Luminous Blue Variables; Quiescent and Eruptive States
The Luminous Blue Variables (LBVs) represent a short-lived (10 000 to 20 000 yrs) episode of the late evolutionary phases of massive stars. At minimum the LBVs define an inclined instability strip in a range of absolute magnitudes and temperatures of − 8 ≳ M ≳ − 10 and 10 000 ≲ T ≲ 35 000 K, respectively. The most luminous LBVs are the hottest ones. The spectra of LBVs in minimum phase show (dependent on luminosity) characteristics of Ofpe/WN9 transition type stars and P Cygni-type stars. At outburst the stars are surrounded by slowly (v ≈ 100 to 200 km s−1) expanding, dense (Ne ≈ 1011 cm−1) envelopes, typically exhibiting an equivalent spectral type of middle A, but with strong P Cygni-type profiles of HI and of singly ionized metals. During the last 10 to 15 years a lot has been learnt about the physical nature of the LBVs and their behaviour during brightening (typically Δ V ∽ 0.5 − 2 mag in timescales of decades) from photometric and high resolution spectroscopic (ground based and IUE) long-term monitoring programs. Within these programs further instances of LBVs, both in the Galaxy and in the LMC have been detected. Results of the present understanding of the LBVs at quiescence and eruptive states mainly obtained from these studies are reviewed.
KeywordsMass Loss Rate Comparison Star Bolometric Luminosity Instability Strip Echelle Spectrograph
Unable to display preview. Download preview PDF.
- Hillier, D.J. 1991, Workshop (Kiel) on “Atmospheres of Early-Type Stars” (preprint).Google Scholar
- Israelian, G., de Groot, M.: 1991, Armagh Observatory, Preprint Series No. 128Google Scholar
- Lamers, H.J.G.L.M.: 1987, Instabilities in Luminous Early-Type Stars, (eds. Lamers and de Loore; Dordrecht, Reidel) p. 99.Google Scholar
- Leitherer, C.: 1991, STScI Workshop Nonisotropic and Variable Outflows from Stars (in press).Google Scholar
- Stahl, O.: 1990, Rev. Mod. Astron. 3; pg. 286 (ed. G. Klare, Springer-Verlag).Google Scholar
- Stahl, O., Wolf, B., Klare, G., Cassatella, A., Krautter, J., Persi, P., Ferrari-Toniolo, M.: 1983, Astr. Ap., 127, 4.Google Scholar
- Zinner, E.: 1952, Bamberg, Kleine Veröffentlichungen, Nr. 7, 1.Google Scholar