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The dust coma of the active Centaur P/2004 A1 (LONEOS)

TNOs: dynamical and physico-chemical properties Catania, 3-7/7/06. The dust coma of the active Centaur P/2004 A1 (LONEOS). Elena Mazzotta-Epifani (1) , P. Palumbo (2) , M.T. Capria (3) , G. Cremonese (4) , M. Fulle (5) , L. Colangeli (1). A CO-driven environment?.

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The dust coma of the active Centaur P/2004 A1 (LONEOS)

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  1. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 The dust coma of the active Centaur P/2004 A1 (LONEOS) Elena Mazzotta-Epifani(1), P. Palumbo (2), M.T. Capria (3), G. Cremonese (4), M. Fulle (5), L. Colangeli (1) A CO-driven environment? (1) INAF-OAC, Napoli, Italy (2) Università Parthenope, Napoli, Italy (3) INAF-IASF, Roma, Italy (4) INAF-OAPd, Padova, Italy (5) INAF-OATs, Trieste, Italy

  2. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Distant activity of Minor Bodies Program started in Autumn 2004 to study a large sample of distant Solar System Minor Bodies (rh > 3-4 AU) in order to investigate the presence of distant activity and to analyse distant dust environment Several observing campaigns performed and programmed (ground telescopes: TNG, CalarAlto; space telescope: AKARI (former ASTRO-F) Up to now: 11 numbered periodic comets, 6 unnumbered periodic comets, 2 new comets  6 undetected (upper limit for nucleus size) or stellar appearence (bare nucleus or unresolved coma), 13 with evident activity (coma and sometimes well developed tail)

  3. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Active Centaurs As for May 2006, ~ 80 objects have been classified as pertaining to the Centaur family Among these, 11 have been reported with cometary activity

  4. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Active Centaurs Chiron Luu & Jewitt, 1990, AJ 100, 913 “Giant comet” 29P/S-W 1 Short term variations of coma morphoogy Jewitt, 1990, ApJ 351, 277

  5. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Active Centaurs 166P/NEAT (former C/2001 T4 NEAT) Puzzling color gradient: even active, it is one of the reddest Centaurs (its V-R color in 2001 exceeded that of Pholus) Bauer et al., 2003, PASP 115, 981 174P/Echeclus (2000 EC98) Inactive up to December 2005. Onset of cometary activity monitored in following months Images from amateurs (R. Ligustri)

  6. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 The Active Centaur P/2004 A1 (LONEOS) N  • Discovered in the course of the LONEOS (Lowell Observatory Near-Earth Object Search) program on 2004. • Perihelion q = 5.46 AU • Eccentricity e = 0.308 • Inclination i = 8.2° • Period P = 22.2 years • Observed at TNG telescope on April 3rd, 2005, when at • r = 5.54 AU • Δ = 4.69 AU E Total exp. time 2400 s ~ 5  105 km

  7. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 The P/2004 A1 (LONEOS) coma general properties • Coma slightly asymmetric: maximum extension in the W (very close to the anti-solar direction) ~ 8.8  104 km • Neck-Line: thin spike extending in the solar direction (antitail) up to 1.5  105 km • Magnitude in the R band (d = 5”): 18.56  0.05. LONEOS is the faintest active Centaur of the observed sample • Af = 334  15 cm For comparison: • 19P/Borrelly: 400-500 cm @ 1.4 AU • 81P/Wild 2: 350 cm @ 2.1 AU • 21P/Giacobini-Zinner: 300-400 cm @ 1 AU • 67P/Churyumov-Gerasimenko: 400 cm @ 1.2 AU isophotes levels: 21.33, 22.08, 22.83, 23.58, 24.34 and 25.09 magR arcsec-2Mazzotta Epifani et al., 2006, submitted to A&A 

  8. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 The P/2004 A1 (LONEOS) dynamical history 30/7/1992 Close encounter with Saturn @ d = 0.03 AU perihelion distance q 9.78  5.46 AU aphelion distance Q 14.56  10.37 AU inclination i 11.4  8.0 ° Mazzotta Epifani et al., 2006, submitted to A&A

  9. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Sources of distant activity Distant activity (rh > 4 AU) cannot be explained (only?) with water sublimation (see for example Meech & Svoren, 2005, in Comets II) CO and other very volatile can be responsible for cometary activity of Centaurs (and even KBOs): CO, CO2,... CO gas trapped in amorphous water ice released when amorphouscristalline transition starts at 100K pure ice released when sublimation starts at 25K Models of thermal evolution and differentiation of the nucles: (Coradini et al., 1997, Icarus 138, 1, 85; Capria et al., 2002, EM&P 90, 1, 217) • the source of a CO-driven activity should be found under the surface • CO tends to flow from the body along most of its orbit • CO flows from everywhere on the nucleus surface • for more details, see talk by Teresa Capria later this morning

  10. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 CO in minor bodies CO is relatively abundant in (typical) comet nuclei IRTF measurement of CO in 21P/G-Z Q = 3.28  1027 mol s-1 FUSE measurement of CO in C/2001 A2 (LINEAR) Q = 1.3  1027 mol s-1 (Mumma et al., 2000, ApJ 531, L155) (Feldman et al., 2002, ApJ 576, L91) ISO measurement of CO (upper limit) in 103P/H 2 Q  4.4  1027 mol s-1 (Colangeli et al., 1999, A&A 343, L87)

  11. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 CO in minor bodies CO measurements in Centaurs (and KBOs) NRAO radio measurement of CO in Chiron Q = 1.5  1028 mol s-1 (Womack & Stern, 1999, Astron. Vestnik, 33, 187) SEST radio measurement of CO in 29P/S-W 1 Q ~ 3  1028 mol s-1 (Festou et al., 2001, Icarus 150, 140) CO (upper limit) derived with radio measurements Q [Centaurs] ~1028 mol s-1 Q [KBOs] ~ 1-5 1028 mol s-1 (Bockelee-Morvan et al., 2001, A&A 377, 343)

  12. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Analysis of the CO-driven dust environment Used as input in the inverse coma model (Fulle, 1989, A&A 217, 283)  to determine the dynamical characteristics of dust grains in cometary coma and tails and study their evolution, starting from the 2D image INPUT: Comet image I(M,N) (M,N: sky coordinates)METHOD: Building up a “theoretical” tail of about 107 dust grains, selected with a Montecarlo method from a set of size and emission time ranges, each emitted with starting velocity v(t,d) = v(t,d0)(d/d0)uand iterative fit with observed isophotes

  13. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Analysis of the CO-driven dust environment EQUATION TO SOLVE: Linear system AF = I (A: matrix with theoretical tail and regularising constants)NON LINEAR PARAMETERS: Derived with a trial and error method: time dependence of dust emission velocity v(t,d0) t time of dust ejection from the inner comad0 reference parameter size dependence of dust emission velocity u=logv(t,d)/ logd v(t,d) = v(t,d0)  (d/d0)u dust emission anisotropy ww half width of the Sun-pointing dust ejection cone MODEL OUTPUT: Solution vector F with physical outputs of the model: grain size distribution n(d) = d-pdust production rate their time evolution from the observation back in time up to the last observable isophote

  14. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Analysis of the CO-driven dust environment

  15. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Analysis of the CO-driven dust environment The dynamical and physical constraints for the application of the model to P/2004 A1 (LONEOS) v(t,d) = v(t,d0)  (d/d0)u with u=logv(t,d)/ logd u = -1/6: very aspheric grains and/or fragmentation during the gas drag. Velocity almost independently on the dust size u = -1/2: perfectly spherical grains  Constant emission velocity from past aphelion: consistent with a CO-driven environment continuous line: u = -1/6, w = 180°; dotted line: u = -1/4, w = 180°; dashed line: u = -1/2, W = 180° Mazzotta Epifani et al., 2006, submitted to A&A

  16. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Analysis of the CO-driven dust environment The dynamical and physical constraints for the application of the model to P/2004 A1 (LONEOS)  = (CprQpr)/(dd) where Cpr = 1.19  10-3 kg m-3 depends on light velocity, Solar mass and G Qpr is the dust scattering efficiency (depends on chemical composition of the grains), assumed to be 1 d dust bulk density, assumed to be 103 kg m-3  (Sub)set of dust size used for the isophote fit: grains larger than 1 cm if 103 kg m-3 density is assumed (at aphelion) Mazzotta Epifani et al., 2006, submitted to A&A

  17. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Analysis of the CO-driven dust environment Automatic output of the inverse dust tail model applied to P/2004 A1 (LONEOS) time dependence of the dust size distribution (sub-set of dust size, variable with time) output with u=-1/2: strong noise  less probable solution output with u=-1/4 and u=-1/6: quite similar and small changes from aphelion (grains larger than 1 cm) to perihelion (grains smaller 1 cm) continuous line: u = -1/6, w = 180°; dotted line: u = -1/4, w = 180°; dashed line: u = -1/2, W = 180° Mazzotta Epifani et al., 2006, submitted to A&A

  18. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Analysis of the CO-driven dust environment Automatic output of the inverse dust tail model applied to P/2004 A1 (LONEOS) Dust production rate: ~ 100-200 kg/s, constant in time Much greater than value obtained for Chiron Afr: ~ 0.5-2 m, computed for a subset of grain size continuous line: u = -1/6, w = 180°; dotted line: u = -1/4, w = 180°; dashed line: u = -1/2, W = 180° Mazzotta Epifani et al., 2006, submitted to A&A

  19. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Conclusions Synchrone-syndyne network for LONEOS on April 2005  = (CprQpr)/(dd) whit: Cpr = 1.19  10-3 kg m-3 (depends on light velocity, Solar mass and G) Qpr dust scattering efficiency (depends on chemical composition of the grains), assumed to be 1 d dust bulk density, assumed to be 103 kg m-3   < 10-4, a > 1 cm amax = 1.57  10-27 Q R-3 cm (Crifo et al., 1999, Icarus 138, 1, 85; see also Meech & Svoren, 2005, in “Comets II”) R = 10 km  QCO = 1030 mol s-1 Cometocentric Earth latitude in comet orbital plane is only 2°

  20. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Conclusions and future prespectives QCO~ 1028 mol s-1 and grains larger than 1 cm  R ~ 2 km QCO + Qdust~ 600 kg/s rather constant over orbit 2-km radius LONEOS with  = 103 kg/m3 would be blown off in ~ 2  103 years Key measurements to solve the question would be:(i) direct estimation of the LONEOS diameter (ii) direct observation of CO production rate (radio measurement)(iii) direct IR spectroscopic measurements of CO content (AKARI next october - hopefully)

  21. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Additional slides orbit computed PA of the Neck-Line antitail 

  22. TNOs: dynamical and physico-chemical propertiesCatania, 3-7/7/06 Additional slides

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