Ultraviolet High Resolution Research Articles

Unravelling the nuclear dust morphology of NGC 1365: a two-phase polar–RAT model for the ultraviolet to infrared spectral energy distribution

ABSTRACT We present a 3D radiative transfer model for the spectral energy distribution (SED) of NGC 1365, which is a ‘changing look’ Seyfert 1.8 type active galactic nucleus (AGN). The SED from the ultraviolet (UV) to the infrared (IR) is constructed using archival data from the Ultra-Violet Imaging Telescope (UVIT) onboard AstroSat, along with IR data from the literature. The skirt radiative transfer code is used to model the SED and derive the geometry and composition of dust in this AGN. Similar to our earlier SED model of NGC 4151, the nuclear region of NGC 1365 is assumed to contain a ring or disc-like structure concentric to the accretion disc, composed of large (0.1–1 $\mu$m) graphite grains in addition to the two-phase dusty torus made up of interstellar-medium-type grains (Ring And Torus or RAT model). We also include, for the first time, an additional component of dusty wind in the form of a bipolar cone. We carry out a detailed analysis and derive the best-fitting parameters from a χ2 test to be Rin, r = 0.03 pc, σ = 26°, and τtotal = 20 for the assumed ring–torus–polar wind geometry. Our results suggest the presence of hot dust at a temperature T ∼ 1216 K at the location of the ring that absorbs and scatters the incident UV radiation and emits in the near-IR. In the mid-IR, the major contributors are the polar cone and warm dust with T ∼ 914 K at Rin, t = 0.1 pc. Not only are our model radii in agreement with IR interferometric observations, but also our study reiterates the role of high-resolution UV observations in constraining the dust grain size distribution in the nuclear regions of AGN.

Development of UPLC-UV-ELSD Method for Fatty Acid Profiling in Polysorbate 80 and Confirmation of the Presence of Conjugated Fatty Acids by Mass Spectrometry, UV Absorbance and Proton Nuclear Magnetic Resonance Spectroscopy

Polysorbate 80 (PS80), a chemical substance composed of sorbitol, ethylene glycol, and fatty acids, is commonly used in pharmaceutical drug products to stabilize formulations. However, recent studies have demonstrated that PS80 may hydrolyze over time and the released free fatty acids (FFAs) may lead to particle formation. Naming conventions of fatty acids in current pharmacopeia and in products’ certificates of analysis (CoA) of PS80 do not typically distinguish between isomeric species of fatty acids in PS80. Thus, methods to fully characterize the fatty acid species present in PS80 raw materials are needed to enhance quality control strategies of pharmaceuticals using PS80. Here, extended effort is taken to characterize fatty acids in hydrolyzed PS80 raw materials and elucidate the identities of isomeric fatty acid species. In this work, a method was developed and optimized for separation and detection of fatty acids in alkaline hydrolyzed PS80 raw materials using ultra performance liquid chromatography (UPLC) with ultra-violet (UV) detection and evaporative light scattering detection (ELSD). Fatty acids not specified in the current pharmacopeias were detected in PS80 raw material by the developed LC-UV-ELSD method including conjugated forms of linoleic and linolenic fatty acid species. Their identities were orthogonally confirmed by retention time agreement with analytical standards, accurate mass by high resolution mass spectrometry, UV absorbance, and proton nuclear magnetic resonance spectroscopy. The detected conjugated fatty acids are theoretically more hydrophobic and less soluble than their unconjugated counterparts and may increase the propensity of PS80 to form particles upon hydrolysis. This work highlights the need for better quality control of PS80 raw material, as it may eventually play a critical role in product quality of therapeutic proteins.

Shock shaping? Nebular spectroscopy of nova V906 Carinae

ABSTRACT V906 Carinae was one of the best observed novae of recent times. It was a prolific dust producer and harboured shocks in the early evolving ejecta outflow. Here, we take a close look at the consequences of these early interactions through study of high-resolution Ultraviolet and Visual Echelle spectrograph spectroscopy of the nebular stage and extrapolate backwards to investigate how the final structure may have formed. A study of ejecta geometry and shaping history of the structure of the shell is undertaken following a spectral line $\rm {\small SHAPE}$ model fit. A search for spectral tracers of shocks in the nova ejecta is undertaken and an analysis of the ionized environment. Temperature, density, and abundance analyses of the evolving nova shell are presented.

