International Ultraviolet Explorer Satellite Research Articles

The Mass–Temperature Relation for B and Early A Stars Based on International Ultraviolet Explorer Spectra of Detached Eclipsing Binaries

Ultraviolet spectra were taken of 25 detached eclipsing binaries (DEBs) with spectral types O, B, and early A with the International Ultraviolet Explorer satellite in the 1150–1900 Å region. The spectra were compared with BOSZ model atmospheres. The composite spectra of the DEBs were modeled by a combination of models representing the hot and cool components, and the temperatures of the hottest components of the systems were determined. From these temperatures a direct mass–temperature relation was obtained for stars close to the main sequence with solar metallicity for B and early A stars: log M/M ⊙ = −5.90 ± 0.27 + (1.56 ± 0.07) × log T. This relation allows a mass to be inferred for comparable stars from an ultraviolet spectrum. The five chemically peculiar Am stars in the sample have larger radii than normal A stars of the same mass.

Inferring Contributions from Unresolved Point Sources to Diffuse Emissions Measured in UV Sky Surveys: General Method and SOHO/SWAN Case Study

Abstract In observations of diffuse emissions like, e.g., the Lyα heliospheric glow, contributions to the observed signal from point sources (e.g., stars) are considered to be a contamination. There are relatively few bright point sources that are usually properly resolved and can be subtracted or masked. We present results of an analysis of the distribution of point sources using UV sky-survey maps from the Solar and Heliospheric Observatory (SOHO)/Solar Wind ANisotropy (SWAN) instrument and spectrophotometry data from the International Ultraviolet Explorer satellite. The estimated distribution suggests that the number of these sources increases with decreasing intensity. Below a certain threshold, these sources cannot be resolved against the diffuse signal from the backscatter glow, that results in a certain physical background from unresolved point sources. Detection, understanding, and subtraction of the point-source background has implications for proper characterization of diffuse emissions and accurate comparison with models. Stars are also often used as standard candles for in-flight calibration of satellite UV observations, thus proper understanding of signal contributions from the point sources is important for the calibration process. We present a general approach to quantify the background radiation level from unresolved point sources in UV sky-survey maps. In the proposed method, a distribution of point sources as a function of their intensity is properly integrated to compute the background signal level. These general considerations are applied to estimate the unresolved-point-source background in the SOHO/SWAN observations that on average amounts to 28.9 R. We also discuss the background radiation anisotropies and general questions related to modeling the point-source contributions to diffuse UV-emission observations.

UV emission line studies of NGC-low redshift Seyfert Galaxies, LINERS and HII regions

Active galaxies as a special class of galaxies are characterized by very strong and broad emission lines. The strong emission lines such as Lyα, NV, Si IV, C IV, and Mg II observed in the UV spectra of Seyfert galaxies and quasars can be used to probe the physical conditions of the gas in the BLR regions surrounding the central accretion discs of these most luminous and exotic objects. In the standard model of broad line emission regions for active galaxies it is assumed that the broad permitted lines are emitted by the photo-ionization of a large number of spherically distributed optically thick clouds which are in Keplerian motion surrounding a central continuum source. However, issues related to variability time-scales, delays in the light curves and BLR sizes etc., remain unexplained consistent with observations. In this paper, a study of emission line properties 9 objects satisfying good SNR (> 5.0) out of 98 NGC (catalogued) IUE observed low redshift active galaxies (z ≤ 0.017) is presented. The International Ultraviolet Explorer (IUE) satellite launched in 1978 by NASA has made low redshift UV spectroscopic observations of many different kinds of UV sources including active galaxies till 1996 and the flux calibrated spectral data of almost all observations have been hosted in NED-IUE database. In the present studies, IUE spectral data of a complete sample of NGC-catalogued active galaxies has been undertaken to understand the emission line properties of low luminosity and low z active galaxies. We find that the emission lines such as Lyα, N V, Si IV, O III], C III], C IV, and Mg II are observed as strong and broad lines in the spectra of only 9 objects owing to the criterion of S/N ≥ 5.0 adopted for the spectral analysis. The Lyα has not been found to be a strong line unlike in high z Seyfert galaxies and quasars observed by IUE satellite. C IV and Mg II lines are observed to be stronger lines in all the nine objects consistent with their usual presence in the remaining (~ 400) active galaxies observed by the IUE satellite. These observations are indicative of different physical and geometrical conditions in the BLR regions surrounding the central accretion disk compared to the intermediate and high redshift Seyfert galaxies and quasars.

