Departamento de Astronomía de la Universidad de Chile

ASTE Observing System

Facility Instruments

During the 2007 observing season, ASTE telescope will have two instrument available for the scientific community as follow

Instrument	Type	Frequency [GHz]	HPBW	# of pixels	Location	Status	Comment
AzTEC	Bolometer Camera	270	30"	144	Cassegrain	Available Jun-Oct	FOV= 7.5' in diameter circular shape.
CATS345	Heterodyne - Two-Side Bands	324 - 372	22"	1	Cassegrain	Available from Nov	IF freq range = 4 - 8 GHz

AzTEC:

The Astronomical Thermal Emission Camera (AzTEC) is a large-format bolometer camera developed at the University of Massachusetts in colaboration with researchers at Caltech, Cardiff, INAOE, Sejong University, and Smith College.

The AzTEC's detector array is composed by 144 pixel, with a pixel size of 30" @ 270 GHz. The field-of-view is of 7.5 arcmin in diameter, with a circular shape. The mapping speed is 10 arcmin² / hr / mJy² (conservative expectation).

AzTEC will be installed at ASTE telescope during April 2007, becoming available for the scientific community during June to Mid October 2007. Further information about AzTEC can be found in the AzTEC official website. A summary of the main AzTEC features is found as follow

Number of pixels	144
Center frequency	270 GHz (1.1 mm)
FWHM	30"
Field-of-view	7.5 arcmin diameter
Mapping speed	10 arcmin² /hr / mJy²

A Excell based integration time calculator for AzTEC can be found at AzTEC-MapSpeed.xls

CATS345 GHz Receiver:

The CATS345 GHz band receiver is a two-single band SIS receiver remotely tunable in the LO frequency range of 324-372 GHz. The expected system noise temperature is comparable to the old SC345 receiver (DSB), with Tsys below 200 K under good conditions (220 GHz opacity is 0.02-0.03). Also, CATS345 will be able to separate the two sidebands with a rejection gain of 13 dB (1/20) or so.

Typical system noise temperatures. Typical system noise temperatures (in DSB), measured under an average atmospheric condition (200 GHz, zenith opacity is 0.06 or PWV is about 1 mm), are shown as a function of LO frequency. Atmospheric transmission (when PWV = 1 mm) is also noted. Noted that the IF frequency is 6 GHz.

The measured main beam efficiencies at 350 GHz are in the range from 0.6 to 0.8 during winter night time. Note that currently day time observations are not recommende due to severe degredation of the main beam efficiency.

Observers are strongly recommended to determine the efficiency by themselves during each observing run (at leaset once per a night) using planets and/or known-intensity standard line sources.

Backends

A digital spectrometer of four XF auto-correlator is current available to the community. The 4 units can be used in the low resolution mode (512 MHz bandwidth) and high resolution mode (128 MHz bandwidth). Each unit has 1024 channels. With the current setting multi-lines observations are possible. A wide bandwidth mode is now currently available.

Instrument

Bandwidth
per unit

# of channels per unit

channel separation

# of unit available

MAC Digital Spectrometer 4-XF

128 MHz

512 Mhz

1024

125 kHz

500 kHz

WHFS Spectrometer

2 GHz

4 GHz

2048

976 kHz

1953 kHz

Some suggested multi-lines observation setups can be found as follow

Line 1	Frequency Line 1 [MHz]	Line 2	Frequency Line 2 [MHz]
CO(3-2)	345795.991	HCO+(4-3)	356734.25
CS(7-6)	342882.95	¹³CO(3-2)	330587.957
SiO(8-7)	347330.58	CH₃OH 4(1)-3(0)E	358605.80
CH₃OH 4(0)-3(1)	350687.73	CH₃OH 1(1)-1(0)	350905.119
HC¹⁸O+(4-3)	340630.7	C¹⁸O(3-2)	329330.546
H¹³CO+(4-3)	346.99854	DCO+(5-4)	360.169830

Observing Modes

AzTEC: The bolometer camera will be using only the raster scan mode, no chopping mode will be implemented. Therefore, it becomes very inefficient to make small size maps, so it is recommended make large maps, with sizes bigger than 15'x15'.

It is recommended to observe point sources.
The reduction procedure for diffuse, extended sources is not established yet. So, if you want to map extended structure, you are encouraged to join the software developing team of AzTEC to develop the software.

CATS345: Currently , ASTE is only working with spectral line observations, under position switching mode.

Currently, ASTE allows to do single-point observations, 5-9 points cross maps, and raster maps observations. On-the fly mapping is currently under testing and will be available to the community in the near future. The currently available observing modes are:

Single-point observation: the observer can specify the on - position in RA and DEC as GAL longitude and GAL latitude (both B1950 or J2000). Off-position can be specified as absolute coordinates or as an offset with respect to the on-position. Until 4 off-positions can be specified.

5-9 point cross maps: the observer specifies the center position of the map, the spacing between the points, and the position angle of the cross map. Off-position can be specified as absolute coordinates or as an offset with respect to the center position. Until 4 off-positions can be specified.

Raster map: the observer specifies the center position of the map, the size and spacing of the grid, and the position angle of the grid. The center of the grid can be specified in RA and DEC as GAL longitude and GAL latitude (both B1950 or J2000). Off-position can be specified as absolute coordinates or as offset with respect to the center position. Until 4 off-positions can be specified.

On-the-fly map: This observing technique efficiently generate
images over large fields with respect to the resolution of the detector. The efficiency is gained by reducing the overhead as the telescope is no longer required to start and stop to discrete points to accumulate integration time. In this mode, the observer specifies the coordinate of the star point of a map, the direction of the scan, lenght of main scan path, spacing between scan, position angle, the acceleration time, scan time of main scan path, transit time, and return time.

Observing tables are prepared in ASTE control room in San Pedro.

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Send comments to Juan Cortés: jcortes@das.uchile.cl