Atomic Absorption Lines Research Articles

Spectro web: oscillator strength measurements of atomic absorption lines in the sun and procyon

We update the online SpectroWeb database of spectral standard reference stars with 1178 oscillator strength values of atomic absorption lines observed in the optical spectrum of the Sun and Procyon (α CMi A). The updated line oscillator strengths are measured with best fits to the disk-integrated KPNO-FTS spectrum of the Sun observed between 4000 Å and 6800 Å using state-of-the-art detailed spectral synthesis calculations. A subset of 660 line oscillator strengths is validated with synthetic spectrum calculations of Procyon observed with ESO-UVES between 4700 Å and 6800 Å. The new log(gf)-values in SpectroWeb are improvements upon the values offered in the online Vienna Atomic Line Database (VALD). We find for neutral iron-group elements, such as Fe I, Ni I, Cr I, and Ti I, a statistically significant over-estimation of the VALD log((gf)-values for weak absorption lines with normalized central line depths below 15 %. For abundant lighter elements (e.g. Mg I and Ca I) this trend is statistically not significantly detectable, with the exception of Si I for which the log(gf)-values of 60 weak and medium-strong lines are substantially decreased to best fit the observed spectra. The newly measured log(gf)-values are available in the SpectroWeb database at http://spectra.freeshell.org, which interactively displays the observed and computed stellar spectra, together with corresponding atomic line data.

Spatial and temporal probing of a laser-induced plasma plume by cavity ringdown spectroscopy

The laser-induced plasma plume of a Ti target in vacuum is probed by the technique of cavity ringdown spectroscopy. A model is developed to perform a forward convolution of atomic absorption line profile measurements. The model accounts for laser-induced plasma characteristics such as anisotropy of the plume and velocity distributions of the ablated particles as well as of the cavity ringdown features such as geometry and time selectivity. The absorption lineshapes of atomic transitions are calculated and discussed for given sets of parameters. Calculated line profiles are fitted to experimental line profiles obtained from nanosecond-laser ablation of the target and provide data about the plume dynamics.

The radio to infrared emission of very high redshift gamma-ray bursts: probing early star formation through molecular and atomic absorption lines

We evaluate the broadband afterglow emission of very high redshift gamma-ray bursts (GRBs) using standard relativistic blastwave models with both forward and reverse shock components. For a broad range of parameters, a generic property for GRBs at redshifts $z \sim$ 5--30 is that the emission peaks in the millimeter to far-infrared bands with milli-Jansky flux levels, first at a few hours after the burst due to the reverse shock, and then again for several days afterwards with somewhat lower flux due to the forward shock. The radio, submillimeter and infrared continuum emission should be readily detectable out to $z \ga 30$ by the Atacama Large Millimeter Array (ALMA), Extended Very Large Array (EVLA), Square Kilometer Array (SKA) and other facilities. For relatively bright bursts, spectroscopic measurements of molecular and atomic absorption lines due to ambient protostellar gas may be possible. Utilizing models of primordial protostellar clouds, we show that under certain conditions, appreciable absorption may be caused by HD rotational transitions even in metal-free environments. After sufficient metal enrichment, absorption from CO rotational transitions and [OI] fine-structure transitions can also become strong. With appropriate observing strategies in combination with optical telescopes, ALMA and/or SKA may be able to detect such lines, offering a unique probe of physical conditions in individual Pop III and early Pop II star forming regions. We also remark on potential near-infrared absorption features due to electronic transitions of H$_2$.

