Observed Energy Distributions Research Articles

Photofragmentation dynamics of 2-chloro-2-nitrosopropane. Scalar correlations of velocity and angular momentum

The 650 nm photodissociation of gas-phase (CH 3) 2 ClCNO (2-chloro-2-nitrosopropane) is studied by measuring the energy distribution in the nitric oxide fragment. The rotational distribution is similar to those previously measured for other nitrosoalkanes Translational distributions were measured in coincidence with single NO ratational states and show clear bimodality and a positive correlation between the rotational energy of the NO photoproduct and the relative translational energy of the recoiling photofragments. Previously applied statistical models for photofragment excitation in nitrosoalkanes fail to predict the translational energy distribution. The observed energy distributions are consistent with dissociation on multiple electronic potential energy surfaces.

Relaxation of the D center in amorphous silicon and how this accounts for the observed energy distributions of deep defects within the mobility gap

Transient capacitance measurements disclose that the mobility gap energy of the D defect in a-Si:H relaxes following a change in its charge state. Using the relaxation parameters thus determined, we solve the resulting dynamical equation to obtain the steady-state energy distributions of both the D − and D 0 sub-bands. These results agree with the experimental distributions determined by modulated photocurrent and steady-state junction capacitance measurements.

G62-46 - an unresolved double degenerate binary containing a magnetic DA component

A detailed analysis of the white dwarf star G62-46 is presented. High signal-to-noise spectroscopy reveals Zeeman splitting of the Hα line profile, indicating the presence of a magnetic field. Model atmosphere calculations are used to demonstrate that the observed energy distribution and line profiles cannot be reconciled with those of a single magnetic hydrogen-line (DA) white dwarf. Instead, G62-46 is shown to be an unresolved double degenerate binary, composed of a featureless DC white dwarf diluting the line profiles of the magnetic DA component. We show from the inferred mass of the DA component that the system most likely has undergone at least one phase of common envelope evolution

THE EVOLUTION OF CARBON STARS

ABSTRACT This dissertation is concerned with the nature of the carbon stars, unusual late-type stars in which the abundance of carbon in the photosphere is greater than that of oxygen. Data from the Infrared Astronomical Satellite (IRAS) survey has shown that carbon stars which were identified from optical surveys and those identified from the SiC dust features in their IRAS Low Resolution Spectrometer LRS spectra have different IRAS colours. The former (which will be referred to as visual carbon stars) are visually bright and have large excesses at 6 microns, while the latter group (which will be referred to as infrared carbon stars) have blackbody energy distributions. The origin of visual carbon stars has been discussed by Chan and Kwok (1988) based on the hypothesis of Willems and de Jong (1988). A complete sample of visual carbon stars detected by IRAS with 12 microns flux densities greater than 5 Jy was selected, and 207 LRS spectra were extracted for those sources without previous \\lrs data. Of these, 152 sources had new LRS spectra with reasonably good signal-to-noise ratio and 575 sources had previously released LRS spectra. All these spectra have been classified with the scheme of Volk and Cohen (1989). When the LRS spectra of these 727 IRAS CCGCS sources were examined, 15 were found to show the 9.7 microns silicate emission feature which is expected to occur only in an oxygen-rich circumstellar shell. Eight of these are reported for the first time in this dissertation. This group of visual carbon stars (hereafter called silicate carbon stars) may represent transition objects between oxygen-rich and carbon stars on the asymptotic giant branch (AGB) because the photosphere is carbon-rich while the circumstellar material resembles that from a typical M-type star. A radiative transfer dust shell model for these silicate carbon stars is presented. The model spectra produce excellent fits to the observed energy distributions of these silicate carbon stars. The J-type stars (13C-rich carbon stars) have been suggested to be transition objects between M-type stars and C-type stars. An optical spectroscopic study of these silicate carbon stars was performed at the Dominion Astrophysical Observatory (DAO) in Victoria in 1991. CCGCS 1653, CCGCS 4222, CCGCS 4923 and CCGCS 5848 have been confirmed to be J stars. CCGCS 1158 and CCGCS 4729 are provisionally identified as J stars. A preliminary spectral analysis has also been carried out. Model calculations are presented on the evolution from the visual carbon stars to infrared carbon stars, and on the evolution of infrared carbon stars. A new empirical opacity function for the SiC grain is derived based on the LRS spectra of a selected sample of infrared carbon stars. A two-shell model has been developed with an oxygen-rich detached shell and a newly-forming SiC dust shell. The energy distributions of ~110 transition objects which are late-stage visual carbon stars or early-stage infrared carbon stars are fitted with this Interrupted Mass Loss Model. Furthermore, the model tracks successfully explain the "C" shaped distribution of the transition objects in the IRAS 12 microns/25 microns/60 microns colour-colour diagram. The energy distributions of ~150 infrared carbon stars are also matched with a radiative transfer dust shell model using only SiC dust. The colour evolution of infrared carbon stars can be explained with a continuous increase in mass loss rate on the AGB. An evolutionary scenario of AGB stars is suggested. There is a branching of M-type and C-type stars on the AGB with each branch evolving independently to the planetary nebula stage. The initial mass of the star in the main sequence may be the factor that determines which branch the star will follow.

