Low-dispersion IUE Spectra Research Articles

New physical elements of HR 7428 and its Hαbehaviour

HR 7428 is a spectroscopic binary composed of a K2 II-III and a main-sequence A2 star. Thanks to a new set of radial velocity measurements from our and IUE spectroscopy we have improved the orbital period determination and the spectroscopic elements of both components. Combining optical photometry and UV low dispersion IUE spectra we have determined new stellar parameters through photospheric synthetic spectra using the NextGen models by Hauschildt et al. (1999a, 1999b). The hot secondary component parameters agree with those of a typical A2 V star while the radius of the primary cool star turns out to be 40 R, i.e. signicantly smaller than a previous estimate of 62 R. The position of the hot and cool component on the H{R diagram is consistent with a normal evolution, without any mass exchange, of this binary system, whose age is in the range 100{200 Myrs. The system displays a lled-in H prole with signicant variations both in depth and width along the orbital phase. In addition to the H chromospheric emission component, we have detected, at some phases, a broad extra-absorption and emission that we relate to an inter-system cloud.

Electron Densities, Radial and Terminal Wind Velocities for the Planetary Nebula NGC 6302 and Its Ovi‐Type Binary Nucleus

Archival high- and low-dispersion IUE spectra of NGC 6302 and its nucleus have been analyzed. The spectra in the NEWSIPS format reveal many high-excitation emission features, including stellar O V, O VI, O VII, and O VIII that identify the nucleus as a new member of the "O VI sequence." Fe II features that are resonantly excited by O VI λ1032 are also observed. Other high-excitation species include [Ne IV], [Ne V], [Mg VI], and [Si VII]. Electron densities were determined from C III], N III], N IV], and [Ne IV] and are compared to IR [Ne V] densities. Radial velocities of strong emission features cluster around -55 km s-1 except for the Bowen O III and [O II] lines that show large positive radial velocities. Results from IUE, optical, ground-based IR, and KAO IR data are summarized. A relatively low terminal wind velocity of -520 ± 200 km s-1 was estimated from the P Cygni profile of the C IV λ1548 feature. A G-type companion to the very hot white dwarf central star is indicated by the LWR/LWP low-dispersion spectra.

The Chromospheres of Carbon Stars

Most oxygen-rich late-type giant stars show evidence for chromospheres in their visual spectra (e.g. Ca ii H & K emission features). Cool (i.e. N-type) non-Mira carbon stars, however, have never been observed to have chromospheric emission in their Ca ii H & K lines. However, faint Mg ii h & k lines were detected in emission in low-dispersion IUE spectra of the brightest cool carbon stars in the early 1980s. May 1984 saw the first (and only) successful high-dispersion IUE spectrum taken of a cool carbon star, TX Psc (N0; C6,2). Armed with this high-dispersion spectrum, as well as low-dispersion IUE and ground-based spectra, Luttermoser et al. (1989) made the first detailed attempt to semiempirically model the chromosphere of a cool carbon star. This model was successful in reproducing the Mg ii lines, but it was not well constrained due to the lack of other observed high-resolution chromospheric profiles for comparison. Modeling carbon star chromospheres can now be addressed more accurately with HST/GHRS high-resolution spectra. New fluoresced emission features have been discovered in the GHRS spectra of carbon stars that are not present in their oxygen-rich counterparts.

TheIUESpectra of the OviSequence Planetary Nebulae NGC 2452, NGC 7026, M3‐30, and Lo 4

We present emission-line fluxes for NGC 2452, NGC 7026, M3-30, and Lo 4 from IUE low-dispersion spectra that have been processed by the New Spectral Image Processing System (NEWSIPS). For NGC 2452, a terminal wind velocity of -4200 ± 300 km s-1 was determined from the C IV λ1549 P Cygni profile, while that of NGC 7026 is -4600 ± 300 km s-1, and -4800 ± 400 km s-1 for M3-30. The spectrum of Lo 4 is a stellar continuum with some absorptions and a questionable C IV λ1549 feature.

The IUE INES System: Improved data extraction procedures for IUE

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 imple- mentation to produce the NEWSIPS output products (extracted spectra) are discussed, and the procedures im- plemented in INES to solve these problems are outlined. The more relevant modications are: 1) the use of a new noise model, 2) a more accurate representation of the spa- tial prole of the spectrum and 3) a more reliable deter- mination of the background. The INES extraction also includes a correction for the contamination by solar light in long wavelength spectra. Examples showing the im- provements obtained in INES with respect to SWET are described. Finally, the linearity and repeatability charac- teristics of INES data are evaluated and the validity of the errors provided in the extraction is discussed.

