Open Access. Powered by Scholars. Published by Universities.®

Physical Sciences and Mathematics Commons™

Open Access. Powered by Scholars. Published by Universities.®

Chapman University

Series

Discipline
Keyword
Publication Year
Publication
File Type

Articles 1201 - 1230 of 1235

Full-Text Articles in Physical Sciences and Mathematics

The High-Energy Spectrum Of Hot Accretion Disks, J. A. Eilek, Menas Kafatos Jan 1983

The High-Energy Spectrum Of Hot Accretion Disks, J. A. Eilek, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

A hot, two-temperature accretion disk can be a strong γ-ray and relativistic particle source. This occurs when the accretion rate is high enough -- M/ M ≥ 3 X 10^-9 α γr^-1 for a canonical Kerr black hole-due to the high ion temperature in the inner disk. We present detailed photon and particle spectra for specific disk models. The predicted γ-ray flux is as high as 10% of the bolometric luminosity in sub-Eddington models. Most of the γ-radiation is continuous, due to the π^0 decay, emitted around 100 MeV but degraded to a few MeV in optically thick models. Spectral …

Go to article

Ultraviolet Observations Of The 1980 Eclipse Of The Symbiotic Star Ci Cygni, R. E. Stencel, A. G. Michalitsianos, Menas Kafatos, A. A. Boyarchuk Jan 1982

Ultraviolet Observations Of The 1980 Eclipse Of The Symbiotic Star Ci Cygni, R. E. Stencel, A. G. Michalitsianos, Menas Kafatos, A. A. Boyarchuk

Mathematics, Physics, and Computer Science Faculty Articles and Research

Secular and eclipse variations of UV lines and continua during the course of nearly a full orbit of the symbiotic binary CI Cygni are presented. High-excitation resonance lines have brightened on an orbital time scale and show minimal effects of eclipse, while intercombination lines have faded and show pronounced but nontotal eclipse effects. The data are discussed in terms of mass transfer from the extended cool envelope of the red giant to a compact secondary. The formation of an accretion disk is a transitory phenomenon in which viscosity eventually dissipates the disk over orbital time scales. A large-scale low-density nebula …

Go to article

Radio And Optical Observations Of The R Aquarii Jet, R. J. Sopka, G. Herbig, Menas Kafatos, A. G. Michalitsianos Jan 1982

Radio And Optical Observations Of The R Aquarii Jet, R. J. Sopka, G. Herbig, Menas Kafatos, A. G. Michalitsianos

Mathematics, Physics, and Computer Science Faculty Articles and Research

VLA observations at 6 cm and Lick Observatory optical plates of R Aquarii indicate the existence of a jetlike feature extending 7" -10" from the central star. A wide field map at 6 cm shows an unresolved compact radio source which lies close to the axis defined by the jet at a distance of ~ 3' from R Aqr. Episodic mass transfer in this symbiotic variable could explain the erratic outbursts that R Aqr is known to undergo. Formation of an accretion disk and the accompanying radio-optical jet may characterize the observed outbursts in this system.

Go to article

A Brightening Of The Symbiotic Variable Sy Muscae, A. G. Michalitsianos, Menas Kafatos, W. A. Feibelman, G. Wallerstein Jan 1982

A Brightening Of The Symbiotic Variable Sy Muscae, A. G. Michalitsianos, Menas Kafatos, W. A. Feibelman, G. Wallerstein

Mathematics, Physics, and Computer Science Faculty Articles and Research

The symbiotic variable SY Muscae has been observed with IUE in September 1980 and June 1981 and in the photographic region in May 1981. The entire ultraviolet spectrum brightened between September and June by about a factor of 5. The spectrum shows high excitation including emission from N v and high electron density, about 10^10 cm^-3 as determined from various line ratios in the ultraviolet. The optical spectrum is dominated by permitted lines; even [0 m] is very weak again indicating high density in the ionized region. The increase in ultraviolet continuum and line emission may be due to enhanced …

Go to article

International Ultraviolet Explorer Observations Of The Aquarii Jet, A. G. Michalitsianos, Menas Kafatos Jan 1982

