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Sitko, M. L.

Publications and source records attributed to Sitko, M. L..

24 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Two multifrequency observations of the BL Lacertae object OJ 287

Results are reported for various sets of X-ray, UV, visual, IR, millimeter, and radio observations of OJ 287. The spectral information is used to constrain nonthermal energy production models for the source, and three possible models are considered. It is found that, in order to describe all the observed flux in the radio to X-ray bands with a synchrotron self-Compton model, a high degree of relativistic beaming is required such that the equivalent Doppler factor ranges from about 20 to 165. It is concluded that submillimeter flux and X-ray spectral measurements could distinguish between the two possible models that fit the present observations.

Worrall, D. M.↗
NASA NTRS1982

Ultraviolet, visual, and infrared observations of the WC7 variable HD 193793

Low-resolution IUE data are used to explore the ultraviolet extinction toward the Wolf-Rayet star HD 193793 and to search for ultraviolet variability that might relate to the infrared variability. High-dispersion IUE observations are used to investigate the nature of the stellar wind of the star and to search for anomalies in the interstellar line spectrum that might be expected to be found toward a star that has recently formed a dust shell. Finally, the ultraviolet and new visual and infrared data are combined to investigate the full energy distribution of this unusual source. The energy distribution is found to extend from 0.12 to 12.5 microns, and the ultraviolet data suggest a normal WC-7 type star. A wind terminal speed of about 3000 km/s is implied by the data, as well as an E(B-V) value of 0.85. The dereddened ultraviolet to visual energy distribution is consistent with a star having effective temperature of about 43,000 K.

Fitzpatrick, E. L.↗
NASA NTRS1981

Spectral energy distributions of hot stars with circumstellar dust

Combined spectral energy distribution curves of six Ae/Be stars (BD+61 deg 154, AB Aur, V380 Ori, HD 259431, ZCMa, and BD+40 deg 4124), five peculiar shell stars (HD 31648, HD 45677, HD 50138, HD 163296, and HD 190073), and the peculiar central object in the Red Rectangle nebula (HD 44179), obtained with the IUE and a variety of ground-based optical and infrared telescope systems, are presented, covering the wavelength range of approximately 1300 A to 12.5 microns. The observations are reviewed, and include ultraviolet observations, low-resolution absolute visual spectrophotometry, moderate-resolution relative visual spectrophotometry, and infrared photometry. For most of the objects the ratio of the flux deficiency for lambda equals less than 1 micron to the flux excess for lambda equals greater than 1 micron is approximately unity. Only two of the objects (AB Aur and HD 163296) possess a strong emission feature at 9.7 microns, while one other (HD 31648) may have a weak 9.7 micron emission feature. Most of the objects have a broad, smooth, infrared emission curve resembling those seen in some WC stars. It is concluded that the dust surrounding these stars may be different from that seen in the diffuse interstellar medium.

Sitko, M. L.↗
NASA NTRS1981

Ultraviolet observations of hot stars with circumstellar dust shells

Absolute fluxes over the wavelength range 1200-3200 A are presented for 13 normal early-type stars and 12 early-type stars known to have large IR excess; the data were obtained to study the UV spectral modifications produced by absorbing circumstellar dust particles. It is found that all the Be/shell stars whose spectral types are later than B6 exhibit greatly enhanced line absorption due to circumstellar Fe II. The circumstellar gaseous line absorption in stars cooler than B6 severely complicates the study of circumstellar dust absorption. However, those B and A stars that exhibit the circumstellar 9.7-micron emission feature have a very large increase in circumstellar absorption for 1800 A; such absorption is expected from circumstellar silicate particles.

Sitko, M. L.↗
NASA NTRS1980

Ultraviolet, visual, and infrared observations of the peculiar Be star HD 45677

The peculiar Be star HD 45677 was observed at low and high resolution by the IUE, and nearly simultaneous optical and IR observations were obtained with ground-based telescopes. These data were used to produce a spectral energy distribution extending from 0.12 to 12.6 microns in order to investigate the conversion of UV to IR radiation in the circumstellar dust shell. The high-resolution spectra indicate a spectral type of B2 in agreement with the optical classification.

Sitko, M. L.↗