Ultraviolet spectropolarimetry with polstar: interstellar medium science

Continuum polarization over the UV-to-microwave range is due to dichroic extinction (or emission) by asymmetric, aligned dust grains. Scattering can also be an important source of polarization, especially at short wavelengths. Because of both grain alignment and scattering physics, the wavelength dependence of the polarization, generally, traces the size of the aligned grains. Similarly because of the differing wavelength dependencies of dichroic extinction and scattering polarization, the two can generally be reliably separated. Ultraviolet (UV) polarimetry therefore provides a unique probe of the smallest dust grains (diameter< 0.09~upmu text{m}), their mineralogy and interaction with the environment. However, the current observational status of interstellar UV polarization is very poor with less than 30 lines of sight probed. With the modern, quantitative and well-tested, theory of interstellar grain alignment now available, we have the opportunity to advance the understanding of the interstellar medium (ISM) by executing a systematic study of the UV polarization in the ISM of the Milky Way and near-by galaxies. The Polstar mission will provide the sensitivity and observing time needed to carry out such a program (probing hundreds of stars in the Milky Way and dozens of stars in the LMC/SMC), addressing questions of dust composition as a function of size and location, radiation- and magnetic-field characteristics as well as unveiling the carrier of the 2175 Å extinction feature. In addition, using high-resolution UV line spectroscopy Polstar will search for and probe the alignment of, and polarization from, aligned atoms and ions - so called “Ground State Alignment”, a potentially powerful new probe of magnetic fields in the diffuse ISM.

In the Trenches of the Solar-stellar Connection. V. High-resolution Ultraviolet and X-Ray Observations of Sun-like Stars: The Curious Case of Procyon

Abstract A joint X-ray (0.2–2 keV) and ultraviolet (1150–3000 Å) time-domain study has been carried out on three nearby bright late-type stars, bracketing the Sun in properties. Alpha Cen A (HD 128620: G2 V) is a near twin to the Sun, although slightly more massive and luminous, slightly metal-rich, but older. Alpha Cen B (HD 128621: K1 V) is cooler than the Sun, somewhat less massive and lower in luminosity. Procyon (HD 61421: F5 IV–V) is hotter, more massive and more luminous than the Sun, half the age, but more evolved. Stellar observations were from Chandra X-ray Observatory and Hubble Space Telescope (HST). The Sun provided a benchmark through high-energy spectral scans from solar irradiance satellites and novel high-dispersion full-disk profiles of key UV species—Mg ii, C ii, and Si iv—from the Interface Region Imaging Spectrograph. Procyon’s flux history was strikingly constant at all wavelengths, in contrast to the other three cycling-dynamo stars. Procyon also displays a strong subcoronal (T ∼ 1 × 105 K) emission excess, relative to chromospheric Mg ii (T ≲ 104 K), although its X-rays (T ∼ 2 MK) appear to be more normal. At the same time, the odd sub-Gaussian shapes, and redshifts, of the subgiant’s “hot lines” (such as Si iv and C iv) are remarkably similar to the solar counterparts (and α Cen AB). This suggests a Sun-like origin, namely a supergranulation network supplied by magnetic flux from a noncycling “local dynamo.”

7Be in the outburst of the ONe nova V6595 Sgr

ABSTRACT We report on the search for the 7Be ii isotope in the outbursts of the classical nova V6595 Sgr by means of high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) observations taken at the European Southern Observatory’s Very Large Telescope in 2021 April, about two weeks after its discovery and under difficult circumstances due to the pandemic. Narrow absorption components with velocities at ∼ −2620 and −2820 km s−1, superposed on broader and shallow absorption, are observed in the outburst spectra for the 7Be ii λλ313.0583, 313.1228 nm doublet resonance lines, as well as in several other elements such as Ca ii, Fe i, Mg i, Na i, H i and Li i. Using the Ca ii K line as a reference element, we infer N(7Be)/N(H) ≈ 7.4 × 10−6, or ≈ 9.8 × 10−6 when the 7Be decay is taken into account. The 7Be abundance is about half of the value most frequently measured in novae. The possible presence of overionization in the layers where 7Be ii is detected is also discussed. Observations taken at the Telescopio Nazionale Galileo in La Palma 91 days after discovery showed prominent emission lines of oxygen and neon, which allow us to classify the nova as ONe type. Therefore, although 7Be is expected to be higher in CO novae, it is found at comparable levels in both nova types.

