Sunday, December 12, 2010

Comet-like appearance of (596) Scheila

CBET nr.2583, issued on 2010, Dec. 12, announced the discovery of a spiral like structure around main belt asteroid (596) Scheila by Steve Larson in the course of Catalina Sky Survey (CSS) through the Catalina 0.68-m Schmidt telescope, on images obtained on 2010, Dec. 11.4. The cometary appearance has been confirmed by other observers.

In the Catalina images, the "coma" is bright (Vtotal~13.5), and extends some 2 arcmin north and 5 arcmin west from the central condensation.

We have been able to confirm this object remotely, using a 0.43-m f/6.8 reflector + CCD located in Nerpio (Spain): on December 12.01, co-adding of 7 unfiltered exposures, 60-seconds each, shows a wide spiral like tail. The longest part of this spiral tail is 1' in PA 280 while the small part is 30" in PA 22. You can see our image below:

According to the "Dictionary of Minor Planet Names" by Lutz D. Schmadel, (596) Scheila was discovered on 1906 Feb. 21 by A. Kopff at Heidelberg. Named in honor of an acquaintance of the discoverer, an English woman student in Heidelberg. (596) Scheila is a main-belt asteroid inclined roughly 14 degree on the ecliptic and it is now 3.1AU from the Sun and 0.8AU out of the ecliptic. With an absolute magnitude H8.9 the estimated diameter is 113Km.

Orbit Diagram of (596) Scheila:

So this object is a potential new member of the recently recognized class of main-belt comets introduced by Jewitt & Hsieh in 2006 . These objects are remarkable for having both the orbital characteristics of asteroids and the physical characteristics of comets: they look like comets because they show comae and tails but they have orbits interior to Jupiter's and Tisserand parameters substantially larger than 3, like asteroids.

The Tisserand parameter of (596) is T_jup = 3.209

UPDATE - December 12, 11:30 UT

We have imaged again (596) Scheila at 08:20UT of December 12, 2010, this time remotely from the GRAS Observatory (near Mayhill, NM) through a 0.25-m, f/3.4 reflector + CCD. Below you can see the new image - stack of 8x120sec exposures:

by Ernesto Guido & Giovanni Sostero


Marshall Eubanks said...

I have to wonder if this is not the result of a meteorite strike on 596 Schella. In that case, I would expect the "tail" to dissipate over the next few weeks at most.

A single epoch's observation should not be sufficient to get an object labeled as a main belt comet, as any body could suffer an impact at any time, and large enough impact could heat the surface material and cause extended outgassing.

Belle said...

Very interesting post. Thanks.

Anonymous said...

Thank you for the heads up on the outburst. I caught an image last night and uploaded it to Wikipedia.

-- Kevin Heider