Resonance Doublet Research Articles

CaII line formation in the spectra of irradiated atmospheres

We have studied the effect of external radiation on the formation of LTE and non-LTECaII lines in the spectra of A-M-star atmospheres. Three frequency distributions were chosen for the external radiation: X-ray radiation specified by the power law \(I_v^ + = I_{0^v } ^{ - 0.6} \) at 1–16.5 keV and UV radiation specified by blackbody distributions with the temperatures Trad=50000 and 15000 K. We analyze the influence of variations in the irradiating flux and its angle of incidence on the profiles and equivalent widths of the λλ3933, 3968 A resonance doublet and the λλ8498, 8542, 8662 A infrared triplet. For any type of external radiation, allowing for deviations from LTE decreases the reflection effects for the CaII lines. We conclude that the CaII profiles do not display emission components in the spectra of optically thick stellar atmospheres irradiated by X-rays. Therefore, CaII emission lines observed in the radiation of cataclysmic variables must be formed in an optically thin plasma. CaII emission lines are likely to form in the spectra of stars with UV irradiation if CaII is the dominant ionization state in atmospheric layers close to the depths at which the continuum is formed. As a result, the spectra of symbiotic variables with hot primaries can contain CaII lines originating on the surfaces of the M-giants and supergiant secondaries due to reflection effects. These lines can be used to analyze the reflection effects and the temperature structure in the atmospheres of the secondaries only if non-LTE effects are included. In the spectra of close binaries with cool white dwarfs, CaII emission lines originate in the irradiated atmospheres of the secondaries under conditions close to thermalization. These lines can be used to study the reflection effects and calcium abundances even in an LTE approximation. We calculated the profiles and equivalent widths of CaII lines in the spectra of the four precataclysmic variables BE UMa, EG UMa, MS Peg, and HR Cam. The observed and theoretical reflection effects in the λλ3933, 8542 A emission lines for the specified parameters of the systems and a solar calcium abundance in the atmospheres of the red dwarfs are in good agreement.

Noise spectroscopy of nonlinear magneto-optical resonances in Rb vapor

Nonlinear magneto-optical (NMO) resonances occurring for near-zero magnetic field are studied in Rb vapor using light-noise spectroscopy. With a balanced detection polarimeter, we observe high contrast variations of the noise power (at fixed analysis frequency) carried by diode laser light resonant with the 5S$_{1/2}(F=2) \to 5$P$_{1/2}(F=1) $ transition of $^{87}$Rb and transmitted through a rubidium vapor cell, as a function of magnetic field $B$. A symmetric resonance doublet of anti-correlated noise is observed for orthogonal polarizations around $B=0 $ as a manifestation of ground state coherence. We also observe sideband noise resonances when the magnetic field produces an atomic Larmor precession at a frequency corresponding to one half of the analysis frequency. The resonances on the light fluctuations are the consequence of phase to amplitude noise conversion owing to nonlinear coherence effects in the response of the atomic medium to the fluctuating field. A theoretical model (derived from linearized Bloch equations) is presented that reproduces the main qualitative features of the experimental signals under simple assumptions.

Optical Studies of V4332 Sagittarii: Detection of Unusually Strong K i and Na i Lines in Emission

We present optical observations of the enigmatic nova-like variable V4332 Sgr. The importance of this object should not be understated since it is considered to be the possible prototype of a new class of eruptive variables. These objects have been the subject of considerable studies at present primarily because of the spectacular eruption of V838 Mon—another member of this class—recently in 2002. The cause of the outburst in such objects is not well understood. Our recent work has shown striking changes in the near-IR spectrum of V4332 Sgr since its 1994 outburst. The optical spectrum presented here confirms that V4332 Sgr is indeed an unusual and extremely interesting object. This spectrum, the first to be taken after a hiatus of nearly 10 years after the outburst, shows several lines in emission but is dominated by exceptionally strong emission in the resonance doublet of K I at 7665 and 7699 A and to a slightly lesser strength in the unresolved Na I doublet at 5890 and 5896 A. The K I lines are shown to be optically thick and considerably broadened. We investigate the site of origin of the K I and Na I emission. Considering the strength of the alkali metal lines—seen at similar strength only in L- and T-type dwarfs (although in absorption)—we discuss whether the outburst of V4332 Sgr was an explosion on an L- or T-type dwarf. However, BVRI photometry does not support such a scenario but rather shows the central object of V4332 Sgr to be an M-type star with a temperature of 3250 K.