A database of synthetic photometry in the GALEX ultraviolet bands for the stellar sources observed with the International Ultraviolet Explorer

The Galaxy Evolution Explorer (GALEX) has produced the largest photometric catalogue of ultraviolet (UV) sources. As such, it has defined the new standard bands for UV photometry: the near UV band (NUV) and the far UV band (FUV). However, due to brightness limits, the GALEX mission has avoided the Galactic plane which is crucial for astrophysical research and future space missions. The International Ultraviolet Explorer (IUE) satellite obtained 63,755 spectra in the low dispersion mode during its 18 years lifetime. We have derived the photometry in the GALEX bands for the stellar sources in the IUE Archive to extend the GALEX data base with observations including the Galactic plane.Good quality spectra have been selected for all IUE classes of stellar sources. The GALEX FUV and NUV magnitudes have been computed using the GALEX transmission curves, as well as the conversion equations between flux and magnitudes provided by the mission (galexgi.gsfc.nasa.gov). Consistency between GALEX and IUE synthetic photometries has been tested using White Dwarfs (WD) contained in both samples. The non-linear response performance of GALEX inferred from this data agrees with the results from GALEX calibration. The photometric data base is made available to the community through the services of the Centre de Donn\'ees Stellaires at Strasbourg (CDS). The catalogue contains FUV magnitudes for 1,631 sources, ranging from FUV=1.81 to FUV=18.65 mag. In the NUV band, the catalogue includes observations for 1,005 stars ranging from NUV = 3.08 to NUV= 17.74 mag . UV photometry for 1,493 not included in the GALEX AIS GR5 catalogue is provided; most of them are hot (O-A spectral type) stars. The sources in the catalogue are distributed over the full sky, including the Galactic plane.

Ultraviolet spectroscopy of V Sagittae in high, intermediate and low states from HST and IUE satellites

We present the first phase resolved ultraviolet spectroscopic study of V Sge in high, intermediate and low states observed with the Hubble Space Telescope High Resolution Spectrograph (HST HRS) and International Ultraviolet Explorer (IUE) during the period 1978–1996 to diagnose the ultraviolet fluxes of C IV 1550 A and He II 1640 A emission lines originating in the accretion disk during different orbital phases. Different spectra showing the variations in line fluxes at different orbital phases are presented. The reddening of V Sge is determined from the 2200 A feature. We concentrated on calculating the line fluxes of C IV & He II emission lines. From HST and IUE data, we derived an accretion luminosity and an accretion rate for V Sge. The average temperature of the outer rim of the accretion disk ${\sim}10000~\mbox{K}$ . Our results show that there are variations in line fluxes, accretion luminosities and accretion rates with time for V Sge. These variations are attributed to the variations of both density and temperature as a result of a changing rate of mass transfer from the secondary star to the white dwarf. These results from the HST and IUE observations are consistent with the binary model consisting of a white dwarf, a disk around the white dwarf, and a lobe-filling main-sequence companion (Hachisu & Kato, Astrophys. J. 598:527H, 2003).

