Knowledge Bank

Observations of molecular bands in the stars $\alpha$ Ori and 19 Psc have been made with the rapid scanner on the one meter optical telescope at Indiana University’s Goethe Link Observatory. The wavelength range 3500-6000 \AA was observed at 20 \AA resolution with the data digitized each 4 \AA, while the range 6000-12000 \AA was covered at 40 \AA resolution, digitized at 6.6 \AA intervals. The spectrometer grating is driven by a stepping motor which is programmed to repeatedly scan the wavelength range of interest at a speed of 667 \AA/sec. The amplified photomultiplier signal is fed to a 1024-channel digital signal averager which is cycled at the grating repetition rate. Forward and reverse scans are accumulated separately in memory so that the accuracy of the scans can be judged from a comparison of the forward and reverse positions. The rapid scan spectrometer is capable of greater accuracy than a conventional single scan instrument because low frequency noise components due to changes in the night sky transparency are avoided. In addition, the observing time can easily be extended to any convenient length necessary for the desired accuracy without laborous averaging of scans. The observed flux errors for the stars 19 Psc and $\alpha$ Ori are three and one percent respectively. The scans of the star 19 Psc show strong bands of the $\Delta v$ = 0, 1, 2, 3 sequences of the $A^{2}$11 - $X2\Sigma$ system of the CN radical from 6000-12000 \AA, and $C2$ Swan bands from 4000-6000 \AA. At wavelengths shorter than 4000 \AA, the light flux from 19 Psc is too small to measure with the accuracy cited above. The star $\alpha$ Ori shows much weaker bands of the red system of CN, and also weak bands of the singlet and triplet electronic systems of TiO throughout this wavelength region. These scans compare favorably with previous work on the same bands in these stars by R. Wing (1967, Ph.D. thesis, U. of Calif., Berkeley) using 27 frequency points between 7500-11000 \AA. The principal advantage of the present work is the detail observed in the structure of these CN and TiO bands at the more than 1500 wavelength points used by the authors. A second advantage is that Wing’s observations are extended from 7500-4000 \AA with photoelectric accuracy at comparable spectral resolution. Methods for calibrating the results and removing the terrestrial $O2$ and $H2O$ bands from the scans at these wavelengths are discussed.