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Coronagraphic Imaging with the Hubble Space Telescope and the Space Telescope Imaging Spectrograph
The unfiltered Space Telescope Imaging Spectrograph (STIS) CCD in tandemwith focal plane wedges and a Lyot stop provides a simple white-lightcoronagraph with a bandpass of 0.2-1.0 μm, which has been used sincelate 1998 to image nebulosity around stars in the ranges0.34<=V<=14 and -0.03<=B-V<=1.65. The residual starlightseen in STIS coronagraphic images includes diffraction spikes due to theHubble Space Telescope (HST) secondary support structure, lacks distinctAiry rings, and varies smoothly with radius from the star. Thepoint-spread function (PSF) shape is a strong function of the sourcespectral energy distribution: we find that the PSF template needs todiffer from the occulted source color by Δ(B-V)<=0.08 mag.Optimal PSF removal is achieved for contemporary template observationsmatched to HST orbital phase of the science observations. Use ofnoncontemporary PSF templates can degrade the limiting contrast by up toa factor of 10-12 at r<=2''. These systematic effects arenegligible when the nebular surface brightness is comparable to theresidual starlight, and they become progressively more important assurface brightness decreases. STIS has been used to detect circumstellarenvelopes and protoplanetary disks with surface brightnesses spanning10-4 to 10-7 per HST resolution element perFstar at 2" from the star, debris disks withFIR/Fstar>=0.001, and emission-line nebulosityassociated with bipolar outflows. The limiting contrast for single-orbitintegrations with the star placed at a location where the coronagraphicwedge is 1.0" wide is 10-8 per HST resolution element perFstar for 6<=V<=8 stars. Deeper imagery can be obtainedby placing the star off the active detector area. When the star is 5"from the detector, a limiting contrast for a single-orbit integration of2.5×10-10 per HST resolution element perFstar is reached. At this contrast level, background objectsand the stellar color variability prevent further improvement byco-adding data from multiple orbits.Based on observations made with the NASA/ESA Hubble Space Telescope,obtained at the Space Telescope Science Institute, which is operated bythe Association of Universities for Research in Astronomy, Inc., underNASA contract NAS 5-26555. This study is part of the STIS IDTprotoplanetary disk key project.
| A Study of the Wavelength Calibration of NEWSIPS High-Dispersion Spectra
In this study we cross-correlate many IUE echellograms of a variety ofwell-observed stars to evaluate systematic error sources in thewavelength zero points (velocities) of all three cameras. We firstevaluate differences between the final archived (``NEWSIPS'') and theoriginally processed (``IUESIPS'') echellograms. These show a markedtime dependence in zero point for the SWP camera resulting from severalrevisions of wavelength calibration coefficients used for IUESIPS.Smaller offsets are present for the LWR camera between the twoprocessings. We also evaluated small-amplitude fluctuations in the zeropoints of the NEWSIPS wavelength calibration spectra themselves. In thecase of the SWP camera, these variations are too complicated to havebeen completely removed in the NEWSIPS wavelength calibration. We alsoexamine wavelength zero-point disparities between data obtained boththrough the small and large entrance apertures as well as forobservations made by different target acquisitions of faint and brightstars. We also find that statistical differences between thesealternative observing modes are virtually nil. For large-apertureobservations, the dominant error source is the placement of the targetin the aperture. These give rise to non-Gaussian, extended ``tails'' inapparent velocity. We also searched for spurious trends. Except for apossible trend for faint objects with SWP camera data, we cannot detectsignificant dependences with time. Additionally, we discovered a trendwith telescope focus for data sets derived from intensive monitoringcampaigns of bright stars. These exhibit a repeatable, 1 day ``radialvelocity variation'' with a semiamplitude of nearly 3 km s-1.This pattern appears to be a by-product of fluctuations in telescopefocus caused by operational procedures to maintain the ambientinstrument temperature. In the second part of the paper, we measure themean zero-point errors of NEWSIPS echellogram data with respect tolaboratory results by using the Goddard High Resolution Spectrograph(GHRS) spectral atlas of the O9 V spectral standard 10 Lacertae as anintermediary reference. We find that the derived apparent velocitydifference for this star is essentially zero: -1+/-3.5 kms-1. Several less precise comparisons lead to similarresults, including cross-correlations of (1) spectra of 10 Lac and twostars with similar spectra, HD 93521 and HD 60753; (2) lines in commonwith the SWP camera and GHRS and STIS atlases of Arcturus and Procyon;and (3) interstellar lines in the GHRS spectrum of the white dwarfG191-B2B. The zero points of the NEWSIPS-processed long-wavelengthcameras are evaluated and are also found to be nearly zero (+/-5 kms-1) relative to the Arcturus and Procyon atlas calibrationsand relative to one another. In general, these results do not supportthe suggestion by González-Riestra and coworkers that correctionsshould be introduced to the wavelength scales of various NEWSIPShigh-dispersion data products. Despite our optimistic results, it isobvious that using small IUE data sets from large-aperture observationsof arbitrarily chosen stars can contain velocity errors of at least afew km s-1.
