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Point-source contamination in high-precision Cosmic Microwave Background (CMB) maps severely affects the precision of cosmological parameter estimates. Among the methods that have been proposed for source detection, wavelet techniques based on ``optimal'' filters have been proposed.In this paper we show that these filters are in fact only restrictive cases of a more general class of matched filters that optimize signal-to-noise ratio and that have, in general, better source detection capabilities, especially for lower amplitude sources. These conclusions are confirmed by some numerical experiments. \keywords{Methods: data analysis -- Methods: statistical, Comment: 6 pages, 3 figures

The colliding-wind binary system WR140 (HD193793, WC7pd+O4-5, P=7.94 yr) was monitored in the ultraviolet by IUE from 1979 to 1994 in 35 short-wavelength high-resolution spectra. An absorption-line radial-velocity solution is obtained from the photospheric lines of the O component, by comparison with a single O star. The resulting orbital parameters, e=0.87 +/- 0.05, w=31 degrees +/- 9 degrees and Ko star=25 +/- 15 km s(-1), confirm the large eccentricity of the orbit, within the uncertainties of previous optical studies. This brings the weighted mean UV-optical eccentricity to e=0.85 +/- 0.04. Occultation of the O-star light by the WC wind and the WC+O colliding-wind region results into orbital modulation of the P-Cygni profiles of the C II, CIV and Si IV resonance lines. Near periastron passage, the absorption troughs of those resonance-line profiles increase abruptly in strength and width, followed by a gradual decrease. In particular, near periastron the blue black-edges of the P-Cygni absorption troughs shift to larger out ow velocities. We discuss that the apparently larger wind velocity and velocity dispersion observed at periastron could be explained by four phenomena: (i) geometrical resonance-line eclipse effects being the main cause of the observed UV spectral variability, enhanced by sightline crossing of the turbulent wind-wind collision zone; (ii) the possibility of an orbital-plane enhanced WC7 stellar wind; (iii) possible common-envelope acceleration by the combined WC and O stellar radiation fields; and (iv) possible enhanced radiatively driven mass loss due to tidal stresses, focused along the orbiting line of centers.

We present here the analysis of ultraviolet spectra from IUE and an X-ray spectrum from ROSAT PSPC observations of the X-ray weak, far-infrared loud AGN, PG 1126-041 (Mrk 1298). The first UV spectra taken in June 1992, simultaneously with ROSAT, show strong absorption lines of NV, CIV and SiIV, extending over a velocity range from -1000 to -5000 km/s with respect to the corresponding line centre. Our analysis shows that the Broad Emission Line Region (BELR) is, at least partially, covered by the material causing these absorption lines. In the IUE spectrum taken in Jan. 1995, the continuum was a factor of two brighter and the UV absorption lines are found to be considerably weaker than in 1992, but only little variation in the emission line fluxes is found. With UV spectral indices of A_{uv} \simeq 1.82 and 1.46 for the 1992 and 1995 data, the far UV spectrum is steep. Based on the emission line ratios and the broad band spectral energy distribution, we argue that the steepness of the UV spectrum is unlikely to be due to reddening. The soft X-ray emission in the ROSAT band is weak. A simple power-law model yields a very poor fit with a UV-to-X-ray spectral index A_{uvx}=2.32. Highly ionized (warm) absorption is suggested by the ROSAT data. After correcting for a warm absorber, the optical to X-ray spectral slope is close to the average of A{uvx}\simeq 1.67 for radio quiet quasars., Comment: 8 pages, 9 postscript figures. Mon. Not. Roy. Astr. Soc., accepted

The World Space Observatory is an unconventional space project proceeding via distributed studies. The present design, verified for feasibilty, consists of a 1.7-meter telescope operating at the second Largangian point of the Earth-Sun system. The focal plane instruments consist of three UV spectrometers covering the spectral band from Lyman alpha to the atmospheric cutoff with R~55,000 and offering long-slit capability over the same band with R~1,000. In addition, a number of UV and optical imagers view adjacent fields to that sampled by the spectrometers. Their performance compares well with that of HST/ACS and the spectral capabilities of WSO rival those of HST/COS., Comment: 11 pages, including 7 figures and 5 tables To be published in Proc SPIE, vol 4854

