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Wu, C.-C.

Publications and source records attributed to Wu, C.-C..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

ANS spectrophotometry - Delta Pictoris as an upper-main-sequence algol system

The early-type eclipsing binary Delta Pictoris has been studied with 260 observations in each of five UV bands. These are the most accurate observations to date, and no strong evidence for light-curve complications produced by circumstellar material has been found. Combined light curves from four epochs separated by intervals of six months do not show any strong dips or shoulders as seen in earlier investigations. The strength of th C IV wavelength 1550 line is independent of phase to better than 0.01 m. The root-mean-square scatterer shown by the light curves ranges from 0.006 m to 0.014 and may be evidence that either or both of the components are intrinsically variable. The integrated colors of the system are consistent with a B1 V spectral type and very little interstellar extinction. A detached solution of the light curves for a Roche model well with the spectroscopic mass ratio, but a semidetached solution cannot be ruled out.

Eaton, J. A.↗
NASA NTRS1983

Prominent ultraviolet emission lines from Type 1 Seyfert galaxies

IUE Explorer data with a 6-A resolution are reported for Ly-alpha, C IV 1550 A, C III semiforbidden line 1909 A, and Mg II 2800 A, as well as the continuum at 1450 A, for 20 Seyfert galaxies and one quasar. Good correlation is found between the continuum and the line fluxes, indicating that photoionization is the dominant heating mechanism for these active galactic nuclei. A combination of the data for Seyferts and high redshift quasars covering five orders of magnitude in continuum luminosity shows the lower luminosity objects to have higher equivalent widths for their emission lines, suggesting that the covering factor increases with decreasing luminosity.

Wu, C.-C.↗
NASA NTRS1983

ANS ultraviolet observations of dwarf Cepheids

Ultraviolet observations of three dwarf Cepheids (VZ Cnc, SX Phe, and AI Vel) are presented. The UV light curves are consistent with those in the visual region. When compared to standard stars, all three dwarf Cepheids exhibit flux deficiencies at the shortest observed wavelengths. The most extreme deficiencies appear for SX Phe; these may be related to the other properties previously noted for this star, including low metallicity, high space motion, and low luminosity.

Sturch, C. R.↗
NASA NTRS1982

Observations of RR Lyrae with the ANS satellite

Photometric observations of RR Lyr in the ultraviolet have been obtained using the Astronomical Netherlands Satellite. The observations are compared with theoretical light curves calculated using synthetic spectra and angular diameters determined as a function of phase for RR Lyr by Manduca et al. from photometry at longer wavelengths. A good agreement is found. A bump in the observed light curves in the phase range 0.6 to 0.8 supports the existence of a shock as predicted by Hutchinson, Hill, and Lillie.

Bonnell, J.↗
NASA NTRS1982

Ultraviolet light curves of the dwarf novae U Geminorum and VW Hydri

The optical light curves of many dwarf novae show a prominent hump. This hump is attributed to a hot spot located where the gas stream from the cool secondary star strikes the accretion disk around the white dwarf primary. In the present investigation, the energy distribution of the hot spot is obtained from the amplitude of the hump in different wavelength regions. The color temperature of the hot spot is derived, and the temperature and optical thickness for thermal free-free emission models for the spot is discussed. The nature of the disk is studied by comparing its UV-optical energy distribution with computed accretion disk models. The ultraviolet light curves of two quiescent dwarf novae, U Gem and VW Hyi is derived by combining Astronomical Netherlands Satellite (ANS) photometry from several different epochs.

Wu, C.-C.↗
NASA NTRS1982

The early-type component in v1 Sagittarii

Four low-resolution UV spectra of v1 Sgr (cK2) were obtained with the IUE satellite to investigate the nature of the hot component in this object, which was detected in the Astronomical Netherlands Satellite UV photometric data. The IUE results show that the spectral energy distribution of v1 Sgr in the FUV is comparable to that of a B9 star. FUV flux level, when compared with that of the mid-ultraviolet flux level, indicates that the luminosity of the hot component is roughly equivalent to that of a main-sequence star, assuming that the mid-ultraviolet flux is dominated almost entirely by a K2 I object. No discernible spectral features are present in the FUV, contrary to what may be expected in a star of B9 spectral type. Two possible interpretations are suggested: the hot component is a rapidly rotating star, or an accretion disk surrounding a central object which could be a collapsed star is being observed.

