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

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

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

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

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

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

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

Earth’s atmosphere http://www.ipac.caltech.edu/outreach/Edu/Windows/transmission.jpg http://www.ipac.caltech.edu/outreach/Edu/Windows/transmission.jpg

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

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

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

Lines at rest approaching Emitting molecules receding

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

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

Redshift to sun Blueshift to sun

Emission lines Absorption lines

Quenching Constraints May 21, better quenching figure is needed…

Mapping Layout OFF ON

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

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

B ½ size = more productive area

Post-perihelion pre-perihelion ~ rh -2.5 C/Garradd Production Rate Gas production rates log(Q) are between 28.13 and 28.26 in mid-June and between 28.2 and 28.6 a few weeks later. Late-July gas production rates are lower, between 27.85 and 28.27. Collisional quenching is present at predicted (Gérard et al. 1998) levels, with 11 July appearing above predictions.

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

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