THE intrinsic extreme ultraviolet (EUV) spectrum of quasars, in which spectral lines of He and CNO ions should appear, is in most cases strongly absorbed by the hydrogen Lyman continuum of intergalactic matter at cosmological distances. The bright quasar HS1700 + 6416 (at redshift z = 2.72), from the Hamburg survey1, is a fortuitous exception, the line of sight towards it being relatively transparent. Here we report detailed ultraviolet spectroscopic measurements of HS1700 + 6416, obtained with the Hubble Space Telescope. We observe a rich absorption line spectrum, in which many EUV resonance lines (including He I, O II to O v, and N III and N IV) are seen. The O/C abundance ratios inferred from the line-strengths are higher than Solar System values by factors of 3 to 5. This suggests that the absorbing material is halo gas of early galaxies, from which population II stars have yet to form, oxygen being a primary nucleosynthesis product from a first generation of massive stars.

Editorial. Part 1: I. Achievements of the Present Generation of Space Observatories. II. Achievements of the Present Generation of Ground--Based Telescopes. III. Stars. IV. Interstellar Medium and Galaxies. V. Cosmology. VI. Observations at Many Wavelengths: Panel Discussion on Coordination of Observations at Many Wavelengths. VII. The New Generation of Large Ground--Based Telescopes. VIII. The New Generation Space Telescopes. IX. New Technologies for Astronomy. X. Summary, Priorities and Objectives for the 21st Century. Part 2: XI. Stars. XII. Interstellar Medium and Galaxies. XIII. New Technologies for Astronomy. Index.

This poster addresses a class of Wolf-Rayet stars which show phenomena of colliding supersonic mass-loss winds: variable non-thermal radio emission, variable IR excesses due to episodic dust formation, variable UV P-Cygni profiles due to instabilities in the wind and eclipse effects, variable excessive X-ray emission, and possibly γ-ray emission.

We present the data and initial results from a combined Hubble Space Telescope (HST)/IUE/ground-based spectroscopic monitoring campaign on the Seyfert 1 galaxy NGC 5548 that was undertaken in order to address questions that require both higher temporal resolution and higher signal-to-noise ratios than were obtained in our previous multiwavelength monitoring of this galaxy in 1988-1989. IUE spectra were obtained once every 2 days for a period of 74 days beginning on 1993 March 14. During the last 39 days of this campaign, spectroscopic observations were also made with the HST Faint Object Spectrograph (FOS) on a daily basis. Ground-based observations, consisting of 165 optical spectra and 77 photometric observations (both CCD imaging and aperture photometry), are reported for the period 1992 October-1993 September, although many of the data are concentrated around the time of the satellite-based program. These data constitute a fifth year of intensive optical monitoring of this galaxy. In this contribution we describe the acquisition and reduction of all of the satellite and ground-based data obtained in this program. We describe in detail various photometric problems with the FOS and explain how we identified and corrected for various anomalies.

The near infrared emission (NIR) of radio quiet active galactic nuclei is commonly attributed to dust, absorbing and re-emitting some of the nuclear UV radiation. The dust can survive only at distances larger than a few light months, and any rapid variation of the nuclear radiation, on timescales of a day or less, will be completely smeared out.

High-resolution spectra of the QSO 3C 273 were obtained in 1989 and added to two spectra recorded in 1982. The coadded spectra represent 600,000 s of integration at a resolution of 30 km/s from 1200 to 2000 A. The line of sight passes through the Virgo Cluster the entire halo of the Milky Way, at Galactic latitude b = 64 deg, and foreground X-ray-emitting material from local disturbed gas. The observed equivalent width of Galactic C IV is greater than the equivalent width of C II, a situation that is uncommon in local gas but is often found in QSO absorption line systems. The lines of C IV, Al III, and Si IV may arise in an extended halo or may be associated with local disturbed gas in a radio loop. The remaining detected species (H I, C II, Si II) arise predominately from the local gas. Most of the gas is probably within 5 kpc, but no firm conclusion is reached. Possible detection of interstellar absorption due to the Virgo Cluster is discussed.

The possibility is considered, and shown to be plausible, that the strong C IV and Si IV absorption lines in low-resolution ultraviolet spectra of gas-rich dwarf galaxies are primarily interstellar, not stellar as has been supposed. The argument is based on analogies with H II regions in the Local Group, on low-resolution equivalent width measurements of gas-rich dwarf galaxies from the literature and on high-resolution UV spectra of NGC 1705.

