A debate has arisen concerning the fundamental nature of luminous blue variables (LBVs) and their role in stellar evolution. While Smith & Tombleson proposed that their isolated environments indicate that LBVs must be largely the product of binary evolution, Humphreys et al. have recently expressed the view that the traditional single-star view still holds if one appropriately selects a subsample of LBVs. This paper finds the claim of Humphreys et al. to be quantitatively unjustified. A statistical test of 'candidate' as opposed to 'confirmed' LBVs shows no significant difference (<1 sigma) between their environments. Even if the sample is further subdivided as proposed, the three most luminous LBVs are spatially dispersed similar to late O-type dwarfs, which have much longer median lifetimes than expected for classical LBVs. The lower luminosity LBVs have a distribution associated with red supergiants (RSGs), but these RSGs are dominated by stars of 10-15 M-circle dot initial mass, with much longer lifetimes than expected for those lower luminosity LBVs. If one's view is restricted to the highest luminosity LBVs, then the appropriate comparison is with early O-type stars that are their presumed progenitors; when this is done, it is clear that even the high-luminosity LBVs are more dispersed than expected. Humphreys et al. also suggest that velocities of LBVs support the single-star view, being inconsistent with runaways. A quantitative analysis of the radial velocity distribution of LBVS in M31 and M33 contradicts this; modest runway speeds expected from mass gainers in binary evolution are consistent with the observed velocities, although the data lack the precision to discriminate.

We present Atacama Large Millimeter Array (ALMA) observations of (CO)-C-12 2-1 emission from circumstellar material around the massive star Eta Carinae (eta Car). These observations reveal new structural details about the cool equatorial torus located similar to 4000 au from the star. The CO torus is not a complete azimuthal loop, but rather, is missing its near side, which appears to have been cleared away. The missing material matches the direction of apastron in the eccentric binary system, making it likely that eta Car's companion played an important role in disrupting portions of the torus soon after ejection. Molecular gas seen in ALMA data aligns well with the cool dust around eta Car previously observed in mid-infrared (IR) maps, whereas hot dust resides at the inner surface of the molecular torus. The CO also coincides with the spatial and velocity structure of near-IR H-2 emission. Together, these suggest that the CO torus seen by ALMA is actually the pinched waist of the Homunculus polar lobes, which glows brightly because it is close to the star and warmer than the poles. The near side of the torus appears to be a blowout, associated with fragmented equatorial ejecta. We discuss implications for the origin of various features north-west of the star. CO emission from the main torus implies a total gas mass in the range of 0.2-1 M-circle dot (possibly up to 5 M-circle dot or more, although with questionable assumptions). Deeper observations are needed to constrain CO emission from the cool polar lobes.

We present optical and near-IR photometry and spectroscopy of SN 2013L for the first 4 yr post-explosion. SN 2013L was a moderately luminous (M-r = -19.0) Type IIn supernova (SN) that showed signs of strong shock interaction with the circumstellar medium (CSM). The CSM interaction was equal to or stronger to SN 1988Z for the first 200 d and is observed at all epochs after explosion. Optical spectra revealed multicomponent hydrogen lines appearing by day 33 and persisting and slowly evolving over the next few years. By day 1509, the Ha emission was still strong and exhibiting multiple peaks, hinting that the CSM was in a disc or torus around the SN. SN 2013L is part of a growing subset of SNe IIn that shows both strong CSM interaction signatures and the underlying broad lines from the SN ejecta photosphere. The presence of a blue Ha emission bump and a lack of a red peak does not appear to be due to dust obscuration since an identical profile is seen in Pa beta. Instead this suggests a high concentration of material on the near-side of the SN or a disc inclination of roughly edge-on and hints that SN 2013L was part of a massive interactive binary system. Narrow Ha P-Cygni lines that persist through the entirety of the observations measure a progenitor outflow speed of 80-130 km s(-1), speeds normally associated with extreme red supergiants, yellow hypergiants, or luminous blue variable winds. This progenitor scenario is also consistent with an inferred progenitor mass-loss rate of 0.3-8.0 x 10(-3) M-circle dot yr(-1).

