Spectral Peculiarities Research Articles

The peculiar optical-UV X-ray spectra of the X-ray weak quasar PG 0043+039

The object PG 0043+039 has been identified as a broad absorption line (BAL) quasar based on its UV spectra. However, this optical luminous quasar has not been detected before in deep X-ray observations, making it the most extreme X-ray weak quasar known today. This study aims to detect PG 0043+039 in a deep X-ray exposure. The question is what causes the extreme X-ray weakness of PG 0043+039? Does PG 0043+039 show other spectral or continuum peculiarities? We took simultaneous deep X-ray spectra with XMM-Newton, far-ultraviolet (FUV) spectra with the Hubble Space Telescope (HST) and optical spectra of PG 0043+039 with the Hobby-Eberly Telescope (HET) and Southern African Large Telescope (SALT) in July, 2013. We have detected PG 0043+039 in our X-ray exposure taken in 2013. We presented our first results in a separate paper (Kollatschny et al. 2015). PG 0043+039 shows an extreme {\alpha}_ox gradient ({\alpha}_ox =-2.37). Furthermore, we were able to verify an X-ray flux of this source in a reanalysis of the X-ray data taken in 2005. At that time, it was fainter by a factor of 3.8 +- 0.9 with {\alpha}_ox=-2.55. The X-ray spectrum is compatible with a normal quasar power-law spectrum ({\Gamma}=1.70_-0.45^+0.57) with moderate intrinsic absorption (N_H=5.5_-3.9^+6.9 +- 10^21cm^-2) and reflection. The UV/optical flux of PG 0043+039 has increased by a factor of 1.8 compared to spectra taken in the years 1990-1991. The FUV spectrum is highly peculiar and dominated by broad bumps besides Ly{\alpha}. There is no detectable Lyman edge associated with the BAL absorbing gas seen in the CIV line. PG 0043+039 shows a maximum in the overall continuum flux at around {\lambda} 2500{\AA} in contrast to most other AGN where the maximum is found at shorter wavelengths. All the above is compatible with an intrinsically X-ray weak quasar, rather than an absorbed X-ray emission.

InAsSbP/InAs0.9Sb0.1/InAs DH photodiodes (λ0.1 = 5.2 μm, 300 K) operating in the 77–353 К temperature range

Double heterostructure back-side illuminated photodiodes with a 10-μm thick InAs0.9Sb0.1 active layer have been fabricated, studied and characterized in the 77–353K temperature range. Spectral response peculiarities and temperature induced peak shift (λ=4–4.8μm) were explained within simple phenomenological model based on proximity of the active layer thickness and hole diffusion length while reasons for a sensitivity decrease at low temperatures are still less evident. Transition from a generation-recombination to a diffusion current flow mechanisms with temperature increase appeared to be close to that for the InAs based diodes.

THERMAL ABSORPTION AS THE CAUSE OF GIGAHERTZ-PEAKED SPECTRA IN PULSARS AND MAGNETARS

We present a model that explains the observed deviation of the spectra of some pulsars and magnetars from the power-law spectra which are seen in the bulk of the pulsar population. Our model is based on the assumption that the observed variety of pulsar spectra can be naturally explained by the thermal free-free absorption that takes place in the surroundings of the pulsars. In this context, the variety of the pulsar spectra can be explained according to the shape, density and temperature of the absorbing media and the optical path of the line-of-sight across that. We have put specific emphasis on the case of the radio magnetar SGR J1745-2900 (also known as Sgr A* magnetar), modeling the rapid variations of the pulsar spectrum after the outburst of Apr 2013 as due to the free-free absorption of the radio emission in the electron material ejected during the magnetar outburst. The ejecta expands with time and consequently the absorption rate decreases and the shape of the spectrum changes in such a way that the peak frequency shifts towards the lower radio frequencies. In the hypothesis of an absorbing medium, we also discuss the similarity between the spectral behaviour of the binary pulsar B1259-63 and the spectral peculiarities of isolated pulsars.

Superattraction mediated by quantum fluctuations of plasmon quasi-continuum.

