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It is shown that the result of calculation of the probability of single-photon emission by a two-dimensional hydrogen-like atom can depend on the choice of the spin operator. Specifically, if it is chosen to be the projection operator of the spin onto the plane of motion, then the result, as expected, agrees with the classical theory of emission of a three-dimensional atom, as was demonstrated by the author in one of his previous works. If, however, it is chosen as the projection operator onto the perpendicular to the plane of motion, the result does not agree with the classical theory. This puts in doubt the results presented in [S. H. Guo, X. L. Yang, F. T. Chan, Phys. Rev. A, 43, No. 3, 1197 (1991)].

The fluxes in the spectral lines of the Lyman series and their variations in solar cycles 23 and 24 are analyzed. They are shown to vary differently with different solar activity throughout the 11-year cycle: the flux in line Lα (λ = 121.6 nm) decreases by about 40% of its magnitude at the activity maximum, and the greatest decrease (by 60–70%) is observed for the flux in line Lβ (λ = 102.57 nm). It is shown for cycle 23 (TIMED observations) that both the fluxes and the half-widths of the spectral line profiles change noticeably depending on the cycle phase, with an increase towards the cycle maximum. Comparative analysis shows that variations in the average annual intensities of the Lyman lines and the radiation flux at a wavelength of 10.7 cm (F10.7) differ for cycles 23 and 24. This fact is attributable to the specificity of cycle 24 and its secondary maximum, which exceeds its primary maximum. Regression dependences are presented for the fluxes in the Lyman lines (based on the daily SDO/EVE measurements) on F10.7, which allow high-accuracy reconstruction of the magnitudes of these fluxes for different levels of solar activity.

The vacuum ultraviolet (VUV) spectroscopy system on the Joint Texas Experimental Tokamak has been upgraded to achieve fast acquisition for the study of impurity transport in transient modulated experiments. In this upgrade, the previous high-energy charge-coupled device detector was replaced by a microchannel plate with a CsI-coated photocathode and P43 phosphor to transform the VUV light to visible light, which is then acquired by a high-speed electron-multiplying charge-coupled device. Two-stage focusing was achieved using a reference slit plate illuminated successively by a green light source and the Lyman series hydrogen spectral lines from the vacuum-conditioning plasma. The spatial resolution was evaluated as ∼4 mm based on the level of image blurring from the alignment plate. A response time of ∼2 ms was obtained with the ten-vertical-track setup.

Data from satellite observations of fluxes in Lyman series lines and their relative variations, both during the 24-th cycle and in individual class M and X flares, are analyzed. The decrement D1 (D1 = F(Lα)/F(Lβ)) has varied over the 24-th activity cycle by roughly 25% from its maximum values to minimum values during 2014, when there was a secondary maximum in the 24-th cycle according to the main indices. Decrement D2 (D2 = F(Lγ)/F(Lβ)) varies by roughly 10% during the cycle, and decrement D3 (D3 = F(Lδ)/F(Lβ)), by roughly 5% during the cycle. D1, D2, and D3 also vary during the cycle at smaller amplitudes with periods analogous to the periods of the quasi-biennial variations of the main activity indices. In flares of x-ray classes from M to X the variations of the Lyman decrements range from 2 to 20%, with the variations in the decrements being larger on the average for flares with higher energies in the soft x-ray range.

In this work we provide experimental insights into the impact of plasma–molecule interactions on the target ion flux decrease during divertor detachment achieved through a core density ramp in the TCV tokamak. Our improved analysis of the hydrogen Balmer series shows that plasma–molecule processes are strongly contributing to the Balmer series intensities and substantially alter the divertor detachment particle balance. We find that Molecular Activated Recombination (MAR) ion sinks from H 2 + (and possibly H − ) are a factor ∼ 5 larger than Electron–Ion Recombination (EIR) and are a significant contributor to the observed reduction in the outer divertor ion target flux. Molecular Activated Ionisation (MAI) appears to be substantial during the detachment onset, but further research is required into its magnitude given its uncertainty. Plasma–molecule interactions enhance the Balmer line series emission strongly near the target as detachment proceeds. This indicates enhancements of the Lyman series, potentially affecting power balance in the divertor. As those enhancements vary spatially in the divertor and are different for different transitions, they are expected to result in a separation of the L y β and L y α emission regions. This may have implications for the treatment and diagnosis of divertor opacity. The demonstrated enhancement of the Balmer series through plasma–molecule processes potentially poses a challenge to using the Balmer series for understanding and diagnosing detachment based only on atom–plasma processes.

