Sharp Absorption Lines Research Articles

Hubble Space Telescope STIS Spectroscopy of Nova T Aurigae 1891

T Aurigae is an eclipsing old nova that exploded in 1891. At a Gaia EDR3 distance of 815–871 pc, it is a relatively nearby old nova. Through ultraviolet spectral modeling and using the new precise Gaia distance, we find that the HST/STIS spectrum of T Aurigae is consistent with an accretion disk with a mass-transfer rate of the order of 10−8 M ⊙ yr−1, for a white-dwarf mass of M wd ≈ 0.7 ± 0.2M ⊙, an inclination of i ∼ 60°, and a Gaia distance of of pc. The sharp absorption lines of metals cannot form in the disk and are likely forming in material above the disk (e.g., due stream disk overflow), in circumbinary material, and/or in material associated with the ejected shell from the 1891 nova explosion. The saturated hydrogen Lyα absorption feature is attributed to a large interstellar-medium hydrogen-column density of the order of 1021cm−2 toward T Aur, as corroborated by the value of its reddening E(B − V) = 0.42 ± 0.08.

Many-Electron System on Helium and Color Center Spectroscopy.

Electrons on the helium surface display sharp resonant absorption lines related to the transitions between the subbands of quantized motion transverse to the surface. A magnetic field parallel to the surface strongly affects the absorption spectrum. We show that the effect results from admixing the intersubband transitions to the in-plane quantum dynamics of the strongly correlated electron liquid or a Wigner crystal. This is similar to the admixing of electron transitions in color centers to phonons. The spectrum permits a direct characterization of the many-electron dynamics and also enables testing the theory of color centers in a system with controllable coupling.

Natural blue zircon from Vesuvius

Zircon from syenitic ejecta of Vesuvius (Campania, Italy) is unusually blue, a property shared with gem zircon from Ratanakiri province (Cambodia), which turns from natural reddish-brown to blue when heated under reducing conditions. Here, the origins of these unusual crystals were traced through geochronology, trace elements, and O-Hf isotopic compositions. The causes of its colour were investigated through optical and electron microscopy, optical absorption spectroscopy, and Raman microspectroscopy. Colour stability upon heating and ultraviolet light (UV) exposure was tested using Ratanakiri zircon as a control. Vesuvius zircon contains vesiculated zones with abundant inclusions ~2.5 μm to <100 nm in diameter (mostly U-rich thorianite and pyrochlore-group minerals), while homogeneous zircon domains are high in Th and U (up to 5.9 and 1.8 wt%, respectively). Its blue colouration is stable under UV radiation, as well as heat-treatment under reducing conditions (1000 °C; >15 h). Turbid domains rich in large inclusions change to yellow-brown after heating under oxidizing conditions, while transparent domains remain pale blue or colourless. Optical absorption spectra display sharp absorption lines attributed to U4+, and slightly elevated absorption towards shorter wavelengths. The ~1007 cm−1 ν3(SiO4) Raman band is broadened due to lattice distortion by non-stoichiometric elements in high-Th/-U zircon, whereas narrow bands in inclusion-rich domains indicate a decrease in lattice strain due to inclusion precipitation. Blue colouration in Vesuvius zircon is explained by the effect of light scattering (Rayleigh and/or Mie scattering) on highly refractive actinide-rich inclusions ranging in size from <1/10 to few multiples of the wavelengths of visible light. Inclusions likely formed during fluid-mediated coupled dissolution-reprecipitation that locally transformed lattice-strained actinide-rich zircon within several hundreds of years prior to eruption.

The CARMENES search for exoplanets around M dwarfs

Context. For years, the standard procedure to measure radial velocities (RVs) of spectral observations consisted in cross-correlating the spectra with a binary mask, that is, a simple stellar template that contains information on the position and strength of stellar absorption lines. The cross-correlation function (CCF) profiles also provide several indicators of stellar activity. Aims. We present a methodology to first build weighted binary masks and, second, to compute the CCF of spectral observations with these masks from which we derive radial velocities and activity indicators. These methods are implemented in a python code that is publicly available. Methods. To build the masks, we selected a large number of sharp absorption lines based on the profile of the minima present in high signal-to-noise ratio (S/N) spectrum templates built from observations of reference stars. We computed the CCFs of observed spectra and derived RVs and the following three standard activity indicators: full-width-at-half-maximum as well as contrast and bisector inverse slope. Results. We applied our methodology to CARMENES high-resolution spectra and obtain RV and activity indicator time series of more than 300 M dwarf stars observed for the main CARMENES survey. Compared with the standard CARMENES template matching pipeline, in general we obtain more precise RVs in the cases where the template used in the standard pipeline did not have enough S/N. We also show the behaviour of the three activity indicators for the active star YZ CMi and estimate the absolute RV of the M dwarfs analysed using the CCF RVs.

Modulating the H-bond strength by varying the temperature for the high pressure synthesis of nitrogen rich carbon nanothreads.

Carbon nanothreads are among the most attractive new materials produced under high pressure conditions. Their synthesis can be achieved by compressing the crystals of aromatic molecules exploiting both the anisotropic stress produced by the unidirectional applied force and that intrinsic to the crystal arrangement. We explored here the transformation of pyridine into a nitrogen rich carbon nanothread crystal by varying the pressure and temperature conditions with the twofold purpose of disclosing the microscopic mechanism of transformation and optimizing the yield and quality of the produced crystalline nanothreads. The best conditions for the synthesis were identified in the 14-18 GPa range at temperatures between 400 and 500 K with a product yield greater than 30%. The comparison of experiments performed under different P-T conditions allowed us to understand the role of high temperature, which is necessary to weaken or even destroy the complex H-bond network characterizing the pyridine crystal and preventing the correct approach of the aromatic rings for nanothread formation. X-ray diffraction data confirm the excellent 2D hexagonal packing of the nanothreads over several tens of microns, whereas the sharp absorption lines observed in the IR spectrum strongly support a substantial order along the threads. Diffraction results suggest a polytwistane structure of the threads derived from a Diels-Alder [4 + 2] polymerization involving molecules arranged in a slipped parallel configuration along the pyridine crystal a and b axes. Electron microscopy evidences an arrangement of the nanothreads in bundles of tens of nanometers.

Terahertz quantum-cascade lasers for high-resolution spectroscopy of sharp absorption lines

Terahertz (THz) quantum-cascade lasers (QCLs) are currently unparalleled for high-resolution spectroscopy of very sharp absorption lines (linewidths below 100 MHz) in the range between 2 and 5.4 THz. Since the frequency range accessible by a single QCL is determined by its typically very limited tuning range, a particular QCL has to be fabricated for each specific application. We quantitatively analyze the frequencies of the modes in THz QCLs with a Fabry–Pérot resonator as a function of its length taking into account waveguide dispersion. Based on these results, we develop a process based on mechanical polishing of the front facet to adjust the emission frequency with a precision of 1 GHz. The demonstrated process makes it possible to reliably fabricate THz QCLs for the spectroscopy of very sharp absorption lines.

Optical defects in milky type IaB diamonds

The optical features of milky type IaB diamonds were studied systematically by non-destructive approaches including FTIR, photoluminescence (PL), and cathodoluminescence (CL) spectroscopy. From 97 type IaB diamonds ranging from 0.2 ct to ~100 ct submitted to GIA's New York laboratory for screening, we found that all the milky type IaB diamonds consistently displayed the hydrogen-related defect with an absorption line at 3107 cm−1, and ~96% of them were accompanied by a weaker line at 3085.4 cm−1, which is undetectable in most non-milky diamonds. Most of the diamond samples display no platelet defect or a very tiny residual platelet peak with a position at larger wavenumber in milky diamonds than in non-milky counterparts. “Amber center” with a weak but sharp absorption line at 4168.8 cm−1 has been observed in ~73% of the milky diamonds and ~24% of the non-milky ones. Photoluminescence (PL) results reveal that several defects with ZPLs at 490.7, 536, 575.9 and 612.4 nm are more common in milky type IaB diamonds than non-milky ones. A zero-phonon line (ZPL) at 536 nm has been confirmed by PL mapping and CL spectra as a product of plastic deformation, and it might be linked with the H4 center (N4V2 defect). A ZPL at 490.7 nm could be related to a nitrogen-vacancy complex. The defects present more often in milky IaB diamonds are generally associated with plastic deformation. The presence of a hydrogen-related peak at 3085.4 cm−1 and a 536 nm center would help effectively distinguish IaB diamonds with subtle milky areas from their non-milky counterparts.

GALEX J184559.8−413827: a new extreme helium star identified using SALT★

A high-resolution spectrum of the helium-rich `hot subdwarf' GALEX J184559.8-413827 (J1845-4138) obtained with SALT HRS demonstrates it to be the first extreme helium (EHe) star to be discovered in nearly 40 years. A quantitative analysis demonstrates it to have an atmosphere described by Teff = 26 170 +/- 750 K, log g /(cm s^-2) = 4.22 +/- 0.10, and a surface chemistry characterised by CNO-processed helium, a 1% contamination of hydrogen (by number), and a metallicity 0.4 dex subsolar. Its distance and position are consistent with membership of the Galactic bulge. Its sharp absorption lines place strong constraints on both the rotation and microturbulent velocities. Spectroscopically, J1845-4138 closely resembles the pulsating EHe star V652 Her, generally considered to be the product of a double helium white dwarf merger evolving to become a helium-rich sdO star.

A YOUNG ECLIPSING BINARY AND ITS LUMINOUS NEIGHBORS IN THE EMBEDDED STAR CLUSTER Sh 2-252E

ABSTRACT We present a photometric and light curve analysis of an eccentric eclipsing binary in the K2 Campaign 0 field, which resides in Sh 2-252E, a young star cluster embedded in an H ii region. We describe a spectroscopic investigation of the three brightest stars in the crowded aperture to identify which is the binary system. We find that none of these stars are components of the eclipsing binary system, which must be one of the fainter nearby stars. These bright cluster members all have remarkable spectra: Sh 2-252a (EPIC 202062176) is a B0.5 V star with razor sharp absorption lines, Sh 2-252b is a Herbig A0 star with disk-like emission lines, and Sh 2-252c is a pre-main-sequence star with very red color.

Coloration of Natural Zircon

Abstract Selected literature data and new results from our own spectroscopic studies using optical absorption, paramagnetic resonance, and Raman spectroscopy are used to give an overview of recent understanding of the coloration of natural zircon. Pure ZrSiO 4 is colorless. Coloration is mainly related to point defects of the electron or hole type, although charge transfer mechanisms and crystal field-dependent internal electron transitions in f - and d -elements may sometimes also play a significant role. There is a common substitution of tetravalent zirconium by trivalent rare earth elements (REE) and yttrium which is frequently not compensated by phosphorus or other elements. As a result, hole defects are the dominant type of coloration centers in reddish and some rose natural zircon crystals. On the other hand, electron centers may be involved in coloration of common yellowish-brownish zircon which displays low REE and yttrium contents. These two coloration mechanisms are the most common in natural zircon. An unspecific absorption increasing steadily from the red to the blue part of the optical absorption spectrum may additionally affect zircon coloration. Color shades of grey, rose, and brown appearing with increasing intensity of this absorption feature may result. This optical characteristic, which is frequently observed in some zircons, is obviously related to the effects of radioactive irradiation and occurs in various types of zircon depending on their uranium and thorium contents. Sharp absorption lines caused by internal electron transitions of the f - f type related to U 4+ or, less typically, to Er 3+ and Nd 3+ substituting for Zr 4+ , occur frequently in the optical absorption spectra of zircon. As a rule, they have no significant influence on the visible color. However, very high U 4+ or Er 3+ contents combined with strong absorption in the blue part of the spectrum may cause greenish coloration. Rarely, green zircon coloration also occurs as a result of various broad absorption bands located in the red part of the spectrum. Very high REE contents in some zircons are the most likely cause for a strong, absorption edge-like feature in the blue part of the optical absorption spectrum, resulting in a rarely observed intense yellow coloration. Blue zircon coloration is mostly artificially induced by heating, but sometimes also occurs in nature. Besides the increase in unspecific absorption causing greyish to brownish colors, there are no simple relationships between zircon coloration, radioactivity, and structural order (or degree of metamictization) of the crystal grains.

Infrared absorption on a complex comprising three equivalent hydrogen atoms in ZnO

A hydrogen-related defect in ZnO which causes two broad IR absorption bands at 3303 and $3321 {\mathrm{cm}}^{\ensuremath{-}1}$ is studied by means of infrared absorption spectroscopy and first-principles theory. In deuterated samples, the defect reveals two sharp absorption lines at 2466 and $2488 {\mathrm{cm}}^{\ensuremath{-}1}$ accompanied by weaker sidebands at 2462 and $2480 {\mathrm{cm}}^{\ensuremath{-}1}$. Isotope substitution experiments with varying concentrations of H and D together with polarization-sensitive measurements strongly suggest that these IR absorption lines are due to stretch local vibrational modes of a defect comprising three equivalent hydrogen atoms. The zinc vacancy decorated by three hydrogen atoms, ${V}_{\mathrm{Zn}}{\mathrm{H}}_{3}$, and ammonia trapped at the zinc vacancy, $({\mathrm{NH}}_{3}){}_{\mathrm{Zn}}$, are discussed as a possible origin for the complex.

Spectroscopic Properties and Ligand-Field Analysis of the Bis(Ethylenediamine Monoacetato-N,N',O)Chromium(III) Moiety

The sharp-line absorption spectrum of (H2en)[Cr(edma)2]2Cl4·2H2O (edma=ethylenediaminemonoacetate) has been measured between 13,000 and 16,000 cm–1 at temperatures down to 5 K. The emission, IR and UV-visible absorption spectra are measured as well. The vibrational intervals of the electronic ground state are extracted from the far-infrared and emission spectra. The nine electronic bands due to spin-allowed and spin-forbidden transitions are assigned. Using the observed electronic transitions, a ligand-fi eld analysis is performed in the framework of the angular overlap model. The zero-phonon line in the sharp-line absorption spectrum splits into two lines that differ by 168 cm–1; the large 2 E g splitting can be reproduced by ligand fi eld theory. The oxygen atoms of the edma ligand are confi rmed to have strong σ- and π-donor properties toward chromium(III).

Synthesis, crystal structure and spectroscopic properties of trans-difluoro(1,4,7,11-tetraazaundecane)chromium(III) perchlorate

The structure of trans-[Cr(2,2,3-tet)F2]ClO4 (2,2,3-tet=1,4,7,11-tetraazaundecane) has been determined by single-crystal X-ray diffraction. The complex crystallizes in the space group P1‾ of the triclinic system with two mononuclear formula units in a cell of dimensions a=5.6741(11), b=9.971(2), c=13.222(3) Å, α=73.76(3)o, β=81.08(3)° and γ=85.12(3)°. The chromium(III) atom is in a slightly distorted octahedral environment coordinated by four N atoms of 2,2,3-tet and two F ligands in a mutually trans (meso RS) geometry. The mean Cr-N(2,2,3-tet) and CrF bond lengths are 2.064(9) and 1.885(7) Å, respectively. The crystal packing is stabilized by several hydrogen bonds. The 5K sharp-line absorption spectrum and the 298K FT-infrared and UV–visible spectra have been measured. Using the electronic transitions, a ligand field optimization has been performed to determine the metal-ligand bonding properties of the coordinated atoms. It is found that the fluoride is a strong σ- and π-donor and the nitrogen atoms of the 2,2,3-tet ligand also have strong σ-donor properties toward the chromium(III).

Absorption Spectrum and Absolute Absorption Cross Sections of CH3O2 Radicals and CH3I Molecules in the Wavelength Range 7473–7497 cm–1

The absorption spectrum of CH3O2 radicals and CH3I molecules has been measured in the range 7473-7497 cm(-1). CH3O2 radicals have been generated by 248 nm laser photolysis of CH3I in the presence of O2, and the relative absorption has been measured by time-resolved continuous-wave cavity ring-down spectroscopy (cw-CRDS). Calibration of the relative absorption spectrum has been carried out on three distinct wavelengths by carefully measuring CH3O2 decays under different experimental conditions and extracting the initial radical concentration (and with this the absolute absorption cross sections) by using the well-known rate constant for the CH3O2 self-reaction. The following, pressure-independent absorption cross sections were determined: 3.41 × 10(-20), 3.40 × 10(-20), and 2.11 × 10(-20) cm(2) at 7748.18, 7489.16, and 7493.33 cm(-1). These values are 2-3 times higher than previous determinations ( Pushkarsky, M. B.; Zalyubovsky, S. J.; Miller, T. A. J. Chem. Phys. 2000, 112 (24), 10695 - 10698 and Atkinson, D. B.; Spillman, J. L. J. Phys. Chem. A 2002, 106 (38), 8891 - 8902). The absorption spectrum of the stable precursor CH3I has also been determined and three characteristic sharp absorption lines with absorption cross sections up to 2 × 10(-21) cm(2) have been observed in this wavelength range.

Disk Origin Narrow Metallic Absortion Lines Observed during the 2009–2011 Eclipse of ∊ Aurigae

Frequent high-resolution spectroscopic observations of $\epsilon$ Aur during the 2009–2011 eclipse revealed temporal appearances of low-excitation absorption lines of neutral iron peak elements. Several 0 eV lines of Fe I were detected near the end of the first half of the eclipse. They had migrated toward shorter wavelength, became much strong after the third contact, and then disappeared after the fouth contact. Curiously, the widths of these temporal absorption lines became broader for about a 100-d period just before the third contact. The radial velocity measured for these lines follows that of the K I line at 7699 Å, implying that these lines originated in a rotating disk around the secondary star, which occulted the primary star. Weak and sharp absorption lines of low excitation neutral metals, such as Sc I, Ti I, V I, Cr I, and Mn I, were observed only for a short period from the third contact to the fourth contact, and they were all blue-shifted by $\sim$ 40 km s$^{-1}$. These observations show that the rotating disk around the secondary star is not axially symmetric, but suggest that a clump of cool gas concentrated in a region observed projected on the primary star near at the end of the eclipse.

Circulation of the Venus upper mesosphere/lower thermosphere: Doppler wind measurements from 2001–2009 inferior conjunction, sub-millimeter CO absorption line observations

Sub-millimeter 12CO (346 GHz) and 13CO (330 GHz) line absorptions, formed within the mesospheric to lower thermospheric altitude (70–120 km) region of the Venus atmosphere, have been mapped across the nightside disk of Venus during 2001–2009 inferior conjunctions, employing the James Clerk Maxwell Telescope (JCMT). Radiative transfer analysis of these thermal line absorptions supports temperature and CO mixing profile retrievals, as described in a companion paper ( Clancy et al., 2012). Here, we consider the analysis of the sharp line absorption cores of these CO spectra in terms of accurate Doppler wind profile measurements at 95–115 km altitudes versus local time (∼8 pm–4 am) and latitude (∼60N–60S). These Doppler wind measurements support determinations of the nightside zonal and subsolar-to-antisolar (SSAS) circulation components over a variety of timescales. The average behavior fitted from 21 retrieved maps of 12CO Doppler winds (obtained over hourly, daily, weekly, and interannual intervals) indicates stronger average zonal (85 m/s retrograde) versus SSAS (65 m/s) circulation at the 1 μbar pressure (108–110 km altitude) level. However, the absolute and relative magnitudes of these circulation components exhibit extreme variability over daily to weekly timescales. Furthermore, the individual Doppler wind measurements within each nightside mapping observation generally show significant deviations (20–50 m/s, averaged over 5000 km horizontal scales) from the simple zonal/SSAS solution, with distinct local time and latitudinal characters that are also time variable. These large scale residual circulations contribute 30–70% of the observed nightside Doppler winds at any given time, and may be most responsible for global variations in nightside lower thermospheric trace composition and temperatures, as coincidentally retrieved CO abundance and temperature distributions do not correlate with solution retrograde zonal and SSAS winds (see companion paper, Clancy et al., 2012). Limited comparisons of these nightside submillimeter results with dayside infrared Doppler wind measurements suggest distinct dayside versus nightside circulations, in terms of zonal winds in particular. Combined 12CO and 13CO Doppler wind mapping observations obtained since 2004 indicate that the average zonal and SSAS wind components increase by 50–100% between altitudes of 100 and 115 km. If gravity waves originating from the cloud levels are responsible for the extension of zonal winds into the thermosphere (Alexander, M.J. [1992]. Geophys. Res. Lett. 19, 2207–2210), such waves deposit substantial momentum (i.e., break) in the lower nightside thermosphere.

Study on the Magnetic Behavior of In-doped Nickel Chromite by Using M?ssbauer Spectroscopy

NiCr1.9−x Fe0.1InxO4 (x = 0.0, 0.1, 0.3, and 0.5) was prepared by using a sol-gel method. The crystal structure at room temperature was determined to be a normal cubic spinel with space group Fd3m. An analysis of the x-ray diffraction patterns was performed using a Rietveld refinement method while the Bragg RB and RF factors were below 5%. The magnetic Neel temperature decreased from 150 K to 77 K with increasing In concentration, which was confirmed by zero-fieldcooled (ZFC) magnetization at applied fields under 100 Oe and by Mossbauer spectra measured at various temperatures. Magnetic hysteresis loops of the samples at 77 K showed drastically increasing magnetization and decreasing coercivity with increasing In concentration. The Mossbauer spectra of the samples were measured at various temperatures ranging from 4.2 to 295 K. The isomer shift value showed that the charge states of the iron ions are ferric. The Mossbauer spectra showed two magnetic phases with two different magnetic spin direction sites for the Cr ion state. Mossbauer spectra below 77 K showed 6 sharp absorption lines and the linewidth became broader with increasing temperature, which indicates a Jahn-Teller distortion and relaxation.

Vibronic line shapes of PTCDA oligomers in helium nanodroplets

Oligomers of the organic semiconductor 3,4,9,10-perylene-tetracarboxylic-dianhydride, C(24)H(8)O(6) (PTCDA) are studied by means of helium nanodroplet isolation spectroscopy. In contrast to the monomer absorption spectrum, which exhibits clearly separated, very sharp absorption lines, it is found that the oligomer spectrum consists of three main peaks having an apparent width orders of magnitude larger than the width of the monomer lines. Using a simple theoretical model for the oligomer, in which a Frenkel exciton couples to internal vibrational modes of the monomers, these experimental findings are nicely reproduced. The three peaks present in the oligomer spectrum can already be obtained taking only one effective vibrational mode of the PTCDA molecule into account. The inclusion of more vibrational modes leads to quasicontinuous spectra, resembling the broad oligomer spectra.

A Novel Observation of “a Sharp Absorption Line" Using Much More Broad Laser Lights: Quantum Interference in the Autoionization Spectra of Sc

The most accurate measurements in physical sciences will be precision spectroscopic experiments which are based on the usage of most narrow lines in cooperation with interference phenomena. We present a novel experimental observation of “a sharp absorption resonance line" with much more broad laser lights. The mechanism of such a novel phenomenon will be elucidated and its implications will be discussed.

Simultaneous Photoacoustic Spectroscopy of Aerosol and Oxygen A-Band Absorption for the Calibration of Aerosol Light Absorption Measurements

The calibration of photoacoustic aerosol optical absorption measurements through simultaneous photoacoustic spectroscopy of the oxygen A-band absorption is demonstrated. While aerosol absorption shows no sharp spectral structures for size-distributed aerosols, the molecular oxygen A-band has sharp absorption lines in the near-infrared (i.e., 760–770 nm) spectral region. Line-strength, shape, and broadening of these lines are well known and molecular oxygen is ubiquitous with a constant concentration in the troposphere. Simultaneous photoacoustic spectroscopy of aerosol and molecular oxygen A-band absorption with a tunable, external cavity diode laser yields a convenient calibration for the photoacoustic measurement of aerosol absorption coefficients without the need for pressurized and potentially toxic calibration gases.