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

TNOs: dynamical and physico-chemical properties Catania, 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 (r h > 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)

TNOs: dynamical and physico-chemical properties Catania, 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 Centaurq (AU)ei (°)P (years)TJ Note 29P/S-W P/Oterma Presently inactive Chiron P/LINEAR P/NEAT P/CINEOS C/2001 M10 (NEAT) Activity questioned P/2004 A1 (LONEOS) P/Echeclus EC 98 P/2005 S2 (Skiff) MPEC2005-T76 P/2005 T3 (Read) MPEC2005-W81

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

TNOs: dynamical and physico-chemical properties Catania, 3-7/7/06 Active Centaurs 166P/NEAT (former C/2001 T4 NEAT) Bauer et al., 2003, PASP 115, 981 Puzzling color gradient: even active, it is one of the reddest Centaurs (its V-R color in 2001 exceeded that of Pholus) 174P/Echeclus (2000 EC 98 ) Inactive up to December Onset of cometary activity monitored in following months Images from amateurs (R. Ligustri)

TNOs: dynamical and physico-chemical properties Catania, 3-7/7/06 The Active Centaur P/2004 A1 (LONEOS) Discovered in the course of the LONEOS (Lowell Observatory Near-Earth Object Search) program on Perihelion q = 5.46 AU Eccentricity e = Inclination i = 8.2° Period P = 22.2 years Observed at TNG telescope on April 3 rd, 2005, when at r = 5.54 AU Δ = 4.69 AU ~ 5  10 5 km Total exp. time 2400 s N E 

TNOs: dynamical and physico-chemical properties Catania, 3-7/7/06 The P/2004 A1 (LONEOS) coma general properties  isophotes levels: 21.33, 22.08, 22.83, 23.58, and mag R arcsec -2 Mazzotta Epifani et al., 2006, submitted to A&A Coma slightly asymmetric: maximum extension in the W (very close to the anti-solar direction) ~ 8.8  10 4 km Neck-Line: thin spike extending in the solar direction (antitail) up to 1.5  10 5 km Magnitude in the R band (d = 5”):  LONEOS is the faintest active Centaur of the observed sample Af  = 334  15 cm For comparison: 19P/Borrelly: AU 81P/Wild 2: AU 21P/Giacobini-Zinner: AU 67P/Churyumov-Gerasimenko: AU

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

TNOs: dynamical and physico-chemical properties Catania, 3-7/7/06 Sources of distant activity Distant activity (r h > 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, CO 2,... pure ice released when sublimation starts at 25K gas trapped in amorphous water ice released when amorphous  cristalline transition starts at 100K 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 CO

TNOs: dynamical and physico-chemical properties Catania, 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  mol s -1 (Mumma et al., 2000, ApJ 531, L155) FUSE measurement of CO in C/2001 A2 (LINEAR) Q = 1.3  mol s -1 (Feldman et al., 2002, ApJ 576, L91) (Colangeli et al., 1999, A&A 343, L87) ISO measurement of CO (upper limit) in 103P/H 2 Q  4.4  mol s -1

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

TNOs: dynamical and physico-chemical properties Catania, 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 10 7 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,d 0 )(d/d 0 ) u and iterative fit with observed isophotes

TNOs: dynamical and physico-chemical properties Catania, 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,d 0 ) t time of dust ejection from the inner coma d 0 reference parameter size dependence of dust emission velocity u=  logv(t,d)/  logd v(t,d) = v(t,d 0 )  (d/d 0 ) u dust emission anisotropy w w 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 -p dust production rate  their time evolution from the observation back in time up to the last observable isophote

TNOs: dynamical and physico-chemical properties Catania, 3-7/7/06 Analysis of the CO-driven dust environment

TNOs: dynamical and physico-chemical properties Catania, 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)  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 v(t,d) = v(t,d 0 )  (d/d 0 ) 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

TNOs: dynamical and physico-chemical properties Catania, 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)  (Sub)set of dust size used for the isophote fit: grains larger than 1 cm if 10 3 kg m -3 density is assumed (at aphelion)  = (C pr  Q pr )/(  d  d) where C pr = 1.19  kg m -3 depends on light velocity, Solar mass and G Q pr is the dust scattering efficiency (depends on chemical composition of the grains), assumed to be 1  d dust bulk density, assumed to be 10 3 kg m -3 Mazzotta Epifani et al., 2006, submitted to A&A

TNOs: dynamical and physico-chemical properties Catania, 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

TNOs: dynamical and physico-chemical properties Catania, 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) 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 Dust production rate: ~ kg/s, constant in time Much greater than value obtained for Chiron Af  : ~ m, computed for a subset of grain size

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

TNOs: dynamical and physico-chemical properties Catania, 3-7/7/06 Conclusions and future prespectives Q CO ~ mol s -1 and grains larger than 1 cm  R ~ 2 km Q CO + Q dust ~ 600 kg/s rather constant over orbit 2-km radius LONEOS with  = 10 3 kg/m 3 would be blown off in ~ 2  10 3 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)

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

TNOs: dynamical and physico-chemical properties Catania, 3-7/7/06 Additional slides