Typical Measurement Uncertainties Research Articles

The Distribution of Metallicities in the Local Galactic Interstellar Medium* *Based in part on observations made with the NASA/ESA Hubble Space Telescope, obtained from the MAST data archive at the Space Telescope Science Institute. The STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Based in part on data obtained from the

In this investigation, we present an analysis of the metallicity distribution that pertains to neutral gas in the local Galactic interstellar medium (ISM). We derive relative ISM metallicities for a sample of 84 sight lines probing diffuse atomic and molecular gas within 4 kpc of the Sun. Our analysis is based in large part on column density measurements reported in the literature for 22 different elements that are commonly studied in interstellar clouds. We supplement the literature data with new column density determinations for certain key elements and several individual sight lines important to our analysis. Our methodology involves comparing the relative gas-phase abundances of many different elements for a given sight line to simultaneously determine the strength of dust depletion in that direction and the overall metallicity offset. We find that many sight lines probe multiple distinct gas regions with different depletion properties, which complicates the metallicity analysis. Nevertheless, our results provide clear evidence that the dispersion in the metallicities of neutral interstellar clouds in the solar neighborhood is small (∼0.10 dex) and only slightly larger than the typical measurement uncertainties. We find no evidence for the existence of very low metallicity gas (as has recently been reported by De Cia et al.) along any of the 84 sight lines in our sample. Our results are consistent with a local Galactic ISM that is well mixed and chemically homogeneous.

Statistical Analysis of Regenerative Air Preheater of Pulverized Coal Fired Boilers

Abstract: The data gathered from the field study and different parameter recorders connected to the data acquisition system of the distributed control system panel for measuring flow, pressure, and temperature are subject to typical systematic instrumentation measurement uncertainties with regard to the primary measuring elements, sensors, transducers, amplifiers, digital converters, and recorders, as well as the effects of the environment. The acceptability of data is statistically confirmed by taking into account the unpredictability of the inaccuracy in recorded parameters for temperature, pressure, and flow measurement. The statistical output on the measured and expected air flow through the APH (ma) in relation to different AAT (Tae) is summarized

A Novel Optical-Based AC Calorimetry Method to Measure In-Plane Thermal Conductivity of Small-Scale Samples

Conventional ac-calorimetry method could accurately measure the in-plane thermal diffusivity of suspended thin films but cannot be applied to small-scale samples due to the large sample size required by this method. This work proposes a novel optical-based ac-calorimetry method that circumvents the limitations of the conventional ac-calorimetry method. This new method uses a modulated continuous-wave laser to heat the sample periodically, and another continuous-wave laser to detect the sample’s temperature response on the surface at different distances from the heating spot via the principle of thermoreflectance. Since this method uses highly focused laser beams with micrometer-scale spot diameters for optical heating and temperature sensing, and this method uses the state-of-the-art thermal model of 3D anisotropic multilayers for signal processing, this method can accurately measure the in-plane thermal conductivity of suspended and supported thin films and bulk materials with sub-millimeter-scale lateral sizes, with a typical measurement uncertainty of less than 5%. This paper describes the details of this technique, including the basic principle, test device, signal acquisition, data processing, and uncertainty analysis. This technique is demonstrated through measurements of a standard sapphire sample, with the phase and amplitude approaches of ac-calorimetry compared. This technique is also compared with some other related optical-based thermal methods for their pros and cons in the end.

Qualification of Fe0.95Co0.05Si2 as a reference material for high temperature measurement of the thermoelectric power factor

Precise characterization of thermoelectric (TE) materials is mandatory for a meaningful validation of scientific results, focusing on traceable determination of the Seebeck coefficient (S), the electric (σ) and thermal (κ) conductivity. These properties form the thermoelectric figure of merit zT = (S2σ/κ)T, which is used for assessment of TE conversion efficiency with respect to the absolute temperature T. The level of metrological standardization is characterized to date by available reference samples for the Seebeck coefficient, publications on best practice measurement approaches, and accomplished international round robin (RR) campaigns on transport property measurements.We report on the qualification of β-Fe0.95Co0.05Si2 (FeSi2) as the first semiconducting high temperature reference material for the TE power factor (PF = S2σ), which is currently developed by the German Aerospace Center (DLR) and the Physikalisch-Technische Bundesanstalt (PTB). The relation between the size of FeSi2 compacts obtained by current-assisted short time sintering and the resulting functional homogeneity of the material is presented, which is studied by spatially resolved Seebeck coefficient measurements at room temperature. Data from temperature dependent characterization of the PF is provided to assess functional stability and homogeneity under integral measurement conditions. The outcome of certification measurements at PTB report on individual uncertainty contributions as the base for a later testimony of FeSi2 as a metrological reference for the PF. Integral measurements have been expanded to further comparative test results obtained by the Korea Electrotechnology Research Institute (KERI), the Indian Institute of Technology Bombay (IITB), and the Netzsch Gerätebau GmbH. The findings give evidence of an excellent homogeneity, reproducibility and stability with low standard deviations for S and σ far below typical measurement uncertainties, which effectively demonstrates the suitability of FeSi2 as a future reference material for TE metrology at elevated temperatures up to 1000 K.

Assessing current-voltage measurements of busbarless solar cells

For measuring the current-voltage ( I–V ) characteristics of busbarless solar cells, there is a certain degree of freedom in the choice of the contacting configuration as none has been defined as standard yet. This leads to the question of how the energy conversion efficiency of a busbarless solar cell should be specified when there are different measured values for it and poses the risk of misinterpreting cell measurements: Designing the measurement system for highest cell efficiencies for example may be tempting but can lead to cell results disassociated from later module performance and reduced cell-to-module power factors. The loss in module efficiency can thereby significantly exceed 5 % rel . It is therefore recommended to always adapt the contacting system to the module interconnection to yield meaningful I–V results in cell measurements. As a remedy for non-adapted measurement conditions, it is shown that I–V results can be converted from various cell measurement configurations to the module configuration. An analytical approach for the conversion of I–V results between measurement systems with different numbers of current contact bars as well as different shading properties is proposed. The approach is validated experimentally on busbarless cells over a large grid resistivity range. For three measurement systems with very different contacting schemes, the differences in fill factor and efficiency between the systems before correction clearly exceeded 10 % rel for high grid resistivities. After correction, good agreement in I–V characteristics within typical measurement uncertainties were shown. Limitations to the analytical approach associated with finger interruptions are identified and discussed. • Study on impact of contacting system on current-voltage characteristics of busbarless solar cells. • Improper contacting systems can lead to increased cell-to-module losses and misdirected cell optimization. • Contacting system should match module interconnection scheme for meaningful cell results. • Proposal and evaluation of correction procedure for conversion of cell results.

Scale Conversion and Uncertainty Calculations in Isotope Delta Measurements

Isotope ratio applications are on the increase and a major part of which are delta measurements, because they are easier to perform than the determination of absolute isotope ratios while offering lower measurement uncertainties. Delta measurements use artefact‐based scales and therefore scale conversions are required due to the lack of the scale defining standards. Such scale conversions often form the basis for comparing data being generated in numerous projects and therefore need to be as accurate as possible. In practice, users are tempted to apply linear approximations, which are not sufficiently exact, because delta values are defined by nonlinear relationships. The bias of such approximations often is beyond typical measurement uncertainties and its extent can hardly be predicted. Therefore, exact calculations are advised. Here, the exact equations and the bias of the approximations are presented, and calculations are illustrated by real‐world examples. Measurement uncertainty is indispensable in this context and therefore, its calculation is described as well for determining delta values but also for scale conversions. Approaches for obtaining a single delta measurement and for repeated measurements are presented. For the latter case, a new approach for calculating the measurement uncertainty is presented, which considers covariances between the isotope ratios.

ON THE ASSESSMENT OF EXPOSURE FROM LTE 800-MHZ DOWNLINK FREQUENCY BAND THROUGH THE TIME-AVERAGED AND INTEGRAL-BASED MEASURE.

Exposure assessment should consider the stochastic nature of the emitted signals. Therefore, the long-term temporal variability of E-field strength, obtained by band selective measurements for long-term evolution in a real mobile network environment, is considered in this paper. Intensive measurements were carried out 24h a day for 2 weeks at an indoor location in the urban area. The repeatability of the measurement results was achieved through descriptive statistics of the 24-h instantaneous, time-averaged and integral-based values. More specifically, we addressed the uncertainties on the temporal variability of the instantaneous exposure levels and the effects of duration of averaging and time-integrating on it. To this aim, a huge amount of signal levels (120960 samples) was collected during the measurement campaign by considering three operators in the 800 MHz downlink band. Results have shown how some factors, such as the time interval in which the measurements are taken, can significantly affect the measurement results and their repeatability. Furthermore, in some cases, such effects become comparable to, or even larger than typical measurement uncertainty. By applying both the 24-h time-averaged and integral-based measure, the variability of daily exposure levels could be reduced to values lower than the measurement uncertainty (i.e. lower than±20% of the mean week value obtained with either measure). Based on such results, an indicator depending on the exposure duration should better quantify the far-field exposure in each location.

