Lyman Series Research Articles

Measurement of Anomalously Strong Emission from the1s−9pTransition in the Spectrum of H-Like Phosphorus Following Charge Exchange with Molecular Hydrogen

We have measured K-shell x-ray spectra of highly ionized argon and phosphorus following charge exchange with molecular hydrogen at low collision energy in an electron beam ion trap using an x-ray calorimeter array with ∼6 eV resolution. We find that the emission at the high end of the Lyman series is greater by a factor of 2 for phosphorus than for argon, even though the measurement was performed concurrently and the atomic numbers are similar. This does not agree with current theoretical models and deviates from the trend observed in previous measurements.

GeV BREAKS IN BLAZARS AS A RESULT OF GAMMA-RAY ABSORPTION WITHIN THE BROAD-LINE REGION

Spectra of the brightest blazars detected by the Fermi Gamma-ray Space Telescope Large Area Telescope cannot be described by a simple power law model. A much better description is obtained with a broken power law, with the break energies of a few GeV. We show here that the sharpness and the position of the breaks can be well reproduced by absorption of gamma-rays via photon--photon pair production on HeII Lyman recombination continuum and lines. This implies that the blazar zone lies inside the region of the highest ionization of the broad-line region (BLR) within a light-year from a super-massive black hole. The observations of gamma-ray spectral breaks open a way of studying the BLR photon field in the extreme-UV/soft X-rays, which are otherwise hidden from our view.

Statistical comparison of the observed and synthetic hydrogen Lyman line profiles in solar prominences

<i>Aims. <i/>We analyse a unique set of prominence SOHO/SUMER Lyman spectra by comparing it with synthetic spectra obtained by 2D multi-thread prominence fine-structure models.<i>Methods. <i/>We employed a novel statistical approach to the analysis of the observed and synthetic Lyman spectra. We compared the statistical distributions of the line properties of the observed and synthetic Lyman spectra using a set of four statistical criteria.<i>Results. <i/>We demonstrate the very good agreement between the observed Lyman spectra and synthetic spectra obtained by modelling.<i>Conclusions. <i/>Our set of statistical criteria is well-suited to analyses of the prominence Lyman spectra because of its sensitivity to a number of different parameters governing the conditions in the prominence fine structures.

Magnetohydrodynamics control of capillary Z-pinch discharge by using a triangular current pulse for lasing a H-like N recombination soft x-ray laser

In expansion cooling phase of pinched nitrogen plasma generated by fast capillary discharge, it might be possible to realize lasing a Blamer α recombination SXRL, which requires a rapid cooling of nonequilibrium plasma. It is effective to decrease the discharge current rapidly in reducing the additional heating caused by the joule heating and the magnetic compression of plasma as quickly as possible. The shaping of discharge current waveform was demonstrated with a transmission line and its effect on expanding plasma dynamics were investigated through magnetohydrodynamics (MHD) calculation, and validity of the MHD calculation in the expansion phase was shown using the discharge photographs taken by using a high speed camera. As a result, strong radiation from the H-like N ion at the maximum pinch, which is in the current decay phase of the triangular current with peak amplitude of over 70 kA and pulse width of 60 ns, has been confirmed in x-ray photodiode signals at wavelength of less than 2.5 nm, to clarify the existence of the Lyman series and continuum of the H-like N ion. Without additional heating by the discharge current after the generation of the fully stripped nitrogen ions, it might be possible to generate the population inversion between the principal quantum number n=2 and 3.

Accurate level energies in the EF1 , GK1 , H1 , B1 , , B′1 , , , J1Δg states of H2

By combining results from a Doppler-free two-photon laser excitation study on several lines in the EF1 − X1 (0,0) band of H2 with results from a Fourier-transform spectroscopic study on a low-pressure discharge in hydrogen, absolute level energies, with respect to the X1 , v = 0, N = 0 ground level, were determined for 547 rovibronically excited states in H2. While for some of the levels in the EF1 and B1 states the uncertainties are as low as 0.0001 cm−1, the accuracy of other levels is lower. The general improvement in the accuracy for the comprehensive data set of level energies is by an order of magnitude with respect to previous measurements. An updated listing of transition wavelengths of the spectral lines in the Lyman and Werner bands is presented, based on combination differences between the presently obtained B1 and level energies and those in the X1 ground state.

