Solar Luminosity Research Articles

Multifractality of the standardized precipitation index: influence of pan evaporation and virtual temperature-based potential evapotranspiration

Hydrological extremes experience an increase in some regions and a decrease in other zones. The objectives of the present work were (i) to introduce Class A pan evaporation data and virtual temperature-based potential evapotranspiration (PETv hereafter) into the Standardized Precipitation–Evapotranspiration Index (SPEIm hereafter) computation and (ii) to describe small and large fluctuations of SPI and SPEIm through multifractal detrended fluctuation (MF-DFA) and multifractal detrended cross-correlation (MF-DCCA) analyses. We used 40 years data (1974–2013) of monthly rainfall (P), mean, minimum and maximum air temperature, pan evaporation (E), relative humidity (RH) and relative sun brightness (RSB). Meteorological variables were collected from Puyo meteorological station, Pastaza Province, Ecuador. SPI time series for 1 and 6 months timescales were determined following two approaches. We computed SPI values using precipitation as the only input variable. Additionally, we incorporated pan evaporation and virtual temperature-based potential evapotranspiration into the standard SPEI computation (SPEIm). The SPEIm revealed some differences as compared with the classical SPI methodology. Five out of fifteen Asymmetry Index (AI) values were positive (0.095 ≤ AI ≤ 0.419).This indicates the relevance of high fluctuations at different time scales. Joint multifractal spectra between SPI (1,6)/SPEIm(1,6) versus RH and RSB rendered negative AI values which suggests the importance of low fluctuations at shorter time scales. The DCCA cross-correlation coefficient allows one to identify those time scales where SPI and SPEIm are influenced by other meteorological variables. Long-term correlation and sub-Gaussian behaviour of meteorological variables (apart from air temperature) are the main causes of multifractal structures.

Proton acceleration in thermonuclear nova explosions revealed by gamma rays

Classical novae are cataclysmic binary star systems in which the matter of a companion star is accreted on a white dwarf (WD). Accumulation of hydrogen in a layer eventually causes a thermonuclear explosion on the surface of the WD, brightening the WD to ~10^5 solar luminosities and triggering ejection of the accumulated matter.They provide extreme conditions required to accelerate particles, electrons or protons, to high energies. Here we present the detection of gamma rays by the MAGIC telescopes from the 2021 outburst of RS Ophiuchi (RS Oph), a recurrent nova with a red giant (RG) companion, that allowed us, for the first time, to accurately characterize the emission from a nova in the 60 GeV to 250 GeV energy range. The theoretical interpretation of the combined Fermi-LAT and MAGIC data suggests that protons are accelerated to hundreds of GeV in the nova shock. Such protons should create bubbles of enhanced Cosmic Ray density, on the order of 10 pc, from the recurrent novae.

Sky Brightness Evaluation at Concordia Station, Dome C, Antarctica, for Ground-Based Observations of the Solar Corona

The evaluation of sky characteristics plays a fundamental role for many astrophysical experiments and ground-based observations. In solar physics, the main requirement for such observations is a very low sky brightness value, less than 10^{-6} of the solar disk brightness (mathrm{B}_{odot }). Few places match such a requirement for ground-based, out-of-eclipse coronagraphic measurements. One of these places is, for instance, the Mauna Loa Observatory (approx 3400~mbox{m} a.s.l.). Another candidate coronagraphic site is the Dome C plateau in Antarctica. In this article, we show the first results of the sky brightness measurements at Dome C with the Extreme Solar Coronagraphy Antarctic Program Experiment (ESCAPE) at the Italian–French Concordia Station, on Dome C, Antarctica (approx 3300~mbox{m} a.s.l.) during the 34th and 35th summer Campaigns of the Italian Piano Nazionale Ricerche Antartiche (PNRA). The sky brightness measurements were carried out with the internally occulted Antarctic coronagraph AntarctiCor. In optimal atmospheric conditions the sky brightness of Dome C has reached values of the order of 1.0 – 0.7 times 10^{-6}~mathrm{B}_{odot }.

