International Ultraviolet Explorer Observations Research Articles

The zonal distribution of hydrogen in the Jovian atmosphere

The Voyager ultraviolet spectrometer disclosed strong longitude variation in the midlatitude Lyman alpha brightness of Jupiter. Minimum brightness of 16 and 14.4 kR were observed from Voyagers 1 and 2, respectively, with the intensity rising to peaks of 21 and 19.6 kR at a longitude near 110°. Observations of Jovian Lyman alpha, made with the International Ultraviolet Explorer (IUE) beginning in December 1978, and continuing through January 1982, also show a region of persistently enhanced but variable flux near a longitude, λ, of 100°; however, IUE measured brightnesses are consistently lower than those of Voyager. Although the Lyman alpha flux from the “normal” region of the plant between λ 200 and 300° remained nearly constant during the period of the IUE observations, that from the “perturbed” region centered on λ 110° varied by ±25% from the mean. The sources of Lyman alpha flux include resonance scattering of solar and interplanetary Lyman alpha, and excitation by charged particle precipitation. That portion of the dayside flux due to charged particle excitation has been variously estimated at between 2.3 and 7 kR. About 1 kR of the dayside flux is due to resonance scattering of the sky background. It is assumed that H and an absorber (CH4) are distributed above the homopause according to the local height distribution of temperature. The daytime equation of radiative transfer is solved to determine the longitudinal distribution of freely scattering atomic hydrogen that would account for the observed flux. This daytime solution shows that if the hydrogen bulge is the result of localized heating and a consequent increase in scale height, the temperature in the perturbed region must be about 100°K warmer than that in the normal region. The nightside Lyman alpha brightness exhibits a longitude variation very similar to that on the dayside. The H distribution derived from the dayside solution is used with the nightside flux to estimate the longitude variation of particle precipitation on the nightside.

Spectrophotometry of extreme helium stars - Ultraviolet fluxes and effective temperatures

view Abstract Citations (58) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrophotometry of extreme helium stars : ultraviolet fluxes and effective temperatures. Drilling, J. S. ; Schonberner, D. ; Heber, U. ; Lynas-Gray, A. E. Abstract Ultraviolet flux distributions are presented for the extremely helium rich stars BD +10 deg 2179, HD 124448, LSS 3378, BD -9 deg 4395, LSE 78, HD 160641, LSIV -1 deg 2, BD 1 deg 3438, HD 168476, MV Sgr, LS IV-14 deg 109 (CD -35 deg 11760), LSII +33 deg 5 and BD +1 deg 4381 (LSIV +2 deg 13) obtained with the International Ultraviolet Explorer (IUE). Broadband photometry and a newly computed grid of line blanketed model atmospheres were used to determine accurate angular diameters and total stellar fluxes. The resultant effective temperatures are in most cases in satisfactory agreement with those based on broadband photometry and/or high resolution spectroscopy in the visible. For two objects, LSII +33 deg 5 and LSE 78, disagreement was found between the IUE observations and broadband photometry: the colors predict temperatures around 20,000 K, whereas the UV spectra indicate much lower photospheric temperatures of 14,000 to 15,000 K. The new temperature scale for extreme helium stars extends to lower effective temperatures than that of Heber and Schoenberner (1981) and covers the range from 8,500 K to 32,000 K. Previously announced in STAR as N83-24433 Publication: The Astrophysical Journal Pub Date: March 1984 DOI: 10.1086/161786 Bibcode: 1984ApJ...278..224D Keywords: Astronomical Spectroscopy; B Stars; Stellar Spectrophotometry; Stellar Temperature; Ultraviolet Spectra; Atmospheric Models; Iue; Stellar Atmospheres; Stellar Color; Stellar Spectra; Astronomy full text sources ADS | data products SIMBAD (17) MAST (1) INES (1)