PHYSICAL CONDITIONS IN THE ULTRAVIOLET ABSORBERS OF IRAS F22456–5125

We present the ultraviolet (UV) and X-ray spectra observed with the Far Ultraviolet Spectroscopic Explorer (FUSE) and the XMM-Newton satellite, respectively, of the low-z Seyfert 1 galaxy IRAS F22456 – 5125. This object shows absorption from five distinct, narrow kinematic components that span a significant range in velocity (~0 to –700 km s–1) and ionization (Lyman series, C III, N III, and O VI). We also show that three of the five kinematic components in these lines appear to be saturated in Lyβ λ1026 and that all five components show evidence of saturation in the O VI doublet lines λλ1032, 1038. Further, all five components show evidence for partial covering due to the absorption seen in the O VI doublet. This object is peculiar because it shows no evidence for corresponding X-ray absorption to the UV absorption in the X-ray spectrum, which violates the 1:1 correlation known for low-z active galactic nuclei (AGNs). We perform photoionization modeling of the UV absorption lines and predict that the O VII column density should be small, which would produce little to no absorption in agreement with the X-ray observation. We also examine the UV variability of the continuum flux for this object (an increase of a factor of 6). As the absorption components lack variability, we find a lower limit of ~20 kpc for the distance for the absorbers from the central AGN.

Fourier-transform spectroscopy of HD in the vacuum ultraviolet at λ = 87–112 nm

Absorption spectroscopy in the vacuum ultraviolet (VUV) domain was performed on the hydrogen-deuteride molecule with a novel Fourier-transform spectrometer based upon wavefront division interferometry. This unique instrument, which is a permanent endstation of the undulator-based beamline DESIRS on the synchrotron SOLEIL facility, opens the way to Fourier-transform spectroscopy in the VUV range. The HD spectral lines in the Lyman and Werner bands were recorded in the 87–112 nm range from a quasi-static gas sample in a windowless configuration and with a Doppler-limited resolution. Line positions of some 268 transitions in the Lyman bands and 141 transitions in the Werner bands were deduced with uncertainties of 0.04 cm−1 (1σ) which correspond to Δλ/λ ∼ 4 × 10−7. This extensive laboratory database is of relevance for comparison with astronomical observations of H2 and HD spectra from highly redshifted objects, with the goal of extracting a possible variation of the proton-to-electron mass ratio (μ = m p /m e ) on a cosmological time scale. For this reason also calculations of the so-called sensitivity coefficients K i were performed in order to allow for deducing constraints on Δμ/μ. The K i coefficients, associated with the line shift that each spectral line undergoes as a result of a varying value for μ, were derived from calculations as a function of μ solving the Schrödinger equation using ab initio potentials.

BLACK HOLE FORMATION IN PRIMORDIAL GALAXIES: CHEMICAL AND RADIATIVE CONDITIONS

In massive primordial galaxies, the gas may directly collapse and form a single central massive object if cooling is suppressed. Line cooling by molecular hydrogen can be suppressed in the presence of a strong soft-ultraviolet radiation field, but the role played by other cooling mechanisms is less clear. In optically thin gas, Lyman-Alpha cooling can be very effective, maintaining the gas temperature below 10^4 K over many orders of magnitude in density. However, the large neutral hydrogen column densities present in primordial galaxies render them highly optically thick to Lyman-Alpha photons. In this letter, we examine in detail the effects of the trapping of these Lyman-Alpha photons on the thermal and chemical evolution of the gas. We show that despite the high optical depth in the Lyman series lines, cooling is not strongly suppressed, and proceeds via other atomic hydrogen transitions, in particular the 2s-1s and the 3-2 transitions. At densities larger than 10^9 cm^{-3}, collisional dissociation of molecular hydrogen becomes the dominant cooling process and decreases the gas temperature to about 5000 K. The gas temperature evolves with density as $T \propto \rho^{\gamma_{\rm eff} - 1}$, with $\gamma_{\rm eff} = 0.97-0.98$. The evolution is thus very close to isothermal, and so fragmentation is possible, but unlikely to occur during the initial collapse. However, after the formation of a massive central object, we expect that later-infalling, higher angular momentum material will form an accretion disk that may be unstable to fragmentation, which may give rise to star formation with a top-heavy IMF.