We investigate the force between a plasmonic nanoparticle and a highly excited two-level system (molecule). Usually van der Waals' force between nanoscale electrically neutral systems is monotonic and attractive at moderate and larger distances and repulsive at small distances. In our system, the van der Waals' force acting on a molecule has a quantum-optical nature. At moderate distances it is attractive as usual but its strength highly increases in narrow distance ranges (lacunas). We show that quantum fluctuations of quasi-continuum of multipole plasmons of high, nearly infinite degree, altogether form an effective environment and determine the interaction force while their spectral peculiarities stand behind the large and narrow lacunas in force. We exactly solve the Hamiltonian problem and discuss the role of the dissipation.

Spectral and kinetic peculiarities of the radiation trapping effect in doped materials

The results of detailed study of the radiation trapping effect in doped materials are presented. A special excitation and detection scheme is developed that allows in fluorescent signals significantly distinguish the contributions from the regions of the crystal excited directly by the laser radiation and excited by radiation transfer of the excitation in the non-irradiated part of the sample. This technique was used to investigate the radiation trapping phenomenon in infrared spectral region around 1.6μm for YAG:Er3+ crystal excited by continuous and pulsed laser radiations at 970nm wavelength. Spectral redistributions in fluorescent bands of the crystal under study were registered due to presence of the radiation trapping effect. The strong dependence of the luminescence decay times on geometry of both excitation and registration is revealed for the material under study. Within the framework of existing models of radiation trapping effect in doped solids, an analysis of the obtained results is carried out.

Luminescent Properties of Nanocomposites on the Basis of Isotactic Polypropylene and Zirconium Dioxide Nanoparticles

At the paper studied luminescent properties of nanocomposites on the basis isotactic polypropylene and zirconium dioxide nanoparticles. Shown that change of nanocomposite colour and maximum amplitude of UV spectres depend on ZrO2 nanoparticles sizes in polypropylene. Found that mean-square roughness of PP +1% ZrO2 composition surface in dependence of cooling rate β changes, i.e. for the samples at regime β1=20 deg/min the roughness is 40-60 nm, whereas for the samples prepared at β2=2 deg/min the roughness is 150-220 nm. Shown that polypropylene matrix works as chemically stable preservative of nanoparticles, preserving its spectral peculiarities. Sufficiently strong interphases interactions between PP matrix and ZrO2 nanoparticles change its luminescent properties.

AN EXPERT COMPUTER PROGRAM FOR CLASSIFYING STARS ON THE MK SPECTRAL CLASSIFICATION SYSTEM

This paper describes an expert computer program (MKCLASS) designed to classify stellar spectra on the MK Spectral Classification system in a way similar to humans—by direct comparison with the MK classification standards. Like an expert human classifier, the program first comes up with a rough spectral type, and then refines that spectral type by direct comparison with MK standards drawn from a standards library. A number of spectral peculiarities, including barium stars, Ap and Am stars, λ Bootis stars, carbon-rich giants, etc., can be detected and classified by the program. The program also evaluates the quality of the delivered spectral type. The program currently is capable of classifying spectra in the violet-green region in either the rectified or flux-calibrated format, although the accuracy of the flux calibration is not important. We report on tests of MKCLASS on spectra classified by human classifiers; those tests suggest that over the entire HR diagram, MKCLASS will classify in the temperature dimension with a precision of 0.6 spectral subclass, and in the luminosity dimension with a precision of about one half of a luminosity class. These results compare well with human classifiers.

Composite spectra XIX: HD 208253, a long‐period binary whose hot secondary has enhanced strontium and barium

AbstractWe separate and analyse the component spectra of the composite‐spectrum binary HD 208253. We find that the cool primary is an evolving star of spectral type G7 III, while its hot secondary is an early‐A dwarf. The giant is currently near the lowest point of the red‐giant branch and is slightly less luminous than its dwarf companion. We provide a set of precise radial‐velocity measurements for both stars. The double‐lined orbit which we derive from them shows that the component mass ratio is close to unity (q = 1.05 ± 0.01). We deduce the physical properties of both stars, determine their respective masses to be 2.75 ± 0.07 Me (giant) and 2.62 ± 0.07 Me (dwarf), and show that the orbit's inclination is within a degree or two of 68°. The spectrum of the A‐type component has quite component has quite narrow lines (we infer a rotational velocity of 18 km s–1), though since the period of the orbit is well over 1 year that component cannot be in synchronous rotation. An intriguing property of the dwarf is its enhanced Sr and Ba, though it does not exhibit the other spectral peculiarities that would signal a classical Am star. While by no means unique amongst the multitude of oddities exhibited by A and early‐F stars, this dwarf which we have uncovered in a long‐period binary offers valuable constraints and challenges to stellar‐evolution theory. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Scanning-tunneling microscopy/spectroscopy and break-junction tunneling spectroscopy of FeSe1–xTex

The iron-chalcogenide superconductor FeSe1–xTex (0.5 < x < 1) was investigated by scanning-tunneling microscopy/spectroscopy (STM/STS) and break-junction techniques. In the STM topography of the samples, randomly distributed Te and Se surface atomic structure patterns correlate well with the bulk composition, demonstrating that nanoscale surface features directly reflect bulk properties. The high-bias STS measurements clarified the gap-like structure at ≈100–300 meV, which is consistent with the break-junction data. These high-energy structures were also found in sulfur substituted FeSe0.1Te0.9. Possible origin of such spectral peculiarities is discussed. The superconducting gap 2Δ ≈ 3.4 ± 0.2 meV at temperature T = 4.2 K was found in the break junction of FeSe1–xTex with the critical temperature Tc ≈ 10 K. The corresponding characteristic gap to Tc ratio 2Δ/kBTc ≈ 4 ± 0.2 indicates moderate superconducting coupling (kB is the Boltzmann constant).

Displacement Spectra Under Isometric Muscle Contraction

The purposes of this work were to detect the microscopic displacements accompanying isometric muscle tissue contraction under different external loads, to explore their spectral characteristics, and to develop physical models capable of explaining the experimental data obtained. By means of a spectral Doppler musculoskeletal ultrasound method, spectral characteristics of local isometric skeletal muscle tissue contraction were studied. In this method, the phased fluctuation (Doppler) algorithm is used to estimate tissue displacements within the given sample volume in real time, and the spectral characteristics of recorded displacements are determined. Observation of local isometric muscle contraction was conducted in the brachioradial muscle of the flexor digitorum profundus. Data obtained from 6 healthy volunteers during observation of muscle contraction in a relaxed state and under different static loads (2, 5, and 10 kg) were processed. The main difference in recorded displacements under different loads was in the displacement fluctuation values, whereas spectral characteristics were almost constant. Differences in the numbers and values of spectral maxima were also observed. These results are explained by a developed physical model assuming that the mechanochemical characteristics of crossbridges between actin and myosin filaments are the main factors influencing the spectral peculiarities of the Doppler response. Both the developed model of the Doppler response and the proposed dynamic model of sarcomere movement establish a link between macroscopic Doppler measurements and the biomechanical processes and behavior of sarcomeres at a subcellular level. The results of these pilot experiments demonstrate the suitability of this spectral Doppler method for a more detailed spectral study of biomechanical processes that occur under muscle contraction. The stability of the spectral characteristics under different loads also testifies to the value of this method as a reliable and valid diagnostic tool for diagnosing neuromuscular disorders.

The manifestation of Coulomb gap in photoluminescence of GaAs/AlGaAs quantum wells with positively charged acceptors

We report results of photoluminescence and photoexcitation studies carried out on GaAs/AlGaAs quantum well structures with positively charged acceptors. We explain the observed spectral peculiarities by an appearance of the Coulomb gap. Another evidence of the Coulomb gap is an anomalously large Stocks shift which has been observed in our experiments.

QU Carinae: Type Ia supernova in the making?

Variable NaI absorption lines have been reported in a number of type Ia supernovae (SNeIa). The presence of this circumstellar material suggests that cataclysmic variables (CVs) with a giant donor star may be the progenitors of these SNeIa (Patat et al. 2007). We present echelle spectra of the CV QU Carinae which strengthen the connection between CVs of the V Sge class, the Accretion Wind Evolution scenario, variable wind features, variable NaI absorption, and SNIa. This thread not only provides insight into the spectral peculiarities of QU Car, but also links SNeIa as a class with their parent systems.

Near-infrared observations of Type Ia supernovae: the best known standard candle for cosmology

We present an analysis of the Hubble diagram for 12 normal Type Ia supernovae (SNe Ia) observed in the near-infrared (NIR) J and H bands. We select SNe exclusively from the redshift range 0.03 < z < 0.09 to reduce uncertainties coming from peculiar velocities while remaining in a cosmologically well-understood region. All of the SNe in our sample exhibit no spectral or B-band light-curve peculiarities and lie in the B-band stretch range of 0.8–1.15. Our results suggest that SNe Ia observed in the NIR are the best known standard candles. We fit previously determined NIR light-curve templates to new high-precision data to derive peak magnitudes and to determine the scatter about the Hubble line. Photometry of the 12 SNe is presented in the natural system. Using a standard cosmology of (H0, Ωm, ΩΛ) = (70, 0.27, 0.73), we find a median J-band absolute magnitude of MJ = −18.39 with a scatter of σJ = 0.116 and a median H-band absolute magnitude of MH = −18.36 with a scatter of σH = 0.085. The scatter in the H band is the smallest yet measured. We search for correlations between residuals in the J- and H-band Hubble diagrams and SN properties, such as SN colour, B-band stretch and the projected distance from the centre of the host galaxy. The only significant correlation is between the J-band Hubble residual and the J − H pseudo-colour. We also examine how the scatter changes when fewer points in the NIR are used to constrain the light curve. With a single point in the H band taken anywhere from 10 d before to 15 d after B-band maximum light and a prior on the date of H-band maximum set from the date of B-band maximum, we find that we can measure distances to an accuracy of 6 per cent. The precision of SNe Ia in the NIR provides new opportunities for precision measurements of both the expansion history of the universe and peculiar velocities of nearby galaxies.

Investigation of the vertical distribution of tropospheric aerosol layers using the data of multiwavelength lidar sensing. Part 3. Spectral peculiarities of the vertical distribution of the aerosol optical characteristics

The spectral peculiarities of the distributions of the backscattering βa(λi, z) and extinction σa(λi, z) coefficients, as well as lidar ratio Sa(λi, z) estimated from the data of multi-wavelength sensing in Tomsk (56° N, 85° E) in the height range from 0.5 to 7.5 km are presented here. Based on observations since April till October 2007 it is shown that in the boundary layer (except of the internal mixing layer) ηβ(532/1064) > ηβ(355/532), and, simultaneously, ησ(532/1064) > ησ(355/532), where ηi are the values of the Agstrom parameter for the respective coefficients. Such a distribution of the Agstrom parameters is caused by prevalence of small particles with mean geometric radius Rf 0.15 μm, and the contribution of large particles is governing. In the boundary layer, the lidar ratio decreases with increasing wavelength; the average values are 59.7 (15) sr at 355 nm, 51.1 (8.3) sr at 532 nm, and 47.3 (13.5) sr at 1064 nm. In the free troposphere, the wavelength behavior of the lidar ratio can be different; the average values are 50.4 (8.5) sr at 355 nm, 49.5 (5.7) sr at 532 nm, and 55.3 (10) sr at 1064 nm. The aerosol contribution of the free troposphere to the total aerosol optical depth grows with decreasing boundary layer height; on average, it is 22 (17)% at 355 nm, 27 (19)% at 532 nm, and 34 (22)% at 1064 nm.

High-latitude supergiants: Anomalies in the spectrum of LN Hya in 2010

High-spectral-resolution observations with the Special Astrophysical Observatory 6-m telescope obtained in 2003–2011 are used to study features of the optical spectrum and the velocity field in the atmosphere of the semiregular variable LN Hya in detail. The weak, symmetric, photospheric absorption lines indicate radial-velocity variations from night to night (by as much as 3 km/s), resulting from small pulsations. Peculiarities and profile variations were found for strong lines of FeI, FeII, BaII, SiII, etc. The profiles of these lines were asymmetric: their short-wavelength wings were extended and their cores were either split or distorted by emission. During the 2010 observing season, the position and depth of the Hα absorption component, the intensities of the short- and long-wavelength emission components, and the intensity ratio of the latter components varied from spectrum to spectrum. Weak emission lines of neutral atoms (VI, MnI, CoI, NiI, FeI) appeared in the spectrum of June 1, 2010. These spectral peculiarities, recorded for the first time, suggest that we have detected rapid changes in the physical conditions in the upper atmospheric layers of LN Hya in 2010.

Spectral peculiarities of high energy X-ray radiation, gamma radiation, and Submillimeter radio emission in the impulsive phase of a solar flare

We analyze experimental data on the temporal behavior of fluxes and energy spectra of hard solar X-ray and gamma radiation in the energy range of 0.015 to 300 MeV, obtained onboard the CORONAS-F satellite during a solar flare on August 25, 2001. These data are compared with measurements of the radio emission fluxes over the wide frequency range of 1–405 GHz. For our analysis, we use data obtained onboard the YOHKOH, TRACE and GOES satellites, along with ground-based observations of this solar event using the Solar Submillimeter Telescope (SST; Argentina). For the first time, we find nearly simultaneous changes in the energy spectra of gamma radiation over the range 10–150 MeV and the frequency spectrum of radio emission at the beginning and during a impulsive phase of this event (whose duration did not exceed three minutes).

Magnetostatic structures in collisionless plasma and their synchrotron radiation

The properties of the magnetostatic structures in a collisionless relativistic plasma found by exactly solving the nonlinear self-consistent kinetic and Maxwell equations using the method of invariants of particle motion are analyzed. These structures include individual neutral current sheets and cylindrically symmetric filaments as well as their ensembles, admitting a wide variety of types of particle energy distribution functions. Relationships are established between the possible parameters of the current sheets and filaments—their sizes, currents and magnetic fields, and the degree of anisotropy of the particle momentum distribution. The extent to which these parameters are conditioned by the properties of the Weibel instability that can produce these structure is also discussed. The spectral peculiarities of the synchrotron radiation from the particles that form the current sheets and filaments are investigated in the special case of power-law energy distribution functions.

Spectral variability of the peculiar A-type supergiant 3Pup

Optical spectra taken in 1997–2008 are used to analyze the spectral peculiarities and velocity field in the atmosphere of the peculiar supergiant 3 Pup. The profiles of strong Fe II lines and of the lines of other iron-group ions have a specific shape: the wings are raised by emissions, whereas the core is sharpened by a depression. The latter feature becomes more pronounced with the increasing line strength, and the increasing wavelength. Line profiles are variable: the magnitude and sign of the absorption asymmetry, and the blue-to-red emission intensity ratios vary from one spectrum to another. The temporal Vr variations are minimal for the forbidden emissions and sharp shell cores of the absorption features of FeII(42), and other strong lines of iron-group ions. The average velocity for the above lines can be adopted as the systemic velocity: Vsys = 28.5 ± 0.5 km/s. The weakest photospheric absorptions and photospheric MgII, Si II absorptions exhibit well-defined day-to-day velocity variations of up to 7 km/s. Quantitative spectral classification yields the spectral type of A2.7±0.3 Ib. The equivalent widths and profiles of Hδ and Hγ, and the equivalent width of the OI 7774 Å triplet yield an absolute magnitude estimate of Mv=−5.5m ± 0.3m, implying the heliocentric distance of 0.7 kpc.

The role of continuum radiation in laser induced plasma spectroscopy

This paper focuses on the interpretation of the origin of the continuum radiation in Laser Induced Plasma (LIP) emission spectra, a subject that has received little consideration in the literature when compared to the analysis of the line emission spectrum. The understanding of the spectral peculiarities observed immediately after the laser pulse, when the continuum radiation prevails on discrete emission lines, can be extremely important to retrieve the initial conditions of LIP and to correlate the produced plasma to the ablation mechanism. In this work, in addition to a qualitative interpretation of the LIP continuum in the initial stage of expansion, a methodology is proposed for a better measurement of the atomic temperature in the expansion stage of the LIP. Such methodology is based on the analysis of the combined Boltzmann and Planck plots. The results obtained stress once again the importance of considering non equilibrium effects in the initial stage of LIP expansion.

Angular and spectral peculiarities of the coherent thermal radiation of the magneto-optical Fabry–Perot resonator in a magnetic field

The influence of magnetic field on the angular and spectral dependences of the coherent thermal radiation of the magneto-optical Fabry–Perot resonators is investigated theoretically and experimentally. The matrix method of multi-beam summation, considering the Faraday rotation, is used to calculate the magneto-optical Fabry–Perot resonator emissivity. It is shown that in conditions of optical resonance the Faraday rotation results in transformation of the spectrum and the directional diagram of coherent thermal radiation. The results of calculations show good agreement with experimental data. The results obtained may be applied for monitoring the parameters of a semitransparent plane-parallel layer and structures, and for developing new magneto-optical devices and controllable sources of infrared radiation.