High-resolution IUE observations of interstellar absorption lines in the VELA supernova remnant

view Abstract Citations (78) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS High-resolution IUE observations of interstellar absorption lines in the VELA supernova remnant. Jenkins, E. B. ; Wallerstein, G. ; Silk, J. Abstract Ultraviolet spectra of 45 stars in the vicinity of the Vela supernova remnant were recorded by the short-wavelength echelle spectrograph aboard the International Ultraviolet Explorer (IUE). Over one-third of the stars show interstellar absorption lines at large radial velocities (greater than 60 km/s). The mapping of these high-velocity components in the sky suggests the motions are chaotic, rather than from a coherent expansion of the remnant material. In accord with earlier conclusions from Copernicus data, the gas at high velocity exhibits higher than normal ionization and shows substantially less depletion of nonvolatile elements than normal interstellar material at low velocities. Relatively strong lines from neutral carbon in the two excited fine-structure states indicate that the neutral clouds within the remnant have had their pressures enhanced by the passage of the blast wave from the supernova. Also, the remnant seems to show a significant enhancement in the abundances of low-velocity Si IV, C IV, and N V over those found in the general interstellar medium. Publication: The Astrophysical Journal Pub Date: March 1984 DOI: 10.1086/161832 Bibcode: 1984ApJ...278..649J Keywords: Interstellar Matter; Nebulae; Stellar Spectra; Supernova Remnants; Ultraviolet Spectra; Absorption Spectra; Abundance; Carbon; Interstellar Gas; Ionized Gases; Iue; Radial Velocity; Velocity Distribution; Astrophysics full text sources ADS | data products SIMBAD (45) MAST (1)

Why high-latitude clouds in our Galaxy and the highly redshifted clouds observed in front of QSOs do not belong to the same parent population

International Ultraviolet Explorer observations of high-latitude gas in our Galaxy reveal the presence of both C II and C IV absorption in the spectra of stars with z>2 kpc. On the other hand, C II is generally absent from unbiased samples of QSO redshift systems with C IV absorption. Comparison between the equivalent-width distributions of the QSO sample and of the galactic sample (which is suitably corrected for contamination by disk absorption) shows that a probability that the two samples are drawn from the same parent population is less than 1% for C II and less than 10% for C IV. Thus, contrary to prevailing opinion, it is highly unlikely that gaseous halos comprised of material with properties of the high-latitude gas are responsible for the bulk of known QSO redshift systems. However, gaseous halos with bimodal states of ionization, or in which the ionization state is a unique function of redshift, are compatible with QSO absorption statistics.

IUE observations of E1405-451 - A new AM Herculis type cataclysmic variable

view Abstract Citations (15) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS IUE observations of E 1405-451 : a new AM Herculis type cataclysmic variable. Nousek, J. A. ; Pravdo, S. H. Abstract International Ultraviolet Explorer observations of the recently discovered AM Herculis type cataclysmic variable E1405-451 reveal a UV spectrum (1000-3000 A) similar to the other members of the type. The continuum flux distribution rises steeply at short wavelength and shows the effects of interstellar extinction. Best fit parameters for a blackbody spectrum are T = 25,500 + or - 2300 K with E(B-V) = 0.13 + or - 0.05. Many strong emission lines appear in the spectrum with similar intensities to those in AM Her. C IV 1550 and He II 1640 show some sign of a P Cygni profile. If these profiles are truly P Cygni, they indicate the intriguing possibility of a magnetically confined, radiatively driven wind present in all AM Her systems but only observable in a subset with an orientation like E1405-451. Publication: The Astrophysical Journal Pub Date: March 1983 DOI: 10.1086/183974 Bibcode: 1983ApJ...266L..39N Keywords: Emission Spectra; Iue; Line Spectra; Ultraviolet Astronomy; Variable Stars; B Stars; Black Body Radiation; Interstellar Extinction; Ultraviolet Spectra; Astrophysics full text sources ADS | data products SIMBAD (1) MAST (1)

Ultraviolet shell formation at V1016 Cygni

A recent 330 minute high-resolution International Ultraviolet Explorer (IUE) spectrogram of V1016 Cygni shows splitting of the 1550 A component of the C IV resonance doublet, suggesting that a nebular shell is in the process of formation. An expansion velocity of 15 km/s is indicated by the IUE data and corresponds to the low range encountered with normal planetary nebulae, but IUE data of V1016 Cyg, taken approximately one year earlier, do not show split C IV lines. The recent IUE observations are consistent with VLA contour maps at 1.3 cm made by Newell and Hjellming (1981) and by Hjellming and Bignell (1982) that morphologically show an extended shell-type object. Thus, V1016 Cyg may have undergone an event which forms a planetary nebula.