The SUMER Ly-α line profile in quiescent prominences

Aims: Out of a novel observing technique, we publish for the first time, SoHO-SUMER observations of the true spectral line profile of hydrogen Lyman-alpha in quiescent prominences. With SoHO not being in Earth orbit, our high-quality data set is free from geocoronal absorption. We study the line profile and compare it with earlier observations of the higher Lyman lines and recent model predictions. Methods: We applied the reduced-aperture observing mode to two prominence targets and started a statistical analysis of the line profiles in both data sets. In particular, we investigated the shape of the profile, the radiance distribution and the line shape-to-radiance interrelation. We also compare Ly-a data to co-temporal 1206 Si III data. Results: We find that the average profile of Ly-a has a blue-peak dominance and is more reversed, if the line-of-sight is perpendicular to the field lines. The contrast of Ly-a prominence emission rasters is very low and the radiance distribution differs from the log-normal distribution of the disk. Features seen in the Si III line are not always co-spatial with Ly-a emission. Conclusions: Our empirical results support recent multi-thread models, which predict that asymmetries and depths of the self-reversal depend on the orientation of the prominence axis relative to the line-of-sight.

New views on the emission and structure of the solar transition region

The Sun is the only star that we can spatially resolve and it can be regarded as a fundamental plasma laboratory of astrophysics. The solar transition region (TR), the layer between the solar chromosphere and corona, plays an important role in solar wind origin and coronal heating. Recent high-resolution observations made by SOHO, TRACE, and Hinode indicate that the TR is highly nonuniform and magnetically structured. Through a combination of spectroscopic observations and magnetic field extrapolations, the TR magnetic structures and plasma properties have been found to be different in coronal holes and in the quiet Sun. In active regions, the TR density and temperature structures also differ in sunspots and the surrounding plage regions. Although the TR is believed to be a dynamic layer, quasi-steady flows lasting from several hours to several days are often present in the quiet Sun, coronal holes, and active regions, indicating some kind of plasma circulation/convection in the TR and corona. The emission of hydrogen Lyman lines, which originates from the lower TR, has also been intensively investigated in the recent past. Observations show clearly that the flows and dynamics in the middle and upper TR can greatly modify the Lyman line profiles.

The impact of Lyman series photons on the intergalactic medium during the Epoch of Reionization

The role of higher order Lyman series photons in the 21 cm absorption or emission signature of the intergalactic medium (IGM) against the background cosmic microwave background (CMB) during the Epoch of Reionization is examined. It is shown that, taking into account the diminishing resonance line scattering cross-section with increasing Lyman order, a non-negligible net scattering rate of higher order Lyman photons is expected. The resulting radiative cascades will substantially enhance the number density of Lyα photons near a radiation source. It is also shown that the higher order Lyman series photons are able to collisionally heat the IGM by amounts of tens to hundreds of degrees kelvin. The possibility that the Wouthuysen-Field effect may be suppressed by the presence of dust near a galaxy is discussed, and it is shown that the higher order Lyman series photons would still induce the effect, but with a somewhat reduced 21 cm radiation efficiency. It is also demonstrated that extended low surface brightness emission-line haloes will be produced from radiative cascades following the scattering of higher order Lyman series photons. These haloes would provide a unique means of confirming that reionization source candidates were surrounded by an IGM that was still largely neutral on large scales.