| SwSt 1: an O-rich planetary nebula around a C-rich central star
The hydrogen-deficient [WCL] type central star HD 167362 and itsplanetary nebula (PN) SwSt 1 are investigated. The central star has acarbon-rich emission-line spectrum, and yet the nebula exhibits a10-μm emission feature from warm silicate dust, perhaps indicating arecent origin for the carbon-rich stellar spectrum. Its stellar andnebular properties might therefore provide further understanding as tothe origin of the [WCL] central star class. The central star optical andUV spectra are modelled with state-of-the art non-LTE codes forexpanding atmospheres, from which the stellar parameters are determined.Using the Sobolev approximation code ISA-Wind, we findTeff=40000K,log(Mȯ/Msolaryr-1)=-6.72,L=8900Lsolar (for a distance of 2.0kpc), andv&infy;~=900kms-1. The abundance mass fractionsfor helium, carbon and oxygen are determined to be 37, 51 and 12 percent, respectively. From this we derive C/O=4.3 (by mass), confirmingthat the star suffered efficient third dredge-up. The nitrogen abundanceis close to zero, while an upper limit of <10 per cent by mass isestablished for H. The model uses a composite beta velocity law whichallows us to reproduce the optical line profiles. The overall shape ofthe dereddened spectrum agrees with the V-scaled[[mV=11.48mag, E(B-V)=0.46mag]] model atmosphere, showing thenebular-derived reddening to be consistent with the reddening indicatedby the stellar analysis. We confirm our model results by using thecomoving frame code CMFGEN, although a few differences remain. The PNhas a high electron density [log(Ne/cm-3)=4.5] anda small ionized radius (0.65arcsec - measured from the HST-WF/PC Hβimages), indicating a young object. Its nebular abundances are notpeculiar. The nebular C/O ratio is close to solar, confirming the PN asan O-rich nebula. The nebular N/O ratio of 0.08 is not indicative of aType-I PN, although the high stellar luminosity points to a relativelyhigh stellar mass. Near-IR spectroscopy is presented and fitted togetherwith IRAS fluxes by using two blackbody curves with temperatures of 1200and 230K, indicating the presence of hot dust. We also report the firstdetection of H2 in this young and compact PN. All of thepublished spectroscopy since the discovery of SwSt 1 in 1895 has beenre-examined, and it is concluded that no clear spectral variability isseen, in contrast to claims in some previously published studies. If anevent occurred that has turned it into a hydrogen-deficient centralstar, it did not happen in the last 100 years.
| Chemical abundances and winds of massive stars in M31: a B-type supergiant and a WC star in OB 10
We present high quality spectroscopic data for two massive stars in theOB 10 association of M31, OB 10-64 (B0 Ia) and OB 10-WR1 (WC6). Mediumresolution spectra of both stars were obtained using the ISISspectrograph on the William Herschel Telescope. This is supplementedwith Hubble Space Telescope STIS UV spectroscopy and Keck I HIRES datafor OB 10-64. A non-local thermodynamic equilibrium (LTE) modelatmosphere and abundance analysis for OB 10-64 is presented, indicatingthat this star has similar photospheric CNO, Mg and Si abundances tosolar neighbourhood massive stars. A wind analysis of this early B-typesupergiant reveals a mass-loss rate ofMȯ=1.6×10-6Msolaryr-1,and v&infy;=1650kms-1. The corresponding windmomentum is in good agreement with the wind momentum-luminosityrelationship found for Galactic early-B supergiants. Observations of OB10-WR1 are analysed using a non-LTE, line-blanketed code, to revealapproximate stellar parameters of logL/Lsolar~5.7, T*~75kK,v&infy;~3000kms-1,Mȯ/(Msolaryr-1)~10-4.3adopting a clumped wind with a filling factor of 10 per cent.Quantitative comparisons are made with the Galactic WC6 star HD 92809(WR23) revealing that OB 10-WR1 is 0.4 dex more luminous, though it hasa much lower C/He ratio (~0.1 versus 0.3 for HD 92809). Our studyrepresents the first detailed, chemical model atmosphere analysis foreither a B-type supergiant or a Wolf-Rayet (WR) star in Andromeda, andshows the potential of how such studies can provide new information onthe chemical evolution of galaxies and the evolution of massive stars inthe local Universe.