Discovery of two cool magnetic white dwarfs

We report the discovery of magnetism in two cool white dwarfs, LHS 1044 and LHS 1734. Optical and infrared photometry, as well as high signal-to-noise spectroscopy, are presented for both objects. The observed energy distributions along with the measured trigonometric parallaxes are used to derive the effective temperatures and surface gravities. LHS 1734, with T(eff) = 5230 K, becomes the coolest observed magnetic white dwarf. The strength of each magnetic field is estimated from a detailed line profile analysis. Offset dipole models with dipole strengths of 16.7 and 7.3 MG, for LHS 1044 and LHS 1734, respectively, are shown to reproduce successfully the observed line profiles. In both objects, the dipole needs to be offset away from the observer by an amount equal to nearly one-fifth of the stellar radius.

Absolute far-ultraviolet spectrophotometry of hot subluminous stars from Voyager

view Abstract Citations (38) References (39) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Absolute Far-Ultraviolet Spectrophotometry of Hot Subluminous Stars from Voyager Holberg, J. B. ; Ali, B. ; Carone, T. E. ; Polidan, R. S. Abstract Observations, obtained with the Voyager ultraviolet spectrometers, are presented of absolute fluxes for two well-known hot subluminous stars: BD + 28 deg 4211, an sdO, and G191 - B2B, a hot DA white dwarf. Complete absolute energy distributions for these two stars, from the Lyman limit at 912 A to 1 micron, are given. For BD + 28 deg 4211, a single power law closely represents the entire observed energy distribution. For G191 - B2B, a pure hydrogen model atmosphere provides an excellent match to the entire absolute energy distribution. Voyager absolute fluxes are discussed in relation to those reported from various sounding rocket experiments, including a recent rocket observation of BD + 28 deg 4211. Publication: The Astrophysical Journal Pub Date: July 1991 DOI: 10.1086/170237 Bibcode: 1991ApJ...375..716H Keywords: Hot Stars; Satellite Observation; Spectral Energy Distribution; Stellar Spectrophotometry; Ultraviolet Spectra; Far Ultraviolet Radiation; Voyager Project; Astrophysics; SPECTROPHOTOMETRY; STARS: INDIVIDUAL ALPHANUMERIC: BD; 28 DEGREES 4211; STARS: INDIVIDUAL ALPHANUMERIC: G191-B2B; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (74) MAST (1) INES (1)

Absolute spectrophotometry of hot subluminous stars from voyager

Abstract We present absolute far UV (900 to 1200 A) spectrophotometry of two hot subluminous stars, BD +28°4211, an sdO, and G191-B2B, a DA white dwarf. These observations, obtained with the Voyager ultraviolet spectrometers, are combined with other data to produce complete absolute energy distributions extending from the Lyman limit at 912 A to 1 μm. For BD +28°4211, this energy distribution is closely approximated by a single power law. Alternately, the energy distribution of G191-B2B is well matched by a single pure H model atmosphere whose effective temperature and gravity are independently determined from spectroscopy. These two distinct results indicate that simple models provide good agreement with observed energy distributions, even at the shortest wavelengths. Comparisons of the Voyager absolute calibration with previous rocket results are discussed, including the recent rocket observations of BD +28°4211 and G191-B2B.