THE KECK + MAGELLAN SURVEY FOR LYMAN LIMIT ABSORPTION. II. A CASE STUDY ON METALLICITY VARIATIONS

We present an absorption line analysis of the Lyman limit system (LLS) at z=3.55 in our Magellan/MIKE spectrum of PKS2000-330. Our analysis of the Lyman limit and full HI Lyman series constrains the total HI column density of the LLS (N_HI = 10^[18.0 +/- 0.25] cm^{-2} for b_HI >= 20 km/s) and also the N_HI values of the velocity subsystems comprising the absorber. We measure ionic column densities for metal-line transitions associated with the subsystems and use these values to constrain the ionization state (>90% ionized) and relative abundances of the gas. We find an order of magnitude dispersion in the metallicities of the subsystems, marking the first detailed analysis of metallicity variations in an optically thick absorber. The results indicate that metals are not well mixed within the gas surrounding high $z$ galaxies. Assuming a single-phase photoionization model, we also derive an N_H-weighted metallicity, <[Si/H]> = -1.66 +/- 0.25, which matches the mean metallicity in the neutral ISM in high z damped Lya systems (DLAs). Because the line density of LLSs is ~10 times higher than the DLAs, we propose that the former dominate the metal mass-density at z~3 and that these metals reside in the galaxy/IGM interface. Considerations of a multi-phase model do not qualitatively change these conclusions. Finally, we comment on an anomalously large O^0/Si^+ ratio in the LLS that suggests an ionizing radiation field dominated by soft UV sources (e.g. a starburst galaxy). Additional abundance analysis is performed on the super-LLS systems at z=3.19.

DISCOVERY OF STRONG RADIATIVE RECOMBINATION CONTINUA FROM THE SUPERNOVA REMNANT IC 443 WITH SUZAKU

We present the Suzaku spectroscopic study of the Galactic middle-aged supernova remnant (SNR) IC 443. The X-ray spectrum in the 1.75-6.0 keV band is described by an optically-thin thermal plasma with the electron temperature of 0.6 keV and several additional Lyman lines. We robustly detect, for the first time, strong radiative recombination continua (RRC) of H-like Si and S around at 2.7 and 3.5 keV. The ionization temperatures of Si and S determined from the intensity ratios of the RRC to He-like K-alpha line are 1.0 keV and 1.2 keV, respectively. We thus find firm evidence for an extremely-overionized (recombining) plasma. As the origin of the overionization, a thermal conduction scenario argued in previous work is not favored in our new results. We propose that the highly-ionized gas were made at the initial phase of the SNR evolution in dense regions around a massive progenitor, and the low electron temperature is due to a rapid cooling by an adiabatic expansion.

New study of the quasi-molecular Lyman-γ satellites due to H-H+ collisions

Context. Quasi-molecular line satellites in the red wings of Lyman series of atomic hydrogen have been identified in the spectra of hydrogen-rich white dwarfs. These features are produced by radiative collisions. Aims. Structures observed about 995 A in the Lyman-γ wing of hot white dwarfs have been shown to be caused by quasi-molecular absorption of H + molecules. Methods. Improvements to previous theoretical calculations of the Lyman-γ line profiles can be achieved by using a unified theory that takes into account the dependence of the dipole moments on internuclear distance during the collision. Results. For the first time, we have computed the transition dipole moments. We measure a significant increase in the region of the formation of the satellites, which alters the general shape of the profile. Conclusions. A large increase in the strength of the two main satellites at 992 and 996 A leads to a deeper broad absorption in the synthetic spectra, which should improve the comparison with observation as previous predicted Lyman-γ satellites were too weak.

Hydrogenic Lamb shift inGe31+and the fine-structure Lamb shift

Using x-ray diffraction and beam-foil spectroscopy, we have determined precise wavelengths for Lyman ${\ensuremath{\alpha}}_{1}$ and Lyman ${\ensuremath{\alpha}}_{2}$ in hydrogenic germanium of $1.166\phantom{\rule{0.2em}{0ex}}993\phantom{\rule{0.2em}{0ex}}8\ifmmode\pm\else\textpm\fi{}33\ifmmode\pm\else\textpm\fi{}169$ and $1.172\phantom{\rule{0.2em}{0ex}}433\phantom{\rule{0.2em}{0ex}}6\ifmmode\pm\else\textpm\fi{}39\ifmmode\pm\else\textpm\fi{}170\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. Hydrogenic germanium ${\mathrm{Ge}}^{31+}$ $1s\text{\ensuremath{-}}2{p}_{3∕2}$ and $1s\text{\ensuremath{-}}2{p}_{1∕2}$ Lamb shifts are measured to be $66\phantom{\rule{0.2em}{0ex}}080\ifmmode\pm\else\textpm\fi{}237\ifmmode\pm\else\textpm\fi{}1121$ and $67\phantom{\rule{0.2em}{0ex}}169\ifmmode\pm\else\textpm\fi{}281\ifmmode\pm\else\textpm\fi{}1237\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, respectively. This $14\phantom{\rule{0.3em}{0ex}}\mathrm{ppm}$ measurement of the wavelengths thus provides a 1.8% measurement of the $2p\text{\ensuremath{-}}1s$ Lamb shift and is an improvement by a factor of 3 over previous work. Fitting the full two-dimensional dispersion relation, including Balmer and Lyman series, limits random and systematic correlation of parameters. Dominant systematics are due to diffraction parameters including crystal thickness and alignment, differential Doppler shifts due to the variable location of spectral emission downstream of the beam-foil target, and dielectronic, $2s\text{\ensuremath{-}}1s$, and $4f\text{\ensuremath{-}}2p$ satellites. Models developed are applicable to all relativistic plasma modeling in beam-foil spectroscopy at accelerators. The technique also reports the germanium $2{p}_{3∕2}\text{\ensuremath{-}}2{p}_{1∕2}$ fine structure as $397\phantom{\rule{0.2em}{0ex}}617\ifmmode\pm\else\textpm\fi{}251\ifmmode\pm\else\textpm\fi{}512\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, representing a 0.14% measurement of the fine structure and a 71% measurement of the QED contribution to the hydrogenic germanium fine structure, an improvement of a factor of 6 over previous work. We also report a precise measurement of heliumlike resonances and fine structure.

