A low resolution spectrum of the prototypical cool giant star Arcturus, also known as alpha Bootes (spectral type K1 III). This star has subtle peaks in its spectrum but it is not too far off the expected spectrum seen at links below.
https://www.cloudynights.com/topic/618666-arcturus-spectrum/
https://www.cloudynights.com/topic/217689-arcturus-spectrum-what-am-i-seeing/
Andy
