New LPV of the Month Article - Alf Ori

American Association of Variable Star Observers (AAVSO)
Fri, 01/31/2020 - 14:40

Clear Skies, 

Rich Roberts (RRIA)

LPV of the Month: Betelgeuse

Just to add a couple of things to Rich Roberts's excellent article: the media hype about a forthcoming supernova assumes that there is a close connection between the pulsating outer layers, and the core where the supernova process occurs.  Actually, the outer layers tend to "do their own thing" in a complex way. 

   Thanks to the decades of AAVSO observations, we know that there is a pulsation period of about 390 days (give or take) and that the pulsation amplitude varies on a time scale of tens of periods, as is the case with other pulsating red giants and supergiants (Percy & Khatu 2014 JAVSO 42, 1).  The peak-to-peak pulsation amplitude has been slowly increasing over the last decade or so, from 0.05 to 0.60.  Furthermore, Betelgeuse has a "long secondary period" (LSP) of about 2100 days (Percy and Sato 2009 JRASC 103, 11), whose peak-to-peak amplitude has also increased over the last decade or so, from 0.18 to 0.30.  We are currently at the minimum of both the pulsation period and the LSP.  In the past, Betelgeuse has faded noticeably (as you can see from the long-term light curve), though not as deep as now. 

   The cause of the pulsation amplitude variation, and of the LSP is not clear, though the large visible convective cells turn over on a time scale of many years, and the star presumably rotates, carrying these cells around the star.

   Pulsation drives mass loss in cool stars and, as others have noted: strong pulsation may increase the mass loss rate temporarily.  This has happened in other cool pulsators, and also in yellow supergiants such as Rho Cas.

   So keep up the good observing!