Supernova 1993J in the spiral galaxy M81 is the brightest supernova since SN 1987A and, like the latter, appears to be another peculiar type II supernova. Its early light curve is characterized by a very sharp initial peak (lasting for less than ten days) followed by a less rapid secondary brightening, which was qualitatively similar to the secondary brightening observed in SN 1987A.

Humphreys et al. (1993) have identified a candidate progenitor consistent with the position of the supernova. Combining their UBVR. photometry with the I magnitude obtained by Blakeslee & Tonry (1993), they concluded that the colors of the apparent progenitor require the presence of at least two bright stars. One star is an early-type supergiant (most likely a late-B to early-A supergiant), the other a late-type supergiant (most likely a G to early-K supergiant). The bolometric magnitudes of both stars are in the range of –6 to –8, with best-fit values of –7 to –7.5 (for an assumed distance of 3.3 Mpc). We have performed our own fits to the photometric data and obtained similar results. These best-fit magnitudes imply mainsequence masses of ∼ 15 M⊙, but the masses could be as low as 8 M⊙ or as large as 20 M⊙. The image of the candidate progenitor appears extended on some plates (Blakeslee & Tonry 1993). This suggests that, at the distance of M81, the two stars do not form a close binary (although either star could have an undetected binary companion).

The historic series of Herstmonceux Conferences was started by the new Astronomer Royal, Sir Richard Woolley, in the late 1950's. The Royal Greenwich Observatory had by then recently finished moving its scientific operations from Greenwich to Herstmonceux Castle in East Sussex. Evidently the first few such conferences were relatively small private affairs, and there are few written records of them, but in later years they grew in size. After the moving of the RGO to Cambridge in 1989, they have been organised jointly with the University's Institute of Astronomy.

Our idea for the 34th Conference was to bring together different astronomical communities who study stellar evolution, stellar winds and the physics of circumstellar media, and to bring out the common physics affecting matter around both high and low-mass stars. This volume presents the proceedings. We have included all the invited reviews and the contributed oral talks, and there is a summary listing the titles and authors of all the poster papers.

Thanks are due to many people for helping to put together what was the largest-ever Herstmonceux Conference. The Organising Committee were Robin Catchpole, Robin Clegg, Peter Meikle, Jim Pringle, Anne Reynolds and Ian Stevens; Anne did a huge job as Conference Secretary and deserves special mention. The Advisory Committee were John Dyson, Alex Filippenko, Claes Fransson, Harm Habing, Alain Omont and Guillermo Tenorio-Tagle. The RGO and the IoA gave financial support, and the International Science Foundation funded speakers from Russia.

Introduction

The detection of narrow emission lines from supernova 1993J gives us a rare opportunity to study the circumstellar medium produced in the preexplosion phase. This can give insights into the evolution and mass loss history of the progenitor star, and test theories of the interaction of a supernova with its surroundings.

Observations

Optical spectra of SN 1993J were obtained with the IDS and ISIS spectrographs on, respectively, the INT and WHT on La Palma. For the first two weeks, spectroscopy was carried out nightly, and less frequently thereafter. The resolution and wavelength coverage varied according to the scheduled observing programme being carried out at the time.

Circumstellar matter in symbiotic stars

By definition, symbiotic stars exhibit simultaneously the absorption features of a cool giant and high excitation emission lines, e.g. HeII, [OIII], of an ionised nebula. Thus the presence of circumstellar material is a necessary classification criterion of these objects. It is now generally accepted that symbiotic stars are binary systems consisting of a red giant and a hot radiation source, in most cases a hot white dwarf. The strong emission lines originate in a dense nebula which is thought to be wind material lost by the cool giant and ionised by the hot companion.

Besides the compact nebula other components of circumstellar material are observed. Enhanced IR emission due to circumstellar dust is found in D-type (D for dust) symbiotic systems. Very extended ionised regions have been mapped with radio interferometers or optical imaging techniques (e.g. Taylor 1988, Solf 1988, Corradi & Schwarz 1993, Schwarz 1993). Some features of the extended structures can be associated with bipolar outflow (velocities ∼ 100 km/s) from the central, unresolved binary system.

In this paper we discuss how the geometric structure of the circumstellar environment of symbiotic systems can be clarified from an analysis of light scattering processes.