International Ultraviolet Explorer Observations Of The Aquarii Jet, A. G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ultraviolet spectra were obtained with the International Ultraviolet Explorer of the newly discovered optical-radio jet feature in the symbiotic variable R Aquarii. The far-UV continuum of the jet is characterized by strong continuum which rises with decreasing wavelength in the 1200-2000 A wavelength range and is considerably different in appearance from the relatively flat continuum exhibited by ionized nebulosity in the central star. Prominent Si III] and Si II emission lines seen in the central region are virtually absent in the jet. This could reflect the depletion of silicon in the feature, the result of grain formation in material that …

Go to article

Iue Observations Of The Peculiar Star Rx Puppis, Menas Kafatos, A. G. Michalitsianos, W. A. Feibelman Jan 1982

Iue Observations Of The Peculiar Star Rx Puppis, Menas Kafatos, A. G. Michalitsianos, W. A. Feibelman

Mathematics, Physics, and Computer Science Faculty Articles and Research

We have obtained the first high-dispersion observations of RX Pup in the wavelength region 1200-2000 A with the International Ultraviolet Explorer. RX Pup has been classified a symbiotic star and has been compared to slow novae as well as to 11 Carinae. The anomalies that we observed in high-excitation lines in RX Pup such as He II, 0 III], C III], C IV, and Si IIIl that show split line profiles, Doppler displaced multiple components, and possible inverse P Cygni profiles inN III] and N IV J suggest dynamic activity in circumstellar material that probably has the form of rings …

Go to article

Ultraviolet Spectrum Of The Crab Nebula, K. Davidson, T. R. Gull, S. P. Maran, T. P. Stecher, R. A. Fesen, R. A. Parise, C. A. Harvel, Menas Kafatos, V. L. Trimble Jan 1982

Ultraviolet Spectrum Of The Crab Nebula, K. Davidson, T. R. Gull, S. P. Maran, T. P. Stecher, R. A. Fesen, R. A. Parise, C. A. Harvel, Menas Kafatos, V. L. Trimble

Mathematics, Physics, and Computer Science Faculty Articles and Research

Data from 65 hours of observation of the Crab Nebula with the International Ultraviolet Explorer are reported, together with new ground-based spectrophotometry. We have measured the important C IV λ1549, He II λ1640, and C III] λ1908 emission line intensities and placed upper limits on other ultraviolet features for the brightest filamentary region in the nebula. We have also measured some ultraviolet continuum surface brightnesses at two places in the Crab. The emission lines imply an average ionic abundance ratio n(C^+2)/n(O^+2 ) in the range from 0.4 to 1.5 in the observed gaseous condensations. The elemental abundance ratio of carbon …

Go to article

Ultraviolet Observations Of Four Symbiotic Stars, A. G. Michalitsianos, Menas Kafatos, W. A. Feibelman, R. W. Hobbs Jan 1982

Ultraviolet Observations Of Four Symbiotic Stars, A. G. Michalitsianos, Menas Kafatos, W. A. Feibelman, R. W. Hobbs

Mathematics, Physics, and Computer Science Faculty Articles and Research

Observations were obtained with the International Ultraviolet Explorer (IUE) of four symbiotic stars. The UV spectra of YY Her, SY Mus, CL Sco, and BX Mon are characterized by varying degrees of thermal excitation. We have analyzed these low resolution spectra in terms of line-blanketed model atmospheres of early A, B, and F type stars in order to identify the nature of the hot companion in these systems. The expected emission from early main sequence stars does not fully explain the observed distribution of UV continuum energy over the entire IUE spectral range (1200-3200 A). More likely the observed continuum …

Go to article

Oh Emission In The Direction Of Tv Gem And Bi Cyg, L. W. Brown, R. W. Hobbs, A. G. Michalitsianos, Menas Kafatos Jan 1981

Oh Emission In The Direction Of Tv Gem And Bi Cyg, L. W. Brown, R. W. Hobbs, A. G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

OH maser main-line emission at 1665 MHz has been detected in the direction of two late-type supergiants, TV Gem (Mllab) and BI Cyg (M3Iab), with the 43-m telescope and 18-cm receiver at NRAO-Green Bank. Detection of two new OH maser sources here is particularly interesting in view of the relatively small number of late-type supergiants that are known as molecular radio sources or associated in close proximity with OH emission clouds. The infrared, ultraviolet, and radio properties of these stars are discussed briefly.

