PI: Warren Brown (SAO) Co-I's: Steve Amato, Maureen Conroy, Giovanni Fazio, John Geary, Joe Hora, Brian McLeod, Michael Pahre, Steve Willner, Bill
Wyatt (SAO), and Emily Bowsher (Wellesley)
Marc Lacasse and I opened the dewar to replace the charcoal
getter. Our goal was to improve vacuum and detector operating
temperature. Tests showed that the detector is working like normal after
One channel on an A/D board failed. We repaired the channel, and
upgraded components on all of A/D boards to prevent this from recurring.
The new Y-band filter is installed and works great! See the exposure
time calculator. The filter wheel problem is fixed.
The new Y-band filter has arrived. Transmissions scans confirm
that the filter has excellent out-of-passband rejection at high incidence
angles. The Y-band filter will be installed before the next SWIRC
SWIRC's filter wheel became stuck in H-band during the second
night of the run, but the instrument continued to obtain excellent science
data (in one filter). The filter wheel problem will be fixed before the
next SWIRC run.
The overhead time between exposures has been halved to nearly 4
seconds, a result of telescope motion flags being updated more rapidly by
the mount computer. However, we had a few streaked images which is
unusual for SWIRC. The streaked image problem was later tracked to
primary mirror hard-point slippage.
The new J-band filter is installed and gives a factor of ~3
improvement in SWIRC's J-band sensitivity. The instrument performance
numbers have been updated accordingly. SWIRC operated in 0.3" seeing at
times during the run.
We bonded a blocking filter to the old J-band filter, and measured
a 3.8x drop in background; the total J-band throughput is down by a factor
of 0.88. The exposure time calculator has been updated
We verified the world coordinate system header information in the
32-channel read-out mode, and exercised a number of new MICE control
features. Our biggest problem, the telescope server repeatedly crashing,
was traced to a Megacam guider server that was unrelated to SWIRC. A few
minor fixes to the MICE interface will be implemented for the May 2005
A new J-band filter, originally scheduled for delivery March 25,
2005, was postponed by the manufacturer to sometime in June.
The 32 channel electronics were completed in September 2004, and
SWIRC's read-out time reduced from 5.7 seconds to 0.7 seconds. The new
electronics provide a reduced readnoise of 31 electrons, and a gain of
4.0. The linearity of the detector is excellent (at 0.1\% level) to
160,000 electrons, and the dark current is very stable. However, one
channel has RMS 75 electron bias fluctuations. Cross-talk is not apparent
We confirmed the J-band filter red leak with transmission scans
taken at large incidence angles. We purchased a blocking filter to reject
this light, and bonded it onto the J-band filter. The composite filter
successfully survived cryogenic temperature cycling. We joined a
consortium filter purchase that has allowed us to purchase a new J-band
and a new Y-band filter (with more stringent specifications) at a
significant cost savings; we expect delivery sometime mid-2005.
We were allocated 5 nights, Oct 22 - 26, for SWIRC engineering and
shared-risk science observations. All 5 nights on the telescope were lost
due to weather. SWIRC worked flawlessly taking darks and flats. A 60 Hz
noise problem was found, traced to a faulty power supply fan (probably
caused by shipment), and eliminated.
Comparison of dome flats suggest that the J-band background has
been reduced by a factor of >3. By comparison, we expected the background
to decrease by a factor of ~15, and the throughput of the composite J-band
filter to decrease by a factor of 0.8. However, until we go on-sky we
cannot verify the new J-band performance or verify the correct orientation
of SWIRC images (we use new software to de-commutate the 32 channel
read-out). These issues will be resolved during engineering in Spring
The new SAO Wide-field InfraRed Camera (SWIRC) was commissioned at the MMT
29 June - 5 July 2004. It was proposed, built, and shipped in 13 months
at a modest cost ($139,000) paid for by Smithsonian IR&D funds.
Throughput is 2.5-3 times that of FLAMINGOS on the MMT. The H-band (1.6
um) sensitivity is comparable to FLAMINGOS, as expected. However, the
J-band background during commissioning was substantially higher than
Sustained seeing of 0.4 arcsec FWHM (2.7 pixel) was observed during
commissioning, so the instrument's optics have good image quality.
Maintaining f/5 secondary collimation and preventing telescope drive
oscillation appear to be the major concerns in maintaining image
quality. SWIRC was returned to the CfA following to implement a
32 channel read-out.
Commissioning image of the globular cluster M3, observed in 0.4 arcsec seeing.