Flux Deficit Research Articles

Probing the magnetic fields of starspots with transit mapping

Starspots, regions of strong magnetic fields, serve as indicators of stellar activity and the dynamo mechanism at play in the interior of stars. The magnetic fields of main-sequence stars play a crucial role in driving stellar activity. An effective approach to better understanding stellar magnetic fields and activity lies in the detailed characterisation of starspot properties. We propose a new method for estimating the magnetic fields of starspots that employs modelling techniques of planetary transit mapping, which provides estimates of the size, intensity, and location of spots on the stellar photosphere. A starspot's maximum magnetic field was calculated using the linear relationship with the spot flux deficit, $ spot $ (the spot's brightness times its area) and the well-characterised relation for sunspots determined in this work, $B_ spot (G). Applying this relationship to previously mapped spots on the photospheres of 14 FGK and M stars yields spot maximum magnetic fields ranging from 2700 G to 4600 G, with an overall average of $3900 400$ G. We looked for correlations between starspot magnetic fields and stellar properties.\ We did not find any correlation between a spot's mean extreme magnetic field and effective temperature, nor the differential shear. However, a weak anti-correlation is seen between the spots' magnetic field and stellar age as well as between the magnetic field and the rotation period. When compared with previous results of small-scale magnetic field measurements, the B values obtained here are basically constant and near the saturation limit found for rapid rotators. This implies that it is not the intensity of the magnetic field of starspots that decreases with age but rather the filling factor. This result offers a unique window into the magnetic dynamo of stars.

Differential Rotation of CoRoT Stars and a Kepler Binary Star from Starspot Transit Mapping

Abstract While direct magnetic field measurements are rare for slowly rotating stars, spots observed during planetary transits provide a potential indicator of magnetic activity on stellar surfaces. Moreover, the rotation of the stellar surface can be probed by monitoring the spots’ position with time in subsequent transits. This study investigates the dynamic interplay of rotational shear and stellar rotation rate in six stars of spectral types F to M, all hosting exoplanets observed by the CoRoT space mission, except for one binary star from Kepler. The analysis, facilitated by the ECLIPSE code, unveils the physical properties of stellar spots, including radius, intensity, temperature, and position. The five CoRoT stars exhibit spot characteristics consistent with those observed in solar type stars. The determination of a spot longitude during different transits allows for the inference of the star’s differential rotation profile, revealing a decreasing trend of rotational shear with the mean stellar rotation period, given by Δ Ω ∝ P ¯ − 0.9 . This implies that, at least for slow rotators (mean rotation period >5 days), as stars age, their differential rotation decreases. Additionally, the six stars analyzed here seem to fall into two categories, according to their spot flux deficit: those with ΔF spot > 0.005 and those with ΔF spot < 0.002.

The Atacama Cosmology Telescope: Millimeter Observations of a Population of Asteroids or: ACTeroids

We present fluxes and light curves for a population of asteroids at millimeter wavelengths, detected by the Atacama Cosmology Telescope (ACT) over 18,000 deg2 of the sky using data from 2017 to 2021. We utilize high cadence maps, which can be used in searching for moving objects such as asteroids and trans-Neptunian Objects, as well as for studying transients. We detect 170 asteroids with a signal-to-noise of at least 5 in at least one of the ACT observing bands, which are centered near 90, 150, and 220 GHz. For each asteroid, we compare the ACT measured flux to predicted fluxes from the near-Earth asteroid thermal model fit to WISE data. We confirm previous results that detected a deficit of flux at millimeter wavelengths. Moreover, we report a spectral characteristic to this deficit, such that the flux is relatively lower at 150 and 220 GHz than at 90 GHz. Additionally, we find that the deficit in flux is greater for S-type asteroids than for C-type.

