comet hale-bopp:
TRANSCRIPT
Paper
New molecules found in comet C/1995 O1 (Hale-Bopp).Investigating the link between cometary and interstellar materialBockelée-Morvan, D., Lis, D., Wink, J.E., et al. 2000A&A 353, 1101
What is a Comet?
• A small (<50km nucleus) icy body orbiting the Sun in a highly elliptical orbit
• Anatomy of a comet:
Historical Significance
Bayeux Tapestry (11th century) image of comet Halley
1857 drawing of a comet hitting Earth
Scientific Significance
• Comets thought to contain pristine material
• Debate over origin of comets:– Interstellar material?– Solar nebula?
• Chemical composition of a comet gives clues about solar system formation
Previous Work• Biver et al. 1999 - production rates• Schleicher et al. 1998 - comet properties
• Greenberg 1982 - interstellar origin theory
• Lewis & Prinn 1980 - solar nebula affected composition
• Several papers about production rates in other comets, most notably Hyakutake and Halley
Comet Hale Bopp• Discovered in 1995 by Alan Hale and Thomas Bopp
• Named “the Great Comet of 1997”
• Perihelion: April 1, 1997, 0.91AU
Scope of Paper
• Use spectroscopy to determine chemical composition of Hale-Bopp
• Compare to composition of interstellar clouds
• Answer questions about the origin of comets, and the origin of our solar system
Observations• Taken during February to April 1997
• Identified six new species from spectra: HC3N, SO, HCOOH, SO2, NH2CHO, HCOOCH3
• HNCO and OCS also confirmed
Fig. 1
Molecular Production Rates and Abundances
• Molecular column density: • Assumes optical thinness• nu calculated using local thermal equilibrium (LTE) approximation
• Local densities of parent and daughter species found with Haser’s model
• For some species, more in-depth modeling was done, yielding similar results to LTE
Sulfur Species
• [SO]: 0.3% and [SO2]: 0.2% relative to water
• SO abundance could vary from comet to comet
• [SO]/[SO2]~1.6 - is SO2 only parent?
Sulfur Species (cont.)
• [OCS]: 0.4% relative to water• In agreement with value found for Hyakutake (Gérard et al. 1998)
• [S]/[O]: 0.02 (solar system value)
N- and CHO-bearing Species
• In agreement with upper limits for other comets (Crovisier et al. 1993)
• HC3N, NH2CHO and other species have low abundances with respect to NH3
• New CHO species have low abundances, do not contribute much to C or O abundance
Volatile Composition
• Abundances are assumed to be abundance of cometary ices
• Does not account for extended sources– Both CO and OCS have additional 50% contribution from distributed source
– H2CO abundance uses extended source calculation
Volatile Composition (cont.)
• Could coma chemical reactions cause minor species?– A model of HCN formation cannot reproduce the abundance
– Ion-molecule interactions could produce new species, but it’s unlikely•Ionic content too small (photoionization takes too long), formation requires two subsequent reactions and more complex ions
Is Hale-Bopp Typical?
• C2 and CN abundances are typical (Schleicher et al. 1998)
• Parent molecules similar to those in other comets (Crovisier 1993)
• Hale-Bopp is assumed to be a representative for all comet-kind
Comparison to Interstellar Medium
• Theories on comet formation range from pure interstellar origin to pure solar condensate origin
• Major constituents were studied, minor species left out
• Compare to hot cores and bipolar flows
Hot Cores
• dense clumps of gas heated to above 100K by UV radiation and shocks from recently formed stars
• Gases may form from sublimation of icy particles
• Typically have large hydrogenated molecule abundance and organic material
Bipolar Flows
Produced by young protostars, also help investigate icy particles sublimated in the presence of low-mass stars
Future Work• Further data on interstellar clouds needed
• Space missions to comets will provide more information about nucleus and composition
For more Information• Deep Impact: http://deepimpact.jpl.nasa.gov/home/index.html
• Rosetta: http://sci.esa.int/science-e/www/area/index.cfm?fareaid=13
• Stardust: http://stardust.jpl.nasa.gov/home/index.html
• Info on Hale-Bopp: http://www2.jpl.nasa.gov/comet/