1. ANALYSIS OF SEQUENCE OF IMAGES MTP003/STP004/TRAIL_001 & TRAIL_002
F. Moreno & OSIRIS Team
A total of 120 WAC images acquired May 17 and May 18, 2014
117 useful images
600 s exposure time. Scale=123 km/px
F12 (red) filter
Very crowded field. Comet projected against galactic plane.
NO TRAIL IS SEEN. Background=8.7±1.5 W/[m2 nm sr] (1-σ)
Lightcurve, Lomb periodogram analysis gives T= h, close to measured h.

5. LIGHTCURVE & LOMB-SCARGLE PERIODOGRAM
T= h

7. Monte Carlo Dust Tail Models of 67P/Churyumov-Gerasimenko
Moreno, F., Snodgrass, C., and the OSIRIS/GIADA Teams

8. Main goal: Analysis of ground-based observations of coma/tail/trail of 67P during the full mission, and in combination with OSIRIS images (during the approach phase), using the Montecarlo dust tail code.
Ground-based observations provide context to in-situ images by giving access to the large-scale structure of the tail. Useful to compare dust parameters derived from completely different distances and aspect angles.
Give insight to possible loss of volatile and grain fragmentation phenomena if take place at large distances from the nucleus.

9. MONTE CARLO DUST TAIL/COMA MODEL (Moreno et al.)
DYNAMICAL/RADIATIVE CODE
- COMPUTE POSITION IN THE SKY PLANE OF PARTICLES EJECTED FROM NUCLEUS SINCE START OF ACTIVITY
CALCULATE TAIL BRIGHTNESS FROM LIGHT SCATTERING PROPERTIES OF DUST GRAINS.
MODEL PARAMETERS:
1)PARTICLE DENSITY, GEOMETRIC ALBEDO, PHASE CORRECTION
2)EJECTION VELOCITY OF GRAINS AS FUNCTIONS OF SIZE
3)SIZE DISTRIBUTION
4)MASS LOSS RATE
5)EJECTION PATTERN
COMPARE SYNTHETIC TAIL WITH OBSERVED TAIL, COMPUTE STANDARD DEVIATION

10. Data OSIRIS/NAC images from April to June, 2014
VLT data (C. Snodgrass) from February to November, 2014, 52 images in total.
Heliocentric distance range: 4.4 to 2.9 AU inbound

11. NAC IMAGES

12. R-SPECIAL VLT IMAGES

13. Distant images  Nucleus contribution to the brightness is important
(e.g. Lamy et al. 1999)
PSF derived from stellar profiles (date-dependent for VLT images).
Coma brightness computed from the Monte Carlo dust tail code.
Nucleus integrated brightness derived from direct Monte Carlo simulation of flux received at OSIRIS NAC/WAC camera or the Earth, from nucleus shape (SHAP4S, facets, Preusker et al. 2015), with surface albedo of 0.060, and linear phase coeff
mag/deg (Fornasier et al 2015).

14. SHAP4S 50000 facets Avg. Surf. Albedo=0.060 Phase coeff: 0.047 mag/deg
(Fornasier et al. 2015)
SHAP4S
50000 facets
May 17-18, 2014

15. Assumed model inputs (4.4 to 2.9 AU)
Particle density ρp=2 g cm-3 (Rotundi et al 2015). Geom. albedo=0.065 (Tubiana et al 2015) (the same as for the nucleus).
Power index of SD α=-3, with α=-4 at r>1 mm (Rotundi et al., 2015, Fulle et al. 2010)
Maximum grain radius ejected: 1cm (Rotundi et al 2015). Rmin=1 micrometer
Start of activity: 4.5 AU
Anisotropic emission pattern: 15% of particles emitted from λ≥60°N, 85% from λ<60°N
Particle terminal velocities: OSIRIS/GIADA results:
From OSIRIS/GIADA data in 3.6 to 3.4 AU, random distribution in the 1-5 m/s range, independent on size (mostly for r > 100 µm)
From GIADA data in 3.37 to 2.32 AU, in the range of particle masses to kg, (r=90 to 400 µm for ρ=1 g cm-3), v is proportional to mass-0.29 (Della Corte et al. submitted), i.e., v proportional to particle radius-0.87, a very steep dependence (remember the canonical r-0.5law).
From OSIRIS/GIADA data at 2.25 and 2.0 AU, “normal” v=K*r-0.51 and v=K*r-0.40 are fitted to the data (always r > 90 µm for ρ=1 g cm-3)

16. PARTICLE TERMINAL VELOCITIES VERSUS SIZE: THREE MODELSȣ ȣ v
r-0.87 ȣ v
r-0.50

17. OSIRIS DATA – MODEL 1
Observation
Model

18. OSIRIS DATA – MODEL 2

19. OSIRIS DATA – MODEL 3

20. OSIRIS DATA – MODEL 1 – ISOTROPIC

22. VLT DATA – MODEL 1

23. VLT DATA – MODEL 2

24. VLT DATA – MODEL 3

25. Goodness of fits: OSIRIS data

26. Goodness of fits: VLT data

27. DUST AND WATER LOSS RATES

28. Conclusion: The dust properties extracted from distant NAC and VLT images by Monte Carlo dust tail models are consistent with those derived from in situ OSIRIS/GIADA data by Rotundi et al.(2015).
d/g≈4±2