Spectra Of Cas Research Articles

An asymmetrical model for high-energy radiation of Cassiopeia A

ABSTRACT The supernova remnant Cassiopeia A (Cas A) shows strong radiation from radio to gamma-ray bands. The mechanism of gamma-ray radiation in Cas A and its possible contribution to PeV cosmic rays are still under debate. The X-ray imaging reveals an asymmetric profile of Cas A, suggesting the existence of a jet-like structure. In this paper, we propose an asymmetrical model for Cas A, consisting of a fast moving jet-like structure and a slowly expanding isotropic shell. This model can account for the multiwavelength spectra of Cas A, especially for the power-law hard X-ray spectrum from ∼60 to 220 keV. The GeV to TeV emission from Cas A should be contributed by both hadronic and leptonic processes. Moreover, the jet-like structure may produce a gamma-ray flux of $\sim 10^{-13}\rm erg\, cm^{-2}\, s^{-1}$ at ∼100 TeV, to be examined by the Large High Altitude Air Shower Observatory (LHAASO) and the Cherenkov Telescope Array (CTA).

DIRECT CONFIRMATION OF THE ASYMMETRY OF THE CAS A SUPERNOVA WITH LIGHT ECHOES

We report the first detection of asymmetry in a supernova (SN) photosphere based on SN light echo (LE) spectra of Cas A from the different perspectives of dust concentrations on its LE ellipsoid. New LEs are reported based on difference images, and optical spectra of these LEs are analyzed and compared. After properly accounting for the effects of finite dust-filament extent and inclination, we find one field where the He I and H alpha features are blueshifted by an additional ~4000 km/s relative to other spectra and to the spectra of the Type IIb SN 1993J. That same direction does not show any shift relative to other Cas A LE spectra in the Ca II near-infrared triplet feature. We compare the perspectives of the Cas A LE dust concentrations with recent three-dimensional modeling of the SN remnant (SNR) and note that the location having the blueshifted He I and H alpha features is roughly in the direction of an Fe-rich outflow and in the opposite direction of the motion of the compact object at the center of the SNR. We conclude that Cas A was an intrinsically asymmetric SN. Future LE spectroscopy of this object, and of other historical SNe, will provide additional insight into the connection of explosion mechanism to SN to SNR, as well as give crucial observational evidence regarding how stars explode.

The Remarkable Be Star HD 110432 (BZ Crucis)

HD 110432 (B1e) has gained considerable recent attention because it is a hard, variable X-ray source with local absorption and also because its optical spectrum is affected by an extensive Be disk. From time-serial echelle data obtained over 2 weeks during 2005 January and February, we have discovered several remarkable characteristics in the star's optical spectrum. The line profiles show rapid variations on some nights, which can most likely be attributed to irregularly occurring and short-lived migrating subfeatures. Such features have been found in spectra of Cas and AB Dor, two stars for which it is believed magnetic fields force circumstellar clouds to corotate over the star's surface. The star's optical spectrum also exhibits a number of mainly Fe II and He I emission features with double-lobed profiles typical of an optically thin circumstellar disk viewed nearly edge-on. Using spectral synthesis techniques for the January data, we find that its temperature and column density are close to 9800 K and roughly 3 × 1022 cm-2, respectively. Its projected disk size covers remarkably large 100 stellar areas, and the emitting volume resides at a surprisingly large distance of 1 AU from the star. Surprisingly, we also find that the absorption wings of the strongest optical and UV lines in the spectrum extend to at least ±1000 km s-1, even though the rotational velocity is 300-400 km s-1. We are unable to find a satisfactory explanation for these extreme line broadenings. Otherwise, HD 110432 and Cas share similarly peculiar X-ray and optical characteristics. These include a high X-ray temperature, erratic X-ray variability on timescales of a few hours, optical metallic emission lines, and submigrating features in optical line profiles. Because of these similarities, we suggest that HD 110432 is a member of a select new class of γ Cas analogs.

