Ejecta Of Core-collapse Supernovae Research Articles

A COOL DUST FACTORY IN THE CRAB NEBULA: AHERSCHELSTUDY OF THE FILAMENTS

Whether supernovae are major sources of dust in galaxies is a long-standing debate. We present infrared and submillimeter photometry and spectroscopy from the Herschel Space Observatory of the Crab Nebula between 51 and 670 micron as part of the Mass Loss from Evolved StarS program. We compare the emission detected with Herschel with multiwavelength data including millimeter, radio, mid-infrared and archive optical images. We carefully remove the synchrotron component using the Herschel and Planck fluxes measured in the same epoch. The contribution from line emission is removed using Herschel spectroscopy combined with Infrared Space Observatory archive data. Several forbidden lines of carbon, oxygen and nitrogen are detected where multiple velocity components are resolved, deduced to be from the nitrogen-depleted, carbon-rich ejecta. No spectral lines are detected in the SPIRE wavebands; in the PACS bands, the line contribution is 5% and 10% at 70 and 100 micron and negligible at 160 micron. After subtracting the synchrotron and line emission, the remaining far-infrared continuum can be fit with two dust components. Assuming standard interstellar silicates, the mass of the cooler component is 0.24(+0.32)(-0.08) Msolar for T = 28.1(+5.5)(-3.2)K. Amorphous carbon grains require 0.11 +/- 0.01 Msolar of dust with T = 33.8(+2.3)(-1.8) K. A single temperature modified-blackbody with 0.14Msolar and 0.08Msolar for silicate and carbon dust respectively, provides an adequate fit to the far- infrared region of the spectral energy distribution but is a poor fit at 24-500 micron. The Crab Nebula has condensed most of the relevant refractory elements into dust, suggesting the formation of dust in core-collapse supernova ejecta is efficient.

55Fe in Supernova 1987A

Observations of newly synthesized radioactive nuclei have provided a wealth of information about the extensively observed supernova 1987A. We add another such study, searching Chandra X-ray spectra of SN 1987A for evidence of 5.9 keV Mn Kα line emission due to the decay of radioactive 55Fe. This isotope is synthesized in explosive silicon burning and in normal freezeout of nuclear statistical equilibrium, mostly as 55Co, in the inner ejecta of core-collapse supernovae. The X-rays from the decay in these regions escape only after 10-20 yr of expansion, depending on the extent of mixing of core material outward in mass. Otherwise generally successful models of SN 1987A predict fluxes at 5.9 keV detectable by Chandra. However, in 400 ks of Chandra ACIS data, we find no evidence for this line emission, with the mean line flux ≤3 × 10-7 cm-2 s-1. We consider the implications for atomic mass A = 55 nucleosynthesis and for the kinematics and mixing of SN 1987A.

The influence of the explosion Mechanism on the Fe-group ejecta of core collapse supernovae

Core collapse supernovae are responsible for at least half of the galactic inventory of Fe-group elements and probably for most of the Fe-group abundances seen in metal poor stars. Recent simulations show the emergence of a proton-rich (Ye > 0.5) region in the innermost ejected mass zones due to the neutrino interaction with matter. We explore the nucleosynthesis implications of these findings that result in enhanced abundances of 45 Sc, 49 Ti, and 64 Zn, which

Carbon Monoxide in the Type Ic Supernova 2000ew

Abstract We present $K$-band (1.9–2.5$\,{\mu \mathrm {m}}$) spectra of the Type Ic SN 2000ew observed with IRCS on the Subaru Telescope. These data show the first detection of carbon monoxide (CO) emission in a Type Ic supernova. The detection of CO in SN 2000ew provides further evidence that molecule formation may be a common occurrence in core-collapse supernova ejecta. The spectrum also contains narrow emission lines of [Fe II] and He I probably from dense clumps of hydrogen-poor circumstellar gas surrounding SN 2000ew. Our spectrum of SN 2000ew shows no trace of an unidentified feature seen near 2.26$\,{\mu \mathrm {m}}$, just blueward of the CO emission, in the spectrum of SN 1987 A; we discuss proposed detections of this feature in other Type II supernovae.

The Chemical Composition of Halo Stars on Extreme Orbits

Presented within is a fine spectroscopic analysis of 11 metal-poor (-2.15 < [Fe/H] < -1.00) dwarf stars on orbits that penetrate the outermost regions of the Galactic halo. Abundances for a select group of light metals (Na, Mg, Si, Ca, and Ti), Fe-peak nuclides (Cr, Fe, and Ni), and neutron-capture elements (Y and Ba) were calculated using line strengths measured from high-resolution (R ? 48,000), high signal-to-noise ratio (S/N ? 110 pixel-1) echelle spectra acquired with the Keck I 10 m telescope and HIRES spectrograph. Ten of the stars have apogalactica, a proxy for stellar birthplace, which stretch between 25 and 90 kpc; however, these outer halo stars exhibit strikingly uniform abundances. The average, Fe-normalized abundances?[Mg/Fe] = +0.23 ? 0.09, [Si/Fe] = +0.24 ? 0.10, [Ca/Fe] = +0.22 ? 0.07, [Ti/Fe] = +0.20 ? 0.08, [Cr/Fe] = 0.02 ? 0.07, [Ni/Fe] = -0.09 ? 0.07, and [Ba/Fe] = +0.01 ? 0.12?exhibit little intrinsic scatter; moreover, the evolution of individual ratios (as a function of [Fe/H]) is generally consistent with the predictions of galactic chemical evolution models dominated by the ejecta of core-collapse supernovae. Only [Y/Fe] = -0.13 ? 0.21 exhibits a dispersion larger than observational uncertainties, which suggests a different nucleosynthesis site for this element. It has been conjectured that stars on high-energy orbits?either those that penetrate the remote halo or ones with extreme retrograde velocities?were once associated with a cannibalized satellite galaxy. Such stars, as shown here, are indistinguishable from metal-poor dwarfs of the inner Galactic halo. The uniformity of the abundances, regardless of kinematic properties, suggests that physically, spatially, and temporally distinct star-forming regions within (or near) the growing Milky Way experienced grossly similar chemical evolution histories. Implications for galaxy formation scenarios are discussed.

Zirconium and Molybdenum in Individual Circumstellar Graphite Grains: New Isotopic Data on the Nucleosynthesis of Heavy Elements

We have analyzed 32 individual graphite grains from the Murchison meteorite for their Mo and/or Zr isotopic compositions by resonant ionization mass spectrometry. Enormous isotopic anomalies were observed in some of these grains for both elements. The data for Zr revealed the largest isotopic anomalies, with 96Zr/94Zr ratios ranging from 0.074 times to 10 times the solar value. The isotopic data on Mo show one population of graphite grains with close-to-terrestrial Mo composition in all isotopes and five grains with an s-process nucleosynthesis signature, i.e., correlated depletions in the p- and r-process isotopes. For eight grains we were able to measure both Mo and Zr isotopic compositions. Three of these eight graphite grains have s-process isotopic characteristics for both Zr and Mo, which suggests low-mass, thermally pulsed asymptotic giant branch stars as their origin. Four grains are puzzling, since they have nearly normal Mo compositions but significant anomalies in Zr, in particular, large depletions or enhancements in the 96Zr/94Zr ratio. Two of these grains have extraordinary enrichments in 96Zr, with 96Zr/94Zr ratios 10.4 ± 1.3 and 2.5 ± 0.3 times the solar system value. These enrichments are suggestive of the r-process, implying that these grains condensed from the ejecta of core-collapse supernovae, but these enrichments could also be made by the s-process if the neutron density were unusually high.