The IUE observations of SN 1987A are presented and the most important results are briefly summarised. The photometric observations of SN 1987A are discussed in some detail in the context of the supernova energetics. Adding the information from spectroscopy and neutrino observations, it is concluded that SN 1987A is a ‘normal’ Type II explosion (i.e. core collapse of a massive star) with an unusually compact initial configuration, just as expected for the progenitor Sk −69°202.

Based on the database of 56 supernovae (SNe) events discovered in 3838 galaxies of the southern hemisphere, we compute the rate of SNe of different types along the Hubble sequence normalized to the optical and near-infrared (NIR) luminosities as well as to the stellar mass of the galaxies. We find that the rates of Type Ia SNe show a dependence on both morphology and colors of the galaxies, and therefore, on the star-formation activity. The rate of SNe Ia can be explained by assuming that at least 15% of Ia events in spiral galaxies originate in relatively young stellar populations. We also find that the rates show no modulation with nuclear activity or environment.

We present the results of over two decades of radio observations of type IIb Supernovae with the Very Large Array and the Australia Telescope Compact Array. These radio studies illustrate the need for multi-wavelength follow-up to determine the progenitor scenario for type IIb events.

We search for massive and evolved galaxies at z ≥ 5 in the Great Observatories Origins Deep Survey (GOODS) southern field. Combining HST ACS, VLT ISAAC and Spitzer IRAC broad–band photometric data, we develop a color selection technique to identify candidates for being evolved galaxies at high redshifts. The color selection is primarily based on locating the Balmer–break using the K- and 3.6 μm bands. Stellar population synthesis models are fitted to the SEDs of these galaxies to identify the final sample. We find 11 candidates with photometric redshifts in the range 4.9 < z < 5.6, dominated by an old stellar population, with ages 0.2-1.0 Gyr, and stellar masses in the range (0.7 − 5) × 1011 M⊙. Most of the candidates have modest amounts of internal dust extinction. The majority of the stars in these galaxies were formed at z>9 and the current star formation activity is a few percent of the inferred initial star formation rate.

The high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd.

An analysis of type Ia supernova (SNIa) events in early type galaxies from the Cappellaro et al. [6] database provides strong evidence that the rate of type Ia supernovae (SNe) in radio-loud galaxies is about 4 times higher than the rate measured in radio-quiet galaxies, i.e. SNIa-rate(radio-loud) SNe per century and per 1010 (SNU) as compared to SNIa-rate(radio-quiet)= 0.11 ± 0.03 SNU. The exact value of the enhancement is still rather uncertain, but is likely to be in the range ~ 2 – 7. We discuss the possible causes of this result and we conclude that the enhancement of the SNIa explosion rate in radio-loud galaxies has the same common origin as their being strong radio sources, but that there is no causality link between the two phenomena. We argue that repeated episodes of interaction and/or mergers of early type galaxies with dwarf companions are responsible for inducing both strong radio activity in ~14% of early type galaxies, and the ~ 1 Gyr old stellar population needed to supply an adequate number SNIa progenitors.

The study of supernovae (SNe) and their environments in host galaxies at the highest possible angular resolution in a number of wavelength regimes is providing vital clues to the nature of their progenitor stars. We are observing SNe in the radio using the Very Large Array (VLA) and VLBI, in the X-rays with Chandra, and in the optical at the subarcsecond resolution of HST.

The radio emission from supernovae provides a direct probe of a supernova’s circumstellar environment, which presumably was established by mass-loss episodes in the late stages of the progenitor’s presupernova evolution. The observed synchrotron emission is generated by the SN shock interacting with the relatively high-density circumstellar medium which has been fully ionized and heated by the initial UV/X-ray flash. The study of radio supernovae therefore provides many clues to and constraints on stellar evolution. We will present the recent results on several cases, including SN 1980K, whose recent abrupt decline provides us with a stringent constraint on the progenitor’s initial mass; SN 1993J, for which the profile of the wind matter supports the picture of the progenitor’s evolution in an interacting binary system; and SN 1979C, where a clear change in presupernova mass-loss rate occurred about 104 years before explosion. Other examples, such as SNe 19941 and 1996cb, will also be discussed.