Excitation-energy transfer in infrared -stimulable CaS doubly doped with Eu and Sm

The photoluminescence emission (PLE) mapping and infrared-stimulated luminescence (ISL) spectra of CaS:Eu,Sm demonstrated that Eu is formed in Eu2+ as a luminescent centre, whereas Sm is formed in Sm3+ as an electron-trapping centre by replacing Ca2+ in the CaS host lattice. It was found that electron trapping occurred in the photoluminescence excitation (PLX) process. A series of concentrations of Eu with a fixed Sm concentration and a series of concentrations of Sm with a fixed Eu concentration in doubly doped CaS:Eu,Sm were studied by the time-related PLE of Eu2+ in the PLX process. According to the electronic energy level(s) of Eu2+ and Sm3+, excitation-energy transfer is realized by translocation of excited electrons from Eu2+ to Sm3+, causing simultaneous ionization of Eu2+ (leaving Eu3+) and capture of excited electrons at Sm3+ (forming Sm2+). ISL is then produced due to the energy released from recombination of de-trapped electrons from the occupied electron-trapping sites (Sm2+) and the previously ionized luminescent centres (Eu3+) under infrared irradiation.

Deep traps in CaS:Eu and CaS:Ce phosphors

The photoluminescence, thermoluminescence, and excitation spectra of CaS:Eu and CaS:Ce phosphors containing various coactivators were measured. The spectra of deep trapping levels in these phosphors were studied for the first time. Optical information writing and storage effects were found in the UV range for both phosphors and in the visible range for CaS:Eu. The written optical information can be readout by IR irradiation.

WSRT HI synthesis absorption study towards Cassiopeia A

We present high resolution images of the entire galactic HI spectrum of Cas A and display the whole data cube in various ways; the spatial resolution is 30 arcsec and the velocity resolution is 0.62 km s-1. In previous studies, observations are described either with lower velocity resolution or with a limited velocity range (below -30 km s-1), Bieging et al. 1991; Reynoso et al. 1997. Here we concentrate the discussion on the local HI gas, with velocities between -10 and +10 km s-1. At a velocity of -1.5 km s-1 we find a cold HI feature with a kinetic temperature of typically 25 K, with a small region of 1 by 2 arcmin with a kinetic temperature below 10 K. This feature can be associated with a 13CO feature observed by Wilson et al. (1993). Based on the new HI absorption results we derive the ratio .

Optical Studies of CaS:Eu, Sm Infrared Stimulable Phosphors

The photoluminescence (PL) and infrared stimulated luminescence (ISL) spectra of CaS:Eu,Sm infrared stimulable phosphors (ISPs) are studied. In addition, the concentration dependence of ISL intensity is examined. Sm3+- and Eu2+-related structures are found in both the PL excitation and emission spectra. Two types of Sm3+ are found, one of which exhibits strong emission at around 650 nm and the other, weak emission compared to the other emissions at around 565 nm and 605 nm. These are assigned to an asymmetric and a symmetric site, respectively. ISL excitation spectra coincide with the Eu2+ 4f7 to 4f65d1 and 4f66s1 transitions and range from 220 to 650 nm. ISL emission spectra coincide with the Eu2+ 4f65d1 to 4f7 transition and range from 550 to 750 nm. ISL stimulation spectra range from 0.8 µm to 1.7 µm and are thought to indicate the Sm2+ ion transition from 4f6 to 4f55d1. The maximum ISL intensity is obtained from a sample with Eu and Sm concentrations of 500 and 130 ppm, respectively.

Electron structure and optical properties of the compound CaS

The zone structure of the compound CaS is calculated by the self-consistent linear combined plane-wave method. The calculation is performed for 89 points of the irreducible portion of the Brillouin zone. The tetrahedron method with quadratic interpolation is used to obtain optical spectra of CaS. Experimental optical spectra are interpreted. The calculations predict a significant degree of covalence in the chemical bond in CaS.

Physical processes and infrared emission from the Cassiopeia A supernova remnant

IRAS 12-100 micron data on the Cas A remnant are presented, and various physical mechanisms and astrophysical sites that may contribute to the observed infrared emission are analyzed. The contributions of various sources of infrared emission to the IRAS fluxes are found to be small. The residual infrared emission is attributed to thermal emission from dust which is swept up by the expanding supernova blast wave and collisionally heated by the postshock X-ray emitting gas. The calculations are consistent with a shock velocity of 1800 km/s and a preshock gas density of about 2/cu cm. The mass of the swept-up gas is about 0.6 solar mass. An excess of 12 micron thermal emission in the spectrum of Cas A suggests the presence of very small particles in the preshocked gas.

