Examination of autocorrelation data in search of the attenuator setting problem in early R8.1 datasets
*
Steve Scott's description of ALMA correlator normalization
The shift log report for
January 13/14, 2012 indicates that the BR1202 track was run in R8_0_3_30_FINAL. In principle, it should not show the problem. Here is an extract from the log:
UT 07:09 steDailySetup -- ALMA-8_0_3_30-FINAL
UT 13:22 SCIVER CII BR1202-0725 B7 v1.0 (Version 1.0)
The shift log report for
January 15/16, 2012 indicates that the next BR1202 track was run in R8_1_0_B. In principle, it should show the problem. Here is an extract from the log:
23:56 almaop steDailySetup -- ALMA-8_1_0-B-JAV-2012-01-11-03-00-00
06:55 SCIVER CII BR1202-0725 B7 v1.1 (Version 1.0)
At first look, both observations appear to have the problem. Here are plots of autocorrelation amplitude vs. elevation for Jan 14 and Jan 16. Orange=BR1202, black=3C279, red=Titan:
April 2011 (ALMA-8_0_0_14) |
January 14, 2012 (ALMA-8_0_3_30) |
January 16, 2012 (ALMA-8_1_0) |
|
|
|
But we need to be careful. On January 14, the PWV increased by 80% from the beginning to the end of the track, while on January 16, the PWV was more constant. So the apparent discrepancy in amplitude on the sky vs. elevation may be explained by this temporal variation.
April 2011 (R8.0.0_14) |
January 14, 2012 (R8.0.3_30) |
January 16, 2012 (R8.1.0) |
|
|
|
Conditions on January 14, 2012 |
Beginning of track |
end of track |
PWV |
1.0 mm |
1.8 mm |
Transmission at 335 GHz at elev=37 deg |
75.1% |
61.2% |
1-T |
24.9% |
38.8% |
38.8/24.9 = 1.56. But roughly half the noise comes from Trx, and is constant, so the expected variation at elev=37 from the beginning to end of the run is sqrt(1.56) = 1.25 ~ 1 dB.
--
ToddHunter - 2012-03-23
Data reduction results
WYSIWYG content - do not remove this comment, and never use this identical text in your topics
Kim reduced the BR1202-0725 (high redshif quasar) data from 14 January. This data had the Tsys measurements but some concerns were expressed about the data quality because of low elevation.
The track includes Titan (amplitude cal), 3c279 (bandpass and phase), and the source (BR1202). The source was observed from about 12:40-13:20 at elevations of 25-35 degrees. So not great but not shameful. 3c279 was higher (~40-50 degrees elevation) and Titan was at ~65 degrees.
The source is clearly detected in both line (redshifted CII) and continuum and resolved into two distinct components, representing a big jump over the SMA data being verified. The source is strong enough for a selfcal, which I added to Kim's scripts.
JIRA: jira.alma.cl/browse/CSV-871
RMS and Flux (flux measured integrating the clean box):
Continuum Image
----------------------------
RMS in
... dirty map [ 0.78966637] mJy
... clean map [ 0.640193] mJy
... selfcal map [ 0.26757087] mJy
Flux in
... dirty map [ 6.55385935] mJy
... clean map [ 15.63448283] mJy
... selfcal map [ 23.22749576] mJy
----------------------------
Line Image
----------------------------
RMS in
... dirty map [ 3.45111964] mJy
... clean map [ 3.34070111] mJy
... selfcal map [ 3.31065012] mJy
Flux in
... dirty map [ 733.32013401] mJy*channel
... clean map [ 840.4469747] mJy*channel
... selfcal map [ 1446.20931582] mJy*channel
--
AdamLeroy - 2012-03-21