The Continuum Detector Laboratory
at the University of Massachusetts, Amherst

BOLOCAM II SPEED Large Millimeter Telescope FSB TopHat

People

Contact

Undergraduate
Opportunities

UMass
Astronomy

CDL Home


This work is funded in part by the National Science Foundation, Grant #s ???? and ???? and the National Aeronautics and Space Administration, Grant # ????


710 N. Pleasant St.
619 E LGRT-B
Amherst, MA 01003
413. 545.1879


Performance Estimates

At this time, the optical designs of Bolocam II are still being optimized, so detailed specifications and performance estimates are unavailable. Some of the changes to the original design that are being analyzed include changing the tertiary mirror with each bandpass, enlarging the FOV to increase mapping speed, and increasing the throughput to improve sensitivity. However, at the current stage of development it is probably most appropriate to simply review some of the instrument’s expected performance estimates on the LMT as if it were an exact copy of the Bolocam I instrument.

On the LMT, the original Bolocam optical design will result in a 2’ field of view (FOV) and a pixel-to-pixel spacing of ~10”. The beam FWHM of each pixel will be approximately 6”, 8”, and 12” for the 1.1mm, 1.4mm, and 2.1mm bands, respectively. Extrapolating from the recently achieved sensitivities of Bolocam at the CSO, the 1.1mm per-pixel sensitivity at the LMT will be approximately 4 mJy/Hz1/2 in an un-chopped scanning mode and 6.2 mJy/Hz1/2 in a chopped mode. A survey mode mapping speed can then be calculated as


with the number of pixels, Npix = 144 (assuming all are operational), and Ωbeam, LMT= 0.0128 arcmin2. A blow-by-blow comparison of similar Bolocam instruments on the LMT and CSO is listed in table 1.

Table 1. Bolocam CSO/LMT 1.1mm Comparison


(1) Instantaneous pixel sensitivity achieved by large majority (>70%) of pixels
(2) BCI currently has only ~110 operational pixels. Values are what they would be if all 144 were operational
(3) Ignoring overhead such as turnaround time, calibration, etc.

When scanning, the edges of the map will have significantly less coverage since the full array never sweeps over those areas. A conservative rule-of-thumb used by Bolocam I team is to assume a loss around the edges of size FOV/2, which leads to the simple mapping efficiency relation


where Lxand Lyare the scanning dimensions in the x and y directions of the scan. The estimated map size and efficiency resulting from 200 hours of scanning are listed in table 1. These efficiency estimates assume a square field map and that each scan spans the entire length of the map.

When on the LMT, Bolocam II will work in conjunction with the SPEED camera to study very distant dusty sources. SPEED is a four-pixel camera, with each pixel comprised of four Frequency Selective Bolometers (FSBs). Bolocam II will efficiently survey large swaths of the sky with the capability of detecting thousands of 1mJy sources in a matter of hours. SPEED will then produce narrow and deep observations of the spectral energy distribution (SED) of the sources detected in the BOLOCAM II surveys. This is accomplished using SPEED’s ability to simultaneously observe at four different frequencies, thus allowing for the measurement of photometric redshifts of the objects.

Back to BOLOCAM II main page.

For further information on BOLOCAM II, contact Grant Wilson or Jay Austermann.