[Vlavlbausers] Special EVLA Proposal Opportunity

[Lori Appel]

***********************************************************************
                   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).