A2010 observer's page Rules of the scavenger hunts:
1. Some questions are labeled (F: first timer) and (R: returnee).
First time attendees should focus on the "F" questions; returnees on the "R" ones.
Everyone should answer the questions without designations.
In all cases,
return attendees shall not
reveal the answers to first timers until sufficient effort is
expended. (And, any bribes must be shared 50:50 will the Scavenger Hunt creators.)
2. You may consult any
source anywhere but please be sure to indicate where you got your information.
And watch out
for bad websites! Actually, if you find any mis-information, make a note
of it for the blog.
UAT13.01 Scavenger Hunt #1:
Using Arecibo and LBW for ALFALFA science
This scavenger hunt will explore some details of how we use Arecibo, ALFA and L-band wide and how we use them together to
undertake ALFALFA followup observations.
1.0 (R) Which of the ALFA
beams were "uphill" when we observed the ALFALFA drift at a Declination of
+35o46'12" (drift 147p2)?
1.1 (F) We do not normally observe in the afternoon. Why not?
1.2 Why are we using L-band wide (LBW) instead of ALFA tonight?
1.3 (F) What does J2000 refer to?
1.4 (R) What is the current velocity of the Earth around the Sun in the
direction the telescope is pointed right now ? Be sure to record the exact time/date when you provide this answer.
(Hint: Observers: we're sure you've seen that somewhere.......)
1.5 (R) At the current moment are the
ALFA amps on or off? Be sure to record the exact time/date when you provide this answer.
1.6 What is the LST time at 3:45 pm AST today
(January 14, 2013)?
1.7 (R) What is the declination of the
A2010 observation that was observed on March 21, 2010? Who conducted those observations?
1.8 (F) In what 1984 movie did the
unsympathetic government agent say:
"Do you seriously expect me to tell the President than an alien has landed, assumed the
identity of a dead housepainter from Madison Wisconsin and is presently out tooling around
the countryside in a hopped up orange and black 1977 Mustang?" 1.9 (R) In a famous movie,
where was Roger Thornhill when he
said "I don't like the way Teddy Roosevelt is looking at me"?
1.10
Position switching with LBW
During the UAT13 workshop, we will begin the ALFALFA followup observing program, using
a technique of total-power position switching, also known as "ON-OFF observing".
a. Why do we need an "OFF" source observation?
b. ALFALFA also uses "position switching" of a sort; how does that work?
c. What is the slew speed of the telecope in azimuth?
d. What is the slew speed of the telescope in zenith angle?
e. What observational consideration(s) led us to hold off a serious campaign of followup observations until now?
f. What famous politician once said "However beautiful the strategy, you should
occasionally look at the results.".
1.11
Setting up the spectrometer
The ALFALFA followup LBW observing setup uses the
interim correlator, not the WAPPs used for the ALFA legacy program. For the drift
scan survey, the frequency range always was set to cover from 1335 to 1435 MHz.
For the followup observations, the center frequency of the spectrum is shifted according
to the expected radial velocity of
the source. For the LBW observations, each spectrum has 2048 "channels" (or "pixels" in
frequency space, "voxels" in velocity space, or "array elements", however you want to think of them).
a. To what velocity does a frequency of 1410.0 MHz correspond for the 21 cm HI line?
b. What is the separation between channels, in km/s? Why is this a trick question?
(Hint: there are two reasons why it is a trick question!)
c. Actually, our correlator setup produces four separate spectra each second. What do the four
spectra correspond to? In what ways are they similar/different?
d. How does the spectral resolution of the 25 MHz observations compare to those obtained for the ALFALFA
legacy observations using the WAPPs?
e. What is meant by "Hanning smoothing"? "Boxcar smoothing"?
f. What is 9-level sampling, and why is it advantageous?
1.12 HI clouds
associated with the Milky Way Galaxy
a. What is the circular speed of the Sun in its orbit around the Galactic Center?
b. The Milky Way is believed to have a halo mass (including
dark matter) of ~2.5 x 1012 solar masses within 50 kpc. In that case,
what is the escape velocity of the Milky Way? Hint: be sure to state what assumptions you make!
c. Suppose we observe a gas cloud moving with a radial velocity (with respect
to the Sun) of -345 km/s. We call it a "high velocity cloud" (HVC). Why?
d. Over what range of frequencies do we expect to observe HI emission associated with the Milky Way?
e. When we look very close to the rest frequency of the HI line (1420.4058 MHz), we sometimes see
the final spectrum show both positive and negative flux. Why is that?
1.13 (F) What is odd about the rotation of Venus, and how and when was
that determined?
1.14 (F) What former Arecibo atmospheric scientist is the author
of the mystery novel "Murder at Arecibo"?
This page created by and for the members of the
ALFALFA Survey Undergraduate team
Last modified: Mon Jan 7 13:50:13 EST 2013 by martha
