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Kirshner, R. P.

Publications and source records attributed to Kirshner, R. P..

36 records · Page 2
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NASA NTRS1982

The Crab Nebula. I - Spectrophotometry of the filaments

Relative line intensities in the 3700-7400 A region are obtained from new spectrophotometric measurements of ten positions in the Crab Nebula. O III forbidden line intensities imply electron temperatures of 11,000-18,300 K, while generally lower temperatures are indicated by the O II, N II and S II forbidden lines. The 6717 and 6731 A forbidden S II line ratio yields electron density estimates of 550-3500/cu cm, with a typical filament value of 1300 cu cm. While Balmer decrements are generally consistent with pure recombination, some filaments show steeper decrements. He line intensities are found to have significant variation. The presence of a moderately strong line at 7378 A, which may be due to the Ni II forbidden line is confirmed. Some filaments are found to exhibit a wide range of ionization states.

Fesen, R. A.↗
NASA NTRS1982

Supernovae, young remnants, and nucleosynthesis

Chemical abundance data from extragalactic supernovae and from supernova remnants (SNR) less than 1000 yrs old are employed to show that nuclear burning beyond helium synthesis actually occurs. Supernova (SN) are classified into types I or II, having no hydrogen lines or featuring hydrogen lines, respectively. The SN I's have been observed as having a preponderance of Fe lines, and emitting from a source at around 12,000 K with a center continuum of approximately 10 AU. Decay chains which could account for detected luminosities and spectra are presented, noting a good fit of Fe II spectrum with observed SN spectra. SNR pass through younger and older stages, going from the outpouring of material to diffusion in the interstellar medium. Expanding flocculi from young SNR show oxygen abundances as well as lines from sulfur, calcium, and argon, with a corresponding necessity of an explosive source of 15 solar masses.

Kirshner, R. P.↗
NASA NTRS1982

An optimist's guide to supernovae

There are some hints that a satisfactory agreement between observations and models is developing in several areas of supernova research. The light curves and spectra of Type I supernovae look so much like the models that they may well have their origin in the synthesis of Ni-56 in the explosion of a compact star. Type II supernovae are found where massive stars form, have light curves that correspond to 10 to the 51st ergs suddenly deposited inside a red supergiant, and may in fact be the explosions of massive stars. Some young supernova remnants, such as Cas A, show abundance patterns that bear a striking resemblance to those seen deep inside models of massive stars on the verge of destruction. Observations of old supernova remnants provide energy estimate of 10 to the 51st ergs - just the amount needed for the models of the outbursts.

Kirshner, R. P.↗
NASA NTRS1982

Optical spectrophotometry of the Cygnus Loop

Cygnus Loop filament optical spectral properties are discussed, with emphasis on comparisons between observational and model data. Some line intensities are correlated among filaments in such a way as to suggest that a well resolved ionization structure behind the shock front is being observed. Departures from the steady flow condition assumed in the present model are found to be necessary in order to improve agreement with observations.

Fesen, R. A.↗
NASA NTRS1980

The discovery of optical emission from the SNR G 126.2 + 1.6

Interference filter photographs were used to identify an arc of nebulosity that is coincident with the radio contours of the galactic supernova remnant G 126.2 + 1.6. Spectrophotometry of the filament shows that the emission line spectrum matches the spectra of other galactic supernova remnants. In particular, the arc shows the usual strong SII, and NII emission lines seen in other remnants and unusually strong OII emission as seen in a few remnants. The spectrum can be adequately matched by a shock of velocity near 100 km/s in an interstellar cloud of density 3. If the SNR is at a distance of 4.5 kpc as indicated by the radio signal-D relation, then the observed pressure in the filament requires an initial energy near 4 x 10 to the 51st power (d/4.5 kpc) to the 3rd power ergs.

Blair, W. P.↗
NASA NTRS1979

A search for stellar remnants of supernovae

The slitless spectra of the stars in the central regions of six galactic supernova remnants Cas A, Kepler, Tycho, SN 1006, RCW 86, and the Cygnus Loop were obtained with the prime focus transmission gratings at the 4M telescopes on Kitt Peak and Cerro Tololo. It was found that no stellar remnant with an unusually blue or peculiar spectrum is present in any of the remnants down to the limit of m sub pg of 18.5. Except for the Cygnus Loop, the area searched in each remnant is large enough that objects with transverse velocities of 1000 km/s would be well within the field. The results are also compared with a computation of emission from gas near a neutron star and with the unpulsed emission from the Crab pulsar; in both cases upper limits were set which place constraints on a possible condensed stellar remnant.

