Beta Pictoris

Beta Pictoris (β Pic, β Pictoris) is the second brightest star in the constellation Pictor. It is located 63.4 light years from the Solar System, and is 1.75 times as massive and 8.7 times as luminous as the Sun. The Beta Pictoris system is very young, only 20 to 26 million years old, although it is already in the main sequence stage of its evolution. Beta Pictoris is the title member of the Beta Pictoris moving group, an association of young stars which share the same motion through space and have the same age. Beta Pictoris shows an excess of infrared emission compared to normal stars of its type, which is caused by large quantities of dust and gas (including carbon monoxide) near the star. Detailed observations reveal a large disk of dust and gas orbiting the star, which was the first debris disk to be imaged around another star. In addition to the presence of several planetesimal belts and cometary activity, there are indications that planets have formed within this disk and that the processes of planet formation may still be ongoing. Material from the Beta Pictoris debris disk is thought to be the dominant source of interstellar meteoroids in the Solar System. The European Southern Observatory (ESO) has confirmed the presence of a planet, Beta Pictoris b, matching previous predictions, through the use of direct imagery, orbiting in the plane of the debris disk surrounding the star. This planet is currently the closest extrasolar planet to its star ever photographed: the observed separation is roughly the same as the distance between Saturn and the Sun. Beta Pictoris is a star in the southern constellation of Pictor, the Easel, and is located to the west of the bright star Canopus. It traditionally marked the sounding line of the ship Argo Navis, before the constellation was split. The star has an apparent visual magnitude of 3.861, so is visible to the naked eye under good conditions, though light pollution may result in stars dimmer than magnitude 3 being too dim to see. It is the second brightest in its constellation, exceeded only by Alpha Pictoris, which has an apparent magnitude of 3.30. The distance to Beta Pictoris and many other stars was measured by the Hipparcos satellite. This was done by measuring its trigonometric parallax: the slight displacement in its position observed as the Earth moves around the Sun. Beta Pictoris was found to exhibit a parallax of 51.87 milliarcseconds, a value which was later revised to 51.44 milliarcseconds when the data was reanalyzed taking systematic errors more carefully into account. The distance to Beta Pictoris is therefore 63.4 light years, with an uncertainty of 0.1 light years. The Hipparcos satellite also measured the proper motion of Beta Pictoris: it is traveling eastwards at a rate of 4.65 milliarcseconds per year, and northwards at a rate of 83.10 milliarcseconds per year. Measurements of the Doppler shift of the star's spectrum reveals it is moving away from Earth at a rate of 20 km/s. Several other stars share the same motion through space as Beta Pictoris and likely formed from the same gas cloud at roughly the same time: these comprise the Beta Pictoris moving group. According to measurements made as part of the Nearby Stars Project, Beta Pictoris has a spectral type of A6V and has an effective temperature of 8,052 K (7,779 °C; 14,034 °F), which is hotter than the Sun's 5,778 K (5,505 °C; 9,941 °F). Analysis of the spectrum reveals that the star contains a slightly higher ratio of heavy elements, which are termed metals in astronomy, to hydrogen than the Sun. This value is expressed as the quantity , the base-10 logarithm of the ratio of the star's metal fraction to that of the Sun. In the case of Beta Pictoris, the value of is 0.05, which means that the star's metal fraction is 12% greater than that of the Sun. Analysis of the spectrum can also reveal the surface gravity of the star. This is usually expressed as log g, the base-10 logarithm of the gravitational acceleration given in CGS units, in this case, cm/s². Beta Pictoris has log g=4.15, implying a surface gravity of 140 m/s², which is about half of the gravitational acceleration at the surface of the Sun (274 m/s²).