The Hubble Space Telescope archive contains a large collection of images of eta Carinae, and this paper analyses those most suitable for measuring its expanding Homunculus Nebula. Multiple intensity tracings through the Homunculus reveal the fractional increase in the overall size of the nebula; this avoids registration uncertainty, mitigates brightness fluctuations, and is independent of previous methods. Combining a 13 yr baseline ofWide Field Planetary Camera 2 images in the F631N filter, with a 4 yr baseline of Advanced Camera for Surveys/ High Resolution Channel images in the F550M filter, yields an ejection date (assuming linear motion) of 1847.1 (+/- 0.8 yr). This result improves the precision, but is in excellent agreement with the previous study by Morse et al., that used a shorter time baseline and a different analysis method. This more precise date is inconsistent with ejection during a periastron passage of the eccentric binary. Ejection occurred well into the main plateau of the Great Eruption, and not during the brief peaks in 1843 and 1838. The age uncertainty is dominated by a real spread in ages of various knots, and by some irregular brightness fluctuations. Several knots appear to have been ejected decades before or after the mean date, implying a complicated history of mass-loss episodes outside the main bright phase of the eruption. The extended history of mass ejection may have been largely erased by the passage of a shock through clumpy ejecta, as most material was swept into a thin shell with nearly uniform apparent age.

While the progenitors of Type Ia supernovae (SNe Ia) have long been thought to be thermonuclear explosions of white dwarf stars, what triggers the explosion are still a topic of debate. This thesis considers constraints on single-degenerate progenitors of SNe Ia based on the presence of a Roche-lobe filling companion. The ejecta strips material from the companion, that maybe detectable via Hα emission during the nebular phase. Using the full structure from simulations produces line widths are larger than those produced in simple models. The structure formed by the ejecta-companion interaction produce a broken reverse shock that may be visible in X-rays via the Fe K&alpha; line at the age of Tycho's supernova remnant (SNR). If the similar structures in Tycho’s SNR are produced this way then the companion star must have been massive, with M ~ 2 M_&odot;. Detections of circumstellar material within the supernova provides another way to indirectly probe the companion star. Mass loss through winds or novae are expected to shape the circumsteller medium for single-degenerate progenitors and the velocities, v ~ 100 km s^-1 appear to be consistent with recurrent nova shells, a model that is tested by analysing simulations of RS Ophiuchi. Models of RS Ophiuchi can explain the absorption lines seen around the 2006 outburst if the mass loss is 10⁻⁶ M_&odot; yr<sup>-1,/sup>. The circumsteller medium is shown to produce in the velocity and relative strengths of the features seen in SN 2006X. However, whether density in the shells is high enough to produce the required recombination timescale and to overcome ionization by &gamma;-rays for shells at 5 × 10¹⁶ cm remains uncertain.

The massive evolved star. Carinae is the most luminous star in the Milky Way and has the highest steady wind mass-loss rate of any known star. Radiative transfer models of the spectrum by Hillier et al. predict that Ha is mostly emitted in regions of the wind at radii of 6-60 au from the star (2.5-25 mas at 2.35 kpc). We present diffraction-limited images (FWHM similar to 25 mas) with Magellan adaptive optics in two epochs, showing that. Carinae consistently appears similar to 2.5-3 mas wider in Ha emission compared to the adjacent 643 nm continuum. This implies that the H alpha line-forming region may have a characteristic emitting radius of 12 mas or similar to 30 au, in very good agreement with the Hillier stellar-wind model. This provides direct confirmation that the physical wind parameters of that model are roughly correct, including the mass-loss rate of M= 10(-3)M(circle dot) yr(-1), plus the clumping factor, and the terminal velocity. Comparison of the Ha images (ellipticity and PA) to the continuum images reveals no significant asymmetries at H alpha. Hence, any asymmetry induced by a companion or by the primary's rotation do not strongly influence the global H alpha emission in the outer wind.

The Hanle effect has been proposed as a new diagnostic of circumstellar magnetic fields for early-type stars, for which it is sensitive to field strengths in the 1-300 G range. In this paper we compute the polarized P Cygni line profiles that result from the Hanle effect. For modeling the polarization, we employ a variant of the "last scattering approximation." For cases in which the Sobolev optical depths are greater than unity, the emergent line intensity is assumed to be unpolarized, while for smaller optical depths, the Stokes source functions for the Hanle effect with optically thin line scattering are used. For a typical P Cygni line, the polarized emission forms in the outer wind, because the Sobolev optical depth is large at the inner wind. For low surface field strengths, weak P Cygni lines are needed to measure the circumstellar field. For high values of the surface fields, both the Zeeman and Hanle diagnostics can be used, with the Zeeman effect probing the photospheric magnetic fields and the Hanle effect measuring the magnetic field in the wind flow. Polarized line profiles are calculated for a self-consistent structure of the flow and the magnetic geometry based on the WCFields model, which is applicable to slowly rotating stellar winds with magnetic fields drawn out by the gas flow. For surface fields of a few hundred gauss, we find that the Hanle effect can produce line polarizations in the range of a few tenths of a percent up to about 2%.

