Engineering Papers⌕ Search

Engineering topics

Wu, C.-C.

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

47 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

The ultraviolet continua of the nuclei of M31 and M81

Ultraviolet measurements of the central 2.5 arcmin of M31 and M81 made with the ANS satellite are reported. A library of standard-star observations is also included for comparison. In agreement with OAO 2 results, it is found that both galaxies exhibit a significant UV excess as compared to expectations for a pure, old metal-rich stellar population including just the main sequence and giant branch. Model calculations show that the excess UV light could be produced either by young stars or by commonly occurring hot stars in an old stellar population. At the present time, several lines of evidence slightly favor old stars. An ultraviolet excess of similar magnitude seems to be common to all early-type galaxies yet observed in the UV and thus may significantly affect the appearance of redshifted galaxies.

Wu, C.-C.↗
NASA NTRS1980

IUE observations of WZ Sagittae in outburst

Preliminary results of the analysis of the low resolution spectra from the recurring nova WZ Sagittae are discussed with reference to the similarity between WZ Sge and dwarf novae and the applicability of accretion disk models. It is found that the spectrum observed on Dec. 1, 1978, is in very good agreement with a simple steady-state disk model of Lynden-Bell (1969) which predicts a power law spectrum over a limited range of frequency. Analysis of the observations within the framework of this model gives a value of the mass of the white dwarf larger than that estimated by Robinson et al (1978).

Holm, A. V.↗
NASA NTRS1979

Interstellar extinction and ultraviolet flux distribution of Scorpius X-1

Measurements of absorption at 2200 A for Sco X-1 indicate an E(B-V) of approximately 0.28. The distance to Sco X-1 is estimated to be 350 pc while the X-ray luminosity is thought to be 5 times 10 to the 36th ergs/sec. It is found that the de-reddened ultraviolet flux distribution closely resembles a blackbody at 26,000 K. Brightness variations and their relation to flickering phenomena are considered.

Wu, C.-C.↗
NASA NTRS1979

Ultraviolet and X-ray observations of Seyfert galaxies and low z QSOs

An analysis of IUE observations of Seyfert galaxies and QSOs indicates that they have the same energy source and heating mechanisms. Neither collisional de-excitation nor simple dust models are sufficient to explain the small L alpha/H beta ratio of Seyfert galaxies and low z QSOs, which is below the recombination value. For Seyfert galaxies, the Log nu (1450) correlates well with Log W lambda (C IV), with a slope similar to that of QSOs. Regarding X-ray fluxes, which were obtained by the A2 experiment onboard the HEAO-1 satellite, the L alpha luminosity correlates well with the continuum luminosity at 1450 A, and there is a positive correlation between the X-ray luminosity and the full line width at zero intensity.

Wu, C.-C.↗
NASA NTRS1979

IUE observations of two high redshift /z more than 3/ QSO's

By means of a collaboration across the Atlantic, very long exposures (about 14 hours) have been made with IUE of two high redshift QSO's during October 1978. Target acquisition and initiation was carried out at Vilspa, and the completion of the exposure and read-out of the image was executed at Goddard. The first object Q 2204-408 is an optical QSO with m(v) = 17.5 and z = 3.18 whose spectrum had just been detected earlier with a 350 minute exposure in the short wavelength spectrograph (Wilson, et al. 1978). In this case two longer exposures were obtained in both spectrographs. The other object is the radio QSO PKS 2126-158 with m(v) = 17.3 and z = 3.27 for which a detectable spectrum was obtained in the short wavelength spectrograph.

Boggess, A.↗
NASA NTRS1978

IUE observations of X-ray sources - HD153919 /4U1700-37/, HDE226868 /Cyg X-1/, HZ Her /Her X-1/

The first UV spectroscopic measurements of binary X-ray sources with IUE show highly variable emission from a photoionized plasma in the object HZ Her, and give evidence for localized circumsystem material in the binary source Cygnus X-1. In addition, a substantial stellar wind is found in one of the brightest identified X-ray sources HD153919. This system may be surrounded by an extensive H II region unusual in its content of high excitation ion species.

Dupree, A. K.↗
NASA NTRS1978

Ultraviolet observations and the extended spectrum of NGC 4151

Five-channel ultraviolet photometry of the Seyfert galaxy NGC 4151 was obtained at three epochs with the ANS. These data are combined with other recent results to illustrate the spectrum of the nucleus of NGC 4151 from 34 microns to 20 MeV, with corrections for galaxy contamination. It is found that no other part of the spectrum has a slope like the best-fitting power law for the X-rays. The C IV emission-line flux is measured; the C IV/H-beta ratio is between 5 and 8, which is similar to the ratio in quasars.

Wu, C.-C.↗
NASA NTRS1978

New observations of ultraviolet variability in Wolf-Rayet stars

Observations of ultraviolet variability in Wolf-Rayet stars have been made with the ANS satellite Ultraviolet Photometer Experiment. Significant variations are detected in several of the observed stars, the timescale of the variability ranging from a few minutes to several months.

Burton, W. M.↗
NASA NTRS1977

Ultraviolet observations of 3C 273 by the ANS

Five-band spectrophotometry between rest wavelengths of 1340 A and 2850 A is presented. The 2200-A absorption feature seems to be present in 3C 273 with a depth appropriate for an internal reddening of E(B-V) = 0.13. The dereddened ultraviolet flux distribution can be described by a power law of spectral index 1.21. This power law can account for the observed flux in X-rays. It provides more photons than needed to excite the observed H-beta by photoionization and Fe II lines by resonance fluorescence. The emission-line flux ratios, Ly-alpha/C IV/ semiforbidden C III/H-beta are 100/80/60/10.

Wu, C.-C.↗
NASA NTRS1972

A study of the unidentified interstellar diffuse features.

The interstellar diffuse lines at 5780 and 5797 A have been observed in 66 stars using the Washburn Observatory echelle spectrograph coupled with an image tube. At a resolution of 0.17 A, the profiles of these diffuse lines are asymmetric and steeper to the blue. There is also a broad, shallow feature shortward of 5780 A. The FWHM of 5780 and 5797 are respectively 2.7 A and 1.1 A. Equivalent widths of 5780, 5797 have been measured at a resolution of 0.26 A, and they present a very tight correlation. It is very likely that these two diffuse lines are carried by the same agent. This investigation proposes that the two lines are produced by the pure electronic transitions of the impurity centers in solid grains, with the broad, shallow absorption feature shortward of 5780 A as the absorption sideband associated with the parent pure electronic line.

Wu, C.-C.↗