For Vega, which is a telluric standard A0V star, the IGRINS Exposure Time Calculator (Version 2.11) gives the estimates shown in the figure below.
The figure shows S/N estimates for 30 & 300 second exposure times with a quad (e.g. ABBA) exposure set.
Park et al. (2014; SPIE Proceedings) find that the observed S/N is ~83% of the predicted value.
Based of IGRINS ETC v2.11 and the deviation from predictions of 83% from Park et al. (2014; SPIE Proceedings), a rough value for the S/N for an A0V star can be estimated using the following equation:
S/N ~ 273*sqrt(N*t)*10^(-0.2*Kmag)
where N = # of exposures, t = exposure time in seconds, Kmag = K-band magnitude.