Fesen, R. A.↗
NASA NTRS1977

Radial distribution of Fe XIV emission in the Cygnus Loop

The one dimensional distribution of Fe 14 emission has been determined along a radius of the Cygnus Loop through the use of a tilting filter photometer. The observed emission extends at least 5 arc minutes outside the optical filaments. A simple Sedov solution model of the temperature and density distribution behind the shock agrees with the observations if the shock front is near the extent of the Fe 14 emission, the shock velocity is from 300 to 250/kms and the density external to the remnant is about 0.7-1.4 cm to three minus 3 power. These parameters are in reasonable agreement with X-ray maps and optical radial velocities.

Woodgate, B. E.↗
NASA NTRS1977

A new optical supernova remnant in Cygnus

The letter reports the discovery of a filamentary emission-line structure at right ascension 19 hr 31 min and declination +31 deg 10 min (1950) during an emission-line survey of the Milky Way. This structure is classified as a supernova remnant on the basis of its similarity to several other SNRs, but is shown not to be part of the Gamma Cygni complex. A physical diameter of about 70 pc is obtained for this SNR along with a distance of approximately 1200 pc, a shock velocity of at least 50 km/s, an initial density of about 0.5 per cu cm, and an age of approximately 300,000 yr.

Gull, T. R.↗
NASA NTRS1975

Supernova 1972e in NGC 5253

Absolute energy distributions of the Type I supernova 1972e in NGC 5253 extending to about 700 days after maximum light have been obtained. A physical model of the expanding envelope, based on the identification of the feature at 6550 A with H-alpha is proposed. It consists of a differentially expanding atmosphere, with electron density ranging from 10 billion near maximum light to about 10 million 340 days later, illuminated by a photosphere with temperature in the range from 10,000 K to 7000 K. Under these conditions, the identifications of Ca II 8600-A, H, and K lines, the Na D lines, and the Mg I b lines forming P Cygni lines are quite plausible. More than 200 days after maximum, the spectrum is dominated by four features between 4200 and 5500 A. Three of these four features match the blended emissions from over 100 Fe II forbidden lines. If this identification is correct, the envelope requires about 0.01 solar mass of iron, which corresponds to an Fe/H ratio about 20 times higher than the cosmic abundance. Possible identifications of the fourth feature with the Mg I 4571-A line or permitted lines of Fe II are also discussed.

Kirshner, R. P.↗
NASA NTRS1975

Supernova 1972 e in NGC 5253

New absolute energy distributions of the Type 1 supernova 1972e in NGC 5253 extending to about 700 days after maximum light were obtained. A physical model of the expanding envelope, based on the identification of the feature at 6550 A with H-alpha, is proposed. It is described as a differentially expanding atmosphere, with electron density ranging from 10 to the 10th power near maximum light to about 10 to the 7th power, 340 days later, illuminated by a photosphere with temperature in the range 10,000 K to 7,000 K. More than 200 days after maximum, the spectrum was dominated by four features between 4200 A and 5500 A. Three of these four features matched the blended emissions from over 100 lines of Fe II. Possible identifications of the fourth feature with Mg I lambda 4571 or permitted lines of Fe II are also discussed.

Kirshner, R. P.↗
NASA NTRS1974

Spectrophotometry of supernovae

Studies were made of a type II supernova (SN 1970g in M 101) and a type I supernova (SN 1972e in NGC 5253) covering the wavelength range from 3200 to 10,000 A. The absolute spectral energy distributions show that both types have a continuum that varies slowly and uniformly with time and carries the bulk of the radiated flux at early epochs. Some lines in both types have P Cygni profiles: broad emissions with broad absorptions at their violet edges. Some lines are common to both types and persist throughout the evolution of the spectrum.

Kirshner, R. P.↗
NASA NTRS1973

The spectra of supernovae.

Progress report on a continuing program of investigation into the nature of the spectra of supernovae. A description of these spectra is presented that is more quantitative and covers a wider wavelength range than heretofore published descriptions. Some preliminary conclusions are suggested in the light of the new data presented.

Kirshner, R. P.↗
NASA NTRS1971

Extreme-ultraviolet observations of a surge.

Observation of a flare surge at the limb in C III 977 A by the Harvard OSO 6 spectroheliometer. The kinematic behavior of the surge is the same in C III and in H alpha. The amount of C III emission is consistent with a model in which the C III ions occupy sheaths with a thickness of about 100 km surrounding the cooler H alpha-emitting threads. The mass of the material containing C III ions is about 0.01 times that emitting H alpha.

Kirshner, R. P.↗