International ultraviolet explorer observations of Hyades stars

view Abstract Citations (29) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS International Ultraviolet Explorer observations of hyades stars. Zolcinski, M. C. S. ; Antiochos, S. K. ; Stern, R. A. ; Walker, A. B. C. Abstract A description is presented of International Ultraviolet Explorer (IUE) satellite observations of transition region and chromospheric emission from a group of Hyades dwarfs which are strong X-ray emitters as seen in a survey conducted by Stern et al. (1981). Short-wavelength spectra (1175-2000 A) and long-wavelength spectra (1900-3200 A) have been obtained. Although the IUE sensitivity limit did not make it possible to detect emission lines in three stars, the presence of chromospheres and transition regions could be confirmed in BD +15 deg 640, 70 Tau, BD +14 deg 693, and BD +16 deg 592. The differential emission measure has been plotted as a function of temperature for the four considered stars. Publication: The Astrophysical Journal Pub Date: July 1982 DOI: 10.1086/160066 Bibcode: 1982ApJ...258..177Z Keywords: Dwarf Stars; Iue; Star Clusters; Stellar Spectrophotometry; Ultraviolet Astronomy; X Ray Sources; Chromosphere; Emission Spectra; Line Spectra; Stellar Spectra; Stellar Temperature; Ultraviolet Spectra; Wavelengths; Astronomy full text sources ADS | data products SIMBAD (7) MAST (1) INES (1)

IUE AND OPTICAL OBSERVATIONS OF MV LYR AT INTERMEDIATE AND LOW STATES.

ABSTRACT Ultraviolet observations of MV Lyrae were obtained with the aid of the International Ultraviolet Explorer (IUE) spacecraft on 1979 December 2 when MV Lyr was at a normal low state and on 1980 December 8. The optical observations were obtained at Kitt Peak, Lick Observatory, and the University of Washington Observatory with various image-tube scanners and photometers. The photometric colors were found to be very blue at the very low state and at the normal low state. Robinson et al. (1981) have identified three components in their very low-state optical spectra. The significance of the observations is discussed.

Observations of interstellar zinc

The International Ultraviolet Explorer observations of interstellar zinc toward 10 stars are examined. It is found that zinc is at most only slightly depleted in the interstellar medium; its abundance may serve as a tracer of the true metallicity in the gas. The local interstellar medium has abundances that apparently are homogeneous to within a factor of two, when integrated over paths of about 500 pc, and this result is important for understanding the history of nucleosynthesis in the solar neighborhood. The intrinsic errors in detecting weak interstellar lines are analyzed and suggestions are made as to how this error limit may be lowered to 5 mA per target observation.

International Ultraviolet Explorer observations of the central stars of the planetary nebulae NGC 6853 and NGC 7293

International Ultraviolet Explorer observations of the central stars of the planetary nebulae NGC 6853 and NGC 7293

Water production models for comet Bradfield /1979 X/

Whipple (1950, 1951) has proposed that water might be the dominant volatile constituent of the cometary nucleus. The considered investigation is concerned with the clues which observations of the cometary coma provide regarding the parents of the dominant observed coma species. In the early part of 1980, comet Bradfield (1979 X) was observed with the aid of the International Ultraviolet Explorer (IUE). These measurements are the first which provide a basis for a comprehensive study of all three water dissociation products, H, O, and OH, simultaneously. The IUE observations of comet Bradfield are compared with the predictions derived from an H2O model. The obtained results indicate that the observed brightnesses of H, O, and OH are certainly consistent with a common water source for all three species.