ULTRAVIOLET SPECTROSCOPY OF PQ Gem AND V405 Aur FROM THEHSTANDIUESATELLITES

Ultraviolet spectra of two intermediate polars (IPs), PQ Gem and V405 Aur, observed with Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph and Faint Object Spectrograph and International Ultraviolet Explorer (IUE) satellites were analyzed during the period between 1994–2000. We estimated the reddening of the two systems from the 2200 A feature. Six spectra of the two systems revealing modulations of line fluxes at different times are presented. PQ Gem and V405 Aur are featured by spectral lines in different ionization states. This paper focuses on the third ionized carbon emission line at 1550 A and the first ionized helium emission line at 1640 A produced in the optically thin outer region of the accretion curtain for the two systems by calculating spectral line fluxes. From HST and IUE data, we deduced ultraviolet luminosities and ultraviolet accretion rates for the two binary stars. The average temperature of the accretion streams for PQ Gem and V405 Aur are ~4500 K and 4100 K, respectively. The results reveal that there are modulations in fluxes of spectral lines, ultraviolet luminosities, and ultraviolet accretion rates with time for both systems. These modulations are referred to the changes of both density and temperature as a result of the variations of mass transfer rate from the secondary star to the primary star. The current results are consistent with an accretion curtain model for IPs.

Ultraviolet spectral behavior of AO Psc and V1223 Sgr from the HST and IUE satellites

We present a spectroscopic study of two intermediate polar systems, AO Psc and V1223 Sgr observed with the Hubble Space Telescope Space Telescope Imaging Spectrograph (HST STIS) and International Ultraviolet Explorer (IUE) during the period 1980–2000. The reddening of two systems is determined from the 2200 A feature. The ultraviolet emission lines are originating in the accretion disk as a result of existing an extra component of emission in the EUV/soft X-ray range with luminosity comparable to the accretion luminosity which reprocessed to produce the observed ultraviolet line strengths. Different spectra for both systems showing the variations in line fluxes at different orbital phases are presented. We concentrated on calculating the line fluxes of C IV 1550 A & He II 1640 A emission lines. From HST and IUE data, we derived an accretion luminosities and an accretion rates for two systems. Our results show that there are variations in line fluxes, accretion luminosities and accretion rates with time for two systems. These variations are attributed to the variations of both density and temperature as a result of a changing rate of mass transfer from the secondary star to the white dwarf. These results from the IUE and HST observations are consistent with the models of Ko et al. (Astrophys. J., 457:363K, 1996).

Ultraviolet spectral variations of FK Comae and V 1794 Cygni

Ultraviolet spectra of FK Comae and V1794 Cygni observed with the Hubble Space Telescope Cosmic Origins Spectrograph (HST COS) and the International Ultraviolet Explorer (IUE) satellites were analyzed for the period 1981–2011. Temporal variations of line fluxes of the O I 1306Å, C II 1336Å, C IV 1550Å, He II 1640Å and Mg II k & h 2800Å, produced in the transition regions and chromospheres of these stars, imply variations in density and temperature changes in the line emitting regions as a result of the rapid rotation and magnetic fields responsible for stellar activity. Results are consistent with the models of Ramsey et al. (1981), Oliveira and Foing (1999), and Korhonen et al. (2000).

Interstellar Dust Models Towards Some IUE Stars

We study the extinction properties of composite dust grains, consisting of host silicate spheroids and graphite as inclusions, using discrete dipole approximation (DDA). We calculate the extinction cross sections of the composite grains in the ultraviolet spectral region, 1200–3200 Å, and study the variation in extinction as a function of the volume fraction of the inclusions. We compare the model extinction curves with the observed interstellar extinction curves obtained from the data given by the International Ultraviolet Explorer (IUE) satellite. Our results for the composite grains show a distinct variation in the extinction efficiencies with the variation in the volume fraction of the inclusions. In particular, it is found that the wavelength of peak absorption at 2175 Å shifts towards the longer wavelength with the variation in the volume fraction of inclusions. We find that the composite grain models with the axial ratios viz. 1.33 and 2.0 fit the observed extinction reasonably well with a grain size distribution, a = 0.005–0.250 μm. Moreover, our results on the composite grains clearly indicate that the inhomogeneity in the grain structure, composition, and the surrounding media modify the extinction properties of the grains.

