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A new generation of solar instruments provides improved spectral, spatial, and temporal resolution, thus facilitating a better understanding of dynamic processes on the Sun. High-resolution observations often reveal multiple-component spectral line profiles, e.g., in the near-infrared He i 10830 Å triplet, which provides information about the chromospheric velocity and magnetic fine structure. We observed an emerging flux region, including two small pores and an arch filament system, on 2015 April 17 with the ‘very fast spectroscopic mode’ of the GREGOR Infrared Spectrograph (GRIS) situated at the 1.5-meter GREGOR solar telescope at Observatorio del Teide, Tenerife, Spain. We discuss this method of obtaining fast (one per minute) spectral scans of the solar surface and its potential to follow dynamic processes on the Sun. We demonstrate the performance of the ‘very fast spectroscopic mode’ by tracking chromospheric high-velocity features in the arch filament system.
We have studied interferometric imaging in the multi-speckle mode by computer simulations. From various simulated data sets diffraction-limited images were reconstructed by the speckle masking method and the iterative building block method. The reconstructed images show the dependence of the signal-to-noise ratio on photon noise.
CIT 3 is an oxygen-rich long-period variable evolving along the Asymptotic Giant Branch and is one of the most extreme infrared AGB objects. Due to substantial mass loss it is surrounded by an optically thick dust shell which absorbs almost all visible light radiated by the star and finally re-emits it in the infrared regime. We present the first near infrared bispectrum speckle-interferometry observations of CIT 3 in the J-, H-, and K′-band (resolution: 48 mas, 56 mas, and 73 mas). The interferograms were obtained with the Russian SAO 6 m telescope. While CIT 3 appears almost spherically symmetric in the H- and K′-band it is clearly elongated in the J-band along a symmetry axis of position angle −28°. Two structures can be identified: a compact elliptical core (eccentricity ~0.8) and a fainter north-western fan-like structure (full opening angle ~ 40°). The development of such asphericities close to the central star suggests that CIT 3 is in the very end of its AGB evolution or even in transition to the proto-planetary nebula phase where most objects are observed in axisymmetric geometry.
The carbon star IRC +10 216 is a long-period Asymptotic Giant Branch (AGB) star suffering from strong stellar winds (several 10-5 M⊙/yr; Loup et al. 1993) which have led to an almost complete obscuration of the star by dust. Due to the high mass-loss rate, long period of P = 649 d (Le Bertre 1992), and carbon-rich chemistry of the dust-shell, IRC +10 216 is obviously in a very advanced stage of its AGB evolution. High-resolution near-infrared imaging of IRC +10 216 has revealed that on sub-arcsecond scales (100 mas) its dust shell is clumpy, bipolar, and changing on a time scale of only ~1 yr (Weigelt et al. 1997, 1998, Haniff & Buscher 1998, Osterbart et al. 2000, Tuthill et al. 2000). Since most dust shells around AGB stars are known to be spherically symmetric, whereas most proto-planetary nebulae (PPN) show an axisymmetric geometry (Olofsson 1996), it appears likely that IRC +10 216 has already entered the transition phase to the PPN stage. This suggests that the break of the dust-shell symmetry between the AGB and post-AGB phase already takes place at the end of the AGB evolution.
We present the first speckle interferometric observations of R CrB, the prototype of a class of peculiar stars which undergo irregular declines in their visible light curves. The observations were carried out with the 6 m telescope at the Special Astrophysical Observatory near maximum light (V = 7, 1996 Oct. 1) and at minimum light (V = 10.61, 1999 Sep. 28). A spatial resolution of 75 mas was achieved in the K-band. The dust shell around R CrB is partially resolved, and the visibility is approximately 0.8 at a spatial frequency of 10 cycles/arcsec. The two-dimensional power spectra obtained at both epochs do not show any significant deviation from circular symmetry. The visibility function and spectral energy distribution obtained near maximum light can be simultaneously fitted with a model consisting of the central star and an optically thin dust shell with density proportional to r−2 and amorphous carbon as its constituent. The inner boundary of the shell is found to be 82 R* (19 mas) with a temperature of 920 K near maximum light. However, this simple model fails to simultaneously reproduce the visibility and spectral energy distribution obtained at minimum light. We show that this discrepancy can be attributed to thermal emission from a newly formed optically thick dust cloud. Simultaneous fits of the observed SED and visibility with models including a thermally emitting dust cloud suggest the presence of a newly formed dust cloud as hot as 1200 K with a radius of 4 – 5R*, in addition to an optically thin dust shell whose inner boundary is ~ 170 R* with a temperature of ~ 690 K. Alternatively the discrepancy can be attributed to an unusual extinction curve of dust grains in the obscuring cloud which was present in front of the star at minimum light. The details of the observations and modeling are described in Ohnaka et al. (2001, A&A 380, 212).