Lithium Abundances in Fast Rotating Bright Giant Stars

We present the results of high resolution spectroscopic observations of Li I resonance doublet at λ 6707.8 Å for fast rotating single stars of luminosity class II and Ib. We present a discussion on the link between rotation and Li content in intermediate mass giant stars, with emphasis on their evolutionary status. At least one of the observed stars, HD 232862, a G8II with an unusual vsini of 20 km/s, present a Li-rich behavior.

A Revised Ephemeris andFUSEObservations of the Supersoft X-Ray Source CAL 83

A new ephemeris has been determined for the supersoft X-ray binary CAL 83 using MACHO photometry. With an improved orbital period of 1.047568 days, it is now possible to phase together photometric and spectroscopic data obtained over the past two decades with new far ultraviolet spectra taken with FUSE. We discuss the properties of the orbital and longterm optical light curves as well as the colors of CAL 83. In the far ultraviolet the only well-detected stellar feature is emission from the O VI resonance doublet. The radial velocity of this emission appears to differ from that of HeII in the optical region, although we only have partial phase coverage for the O VI line. The FUSE continuum variations are similar to the optical light curve in phase and amplitude.

Effects of averaging of spin packets of interacting resonances in Gd3+ EPR spectra of scheelites

The EPR spectra of Gd3+ tetragonal centers in crystals with a scheelite structure are analyzed. It is found that the EPR spectra exhibit additional signals in the vicinity of coincidence of the resonance lines attributed to Gd3+ EPR transitions. It is shown that these signals are caused by averaging (due to relaxation spin-lattice transitions between the resonance doublets) of the internal part of the quasi-symmetric system of spin packets corresponding to the inhomogeneously broadened initial EPR lines. The quasi-symmetric arrangement of the spin packets is associated with the mosaic structure of the studied crystals.

Far Ultraviolet Spectroscopic ExplorerSpectra of the Black Hole Binary LMC X-3

Far-ultraviolet spectra of LMC X-3 were taken covering photometric phases 0.47?0.74 in the 1.7 day orbital period of the black hole binary (phase zero being superior conjunction of the X-ray source). The continuum is faint and flat but appears to vary significantly during the observations. Concurrent RXTE/ASM observations show the system was in its most luminous X-ray state during the Far Ultraviolet Spectroscopic Explorer (FUSE) observations. The far-UV spectrum contains strong terrestrial airglow emission lines, while the only stellar lines clearly present are emissions from the O VI resonance doublet. Their flux does not change significantly during the FUSE observations. These lines are modeled as two asymmetric profiles, including the local ISM absorptions due to C II and possibly O VI. Velocity variations of O VI emission are consistent with the orbital velocity of the black hole and provide a new constraint on its mass.

Lithium in the symbiotic Mira V407 Cyg

We report an identification of the lithium resonance doublet Li i 6708 A in the spectrum of V407 Cyg, a symbiotic Mira with a pulsation period of about 745 d. The resolution of the spectra used was R=λ/Δλ≈ 18 500 and the measured equivalent width of the line is ∼0.34 A. It is suggested that the lithium enrichment is due to hot bottom burning in the intermediate-mass asymptotic giant branch (AGB) variable, although other possible origins cannot be totally ruled out. In contrast to lithium-rich AGB stars in the Magellanic Clouds, ZrO λλ5551, 6474 absorption bands were not found in the spectrum of V407 Cyg. These are the bands used to classify the S-type stars at low-resolution. Although we identified weak ZrO λλ5718, 6412 these are not visible in the low-resolution spectra, and we therefore classify the Mira in V407 Cyg as an M type. This, together with other published work, suggests lithium enrichment can precede the third dredge up of s-process enriched material in galactic AGB stars.

The spectrum of the roAp star HD 101065 (Przybylski's star) in the Li I 6708 Å spectral region

We carried out a detailed analysis of spectra of the unique roAp star HD 101065 (Przybylski's star) near the resonance doublet Li I 6708 A, using a most complete line list including all possible transitions between REE levels of the NIST database. Our model calculations were performed under two assumptions: a blend of Li and REE lines, and a blend of REE lines only. They prove that Li lines are present in the range 6707.72−6708.02 A and that the resulting Li abundance is 3.1 dex (in the scale log N(H) = 12.0), while the isotopic ratio 6 Li/ 7 Li is near to 0.3.