Scattering processes in the circumstellar environment of symbiotic stars

Polarisation measurements are a well known tool for studying scattering processes. Polarimetric observations of symbiotic stars in broad and narrow band filters have shown that these objects are often intrinsically polarised (e.g. Piirola 1983, Schulte-Ladbeck 1985, Schulte-Ladbeck et al. 1990).

Introduction

The defining characteristic of type II SNe is the presence of very broad Hα emission with a strong P-Cygni profile. A small number of peculiar type II SNe have been found in recent years which are either very bright in the optical continuum with very strong and broad Hα emission without a P-Cygni profile, or are strong radio sources then called radio supernovae.

Introduction

The circumstellar gas (CSG) around supernovae (SNe) provides information on the mass loss history of the dying star. When the SN explodes, the CSG is ionized by the radiation from both the SN and the gas shocked by the expanding ejecta. By looking at spectral signatures from the ionized CSG at increasingly large radii, we may peer deeper and deeper back through time into the mass loss history of the pre-SN. The recent bright and well-studied Type II SNe 1987A and 1993J have given us an unprecedented chance of doing so. Here we briefly discuss the CSG of these two SNe.

SN 1987A

Light curves for the narrow UV emission lines from SN 1987A (Sonneborn et al. 1994) show that the emission starts ∼ 70 days after the outburst with a roughly linear increase in strength until day ∼ 400, followed by a gradual decline up to day ∼ 1000 when the lines start to fall below detectability. In the optical there is very good information on the spatial flux distribution from observations with the NTT (Wampler et al. 1990; Wang & Wampler 1992) and the HST (Jakobsen et al. 1991; Plait et al. 1994); the emission mainly comes from a patchy, elliptically shaped ring with semimajor and semiminor axes of ∼ 0.830 (corresponding to ∼ 6.2 × 1017 cm at 50 kpc) and ∼ 0.605 arcsec, respectively.

Introduction

Supernovae are important for the study of several astrophysical problems – nuclear processing in stellar interiors, distance scale determinations, and the chemical enrichment of the interstellar medium have all been explored. Additionally, they may be used as background probes of interstellar gas by studying, for example, NaI and CaII lines, sampling the gas in the host galaxy, the Milky Way halo gas, and any intervening intergalactic gas. SN 1987A allowed the detailed study of gas towards and within the LMC to a distance D ≃ 0.05 Mpc (Vidal-Madjar et al. 1987, de Boer et al. 1987). With the unusually bright SN 1993J in M81 it is now possible to extend the search for interstellar/intergalactic absorptions beyond the local group of galaxies, out to the distance of the M81 group at a distance of D~3.25 Mpc. In this paper we present a preliminary study of high resolution optical interstellar spectra towards SN 1993J. The observations are described in section 2. The origin of the absorption lines, which fall into three distinct groups are discussed in section 3.

Observations

The observations of SN 1993J were obtained during the nights 1993 April 4–8, using the Utrecht Echelle Spectrograph on the William Herschel Telescope at the Observatorio del Roque de los Muchachos, La Palma.

Introduction

An early result from ultraviolet astronomy was that OB stars with bolometric magnitudes brighter than Mbol ≃ −6 suffer significant mass loss (Snow & Morton 1976). At about the same time the framework was laid down by Castor, Abbott & Klein (1975; hereafter CAK) for what, has proved since to be a very successful theory of mass loss from OB and other similarly high-luminosity stars. In bare outline the physical model is a simple one in which the outward force able to overcome gravity is the pressure exerted by the hot star's radiation field on its own atmosphere. In practical application, complexity arises from the fact that it is overwhelmingly the scattering of radiation in spectral lines that, mediates the force (a point first appreciated by Lucy & Solomon 1970).

Introduction

The standard picture of a Type II SN progenitor star is a red supergiant (RSG) that has evolved from a massive star with an initial main-sequence mass above ∼ 10M⊙. These RSGs are observed to have very massive, slow winds with terminal speeds in the range of 10 − 50 km s−1, and mass loss rates in the range of 10−7 − 10−5M⊙yr−1. These slow winds will gradually blow a stellar wind bubble of RSG wind into the relic main-sequence stellar wind bubble, building up a shell of shocked RSG wind at the edge of the expanding bubble.

