Try to finish this activity by 4pm on Monday afternoon

Useful links:
  • Using Arecibo for ALFALFA
  • Using ALFALFA for science
  • AO telescope schedule
  • A2010 observer's page
  • Observing checklist for LBW observing
  • L-band wide (LBW) observing for ALFALFA followup
  • Standard ALFALFA LBW followup observing modes
  • Instructions on reducing LBW data using IDL_LBW

    Rules of the scavenger hunts:   (1): In all cases, return attendees shall not reveal the answers to first timers until sufficient effort is expended. (2): Any bribes must be shared 50:50 with the Scavenger Hunt creators. (3): 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.

    UAT15.01 Scavenger Hunt #1:   Using Arecibo and LBW for ALFALFA followup science

    This scavenger hunt will explore some details of the L-band wide observations we are conducting during the workshop by examining some of the similar data obtained by the awesome UAT in November 2014. Be sure to familiarize yourself with the various links above in order to figure out the answers to these questions.

    1.0   During the 2015 UAT workshop, we are conducting observations under what Arecibo observing program?   What was the program designation in November 2014?

    1.1   Position Switching with LBW
    The LBW followup observations using a technique referred to as "total power position switching", also known as "ON-OFF" observing.

    a.   Why do we need an "OFF-source" observation?

    b.   How is the position of the OFF-source specified? What assumptions are involved?

    c.   Our LBW observing technique consists of five distinct steps, four of which produce separate raw datasets (which then get bundled into one file for us). One of the five steps is a telescope movement when no data are recorded. What are the other four? Write them in the proper order below.
    1. Step 1

    2. Step 2

    3. Step 3

    4. Step 4

    5. Step 5

    d.   What is the slew speed of the telescope in azimuth?

    e.   What is the slew speed of the telescope in zenith angle?

    f.   Why is the unit of flux density called a Jansky?

    g.   What is the continuum flux density of the radio source 3C 286 at 21cm? Where did you find the answer?

    h.   What is the "radiometer equation"?

    1.2   Setting up the Spectrometer
    a.   What do we mean by "heliocentric" velocity?

    b.   To what velocity does a frequency of 1400 MHz correspond for the 21 cm HI line?

    c.   The 2015 correlator setup we adopt produces eights separate spectra each second. What do these eight spectra correspond to and in what ways are they the same/different?

    d.   How can you determine the separation, in frequency, between channels for a given spectrum? How does that convert to a separation in velocity? What's the complication in the 2nd case?

    e.   With the correlator setup we are using in 2015, what is the total velocity coverage (all spectra)?

    f.   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.......)

    1.3   Intro to LBW spectra: A quicklook at some targets observed in 2014
    While we are observing, it is possible to take a quick look at the data at the end of every ON-OFF pair. (Actually, in practice, you cannot do this easily until the subsequent scan is started.). The observing team does this during the observing run so that they can enter notes in the log file. We can also look at data taken previously using the same command. Here, let's look at some of the spectra we acquired in Nov 2014 during the test of our search mode to give you a feeling for what real observations look like.

    Refer to the Observing checklist for LBW observing to find the commands associated with the routine lbwquicklook in the section titled Check the spectrum produced for each ON-OFF pair.

    a.   In this Scavenger Hunt, the spectra we use were taken in Nov 2014 under a different project name (see you answer to question 1.0). At that time, WAPP Board 3 was dead so, for most of the run, we swapped around the IF/LO settings for Boards 3 and 4. How can you figure out what was changed and when it took place? What does such a change of setup do to the display presented in this exercise as compared to what we will be seeing at the telescope during this run?

    Getting started in IDL
    Here at the UAT workshop, please follow these instructions exactly:

    In each of the following, you are given a file containing the ON-OFF pair of a particular galaxy.

    b.   Use the file /share/pserverf.sda3/wappdata/wapp.20141127.a2899.0001.fits
    c. Use the file /share/pserverf.sda3/wappdata/wapp.20141127.a2899.0021.fits
    d.   Hypothetically, ALFALFA team observers take careful notes on each observing run, allowing us to find the data afterwards. You should be able to find everything you need via the A2010 observer's page.

    1.4   Reducing an LBW detection
    Now let's work through the procedure to fully reduce one of the spectra of a galaxy detected in HI by the awesome UAT in November 2014 to the point where we can extract the numbers we need to do science . For this part of the exercise, we will use data taken with the interim correlator, so you need to review that setup. Look at the section on LBW observing modes.

    a.   Assess your approach to the data reduction:
    Study the documentation supplied as the LBW Data Reduction Instructions. As before, some commands may be slightly different because of the special circumstances of the workshop (i.e. the account we are using, the data we are examining). Be sure you work in the right place.

    For starters, you need to exit IDL at this point and restart it using the routines that work on "corfiles" not "wappfiles". Start IDL again, but use @corinit rather than @wasinit. The interim correlator spectral data files are found in /share/olcor and you can figure out what file to grab by looking in the observing log (as always).

    b.   Fitting a baseline and measuring the RMS
    Because of the ON-OFF technique, there is often some residual difference across the bandpass that we want to subtract off. This is called the spectral baseline, and we want to remove it.

    c.   Measuring the HI line parameters
    Remind yourself what the shape of the profile looks like (single or double peaked) and choose the appropriate branch of the data reduction scheme as you proceed with lbwmeasure.

    d.   Save your work and make a plot.
    Once you are happy that you have done a good job on reducing the source, you want to save the information into the IDL structure and then write the file to disk so that it can be read in again.

    e.   Repeat the baselining, measuring and saving steps on the other spectrum (high res or low res; i.e., the one you did not select in above). How do the measurement results differ? Which do you believe is more robust? Did you make the right decision before?

    1.5   Dealing with non-detections
    Not all of the sources we look at in the LBW observations will be confirmed. When the source is not confirmed, we want to recordthe RMS noise in the basedlined spectrum so that we can derive an upper limit on the HI line flux density. We can do that following the steps above.

    a.   Use the file /share/olcor/corfile.25nov14.a2899.24 to baseline and then measure the RMS of the high resolution spectrum. Save you result.

    b.   Suppose we want to know the upper limit of the HI mass of this source. How would you go about making an estimate of that upper limit? What assumptions do you need to make?

    1.6   Mysteries, discoveries and bad data
    If everything were predictable, science would be boring! Explore the selection of spectra below using the tools you have at hand to interpret what you see. In each case, we give you the filename containing the target to explore. Since these are data taken with a project back in 2012, the files are in a different location not /share/oldcor/. Sometimes the /proj directory is not mounted on a machine; you might have to hunt around for one that has it mounted.

    a.   Use the file /proj/a2669/corfile.26mar12.a2669.11
    What is going on here?

    b.   Use the file /proj/a2669/corfile.23mar12.a2669.7
    What is going on here?

    c.   Use the file /proj/a2669/corfile.23mar12.a2669.5
    What is going on here?

    1.7   Movie and Arecibo trivia   (Some of us think this is important too!)

    a.   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?"

    b.   In a famous movie, where was Roger Thornhill when he said " I don't like the way Teddy Roosevelt is looking at me"?

    c.   What is odd about the rotation of Venus, and how and when was that determined?

    d.   In the movie "Some Like It Hot", who (what actor) utters the famous closing words "Well, nobody's perfect."?

    e.   What is the temperature at which paper burns, according to the famous futuristic 1967 film starring Julie Christie and Oskar Werner?

    This page created by and for the members of the ALFALFA Survey Undergraduate team

    Last modified: Wed Jan 7 18:35:10 EST 2015 by martha