Impact of 3D radiative transfer on airborne NO<sub>2</sub> imaging remote sensing over cities with buildings

Abstract. Airborne imaging remote sensing is increasingly used to map the spatial distribution of nitrogen dioxide (NO2) in cities. Despite the small ground-pixel size of the sensors, the measured NO2 distributions are much smoother than one would expect from high-resolution model simulations of NO2 over cities. This could partly be caused by 3D radiative transfer effects due to observation geometry, adjacency effects and effects of buildings. Here, we present a case study of imaging a synthetic NO2 distribution for a district of Zurich using the 3D MYSTIC (Monte carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres) solver of the libRadtran radiative transfer library. We computed NO2 slant column densities (SCDs) using the recently implemented 3D-box air mass factors (3D-box AMFs) and a new urban canopy module to account for the effects of buildings. We found that for a single ground pixel (50 m × 50 m) more than 50 % of the sensitivity is located outside of the pixel, primarily in the direction of the main optical path between sun, ground pixel, and instrument. Consequently, NO2 SCDs are spatially smoothed, which results in an increase over roads when they are parallel to the optical path and a decrease otherwise. When buildings are included, NO2 SCDs are reduced on average by 5 % due to the reduced sensitivity to NO2 in the shadows of the buildings. The effects of buildings also introduce a complex pattern of variability in SCDs that would show up in airborne observations as an additional noise component (about 12 µmol m−2) similar to the magnitude of typical measurement uncertainties. The smearing of the SCDs cannot be corrected using 1D-layer AMFs that assume horizontal homogeneity and thus remains in the final NO2 map. The 3D radiative transfer effects by including buildings need to be considered to compute more accurate AMFs and to reduce biases in NO2 vertical columns obtained from high-resolution city-scale NO2 remote sensing.

Boreas: A Sample Preparation-Coupled Laser Spectrometer System for Simultaneous High-Precision In Situ Analysis of δ13C and δ2H from Ambient Air Methane.

We present a new instrument, “Boreas”, a cryogen-free methane (CH4) preconcentration system coupled to a dual-laser spectrometer for making simultaneous measurements of δ13C(CH4) and δ2H(CH4) in ambient air. Excluding isotope ratio scale uncertainty, we estimate a typical standard measurement uncertainty for an ambient air sample of 0.07‰ for δ13C(CH4) and 0.9‰ for δ2H(CH4), which are the lowest reported for a laser spectroscopy-based system and comparable to isotope ratio mass spectrometry. We trap CH4 (∼1.9 μmol mol–1) from ∼5 L of air onto the front end of a packed column, subsequently separating CH4 from interferences using a controlled temperature ramp with nitrogen (N2) as the carrier gas, before eluting CH4 at ∼550 μmol mol–1. This processed sample is then delivered to an infrared laser spectrometer for measuring the amount fractions of 12CH4, 13CH4, and 12CH3D isotopologues. We calibrate the instrument using a set of gravimetrically prepared amount fraction primary reference materials directly into the laser spectrometer that span a range of 500–626 μmol mol–1 (CH4 in N2) made from a single pure CH4 source that has been isotopically characterized for δ13C(CH4) by IRMS. Under the principle of identical treatment, a compressed ambient air sample is used as a working standard and measured between air samples, from which a final calibrated isotope ratio is calculated. Finally, we make automated measurements of both δ13C(CH4) and δ2H(CH4) in over 200 ambient air samples and demonstrate the application of Boreas for deployment to atmospheric monitoring sites.

Technique for measuring very small angle changes.

A method for making accurate and precise measurements of small angles is described using an interferometer and a test fixture with reference control surfaces. The test is relatively insensitive to test fixture alignment. Typical measurement uncertainties are better than 0.2 arcsec (1σ). This technique is applicable for verifying the angular stability of opto-mechanical systems that must undergo rigorous environmental testing.

