An asymptotic solution of conical shells of constant thickness Progress report no. 6

Asymptotic solution of thin walled conical shell of revolution under lateral stres

VLT observations of the highly ionized nebula around Brey2

We present the first high resolution HeII 4686 images of the high excitation nebula around the WR star Brey 2 in the LMC. This nebula presents a striking morphology: a small arc-like feature some 3.6pc in radius is particularly prominent in the HeII 4686 line. We further discover a previously unknown faint HeII emission that extends over an area of 22*17 pc^2. An even fainter HeII emission is apparently associated with the interstellar bubble blown by the progenitor of Brey2. The total HeII flux corresponds to an ionizing flux of 4*10^{47} photons/s. Halpha, [OIII], and HeI 5876 images and long-slit spectra are also examined in this letter, enabling us to investigate the detailed physical properties at various locations of the nebula.Comment: 4 pages, 3 figures (2 in jpg), accepted by A&A Letters, also available from http://vela.astro.ulg.ac.be/Preprints/P80/index.htm

Circumstellar Nebulae in Young Supernova Remnants

Supernovae descendent from massive stars explode in media that have been modified by their progenitors' mass loss and UV radiation. The supernova ejecta will first interact with the circumstellar material shed by the progenitors at late evolutionary stages, and then interact with the interstellar material. Circumstellar nebulae in supernova remnants can be diagnosed by their small expansion velocities and high [N II]/H$\alpha$ ratios. The presence of circumstellar nebulae appears ubiquitous among known young supernova remnants. These nebulae can be compared to those around evolved massive stars to assess the nature of their supernova progenitors. Three types of archeological artifacts of supernova progenitors have been observed in supernovae and/or young supernova remnants: (1) deathbed ejecta, (2) circumstellar nebulae, and (3) interstellar bubbles. Examples of these three types are given.Comment: 9 pages, 5 figures, proceedings of the 11th October Astrophysics conference in Maryland, "Young Supernova Remnants", eds. Holt and Hwan

A Critical Examination of Hypernova Remnant Candidates in M101. II. NGC 5471B

NGC 5471B has been suggested to contain a hypernova remnant because of its extraordinarily bright X-ray emission. To assess its true nature, we have obtained high-resolution images in continuum bands and nebular lines with the Hubble Space Telescope, and high-dispersion long-slit spectra with the Kitt Peak National Observatory 4-m echelle spectrograph. The images reveal three supernova remnant (SNR) candidates in the giant HII region NGC 5471, with the brightest one being the 77x60 pc shell in NGC 5471B. The Ha velocity profile of NGC 5471B can be decomposed into a narrow component (FWHM = 41 km/s) from the background HII region and a broad component (FWHM = 148 km/s) from the SNR shell. Using the brightness ratio of the broad to narrow components and the Ha flux measured from the WFPC2 Ha image, we derive an Ha luminosity of (1.4+-0.1)x10^39 ergs/s for the SNR shell. The [SII]6716,6731 doublet ratio of the broad velocity component is used to derive an electron density of ~700 cm^-3 in the SNR shell. The mass of the SNR shell is thus 4600+-500 Mo. With a \~330 km/s expansion velocity implied by the extreme velocity extent of the broad component, the kinetic energy of the SNR shell is determined to be 5x10^51 ergs. This requires an explosion energy greater than 10^52 ergs, which can be provided by one hypernova or multiple supernovae. Comparing to SNRs in nearby active star formation regions, the SNR shell in NGC 5471B appears truly unique and energetic. We conclude that the optical observations support the existence of a hypernova remnant in NGC 5471B.Comment: 27 pages, 9 figures, to appear in May 2002 issue of The Astronomical Journa