The answers to the Hunt#0 questions:

1. What is the beginning and ending RA of the drift sequence we took?
   According to Sabrina's excellent and helpful log, we quickly find that the first drift started at 13h31m15s and the last one ended at 15h02m.

2. What are the declinations of the drifts of each individual beam?
   
   • Our observations covered the drift assignment designated "22p1"? What does that tell you about the declination?
     From the ALFALFA master list, we find that drift22p1 places beam 0 at Dec(J2000) = +05d13m54s

   • To what angle do we rotate the array when we conduct ALFALFA observations?
     19 degrees

   • Why do we do that?
     We desire to orient the array so that the different beams trace drifts that are equally spaced in declination. For drifts conducted with the azimuth arm on the meridian (0 degrees or 180 degrees), an array rotation of 19 degrees produces such a layout. Note that ALFA has 6-fold symmetry, so that there are several possible configurations yielding similar spacings.

   • Now figure out the declinations of all 7 beam tracks and list them in order of increasing declination, indicating which beam is which.
     The ALFALFA precursor team A1946 memo on ALFA beam rotation indicates the layout of the beams on the sky for a source south of the Arecibo zenith when the array is rotated by 19 degrees. Since we know the declination tracked by Beam 0 and that the beam separation for the adopted configuration at transit is 2.1 arcmin, we can calculate the answers assuming we've got the beam spacing correctly:
     Beam 4     +05d 07m 36s
     Beam 3     +05d 09m 42s
     Beam 5     +05d 11m 48s
     Beam 0     +05d 13m 54s
     Beam 2     +05d 16m 00s
     Beam 6     +05d 18m 06s
     Beam 1     +05d 20m 12s
     Since she was working on the data, Adrienne checked the answer to this by looking into the IDL dred structures themselves. The parameter dred[0,0,*].decdeg shows the declinations in decimal format; these are based on a more precise model of ALFA and hence should be more accurate than the ssumption above (but note the difference is insignificant given the size of an ALFA beam!):
     Beam 4     +05d 07m 37s
     Beam 3     +05d 09m 44s
     Beam 5     +05d 11m 51s
     Beam 0     +05d 13m 55s
     Beam 2     +05d 16m 01s
     Beam 6     +05d 18m 07s
     Beam 1     +05d 20m 12s

3. Which data file contains the best drift covering NGC 5363, and which beam track should show the maximum signal from that galaxy?
   • First we check NED or some other database and record the coordinates of NGC 5363:
     RA(J2000) = 13h56m07.2s, Dec(J2000)= +05d15m17s. Therefore we predict that the center of the galaxy will cross about halfway between beams 0 and 2.
     Note that although NGC 5363 will track slightly closer to Beam 2, the sensitivity of Beam 0 is 30% higher.

   • We check Sabrina's log file (and we express our eternal gratitude for her excellent log keeping) and note that there are 9 drifts of 600 seconds each (with a few seconds lost in between for the cal firing and dead time). We see that the 3rd drift starts at about RA: ~13h51m, and because drifts are 10 minutes long, goes until about ~14h01m. So the highest signal-to-noise signal expected from NGC 5363 should occur in Beam 0 around the middle of the third drift.
     Adrienne checked the data files themselves and noted that the 3rd drift starts at RA: 13h51m 29s, and because drifts are 10 minutes long, goes until 14h01m29s.

4. Which is the bad beam? Do you remember what was wrong with it?
   Beam 1, Pol 1 is taking data, but it is highly attenuated (fancy radio science/electronics word for reduced). This is an indication that a low noise amplifier (LNA) might be having a problem. Currently Arecibo engineers are consulting with the CSIRO engineers who built ALFA, but more analysis is needed on the system. The first step will be to "warm" ALFA up, and then pump it back down to a cold temperature. Radio receivers are cyrogenically cooled to reduced the noise level. If the problem persists, ALFA will have to come down out of the Gregorian dome for repair.

   Check out the block diagram here: Link

   For extra credit, find the LNAs and their performance parameters. Take a look at "Radio Astronomy, 2nd ed." by Kraus to read further on radio receivers. Check with Brian for updates...

5. There is a HI emission source at 14h39m11s seen in beams 1 and 6 (at least). What is it?
   The source in beams 6 and 1 at 14h39m11s is NGC 5701 (UGC 09436), a nearly face-on spiral.
   Adrienne points out that Fouqué (1984) found that its HI line flux drops to 7.3% of the peak at 8 arcmin from the center. In our data, HI is visible (by eye so far...) in the Beam 6 drift from RA = 14h38m32.7s to 14h39m56s. This corresponds to roughly 20 arcmin on the sky. The optical extent of the galaxy is 4.3 arcmin by 4.1 arcmin, which is nearly a fifth of the size of the HI extent. We'll look a bit more at this in the next "Scavenger Hunt" (coming soon)...

6. What questions do you have for the rest of us?