VB 10 or Van Biesbroeck's star/vænˈbiːzbrʊk/[7] is a small and dim red dwarf[2] located in the constellationAquila. It is part of a binary star system. VB 10 is historically notable as it is one of the faintest known stars to exist.[8] Although it is relatively close to Earth, at about 19 light years, VB 10 is a dim magnitude 17, making it difficult to image with amateur telescopes as it can get lost in the glare of the primary star.[1]
VB 10 has an extremely low luminosity with a baseline absolute magnitude of nearly 19 and an apparent magnitude of 17.3 (somewhat variable), making it very difficult to see.
Mathematical formulae[9] for calculating apparent magnitude show that, if VB 10 occupied the place of the Sun, it would shine on Earth's sky at a magnitude of −12.87—approximately the same magnitude of that of the full moon.[10]
Later researchers also noted that its mass, at 0.08 solar mass (M☉), is right at the lower limit needed to create internal pressures and temperatures high enough to initiate nuclear fusion and actually be a star rather than a brown dwarf. At the time of its discovery it was the lowest-mass star known. The previous record holder for the lowest mass was Wolf 359 at 0.09 M☉.[11]
VB 10 is also notable by its very large proper motion, moving more than one arc second a year through the sky as seen from Earth.[1]
Flare star
VB 10 is a variable star and is identified in the General Catalogue of Variable Stars as V1298 Aquilae. It is a UV Ceti-type variable star and is known to be subject to frequent flare events.[2] Its dynamics were studied from the Hubble Space Telescope in the mid-1990s. Although VB 10 has a normal low surface temperature of 2600 K it was found to produce violent flares of up to 100,000 K.[11] This came as a surprise to astronomers. It had previously been assumed that low mass red dwarfs would have insignificant or nonexistent magnetic fields, which are necessary for the production of solar flares. The dwarfs were believed to lack the radiative zone just outside the star's core that powers the dynamo of stars like our Sun. Nevertheless, the detection of solar flares indicates some as yet unknown process allows the solely convective cores of low mass stars to produce sufficient magnetic fields to power such outbursts.[12]
VB 10 is the secondary star of a bound binary star system. The primary is called Gliese 752, and hence VB 10 is also referred to as Gliese 752 B. The primary star is much larger and brighter. The two stars are separated by about 74 arc seconds (~434 AU).[4]
Claims of a planetary system
In May 2009, astronomers from NASA's Jet Propulsion Laboratory, Pasadena, California, announced that they had found evidence of a planet orbiting VB 10, which they designated VB 10b. The 200 in (5.1 m) Hale telescope at the Palomar Observatory was used to detect evidence of this planet using the astrometry method.[6][13] The new planet was claimed to have a mass 6 times that of Jupiter and an orbital period of 270 days. However, subsequent studies using Doppler spectroscopy failed to detect the radial velocity variations that would be expected if such a planet was orbiting this small star.[14][15] The claimants of VB 10b note that these Doppler measurements only rule out planets more massive than 3 times the mass of Jupiter, but this limit is only half the reported best-fit mass of the planet as originally claimed.[16] The claims for this planet thus fall into a long history of claimed astrometric extrasolar planet detections that were subsequently refuted.[14]
By 2016, it was suspected that the asymmetric debris disk signal was mistaken for the long-period planet.[17]
^ abLinsky; Wood, Brian E.; Brown, Alexander; Giampapa, Mark S.; Ambruster, Carol (December 20, 1995). "Stellar Activity at the End of the Main Sequence: GHRS Observations of the M8 Ve Star VB 10". The Astrophysical Journal. 455: 670–676. Bibcode:1995ApJ...455..670L. doi:10.1086/176614. hdl:2060/19970022983.