Polarimetric Observations of Active Cool Binaries

For a sample of RS CVn binaries Busso and collaborators (Busso et al., 1987, 1988; Busso and Scaltriti, 1990) compared the observed energy distribution from the UV to the near-IR (and to IRAS bandpasses for some objects) with those calculated from the known radii and spectral types of the stellar components. About 25% of the sample gave evidence of an IR excess up to 0.7 mag, generally starting from the I-band. The excess is significantly larger than observational error. These same authors ascribe the excess to a thin dust shell surrounding the binary. Using the “dirty silicates” model by Jones and Merrill (1976) they find for the shell a temperature range of 1500 K to 2000 K, an optical depth of about 0.01 at 10 micrometers in the shell, and a distance of the shell from the stars to be typically about 100 times the radius of the larger star.

Infrared polarimetry of radio luminous OH/IR stars

view Abstract Citations (18) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Infrared Polarimetry of Radio Luminous OH/IR Stars Jones, Terry Jay ; Gehrz, Robert D. Abstract Polarimetry from 1 to 2.5 microns is presented for 14 radio luminous OH/IR stars. All of the stars show significant polarization. Four stars show only interstellar polarization, four show a combination of interstellar and intrinsic polarization, and six were too red to measure at any wavelength other than 2.2 microns. The interstellar polarization is substantial, and clearly indicates that interstellar extinction is a significant factor in the observed energy distributions of these stars. The intrinsic component is also substantial, and requires large asymmetries in the geometry of the circumstellar dust shells. Publication: The Astronomical Journal Pub Date: July 1990 DOI: 10.1086/115512 Bibcode: 1990AJ....100..274J Keywords: Giant Stars; Hydroxyl Emission; Infrared Stars; Late Stars; Polarimetry; Radio Stars; Energy Distribution; Interstellar Extinction; Stellar Luminosity; Astrophysics; STARS: LONG-PERIOD VARIABLES full text sources ADS | data products SIMBAD (15)

High-order multiphoton ionization photoelectron spectroscopy of nitric oxide

Resonance-enhanced and nonresonant five- and six-photon ionization of NO was studied using angle resolved photoelectron spectroscopy. The (3+3) resonance-enhanced multiphoton ionization photoelectron spectrum (REMPI-PES) of NO via the A 2 Σ+ (v=0) level yielded a distribution of electron energies corresponding to all accessible vibrational levels (v+ =0–6) of the nascent ion. The observed energy distributions suggest near resonant enhancement due to vibrational levels of the D 2 Σ+ and C 2 Π states at the fourth photon level. Angular distributions of photoelectrons corresponding to v+ =0 and v+ =3 (rotationally unresolved) were significantly different, perhaps reflecting these different pathways. The (3+2) REMPI via the A 2 Σ+ (v=1) level produced only one low-energy electron peak corresponding to v+ =1. Nonresonant MPI at 532 nm yielded a distribution of photoelectron energies corresponding to both four- and five-photon ionization. Prominent peaks in the five-photon ionization photoelectron spectrum show that near resonant enhancement occurs via the A 2 Σ+ (v=5), the C 2 Π(v=2) and the D 2 Σ+ (v=1) states at the three-photon level. This study amply demonstrates the utility of angle resolved MPI-PES in understanding high-order multiphoton ionization processes. Finally, measurements of the ratio of NO+ ion signal for circular and linear polarized light when tuning near the A 2 Σ+ (v=0) and A 2 Σ+ (v=1) levels are reported and compared with theory.

The transition from oxygen-rich to carbon stars

Evolutionary tracks for the transition from oxygen-rich to carbon-rich stars are calculated, using the model of Willems and de Jong (1988). It is found that model spectra produce excellent fits to the observed energy distributions of carbon stars. The mass-loss rate and the time since shell detachment can be determined for each individual object by comparing observed data with the models. 76 references.

