Shell Spectra Research Articles

Omicron Andromedae Photometry, Polarimetry, and a Tentative Model of the Light Variability

Basic information about the star o and (HR 8762, HD 217675-6) is a bright (V=3.55m, B-V=-0.11m U-B=-0.50m) B6 III-Ve star. Its emission-line and shell spectrum is known to come and go on a time scale of years. In fact, the presence of a strong shell spectrum misled the authors of the HD catalogue to assign the star two HD numbers.o and is a prototype of Be rapid light variables in the sense that it has the longest record of photoelectric monitoring which goes back to 1915! The long history of attempts to understand the variations of this star has recently been summarized by Harmanec (1983). Collecting and analyzing all historical photoelectric observations, Harmanec (1984) concluded that the light variations of o And can be understood as a superposition of a long-term cyclic (8.5y) variation with an amplitude over 0.1m (the star being faintest at the recorded shell maxima) and a rapid periodic variation with a period of 1.571272 days.

Electron correlation effects in the valence shell photoelectron spectra of haloethenes

Calculations have show that ionization from the inner valence shells of haloethenes cannot be treated on a one-electron basis and that photoelectron spectra should show additional bands corresponding to final ionized states of mixed character. The spectra of a range of haloethenes have been recorded using synchrotron radiation with photon energies of up to 75 eV and the inner valence shell spectra have been shown to be in good agreement with predictions. The measurements have also been used to extend existing photoelectron assignments providing complete valence shell assignments for the molecules studied.

CH CYGNI IN 1983-1984 : TRANSITION TO A REAL SYMBIOTIC STAR ?

ABSTRACT The authors report the end of the shell spectrum phase of CH Cyg and its transformation into a symbiotic star. A Reticon spectrum of moderate dispersion showing forbidden and permitted emission lines as well as strong absorption by Ca I and Al I is displayed. The absence of Sr II absorption in the shell during prior years may be explained by ionization from the first excited state by Lα photons. Sr II absorption gradually reappeared in 1983 - 84.

Extraction of the Shell Spectrum of Epsilon Aurigae

AbstractA sample of high-dispersion optical spectrograms of ε Aur,taken on different epochs before and during eclipse, has been processed by computer in order to extract the shell spectrum, produced by the eclipsing body. Using an uneclipsed spectrum as reference, the primary’s dominant contribution was removed, and this makes it possible for the first time to study the secondary body spectrum separately at all eclipse phases. As the first striking result, one finds that the internal regions of the extended eclipsing body are hotter than the outer zones.

CARBON AND OXYGEN K-SHELL EXAFS OF GASES STUDIED BY ELECTRON ENERGY LOSS SPECTROSCOPY

EXAFS in the soft X-ray range from intramolecular, low Z backscattering has been investigated in the inner shell spectra of gaseous CO, CO2, CF4, c-C6H12, C6H6 and C6F6, recorded by inelastic electron scattering in the dipole regime. The 01s continua of CO and CO2 do not exhibit the oscillations recently reported by Yang et al (Phys. Lett A110 (1985) 301). The Cls spectrum of CF4 contains extended continuum features similar to those reported previously. The Cls continua of c-C6H12, C6H6 and C6F6 exhibit weak extended continuum features which appear to be EXAFS although the analysis procedures used so far are not able to reproducibly extract accurate bond lengths.

Two-dimensional space-resolved soft x-ray spectroscopy of hot dense plasmas

Two-dimensional spatially resolved K shell spectra from hot (Te≂40–400 eV), dense (ne≂1019–1021 cm−3) aluminum plasmas have been recorded using a convex curved KAP crystal spectrograph in a dispersion mapping mode with an orthogonal imaging slit. The approximately 1-cm-diameter, 2-cm-long cylindrical source was viewed on end, yielding axially and temporally integrated spectra. The relative intensities of the lines and recombination continua were used to estimate local temperatures and densities. The measurement technique is reviewed and representative analysis and results are presented in this paper.

Two-dimensional space-resolved soft x-ray spectroscopy of hot dense plasmas (abstract)

Two-dimensional spatially resolved K shell spectra from hot (Te≂40–400 eV) dense (ne≂1019–1021 cm−3) aluminum plasmas have been recorded using a convex curved KAP crystal spectrograph in a dispersion mapping mode1 with an orthogonal imaging slit. The approximately 1-cm-diameter, 2-cm-long cylindrical source was viewed on end, yielding axially and temporally integrated spectra. The relative intensities of the lines and recombination continua were used to estimate local temperatures and densities. The measurement technique is reviewed and representative analysis and results presented in this paper.