Evolutionary status of the spectral variable BD + 48°1220 = IRAS 05040+4820

Based on high-resolution observations (R = 60 000 and 75 000), we have studied the optical spectral variability of the star BD + 48°1220, identified with the IR source IRAS 05040+4820. We have measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths from 4500 A to 6760 A, as well as the corresponding radial velocities. We use model atmospheres to determine the effective temperature T eff = 7900 K, surface gravity log g = 0.0, microturbulence velocity ξ t = 6.0, and the abundances for 16 elements. The star’s metallicity differs little from the solar value: [Fe/H] = −0.10 dex. The main peculiarity of the chemical composition of the star is a large helium excess, derived from the Hel λ 5876 A absorption, [He/H] = +1.04, and the equally large oxygen excess, [O/Fe] = +0.72 dex. The carbon excess is small, [C/Fe] = +0.09 dex, and the ratio [C/O] < 1. We obtained an altered relation for the light-metal abundances: [Na/Fe] = +0.87 dex with [Mg/Fe] = −0.31 dex. The barium abundance is low, [Ba/Fe] = −0.84 dex. It is concluded that the selective separation of elements onto dust grains of the envelope is probably efficient. The radial velocity of the star measured from photospheric absorption lines over three years of observations varies in the interval V ⊙ = −(7–15) km/s. Time-variable differential line shifts have been revealed. The entire set of available data (the luminosity M v ≈ −5 m , velocity V lsr ≈ −20 km/s, metallicity [Fe/H] = −0.10, and peculiarities of the optical spectrum and chemical composition) confirms the status of BD + 48°1220 as a post-AGB star with He and O excesses belonging to the Galactic disk.

Near‐Infrared Spectra of the Black Hole X‐Ray Binary A0620‐00

We present broadband NIR spectra of A0620-00 obtained with SpeX on the IRTF. The spectrum is characterized by a blue continuum on which are superimposed broad emission lines of HI and HeII and a host of narrower absorption lines of neutral metals and molecules. Spectral type standard star spectra scaled to the dereddened spectrum of A0620-00 in K exceed the A0620-00 spectrum in J and H for all stars of spectral type K7V or earlier, demonstrating that the donor star, unless later than K7V, cannot be the sole NIR flux source in A0620-00. In addition, the atomic absorption lines in the K3V spectrum are too weak with respect to those of A0620-00 even at 100% donor star contribution, restricting the spectral type of the donor star in A0620-00 to later than K3V. Comparison of the A0620-00 spectrum to scaled K star spectra indicates that the CO absorption features are significantly weaker in A0620-00 than in field dwarf stars. Fits of scaled model spectra of a Roche lobe-filling donor star to the spectrum of A0620-00 show that the best match to the CO absorption lines is obtained when the C abundance is reduced to [C/H] = -1.5. The donor star contribution in the H waveband is determined to be 82+-2%. Combined with previous published results from Froning & Robinson (2001) and Marsh et al. (1994), this gives a precise mass for the black hole in A0620-00 of M_BH = 9.7+-0.6 M_solar.

The CH$_\mathsf{2}$CN- molecule: carrier of the $\mathsf{\lambda}$8037 diffuse interstellar band?

The hypothesis that the cyanomethyl anion CH2CN is responsible for the relatively narrow di use interstellar band (DIB) at 8037:8 0:15 A is examined with reference to new observational data. The 0 0 absorption band arising from the 1 B1 ˜ X 1 A 0 transition from the electronic ground state to the first dipole-bound state of the anion is calculated for a rotational temperature of 2.7 K using literature spectroscopic parameters and results in a rotational contour with a peak wavelength of 8037.78 A. By comparison with di use band and atomic line absorption spectra of eight heavily-reddened Galactic sightlines, CH2CN is found to be a plausible carrier of the 8037 di use interstellar band provided the rotational contour is Doppler-broadened with a b parameter between 16 and 33 km s 1 that depends on the specific sightline. Convolution of the calculated CH2CN transitions with the optical depth profile of interstellar Tiii results in a good match with the profile of the narrow 8037 DIB observed towards HD 183143, HD 168112 and Cyg OB2 8a. The rotational level populations may be influenced by nuclear spin statistics, resulting in the appearance of additional transitions from Ka = 1 of ortho CH2CN near 8025 and 8050 A that are not seen in currently available interstellar spectra. For CH2CN to be the carrier of the 8037 di use interstellar band, either a) there must be mechanisms that convert CH2CN from the ortho to the para form, or b) the chemistry that forms CH2CN must result in a population of K 00 levels approaching a Boltzmann distribution near 3 K.