Energy distributions of neutral atoms sputtered by very low energy heavy ions

Polycrystalline Cu was sputtered by normally incident, very low energy Ar + ions ( E 0 = 40–1000 eV). The kinetic energy ( E) distributions of the neutral Cu atoms sputtered normally from the Cu surface were measured, using secondary neutral mass spectrometry. For values of E 0 above approximately 600 eV, the observed energy distributions agreed closely with the Thompson-Sigmund theory. For values of E 0 less than about 600 eV the distributions fell off faster than predicted by the Thompson-Sigmund theory, and the peak value of the distribution shifted to somewhat lower energies. Both these effects were exaggerated as E 0 was further lowered. The average kinetic energy of the sputtered neutral Cu atoms increased with increasing E 0. The rate of this increase was less at higher values of E 0.

A survey of IRAS data on 41 classical novae

The IRAS database has been searched for detections of 41 classical novae using coadditions of survey scans; 15 were detected. IRAS temporal observations of novae in outburst are discussed. The observed long-wavelength infrared distributions of DQ Her, and possibly HR Del, can be explained by emission from small (a of about 0.1 microns) dust grains heated by the central object. An alternative explanation for the energy distributions of DQ Her and HR Del is emission from fine-structure lines. FH Ser and LW Ser display energy distributions that have color temperatures much too hot to be due to heating of dust by the central source in any plausible scenario. Line emission is probably the best explanation of their observed energy distributions. The novae NQ Vul and LV Vul have energy distributions that may be contaminated by emission from galactic cirrus. The unusual object PL 1547.3-5612 exhibits an energy distribution that does not resemble those of planetary nebulae or other novae detected in this sample. An IRAS low-resolution spectrum of RR Tel shows the 10-micron silicate emission feature.

A SPHERICAL, NON-LTE, BLANKETED MODEL STELLAR ATMOSPHERE FOR PHI CASSIOPEIAE (F0 IA)

By constructing a model atmosphere, I have calculated the theoretical energy distribution of the emergent radiation that best matches the observed energy distribution of the star Cassiopeiae, and so derived its effective temperature and surface gravity. For an accurate comparison between theory and observations, it is desirable to determine the interstellar extinction situ and then correct the observations for it. Fortunately, (J) Cas is very likely a member of the open cluster NGC 457. Five early-B-type stars near the main-sequence turnoff in NGC 457 were observed at low dispersion with the WE satellite. In order to use the pair to derive the extinction curve for NGC 457, 1 have developed a new method of choosing a lightly reddened comparison star. It consists of matching the equivalent widths of spectral features that are particularly strong and sensitive to temperature and luminosity. The UV extinction in NGC 457 deviates from the average extinction for the Milky Way and is uniform across the cluster. For the visible region, monochromatic fluxes of 4> Cas were dereddened with a mean extinction curve. Thus, the intrinsic energy distribution of § Cas was determined from 1500 A to 5800 A. A detailed new spherical model atmosphere was constructed. The equation of transfer was solved with the constraints of hydrostatic and pure radiative equilibrium. The statistical equilibrium of 106 transitions was treated. Several tests have demonstrated this model to be reliable. Comparison of the observed UV and visible energy distributions and the HO, Ca II K, and Mg II h and k line profiles with the theoretical results indicates that the best model for Cas.

The 193 (and 248) nm photolysis of HN3: Formation and internal energy distributions of the NH (a 1Δ, b 1∑+, A 3Π, and c 1Π) states

The UV photolysis of HN3 at 193 nm was investigated in detail in the bulk phase at 300 K. NH radicals in the X, a, b, A, and c states were found to be formed with quantum yields ≤0.0019, 0.4, 0.017, 0.000 15, and 0.000 61, respectively. Relative rotational and vibrational populations were measured for all states except for NH(X). Average translational energies were estimated for NH(a,v=0 and 1) and NH(b,v=0). The 248 nm photolysis of HN3 was reinvestigated with respect to processes forming NH radicals other than NH(a). The observed energy distributions differ for both laser wavelengths and for high and low lying NH states. The distribution can be better described by a simple impulsive than by a statistical model. Some conclusions are drawn concerning the upper HN3 potential surfaces involved.

