Astronomical Observations and Technology: Homework 1

This homework must be submitted in hardcopy before class on Thursday, Sep 20. It is possible that you might not have some of the information required to solve parts of these problems. Please please please ask me for help if that is the case. Perhaps we will discuss them in class before they are due.

  1. Oh, no! The Sun spontaneously and completely turns into a giant, fluffy ball of neutrons!

    1. How many neutrino-neutron interactions will be recorded in the SAGE detector?
    2. Some of these neutrinos will interact with the nuclei within human bodies. For a typical adult human, estimate the increase in body temperature due to the interactions. (Don't worry too much about this one, everybody will soon die anyway -- the Sun has stopped shining)
  2. The star HD 13379 has spectral class A0V. Since stars of this spectral class should have an intrinsic color (B-V) = 0.00, they make good examples. Let's examine the properties of this star, and see if they make sense.

    1. What is the (RA, Dec) position of this star?
    2. Use the UCAC4 catalog to look up the apparent magnitudes of this star, in the B and V passbands: mB and mV. I suggest the Vizier interface to UCAC4, at
    3. What is the measured color (B-V) of this star?
    4. The difference between the measured (B-V) color and the intrinsic (B-V) color is written as E(B-V), and called the "color excess" or reddening of the star.
    5. Using the standard extinction law, based on this reddening, what should the V-band extinction be for this star? In other words, compute AV using (B-V).
    6. Now, let's see if that's the actual extinction in V-band. Stars of spectral class A0V should have an absolute magnitude of roughly MV = +0.80.

    7. Use the "Search" tool at the Gaia archive website (or another search engine of your choice) to look up the Gaia-based parallax of this star. What is the parallax in milli-arcseconds?
    8. Use this parallax to compute the distance D to the star in parsecs.
    9. Now that you know the apparent magnitude m and the absolute magnitude M for this star, compute the distance modulus to the star:
                  (m - M) = 5*log(D) - 5
    10. Using the apparent V-band magnitude, and the distance modulus, calculate the absolute V-band magnitude for the star.
    11. How much fainter is this than the expected absolute magnitude for an A0V star?
    12. Does this actual extinction match the expected extinction, based on the apparent color of the star?
  3. Lucky you! You are observing a galaxy with the Subaru Telescope, on top of Mauna Kea in Hawaii, on a night which is clear and dark. No clouds at all. Your target is a star-forming galaxy at redshift z = 0.10, and you are using a spectrograph to measure the oxygen [OIII] emission line at a REST wavelength of 5007 Angstroms.

    1. What is the OBSERVED wavelength of this emission line in your spectrum? (Not sure how to figure this out? Please ask)
    2. At midnight, this galaxy is DIRECTLY overhead. Awesome!

    3. What is the declination of this galaxy?
    4. You take a 1-minute exposure, and measure the bright emission line to have 3000 counts. That's a nice, high signal.

      Two hours later, you decide to go back to the galaxy and take another 1-minute exposure with exactly the same instrument setup.

    5. How many counts will you measure in this spectrum?