Epoch J2000 Equinox J2000
|Right ascension||05h 55m 32.6868s|
|Declination||−57° 17′ 26.064″|
|Apparent magnitude (V)||9.98 / 10.76|
|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)|
|Mass||1.13 ± 0.08 M☉|
|Surface gravity (log g)||4.18 ± 0.21 cgs|
|Temperature||6461 ± 124 K|
|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|
|Radius||0.94 ± 0.08 R☉|
|Temperature||5717 ± 124 K|
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 ± 4 Jupiter masses, or 0.081 Solar masses. The star has a radius comparable to that of Saturn. EBLM J0555-57Ab is situated at the lower mass limit for hydrogen-burning stars predicted by current stellar models. 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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