A survey for redshifted molecular and atomic absorption lines - I. The Parkes half-Jansky flat-spectrum red quasar sample

We are currently undertaking a large survey for redshifted atomic and molecular absorption lines at radio frequencies. In this paper, we present the results from the first phase of this survey: the search for Hi 21-cm and OH 18-cm absorption lines in the hosts of reddened quasars and radio galaxies. Although we observed each source for up to several hours with two of the world's most sensitive radio telescopes, the Giant Metrewave Radio Telescope (GMRT) and Westerbork Synthesis Radio Telescope (WSRT), only one clear and one tentative detection were obtained: H I absorption at z = 0.097 in PKS 1555-140 and OH absorption at z = 0.126 in PKS 2300-189, respectively, with the Australia Telescope Compact Array (ATCA). For the latter, no H i absorption was detected at the same redshift as the borderline OH detection. In order to determine why no clear molecular absorption was detected in any of the 13 sources searched, we investigate the properties of the five redshifted systems currently known to exhibit OH absorption. In four of these, molecules were first detected via millimetre-wave transitions, and the flat radio spectra indicate compact background continuum sources, which may suggest a high degree of coverage of the background source by the molecular clouds in the absorber. Furthermore, for these systems we find a relationship between the molecular line strength and red optical-near-infrared (V - K) colours, thus supporting the notion that the reddening of these sources is due to dust, which provides an environment conducive to the formation of molecules. Upon comparison with the V - K colours of our sample, this relationship suggests that, presuming the reddening occurs at the host galaxy redshift at least in some of the targets, many of our observations still fall short of the sensitivity required to detect OH absorption, although a confirmation of the 'detection' of OH in 2300-189 could contravene this.

Detection of spectral variability of the optical component of the IR source IRAS 20508+2011

Our high-resolution spectral observations have revealed variability of the optical spectrum of the cool star identified with the IR source IRAS 20508+2011. We measured the equivalent widths of numerous absorption lines of neutral atoms and ions at wavelengths 4300–7930 A, along with the corresponding radial velocities. Over the four years of our observations, the radial velocity derived from photospheric absorption lines varied in the interval V r⊙ = 15–30 km/s. In the same period, the Hα profile varied from being an intense bell-shaped emission line with a small amount of core absorption to displaying two-peaked emission with a central absorption feature below the continuum level. At all but one epoch, the positions of the metallic photospheric lines were systematically shifted relative to the Hα emission: ΔV r = V r(met) − V r(Hα, emis) ≈ −23 km/s. The Na D doublet displayed a complex profile with broad (half-width ≈ 120 km/s) emission and photospheric absorption, as well as an interstellar component. We used model atmospheres to determine the physical parameters and chemical composition of the star’s atmosphere: T eff = 4800 K, log g = 1.5, ξt = 4.0 km/s. The metallicity of the star differs little from the solar value: [Fe/H]⊙ = −0.36. We detected overabundances of oxygen [O/Fe]⊙ = +1.79 (with the ratio [C/O] ≈ −0.9), and α-process elements, as well as a deficit of heavy metals. The entire set of the star’s parameters suggests that the optical component of IRAS 20508+2011 is an “O-rich” AGB star with luminosity M v ≈ −3m that is close to its evolutionary transition to the post-AGB stage.

Measuring the Magnetic Field of the Classical T Tauri Star TW Hydrae

We present infrared (IR) and optical echelle spectra of the classical T Tauri star TW Hydrae. Using the optical data, we perform detailed spectrum synthesis to fit atomic and molecular absorption lines and determine key stellar parameters: Teff = 4126 ± 24 K, log g = 4.84 ± 0.16, [M/H] = -0.10 ± 0.12, and log g = 5.8 ± 0.6 km s-1. The IR spectrum is used to look for Zeeman broadening of photospheric absorption lines. We fit four Zeeman-sensitive Ti I lines near 2.2 μm and find that the average value of the magnetic field over the entire surface is B = 2.61 ± 0.23 kG. In addition, several nearby magnetically insensitive CO lines show no excess broadening above that produced by stellar rotation and instrumental broadening, reinforcing the magnetic interpretation for the width of the Ti I lines. We carry out extensive tests to quantify systematic errors in our analysis technique that may result from inaccurate knowledge of the effective temperature or gravity, finding that reasonable errors in these quantities produce a ~10% uncertainty in the mean field measurement.

Abundance Survey of M and K Dwarf Stars

We report the measurement of chemical abundances in 35 low-mass main sequence (M and K dwarf) stars. We have measured the abundance of 12 elements in Kapteyn's Star, a nearby halo M subdwarf. The abundances indicate an iron abundance of [Fe/H] = −0.98, which is about 0.5 dex smaller than that measured in the only previous published measurement using atomic absorption lines. We have measured Fe and Ti abundances in 35 M and K dwarfs with −2.39 ⩽ [Fe/H] ⩽ +0.21 using atomic absorption lines, mostly in the 8000A λ

Metallicity measurements using atomic lines in M and K dwarf stars

We report the first survey of chemical abundances in M and K dwarf stars using atomic absorption lines in high resolution spectra. We have measured Fe and Ti abundances in 35 M and K dwarf stars using equivalent widths measured from (lambda / Delta lambda) = 33,000 spectra. Our analysis takes advantage of recent improvements in model atmospheres of low-temperature dwarf stars. The stars have temperatures between 3300 and 4700 K, with most cooler than 4100 K. They cover an iron abundance range of -2.44 < [Fe/H] < +0.16. Our measurements show [Ti/Fe] decreasing with increasing [Fe/H], a trend similar to that measured for warmer stars where abundance analysis techniques have been tested more thoroughly. This study is a step toward the observational calibration of procedures to estimate the metallicity of low-mass dwarf stars using photometric and low-resolution spectral indices.

Vacuum ultraviolet absorption in Xe+CF4 and Kr+CF4 mixtures

The absorption spectra of Xe + CF4 and Kr + CF4 mixtures in the vacuum ultraviolet region are presented. A considerable broadening of the short-wavelength wings of the atomic absorption lines is explained by a repulsive character of the Rg*-CF4 interaction potential. This repulsive character is also considered to be the most probable reason for the anomalously small cross sections of the quenching of electronically excited atoms of rare gases by CF4 molecules. The influence of CF4 on the emission rate of the trapped resonance radiation of Xe from the cell is discussed.

The cool circumstellar environment of IRAS 08182-6000: radiative transfer modelling of TiO absorption bands

IRAS 08182−6000 has very red infrared colours, with an excess at K and L, and a silicate absorption feature at 9.7 μm. Optical spectra show strong, narrow absorption bands of TiO and AlO and weaker bands of VO that are indicative of formation in a very cool region, superimposed on a late F-type or early G-type spectrum. It is similar to the unusual star U Equ = IRAS 20547+0247 and both are high-velocity stars. These characteristics, together with spectroscopic indications of low surface gravity, suggest that these stars are of low mass and are possibly at a post-AGB stage of evolution. IRAS 08182−6000 brightened by several magnitudes during 12 yr of photometric observation. Photospheric and some circumstellar atomic absorption lines are evident, as well as atomic lines seen in emission that differ in radial velocity from those in absorption by c. 50 km s−1. Molecular bands of the γ, γ′ and α systems of circumstellar TiO have been modelled using a one-dimensional radiative transfer code that makes use of the most recent laboratory and theoretical spectroscopic data on TiO. It was found necessary to invoke a non-local thermodynamic equilibrium model, which resulted in the determination of different rotational, spin–orbit and vibrational temperatures for the TiO gas, all of which lie well below the temperature at which TiO begins to deplete from the gas phase due to grain formation.

Wavelength references for 1300-nm wavelength-division multiplexing

We have conducted a study of potential wavelength calibration references for use as both moderate-accuracy transfer standards and high-accuracy National Institute of Standards and Technology (NIST) internal references in the 1280-1320-nm wavelength-division-multiplexing region. We found that most atomic and molecular absorption lines in this region are not ideal for use as wavelength references owing to factors such as weak absorption, complex spectra, or special requirements (for example, frequency-doubling or excitation with an additional light or discharge source). We have demonstrated one of the simpler schemes consisting of a tunable diode laser stabilized to a Doppler-broadened methane absorption line. By conducting a beat-note comparison of this reference to a calcium-based optical frequency standard, we measured the methane line center with an expanded uncertainty (2/spl sigma/) of /spl plusmn/2.3 MHz. This methane-stabilized laser now serves as a NIST internal reference.

Molecular Hydrogen, Deuterium, and Metal Abundances in the Damped Lyα System atzabs = 3.025 toward Q0347−3819

We have detected in high-resolution spectra of the quasar Q0347-3819 obtained with the UV-Visual Echelle Spectrograph (UVES) at the VLT/Kueyen telescope over 80 absorption features in the Lyman and Werner H2 bands at the redshift of a damped Lyα (DLA) system at zabs = 3.025. At the same redshift, numerous absorption lines of atoms and low ions (H I, D I, C II, C II*, N I, O I, Si II, P II, Ar I, Cr II, Fe II, and Zn II) were identified. The zabs = 3.025 system spans over ~80 km s-1 and exhibits a multicomponent velocity structure in the metal lines. The main component at zabs = 3.024855 shows a total H2 column density N(H2) = (4.10 ± 0.21) × 1014 cm-2 and a fractional molecular abundance fH2 = (1.94 ± 0.10) × 10-6 derived from the H2 lines arising from the J = 0-5 rotational levels of the ground electronic vibrational state. In the second strong component at zabs = 3.024684 we were able to set a stringent upper limit to fH2 of 3.3 × 10-9 (3 σ c.l.). The population of the J levels can be represented by a single excitation temperature of Tex = 825 ± 110 K. The ortho-H2 : para-H2 ratio equals 3.1 ± 0.3. This ratio is comparable to that calculated from hot H2 formation upon grain surfaces (ortho-H2 : para-H2 = 3 : 1) but is higher than the "freezeout" quantity (ortho-H2 : para-H2 = 1 : 4) predicted for cosmological epochs at z < 20, implying recent formation of the hydrogen molecules following photodissociation of pristine H2. In the main component the properties of the neutral atoms and low ions can be described with the same broadening parameter b ≃ 3 km s-1 of the H2 cloud. The rate at which UV photons are absorbed in the Lyman and Werner bands is found to be β0 ≃ 2 × 10-9 s-1. Taking into account that similar β0 values are observed in the Galactic diffuse molecular clouds, it shows that the UV radiation fields in the DLA and in the Milky Way are very much alike. We also found the H2 formation rate of RnH ≃ 3 × 10-16 s-1 at zabs = 3.025, which is consistent with observations in the Galactic disk diffuse clouds where nH2 is low. Comparing the relative rotational population ratios of H2 with the measured C II*/C II ratio, we can infer that nH ≃ 6 cm-3 in the main component, which gives a size of D ≃ 14 pc along the line of sight. The mean value of the dust-to-gas ratio estimated for the whole zabs = 3.025 system from the [Cr/Zn] ratio is equal to = 0.032 ± 0.005 (in units of the mean Galactic interstellar medium value). For the first time we unambiguously reveal a pronounced [α-element/iron peak] enhancement of [O,Si/Zn] = 0.6 ± 0.1 (1 σ c.l.) at high redshift. The simultaneous analysis of metal and hydrogen lines leads to D/H = (3.75 ± 0.25) × 10-5. This value is consistent with standard big bang nucleosynthesis if the baryon-to-photon ratio, η, lies within the range 4.37 × 10-10 ≲ η ≲ 5.32 × 10-10, implying 0.016 ≲ Ωbh ≲ 0.020.

