1. Spectroscopic Mapping of Comets at Radio Frequencies Amy Lovell, Agnes Scott College

2. Comet “Anatomy” nucleus (<30km) atmosphere (near sun)
Neutral (dust/gas) tails
Magnetic fields direct ions
Comet 1P/Halley -->

3. Tempel 1
The largest dimension is shorter than the distance from Decatur to downtown Atlanta
7.6km x 4.8km

4. 67P/Churyumov-Gerasimenko Rosetta .
550 km distance 55m/pix – about 4km long
~4km

5. Why Comets? Remnants of planet formation era
- some comets preserved/frozen early
- others more processed by solar heating
Coma gases sublimate from the nucleus ices
-composition & physical conditions

6. Interesting Chemistry & Physics
production/flow of sublimating gases off nucleus
release of dust from nucleus*
collisions between particles in inner coma
UV dissociation of “parent” molecules into “daughters”
chemical reactions
interactions with the solar wind
Orbital characteristics
Coma composition (inferred nucleus comp)
Gas-to-dust ratios
Gas and dust production varies along orbit
Nucleus size
Physical properties, density, strength

7. Radio Astronomy Complementary observing opportunities
Energetics appropriate for parent molecules
Velocity details in high-resolution spectra
3rd dimension to images
H2O, HDO, OH, H2O+, CO, CO2, CO+, HCO+, H2S, SO, SO2, OCS, CS, CH3OH, H2CO, HCOOH, HCN, CH3CN, HNC, HC3N, HNCO, CN, NH2, NH, CH4, C2H2, C2H6, C3, C2, Na, H13CN, HC15N, C34S

8. Earth’s atmosphere

9. Green Bank Telescope (100m GBT) Spatial resolution 7.4' Arecibo 305m
Mapping pattern, spectral & spatial resolution

10. Radio spectra (and maps) can assess:
Gas production rates
Gas outflow velocities
Outgassing Asymmetries
Coma excitation conditions/density
Support optical/IR observations

11. Parents (from ice)
HCN, H2O UV
Daughters (secondary products) CN, OH

12. Lines at rest
approaching
Emitting molecules
receding

13. Line width shows expansion velocity
Width = outflow velocity
Height relates to quantity of gas
Shape = where gas is emitted
Line width shows expansion velocity
Line shape suggests a/symmetry, acceleration
Line area relates to gas production

14. OH Radio Bands OH is visible in the 18cm L-doublet
1667 and 1665 MHz primary lines,
Pumped by solar UV
amplifies or absorbs the cosmic background
Despois et al. (A&A, 1981); Schleicher & A'Hearn (ApJ, 1988)
Mapping pattern, spectral & spatial resolution

15. Redshift to sun
Blueshift to sun

16. Emission lines
Absorption lines

17. Quenching Constraints
May 21, better quenching figure is needed…

18. Mapping Layout
OFF ON

19. Monte Carlo OH coma simulation
H2O lifetime 82,000 s
random time, direction
OH lifetime 150,000s
“kick” v=1.05 km/s
Surviving OH forms synthetic spectrum
binned by observed Doppler velocity

20. Mapping simulation Fits minimize c2 data
Outflow velocity & quenching, possible asymmetry across the coma
Arecibo rH = 2 AU 4’ 205,000 km

21. B ½ size = more productive area

22. Post-perihelion pre-perihelion ~ rh -2.5 C/Garradd Production Rate
Gas production rates log(Q) are between and in mid-June and between 28.2 and 28.6 a few weeks later. Late-July gas production rates are lower, between and Collisional quenching is present at predicted (Gérard et al. 1998) levels, with 11 July appearing above predictions.

23. Gas outflow velocity Distance to sun (AU)
High variability near the sun – levels off at larger distances
Distance to sun (AU) 25

24. Summary Radio Observations reveal unique physics “big picture” view
supplement multiwavelength campaigns
Velocity results challenge predictions
Mapping spectroscopy is best constraint