Introduction

Axisymmetric outflows are associated with many nebulae (e.g. He 2-36, BI Cru, My Cn 18, IC 4406, K 3-72, Corradi & Schwarz 1993a, b, c; OH 17.7–2.0, La Bertre 1986; R Aquarii, Burgarella & Paresce 1992) and with Be stars. I will concentrate in the present review mainly on planetary nebulae (PNe).

An examination of the catalogue of narrow band images of Schwarz, Corradi and Melnick (1992) and other images in the literature reveals a few interesting morphologies. In some cases, almost perfect rings are observed (e.g. ScWe 3, ScWe 2, Schwarz, Corradi & Melnick 1992; Hen 1357, Bobrowsky 1993).

Introduction

If a supernova progenitor has undergone significant mass-loss then the expanding supernova ejecta will eventually collide with this circumstellar material (CSM). Shock waves arising from the collision will compress and heat both the ejecta and the CSM. The emission from the shocked material depends strongly on the density distributions of the ejecta and the CSM, thereby providing important information about the nature of the CSM.

SN 1987A

Images from the European Southern Observatory (ESO) (Wampler et al. 1990) and the Hubble Space Telescope (HST) (Jakobsen et al. 1991) revealed the presence of a ring-like structure at ∼ 6 × 1017 cm from SN 1987A. The outermost part of the supernova, ejecta is expanding at ∼ 104 km s−1 (Shigeyama & Nomoto 1990) and so is expected to collide with the ring ∼ 10 years after the explosion.

Hydrodynamical model

The progenitor of SN 1987A went through a red supergiant (RSG) phase, and then contracted to a blue supergiant (BSG) before the explosion (for reviews, see Arnett et al. 1989, Hillebrandt & Höflich 1989, Podsiadlowski 1992, and Nomoto et al. 1993a). This evolutionary scenario implies that the SN 1987A environment was formed as follows: the progenitor blew a stellar wind with a velocity ∼ 10 km s−1 and a mass loss rate ∼ 10−5M⊙ yr−1 during the RSG stage, and with corresponding values of ∼ 550 km s−1 and ∼ 10−6M⊙ yr−1 during the BSG stage (Lundqvist & Fransson 1991).

Introduction

The dusty envelopes of late type stars are fascinating objects on their own; they are also interesting for what they teach us about IS chemistry. From their velocity field and density profile, we can study the mass loss during a crucial phase of stellar evolution: since the gas expands at nearly constant velocity in all, but the innermost envelope, the velocity maps yield a 3-D view of the molecule spatial distribution; the distributions of the different molecular species show how photochemical, molecule-molecule and grainsurface reactions proceed with time in a well behaved environment.

The closest massive envelopes lie a few hundred parsecs away and have small angular sizes. The construction of large millimeter-wave interferometers, in particular the IRAM Plateau de Bure interferometer (Guilloteau et al. 1992), has provided a major breakthrough in their investigation.

Molecular emission in IRC+10216

The most remarkable and probably closest massive envelope surrounds the bright IR object IRC+10216 (CW Leo). Its outer radius, observed in the mm lines of 12CO, the most abundant molecule and the best shielded from photodissociation after H2, is R = 3′ (Guélin & Cernicharo, in preparation).

Introduction

The LMC star S119 is a member of the group of Ofpe/WN9 stars listed by Bohannan and Walborn (1989). The Ofpe/WN9 category, first defined by Walborn (1982), identifies peculiar supergiants whose spectra combine the typical Of characteristic emission lines of He II and N III with equally strong lower ionization emission features, such as those of He I and N II, and are believed to represent a transition phase in the evolution between massive O stars and WR stars.

High Resolution Echelle Observations

We have observed S119 with the high resolution echelle spectrograph EMMI, coupled to the NTT, ESO La Silla, on September 18, 1991. The spectra cover the wavelength range 4100Å- 7800Å, with a spectral resolution of 0.089 Å/pixel at 6563 Å. The selected slit width was 1.5″ × 5″, with a plate scale on the detector of 0.345″/pixel. In the spectrum, previously undetected nebular lines of Hα, Hβ, [NII], [SII] appear strong and spatially extended, an indication that S119 is surrounded by a bright gaseous nebula. We detect clear splitting of all the observed nebular lines. In Figure 1 we show the radial velocity map obtained from the [NII] 6583 Å line profile. During the observation the slit was oriented EW, and the star was not centered in the aperture, so that only the eastern portion of the nebula lies completely within the slit, while the western region is marginally covered (≃ 2″).