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Analyzing and modeling snow loss and snow loss accumulation in ground-mounted photovoltaic systems
No full textSnow can cause significant energy loss in photovoltaic systems, making it essential to account for in performance modeling for all snow-prone regions. Previous snow loss research has been conducted primarily for roof mounted systems, and there is a lack of reported snow losses and validation of snow loss models for ground mounted systems. The aim of this work is to quantify snow loss and validate the Marion snow loss model for ground mounted PV systems using data from two scientific test sites in Norway. The quantification of snow losses indicates that ground mounted systems have lower snow losses compared to what have previously been documented for roof mounted systems in Norway and similar climates. Additionally, monofacial and bifacial arrays experienced similar losses. At the same test site, the bifacial array’s monthly losses were, on average, 0.2 percentage points higher than those of the monofacial array. In the snow loss model validation, the impact of snow data quality was evaluated. The global weather snow data sources assessed (ERA5-Land and ERA5 global) had a large share of snowfall events not giving snow accumulation. These events were linked to both small snowfalls and higher temperatures. The default pvlib implementation of the Marion model typically underestimates losses, but the error in relative yearly losses is less than 0.5 percentage points. The error in the modeling is mainly related to periods where the temperature is close to zero, when both the snow input data and the prediction of snow shedding are more uncertain. Ground interference due to large snow depths also leads to slower shedding and underestimation of losses in the model
How our proto-nuclear star cluster formed and grew due to early globular cluster disruption
No full textContext. To date, two main mechanisms have been proposed for the formation and growth of nuclear star clusters (NSCs) in galaxies. The first suggests in situ star formation from gas that has migrated to the central regions from the galaxy’s outskirts, while the second involves the accretion of stars from disrupted globular clusters (GCs) onto the galactic centre. However, the relative importance of these mechanisms in the evolution of NSCs across different galaxy morphologies remains an open question.
Aims. We investigate the accretion of GC stars on early cosmological timescales through detailed N-body simulations of theoretical GC models to assess the role of this mechanism in Milky Way-like (MW-like) galaxies.
Methods. For the dynamical modelling, we used the updated parallel N-body code ϕ-GPU, including stellar evolution. We prepared three sets of GC models with different half-mass radii (rhm), each consisting of 50 full N-body GC models, and integrated these models in an external, time-variable MW-like potential taken from the cosmological database IllustrisTNG-100. The simulations cover the time interval from −10 Gyr to −5 Gyr, enabling us to assess the rate of early stellar accretion onto the proto-NSC.
Results. We find that GC models with average orbital eccentricities of 0.4−0.5 and orbits oriented perpendicular to the galactic disc contribute most significantly to the mass of the proto-NSC formation. Accretion is especially efficient in the first billion years (Gyr) and in compact GC models with rhm=1 pc. In all sets, the dominant accreted stellar population consists of low-mass stars (≈ 0.33 M⊙). However, the accreted mass alone is insufficient to fully account for the current NSC mass.
Conclusions. Based on our extended set of numerical simulations, we obtained an average lower limit of mass contribution (≈ 6%) to the NSC from investigated GCs. The fraction of mass contribution from individual disrupted GCs can significantly vary from 0.1% up to 90%. Generally, we conclude that the GC stellar accretion channel alone might not be sufficient to ensure the present-day MW galaxy’s NSC mass budget
Substellar initial mass function of Trumpler 14
No full textContext. Young, massive stellar clusters offer a prime setting to explore brown dwarf (BD) formation under high densities and intense UV radiation. Trumpler 14 (Tr 14), a ∼1 Myr old cluster located at a distance of 2.4 kpc that is particularly rich in O-type stars, is an ideal target for such a study.
Aims. Our goal is to measure the initial mass function (IMF) in the young massive, high-UV-flux cluster.
Methods. We present the deepest study to date of the IMF in Tr 14, based on Gemini Multi-Conjugate Adaptive Optics System/Gemini-South Adaptive Optics Imager imaging. We constructed the IMF using both the Besançon Galactic model and an observational control field from VISTA for background correction. Completeness was assessed using artificial star tests and applied to the IMF derivation.
