Observations and Analysis of the Aquarii Jet
Menas Kafatos and Andrew G. Michalitsianos
Ultraviolet, optical and radio observations of the symbiotic star R Aquarii are discussed in the light of the discovery of a bright radio and optical jet from this star. The star is probably a binary with a period of 44 years. The VLA maps of the jet reveal a protruding structure extending-10 arc sec from the central radio source with a position angle virtually identical to that of the optical jet observed at Lick. We interpret the observations of R Aqr as indicating the existence of an accretion disk around an unseen companion. The hot subdwarf has effective temperature ,(65,000 K. We believe that the Mira primary and the hot secondary are in orbit around each other with a high eccentricity. At periastron the hot subdwarf accretes at super critical rates and a jet forms. It is difficult to understand how an accretion disk would have eclipsed the Mira in 1928-1935 and 1974-1980. We prefer to interpret the suppression of maximum light in these two periods as due to a distortion of the Mira envelope at periastron by the tidal interaction with the secondary. The jet may help to explain the excitation of the R Aqr nebula. It is possible that R Aqr flared up as a nova N1OOO years ago forming the nebula.
UV Emission from the M1 Supergiant TV Gem
Andrew G. Michalitsianos and Menas Kafatos
Low and high dispersion ultraviolet spectra were obtained of the Ml supergiant TV Gem with IUE. Previous IUE observations of this late type supergiant revealed unexpected W continuum emission, perhaps arising from an early B companion. Low resolution spectra obtained approximately one year apart suggest that the strong Si I11 in-combination perhaps with 0 I at wavelengths % A1300 A varies considerably with time. Large variation the column density is required to explain these changes. Sporadic mass expulsion with mass loss rates dM/dt * 10-5 S y r - l from the M supergiant could lead to a dense circumstellar wind near the hot early companion, and thus could account for these observed variations in equivalent width. The high resolution spectrum in the A2000 to 3200 A wavelength range is characterized by narrow absorption lines primarily due to Fe 11, Mn I1 and Mg I1 (h and k), which are skewed in profile with an extended red wing, We tentatively attribute this profile structure to interstellar absorption and an intervening differentially moving cloud in the direction of Gem OB1, of which TV Gem is a known association member.
Ci Cygni Since the 1980 Eclipse
R. E. Stencel, Andrew G. Michalitsianos, and Menas Kafatos
Following the 1980 eclipse of the 855 day period symbiotic binary CI Cyg, we were confronted with a data set showing high excitation resonance lines which were largely uneclipsed but brightening on an orbital timescale, and intercombination lines exhibiting pronounced but nontotal eclipses and which were fading on an orbital timescale. Our model invoked a low density dissipating nebula surrounding the hot companion to explain the intercombination lines, and a shock between stellar winds to interpret the resonance lines. Subsequent synoptic observations have revealed continuing changes in the W emission line fluxes, consistent with those described above, except for the brightening of Mg I1 and the emergence of strong, not previously seen [Mg VI emission. Post-outburst and phase dependent changes must be included in any interpretation of this system as the archetypal symbiotic binary. We anticipate that critical observations will be made during the 1982 October eclipse.
Preliminary Report on IUE Spectra of Crab Nebula
K. Davidson, T. R. Gull, S. P. Maran, T. P. Stecher, Menas Kafatos, and V. L. Trimble
The Crab Nebula is marginally observable with the IUE. Observations of the optically brightest filamentary regions, made with IUE in August 1979, show the C IV x1549, He II x1640, and C III] x1909 emission lines. The intensities of these lines have been compared with visual-wavelength data. It appears that carbon is not overabundant in the Crab; carbon/- oxygen is approximately "normal" oxygen is slightly scarcer than "normal" as a fraction of the total mass.
T. R. Gull, F. C. Bruhweiler, Menas Kafatos, and S. Sofia
Individual massive stars with Mbol < -6 have huge stellar winds that create interstellar bubbles. Stars with masses greater than 8Mo (4Mo?) are considered supernova progenitors. These massive stars are numerous in OB associations where few supernova remnants are detected. Model calculations describing the evolution of an association show: i) that large, hot cavities are formed by pushing the ambient gas into neutral shells; 2) that the shell radii change with galactocentric radius, 3) that only thirty percent of the interstellar medium is in the form of supercavities and 4) that a consequence is that only a small fraction of supernovae form supernova remnants. These results have strong bearing on interpretation of interstellar studies being done by IUE and by HEAO-B.
