Nov Boston Meeting1 Mercury at the TNG Cesare Barbieri Dept. of Astronomy University of Padova With the collaboration of: Gabriele Cremonese, Stefano Verani, Valeria Mangano and Francois Leblanc

Nov Boston Meeting2 Mercury’s Exosphere with the TNG Four TNG campaigns: (Barbieri et al. PSS, 2003) (Leblanc et al. Icarus, 2006) -we could not observe in (Mangano et al. EGU 2006) (June in preparation, bad weather in October) Our program to observe with the High Resolution Spectrograph (SARG) of the TNG started in The observing period is very short, less than 60 min (only at sunset).

Nov Boston Meeting3 SARG Characteristics SARG main parameters Spectrograph resolution Slit length and width26.7 x 0.40 arcsec Pixel dimension and scale0.022 A, 0.16 arcsec (binned x2 to 0.32) CCD dimension2K x 4K pixels A Na-D 60 A wide filter is inserted before the slit to suppress unwanted orders, so we imagine 0.32x27 arccsec in the sky.

Nov Boston Meeting4 From raw to reduced Subtract background and scattered light Fit a Voigt profile Extract the Na-D emissions

Nov Boston Meeting5 Two examples from 2005 The slit was kept aligned in Right Ascension. The Na measured counts (ADUs) along the slit. June 29, 2005 July 1, 2005

Nov Boston Meeting6 Radial velocity verification Topocentric Radial velocity of Na-D emissions. Table from the 2002 data. The precision is slightly worse than expected, but until now we didn’t try to do a better analysis. DateMercury’s Radial velocity (Horizon JPL) Measured Na Radial Velocity Difference (JPL-TNG) (km/s) 23/08/ (  0.6) /08/ (  0.6) /08/ (  0.6) /08/ (  0.6) /08/ (  0.6) /08/ (  0.6) -0.2

Nov Boston Meeting7 PROBLEMS! Slit position Hapke’ method and physical calibration Background substraction ??, electronics instabilities associated with dome opening??

Nov Boston Meeting8 Problems with slit position One of our major present difficulties is the determination of the slit position on Mercury’s disk. The slit field is imaged by a TV camera that takes an image every 0.1 seconds or so, and which is positioned after the NaD narrow filter. So, we could obtain at the same time useful planet’s images. Unfortunately, the slit plane has no good optical qualty, as shown here: An image obtained in 2003 An image obtained in 2006 The situation has been slightly improved in 2006 with a new TV camera, but a drastic remedy is necessary. We are trying to have a better slit for next run. On the data obtained till now,we cannot claim a positioning accuracy better than  1” (  1/6 th Mercury radii).

Nov Boston Meeting9 Problems with scattered background We are obliged to observe only in the evening. Therefore, we start the observations when the Sun is still several degrees above the horizon. The dome has fairly reflective walls very close to the telescope. Even raising the perforated wind screen has little effect on a strong rapidly varying background. Sometimes we are even forced to start observing with the dome shutters only partially open. Therefore, the background level of the first images is sometimes erratic and difficult to remove from the data. As a consequence, the absolute calibration of the brightness of the lines via Hapke’s method is very uncertain on the earliest spectra. The problem seems aggravated in 2005 and 2006 data.

Nov Boston Meeting10 Applying Sprague et al. (1997) Method Systematic search of an optimum for two free parameters: - position of the slit on the disk (  1”.5 from the theoretical position) - seeing values (between 0”.7 and 2”.5) By fitting the theoretical Hapke’s continuum, the Na-D intensities are calibrated in Rayleigh. The original program was obtained from A. Sprague, and recently modified by F. Leblanc.

Nov Boston Meeting11 Results for the June 16, 2006 evening - 1

Nov Boston Meeting12 Results for the June 16, 2006 evening - 2 Log 10 scale D2 For better visual clarity, I show only the D2 intensities. 46,55 44,48

Nov Boston Meeting13 Results for the June 16, 2006 evening - 3 Difference due to dome? No change Comparison of the measured emission (ADU) at different positions D1 D2

Nov Boston Meeting14 Results for the June 17, 2006 evening - 1

Nov Boston Meeting15 Log 10 scale 41, 42, 49, 47, 51, 53, 54 62, 66 43, 61, 63, 65 Results for the June 17, 2006 evening - 2 For better visual clarity, I show only the D2 intensities

Nov Boston Meeting16 Comparison of the measured emission (ADU) at different positions D2 (same behavior for D1) Results for the June 17, 2006 evening - 3 Change due to dome ? Same position No change

Nov Boston Meeting17 Results for the June 18, 2006 evening - 1 Bad Night!!

Nov Boston Meeting18 Log 10 scale 47, 50 Results for the June 18, 2006 evening - 2 For better visual clarity, only the D2 intensities are shown. The slit was rotated in the celestial declination direction, and spectra taken across the disk, in front to the planet and in the anti-Sunward direction.

Nov Boston Meeting19 Comparison of the measured emission (ADU) at different positions D1 and D2 Dome effect? Results for the June 18, 2006 evening - 3

Nov Boston Meeting20 Results for the June 19, 2006 evening - 1

Nov Boston Meeting21 Log 10 scale 56, 57 44, 45, 48, 51, 61 46, 54, 55 The slit was rotated in the equatorial declination direction, and spectra taken across the disk, in front to the planet and in the anti-Sunward direction. Only D2 is shown. Results for the June 19, 2006 evening - 2

Nov Boston Meeting22 Comparison of the measured emission (ADU) at different positions D2 Same position Results for the June 19, 2006 evening - 3

Nov Boston Meeting23 Excellent data of the sodium emissions for three nights 06/16/06 06/17/06 06/19/06 ( the 06/18/06 not very good) Problem of calibration has to be solved Analysis of the Doppler shift of the emission lines to be refined: at moment, no good precision on the radial component, pixel dispersion ~1 km/s: when divided by phase angle this dispersion is equal to 10 km/s on the radial velocity during the two first nights (Phase Angle 94° and 96°), down to 7 km/s for the two last nights (Phase Angle 98° and 100.6°), whereas the expected velocity range in the tail is between 0 and 12 km/s CONCLUSIONS 2006