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Optical observations of comet P/Tempel 1

Heike Rauer, JÆrg Knollenberg, Michael Weiler DLR, Institut fÝr Planetenforschung Berlin-Adlershof


Observations of comet P/Tempel 1 at optical wavelengths
Before and after impact: monitoring · Gas production rates -,,classical" optical long- slit spectroscopy: CN, C3, C2, NH2 - variation along heliocentric distance: difference before ­ after? - compare with measurements of parent species at radio, IR · Dust production rates - measure Afrho parameter, compute d ust production rate with model - variation along heliocentric distance: difference before ­ after? - combine with IR data to determine d ust parameters · Coma morphology - presence of jets and /or outbursts - new features d uring impact? - d uration of new features (jets, shells)?


Example: Long-term monitoring of the gas activity of comet Hale-Bopp

Ra ue r e t a l., 20 03 , A&A 3 9 7, 110 9- 1122

- optical long-slit spectra of comet Hale-Bopp, r = 4.6 - 2.9 AU, r = 2.8 ­ 12.8 AU - derive CN production rates comparison with HCN shows no indications for significant additional sources of CN dependence of production rates on r indicates near-surface sublimation


Gas production rates of C2 H2 and C2 H6 from C2 and C3
· Simultaneous long-slit spectra of C2 and C3 (Hale-Bopp observi ng campai gn) · use chemical model of related Cchemistry (ComChem model, e.g.:
Huebner et a l., 1987; Boi ce e t a l., 1998)

· compute spatial coma profiles of C2 and C3 · scale by factor to measured profiles determine parent production rates very good agreement with direct measurements of C2H2 and C2H6

J. He lbe rt, P hd the s is , 200 3

We currently investigate use of simplified model approach.


Observations of comet P/Tempel 1 at optical wavelengths
Before and after impact: monitoring · Gas production rates -,,classical" optical long- slit spectroscopy: CN, C3, C2, NH2 - variation along heliocentric distance: difference before ­ after? - compare with measurements of parent species at radio, IR · Dust production rates - measure Afrho parameter, compute d ust production rate with model - variation along heliocentric distance: difference before ­ after? - combine with IR data to determine d ust parameters · Coma morphology - presence of jets and /or outbursts - new features d uring impact? - d uration of new features (jets, shells)?


Model for computation of dust production rates
- 1- D, isotropic em iss ion - Eu ler- equ ation s solved for gas flow - On su rface: T from en ergy balan ce (irradiation , su blim ation of H 2O an d reradiation ) - active su rface fraction , f - gas produ ction rate s caled from OH observation s an d f - du st treated as tes t particles - Equ ation of m otion of a s perical du st particle in th e gas flow, in flu en ced by gas drag an d n u cleu s gravity - com pu te th e m ax im u m du s t s ize lifted of th e n u cleu s: ama x res u lts from th e balan ce of gravity an d acceleration du e to gas drag - with th e resu ltin g du s t term in al velocity v(a), th e du st m ass produ ction rate can be determ in ed with assu m ption s on th e albedo, ph as e fu n ction , du st den sity an d du st s ize distribu tion u sin g (J orda 1995):

2 A f QM = ( 3 AB D( )

a

mx a


a

1

f ( a) a2 - d) a v( a)

a 1

mx a


a



dst u

( a) a 3 f (a) d a

1


The dust-to-gas ratio of comet Hale-Bopp versus heliocentric distance.

Weiler et a l. 2003, A&A 403, 313

-

Afrho determined in spectra of Hale-Bopp long-term observing campaign The Afrho/ gas ratio varies more than one order of magnitude The dust to gas mass ratio computed with our model remains nearly constant. The difference is caused by the variation of dust velocity with heliocentric distance.


Dust velocities versus heliocentric distance

Slope of gas velocity versus distance differs significantly from simple sqrt(r) dependency use gas dynamical model Resulting dust velocities are in good agreement with observed velocities.


The dust-to-gas ratio of comet Hale-Bopp versus heliocentric distance.