Low-Temperature Synthesis of ZnO Nanoparticles with Controlled Crystal Growth for Efficient Ultraviolet Photocatalyst

In this paper, we report that an effective and simple chemical method under the low temperature (60 °C) could synthesize zinc oxide (ZnO) nanoparticles and effectively control the crystal growth based on the hydrothermal method. X-ray diffraction, X-ray electron spectroscopy, high resolution transmission electron microscopy and ultra violet visible spectroscopy were used to characterize the structure and performance of the samples. It is shown that the ZnO nanoparticles synthesized under the optimal reaction conditions are strong ultraviolet absorption, high-uniformed sphere and high specific surface. In the photodegradation of rhodamine B (RhB) tests, ZnO nanoparticles thrived well during the reaction and degraded the material in 50 minutes. Since ZnO nanoparticles towards RhB degradation shows a good stability, it might provide an effective way to tackle environmental pollution.

High-resolution synthetic UV–submm images for simulated Milky Way-type galaxies from the Auriga project

ABSTRACT We present redshift-zero synthetic observational data considering dust attenuation and dust emission for the 30 galaxies of the Auriga project, calculated with the skirt radiative transfer code. The post-processing procedure includes components for star-forming regions, stellar sources, and diffuse dust taking into account stochastic heating of dust grains. This allows us to obtain realistic high-resolution broad-band images and fluxes from ultraviolet (UV) to submillimetre (submm) wavelengths. For the diffuse dust component, we consider two mechanisms for assigning dust to gas cells in the simulation. In one case, only the densest or the coldest gas cells are allowed to have dust, while in the other case this condition is relaxed to allow a larger number of dust-containing cells. The latter approach yields galaxies with a larger radial dust extent and an enhanced dust presence in the interspiral regions. At a global scale, we compare Auriga galaxies with observations by deriving dust scaling relations using spectral energy distribution fitting. At a resolved scale, we make a multiwavelength morphological comparison with nine well-resolved spiral galaxies from the DustPedia observational data base. We find that for both dust assignment methods, although the Auriga galaxies show a good overall agreement with observational dust properties, they exhibit a slightly higher specific dust mass. The multiwavelength morphological analysis reveals a good agreement between the Auriga and the observed galaxies in the optical wavelengths. In the mid- and far-infrared wavelengths, Auriga galaxies appear smaller and more centrally concentrated in comparison to their observed counterparts. We publicly release the multi-observer images and fluxes in 50 commonly used broad-band filters.

A High Resolution Ultraviolet Spectroradiometer and its Application in Solar Radiation Measurement

