THEMIS Observations (2007)

1. THEMIS Observations (2007) F. Leblanc (Service d'Aéronomie), A. Doressoundiram (Observatoire de Paris),V. Mangano (IFSI), A. López Ariste (THEMIS), C. Lemen(THEMIS), B. Gelly (THEMIS), C. Barbieri (Padova University), G. Cremonese (INAF, Padova) and N. Schneider(LASP)

2. THEMIS, Tenerife, Canarias 0.90-m Solar telescope Spectral range 400 to 1000 nm at R ~ 220000 Slit: 0.5" & 2’ long Resolution of 450,000 with Slit: 0.25" & 74 "long May and October 2007 campaigns Spectral resolution 0.027 Å Spectral dispersion 10.2 mÅ Four individual cameras D1 Na at 5896 Å OK D2 Na at 5889 Å OK D1 K at 7699 Å No ident. Li at 6707 Å No ident.

3. Two years of observations Scanning of Mercury’s exosphere: typically 17 exposures of ~8 mm separated by the width of the slit (0.5″) + tip tilt + tracking

4. Hapke Model May Campaign 01/06/2007 • Use of Mercury’s surface (Hapke 1986; Mallama et al. 2002) to : • Measure Seeing value and variation • (here 2.05″±0.36″) • Calibrate (taking into • account absorption effects) Measured D2 continuum

5. D2 Na • Observed D2 and D1 • emission intensities • Total: • D2: 1.34±0.10 105 kR • D1: 1.04±0.06 105 kR • Uncertainty taking into account: • Noise level • Uncertainty on seeing value • Uncertainty on position of Mercury D1 Na

6. D2 Na Observed D2 and D1 emission intensities Simultaneous peaks of emission Following Potter et al. (2006) due to solar pressure effect inducing a strong recycling  Solar pressure acceleration = 35% of gravity acceleration D1 Na

7. Observed Doppler width Fit of the spectral line by Gaussian distribution 1.37 km/s resolution of THEMIS But 2.5 – 2.8 km/s doppler width of exospheric line and optical thin D2 = 0.3 D1 = 0.15 D2 Na D1 Na

8. D2 Na • Observed Doppler width • 10-6 probability to find these values at these places • Equivalent temperature: • - 810 - 960 K for “cold” regions • 890-990 K for “hot” regions • Good agreement with Killen et al. (1999) D1 Na

9. Conclusions of 06/01/2007 observations • The high latitude peaks are produced by an energetic process with respect to the bulk exosphere • Cannot be thermal desorption • Meteoroid vaporization, difficult to produce symmetric peaks • Could be photon stimulated desorption if local peaks of surface density are formed (following Potter et al. (2006) suggestions) • Most probably solar wind sputtering but how to have symmetric magnetospheric impact?

10. October’s campaign: 10/14/2007, D2 Na 13:46 UT - SeeingFWHM = 0.48 RM Tot. Emiss. = 1.86±0.79 105 kR 15:38 UT - SeeingFWHM = 0.54 RM Tot. Emiss. = 1.95±0.76 105 kR 16:48 UT - SeeingFWHM = 0.58 RM Tot. Emiss. = 1.66±0.58 105 kR 14:34 UT - SeeingFWHM = 0.55 RM Tot. Emiss. = 1.62±0.22 105 kR

11. 10/16/2007 D2 Na 14:35 UT - SeeingFWHM = 0.45 RM Tot. Emiss. = 1.74±0.23 105 kR 16:16 UT - SeeingFWHM = 0.40 RM Tot. Emiss. = 2.00±0.31 105 kR 17:19 UT - SeeingFWHM = 0.52 RM Tot. Emiss. = 2.46±0.47 105 kR

12. D1 Continuum D2 Continuum

13. FWHM D2 Doppler D2

14. Comparison with Potter et al. data set (2006) A rather good agreement  A steady exosphere to model…

15. Expected coverage at the end of 2008 campaign Red dawn side Orange dusk side A 2009 campaign?