The tenth recorded outburst of the recurrent eclipsing nova U Sco was observed simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9 after the outburst. Two full passages of ...the companion in front of the nova ejecta were observed, as was the reformation of the accretion disk. On day 22.9, we observed smooth eclipses in UV and optical but deep dips in the X-ray light curve that disappeared by day 34.9, yielding clean eclipses in all bands. X-ray dips can be caused by clumpy absorbing material that intersects the line of sight while moving along highly elliptical trajectories. Cold material from the companion could explain the absence of dips in UV and optical light. The disappearance of X-ray dips before day 34.9 implies significant progress in the formation of the disk. The X-ray spectra contain photospheric continuum emission plus strong emission lines, but no clear absorption lines. Both continuum and emission lines in the X-ray spectra indicate a temperature increase from day 22.9 to day 34.9. We find clear evidence in the spectra and light curves for Thompson scattering of the photospheric emission from the white dwarf. Photospheric absorption lines can be smeared out during scattering in a plasma of fast electrons. We also find spectral signatures of resonant line scattering that lead to the observation of the strong emission lines. Their dominance could be a general phenomenon in high-inclination systems such as Cal 87.
The thermodynamic temperature of the point of inflection of the melting transition of Re-C, Pt-C and Co-C eutectics has been determined to be 2747.84 ± 0.35 K, 2011.43 ± 0.18 K and 1597.39 ± 0.13 K, ...respectively, and the thermodynamic temperature of the freezing transition of Cu has been determined to be 1357.80 ± 0.08 K, where the ± symbol represents 95% coverage. These results are the best consensus estimates obtained from measurements made using various spectroradiometric primary thermometry techniques by nine different national metrology institutes. The good agreement between the institutes suggests that spectroradiometric thermometry techniques are sufficiently mature (at least in those institutes) to allow the direct realization of thermodynamic temperature above 1234 K (rather than the use of a temperature scale) and that metal-carbon eutectics can be used as high-temperature fixed points for thermodynamic temperature dissemination. The results directly support the developing mise en pratique for the definition of the kelvin to include direct measurement of thermodynamic temperature.
Seventeen years (1998–2014) of satellite-derived chlorophyll concentration (Chl) are used to analyse the seasonal and non-seasonal patterns of Chl variability and the long-term trends in ...phytoplankton phenology in the Mediterranean Sea. With marked regional variations, we observe that seasonality dominates variability representing up to 80% of total Chl variance in oceanic areas, whereas in shelf-sea regions high frequency variations may be dominant representing up to 49% of total Chl variance. Seasonal variations are typically characterized by a phytoplankton growing period occurring in spring and spanning on average 170 days in the western basin and 150 days in the eastern basin. The variations in peak Chl concentrations are higher in the western basin (0.88 ± 1.01 mg m−3) compared to the eastern basin (0.35 ± 1.36 mg m−3). Differences in the seasonal cycle of Chl are also observed between open ocean and coastal waters where more than one phytoplankton growing period are frequent (>0.8 probability). During the study period, on average in the western Mediterranean basin (based on significant trends observed over ~95% of the basin), we show a positive trend in Chl of +0.015 ± 0.016 mg m−3 decade−1, and an increase in the amplitude and duration of the phytoplankton growing period by +0.27 ± 0.29 mg m−3 decade−1 and +11 ± 7 days decade−1 respectively. Changes in Chl concentration in the eastern (and more oligotrophic) basin are generally low, with a trend of −0.004 ± 0.024 mg m−3 decade−1 on average (based on observed significant trends over ~70% of the basin). In this basin, the Chl peak has declined by −0.03 ± 0.08 mg m−3 decade−1 and the growing period duration has decreased by −12 ± 7 days decade−1. The trends in phytoplankton Chl and phenology, estimated in this study over the period 1998–2014, do not reveal significant overall decline/increase in Chl concentration or earlier/delayed timings of the seasonal peak on average over the entire Mediterranean Sea basin. However, we observed large regional variations, suggesting that the response of phytoplankton to environmental and climate forcing may be complex and regionally driven.
•Trends in phytoplankton phenology in the Mediterranean Sea during 1998–2014•Basin and regional scale differences exist throughout the Mediterranean Sea.•Bloom duration and intensity increased in the western but reduced in the east basin.•Non-seasonal variability is locally important at straits and channels.•Regional processes are important in the modulation of phytoplankton phenology.
After measuring thermodynamic temperatures in the range from 900 °C to 2500 °C, The Centro Español de Metrologia (CEM) in collaboration with the Instituto de Óptica of the Consejo Superior de ...Investigaciones Científicas (IO-CSIC) are currently involved in the measurement of thermodynamic temperatures down to 400 °C using radiometers based on InGaAs detectors with central wavelengths in the near-infrared spectral range (NIR). This communication summarizes the progress towards the extension of absolute radiation thermometry measurement range to lower temperatures.
Context. Classical novae (CNe) have recently been reported to represent the major class of supersoft X-ray sources (SSSs) in the central region of our neighbour galaxy M 31. Aims: We carried out a ...dedicated monitoring of the M 31 central region with XMM-Newton and Chandra in order to find SSS counterparts of CNe, determine the duration of their SSS phase and derive physical outburst parameters. Methods: We systematically searched our data for X-ray counterparts of CNe and determined their X-ray light curves and spectral properties. Additionally, we determined luminosity upper limits for all novae from previous studies which are not detected anymore and for all CNe in our field of view with optical outbursts between May 2005 and March 2007. Results: We detected eight X-ray counterparts of CNe in M 31, four of which were not previously known. Seven sources can be classified as SSSs, one is a candidate SSS. Two SSSs are still visible more than nine years after the nova outburst, whereas two other nova counterparts show a short SSS phase of less than 150 days. Of the latter sources, M31N 2006-04a exhibits a short-time variable X-ray light curve with an apparent period of (1.6±0.3) h. This periodicity could indicate the binary period of the system. There is no X-ray detection for 23 out of 25 CNe which were within the field of view of our observations and had their outburst from about one year before the start of the monitoring until its end. From the 14 SSS nova counterparts known from previous studies, ten are not detected anymore. Additionally, we found four SSSs in our XMM-Newton data without a nova counterpart, one of which is a new source. Conclusions: Out of eleven SSSs detected in our monitoring, seven are counterparts of CNe. We therefore confirm the earlier finding that CNe are the major class of SSSs in the central region of M 31. We use the measured SSS turn-on and turn-off times to estimate the mass ejected in the nova outburst and the mass burned on the white dwarf. Classical novae with short SSS phases seem to be an important contributor to the overall population.
At present, numerical simulations are the common method to predict the response of quantum efficient detectors based on induced-junction diodes. As alternative, this work proposes an analytical model ...based on photocurrent analysis where surface and bulk losses are modelled considering design and operation photodiode parameters and the characteristics of the incident beam. The model shows how, at short wavelengths, the surface recombination velocity dominates the losses that are directly proportional, whereas the bulk doping and reverse bias voltage determine the losses at long wavelengths. The results obtained by the here proposed analytical model are discussed for different values of surface recombination velocity and compared with simulations reported by other authors. For wavelengths from 400 nm up to 700 nm, the losses calculated by the analytical model at room temperature are in the order of tens of ppm for values between 1000 cm/s and 10000 cm/s of surface recombination velocity. Some simulations agree with a maximum difference of 80 ppm up to 700 nm, where the abrupt rise of bulk losses starts for the analytical model but it is shifted around 800 nm for reported simulations.
Two XMM-Newton observations of the fast classical nova V2491 Cyg were carried out in short succession on days 39.93 and 49.62 after discovery, during the supersoft source (SSS) phase, yielding ...simultaneous X-ray and UV light curves and high-resolution X-ray spectra. The first X-ray light curve is highly variable, showing oscillations with a period of 37.2 minutes after an extended factor of three decline lasting ~3 hr, while the second X-ray light curve is less variable. The cause of the dip is currently unexplained and has most likely the same origin as similar events in the early SSS light curves of the novae V4743 Sgr and RS Oph, as it occurred on the same timescale. The oscillations are not present during the dip minimum and also not in the second observation. The UV light curves are variable but contain no dips and no period. High-resolution X-ray spectra are presented for four intervals of differing intensity. All spectra are atmospheric continua with deep absorption lines and absorption edges. Two interstellar lines of O I and N I are clearly seen at their rest wavelengths, while a large number of high-ionization absorption lines are found at blueshifts indicating an expansion velocity of 3000-3400 km s--1, which does not change significantly during the epochs of observation. Comparisons with the slower nova V4743 Sgr and the symbiotic recurrent nova RS Oph are presented. The SSS spectrum of V4743 Sgr is much softer with broader and more complex photospheric absorption lines. The ejecta are extended, allowing us to view a larger range of the radial velocity profile. Meanwhile, the absorption lines in RS Oph are as narrow as in V2491 Cyg, but they are less blueshifted. A remarkable similarity in the continua of V2491 Cyg and RS Oph is found. The only differences are smaller line shifts and additional emission lines in RS Oph that are related to the presence of a dense stellar wind from the evolved companion. Three unidentified absorption lines are present in the X-ray spectra of all three novae, with projected rest wavelengths 26.05 A, 29.45 A, and 30.0 A. No entirely satisfactory spectral model is currently available for the soft X-ray spectra of novae in outburst, and careful discussion of assumptions is required.