A Joint Discussion on the Topic of Cold Gas and Dust at High Redshift

The number of spectroscopically confirmed galaxies at high redshift is increasing rapidly, with many being found efficiently by deep optical imaging and color selection. In parallel, a confluence of technical developments is bringing rapid progress to the domain of observations of cold gas and dust at high redshift. Large telescopes operating at high, dry sites, with a new generation of sensitive detectors, together with recent satellite missions, are opening up new areas of study through observations of dust continuum emission and associated atomic and molecular emission and absorption lines. These data bear directly on fundamental questions of cosmic evolution by probing the ordinary cool material that forms stars and fuels active galactic nuclei. Analysis of data from the COBE satellite confirms the presence of a diffuse far-infrared background from a widespread population of distant dusty objects. The global energetics of the optical and far-infrared backgrounds suggest that perhaps half of distant activity may be enshrouded by dust. Understanding the nature and redshifts of the sources responsible for these emissions is profoundly important. The intent of Joint Discussion 9, between Division X (Radio Astronomy) and Division XIII (Galaxies and the Universe), was to provide a forum to present observations from this newly accessible realm and to consider the astrophysical implications.

Frequency-dependent optical pumping in atomic Λ-systems

We consider the effects of optical pumping on the conversion of laser-frequency modulation into intensity modulation by an atomic absorption line in a vapor of alkali atoms driven in a ?-configuration. It is found that, due to optical pumping in combination with the excited-state hyperfine structure, the absorption line shape is distorted substantially as the Fourier frequency of the FM is changed. The most significant effect of the distortion is a shift of the apparent line center, which depends on how the frequency of the modulation compares with the optical pumping rate. This shift has implications for locking lasers to atomic transitions and also for FM-AM noise conversion in atomic vapors.

Power broadening revisited: theory and experiment

The spectral width of an atomic absorption line, observed with a steady light source, typically increases as the light intensity increases, an effect known as power broadening. In this paper, we point out classes of pulsed-light observations where power broadening does not always occur. We present analytical and numerical results, supported by experimental data of coherent pulsed excitation probed by photoionization, which show that the extent of power broadening depends crucially upon the nature of excitation and the type of measurement. In particular, we show that a spectral line obtained from measurement performed after pulsed excitation exhibits no power broadening. For pulsed excitation and continuous measurement, the spectral line contains two components: a power-broadened signal collected during the excitation and an unbroadened signal collected after the excitation.

Unidirectional ring TI3+:Al2O3 laser generation at the wavelength of an atomic absorption line by bidirectional passive self-injection locking

A simple, purely optical approach to produce, in a ring Ti:Al2O3 laser, a pulsed unidirectional generation, spectrally fixed at a reference atomic absorption line is described. The control relies on the unbalance between two opposite, passive, wavelength-scanned self-injections that is produced by the absorption at the reference line. It is shown both experimentally and theoretically that: (i) the emitted spectrum is centered at the absorption maximum and (ii) due to the nonlinear character of the process the spectrum is narrowed several times compared with an absorption linewidth.

Phonon Bands Associated with the Inner-Shell Electronic Absorption Lines of Eu Atoms in Bulk Liquid Helium

The phonon bands associated with the inner-shell electronic absorption lines of Eu atoms have been studied in bulk liquid helium in the temperature range between 1.6 and 3.1 K. Profiles of the phonon bands show the remarkable temperature dependence from a broad peak at 1.6 K to a monotonic decrease of the intensity by energy at higher temperatures. Two phonon bands, measured at about 1.9 K for two different lines with different interaction energies with the liquid, are found to show identical profiles, suggesting that the profiles depend only on the temperature. The broad peak at 1.6 K has been interpreted as temperature-broadened roton/maxon peaks, while the monotonically decreasing profiles have not been well understood yet.