Merill-Sanford (MS) absorption bands are molecular absorption bands of SiC2 in the blue-green spectra of carbon stars. I have tried to detect these rather weak but famous bands using the SA-100 (R=100 in my setup) and VX And as object (red curve; 38 spectra at 180 sec. each were stacked). As reference object I used a spectrum of RY Dra from the BAA-database (R=430; blue curve) (https://britastro.or...ment=&plot=Plot).
The most intense MS-band at 4985 A is already visible in the original SA-100 spectrum. Two more MS-bands could be detected:
VX And is classified as C-J4.5 J 5 MS 5
RY Dra is classified as C-N3 III: C2 6.5 J 3.5 MS 4.5
(MK classification: https://iopscience.i...1086/133252/pdf)
The structure of SiC2 is quite interesting showing a T-shaped form (see Fig. 1 as inset; taken from http://theop11.chem....7_1195_SiC2.pdf) with a C2v-symmetry (vetrical symmetry plane with a 180 degrees rotational symmetry axis). The broad shape of the bands is due to overlapping electronic and vibrational energy levels (see inset showing the assignments; taken from https://iopscience.i...1086/310336/pdf).
A comparison of VX And with another SA-100 carbon star spectrum of Z Psc (C-N5 C24) shows the absence of these MS-bands and demonstrates that carbon stars can, indeed, be classified using a low resolution setup.
SiC2 bands are possibly generated in cooler material high above in the photosphere. Real cool chemistry in cool stars!
Edited by mwr, 17 November 2019 - 06:29 AM.