CO, H2O, and CH4 in the dusty atmosphere of a ≲5 Myr-old exoplanet

ABSTRACT Very young massive planets are sufficiently luminous by their internal heat of formation to permit detailed studies, including spectroscopy of their atmospheres with large telescopes at sufficient resolution (λ/Δλ ≳ 1000) to identify major constituents to inform models of planet formation and early evolution. We obtained 1–2.4 μm (YJHK) spectra of the planetary-mass ‘b’ companion of 2MASS J04372171+2651014, a 1–3 Myr-old M dwarf member of the Taurus star-forming region, and one of the youngest such objects discovered to date. These indicate the presence of CO and possibly H2O and CH4 in the atmosphere, all suggesting a Teff of around 1200 K, characteristic of a L-T transition spectral type and consistent with previous estimates based on its luminosity and age. The absence or attenuation of spectral features at shorter wavelengths suggests the presence of micron-size dust, consistent with the object’s red colour. The spectrum of 2M0437b resembles those of the HR 8799 planets, especially the innermost ‘b’ planet, with the exception of a pronounced flux deficit in the H-band of uncertain origin.

Climate change impacts on water flux dynamics in Shingoda basin having agriculture and forest ecosystems: A comprehensive analysis

An assessment of climate chnage and its impacts on water fluxes in the Shingoda basin of the Saurashtra region having 14% agriculture and 75% forest were made through analysis of time series (1951-2100) of bias corrected maximum/minimum temperature and rainfall (RCP4.5), rreference evapotranspiration (ETo), evapotranspiration (ETc) and runoff. Results showed significant climate changes in the basin, with day mean temperature rising from 24.4°C in the second half of the 20th century to 26.5°C and 27.9°C in the first and second half of the 21st century, respectively. During the first and second half of the 21st century, seasonal rainfall increased by 23.0% and 46.33%, and runoff rose by 46.78% and 86.40% compared to the second half of the 20th century. However, annual reference evapotranspiration (ETo) decreased by -1.41% and -6.5%, and crop evapotranspiration (ETc) decreased by -3.2% and -9.8% in the same periods. The analysis also revealed a deficit of -16.10% in downward water flux (rainfall) in the first half of the 20th century, followed by a surplus of 8.46% and 28.37% compared to the upward flux (ETc) in subsequent periods. The upward water flux deficit during 2nd half of 20th century were supported by evidence of depleted groundwater levels and seawater intrusion in the study area.

Satellite-based investigation of water stress at the basin scale: an integrated analysis of downscaled GRACE estimates and remotely sensed data

Abstract Freshwater availability is a very determining issue, especially in semiarid and arid regions, for sustainable development and secured food production. In this premise, the detection and assessment of water stress are of utmost importance. In this study, the satellite-based Potential Available Water Storage (PAWS) index is used to test its feasibility for a basin-scale analysis of water stress in the Western Mediterranean Basin (WMB) in Türkiye. The coarse-resolution GRACE (Gravity Recovery And Climate Experiment) estimates were downscaled based on the Random Forest (RF) model and then were integrated with fine-resolution precipitation data to derive fine-resolution PAWS values. The accuracy of the index was validated against the net water flux (NWF) and water storage deficit (WSD) values over the basin. The results revealed a good performance for the PAWS index for a local scale evaluation of water stress. The PAWS variations turned out to be highly correlated with the NWF (r = 0.72) and WSD (r = 0.66). The PAWS indicates that the WMB has suffered from a critical hydrological situation from 2003 to 2020 during which the basin has been under stress with the most critical situation in 2018 when the per capita water has fallen below 500 m3 suggesting an absolute water stress status.

First Measurement of High-Energy Reactor Antineutrinos at Daya Bay.

This Letter reports the first measurement of high-energy reactor antineutrinos at Daya Bay, with nearly 9000 inverse beta decay candidates in the prompt energy region of 8-12MeV observed over 1958days of data collection. A multivariate analysis is used to separate 2500 signal events from background statistically. The hypothesis of no reactor antineutrinos with neutrino energy above 10MeV is rejected with a significance of 6.2 standard deviations. A 29% antineutrino flux deficit in the prompt energy region of 8-11MeV is observed compared to a recent model prediction. We provide the unfolded antineutrino spectrum above 7MeV as a data-based reference for other experiments. This result provides the first direct observation of the production of antineutrinos from several high-Q_{β} isotopes in commercial reactors.