The evolving mise en pratique for the definition of the kelvin (MeP-K)
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,
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will, in its forthcoming edition, encourage the realization and dissemination of the thermodynamic temperature either ...directly (primary thermometry) or indirectly (relative primary thermometry) via fixed points with assigned reference thermodynamic temperatures. In the last years, the Centro Español de Metrología (CEM), in collaboration with the Instituto de Óptica of Consejo Superior de Investigaciones Científicas (IO-CSIC), has developed several setups for absolute calibration of standard radiation thermometers using the radiance method to allow CEM the direct dissemination of the thermodynamic temperature and the assignment of the thermodynamic temperatures to several fixed points. Different calibration facilities based on a monochromator and/or a laser and an integrating sphere have been developed to calibrate CEM’s standard radiation thermometers (KE-LP2 and KE-LP4) and filter radiometer (FIRA2). This system is based on the one described in
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placed in IO-CSIC. Different light sources have been tried and tested for measuring absolute spectral radiance responsivity: a Xe-Hg 500 W lamp, a supercontinuum laser NKT SuperK-EXR20 and a diode laser emitting at 6473 nm with a typical maximum power of 120 mW. Their advantages and disadvantages have been studied such as sensitivity to interferences generated by the laser inside the filter, flux stability generated by the radiant sources and so forth. This paper describes the setups used, the uncertainty budgets and the results obtained for the absolute temperatures of Cu, Co-C, Pt-C and Re-C fixed points, measured with the three thermometers with central wavelengths around 650 nm.
The capability of L-band radiometry to monitor surface soil moisture (SM) at global scale has been analyzed in numerous studies, mostly in the framework of the ESA SMOS and NASA SMAP missions. To ...retrieve SM from L-band radiometric observations, two significant effects have to be accounted for, namely soil roughness and vegetation optical depth. In this study, soil roughness effects on retrieved SM values were evaluated using brightness temperatures acquired by the L-band ELBARA-II radiometer, over a vineyard field at the Valencia Anchor Station (VAS) site during the year 2013. Different combinations of the values of the model parameters used to account for soil roughness effects (HR, QR, NRH and NRV) in the L-MEB model were evaluated. The L-MEB model (L-band Microwave Emission of the Biosphere) is the forward radiative transfer model used in the SMOS soil moisture retrieval algorithm. In this model, HR parameterizes the intensity of roughness effects, QR accounts for polarization effects, and NRH and NRV parameterize the variations of the soil reflectivity as a function of the observation angle, θ, respectively for both H (Horizontal) and V (Vertical) polarizations. These evaluations were made by comparing in-situ measurements of SM (used here as a reference) against SM retrievals derived from tower-based ELBARA-II brightness temperatures mentioned above. The general retrieval approach consists of the inversion of L-MEB. Two specific configurations were tested: the classical 2-Parameter (2-P) retrieval configuration where SM and τNAD (vegetation optical depth at nadir) are retrieved, and a 3-Parameter (3-P) configuration, accounting for the additional effects of the vineyard vegetation structure.
Using the 2-P configuration, it was found that setting NRp (p=H or V) equals to −1 provided the best SM estimations in terms of correlation and unbiased Root Mean Square Error (ubRMSE). The assumption NRV=NRH=−1 simplifies the L-MEB retrieval, since the two parameters τNAD and HR can then be grouped and retrieved as a single parameter (method here defined as the Simplified Retrieval Method (SRP)). The main advantage of the SRP method is that it is not necessary to calibrate HR before performing the SM retrievals. Using the 3-P configuration, the results improved, with respect to SM retrievals, in terms of correlation and ubRMSE, as the structural characteristics of the vineyards were better accounted for. However, this method still requires the calibration of HR, a disadvantage for operational applications. Finally, it was found that the use of in-situ roughness measurements to calibrate the roughness model parameters did not provide significant improvements in the SM retrievals as compared to the SRP method.
•Roughness parameterizations at L-band were evaluated using in situ radiometric data.•2-P and 3-P retrievals, accounting for changes in vegetation structure, were tested.•Lower performances in SM retrievals were obtained for increasing values of HR.•Best SM retrievals were generally obtained using NRV=NRH=−1.•The use of in situ roughness measurements did not improve SM retrievals.
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