Highly Efficient Solar Laser Pumping Using a Solar Concentrator Combining a Fresnel Lens and Modified Parabolic Mirror

Solar-pumped lasers (SPLs) allow direct solar-to-laser power conversion, and hence, provide an opportunity to harness a renewable energy source. Herein, we report significant improvements in end-side-pumped solar laser collection efficiency and beam brightness using a novel 1.5-m-diameter compound solar concentrator combining a Fresnel lens and modified parabolic mirror. A key component of this scheme is the off-axis-focused parabolic mirror. An original dual-parabolic pump cavity is another feature. To determine the dependence of the SPL performance on the distance between the focus and central axis of the modified parabolic mirror, several systems with different distances were optimized using TracePro and ASLD software. It was numerically calculated that end-side pumping a 5-mm-diameter, 22-mm-long Nd:YAG crystal rod would generate 74.6 W of continuous-wave solar laser power at a collection efficiency of 42.2 W/m2, i.e., 1.1 times greater than the previous record value. Considering the laser beam quality, a brightness figure of 0.063 W was obtained, which is higher than that of other multimode SPL designs with end-side pumping. Thus, our SPL concentrator offers the possibility of achieving a beam quality as high as that obtainable via side pumping, alongside highly efficient energy conversion, which is characteristic to end-side pumping.

A Multiscale Normalization Method of a Mixed-Effects Model for Monitoring Forest Fires Using Multi-Sensor Data

This paper points out the shortcomings of existing normalization methods, and proposes a brightness temperature inversion normalization method for multi-source remote sensing monitoring of forest fires. This method can satisfy both radiation normalization and observation angle normalization, and reduce the discrepancies in forest fire monitoring between multi-source sensors. The study was based on Himawari-8 data; the longitude, latitude, solar zenith angle, solar azimuth angle, emissivity, slope, aspect, elevation, and brightness temperature values were collected as modeling parameters. The mixed-effects brightness temperature inversion normalization (MEMN) model based on FY-4A and Himawari-8 satellite sensors is fitted by multiple stepwise regression and mixed-effects modeling methods. The results show that, when the model is tested by Himawari-8 data, the coefficient of determination (R2) reaches 0.8418, and when it is tested by FY-4A data, R2 reaches 0.8045. At the same time, through comparison and analysis, the accuracy of the MEMN method is higher than that of the random forest normalization method (RF) (R2=0.7318), the pseudo-invariant feature method (PIF) (R2=0.7264), and the automatic control scatter regression method (ASCR) (R2=0.6841). The MEMN model can not only reduce the discrepancies in forest fire monitoring owing to different satellite sensors between FY-4A and Himawari-8, but also improve the accuracy and timeliness of forest fire monitoring.

Faint intermediate luminosity optical transients (ILOTs) from engulfing exoplanets on the Hertzsprung gap

ABSTRACT We follow the evolution of four observed exoplanets to the time when the respective parent star of each planet evolves off the main sequence and engulfs its planet to start a common envelope evolution (CEE), concluding that in each case this process powers an intermediate luminosity optical transient (ILOT; luminous red nova). We characterize the final thousands of days of the orbital decay towards a CEE and determine the properties of the star at the onset of the CEE. We scale the properties of the ILOT V1309 Scorpii to the properties of a planet that enters a CEE inside a star on and near the Hertzsprung gap to estimate the duration and luminosity of the expected ILOT. Based on these, we estimate that for a planet of Jupiter mass the ILOT will last for several days and reach a luminosity of several thousand solar luminosity. This type of ILOTs are less luminous than classical novae. Because of the small amount of expected dust and the small amount of energy that an accretion process on to the planet can release, such ILOTs can teach us on the merger at the onset of CEE of stellar companions. Our study adds to the variety of ILOTs that planets can power as they interact with a more massive companion.

Planetary Emittance And Feedback Parameters Through Varying Climates In Basic Modelling

In search for reproducibility of the results from sophisticated scientific research, the present work focuses on the planetary (longwave) emittance variabilities. A simple model appears applicable through the entire range from very cold to extremely warm climates and for different climate driving forces, i.e. solar luminosity variation and CO2 concentration change. The results interrelate effects from lapse rate, water vapor, CO2 , and clouds for equilibrium climate states. Feedback parameters are analysed for the emittance decomposition into the atmospheric window, clouds, and the cloud-free atmosphere. A view is devoted to the faint young Sun problem.

