The Spinning Enhanced Visible and Infrared Imager (SEVIRI) measurements from the Meteosat Second Generation (MSG) satellites enable global monitoring of the distribution of clouds during day and ...night, with a spatial, temporal and spectral resolution that allows for better understanding of the role of clouds in global radiation budget and in climate in general. A method to retrieve cloud properties from nighttime SEVIRI measurements is described in this paper. The method is applicable to single-layer water clouds over sea surfaces and it is based on the inversion of a forward theoretical radiative transfer model, that simulates the radiances reaching the SEVIRI infrared detectors from a specified configuration of the earth–cloud–atmosphere system. This model accounts for scattering and absorption processes in the assumed horizontally homogeneous adiabatic cloud layer. For the inversion of this model, artificial neural networks techniques have been used in this work. The main advantage that these techniques provide is their low computational cost, which makes them suitable for the implementation of operational retrieval procedures. Results obtained by the proposed method are compared with the values provided by the CloudSat derived 2B-TAU product, and those derived from NOAA-AVHRR nighttime imagery, obtaining good agreements.
► Remote sensing of nighttime boundary layer cloud properties from MSG-SEVIRI. ► Use of artificial neural networks techniques to invert a radiative transfer model. ► Cloud properties retrieval at near real-time. ► Validation of retrievals using 2B-TAU CloudSat product and NOAA-AVHRR data.
Hydraulic lift (HL) has been shown to improve performance of species occurring next to a plant engaged in HL, but whether this process plays an important role in seedling survival and growth in arid ...environments remains largely unknown. Here, we tested the influence of HL on the interaction between
Retama sphaerocarpa, a nurse lifter shrub from western Mediterranean basin, and the protégé shrub
Marrubium vulgare. Seedlings of
Marrubium were planted under the canopy of
Retama in three tube types inserted into the soil. Tubes either did not affect (Mesh), reduced (Netting) or fully prevented root competition (PVC). At the same time, these tubes allowed (Mesh, Netting) or prevented (PVC) soil water flux to/from the tube. Additional seedlings were planted in Mesh tubes in gaps (open spaces between shrubs). Hydraulic lift was measured using soil psychrometers. We detected HL patterns only in mesh and Netting tubes but not in solid-walled PVC tubes. Seedling survival was comparable where root competition was reduced and HL allowed (Netting) and where they were fully prevented (PVC) while survival was 23% lower in Mesh tubes (full root competition plus HL) and no seedlings survived in gaps. Differences in seedlings biomass showed somehow similar patterns, although biomass was greatest in PVC tubes followed by Netting tubes. These results show that, although HL might have contributed to seedling performance under the canopy of
Retama, it did not offset root competition from neighbours; when full root competition and HL occurred, competitive effects were stronger than facilitative effects of HL. Overall, intense root competition underneath nurse plants may outweigh the positive effects of the extra water meant by HL. Rather, microclimate amelioration and increased soil fertility under shrubs could account for the reported facilitation of
Marrubium seedlings by
Retama.
Ecosystems will likely be affected by changing rainfall patterns in dry environments and roots will play a major role in plant responses. However, little is known on root dynamics in response to ...changing rainfall in nature. In a rainout shelter experiment conducted in a semiarid shrub-steppe in south-eastern Spain, we manipulated both the amount (30% reduction all year round) and seasonal rainfall distribution according to climate change scenarios, with increases (30%) or subtle reductions (10%) in winter rainfall, and reductions in the remaining seasons (15% in spring and autumn or 40% in spring and autumn and 30% in summer). Minirhizotron tubes were used to monitor fine root dynamics beneath the canopy of the dominant shrub in a year that was above the average rainfall. We found higher root length density and enhanced root length production in the 30% reduction in annual rainfall compared to ambient (control) or any of the altered seasonality treatments. There were no differences among the three other treatments. By contrast, root length loss and root length turnover were not consistently influenced by rainfall treatments. These results evidence that moderate rainfall reductions all year round would have the largest impact on root dynamics in this arid shrubland. Increased or subtle rainfall reductions in rainy winters may have lower impact, due to moisture replenishment at the beginning of the growing season. These findings are stimulating for further research in larger time scales and in years with contrasting precipitation.
•Root density and production increased under 30% reduced annual rainfall.•Root loss and turnover was not affected consistently by rainfall amount or pattern.•Altered rainfall seasonality had no consistent effect on root dynamics.
