The IUE Final Archive: Conception to Completion

Nichols-Bohlin, J.; Pena, Michele De La; Linsky, Jeffrey L.; Kondo, Y.; Michalitsianos, A. G.; Ponz, D.; Talavera, A.; González‐Riestra, R.; Wamsteker, W.

doi:10.1007/978-94-011-0794-5_121

Cited by 3 publications

(9 citation statements)

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“…Nichols identified the sources of fixed pattern noise (FPN) in the original image processing system (IUESIPS) and quantified the improvement in S/N that could be achieved by developing new processing algorithms. The results of these investigations supported the feasibility of developing a new processing system by showing the two-dimensional fixed pattern to be generally constant in raw space with time, providing a possible fiducial pattern for fine-scale image registration (Nichols-Bohlin 1988a). The predicted improvements in S/N of extracted spectral data were of sufficient magnitude to justify a major effort by the IUE Project to implement such a system.…”

Section: Introductionmentioning

confidence: 54%

“…Figures 1(b) and 1(c) show similar information for the LWP and LWR cameras, respectively. The improvement in S/N using found reseau marks for alignment is clearly seen in all four areas of the image and was found to be a factor of 1.5-2.0 compared to the original IUESIPS processing (Nichols-Bohlin 1988b). The variation in S/N with time seen in these plots was the first information concerning the critical time dependency of the ITF data, which was not discernible with the IUESIPS data.…”

Section: Introductionmentioning

confidence: 84%

“…A video that they produced to describe this technique played an important role in stimulating the Final Archive project. Subsequently, a much simpler form of crosscorrelation of the two-dimensional raw images with the ITF image over much of the target region showed the fixed pattern in IUE raw data to be easily recognizable as a twodimensional pattern and relatively constant in time (Nichols-Bohlin 1988a).…”

Section: Introductionmentioning

confidence: 99%

“…One important source of fixed pattern noise in IUE images was traced to misalignment of the ITF images with respect to the science images during the photometric linearization step of the image processing (Nichols-Bohlin 1988b, 1989a. Reseau marks etched on the camera faceplates are intended to be used as the geometric image fiducials and are apparent on flat-field flood lamp exposures as a 13X13 grid of zero-flux points.…”

Section: Introductionmentioning

confidence: 99%

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The Final Archive and Recalibration of the International Ultraviolet Explorer (IUE) Satellite

Nichols¹,

Linsky²

1996

The Astronomical Journal

125

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Since 1978 the International Ultraviolet Explorer (IUE) satellite has been acquiring the largest collection of astronomical ultraviolet spectra that will likely be obtained in the foreseeable future. The more than 100 000 spectral images, from which low and high dispersion spectra are extracted, include a very broad range of sources from solar system objects, stars of all types, interstellar and Galactic halo gas, normal galaxies, and active galactic nuclei. The Final Archive of IUE data will contain all of these spectral images and extracted spectra, reprocessed with uniform software and calibrations that enhance the quality of the data products. This paper summarizes the rationale for and content of the new processing algorithms, together with the calibration chronology of the IUE scientific instrument. Examples of spectra processed for the Final Archive demonstrate an increased signal-to-noise ratio of 10%-50% for low dispersion data and-100% or more for high dispersion data compared to the old processing scheme, the extension of the usable spectral range down to 1150 and up to 3400 Â, and the emergence of new spectral features from the fixed pattern noise that is now largely eliminated.

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Section: Introductionmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Final Archive and Recalibration of the International Ultraviolet Explorer (IUE) Satellite

Nichols¹,

Linsky²

1996

The Astronomical Journal

125

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“…The IUE ULDA (Wamsteker et al 1989) provides a unique source of archival data which satisfies the requirements for a comprehensive study of a large sample of objects owing to its uniform quality and the large number of spectra accumulated over the long life of IUE . Although the IUE final archive (Nichols-Bohlin et al 1994) has since superseded the ULDA, the reprocessing effort of the final archive had not begun when this study was begun in 1992. To build the data sample, the IUE Merged Log was searched using software at the IUE Regional Analysis Facility, then at the University of Colorado.…”

Section: Discussionmentioning

confidence: 99%

Ultraviolet Emission‐line Ratios of Cataclysmic Variables

Mauche

Lee

Kallman

1997

ApJ

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We present a statistical analysis of the ultraviolet emission lines of cataclysmic variables (CVs) based on ≈ 430 ultraviolet spectra of 20 sources extracted from the International Ultraviolet Explorer Uniform Low Dispersion Archive. These spectra are used to measure the emission line fluxes of N V, Si IV, C IV, and He II and to construct diagnostic flux ratio diagrams. We investigate the flux ratio parameter space populated by individual CVs and by various CV subclasses (e.g., AM Her stars, DQ Her stars, dwarf novae, nova-like variables). For most systems, these ratios are clustered within a range of ∼ 1 decade for log Si IV/C IV ≈ −0.5 and log He II/C IV ≈ −1.0 and ∼ 1.5 decades for log N V/C IV ≈ −0.25. These ratios are compared to photoionization and collisional ionization models to constrain the excitation mechanism and the physical conditions of the line-emitting gas. We find that the collisional models do the poorest job of reproducing the data. The photoionization models reproduce the Si IV/C IV line ratios for some shapes of the ionizing spectrum, but the predicted N V/C IV line ratios are simultaneously too low by typically ∼ 0.5 decades. Worse, for no parameters are any of the models able to reproduce the observed He II/C IV line ratios; this ratio is far too small in the collisional and scattering models and too large by typically ∼ 0.5 decades in the photoionization models.

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Signal-to-noise ratios in IUE low-dispersion spectra. II - Photometrically corrected images

Ayres

1993

PASP

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The character of detector noise is explored in photometrically corrected images from the short-wavelength and long-wavelength prime intensified vidicon cameras of the International Ultraviolet Explorer A protocol is proposed for deriving realistic "noise models"-crucial to the application of Optimal extraction algorithms like that of Kinney, Bohlin, and Neill (1991, PASP, 103, 694)-from the available collections of UV-Flood calibration images. The protocol includes evaluation of the "noise-filtering" properties of the SWP and LWP cameras through 2-D spatial power spectrum analysis. The two vidicon cameras behave nearly identically. For both, the incomplete removal of the pixel-to-pixel sensitivity pattern can lead to a factor of up to two enhancement in the apparent noise, depending on position in the image. Even with good suppression of the pixel granularity, however, the remaining random noise can exhibit saturation behavior that causes the S/N to cease improving with increasing exposure. The random noise itself exhibits a two-component character: a normal white-noise field superimposed on a filtered (Gaussian-like smoothing) background. The influence of the smooth component varies strongly with position. Nevertheless, when all of the relevant effects are considered, the underlying "pristine" noise models show essentially no dependence on spatial position, except for an unusually noisy patch on the LWP camera. Two additional sources of noise, beyond the largely photometric contributions documented above, are microphonics and cosmic particle radiation. Microphonics are important in only a few exceptional circumstances, but cosmic ray "bright spots" set an effective limit of ~ 4 hr on useful SWP-LO exposures of (unresolved) emission-line objects, even those conducted during low-radiation time.

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The IUE Final Archive: Conception to Completion

Cited by 3 publications

References 0 publications

The Final Archive and Recalibration of the International Ultraviolet Explorer (IUE) Satellite

The Final Archive and Recalibration of the International Ultraviolet Explorer (IUE) Satellite

Ultraviolet Emission‐line Ratios of Cataclysmic Variables

Signal-to-noise ratios in IUE low-dispersion spectra. II - Photometrically corrected images

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