arXiv subjects

W. Wamsteker

Publications and source records attributed to W. Wamsteker.

26 records · Page 2Linked to original sources

arXiv1999

The INES System III: Evaluation of IUE NEWSIPS High Resolution Spectra

This paper discusses the overall quality of IUE high resolution data processed with the NEWSIPS software in terms of flux and wavelength accuracy. It also describes the processing of NEWSIPS high resolution spectra within the framework of the ESA ``IUE Newly Extracted Spectra'' (INES) System. This system provides the IUE high resolution data in two formats: the high resolution ``concatenated'' spectra, in which the spectral orders are connected, eliminating the overlap regions through a procedure designed to optimize the signal-to-noise ratio at the edges of the orders, and the ``rebinned'' spectra, i.e. the high resolution concatenated spectra resampled into the low resolution wavelength domain. Our study reveals the existence of a significant discrepancy in the wavelength scales of short and long wavelength NEWSIPS high resolution spectra. The INES processing applies a correction of +17.7 km/s to the wavelength scale of the high resolution SWP spectra in order to provide an internally consistent velocity scale. Similarly, suitable corrections have been applied to long wavelength small aperture spectra. The new wavelength scale is, within the errors, in good agreement with the optical velocity scale.

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arXiv1999

The INES System II: Ripple Correction and Absolute Calibration for IUE High Resolution Spectra

In this paper we document the results of the study which led to the ripple correction and absolute calibration algorithms applied to the high resolution spectra processed with the NEWSIPS software for the Final Archive of the IUE Project. In this analysis, based on a very large number of spectra, we find that both K and the alpha parameters (not only the former as previously believed) vary with order number. This fact, together with the finding that the central peaks of the blaze function vary also as a function of the THDA temperature (for the SWP camera) and of the date of observations (for the LWP and LWR cameras), makes the ripple correction algorithm more complex than previously considered but, at the same time, considerably more reliable. As for the high resolution absolute calibration, the method followed is similar to the one implemented in IUESIPS. The internal accuracy of the high resolution calibration is about 4%. We note that the ripple correction and absolute calibration algorithms here described apply also to IUE data processed and distributed with the INES system.

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arXiv1999

Improved data extraction procedures for IUE Low Resolution Spectra: The INES System

We present the extraction and processing of the IUE Low Dispersion spectra within the framework of the ESA ``IUE Newly Extracted Spectra'' (INES) System. Weak points of SWET, the optimal extraction implementation to produce the NEWSIPS output products (extracted spectra) are discussed, and the procedures implemented in INES to solve these problems are outlined. The more relevant modifications are: 1) the use of a new noise model, 2) a more accurate representation of the spatial profile of the spectrum and 3) a more reliable determination of the background. The INES extraction also includes a correction for the contamination by solar light in long wavelength spectra. Examples showing the improvements obtained in INES with respect to SWET are described. Finally, the linearity and repeatability characteristics of INES data are evaluated and the validity of the errors provided in the extraction is discussed.

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arXiv1999

Ionized Ultraviolet and Soft-X-ray Absorptions in the Low Redshift Active Galactic Nucleus PG1126-041

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.

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arXiv1998

30 years of multi-wavelength observations of 3C 273

We present a wide multi-wavelength database of most observations of the quasar 3C 273 obtained during the last 30 years. This database is the most complete set of observations available for an active galactic nucleus (AGN). It contains nearly 20'000 observations grouped together into 70 light curves covering 16 orders of magnitude in frequency from the radio to the gamma-ray domain. The database is constituted of many previously unpublished observations and of most publicly available data gathered in the literature and on the World Wide Web (WWW). It is complete to the best of our knowledge, except in the optical (UBV) domain where we chose not to add all observations from the literature. In addition to the photometric data, we present the spectra of 3C 273 obtained by the International Ultraviolet Explorer (IUE) satellite. In the X-ray domain, we used the spectral fit parameters from the literature to construct the light curves. Apart from describing the data, we show the most representative light curves and the average spectrum of 3C 273. The database is available on the WWW in a homogeneous and clear form and we wish to update it regularly by adding new observations.

