README for HAWK-I SV programme 60.A-9284(I)

Proper motions in HH212: tying down the reference frame and
extending the baseline

PI: Mark McCaughrean, University of Exeter (mjm@astro.ex.ac.uk)

Description:

This is a simple programme involving direct imaging of the young stellar
jet HH212 with HAWK-I through the narrow-band H2 filter at 2.12 microns.
The jet has been monitored over several years with ISAAC to measure proper 
motions: the HAWK-I data will be used to provide an accurate astrometric
reference frame to allow removal of variable ISAAC image distortion problems.

The associated finding chart shows an H2 image of the HH212 jet taken with
the wide-field Omega-Prime camera on Calar Alto covering 515 x 515 arcsec
(no larger H2 image of the field is available).

The smaller HAWK-I field-of-view is superimposed with the jet centred in
one quadrant (217 x 217 arcsec) and fully covered by rotating the HAWK-I
FOV 23 degrees W of N. The central coordinate is part way along the jet
axis (i.e. not at the symmetric centre), as the jet is longer to the SW
than the NE.

Strategy:

The jet is to be imaged in each of the 4 HAWK-I quadrants sequentially,
i.e. by placing the coordinate given in the finding chart at the centre
of each quadrant in turn. A total of 3 minutes should be spent in each 
quadrant: DIT=60 sec, NDIT=3 is likely to be good, but should be checked
to avoid too saturation on jet knots or sky. 

There should be small jitter (<10 arcsec) between the 3 DITS at each
position to allow removal of bad pixels and to aid sky subtraction. There
is no need to cover the HAWK-I inter-quadrant gaps: it is more important
that the whole jet remain within a quadrant at each position. 

Also, when HH\,212 is in one quadrant, HAWK-I will be measuring sky in the 
other 3, and thus by stepping around all 4 quadrants a total of 5 times until 
a total of 1 hour of integration time is achieved, suitable blank sky images 
can be built up for sky subtraction from each quadrant.

In turn, this will yield four separate 15 minute images of HH\,212, one from 
each quadrant. Rather than resample and co-add them, we will use each 
independently as a template for resampling the ISAAC data and measuring 
proper motions: this will help reduce errors in our final results. The
high sensitivity of HAWK-I should yield roughly the same S/N in 15 mins
as our ISAAC data did in 1 hour. 

Important constraints:

All of the existing ISAAC data were taken in 0.4 arcsec FWHM seeing or better. 
The same must be true of the new HAWK-I data to ensure the most accurate 
astrometry and to allow best measurement of a new proper motion epoch as 
proposed.

The sky should be clear.
There is no constraint on lunar illumination.
There are no constraints on airmass as long as the seeing constraint is met.