The dust coma of the active Centaur P/2004 A1 (LONEOS) A CO-driven environment? TNOs: dynamical and...

The dust coma of the active Centaur P/2004 A1

(LONEOS)

A CO-driven environment?

TNOs: dynamical and physico-chemical propertiesCatania, 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


Distant activity of Minor BodiesProgram 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 environmentSeveral 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 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

Centaur q (AU)

e i (°)

P (years)

TJ Note

29P/S-W 1 5.724 0.044

9.4 14.7 2.984

39P/Oterma 5.471 0.245

1.9 19.5 3.005

Presently inactive

Chiron 8.454 0.383

6.9 50.7 3.356

165P/LINEAR 6.830 0.621

15.9

76.4 3.095

166P/NEAT 8.564 0.384

15.4

51.9 3.285

167P/CINEOS 11.788

0.269

19.1

64.8 3.527

C/2001 M10 (NEAT)

5.303 0.801

28.1

138 2.586

Activity questioned

P/2004 A1 (LONEOS)

5.463 0.308

10.6

22.2 2.963

174P/Echeclus 5.826 0.457

4.3 35.1 3.032

2000 EC98

P/2005 S2 (Skiff) 6.398 0.197

3.1 22.5 3.076

MPEC2005-T76

P/2005 T3 (Read) 6.202 0.174

6.3 20.6 3.045

MPEC2005-W81


Chiron

“Giant comet”

29P/S-W 1

Luu & Jewitt, 1990, AJ 100, 913

Jewitt, 1990, ApJ 351, 277

Short term variations of

coma morphoogy


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 EC98)

Inactive up to December 2005.

Onset of cometary activity monitored in following

months

Images from amateurs (R. Ligustri)


The Active Centaur P/2004 A1 (LONEOS)

• 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

~ 5 ~ 5 10 1055 kmkm

Total exp. time 2400 sTotal exp. time 2400 s

N

E


The P/2004 A1 (LONEOS) coma general properties

isophotes levels: 21.33, 22.08, 22.83, 23.58, 24.34 and 25.09 magR

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) ~ 8.8 104 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


The P/2004 A1 (LONEOS) dynamical history


30/7/1992Close encounter

with Saturn

@ d = 0.03 AU

perihelion distance q

9.78 5.46 AU

aphelion distance Q

14.56 10.37 AU

inclination i11.4 8.0 °


Sources of distant activityDistant 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,...

pure icereleased when sublimation

starts at 25K

gas trapped in amorphous water ice

released when amorphouscristalline

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 surfacefor more details, see talk by Teresa Capria later this morning

CO

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-ZQ = 3.28 1027 mol s-1

(Mumma et al., 2000, ApJ 531, L155)

FUSE measurement of CO in C/2001

A2 (LINEAR)Q = 1.3 1027 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 1027 mol s-1

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)

(Festou et al., 2001, Icarus 150, 140)

SEST radio measurement of CO in 29P/S-W 1

Q ~ 3 1028 mol s-1

(Bockelee-Morvan et al., 2001, A&A 377, 343)

CO (upper limit) derived with radio measurements

Q [Centaurs] ~ 1028 mol s-1

Q [KBOs] ~ 1-5 1028 mol s-1

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

environmentUsed 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)u and iterative fit with observed isophotes


environmentEQUATION 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)/ logdv(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-p

dust production rate

their time evolution from the observation back in time up to the last observable isophote


environment


environmentThe 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°


v(t,d) = v(t,d0) (d/d0)u

withu=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


environmentThe 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 103 kg m-3 density is assumed (at aphelion)

= (CprQpr)/(dd)

whereCpr = 1.19 10-3 kg m-3 depends on light

velocity, Solar mass and GQpr is the dust scattering efficiency (depends on chemical composition of the grains), assumed to

be 1d dust bulk density, assumed to be 103 kg m-3



environmentAutomatic 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)




environmentAutomatic output of the inverse dust tail model applied

to P/2004 A1 (LONEOS)



Dust production rate: ~ 100-200 kg/s, constant in timeMuch greater than value

obtained for Chiron

Af: ~ 0.5-2 m, computed for a subset of grain size


Conclusions

Synchrone-syndyne network for LONEOS on April 2005 = (CprQpr)/(dd)

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 cmamax = 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°


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)


Additional slides

orbitantitailcomputed PA of the Neck-

Line


Additional slides

The dust coma of the active Centaur P/2004 A1 (LONEOS) A CO-driven environment? TNOs: dynamical and...

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