Go to article

On Some Dependencies Between Functional Forms In Functional Programming Systems, Atanas Radenski Jan 1981

On Some Dependencies Between Functional Forms In Functional Programming Systems, Atanas Radenski

Mathematics, Physics, and Computer Science Faculty Articles and Research

In the present paper, some dependencies between functional forms in functional programming systems are demonstrated. It is shown that any functional form can be expressed by using only the forms composition, condition and construction.

Go to article

Gamma Rays From Penrose Powered Black Holes In Centaurus A, 3c 273, And Ngc 4151, Menas Kafatos Jan 1980

Gamma Rays From Penrose Powered Black Holes In Centaurus A, 3c 273, And Ngc 4151, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Gamma-ray observations of active galaxies have important consequences for theories of the activity in their nuclei. The observations of Cen A, 3C 273, and NGC 4151 are examined under the assumption that Penrose collision processes in the ergospheres of massive black holes power their nuclei. The observed sharp break in the MeV region of the NGC 4151 spectrum cannot be due to the γ-γ pair production process. We attribute this break to the Penrose Compton scattering (PCS), in which γ-rays escape from the ergosphere as a result of Penrose processes involving electrons and lower energy X-ray photons in the ergosphere …

Go to article

Iue Observations Of A Luminous M Supergiant That Exhibits Emission Continuum In The Far Ultraviolet, A. G. Michalitsianos, Menas Kafatos, R. W. Hobbs Jan 1980

Iue Observations Of A Luminous M Supergiant That Exhibits Emission Continuum In The Far Ultraviolet, A. G. Michalitsianos, Menas Kafatos, R. W. Hobbs

Mathematics, Physics, and Computer Science Faculty Articles and Research

IUE observations of the late-type M supergiant TV Gem (M1 lab) have been obtained that reveal strong UV continuum between 1200 and 3200 A. The continuum is essentially featureless with the exception of a number of broad absorption features in the short wavelength spectral range. UV emission from this star is unexpected because earlier ground-based observations give no indication of a possible association with an early companion or circumstellar ionized nebulosity. We find that a B9 or A1 III-IV type star approximately 2-3 magnitudes fainter than the M star could explain the level of UV continuum observed, but a fully …

Go to article

Iue Observations Of Circumstellar Emission From The Late Type Variable R Aquarii (M7 + Pec), A. G. Michalitsianos, Menas Kafatos, R. W. Hobbs Jan 1980

Iue Observations Of Circumstellar Emission From The Late Type Variable R Aquarii (M7 + Pec), A. G. Michalitsianos, Menas Kafatos, R. W. Hobbs

Mathematics, Physics, and Computer Science Faculty Articles and Research

IUE observations of R Aquarii (M7 + pec) have been obtained in low dispersion in order to study its circumstellar emission. Strong permitted, semiforbidden, and forbidden emission lines are identified that are superposed on a bright ultraviolet continuum. From our analysis we deduce that the strong emission-line spectrum that involves C III], C IV, Si III], [0 II], and [0 III] probably arises from a dense compact nebula the size of which is comparable to the binary system of which R Aqr is the primary star. Low-excitation emission lines of Fe II, Mg II, 0 1, and Si II suggest …

Go to article

The Evolution Of Supernova Remnants In Different Galactic Environments, And Its Effects On Supernova Statistics, Menas Kafatos, S. Sofia, C. Bruhweilier, T. R. Gull Jan 1980

The Evolution Of Supernova Remnants In Different Galactic Environments, And Its Effects On Supernova Statistics, Menas Kafatos, S. Sofia, C. Bruhweilier, T. R. Gull

Mathematics, Physics, and Computer Science Faculty Articles and Research

By examining the interaction between supernova (SN) ejecta and the various environments in which the explosive event might occur, we conclude that only a small fraction of the many SNs produce observable supernova remnants (SNRs). This fraction, which is found to depend weakly upon the lower mass limit of the SN progenitors, and more strongly on the specific characteristics of the associated interstellar medium, decreases from approximately 15% near the galactic center to 10% at R8a1 -10 kpc and drops nearly to zero for Rga~> 15 kpc. Generally, whether a SNR is detectable is determined by the density of the …

