Observed evolutionary changes in the visual magnitude of the luminous blue variable P Cygni.
Abstract
Historical observations of the star P Cygni (B1 Ia(+)) show that the star has steadily increased its visual brightness between 1700 and 1988 by 0.15 +/- 0.02 magn/century. If we assume that the luminosity of the star remained constant, (as predicted by evolutionary tracks of massive stars) the increase in brightness must be due to a steady decrease of the Bolometric Correction and hence of Teff at a rate of 6 +/- 1 percent per century. This is the first time ever that the evolution of a star has been observed in secular photometric variations. The redward evolution of P Cyg in the HR-diagram occurs on a Kelvin-Helmholtz time scale for core-contraction and envelope expansion, but the observed rate of change is a factor of two faster than predicted by the evolutionary tracks. The discrepancy can be explained by either assuming that dynamical effects speed up the post main-sequence evolution of massive stars or that the core mass of the star is smaller than predicted. We briefly discuss the absolute bolometric magnitude of P Cygni during the outbursts in the seventeenth century derived from the observed color and the visual brightness.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- April 1992
- Bibcode:
- 1992A&A...257..153L
- Keywords:
-
- Blue Stars;
- Stellar Evolution;
- Stellar Luminosity;
- Stellar Magnitude;
- Variable Stars;
- Hertzsprung-Russell Diagram;
- Kelvin-Helmholtz Instability;
- Light Curve;
- Stellar Color;
- Stellar Spectrophotometry;
- Astrophysics