| The INES system. IV. The IUE absolute flux scale
This paper deals with the definition of the input fluxes used for thecalibration of the IUE Final Archive. The method adopted consists in thedetermination of the shape of the detector's sensitivity curves usingIUE low resolution observations with model fluxes of the DA white dwarfG191-B2B. A scale factor was then determined so that the IUEobservations of some bright OAO-2 standards match the originalmeasurements from Meade (\cite{meade}) in the spectral region 2100-2300Å. The ultraviolet fluxes of six standard stars used as input forthe Final Archive photometric calibration together with the model fluxesof G191-B2B normalized to the OAO-2 scale are given. A comparison withthe independent FOS calibration shows that the IUE flux scale for theUltraviolet is 7.2% lower. We consider this mainly to be caused by thedifferent normalization procedures. It is shown that the present fluxcalibration applies to spectra processed with the INES low resolutionextraction software.
| A Recalibration of IUE NEWSIPS Low-Dispersion Data
While the low-dispersion IUE New Spectroscopic Image Processing System(NEWSIPS) data products represent a significant improvement overoriginal IUE Spectroscopic Image Processing System (SIPS) data, theystill contain serious systematic effects which compromise their utilityfor certain applications. We show that NEWSIPS low-resolution data areinternally consistent to only 10%-15% at best, with the majority of theproblem due to time-dependent systematic effects. In addition, theNEWSIPS flux calibration is shown to be inconsistent by nearly 10%. Weexamine the origin of these problems and proceed to formulate and applyalgorithms to correct them to the ~3% level-a factor of 5 improvement inaccuracy. Because of the temporal systematics, transforming thecorrected data to the IUE flux calibration becomes ambiguous. Therefore,we elect to transform the corrected data onto the Hubble Space TelescopeFaint Object Spectrograph system. This system is far moreself-consistent, and transforming the IUE data to it places data fromboth telescopes on a single system. Finally, we perform a detailed erroranalysis of the corrected NEWSIPS data. We demonstrate that much of theremaining 3% systematic effects in the corrected data is traceable toproblems with the NEWSIPS intensity transformation function (ITF). Theaccuracy could probably be doubled by rederiving the ITF.
| Space Telescope Imaging Spectrograph Coronagraphic Observations of β Pictoris
We present new coronagraphic images of β Pictoris obtained with theSpace Telescope Imaging Spectrograph (STIS) in 1997 September. Thehigh-resolution images (0.1") clearly detect the circumstellar disk asclose to the star as 0.75", corresponding to a projected radius of 15AU. The images define the warp in the disk with greater precision and atcloser radii to β Pic than do previous observations. They show thatthe warp can be modeled by the projection of two components: the maindisk and a fainter component, which is inclined to the main component by4°-5° and extends only as far as ~4" from the star. We interpretthe main component as arising primarily in the outer disk and the tiltedcomponent as defining the inner region of the disk. The observedproperties of the warped inner disk are inconsistent with a drivingforce from stellar radiation. However, warping induced by thegravitational potential of one or more planets is consistent with thedata. Using models of planet-warped disks constructed by Larwood &Papaloizou, we derive possible masses of the perturbing object. Based onobservations with the NASA/ESA Hubble Space Telescope, obtained at theSpace Telescope Science Institute, which is operated by the Associationof Universities for Research in Astronomy, Inc., under NASA contractNAS5-26555.