Improved field-portable system to measure Cs-137 in wildlife

We have developed an improved system to measure Cs-137 in wildlife at the Savannah River Site. This field-portable system consists of a shielded 5 cm by 10 cm by 40 cm NaI detector controlled by an Ametek Ortec Digibase. Measurement of an animal’s radioactivity is made by placing the animal at a predefined location on the detector system for a one minute count-time. The counts, animal type, and animal weight are then used as inputs to an algorithm which calculates the amount of Cs-137 within the whole animal and within the edible meat portion of the animal. The results from these calculations are used to estimate the received dose from eating this animal and is included in the Savannah River Site’s Hunter Dose Tracking System. This system has a detection limit of 0.60 pCi/g (22.20 Bq/kg) with a typical measurement uncertainty of less than 0.32 pCi/g (11.84 Bq/kg).

The effect of multiple scattering on optical measurement of soot emissions in atmospheric plumes

Measurements of soot/black carbon emissions via optical observations of atmospheric plume transmittance require a correction to account for bias in perceived plume brightness due to inscatter of ambient light. The ability to accurately correct for inscattering is hampered, however, by the potential for multiple scattering (MS) within the plume, which cannot be directly considered without detailed knowledge of the turbulent plume's structure. MS is thus oft-ignored within such measurement techniques, resulting in an inherent upward bias in calculated emissions. In this work, Monte Carlo “ray tracing” (MCRT) analyses for realistic lines-of-sight through large-eddy simulated, soot-laden atmospheric plumes of gas flares were used as case study data for analysis of MS effects. Through a reverse MCRT procedure, a remarkably simple yet accurate model was derived that relates the quantity of inscattered light under MS conditions to an estimate assuming single-scattering. Case study data from previous field measurements of gas flares using the sky-LOSA technique demonstrate that neglecting MS effects can bias reported soot emission rates by up to and exceeding one-quarter of typical measurement uncertainties. Coupling this model with an additional procedure to correct for minor model biases allows the complex influence of multiple scattering to be directly and accurately considered in optical measurements of soot emissions.

The Evolution and Origin of Ionized Gas Velocity Dispersion from z ∼ 2.6 to z ∼ 0.6 with KMOS3D ∗

Abstract We present the 0.6 < z < 2.6 evolution of the ionized gas velocity dispersion in 175 star-forming disk galaxies based on data from the full integral field spectroscopic survey. In a forward-modeling Bayesian framework including instrumental effects and beam-smearing, we fit simultaneously the observed galaxy velocity and velocity dispersion along the kinematic major axis to derive the intrinsic velocity dispersion σ 0. We find a reduction of the average intrinsic velocity dispersion of disk galaxies as a function of cosmic time, from σ 0 ∼ 45 km s−1 at z ∼ 2.3 to σ 0 ∼ 30 km s−1 at z ∼ 0.9. There is substantial intrinsic scatter ( ) around the best-fit σ 0–z relation beyond what can be accounted for from the typical measurement uncertainties (δσ 0 ≈ 12 km s−1), independent of other identifiable galaxy parameters. This potentially suggests a dynamic mechanism such as minor mergers or variation in accretion being responsible for the scatter. Putting our data into the broader literature context, we find that ionized and atomic+molecular velocity dispersions evolve similarly with redshift, with the ionized gas dispersion being ∼10–15 km s−1 higher on average. We investigate the physical driver of the on average elevated velocity dispersions at higher redshift and find that our galaxies are at most marginally Toomre-stable, suggesting that their turbulent velocities are powered by gravitational instabilities, while stellar feedback as a driver alone is insufficient. This picture is supported through comparison with a state-of-the-art analytical model of galaxy evolution.

Dust attenuation in 2 < z < 3 star-forming galaxies from deep ALMA observations of the Hubble Ultra Deep Field

We present the results of a new study of the relationship between infrared excess (IRX), UV spectral slope (beta) and stellar mass at redshifts 2<z<3, based on a deep Atacama Large Millimeter Array (ALMA) 1.3-mm continuum mosaic of the Hubble Ultra Deep Field (HUDF). Excluding the most heavily-obscured sources, we use a stacking analysis to show that z~2.5 star-forming galaxies in the mass range 9.25 <= log(M/Msun) <= 10.75 are fully consistent with the IRX-beta relation expected for a relatively grey attenuation curve, similar to the commonly adopted Calzetti law. Based on a large, mass complete, sample of 2 <= z <= 3 star-forming galaxies drawn from multiple surveys, we proceed to derive a new empirical relationship between beta and stellar mass, making it possible to predict UV attenuation (A_1600) and IRX as a function of stellar mass, for any assumed attenuation law. Once again, we find that z~2.5 star-forming galaxies follow A_1600-mass and IRX-mass relations consistent with a relatively grey attenuation law, and find no compelling evidence that star-forming galaxies at this epoch follow a reddening law as steep as the Small Magellanic Cloud (SMC) extinction curve. In fact, we use a simple simulation to demonstrate that previous determinations of the IRX-beta relation may have been biased toward low values of IRX at red values of beta, mimicking the signature expected for an SMC-like dust law. We show that this provides a plausible mechanism for reconciling apparently contradictory results in the literature and that, based on typical measurement uncertainties, stellar mass provides a cleaner prediction of UV attenuation than beta. Although the situation at lower stellar masses remains uncertain, we conclude that for 2<z<3 star-forming galaxies with log(M/Msun) >= 9.75, both the IRX-beta and IRX-mass relations are well described by a Calzetti-like attenuation law.