On the Nature of Ultracool White Dwarfs: Not so Cool after All

A recent analysis of the 100 pc white dwarf sample in the SDSS footprint demonstrated for the first time the existence of a well-defined ultracool—or IR-faint—white dwarf sequence in the Hertzsprung–Russell diagram. Here we take advantage of this discovery to enlarge the IR-faint white dwarf sample threefold. We expand our selection to the entire Pan-STARRS survey footprint as well as the Montreal White Dwarf Database 100 pc sample and identify 37 candidates with strong flux deficits in the optical. We present follow-up Gemini optical spectroscopy of 30 of these systems and confirm all of them as IR-faint white dwarfs. We identify an additional set of 33 objects as candidates based on their colors and magnitudes. We present a detailed model atmosphere analysis of all 70 newly identified IR-faint white dwarfs together with 35 previously known objects reported in the literature. We discuss the physics of model atmospheres and show that the key physical ingredient missing in our previous generation of model atmospheres was the high-density correction to the He− free–free absorption coefficient. With new model atmospheres calculated for the purpose of this analysis, we now obtain significantly higher effective temperatures and larger stellar masses for these IR-faint white dwarfs than the T eff and M values reported in previous analyses, thus solving a two-decade-old problem. In particular, we identify in our sample a group of ultramassive white dwarfs in the Debye cooling phase with stellar parameters never measured before.

Modelling the spectra of the kilonova AT2017gfo – I. The photospheric epochs

ABSTRACT The kilonova (KN) associated with the binary neutron star (BNS) merger GW170817 is the only known electromagnetic counterpart to a gravitational wave source. Here we produce a sequence of radiative transfer models (using tardis) with updated atomic data, and compare them to accurately calibrated spectra. We use element compositions from nuclear network calculations based on a realistic hydrodynamical simulation of a BNS merger. We show that the blue spectrum at +1.4 d after merger requires a nucleosynthetic trajectory with a high electron fraction. Our best-fitting model is composed entirely of first r-process peak elements (Sr and Zr) and the strong absorption feature is reproduced well by Sr ii absorption. At this epoch, we set an upper limit on the lanthanide mass fraction of $X_{{\small LN}} \lesssim 5 \times 10^{-3}$. In contrast, all subsequent spectra from +2.4 to 6.4 d require the presence of a modest amount of lanthanide material ($X_{{\small LN}} \simeq 0.05^{+0.05}_{-0.02}$), produced by a trajectory with Ye = 0.29. This produces lanthanide-induced line blanketing below 6000 Å, and sufficient light r-process elements to explain the persistent strong feature at ∼0.7–1.0 $\mu$m (Sr ii). The composition gives good matches to the observed data, indicating that the strong blue flux deficit results in the near-infrared (NIR) excess. The disjoint in composition between the first epoch and all others indicates either ejecta stratification, or the presence of two distinct components of material. This further supports the ‘two-component’ KN model, and constrains the element composition from nucleosynthetic trajectories. The major uncertainties lie in availability of atomic data and the ionization state of the expanding material.

Environmental factors driving evapotranspiration over a grassland in a transitional climate zone in China

AbstractThe surface evapotranspiration (ET) process is the key link in the interaction between land and atmosphere. However, the influence of different environmental factors on ET over transitional climate zones and the physical pattern of the interaction between multiple factors remain unclear. Therefore, based on the continuous observation data during the vegetation growing season of a typical grassland in the Semi‐Arid Climate and Environment Observation of Lanzhou University (SACOL) station from 2007 to 2012, the influence pattern of multiple environmental factors on ET over China's transitional climate zone was analysed. Each environmental factor exhibited significant seasonal and interannual variations. The mean value of ET was 1.67 mm day−1. Although the maximum values of sensible heat flux and vapour pressure deficit occurred in April and June, respectively, the maximum values of other environmental factors appeared from July to August. Net radiation, soil moisture, and normalized difference vegetation index (NDVI) were the main controlling factors of ET over the grassland, with correlation coefficients of 0.54, 0.52, and 0.46, respectively. The analysis of multiple environmental factors showed that when soil moisture, wind speed, net radiation, and NDVI reached 0.2 m3 m−3, 2 m s−1, 100 W m−2, and 0.2, respectively, ET varied in contrast with vapour pressure, vapour pressure deficit, and air temperature under the influences of weather processes, land–atmosphere coupling, and drought stress. These findings deepen our understanding of the role of ET in the land–atmosphere coupling process over the transitional climate zone in China.

Estimating Bulk Stomatal Conductance in Grapevine Canopies

In response to changes in their environments, grapevines regulate transpiration using various physiological mechanisms that alter conductance of water through the soil-plant-atmosphere continuum. Expressed as bulk stomatal conductance at the canopy scale, it varies diurnally in response to changes in vapor pressure deficit and net radiation, and over the season to changes in soil water deficits and hydraulic conductivity of both the soil and plant. To help with future characterization of this dynamic response, a simplified method is presented for determining bulk stomatal conductance based on the crop canopy energy flux model by Shuttleworth and Wallace using measurements of individual vine sap flow, temperature and humidity within the vine canopy, and estimates of net radiation absorbed by the vine canopy. The methodology presented respects the energy flux dynamics of vineyards with open canopies, while avoiding problematic measurements of soil heat flux and boundary layer conductance needed by other methods, which might otherwise interfere with ongoing vineyard management practices. Based on this method and measurements taken on several vines in a non-irrigated vineyard in Bordeaux France, bulk stomatal conductance was estimated on 15-minute intervals from July to mid-September 2020 producing values similar to those presented for vineyards in the literature. Time-series plots of this conductance show significant diurnal variation and seasonal decreases in conductance associated with increased vine water stress as measured by predawn leaf water potential. Global sensitivity analysis using non-parametric regression found transpiration flux and vapor pressure deficit to be the most important input variables to the calculation of bulk stomatal conductance, with absorbed net radiation and bulk boundary layer conductance being much less important. Conversely, bulk stomatal conductance was one of the most important inputs when calculating vine transpiration, emphasizing the usefulness of characterizing its dynamic response for the purpose of estimating vine canopy transpiration in water use models.

High-order multirate explicit time-stepping schemes for the baroclinic-barotropic split dynamics in primitive equations

In order to treat the multiple time scales of ocean dynamics in an efficient manner, the baroclinic-barotropic splitting technique has been widely used for solving the primitive equations for ocean modeling. Based on the framework of strong stability-preserving Runge-Kutta approach, we propose two high-order multirate explicit time-stepping schemes (SSPRK2-SE and SSPRK3-SE) for the resulting split system in this paper. The proposed schemes allow for a large time step to be used for the three-dimensional baroclinic (slow) mode and a small time step for the two-dimensional barotropic (fast) mode, in which each of the two mode solves just need to satisfy their respective CFL conditions for numerical stability. Specifically, at each time step, the baroclinic velocity is first computed by advancing the baroclinic mode and fluid thickness of the system with the large time-step and the assistance of some intermediate approximations of the barotropic mode obtained by substepping with the small time step; then the barotropic velocity is corrected by using the small time step to re-advance the barotropic mode under an improved barotropic forcing produced by interpolation of the forcing terms from the preceding baroclinic mode solves; lastly, the fluid thickness is updated by coupling the baroclinic and barotropic velocities. Additionally, numerical inconsistencies on the discretized sea surface height caused by the mode splitting are relieved via a reconciliation process with carefully calculated flux deficits. Two benchmark tests from the “MPAS-Ocean” platform are carried out to numerically demonstrate the performance and parallel scalability of the proposed SSPRK-SE schemes.

Buildup of the Magnetic Flux Ropes in Homologous Solar Eruptions

Abstract Homologous coronal mass ejections (CMEs) are an interesting phenomenon, and it is possible to investigate the formation of CMEs by comparing multi-CMEs under a homologous physical condition. AR 11283 had been present on the solar surface for several days when a bipole emerged on 2011 September 4. Its positive polarity collided with the preexisting negative polarity belonging to a different bipole, producing recurrent solar activities along the polarity inversion line (PIL) between the colliding polarities, namely the so-called collisional PIL (cPIL). Our results show that a large amount of energy and helicity were built up in the form of magnetic flux ropes (MFRs), with recurrent release and accumulation processes. These MFRs were built up along the cPIL. A flux deficit method is adopted and shows that magnetic cancellation happens along the cPIL due to the collisional shearing scenario proposed by Chintzoglou et al. The total amount of canceled flux was ∼0.7 × 1021 Mx with an uncertainty of ∼13.2% within the confidence region of the 30° Sun-center distance. The canceled flux amounts to 24% of the total unsigned flux of the bipolar magnetic region. The results show that the magnetic fields beside the cPIL are very sheared, and the average shear angle is above 70° after the collision. The fast expansion of the twist kernels of the MFRs and the continuous eruptive activities are both driven by the collisional shearing process. These results are important for better understanding the buildup process of the MFRs associated with homologous solar eruptions.

Feasibility study of muon tomography application in a non-invasive representation of tumulus

Within the frame of the EKATϒ programme, whose purpose is the innovative imaging of the subsurface of archaeological sites and the interior of structural elements of monuments in “three” and “four” dimensions, the applicability of Muon Tomography technique in the representation of a tumulus is tested in the present work. The scanning of its internal structure is accomplished by measuring the flux deficit of cosmic muon tracks in the presence of an object inside the tumulus, compared to the muon flux when traversing a uniform tumulus (transmission muography). The feasibility study of the method is achieved with a simulation of the tumulus geometry and the structure under investigation. Following the simulation process, a tracking telescope, consisting of four MicroMegas detectors and two trigger plastic scintillators, will be placed near Apollonia’s tumulus to collect data. For the specific latitude where the Apollonia’s tumulus is located, the energy and angular muon distribution at sea level is studied. Implementing the dimensions of the telescope in the simulation, the back-projection method is examined for the localization of the hidden object and the estimation of its dimensions. The method is tested for the telescope optimal position, placed under the tumulus, and the realistic one, placed near the tumulus at the level of its base.

Observation of the cosmic ray shadow of the Sun with the ANTARES neutrino telescope

ANTARES is the largest undersea neutrino telescope and it has been taking data in its final configuration for more than ten years. On their journey to the Earth, cosmic rays can be absorbed by celestial objects, like the Sun, leading to a deficit in the atmospheric muon flux measured by the ANTARES detector, the so-called Sun "shadow" effect. This phenomenon can be used to evaluate fundamental telescope characteristics: the detector angular resolution and pointing accuracy. This work describes the study of the Sun "shadow" effect using the ANTARES data collected between 2008 and 2017. The statistical significance of the Sun shadow observation is 3.7σ and the estimated angular resolution value of the ANTARES telescope for downward-going muons is 0.59°±0.10°, which is consistent with the expectations obtained from the Monte Carlo simulations and also with the estimation from the Moon "shadow" analysis of 2007-2016 years. No evidence of systematic pointing shift is found and the resulting pointing accuracy is consistent with the expectations.

Coronal Hole Detection and Open Magnetic Flux

Abstract Many scientists use coronal hole (CH) detections to infer open magnetic flux. Detection techniques differ in the areas that they assign as open, and may obtain different values for the open magnetic flux. We characterize the uncertainties of these methods, by applying six different detection methods to deduce the area and open flux of a near-disk center CH observed on 2010 September 19, and applying a single method to five different EUV filtergrams for this CH. Open flux was calculated using five different magnetic maps. The standard deviation (interpreted as the uncertainty) in the open flux estimate for this CH ≈ 26%. However, including the variability of different magnetic data sources, this uncertainty almost doubles to 45%. We use two of the methods to characterize the area and open flux for all CHs in this time period. We find that the open flux is greatly underestimated compared to values inferred from in situ measurements (by 2.2–4 times). We also test our detection techniques on simulated emission images from a thermodynamic MHD model of the solar corona. We find that the methods overestimate the area and open flux in the simulated CH, but the average error in the flux is only about 7%. The full-Sun detections on the simulated corona underestimate the model open flux, but by factors well below what is needed to account for the missing flux in the observations. Under-detection of open flux in coronal holes likely contributes to the recognized deficit in solar open flux, but is unlikely to resolve it.

Identifying dominant environmental predictors of freshwater wetland methane fluxes across diurnal to seasonal time scales.