High resolution carbon 1 s and valence shell electronic excitation spectra of trans-1,3-butadiene and allene studied by electron energy loss spectroscopy

The high resolution inner shell electron energy loss spectra of trans-1,3-butadiene and alllene are presented. Also reported are the wide range (5–25 eV) valence shell electron energy loss spectra of these molecules. The inner shell spectra show intense C 1 s→ * transitions well below the Rydberg structure. Transitions to both π * levels in trans-1,3 butadiene are clearly identified. Both molecules show significant structures above the C Is edges which are attributed to σ * shape-resonances as well as double excitations and “shake-up”. Comparisons are made between the inner shell and valence shell spectra. The transitions identified in the inner shell spectra of butadiene and allene help clarify the assignments of the valence shell spectra because of the essential transferability of Rydberg term values. The assignments of the valence shell spectrum of allene are, in turn, helpful in assessing the great variety of published theoretical investigations of this spectrum. In particular, earlier predictions of the π→π * transition in allene at 7.2eV are supported, in disagreement with a more recent calculation.

Electron energy loss spectra of the silicon 2 p, 2 s, carbon 1 s and valence shells of tetramethylsilane

Inner shell excitation spectra of tetramethylsilane, (CH 3) 4Si, have been measured in the silicon 2 s, 2 p ( L I,II,III-shell) and carbon is ( K-shell) regions using electron energy-loss spectroscopy at an impact energy of 2.5 keV and a scattering angle of ~1°. The high-resolution valence shell spectrum has also been observed at an impact energy of 3 keV and a zero degree scattering angle. The silicon 2 p spectra are compared and contrasted with published photoabsorption spectra of SiF 4, SiH 4, and other related Si-containing molecules with varying ligands.

Influence of Lyman-series fine-structure opacity on theK-shell spectrum and level populations of low-to-medium-Zplasmas

As laboratory plasmas of increasing atomic number, temperature, size, and/or density are produced, it becomes likely that the details of the doublet opacity profiles of the Lyman series will influence the $K$-shell level populations and spectrum. Accordingly, we have analyzed these effects for a range of plasma parameters, confined to densities low enough for Stark broadening to be unimportant. An analytic model is developed which predicts line power enhancements and level-population changes for $K$-shell plasmas. This model is based upon photon escape probability and collisional quenching concepts and is valid for plasmas of atomic number \ensuremath{\sim}13-26. Additionally, an extensive set of numerical calculations of line ratios, line profiles, and level populations has been carried out for $K$-shell argon plasmas. Each computation was performed both with detailed fine-structure opacity profiles and with a single-Voigt-profile approximation. The results of these calculations may be scaled for plasmas of atomic number other than 18 using a simple set of rules discussed in the text.

Shell spectrum of CH Cyg at the brightening of the star at the end of 1981

When CH Cyg brightned at the end of 1981, it had a well-developed shell spectrum. The shell of the star has been investigated on the basis of two spectrograms with reciprocal dispersion 4.2 A/mm. It is shown that the shell lines are formed around the hot component of CH Cyg. An ionization temperature of 10,000 K, an electron density of 10 to the 12th/cu cm, and a dilution coefficient of W 0.1 - 0.001 were determined by the curve-of-growth method. It is concluded that the physical conditions in the accreting shell are close to the conditions in the atmospheres of very bright supergiants. 20 references.

Inner shell excitation, valence excitation and core ionization in NF 3 studied by electron energy-loss and X-ray photoelectron spectroscopies

Electron energy-loss Spectroscopy (EELS) at impact energies of 2.5–3 keV has been used to obtain the electron excitation spectra for the N 1 s ( K-shell), F 1 s ( K-shell) and valence shell regions of NF 3. The inner shell spectra were recorded using small angle scattering (⩽1° ) while the valence shell spectrum was obtained at zero degree scattering angle. The inner shell excitation spectra show a strongly enhanced 1 s→ δ * type transition and continuum features which are typical for molecules with highly electronegative ligands. One of the peaks in an earlier published photoabsorption study of the N 1 s region has been shown to be due to a N 2 impurity. The valence shell electron energy-loss spectrum shows a number of transitions which are considered to be mainly due to valence-valence type transitions, with also some evidence of Rydberg structure. The X-ray photoelectron spectra (XPS) of the N 1 s and F 1 s electrons along with their associated satellite structures have also been recorded using Al Kα (1486.58 eV) radiation. The vertical ionization potentials for the N 1 s and F 1 s electrons were found to be 414.36 (10) eV and 693.24 (10) eV, respectively. Both spectra exhibit a rich and different satellite structure. These “shake-up” features in the satellite XPS spectra are compared with continuum features of the inner shell electron energy-loss spectra and also with the valence shell spectrum.

