Collapsed datacubes showing HR 2562B in each of the four modes observed with GPI and reduced using KLIP. The K2 image is from February 2016 and demonstrates two possible solutions for the inner edge of the disk (38 and 75 AU with dashed and dotted-dashed lines respectively) assuming inclination of 78 degrees and position angle of 120 degrees. Credit: Konopacky et al., 2016.
Astronomers have detected a brown dwarf orbiting HR 2562 – a nearby star known to host a debris disk. HR 2562, 110 light years away, is an F5V star, about 30% more massive than the sun. It has a debris disk—a circumstellar belt of dust and planetesimals left over from planetary formation. The disk around HR 2562, spans from 38 to 75 AU away from the host star.
In early 2016, a team of researchers, led by Quinn Konopacky, UCSD, observed HR 2562 using the Gemini Planet Imager (GPI), mounted on Gemini South Telescope in Chile. GPI is a high-contrast imaging instrument, allowing imaging and integral field spectroscopy of extrasolar planets. The observations were conducted as part of the Gemini Planet Imager Exoplanet Survey (GPIES), that images young Jupiters and debris disks around nearby stars.
However, their search for a young, Jupiter-like planet resulted in a discovery of a much more massive substellar object. The data allowed the team to confirm the existence of a brown dwarf that could have at least 15 Jupiter masses. The newly found companion is separated by about 20 AU from the host star and was designated HR 2562B. “We present the discovery of a brown dwarf companion to the debris disk host star HR 2562. This object, discovered with the Gemini Planet Imager, has a projected separation of 20.3±0.3 AU from the star,” the researcherssaid. Separation by only 20 AU means that HR 2562B lies within the inner hole of the debris disk; significantly, it is the first known brown dwarf residing inside such a gap. The scientists also noted that so far, only few substellar companions have been imaged within 100 AU from their host stars.
While the separation of HR 2562B has been precisely estimated, its mass remains uncertain. Its minimum mass is at least 15 Jupiter masses. However, the brown dwarf could be even 45 times more massive than Jupiter as well. Thus, the mean value was calculated to be 30 Jupiter masses. The host star’s age also remains to be determined, as previous observations delivered conflicting results, ranging from 20 million to 1.6 billion years. However, for the purposes of the recent study, the team adopted a nominal age range of 300 to 900 million years.
The findings could be useful in understanding the formation process of circumstellar companions; it is widely debated whether these objects form within a circumstellar disk and reach a mass above the deuterium burning limit or via cloud fragmentation, as in binary systems with a high mass ratio. Future studies of the HR 2562 system should focus on constraining the true mass and orbit of the companion. It could be essential to determine its possible origin, which could offer evidence of planet formation above the deuterium burning limit. http://phys.org/news/2016-08-astronomers-brown-dwarf-companion-nearby.htmljCp
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