EBLM J0555-57

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 J0555-57AB

Resolved image of EBLM J0555-57A (left) and EBLM J0555-57B (right) taken with the Leonhard Euler Telescope at the ESO's La Silla Observatory[1]
Credit: ESO
Observation data
Epoch J2000      Equinox J2000
Constellation Pictor
Right ascension 05h 55m 32.6868s[2]
Declination −57° 17′ 26.064″[2]
Apparent magnitude (V) 9.98 / 10.76[1]
Characteristics
EBLM J0555-57A
Spectral type F8[3]
Variable type Eclipsing[1]
EBLM J0555-57B
Spectral type G0V
Astrometry
Radial velocity (Rv)23.419 ± 0.74[4] km/s
Proper motion (μ) RA: 3.858[2] mas/yr
Dec.: -39.713[2] mas/yr
Parallax (π)5.16 ± 0.36[2] mas
Distance630 ± 40 ly
(190 ± 10 pc)
Position (relative to A)
ComponentB
Epoch of observation1998
Angular distance2.50″ [3]
Position angle254° [3]
Observed separation
(projected)		479 AU [1]
Orbit[1]
PrimaryAa
CompanionAb
Period (P)7.757676+0.000029
−0.000025 d
Semi-major axis (a)0.0817 ± 0.0019 au
Eccentricity (e)0.0894+0.0035
−0.0036
Inclination (i)89.84+0.2
−1.8°
Argument of periastron (ω)
(secondary)		−53.7+1.5
−1.8°
Details[1]
EBLM J0555-57Aa
Mass1.13 ± 0.08 M☉
Radius0.99+0.15
−0.03 R☉
Surface gravity (log g)4.18 ± 0.21 cgs
Temperature6461 ± 124 K
Metallicity [Fe/H]−0.24 ± 0.16 dex
Rotational velocity (v sin i)7.60 ± 0.28 km/s
EBLM J0555-57Ab
Mass85.2+4.0
−3.9 MJup
Radius0.84+0.14
−0.04 RJup
Surface gravity (log g)5.50+0.03
−0.13 cgs
EBLM J0555-57B
Radius0.94 ± 0.08 R☉
Temperature5717 ± 124 K
Other designations
CD−57 1311, CPD−57 913, WDS J05555-5717, TYC 8528-926-1, 2MASS J05553262-5717261
Database references
SIMBADdata

System

EBLM J0555-57, also known as CD−57 1311, is a triple star system[1][5] 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.[1]

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.[1]

EBLM J0555-57Ab

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.[1] 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),[1] using data collected by the WASP project. WASP (Wide Angle Search for Planets) is searching for exoplanets using the transit method.[6] 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.[1]

References
  1. 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 Saturn-size 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.
  2. 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.
  3. 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.
  4. 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.
  5. Wenz, John (11 July 2017). "This Is the Smallest Star Ever Discovered". Popular Mechanics. Retrieved 17 July 2017.
  6. "Smallest-ever star discovered by astronomers". Phys.org. 12 July 2017. Retrieved 12 July 2017.
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