SSP-4 Photometer Observation Report and Analysis #2

In this report I develop the relationship between the signal-to-noise (SNR) and the error in magnitude for a single five second integration with the SSP-4. The SNR is calculated from the ratio (average counts for n measurements)/(standard deviation for n measurements). Note that the standard deviation is for a single measurement not for the mean. For the observations shown in figures 1 and 2, n was seven or eight, in other words, I took seven or eight five second integrations per band. The sky background count was an average of three five second integrations. The telescope used was a Meade LX200 0.2m SCT and the observing setting is suburban. I can typically see 4+ magnitude stars naked eye near zenith. Figures 1 and 2 show the dependence of the SNR upon the magnitude of the star.

In table 1, the columns labeled “J Band SNR” and “H Band SNR” represents the average SNR that would be expected for stars with magnitudes between -2 and 4. These numbers are derived from the exponential formulas contained in figures 1 and 2. The columns with labels “J Band Error” and “H Band Error” represent the expected error (one sigma) associated with each value of SNR. The formula for calculation of the estimated error is 1.0857/SNR.

Table 1 - Estimated SNR and Error as a Function of Magnitude

A couple of general comments. I need to complete figures 1 and 2 with observations for stars fainter that 2.5 magnitude. In figure 2, the SNR drops lower than would be expected for stars brighter that 0th magnitude. I am not sure if this an observational problem or an instrumentation problem or just an odd coincidence. More observations are needed to clarify these points. In my next report I will cover color the transformation coefficients and the airmass extinction parameters.

Figure 1 - Dependence of SNR with J magnitude.

Figure 2 - Dependence of SNR with H magnitude.