ESO: Two Families of Comets Found around β Pictoris

[bystander]

Two Families of Comets Found around Nearby Star
European Southern Observatory | HARPS | 2014 Oct 22

Biggest census ever of exocomets around Beta Pictoris

[url=http://www.eso.org/public/images/eso1432a/][b][i]Artist’s impression of exocomets around Beta Pictoris[/i][/b][/url] [b][i](Credit: ESO/L. Calçada)[/i][/b]

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The HARPS instrument at ESO’s La Silla Observatory in Chile has been used to make the most complete census of comets around another star ever created. A French team of astronomers has studied nearly 500 individual comets orbiting the star Beta Pictoris and has discovered that they belong to two distinct families of exocomets: old exocomets that have made multiple passages near the star, and younger exocomets that probably came from the recent breakup of one or more larger objects. The new results will appear in the journal Nature on 23 October 2014.

Beta Pictoris is a young star located about 63 light-years from the Sun. It is only about 20 million years old and is surrounded by a huge disc of material — a very active young planetary system where gas and dust are produced by the evaporation of comets and the collisions of asteroids.

Flavien Kiefer (IAP/CNRS/UPMC), lead author of the new study sets the scene: “Beta Pictoris is a very exciting target! The detailed observations of its exocomets give us clues to help understand what processes occur in this kind of young planetary system.”

For almost 30 years astronomers have seen subtle changes in the light from Beta Pictoris that were thought to be caused by the passage of comets in front of the star itself. Comets are small bodies of a few kilometres in size, but they are rich in ices, which evaporate when they approach their star, producing gigantic tails of gas and dust that can absorb some of the light passing through them. The dim light from the exocomets is swamped by the light of the brilliant star so they cannot be imaged directly from Earth. ...

Two families of exocomets in the β Pictoris system - Flavien Kiefer et al

• Nature 514(7523) 462 (23 Oct 2014) DOI: 10.1038/nature13849 (pdf)

[BDanielMayfield]

I found this article to be very interesting. There is a veritable swarm of comets around the young star Beta Pictoris.

http://www.skyandtelescope.com/astronom ... s-10272014

The first few paragraphs state:

Eight years of measurements from the HARPS spectrograph in Chile have revealed two distinct populations of comets in the forming planetary system around Beta Pictoris, Flavien Kiefer (Paris Institute of Astrophysics) and colleagues report in the October 23rd Nature.

Astronomers already knew cometary bodies fill the disk around Beta Pic: work by members of the same team in the 1980s and 1990s found hints of evaporating bodies traversing in front of the star. These bodies block certain wavelengths of starlight when they pass between us and Beta Pic, leaving absorption features in the light that come and go over the course of several hours.

The new results are an analysis of 1,106 spectra taken from 2003 to 2011, containing variable calcium absorption features from an estimated 493 exocomets. (To avoid double-counting, the team only looked at one spectrum per day.) To make the signals clearer, the team averaged spectra over 30 minutes to boost the detections. Still, there are so many evaporating bodies in this infant planetary system that, in each 30-minute spectrum, there’s an average of six comets passing in front of the star.