We have obtained new observations of the absorption system at $z_\mathrm{abs}=0.48$ toward QSO Q0454-220, which we use to constrain its chemical and physical conditions. The system features metal-enriched gas and previously unknown low-metallicity gas detected $\sim 200 \, \mathrm{km \, s^{-1}}$ blueward of the metal-enriched gas. The low-metallicity gas is detected in multiple Lyman series lines but is not detected in any metal lines. Our analysis includes low-ionization (e.g., Fe II, Mg II) metal lines, high-ionization (e.g., C IV, O VI, N V) metal lines, and several Lyman series lines. We use new UV spectra taken with HST/COS along with data taken from HST/STIS, Keck/HIRES, and VLT/UVES. We find that the absorption system can be explained with a photoionized low-ionization phase with $\mathrm{[Fe/H]} \sim -0.5$ and $n_\mathrm{H} \sim 10^{-2.3} \, \mathrm{cm}^{-3}$, a photoionized high-ionization phase with a conservative lower limit of $-3.3 < \mathrm{[Fe/H]}$ and $n_\mathrm{H} \sim 10^{-3.8} \, \mathrm{cm}^{-3}$, and a low-metallicity component with a conservative upper limit of $\mathrm{[Fe/H]} < -2.5$ that may be photoionized or collisionally ionized. We suggest that the low-ionization phase may be due to cold-flow accretion via large-scale filamentary structure or due to recycled accretion while the high-ionization phase is the result of ancient outflowing material from a nearby galaxy. The low-metallicity component may come from pristine accretion. The velocity spread and disparate conditions among the absorption system's components suggest a combination of gas arising near galaxies along with gas arising from intergroup material., 18 pages, 9 figures; updated author affiliation

The CAFE (Census of warm-hot intergalactic medium, Accretion, and Feedback Explorer) and LyRIC (Lyman UV Radiation from Interstellar medium and Circum-galactic medium) have been proposed to the space agencies in China respectively. CAFE was first proposed as a joint scientific CAS-ESA small space mission in 2015. LyRIC was proposed as the independent external payload operating on the Chinese Space Station (CSS) in 2019. Both missions are dedicated to mapping the Lyman UV emissions ( ionized oxygen (OVI) resonance lines at 103.2 and 103.8 nm, and Lyman series) for the diffuse sources either in our Galaxy or the circum-galactic mediums of the nearby galaxies. We present the primary science objectives, mission concepts, the enabling technologies, as well as the current status.

Vacuum ultraviolet (VUV) radiation corresponds to photon energies exceeding 6.2 eV and provides access to atomic and molecular resonant transitions in various plasmas. Determining population densities of electronic levels directly connected to the ground state requires an absolute intensity calibration of the VUV spectrometer. For this purpose, synchrotron radiation from electron storage rings is the typical primary standard source associated with transport effort and operating costs. Alternatively, a complex procedure using several secondary standards and discharges directly at the setup in use can be applied. In this work, an absolute intensity calibration avoiding synchrotron radiation to cover the wavelength range 46–300 nm accessible with two detectors—a photomultiplier tube and a channel electron multiplier—is presented. A combination of different standard sources—two deuterium arc lamps, branching-ratios of a nitrogen plasma and a high current hollow cathode—is applied for the relative calibration. The absolute calibration is based on simultaneous measurements of atomic lines in a low pressure helium discharge with the VUV spectrometer and an absolutely calibrated optical emission spectrometer. Special focus is laid on the uncertainties of the relative and absolute calibration depending on the wavelength range. The applicability of the intensity calibration is demonstrated at a hydrogen plasma in the wavelength range 80–300 nm. Using the emissivity of the Lyman series, population densities of the first six excited atomic states are calculated considering opacity effects. The excellent agreement with results from the Balmer series by optical emission spectroscopy manifests the high validity of the performed absolute intensity calibration.

