News for VLA Observers
November 27, 2012: OPT 1.14 released
We present a summary of new capabilities
August 16, 2012: New Scheduling Block Length
Scheduling blocks must be a multiple of 15 minutes in total duration. For example: 00:30:00, 00:45:00, 01:15:00, 01:45:00, 02:00:00 etc.
July 31, 2012: New Scan Length Limit
The new scan length limit is 10min for all scans, independent of the hardware setup or the integration time. CASA can now handle these longer scans, therefore the 90s x integration time rule has been lifted.
April 24, 2012: Spectral-line polarization Science (including Zeeman Effect)
EVLA observations of strong lines with high spectral resolution were subject to an unanticipated spectral response ("spectral splatter") described in detail in EVLA memoranda 148, 157, and 160 (Sault 2010, 2011, 2012). This significantly complicates the analysis of observations of strong lines with high spectral resolution. Polarization studies, which rely on the detection of subtle differences between strong signals, are particularly vulnerable, with the Zeeman effect being an unfortunate example. Data taken with the WIDAR correlator before August 2011 are the most severely affected and should not be used for any spectral line polarization studies, linear or circular. Data taken between August 2011 and April 2012 may be more reliable but should be treated with considerable caution. We believe that data taken after April 2012 are free from these effects, though as with all correlators very subtle, low-level artifacts may persist for particularly challenging observations -- see the aforementioned memoranda for details.
February 21, 2012: Scan Intent Change in Measurement Set
This change is primarily of interest to those who are using scan intents during post-processing, in particular those who are running a pipeline. Certain scan intent definitions have been changed, which has the potential to affect operation of your pipeline. If this applies to you please contact the helpdesk for further details.
January 23, 2012: Missing Weather Station Data
From 23 December 2011, 19:12 UT to 12 January 2012, 23:37 UT the weather station located on the EVLA site failed to produce reliable data. This has consequences for the zenith opacities systems such as CASA and AIPS derive. During the time interval above these zenith opacities should be based on the seasonal model only instead of a weighted average of actual weather data and the seasonal model. This can be accomplished as follows:
AIPS - delete version 1 of the CL table, and create a new version 1 by running the task INDXR with BPARM(1)=0 and BPARM(10)=-1.
CASA - derive the zenith opacity by running the contributed task plotWX with seasonal_weight=1.0 (more information on plotWX).
January 4, 2012: Correlator Back-End problem January 2-3
From 08:22 UT January 2, 2012 to 13:50 UT January 3, 2012 a temporary CBE problem can cause data to be missing. Antennas are blanked out in pairs, e.g. antenna 1 and 2, 5 and 6, 9 and 10, etc. Observers during this time are strongly advised to check their data extra carefully for missing data or amplitudes identical zero.
December 12, 2011: Data averaging problem on the EVLA
Between the dates of September 20 23:00 UT and December 3 00:00 UT a bug in the EVLA's Correlator Back End (CBE) computer resulted in only 1 second's worth of data being saved per integration, no matter what averaging time was selected in the observing script. We regret the impact this will have on the sensitivity that will be achieved for many projects observed in the current D configuration. We are making every attempt to repeat the most severely affected, priority A, scheduling blocks, and will be extending the D configuration by 1 week to accommodate this make-up time. A revised configuration schedule is available here. Please report any problems with your data through the NRAO Helpdesk.
June 30, 2011: Call for proposals for semester 2012A
The June 30, 2011 NRAO eNews contains the Call for Proposals for the GBT, EVLA, and VLBA/HSA/VLBI, along with general news for proposers.
April 20, 2011: 74-MHz dipole installation
The 74-MHz dipoles will be installed on April 26, in preparation for a low frequency campaign that will span the end of B-configuration, BnA-configuration, and the beginning of the A-configuration. The 74-MHz dipoles impact the performance of the L-band, and probably also the S-band, systems on the EVLA. In particular, the sensitivity at the field center will be reduced by approximately 8% at L-band, and probably half of this at S-band. Furthermore, the dipoles introduce elevation-dependent D-terms at L-band, preventing polarimetric observations. L-band polarimetry will not be scheduled after April 25.