Results. We estimated the IMF down to the 20% completeness limit found at ∼0.01 M⊙. Using the control-field-based IMF as our primary result, we find a slope of α = 0.14 ± 0.19 for masses between 0.01 and 0.2 M⊙, and α = 1.72 ± 0.04 for 0.2–4.5 M⊙, where dN/dM ∝ M−α. The low-mass slope is largely influenced by the incompleteness-affected lowest bin; excluding it brings our results into agreement with those for other young clusters. The resulting median for the star-to-BD ratio in the 0.03–1 M⊙ mass range is 4.0, with a 95% confidence interval of 2.8–5.8.
Conclusions. Our analysis reveals that Tr 14 hosts a relatively flat substellar IMF, but this is strongly influenced by the lowest-mass bin, which may be affected by incompleteness. When that bin is excluded, the IMF becomes consistent with those of other regions. The star-to-BD ratio falls within the usually observed ∼3–6 range, indicating that BDs with masses above ∼0.03 M⊙ form with similar efficiencies across environments. However, the relative lack of objects below this threshold suggests that the presence of an environment with both high stellar density and far-UV flux plays a role in shaping the IMF by suppressing the formation of BDs at masses <0.03 M⊙
Refractive indices of photochemical haze analogs for Solar System and exoplanet applications: A cross-laboratory comparative study between the PAMPRE and COSmIC experimental setups
No full textPrevious observations of Titan, Pluto, and Solar System gas giants, along with recent observations of exoplanet atmospheres with the James Webb Space Telescope, have taught us that photochemical hazes are ubiquitous and form in a variety of temperature, gas composition, and irradiation environments. Despite their crucial role in understanding their impact on observations and on the planetary radiative budget, the refractive indices of these haze particles remain unknown and are strongly influenced by changes in gas-phase chemistry. In this study, we performed a cross-laboratory investigation to assess the effect of the experimental setup and gas composition on the refractive indices of Titan, Pluto, and exoplanet haze analogs. We report new data in a broad spectral range from UV to far-IR (up to 200 μm) for future use in climate models and retrieval frameworks. We compare the refractive indices of laboratory haze analogs produced from six different gas compositions, in which we varied the relative abundances N2/CH4 and CH4/CO in the initial gas mixture, using the PAMPRE (LATMOS, France) and COSmIC (NASA Ames Research Center, USA) experimental setups. We observed strong variations in the k values in the spectral range from UV to near-IR between the different analogs, which are caused by both the experimental setup and changes in the gas N2/CH4 ratio. We find that the gas N2/CH4 ratio has a stronger influence on the haze refractive indices in the entire spectral range compared to the gas CH4/CO ratio. The experimental setup is the primary factor affecting the refractive indices, confirming that the gas residence time, irradiation, pressure, and gas temperature are important parameters influencing the composition of the solid analog. The higher n and k values in the UV-visible range, along with the stronger amine, alkene, aromatic, and/or hetero-aromatic signatures in the mid-IR for the COSmIC analogs, are consistent with a greater incorporation of nitrogen into the COSmIC solid analogs compared to the PAMPRE analogs, even at similar nitrogen abundances in the gas phase. Haze analogs produced in gas mixtures without nitrogen, similar to the stratospheres of Solar System gas giants and the H2-dominated atmospheres of sub-Neptunes, are generally more transparent with lower n values across the entire spectral range from UV to mid-IR and should therefore be carefully considered in climate and observational applications. The variations in IR absorption features between hazes produced with and without nitrogen could help constrain the presence of N2 in exoplanet atmospheres
Dynamical evolution of massless particles in star clusters with
No full textContext. Comets, asteroids, planetesimals, free-floating planets, and brown dwarfs are continuously injected into the intracluster environment after expulsion from their host-planetary systems or binary system. The dynamics of large populations of such free-floating comets (ff
Superhot (> 30 MK) flare observations with STIX: Joint spectral fitting
No full textContext. Spectroscopic analysis of large flares (> X1) in the hard X-ray (HXR) range offers unique insights into the hottest (> 30 MK) flare plasma, the so-called superhot thermal component. To manage the high count rates in large flares, an attenuator is typically placed in front of the HXR detectors. However, this significantly limits the spectral diagnostic capabilities at lower energies, and consequently, it restricts the analysis of the lower temperatures in flares.
Aims. The Spectrometer/Telescope for Imaging X-rays (STIX) on board the Solar Orbiter mission was designed to observe solar flares in HXRs. The imaging detectors use an attenuator during periods of high flux. In contrast, the background (BKG) detector of STIX is never covered by the attenuator and is therefore dedicated to measuring the unattenuated flux using differently sized apertures placed in front of the detector. We aim to demonstrate that joint spectral fitting using different detector configurations of STIX allows us to reliably diagnose both the hot and the superhot components in large flares.
Methods. We jointly fit the HXR spectra of the STIX BKG detector and the STIX imaging detectors using the SUNKIT-SPEX software package to determine the spectral parameters of both the hot and superhot thermal components in solar flares.
Results. Using joint fitting on 32 STIX flares, we corroborated that for GOES X-class flares the HXR spectrum is better represented by two thermal components instead of an isothermal component. At the temperature peak time, the superhot HXR flux above ∼15 keV is typically stronger than the hot HXR flux. The GOES long-wavelength channel is dominated by the hot component with a superhot contribution up to 10%.
Conclusions. This paper demonstrates that joint spectral fitting of the same detector type with different attenuation schemes is a simple and powerful method of monitoring multithermal flare plasma
Solar limb faculae: Intensity contrast from two vantage points
No full textContext. Small-scale magnetic-flux concentrations contribute significantly to the brightness variations of the Sun, yet observing them – particularly their magnetic field – near the solar limb remains challenging. The Solar Orbiter mission offers an unprecedented second vantage point for observing the Sun. When combined with observations from the perspective of Earth, this enables simultaneous dual-viewpoint measurements of these magnetic structures, thereby helping to mitigate observational limitations.
Aims. Using such a dual-viewpoint geometry, we characterised the brightness contrast of faculae near the limb as a function of both their associated magnetic field strength and the observation angle.
Methods. We analysed data from the Polarimetric and Helioseismic Imager on board the Solar Orbiter (SO/PHI), obtained during an observation programme conducted in near-quadrature configuration with Earth, in combination with data from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory (SDO/HMI). The High Resolution Telescope of SO/PHI observed a facular region located near the disc centre as seen from its vantage point, while the same region was simultaneously observed near the solar limb by SDO/HMI. We identified faculae and determine their magnetic field strength from the disc-centre observations, and combined these with continuum intensity measurements at the limb to derive dual-viewpoint contrast curves. We then compared these with contrast curves derived from SDO/HMI alone.
Results. Using two viewpoints, we consistently find higher facular contrast near the limb than from a single viewpoint. A comparison of the facular line-of-sight magnetic field derived from limb observations with that derived from disc-centre observations (and re-projected to the limb) reveals significant differences between the two. Co-temporal observations of limb faculae from a second, disc-centre viewpoint enable a more precise determination of their associated magnetic field
Peak-intensity energy spectra of intense solar energetic electron events measured with Solar Orbiter in 2020–2022
No full textContext. The energy spectra of energetic particles offer valuable insights into particle acceleration processes. While the commonly observed spectral breaks in solar energetic electron (SEE) spectra could serve as fingerprints of the acceleration process, several transport-related effects have been proposed to be responsible as well. Here, we analyse the energy spectra of intense SEE events measured with Solar Orbiter’s Energetic Particle Detector (EPD) between December 2020 and December 2022.
Aims. We investigate the shape of SEE spectra by fitting them with various mathematical models. We compare our results with previous studies and explore possible links to transport-related effects. We aim to identify potential correlations between spectral features and meaningful parameters, such as the radial distance, or the properties of associated solar events.
Methods. We determined the background-subtracted peak-intensity spectra as observed by EPD, accounting for velocity dispersion. We fit the spectra of STEP and EPT with various mathematical models, using an automated method that chooses the best possible fit.
Results. We found four different spectral shapes in our analysis: single power law, double power law and two types of triple power law: a knee-knee (KK) and an ankle-knee (AK) triple power law. No significant correlations with radial distance were identified; although the observed spectral shapes display an ordering with the longitudinal separation between the spacecraft and the associated solar flare. We also observed a correlation between the spectral index in the intermediate energy range at 70 keV and the strength of the associated solar flare. The correlation disappears at lower and higher energies, suggesting a stronger influence of transport effects at those energies.
