12 Meter Description

The ARO 12 Meter Telescope began as the 36 Foot Telescope, the telescope responsible for the birth of millimeter-wavelength molecular astronomy. During a period of explosive growth in this new area of astronomical research dozens of molecular species known to exist in the interstellar medium were first detected at the 36 Foot. In 1984, the telescope's reflecting surface and surface support structure were replaced and the 36 Foot was re-christened the 12 Meter. Subsequently, the scientific program has evolved from one dominated by observing programs in Astrochemistry to one with a broader mix of studies of molecular clouds and Galactic star formation, evolved stars, Astrochemistry, and external galaxies. The 12m offers users flexibility and the opportunity to respond quickly to new scientific developments. The Observatory maintains low-noise receiving systems covering all atmospheric windows form 68 GHz to 180 GHz. Operational reliability throughout is emphasized. Flexible spectral line and continuum backends allow the observer to match the instrument to the scientific goals. The telescope control system offers great flexibility, efficiency, and convenience, and provides a proven remote observing capability.

Telescope:

**Table 1:** Telescope and Site Characteristics
Site
	East Longitude:	-111 36 53.475
	North Latitude:	+31 57 12.0
	Elevation:	1914 meters (6280 feet)
Telescope
	Primary Reflector Diameter:	12.0 meters

	Focal Ratio (f/D)
	Prime Focus:	0.42
	Cassegrain Focus:	13.8

	Surface Accuracy :	75 µm rms
	Mount:	Elevation over Azimuth
	Slew Rate :	68"/minute
	Pointing Accuracy :	5" rms
	Elevation Limit :	14.7 degrees
	Enclosure:	Tracking astrodome with movable door
	Aperture Efficiencies:	52% at 70 GHz
		49% at 115 GHz

Present Instrumentation:

Receivers

As many as four receivers are mounted simultaneously at offset Cassegrain foci on the telescope. Receiver selection is by means of a rotating central mirror and can be accomplished in minutes. The receivers are configured remotely from the control room with a computer-aided tuning system. The standard receiver system at the 12 Meter telescope consists of a 4 K closed-cycle cryostat containing up to 6 SIS receivers. A complete set of dual-channel SIS receivers is operational over the entire 68 - 180 GHz range.

Spectrometers

Filters:

Table 3: 12m Filter Spectrometer Characteristics

Filter Resolution	Channels per Bank	Filter Banks Available
2 MHz	256	2
1 MHz	256	2
500 kHz	256	1
250 kHz	256	1
100 kHz	256	1
30 kHz¹	128	1

¹ Series option only.

Millimeter Auto Correlator (MAC):