Realm of the Nebulae - M57 vs M31
EL Obs 4
SPU-21 Fall 2014
In this lab, we will measure two very different "nebulae": the Planetary Nebula, M57 (The Ring Nebula), and the Andromeda Nebula (as it was originally called), M31, which is of course our closest spiral galaxy. We'll observe M57 first since it is setting; then M31.
Fro M57, our goals for this Observation Report are to measure the B and V magnitudes of two parts of the Planetary Nebula (PN): its central hot white dwarf, which is the core of the star that ejected the PN, and the "ring" itself. Your Analysis of these observations will come in the Final Evelab Report in which you will use your measured B-V colors to estimate the blackbody temperature and luminosity of the WD and the Ring, and for the Ring to then deduce what type of radiation it really must be.
For M31, we shall measure the Bulge magnitudes (again in B and V) over a range of aperture sizes and in your later Analysis (Final Evelab Report) deduce from this the distribution of mass in the Bulge both within each aperture (a "cumulative" measurement) and in the annuli between each aperture (a "differential" measurement). The B-V colors in each annulus will allow you to estimate the approximate type of stars contributing to its light.
M57 Observations:
For this we can observe both M57 and our standard star in the same field.
- Slew to the position of M57 using the Sky program or enter coordinates: RA, DEC = 18:53:35.079, +33:01:45.03
- The standar star Tyc 264-509-1 is at RA, DEC = 18:53:11.536, +33:03:12.73, with magnitudes B = 12.31, V = 11.09
Then for your exposures on M57 and your standard, take 2 exposures in each of the following filters for the times given: B (45 sec), V (30 sec) and R (30 sec). You will only use B and V for the analysis bur you can combine those images with the R band images for an RGB color image of M57 for your own pleasure (or to add as a nice figure in your Final Evelab Report). Enter in observations table (pdf or docx).
M31 Observations:
- We must begin by observing our standard star for calibration.
- We will choose a bright star (V=4.52, B=4.39) that is only ~1 degree NW of M31 at J2000 coords: RA, DEC = 00:49:48.847, +41:04:44.08
- This star is ν-Andromeda, a B star with an F star companion (spectroscopic binary and not variable).
- Slew to this object and take 2 exposures of ~3seconds in each of the B, V, R filters. Enter in observations table (pdf or docx). In the images, also note the sky background counts in each filter (well removed from the star).
- NOTE: FALL 2014 we used the standard Tycho 3266-180-1 at RA, DEC = 00:49:46.688, +47:06:07.93 with magnitudes B = 12.17, V = 10.53 - take 2 exposures of ~30-45 sec in each of the B, V and R filters.
- Now let's take our Andromeda images!
- Use TheSky program to slew to M31.
- Using the eyepiece, center on the bright core of the bulge of the galaxy. The light you are seeing left the galaxy 2 million years ago!
- Now take a test exposure of 10 seconds in B, V, and R to ensure that the center pixels are < 30,000 counts/pixel and that out to 1 arcmin radius from the center there are still > 2,000 counts/pixel above the sky background (use the sky background, scaled to exp. time used for Andromeda).
- Once you have the appropriate exposure times, take 2 exposures in each filter and again enter the observations in your observations table.
- If you have extra time, move the telescope so you are slightly off-center from the bulge and re-take you B, V, and R image. You can then make a really nice "true" color image (to the right) of the central disk region of Andromeda - not just the Bulge!
Reductions:
- For each field we must first reduce the data manually for the calibration star you used to derive the "const" in Equation 1 below,
- Apparent mag (B or V) = -2.5log[S/T] + Bconst or Vconst
where S is the total star counts with the sky background already subtracted, as done for you by the TFs in the datafiles you received, and T is hte exposure time in sec. Use the B and V magnitudes given above for the standard stars for each field and then solve for the const in each filter, B and V. These will be differernt for the M57 and M31 fields.
- Then use the Bconst and Vconst values and the counts you measured for each aperture and eacg exopsure (you should have 2 exposures in each B and V) to then solve for the B and V magnitudes in each aperture, or circular region in your B and V image.
- For M57, you derive B, V magnitudes for 3 apertures of radius 4, 12 and either 17 (reduction 1) or 20 (reduction 2) pixels. For the 4 pixel radius, your B and V magnitudes are for the image inside that radius, whereas for the 12 and 17 0r 20 pixel radius apertures, you are deriving a B and V magnitude for the image between those two radii, the "Ring".
- For M31, you derive B, V magnitudes for 4 apertures of radius 16,32,48, and 96 pixels. Note that the "96" pixel radius came from your first binning the image in 2x2 pixel bins and then taking 24 of those bins (2x24=48), and your "96" pixel radius came from similarly binning your image in 3x3 pixel bins and taking 32 of those (3x32=96). You should produce 2 values of B and V magnitudes for EACH aperture, since you took 2 exposures in each of B and V filters.
- Enter these values in the reductions table (pdf or docx), one for each object (M57 and M31). Give your derived values for Bconst and Vconst in the first row of this Table. Each subsequent row of this table gives the exposure time and magnitude values for each exposure in B (exp. 1, 2, and then average) and then the same values for V, all for a given Aperture radius. So each row represents data results for a given Aperture.
- In your Observation Report, you shoudl comment on your reduced data; do the magnitudes in each filter and colors (B-V) look "reasonable"? That is, if you find a value for B-V = -3 or +5 you can be sure something went wrong. For this EL4-ObsReport, there is no need for interpretive analysis (yet) for either M57 or M31. Once again, this will be done in your Final Evelab Report.