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1MHz * 2048 Channels

Observing Options: 1 * 2048 Channels, 2 * 1024 Channel, 4 * 512 Channels.

250 KHz * 512 Channels

Observing options: 2 * 256, 4 * 128 

Status report can be viewed here.


Acousto-Optical-Spectrometers: (AOS's)


The MPIfR installed two 1 GHz bandwidth AOS's for spectral line work in early 1997. The mean resolutions are 934 kHz for AOSA and 913 kHz for AOSB. The AOS's use 2048 element linear CCD's and thus over sample the spectra by about a factor 2. Therefore, the channel widths in CLASS spectra are about a half of the AOS's resolution.

The latest maintenance measurements of 22 March 05 are shown in the following two graphs (click on images to get a larger version). The results are similar to the measurements of 1998. The AOSB resolution was slightly better in 1998 (915 vs 996 MHz). (Since 1998, the light pens had to be replaced in all three AOS's and then their optics were adjusted to accommodate the new pens.)

AOSA comb results

PostScript version  PDF Version


AOSB comb results

PostScript version  PDF Version


250 MHz AOS: (AOSC)

The MPIfR 250 MHz bandwidth AOS was installed in the fall of 1997. At that time it had a mean resolution of 385 kHz. The same 2048 channel linear CCD is used to detect the spectra which are therefore over sampled by about a factor 3. Thus, the CLASS channel width for spectra taken with this AOS is about a third of the resolution.

The following graph shows the results of the 22 March 05 maintenance (click on image to get a larger version). Its linearity is comparable to that of 1997 and its resolution is slightly better (370 kHz).

AOSC comb results

PostScript version  PDF Version


Long integration (~4 hours) data on sky using the 230 GHz receiver with the wobbler are available for AOSB and AOSC. Both AOS's do not show any significant deviation from the expected 1/sqrt(time) law.

AOSB long integration results (GIF)
AOSB long integration results

(PostScript version)

AOSC long integration results (GIF)
AOSC long integration results

(PostScript version)

Chirp Transform Spectrometers: (CTS)

These are spectrometers with a bandwidth of about 215 MHz. There were originally three of these with a resolution of 60-80 kHz. They had about 30%more noise than an ideal spectrometer due to defects in their Surface Acoustic Wave filters.

In August 2004, a 2nd prototype of a CTS based on digital technology was installed. This one only has <10% more noise compared to an ideal spectrometer and it has even higher resolution (about 40 kHz). It will eventually be replaced by three digital CTS's. The new ones will be more carefully adjusted and perhaps will have even less noise than the prototypes.

The CTS backend cannot be reliably used for OTF mapping.

The 250 KHz filterbanks and AOSC and the CTS use the same IF processor. Due to the different input IF frequencies required for these instruments, the CTS and AOSC can only be used if the 250 KHz filters are turned off.

CTS-A Comb Results

Postscript Version   PDF Version

Below are four spectra showing a comparison of the newest CTS with the AOS's.

Sample 12CO(2-1) spectrum of NGC 7027 taken with the 1.3mm JT receiver and the wide band AOS, AOS-A. This was a beam switched observation with a 4 minute integration time. Unlike the old receivers, the JT receivers have a
bandwidth larger than the bandwidth of the AOS-A and AOS-B, so all 2048 channels are shown in this plot.
Sample spectrum of W75N taken with the 1.3mm JT receiver and the other wide band AOS, AOS-B. This was a position switch observation with a 44 minute integration time. The receiver was tuned double sideband with the 12CO(2-1) line in the upper sideband. The line at about -180 km/sec is actually the 13CO(2-1) line in the lower sideband. (There is a 13CO line is in the AOS-A spectrum too, but there only barely enough integration in that one to detect it.)
Same as the AOS-B spectrum, but taken with the narrower band AOS-C.
Same as the AOS-B spectrum, but taken with the high resolution Chirp Transform Spectrometer. This spectrometer has a bandwidth of 215 MHz and a resolution of 40 kHz (0.06 km/sec at the 12CO(2-1) line).

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For problems or questions regarding this web contact [tfolkers{at}email{dot}arizona{dot}edu].
Last updated: 11/08/11.