The prototypical dust-enshrouded carbon Mira IRC +10216 is known to exhibit intrinsic changes on a time scale of the order of only a few years as revealed, e.g., by CO infrared line profiles (Winters et al. 2000a), its infrared light curves, and by high spatial resolution monitoring in the infrared (Osterbart et al. 2000; Tuthill et al. 2000). In particular, the infrared light curves indicate a possible periodicity on a ≈ 20 yr time scale, i.e. that a recurrent phenomenon might lead to the observed variations. Such multi-periodicity time scales of several (≈ 10) stellar pulsation periods are predicted by consistent hydrodynamical models which include a proper treatment of dust formation (e.g. Winters et al. 2000b). In these models discrete dust layers form in time intervals which are several times longer than the typical pulsation period of an AGB star (Fleischer, Gauger, & Sedlmayr 1995; Höfner, Feuchtinger, & Dorfi 1995).
We present speckle masking observations of Seyfert galaxies with the Russian 6 m telescope. Diffraction-limited resolution of 76 mas in the K-band was obtained for the first time. This resolution is similar to the resolution of recent MERLIN and VLA observations of galactic centers, thus allowing us to study the radio-IR spectrum of the same structures. Figure 1 shows the decreasing K-band visibility function of NGC 1068 and the contour plot of our reconstructed image. The results show that NGC 1068 is resolved with a FWHM diameter of 30 mas or 2 pc for an assumed Gaussian flux distribution. The image is elongated in northern direction, which is approximately the direction of the radio jet. In the right panel of figure 1 the observed flux values at 5,15 and 22 GHz (from) are plotted together with our K-band flux. The spectral index between 5 GHz and the K-band is approximately 1/3. This spectrum can be explained by synchrotron emission of quasi-monoenergetic relativistic electrons (as for our Galactic Center by). Assuming that the observed flux is mainly nuclear light (from, for example, scattering lobes above and below a torus, without absorption and re-emission) we use the same synchrotron model as has been used for the Galactic Center to explain our data. With this model, we find a source radius of R ∼ 1015 cm, a magnetic field of B ∼ 11 G, a electron number density of ne ∼ 1.1103 cm−3 and a mean electron energy of ∼ 2.7 GeV. The corresponding model spectrum is shown in the right panel of fig. 1. The observed flux value at 2.2 μm lies slightly above the model spectrum. This could be caused by flux contributions from additional components, for example, a central stellar cluster, an accretion disk or thermal radiation from a dusty torus. We have also observed the central regions of other galaxies. For example, for NGC 4151, we found a dominant central core, which is not resolved, and therefore has a diameter of < 20 mas.
We present high-resolution J–, H–, and K–band observations of the carbon star IRC+10 216. The images were reconstructed from 6 m telescope speckle interferograms using the speckle masking bispectrum method. The H image has the unprecedented resolution of 70 mas. The H and K images consist of at least five dominant components within a 0.21 arcsec radius and a fainter asymmetric nebula. The J-, H-, and K—band images seem to have an X-shaped bipolar structure. A comparison of our images from 1995, 1996, 1997, and 1998 shows that the separation of the two brightest components A and B increased from ∼ 193 mas in 1995 to ∼ 246 mas in 1998.
The cometary shapes of component A in the H and J images and the 0.79 μm and 1.06 μm HST images suggest that the core of A is not the central star, but the southern (nearer) lobe of the bipolar structure. The position of the central star is probably at or near the position of component B, where the H—K color has its largest value of H—K = 4.2.