Evidence of Chromospheric Activity on HR 1099

We present an observational evidence of the chromospheric activity on HR1099. The IUE spectra of HR 1099 were used for the ultraviolet photometry and for the intensity variation of chromospheric emission line. Ultraviolet light curves were made from the low and high dispersion IUE spectra and were compared with a optical light curve. We have analyzed the ultraviolet and optical light curves by the Wilson and Devinney computing code including dark spots. The intensity variation of Mg II emission line depends on the orbital phase. The maximum intensity of Mg II emission line occurs at the phase of light minimum where dark spot visibility is maximum due to strong chromospheric activity.

A REASSESSMENT OF THE IUE EMISSION LINE SPECTRUM OF THE PLANETARY NEBULA NGC 5189 AND ITS CENTRAL STAR

ABSTRACT Archival high-and low-dispersion IUE spectra of NGC 5189 and its central star were reexamined. It was found that earlier published results misinterpreted nebular features for stellar emission lines due to incorrect coordinates and/or incorrect pointing of the spacecraft. NGC 5189 has a UV spectrum rich in emission lines of He II, C II], C III, C III], C IV, C V, N III], N IV], O I, O III], O IV], O V, O VI, O VII, O VIII, [Ne III], [Ne IV], [Ne V], [Mg V], [Ar IV], Si III], and Fe II. The data were reextracted and the emission line fluxes were measured. Electron density for C III] and terminal wind velocities from C IV P Cygni profiles were determined. Comparisons of the IUE spectra of NGC 5189 and NGC 6905 show that these objects have very similar characteristics.

THE IUE SPECTRUM OF THE BINARY NUCLEUS OF THE PLANETARY NEBULA NGC 1514

ABSTRACT Archival IUE low-dispersion spectra and the first ultraviolet high-dispersion spectrum of the binary nucleus of NGC 1514 have been analyzed. Both SWP and LWR low-dispersion spectra show variability by as much as a factor of two in the continuum level between the years 1978 and 1989. Weak P Cygni features for OV lambda 1371 and C IV lambda 1549 yield terminal wind velocities of -105 plus or minus 25 and -960 plus or minus 150 km s-1, respectively. No nebular emission lines were detected, but several photospheric and interstellar absorption features were observed. Absorption lines of Fe VII are suspected. The He II lambda 1640 absorption line has a radial velocity of +49 plus or minus 3 km s-1 and is in good agreement with optical data. The peculiar energy distribution of the SWP continuum for NGC 1514 can be synthesized by the coaddition of spectral type A0 - A3 III plus hot subdwarf IUE spectra.

THE WHITE-DWARF COMPANIONS OF 56 PERSEI AND HR 3643

ABSTRACT We have obtained low-dispersion IUE spectra of the stars 56 Persei (F4 V) and HR 3643 (F7 II), as part of a survey of late-type stars with a 1565A flux excess in the TD-1 ultraviolet sky survey. The IUE spectrum of each star reveals the presence of a hot white dwarf companion. We fit the Ly-alpha profile and ultraviolet continuum using pure hydrogen models, but the distance of the primary star is also needed to uniquely constrain the white dwarf parameters. We derive Teff = 16,420 ± 420 K, log g= 8.46 ± 0.2 for the white dwarf companion to 56 Per, using the photometric distance of 30.1 ± 2.8 pc. The implied white dwarf mass is 0.90 ± 0.12 solar mass, considerably above the median mass (~0.6 solar mass) of single white dwarfs. The parameters of the white dwarf in HR 3643 are not well constrained, mainly due to a large uncertainty in the distance. By assuming a reasonable range of gravity for the white dwarf (7.3 < log g < 9.0), we derive -1.4 < MV < 0.6 for the F7 II star, adn 28,970 < Teff < 35,990 K for the white dwarf. Prompted by our detection of a white dwarf companion of a luminous F star, we have examined the IUE archives to assess the upper limits on possible white dwarf companions to Cepheids. The detection of a Cepheid--white dwarf binary would provide important insights concerning the most massive progenitors of white dwarfs. Only for the cases of alpha UMi and Beta Dor are existing IUE spectra of Cepheids sufficiently deep to rule out the presence of a white dwarf companion.

