Betelgeuse relative intensity in the near infrared

Forums Variable Stars VSS Circular 186 now available Betelgeuse relative intensity in the near infrared

Hugh Allen

Thanks for your feedback Andrew, and Robin as well. By normalising the relative flux near the centre of the V-band filter, I wondered if the changes in the relative flux in the near IR could then be monitored in a useful way compared to changes in the observed V magnitude (essentially a way of quantifying changes in the shape of the spectrum as the visual magnitude varies). But I can see some of the dangers, not least the initial process of corrrecting the shape of the spectrum for atmospheric effects. In the BAA database, Robin has a number of Alpy 600 spectra of Betelgeuse on which I made the same analysis:

There is an offset between our two methods of atmospheric correction. However the difference should just be a constant factor which can be best estimated from our almost simultaneous observations on JD 2458867.4 (2020 Jan 18), marked as point 1 in the adjusted chart below which shows all of the points from Robin’s data adjusted by the same factor. Once adjusted both our data follows a consistent trend. Point 2 is very interesting. It was my last observation of Betelgeuse on JD 2458954.3 (2020 Apr 14) before it disappeared into twilight and shows a significant increase in the relative intensity in the near IR even though the V mag was also continuing to increase: