CIV Line Research Articles

At the end of the rainbow

The flux of ionizing photons, the profiles of Ly α and CIV lines and the soft x-ray emission in radio loud quasars and radio quiet quasars are compared. The similarity of these properties in these quasars suggests that either the opening angle of the obscuring torus in high luminosity AGNs is larger than that in Seyfert galaxies or there is no obscuring torus at high luminosities.

Coordinated SPDE rocket, Yohkoh and ground observations of an emerging flux region and a filament

During the first flight of the Solar Plasma Diagnostic Experiment (SPDE), May 12, 1992, we obtained UV filtergrams at high resolution (full Sun 0.82″ spatial resolution in the 160 nm continuum, the CIV lines and Lyman α) with the Ultraviolet Filtergraph Camera (UVFC). Closely coordinated observations were obtained with the Soft X-ray Telescope (SXT) of the Yohkoh satellite and from dedicated ground programs in particular at Sacramento Peak, La Palma and Pic-du-Midi observatories. With this unique set of data we cover the solar atmosphere as a whole, from the temperature minimum to the high corona with essential steps in the chromosphere and transition region. After the necessary calibrations of the data set, we present the first results of the multitemperature development of an emerging flux region and of a filament that rapidly changed right during the rocket short lifetime.

HST FOS Observations of YY Dra

AbstractThe UV continuum of YY Dra exhibits a sinusoidal modulation with 15.5% semi-amplitude and period 264.7 s, commensurate with one half the white dwarf spin period. The Civ line profile varies with spin phase, implying accretion onto, and visibility of, both magnetic poles. The line width is greatest at the phases of continuum pulsation maximum, when the wings extend out to ±3000 km s−1. This implies a minimum white dwarf mass of 0.62 M⊙, and constrains the angle between the line of sight and the magnetic axis.

Impurity transport modelling and simulation analysis of impurity behavior in JT-60U

A two-dimensional impurity code based on Monte Carlo techniques (IMPMC) has been developed, in order to study the impurity behavior in the divertor plasma. The model includes (1) impurity generation at the divertor plate, (2) ionization of sputtered neutrals, (3) parallel motion of impurity ions along field lines, (4) Coulomb scattering, (5) cross-field diffusion, and (6) atomic processes. This model is applied to the carbon impurity behavior in a JT-60U NB heated plasma. The impurity generation mechanism, the effect of the thermal force on impurity sheilding, and the contribution of charge exchange recombination to C 3+ ion density near the plates are clarified. The measured spatial profile of the CIV line indicates that the diffusion coefficient, D ⊥ is around 1 m 2/s. The ion temperature measured by Doppler broadening of the CIV line is found to be shifted to lower temperature side due to the overspread distribution of C 3+ ions in the SOL by the thermal force.

Multiwavelength study of the WO star Sand 2

We present the results of a multifrequency observation of the WO star Sand 2 in the LMC. Two ROSAT PSPC observations, with exposure times of 8953 s and 4540 s, are used to investigate possible X-ray emission from Sand 2. The optical spectrum observed with the ESO 2.2m telescope close to the time of the ROSAT observations, shows strong emission lines of HeII, CIV, OV and OVI. All lines have a velocity broadening of 4 200±100 km s−1. The UV spectrum from the IUE archive shows a CIV resonance doublet at 155 nm with a P-Cygni absorption at ∼ −5 000 km s−1, with wings extending to about −8 000 km s−1. A combination of two different BB temperatures (80 000 K and 25 000 K) are required to fit the UV-optical continuum, dereddened by EB-V = 0.25.

IUE monitoring of WR140 (WC7+O4-5)

We present the first results of the IUE monitoring campaign of the WC7+O4-5 binary system WR140. Thirty-four high-resolution short-wavelength spectra were obtained in 1979—93, i.e., over more than one orbital period of 7.9 yr. The spectra show variations in the strong resonance lines of CIV and SiIV: large variations occur at the blue edges of the absorption parts of their P-Cygni profiles just after periastron passage. The observed profile changes are discussed in terms of a velocity variation at periastron passage and/or turbulence in the sightline to the O4—5 star at this time.

UV spectral classification and stellar winds in a sample of Be and standard stars

Equivalent widths of 16 lines of CI, CII, CIII, CIV, SiII, SiIII, SiIV, AlII, AlIII, FeII, and FeIII, plus centroid and edge velocities of the SiIV and CIV lines, were measured in IUE spectra of 39 Ble–B8e and 18 B1–B8 standard stars. These suggest the following: 1.Certain line ratios of Sill/III, CII/III, A1II/III, and Fell/Ill are very sensitive to spectral type and represent excellent UV criteria for spectral classification.2.UV line strengths and line ratios show that there are no significant differences between the photospheric line spectra of Be and normal, nonemission stars of corresponding type.3.Despite the fact that the SilV and CIV wind lines are variable in the Be stars, certain conclusions can be drawn from a statistical “snapshot” study such as this:a)The SilV and CIV wind lines in the Be stars are correlated with both spectral type and luminosity class in the sense that the hottest stars have the strongest lines, and the giants and subgiants (at least for the B1-B3 stars) have stronger lines than the main-sequence stars, (see Fig. 1 and 2).b)The SilV wind lines persist to spectral type B8 in both the Be stars and the standard stars but are stronger in the Be stars than in the standards for the earlier types (B1-B3). (See Fig. 1)c)The CIV wind lines persist to spectral type B8 in the Be stars but only to B3 in the standard stars. They are stronger in the Be stars than in the standards at all spectral types, (see Fig. 2).d)The equivalent widths of the SilV and CIV wind lines are only very weakly correlated with vsini, if at all, but a threshold in vsini near 150 km s− 1 (as found earlier by Grady et al.) exists below which no large equivalent widths of SilV or CIV may be seen. Assuming that the Be stars are all rapid rotators, such a correlation is essentially a correlation with i and suggests that the winds from Be stars arise preferentially from the equatorial regions. The aforementioned conclusion is supported by a plot of SilV 1394 centroid velocities versus vsini, which shows that stars with large velocity shifts also have large vsini, while those with unshifted lines all have vsini less than about 150 km s− 1. Again, it seems that strong stellar winds are more likely to arise from equatorial than polar regions.e)Additional evidence that the winds are stronger for Be stars of early type comes from the SilV and CIV centroid velocities, which are much larger for the hotter Be stars. The stars with the strongest lines also tend to have the largest velocity shifts, suggesting that winds with more mass are also faster moving.f)The SilV and CIV lines in the standard stars, while they may be asymmetric, never show displaced line centers.g)The edge velocities for both the SilV 1394 and the CIV 1548 Unes increase with earlier spectral type in the Be stars (therefore, stronger winds in the hotter stars), and are considerably higher in the Be stars than in the standard stars, suggesting again that the winds are stronger in the Be stars.h)Shell stars have weaker CIV absorption and smaller edge and centroid velocities than other Be stars, suggesting that they have weaker winds. Since there is considerable evidence that these are stars with cool, low-velocity disks which axe being viewed edge-on or nearly edge-on, the winds may be inhibited and modified by the denser material in the equatorial regions.4.Mg II emission is detected in about half of the program Be stars with long wavelength IUE spectra, and seems not to be correlated with spectral type, vsini, or strength of the SilV wind lines. Since the Mgll emission presumably originates in the cool, low velocity envelope and since Mgll emission also correlates with hydrogen Balmer emission in the Be stars, this suggests that there is no strong physical relationship between the stellar winds and the cool disk.

Long-term periodic variability in UV absorption lines of the Be star γ Cas: on the relation with V/R variations in the Hβ line

We present a quantitative study of the variability in ultraviolet resonance lines of Nv, Siiv and Civ of the Be star γ Cas, following up on the work of Henrichs et al. (1983). For this purpose we used 133 IUE spectra obtained over a period of eleven years. Variability occurs in the form of discrete absorption components (DACs), which are formed in the fast-outflowing radiatively driven part of the stellar wind. We constructed a template spectrum from spectra containing no or minor extra absorption due to DACs and modelled the isolated DACs in the obtained quotient spectra. Besides the frequently observed narrow components (vt typically ≤ 250 km/s) at high velocity, we found several broad components occurring at low and intermediate wind velocities.We confirm the finding of Doazan et al. (1987) who reported that the number of observed DACs is associated with the cyclic V/R variability of the Balmer-emission lines. This V/R variability most probably originates in the slowly outflowing high-density equatorial disc-like wind of the star (see e.g. Telting et al. 1993 for the case of γ Cas). We show that when V/R≪1 the central optical depth of DACs is significantly lower than when V/R≪1. In our interpretation this is due to a correlation between the column density associated with the DACs and the phase of the V/R cycle.We find that the Hβ observations of Doazan et al. are consistent with a model in which the cyclic V/R variability is due to a global, one-armed oscillation moving through an equatorial disc (Okazaki 1991, Papaloizou et al. 1992, Savonije and Heemskerk 1993). We suggest that the higher column density of DACs in phases of V/R≪1 is the result of the higher density in the region of their origin, namely close to or in the part of the equatorial disc which is rotating towards the observer.

An upper limit on possible time variation of the fine-structure constant from qso absorption spectra

Abstract A statistical analysis of 1185 fine splittings of CIV, NV, OVI, MgII, AlIII and SiIV doublet absorption lines with redshifts z = 0.2–3.7 in QSO spectra is carried out in order to estimate a possible time variation of the fine-structure constant α = e2/hc at cosmological time scales t ∼101° yr. Robust statistical estimates like the “trimmed mean” are used as well as least squares. No statistically significantly time variations of α is found. The estimate α−1 dα/dz = (-1.2 ± 2.9) × 10−4 is obtained. For the 95% confidence level, the upper limit on the rate of a relative variation of the fine-structure constant is |α−1 dα/dz| < 6.4 × 10−4, which approximately corresponds to |α−1dα/dt| < 4 × 10−14 yr−1. This limit reprents the strongest up-to-date restriction on the possible time variation of α for the epoch 0.2 ≤ z ≤ 4.

β Cep: a Magnetic Be Star?

AbstractBesides the well-known pulsation period of 4h34m, the B1 IV star β Cep has a very significant period of 6 or possibly 12 days in the equivalent width of the ultraviolet resonance lines. This was discovered by Fishel and Sparks (1972) with the OAO-2 satellite, and later confirmed with IUE data. Until now, no explanation has been put forward for this period.We propose that the UV periodicity arises from a 12 day rotational period of the star and that the stellar wind is modulated by an oblique dipolar magnetic field at the surface.Support for this hypothesis is given by the striking similarity between the UV-line behavior of β Cep and of known rotating magnetic B stars, for example the B2 V helium-strong star HD 184927 (Barker et al. 1982), and by the measured magnetic field strength of B ± σ = (810 ± 170) G for β Cep itself by Rudy and Kemp (1978). A rotational period of 12 days corresponds well with an adopted radius between 6 and 10 R⊙, given the reported values of 20 - 43 km/s for vsini.To verify our hypothesis we carried out new magnetic field measurements simultaneously with UV spectroscopy. We confirm the 12 day UV period in the equivalent width of the stellar wind lines of CIV, Si III, Si IV and N V (see Figs. 1 and 2), but find a lower and likely variable field strength (Fig. 3), which is consistent with a 12 day period, but not conclusive.It remains puzzling why our new magnetic field measurements show a lower field than in 1978. It is interesting to recall the recent discovery (Mathias et al. 1991) that β Cep has entered a new Be phase (July 1990), when Hα turned into emission (see Fig. 4). This opens the suggestion that the lower magnetic field is related to the emission phase. Because the UV period is still the same, the field must still be strong enough to modulate the wind. A possibly higher equivalent width of the 1991 UV data with respect to the 1979 data might also be related to this transition, but this needs to be confirmed.The star β Cep appears to be the only star in its class which shows this wind variability and in this respect β Cep is an exceptional β Cep star.

