SHARCII Instrument Status

Darren Dowell -- (626)395-6675 (office), 796-8806 (FAX)
Last modified Thursday, 07-Aug-2003 12:45 PDT
cdd@submm.caltech.edu

February 2003

Array

We now have capability to read the full 12x32 array. Approximately 330 of the detectors have good performance.

Filters

SHARC II has 3 filters in a manually-operated wheel: 350 microns, 450 microns, and 850 microns. We observe nearly background-limited performance at 350 microns and expect the same at 450 microns. At 850 microns, we expect an NEFD of about 1-2 Jy s1/2 -- 10-20x worse than SCUBA. We anticipate very little observing at 850 microns.

Sensitivity


NEFD, Jan. 2003
Preliminary 350 micron NEFD measurements (points) from the Jan. 2003 commissioning run compared to the theoretical expectation (line). We confirm the performance of ~1 Jy s1/2 for tau(225 GHz) = 0.05.

We do not yet have NEFD measurements at 450 microns.

Field Rotation

SHARC II sits on an instrument rotator, which in principle can be used to correct for parallactic angle rotation. The user should verify that the actual rotator position (APA on antenna monitor) is close to the requested rotator position (RPA), and also watch out for rotation-dependent pointing offsets. Cable restrictions are fairly minor if things are set up well, but should be monitored for large rotations.

Availability of Other Instruments with SHARC II Installed

SHARC II sits on the right port of the Cassegrain relay optics, the same as SHARC I. With SHARC II on the telescope, the standard facility heterodyne receivers in the sidecab can be used by positioning the swinging tertiary mirror appropriately.  SHARC II conflicts with the 850 GHz heterodyne receiver and probably most other instruments which mount on the left port of the relay optics. At this time, it is not possible to switch conveniently from SHARC II to Bolocam due to their different Cassegrain structures.

Observing Modes

The primary observing mode of SHARC II is scanning without chopping. We have developed two routines to collect data while performing linear and curved controlled scans; they are called "SWEEP" and "BOX_SCAN" in the UIP. SWEEP is most appropriate for maps comparable to the size of the detector array, and BOX is better for larger maps.  The stability timescale of a SHARC II bolometer is approximately 10 seconds; to achieve full sensitivity, one should scan from off source to on source to off source within this time.

We do not yet support chopped observations. Data have been acquired and analyzed using a slow (1 Hz) chop, but this mode is not "released". Supporting fast (>=3 Hz) chopping (which was used with SHARC I) is unlikely to become a priority.

Analysis Software

Analysis software is under development at Caltech and Goddard. Operating it away from the CSO may require Solaris or Linux and possibly JAVA or IDL. More information will be made available when the software is near release. Carrying out analysis in a timely fashion may require modern (>= 400 MHz) processor speeds.

Raw SHARC II data will be large in size (3 Gbytes on a good night), probably too large for Internet transfer. We hope that users will be transporting reduced data back to their institutions. Transporting raw data may require purchasing storage media.

Go to SHARC II home page...