On the spectroscopic detection of neutral species in a low-pressure plasma containing boron and hydrogen

Spectroscopic studies of microwave discharges in H2–Ar–B2H6 gas mixtures (f = 2.45 GHz, P = 1.2–3.5 kW, p = 1–8 mbar) have been performed to improve the possibilities of diagnostics of non-equilibrium, low-pressure plasmas containing boron and hydrogen. For this purpose, UV–VIS optical emission spectroscopy and infrared absorption spectroscopy with tunable diode lasers (TDLAS) have been applied. It is shown that information about neutral species and the gas temperature may be obtained by means of new and modified spectroscopic methods. A method for the determination of the absolute number density of boron atoms from measured relative intensities of the components of the boron resonance doublet (distorted by reabsorption) is proposed and tested for validity. The maximum of the density was found to be 3.8×1011 atoms cm−3 at an admixture of diborane of about 2%. The gas temperature was determined from the intensity distributions in the rotational structure of the emission bands of BH and H2 and from Doppler broadening of the absorption line profiles of the BH molecule. It was observed that values of the gas temperature obtained from the rotational intensity distributions are in good agreement with those obtained from Doppler widths (Tg = 700–1070 K). Based on measurements of the relative line intensities of atomic and molecular hydrogen and the gas temperature, and using a simple excitation–deactivation model, the density of molecular hydrogen was found to be about 40 times higher than the density of atomic hydrogen. It is shown that some absorption lines of boron hydrides (B2H6, BH3 and BH) detected by TDLAS may be used for plasma diagnostics.

Properties of Solar Plasmas near Solar Maximum above Two Quiet Regions at Distances of 1.02–1.34R⊙

In the present work we have analyzed the spectra emitted by two quiet solar regions observed off the solar disk by the SUMER instrument on board the SOHO satellite. The two complete spectra were recorded when the SOHO north-south axis was rotated relative to the Sun north-south axis by 150° clockwise. As a result, the SUMER slit could be placed so that it is perpendicular to the solar limb in an intermediate orientation between the equator and the poles. The SUMER fields of view consisted of two 1'' wide radial strips of the solar corona from 1.02 to 1.34 R☉. The aim of the present work was to measure the physical properties of the emitting plasma, namely, the electron density and temperature, the plasma emission measure, and the nonthermal mass motions, as a function of the distance from the solar limb. The measurement of the plasma absolute element abundances is deferred to a future paper. In measuring the nonthermal velocities of both source regions, we have discovered a residual instrumental systematic effect to line widths. The plasma in the SUMER field of view is nearly isothermal. The measurements of electron density and temperature allow us to check the hydrostatic assumption commonly adopted in the literature and to find that the plasma is denser than predicted. The wide wavelength range covered by the SUMER instrument includes several Li-like ions, allowing us to investigate the relative contribution of the radiative and collisional excitation mechanisms in the Li-like resonance doublet formation. We confirm the earlier findings that a significant radiative excitation occurs for O VI and Ne VIII resonance lines even at low altitudes.

Characteristic features of the spectrum of the unique roAp star HD 101065 near the 6708 Å lithium resonance doublet

Synthetic spectrum of the peculiar roAp star HD 101065 (Przybylski’s Star) have been computed in the wavelength interval 6705.8–6708.7 A in order to describe the observed spectrum in the vicinity of the 6708 A lithium line. Our detailed computations of the synthetic spectrum allowing for the hyperfine structure of the lithium line, lithium isotopic composition, and blending due to lines of rare-earth elements (CeII, NdII, SmII, and others) have yielded estimates of the atmospheric lithium abundance of the star and its 6Li/7Li isotopic ratio.

A search for OVI in the winds of B-type stars

We have conducted a survey of FUSE spectra of 235 Galactic B-type stars in order to determine the boundaries in the H-R diagram for the production of the superion $\ion{O}{vi}$ in their winds. By comparing the locations and morphology of otherwise unidentified absorption features in the vicinity of the $\ion{O}{vi}$ resonance doublet with the bona fide wind profiles seen in archival IUE spectra of the resonance lines of $\ion{N}{v}$, $\ion{Si}{iv}$ and $\ion{C}{iv}$, we were able to detect blueshifted $\ion{O}{vi}$ lines in the spectra of giant and supergiant stars with temperature classes as late as B1. No features attributable to $\ion{O}{vi}$ were detected in dwarfs later than B0, or in stars of any luminosity class later than B1, although our ability to recognize weak absorption features in these stars is severely restricted by blending with photospheric and interstellar features. We discuss evidence that the ratio of the ion fractions of $\ion{O}{vi}$ and $\ion{N}{v}$ is substantially different in the winds of early B-type stars than O-type stars.