IUE observations of two elliptical galaxies - NGC 3379 and NGC 4472

The International Ultraviolet Explorer observations of the nuclei of the elliptical galaxies NGC 3379 and NGC 4472 show that the flux drops rapidly with decreasing wavelength until about 2300 A, below which the flux increases rapidly. The hot UV component of the radiation can be approximately represented by a blackbody at 30,000 K. The spectra of NGC 3379, NGC 4472, and M31 are very similar from 1260 to 8000 A. The hot UV component is abnormally weak in M 32 and abnormally strong in M 87. The UV spectrum from 1300 to 3200 A of the metal-rich globular cluster NGC 6624 resembles those of NGC 3379, NGC 4472, and M 31, and shows evidence for hot blue stars. A comparison of the UV fluxes with those measured in large-redshift normal galaxies shows good agreement, although allowance must be made for the line-strength differences found between the integrated galaxy spectra and the nuclear-region spectra.

Extragalactic Work with IUE

The International Ultraviolet Explorer (IUE) is an 18 inch (45 cm) space telescope for ultraviolet spectrophotometry in geosynchronous orbit and is a joint project of the European Space Agency, the American National Aeronautics and Space Administration and the British Science Research Council. (Boggess et al. 1978 ab). It is a small instrument to use for objects of truly high redshift and therefore IUE observations relevant to extragalactic astronomy in general will be covered here.

IUE observations of gas stream effects in the ultraviolet spectrum of U Cephei

view Abstract Citations (33) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS IUE observations of gas stream effects in the ultraviolet spectrum of U Cephei. Kondo, Y. ; McCluskey, G. E. ; Stencel, R. E. Abstract The eclipsing binary U Cephei has been observed with the International Ultraviolet Explorer (IUE) satellite. Nine high-resolution spectra in the mid-ultraviolet (1900-3200 A) and one high-resolution spectrum in the far-ultraviolet (1200-1900 A) were obtained. The effects of gas streaming are clearly seen in the mid-ultraviolet resonance lines of Fe II (2599 A) and Mg II (2795 and 2802 A). The data indicate that much of the gas leaving the G star circles behind the B star and leaves the system. It is suggested that g-mode oscillations in the G star supply part of the energy required to drive the gas out of the system. Publication: The Astrophysical Journal Pub Date: November 1979 DOI: 10.1086/157452 Bibcode: 1979ApJ...233..906K Keywords: B Stars; Eclipsing Binary Stars; Gas Streams; Spaceborne Astronomy; Ultraviolet Spectra; Absorption Spectra; Far Ultraviolet Radiation; G Stars; High Resolution; Iue; Line Spectra; Radial Velocity; Astrophysics; Eclipsing Binaries:UV Spectra full text sources ADS | data products SIMBAD (2) MAST (1) Related Materials (1) Erratum: 1983ApJ...264..746K

IUE Observations of White Dwarfs and Hot Subdwarfs

The International Ultraviolet Explorer (IUE) has been used by Greenstein and Oke to obtain low resolution spectra from 1150 to 3200 Å of a selection of white dwarfs and hot subdwarfs.The observations can be converted to absolute fluxes so that, by including energy distributions measured with the multichannel spectrometer on the Hale telescope, fluxes can be derived between 1150 and 11000 Å. The IUE absolute fluxes show erratic level shifts of up to 20 percent and probably also smaller changes in the slope. These shifts are probably associated with the level of the radiation induced background coupled with uncertainties in the calibration of the non-linear detectors. In many cases, these anomalies in the fluxes are obvious, but they do decrease the accuracy with which temperatures and gravities can be determined.

IUE observations of the eclipsing binary Epsilon Aurigae

THE eclipsing binary Epsilon Aur is almost peculiar binary system and it has not been explained satisfactorily. We report here our observations of this system using the International Ultraviolet Explorer (IUE) collected at the Villafranca Satellite Tracking Station of the European Space Agency (SA).