Go to article

Iue Observations Of Rw Hydrae (Gm2 + Pec), Menas Kafatos, A. G. Michalitsianos, R. W. Hobbs Jan 1980

Iue Observations Of Rw Hydrae (Gm2 + Pec), Menas Kafatos, A. G. Michalitsianos, R. W. Hobbs

Mathematics, Physics, and Computer Science Faculty Articles and Research

IUE observations of the late type star RW Hya (gM2 + pec) have been obtained. Analysis of the intense UV continuum observed between 1100 and 2000 A suggests that this object is a binary system in which the secondary is identified as the central star of a planetary nebula with Teff 105 K. The ultraviolet spectrum is characterized by semiforbidden and allowed transition lines, of which the C IV (1548 A, 1550 A) doublet is particularly strong. A general absence of strong forbidden line emission suggests that the compact nebula in which both primary and secondary stars are embedded has …

Go to article

Iue Observations Of Two Late Type Stars: R Aql And W Hya, Menas Kafatos, A. G. Michalitsianos, R. W. Hobbs Jan 1980

Iue Observations Of Two Late Type Stars: R Aql And W Hya, Menas Kafatos, A. G. Michalitsianos, R. W. Hobbs

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ultraviolet spectra of two late type M stars R Aql and W Hya were obtained with the International Ultraviolet Explorer (IUE). Spectra were obtained of R Aql near maximum (cf>=0.21) and minimum (cf>=0.65) of the visible light curve. We find that the absolute flux intensity of the Mgn resonance doublet (2796 A, 2803 A) is essentially the same at these phases in the visible light curve. A nebular emission feature at 3133 A is detected at minimum light in R Aql that is possibly due to 0 III. Mg II emission is totally absent in W Hya, which …

Go to article

Forbidden Lines Of Np^Q Ions. I. Detailed Balance And Line Intensity Ratios, Menas Kafatos, J. P. Lynch Jan 1980

Forbidden Lines Of Np^Q Ions. I. Detailed Balance And Line Intensity Ratios, Menas Kafatos, J. P. Lynch

Mathematics, Physics, and Computer Science Faculty Articles and Research

Ground state forbidden transitions of np^q ions of C, N, 0, Ne, Mg, Si, S, and Fe can provide important information on the state of cosmic ionized gases. Wavelengths of these lines are in the far- and near-UV visible and near-- and far-IR regions of the spectrum. The line intensity ratios of particular transitions in q = 2, 4 ions can provide information on the temperature of the gas and in q = 3 ions information on the density of the gas. In the present work we have tabulated the line intensities of 95 transitions of these ions, which include …

Go to article

150 Ghz Observations Of Three Radio Galaxies, Menas Kafatos, R. W. Hobbs, S. P. Maran, L. W. Brown Jan 1980

150 Ghz Observations Of Three Radio Galaxies, Menas Kafatos, R. W. Hobbs, S. P. Maran, L. W. Brown

Mathematics, Physics, and Computer Science Faculty Articles and Research

Radio galaxies were observed for the first time at 150 GHz. The central sources in Cyg A and 3C Ill were detected, as were the two radio lobes of Cyg A. No emission was found from the central source in 3C 236. Each of these three central sources has been previously discussed as the site of the energy supply for the associated distant components. The millimeter-wavelength emission from the central sources in Cyg A and 3C 111 is probably due in each case to a compact component that is optically thin to synchrotron radiation above about 35 GHz. These components …

Go to article

Sporadic Mass Ejection In Red Supergiants, Menas Kafatos, A. G. Michalitsianos Jan 1979