We report sub-arcsecond narrow band imaging in the lines of H2 2.1218 μm, Brγ 2.16 μm, [Fe II] 1.664 μm of the Planetary Nebulae NGC 7027. Data were obtained at the 3.5 m telescope at Calar Alto Observatory (Spain), using MAGIC. A false color image was produced by combining these three narrow band images. Thus, and due to extraordinary seeing (0″.6 arcsecond) conditions, allow us to reveal the morphology of the excited molecular and ionized gas. The Brγ and the [Fe II] images allowed us to study the structure of the ionized gas at slightly different excitation levels, according to the ionization potentials of the ions involved in the corresponding transitions (13.6 eV to ionize hydrogen, versus 17.4 eV for iron ionizaton). Since NGC 7027 is a high excitation nebula, the iron is readily double– ionized in the hotter regions, thus what we really see in the [Fe II] image is the low–intermediate excitation zones. By studying the [Fe II] and Brγ images together we infer that: the (non–reddened) low–ionization gas morphology consists of a regular, smooth ring reminder of a projected cylindrical structure. In addition to a brightness level that is at least thirty times the brightness of the maximum [Fe II] emission, the ionized hydrogen image exhibit a strong brightness gradient between the mentioned ring and the outer regions, and the emission is comparatively negligible outside the ring–like feature of about 12 × 10 arcsec (the measures refer to the major and minor axes of the ellipse–like shape). The [Fe II] morphology is less so ring–like and regular, and it seems to indicate smaller scale structure, such as clumps and filaments, at the resolution scale–level. The dishomogeneity in the [Fe II] emission could be ascribed to gradients in the elemental distribution, as well (and more probably so) as to the plasma temperature and density inhomogeneities. The H2 molecular image completely embeds the ionized gas zones, up to a size of about 16 × 11 arcsec. The smaller size refers here to the waist of the markedly bipolar shape, similar to a projected peanut; the larger size is the dimension of the two main lobes. The highest brightness through the molecular filters corresponds to the inner ring, slightly less extended than the ionized one, and to an outer envelope that is not seen in the ionized gas, and has a maximum diagonal extension of about 24 arcsec. Spatially resolved low resolution spectra (R 200) were obtained in the H and K band.

Observations with the Wide Field Camera on HST were examined, and 27 Cepheids were discovered. Photometry and period analysis have produced unambiguous light curves free of alias. The observed P-L relation has a slope consistent with seminal calibration studies of Galactic and LMC Cepheids. An apparent distance modulus (in V) of 28.47 ± 0.10 to IC 4182 is derived. This implies that Mv(max) for SNIa 1937C is -19.92 ± 0.2 mag, independent of everything except differential absorption between the Cepheids and the supernova. Using this to calibrate Hubble diagrams for SNIa by several authors, and allowing for a 1-σ uncertainty in the absolute magnitude from the calibration of only one SNIa, we obtain H0 = 45 ± 14kms-1Mpc-1.

We present and discuss the first images of SN 1987A obtained on day 1278 with the FOC on board the Hubble Space Telescope. The supernova is well detected and resolved spatially in the four observed bands. The UV luminosity of SN 1987A is found to be comparable to that emitted in the visible and infrared spectrum. Narrow-band [OUI] imaging reveals that the circumstellar nebula surrounding SN 1987A has the shape of a perfectly elliptical ring, implying an inclination of 43° ±3°. A comparison of the ring angular size with its absolute size derived from an analysis of the light curves of narrow UV lines measured with IUE, gives an accurate determination of the distance to SN 1987A, i.e. d(1987A) = 51.2±3.1 kpc. Allowing for the relative position of SN 1987A within the LMC, the distance to the center of the LMC turns out to be 50.1 ± 3.1 kpc. This value agrees very well with the determinations obtained from light curve analyses of variable stars.

Three supernovae have so far been detected in the radio range shortly after their optical outbursts. All are Type IIs. A fourth supernova, a Type I, is being monitored for radio emission but, at an age of approximately one year, has not yet been detected. For two of the supernovae, extensive data are presented on their “light curves” and spectra and models which have been suggested in the literature are discussed.

From consideration of the observed properties of the envelopes produced by mass loss in WR stars we find that:

1. a) The velocity at the optical photosphere is in the range 200–800 km s

2. b) The effective photospheric radius for the continuous radiation capable to ionize helium twice (γ < 228 A) is typically 5 to 15 times the optical photospheric radius.