Absolute redshifts in the C iv 1548 � line in the transition region of the quiet Sun

Observations with the UVSP instrument on the SMM spacecraft were made at the polar limb and disk center for the accurate determination of Doppler shifts of the Civ 1548 A emission line formed at 105 K in the transition region of the quiet Sun. Individual data points representing 3 arc sec square pixels yield both redshifts and blueshifts, but the mean values from four different days of observations are toward the red. The mean redshifts are in the range 4–8 km s-1 and are produced by nearly vertically directed flows; the uncertainty associated with the mean values correspond to ±0.5 km s-1. The redshift increases with brightness of the Civ line.

The relation between cerenkov redshift of H-I lines of quasars and the intensity ratio lyman-alpha / CIV

In the framework of the Cerenkov line enission theory we discuss the intrinsic relation between the Cerenkov redshift of HI emission lines of quasars and the line intensity ratio I(Lyα) I(Hβ) . Neglecting the contributions of HI recombination lines in the outer optically thin zones of quasars we can use the observed relative shift of the Lyα line with respect to the CIV line, i.e., the Cerenkov redshift, to obtain an estimate of the particle population at the 2nd energy level, R 2≈ 0.02. We can also use the observed 〈 I(Hα) I(Hβ) 〉 value to estimate the parameter Xβ ≈ 14.0. For a temperature of ∼11000 K, the predicted Cerenkov redshifts of HI Balmer lines and the intensity ratio I(Lyα) I(Hβ) are then both in good agreement with the observations. This is a strong support for the Cerenkov line emission theory.

Theoretical study of electron-beam-heated carbon plasma C+++ emission

The response of an electron beam heated carbon plasma is studied with particular attention given to Civ(C+++) line emission at 2530 Å which has shown promise in plasma lasing schemes. A theoretical model which follows the plasma’s hydrodynamics, ionization dynamics, and beam-plasma interactions is used to identify two distinct plasma responses which depend upon the heating rate. The response’s difference is caused by variation of radiated power with plasma temperature and density. The model’s predictions qualitatively agree with experimental observations at the University of Michigan.

Non-LTE Spectral Analysis of PG 1159–035

We present first preliminary results from an exploratory spectral analysis of PG1159-035. An effective temperature of 120000 K (±20000 K) and a surface gravity of about log g=7 are derived from optical and ultraviolet profiles of carbon and helium lines. NLTE model atmospheres are used which are composed of H (1%), He (19%), C (40%) and O (40%, mass fractions). The abundances adopted are in accordance with predictions of stellar pulsation theory. A direct spectroscopic determination is under way. The analysis of optical CIV lines is rendered difficult due to the lack of a reliable line broadening theory which would have to account for a gradual change to broadening by linear Stark effect. Due to the complexity of the spectral analysis, reliable abundance ratios can only be derived from a systematic investigation employing a large grid of models.

Optical observations of jets in the Seyfert nucleus NGC 4151

18 spectra of the Seyfert nucleus NGC 4151 in the 4050–5000 Å spectral range from March 3 to April 11, 1986 and several high resolution spectra (3800–4900 Å) of March–May, 1987 are inferred from 6 -m telescope observations. When observed, the object was at a low -brightness level and did not exhibit photometric variability. The analysis of radial velocities of low-intensity features of the spectrum suggests that they should partly be the narrow satellites of Hp, H 8, H δ, H σ, and probably He II 4686 Å lines. The radial velocities of the satelites (−7500 km/s and 9400 km/s) are close, but not equal, to the velocities found by [10] for CIV 1550 Å. If the satellites are produced in jets, then the CIV lines are generated nearer to the nucleus center than the hydrogen lines and the nucleus mass is 10 8–10 9 M.