If the star is located at or near B, then the components A, C, and D are located close to the inner boundary of the dust shell at separations of ∼200 mas ∼30 AU (projected distance) ∼6 stellar radii for a distance of ∼ 150 pc, in agreement with our 2-dimensional radiative transfer modelling.
In addition to IRC+ 10 216 we studied the stellar disks and the dust shells of several related objects. Angular resolutions of 24 mas at 700 nm or 57 mas 1.6 μm were achieved.
We analysed calibrated Stokes V magnetograms and simultaneously measured Stokes I spectra of high spatial and spectral resolution taken in a medium sized sunspot. We found a clear (anti-) correlation between the brightness variation of penumbral structures and the longitudinal component (B*cosγ) of the magnetic field. No azimuthal variation of the amount of the magnetic field strength (B) was observed across dark and bright structures. There the field is more vertical in bright filaments compared to dark ones.
The infrared-optical properties of GaAs/GaNxAs1−x superlattice (SL) heterostructures (0 < x < 3.3%) are studied by variable angle-of-incidence infrared spectroscopic ellipsometry (IRSE) for wavenumbers from 250 cm−1 to 700 cm−1. The undoped SL structures where grown on top of a 300 nm thick undoped GaAs buffer layer on Te-doped (001) GaAs substrates by metal-organic vapor phase epitaxy (MOVPE). We observe the well-known Berreman-polariton effect within the GaAs LO-phonon region. We further observe a strong polariton-like resonance near the coupled longitudinal-optical plasmon-phonon frequency of the Te-doped substrate at 306 cm−1. For analysis of the IRSE data we employ the harmonic oscillator dielectric function model and the Drude model for free-carrier response. The additional resonance feature is explained by pseudo surface polariton (PSP) interface modes between the Te-doped GaAs and the undoped GaAs buffer layer / SL film. We find that the PSP modes are extremely sensitive to free-carrier properties within the SL structures, and we obtain a strong increase in free-carrier concentration within the GaNAs SL sublayers with increasing x from analysis of the IRSE data. We further observe the localized vibrational modes of nitrogen at 470 cm−1 in the GaNxAs1−x SL sublayers with a polar strength that increases linearly with x, and which can be used to monitor the nitrogen concentration in GaNxAs1−x.
We report on mid-infrared (600 – 4000 cm-1), refection-type optical-Hall effect measurements on epitaxial graphene grown on C-face silicon carbide and present Landau-level transition features detected at 1.5 K as a function of magnetic field up to 8 Tesla. The Landau-level transitions are detected in reflection configuration at oblique incidence for wavenumbers below, across and above the silicon carbide reststrahlen range. Small Landau-level transition features are enhanced across the silicon carbide reststrahlen range due to surface-guided wave coupling with the electronic Landau-level transitions in the graphene layer. We analyze the spectral and magnetic-field dependencies of the coupled resonances, and compare our findings with previously reported Landau-level transitions measured in transmission configuration [4,5,6]. Additional features resemble transitions previously assigned to bilayer inclusion , as well as graphite . We discuss a model description to account for the electromagnetic polarizability of the graphene layers, and which is sufficient for quantitative model calculation of the optical-Hall effect data.
A modified critical point model dielectric function for graphene is derived here and used to analyze spectroscopic ellipsometry data obtained over a wide spectral range from 3 to 9 eV. Critical point and exciton resonance energies are extracted and discussed. Our findings indicate that epitaxial graphene on SiC to exhibits equivalent exciton behavior to that of suspended graphene. We further apply our model dielectric function to evaluate dielectric function data for highly oriented pyrolytic graphite reported in the literature. Excellent agreement is found between the critical point model developed here and the literature data even for the low energy spectral range up to 1 eV.
We demonstrate that the anisotropic optical response of metal (cobalt) slanted columnar thin films (STF) at THz frequencies strongly depends on the dielectric properties of the dielectric ambient surrounding the slanted columnar thin films. An effective medium dielectric function approach is used to describe the combined optical response of metal slanted columnar thin film and dielectric ambient. Our observations indicate that metal (cobalt) slanted columnar thin films can be used as sensors which will enable detection and characterization of minute amounts of dielectrics at THz frequencies, such as for flow-based detection of liquid chemical constituents.
