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Brown Dwarf Found Orbiting a Young Sun-like Star

PZ Tel

PZ Tel A and B. The vast majority of light from PZ Tel A has been removed from this image using specialized image analysis techniques. The size of the orbit of Neptune is shown for comparison. PZ Tel B would lie within Neptune's orbital dimensions and is one of few brown dwarfs or exoplanets imaged at a distance of less than 30 AU from its parent star. Credit: Beth Biller and the Gemini NICI Planet-Finding Campaign, Gemini Observatory/AURA.

A team led by IfA astronomers Beth Biller, Michael Liu, and Zahed Wahhaj has taken a picture of a very young brown dwarf (or failed star) in a tight orbit around a young nearby Sun-like star.  This discovery is a rare find:  The brown dwarf companion, dubbed "PZ Tel B," has a mass 36 times that of Jupiter and resides only 18 astronomical units (AU) from its primary star, a distance similar to that of Uranus from the Sun.

Most young brown dwarf and planetary companions found by direct imaging are at orbital separations greater than 50 AU—farther than the orbit of Pluto (40 AU). In addition to observing its small current separation, in just the past year, the researchers saw PZ Tel B moving quickly outward from its parent star. As recently as 2003, PZ Tel B was completely obscured by its parent star, indicating its orbit is more oval than circular.

The host star, PZ Tel A, has a mass similar to that of the Sun, but is only 12 million years old, while our Sun has been shining for about 5 billion years. In fact, PZ Tel is young enough to still possess significant amounts of cold circumstellar dust, which may have been sculpted by the gravitational interaction with the young brown dwarf companion. This makes the PZ Tel system an important laboratory for studying the early stages of solar system formation. PZ Tel B's orbital motion has significant implications for what type of planets can form (and whether planets can form at all) in the PZ Tel system.

PZ Tel B was discovered using the Near-Infrared Coronagraphic Imager (NICI; see Na Kilo Hoku no. 35) on the Gemini South Telescope. NICI is a powerful instrument designed for imaging brown dwarfs and planets around other stars. It is the highest contrast camera in operation today and can detect companions 1 million times fainter than the host star at just 1 arcsecond separations.

An international team of researchers is currently carrying out a 300-star survey with NICI, the largest high-contrast imaging survey conducted to date. NICI Campaign leader Michael Liu says, "We are just beginning to glean the many configurations of solar systems around stars like the Sun. The unique capabilities of NICI provide us a powerful tool for studying their constituents using direct imaging."

Because PZ Tel B is so close to its parent star, special techniques were needed to distinguish the faint light of the companion from the light of the primary star. PZ Tel B is separated by less than 0.4 arcsecond from PZ Tel A, equivalent to a dime seen at a distance of 5 miles (about 8 km). NICI was able to take pictures PZ Tel B because it has both an advanced adaptive optics system, which corrects for the blurring of astronomical images caused by turbulence in Earth's atmosphere, and a coronagraph that blocks out excess starlight. The team applied specialized analysis techniques to the images to detect PZ Tel B and measure its orbital motion.

The discovery of PZ Tel B is described in a paper published by the Astrophysical Journal Letters.