VARIABILITY OF IUE SPECTRA OF THE PULSATING NUCLEUS OF THE PLANETARY NEBULA K 1-16

ABSTRACT We report on some subtle changes which were detected in old IUE low dispersion spectra of the pulsating central star of the planetary nebula K 1-16. Although most of the data were taken more than ten years ago, the improved data reduction techniques and more accurate line identifications that have become available only recently permit measurement of variability in absorption lines. These changes are suspected of being caused by variations of O VI and high-excitation C IV transitions that on low-dispersion spectra are unresolved from interstellar Si II and may also mimic He II lambda-1640 absorption. We compare features in low- and high-resolution spectra of K 1-16 with those found in other PG 1159- and O VI-type central stars.

FAR-ULTRAVIOLET AND OPTICAL SPECTROSCOPY OF THE DETACHED WHITE DWARF-M DWARF BINARY RE J1629+780

ABSTRACT We present optical and far ultraviolet observations, including IUE high and low dispersion spectroscopy of the (DA2+dM4-5) close binary, RE J1629+780, a very bright ROSAT EUV source. The optical data reveal emission reversals in the cores of the Balmer lines, which vary in strength but reveal no evidence of wavelength shifts reflecting orbital motion, suggesting that the red dwarf and the white dwarf are widely separated. Thus it is unlikely that irradiation plays a dominant role in the activity of the red dwarf. One dramatic increase in the intensity of the H-beta emission strength in the course of one hour indicates that the observed intensity variations are most likely related to flare activity on the red dwarf. Our analysis of Balmer and Lyman alpha features yield Teff = 42,500 ± 1300K and log g = 7.6 ± 0.3 for the DA2 white dwarf, which is consistent with the overall 900 A to 3200 A energy distribution derived from Voyager and IUE low dispersion spectra. Our analysis of three IUE echelle spectra reveal numerous lines of interstellar origin. Using a total of 13 ISM features we find a mean radial velocity of -13.57 ± 1.66 km/s for the interstellar features. However we found no evidence of trace metal absorbers levitated or accreited in the white dwarf photosphere nor any evidence of circumstellar or wind features. We estimate a lower limit hydrogen layer mass of 2.1 X 10-15 Msun for a stratified atmosphere based upon the non-detection of He II (1640). Tighter constraints on the helium abundance and the hydrogen layer mass, from EUV and X-ray data, are presented for both homogeneous and stratified atmospheric configurations.

Synthetic UV Lines of SI iv, C iv, and He II from a Population of Massive Stars in Starburst Galaxies

view Abstract Citations (80) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Synthetic UV Lines of Si IV, C IV, and He II from a Population of Massive Stars in Starburst Galaxies Robert, Carmelle ; Leitherer, Claus ; Heckman, Timothy M. Abstract We present the first results of our study of the massive star population in starburst galaxies based on UV data. We have synthesized the Si IV 1400, C IV 1550 and He II 1640 lines for both a continuous and an instantaneous burst of star formation with approximately solar chemical composition. Our code uses the latest generation of stellar evolutionary models, stellar atmosphere codes, and a library of high-dispersion lUE spectra of hot stars. Models were computed for various values of the IMF parameters. Si IV λ1400 and C IV λ1550 develop P Cygni profiles when formed in strong stellar winds from the most massive stars. The velocity shifts predicted for these lines give a tight constraint on the value of the IMF upper mass cutoff: strong blueshifts in both lines are produced if stars with an initial mass larger than 30-60 Msun are included in the models. Based on the line velocity shifts, it also seems possible to put limits on the burst age. The models show only a small dependence of the line velocity shifts on the IMF slope. We also find a significant dependence of the equivalent widths of Si IV λ1400 and C IV λ1550 on the burst age, the IMF upper cutoff mass, and the IMF slope. The He II λ1640 line shows a strong broad emission profile when formed in winds from evolved massive stars. It offers additional important clues to the burst age and the IMF upper cutoff mass. We have compared the model parameters with data obtained for an average galaxy spectrum formed by combining low-dispersion IUE spectra of 13 starburst galaxies with nearly solar chemical composition. The most interesting result, based on the Si IV λ1400 and C IV λ1550 line velocity shifts and the strength of the broad He II λ1640 emission line, is that evolved massive stars with an initial mass larger than 30 Msun must be present in most of these galaxies. We find a good fit to the data for a model of an instantaneous burst of age ≃5 × 106 yr or a model for which star formation is proceeding at a constant rate for ≃107 yr. Hubble Space Telescope data with higher spectral resolution will be required to test these ideas and to allow us to fully exploit our method. Publication: The Astrophysical Journal Pub Date: December 1993 DOI: 10.1086/173432 Bibcode: 1993ApJ...418..749R Keywords: GALAXIES: STARBURST; STARS: EVOLUTION; STARS: FORMATION; STARS: MASS LOSS; ULTRAVIOLET: GALAXIES full text sources ADS | data products SIMBAD (212) MAST (1)

High-velocity spectral features in V854 Centauri: evidence for dust formation?