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arXiv1998

Steps towards determination of the size and structure of the Broad-Line Region in Active Galactic Nuclei. XIII. Ultraviolet observations of the Broad-Line Radio Galaxy 3C 390.3

As part of an extensive multi-wavelength monitoring campaign, the International Ultraviolet Explorer satellite was used to observe the broad-line radio galaxy 3C 390.3 during the period 1994 December 31 to 1996 March 5. Spectra were obtained every 6-10 days. The UV continuum varied by a factor of 7 through the campaign, while the broad emission-lines varied by factors of 2-5. Unlike previously monitored Seyfert 1 galaxies, in which the X-ray continuum generally varies with a larger amplitude than the UV, in 3C 390.3 the UV continuum light-curve is similar in both amplitude and shape to the X-ray light-curve observed by ROSAT. The UV broad emission-line variability lags that of the UV continuum by 35-70 days for Ly-alpha and CIV 1549; values larger than those found for Seyfert 1 galaxies of comparable UV luminosity. These lags are also larger than those found for the Balmer lines in 3C 390.3 over the same period. The red and blue wings of CIV and Ly-alpha vary in phase, suggesting that radial motion does not dominate the kinematics of the UV line-emitting gas. Comparison with archival data provides evidence for velocity-dependent changes in the Ly-alpha and CIV line profiles, indicating evolution in the detailed properties and/or distribution of the broad-line emitting gas.

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arXiv1997

Patchy intergalactic HeII absorption in HE 2347-4342. - The possible discovery of the epoch of He-reionization

We report on observations of redshifted HeII 304 A absorption in the QSO HE 2347-4342 (z=2.885, V=16.1) with the GHRS on board HST (FWHM=0.7 A). At the expected position of HeII 304 A absorption, HE 2347-4342 is the most UV-bright high redshift QSO discovered so far. We show that the HeII opacity as a function of redshift is patchy showing spectral regions with low HeII opacity (voids) and regions with high HeII opacity (troughs) and no detectable flux. Combination with high-resolution optical spectra of the Ly_alpha forest using CASPEC at the ESO 3.6m telescope shows that the voids can be explained either exclusively by Ly_alpha forest cloud absorption with a moderate N(HeII)/N(HI) ratio of 100 and turbulent line broadening or by a combination of Ly_alpha forest with N(HeII)/N(HI)=45 and thermal broadening plus a diffuse medium with tau_GP_HeII=0.3. Thus a strict upper limit to a diffuse medium is Omega_diff<= 0.02 h_50^(-1.5) at z=2.8. In the troughs an additional continuous HeII 304 A opacity tau > 2.8 is required. In case of photoionization, the troughs would require a diffuse component with a density close to Omega = 0.059 h_50^(-1.5), i.e. all baryons in the universe, which is inconsistent with the observed absence of such a component in the voids. A tentative interpretation is that we observe the epoch of partial HeII reionization of the universe with patches not yet reionized. In that case a diffuse component with Omega_diff >= 1.3 10^(-4) h_50^(-1) would be sufficient to explain the ``trough'' opacity.

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arXiv1996

The evolution of ultraviolet emission lines from the circumstellar material surrounding SN 1987A

The presence of narrow high-temperature emission lines from nitrogen-rich gas close to SN 1987A has been the principal observational constraint on the evolu- tionary status of the supernova's progenitor. A new analysis of the complete five-year set of low and high resolution IUE ultraviolet spectra of SN 1987A (1987.2--1992.3) provide fluxes for the N V 1240, N IV] 1486, He II 1640, OIII] 1665, NIII] 1751, and CIII] 1908 lines with significantly reduced random and systematic errors and reveals significant short-term fluctuations in the light curves. The N V, N IV] and N III] lines turn on sequentially over 15 to 20 days and show a progression from high to low ionization potential, implying an ioni- zation gradient in the emitting region. The line emission turns on suddenly at 83+/-4 days after the explosion, as defined by N IV]. The N III] line reaches peak luminosity at 399+/-15 days. A ring radius of (6.24+/-0.20)E{17} cm and inclination of 41.0+/-3.9 is derived from these times, assuming a circular ring. The probable role of resonant scattering in the N V light curve introduces systematic errors that leads us to exclude this line from the timing analysis. A new nebular analysis yields improved CNO abundance ratios N/C=6.1+/-1.1 and N/O=1.7+/-0.5, confirming the nitrogen enrichment found in our previous paper. From the late-time behavior of the light curves we find that the emission origi- nates from progressively lower density gas. We estimate the emitting mass near maximum (roughly 400 days) to be roughly 4.7E{-2} solar masses, assuming a filling factor of unity and an electron density of 2.6E4 cm^{-3}. These results are discussed in the context of current models for the emission and hydrodynamics of the ring.

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