UKIRT Newsletter : Issue 4 : Special Report : UKIRT Mini Wide-Field Survey
The UKIRT Mini Wide-Field Survey
Stuart Ryder, Frossie Economou and Malcolm Currie
UKIRT, Joint Astronomy Centre, 660 N. A'ohoku Place, Hilo,
Hawaii 96720, USA
As a result of a last-minute delay in the delivery of UFTI,a
gap opened up in the UKIRT schedule for the nights of 15,16 and 17 September
1998, which could not easily be filled up by engineering or reactive recovery.
After seeking suggestions from the UKIRT scientific staff, the former Director
of UKIRT,Tom Geballe, elected to award these 3 nights to us for the purpose
of conducting the UKIRT Mini Wide-Field Survey. While the title
of this program may sound a little oxymoronic, the aims of this survey
were twofold:
a) to reveal what types and number densities of objects we
can expect to turn up in surveys with a dedicated UKIRT wide-field facility,
both at high and low Galactic latitude; and
b) to provide a partial testbed for the ORACDR software (and
its mosaicing recipes in particular) in advance of actual testing with
UFTI.
We set out to map two fields, each roughly 10' x 10', with our existing
camera system |
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IRCAM3. While somewhat less than the anticipated field of view of a
wide-field instrument, this was a necessary compromise between time available,
area coverage, and depth.
The two fields would be spaced about 5 hours apart in RA (since no one
field would be up for the full 10 hour night), and close to either the
northern Dec limit of UKIRT, or to the celestial equator, so as to minimise
the change in airmass during the observations. One field should be near
the Galactic Plane (GP), to give a high density of field stars and embedded
sources, while the other should be a comparatively empty field at High
Galactic Latitude (HL). The GP field chosen was centered on RA=22:00, Dec=+55:00
(l=100o, b=0o),near the border of Cepheus
and Cygnus. For the HL field, we selected an area centred on RA=03:05,
Dec=-09:35 (l=190o, b=-53o) in Eridanus.
This area was the site of a deep ISOCAM observation (Clements et al. 1999,
A&A, in press), and so has the advantage of having a well determined
12 micron source population. |
| The fields would be mosaiced with IRCAM3 (without magnifier),
stepping along by 60 arcsec in each axis, then imaged again with the field
centres shifted by 30 arcsec, assuring complete redundancy. We aimed to
reach J=H=K~19 on both the GP and HL fields (for comparison, the 2MASS
survey expects to reach 5-sigma for Ks=15.8 in a total of 7.8
sec, but with a pixel scale of 1'' x 1'', after sub-sampling).
We were fortunate that all 3 nights were photometric, with seeing averaging
0.6'' in K. This enabled us to map the full extent of the HL field, and
two-thirds of the GP field, in J and K. The award of half a night of Director's
Discretionary Time on 28 September 1998 by the new Head of UKIRT, Andy
Adamson, allowed us to cover the same area of the GP field in the H filter. |
|
The accompanying figure shows one of the first "sub-mosaics"
produced with ORACDR, a 3.7' x 1.8' region in the centre of the GP field
observed in K, made up of 6 overlapping IRCAM3 frames. The faintest objects
we can measure on this image are at K=19.0 or slightly fainter. Processing
of the full dataset and catalogues will be made freely available to the
astronomical community, and interest has already been expressed in doing
comparisons with other surveys (e.g., from the wide-field imaging facility
on the INT). Interested persons should keep an eye on the UKIRT Web page,
or contact the authors for more information.
Incidentally, at this rate of data collection, we calculate it would
take us only another 250 years to map the entire sky accessible to UKIRT
with IRCAM3... Roll on the true Wide-Field facility! |
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