Axion string signatures: a cosmological plasma collider

We study early and late time signatures of both QCD axion strings and hyperlight axion strings (axiverse strings). We focus on charge deposition onto axion strings from electromagnetic fields and subsequent novel neutralizing mechanisms due to bound state formation. While early universe signatures appear unlikely, there are a plethora of late time signatures. Axion strings passing through galaxies obtain a huge charge density, which is neutralized by a dense plasma of bound state Standard Model particles forming a one dimensional “atom”. The charged wave packets on the string, as well as the dense plasma outside, travel at nearly the speed of light along the string. These packets of high energy plasma collide with a center of mass energy of up to 109 GeV. These collisions can have luminosities up to seven orders of magnitude larger than the solar luminosity, and last for thousands of years, making them visible at radio telescopes even when they occur cosmologically far away. The new observables are complementary to the CMB observables for hyperlight axion strings that have been recently proposed, and are sensitive to a similar motivated parameter range.

A breviary of Earth’s climate changes using Stephan-Boltzmann law

Earth’s surface temperature oscillated greatly throughout time. From near congelation during “snowball Earth” 2.9Gya to an ice-free world in the Paleocene-Eocene Thermal maximum 55Mya. These changes have been forced by internal (e.g. changes in the chemical composition of the atmosphere) or external (e.g. changes in solar luminosity) drivers that varied through time. Thus, if we understand how the radiation budget evolved in different times, we can closely calculate past global climate; a fundamental comparison to situate current climate change in the context Earth’s history. Here I present an analytical framework employing a simple energy balance derived from the Stephan-Boltzmann law, that allows for quick comparison between drivers of global temperature and at multiple moments in the history of our planet. My results show that current rates of increase in global temperature are at least four times faster than any previous warming event.

On the Possible Evolutionary History of the Water Ocean on Venus

We have investigated the possible evolutional history of the water ocean on Venus, adopting the one dimensional radiative-convective model,including the parameters as albedo and relative humidity. Under this model, it has the possibility that the habitable zone could include Venus. It could continue for $\sim 1$ Gy in faint young solar flux increasing, with modest parameters such as albedo = 0.3, relative humidity (RH=1), and $p_{n0}=10^5 $Pa. If we relax parameters considering the 3-Dimensional calculations, the ocean could exist there longer than $\sim$ 4.6 Gy. In such cases, we have to consider the cause of runaway other than just solar luminosity increasing. It is important to investigate Venus history for the coming future of Earth and observations of exoplanets for their historical habitable zones.

Searching for High-Energy Neutrinos from Ultra-Luminous Infrared Galaxies with IceCube

This work presents an IceCube search for high-energy neutrinos from Ultra-Luminous Infrared Galaxies (ULIRGs). ULIRGs are the most luminous infrared objects in the sky, with infrared luminosities exceeding 1012 solar luminosities. They are mainly powered by starbursts that exhibit star-formation rates larger than 100 solar masses per year. In addition, an active galactic nucleus (AGN) can also contribute significantly to the ULIRG luminosity output. The acceleration of hadrons, and consequently the production of neutrinos, can occur both in starburst and AGN environments. As such, ULIRGs form a source population that could be responsible for a significant fraction of the diffuse neutrino flux observed by IceCube. In this study we perform a stacking analysis on a representative sample of 75 ULIRGs with redshift z ≤ 0.13 using 7.5 years of IceCube data. We find no evidence for astrophysical neutrinos correlated with our selection of ULIRGs. We therefore compute upper limits on the contribution of the ULIRG source population to the diffuse neutrino observations, and also use these limits to constrain model predictions.

Reading runes with the sun. A geosemiotic analysis of the Rök runestone

In the field of runestone research, the importance of multimodal understanding has been downplayed although it is obvious that several semiotic resources interact when it comes to carving a stone and erecting it in the landscape. This study examines if it is possible to deal with the methodological challenges of a historical material and make a multimodal approach deepen our understanding of the Rök runestone, one of the most famous and enigmatic Viking Age runestones. The study applies Scollon and Scollon’s geosemiotic framework (2003). Through an investigation of how the visual semiotics interacts with place semiotics and interaction order, it turns out that the marked reading direction of the lines of the inscription symbolizes the movement of the sun, and that the change of font size in two lines probably mimics the change of solar brightness at sunrise and sunset. Further, it is suggested that the big crosses of cipher runes and the small crosses between some information units may represent the sun and stars, respectively. The conclusion is that the monument was risen for the enactment of a counsel of the gods with the aim of securing the rhythm of celestial light. Finally, implications for multimodal research are discussed.