| Far Ultraviolet Spectroscopic Explorer Spectroscopy of the O VI Resonance Doublet in Sand 2 (WO)
We present Far Ultraviolet Spectroscopic Explorer spectroscopy of Sand2, an LMC WO-type Wolf-Rayet star, revealing the O VI resonance P Cygnidoublet at 1032-1038 Å. These data are combined with Hubble SpaceTelescope Faint Object Spectrograph ultraviolet and Mount Stromlo 2.3 moptical spectroscopy and analyzed using a spherical, non-LTE,line-blanketed code. Our study reveals exceptional stellar parameters:T*~150,000 K, v&infy;=4100 km s-1,log(L/Lsolar)=5.3, and M=1×10-5Msolar yr-1, if we adopt a volume filling factorof 10%. Elemental abundances of C/He~0.7+/-0.2 andO/He~0.15+0.10-0.05 by number qualitativelysupport previous recombination line studies. We confirm that Sand 2 ismore chemically enriched in carbon than LMC WC stars and that it isexpected to undergo a supernova explosion within the next5×104 yr.
| The INES system. III. Evaluation of IUE NEWSIPS high resolution spectra
This paper discusses the overall quality of IUE high resolution dataprocessed with the NEWSIPSlinebreak software in terms of flux andwavelength accuracy. It also describes the processing of NEWSIPS highresolution spectra within the framework of the ESA ``IUE Newly ExtractedSpectra'' (INES) System. This system provides the IUE high resolutiondata in two formats: the high resolution ``concatenated'' spectra, inwhich the spectral orders are connected, eliminating the overlap regionsthrough a procedure designed to optimize the signal-to-noise ratio atthe edges of the orders, and the ``rebinned'' spectra, i.e. the highresolution concatenated spectra resampled into the low resolutionwavelength domain. Our study reveals the existence of a significantdiscrepancy in the wavelength scales of short and long wavelengthNEWSIPS high resolution spectra. The INES processing applies acorrection of +17.7 km s-1 to the wavelength scale of thehigh resolution SWP spectra in order to provide an internally consistentvelocity scale. Similarly, suitable corrections have been applied tolong wavelength small aperture spectra. The new wavelength scale is,within the errors, in good agreement with the optical velocity scale.
| 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 theripple correction and absolute calibration algorithms applied to thehigh resolution spectra processed with the NEWSIPS software for theFinal Archive of the IUE Project. In this analysis, based on a verylarge number of spectra, we find that both the K and 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 blazefunction vary also as a function of the THDA temperature (for the SWPcamera) and of the date of observations (for the LWP and LWR cameras),makes the ripple correction algorithm more complex than previouslyconsidered but, at the same time, considerably more reliable. As for thehigh resolution absolute calibration, the method followed is similar tothe one implemented in IUESIPS. The internal accuracy of the highresolution calibration is about 4%. We note that the ripple correctionand absolute calibration algorithms here described apply also to IUEdata processed and distributed with the INES system.
| The IUE INES System: Improved data extraction procedures for IUE
We present the extraction and processing of the IUE Low Dispersionspectra within the framework of the ESA ``IUE Newly Extracted Spectra''(INES) System. Weak points of SWET, the optimal extractionimplementation to produce the NEWSIPS output products (extractedspectra) are discussed, and the procedures implemented in INES to solvethese problems are outlined. The more relevant modifications are: 1) theuse of a new noise model, 2) a more accurate representation of thespatial profile of the spectrum and 3) a more reliable determination ofthe background. The INES extraction also includes a correction for thecontamination by solar light in long wavelength spectra. Examplesshowing the improvements obtained in INES with respect to SWET aredescribed. Finally, the linearity and repeatability characteristics ofINES data are evaluated and the validity of the errors provided in theextraction is discussed.
