From lappel at nrao.edu Wed Mar 12 13:20:19 2008 From: lappel at nrao.edu (Lori Appel) Date: Wed, 12 Mar 2008 11:20:19 -0600 Subject: [Vlavlbausers] Special EVLA Proposal Opportunity Message-ID: <47D810D3.3020109@aoc.nrao.edu> *********************************************************************** Special EVLA Proposal Opportunity Expanded L-Band Tuning Available, 1.0-1.2 GHz March 12, 2008 *********************************************************************** Test observations below 1200 MHz have recently been carried out with the EVLA to assess the feasibility of pursuing spectral-line observations for redshifted HI 21cm or other spectral-line transitions at frequencies where the VLA has severe limitations and/or simply cannot observe. The results of observing two known HI 21cm absorbers, one at z=0.2467 (~1139 MHz) and the other at z=0.3127 (~1082 MHz) can be found at the "EVLA returns" web page, at http://www.vla.nrao.edu/astro/guides/evlareturn/Lband_expanded.shtml These test observations show that successful observations are possible with the EVLA at frequencies that are believed to be dominated by RFI due to aeronautical navigation transponders, at least at night time and in A and B configurations. We expect that daytime observations, and observations in C and D configurations, may be much more difficult. It should also be noted that for observations below 1200 MHz, only IF pair B and D can be used at this time. Furthermore, the polarization performance below 1200 MHz is severely compromised, with the polarization impurity reaching 40% at 1 GHz. Nevertheless, this new 1.0-1.2 GHz capability on the EVLA is now available for users, and NRAO will consider exploratory proposals to use it in the current configuration through the end of D configuration, 15 September 2008. Please ensure that any proposals are labeled as "Rapid Response--Exploratory Time." Details of the expected sensitivity based on the tests described above can be found at the "EVLA returns" web page, at http://www.vla.nrao.edu/astro/guides/evlareturn/ and any further information or test results will also be posted at this page. It will be assumed that all proposals submitted are suitable for dynamic scheduling unless explicitly justified in the proposal and in the "comments" field of the sessions section of the cover sheet. At present this excludes the use of subarrays, although this may change in the future. Please consult the EVLA returns web page above for the latest information. Potential users are advised that these are "shared risk" observations. We cannot guarantee success, especially for daytime observations that might be severely affected by RFI, but we will provide reasonable assistance. Users are also reminded of the aliasing of continuum emission in the bottom 0.7 MHz of baseband that affects narrow-bandwidth observing with the EVLA antennas, and should consult the EVLA returns web page for recommendations on its mitigation. Note that proposals for A configuration should be submitted as usual at the 2 June 2008 deadline. Technical questions about observing below 1200 MHz should be directed to Emmanuel Momjian (emomjian at nrao.edu) or vlahelp at nrao.edu. For information about this special call for exploratory proposals to use the new tuning capabilities please contact Claire Chandler (cchandle at nrao.edu). From analysts at nrao.edu Wed Mar 12 15:46:56 2008 From: analysts at nrao.edu (Data Analysts) Date: Wed, 12 Mar 2008 13:46:56 -0600 Subject: [Vlavlbausers] Error in AIPS task FILLM for polarimetry data Message-ID: <47D83330.1040907@aoc.nrao.edu> To: All VLA users Subject: Error in AIPS task FILLM for polarimetry data Dear colleague, We have recently discovered an error in the AIPS task FILLM whereby cross-polarization data (LR and RL) from the VLA may be scaled and weighted incorrectly, in a manner that cannot be corrected by calibration. The specific instances of when this incorrect scaling and weighting occurs are described below. The 31DEC08 (TST) version of FILLM was corrected on March 5, 2008, and is available for download via the midnight job. A patch is also available for AIPS version 31DEC07 (NEW). Please note that 31DEC06 (OLD) has not been patched, and should no longer be used to load VLA data into AIPS. More details: FILLM has been scaling cross-hand data incorrectly since the Modcomps were turned off on June 27, 2007, for data saved by the on-line system in raw correlation coefficients but loaded scaled by the nominal sensitivity (the default option). This problem occurs on those baselines for which the antenna order in the on-line system is reversed from that required by AIPS (e.g., where the on-line system provides a visibility for baseline 11-6 rather than 6-11). Once the data have been loaded into AIPS it is not possible to tell which baselines may have undergone this switch. The problem also affects data obtained in the Modcomp-era that are loaded as correlation coefficients by FILLM, where FILLM has had to "undo" the on-line nominal sensitivity scaling. Thus all solar data taken with the Modcomps, which were always converted to correlation coefficients by FILLM, have had their cross-hand data incorrectly scaled. FILLM has also been calculating the weights for the same cross-hand data incorrectly, although this has a much less serious effect on the data. The fix for this problem is to: 1) re-load data using a corrected version of FILLM in 31DEC07 or 31DEC08 2) copy all calibration and flag tables from any previous reduction to the new dataset, and check that the data were not overly flagged previously due to poor cross-hand results 3) re-do any polarization processing Parallel-hand (RR and LL) data reductions are unaffected, so most total-intensity experiments will be fine. Please contact daip at nrao.edu if you have any further questions about the quality of your data. Claire Chandler Deputy Assistant Director for Science, NM Operations