Narrow Line Spectra Research Articles

Type Ic supernova of a 22 M⊙ progenitor

ABSTRACT Type Ic supernovae (SNe Ic) are a sub-class of core-collapse SNe that exhibit no helium or hydrogen lines in their spectra. Their progenitors are thought to be bare carbon–oxygen cores formed during the evolution of massive stars that are stripped of their hydrogen and helium envelopes sometime before collapse. SNe Ic present a range of luminosities and spectral properties, from luminous GRB-SNe with broad-lined spectra to less luminous events with narrow-line spectra. Modelling SNe Ic reveals a wide range of both kinetic energies, ejecta masses, and 56Ni masses. To explore this diversity and how it comes about, light curves and spectra are computed from the ejecta following the explosion of an initially 22 M⊙ progenitor that was artificially stripped of its hydrogen and helium shells, producing a bare CO core of ∼5 M⊙, resulting in an ejected mass of ∼4 M⊙, which is an average value for SNe Ic. Four different explosion energies are used that cover a range of observed SNe. Finally, 56Ni and other elements are artificially mixed in the ejecta using two approximations to determine how element distribution affects light curves and spectra. The combination of different explosion energy and degree of mixing produces spectra that roughly replicate the distribution of near-peak spectroscopic features of SNe Ic. High explosion energies combined with extensive mixing can produce red, broad-lined spectra, while minimal mixing and a lower explosion energy produce bluer, narrow-lined spectra.

Light echoes from the plateau in Eta Carinae’s Great Eruption reveal a two-stage shock-powered event

ABSTRACT We present multi-epoch photometry and spectroscopy of a light echo from η Carinae’s 19th century Great Eruption. This echo's light curve shows a steady decline over a decade, sampling the 1850s plateau of the eruption. Spectra show the bulk outflow speed increasing from ∼150 km s−1 at early times, up to ∼600 km s−1 in the plateau. Later phases also develop remarkably broad emission wings indicating mass accelerated to more than 10 000 km s−1. Together with other clues, this provides direct evidence for an explosive ejection. This is accompanied by a transition from a narrow absorption line spectrum to emission lines, often with broad or asymmetric P Cygni profiles. These changes imply that the pre-1845 luminosity spikes are distinct from the 1850s plateau. The key reason for this change may be that shock interaction with circumstellar material (CSM) dominates the plateau. The spectral evolution of η Car closely resembles that of the decade-long eruption of UGC 2773-OT, which had clear signatures of shock interaction. We propose a two-stage scenario for η Car’s eruption: (1) a slow outflow in the decades before the eruption, probably driven by binary interaction that produced a dense equatorial outflow, followed by (2) explosive energy injection that drove CSM interaction, powering the plateau and sweeping slower CSM into a fast shell that became the Homunculus. We discuss how this sequence could arise from a stellar merger in a triple system, leaving behind the eccentric binary seen today. This gives a self-consistent scenario that may explain interacting transients across a wide range of initial mass.

EPR Study of H and D Atoms in Quench-Condensed Solid D $$_{2}$$ 2

We present an experimental study of H and D atoms trapped in a solid D\(_{2}\) matrix. The samples were prepared by quench condensing gaseous \(n\)D\(_{2}\) with small (0.15 %) admixture of molecular \(n\)H\(_{2}\) on a substrate at 1.3–4.2 K. An EPR observation revealed two types of H and D atoms: with narrow- and broad-line spectra. In order to elucidate the origin of the centers we performed an analysis that included comparing the matrix shifts of the hyperfine structure constants, considering the saturation and spin-relaxation times, estimation of the superhyperfine broadening, and evaluation of an effect which the tunneling isotope exchange reaction has on the H and D atoms relative EPR intensities. As a result, the broad-line H and D spectra were attributed to atoms at the substitutional positions in the regular D\(_{2}\) lattice, while the narrow-line spectra were due to atoms trapped at the one-dimensional structure imperfections (like dislocations). These trapped atoms are capable of moving quickly along the defects with a diffusion coefficient \(D\approx 4\times 10^{-6}\) cm\(^{2}\)/s. The results were compared to earlier observations which allowed us to build a suggestion about the nature of previously found atomic centers in D\(_{2}\) not explained in the literature.

Broadening of the lines due to the 4f n -4f n − 15d transitions of Ce3+, Pr3+, and Tb3+ ions in the absorption spectra of CdF2 crystals

The structure of the absorption spectra of Ce3+, Pr3+, and Tb3+ ions in the vicinity of 4f-5d transitions has been investigated. At low temperatures the absorption spectra exhibit a weakly pronounced fine structure, in contrast to narrow-line spectra in crystals of Ca, Sr, and Ba fluorides. The spectra of Ce3+, Pr3+, and Tb3+ ions in CdF2 can be considered as the absorption spectra of these ions in alkali-earth fluorides, broadened by 60–75 cm−1. The broadening is related to the autoionization of electron from the local 5d(eg) level to the energy-degenerate states of the conduction band of CdF2 crystal.

THE QUASAR SDSS J105041.35+345631.3: BLACK HOLE RECOIL OR EXTREME DOUBLE-PEAKED EMITTER?

The quasar SDSS J105041.35+345631.3 (z = 0.272) has broad emission lines blueshifted by 3500 km/s relative to the narrow lines and the host galaxy. Such an object may be a candidate for a recoiling supermassive black hole, binary black hole, a superposition of two objects, or an unusual geometry for the broad emission-line region. The absence of narrow lines at the broad line redshift argues against superposition. New Keck spectra of J1050+3546 place tight constraints on the binary model. The combination of large velocity shift and symmetrical H-beta profile, as well as aspects of the narrow line spectrum, make J1050+3546 an interesting candidate for black hole recoil. Other aspects of the spectrum, however, suggest that the object is most likely an extreme case of a ``double-peaked emitter.'' We discuss possible observational tests to determine the true nature of this exceptional object.

Difference in Narrow-Emission-Line Spectra of Seyfert 1 and 2 Galaxies

In the unification scheme of Seyfert galaxies, a dusty torus blocks the continuum source and broad line region in Seyfert 2 galaxies. However it is not clear whether or not and to what extent the torus affects the narrow line spectra. In this paper, we show that Seyfert 1 and Seyfert 2 galaxies have different distributions on the [OIII]/H$\beta $ vs [NII]/H$\alpha$ diagram (BPT diagram) for narrow lines. Seyfert 2 galaxies display a clear left boundary on the BPT diagram and only 7.3% of them lie on the left. By contrast, Seyfert 1 galaxies do not show such a cutoff and 33.0% of them stand on the left side of the boundary. Among Seyfert 1 galaxies, the distribution varies with the extinction to broad lines. As the extinction increases, the distribution on BPT diagram moves to larger [NII]/H$\alpha$ value. We interpret this as an evidence for the obscuration of inner dense narrow line region by the dusty torus. We also demonstrate that the [OIII] and broad line luminosity correlation depends on the extinction of broad lines in the way that high extinction objects have lower uncorrected [OIII] luminosities, suggesting that [OIII] is partially obscured in these objects. Therefore, using [OIII] as an indicator for the nuclear luminosity will systematically under-estimate the nuclear luminosity of Seyfert 2 galaxies.

LOW-MASS SEYFERT 2 GALAXIES IN THE SLOAN DIGITAL SKY SURVEY

We describe a sample of low-mass Seyfert 2 galaxies selected from the Sloan Digital Sky Survey (SDSS), with a median absolute magnitude of Mg = –19.0 mag. These galaxies are Type 2 counterparts to the Seyfert 1 galaxies with intermediate-mass black holes identified by Greene & Ho. Spectra obtained with the Echellette Spectrograph and Imager at the Keck Observatory are used to determine the central stellar velocity dispersions and to examine the emission-line properties. Overall, the stellar velocity dispersions are low (~40-90 km s–1), and we find 12 objects having σ < 60 km s–1, a range where very few Seyfert 2 galaxies were previously known. The sample follows the correlation between stellar velocity dispersion and FWHM([O III]) seen in more massive Seyfert galaxies, indicating that the narrow-line FWHM values are largely determined by virial motion of gas in the central regions of the host galaxies, but the [O III] emission lines exhibit a higher incidence of redward asymmetries and double-peaked profiles than what is found in typical Seyfert samples. Using estimates of the black hole masses and active galactic nucleus (AGN) bolometric luminosities, we find that these galaxies are typically radiating at a high fraction of their Eddington rate, with a median L bol/L Edd = 0.4. We identify one galaxy, SDSS J110912.40+612346.7, as a Type 2 analog of the nearby dwarf Seyfert 1 galaxy NGC 4395, with a nearly identical narrow-line spectrum and a dwarf spiral host of only Mg = –16.8 mag. The close similarities between these two objects suggest that the obscuring torus of AGN unification models may persist even at the lowest luminosities seen among Seyfert galaxies, below L bol = 1041 ergs s–1. Spectropolarimetry observations of four objects do not reveal any evidence for polarized broad-line emission, but SDSS J110912.40+612346.7 has a continuum polarization significantly in excess of the expected Galactic foreground polarization, a possible indication of scattered light from a hidden nucleus. Forthcoming observations of this sample, including X-ray and mid-infrared spectroscopy, can provide new tests of the obscuring torus model for active galaxies at low luminosities.

Thermodynamic consideration of the positronium decay

Electron-positron annihilation has mainly two decay channels. Firstly into two gamma-photons of equal energy forming a narrow line spectrum, and secondly into three gamma-photons forming a continuous energy spectrum. The ratio of decay events N 3 /N 2 is experimentally found with about 1:379 and depends only on the fine-structure constant a like N 3 /N 2 = 4(π 2 - 9)a/37r to the first QED expansion order. The given consideration tries to understand this ratio of decay events in a thermodynamic way and allows the computation of a theoretical ratio of 1:356 on the base of the Boltzmann distribution and the calculated temperatures of the 27-decay with k B T ≅ 1.04737·mc 2 and the 3γ-decay with k B T ≅ 1/8.0125·mc 2 . The radiation entropy produced at the 2γ-decay was calculated with 1.90975 k B and the radiation entropy of the 3γ-continuum with 5.9663 k B . The positronium system could be seen in some kind of conflict: Due to the smallness of a the construction of an additional third gamma-photon is improbable. On the other hand, much more entropy could be generated by three gamma quanta. This antagonism could be transformed into an understanding of the ratio of decay events and thus the actual value of the fine-structure constant. Due to entropy, this seems to be the optimal value for the positronium ecay-or, more general -the optimal value for the building probability of a photon. As entropy is an observable physical quantity, the calculated values should experimentally be measurable, so that the given calculations could experimentally be verified.

Narrow line spectra induced by Er 3+ in silica glasses containing SnO 2 nanocrystals

Silica glasses containing SnO2 nanocrystals and Er3+ ions were prepared by the sol-gel route and proper annealing treatments. A few samples were prepared with fluorinated Si precursors. Er3+ transitions from the ground 4I15/2 to the 4I13/2, 4I11/2, 4I9/2, 4F9/2, 4S3/2, 2H11/2, and 4F7/2 excited manifolds were monitored by means of high resolution (as fine as 0.1 cm–1) Fourier Transform spectroscopy in the wave number (6000–22000 cm–1) and temperature (9–300 K) range, respectively. Broad absorption spectra were observed in silica samples simply doped with Er3+, as expected for Er3+ in a glassy environment. In samples containing also SnO2 nanocrystals, complex, narrow line Er3+ related spectra were monitored. The lines become sharper and sharper by lowering the temperature to 9 K, as expected for Er3+ ions embedded in an ordered (crystalline) environment. The nature and origin of different surroundings probed by the Er3+ line spectra are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Vibronic Transitions of Trivalent Er and Ce in BaY2F8 Single Crystals

High resolution (0.02 cm−1) Fourier transform spectroscopy was applied in the 9–300 K and 100–24,000cm−1 ranges, respectively, to detect in Er3☎ and Ce3☎ doped BaY2F8 single crystals (1) the narrow line spectra due to the intraconfigurational 4f→4f transitions of the rare earths (RE) and (2) the possible vibronic tails accompanying the zero-phonon lines. The 2F5/2→2F7/2 transition was monitored for the Ce3☎-doping and the crystal field splitting of the initial and final manifold was determined. Weak vibronic spectra accompanying six among the nine investigated 4f→4f transitions of Er3☎ and the 2F5/2→2F7/2 transition of Ce3☎ were detected. The vibronic spectra amplitude was found to scale with the RE contents. On the basis of the IR- and Raman-active vibrational modes, either measured or quoted in the literature, most of the vibronic lines could be successfully assigned to the lattice modes. Violations of the selection rules were envisaged and discussed.

Archival [ITAL]HST[/ITAL] and [ITAL]IUE[/ITAL] Study of the Dwarf Novae AH Herculis and CM Delphini: Exposed White Dwarfs?

We have analyzed Hubble Space Telescope (HST) archival and IUE NEWSIPS archival SWP spectra of the dwarf novae CM Del and AH Her obtained when AAVSO light-curve data indicated the occurrence of dwarf nova quiescence. We have computed synthetic, high-gravity spectra in LTE with solar composition using TLUSTY195 and SYNSPEC42 and have carried out fits of these models to the far-UV continuum and narrow absorption line spectra. For CM Del, we find that the far-UV spectrum is dominated by a hot (Teff = 22,000 K and log g = 8) white dwarf, but reliable information on the metal abundances is unavailable because of the quality of the data. For AH Her, we find evidence for a hot white dwarf with Teff = 27,000 K and log g = 8, with subsolar abundance for Si. An HST spectrum (GHRS G160M) of AH Her reveals blue-asymmetric Si IV profiles. If this is due to wind outflow, we derive a single-scattering, upper limit, mass-loss rate of 10-9 M⊙ yr-1. Synthetic profile fits to 12 co-added HST medium-resolution G160M spectra of the Si IV (1393, 1402 A) resonance doublet of CM Del yield a white dwarf rotational velocity estimate of v sin i = 400 km s-1 and Si/H = 1 times solar. The value of v sin i for CM Del is discussed in the context of angular momentum transfer and rotation rates for other cataclysmic variable, primary degenerate stars.

Grazing-incidence flat-field spectrometer for high-order harmonic diagnostics

The design and performances of an EUV spectrometer for diagnostics of high-order harmonics generated by an ultrashort (<30 fs) pulsed laser focused onto a gas jet are presented. The system consists of a toroidal mirror, an entrance slit, a spherical variable-line-spaced grating and a bidimensional detector. The mirror focuses astigmatically the radiation from the gas jet, with the tangential focus on the entrance slit. The grating diffracts the radiation coming out from the slit, spectrally focusing the 5 to 40 nm wavelength range in an almost straight focal curve, where the detector is located. The latter is a 40 mm diameter microchannel-plate intensifier. The spatial focal point of the toroidal mirror lies before the spectral focal plane of the spectrometer, so measurement of the height of the spectral lines gives the beam divergence. The spectral resolution of the spectrometer was measured using the narrow line spectra obtained by a microfocus soft x-ray source. Also the absolute response of the system, that is grating efficiency plus detector efficiency, was measured.

The Surface Temperatures of White Dwarf Accretors in Dwarf Novae: The Active Dwarf Nova CN Orionis during Quiescence

ABSTRACTWe have carried out a synthetic spectral analysis of five IUE NEWSIPS archival spectra of the peculiar, very active dwarf nova CN Orionis taken at the system’s lowest flux levels during quiescence. AAVSO data indicate the visual magnitude V∼14 for CN Ori at this time. On the assumption that the white dwarf contributes significantly to the far‐UV light of the system, we have computed a two‐parameter grid of synthetic, high‐gravity spectra in LTE with solar composition using TLUSTY195 and SYNSPEC42 and carried out fits of these pure photospheric models to the far‐UV continuum and narrow absorption line spectra. We find that the far‐UV spectrum in quiescence is well represented by a hot (Teff = 30,000 K, log g = 7) white dwarf with probable subsolar silicon abundance and all other observed metal transitions at essentially their solar values. For comparison, we have fitted optically thick accretion disk models to the same spectra for Mwd = 0.80 M⊙ and disk inclination angle i = 60° for accretion rates M˙ = 10-10.5 and 10−9.5 M⊙ yr−1. We compare the Teff of CN Ori, one of a handful of dwarf novae above the period gap with a model photospheric analysis, to all other dwarf novae with white dwarfs of known Teff derived using white dwarf model atmospheres. We find evidence that the white dwarfs in dwarf novae above the period gap are hotter than the ones below the gap. This trend suggests more heated, younger degenerates above the gap and is consistent with the overall empirical evidence that mass transfer rates in dwarf novae above the period gap are higher than mass transfer rates in systems below the gap.

A Search for “Dwarf'' Seyfert Nuclei. V. Demographics of Nuclear Activity in Nearby Galaxies

We use the sample of emission-line nuclei derived from a recently completed optical spectroscopic survey of nearby galaxies to quantify the incidence of local (z ≈ 0) nuclear activity. Particular attention is paid to obtaining accurate measurements of the emission lines and reliable spectral classifications. The resulting database contains the largest collection of star-forming nuclei and active galactic nuclei (AGNs) currently known for nearby galaxies. It consists of 420 emission-line nuclei detected from a nearly complete, magnitude-limited sample of 486 galaxies with BT ≤ 12.5 mag and declination greater than 0°; the equivalent width detection limit of the brightest emission line, usually Hα, is ~0.25 A. As is consistent with previous studies, we find detectable amounts of ionized gas in the central few hundred parsecs of most galaxies (86%); emission lines are present in essentially every spiral galaxy and in a large fraction of ellipticals and lenticulars. Based on their narrow-line spectra, half of the objects can be classified as H II or star-forming nuclei and the other half as some form of AGN, of which we distinguish three classes: Seyfert nuclei, low-ionization nuclear emission-line regions (LINERs), and transition objects that we assume to be composite LINER/H II-nucleus systems. The population of AGNs is consequently very large; approximately 43% of the galaxies in our survey can be regarded as active, although, for a number of reasons, this fraction is still rather uncertain. Most of the objects have much lower luminosities than commonly studied AGNs; the median luminosity of the narrow Hα line, after correcting for extinction, is only 2 × 1039 ergs s-1. Our sample therefore occupies the extreme faint end of the AGN luminosity function. We detect signatures of a broad-line region, as revealed by visible broad Hα emission, in ~20% of the AGN sample. Seyfert nuclei, both type 1 and type 2, reside in ~10% of all galaxies. LINERs make up the bulk (1/2-3/4) of the AGN population and a significant fraction (1/5-1/3) of all galaxies. A nonnegligible subset of LINERs emit broad Hα emission, furnishing direct evidence that a least some LINERs are indeed physically related to the AGN phenomenon. The dominant ionization mechanism of the nuclear emission depends strongly on the morphological type and luminosity of the host galaxy. AGNs are found predominantly in luminous, early-type (E-Sbc) galaxies, while H II nuclei prefer less luminous, late-type (Sbc and later) systems. The various AGN subclasses have broadly similar host galaxies.

Locally Optimally Emitting Clouds and the Narrow Emission Lines in Seyfert Galaxies

The narrow emission line spectra of active galactic nuclei are not accurately described by simple photoionization models of single clouds. Recent Hubble Space Telescope images of Seyfert 2 galaxies show that these objects are rich with ionization cones, knots, filaments, and strands of ionized gas. Here we extend to the narrow line region the ``locally optimally emitting cloud'' (LOC) model, in which the observed spectra are predominantly determined by powerful selection effects. We present a large grid of photoionization models covering a wide range of physical conditions and show the optimal conditions for producing many of the strongest emission lines. We show that the integrated narrow line spectrum can be predicted by an integration of an ensemble of clouds, and we present these results in the form of diagnostic line ratio diagrams making comparisons with observations. We also predict key diagnostic line ratios as a function of distance from the ionizing source, and compare these to observations. The predicted radial dependence of the [O III]/[O II] ratio may be matched to the observed one in NGC4151, if the narrow line clouds see a more intense continuum than we see. The LOC scenario when coupled with a simple Keplerian gravitational velocity field will quite naturally predict the observed line width versus critical density relationship. The influence of dust within the ionized portion of the clouds is discussed and we show that the more neutral gas is likely to be dusty, although a high ionization dust-free region is most likely present too. This argues for a variety of NLR cloud origins.

The vibronic structure of mixed ligand Os(IV) complexes III: Low temperature absorption spectra in high resolution

Low temperature (2 K) absorption spectra in the region 4800–20 000 cm −1 of hexahalogeno Os(IV) complexes have been recorded, for the near infrared by the use of a vacuum interferometer. The resolution of bands assigned to d–d transitions is remarkably improved to that obtained earlier from these and similar complexes which supply narrow line spectra. The compounds investigated are Cs- and tetrabutylammonium (TBA) salts of OsCl 2− 6, Cs 2OsBr 6 and the mixed halogen complexes Cs 2[OsCl 5Br], Cs 2[OsCl 4Br 2] ( cis and trans), Cs 2[OsBr 4Cl 2] ( cis) and Cs 2[OsBr 5Cl]. Peak assignments to zero-phonon transitions (electronic origins) and vibrational side bands, the latter in general having higher intensity, show that selection rules valid for octahedral coordination largely hold as well for complexes of definitely lower symmetry. This is also true for vibronic transitions promoted by vibrational modes which are resultants from the corresponding parent compounds, i.e. from ν 3( t 1u), ν 4( t 1u) and ν 6( t 2u) of octahedral symmetry. Apparently localization of d-electrons on the metal overrules the requirements imposed by molecular symmetry. The compounds are synthesized following a prescription in the literature, with an improvement of the separation procedure for avoiding contaminations with compounds of other halogen ligand composition.

The HST Sample of Radio-Loud Quasars: Fe II and Other Correlations

We are analyzing the emission lines and continuum spectra of a sample of ~61 radio-loud quasars to investigate dependences amongst various spectral, radio, and X-ray parameters, in particular to look for dependences of spectral properties on inclination of the the radio-jet axis (Wills et al. 1997).We have carried out conventional correlation analyses, as well as spectral principal-component analyses (SPCA) as described in the previous paper (Wills et al. 1997). We found that the single largest contribution to the spectrum-tospectrum variations was from a component — the ‘first principal component’ (PC1) — that has a more UV (or less red) continuum than the mean spectrum, and a weaker narrow-line (NLR) spectrum. The ‘second principal component’ (PC2) accounts for only 8–12% of the spectrum-to-spectrum variation, contributing a weaker UV, and stronger red continuum, and showing stronger narrow emission lines. There is also a tendency for the broad (BLR) lines in the second principal component spectrum to be narrower (note the sharper He II λ1640 and [O III] λ1663 features redward of the stronger C IV λ1549 emission line, and perhaps a narrow component of the N V λ1240 line redward of Lyα).

The Ultraviolet Spectrum of the Liner NGC 4579

view Abstract Citations (46) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Ultraviolet Spectrum of the Liner NGC 4579 Barth, A. J. ; Reichert, G. A. ; Filippenko, A. V. ; Ho, L. C. ; Shields, J. C. ; Mushotzky, R. F. ; Puchnarewicz, E. M. Abstract We present a Hubble Space Telescope ultraviolet spectrum of the LINER nucleus of NGC 4579, spanning the wavelength range 1160-3270 A. The data reveal a low-excitation spectrum of narrow (FWHM ~1200 km s^-1^) and broad (FWHM ~ 6600 km s^-1^) emission lines, which provide new diagnostics of the physical conditions within the emission-line regions. A featureless ultraviolet continuum is detected unambiguously, with fnu) is proportional to ν^-1.0^ over the range 1300-2200 A and ν^-2.4^ over 2200-3000 A. The 2200 A continuum flux is a factor of 3.3 lower than the value reported by Maoz et al. (1995) based on an HST image taken 19 months earlier; this is the first time that UV variability has been discovered in a LINER. The predictions of fast shock models are incompatible with the narrow-line spectrum, because the high-excitation lines produced in fast shocks are weak or absent in NGC 4579. Models of a single slab of gas photoionized by a power-law spectrum do not reproduce the observed line ratios well either, and it appears that the narrow-line region cannot be characterized by a unique value of the ionization parameter. We argue that the narrow-line region is photoionized by the central UV/X-ray source, and that more sophisticated photoionization calculations, incorporating the effects of density and/or ionization stratification and different continuum shapes, can yield results in better agreement with the data. Publication: The Astronomical Journal Pub Date: November 1996 DOI: 10.1086/118145 Bibcode: 1996AJ....112.1829B Keywords: GALAXIES: INDIVIDUAL: NGC 4579; GALAXIES: ACTIVE; GALAXIES: NUCLEI full text sources ADS | data products SIMBAD (5) NED (1) MAST (1) ESA (1)

Progress with optical gas sensors using correlation spectroscopy

The paper reviews recent progress on gas detection using real-time correlation spectroscopy. The general method relies on using a gas sample in a reference cell as a matched optical filter to detect, preferentially, similar absorption spectra in a measurement cell. All variations of the method have the advantage of excellent selectivity for gases with narrow line spectra, even when using broadband sources for illumination. They are also suitable for remote detection over optical-fibre leads. The recent progress is in two main areas. First, the earlier reported Stark modulation method has been extended to investigate a novel hygrometer. Secondly, we have developed a novel multi-line light source by combining a broadband optical source with a Michelson interferometer, where the latter contains a gas in one arm.

Narrow-line spectra of fullerene molecules in a crystalline matrix

The new allotropic form of carbon, the fullerenes, which possess unusual physical properties and are promising for various practical applications, have received much attention in recent years. Revealing the energy structure of fullerenes is one of the pressing problems of the physics of these novel materials. Rich information on their electronic and vibrational states could be obtained from optical spectra. However, until recently only wide-band absorption and emission spectra of fullerenes were observed in both solutions and the crystalline state (in fullerites), which did not allow full advantage of to be taken optical spectroscopy. The possibility of producing narrow-line spectra of fullerene C{sub 70} molecules in solid solutions of organic crystals at low temperatures was established. The present paper contains more detailed information on these spectra. In addition, observation of the narrow-line spectrum of the fullerene C{sub 60} molecule is reported for the first time. First the authors consider C{sub 70} spectra.