We apply infrared spectroscopic ellipsometry (IRSE) in combination with near-infrared to vacuum-ultraviolet ellipsometry to study the concentration and mobility of holes in a set of Mg-doped In-polar InN samples of different Mg-concentrations. P-type behavior is found in the IRSE spectra for Mg-concentrations between 1x1018 cm-3 and 3x1019 cm-3. The free-charge carrier parameters are determined using a parameterized model that accounts for phonon-plasmon coupling. From the NIR-VUV data information about layer thicknesses, surface roughness, and structural InN layer properties are extracted and related to the IRSE results.
Several nanoindentation techniques were applied to the surface, the reverse side and cross-sections of PECVD ultralow-k (ULK) film stacks to characterize their elasto-plastic properties quantitatively. Results showed good agreement of the reduced modulus (Er) values measured from above and on cross-sections, respectively. Er decreased by 10-22% from the upper to the lower surface of the films. This gradient suggests that UV light absorption inside the film leads to slightly reduced curing at the rear side of the films compared to the surface of the ULK layers. Both quasi-static nanoindentation and dynamic mechanical mapping showed this trend. It is demonstrated that quantitative mechanical mapping can be performed with a lateral resolution ≤ 100nm. Slight local variations of Er were detected on ULK/SiCxNy films stacked on top of Cu-low-k interconnect structures.
We present an infrared spectroscopic ellipsometry investigation of SixNy films deposited on textured Si substrates employed for photovoltaic cells. A multiple-sample data analysis scheme is used in order to determine the SixNy dielectric function and thickness parameters regardless of the surface morphology of the substrate. We observe changes in the dielectric function of the silicon nitride film which suggest variations in the chemical composition of the films depending on the substrate morphology.
We report the synthesis of a series of highly functional metal chelated silyl- and tert-butyl-protected 2, 3-diaminomethyl norbornene derivatives. Subsequent alterations to the previously synthesized norbornene adducts afford many other derivatives containing such functionalities as alkyl, cyano, esters, and ethers. These derivatives are then subjected to ring-opening metathesis polymerization (ROMP) employing a ruthenium homogeneous catalyst to afford phase separated block polymers. The block polymers formed serve as unique templates for the formation of size controlled metal nanoclusters having a narrow dispersion. These metal nanoclusters containing diblock polymers are evaluated as unique electrical and optical materials.
This paper presents new findings regarding the effects of precursor drop size and concentration on product particle size and morphology in ultrasonic spray pyrolysis. Large precursor drops (diameter >30 μm) generated by ultrasonic atomization at 120kHz yielded particles with holes. Precursor drops 6-9 μm in diameter, generated by an ultrasonic nebulizer at 1.65MHz and 23.5W electric drive power, yielded uniform spherical particles 150nm in diameter under proper control of heating rate and precursor concentration. Moreover, air-assisted ultrasonic spray pyrolysis at 120kHz and 2.3W yielded spherical particles of which nearly half were smaller than those produced by the ultrasonic spray pyrolysis of the 6-9 μm precursor drops, despite the much larger precursor drop sizes (28 μm peak diameter versus 7 μm mean diameter). These particles are much smaller than those predicted by the conventional one particle per drop mechanism, suggesting that a vapor condensation mechanism may also be involved in spray pyrolysis. It may be concluded that through this new mechanism air-assisted ultrasonic spray pyrolysis can become a viable process for mass production of nanoparticles.
Cd1-xZnxTe ZriTe crystals grown by the travelling heater methode (THM) have been investigated by low temperature photoluminescence (PL). The excitonic energy gap as a function of the alloy composition was determined for the complete range of x - 0 to x - 1. The composition dependent broadening of the neutral acceptor bound exciton (A°X) line was measured and compared to theoretical calculations. The Donor - Acceptor pair luminescence in the crystals is a superposition of recombinations due to residual Cu acceptors and A - centers (anion vacancy - donor pairs ).
The optical properties of the red modification of mercuric iodide (HgJ2) were studied by optical absorption, magnetic circular dichroism, photoluminescence and optically detected magnetic resonance investigations. The experiments demonstrate the involvment of acceptors with energy levels at Ev + 0.14 ± 0.01 eV and 0.15 ± 0.01 eV in the absorption and recombination at 2.2 eV. The g - values are 0.85 and 0.74, respectively.