Kondo, Y.↗
NASA NTRS1982

The circumstellar extinction of RY Sagittarii

In 1979-80, ultraviolet spectrophotometry of RY Sgr was obtained by the International Ultraviolet Explorer (IUE) during the star's recovery from its 1977-78 minimum. The wavelength dependence of the extinction of this R Coronae Borealis-type variable was determined by comparison of spectra obtained at different times but with nearly the same pulsational phase. The measured wavelength dependence is compatible with theoretical predictions of extinction by spherical graphite particles having a radius of 0.043 micron and with the extinction observed for amorphorus carbon smoke.

Holm, A. V.↗
NASA NTRS1982

Infrared, optical, and ultraviolet observations of hydrogen line emission from Seyfert galaxies

Nearly simultaneous observations are reported of P-alpha, H-alpha, and H-beta emission from 18 Seyfert galaxies and of Ly-alpha from eight of these galaxies. In many cases, P-alpha is stronger relative to the Balmer lines than is predicted by recombination calculations; reddening appears to be required. Dispersion in the P-alpha/H-alpha/H-beta ratios orthogonal to the reddening track indicates that high densities or optical depths also affect the line flux ratios. Several galaxies, notably NGC 1275, have very low P-alpha/H-alpha ratios. High densities, large optical depths, and reddening probably all contribute to the low observed Ly-alpha/H-beta ratios.

Lacy, J. H.↗
NASA NTRS1982

The gaseous galactic halo as inferred from the line spectra of the galaxies Markarian 509 and Fairall 9

Narrow interstellar absorption lines of S II 1259.52, Si II 1260.42, and Fe II 1608.46 due to gas in the disk and the halo of the Galaxy have been detected in the spectrum of the Seyfert galaxy Mrk 509 with the International Ultraviolet Explorer. This gas is also seen at higher resolution in the Ca II and Na I absorption lines in two components at LSR velocities of +6 and +62 km/s. In addition, narrow Ly-alpha and C IV absorption near the Seyfert redshift seem to be present in the spectrum. Si II 1260.42 absorption from the galactic disk and from the Magellanic Stream or the halo of the SMC have been detected with the IUE in the spectrum of Fairall 9. The observations of these two objects when combined with existing results are shown to be consistent with a corotating galactic halo having a height of less than 10 kpc at the sun.

York, D. G.↗
NASA NTRS1982

ANS spectrophotometry - The bright X-ray binaries Hercules X-1 /HZ Herculis/ and Cygnus X-1 /HDE 226868/

Complete ultraviolet light curves for HZ Her immediately after a well-defined X-ray turn-on in 1975 are obtained. The features of the curve are found to correspond well with features seen in the optical. The absolute level of emission at maximum light at 1550 A is in good agreement with the calculations of the X-ray reflection effect of Milgrom and Salpeter (1975). It is found that at 1550 A approximately 20% of the light at maximum comes from the accretion disk. Similar observations of Cyg X-1 make it possible to determine the degree of reddening, equivalent to E(B-V) = 0.95 + or - 0.07, from the strength of the 2200 A interstellar absorption feature. The distance inferred from this amount of reddening requires that the optical star be luminous and, therefore, massive. Observations obtained during the May 1975 X-ray transition show ultraviolet excess when compared with the data obtained six months later.

Wu, C.-C.↗
NASA NTRS1981

Five-color band ultraviolet photometry of fourteen close binaries

Photometric observations obtained with the Astronomical Netherlands Satellite in five ultraviolet wavelength regions for 14 close binaries are presented. Strong excess far-ultraviolet flux is detected in four objects. The binaries TT Hya, RX Cas, and SX Cas exhibit a pronounced excess of far-ultraviolet flux, which is thought to be the result of mass transfer phenomena in these systems. Observations of the binary R Ara show very peculair variations; its far ultraviolet flux at 1550 A brightened by 0.4 mag between phases 0.7 and 0.8, while its near ultraviolet flux at 3300 A decreased by 0.5 mag over this same half-day interval. The A0 II-III component in the system RZ Sct is seen to dominate the ultraviolet spectrum.

