The astrometric binary Mu Cas: Photographically almost resolved, and its implications on the primordial helium abundance

The Population 2 sub-dwarf star mu Cas was photographed, yielding elongated images from which the separation magnitude of the unseen component can be derived

An atlas of emission line fluxes of planetary nebulae in the 1150-3200 A region

Emission line fluxes for 28 planetary nebulae are presented. The nebulae were chosen to cover a wide range of excitation classes, apparent diameters, location in the sky, and types of central stars. All objects were observed in the low dispersion mode of the IUE spectrographs, using the large entrance aperture

Blackbody curves for the IUE spectral range lambda 1150 to lamda 3200 from 6,000 to 200,000 K

Two sets of blackbody curves are presented for the wavelength region covering the international ultraviolet explorer spectrographs. One set is normalized to unity at 3200 A, the other is normalized at 1900 A for those astronomers primarily interested in data for the SWP range. The blackbody curves extend from 1150 to 3200 A and cover the temperature range from 6,000 to 200,000K

The transit of Mercury of 10 November 1973

The transit of Mercury of November 10, 1973 was observed from Silver Spring, Maryland (76 deg 58' W, 39 deg 01' N) for the period 6:48:00 EST, near sunrise, to 8:17:18 (contact 4). A total of 24 frames of 35mm Pan X film were taken through a Questar telescope equipped with a sun filter of 40mm aperture. The diameter of the solar image is 13mm on the film. Transit photographs from the observation are included

The spectrum of HM Sagittae: A planetary nebula excited by a Wolf-Rayet star

A total of image tube spectrograms of HM Sagittae were obtained. More than 70 emission lines, including several broad emission features, were identified. An analysis of the spectra indicates that HM Sagittae is a planetary nebula excited by a Wolf-Rayet star. The most conspicuous Wolf-Rayet feature is that attributed to a blend of C III at 4650 A and He II at 4686 A

On a suspected ring external to the visible rings of Saturn

The reexamination of a photograph of Saturn taken on 15 November 1966 when the earth was nearly in the ring plane is investigated which indicates that ring material does exist outside the visible rings, extending to more than 6 Saturnian radii. The observed brightness in blue light was estimated per linear arc second, implying a normal optical thickness, for ice-covered particles

IUE Observations of the Peculiar Star RX Puppis

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 and/or gas streamers between the cool giant and the hot companion. The continuum observed by us in low dispersion is fairly flat in the wavelength region 1200-2000 A and rises toward longer wavelengths in the region 2000-3200 A. It cannot be due to a star earlier than AO II. Alternatively it may be from an accretion disk. We find electron densities in the line-emitting region in the range 109-1011 em- 3 , temperatures in the range 10,000-20,000 K, and linear sizes :S a few x 1013 em. We find that the photoionizing radiation may be due to the presence of an unseen, hot subdwarf with most probable effective temperature in the range 75,000-90,000 K. Alternatively it may be due to an accretion disk around a secondary with boundary layer temperature -105 K. Short-range as well as long-range monitoring of this very interesting object in the far-UV would be very helpful in understanding the nature of its peculiar properties and the connection between slow novae and symbiotic stars

Ultraviolet Observations of Four Symbiotic Stars

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 may be originating from an accretion disk and/or hot subdwarf that photoionizes circumstellar material, and gives rise to the high excitation lines we have detected. The Bowen fluorescent excited lines of 0 III in SY Mus exhibit slightly broadened profiles that suggest possible turbulent motions in an extended circumstellar cloud with characteristic velocities ~ 300 km s^-1

Grains in Ionized Nebulae: Spectral Line Diagnostics

The depletion of condensable elements onto grains in gaseous nebulae can provide evidence that dust is well mixed with the ionized gas. Al and CA are two of the most depleted elements in the general interstellar medium, and it is therefore important to measure their abundances within the ionized region of nebulae. We compute a large grid of photoionization models and identify sets of line ratios which are relatively insensitive to stellar and nebular parameters, and are thus excellent diagnostics for determining relative abundances. Based on the absence of the [Ca II] λλ7291, 7324 doublet and the detection of Al II] λλ2660, 2669 in the ultraviolet, we determine the extent of aluminum and calcium depletion onto grains in NGC 7027 and the Orion Nebula. Our results show a approximately 0.3 dex depletion for Al, but a depletion of more than two and a half orders of magnitude for Ca. A similar calculation based on Mg II λ2798 yields roughly a 0.8 dex depletion for Mg. This reaffirms the discrepancy between depletion determined from high and low ionization Mg lines. We also find evidence for a \u27depletion gradient\u27 in Ca in NGC 7027, since the calcium depletion we infer for the outer, more neutral regions using [Ca II] is somewhat higher than that inferred for the inner high-ionization region, using [Ca v]. This gradient can test current models of the survival of grains within hot ionized gas

A Brightening of the Symbiotic Variable SY Muscae

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 mass transfer from the cool star whose period is 623 d and whose maximum was predicted to occur very close to the time of the June 1981 observations. Alternatively the hot star and much of the emitting gas could have been in eclipse in September 1980