AbstractA recent laboratory study suggests that water vapor displays structured absorption features over the 290–350 nm region, with maximum and minimum cross‐sections of 8.4 × 10−25 and 1.4 × 10−25 cm2/molecule at room temperature (Pei et al. 2019, https://doi.org/10.1029/2019jd030724; Du et al., 2013, https://doi.org/10.1002/grl.50935). To observe water vapor absorption features in the ultraviolet (UV) region in the atmosphere, a United States Department of Agriculture reference spectroradiometer was upgraded with a new fore‐optical module, enabling it to measure direct solar beam and sky radiance at given azimuth and elevation angles. This double Czerny‐Turner spectroradiometer enables wavelength scanning from 290 to 410 nm, with a nominal bandwidth of 0.1 nm. It can operate with a step‐size of 0.0005 nm and a full width at half maximum of 0.1 nm. It has an out‐of‐band rejection ratio of approximately 10−10. This high resolution spectroradiometer can be used as a reference instrument for UV radiation measurements and for monitoring atmospheric gases such as O3, SO2, and NO2. A series of field observations were made using this spectroradiometer in the University at Albany campus. A residual analysis method is developed to analyze absorption by atmospheric components and to retrieve atmospheric optical depth. The residual optical depth was calculated by subtracting the optical depths of Rayleigh scattering, aerosol extinction, and absorption of typical atmospheric gases such as O3, SO2, and NO2 from the retrieved total optical depth. Multiple case studies show that residual optical depth from the observed UV spectra is sensitive to the atmospheric water vapor amount. The greater the water vapor path, the larger the magnitude of residual optical depth. The ozone amount was inferred from the residual analysis; it is comparable to the satellite measurements. For example, in a case with water vapor path of 13 mm on October 24, 2019, the inferred ozone amount from residual analysis is 2.7% lower than retrievals from the Ozone Monitoring Instrument‐Total Ozone Mapping Spectrometer.

Meteosat Third Generation (MTG): Continuation and Innovation of Observations from Geostationary Orbit

AbstractWithin the next couple of years, the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT) will start the deployment of its next-generation geostationary meteorological satellites. The Meteosat Third Generation (MTG) is composed of four imaging (MTG-I) and two sounding (MTG-S) platforms. The satellites are three-axis stabilized, unlike the two previous generations of Meteosat that were spin stabilized, and carry two sets of remote sensing instruments each. Hence, in addition to providing continuity, the new system will provide an unprecedented capability from geostationary orbit. The payload on the MTG-I satellites are the 16-channel Flexible Combined Imager (FCI) and the Lightning Imager (LI). The payloads on the MTG-S satellites are the hyperspectral Infrared Sounder (IRS) and a high-resolution Ultraviolet–Visible–Near-Infrared (UVN) sounder Sentinel-4/UVN, provided by the European Commission. Today, hyperspectral sounding from geostationary orbit is provided by the Chinese Fengyun-4A (FY-4A) satellite Geostationary Interferometric Infrared Sounder (GIIRS) instrument, and lightning mappers are available on FY-4A and on the National Oceanic and Atmospheric Administration (NOAA) GOES-16 and GOES-17 satellites. Consequently, the development of science and applications for these types of instruments have a solid foundation. However, the IRS, LI, and Sentinel-4/UVN are a challenging first for Europe in a geostationary orbit. The four MTG-I and two MTG-S satellites are designed to provide 20 and 15.5 years of operational service, respectively. The launch of the first MTG-I is expected at the end of 2022 and the first MTG-S roughly a year later. This article describes the four instruments, outlines products and services, and addresses the evolution of the further applications.

Strategy of All-Inorganic Cs3Cu2I5/Si-Core/Shell Nanowire Heterojunction for Stable and Ultraviolet-Enhanced Broadband Photodetectors with Imaging Capability.

In this study, for the first time, the integration of nontoxic ternary copper halide Cs3Cu2I5 with one-dimensional Si nanowires (NWs) was reported to achieve an ultraviolet (UV)-enhanced Si NW broadband photodetector. A compact and uniform coverage of Cs3Cu2I5 on the top and sidewall of Si NWs formed a core/shell heterostructure, in which Si NWs served as the growth template and the electron-transport layer, and Cs3Cu2I5 was employed as the UV photoactive material and the hole-transport layer. The as-fabricated Cs3Cu2I5/Si-core/shell NW photodetector demonstrates a multiband photodetection from the deep UV to near-infrared region, a fast response speed of 92.5/189.2 μs (265 nm), and a high photoresponsivity of 130 mA/W, nearly 600 times as much as the reference device constructed using Si NWs. More importantly, the proposed photodetector exhibits an excellent stability in air ambient. Typically, it could endure a high temperature of 60 °C for 11 h consecutive working; after storage in air ambient for two weeks, its photodetection ability can almost be retained. Additionally, high-resolution UV imaging applications were presented by employing the proposed photodetector as sensing pixels. These obtained results verify the effectiveness of the Cs3Cu2I5/Si-core/shell NW heterojunction strategy for UV-enhanced broadband photodetection, making such a device really possible for practical applications.

