*4.3. P Cygni*

As was mentioned above P Cygni is one of the classical giant eruption LBVs, with an eruption observed in 1600. In the Van Genderen classification it is currently a weakly active LBV. The nebula around P Cygni has at least, two distinct parts. One larger structure with a diameter of 0.8 to 0.9 pc named the outer shell or OS which is rather spherical and a much smaller and clumpy structure the inner shell or IS which is less than 0.2 pc across [85]. Beside the IS and OS Meaburn et al. [86] reported 1999 a giant lobe to associated with the stars. Its has a PA = 50◦ to the other nebulae and stretches to an extend of 7 arcminutes or up 3.6 pc. He finds expansion velocities around 110 to 140 km/s (depending on which line he uses) associate with the inner shell and structures as high 185 km/s in the outer shell.

With a diameter of only 0.2 pc the IS is in most images barely resolved. A new LBT/LUCI AO image (Figure 5) we made recently shows the large amount of fine structure and details of inner nebula for the very first time. With a resolution down to 85 AU size structures it is an improvement from the previously published LBT image by Arcidiacono et al. [87].

**Figure 5.** An LBT LUCI AO [FeII] image of the inner nebula (or inner shell) of P Cygni (Weis et al., in prep). The images has pixel scale of 0.015"/pixel and resolve scales down to 85 AU.

Mapping the nebulae with KPNO high resolution longslit Echelle Spectra we measured the expansion velocity of the inner nebula is 100–150 km/s, this is well in agreemen<sup>t</sup> to Meaburns values. This would assuming no larger acceleration or deceleration match to the inner shell having been ejected during the 1600 giant eruption. With the spectra we can also associate velocities to distinct clumps that appear in the spectra and can be identified on the image (Weis et al. in prep.).

### *4.4. η Carinae — the Most Peculiar LBV?*

*η* Carinae used to be the most classical giant eruption LBV or *η* Carinae variable. With the discovery of many unique and unusual characteristics *η* Carinae or the *η* Carinae system is not the LBV par excellence anymore. A book devoted to *η* Carina and the Supernova impostors [88] can be consulted for all details on this object. Here a short summary of the characteristics:


The Homunculus was identified first and photographed in 1950 by Gaviola [90], the name of the nebula was motivated by the first images showing a man like morphology. The little Homunculus resides within the Homunculus and was revealed only using HST STIS long slit spectroscopy by Ishibashi et al. [91]. The outer ejecta as the name implies surrounds the Homunculus. It consists of a countless number of clumps and filaments. A first report and catalog with designation of several part of the outer ejecta was made 1976 by Walborn [92]. A summary of more recent optical, x-ray and kinematic studies of the outer ejecta is given by Weis [59]. Today we know that all three sections of the nebula are of bipolar morphology. The expansion velocities are with up to 3000 km/s faster than in any other LBV nebula. Shocks of these extremely fast structures in the outer ejecta create X-ray emission [93,94]. This emission is shown in the right section of Figure 6, here a a CHANDRA image is color coded and in indicates in red soft Xray emission of the outer ejecta is, in blue the more central emission results mark shocks of the central stellar system not the Homunculus nebula!

**Figure 6.** The nebula around *η* Carinae in the optical and X-ray. **Left**: An optical F658N HST image in greyscale, the Homunculus nebula additionally marked in contour to distinguish it from the outer ejecta, shown only in grey scale [58]. **Right**: A CHANDRA Xray image with color coded energy regimes, green:0.2-0.6 keV, red: 0.6–1.2 keV and blue 1.2–12 keV color version of Figure 1 in [95].

### **5. Instabilities and the Origin of Variability**

What are possible origins of the LBV variability. First we have to differentiate between the S Dor variability and giant eruptions. The latter are in need of much larger energy being released. Already in their 1994 paper Humphreys and Davidson [41] discussed what could cause the variabilities

and whether one or more mechanism are at work. They argue and cite several works showing that a classical *κ*-mechanism seems not to work. A more likely cause also discussed in that paper is the proximity of LBV to the Eddington, or in case of rotation ΩΓ limit. This limit indeed lies in the HRD in the same region as the Humphreys Davison limit, which also resembles the cool position of an LBV in the S Dor cycle. Clearly the properties of the stellar winds and their dependence of metallicity have to be a major contributor to the mechanisms creating the variability. For various more detailed theoretical works the reader is referred a review by Glatzel [96] a newer overviews by Vink [97] and Owocki [98]. Alternative models like non-radial gravity mode oscillations have been proposed by Guzik [99]. The potential importance of pulsations for the driving of the S Dor mechanism was discussed in [100]. The analysis of long, well sampled lightcurves may provide more information about the properties of the S Dor process [20,101]. Still, the link of low amplitude variability patterns with LBV nature is far from clear. Kalari et al. [101] showed that SMC blue supergiant AzV 261 exhibits variability patterns consistent with other LBVs in a 3 year time span and nearly nightly photometric observations, but their detailed analysis of high dispersion spectra showed no temperature changes typical for an S Dor cycle over a decade, precluding a classification as LBV.