Low-dispersion IUE spectra of V854 Cen show apparent shifts or splitting in the λ2325 C II], λ2800 Mg II, λ2851 Mg I and λ2965 C I lines which, if kinematic, indicate velocities in excess of 1000 km s −1 . The variations are seen in all the UV emission lines simultaneously. The line splitting seems to occur at times near phase 0.0 (maximum light) of the pulsation cycle of the star. Dust formation episodes in V854 Cen also occur at this phase. New high-dispersion spectra of V854 Cen of the Na I D lines show many high-velocity features, both red- and blueshifted, including one at almost −400 km s −1 . The line profile variations may be a spectral signature of the gas from which the dust is condensing

THE HOT WHITE DWARF COMPANIONS OF HR 1608, HR 8210, AND HD 15638

ABSTRACT We have obtained low-dispersion IUE spectra of the late-type stars HD 15638 (F3 V), HR 1608 (=63 Eri, K0 IV), and HR 8210 (A8m). Each of these stars had been detected as a strong EUV source with the Wide Field Camera (WFC) aboard the ROSAT satellite. The short-wavelength IUE spectrum of each star reveals the presence of a hot white dwarf companion. We have fit the Ly-alpha profile and ultraviolet continuum of each white dwarf using pure hydrogen models. The excellent fit of the data to the models provides confirmation of the Finley and Koester absolute calibration of the SWP camera of IUE. The ultraviolet data alone are insufficient to constrain the model gravity, but an additional constraint is provided by the photometric distance to the late-type primary. We derive Teff = 50,000 K, log g = 8.15 for the white dwarf companion to HD 15638, Teff = 26,000 ± 1500 K, log g = 7.5 ± 0.5 for the companion to HR 1608, and Teff = 35,500 ± 1500 K and log g = 9.0 for the companion to HR 8210. The most interesting of the three white dwarfs is the companion to HR 8210 for which our results imply a mass of 1.15 M. This result is in good agreement with the lower limit on the mass derived from the spectroscopic orbit (M > 1.1 solar mass), provided that the inclination is close to 90 degrees. HR 8210 thus shows similarities to the Sirius system, although with a cooler primary (7700 K vs. 10,000 K), a hotter white dwarf (35,500 K vs. 25,000 K), and a 100 times smaller component separation (3 x 107 km vs. 3 x 109 km). We discuss the importance of future observations of HR 8210 for the study of high mass white dwarfs, and for scenarios of binary star evolution.

A new look at the dust toward Omicron Persei and Sigma Scorpii with the International Ultraviolet Explorer

The first IUE low dispersion spectra for Omicron Persei and Sigma Scorpii have been obtained and extinction curves from 1150 to 3250 A are presented. It is of interest to consider Omicron Persei and Sigma Scorpii dust in the context of the average extinction law of Cardelli et al (1989), here referred to as 'CCM', which depends on the R(v) parameter; this is defined as the ratio of total to selective extinction. Omicron Persei lies behind the edge of a dark cloud, and its dust shows a broad bump shifted to shorter wavelengths, similar to other dark cloud lines of sight, but shows no deviation from the CCM average curve in the far UV. Sigma Scorpii lies within the H II region near a dark cloud, and its dust shows a marked deviation from the CCM law in the far UV. These deviations are more typical of dark clouds or diffuse lines of sight, rather than of bright nebula lines of sight. The Omicron Persei and Sigma Scorpii dust characteristics exemplify a continuum of characteristics observed along various lines of sight, depending on the local dust environemnts.

The Blazhko Effect in RR Lyrae

AbstractThe cause of the Blazhko effect, the long-term modulation of the light and radial velocity curves of some RR Lyr stars, is still not understood. The observational characteristics of the Blazhko effect are discussed in §1. Some preliminary results are presented from aomw recent of campaigns to observe RR Lyr, using the International Ultraviolet Explorer along with ground-based spectroscopy and photometry, throughout a pulsation cycle, at a variety of Blazhko phases. A set of ultraviolet light curves have been generated from low dispersion IUE spectra. In addition, the (visual) light curves from IUE's Fine Error Sensor are analyzed using the Fourier decomposition technique. The values of the parameters ϕ21 and R21 at different Blazhko phasas of RR Lyr span the range of values found for non-Blazhko variables of similar period.