Ultraviolet spectral behavior of IP Peg and DW UMa in high, intermediate and low states from the HST and IUE satellites

Ultraviolet spectra of IP Peg and DW UMa observed with Hubble Space Telescope Space Telescope Imaging Spectrograph & Faint Object Spectrograph (HST STIS FOS) and International Ultraviolet Explorer (IUE) satellites were analyzed during the period between 1989–1994 and 1985–2004. Different profiles of two systems showing variations of line fluxes at different orbital phases are presented. Both IP Peg and DW UMa are characterized by emission lines in high, intermediate and low states. DW UMa is characterized by absorption lines in an unusual low state. This paper focuses on the C IV emission line at 1550Å produced in an accretion disk for two systems (Saito et al., 2005; Knigge et al., 2000), by calculating spectral line fluxes. Our results show that there are significant variations of line fluxes with time for two systems. The variations of line fluxes are attributed to the variations of both density and temperature as a result of a changing rate of mass transfer from the secondary star to the white dwarf (Saito et al., 2005; Knigge et al., 2000). These results from the IUE and HST observations support a white dwarf model atmospheres of IP Peg and DW UMa producing sufficient UV flux for orbital modulations.

FAR-ULTRAVIOLET DETECTION OF THE SUSPECTED SUBDWARF COMPANION TO THE Be STAR 59 CYGNI

We report on the detection of a hot subdwarf component in the Be binary system, 59 Cygni. The spectral signature is found in cross-correlation functions of photospheric model spectra with far-ultraviolet spectra obtained by the International Ultraviolet Explorer Satellite, and we used radial velocities from the cross-correlation functions to determine a double-lined spectroscopic orbit. The individual spectra of the binary components were extracted using a Doppler tomography algorithm. The flux of the system is dominated by the rapidly rotating Be star. However, the subdwarf contributes approximately 4% of the UV flux, and its spectrum bears a strong resemblance to that of the hot sdO star BD +75°325. Based on the appearance of the UV spectrum and the orbital elements, we present estimates for the stellar masses, radii, and temperatures. The presence of the hot companion causes excess emission from the outer part of the Be disk facing the companion. We present a set of red spectra that show the orbital phase variations of the He I λ6678 emission formed in the heated region of the disk, which probably occurs near the disk outer boundary. 59 Cygni, FY Canis Majoris, and Persei comprise the known set of Be binaries with detected hot evolved companions, which are the stripped down remains of mass transfer. Their properties demonstrate that some fraction of Be stars were spun up through angular momentum transfer by Roche lobe overflow.

Looking for Discrete UV Absorption Features in the Early‐Type Eclipsing Binaries μ1 Scorpii and AO Cassiopeiae

ABSTRACTA search for discrete absorption components in the ultraviolet spectra of the early‐type binaries μ1 Scorpii and AO Cassiopeiae has been undertaken by analyzing material secured with the International Ultraviolet Explorer satellite during an exclusively assigned interval of nearly 50 hr. While the spectra of μ1 Sco definitely do not show the presence of such lines, the spectra of AO Cas do confirm them and permit us to draw some conclusions about where they may be formed.

Heavy Element Abundances in Late‐B and Early‐A Stars. I. Co‐AddedIUESpectra of HgMn Stars