RENEWABLE ENERGIES RESOURCES EVALUATION USING A GEOGRAPHIC INFORMATION SYSTEMS IN THE COLOMBIAN CARIBBEAN REGION

This manuscript presents an integral evaluation of the use of wind and solar resources in the Colombian Caribbean region. For the use of solar and wind energy sources, spatial restrictions according to topography, natural parks, water reserves, indigenous and sacred reserves were taken into account. In addition, studies of the energy potential of wind and solar radiation were carried out through geostatistical analysis of different points in meteorological stations located in the region. Finally, areas with wind and solar potential were determined using the Geographic Information System for Renewable Energies (SIGER). The results show that the department of Guajira has the highest values of solar brightness (229-240 Month day), while the departments of Valledupar, Cesar, and part of Magdalena decrease in the range of 229 to 207 Month day. In terms of solar radiation, the departments of Guajira and Atlántico showed global solar radiation values of up to 6,015 W/m2. The departments of Cesar, Magdalena, and part of Bolivar showed values close to 5,259 W/m2; while Sucre, and Cordoba showed low solar radiation values of 4,502 W/m2. It is concluded that the departments of Atlántico and Guajira are excellent candidates for solar and wind energy projects due to their characteristics. The results of this manuscript are a fundamental basis for future technical-economic feasibility studies of renewable energy in the Colombian Caribbean region. In addition, it allows the elaboration of energy policies that encourage the execution of this type of study at a real level.Keywords: SIGER, renewable energies, solar energy, wind energy, wind potentialJEL Classification: Q42DOI: https://doi.org/10.32479/ijeep.11612

Faint young Sun problem and variable physical constants

ABSTRACT The faint young Sun problem has been of great concern to astrophysicists and paleoclimatologists at least for the past five decades. Solar evolution models predict that the luminosity of the Sun 4.6 billion yr ago was less than 75 per cent of what it is today. This would mean that all water on Earth was frozen, and thus life could not have evolved as we know it. We attempt to show here that the variable physical constants (VPCs) approach, wherein constants are treated as scalar fields, could naturally resolve the problem. We use an analytical model that predicts the solar luminosity to be lower in the past to show that by properly including the VPCs in the model, the faint young Sun problem is mostly resolved: The young Sun flux intercepted by Earth was only 6 per cent lower 4.6 Gyr ago than it is today. We introduce the concept of cosmological and local energies in the context of VPC scalar fields, which is compliant with general relativity and cosmology: The cosmological energy is not available for conversion into thermal and radiative energies, whereas the local energy is.

Optical Transients from Fast Radio Bursts Heating Companion Stars in Close Binary Systems

Abstract Fast radio bursts (FRBs) are bright radio transients with short durations and extremely high brightness temperatures, and their physical origins are still unknown. Recently, a repeating source, FRB 20200120E, was found in a globular cluster in the very nearby M81 galaxy. The associated globular cluster has an age of ∼9.13 Gyr, and hosts an old population of stars. In this work, we consider that an FRB source is in a close binary system with a low-mass main-sequence star as its companion. Due to the large burst energy of the FRB, when the companion star stops the FRB, its surface would be heated by the radiation-induced shock, and make reemission. For a binary system with a solar-like companion star and an orbital period of a few days, we find that the reemission is mainly at an optical band, with delays of a few seconds after the FRB. Its luminosity is several times larger than the solar luminosity, and the duration is about hundreds of seconds. Such a transient might be observable in a future multiwavelength follow-up observation for Galactic FRB sources.

A [C ii] 158 μm emitter associated with an O i absorber at the end of the reionization epoch

The physical and chemical properties of the circumgalactic medium (CGM) at $z\gtrsim6$ have been studied successfully through the absorption in the spectra of background Quasi-Stellar Objects (QSOs). One of the most crucial questions is to investigate the nature and location of the source galaxies that give rise to these early metal absorbers. Theoretical models suggest that momentum-driven outflows from typical star-forming galaxies can eject metals into the CGM and the intergalactic medium (IGM) at z=5-6. Deep, dedicated surveys have searched for Ly$\alpha$ emission associated with strong CIV absorbers at $z\approx 6$, but only a few Ly$\alpha$ emitter candidates have been detected. Interpreting these detections is moreover ambiguous because Ly$\alpha$ is a resonant line, raising the need for complementary techniques for detecting absorbers' host galaxies. Here, using Atacama Large Millimeter Array (ALMA), we report a [C II] 158$\mu$m emitter associated with a strong low-ionization absorber, OI, at $z=5.978$. The projected impact parameter between OI and [C II] emitter is 20.0 kpc. The measured [C II] luminosity is $7.0\times 10^7$ solar luminosities. Further analysis indicates that strong OI absorbers may reside in the circumgalactic medium of massive halos one to two orders of magnitude more massive than expected values.

