Astron. Astrophys. Suppl. Ser.
Volume 124, Number 3, September 1997
|Page(s)||517 - 531|
|Published online||15 September 1997|
New perceptions on the S Doradus phenomenon and the micro variations of five Luminous Blue Variables (LBVs)*
Leiden Observatory, Postbus 9513, 2300 RA Leiden, The Netherlands
2 Armagh Observatory, College Hill, Armagh BT61 9DG, Northern Ireland
3 University of Brussels (VUB), Pleinlaan 2, 1050 Brussels, Belgium
Send offprint request to: A.M. van Genderen
Accepted: 17 December 1996
We investigated the photometric histories of the LBVs HR Car in the Galaxy, R 127, R 110 and R 71 in the LMC, and R 40 in the SMC by collecting all available photometry. All these objects have been reasonably well observed over the last few decades and a number of "S Dor (SD) phases” (episodes of enhanced light) is well documented. Time-scales lie between 1.4 and 25 y. During the SD cycles two different types of micro-variations (amplitudes ) are present: one near the minima (time-scale from 2 to 6 weeks; colours generally blue in the maxima and red in the minima) and the other one near the maxima (time-scale ; colours generally red in the maxima and blue in the minima). Halfway the ascending and descending branches of the SD cycles the stars switch rather abruptly from one type to the other. We argue that the two types of SD phases are probably caused by different instability mechanisms.
Key words: technique: photometric / stars: individual HR Car = HD 90177, R 127 = HDE 269858f, R 40 = HD 6884, R 71 = HDE 269006, R 110 = HDE 269662 / stars: variables / stars: supergiants / stars: oscillations
© European Southern Observatory (ESO), 1997