Tangential velocity
v_t (km/s) = 4.74 * pm * d
(pm in mas/yr; d in kpc)
Converting heliocentric to Galactocentric RVs
Assuming (U,V,W) = (10.0,5.2,7.2) km/s
v_gal = v_hel + 10.0*cos(l)*cos(b) + 7.2*sin(b) + (v_lsr+5.2)*(sin(l)*cos(b))
Note: v_lsr = 220 km/s (standard) to 244 km/s (Bovy et al 2009)
(Ref: Xue et al 2008)
SDSS extinction
A_u = 1.579 A_V
A_g = 1.161 A_V
A_r = 0.843 A_V
A_i = 0.639 A_V
A_z = 0.453 A_V
Reading FITS binary tables to IDL
a=mrdfits('table.fits',1,hdr)
reads the table to the structure 'a' and the table header to 'hdr'
Telescope plate scale
plate scale ("/pix) = 0.206265 * pix size (microns)/focal length (m)
Finding gain/RN
(i) take two bias and flat frames (b1, b2; f1, f2)
(ii) difference the frames (b1 - b2, f1 - f2)
gain = ( E(f1+f2) - E(b1+b2) ) / (sigma^2 (f1-f2) - sigma^2 (b1-b2))
RN = gain*sigma(b1-b2) / sqrt(2)
Cluster structure
For a King profile with c=30:
r_eff = 1.48*FWHM
Remember: Don't make a goat the watchman for a breadnut tree.