April 20, 2011: B-Configuration not to be extended
Although a large number of approved projects remain in the dynamic queue for B-configuration at this time the configuration will not be extended, and the move to the BnA hybrid will proceed as originally scheduled on May 9. Observers can manage which of their scheduling blocks are available for scheduling by submitting only their highest priority SBs for a given LST.
January 7, 2011: Call for proposals for semester 2011B
The January 7, 2011 NRAO eNews contains the Call for Proposals for the GBT, EVLA, and VLBA/HSA/VLBI, along with general news for proposers.
December 9, 2010: EVLA C-configuration extended by 2 weeks
The extension of D-configuration earlier this year has resulted in the high-pressure LST range 12 to 18 hours coinciding with day time EVLA commissioning activities in the C-configuration. In order to complete some of the high priority science programs that fall in this LST range NRAO is extending the C-configuration by 2 weeks, and adjusting its commissioning and test activities for the remainder of the configuration to accommodate science. The move from C to CnB configuration is now scheduled to begin on January 18, 2011.
September 27, 2010: 4-band (74 MHz) for trimester 2011A
At the call for proposals for trimester 2011A NRAO will consider proposals for use of the 74 MHz band (4-band) on the EVLA. We expect to have 4-band dipoles installed on all antennas during the last couple of weeks of the B configuration, all of the BnA configuration, and during the first couple of weeks of the A-configuration. Recent tests indicate that a reasonable response can be obtained ranging from 62 - 78 MHz. Click here for an example.
Although we have good reasons to believe that the new system will provide improved sensitivity compared to the old system, until we have a better estimate you should continue to base your observing time request on the sensitivity of the old 4-band system.
Note that these experiments will use a much larger fractional bandwidth (15-20%) than we have used so far. We are actively working on imaging software to deal with this, but be aware of the risk that not all post-processing issues will have been resolved by the time the observations take place.
We plan for the OPT to support 4-band observing well before the new receivers become operational. For the most up-to-date information please refer to the EVLA Observational Status Summary (OSS).
Observers who during the previous round of 4-band observing were seriously affected by the aliasing problem plaguing the transition system at the time may consider reapplying for time.
September 15, 2010: Call for proposals for trimester 2011A
The September 15, 2010 NRAO eNews contains the Call for Proposals for the GBT, EVLA, and VLBA/HSA/VLBI, along with general news for proposers.
July 29, 2010: EVLA D-configuration extended until September 13, 2010
Wideband operation of the EVLA, with up to 2 GHz per polarization, was achieved at the beginning of July. Commissioning of wideband observing has been proceeding over the last few weeks. The delay in commissioning the wideband observing modes has limited the time available for the Resident Shared Risk Observing program. NRAO has therefore decided to further extend the current D-configuration until September 13, 2010. All future array configurations will remain at their originally-planned durations, but will have their start dates offset. The revised configuration dates may be found here.
June 1, 2010: EVLA D-configuration extended by 6 weeks
In order to complete observations for the Resident Shared Risk Observing program and to further test and commission the modes that will be needed to support future higher-bandwidth capabilities, NRAO has extended the current D-configuration of the EVLA for approximately seven additional weeks. All future array configurations will remain at their originally-planned durations, but will have their start dates offset.
Observers with approved projects for the D-configuration should continue to submit new scheduling blocks as required. D-configuration Rapid Response Science will continue to be supported until the move to DnC begins in July. Revised configuration dates may be found here.
To learn about current restrictions on Open Shared Risk Observing and to access the EVLA Observation Preparation Tool, please visit the OPT web page.
May 14, 2010: Call for proposals for trimester 2010C
The May 14, 2010 NRAO eNews contains the Call for Proposals for the GBT, EVLA, and VLBA/HSA/VLBI, along with general news for proposers.