Weiler et a l. 2003, A&A 403, 313

-

Afrho determined in spectra of Hale-Bopp long-term observing campaign The Afrho/ gas ratio varies more than one order of magnitude The dust to gas mass ratio computed with our model remains nearly constant. The difference is caused by the variation of dust velocity with heliocentric distance.


Comet P/Churyumov-Gerasimenko
Dust mass production rates Dust number production rates

Dust to gas mass ratio

Maximum dust grain size

Data for Afrho and OH from LOCD data base

We ile r e t a l., 20 0 4 , s ubmitte d


Observations of comet P/Tempel 1 at optical wavelengths
Before and after impact: monitoring · Gas production rates -,,classical" optical long- slit spectroscopy: CN, C3, C2, NH2 - variation along heliocentric distance: difference before ­ after? - compare with measurements of parent species at radio, IR · Dust production rates - measure Afrho parameter, compute d ust production rate with model - variation along heliocentric distance: difference before ­ after? - combine with IR data to determine d ust parameters · Coma morphology - presence of jets and /or outbursts - new features d uring impact? - d uration of new features (jets, shells)?


Comet P/Churyumov-Gerasimenko
- observed at ThÝringer Landessternwarte Tautenburg, Germany - 2m Schmidt telescope - date: 27.3.2003 - FOV: 16,8x16,8 arcmin (sub-frame, total FOV: 3x3 degree) - R filter - 36 min exposure time - comet magnitude: ~14 mag - r = 2.6 AU , = 1.7 AU


Comet P/Churyumov-Gerasimenko

- left: R-filter image after subtraction of a mean coma intensity profile (taken in March 2003 with the 2m telescope at TLS) - r ight: deviation of the coma intensity from the mean intensity Weiler et al., 2004, A&A, in press.


Comet P/Churyumov-Gerasimenko

-1.93m at Observatoire de Haute Provence, France - CARELEC medium-resolution spectrograph - date: 10/ 11.2.1996 - exposure time: 50 min - comet magnitude: ~11 mag - r = 1.3 AU, = 1.2 AU


Comet P/Tempel 1: example for dust model application
Model parameters used: - Q(OH) = ~1028 s1

(

Os ip e t a l., 19 9 2)

- active fraction: 4.6 % - nucleus radius: 3 km
(Fe rna nd e z e t a l., 200 3)

· maximum grain size: 5-14 cm · terminal gas velocity: 837-845 m/ s · r = 1.91 AU, Q(dust) = 328 kg/ s · r = 1.586 AU, Q(dust) = 471 kg/ s


Observing P/Tempel 1
Before and after impact: monitoring

· Opti cal i magi ng i n broad-band fi lte rs + na rrow band (li ght c urve, c olour, je ts, depe ndence on r) · medi um-re soluti on long-sli t s pe c trosc opy (CN, C2, C3 , NH2) · capa bi li ty to swi tch betwee n i ma gi ng a nd s pec tra VLT a llows to sea rch for ga s e mi ssi ons ,,e arly" i n r (e .g. usi ng FORS)


Observing comet P/Tempel 1
Around impact time: · Coma morphology - follow d evelopment of jets, shells · Gas prod uction rates -,,classical" optical long- slit spectroscopy: CN, C3, C2, NH2 - d etermine increase in activitiy for species detected · Dust production rates - d etermine increase in activitiy for species detected · Na observations (source from dust particle sputtering?) · High- resolution spectroscopy


Proposed observations for P/Tempel 1
During impact: Need for high temporal and spatial resolution (1arcsec ~ 700 km at the comet)

· Switching between spectra and imaging at the same instrument takes time · may be done in parallel at different telescopes · use VI MOS for inner coma (2 7x2 7 arcs ec) imaging spectroscopy at VLT ?


Summary
· Long-slit spectroscopy and imaging observations pre- and post- impact · High-resolution, narrow band filters around impact
· Use small telescopes (TLS) for (pre-)impact observations of dust coma morphology

Data analysis based on tools developed for previous observing campaigns: - reduction and analysis of spectra and imaging observations - hydrodynamical model to compute dust production rates - chemical model to link daughter species to parent abundances