Sporadic Mass Ejection In Red Supergiants, Menas Kafatos, A. G. Michalitsianos

Mathematics, Physics, and Computer Science Faculty Articles and Research

We have applied a general mechanism first proposed by J. A. Burke to red supergiants for determining the spin-down rate and angular momentum loss of rotating stars. This model relies principally on sporadic mass ejection, which is assumed to be the result of turbulent elements accelerating material in cool supergiant.atmospheres. Mass is preferentially expelled in the forward direction of rotation, resulting in a rapid loss of angular momentum on time scales of 1Q^4-10^6 years in the supergiant evolutionary phase. Such rotational breaking will occur if the turbulent elements have characteristic sizes a few percent of the stellar radius, and rms …

Go to article

Penrose Pair Production As A Power Source Of Quasars And Active Galactic Nuclei, Menas Kafatos, D. Leiter Jan 1979

Penrose Pair Production As A Power Source Of Quasars And Active Galactic Nuclei, Menas Kafatos, D. Leiter

Mathematics, Physics, and Computer Science Faculty Articles and Research

In this paper we propose a new mechanism, Penrose pair production in massive, canonical (with a/M = 0.998) Kerr black holes, as a power source in quasars, Seyfert galaxies, radio galaxies, and BL Lac objects (i.e., what one usually refers to as active nuclei). As a working hypothesis, we postulate that massive (10^8 M0 or around this value) Kerr black holes reside in the centers of these objects. We also postulate that an accretion disk is formed. In a variety of models, hot, inner disks are expected. If the temperature is sufficiently high-as, for example, in the two-temperature model-then MeV …

Go to article

Penrose Pair Production In Massive, Extreme Kerr Black Holes, D. Leiter, Menas Kafatos Jan 1978

Penrose Pair Production In Massive, Extreme Kerr Black Holes, D. Leiter, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

We show that in the case of very massive (M > 108 M0 ) Kerr black holes with extreme ranges of angular momentum 1 ≥ a/M > 0.998, the possibility of photon-induced Penrose pair production (PPP) in the ergosphere is very plausible. The pairs that escape the ergosphere are very high energy and on the order of the GeV rest mass of the Penrose accreted protons which participate in the photon-induced pair production process. Application of this model to the case of quasistellar objects (QSOs) is shown to lead to reasonable predictions about their masses, lifetimes, and luminosities. The physical mechanism is …

Go to article

Mass Loss And Oh Maser Emission From Mira Variables, A. G. Michalitsianos, Menas Kafatos Jan 1978

Mass Loss And Oh Maser Emission From Mira Variables, A. G. Michalitsianos, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

We have estimated the mass, radius, and luminosity of 26 Mira variables that are known OH sources of radio emission at 1612 MHz. The time-independent solution of Salpeter's stellar wind equation and a period-density relation are used to solve for basic stellar parameters, with the aid of the terminal expansion velocity of the OH maser cloud. Masses obtained from these calculations are consistent with other estimated values for masses of Mira variables. Good agreement is obtained when comparing the rate of mass loss as determined from Reimers's semiempirical relation to estimates of the mass loss rate as deduced from theoretical …

Go to article

The Central, Compact Source In The Cygnus A Galaxy, Menas Kafatos Jan 1978

The Central, Compact Source In The Cygnus A Galaxy, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Single, optically thin, component models as well as double, optically thick at low frequencies, component models have been examined in trying to explain the central source in the nucleus of Cygnus A. In the course of exploring those models, it is found that this compact radio source may be quite similar to other compact and variable sources in Seyfert galaxies and quasars. Double component models generally do better because they fit the X-rays, and there is a good chance that the X-rays arise in the central source; these models can naturally explain variability which may already have been detected in …

Go to article

Cygnus A At 99 Ghz: Observations Of The Three Principal Components And The Interpretation Of The Central Source, R. W. Hobbs, S. P. Maran, Menas Kafatos, L. W. Brown Jan 1978

Cygnus A At 99 Ghz: Observations Of The Three Principal Components And The Interpretation Of The Central Source, R. W. Hobbs, S. P. Maran, Menas Kafatos, L. W. Brown

Mathematics, Physics, and Computer Science Faculty Articles and Research

The three principal emission components of Cygnus A have been observed at 99 GHz, the highest frequency at which radio measurements of this source have been accomplished. The observations show no definite indication of a high-frequency cutoff in the spectrum of the compact central component, which perhaps may be attributed to an optically thin synchrotron source that peaks at a frequency of several hundred GHz.