The AMIGA sample of isolated galaxies

Context. We present the largest catalogue of HI single dish observations of isolated galaxies to date, as part of the multi-wavelength compilation being performed by the AMIGA project (Analysis of the interstellar Medium in Isolated GAlaxies). Despite numerous studies of the HI content of galaxies, no revision focused on the HI scaling relations of the most isolated L∗ galaxies has been made since Haynes &amp; Giovanelli (1984, AJ, 89, 758). Aims. The AMIGA sample has been demonstrated to be almost “nurture free”, therefore, by creating scaling relations for the HI content of these galaxies we will define a metric of HI normalcy in the absence of interactions. Methods. The catalogue comprises of our own HI observations with Arecibo, Effelsberg, Nançay and GBT, and spectra collected from the literature. In total we have measurements or constraints on the HI masses of 844 galaxies from the Catalogue of Isolated Galaxies (CIG). The multi-wavelength AMIGA dataset includes a revision of the B-band luminosities (LB), optical diameters (D25), morphologies, and isolation. Due to the large size of the catalogue, these revisions permit cuts to be made to ensure isolation and a high level of completeness, which was not previously possible. With this refined dataset we fit HI scaling relations based on luminosity, optical diameter and morphology. Our regression model incorporates all the data, including upper limits, and accounts for uncertainties in both variables, as well as distance uncertainties. Results. The scaling relation of HI mass with D25 is in good agreement with that of Haynes &amp; Giovanelli (1984), but our relation with LB is considerably steeper. This disagreement is attributed to the large uncertainties in the luminosities, which introduce a bias when fitting with ordinary least squares regression (as was done in previous works), and the different morphology distributions of the samples. We find that the main effect of morphology on the D25-relation is to increase the intercept towards later types, while for the LB-relation it is to flatten the slope. These trends were not evident in previous works due to the small number of detected early-type galaxies. Applying our relations to HI detected galaxies in the Virgo cluster we find that although the typical HI-deficiency is only ~0.3 dex, the tail of the distribution extends over an order of magnitude beyond that of the AMIGA sample. These results are in general agreement with previous studies of HI-deficiency in the Virgo cluster. Conclusions. The HI scaling relations of the AMIGA sample define an up-to-date metric of the HI content of almost “nurture free” galaxies. These relations allow the expected HI mass, in the absence of interactions, of an individual galaxy to be predicted to within 0.25 dex (for typical measurement uncertainties). These relations are thus suitable for use as statistical measures of the impact of interactions on the neutral gas content of galaxies.

A Stacked Dual-Frequency Microstrip Patch Antenna for Simultaneous Shear and Pressure Displacement Sensing

This paper presents a simultaneous shear and pressure displacement sensor based on the microstrip patch antenna technology. The antenna sensor consists of a dual-frequency patch antenna, a superstrate, and a rectangular director. The two fundamental resonant frequencies of the patch antenna are influenced by the lateral and vertical positions of the director with respect to its radiation patch. Therefore, the shear and pressure displacements of the director can be determined simultaneously from two fundamental antenna resonant frequencies. The antenna sensor was designed, fabricated, and tested to characterize its sensing performance. An algorithm was developed to inversely determine the shear and pressure displacements from the measured antenna frequencies. We validated that the typical measurement uncertainties of the antenna sensor is ±0.3 mm for the shear displacement and ±0.15 mm for the pressure displacement. The presented shear/pressure displacement sensor is intended for monitoring the interaction between the human body and assistive medical devices (e.g., prosthetic liners, diabetic shoes, seat cushions, and so on).