Scanner observations of shell stars ? Persei and ? Persei

Spectrophotometric energy distribution data of the shell stars ϕ Per and ψ Per are reported in the wavelength range λλ3200–8000 A. The effective temperature of these stars is derived by comparison of observed energy distribution with theoretical models. Both the stars show higher values of derived effective temperature. The continuum energy distribution in the ultraviolet region has also be discussed.

Modeling the extended atmospheres of WN stars

view Abstract Citations (178) References (61) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Modeling the Extended Atmospheres of WN Stars Hillier, D. J. Abstract A detailed study of WN stars with particular reference to HD 50896 is initiated. Using radiative transfer calculations in the comoving frame, the author examines the behavior of the He II, He I, and H departure coefficients in a dense extended atmosphere. The models indicate that in HD 50896 (WN5) the helium ionization decreases strongly with radius, so that helium is predominantly singly ionized in the radio emitting region. This will necessitate the revision of mass loss rates for Wolf-Rayet (W-R) stars similar to HD 50896, which have been derived from radio data. It is shown that a star with a small core (2.5 R_sun;) and a dense stellar wind (M≈ 5×10-5M_sun;yr-1) can explain the observed energy distribution of W-R stars similar to HD 50896. Publication: The Astrophysical Journal Supplement Series Pub Date: April 1987 DOI: 10.1086/191187 Bibcode: 1987ApJS...63..947H Keywords: Atmospheric Models; Stellar Atmospheres; Stellar Models; Wolf-Rayet Stars; Atmospheric Composition; Equilibrium Equations; Helium Atoms; Hydrogen Atoms; Radiative Transfer; Resonance Lines; Stellar Temperature; Astrophysics; STARS: ATMOSPHERES; STARS: INDIVIDUAL HENRY DRAPER NUMBER: HD 50896; STARS: WOLF-RAYET full text sources ADS | data products SIMBAD (2)

Spectrophotometric observations and evolutionary status of ten Be stars

The continuum energy distribution data of ten Be stars — namely, HR 1761, HR 1786, HR 1820, σOri, ωOri, OT Gem, βLyr, HR 7983, νCyg, and 59 Cyg — have been presented in the wavelength range λλ3200–8000 A. The observed energy distribution curve shows near infrared excess for majority of Be stars and a double Balmer jump for HR 8047 and HR 8146. Empirical effective temperatures of these stars have been estimated by comparing the observed continuum energy distributions with that of computed theoretical models given by Kurucz (1979). On the basis of an HR diagram with evolutionary tracks for different solar masses the masses of these Be stars have been estimated. Position of these studied stars on the HR diagram suggests that these Be stars may be in the stage of core contraction after exhausting hydrogen at the centre and have undergone hydrogen exhaustion in the thick shell.

Effective temperatures of normal stars of classes O9-A0

In order to determine the effective temperatures of stars of classes 09-A0, a comparison was made between the mean observed energy distributions in their spectra and the corresponding data calculated for various models of atmospheres. In the case of LTE models and plane-parallel approximation, the temperatures obtained for supergiants of all subclasses are found to be below the temperatures of main sequence stars, while when models of static extended atmospheres were used for hot supergiants their temperatures proved to be higher, and were practically the same as the temperatures of main sequence stars found by the use of models which take into account deviations from LTE.

Ion extraction from the cathode-fall region of Ar, N 2 and O 2 discharges

A relatively simple experimental apparatus has been developed to extract ions from several d.c. plasmas, involving a symmetrical three-element einzel lens and mass spectrometric detection. The measured ion energy distributions obtained for Ar d.c. plasmas are in good agreement with the classical results of Davis and Vanderslice and conform to their model except that there must be at least one other type of ion which contributes to the observed energy distributions in addition to those which experienced charge exchange during their last collision in the cathode-fall region. This additional group of ions has been tentatively identified. The distributions from N 2 d.c. plasmas show larger deviations from the Davis and Vanderslice model; two consecutive processes may be at work which also have been specified. The O 2 + and O + results obtained were non-reproducible, presumably because of changes of the internal surfaces which affected the electrical fields in the ion optics.