While wetlands are the largest natural source of methane (CH4 ) to the atmosphere, they represent a large source of uncertainty in the global CH4 budget due to the complex biogeochemical controls on CH4 dynamics. Here we present, to our knowledge, the first multi-site synthesis of how predictors of CH4 fluxes (FCH4) in freshwater wetlands vary across wetland types at diel, multiday (synoptic), and seasonal time scales. We used several statistical approaches (correlation analysis, generalized additive modeling, mutual information, and random forests) in a wavelet-based multi-resolution framework to assess the importance of environmental predictors, nonlinearities and lags on FCH4 across 23 eddy covariance sites. Seasonally, soil and air temperature were dominant predictors of FCH4 at sites with smaller seasonal variation in water table depth (WTD). In contrast, WTD was the dominant predictor for wetlands with smaller variations in temperature (e.g., seasonal tropical/subtropical wetlands). Changes in seasonal FCH4 lagged fluctuations in WTD by ~17±11days, and lagged air and soil temperature by median values of 8±16 and 5±15days, respectively. Temperature and WTD were also dominant predictors at the multiday scale. Atmospheric pressure (PA) was another important multiday scale predictor for peat-dominated sites, with drops in PA coinciding with synchronous releases of CH4 . At the diel scale, synchronous relationships with latent heat flux and vapor pressure deficit suggest that physical processes controlling evaporation and boundary layer mixing exert similar controls on CH4 volatilization, and suggest the influence of pressurized ventilation in aerenchymatous vegetation. In addition, 1- to 4-h lagged relationships with ecosystem photosynthesis indicate recent carbon substrates, such as root exudates, may also control FCH4. By addressing issues of scale, asynchrony, and nonlinearity, this work improves understanding of the predictors and timing of wetland FCH4 that can inform future studies and models, and help constrain wetland CH4 emissions.

Damped neutrino oscillations in a conformal coupling model

Flavor transitions of Neutrinos with a nonstandard interaction are studied. A scalar field is conformally coupled to matter and neutrinos. This interaction alters the neutrino effective mass and its wavefunction leading to a damping factor, causing deficits in the probability densities and affecting the oscillation phase. As the matter density determines the scalar field's behavior, we also have an indirect matter density effect on the flavor conversion. We explain our results in the context of screening models and study the deficit in the total flux of electron-neutrinos produced in the Sun through the decay process and confront our results with observational data.

Space Telescope and Optical Reverberation Mapping Project. XIII. An Atlas of UV and X-Ray Spectroscopic Signatures of the Disk Wind in NGC 5548

Abstract The unusual behavior of the spectral lines of NGC5548 during the STORM campaign demonstrated a missing piece in the structure of AGNs. For a two-month period in the middle of the campaign, the spectral lines showed a deficit in flux and a reduced response to the variations of the UV continuum. This was the first time that this behavior was unequivocally observed in an AGN. Our previous papers explained this as being due to a variable disk wind that acts as a shield and alters the SED. Here, we use Cloudy to create an atlas of photoionization models for a variety of disk winds, in order to study their effects on the SED. We show that the winds have three different cases: Case 1 winds are transparent, fully ionized, and have minimal effects on the intrinsic SED, although they can produce some line emission, especially He ii or FeKα. We propose that this is the situation in most of the AGNs. Case 2 winds, which have a He++–He+ ionization front, block part of the XUV continuum but transmit much of the Lyman continuum. They lead to the observed abnormal behavior. Case 3 winds have a H+ ionization front and block much of the Lyman continuum. The results show that the presence of these winds has important effects on the spectral lines of AGNs. They will thus have an effect on the measurements of the black hole mass and the geometry of the AGN. This atlas of spectral simulations can serve as a guide to future reverberation campaigns.

Observation of the cosmic ray shadow of the Sun with the ANTARES neutrino telescope

The ANTARES detector is an undersea neutrino telescope in the Mediterranean Sea. The search for point-like neutrino sources is one of the main goals of the ANTARES telescope, requiring a reliable method to evaluate the detector angular resolution and pointing accuracy. This work describes the study of the Sun "shadow" effect with the ANTARES detector. The shadow is the deficit in the atmospheric muon flux in the direction of the Sun caused by the absorption of the primary cosmic rays. This analysis is based on the data collected between 2008 and 2017 by the ANTARES telescope. The observed statistical significance of the Sun shadow detection is $3.7\sigma$, with an estimated angular resolution of $0.59^\circ\pm0.10^\circ$ for downward-going muons. The pointing accuracy is found to be consistent with the expectations and no evidence of systematic pointing shifts is observed.