Search for 7Be in the outbursts of four recent novae

ABSTRACT Following the recent detection of 7Be ii in the outburst spectra of classical novae, we report the search for this isotope in the outbursts of four recent bright novae by means of high-resolution Ultraviolet and Visual Echelle Spectrograph (UVES) observations. The 7Be ii λλ313.0583, 313.1228 nm doublet resonance lines are detected in the high-velocity components of Nova Mus 2018 and ASASSN-18fv during outbursts. However, 7Be ii is not detected in ASASSN-17hx and possibly not in Nova Cir 2018, which shows that 7Be is not always ejected in the thermonuclear runaway. Taking into account the 7Be decay, we find X(7Be)/X(H) ≈ 1.5 × 10−5 and 2.2 × 10−5 in Nova Mus 2018 and ASASSN-18fv, respectively. A value of 7Be/H ≈ 2 × 10−5 is found in five out of the seven extant measurements, and it can be considered as a typical 7Be yield for novae. However, this value is almost one order of magnitude larger than predicted by current theoretical models. We argue that the variety of high 7Be/H abundances could be the result of a higher than solar content of 3He in the donor star. The cases with 7Be not detected might be related to the small mass of the white dwarf (WD) or to relatively little mixing with the core material of the WD. The 7Be/H, or 7Li/H, abundance is ≈ 4 dex above meteoritic abundance, thus confirming the novae as the main sources of 7Li in the Milky Way.

Analysis of Wide-Bandgap Material OPFET UV Detectors for High Dynamic Range Imaging and Communication Applications

The ultraviolet (UV) photoresponses of Wurtzite GaN, ZnO, and 6H-SiC-based Optical Field Effect Transistor (OPFET) detectors are estimated with an in-depth analysis of the same considering the generalized model and the front-illuminated model for high resolution imaging and UV communication applications. The gate materials considered for the proposed study are gold (Au) and Indium-Tin-Oxide (ITO) for GaN, Au for SiC, and Au and silver dioxide (AgO2) for ZnO. The results indicate significant improvement in the Linear Dynamic Range (LDR) over the previously investigated GaN OPFET (buried-gate, front-illuminated and generalized) models with Au gate. The generalized model has superior dynamic range than the front-illuminated model. In terms of responsivity, all the models including buried-gate OPFET exhibit high and comparable photoresponses. Buried-gate devices on the whole, exhibit faster response than the surface gate models except in the AgO2-ZnO generalized OPFET model wherein the switching time is the lowest. The generalized model enables faster switching than the front-illuminated model. The switching times in all the cases are of the order of nanoseconds to picoseconds. The SiC generalized OPFET model shows the highest 3-dB bandwidths of 11.88 GHz, 36.2 GHz, and 364 GHz, and modest unity-gain cut-off frequencies of 4.62 GHz, 8.71 GHz, and 5.71 GHz at the optical power densities of 0.575 μW/cm2, 0.575 mW/cm2, and 0.575 W/cm2 respectively. These are in overall, the highest detection-cum-amplifi-cation bandwidths among all the investigated devices. The same device exhibits the highest LDR of 73.3 dB. The device performance is superior to most of the other existing detectors along with comparable LDR, thus, emerging as a high performance photodetector for imaging and communication applications. All the detectors show considerably high detectivities owing to the high responsivity values. The results have been analyzed by the photovoltaic and the photoconductive effects, and the series resistance effects and will aid in conducting further research. The results are in line with the experiments and the commercially available software simulations. The devices will greatly contribute towards single photon counting, high resolution imaging, and UV communication applications.