The shell spectrum of CH Cygni in 1981

The shell spectrum of CH Cyg observed in 1981 has been analyzed by the curve of growth method and using the equivalent widths of Balmer lines. The following parameters for the region of the shell where the absorption spectrum is formed have been obtained: excitation temperatureTex=9000 K, microturbulent velocityv t =16 km s−1, electron densityne=6.3×1012, number of active hydrogen atoms in the second excited stateN0.2=5.8×1015, and the effective height of the absorption spectrum formation regionH=105 km.

Spectroscopic Study of Pleione in 1977–1979

Shell spectra of Pleione in 1977–1979 are characterized by further increase in their strengths and by the development of the blue-winged profiles without noticeable variation of their radial velocities. The MgII resonance lines at λ2800A have the blue-shifted components with a velocity of-35 km/s relative to the other shell lines. The development of the shell structure is derived. The mass loss rate was 7×10−11 M⊙/yr.

V923 AQL.

ABSTRACT Spectrographic observations of the early-type shell star V923 Aquilae are presented. The observations were made at Cerro Tololo Inter-American Observatory in July 1980, when the shell was apparently entering the positive velocity phase of a cyclic V/R variable. The stellar spectrum of the object confirms its previous classification as B5, and indicates an effective temperature of about 15,000 K, log g of 4 and rotational velocity between 275 and 300 km/sec. The shell spectrum displays three absorption components in H lines, two of which have mean radial velocities of -35.9 and -20.2 km/sec, metallic lines identified with Mg I, Cr II, Ti II, Ni II, Mn II and Fe II associated with radial velocities of about 40, -15 and -20 km/sec, and Na I and Ca II lines with components at radial velocities to the blue of -20 km/sec. The only prominent emission is identified with H-alpha, which appears as the superimposition of two emission profiles. The three absorption components are interpreted as expanding shell regions, while the region of H-alpha emissions must be different from the absorption regions. Simultaneous ultraviolet and photographic observations are required to more fully understand the envelope structure.

Recent developments in the spectra of shell stars. I - The stable shell stars

view Abstract Citations (15) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Recent developments in the spectra of shell stars. I. The stable shell stars. Gulliver, A. F. Abstract Two of the three previously known stable shell stars, HD 193182 and HD 195325, are described. A third such star, HD 179343, is identified and a marked intensity change is observed in an otherwise stable shell, HD 192954. No changes in the shell velocities or spectra of the stable shell stars have been observed for up to half a century. The underlying stellar spectra are restricted to spectral types B6 to B9. The individual shell spectra range in intensity but are qualitatively similar. A very broad Ca II K shell line component is found in several stars. Publication: The Astrophysical Journal Pub Date: August 1981 DOI: 10.1086/159146 Bibcode: 1981ApJ...248..222G Keywords: B Stars; Line Spectra; Shell Stars; Stellar Envelopes; Stellar Spectra; Calcium; Dynamic Stability; H Beta Line; K Lines; Radial Velocity; Astrophysics full text sources ADS | data products SIMBAD (4)

Outflow of matter in the chromosphere of α Orionis

The spectrum of α Orionis is composite and consist of three components: 1) a photospheric spectrum characterized by symmetric absorption lines more or less typical of the spectrum of an M2 supergiant, except for their very great widths; 2) a shell spectrum consisting of P Cygnitype profiles of neutral and singly-ionized metallic lines of very low excitation potential; and 3) asymmetric absorption lines, including Hα Hβ , Fel lines of intermediate excitation potential and the infrared triplet of Ca+, which appear to be formed in a relatively warm layer, probably an extended chromosphere.

The perplexing spectrum of AFGL 2789 /V645 CYGNI/

Visual spectra and photometry from 0.35 to 18 microns show that AFGL 2789 may be one of the most interesting of the infrared sources now identified with reflection nebulae. It has an Ae-type shell spectrum with strong emission lines of hydrogen, Fe II, Cr II, and Ti II, but the most remarkable feature is a broad absorption band near 5500 A, presumably molecular, with three possible band heads. This absorption band was present on only one of two spectra taken one night apart. The two known molecules with wavelengths closest to the observed band heads are C2 and H2O(+), although there are problems with either of these as possible identifications.

Vibrations of axially compressed laminated orthotropic cylindrical shells, including transverse shear deformation

The free vibrations, buckling and the effect of initial prestress upon the frequency spectrum of orthotropic composite cylindrical shells are examined in the context of a theory that includes transverse shear deformation. Results obtained are compared with the predictions of refined Love-type theory and simplified Donnell-type theory that do not consider shear deformation.

The shell spectrum of the optical counterpart of GX 304 –1 (4U 1258 –61)

The shell spectrum of the optical counterpart of GX 304 –1 (4U 1258 –61)