Solar transition region above sunspots

We study the TR properties above sunspots and the surrounding plage regions, by analyzing several sunspot spectra obtained by SUMER in March 1999 and November 2006. We compare the SUMER spectra observed in the umbra, penumbra, plage, and sunspot plume regions. The Lyman line profiles averaged in each region are presented. For the sunspot observed in 2006, the electron densities, DEM, and filling factors of the TR plasma in the four regions are also investigated. The self-reversals of the Lyman line profiles are almost absent in umbral regions at different locations (heliocentric angle up to $49^\circ$) on the solar disk. In the sunspot plume, the Lyman lines are also not reversed, whilst the lower Lyman line profiles observed in the plage region are obviously reversed. The TR densities of the umbra and plume are similar and one order of magnitude lower than those of the plage and penumbra. The DEM curve of the sunspot plume exhibits a peak centered around $\log(T/\rm{K})\sim5.45$, which exceeds the DEM of other regions by one to two orders of magnitude at these temperatures. We also find that more than 100 lines, which are very weak or not observed anywhere else on the Sun, are well observed by SUMER in the sunspot, especially in the sunspot plume. We suggest that the TR above sunspots is higher and probably more extended, and that the opacity of the hydrogen lines is much smaller above sunspots, as compared to the TR above plage regions. Our result indicates that the enhanced TR emission of the sunspot plume is very likely to be the result of a large filling factor. The strongly enhanced emission at TR temperatures and the reduced continuum make many normally weak TR lines stick out clearly in the spectra of sunspot plumes.

Time Ordering Effects on Hydrogen Zeeman-Stark Line Profiles in Low-Density Magnetized Plasmas

Stark broadening of hydrogen lines is investigated in low-density magnetized plasmas, at typical conditions of magnetic fusion experiments. The role of time ordering is assessed numerically, by using a simulation code accounting for the evolution of the microscopic electric field generated by the charged particles moving at the vicinity of the atom. The Zeeman effect due to the magnetic field is also retained. Lyman lines with a low principal quantum number n are first investigated, for an application to opacity calculations; next Balmer lines with successively low and high principal quantum numbers are considered for diagnostic purposes. It is shown that neglecting time ordering results in a dramatic underestimation of the Stark effect on the low-n lines. Another conclusion is that time ordering becomes negligible only when ion dynamics effects vanish, as shown in the case of high-n lines.