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Identifying the mechanisms driving the escape of Lyman Continuum (LyC) photons is crucial to find Lyman Continuum Emitter (LCE) candidates. To understand the physical properties involved in the leakage of LyC photons, we investigate the connection between the HI covering fraction, HI velocity width, the Lyman alpha (LyA) properties and escape of LyC photons in a sample of 22 star-forming galaxies including 13 LCEs. We fit the stellar continua, dust attenuation, and absorption lines between 920 and 1300 A to extract the HI covering fractions and dust attenuation. Additionally, we measure the HI velocity widths of the optically thick Lyman series and derive the LyA equivalent widths (EW), escape fractions (fesc), peak velocities and fluxes at the minimum of the LyA profiles. Overall, we highlight strong correlations between the presence of low HI covering fractions and (1) low LyA peak velocities; (2) more flux at the profile minimum; and (3) larger EW(LyA), fesc(LyA), and fesc(LyC). Hence, low column density channels are crucial ISM ingredients for the leakage of LyC and LyA photons. Additionally, galaxies with narrower HI absorption velocity widths have higher LyA equivalent widths, larger LyA escape fractions, and lower LyA peak velocity separations. This suggests that these galaxies have low HI column density. Finally, we find that dust regulates the amount of LyA and LyC radiation that actually escapes the ISM. Overall, the ISM porosity is one origin of strong LyA emission and enables the escape of ionizing photons in low-z leakers. However, this is not enough to explain the largest fesc(LyC) observed, which indicates that the most extreme LCEs are likely density-bounded along all lines of sight to the observer. Overall, the neutral gas porosity constrains a lower limit to the escape fraction of LyC and LyA photons, providing a key estimator of the leakage of ionizing photons., Comment: Accepted for publication in A&A. 28 pages, 23 figures, 7 tables

The widths of the spectral emission lines of a hydrogen-like atom in a superstrong magnetic field B >> (Zα)2 B 0, B 0 = m e 2 / e ≈ 4.41·1013 G, have been calculated. Specifically, the width of the α-line of the Lyman series is roughly 2 times smaller than in the absence of a magnetic field. Along with linear polarization of radiation, this makes it possible to determine the magnitude of the magnetic field of magnetars within the limits of the inequality B >> (Zα)2 B 0 from an analysis of the hydrogen emission spectrum. The general expression, so obtained, for the spectral width for an n → n′ transition with emission of a photon allows one in principle to calculate the width of any line of the emission spectrum of hydrogen in such a field with expansion of the possibilities of experimental identification of the latter.

We review studies of the intergalactic medium (IGM) via HI absorption with emphasis on the decades of previous research with quasar absorption line studies. The chapter begins with a historical perspective and then offers a pedagogical description of the quantum mechanics underlying the Lyman series and Lyman continuum opacity of the HI atom. We describe the manifestation of these opacities in absorption spectroscopy and the challenges related to normalization of quasar emission. Standard measurement techniques (equivalent width, line-profile fitting) are introduced. We then introduce the \(N_\mathrm{HI}\) frequency distribution \(f(N_\mathrm{HI})\) and efforts to constrain this distribution across cosmic time with emphasis on the optically thin Ly\(\alpha \) forest. A discussion of optically thick gas (Lyman limit systems and damped Ly\(\alpha \) systems) and its relation to the mean free path is presented. Online presentations and Python notebooks supplement this chapter with examples, a review of modern work, and thoughts on future progress. See https://github.com/profxj/SaasFee2016 for additional resources.

The first non-vanishing term in the perturbation expansion of the electron contribution to the line width, commonly used in spectral line broadening by plasmas, was previously expressed in terms of the thermally averaged bremsstrahlung Gaunt factor. The approximations in the derivation, however, suggest that the result is uncertain. The electron width formula is tested with the hydrogen Balmer series and found suspect. Calculations for the He II Lyman series also display similar difficulties. The limitation of this electron width formulation is traced to the absence of an explicit strong collision cutoff beyond which the second-order theory is invalid.

