ASTR 306 - HW #1

Note: Many times problem will have information missing. This is intentional, and meant to get you in the habit of using online sources to find the data you need. You must cite your sources, and the data must come from professional scientific sources (journal articles, observatory websites, data archives, NED, etc), not Wikipedia or amateur astronomy sources (ie SEDS and the like).

1. Star A has coordinates (alpha,dec) = (45.58o, +21.5o). Star B has coordinates (88.2o, +19.6o) From Cleveland, what the altitude (in degrees) of Star A when it transits? About how long after Star A transits will Star B transit? What time of the year is the best for observing Star A? Do this problem without using online calculators.

For the rest of the problems, it's okay to use online calculators when necessary.

2. When I observe, to minimize problems with the atmosphere, I won't observe my objects at airmasses greater than 1.5. How low in altitude is this? I will admit, though, having been desperate enough to chase something down to 2 airmasses. How low (in altitude) is that?

3. Track down and report values for extinction coefficients for KPNO broadband imaging. Make a plot of how much a star is extincted (in V magnitudes) as you go from sec(z)=1-3. Make another plot showing how much its B-V color is changed by atmospheric extinction over this same range of airmass.

4. We want to observe the galaxy pair NGC 4038/4039 using the 4m telescope at Kitt Peak (KPNO). When is the best time of the year to observe it, and at that time how long is it above 1.5 airmasses? How does your answer change if we used the 4m telescope at Cerro Tololo instead?

5. What are the J2000 coordinates of the galaxies M81 and M82? What time of the year are they best visible? How far apart are these two galaxies on the sky? At their distance, what does this separation translate to in terms of a physical (projected) separation?

6. What is the Crab Nebula's B1950 coordinate? Its J2000 coordinate? Its coordinate today? You're observing this fall using the KPNO 4m mosaic imager. If you mistakenly pointed your telescope at the Crab tonight using its B1950 coordinate, how far off would your pointing be? Would you see it in your image?

7. I am using the KPNO 4m to do a spectroscopic survey of Ap stars. If each observation takes an hour, and I don't want to observe below 1.5 airmasses, what is the declination limit of my sample? Think about both the northern and southern declination limits.

8. Data analysis check: Here is a simple dataset of standard star photometry. It has several observations of one star (of known apparent magnitude mV=12.40), taken at different airmasses (column1=airmass, column2=instrumental magnitude). Read and plot the data, and do a linear fit to work out the airmass term and photometric zeropoint (i.e, do a fit to the relationship truemag = instmag - K*secz + zp, and give the values of K and zp). Show a plot of the data, with your fit overplotted.

ASTR 406 extras:

11. We will be observing the galaxy M101 this spring from Kitt Peak. We need to be observing it at airmass<1.5 and with the Moon down, and we want to be able to observe at least 4 hours per night. In March, April, and May, what are the range of usable dates?