Supernova Remnants In M82 Research Articles

An atlas of confirmed and candidate supernova remnants in M33

Thirty emission nebulae in M33 have been discovered which, on the basis of strong forbidden S II compared with H-alpha, are almost certainly supernova remnants. The total number of known supernova remnants in M33 is now about 50. The cumulative number versus diameter relationship for the nebulae in the sample appears to show evidence of shock deceleration. The number of supernova remnants in M33 is consistent with a supernova rate of one per 26-300 yr. The observations are described and positions, diameters, line ratios, and images of the new candidates are presented, as well as 10 previously known and two suggested supernova remnants in M33 that were in the survey region. 57 refs.

Long Slit Echelle Spectroscopy of Supernova Remnants in M33

AbstractWe have obtained long slit echelle spectroscopy for 10 of the brightest supernova remnants in M33 using the KPNO 4 m telescope. The profiles at Hα indicate bulk motions in the range 100–350 km s−1 in these remnants. Nearly all of the objects show signs of contamination by low velocity H II emission at some level. This affects the line intensities measured from low resolution data and may affect diameter measurements of these remnants.

New Supernova Remnants in M33

AbstractExisting catalogues of supernova remnants (SNRs) in external galaxies are very incomplete. Potentially however, such samples are of great importance in understanding SNRs, since the distances to objects in a given sample are essentially the same and since absorption is small (compared to galactic SNRs). We have recently obtained Hα+[NII], Hβ, [SII], [OIII], and 6100 Å continuum CCD images of nine selected areas in M33 using the KPNO 4m. In addition to the six SNRs already known to exist in the fields we have surveyed, we have identified 21 other nebulae with [SII]:Hα+[NII] ratios which may be SNRs. Spectra of seven of these nebulae were obtained subsequently and show that the majority are indeed SNRs. A more detailed analysis of regions containing significant HII region contamination and a search for very small diameter remnants is currently underway.

A radio search for Crab-like nebulae in M33

The results of a search for Crablike supernova remnants in M33 using the VLA and spectral indices and center-brightened morphology as discriminants are reported. The observations show that seven of the 12 are unresolved with a 0.3 arcsec beam. Of the five resolved sources, three have morphologies typical of background radio galaxies, and one may be a shell supernova remnant in M33. However, one 'source' is shown at high resolution to be composed of a complex of sources, mostly steep-spectrum, but containing one unresolved component with a flux at both frequencies of about 0.5 mJy. While this could be a Crablike remnant with a very flat spectrum, its properties are also consistent with those of a normal compact H II region. None of the other 11 objects fits the observational definition of a Crablike remnant. Thus M33 joins M31 and the Galaxy in exhibiting far fewer Crablike remnants than theory would predict.

Improved optical spectrophotometry of supernova remnants in M33

Optical spectra of SNRs in M33 have been used to investigate abundance gradients and SNR evolution in this galaxy. Abundances of O, N, and S are derived from the spectra using new shock models by Dopita et al. (1984). The results for N and S show abundance gradients similar to those in NGC 300 and the Galaxy. The O abundances may be affected by possible contamination from H II regions and low-velocity shocks. Electron densities derived from the forbidden S II 6717 A/6731 A line ratio are used with a pressure equilibrium argument to estimate the initial explosion energy for each SNR. Evolutionary models for the remnants are investigated, and the distribution of the number of remnants with diameter is found to be consistent with free expansion of the SNRs to diameters of about 26 pc. The results may also be consistent with Sedov evolution if the ranges of initial supernova energies and surrounding interstellar medium densities are large enough.

Radio observations of three supernova remnants in M33

Radio observations of three supernova remnants in M33

Spectra of supernova remnants in M33

Spectra of supernova remnants in M33