| The circumstellar envelope of AFGL 4106
We present new imaging and spectroscopy of the post-red supergiantbinary AFGL 4106. Coronographic imaging in Hα reveals the shapeand extent of the ionized region in the circumstellar envelope (CSE).Echelle spectroscopy with the slit covering almost the entire extent ofthe CSE is used to derive the physical conditions in the ionized regionand the optical depth of the dust contained within the CSE. The dustshell around AFGL 4106 is clumpy and mixed with ionized gas. Hαand [N ii] emission is brightest from a thin bow-shaped layer justoutside of the detached dust shell. On-going mass loss is traced by [Caii] emission and blue-shifted absorption in lines of low-ionizationspecies. A simple model is used to interpret the spatial distribution ofthe circumstellar extinction and the dust emission in a consistent way.Based on observations obtained at the European Southern Observatory, LaSilla, Chile
| Spatially resolved nebulae around the Ofpe/WN9 stars S 61 and BE 381
We present new high-resolution coronographic imaging andmedium-resolution spectroscopy of the circumstellar region around S 61and BE 381, two Ofpe/WN9 stars in the Large Magellanic Cloud. Theobservations were carried out at the ESO/NTT (La Silla) in January 1996and July 1998. The excellent seeing conditions allowed the circumstellarnebulae associated with both S 61 and BE 381 to be spatially resolvedfor the first time. The nebula surrounding S 61 has the appearance of ashell with a mild central axisymmetry. The surface brightness is notuniform, and the northern region of the nebula is the brightest. Thenebula exhibits a bipolar structure with an overall morphology verysimilar to nebulae around other LBVs or Opfe/WN9 stars, especially S119.The diameter of the shell is 7.3'', corresponding to a linear size of1.8 pc. From the profile of nebular emission lines we clearly detect anexpansion motion with a velocity of 28 km s(-1) , which indicates adynamical age of ~ 30000 yrs. We find an electron density of 400 cm(-3)and an electron temperature of 6120 K. The nebula is similar to otherLBV nebulae in that it is nitrogen enriched. The observed chemical anddynamical properties confirm that the nebula is associated with thecentral star and is of stellar origin. This result implies that S 61 islikely to have undergone a LBV-type ouburst and, therefore, strenghtensthe suggestion that Ofpe/WN9 stars are quiescent LBVs. The situation isdifferent for BE 381. The Hα images of BE 381 also reveal thepresence of a faint nebulosity around the star; most of the nebular fluxappears to be emitted by an arc of gas located to the east of BE 381,while a much dimmer arc is detectable on the western side. The arcsdelineate a shell of 13'' in diameter, corresponding to a linear size of3.2 pc, which appears to be expanding with a velocity of 14 km s(-1) .From the nebular emission lines we derive an electron density rangingbetween 30 cm(-3) and 120 cm(-3) (assuming T_e = 10000 K), and a N(+)/S(+) ratio between 1.5 and 2.3, which are typical of HII regions. Wetherefore conclude that the shell detected around BE 381 is not ofstellar origin and probably represents the relic of the interstellarbubble blown by BE 381 during its O main-sequence phase. Based onobservations obtained at the European Southern Observatory, La Silla,Chile
| A survey of vacuum-ultraviolet extinction curves based on International Ultraviolet Explorer spectra
This paper presents the interstellar extinction curves derived from theIUE spectra with the aid of the already published 'artificialstandards'. The variety of possible shapes of the curves, demonstratedearlier on spectra from the TD/1 satellite, is fully confirmed.
| The WC10 central stars CPD-56 deg 8032 and He 2-113. I - Distances and nebular parameters
We present the results of an analysis of the WC10 central stars CPD-56deg 8032 and He 2-113 and of their surrounding planetary nebulae (PNe).UCL Echelle Spectrograph spectra with a resolving power of R = 50,000,covering the wavelength range 3600-9500 A, were obtained for bothobjects. Expansion and radial velocities are derived from the nebularBalmer lines. We also present deconvolved pre-COSTAR HST H-beta images,from which we derive nebular angular sizes of 1.6 x 2.1 sq arcsec forCPD-56 deg 8032 and 1.4 x 1.1 sq arcsec for He 2-113.