Hydrogen Lyman-α and Lyman-β spectral radiance profiles in the quiet Sun

<i>Aims. <i/>We extend earlier work by studying the line profiles of the hydrogen Lyman-<i>α<i/> and Lyman-<i>β<i/> lines in the quiet Sun. They were obtained quasi-simultaneously in a raster scan with a size of about 150″ 120″ near disk center.<i>Methods. <i/>The self-reversal depths of the Ly-<i>α<i/> and Ly-<i>β<i/> profiles. we are quantified by measuring the maximum spectral radiances of the two horns and the minimum spectral radiance of the central reversal. The information on the asymmetries of the Ly-<i>α<i/> and Ly-<i>β<i/> profiles is obtained through calculating the 1st and 3rd-order moments of the line profiles. By comparing maps of self-reversal depths and the moments with radiance images of the Lyman lines, photospheric magnetograms, and Dopplergrams of two other optically thin lines, we studied the spatial distribution of the Ly-<i>α<i/> and Ly-<i>β<i/> profiles with different self-reversal depths, and investigated the relationship between profile asymmetries and flows in the solar atmosphere.<i>Results. <i/>We find that the emissions of the Lyman lines tend to be more strongly absorbed in the internetwork, as compared to those in the network region. Almost all of the Ly-<i>α<i/> profiles are self-reversed, while about 17% of the Ly-<i>β<i/> profiles are not reversed. The ratio of Ly-<i>α<i/> and Ly-<i>β<i/> intensities seems to be independent of the magnetic field strength. Most Ly-<i>α<i/> profiles are stronger in the blue horn, whereas most Ly-<i>β<i/> profiles are stronger in the red horn. However, the opposite asymmetries of Ly-<i>α<i/> and Ly-<i>β<i/> are not correlated pixel-to-pixel. We also confirm that when larger transition-region downflows are present, the Ly-<i>α<i/> and Ly-<i>β<i/> profiles are more enhanced in the blue and red horns, respectively. The first-order moment of Ly-<i>β<i/>, which reflects the combined effects of the profile asymmetry and motion of the emitting material, strongly correlates with the Doppler shifts of the Si iii and O vi lines, while this correlation is much weaker for Ly-<i>α<i/>. Our analysis shows that both Ly-<i>α<i/> and Ly-<i>β<i/> might be more redshifted if stronger transition-region downflows are present. We also find that the observed average Ly-<i>β<i/> profile is redshifted with respect to its rest position.

Lyman-αtransfer in primordial hydrogen recombination

Cosmological constraints from the cosmic microwave background (CMB) anisotropies rely on accurate theoretical calculations of the cosmic recombination history. Recent work has emphasized the importance of radiative transfer calculations due to the high optical depth in the HI Lyman lines. Transfer in the Lyman-alpha line is dominated by true emission and absorption, Hubble expansion, and resonant scattering. Resonant scattering causes photons to diffuse in frequency due to random kicks from the thermal velocities of hydrogen atoms, and also to drift toward lower frequencies due to energy loss via atomic recoil. Past analyses of Lyman-alpha transfer during the recombination era have either considered a subset of these processes, ignored time dependence, or incorrectly assumed identical emission and absorption profiles. We present here a fully time-dependent radiative transfer calculation of the Lyman-alpha line including all of these processes, and compare it to previous results that ignored the resonant scattering. We find a faster recombination due to recoil enhancement of the Lyman-alpha escape rate, leading to a reduction in the free electron density of 0.45% at z=900. This results in an increase in the small-scale CMB power spectrum that is negligible for the current data but will be a 0.9 sigma correction for Planck. We discuss the reasons why we find a smaller correction than some other recent computations.

FUSE observations of intermediate temperature DA: Atmospheric parameters and metal abundances

We present results from our analysis of a sample of DA white dwarfs having effective temperature below 25,000 K observed with the FUSE satellite with the goals of better understanding the origin of metals detected in the atmosphere of these stars. When possible, we combine the FUSE spectra with the IUE spectra and determine atmospheric parameters by fitting the Lyman line profiles. In general we find a good agreement with published values based on fits of the Balmer series. We observe that the continuum in the blue wing of the Lyman α line profile is generally lower in comparison with model spectra and that the discrepancy appears to become less important at higher effective temperature. The agreement between models and observations is excellent at wavelengths shorter than 1100 Å, which gives us confidence in the determination of atmospheric parameters. Finally, using adopted atmospheric parameters; we have performed a detailed analysis of the composition of these stars. In several instances, we have observed the presence of silicon and in one case that of carbon. For each star in the sample we have either measured or set an upper limit on the presence of key species such as CII, CIII, SiIII, and SiIV. We then compare the measured abundances with equilibrium abundance predicted by radiative levitation theory for each star. In this limited sample, we find that when detected, the abundance of silicon is in good agreement with theory. However there are several cases where the upper limits are smaller than the predictions and one case where it is considerably larger.