Recently, new 3d radiation hydrodynamic simulations of 80 and 35 M performed and the results point at variations of the He opacity as a possible cause of the S Dor variability and link the shorter time scale irregular oscillations to convection [102]. Other ideas for the origin of the S Dor variability were already discussed in Section 3.

### **6. The LBV Wolf-Rayet Star Connection**

In the last years it has been found that the masses of Wolf-Rayet stars in that state (not their initial mass) is much lower as can be explained by the stellar winds only. Furthermore the empirical mass loss rates for hot, massive stars have also been seriously questioned, mainly because of the effects of wind clumping [103,104]. Wind clumping will reduce the mass loss rate and leave us with even higher mass in evolved stars. Stellar evolution models use theoretical mass loss rates, generally lower that the empirical ones even without clumping. A phase of enhanced mass loss with a different mechanism may be needed [105].

The LBVs phase would just fit. It is passed right before the WR phase and is known for high mass loss as well as the formation of massive nebulae. A LBV phase therefore might be mandatory to explain at least some WR classes and the lower WR star masses. One might even speculate that WR nebula are only by fast WR winds blown up, enlarged former LBV nebulae. Indications for such a hypothesis are the somewhat larger size of WR nebulae in combination with a N enhancement. The latter being a well known attribute of LBV nebula. Most WR nebula are not found around WO or WC but WN type stars, the natural and direct predecessor of LBVs.

First hints for such a scenario have been shown for the Wolf-Rayet stars WR 124 with its nebula M1-67 and the LBV He 3-519 [55]. The M1-67 WR nebula is one of few if not the only one that has a bipolar morphology and a size of only 2pc. As described above these are very typical values for LBV nebula. One might picture WR 124 as an old LBV that has just left the LBV and entered the WR phase, matching well to its current WN 8 spectrum. The scenario for He 3-519 might be just reversed, the stars is an LBV that is turning into an WR right now. This would also explain why no S Dor variability is seen for that star. Its current spectra type is already that of a WN 11. The nebula is only weakly bipolar and with 2 × 2.5 pc rather large for an galactic LBV see HST image in Figure 4. It looks more like an old LBV nebula that by inflation via the strong WR stars wind has already increased its size. Doing so also caused bipolarity to fade o[55]. For a more general review about WR stars see the contribution by Kathryn Neugent and Philip Massey in this volume.

### **7. Links of SN Impostors and LBVs**

In recent years several projects and monitoring surveys that search for supernovae found what has become known as *SN impostors*. These transients show spectra similar to core-collapse SN, especially of the type SNIIn, but are generally significant fainter than core-collapse SN. SN impostors show lightcurves quite different from all core collapse SN, sometimes even showing strong fluctuations on short timescales some time after the initial eruption, see e.g., [106]. It is interesting to note, that the brightest impostors events even overlap in energy with the faint SN IIP, e.g., [107,108]. A very tempting and likely explanation is to identify at least a subset of these SN impostors with giant eruptions or even S Dor variabilities of LBVs [109] in distant galaxies. Note in this context that while a LBV giant eruption will look like a SN impostor, not all SN impostors might indeed be LBV giant eruptions!

With the current list of about 40 SN impostors [110], light curves and spectra during the eruption, and especially the pre- and post-eruption behavior imply at least two different object classes are summarized in the name Impostor: the transients with strong narrow emission lines and erratic lightcurves with secondary, smaller outbursts following the first eruption, and the transients, which are followed with less than a decade by a true supernova explosion, e.g., [111]. This diversity of the lightcurves and spectra of the transients denoted as SN impostor was also noted by Smith [112]. It is potentially important, that the rise of the eruptions can be very steep [106,110,113], putting interesting limits on the kinetic energy and size scales evolved.

SN impostors will be discussed in detail in this volume by Kris Davidson.