| The Bipolar HR Carinae Nebula: Dynamics and Chemical Abundances
We present the results of a new set of medium resolution spectroscopicobservations and high-resolution coronographic images of the nebulaaround the Galactic luminous blue variable (LBV) HR Carinae. Theobservations were carried out at the ESO/NTT (La Silla) in 1995 May and1996 January. The nebular morphology and kinematics confirm that thenebula around HR Carinae is truly bipolar and very reminiscent of theeta Carinae nebula. The previously identified "filaments" outline theedges of two symmetrical expanding bubbles, originating from the starand located, respectively, in the NW and SE quadrants. The small compactinner nebula, a few arcsec in size, previously detected, represents the"waist" of the bipolar distribution. The orientation in the images andthe kinematical study have allowed us to define the true orientation ofthe bubbles, whose major axis lies at an angle of ~=50 deg with theplane of the sky, at an inclination of approximately 30 deg on the lineof sight. The maximum projected expansion velocity is of the order of~=100 km s-1. In the light of these new kinematical data, we revise thedynamical timescale to a younger age of ~=5000 yr. The nebula around HRCarinae is relatively young and fast, at variance with other well knownLBV nebulae such as AG Carinae's. Spectroscopically, the nebula is oflow excitation with [O III] absent, and [N II] fairly strong. [Ni II]lambda 6667 is detected, but only in the inner regions (<=5"). Wefind that the electron density increases from 400 cm-3 in the outerregions to more than 104 cm-3 in the innermost regions. An analysis ofthe chemical abundances in different regions of the nebula finds that Nis overabundant, indicating that the nebula is composed of CNO processedstellar material. We find that the filamentary H II region, seen to theNW of HR Carinae, is at the same distance and is composed of materialwith typical H II region abundances, and has a morphology that suggestsit has been shaped by the wind of HR Carinae.
| The Final Archive and Recalibration of the International Ultraviolet Explorer (IUE) Satellite
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996AJ....111..517N&db_key=AST
| Vitesses radiales. Catalogue WEB: Wilson Evans Batten. Subtittle: Radial velocities: The Wilson-Evans-Batten catalogue.
We give a common version of the two catalogues of Mean Radial Velocitiesby Wilson (1963) and Evans (1978) to which we have added the catalogueof spectroscopic binary systems (Batten et al. 1989). For each star,when possible, we give: 1) an acronym to enter SIMBAD (Set ofIdentifications Measurements and Bibliography for Astronomical Data) ofthe CDS (Centre de Donnees Astronomiques de Strasbourg). 2) the numberHIC of the HIPPARCOS catalogue (Turon 1992). 3) the CCDM number(Catalogue des Composantes des etoiles Doubles et Multiples) byDommanget & Nys (1994). For the cluster stars, a precise study hasbeen done, on the identificator numbers. Numerous remarks point out theproblems we have had to deal with.
| Photometric calibriation of the international Ultraviolet Explorer (IUE) for high resolution spectra
We present and discuss the high resolution absolute calibration for theSWP, LWP and LWR cameras on board IUE. The calibration was implementedin routine processing on 27 December, 1987 at VILSPA and on 30 August,1990 at GSFC. The calibration is applicable to high resolution spectraprocessed with the 'new' version of the IUE spectral image processingsoftware which was implemented in routine on 10 November, 1981 at GSFCand 11 March, 1982 at VILSPA. The high resolution calibration, for theway it is defined, is primarily determined by the efficiency of theshort or long wavelength spectrographs in the high resolution, relativeto the low resolution observing modes. This interpretation is consistentwith the high resolution calibration being the same for LWP and LWRspectra (which are obtained through the same spectrograph) and beingconstant with time. It is shown that the data extraction becomescritical for the higher orders of the IUE echelle spectrographs, causinghigh resolution calibration to depend on the data extraction algorithmused below about 1350 A in the SWP and below about 2350 A in the LWP andLWR cameras.
| Spectroscopic binary orbits from ultraviolet radial velocities. IX - Y Cygni (HD 198846)
The paper presents spectroscopic binary orbits of Y Cygni obtained fromthe results of a three-day observations (covering 16 hours of each day)of this eclipsing binary, made by the IUE satellite at the end of May1990. Full cross-correlation reduction of high-dispersion spectrasecured over the three days allowed the production of an orbitalsolution with a precision comparable to the best results obtained fromthe ground. Spectroscopic determination of apsidal motion, yields avalue very similar to that obtained by Gimenez et al. (1987).
