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The NGC 2903 ALFA Survey

Notes on the first observing run: Nov 28-Dec 6, 2004


Observers:

Riccardo Giovanelli, Martha Haynes, Mary Putman, Barbara Catinella and Emmanuel Momjian

The ALFA Fixed Azimuth Drift Mode

A1963 uses an extension of the A1946 fixed azmith drift mode. See the A1946 memo which explains this mode in some detail.

Basic setup: SPECTRAL LINE OBSERVING

Setup SettingComment
Center Freq 1417 MHz  
LO tracking None (Topocentric) Best for rfi identification; unfortunately Doppler correction, although computed, not recorded in FITS file.
Bandwidth 12.5 MHz  
Sampling 9 level auto Best for sensitivity and rfi mitigation
# channels 2048/pol (9 level reduces total # chans by half)
Drift length 480 seconds The drift then lasts 8 minutes, and is set to begin when Beam 0 crosses RA(NGC2903) - 4 min. The CAL time is additional.
Cal mode loopend or loopstart All except Dec03 done in loop end. LIVEDATA requires loop start which Mary used on 12/03. However, then the actual drift start/stop times are not fixed, and this complicates true position checking vs. header positions (needed for continuum tests). Concerns raised about possible firing of cal on top of continuum source if fired at fixed point on sky throughout night. Mikael will add option for loopstart+loopend before run 2.
Note that it takes 7 or 8 seconds beyond the end of the 480 sec drift to complete the 1 sec CalON plus 1 sec CalOFF. If we decide to select loopstart+loopend, that may require an additional overhead of 5-8 secs.
CIMA files FixedAzdrift Sources /home/lerner/fixedAZ2.tcl (executive) and /home/lerner/fixedAZ2_widget.tcl (gui)
  "Saved state" a1963_hiline.gui

Basic setup: CONTINUUM BEAM MAP OBSERVING

Setup SettingComment
Center Freq 1405 MHz  
LO tracking None (Topocentric) Best for rfi identification; unfortunately Doppler correction, although computed, not recorded in FITS file.
Bandwidth 50 MHz  
Sampling 9 level auto Best for sensitivity and rfi mitigation
# channels 2048/pol (9 level reduces total # chans by half)
Drift length 240 seconds The drift then lasts 4 minutes, and is set to begin when Beam 0 crosses RA(calibrator) - 2 min. The CAL time is additional.
Cal mode loopend Better idea for position checks. See note above.
CIMA files FixedAzdrift Sources /home/lerner/fixedAZ2.tcl (executive) and /home/lerner/fixedAZ2_widget.tcl (gui)
  "Saved state" a1963_beammaps.gui

This page created for the NGC2903 group by Martha Haynes and maintained by Barbara Catinella

Last modified: Mon Dec 6 14:47:46 AST 2004 by mph