NAME: inst2std PURPOSE: (one line) Apply photometric transformation from instrumental to standard mags. DESCRIPTION: The formula for applying transformation to a photometric measurement follows the basic formalism (including signs) from Hardie. A time dependent term has been added. The formula looks like this: m0 = m - kX - n(t-t0)X - k"CX + eC + Z where m = instrumental magnitude k = extinction coefficient, mag/airmass X = airmass n = coefficient of the 1st order expansion of extinction as a function of time t = Time of observation (in hours) t0 = Reference time for n, time dependent correction is zero at this time, usually is the middle of the observation set. k" = second order extinction coefficient C = Standard system color of the object e = color term Z = zero point m0 = Standard magnitude This routine also supports two extra terms that fill out the second order expansion. These terms are: + fX^2 + gC^2 CATEGORY: Photometry CALLING SEQUENCE: inst2std,jd,am,inst,instsig,color,colorsig, $ tran,transig,jdref,std,stdsig INPUTS: jd - Julian date of observation for each entry. am - Floating point array of the airmass of observations. inst - Instrumental magnitude instsig - Uncertainty of the instrumental magnitude color - Standard system color for object. colorsig - Uncertainty on the standard color tran - Transformation coefficients (vector) tran[0] = (k) principal extinction coefficient tran[1] = (k") second order extinction coefficient tran[2] = (e) color term tran[3] = (Z) zero-point tran[4] = (n) time-dependent extinction term if provided: tran[5] = (f) airmass squared term tran[6] = (g) color squared term transig - Uncertainty on the transformation coefficients (vector). (no uncertainty on reference time) tran and transig can either be 5-element vectors or 5xN element arrays. or either be 7-element vectors or 7xN element arrays. These two arrays must match in rank and size jdref - Time reference point for extinction must match the number of transformation sets provided OPTIONAL INPUT PARAMETERS: KEYWORD INPUT PARAMETERS: REFAM - Optional air mass reference for the transformation. The default is an airmass=0. The rules for this input are the same as REFCOLOR. Either scalar or length N from TIDX. REFCOLOR - Optional color reference for the color term transformation. This term is normally C * (B-V) or some other standard color. As written, the reference color is zero and this is the default. By providing this value you are using C * ( (B-V) - REFCOLOR ) for the term instead. This can either be a scalar or a vector. If a vector it must match the length N in TIDX. Vector input is not allowed if you are not using an array of coefficients. TIDX - Indexing array, same length as the input observations. This keyword is ignored if the input transformation vectors is a simple 5-element vector. If the transformation is provided as a 5xN array then this keyword is REQUIRED. Each element gives the index into the set of transformation values. This allows combining data that have different photometric transformation coefficients. KEYWORD OUTPUT PARAMETERS: OUTPUTS: std - Standard magnitude. stdsig - Uncertainty of the standard magnitude. COMMON BLOCKS: SIDE EFFECTS: RESTRICTIONS: PROCEDURE: MODIFICATION HISTORY: Written: Marc W. Buie, Lowell Observatory, 1992/03/31. 1997/02/10, MWB, total rewrite 2013/06/02, MWB, allow option for data to be covered by different transformation coefficients. 2013/06/25, MWB, added REFCOLOR keyword 2014/02/26, MWB, added vector option for REFCOLOR, added REFAM keyword, added option for extra transformation terms