IUE and optical spectrophotometry of the HZ Herculis/Hercules X-1 system

Photometric (B-filter) data of HZ Herculis obtained between 1972 and 1974 have been fitted by a model consisting of Roche-lobe-filling star transferring material to a neutron star via a tilted, preccessing, accretion disc. The disc inclination was found to be small, thus avoiding theoretical difficulties experienced with high-inclination discs. We compared a second set of B-fliter data obtained between 1980 and 1983 with the model predictions and found that the system's observed luminosity was lower during the period 1980–1983 than predicted. This is interpreted as a result of a reduction in the flux of X-rays incident upon the heated hemisphere of HZ Herculis; this conclusion seems confirmed by periodogram analysis of the two datasets. The 71 IUE low resolution spectra available have been uniformly extracted and examined. In addition to the expected orbital and X-ray cycle effects, we have observed short episodes when the CIV (λ1550) line is unusually strong.

Ultraviolet Observations of CX Draconis

CX Draconis /HD 174237, B2.5Ve, v.sin i = 160 km.s-1/ is a typical Be star displaying most of the well known spectroscopic and photometric characteristics of these stars.Koubský /1978/ disclosed that CX Dra is a SB1 /P=6.69603d, K = 35 km.s-1, e = 0/. Penrod /1985/ confirmed that the secondary is a F star. Peters and Polidan /1984/ reported strong, variable lines of NV, CIV and SilV from high-resolution spectra secured with IUE satellite. These features were interpreted to arise from gas stream and accretion close to the photosphere of the B-component of the system.

IUE Spectra of the Be Star HD 174237

AbstractHigh-resolution spectra of the Be star HD 174237 taken on September 9, 1980 will be presented. They show stellar absorption lines and superionized NV lines shifted redward equivalent to a velocity of 20 km s-1. This velocity when compared to the earlier measured velocity of - 20 km s-1 (cf. Hoffleit) suggests that the Be star HD 174237 is really a binary and the IUE and previous observations are in different phases of binary motion. The spectra also show strong A1III and SilV absorption lines together with strong NV lines but surprisingly the CIV lines are very weak. It appears that the A1III doublet is associated with a narrow blue-shifted component suggesting an outflow of cool gas from the star.

Discrete subresolution structures in the solar transition zone

During operations on the Spacelab-2 Shuttle mission, the NRL High Resolution Telescope and Spectrograph (HRTS) recorded spectra of a variety of solar features in the 1200–1700 A wavelength region which contains spectral lines and continua well suited for investigating the temperature minimum, the chromosphere and transition zone. These data show that, at the highest spatial resolution, the transition zone spectra are broken up from a continuous intensity distribution along the slit into discrete emission elements. The average dimensions of these discrete transition zone structures is 2400 km along the slit, but an analysis of their emission measures and densities shows that the dimensions of the actual emitting volume is conciderably less. If these structures are modelled as an ensemble of subresolution filaments, we find that these filaments have typical radii of from 3 to 30 km and that the cross-sectional fill factor is in the range from 10−5 to 10−2. The transport of mass and energy through these transition zone structures is reduced by this same factor of 10−5 to 10−2 which has significant consequences for our understanding of the dynamics of the solar atmosphere. Because the HRTS transition zone line profiles are not broadened by resolved large-spatial-scale solar velocity fields, the line widths of the Civ lines have been analyzed. The average line width is 0.195 A (FWHM) and requires an average nonthermal velocity of 16 km s−1 (most-probable) or 19 km s−1 (root-mean-square) which is lower than previously observed values.

Photospheric and “Chromospheric” CIV Lines in B-Main-Sequence Stars

The presence in the far-UV spectra of early-type stars of spectral lines of superionized atoms is argument of controversial debate among astronomers. Presently there is agreement on the non-radiative origin of these ions but not on the proposed mechanisms for their production nor on the proposed locations in the stellar atmosphere where they are abundant. Cassinelli et al. (1978) suggest that the Auger mechanism is operative in a cool wind blowing above a narrow corona to produce these ions; Lucy and White (1980) introduce radiative instabilities growing into hot blobs distributed across the stellar wind; Doazan and Thomas (1982) make these ions to be formed in both pre- and post-coronal, high temperature regions at low and high velocity respectively.