VEGAS Commissioning Memo Data Reduction Notes


This page is for shared work on the data reduction for the VEGAS commissioning memo. Eventually, the contents should transfer pretty painlessly into the memo.

Commissioning data consists of:
  • Engineering Tests (Anish)
  • Ripple Tests (Amanda)
  • Astronomical Tests (Richard, Sam, Adam)
    • RRL tests
    • Continuum Tests
    • Deep integration tests

GBIDL and python for these tests should be kept around - they will form the basis of long-term unit / regression tests.

To Do List For Astronomical Tests

  • Priority order is TP on W3, TP on 3C147, FSW on W3, long integration.
  • create a shared SDFITS file with all of the observations
  • create a GBTIDL to flag the center channel of every ifnum and plnum of every scan, before we do any other processing. Is it N/2 or N/2+1 ?
  • run getps or getfs and look at every scan, ifnum and plnum - need a procedure to run through all of these.
    • inspect every plot visually, but only print out discrepant ones
    • make a note of RFI (I have seen something that looks like that), duff scans (maybe Bank H), etc

RRL Scans

  • Get Tsys for every scan, ifnum and plnum - put in a database. Plot histograms of this. Plot against elevation.
    • do we need to do this for every integration? I hope not!
  • Get rms for every scan, ifnum, plnum. Compare to radiometer equation. Plot histograms of this.
  • create a routine to fit a baseline and Gaussian for every scan, ifnum and plnum.
  • create a database of frequency and intensity for all RRLs. Compare to established values
  • Do above for TP and SP

3C147 scans

  • Get Ta as a function of frequency for all windows, etc.
  • Plot against spectral index of 3C147. Deduce scatter in intensity measurements.

Deep Integrations

  • Plot Tsys, Trms and Tline as a function of integration time

Commissioning Memo


Observations were made using VEGAS and the X-band (8-10 GHz) receiver of a number of radio recombination lines (RRL) in W3, as well as two calibrators, 3C147 and 3C395. A source position of 02:25:44.40, +62:06:11 (J2000) and an LSRK velocity of -40.9km/s was used (Dana Balser, private communication). The majority of the observations were made over the weekend of 18 - 20th July, with observations running from noon until 10pm. Some additional observations were made later in the month, to fill in some data which had been lost due to faults. During all of the observation periods, the weather was poor, with the sky completely overcast, and occasional light rain.Observations were made with the active surface turned on, and Peak / Focus observations were made (on calibrators chosen by AutoPeakFocus) every one-two hours. A log of observations is given in Table 1. Data were "filled" using sdfits-test, version 1.20.

A "typical" position-switched spectrum is shown in Figure 1. This was made in Mode 25, and only one of 64 windows (covering the H89alpha line) is shown, Typical off-source system temperatures were ~ 30k (to be confirmed by Sam), and on-source system temperatures 85K 9to be confirmed). Typical observations were made with five minutes Off, and five minutes On, with the offset chosen so that the telescope would follow the same (az,el) trajectory in each case.

  • Scan 6 position-switched plot plot of a typical position-switched scan. No processing has been performed on the data apart from that applied by the GBTIDL "getps" command.

Observations were made in modes 3 through 29, with the exceptions of modes 14 and 19, which were not available at the time the observations were made (list ones we didn't use in 20-29. We went bacl and did 1-3, for what?) For single-subband modes, each of the eight spectrometer banks was tuned to a different line, using a scheduling block provided by Dana Balser. For eight subband mode, the 64 subbands of the eight spectrometers were tuned to 64 different lines. The relevant scheduling blocks are attached here:

BOF files

The BOF files (FPGA personalities) in use at the time of the observations were as follows:

Mode BOF file
1 h1k_ver108_1500_2014_Jul_15_0006.bof
2 h16k_ver110_2014_Apr_08_1753.bof
3 h16k_ver110_1080_2014_Jul_15_0728.bof
4 l1_ver116_1500_2014_Jul_16_0619.bof
5 l1_ver116_1500_2014_Jul_16_0619.bof
6 l1_ver116_1500_2014_Jul_16_0619.bof
7 l1_ver116_800_2014_Jul_16_0616.bof
8 l1_ver116_800_2014_Jul_16_0616.bof
9 l1_ver116_800_2014_Jul_16_0616.bof
10 l8_ver139_1500_2014_Jul_16_2223.bof
11 l8_ver139_1500_2014_Jul_16_2223.bof
12 l8_ver139_1500_2014_Jul_16_2223.bof
13 l8_ver139_1500_2014_Jul_16_2223.bof
15 l8_ver139_750_2014_Jul_16_2242.bof
16 l8_ver139_750_2014_Jul_16_2242.bof
17 l8_ver139_750_2014_Jul_16_2242.bof
18 l8_ver139_750_2014_Jul_16_2242.bof
20 l8_ver139_1500_2014_Jul_16_2223.bof
22 l8_ver139_1500_2014_Jul_16_2223.bof
24 l8_ver139_1500_2014_Jul_16_2223.bof
25 l8_ver139_1080_2014_Jul_16_2244.bof
29 l8_ver139_1080_2014_Jul_16_2244.bof

Observing Log

Scans Source Mode Switching Comments
6-7 W3 25 TP  
9-10 W3 29 TP  
11-12 W3 20 TP  
13-14 W3 24 TP  
20-21 W3 15 TP  
22-23 W3 16 TP  
24-25 W3 17 TP  
26-27 W3 18 TP  
33-34 W3 10 TP  
35-36 W3 11 TP  
37-38 W3 12 TP  
39-40 W3 13 TP  
47-48 3C147 10 TP  
49-50 3C147 11 TP  
51-52 3C147 12 TP  
53-54 3C147 13 TP  
55-56 3C147 15 TP  
57-58 3C147 16 TP  
59-60 3C147 17 TP  
61-62 3C147 18 TP  
68-69 3C147 20 TP  
70-71 3C147 24 TP  
72-73 3C147 25 TP  
74-75 3C147 29 TP  
91 W3 10 SP  
92 W3 11 SP  
93 W3 12 SP  
94 W3 13 SP  
95 W3 14 SP  
96 W3 15 SP  
97 W3 16 SP  
98 W3 17 SP  
99 W3 18 SP  
104 W3 20 SP  
105 W3 24 SP  
106 W3 25 SP  
211-212 W3 4 TP  
213-214 W3 5 TP  
215-216 W3 6 TP  
217-218 W3 7 TP  
219-220 W3 8 TP  
221-222 W3 9 TP
234-235 3C147 1 TP IF Manager flaky - data may be no good
236-237 3C147 2 TP as above
238-239 3C147 3 TP as above
240-241 3C147 4 TP as above
242-243 3C147 5 TP as above
246-247 3C147 6 TP as above
248-249 3C147 7 TP as above
250-251 3C147 8 TP as above
252-253 3C147 9 TP as above
259-278 W3 29 TP deep integration
308-327 NCP ?? TP Deep integration, mislabelled W3
328-343 NCP ?? TP Deep integration, mislabelled W3

Columns: Scan number(s), Source Name, VEGAS Mode, Switching scheme (TP = total power with cal, SP = frequency switched with cal), Notes.

Comparison Spectrometer Data

Bania et al (private communication) have made similar observations as those described here, but with the old GBT Autocorrelation Spectrometer. The summary of their results is in the attached file:

Topic attachments
I AttachmentSorted descending Action Size Date Who Comment
W3.RRLs.datdat W3.RRLs.dat manage 5 K 2014-07-28 - 16:00 RichardPrestage Tom Bania's RRL results
scan6ps.pdfpdf scan6ps.pdf manage 44 K 2014-07-28 - 11:05 RichardPrestage Scan 6 position-switched plot
RRLlines8.sbsb manage 531 bytes 2014-07-28 - 11:36 RichardPrestage eight subband lines
RRLlines64.sbsb manage 2 K 2014-07-28 - 11:37 RichardPrestage 64 sub-bans lines
Topic revision: r7 - 2015-01-27, RichardPrestage
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