HD-145875 Spectrogram: a Red Dwarf (Joel Shepherd)

HD-145875 Spectrogram: a Red Dwarf

This was a bit of an adventure. I was capturing a spectrum of Yed Prior (Delta Ophiuchi) when I noticed a faint but more interesting spectrum in the background. It almost looked like a Wolf-Rayet. So after some efforts to bring it into focus and figure out a reasonable exposure time, I finally captured it and started to figure out what it was. It was HD-145875, on the other end of the spectrum (so to speak) from a Wolf-Rayet: a relatively cool, M3 red dwarf.

Red dwarfs are actually quite common, at least in our galaxy, but hard to capture spectra of because of their small size and inherit dimness. This one is roughly 8.9 visual magnitude. Probably 1650-1850 light-years distant, HD-145875 is a little under half the diameter of our sun, with an estimated surface temperature of 3540K. My rough estimate using Wien's Law puts it at 3870K, about a 9% error. HD-145785 is variously classified as a K5 or M3 star: the reference spectrum, shown in blue, is for an M3 iii and is the closest fit I could find in the Pickles reference curves.

Note the barely-there hydrogen lines, and the much more prevalent TiO and other molecular bands. I'm not sure what is causing the shift apparent on the red end of the spectrum but suspect calibration errors.

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