mercury at the tng

Nov. 20. 2006 Boston Meeting 1

Mercury at the TNG

Cesare BarbieriDept. of Astronomy

University of [email protected]

With the collaboration of: Gabriele Cremonese, Stefano Verani, Valeria Mangano and

Francois Leblanc


Mercury’s Exosphere with the TNG

Four TNG campaigns: - 2002 (Barbieri et al. PSS, 2003) -2003 (Leblanc et al. Icarus, 2006) -we could not observe in 2004-2005 (Mangano et al. EGU 2006)-2006 (June in preparation, bad weather in October)

Our program to observe with the High Resolution Spectrograph (SARG) of the TNG started in 2002. The observing period is very short, less than 60 min (only at sunset).


SARG CharacteristicsSARG main parameters

Spectrograph resolution 115000

Slit length and width 26.7 x 0.40 arcsec

Pixel dimension and scale 0.022 A, 0.16 arcsec

(binned x2 to 0.32)

CCD dimension 2K 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.


From raw to reduced

Subtract background and scatteredlight

Fit a Voigtprofile

Extract the Na-D emissions


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


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.

Date Mercury’s Radial velocity

(Horizon JPL)

MeasuredNa Radial Velocity

Difference(JPL-TNG)

(km/s) (km/s) (km/s)

23/08/2002 -23.2364 -22.4 (0.6) -0.8

23/08/2002 -23.2136 -23.6 (0.6) +0.4

24/08/2002 -23.5354 -22.7 (0.6) -0.8

24/08/2002 -23.5121 -23.0 (0.6) -0.5

26/08/2002 -24.1171 -23.9 (0.6) -0.2

26/08/2002 -24.0843 -23.9 (0.6) -0.2


PROBLEMS!

•Slit position

•Hapke’ method and physical calibrationBackground substraction ??, electronics instabilities associated with dome opening??


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” ( 1/6th Mercury radii).


Problems with scattered backgroundWe 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.


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.


Results for the June 16, 2006 evening - 1


Results for the June 16, 2006 evening - 2Log10 scaleD2

For better visual clarity, I show only the D2 intensities.

46,5544,48



Difference due to dome? No change

Comparison of the measured emission (ADU) at different positions D1 D2


Log10 scale

41, 42, 49, 47,51, 53, 54

62, 66

43, 61, 63, 65Results for the June 17, 2006 evening - 2

For better visual clarity, I show only the D2 intensities


Comparison of the measured emission (ADU) at different positionsD2 (same behavior for D1)


Change due to dome ?

Same position

No changeNo change

No change



Bad Night!!


Log10 scale

47, 50


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.


Comparison of the measured emission (ADU) at different positionsD1 and D2

Dome effect?



Log10 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.



Comparison of the measured emission (ADU) at different positionsD2

Same position



• 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

mercury at the tng

Documents

better slit

slit plane

slit field

boston meetingproblems

slit positionhapke method

boston meetingapplying

theoretical position

reducedsubtract background