A study on the electroluminescence spectrum of CaS:Sm and CaS:Dy

A study on the electroluminescence spectrum of CaS:Sm and CaS:Dy

A study of the electroluminescence spectrum of CaS:Er phosphor and the energy level splitting in Er3+ions

The electroluminescence spectrum of CaS:Er phosphor is found to exhibit nine bands covering the ultraviolet, visible and near-infrared regions. The most intense bands, which occur at 530 and 550 nm, are split into as many as seven sharp lines. Calculations based on the theory of crystal-field splitting indicate that Er3+ ions can occupy the sulphur-ion vacancy position as well as the Ca2+ substitutional site.

The 26.13 MHz absorption line in the direction of Cassiopeia A.

It has recently been suggested1 that the absorption line v = 26.13 MHz that we had detected2 in the direction of Cassiopeia A might be a recombination line due either to carbon (C631α) present in H I clouds or to heavier elements of hot gas. Observations reported here taken in February 1981 suggest that the low-frequency attenuation in the spectrum of Cas A is due to the presence of a cold cloud of ionized carbon.

Abundance inhomogeneities in the Cassiopeia A supernova remnant

view Abstract Citations (163) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Abundance inhomogeneities in the Cassiopeia A supernova remnant. Chevalier, R. A. ; Kirshner, R. P. Abstract Quantitative spectral information has been obtained for several of the fast-moving knots in Cas A. It is found that the strengths of S II, Ar III, and Ca II forbidden lines are correlated with each other and this group of lines can vary by large factors relative to lines of oxygen. Sulfur, argon, and calcium are the products of oxygen burning, so a simple interpretation of the result is that different parts of the remnant come from portions of a stellar interior that have undergone different amounts of oxygen burning. The abundance ratios are uncorrelated with the kinematic properties of the knots. Minkowski's (1957) spectra of Cas A are examined, and it is confirmed that neon is present in one of the fast knots, although the location of the knot is not known. Publication: The Astrophysical Journal Pub Date: October 1979 DOI: 10.1086/157377 Bibcode: 1979ApJ...233..154C Keywords: Abundance; Astronomical Spectroscopy; Cassiopeia A; Nebulae; Supernova Remnants; Filaments; Inhomogeneity; Line Spectra; Neon; Spectral Line Width; Stellar Interiors; Astrophysics; Nucleosynthesis:Supernova Remnants; Supernova Remnants:Element Abundances full text sources ADS | data products SIMBAD (1)

Further studies of particle acceleration in Cassiopeia A

We have further investigated models for statistical particle acceleration in the supernova remnant Cas A. Simple (three-parameter) models involving continuous second order Fermi acceleration and variable relativistic particle injection can reproduce the observed radio properties of Cas A, including the low-frequency flux anomaly first noted by Erickson and Perley. Models dominated by adiabatic expansion losses are preferable to those dominated by particle escape. The gain time determined from these models agrees well with that predicted from the hydrodynamic situation in Cas A. A model predicting the high-frequency nonthermal spectrum of Cas A indicates that the spectrum turns down in the optical regime due to synchrotron losses. The maximum relativistic particle energy content of Cas A was probably about several times 10/sup 49/-10/sup 50/ ergs, which can be compared with an estimated initial kinetic energy in the range 0.24 to 1.0 x 10/sup 52/ ergs. If relativistic particles can escape from Cas A, their spectra will have certain characteristics: the electron spectrum will have a turnover due to synchrotron losses and the proton spectrum will have a cutoff due to the particle gyroradii becoming larger than the sizes of the magnetic scattering centers. The observed bend in the galactic cosmic raymore » spectrum could be due to energy losses within the source remnant itself instead of losses incurred during propagation through the Galaxy. We also comment on other models for the relativistic electron content of Cas A.« less

Anomalous OH absorption in the direction of Cassiopeia A

At radial velocities around zero, the optical depths in the 1665- and 1667-MHz OH absorption lines in the spectrum of Cas A are in the expected ratio, 5 : 9. In both lines, the zero-velocity component is split into two clearly-resolved features. However, neither the 1612- nor the 1720-MHz lines shows any splitting. Absorption in the 1612-MHz line is stronger than expected, while the 1720-MHz line shows evidence of emission.

Note: an Attempt to Measure the Galactic Magnetic Field.

An attempt to measure the galactic magnetic field by the Zeeman splitting of the 21-cm line is described. The observations were confined to the absorption lines in the spectra of Cas A and the Crab Nebula. (C.E.S.)