The Five College Radio Astronomy Observatory operates the 14 meter radio telescope located in New Salem, Massachusetts. Commissioned in 1976, the 14-m has played a leading role in the study of the molecular interstellar medium, in the development of leading edge technologies and millimeter-wave intrumentation, and in providing a valuable educational resource for graduate and undergraduate students from institutions throughout the world.
The 14m antenna is enclosed in a metal frame radome covered by a GoreTex fabric which provides protection from wind and precipitation and has high transparency within the 3mm band. The environment within the radome is regulated by fans and vents to limit temperature gradients across the antenna. Pointing of the telescope to account for gravitational deformations is controlled by a model whose rms is 5arcsecs;.
The ONLY frontend system on the FCRAO 14m telescope is the single sideband 32 element focal plane array receiver SEQUOIA. SEQUOIA is comprised of low noise MMIC based amplifiers. The footprint configuration is shown below. The 32 pixels are tuned automatically under computer control but such tuning is typically unneccessary since the amplifiers have a simultaneous bandwidth of 30 GHz.
The table below lists recommended Tsys values to estimate observating time as a function of frequency. These are typically values averaged over the transit of a source (25 < el < 75 degrees). On cold, dry days, lower values of Tsys can be achieved.
|Frequency (GHz)||Tsys (K)|
The IF signal from SEQUOIA can be fed into 2 backend systems. The dual channel correlator (DCC) allows the user to observe 2 frequencies simultaneously within the 85-100 GHz or 100-115 GHz bands for all 32 pixels of SEQUOIA. The user generates 32x2=64 spectra for each read of the DCC. The Quarry extragalactic filterbanks (QEFs) provide 16 backends over wide bandwidths to observe galaxies or the galactic center. The configurations of these backend systems are summarized the table below.
|Backend>||Pixels||IFs/Pixel||Spectra||Bandwidth (MHz)||Channels/pixel||Channel Spacing (kHz)|
On the Fly Mapping is required for most observational programs with SEQUOIA on the 14m telescope. See OTF Mapping with SEQUOIA for more information.
OTFCALC is a JAVA based tool to calculate 1) the time to complete an OTF Map and 2) the rms achieved after regridding the raw data,
The telescope computer system consists of a ModComp Classic which runs the telescope tracking program, a distributed network of microprocessors which operate individual instruments, and a Pentium II Linux Workstation and a Sparc 10 workstation for data analysis. The tracking program allows for straightforward input of source positions in equatorial or galactic coordinates, or from a user-supplied ephemeris for solar system objects. Position-switched and frequency-switched modes of observation are available. The tracking program is designed to map efficiently with the receiver array system, and can easily be used to generate maps with full-beam or half-beam spacing at any position angle on the sky. To reduce overhead on position-switched maps, a single reference observation can be used for many on-source positions.
Position switched observations are written to disk on the ModComp in a format readable by the SPA data analysis and the Grenoble CLASS programs. Data may be analyzed on either the LINUX or SUN workstations using these programs, or can be converted into FITS format for exportation to other data analysis programs.
OTF Data are written onto a disk array (capacity 600 GBytes) and processed with the otftool (gui based) or otfmap (command line) programs. The output of these programs are regridded spectra written into either CLASS files or FITS data cubes.