Conclusions. We conclude that multiple processes are likely involved in shaping SEE spectra. Our results suggest that the two breaks of the KK triple power law spectra arise from distinct effects, Langmuir-wave generation, and pitch-angle scattering, respectively. Our results also suggest that the break in the double power laws could represent a merger between the first and second breaks of KK triple power laws
Influence of the Martian crustal magnetic fields on oxygen ion escape at Mars
No full textContext. The escape of oxygen ions from Mars has played a crucial role in the planet’s long-term atmospheric evolution and habitability. The crustal magnetic fields influence ion escape, but the exact role remains debated. Previous studies have presented contrasting conclusions, suggesting that the crustal fields may either suppress or enhance oxygen ion escape. To date, the extent and mechanisms of this influence remain insufficiently understood.
Aims. This study aims to investigate the influence of the Martian crustal magnetic fields on the oxygen ion escape at Mars.
Methods. Several groups of 3D global hybrid simulations of Mars-solar wind interaction were performed, with the escaping oxygen ion trajectories traced. The results from the simulations with or without the crustal fields and under different interplanetary magnetic field conditions were then compared.
Results. The simulation results show that the presence of crustal fields enhances the ionospheric oxygen ion escape, while the exospheric oxygen ion escape rate remains largely unaffected. The crustal magnetic fields alter the local electric and magnetic environments and, subsequently, modify the local oxygen ion density and flow direction in the ionosphere. First, the steep magnetic inclination and large magnetic strength in crustal field regions increase the density of low-altitude ionospheric oxygen ions and facilitate their outward transport, thereby promoting ion escape. Second, the crustal fields modify the local electric field structure, which also affects ion acceleration and escape. When strong crustal fields are located on the dayside, their obstruction of the upstream plasma flow weakens the dayside radial electric field at low altitudes in the southern hemisphere. The weakened electric field tends to assist or reduce ion escape, depending on whether it points toward or away from Mars, respectively. In any case, the influence of the magnetic field topology change (the steep magnetic inclination and large magnetic strength) in crustal field regions dominates the effect of weakened electric field, resulting in a higher escape rate than that without the crustal fields. Additionally, when strong crustal fields are on the nightside, the dayside moderate crustal fields still enhance the local density and outward transport of ionospheric oxygen ions, while their impact on the local electric field remains limited. The net effect is enhanced ion escape over the +E hemisphere where the solar wind motional electric field points away from Mars
Selection and characterisation of the M dwarf targets in the PLATO Input Catalogue
No full textContext. The aim of the European Space Agency’s PLAnetary Transits and Oscillations of Stars (PLATO) mission is to detect planets orbiting around dwarfs and subgiant stars with spectral type F5 or later, including M dwarfs. The PLATO Input Catalogue (PIC) contains all PLATO targets available for observation by the PLATO nominal science. The latest version, PIC2.1.0.1, focuses on the Southern PLATO field, named LOPS2, selected as the first long observation field, and includes the P4 sample, one of the four target samples outlined in the Science Requirement Document. P4 includes the M dwarfs with magnitudes brighter than V=16 located within LOPS2.
Aims. A characterisation of the M dwarfs in the PIC is essential for assessing their potentiality to host exoplanets, and eventually for estimating the hosted planet(s) properties. The purpose of this paper is to describe how we selected the P4 M dwarf targets, and obtained their fundamental parameters and properties.
Methods. Measuring stellar parameters is a challenging task. Interferometry provides direct estimates of radii, whereas alternative approaches relying on theoretical assumptions are still affected by significant uncertainties. In this work, we introduce the P4 sample and detail the methodologies, all based on photometric criteria, adopted for the measurement of their stellar parameters.
Results. Based on a statistical analysis of the P4 sample, we assess both the photometric and volume completeness, and classify the stellar populations according to their Galactic spatial-velocity components. The adopted stellar parameters are validated by comparison with independent methods from the literature used to estimate stellar radii.
Conclusions. We conclude that the P4 sample is compliant with the PLATO science requirements. Being magnitude limited, its volume completeness decreases going towards distances larger than 30 pc, where late-type targets are progressively less covered. The observed large spread in the colour-magnitude diagram is likely due to the combination of several effects such as metallicity, age, binarity, and activity. The strategy we adopted for deriving stellar parameters provides results consistent with those obtained in the literature with different and independent methods