Figure 7.25. Rotational support correlations for Be stars. From Hanuschik et al. (1988).
Cygni-profile" line is shown in Figure 7.27. The broad blue absorption edge coupled with a redder emission edge is indicative of a strongly cooling wind outflow from a star. The wind regions closest to the stellar photosphere are exposed to the hard radiation field from the star, producing uniform line emission. However, the bluest features arise from the portion of the wind moving directly towards the observer - which of course means that those photons must traverse even-cooler material moving at the same projected velocity as the emitting material, creating strong line absorption. The line of sight to line-emitting material moving significantly away from the "head-on" direction also traverses cooler material, but with different projected velocities, which make the material effectively transparent to the line emission.
LBV stars are somewhat famously "eruptive" in their nature - during much of the 1800 s, n Car went from relative obscurity at mV > 7 mag to being the brightest star
in the sky, before fading away again a few decades later. This eruption resulted in the formation of the famous "Homunculus" cloud of material surrounding n Car now (Figure 7.28).
The optical spectra of LBVs are typically dominated by Balmer lines, He I emission, and Fe and [Fe] lines, most with strong P Cygni profiles. Their IR spectra show the same features, though they also often include Mg II and Na I emission as well.
Another interesting set of LBVs is the IR-discovered stars the "Pistol Star" (Figer et al. 1997) and LBV 1806-20 (van Kerkwijk et al. 1995; Eikenberry et al. 2004). Both of these stars have very high luminosities of ^(3 — 5) x 106L0 (Figer et al. 1997; Eikenberry et al. 2004), and there is evidence of nebular remnants and/or radio shells indicating LBV-type past eruptions. Their IR spectra are remarkably similar to each other, and closely resemble those of other LBVs - particularly AG Car and n Car (see Figure 7.29). Together with n Car, they three constitute what appear to be the three most-luminous stars known in the Milky Way to date. It is important to note that two of the three most-luminous stars in the Galaxy were discovered serendipitously in the past decade. One would think that their instrinsic luminosity would make such stars obvious targets. However, neither of these two is easily visible in the optical due to AV ~ 25—30 mag of extinction. This again emphasizes the importance of more IR observational work -particularly spectroscopy - for probing the massive-stellar content of our own Galaxy.
Wolf-Rayet (WR) stars are massive objects that tend to show strong He emission, but relatively weak H emission. This is thought to indicate that WR stars have shed
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