UV‐activated room temperature single‐sheet ZnO gas sensor

Room temperature sensor is a research hot for metal–oxide gas sensors. However, electron activation is a bottleneck to improve sensitivity for room temperature sensors. Here, an ultraviolet (UV)-activated gas sensor based on a single-sheet porous single-crystalline (PSC) zinc oxide (ZnO) sheet has been fabricated instead of heating activation, which works at room temperature. The PSC ZnO nanosheets were first prepared by a one-pot wet-chemical method. Then, the precursors were annealed for 2 h in air to obtain the PSC ZnO nanosheets. They were characterised by scanning electron microscopy, high-resolution transmission electron microscopy and UV–visible spectrum. Finally, the single-sheet ZnO gas sensors were fabricated by focused ion beam technology, which exhibited good responses to 1–300 ppm of ethanol. The single-sheet ZnO UV-activated sensing mechanism was also put forward to explain the excellent sensing property.

Magnetic Flux Rope Shredding By a Hyperbolic Flux Tube: The Detrimental Effects of Magnetic Topology on Solar Eruptions

Abstract We present the analysis of an unusual failed eruption captured in high cadence and in many wavelengths during the observing campaign in support of the Very high Angular resolution Ultraviolet Telescope (VAULT2.0) sounding rocket launch. The refurbished VAULT2.0 is a Lyα (λ 1216 Å) spectroheliograph launched on 2014 September 30. The campaign targeted active region NOAA AR 12172 and was closely coordinated with the Hinode and IRIS missions and several ground-based observatories (NSO/IBIS, SOLIS, and BBSO). A filament eruption accompanied by a low-level flaring event (at the GOES C-class level) occurred around the VAULT2.0 launch. No coronal mass ejection was observed. The eruption and its source region, however, were recorded by the campaign instruments in many atmospheric heights ranging from the photosphere to the corona in high cadence and spatial resolution. This is a rare occasion that enabled us to perform a comprehensive investigation on a failed eruption. We find that a rising Magnetic Flux Rope (MFR)-like structure was destroyed during its interaction with the ambient magnetic field, creating downflows of cool plasma and diffuse hot coronal structures reminiscent of “cusps.” We employ magnetofrictional simulations to show that the magnetic topology of the ambient field is responsible for the destruction of the MFR. Our unique observations suggest that the magnetic topology of the corona is a key ingredient for a successful eruption.

On the possible triple central star system of PN SuWt 2: no ménage à trois at the heart of the Wedding Ring

SuWt 2 is a planetary nebula consisting of a bright ring-like waist from which protrude faint extended lobes – a morphology believed to be typical of progenitors which have experienced a close-binary evolution. Previous observations of NSV 19992, the star at the projected centre of SuWt 2, have found it to comprise two A-type stars in a 4.9 d eclipsing orbit, neither of which could be the nebular progenitor. Radial velocity studies provided a hint that the systemic velocity of this double A-type binary might be varying over time, suggesting the presence of a third component hypothesized to be the nebular progenitor. Here, we present an extensive radial velocity monitoring study of NSV 19992, performed with the high-resolution Ultraviolet and Visual Echelle Spectrograph mounted on the European Southern Observatory's Very Large Telescope, in order to constrain the possible variation in the systemic velocity of the A-type binary and its relation to the progenitor of SuWt 2. The observations, acquired over a period of approximately one year, show no evidence of variability in the systemic velocity of NSV 19992. Combining these new observations with previous high-resolution spectroscopy demonstrates that the systemic velocity is also stable over much longer periods and, moreover, is distinct from that of SuWt 2, strongly indicating that the two are not associated. We conclude that NSV 19992 is merely a field star system, by chance lying in the same line of sight as the nebular centre, and that it bears no relation to SuWt 2 or its, as yet unidentified, central star(s).

Investigation of the Chromosphere–Corona Interface with the Upgraded Very High Angular Resolution Ultraviolet Telescope (VAULT2.0)

Very high angular resolution ultraviolet telescope (VAULT2.0) is a Lyman-alpha (Ly[Formula: see text]; 1216[Formula: see text]Å) spectroheliograph designed to observe the upper chromospheric region of the solar atmosphere with high spatial ([Formula: see text]) and temporal (8[Formula: see text]s) resolution. Besides being the brightest line in the solar spectrum, Ly[Formula: see text] emission arises at the temperature interface between coronal and chromospheric plasmas and may, hence, hold important clues about the transfer of mass and energy to the solar corona. VAULT2.0 is an upgrade of the previously flown VAULT rocket and was launched successfully on September 30, 2014 from White Sands Missile Range (WSMR). The target was AR12172 midway toward the southwestern limb. We obtained 33 images at 8[Formula: see text]s cadence at arc second resolution due to hardware problems. The science campaign was a resounding success, with all space and ground-based instruments obtaining high-resolution data at the same location within the AR. We discuss the science rationale, instrument upgrades, and performance during the first flight and present some preliminary science results.