We present a systematic investigation of the circumgalactic medium (CGM) within projected distances d1e11 M_sun. Combining far-ultraviolet Cosmic Origin Spectrograph spectra from the Hubble Space Telescope and optical echelle spectra from the ground enables a detailed ionization analysis based on resolved component structures of a suite of absorption transitions, including the full HI Lyman series and various ionic metal transitions. By comparing the relative abundances of different ions in individually-matched components, we show that cool gas (T~1e4 K) density and metallicity can vary by more than a factor of ten in in an LRG halo. Specifically, metal-poor absorbing components with, Accepted for publication in MNRAS after a minor revision. 23 pages, 14 figures, and a 29-page Appendix with 27 additional figures

The hydrogen spectrum is one of the most commonly demonstrated and most commonly studied. After the visible spectral lines (Balmer series) are explained by the Rydberg’s formula, it becomes immediately apparent that there will also be similar infrared and ultraviolet series. As you may have taught your students, these are called the Paschen and the Lyman series, respectively. But do they really exist? In this article I explain how these wavelengths were first detected and go further to provide advice on modern means to more simply detect and measure invisible spectral lines. The history of these spectral lines is also presented, which gives a good flavor for the different roles of theoretical physics and applied physics in investigating a given phenomenon.

Lyman spectra and line ratios are reported for soft-x-ray emissions following the charge exchange process in 293, 414, 586, and 1256 km/s ${\mathrm{O}}^{8+}$ and Kr collisions. Lyman series from Ly-$\ensuremath{\alpha}$ to Ly-$\ensuremath{\varepsilon}$ were resolved for the ${\mathrm{O}}^{7+}$ ion using a high-resolution x-ray quantum microcalorimeter detector. It is found that the observed line ratios are dependent on the $nl$ distribution of the captured electron, and the Ly-$\ensuremath{\alpha}$ and Ly-$\ensuremath{\beta}$ x-ray emissions are enhanced. Moreover, by comparing the measured line ratios to the constructed theoretical single charge exchange line ratios for ${\mathrm{O}}^{8+}+\text{H}$, it is suggested that autoionizing double capture plays a significant role in the enhancement of Ly-$\ensuremath{\alpha}$ and Ly-$\ensuremath{\beta}$ emissions for the present system.

We present a 30h integration Very Large Telescope X-shooter spectrum of the Lyman series forest towards the $z = 7.084$ quasar ULAS J1120+0641. The only detected transmission at ${\rm S/N}>5$ is confined to seven narrow spikes in the Ly$\alpha$ forest, over the redshift range $5.858 5.5$. The data nevertheless provide only a weak limit on the volume-weighted hydrogen intergalactic (IGM) neutral fraction at $z\sim 6.5$, $x_{{\rm HI}} > 10^{-4}$, similar to limits at redshift $z\sim6$ from less distant quasars. The new observations cannot extend measurements of the neutral fraction of the IGM to higher values because absorption in the Ly$\alpha$ forest is already saturated near $z\sim6$. For higher neutral fractions, other methods such as measuring the red damping wing of the IGM will be required., Comment: Accepted for publication in A&A. 11 pages, 10 figures

We reveal multiple components of an interacting galaxy system at $z\approx3.35$ through a detailed analysis of the exquisite high-resolution Keck/HIRES spectrum of the afterglow of a gamma-ray burst (GRB). Through Voigt-profile fitting of absorption lines from the Lyman-series, we constrain the neutral hydrogen column density to $N_{\mathrm{HI}} \leq 10^{18.35}$ cm$^{-2}$ for the densest of four distinct systems at the host redshift of GRB~080810, among the lowest $N_{\mathrm{HI}}$ ever observed in a GRB host, despite the line of sight passing within a projected 5 kpc of the galaxy centres. By detailed analysis of the corresponding metal absorption lines, we derive chemical, ionic and kinematic properties of the individual absorbing systems, and thus build a picture of the host as a whole. Striking differences between the systems imply that the line of sight passes through several phases of gas: the star-forming regions of the GRB host; enriched material in the form of a galactic outflow; the hot and ionised halo of a second, interacting galaxy falling towards the host at a line-of-sight velocity of 700 km s$^{-1}$; and a cool, metal-poor cloud which may represent one of the best candidates yet for the inflow of metal-poor gas from the intergalactic medium., Comment: 18 pages, 15 figures. A&A, Accepted. Updated to accepted version

Geocoronal H α and H β intensity measurements using the Wisconsin H α Mapper Fabry-Perot are used to determine the intensity of the H α cascade component. From basic atomic physics and the work of Meier (1995), we show that the total cascade in geocoronal H α emission is 0.52 ± 0.03 times the geocoronal H β intensity, I(H β), for solar Lyman series excitation of geocoronal hydrogen. The results are consistent with the H α cascade measurements of Mierkiewicz et al. (2012), which were determined directly from the analysis of H α line profile measurements, and significantly narrow the range of uncertainty in the cascade measurement. Accounting for cascade is essential in determining exospheric effective temperatures and dynamics from the shape of the geocoronal H α line.