We present spectral line mapping observations towards four massive star-forming regions Cepheus A, DR21S, S76E and G34.26+0.15 - with the IRAM 30-m telescope at the 2 and 3 mm bands. In total, 396 spectral lines from 51 molecules, one helium recombination line, 10 hydrogen recombination lines and 16 unidentified lines were detected in these four sources. An emission line of nitrosyl cyanide (ONCN, 14(0), 14-13(0), (13)) was detected in G34.26+0.15, as the first detection in massive star-forming regions. We found that c-C3H2 and NH2D show enhancement in shocked regions, as suggested by the evidence of SiO and/or SO emission. The column density and rotational temperature of CH3CN were estimated with the rotational diagram method for all four sources. Isotope abundance ratios of C-12/C-13 were derived using HC3N and its C-13 isotopologue, which were around 40 in all four massive star-forming regions and slightly lower than the local interstellar value (similar to 65). The N-14/N-15 and O-16/O-18 abundance ratios in these sources were also derived using the double isotopic method, which were slightly lower than in the local interstellar medium. Except for Cep A, the S-33/S-34 ratios in the other three targets were derived, which were similar to that in the local interstellar medium. The column density ratios of N(DCN)/N(HCN) and N( DCO+)/N(HCO+) in these sources were more than two orders of magnitude higher than the elemental [D]/[H] ratio, which is 1.5 x 10(-5). Our results show that the later stage sources, G34.26+0.15 in particular, present more molecular species than earlier stage sources. Evidence of shock activity is seen in all stages studied.

Supernova (SN) 2005ip was a Type IIn event notable for its sustained strong interaction with circumstellar material (CSM), coronal emission lines and infrared (IR) excess, interpreted as shock interaction with the very dense and clumpy wind of an extreme red supergiant. We present a series of late- time spectra of SN 2005ip and a first radio detection of this SN, plus late-time X-rays, all of which indicate that its CSM interaction is still strong a decade post- explosion. We also present and discuss new spectra of geriatric SNe with continued CSM interaction: SN 1988Z, SN 1993J and SN 1998S. From 3 to 10 yr post- explosion, SN 2005ip's Ha luminosity and other observed characteristics were nearly identical to those of the radio- luminous SN 1988Z, and much more luminous than SNe 1993J and 1998S. At 10 yr after explosion, SN 2005ip showed a drop in Ha luminosity, followed by a quick resurgence over several months. We interpret this Ha variability as ejecta crashing into a dense shell located less than or similar to 0.05 pc from the star, which may be the same shell that caused the IR echo at earlier epochs. The extreme Ha luminosities in SN 2005ip and SN 1988Z are still dominated by the forward shock at 10 yr post- explosion, whereas SN 1993J and SN 1998S are dominated by the reverse shock at a similar age. Continuous strong CSM interaction in SNe 2005ip and 1988Z is indicative of enhanced mass- loss for similar to 10(3) yr before core collapse, longer than Ne, O or Si burning phases. Instead, the episodic mass- loss must extend back through C burning and perhaps even part of He burning.

The Galactic blue supergiant SBW1 with its circumstellar ring nebula represents the best known analogue of the progenitor of SN 1987A. High-resolution imaging has shown H alpha and infrared structures arising in an ionized flow that partly fills the ring's interior. To constrain the influence of the stellar wind on this structure, we obtained an ultraviolet (UV) spectrum of the central star of SBW1 with the Hubble Space Telescope Cosmic Origins Spectrograph. The UV spectrum shows none of the typical wind signatures, indicating a very low mass-loss rate. Radiative transfer models suggest an extremely low rate below 10(-10) M-circle dot yr(-1), although we find that cooling time-scales probably become comparable to (or longer than) the flow time below 10(-8) M-circle dot yr(-1). We therefore adopt this latter value as a conservative upper limit. For the central star, the model yields T-eff = 21 000 +/- 1000 K, log(g(eff)) = 3.0, L similar or equal to 5 x 10(4) L-circle dot, and roughly Solar composition except for enhanced N abundance. SBW1' s very low mass-loss rate may hinder the wind's ability to shape its nebula and to shed angular momentum. The spin-down time-scale for magnetic breaking is more than 500 times longer than the age of the ring. This, combined with the star's slow rotation rate, constrains merger scenarios to form ring nebulae. The mass-loss rate is at least 10 times lower than expected from mass-loss recipes, without any account of clumping. The physical explanation for why SBW1' s wind is so weak presents an interesting mystery.