Growth of H(II) centers in natural silica after UV laser exposure

The post-irradiation increase in the amplitude of the electron spin resonance doublet split by 11.8 mT, associated with the H(II) centers (Ge H), was measured in dry and wet natural silica irradiated at room temperature with UV photons at 266 nm from a Nd:YAG laser. The concentration of these paramagnetic defects increases on increasing the delay time after the UV exposure, in a time scale of few hours and its final magnitude depends on the number of laser shots and on the OH content. The generation of H(II) centers is correlated with the bleaching of the 5.1 eV absorption band ascribed to the twofold coordinated Ge (Ge ) so supporting the occurrence of a conversion process between these defects whose kinetics is governed by the diffusion of molecular hydrogen in the silica matrix.

Calculation of profiles of CIV, NV, OVI, and SiIV resonance lines formed in accretion shocks in T Tauri stars: A plane layer

We have calculated profiles of the CIV 1550, NV 1240, OVI 1035, and SiIV 1400 resonance doublets for a plane-parallel shock viewed at various angles. Calculations were performed for the range of preshock gas velocities V0 and gas densities ρ0 appropriate for classical T Tauri stars. The parameters of accretion shocks in young stars can be determined by comparing the calculated and observed profiles of the studied lines and their relative intensities. It is not possible to derive the parameters of the accreting gas from the line profiles without knowing the geometry of the accretion zone. The relation Iν (µ, V0 ,ρ 0) for a plane shock, where Iν is the intensity µ =c osθ, can be used to determine the accretion parameters by either choosing a geometry for the radiating region or using a technique similar to Doppler tomography. The results obtained for DR Tau, T Tau, and RY Tau indicate that, in contrast to current concepts, the inner regions of the accretion disk are not disrupted by the magnetic field of the star, and the disk reaches the stellar surface. As a result, only a small fraction of the accreted matter passes through the shock and falls onto the star. c � 2003 MAIK "Nauka/Interperiodica".

Multiwavelength studies of the Seyfert 1 galaxy NGC 7469 I. Far UV observations with FUSE

We obtained far-ultraviolet spectra of the Seyfert 1 galaxy NGC 7469 using the Far Ultraviolet Spectroscopic Explorer on 1999 December 6. Our spectra cover the wavelength range 990-1187 A with a resolution of0:05 A. We see broad emission lines of Ciii ,N iii ,O vi ,a nd Heii as well as intrinsic absorption lines in the O vi1032; 1038 resonance doublet. The absorption arises in two distinct kinematic components at systemic velocities of 569 km s 1 and 1898 km s 1 . Both components are very highly ionized - no significant Ly absorption is present. The higher blueshift component is not quite saturated, and it has a total O vi column density of 8 10 14 cm 2 . It covers more than 90% of the continuum and broad- line emission. The lower blueshift component is heavily saturated and covers only 50% of the continuum and broad-line emission. It too has a column density of 8 10 14 cm 2 , but this is less certain due to the high saturation. We set an upper limit of<1:5 10 18 cm 2 on the O vi column density of this component. Its line depth is consistent with coverage of only the continuum, and thus this component may lie interior to the broad emission-line gas. The component at 569 km s 1 has a velocity comparable to the high-ionization X-ray absorption lines seen in the XMM-Newtongrating spectrum of NGC 7469, and photoionization models show that the observed column densities of O vi and H i are compatible with their formation in the same gas as that causing the X-ray absorption. The gas at 1898 km s 1 has lower ionization and column density, and no

Excitation of resonance lines of the cadmium ion by monoenergetic electrons

The excitation of resonance lines at 226.5 and 214.4 nm, corresponding to the transitions 226.5 (5p 2 P 1 2/0 →5s 2 S 1/2) and 5p 2 P 3 2/0 → 5s 2 S 1/2, respectively, in the Cd+ ion upon collisions with monoenergetic electrons with an energy in the range of 4–130 eV is studied with high precision by a spectroscopic method in crossing beams. It is found that the dependence of the effective excitation cross sections of the resonance doublet components on the energy of the electrons has a distinct resonance structure. It is shown that the dominant mechanism responsible for this structure is the capture of an incident electron by a Cd+ ion with the simultaneous excitation of an electron from the subvalence 4d 10 shell to the autoionizing states of the Cd atom with their subsequent decay (directly or via cascade transitions) to resonance levels of the ion. The results obtained are compared with data from other experiments and with the results of the R-matrix strong-coupling calculation of 15 states and of semiempirical calculation using the Van Regemorter formula.

