Sunday 26 February 2012

Planetary formation around GM Cephie.

GM Cephei is a young (about four million years old) variable star in the Elephant's Trunk Nebula (Trumpler 37), about 2450 light years from Earth; the name GM Cepei means 195th variable star in the constellation of Cepheus. CM Cephei has an estimated mass of 2.1 times that of our sun, and a volume between 100 and 900 times as great (this is not unusual in a star still collapsing under its own weight, which is how stars form). It is classified as a Type II T Tauri irregular variable star, a young star with a variable output due to patchy heat distribution and material still accreting onto its surface.

The Elephants Trunk Nebula (Trumpler 37). Image from NASA's Spitzer Space Telescope.

In a paper published on the arXiv online database at Cornell University Library on 23 February 2012, and due to be printed in a forthcoming edition of the Astronomical Society of the Pacific Conference Series, a team of scientists led by Chia-Ling Hu, of the Institute of Astronomy at the National Central University of Taiwan and the Taipei Astronomical Museum, describe the discovery of a regular pattern in the variability of GM Cephie, and the conclusions drawn from it. The discovery was made from results obtained by the Lulin Observatory in Taiwan and the Tenagra Observatory in Arizona, which were studying the system as part of the international Young Exoplanet Transit Initiative (YETI), which is concentrating on the stellar nurseries of Trumpler 37 and 25 Ori.

The YETI team observed that GM Cephie dimmed every 311 day for a period of 39 days, and that it turned slightly bluish as it did so. They theorize that this dimming is caused by a cloud of material orbiting the star at a distance of 1.16 AU, with a volume in excess of 4 million times that of our sun. They calculate this cloud of material would contain about 2.269 × 10¹⁸ kg (that's 2 269 000 000 000 000 000 kg) of silica dust, enough for a small-to-medium-sized asteroid.