Among the sample of Galactic transient X-ray binaries (SXTs) discovered to date, about 70 have been proposed as likely candidates to host a black hole. Yet, only 19 have been dynamically confirmed. ...Such a reliable confirmation requires phase-resolved spectroscopy of their companion stars, which is generally feasible when the system is in a quiescent state. However, since most of the SXT population lies in the galactic plane, which is strongly affected by interstellar extinction, their optical brightness during quiescence usually falls beyond the capabilities of the current instrumentation (
R
≳ 22). To overcome these limitations and thereby increase the number of confirmed Galactic black holes, a correlation between the full-width at half maximum (FWHM) of the H
α
line and the semi-amplitude of the donor’s radial velocity curve (
K
2
) was presented in the past. Here, we extend the FWHM–
K
2
correlation to the near-infrared (NIR), exploiting disc lines such as He
I
λ
10830, Pa
γ
, and Br
γ
, in a sample of dynamically confirmed black-hole SXTs. We obtain
K
2
= 0.22(3) FWHM, in good agreement with the optical correlation derived using H
α
. The similarity of the two correlations seems to imply that the widths of H
α
and the NIR lines are consistent in quiescence. When combined with information on orbital periods, the NIR correlation allows us to constrain the mass of the compact object of systems in quiescence by using single-epoch spectroscopy. We anticipate that this new correlation will give access to highly reddened black hole SXTs, which cannot be otherwise studied at optical wavelengths.
MAXI J1348–630 is a low mass X-ray binary discovered in 2019 during a bright outburst. During this event, the system experienced both hard and soft states following the standard evolution. We present ...multi-epoch optical and near-infrared spectroscopy obtained with X-shooter at the Very Large Telescope. Our dataset includes spectra taken during the brightest phases of the outburst as well as the decay towards quiescence. We study the evolution of the main emission lines, paying special attention to the presence of features commonly associated with accretion disc winds, such as blueshifted absorptions, broad emission line wings and flat-top profiles. We find broad emission line wings in H
α
during the hard-to-soft transition and blueshifted absorption troughs at ∼ − 500 km s
−1
in H
β
, He
I
–5876, H
α
and Pa
β
during the bright soft-intermediate state. In addition, flat-top profiles are seen throughout the outburst. We interpret these observables as signatures of a cold (i.e., optical-to-infrared) accretion disc wind present in the system. We discuss the properties of the wind and compare them with those seen in other X-ray transients. In particular, the wind velocity that we observe is low when compared to those of other systems, which might be a direct consequence of the relatively low binary inclination, as suggested by several observables. This study strengthens the hypothesis that cold winds are a common feature in low mass X-ray binaries and that they can also be detected in low inclination objects via high-quality optical and infrared spectroscopy.
The black hole transient GRS 1915+105 entered a new phase of activity in 2018, generally characterised by low X-ray and radio fluxes. This phase has only been interrupted by episodes of strong and ...variable radio emission, where high levels of X-ray absorption local to the source were measured. We present 18 epochs of near-infrared spectroscopy (2018–2023) obtained with GTC/EMIR and VLT/X-shooter, spanning both radio-loud and radio-quiet periods. We demonstrate that radio-loud phases are characterised by strong P-Cygni line profiles, indicative of accretion disc winds with velocities of up to ∼3000 km s
−1
. This velocity is consistent with those measured in other black hole transients. It is also comparable to the velocity of the X-ray winds detected during the peak outburst phases in GRS 1915+105, reinforcing the idea that massive, multi-phase outflows are characteristic features of the largest and most powerful black hole accretion discs. Conversely, the evolution of the Br
γ
line profile during the radio-quiet phases follows the expected trend for accretion disc lines in a system that is gradually decreasing its intrinsic luminosity, exhibiting weaker intensities and more pronounced double-peaks.
Optical spectroscopy of 4U 1812–12 Armas Padilla, M.; Muñoz-Darias, T.; Jiménez-Ibarra, F. ...
Astronomy and astrophysics (Berlin),
12/2020, Volume:
644
Journal Article
Peer reviewed
The persistent low-luminosity neutron star X-ray binary 4U 1812−12 is a potential member of the scarce family of ultra-compact systems. We performed deep photometric and spectroscopic optical ...observations with the 10.4 m Gran Telescopio Canarias in order to investigate the chemical composition of the accreted plasma, which is a proxy for the donor star class. We detect a faint optical counterpart (
g
∼ 25,
r
∼ 23) that is located in the background of the outskirts of the Sharpless 54 H
II
region, whose characteristic nebular lines superimpose on the X-ray binary spectrum. Once this is corrected for, the actual source spectrum lacks hydrogen spectral features. In particular, the H
α
emission line is not detected, with an upper limit (3
σ
) on the equivalent width of < 1.3 Å. Helium (He
I
) lines are also not observed, even though our constraints are not restrictive enough to properly test the presence of this element. We also provide stringent upper limits on the presence of emission lines from other elements, such as C and O, which are typically found in ultra-compact systems with C−O white dwarfs donors. The absence of hydrogen features, the persistent nature of the source at low luminosity, and the low optical–to–X-ray flux ratio confirm 4U 1812−12 as a compelling ultra-compact X-ray binary candidate, for which we tentatively propose a He-rich donor based on the optical spectrum and the detection of short thermonuclear X-ray bursts. In this framework, we discuss the possible orbital period of the system according to disc instability and evolutionary models.