3. c) The radiation temperature in the Lyman continuum (γ < 912 Å) is around 5 × 104K. Therefore, most of the stellar radiation is emitted in the far UV and the total luminosity is considerably higher than currently estimated.

4. d) Multiple scattering (N ≃ 20) of radiation in the interval 228–504 Å can provide most of the momentum needed to accelerate the wind up to the observed terminal velocities.

We report here on preliminary infrared photometry of six WN stars in the Large Magellanic Cloud. Besides R136, the central object of the 30 Doradus Nebula, the sample includes three stars (R139, R140, R145) located near the center of the region (within ∼ 1 arcmin) and two more stars (R144, R147) at a distance of ∼ 5 arcmin from R136.

In this paper we report briefly on a study of the mass loss of early type stars in the infrared. Up to now near infrared (1.25 - 4.8 μ ) broad band photometry of 70 southern OB stars of various luminosity class has been secured. Program stars have been selected, among those bright enough in the infrared to give a suitable photometric accuracy, in order to cover a wide range of spectral types (Fig. 1).

37 stars are found to exhibit emission in excess over a blackbody photospheric continuum, which is interpreted in terms of gas ejected in the form of an accelerated wind. By means of model calculations the corresponding mass loss rates are derived. The obtained values compare well with those determined indipendently by various Authors for stars in common. Our data show that mass loss rates increase with luminosity and are a decreasing function of surface gravity.

Eight O-type giants and supergiants, selected for being relatively isolated in the sky, have been observed at 5 GHz with 17 antennae of the partially completed VLA (NRAO, Socorro, New Mexico: The National Radio Astronomy Observatory is operated by Associated Universities under contract with the National Science Foundation) on October 7 and 8, 1979. The integration times ranged between 38 and 187 minutes. The results are displayed in Table 1. Most of the stars (6 out of 8) were not detected. The upper limits given in Table 1 for these stars correspond to the 3σ noise level. Possible detection has been achieved for the two supergiants HD 225160 and HD 30614 both with a flux density of 0.15 mJy. Although this flux is equal to the 3a noise level, the detections can be considered to be real because 1) Excellent positional coincidence is found between stars and the radio peaks (better than 1”) 2) The observed source pattern corresponds very well to the expected response to a point-like source.

Plerions, i.e. supernova remnants resembling the Crab Nebula, are characterized at radio wavelengths by having: 1) a centrally peaked brightness distribution, 2) flat radio spectrum (α > −0.3, Sν να), 3) high linear polarization, and 4) a highly ordered magnetic field. At higher frequencies (1011–1013 Hz depending upon the age) the spectrum turns over and attains a slope of α ~ −1. In particular, for the Crab Nebula the turnover frequency occurs at νc ~ 3×1012 Hz (cf. Fig. 1). Moreover, the optical spectrum displays a slope of −0.9 and the radiation is linearly polarized. Nonthermal emission is also detected in the X-ray and γ-ray domains (Fig.1). Similar spectral characteristics are found for other bona fide plerions. As discussed by Weiler and Panagia (1980), the plerion phenomenon is determined by the presence of a highly energetic and active central object (a fast spinning neutron star) which is able to both accelerate and inject continuously relativistic electrons into the remnant with a typically flat energy distribution roughly proportional to E−1.

The galactic luminosity for 0.1 < Eγ < 2 GeV can be evaluated directly from observational data and the commonly accepted value is 5 1038 erg s−1. Various contributions to the γ-ray emission can be recognized, namely i) strong sources, ii) pulsars, and iii) diffuse processes. Their relative importance is discussed in the following.

The processes of radiative acceleration of stellar winds in OB stars by single and multiple photon scattering are considered. Single scattering can be the dominant accelerating process for stars later than B2 (Teff < 2 x 104 K) and can account for terminal velocities up to 500 – 1000 km s-1 . Multiple scattering of photons in the approximate range 200 – 500 A provides additional wind acceleration for stars earlier than B2 to reach terminal velocities of up to 2000 – 4000 km s-1 A systematic increase of the terminal velocity as a function of the effective temperature is predicted. Observational data confirm this expectation quite well.