Kondo, Y.↗
NASA NTRS1981

The C IV 1550 profile in type 1 Seyfert galaxies

The paper presents C IV 1550 A line profiles for the type 1 Seyfert galaxies NGC 5548, Mrk 509, NGC 7469, and MCG-2-58-22. Several line broadening mechanisms and theoretical line profiles are considered, and random motion of discrete clouds is ruled out. A spherical ensemble of discrete clouds with steady outflow or inflow produces a logarithmic profile, but does not account for the highly extended wings. A spherical ensemble with ballistic outflow produces a profile of the first exponential integral function, and fits the observed profile to the continuum level. Although C IV profiles favor the ballistic model, both Mrk 509 and NGC 7469 have significant asymmetry, and Balmer lines with a higher optical depth show higher asymmetry and redshift than all four galaxies.

Wu, C.-C.↗
NASA NTRS1981

Empirical relationship of ultraviolet extinction and the interstellar diffuse bands

New ultraviolet colors are presented for 110 hot stars. These data are combined with infrared colors and diffuse-band measurements to study the relationship of diffuse interstellar bands (4430, 5780, 6284 A) to the overall extinction curve. Equivalent widths of 5780 A and 6284 A are not well correlated with infrared, visible, or ultraviolet extinction measurements for stars in this sample. The central depth of 4430 A is well correlated with visible and infrared extinction, but less well correlated with UV extinction at 1800 A. The wavelength 4430 A is strongly correlated with the strength of the 2200-A bump. The data suggest that if small grains account for the general rise in UV extinction, the diffuse bands are not formed in these grains. The wavelength 4430 A may well arise in large grains and/or in the material responsible for the 2200-A bump. Correlations with UV extinctions derived by other authors are discussed in detail. It is suggested that definitions of extinction parameters and band shapes, as well as selection effects in small samples of stars, may still compromise conclusions based on correlation studies such as are being attempted.

Wu, C.-C.↗
NASA NTRS1980

An ultraviolet extinction study of the rho Ophiuchi dark cloud

Five-band ultraviolet spectrophotometry has been carried out for 54 stars in the upper Scorpius complex. Of these, 14 stars in the rho Ophiuchi dark cloud and 13 in the surrounding area are found to be free of spectral peculiarities and contamination by scattered light from nearby bright stars. The dark cloud stars give extinction curves which are significantly lower than the average extinction curves derived by other investigators and also those observed for localized regions such as the area around Cygnus X-1 and the Cepheus OB III cluster. This implies that the dust in the upper Scorpius region, especially that in the rho Ophiuchi dark cloud has larger average size than the normal interstellar medium. R, the ratio of total-to-selective extinction, is found to be 4.2. The effects of a lower extinction curve on the chemistry of a dark cloud is also briefly discussed.

Wu, C.-C.↗
NASA NTRS1980

Ultraviolet colors of W Ursae Majoris - Gravity darkening, temperature differences, and the cause of W-type light curves

The paper presents photometry of the prototype W UMa binary system in three ultraviolet bands with the ANS satellite. It was found that W UMa has low-gravity darkening beta of 0.03; that temperature differences between the components not established by gravity darkening are insignificant; and that the bolometric albedo is not very large. It was also found that W UMa is limb-darkened in the ultraviolet region, and that the inner hemisphere of the less massive component is hotter than that predicted by gravity darkening and the reflection effect. It was concluded that about 20% of the surface area of the component responsible for large gravity darkening is covered by dark spots distributed uniformly in the longitudinal direction. An observational value of the convective darkening exponent of 0.054 plus or minus 0.02 is proposed.

Eaton, J. A.↗
NASA NTRS1980

Colors and magnitudes predicted for high redshift galaxies

Ultraviolet observations of nearby galaxies with the ANS are used to derive ultraviolet spectra for different galaxy types. These spectra are used with existing visible spectrophotometry to calculate K-corrections, and to predict colors and magnitudes for various galaxy types as a function of redshifts, to z = 2. No evolutionary effects are considered. It appears that the first-ranked cluster galaxies on blue emulsions should be spirals for z greater than or approximately equal to 0.5.

Coleman, G. D.↗