The objective of this study was to assess the pharmacokientic parameters of regular nimodipine (Bayer), 30 mg, given every 6 h and nimodipine AP (nimodipine in micro particles with programmed action ...contained in tablets, developed by Biocontrolled-Leti Group Laboratories), 120 mg, given every 24 h. Subjects (19 healthy volunteers, five female; 14 male: age: 21 +/- 0.7 years) received one formulation over 5 days. Then, after a washout period of 7 days, the other formulation was given. The analyst was blinded to the relationship in formulation received. Antecubital blood samples were taken before the first tablet was taken and after 15, 45, 60 min and 2, 4, 6, 8, 12, 13, 18 and 24 h on day 1 and five of each formulation. Nimodipine blood levels were analysed by HPLC. At steady-state regular nimodipine reached a C-max of 10.208 +/- 0.317 ng/ml, at a t-max of 1 h; minimum concentration 6 h after dosage was 1.2929 +/- 0.411 ng/ml, half-life was estimated in 2.9 h. Meanwhile nimodipine AP 120 mg reach a C-max of 11.885 +/- 0.403 ng/ml; a t-max of 1 h with a minimum concentration 24 h after the last dose of 4.2387 +/- 0.353 ng/ml (P < 0.001). Apparent half-life was calculated in 17.8 h (P < 0.001). Area under the curve for the 24 h period was 143.76 ng/ml/min for regular nimodipine and 183.7 ng/ml/min for nimodipine AP 120 mg (P < 0.001), indicating better bioavailability. In conclusion nimodipine in AP formulation 120 mg produced similar peak plasma levels (C-max) than regular nimodipine, but with higher trough (C-min) values and stable plasma levels with one administration every 24 h. This formulation would be more suitable when nimodipine chronic therapy is indicated.
Context.
Markarian 501 (Mrk 501) is a very high-energy (VHE) gamma-ray blazar located at
z
= 0.034, which is regularly monitored by a wide range of multi-wavelength instruments, from radio to VHE ...gamma rays. During a period of almost two weeks in July 2014, the highest X-ray activity of Mrk 501 was observed in ∼14 years of operation of the
Neil Gehrels Swift
Gamma-ray Burst Observatory.
Aims.
We characterize the broadband variability of Mrk 501 from radio to VHE gamma rays during the most extreme X-ray activity measured in the last 14 years, and evaluate whether it can be interpreted within theoretical scenarios widely used to explain the broadband emission from blazars.
Methods.
The emission of Mrk 501 was measured at radio with Metsähovi, at optical–UV with KVA and
Swift
/UVOT, at X-ray with
Swift
/XRT and
Swift
/BAT, at gamma ray with
Fermi
-LAT, and at VHE gamma rays with the FACT and MAGIC telescopes. The multi-band variability and correlations were quantified, and the broadband spectral energy distributions (SEDs) were compared with predictions from theoretical models.
Results.
The VHE emission of Mrk 501 was found to be elevated during the X-ray outburst, with a gamma-ray flux above 0.15 TeV varying from ∼0.5 to ∼2 times the Crab nebula flux. The X-ray and VHE emission both varied on timescales of 1 day and were found to be correlated. We measured a general increase in the fractional variability with energy, with the VHE variability being twice as large as the X-ray variability. The temporal evolution of the most prominent and variable segments of the SED, characterized on a day-by-day basis from 2014 July 16 to 2014 July 31, is described with a one-zone synchrotron self-Compton model with variations in the break energy of the electron energy distribution (EED), and with some adjustments in the magnetic field strength and spectral shape of the EED. These results suggest that the main flux variations during this extreme X-ray outburst are produced by the acceleration and the cooling of the high-energy electrons. A narrow feature at ∼3 TeV was observed in the VHE spectrum measured on 2014 July 19 (MJD 56857.98), which is the day with the highest X-ray flux (>0.3 keV) measured during the entire
Swift
mission. This feature is inconsistent with the classical analytic functions to describe the measured VHE spectra (power law, log-parabola, and log-parabola with exponential cutoff) at more than 3
σ
. A fit with a log-parabola plus a narrow component is preferred over the fit with a single log-parabola at more than 4
σ
, and a dedicated Monte Carlo simulation estimated the significance of this extra component to be larger than 3
σ
. Under the assumption that this VHE spectral feature is real, we show that it can be reproduced with three distinct theoretical scenarios: (a) a pileup in the EED due to stochastic acceleration; (b) a structured jet with two-SSC emitting regions, with one region dominated by an extremely narrow EED; and (c) an emission from an IC pair cascade induced by electrons accelerated in a magnetospheric vacuum gap, in addition to the SSC emission from a more conventional region along the jet of Mrk 501.
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