The ultraviolet spectrum of NGC 4151 from 1978 to 1990 - General characteristics and evolution

view Abstract Citations (65) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Ultraviolet Spectrum of NGC 4151 from 1978 to 1990: General Characteristics and Evolution Ulrich, M. -H. ; Boksenberg, A. ; Bromage, G. E. ; Clavel, J. ; Elvius, A. ; Penston, M. V. ; Perola, G. C. ; Snijders, M. A. J. Abstract From the examination of all the low-dispersion IUE spectra of NGC 4151 taken since the launch of IUE in 1978, including the latest data taken in 1990, we follow the evolution of this active nucleus on time scales ranging from days to 10 years. We concentrate our analysis on the campaigns of observations during which the nucleus was not continuously in a minimum state. Regarding the continuum, we find that the short variability time scales (a few days) in the optical and ultra-violet ranges rule out the possibility that the continuum intensity variations in these wavelength intervals are due to variations in the accretion rate of the possibly present accretion disk. Possible origins could be instabilities in the inner radiation-dominated part of the disk or irradiation of the disk by the variable X-ray flux. We study in detail the long- and short-term temporal behavior of the wings of the C IV and Mg II lines (|v| > 3870 km s^-1^) and the variations of the C III] line. The C IV line maintains a high degree of symmetry during the decrease and increase branches of the deep minimum of 1988 November 29-1989 January 30, but, in general, there are large changes in the C IV wings intensity ratio from campaign to campaign, and different responses of the blue and red wings to the continuum variations are frequently observed during a campaign. Our preferred interpretation of these effects is the redistribution or rearrangement of the fast- moving gas on a time scale of one to a few years, probably in the form of the arrival of a new gas cloud in the inner part of the broad-line region. We speculate that the gas clouds are being detached from stars or from the accretion disk itself. Publication: The Astrophysical Journal Pub Date: December 1991 DOI: 10.1086/170735 Bibcode: 1991ApJ...382..483U Keywords: Active Galactic Nuclei; Galactic Evolution; Seyfert Galaxies; Ultraviolet Spectra; Astronomical Spectroscopy; Emission Spectra; Interstellar Gas; Iue; Light Curve; Line Spectra; Astrophysics; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4151; GALAXIES: NUCLEI; GALAXIES: SEYFERT; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (4) NED (1) MAST (1)

Magnetically controlled circumstellar matter in the helium-strong stars

This paper reports the observation and interpretation of the ultraviolet spectrum variations of nine helium-strong stars: HD 36485, 37017, 37479, 37776, 58260, 60344, 64740, 96446, and 133518. A unified model is developed to account for the observed correlation among three stellar properties: the line profile characteristics of the C IV and Si IV resonance doublets, the variations in the strength of these lines, and the inferred magnetic field geometry. It is proposed that circumstellar plasma is trapped in the stellar magnetosphere near the magnetic equator or is channeled to form jetlike outflows from the magnetic polar regions. These results, together with those of a previous study of the helium-weak sn stars, show that both helium-weak and helium-strong stars can possess magnetospherically trapped plasma, notwithstanding their different photospheric properties. New results for radii and temperatures of the helium-strong stars in Ori OB 1 and for HD 64740 from low-dispersion IUE spectra are also presented.

The mass of the classical Cepheid SU Cygni

Radial velocity differences between the classical Cepheid SU Cyg and a hot companion have been measured from IUE high dispersion spectra. The blue star is itself a member of a close binary system. The triple system solution provides the ratio of the Cepheid mass to the sum of the masses of the companions. IUE low dispersion spectra are used to infer the masses of the companions. A mass of 6.3 M⊙ is derived for the Cepheid, with a range from 7.0 M⊙ to 5.9 M⊙, which is in agreement with the evolutionary mass.

THE ORBIT AND COLORS OF THE CEPHEID S MUSCAE

ABSTRACT A new orbit has been computed for the binary Cepheid S Mus combining new data from Mount John Observatory with previous data. Corrections to the colors and reddening due to the light from the companion are derived. The spectral type determined from IUE low-dispersion spectra is used for these corrections. The corrections are small, even though the companion is one of the hottest (B5 V) known for a Cepheid.