1. Using the Rosetta Navigation Camera and Star Trackers to study comet outbursts and dust properties Bernhard Geiger
SSW#9 – Akersloot – 7-9 November 2016

2. Content Comet outbursts imaged by the NAVCAM.
Continuous measurements by the Star Trackers.
Characterisation of the properties of dust particles.
Radiometric calibration of the NAVCAM.

3. 1. Comet outbursts imaged by the NAVCAM
Regular images were acquired with the NAVCAM for navigation purposes. In addition, context images for science instruments were scheduled.
A number of outbursts were caught by the NAVCAM which were not seen by the OSIRIS camera.
Some individual cases were looked at in detail by the Rosetta community.
A systematic analysis of available images has not yet been done.
-> ESA-SCI funded project, NAVCAM work by the University of Stuttgart

4. Comet outburst examples
~150km, ~250km

5. 2. Continuous star tracker measurements
Star Trackers continuously measure the background signal in up to 9 sub-windows centred on tracked stars.
Information is reported via AOCS housekeeping telemetry.
A rough radiometric calibration has been applied.
The Star Tracker information was used as an additional source of information for studying individual outburst events, complementing the measurements of the scientific instruments.

6. Outburst on 19 February 2016: OSIRIS
35km.
Grün et al. (MNRAS, 2016)

7. Outburst on 19 February 2016: Star Tracker
Grün et al. (MNRAS, 2016)

8. Outburst on 3 July 2016: OSIRIS+STR
10km
Agarwal et al. (in prep.)

9. Signal evolution over the mission
Note: The graph shows un-cleaned data with artefacts.

10. Signal evolution over the mission
Note: The graph shows un-cleaned data with artefacts.

11. 3. Characterisation of dust particles
Characterisation of Dust Grains from Rosetta Navigation Camera Images
Florencia Calandra, Esteban García Migani, Mariela Huamán, Cecilia Lopez Sisterna, Ximena Ramos, Macarena Zinardi, Bernhard Geiger
Results obtained during the COSPAR Capacity Building Workshop on Planetary Data Analysis, Guaratinguetá, Brazil, 26 October - 6 November 2015

12. Resolved dust particles in the images
number of particles
instrumental magnitude
There are two orders of magnitude more objects detected than stars expected.
-> dust particles km
T10:41:02

13. Out of focus images of dust particles
number of particles
10m
60m
distance
size of image circles -> distance of particles
flux -> size of particles ~0.1mm to 0.5mm
T21:11:30

14. Histogram of particle distances
dark
number of particles
bright
200m
1000m
distance

15. 4. Radiometric Calibration of the NAVCAM
Difficulties:
Instrument was developed ~15-20 years ago.
Relevant information and laboratory data not available.
Broad spectral sensitivity band.
Methods:
Manufacturer calibration: “Instrumental magnitudes” for point sources.
Calibration studies based on stellar images.
Cross-calibration with OSIRIS images of the comet nucleus. (Extended source.)

16. NAVCAM Stellar Calibration

17. NAVCAM Cross-Calibration with OSIRIS
NAVCAM August OSIRIS
spectral radiance
relative frequency
-> determination of the calibration factor to convert NAVCAM digital number counts to average spectral radiance
Statella and Geiger (in preparation)

18. Summary
NAVCAM:
Un-calibrated images (Level2) are all available in the PSA.
Calibrated image datasets (Level 3) will be available in 2017.
(to be documented in detail in Geiger et al., in preparation)
Images have been used for scientific purposes by the Rosetta community.
Project for systematic analysis on-going.
Star Tracker:
Data have been used scientifically in individual cases. More potential.
Archiving of the data pending.

19. NAVCAM Spectral Sensitivity Curve