In this work we investigate the cooling channels of diffuse gas (i.e. n_H, 24 pages, 19 figures. Accepted for publication in MNRAS

Gaseous and dust debris disks around white dwarfs (WDs) are formed from tidally disrupted planetary bodies. This offers an opportunity to determine the composition of exoplanetary material by measuring element abundances in the accreting WD's atmosphere. A more direct way to do this is through spectral analysis of the disks themselves. Currently, the number of chemical elements detected through disk emission-lines is smaller than that of species detected through lines in the WD atmospheres. We assess the far-ultraviolet (FUV) spectrum of one well-studied object (SDSS J122859.93+104032.9) to search for disk signatures at wavelengths, 5 pages, 5 figures, accepted for publication in A&A

Dissociative excitation of thymine following electron impact was studied in the energy range up to 430 eV. Emissions in the vacuum ultra-violet spectral region below 150 nm were studied and found to be dominated by the hydrogen Lyman series. Emission cross section data reveal that Lyman-α excitation displays a broad maximum at an electron impact energy of 160 eV. The probability of extracting other excited atoms from the parent molecule is found to be insignificant. Possible excitation and dissociation mechanisms in the parent molecule are discussed.

We report on the detection of Lyman continuum radiation in two nearby starburst galaxies. Tol 0440-381, Tol 1247-232 and Mrk 54 were observed with the Cosmic Origins Spectrograph onboard the Hubble Space Telescopes. The three galaxies have radial velocities of ~13,000 km/s, permitting a ~35 A window on the restframe Lyman continuum shortward of the Milky Way Lyman edge at 912 A. The chosen instrument configuration using the G140L grating covers the spectral range from 912 to 2,000 {\AA}. We developed a dedicated background subtraction method to account for temporal and spatial background variations of the detector, which is crucial at the low flux levels around 912 A. This modified pipeline allowed us to significantly improve the statistical and systematic detector noise and will be made available to the community. We detect Lyman continuum in all three galaxies. However, we conservatively interpret the emission in Tol 0440-381 as an upper limit due to possible contamination by geocoronal Lyman series lines. We determined the current star-formation properties from the far-ultraviolet continuum and spectral lines and used synthesis models to predict the Lyman continuum radiation emitted by the current population of hot stars. We discuss the various model uncertainties such as, among others, atmospheres and evolution models. Lyman continuum escape fractions were derived from a comparison between the observed and predicted Lyman continuum fluxes. Tol 1247-232, Mrk 54 and Tol 0440-381 have absolute escape fractions of (4.5 +/- 1.2)%, (2.5 +/- 0.72)% and, Comment: Accepted by The Astrophysical Journal

The reported observations of an unidentified X-ray line feature at $\sim$3.5 keV have driven a lively discussion about its possible dark matter origin. Motivated by this, we have measured the \emph{K}-shell X-ray spectra of highly ionized bare sulfur ions following charge exchange with gaseous molecules in an electron beam ion trap, as a source of or a contributor to this X-ray line. We produce $\mathrm{S}^{16+}$ and $\mathrm{S}^{15+}$ ions and let them capture electrons in collision with those molecules with the electron beam turned off while recording X-ray spectra. We observed a charge-exchanged-induced X-ray feature at the Lyman series limit (3.47 $\pm$ 0.06 keV). The inferred X-ray energy is in full agreement with the reported astrophysical observations and supports the novel scenario proposed by Gu and Kaastra (A \& A \textbf{584}, {L11} (2015))., 7 pages, 6 figures, accepted for publication in ApJ

By revisiting the Suzaku and XMM-Newton data of the North Polar Spur, we discovered that the spectra are inconsistent with the traditional model consisting of pure thermal emission and neutral absorption. The most prominent discrepancies are the enhanced O VII and Ne IX forbidden-to-resonance ratios, and a high O VIII Ly$\beta$ line relative to other Lyman series. A collisionally ionized absorption model can naturally explain both features, while a charge exchange component can only account for the former. By including the additional ionized absorption, the plasma in the North Polar Spur can be described by a single-phase CIE component with temperature of 0.25 keV, and nitrogen, oxygen, neon, magnesium, and iron abundances of $0.4-0.8$ solar. The abundance pattern of the North Polar Spur is well in line with those of the Galactic halo stars. The high nitrogen-to-oxygen ratio reported in previous studies can be migrated to the large transmission of the O VIII Ly$\alpha$ line. The ionized absorber is characterized by a balance temperature of $0.17-0.20$ keV and a column density of $3-5 \times 10^{19}$ cm$^{-2}$. Based on the derived abundances and absorption, we speculate that the North Polar Spur is a structure in the Galactic halo, so that the emission is mostly absorbed by Galactic ISM in the line of sight., Comment: Accepted for publication in Astronomy and Astrophysics

