Wednesday 29 February 2012

A second star in the T Chamaeleontis system.

T Chamaeleontis is a young star (about 7 million years old) roughly 326 light years from Earth in the constellation of Chamaeleon. It has a mass of about 1.5 × that of our sun, and is surrounded by an accretionary disk; a disk of dust and gas from which planets can potentially form. In February 2011 a team of scientists lead by Nuria HuĂ©lamo, of the Centro de AstrobiologĂ­a at European Space Astronomy Centre Campus in Madrid, announced the discovery of a planet orbiting T Chamaeleontis at a distance of 6.7 AU (6.7 times as far from the star as the Earth is from the Sun, or slightly greater than the distance at which Jupiter orbits), within a gap in the disk surrounding the star, in a paper in the journal Astronomy & Astrophysics.

Simulation of a journey through the T Chamaeleontis System.

In a paper published on the online arXiv database at Cornell University Library on 1 February 2012, a team of scientists lead by Joel Kastner of the Center for Imaging Science and Laboratory for Multiwavelength Astrophysics at the Rochester Institute of Technology, describe a new study of the T Chamaeleontis system, made from the Australian National University’s Siding Spring Observatory in New South Wales, from which they conclude that the neighboring star 2M1155–79 is in fact a part of the T Chamaeleontis system.

2M1155–79 is a young (about ten million years old) Red Dwarf star with a mass 30% of that of the Sun, and an effective temperature of 3400 K (compared to 5770 K for our sun). It is separated from T Chamaeleontis by a distance of about 38 kAU (38 000 times as far from T Chamaeleontis as the Earth is from the sun).

This may at first seem a little far out to be part of the same system, but on the scales at which star distances are measured is not that far. The Earth is 50 light seconds from the Sun, giving a separation between 2M1155–79 and T Chamaeleontis of 1 900 000 light seconds, or 22 light days. The nearest star to our Sun, the Red Dwarf Proxima Centauri, is 4.2 light years away, so 2M1155–79 is 70 times as close to T Chamaeleontis as Proxima Centauri is to the Sun.

Kastner et al. propose that 2M1155–79 will take a million years to orbit T Chamaeleontis, and suggest that it be renamed T Chamaeleontis B (with T Chamaeleontis becoming T Chamaeleontis A). Furthermore they note that binary partners for very young stars seem to be far more common than for the general population of stars, and that the presence of these stars, and their gravity, must have a profound effect on the formation of planets.

An artists impression of the T Chamaeleontis system. European Southern Observatory.