1RXS J160929.1−210524 (also known as GSC 6213-1358 or PZ99 J160930.3−210459) is a pre-main-sequence star approximately 456

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

of Scorpius. The star was identified as a member of the Upper Scorpius subgroup of the

Scorpius–Centaurus association The Scorpius–Centaurus association (sometimes called Sco–Cen or Sco OB2) is the nearest OB association to the Sun. This stellar association is composed of three subgroups (Upper Scorpius, Upper Centaurus–Lupus, and Lower Centaurus–Crux) ...

by Thomas Preibisch and coauthors in 1998, and originally assigned an age of years old based on its group membership. A more recent analysis of the ages of the stars in the Upper Scorpius group pegs its average age at 11 million years.

Stellar characteristics

This star was identified as a young object belonging to the Upper Scorpius subgroup of the

in two papers published in 1998 and 1999, based on its lithium abundance, X-ray emission, and position in the H–R diagram. The spectrum of 1RXS J160929.1-210524 reveals it to be cooler than the Sun with a spectral type that has been estimated at K7 or M0, so the star can be considered an orange dwarf or a

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...

. The star is estimated to be around 0.85 times as massive as the Sun and to have an

effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...

of 4,060 K. The Upper Scorpius association is quite young and only stars earlier (hotter) than type A3 have reached the

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

; less massive stars, such as 1RXS J160929.1−210524, are still in the process of contraction during the pre-main sequence phase. Originally, the association was estimated to be around 5 million years old, but a recent 2012 paper made a significant revision of this value to 11 million years, which is therefore considered to be the age of 1RXS J160929.1-210524.

Planetary system

On 8 September 2008, it was announced that astronomer David Lafrenière and collaborators used the Gemini Observatory to take pictures of the star which appeared to show a planet (designated ''1RXS J160929.1-210524 b''). The apparent planet is very large—about eight times the mass of Jupiter, orbiting the star at a distance of (roughly or miles). The orbital status of the companion planet was confirmed in a paper submitted on 2010 to '' The Astrophysical Journal''. This made it the smallest known

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

orbiting its host at such a distance. It is also the second announced directly imaged exoplanet orbiting a sun-like star (after GQ Lup b), and the 2nd directly imaged exoplanet to have spectrum taken (after

2M1207b 2M1207b is a planetary-mass object orbiting the brown dwarf 2M1207, in the constellation Centaurus, approximately 170 light-years from Earth.

). The discoverers note that the object's location far from its star presents serious challenges to current models of planetary formation: the timescale to form a planet by core accretion at this distance from the star would be longer than the age of the system itself. One possibility is that the planet may have formed closer to the star and migrated outwards as a result of interactions with the disk or with other planets in the system. An alternative is that the planet formed ''in situ'' via the disk instability mechanism, where the disk fragments because of gravitational instability, though this would require an unusually massive protoplanetary disk. With the upward revision in the age of the Upper Scorpius group from 5 million to 11 million years, the estimated mass of 1RXS J1609b is approximately 14 Jupiter masses, i.e. above the deuterium-burning limit. An older age for the J1609 system implies that the luminosity of J1609b is consistent with a much more massive object, making more likely that J1609b may be simply a brown dwarf which formed in a manner similar to that of other low-mass and substellar companions. A 2013 study, using data from the

Spitzer Space Telescope The Spitzer Space Telescope, formerly the Space Infrared Telescope Facility (SIRTF), was an infrared space telescope launched in 2003. Operations ended on 30 January 2020. Spitzer was the third space telescope dedicated to infrared astronomy, f ...

, detected a moderate

excess Excess may refer to: * Angle excess, in spherical trigonometry * Insurance excess, similar to a deductible * Excess, in chemistry, a reagent that is not the limiting reagent * "Excess", a song by Tricky from the album '' Blowback'' * ''Excess'' ( ...

of infrared radiation at 24

μm The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...

coming from this system, indicating the presence of a dusty debris disk, but could not determine whether the excess was coming from the star or the substellar companion (or both). In 2015, observations with the Magellan Clay Telescope found evidence that the light from the substellar object is obscured and reddened by 4.5 visual magnitudes of circumstellar extinction, which indicated that the object is surrounded by a dusty disk responsible for the infrared excess. When considering the extinction in modeling the object's spectrum, its effective temperature was increased to 2,000 K and the spectral type to L2.

References

External links

* * * Astronomy Picture of the Day �
Companion of a Young, Sun-like Star Confirmed
– 2010 July 4 {{DEFAULTSORT:1RXS J160929.1-210524 K-type main-sequence stars Pre-main-sequence stars Scorpius (constellation) Planetary systems with one confirmed planet T Tauri stars ROSAT objects Upper Scorpius

Stellar characteristics

Planetary system

See also

References

External links