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Some miles before reaching our destination we
passed the snow line and saw the devastation caused by the forest fires
that came close to destroying the CSS observatories back in the summer
of 2003. Once we arrived at the summit of Mt. Lemmon (9200ft above sea
level), the Large Binocular Telescope on the summit of Mt. Graham 50
miles to the northwest was plainly visible, with the lengthening shadow
of Mt. Lemmon pointing almost directly at it.
The shadow of Mt. Lemmon pointing almost directly at the Large Binocular
Telescope on Mt. Graham 50 miles away (top right in insert) As
the Sun was setting, Ed opened up the dome of the 1.5-m reflector
(observatory code G96) and started the initialisation of the equipment before the
beginning of
the nights NEO surveying.
Ed Beshore opens up
the lower shutter of the Mt. Lemmon 1.5-m telescope There are
currently seven telescopes on Mt. Lemmon, the 1.5-m reflector being the
largest, this view looking south from inside the dome of the big
reflector shows more than half a dozen other domes and buildings nearby
Looking south, out of the dome of the 1.5-m reflector
The observer for the night, Alex Gibbs arrived and continued preparing
the telescope. The 4K x 4K CCD is normally operated at -100°C
but that temperature has recently been difficult to get down to, an air
dryer unit used to extract water from the cooling system suspected of
being full of water and needing replacing soon. Alex kept an eye on the
CCD temperature and ran through focussing sequences and also started
choosing fields
in the early evening sky ready for the survey work to start. Two
computer flat screen monitors arranged side-by-side displayed the sky
divided up into the fixed 1.2° x 1.2° field centres that are used night
after night for all the survey work with the 1.5-m telescope. Settings allowed the areas of sky
that CSS and the other surveys such as LINEAR and Spacewatch had covered
in recent nights to be colour-coded so that fresh unsurveyed sky could
be targeted that evening.
Field centres for the 1.5-m telescope, colour-coded
showing where NEO surveying had been done in recent nights by other
surveys Alex clicked on sets of 12 adjacent fields with the
mouse, each set of 12 fields would be automatically imaged one after
another, going around the set a total of four times. All the images
would then be fed into the processing pipeline for automatic moving
object detection. Lines on the computer screen marking out 60° elongation
from the Sun indicate the westernmost boundary and surveying then
proceeds to the east as the night progresses, with the observer manually
choosing the areas of sky to be targeted. Earlier in the week Pan-STARRS
had been given a complete night dedicated to NEO detection, resulting in
27 Pan-STARRS objects being on the NEO Confirmation Page, most very
faint at mag. 22-23 and out of the reach of amateurs. Alex selected some
of the sets of survey fields to cover the uncertainty areas where some
of the Pan-STARRS objects were located to try and help recover them. As
astronomical twilight ended the exposures started and soon the first set
of 12 x 4 images had been processed and was ready for examination.
Alex Gibbs
selecting fields at the start of a night of NEO surveying by the 1.5-m
Mt. Lemmon telescope
The CSS software detects objects that
have consistent movement on all four frames of each field, down to a
signal-to-noise threshold of about 1.2 (i.e. deep into the random noise
in the images) and then matches those detections against the latest
orbits in the MPC's MPCORB Minor Planet database. Each set of four
images is then blinked, with known objects marked in green. All the
remaining detections are then visually checked by the observer and those
that look convincing are manually selected, the rest discarded. A score
is then determined for each new object depending on its rate and
direction of motion, together with where it is located in the sky to
indicate its chance of being a NEO. Astrometry is measured for all the
objects and sent off to the MPC, any objects that look like they are
particularly interesting have further exposures scheduled for later in
the night to help with the follow-up effort.
With the 1.5-m
telescope in full operation, Ed and I left to drive the 7 miles down to
Mt. Bigalow where the CSS 0.68-m Schmidt is located (observatory code
703), 1000ft below the Mt. Lemmon telescope.
The 0.68-m Schmidt at night during a brief interruption
from NEO surveying
That night Andrea Boattini
was the observer (he was the only member of the CSS team I had met
before, at the
MACE meeting in Mallorca in 2003) and as we arrived he
was busy blinking a set of images with 100+ moving objects, expertly
selecting or rejecting the automatic detections at a remarkably fast
rate!
Andrea Boattini
blinking newly detected moving objects at the controls of the CSS 0.68-m
Schmidt
Ed and Andrea
discussed recent adjustments to their procedures for the Schmidt,
increasing exposure length to 60 seconds to try and detect fainter
objects, at the expense of reducing the amount of sky they would be able
to cover per night. We left Andrea blinking the latest set of images
processed through the pipeline and drove back down the mountain with
both telescopes continuing to work flat out. What a night... |
