GAIA: SOLAR SYSTEM ASTROMETRY IN DR2

Transcription

1 GAIA: SOLAR SYSTEM ASTROMETRY IN DR2 P. Tanga 1, F. Spoto 1,2 1 Observatoire de la Côte d Azur, Nice, France 2 IMCCE, Observatoire de Paris, France

2 2 Gaia is observing asteroids - Scanning the sky since July 2014 (operational phase) - Solar elongations 45 to Limiting magnitude V~ asteroid observations (CCD level) / day 45 Sun

3 P. Tanga Gaia and the Solar System Gaia DR2 - Solar System On the base of a pre-selected list of known objects > 10 FOV transits over the 22 months of DR2 August 5, May 23, 2016 Objects Epoch astrometry Typ. accuracy CCD positions transits (52% : photometry) <1 mas (along scan) 3

4 4 Gaia DR2 - Solar System statistics 1:0e e e e e G mag Number of observations per object a (AU)

5 5 Gaia DR2 - Solar System - single transit astrometric performance Residuals from the orbital fit of Gaia DR2 data only (along-scan direction) Spoto et al. 2018

6 6 Asteroid (386) Siegena - residuals from orbital fit Combining archive data (2776 obs.) to GDR2 0:4 4 0:3 0:03 Dec residual (as) Dec residual (as) 0:2 0:1 0 0:1 Dec residual (as) 0:02 0:01 0 0:01 0:2 0:02 4 0:3 0: RA residual (as) 0:4 0:4 0:3 0:2 0:1 0 0:1 0:2 0:3 0:4 RA residual (as) 0:02 0 0:02 RA residual (as) factor 100 X improvement!

7 7 The situation, before Gaia 1.9 x 108 measurements in the archives of the Minor Planet Center mostly CCD imaging average accuracy: 0.4 as ~2000 radar ranging measurements equivalent accuracy : mag

8 8 Some challenges for asteroid astrometry Discover asteroid satellites New / precise asteroid masses from their wobbling mas 1000s encounters/year > 10 mas Improve predictions of stellar occultations ~a few mas Measure the orbital drift due to Yarkovsky force

9 9 Yarkovsky effect: why we care Yarkovsky applications: NEO and meteorite transport physical properties (spin, density ) family dispersion, ages Spoto et al The challenge: measure a few, apply to many > connection to spectro- photometry by Gaia: low-res spectra: taxonomy in the visible mmag photometry: shape determinations Large sample by end of mission: ~ Delbo, Galluccio, De Angeli, ESA/Gaia/DPAC

10 10 Yarkovsky and Gaia? ~ 3 x 10-9 AU Pre-Gaia orbit quality (MPC data) 1/D (1/km) In DR2: 3 NEOs with measured Yarkovsky 5 NEOs with marginal detection about 20 good MB candidates Orbit uncertainty (km)

11 11 Asteroid family members in DR family members in DR2 (from AstDys membership) 0:6 0:5 0:4 sin(i) 0:3 0:2 0:1 0 1:6 1:8 2:0 2:2 2:4 2:6 2:8 3:0 3:2 3:4 3:6 3:8 4:0 a (AU)

12 12 Joint exploitation Gaia + pre-gaia astrometry: bias example Asteroid (1132) Hollandia Liverpool Telescope + VST (8 hours apart) & MPC ground-based data (~1900 positions) PPMXL calibration Gaia calibration 0.1 VST 0.1 LT+VST O-C Dec (as) O-C Dec (as) LT O-C RA (as) O-C RA (as) (credits: Gaia GBOT team)

13 13 The occultation astrometry with Gaia DR2 already successfully exploited Triton (Octobre 3, 2017) 2014 MU69 (V=27.5, 50 km KBO, ~1.4 mas)!! Occultations: very accurate asteroid position at the level of the star astrometry Beyond the duration of Gaia! Occultations ¾a(au) 1e 4 1e 5 1e 6 1e 7 1e 8 equal accuracy 1e 9 1e 9 2e 9 5e 9 1e 8 2e 8 All observations ¾ a (au) N occultations

14 14 Robotic observations of asteroid occultations Extension to faint magnitudes and small asteroids Only method providing ~Gaia accuracy 50 cm robotic telescope at OCA, France ASTROMETRIC DATA OBSERVATIONS EXPLOITATION: YARKOVSKY, IMPROVED DYNAMICAL MODEL AND ORBITS OCCULTATION PREDICTIONS

15 15 Conclusions Gaia DR2 asteroid data: the first sample, already useful to test subtle dynamical effects Yarkovsky determination general orbit improvement application to stellar occultations Combination with other observations: it starts to work but weighting of the data is critical accurate debiasing is required a new method successfully implemented and tested Yarkovsky detection in the Main Belt is getting closer

16 16 P. Tanga Gaia and the Solar System Diffusion of asteroid alerts From the Gaia-FUN-SSO web site (the red contours are computed by the SSO-ST pipeline and show the search area on the sky, on three different dates): Topocentric predictions B. Carry (OCA), W. Thuillot (IMCCE) d n a r e t s i Reg! e t u b i r t n co