New 3,4-seco-cycloartane triterpenes from Gardenia sootepensis

Two new 3,4-seco-cycloartane triterpenes, named sootepins H (1) and I (2), were isolated from the ethyl acetate extract of the leaves and twigs of Gardenia sootepensis. Their structures were elucidated on the basis of 1D- and 2D-nuclear magnetic resonance (NMR) analysis, as well as high-resolution mass spectrometry (HR-MS), infrared (IR), and ultra violet (UV).

Comparison of solar photospheric bright points between Sunrise observations and MHD simulations

Bright points (BPs) in the solar photosphere are radiative signatures of magnetic elements described by slender flux tubes located in the darker intergranular lanes. They contribute to the ultraviolet (UV) flux variations over the solar cycle and hence may influence the Earth's climate. Here we combine high-resolution UV and spectro-polarimetric observations of BPs by the SUNRISE observatory with 3D radiation MHD simulations. Full spectral line syntheses are performed with the MHD data and a careful degradation is applied to take into account all relevant instrumental effects of the observations. It is demonstrated that the MHD simulations reproduce the measured distributions of intensity at multiple wavelengths, line-of-sight velocity, spectral line width, and polarization degree rather well. Furthermore, the properties of observed BPs are compared with synthetic ones. These match also relatively well, except that the observations display a tail of large and strongly polarized BPs not found in the simulations. The higher spatial resolution of the simulations has a significant effect, leading to smaller and more numerous BPs. The observation that most BPs are weakly polarized is explained mainly by the spatial degradation, the stray light contamination, and the temperature sensitivity of the Fe I line at 5250.2 \AA{}. The Stokes $V$ asymmetries of the BPs increase with the distance to their center in both observations and simulations, consistent with the classical picture of a production of the asymmetry in the canopy. This is the first time that this has been found also in the internetwork. Almost vertical kilo-Gauss fields are found for 98 % of the synthetic BPs. At the continuum formation height, the simulated BPs are on average 190 K hotter than the mean quiet Sun, their mean BP field strength is 1750 G, supporting the flux-tube paradigm to describe BPs.

Raman Spectroscopy Using a Spatial Heterodyne Spectrometer: Proof of Concept

The use of a spatial heterodyne interferometer-based spectrometer (SHS) for Raman spectroscopy is described. The motivation for this work is to develop a small, rugged, high-resolution ultraviolet (UV) Raman spectrometer that is compatible with pulsed laser sources and that is suitable for planetary space missions. UV Raman is a particular technical challenge for space applications because dispersive (grating) approaches require large spectrographs and very narrow slits to achieve the spectral resolution required to maximize the potential of Raman spectroscopy. The heterodyne approach of the SHS has only a weak coupling of resolution and throughput, so a high-resolution UV SHS can both be small and employ a wide slit to maximize throughput. The SHS measures all optical path differences in its interferogram simultaneously with a detector array, so the technique is compatible with gated detection using pulsed lasers, important to reject ambient background and mitigate fluorescence (already low in the UV) that might be encountered on a planetary surface where samples are uncontrolled. The SHS has no moving parts, and as the spectrum is heterodyned around the laser wavelength, it is particularly suitable for Raman measurements. In this preliminary report we demonstrate the ability to measure visible wavelength Raman spectra of liquid and solid materials using an SHS Raman spectrometer and a visible laser. Spectral resolution and bandpass are also discussed. Separation of anti-Stokes and Stokes Raman bands is demonstrated using two different approaches. Finally spectral bandpass doubling is demonstrated by forming an interference pattern in both directions on the ICCD detector followed by analysis using a two-dimensional Fourier transform.