AS 209 is a young pre-main-sequence

K-type star In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

located in the Ophiuchus star formation region about 126 parsecs from the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. It has a mass of 0.9 solar masses and a luminosity of 1.5 solar luminosity. It is only somewhere between 0.5-1.0 million years old. Surrounding AS 209 is a remarkable

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk; while the two are sim ...

. This disk is separated into several distinct parts. There the central core and extending from it lies two prominent rings at 75 AU and 135 AU. These rings have different widths and depths with the inner one being narrower and shallower. V1121OphLightCurve

AS 209 was found to be a

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are ...

in 1968. and it was given the

variable star designation In astronomy, a variable-star designation is a unique identifier given to variable stars. It extends the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constellation in whic ...

V1121 Ophiuchi, in 1970. The International Variable Star Index classifies it as both a classical

T Tauri star T Tauri stars (TTS) are a class of variable stars that are less than about ten million years old. This class is named after the prototype, T Tauri, a young star in the Taurus Molecular Cloud, Taurus star-forming region. They are found near mo ...

and a T Tauri star showing periodic variability due to starspots. The

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of ...

data for the star shows periodic variability. S. A. Artemenko ''et al.'' determined that the period is 8.60 days, in 2012. The gap of the outer disk suggest that there might be a Saturn-like (0.7 Saturn mass)

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first confirmed detection of an exoplanet was in 1992 around a pulsar, and the first detection around a main-sequence star was in 1995. A different planet, first det ...

orbiting the star at a distance of 62 AU. There may also be a second

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

with 0.1 Jupiter masses orbiting closer to the star than the first planet. The discovery of such planets around a young less than a million year old star shows that giant planets are able to form far from their

stars A star is a luminous spheroid of plasma held together by self-gravity. The nearest star to Earth is the Sun. Many other stars are visible to the naked eye at night; their immense distances from Earth make them appear as fixed points of ...

on wide orbits.

References

{{Ophiuchus Ophiuchus K-type stars Circumstellar disks 082323 Ophiuchi, V1121