Very heavy elements (Pt, Au, Hg, Tl, and Bi) are found to be enhanced inthe atmospheres of the chemically peculiar stars of the upper mainsequence by up to a million times the solar system levels. Suchenhancements are believed to result from atmospheric dynamics (i.e.,diffusion) rather than scenarios that dredge up nuclear-processedmaterial to the surface or transfer processed material between binarycompanions. However, the theoretical framework needs to be furtherconstrained by observations beyond the realm of the spectral types forwhich such abundance enhancements are observed at optical wavelengths.The International Ultraviolet Explorer (IUE) satellite collected spectraof bright stars for which chemical peculiarities have been derived fromground-based data. For several elements the abundance enhancements haveonly been recently measured using Hubble Space Telescope data and havetherefore not yet been exploited in the IUE data. We have initiated aprogram to analyze IUE high-dispersion spectra to more fullycharacterize the pattern of very heavy element enhancement for manymercury-manganese (HgMn) stars and to potentially extend the spectralclass (effective temperature) boundaries over which these abundanceanomalies are known to exist. The abundances of very heavy elements inchemically normal B and A-type stars provide a base level that may becompared with the solar system abundances. These early spectral typestars may therefore reveal clues for galactic chemical evolution studiessince they were formed at a later epoch than the Sun in the history ofthe Galaxy. This first paper presents the motivation for the analyses tofollow, outlines our spectral co-addition technique for IUE spectra, anddiscusses the choice of model atmospheres and the synthetic spectrumprocedures, while initiating the study by highlighting the abundance ofgold in several HgMn stars.

An Archive of IUE Low‐Dispersion Spectra of the White Dwarf Stars

We have produced an archive of the ultraviolet low-dispersion spectra for the full set of white dwarf stars observed with the International Ultraviolet Explorer (IUE) satellite over the course of its 18 yr mission. This archive contains the spectra of 322 individual degenerate stars which have been processed to optimize the signal-to-noise for each star. In particular, all spectra have been corrected for residual temporal and thermal effects and placed on the Hubble Space Telescope Faint Object Spectrograph absolute flux scale using procedures described by Massa & Fitzpatrick. Wherever possible, multiple observations of individual stars have been co-added to further enhance signal-to-noise and have been combined into a single spectrum

Ultraviolet light curves of eclipsing binary stars. I. The catalogue of IUE data

The catalogue contains eclipsing and ellipsoidal variable stars observed by International Ultraviolet Explorer satellite (IUE). As examples we discuss IUE data for Algol (β Persei) and MR Cygni.

Far-Ultraviolet light curves of the δ Scuti variable: β Cassiopeiae

Ultraviolet spectra of β Cas (Sp F2 III–IV) were acquired with the International Ultraviolet Explorer (IUE) satellite. The observed flux level changes rapidly from F λ ≈ 2.5 · 10 −13 to 2.0 · 10 −10 erg/cm 2/s/Å at λ = 1280 A ̊ and 3000 Å, respectively. Chromospheric emission in UV spectra is seen both in spectral lines (e.g. SiIV 1400, CIV 1550, MgII 2800 Å) and continuum (for λ < 1700 A ̊ ). To obtain the basic photospheric parameters of this star we took the mean IUE spectrum only for λ > 2300 A ̊ as well as the ground based observations in the spectral range of 3200–10800 Å. We found log T eff = 3.85, log g = 3.40, log L/ L ⊙ = 1.43 and θ = 2.0 mas. β Cas is a δ Scuti variable and time sequences of the low resolution SWP (1150–1950 Å) spectra and high resolution LWP (1900–3200 Å) spectra made in the large aperture allowed us to construct the light curves at selected wavelength passbands. In general, the amplitude grows with decreasing wavelength. Our results also indicate pulsational variability of the lower chromosphere, as seen at λ < 1700 A ̊ .

The Mass of the Central Black Hole in the Seyfert Galaxy NGC 3783

Improved analysis of ultraviolet and optical monitoring data on the Seyfert 1 galaxy NGC 3783 provides evidence for the existence of a supermassive, (8.7 +/- 1.1) x 10(exp 6) solar mass, black hole in this galaxy. By using recalibrated spectra from the International Ultraviolet Explorer satellite and ground-based optical data, as well as refined techniques of reverberation mapping analysis, we have reduced the statistical uncertainties in the response of the emission lines to variations in the ionizing continuum. The different time lags in the emission-line responses indicate a stratification in the ionization structure of the broad-line region and are consistent with the virial relationship suggested by the analysis of similar active galaxies.