IUE Observations of Circumstellar Emission from the Late Type Variable R Aqr (M7 + pec)
R. W. Hobbs, Andrew G. Michalitsianos, and Menas Kafatos
As part of a program to observe circumstellar emission from late type stars, IUE observations of R Aqr (M7 + pec) have been obtained in low dispersion. Strong permitted, semi-forbidden and forbidden emission lines are seen, superimposed on a bright ultraviolet continuum. We deduce that the strong emission line spectrum that involves C III], C IV, Si III], [0 II] and [0 lll] probably arises from a dense compact nebula the size of which is comparable to the orbital radius of the binary system of which R Aqr is the primary star. The low excitation emission lines of Fe II, Mg II, 0 1 and Si II probably arise in the chromosphere (T_IO,O00 K) of the R Aqr. The secondary is probably a white dwarf, comparable to or somewhat brighter than the sun, since such a star can produce enough ionizing photons to excite the continuum and emission line spectrum and yet be sufficiently faint as to escape detection by direct observation. We attribute the UV continuum to Balmer recombination from the dense nebula and not to blackbody emission from the hot companion.
IUE Observations and Interpretation of the Symbiotic Star RW Hya
Menas Kafatos and Andrew G. Michalitsianos
IUE observations of the high excitation symbiotic star RW Hya (gM2 + pec) have been obtained. Analysis of the intense UV continuum observed between II00 A to 2000 A suggests this star is a binary system in which the secondary is identified as a hot subdwarf with T _. _I0 D K. We deduce a distance to the system of ~1000 pc. The UV spectrum consists of mainly semi-forbidden and allowed transition lines of which the ClV (1548 A, 1550 A) emission lines are particularly strong, and UV continuum at both shorter and longer wavelengths. Strong forbidden lines seem to be absent suggesting the presence of a nebula of high densities, in the approximate range 10^8 - 10^9 cm^-3. Tidal interaction between the red giant primary and the hot subdwarf is suggested as a likely means to form the observed nebula. RW Hya is suggested as a possible source of soft X-ray emission from material accreting onto the surface of the hot subdwarf. Detection of such emission with HEAO-B ("Einstein") would give us information if this accretion is taking place via Roche lobe overflow or via capture from a stellar wind emitted by the primary. A general discussion of elemental and ionic abundances in the nebula is also presented.
IUE Observations of Two Late Type Stars BX Mon (M4 + pec) and TV Gem (M1 Iab)
Andrew G. Michalitsianos, R. W. Hobbs, and Menas Kafatos
IUE observations of two late type stars BX Mon and TV Gem have been obtained that reveal the emission properties in the ultraviolet of subluminous companions. Analysis of the continuum emission observed from BX Mon suggests the companion is a middle A III star. High excitation emission lines observed between 1200 A and 2000 A (C IV, Si Ill], C III ) that generally do not typify emission observed in either late M type variables or A type stars are also detected. It is suggested that these strong high-excitation lines arise in a large volume of gas heated by non-radiation processes that could be the result of tidal interaction and mass exchange in the binary system. In contrast to stars such as BX Mon that are observed in the visible to have emission lines superimposed on the strong absorption of the M giant_ the luminous MI supergiant TV Gem shows unexpected intense UV continuum throughout the sensitivity range of IUE. The UV spectrum of TV Gem is characterized by intense continuum with broad absorption features detected in the short wavelength range. Our analysis shows that the companion could be a B9 or A1 Ill-IV star, although a fully self-consistent model including the observed color index has as yet not been fully developed. Alternate suggestions are presented for explaining the UV continuum in terms of an accretion disk in association with TV Gem.
Ingress Observations of the 1980 Eclipse of the Symbiotic Star CI Cygni
R. E. Stencel, Andrew G. Michalitsianos, Menas Kafatos, and Alexander A. Boyarchuk
One of the major results from the IUE may prove to be the new knowledge gained by studies of the ultraviolet spectra of symbiotic stars. Symbiotics combine spectral features of a cool M giant-like photosphere with strong high excitation emission lines of nebular origin, superposed. An excellent pre-UV review has been given by Swings (i). The UV spectra are dominated by intense permitted and semi-forbidden emission lines and weak continua indicative of hot compact objects and accretion disks. Two symbiotics, AR Pay and CI Cyg are thought to be eclipsing binaries, and we have begun IUE observations during the predicted 1980 eclipse of CI Cygni.
On the Thermoelectric Effect in a Superconducting Ring
Armen Gulian and G. F. Zharkov
Thermoelectric effects in superconductors attracted much attention recently (see review paperl). In particular, when the temperature gradient in a superconducting bimetallic ring is present, the magnetic flux and thermoelectric current arise, which have inductive origin.1 In Ref. 2 it was pointed out that an additional contribution to the magnetic flux arises if the mutual transformation of the superconducting and normal currents is taken into account. This additional effect is considered in more details in the present paper.
Below you may find selected books and book chapters from Mathematics, Physics, and Computer Science faculty in the Schmid College of Science and Technology.
Printing is not supported at the primary Gallery Thumbnail page. Please first navigate to a specific Image before printing.