of the orbit gives a period of 7 days and 18 hours, with a low eccentricity of 0.09, an almost edge-on inclination of 89.84°, and a semi-major axis of 0.08 AU.
EBLM J0555-57Ab has a mass of about 85.2±4 ( probably 83 ) Jupiter masses, or 0.081 Solar masses. Its radius is 0.08 Solar radii (about 59,000 km), slightly smaller than Saturn's equatorial radius of 60,268 km, although the star is about 250 times more massive than Saturn.  Current stellar models put its mass at the lower limit for hydrogen-burning stars. EBLM J0555-57Ab was discovered by a group of scientists at the University of Cambridge associated with the EBLM project (Eclipsing Binary, Low Mass), using data collected by the WASP project. WASP (Wide Angle Search for Planets) is searching for exoplanets using the transit method. Additional properties of the star were determined using Doppler spectroscopy, to measure the periodic radial velocity variation of the primary star due to the gravitational influence of its companion.
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EBLM J0555-57Ab is the smallest star currently known.
- 2MASS J0523-1403
- OGLE-TR-122 - This binary stellar system contained one of the smallest red dwarfs known when it was discovered.
- List of smallest stars
- von Boetticher, Alexander; Triaud, Amaury H. M. J.; Queloz, Didier; Gill, Sam; Lendl, Monika; Delrez, Laetitia; Anderson, David R.; Collier Cameron, Andrew; Faedi, Francesca; et al. (2017). "The EBLM project III. A smaller than Saturn low-mass star at the hydrogen-burning limit". Astronomy and Astrophysics. 1706: L6. arXiv:1706.08781. Bibcode:2017A&A...604L...6V. doi:10.1051/0004-6361/201731107. S2CID 54610182.
- Gaia Collaboration (2016). "Gaia Data Release 1". Astronomy & Astrophysics. 595: A2. arXiv:1609.04172. Bibcode:2016A&A...595A...2G. doi:10.1051/0004-6361/201629512. S2CID 1828208.
- Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
- Kunder, Andrea; Kordopatis, Georges; Steinmetz, Matthias; Zwitter, Tomaž; McMillan, Paul J.; Casagrande, Luca; Enke, Harry; Wojno, Jennifer; Valentini, Marica; Chiappini, Cristina; Matijevič, Gal; Siviero, Alessandro; De Laverny, Patrick; Recio-Blanco, Alejandra; Bijaoui, Albert; Wyse, Rosemary F. G.; Binney, James; Grebel, E. K.; Helmi, Amina; Jofre, Paula; Antoja, Teresa; Gilmore, Gerard; Siebert, Arnaud; Famaey, Benoit; Bienaymé, Olivier; Gibson, Brad K.; Freeman, Kenneth C.; Navarro, Julio F.; Munari, Ulisse; et al. (2017). "The Radial Velocity Experiment (RAVE): Fifth Data Release". The Astronomical Journal. 153 (2): 75. arXiv:1609.03210. Bibcode:2017AJ....153...75K. doi:10.3847/1538-3881/153/2/75. S2CID 118835808.
- Wenz, John (11 July 2017). "This Is the Smallest Star Ever Discovered". Popular Mechanics. Retrieved 17 July 2017.
- "Smallest-ever star discovered by astronomers". Phys.org. 12 July 2017. Retrieved 12 July 2017.
- Smallest ever star discovered by astronomers University of Cambridge