One of the reasons why the bright supernova SN1987A is of such importance is the fact that its proximity would allow for the first time, the identification of a supernova progenitor star. Attempts to establish which star was the progenitor have led to uncertainties, however. Here we use spatial and spectroscopic information from International Ultraviolet Explorer (IUE) spectra in the range 1,150–1,950A to demonstrate that Sk–69 202, the star coinciding positionally with the Large Magellanic Cloud (LMC) supernova, has disappeared from sight. Two weaker sources, named star 2 and star 3 in the astrometric analysis of the image of Sk–69 202 before the supernova outburst, are still present in the ultraviolet spectra. We isolate their spectra and give a spectral classification. We conclude that Sk-69 202 is the progenitor the LMC supernova.

SummaryRecent EXOSAT observations of active galactic nuclei are presented. Unlike earlier X-ray satellites (all of which flew in low earth orbit), the deep orbit of EXOSAT allows long continuous observations of celestial X-ray sources, uninterrupted by earth occultation etc. We present the results of EXOSAT observations of several AGN which have been seen to vary rapidly (timescale 0.2–6 hours). We also consider the implications of rapid variability in AGN. For Seyfert galaxies and quasars, we find a highly significant correlation between the timescale of variability and their X-ray luminosity. They are not, howwever, bounded either by the (classical) Eddington limit nor by efficiency arguments. We sugest, rather, that the emitting plasma is dominated by electron-positron pairs.

In 1985 April, the WC7+abs star WR140 = HD 193793 was observed to have brightened by over two mag. in the infrared owing to the formation of a new dust shell. The growth and evolution of the shell was monitored by infrared observations using UKIRT during the remainder of 1985. Examination of infrared photometry of this star since 1979 and previously published data indicate that the dust formation occurs at intervals of 7.9 years. Phasing the published radial velocities of the absorption line component with this period confirms that it is a member of an eccentric (e = 0.7-0.8) binary system having periastron passage shortly before dust formation. Further evidence of the distortion of the stellar wind from the WC7 component is provided by changes in the P Cygni profile of the C IV lines observed with IUE while the dust was forming. The X-ray spectrum also changed between 1984 and 1985 in becoming significantly “harder” while the non-thermal radio source was extinguished. An interpretation is sought in terms of a model wherein the non-thermal radio and X-ray emission is excited by collision of the WC and O star winds and modulated by the orbital motion. A suitably compressed region of the wind must be advected far enough from the stars to form dust.

The behavior of the C IV 1550 A emission line strength in variable active galactic nuclei (AGNs) such as Seyfert 1 galaxies and one broad-line radio galaxy (BLRG) is discussed on the basis of low-resolution spectra from IUE. The results are compared with those obtained previously for QSO samples. The variation of individual AGNs indicate that they present matter-bounded conditions when the AGN is in a high-luminosity state. Such behavior is illustrated by the variations seen in the Seyfert 1 galaxy F9, where the transition from photon-bounded to matter-bounded occurs at a transition luminosity of ergs/sec per Hz. The results indicate the existence of a transition luminosity, which appears to be typical for an individual galaxy. An absolute luminosity limit also appears to be present both in the C IV line at 45.0 ergs/sec and for the continuum at 31.7 ergs/sec per Hz. 25 references.

Averaged low-resolution IUE spectra of the Seyfert I galaxy NGC 3783 at two brightness levels are presented. The wavelength interval 1250-1400 A, which is essentially free of emission lines in active galaxies, contains two absorption lines at 1303 A and 1335 A. The line at 1303 A shows, in contrast to the line at 1335 A, considerable variations with continuum brightness. This is interpreted as variations in the Si III (4) metastable absorption at 1294-1305 A, with an outflow velocity of about 3000 km/s. C IV absorption at the same velocity is present when the galaxy is bright. This indicates the presence of outflow of material, which is optically thin to the variable ionizing UV continuum. The variable UV continuum has to extend at least until 50 eV (about 250 A). 10 references.

A 1-micron CCD picture and maps of the Ne II and Ar III fine-structure lines have been obtained in a region roughly one arcmin in size centered on the core of the compact H II region G333.6 - 0.2. The two emission-line maps show nearly identical intensity distributions, although much different fluxes. The maps are similar to the 1-micron picture smoothed to their angular resolutions. The infrared line of S IV also was detected and appears to have a spatial intensity distribution similar to that of the other fine-structure lines. The 1-micron picture reveals a small number of objects of nearly stellar appearance in the core, suggesting that G333.6 - 0.2 is powered by a compact cluster of sources. Stellar continuum radiation probably is responsible in part for the low equivalent width of the B-gamma line in the core.