Spectroscopic diagnostics of UV power and accretion in T Tauri stars

It is known that in the upper atmospheres of the Sun and some late-type stars there is a systematic relationship between the optically thin total radiated power and the power emitted by single spectral lines. Using recently derived emission-measure distributions from IUE spectra for BP Tau, CV Cha, RY Tau, RU Lupi and GW Ori, we demonstrate that this is also true for classical T Tauri stars (CTTSs). As in the solar case it is found that the C IV resonance doublet at 1548 A is also the most accurate indicator of the total radiated power from the atmospheres of CTTSs. Since the total radiated-power density in CTTSs exceeds that of the Sun by over three orders of magnitude we derive new analytic expressions that can be used to estimate the values for these stars. We also discuss the implications of these results with regard to the influence or absence of accretion in this sample of stars and suggest that the method can be used to infer properties of the geometrical structure of the emission regions. As a demonstration case we also use archived HST-GHRS data to estimate the total radiative losses in the UV emitting region of BP Tau. We find values of 4.57 × 10 9 erg cm - 2 s - 1 and 5.11 x 10 3 2 erg s - 1 dependent on the geometry of the emission region. These results are several orders of magnitude larger than would be expected if the UV emission came primarily from an atmosphere covered in solar-like active regions and are closer to values associated with solar flares. They lead to luminosity estimates of 0.07 and 0.13 L O ., respectively, which are in broad agreement with results obtained from theoretical accretion shock models. Taken together they suggest that accretion may well be the dominant contributor to the UV emission in BP Tau.

Beryllium Abundances in F and G Dwarfs in the Coma Cluster and the Ursa Major Moving Group from Keck HIRES Observations

The study of both light elements Li and Be in open clusters of known properties can reveal the internal structure and the mechanisms of mixing in main-sequence stars as a function of age and composition. In previous work, we have investigated the older Hyades cluster and the younger Pleiades and α Per clusters. The Coma Berenices cluster and the UMa moving group are intermediate in age between the Hyades and Pleiades and provide a good linchpin for the influence of stellar age on light-element abundances; there are dips in the mid-F stars in both Li and Be in the Hyades but no Be dip and only a minor Li dip in the Pleiades. We have made observations of the resonance doublet of Be II near 3130 A in 13 Coma and six UMa stars with the Keck I telescope and the High Resolution Echelle Spectrometer. The Be abundances were determined by spectrum synthesis. In the F dwarfs in Coma, there are both Li and Be deficiencies, indicating that the depletions occur during the main-sequence phase of evolution but do not become evident until an age of 200-300 Myr. For both UMa and Coma stars, the Li depletion is greater than the Be depletion at all temperatures, but there is little, if any, Be depletion in stars with Teff < 6000 K. In the four clusters studied for Be, the mean Be abundance for stars with temperatures less than 6000 K is log N(Be/H) + 12.00 = 1.27, independent of age or metal content. For the hotter stars (5850-6680 K), the Li and Be abundances are correlated, indicating that the depletion probably occurs simultaneously; this matches the results for the field stars and the Hyades and the predictions of Li and Be depletion by rotationally induced mixing.

Origins of the Highly Ionized Gas along the Line of Sight toward HD 116852

We present Hubble Space Telescope Imaging Spectrograph (HST/STIS) and Far Ultraviolet Spectroscopic Explorer (FUSE) observations of high ion interstellar absorption along the sight line to HD 116852. At a distance of 4.8 kpc, HD 116852 is an O9 III star lying in the low Galactic halo, -1.3 kpc from the plane of the Galaxy in the direction l = 304.9, b = -16.1. The STIS E140H grating observations provide high-resolution (FWHM = 2.7 km/s) spectra of the resonance doublets of Si IV, C IV, and N V. These data are complemented by medium-resolution (FWHM = 20 km/s) FUSE spectra of O VI. We find evidence for three distinct types of highly ionized gas present in the data. First, two narrow absorption components are resolved in the Si IV and C IV profiles, at approximate LSR velocities of -36 and -10 km/s. These narrow components appear to be produced in gas associated with the Norma and Sagittarius spiral arms, at approximate z-distances of -1.0 and -0.5 kpc, respectively. Second, we detect an intermediate-width component in C IV and Si IV, at 17 km/s, which we propose could arise at the conductive interface at the boundary between a low column density neutral or weakly ionized cloud and the surrounding hot medium. Finally, a broad collisionally ionized component of gas responsible for producing the smooth N V and O VI profiles is observed; such absorption is also present to a lesser degree in the profiles of Si IV and C IV. The broad O VI absorption is observed at a velocity displaced from the broad C IV component by almost 20 km/s, an amount large enough to suggest that the two ions may not co-exist in the same physical location.