Zigzag Multirod Laser Beam Merging Approach for Brighter TEM00-Mode Solar Laser Emission from a Megawatt Solar Furnace

An alternative multirod solar laser end-side-pumping concept, based on the megawatt solar furnace in France, is proposed to significantly improve the TEM00-mode solar laser output power level and its beam brightness through a novel zigzag beam merging technique. A solar flux homogenizer was used to deliver nearly the same pump power to multiple core-doped Nd:YAG laser rods within a water-cooled pump cavity through a fused silica window. Compared to the previous multibeam solar laser station concepts for the same solar furnace, the present approach can allow the production of high-power TEM00-mode solar laser beams with high beam brightness. An average of 1.06 W TEM00-mode laser power was numerically extracted from each of 1657 rods, resulting in a total of 1.8 kW. More importantly, by mounting 399 rods at a 30° angle of inclination and employing the beam merging technique, a maximum of 5.2 kW total TEM00-mode laser power was numerically extracted from 37 laser beams, averaging 141 W from each merged beam. The highest solar laser beam brightness figure of merit achieved was 148 W, corresponding to an improvement of 23 times in relation to the previous experimental record.

Stellar activity cycles as revealed by long-term beat-like patterns from light curves of Kepler

Stellar activity cycles have been found on many stars through different methods. Although in debate, an empirical relation has been found where a period of stellar activity cycle P cyc is positively correlated with rotation period P rot along some segregated branches. In this work, we built a systematic process to search for the Kepler objects that are analogous to the long-term solar brightness variations and investigate their possible origins. After a rigorous selection, we obtained 43 objects that all exhibit clear long-term beat-like patterns and their variability (amplitude of rotational modulation) periods and rotation periods were derived. Due to the 4-year duration of the Kepler mission, our targets are located in the region where the cycle periods are longer than ∼1 yr and shorter than ∼2.5 yr. However, all of our targets exhibit clear and notable quasi-periodic variations in variability, yet we cannot confirm any linear trends that were predicted by previous research independently. This may suggest that in the Kepler realm of the P cyc–P rot diagram, these relations would mix with each other or the beat-like patterns may not be related to the stellar cycle unless other evidence is provided.

The Climates of Earth’s Next Supercontinent: Effects of Tectonics, Rotation Rate, and Insolation

AbstractWe explore two possible Earth climate scenarios, 200 and 250 million years into the future, using projections of the evolution of plate tectonics, solar luminosity, and rotation rate. In one scenario, a supercontinent forms at low latitudes, whereas in the other it forms at high northern latitudes with an Antarctic subcontinent remaining at the south pole. The climates between these two end points are quite stark, with differences in mean surface temperatures approaching several degrees. The main factor in these differences is related to the topographic height of the high latitude supercontinents where higher elevations promote snowfall and subsequent higher planetary albedos. These results demonstrate the need to consider multiple boundary conditions when simulating Earth‐like exoplanetary climates.

Light scattering due to particulate contamination over the primary mirror of Visible Emission Line Coronagraph on board Aditya-L1 mission

To meet the proposed science goals of the Visible Emission Line Coronagraph on board the Aditya-L1 mission, the total scattered light should be less than 5 ppm (parts per million) of solar disk brightness over the field of view (FOV). Major contributors to the scatter light are microroughness and contamination over the surface of the primary mirror (M1). A detailed study to derive the microroughness specifications of the M1 provides a fair idea of the effect of the contamination on the mirror in terms of the scatter generated from the surface: 1.53 Å band-limited RMS microroughness on the M1 surface contributes toward a total scatter of 4 ppm over the FOV. This restricts the scatter over the FOV due to contamination being less than 1 ppm, and it is equally apportioned to scatter due to both particulate and molecular contamination. Hence, the scatter over the FOV due to particulate contamination should be limited to 0.5 ppm. Our paper provides a detailed explanation of the studies carried out to determine the maximum allowable particulate contamination levels on the M1.