[Note: while this project can’t be done in May-June, it addresses important system performance issues. It is included to stimulate thinking about similar science on more accessible targets.]
Science:
The project is to obtain very deep narrowband line images in Br g, 2.122 micron H2, and 1.64 micron [Fe II], along with shorter exposures in J H KS . These lines are diagnostic of physical conditions in shock-excited gas, and frequently identify morphologically interesting compact objects. The science has two threads, investigations of the ISM and of the stellar content of this extensive nearby region of star formation:
NEWFIRM on the 4-m telescope offers
the opportunity to survey a large spatial extent of Orion A to a deep
sensitivity limit. This extended field, or portions of it, are being observed
in a variety of surveys, including 1.1 mm continuum (Bolocam), 21 and 6 cm
(IGPS and VLA), IR (Spitzer), and optically. The field location is chosen to
match the optical narrowband imaging survey conducted on the 4-m with Mosaic
CCD camera. There is also a rich heritage of data at all wavelengths in the
literature and in electronic form. So there is both significant immediate
science return and substantial archival value for the dataset.
System performance issues:
The broadband imaging is similar to
what has been done before, just over more area. The project stresses use of the
narrowband filters. Observations will very likely be background limited—if not,
serious performance issues will have been uncovered! Data rates will be
moderate for the broadband imaging, ~1 frame/minute, and low for the narrowband
imaging, ~1 frame every 5-10 minutes. Performance issues of interest include
·
Electronic and thermal stability of
the arrays with exposure times of many minutes—for example, signal offset due
to readout-induced self-heating
·
Does this impact mixing broadband
and narrowband exposures during observing?
·
Use of the reference pixels
incorporated in the array structure to correct such effects in pipeline
processing
·
Guider performance—is microstepping
possible?—and PSF stability over hours, for intercomparison of images in
different filters at finest possible spatial scales
·
Optimal data taking protocol when
the airmass is changing rapidly, as it does for this region when X > 2
·
Definition of best quick-look
reductions and realtime diagnostics for narrowband imaging
·
How best to use broadband images for
continuum subtraction, a photometrically iterative process
·
Mosaicking over a very extended
area, including photometric and astrometric problems, e.g. background matching,
preservation of consistent and high accuracy coordinate system
·
Uncovering systematics of whatever
origin—instrument, telescope, sky—that may limit ultimate sensitivity for
narrowband imaging
Observing strategy:
We will obtain very deep narrowband
images, with commensurate shorter exposures in J, H, KS
to reach the same stellar flux limits as in the narrowband filters. Integration
times per filter are estimated from our previous experience.
Area coverage: Survey the 4 square
degree portion of the Orion A cloud from NGC 1977 (30' North of the Orion
Nebula), to about 3 degrees South (covering the region imaged with Mosaic
in 2001). This is 16 NEWFIRM pointings. Mean background sky frames and
flatfields will be derived from the on-source data.
Telescope time, including allowance
for overheads:
3
NB filters, x 1800 sec / filter = 2 hrs/ field, x 16 fields = 32 hours
3
BB filters, x 300 sec / filter = 0.5 hr/ field, x 16 fields = 8 hours
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Total
time 40 hours
This region is accessible from