Leo II stellar population selection

Bootes I was not clear in the spatial plot data after doing color-magnitude population selection, so the process is repeated here on Leo II with much better results.

Color-magnitude diagram, isochrone shifted according to NED listing for average published distance modulus for Leo II:

First all of the SDSS data is plotted spatially. The ring-like overdensity in this image is Leo II, though the hope is that the CMD population selection will clean up the data and make it even clearer.

Below is the spatial plot for the population selected initially (shown in red on first plot, distance less than or equal to 0.2 from isochrone).

The plot as a whole is much less dense, and Leo II is still easily seen. Doing a new selection (on points distance to isochrone less than or equal to 0.4) makes the picture a little clearer:

Bootes I: stellar population selection

Now using SDSS data to look at Bootes I. Different theoretical isochrone (older; 10 Gyr with Fe/H = -2), again plotted in yellow. Red points are stars within 0.2 of the isochrone, what I select as the stellar population. 

[SDSS data is ra between 209.5 and 210.5, dec between 14 and 15] 

Color-magnitude diagram:

The first of the next two plots is the SDSS data plotted spatially. The second spacial plot is only the subset of the data identified above as being in the stellar population.

All data, spatial plot:

Selected stellar population, spatial plot:

Here we do not see Bootes I distinctly, though at least some bad data has been removed (see straight line in upper-right of first graph does not appear in second).

M67 Data Plotting in IDL

Finishing up a HW problem as an introduction to IDL, color-magnitude, color-color, reddening/extinction, distance modulus, etc:

Plotted color-color diagram of M67 data (white) with theoretical isochrone (yellow). Graph is (g-r) vs (r-i), corrected for reddening caused by dust in line of sight. This fit created by varying E(B-V), allowing set equations to then change A(g), A(r), A(i) appropriately.

Overplotting stars close to isochrone in red to see quality of fit:

NED gives an E(B-V) value of 0.035. The fit above is using E(B-V) = 0.05. 

Applying this reddening correction to a color-magnitude plot ((g-r) vs (r)) gives the following graph after vertically fitting the isochrone. Once again, stars close to the isochrone are overplotted in red, as those are the stars we actually want (in M67, same age and distance):

[note: obvious gap in red near bottom due to isochrone being non-continuous, fixable by extrapolating further points along the isochrone line]

The vertical fit needed to fit the isochrone to the data after adjusting for extinction reddening is the distance modulus µ. Here µ = 9.5, close to the literature value of 9.48. Using the formula µ = 5*log10(d) – 5, the distance d is found to be ≈749.328 parsecs, or about 0.794 kpc. One published paper gives the distance to M67 as 0.843 ± ~0.120 kpc, a range the distance here falls well within.