Figure 7.27. Typical P Cygni line profile and schematic illustration. Adapted reproduced from Kudritzki (2000).

most/all of their hydrogen envelope, and are thus highly evolved massive stars. They may be the final evolutionary phase for massive stars before their life-ending supernova explosions. There are two primary subtypes of WR stars - the "WN" stars, which typically have strong NII and N Ill emission lines (see Figure 7.30); and those of "WC" subtype, which have the same N lines as well as C III and C IV emission features. The WC9d stars also have thermal excess in the IR, indicating the presence of dusty envelopes (see Figure 7.31).

FIGURE 7.28. The Homunculus structure surrounding Eta Carina (figure reproduced from the

Hubble Space Telescope website).

FIGURE 7.28. The Homunculus structure surrounding Eta Carina (figure reproduced from the

Hubble Space Telescope website).

Tubofiale Nuova Ompi

2.00 2.05 2.10 2.15 2.20 2.25 2.30 Wavelength (iam)

FIGURE 7.29. The near-IR spectrum of LBV 1806-20. Adapted from Eikenberry et al. (2004).

Wolf Rayet Star Spectrum
Figure 7.30. The near-IR spectrum of the WN Wolf-Rayet star near LBV 1806-20.

7.4.3 Magnetospherically active stars

In some sense, the Sun itself is a Galactic source of emission lines. The Sun has an active magnetosphere, which produces detectable line emission. These lines are in fact crucial diagnostics for many aspects of Solar physics. As far as we can tell, probably all stars have emission lines from their magnetospheres. However, "normal" stars like the Sun are seldom considered "emission-line objects," largely because the line luminosity is very low - both in absolute terms and as a fraction of the total system luminosity.

The dM stars also have low-luminosity line emission, but as a fraction of total luminosity it can be quite significant, resulting in moderate-to-high equivalent widths. These are magnetospherically active objects, and other magnetospherically active stars also possess emission lines. However, this class (like stars in general) is numerically dominated by the low-mass M stars. While the luminosities for these objects are low, they are so numerous that they are often found as foreground contaminants for surveys of more-distant/luminous objects. Figure 7.32 shows some dM star spectra, including a "normal" stellar continuum with Ha in emission. Even magnetospherically active brown dwarfs with Ha emission have recently been discovered.

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