Aging Star Has Bullets and Horns
September 29, 2002
Observers: Toshiya Ueta, David Fong, and Margaret Meixner (University of Illinois at Urbana-Champaign)
Object Name: Bipolar Planetary Nebula AFGL 618
Position: 04h42m53.6s +36d06m53.6s (Constellation: Auriga)
Telescope: Subaru Telescope / Cassegrain Focus
Instrument: Infrared Camera and Spectograph (IRCS)
Filters: J (1.3 +-0.2microns), H (1.6 +-0.3 microns), K' (2.1 +-0.4microns), Molecular Hydrogen (2.12+-0.03 microns) Date: February 5, 2001 (UT)
Field of View: 23.2 arcsec x 14.5 arcsec
Image Resolution: 0.058 arcsec/pixel
Orientation: North up, east left
Distance from Earth: About 450 light years. (Estimates range from 280 light years to 630 light years.)
Using Subaru Telescope's Infrared Camera and Spectrograph (IRCS), astronomer Toshiya Ueta and his colleagues from the University of Illinois at Urbana-Champaign have detected structures resembling "bullets" and "horns" in the gas and dust surrounding an aging star called AFGL 618. This is the first detection of these structures in the near-infrared (the wavelength region beyond the reddest light humans can see). The high resolution and sensitivity of the Subaru data bring new detail to our understanding of the complex processes that accompany the aging of a low-mass star like our own Sun.
AFGL 618 is a popular subject of study among astronomers as a prime example of a very young bipolar planetary nebula. The name "planetary nebula" can be misleading, since planetary nebulae have nothing to do with planets, but instead consist of an aging star and an envelope of gas and dust which this star has ejected. AFGL 618 is called a bipolar planetary nebula because its nebulosity appears to have two preferred directions. It was along these directions that the team of astronomers found the bullets and horns. The "bullets" are the three dot-like structures at the end of the lobe to the right (the top most dot is very faint), and the "horns" are the two elongated structures at the end of the lobe to the left. The cinch in the middle of the structure is called a "dust waist" and is caused by dust grains obscuring our view to the central star.
Team members suspect that the bullets and horns are located where rapid outflows of gas from the aging central star hit previously-ejected material. Their most recent observations of the object using the Wisconsin-Indiana-Yale-NOAO (WIYN) telescope at Kitt Peak, Arizona support this view. Further observations have also been made with the Berkeley-Illinois-Maryland Association (BIMA) radio interferometer in Northern California. BIMA observes at long radio wavelengths which are able to see through the dust surrounding AFGL 618 to study the distribution and movement of the underlying molecular gas. By combining these observations with the data from the Subaru and WIYN telescopes, the team hopes to solve the mystery of the bullets and horns.