The Massive Close Binary in the δ Ori A Triple System

AbstractWe present an analysis of short-wave, high-dispersion ultraviolet spectra of the triple star δ Ori A from the International Ultraviolet Explorer Satellite’s (IUE) Final Archive. These spectra were cross-correlated against AE Aur to find the components’ radial velocities, which were then used to produce the system’s orbital elements. The long-period tertiary star in the δ Ori A system was not seen in the resulting cross-correlation functions (CCFs). The close binary’s eclipses allow the orbit’s inclination to be estimated by modeling of its Hipparcos light curve. The primary star appears to have a mass of 11.2 M⊙ and the secondary seems to have a mass of 5.6 M⊙, both of which are about 1/3 of the expected values for stars of their MK types. Although we expected the massive close binary in the δ Ori A system to be a pre-Roche lobe overflow (RLOF) system, these masses appear to require that it be a post-RLOF system. The full description of this work, including the tomographic separation of the spectra for the close binary’s components, appears in Harvin et al. (2002).

IUE Absorption‐Line Observations of the Moderately and Highly Ionized Interstellar Medium toward 164 Early‐Type Stars

We present measurements of Galactic interstellar Al III, Si IV, and C IV absorption recorded in high-resolution archival ultraviolet spectra of 164 hot early-type stars observed by the International Ultraviolet Explorer (IUE) satellite. The objects studied were drawn from the list of hot stars scheduled to be observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite as part of observing programs designed to investigate absorption by O VI in the Galactic disk and halo. Multiple IUE echelle-mode integrations have been combined to produce a single ultraviolet (1150-1900 A) spectrum of each star with a spectral resolution of ~25 km s-1 (FWHM). Selected absorption-line profiles are presented for each star along with plots of the apparent column density per unit velocity for each line of the Al III, Si IV, and C IV doublets. We report absorption-line equivalent widths, absorption velocities, and integrated column densities based on the apparent optical depth method of examining interstellar absorption lines. We also determine column densities and Doppler parameters from single-component curve-of-growth analyses. The scientific analysis of these observations will be undertaken after the FUSE satellite produces similar measurements for absorption by interstellar O IV, Fe III, S III, and other ions.

MgiiEmission Lines of Hyades F Stars

With the Hubble Space Telescope (HST) we have observed Hyades F stars, using the Space Telescope Imaging Spectrograph (STIS), in order to get more information about the heating mechanism(s) for the chromospheres and transition layers and their dependence on rotation and age. In this paper we study the Mg II lines at 2800 A. We include earlier observations with the International Ultraviolet Explorer (IUE) satellite. The Mg II emission lines become observable for B - V > 0.3. The emission line fluxes increase steeply until B - V ~ 0.40. For single stars there is a steep decrease in flux between B - V = 0.41 and B - V = 0.44, similar to the behavior of the Ca II emission line cores. For larger B - V the Mg II emission line fluxes again increase, but much more slowly than for the Ca II lines. Generally, the low point of the emission is reached between B - V = 0.43 and B - V = 0.45, i.e., similar to the Ca II emission cores. For the Hyades F stars there appears to be a difference between the emissions for single stars and those for binaries. We find that for Hyades stars with surface line fluxes larger than 106 ergs cm-2 s-1 the emission line fluxes decrease with increasing v sin i. For smaller fluxes they may increase with increasing v sin i. We have only three stars that perhaps show this. We study the flux ratios of the Mg II k and h lines at 2795.7 and 2802.5 A in order to determine where the lines fall on the curve of growth. For the earliest F stars studied here the ratio is close to 2, as expected for optically thin lines. Generally, it seems that the optical depths in the line centers are less than 10. There remain problems in understanding the size of the line widths. We discuss the interpretation of the Wilson-Bappu effect. For the Hyades F stars there is a strong dependence of the line width on the effective temperature.