Observing List Compiled and Four New Clusters

Part of the morning was involved in a follow up on the photometry of FGD459 from yesterday. The systematic error between my measurements was never completely explained.

I have analyzed four new clusters, yet one needed to be dropped since I forgot to check if it was visible in July. One cluster has a low metallicity of -0.16 which reduces the planeticity, but other aspects of the cluster make it good for the survey. Another cluster's stars have masses of 4.5 solar masses. This is the largest I've analyzed yet by about an entire solar mass. Lovis and Mayor did include stars in this range, so I think they are legitimate to include.

I also transferred all necessary data into an observing list format. To complete this, I also had to calculate exposure times. I am uncertain as to the correctness of my method to calculate exposure time.

The Handbook of CCD Astronomy says that, for high values, the signal to noise ratio is dominated by error from source and is proportional to the square root of the number of pixels received. This follows from the incoming photons having a Poisson distribution. The number of photons is the flux times the exposure time. Flux can be expressed as 10^((m-48.6)/2.5) ergs/sec, with m in the AB system. AB magnitudes are only slightly off from the Johnson system, so I just used the V magnitude listed. The conversion from ergs/sec to photons/sec I just absorbed into the constant of proportionality. These all give the formula
S/N = C * 10^((m-48.6)/5) * sqrt(t)
where C is a constant of 4.4e12 determined from the rule of thumb "A 8th mag star takes 90s to get S/N=200".

I set the signal to noise ratio equal to 90, solved for t, and rounded up to the nearest convenient number. For stars dimmer than 12th mag, this gives times in excess of a thousand seconds. This seems an inefficient use of time, so those clusters should go to lower priority values.

Tomorrow I intend to search through the literature to find any possible problems with the new prospective stars to eliminate variables, non-members, spectroscopic binaries, etc.

Current Survey Total
Stars: 37
Clusters: 11