Go to article

Structure Of The Information Base And Operations On The Entities In A System For Information Servicing Of Collectivities, Peter H. Barnev, Atanas Radenski Jan 1978

Structure Of The Information Base And Operations On The Entities In A System For Information Servicing Of Collectivities, Peter H. Barnev, Atanas Radenski

Mathematics, Physics, and Computer Science Faculty Articles and Research

This paper treats, from an user point of view, the structure of the entities in the information base (IB) of a System for information servicing of collectivities (SISC) as well as the operations on these entries.

Go to article

Thermal Instability In Supernova Shells, R. Mccray, R. F. Stein, Menas Kafatos Jan 1975

Thermal Instability In Supernova Shells, R. Mccray, R. F. Stein, Menas Kafatos

Mathematics, Physics, and Computer Science Faculty Articles and Research

Thermal instability in the radiative cooling region behind a shock will cause upstream density fluctuations to collapse into thin sheets aligned parallel to the shock front. A linearized calculation demonstrates the development of this instability. Thermal conduction suppresses the development of small-scale perturbations. Estimates of the scale sizes for the fully developed condensations agree roughly with the scale sizes of fine structure observed in supernova shells such as the Cygnus Loop.

Go to article

Sources Of Excitation Of The Interstellar Gas And Galactic Structure, J. J. Cowan, Menas Kafatos, W. K. Rose Jan 1975

Sources Of Excitation Of The Interstellar Gas And Galactic Structure, J. J. Cowan, Menas Kafatos, W. K. Rose

Mathematics, Physics, and Computer Science Faculty Articles and Research

The excitation of the interstellar gas. is discussed in the light of recent evidence from γ-ray, molecular, and 21-cm line observations. Previous studies of the excitation of the interstellar gas have not taken into account the substantial density contrast that exists between spiral arms and interarm regions. We examine the role played by the galactic distribution of three sources of excitation (supernovae, OB stars, and ultraviolet stars) in determining the physical state of the interstellar gas in arm and interarm regions.

Go to article

An Algorithm For Finding All Isomorphisms Of Two Graphs, Atanas Radenski Jan 1975

An Algorithm For Finding All Isomorphisms Of Two Graphs, Atanas Radenski

Mathematics, Physics, and Computer Science Faculty Articles and Research

No abstract provided.

Go to article

Ionization Of Carbon And Nitrogen In The Intercloud Medium, Menas Kafatos, H. Gerola, S. Hatchett, R. Mccray Jan 1974

Ionization Of Carbon And Nitrogen In The Intercloud Medium, Menas Kafatos, H. Gerola, S. Hatchett, R. Mccray

Mathematics, Physics, and Computer Science Faculty Articles and Research

If the intercloud medium in the solar neighborhood was suddenly ionized less than 106 years ago, the subsequent relaxation of the gas can account for the very low observed column density of C III and N III yet still leave a significant fraction ("'0.05) of ionized hydrogen and of C I in a cold (T ≈ 20° K) intercloud medium. The OAO-C Copernicus observations in the direction of X Sco are consistent with cosmic abundances and a uniform-density medium, except for C III whose predicted column density from the C m ionization zone surrounding the star is a factor ~1Q …

Go to article

Statistical Time-Dependent Model For The Interstellar Gas, H. Gerola, Menas Kafatos, R. Mccray Jan 1974

Statistical Time-Dependent Model For The Interstellar Gas, H. Gerola, Menas Kafatos, R. Mccray

Mathematics, Physics, and Computer Science Faculty Articles and Research

We present models for temperature and ionization structure of low, uniform-density (n ~ 0.3 cm^-3) interstellar gas in a galactic disk which is exposed to soft X-rays from supernova outbursts occurring randomly in space and time. The structure was calculated by computing the time record of temperature and ionization at a given point by Monte Carlo simulation. The calculation yields probability distribution functions for ionized fraction x, temperature T, and their various observable moments. These time-dependent models predict a bimodal temperature distribution of the gas with structure in x, T that agrees with various observations. Cold regions in the low-density …

Go to article

First Prev Next Last