Liquid Viscosity and Surface Tension of n-Dodecane, n-Octacosane, Their Mixtures, and a Wax between 323 and 573 K by Surface Light Scattering

The present contribution provides experimental data for the liquid viscosity and surface tension of n-alkane based model systems at temperatures up to 573 K. The fundamental advantage of the used surface light scattering (SLS) method lies in its application in thermodynamic equilibrium without calibration in a contactless way. The investigated systems comprise the pure fluids n-dodecane (n-C12H26) and n-octacosane (n-C28H58), their binary mixture at a n-C12H26 mole fraction of about 0.3, and the commercially available hydrocarbon wax SX-70 representing a multicomponent mixture of n-alkanes with a broad chain length distribution. For the first time, it could be demonstrated that the SLS method can simultaneously access the liquid viscosity and surface tension of such medium- to long-chained n-alkane systems close to saturation conditions over a broad temperature range from 323 to 573 K. Typical measurement uncertainties of 2% based on a coverage factor k = 2, i.e., a level of confidence of more than 95%, were obtained. Over the entire temperature range, a simple polynomial equation for the dynamic viscosity and a modified van der Waals equation for the surface tension represent the measured data of the pure and binary systems well. The present investigations improve the data situation for hydrocarbon systems in the high-temperature range where no measurement results exist in literature.

The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies

Past UV and optical observations of stars hosting hot Jupiters have shown that some of these stars present an anomalously low chromospheric activity, significantly below the basal level. For WASP-13, observations have shown that the apparent lack of activity is possibly caused by absorption from the intervening ISM. Inspired by this result, we study the effect of ISM absorption on activity measurements (S and logR'$_{\rm HK}$ indices) for main-sequence late-type stars. To this end, we employ synthetic stellar photospheric spectra combined with varying amounts of chromospheric emission and ISM absorption. We present the effect of ISM absorption on activity measurements by varying several instrumental, stellar, and ISM parameters. We find that for relative velocities between the stellar and ISM lines smaller than 30-40 km/s and for ISM CaII column densities logN$_{\rm CaII}$>12, the ISM absorption has a significant influence on activity measurements. Direct measurements and three dimensional maps of the Galactic ISM absorption indicate that an ISM CaII column density of logN$_{\rm CaII}$=12 is typically reached by a distance of about 100 pc along most sight lines. In particular, for a Sun-like star lying at a distance greater than 100 pc, we expect a depression (bias) in the logR'$_{\rm HK}$ value larger than 0.05-0.1 dex, about the same size as the typical measurement and calibration uncertainties on this parameter. This work shows that the bias introduced by ISM absorption must always be considered when measuring activity for stars lying beyond 100 pc. We also consider the effect of multiple ISM absorption components. We discuss the relevance of this result for exoplanet studies.

NEW PARALLAXES AND A CONVERGENCE ANALYSIS FOR THE TW Hya ASSOCIATION

ABSTRACT The TW Hya Association (TWA) is a nearby stellar association with an age of ∼5–10 Myr. This is an important age for studying the late stages of star and planet formation. We measure the parallaxes of 14 candidate members of TWA. That brings to 38 the total number of individual stars with fully measured kinematics, i.e., proper motion, radial velocity, and parallax, to describe their motions through the Galaxy. We analyze these kinematics to search for convergence to a smaller volume in the past, but we find that the association is never much more compact than it is at present. We show that it is difficult to measure traceback ages for associations such as TWA that have expected velocity dispersions of 1–2 km s−1 with typical measurement uncertainties. We also use our stellar distances and pre-main-sequence evolutionary tracks to find the average age of the association of 7.9 ± 1.0 Myr. Additionally, our parallax measurement of TWA 32 indicates that it should be considered a bona fide member of TWA. Two new candidate members have high membership probabilities, and we assign them TWA numbers: TWA 45 for 2MASS J11592786–4510192 and TWA 46 for 2MASS J12354615–4115531.

Sensitivity of Alpine3D modeled snow cover to modifications in DEM resolution, station coverage and meteorological input quantities

This study presents a comprehensive sensitivity and uncertainty assessment of important input parameters on the Alpine3D modeled snow water equivalent (SWE) for two different alpine catchments. Horizontal resolution of the DEM grid, station coverage and several meteorological input quantities were modified. Decreasing the horizontal resolution from 25 m to 1000 m leads to a 10% higher SWE. Modifications in the spatial coverage of meteorological stations influences the SWE up to 20%. Modifications of meteorological input quantities within some plausible ranges lead to changes in SWE up to 30%. The results demonstrate that Alpine3D input uncertainties are in general in the same range as the typical measurement uncertainty of SWE and the uncertainty of the typical scenario spread of GCM-RCM ensemble runs.