We use electronic Raman scattering for studying the band structure of the n s boron acceptor states in diamond. For the first time, the spin–orbit splitting of these acceptor states and the 1 s → n s Lyman series of transitions are observed. The spin–orbit splitting linearly increases with n number. Lyman series exhibit fine structure consisting of four bands each. The energy spacing between series is equal to ∼ 13 meV . Evolution of Raman spectra of the boron-doped diamond with increasing boron concentration is shown. Mott transition is revealed in Raman spectrum. Correct values of Luttinger parameters for diamond are specified.

We estimate the He II to H I column density ratio, \eta = N(He II)/N(H I), in the intergalactic medium towards the high redshift (z_{em} = 2.885) bright quasar QSO HE 2347-4342 using Voigt-profile fitting of the H I transitions in the Lyman series and the He II Lyman-$\alpha$ transition as observed by the FUSE satellite. In agreement with previous studies, we find that $\eta > 50$ in most of the Lyman-$\alpha$ forest except in four regions where it is much smaller ($\eta \sim 10-20$) and therefore inconsistent with photo-ionization by the UV background flux. We detect O VI and C IV absorption lines associated with two of these regions ($z_{\rm abs}$ = 2.6346 and 2.6498). We show that if we constrain the fit of the H I and/or He II absorption profiles with the presence of metal components, we can accommodate $\eta$ values in the range 15-100 in these systems assuming broadening is intermediate between pure thermal and pure turbulent. While simple photo-ionization models reproduce the observed N(O VI)/N(C IV) ratio, they fail to produce low $\eta$ values contrary to models with high temperature (i.e T $\ge 10^5$ K). The Doppler parameters measured for different species suggest a multiphase nature of the absorbing regions. Therefore, if low $\eta$ values were to be confirmed, we would favor a multi-phase model in which most of the gas is at high temperature ($>$ 10$^5$ K) but the metals and in particular C IV are due to lower temperature ($\sim$ few $10^4$ K) photo-ionized gas.

The fraction of ionizing photons that escape high-redshift galaxies sensitively determines whether galaxies reionized the early universe. However, this escape fraction cannot be measured from high-redshift galaxies because the opacity of the intergalactic medium is large at high redshifts. Without methods to indirectly measure the escape fraction of high-redshift galaxies, it is unlikely that we will know what reionized the universe. Here, we analyze the far-ultraviolet (UV) H I (Lyman series) and low-ionization metal absorption lines of nine low-redshift, confirmed Lyman continuum emitting galaxies. We use the H I covering fractions, column densities, and dust attenuations measured in a companion paper to predict the escape fraction of ionizing photons. We find good agreement between the predicted and observed Lyman continuum escape fractions (within $1.4\sigma$) using both the H I and ISM absorption lines. The ionizing photons escape through holes in the H I, but we show that dust attenuation reduces the fraction of photons that escape galaxies. This means that the average high-redshift galaxy likely emits more ionizing photons than low-redshift galaxies. Two other indirect methods accurately predict the escape fractions: the Ly$\alpha$ escape fraction and the optical [O III]/[O II] flux ratio. We use these indirect methods to predict the escape fraction of a sample of 21 galaxies with rest-frame UV spectra but without Lyman continuum observations. Many of these galaxies have low escape fractions ($f_{\rm esc} \le 1$\%), but 11 have escape fractions $>1$\%. The methods presented here will measure the escape fractions of high-redshift galaxies, enabling future telescopes to determine whether star-forming galaxies reionized the early universe., Comment: Accepted for publication in A&A. 12 pages, 5 figures

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.