| Radial velocities of the IUE calibration stars
Not Available
| Photometric calibration of the International Ultraviolet Explorer (IUE) at low resolution - The LWP camera
We present and discuss the low resolution absolute calibration for theLWP camera of the International Ultraviolet Explorer (IUE). Thecalibration, implemented in routine processing of LWP low resolutionimages on December 22, 1987 at both GSFC and VILSPA IUE ground stations,is based on the last set of Intensity Transfer Function (ITF 2) obtainedin September 1984 and on a substantially larger amount of IUEobservations of standard stars than used for the preliminary calibrationby Cassatella & Harris (1983) based on the earlier ITF (ITF 1). Thenew ITF and the associated calibration provide upgraded performances influx accuracy, signal-to-noise ratio and linearity with respect to theearlier LWP ITF1 which was implemented in processing LWP data obtainedin the period from October 16, 1983 until December 21, 1987.
| The ultraviolet calibration of the Hubble Space Telescope. IV - Absolute IUE fluxes of Hubble Space Telescope standard stars
UV fluxes are presented for 37 stars selected as calibration standardsfor the Hubble Space Telescope (HST). In order to provide data ofmaximum precision, new absolute calibrations have been derived for theIUE SWP and LWR cameras for point sources in the large apertures, whilethe sensitivities of the trail and small aperture observing modesrelative to the large apertures are updated for all three IUE cameras.More than 2700 individual spectra are used to define the absolute fluxdistributions of the 37 HST standard stars in the wavelength range1150-3300 A. A comparison with white dwarf model atmosphere calculationssuggests that the systematic external errors in the fluxes are less than15 percent, while comparison with ANS flux measurements demonstrates aninternal consistency of the IUE spectrophotometry of 2 percent, over adynamic range of 10,000, in bandpasses of 100 A or greater.
| An atlas of Hubble Space Telescope photometric, spectrophotometric, and polarimetric calibration objects
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99.1243T&db_key=AST
| Empirical temperature calibrations for early-type stars
Three temperature calibrations of suitable photometric quantities havebeen derived for O and B stars. A sample of 120 stars with reliableT(eff.) determinations has been used for establishing each calibration.The different calibrations have been critically discussed and compared.Temperature determinations for 1009 program stars have been obtainedwith an accuracy of the order of 10 percent.
| The recalibration of the IUE scientific instrument
The IUE instrument was recalibrated because of long time-scale changesin the scientific instrument, a better understanding of the performanceof the instrument, improved sets of calibration data, and improvedanalysis techniques. Calibrations completed or planned include intensitytransfer functions (ITF), low-dispersion absolute calibrations,high-dispersion ripple corrections and absolute calibrations, improvedgeometric mapping of the ITFs to spectral images, studies to improve thesignal-to-noise, enhanced absolute calibrations employing correctionsfor time, temperature, and aperture dependence, and photometric andgeometric calibrations for the FES.
| Merged log of IUE observations.
Not Available
| The ultraviolet calibration of the Hubble Space Telescope. III - A correction for the change in sensitivity of the LWR camera on IUE
The absolute photometric calibration of the Hubble Space Telescope (HST)in the UV will be based on low-dispersion spectra obtained by IUE.Therefore, these data must be corrected for the substantial changesobserved in the sensitivities of the IUE SWP and LWR cameras. A previouspaper specified the correction in 5 A bins for SWP through 1986.36. Thispaper details the corrections for LWR and provides an update for SWPthrough 1987.36. A total of 764 LWR spectra of five standard stars areanalyzed to derive the annual change spectra for the the low-dispersionobserving modes.
| The ultraviolet calibration of the Hubble Space Telescope. II - A correction for the change in sensitivity of the SWP camera on the IUE
The IUE data on standard stars that will be the basis of UV absolutephotometric calibration for the Hubble Space Telescope must be correctedfor the changes that are apparent in the low-dispersion spectra of thefive standard stars. A set of 895 spectra is presently analyzed in orderto determine the change in sensitivity of the SWP camera for the first 8years of flight operations. Sensitivity loss is noted to be most acuteat the shortest (1400-1500 A) wavelengths, as well as beyond 1800 A,where total degradation often exceeds 10 percent.
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Наблюдательные данные и астрометрия
| Созвездие: | Корма |
| Прямое восхождение: | 07h33m27.32s |
| Склонение: | -50°35'03.3" |
| Видимая звёздная величина: | 6.673 |
| Расстояние: | 1204.819 парсек |
| Собственное движение RA: | -2.2 |
| Собственное движение Dec: | 5.4 |
| B-T magnitude: | 6.567 |
| V-T magnitude: | 6.665 |
Каталоги и обозначения:
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