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., Comment: 5 pages, 3 figures, accepted at ApJL

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 hydrogen and helium lines are the most prominent lines in the solar prominences spectra. Observations with the SUMER spectrometer onboard SOHO showed that there are weak lines in the blue wings of the Lyman series which affect their profiles. They were all identified as He ii lines in the Lyman series wings, except for the Lα line whose profile was affected by the use of an attenuator. The He ii lines are the even Balmer lines of the He ii system, a set of lines that we complete with the odd ones. We characterize them by comparison with the blue wings of the Lyman series in order to improve the H Lyman series observations and modeling, on one hand and to provide He ii lines observations for further combined H – He i – He ii modeling, on the other hand.

The first, self-consistent calculations of the cosmological H_2 dissociating UV background produced during the epoch of reionization (EOR) by the sources of reionization are presented. Large-scale radiative transfer simulations of reionization trace the impact of all the ionizing starlight on the IGM from all the sources in our simulation volume down to dwarf galaxies of mass ~ 10^8 solar mass, identified by very high-resolution N-body simulations, including the self-regulating effect of IGM photoheating on dwarf galaxy formation. The UV continuum emitted below 13.6 eV by each source is then transferred through the same IGM, attenuated by atomic H Lyman series resonance lines, to predict the evolution of the inhomogeneous background in the Lyman-Werner band of H_2 between 11 and 13.6 eV., Comment: First Stars III Conference Proceedings; This is a summarized version of the journal paper to be submitted soon

A review is given of measurements involving the K-shell (np → 1s) transitions of hydrogenlike ions. In many experiments carried out, for example, on electron-beam ion traps and tokamaks, the calculated energies of the Lyman-series lines are utilized as calibration standards for measuring the energies of lines from more complex ions. Examples given include measurements of the transition energies of L-shell lines in neonlike ions. The Lyman lines of low-Z ions are also used as a bootstrap for measuring the contributions of quantum electrodynamics (QED) in very high-Z ions, such as U81+ and U89+. The lowest energy member of the Lyman series, Lyman-α, is commonly the target of absolute-energy measurements so as to test the reliability of the calculations of atomic structure in general and of the 1s QED terms in particular. A review of 42 measurements of 1s QED measurements indicates an apparent bias toward wanting to agree with calculations.PACS Nos.: 32.30.Rj, 31.30.Jv, 12.20.–m

Energies and probabilities of Lyman transitions of high rovibrationally excited H 2 , HD and D 2 molecules have been measured and compared with calculations. The experimental results are obtained from laser-induced fluorescence spectra that have been recorded in the spectral range from 60 500 to 83 500 cm −1 , covering 2/3 of the hydrogen Lyman band system. The necessary vacuum-UV radiation is produced by stimulated anti-Stokes Raman scattering, providing a widely tunable radiation source with narrow spectral bandwidth to resolve single Lyman transitions. The highest internal energies of detected hydrogen isotopologues are close to the dissociation limit. This extends the available data base of Lyman transitions from and to higher rotational states ( J > 10) of HD and D 2 .

Context. An accurate determination of the line broadening of the Lyman series of atomic hydrogen has been shown to be fundamental to interpretating UV and FUV spectra of DA white dwarfs. Quasi-molecular lines have been detected in the red wing of Lyman-α, Lyman-β, and Lyman-γ. They arise from radiative collisions of excited atomic hydrogen with unexcited neutral hydrogen atoms or protons. Aims. The aim of this paper is twofold. First, we examine the range of validity of the one-perturber approximation widely used to calculate the line wing. Second, we study the relative contributions of the two main transitions contributing to the far wing of the Lyman-α line profile according to the effective temperature and perturber density. Methods. In cool white dwarfs, the perturber density is so high that the one-perturber approximation breaks down and the collisional effects must be treated by using the autocorrelation formalism in order to take into account simultaneous collisions with more than one perturbing atom. Results. We show that, at the low temperatures of cool white dwarfs, the contribution of the singlet X 1 Σ + → B 1 Σ + transition cannot be neglected in the calculation of Lyman-α profile perturbed by neutral hydrogen. A comparison with experimental laboratory spectra shows that the effects of multiple H-perturbers appear in the far wing. Conclusions. A reliable determination of the line profiles for the physical conditions of cool white dwarfs requires a unified theory that takes account of both the singlet and triplet transitions contributing to Lyman-α using accurate interaction potentials and radiative dipole transition moments. Multiple perturber effects must be considered and the autocorrelation formalism permits calculations for the densities of the atmospheres of cool white dwarfs.