scholarly journals Impact of magnetic activity on inferred stellar properties of main-sequence Sun-like stars

2021 ◽  
Vol 502 (4) ◽  
pp. 5808-5820
Author(s):  
Alexandra E L Thomas ◽  
William J Chaplin ◽  
Sarbani Basu ◽  
Ben Rendle ◽  
Guy Davies ◽  
...  
Keyword(s):  
Magnetic Activity ◽  
Frequency Separation ◽  
Near Surface ◽  
Global Properties ◽  
Modelling Analysis ◽  
Inclination Angles ◽  
Stellar Properties ◽  
Oscillation Frequencies ◽  
Frequency Ratios ◽  
The Impact

ABSTRACT The oscillation frequencies observed in Sun-like stars are susceptible to being shifted by magnetic activity effects. The measured shifts depend on a complex relationship involving the mode type, the field strength, and spatial distribution of activity, as well as the inclination angle of the star. Evidence of these shifts is also present in frequency separation ratios that are often used when inferring global properties of stars in order to avoid surface effects. However, one assumption when using frequency ratios for this purpose is that there are no near-surface perturbations that are non-spherically symmetric. In this work, we studied the impact on inferred stellar properties when using frequency ratios that are influenced by non-homogeneous activity distributions. We generate several sets of artificial oscillation frequencies with various amounts of shift and determine stellar properties using two separate pipelines. We find that for asteroseismic observations of Sun-like targets we can expect magnetic activity to affect mode frequencies that will bias the results from stellar modelling analysis. Although for most stellar properties this offset should be small, typically less than 0.5 per cent in mass, estimates of age and central hydrogen content can have an error of up to 5 per cent and 3 per cent, respectively. We expect a larger frequency shift and therefore larger bias for more active stars. We also warn that for stars with very high or low inclination angles, the response of modes to activity is more easily observable in the separation ratios and hence will incur a larger bias.

scholarly journals On the impact of the structural surface effect on global stellar properties and asteroseismic analyses

2020 ◽  
Vol 500 (4) ◽  
pp. 4277-4295
Author(s):  
Andreas Christ Sølvsten Jørgensen ◽  
Josefina Montalbán ◽  
George C Angelou ◽  
Andrea Miglio ◽  
Achim Weiss ◽  
...  
Keyword(s):  
Surface Effect ◽  
Outer Boundary ◽  
Space Mission ◽  
Stellar Structure ◽  
Time Step ◽  
Near Surface ◽  
Seismic Properties ◽  
Stellar Properties ◽  
Mixing Length Theory ◽  
The Impact

ABSTRACT In a series of papers, we have recently demonstrated that it is possible to construct stellar structure models that robustly mimic the stratification of multidimensional radiative magnetohydrodynamic simulations at every time-step of the computed evolution. The resulting models offer a more realistic depiction of the near-surface layers of stars with convective envelopes than parametrizations, such as mixing length theory, do. In this paper, we explore how this model improvement impacts on seismic and non-seismic properties of stellar models across the Hertzsprung–Russell diagram. We show that the improved description of the outer boundary layers alters the predicted global stellar properties at different evolutionary stages. In a hare and hound exercise, we show that this plays a key role for asteroseismic analyses, as it, for instance, often shifts the inferred stellar age estimates by more than 10 per cent. Improper boundary conditions may thus introduce systematic errors that exceed the required accuracy of the PLATO space mission. Moreover, we discuss different approaches for computing stellar oscillation frequencies. We demonstrate that the so-called gas Γ1 approximation performs reasonably well for all main-sequence stars. Using a Monte Carlo approach, we show that the model frequencies of our hybrid solar models are consistent with observations within the uncertainties of the global solar parameters when using the so-called reduced Γ1 approximation.

Asteroseismology: The Impact of Solar Space Observations

1993 ◽  
Vol 137 ◽  
pp. 43-50
Author(s):  
H.S. Hudson
Keyword(s):  
Solar Flares ◽  
Coronal Holes ◽  
Magnetic Activity ◽  
Solar Interior ◽  
Small Bodies ◽  
Solar Observations ◽  
Global Properties ◽  
Stellar Convection ◽  
Technical Report ◽  
The Impact

AbstractObservations from space relevant to solar global properties (oscillations, magnetic activity, etc.) are helpful both scientifically and technically in preparing for stellar observations. This paper summarizes the results from the main previous experiments (ACRIM, SOUP, and IPHIR), and also give an initial technical report from the SXT instrument on board Yohkoh, launched in August 1991. The solar observations to date demonstrate the existence of several mechanisms for low–level variability: spots, faculae, the photospheric network, granulation, and p–mode oscillations. The observations of oscillations have been particularly helpful in setting limits on solar interior rotation. In addition to the solar processes, stars of other types may have different mechanisms of variability. These may include the analogues of coronal holes or solar flares, modes of oscillation not detected in the Sun, collisions with small bodies, duplicity, and probably mechanisms not invented yet but related in interesting ways to stellar convection and magnetism.

scholarly journals Frequency shifts of resonant modes of the Sun due to near-surface convective scattering

2015 ◽  
Vol 11 (A29B) ◽  
pp. 614-619
Author(s):  
J. Bhattacharya ◽  
S. M. Hanasoge ◽  
H. M. Antia
Keyword(s):  
Wave Equation ◽  
Small Scale ◽  
Systematic Effect ◽  
The Sun ◽  
Resonant Frequencies ◽  
Near Surface ◽  
Oscillation Frequencies ◽  
3D Flows ◽  
Surface Convection ◽  
The Impact

AbstractMeasurements of oscillation frequencies of the Sun and stars can provide important independent constraints on their internal structure and dynamics. Seismic models of these oscillations are used to connect structure and rotation of the star to its resonant frequencies, which are then compared with observations, the goal being that of minimizing the difference between the two. Even in the case of the Sun, for which structure models are highly tuned, observed frequencies show systematic deviations from modeled frequencies, a phenomenon referred to as the “surface term.” The dominant source of this systematic effect is thought to be vigorous near-surface convection, which is not well accounted for in both stellar modeling and mode-oscillation physics. Here we bring to bear the method of homogenization, applicable in the asymptotic limit of large wavelengths (in comparison to the correlation scale of convection), to characterize the effect of small-scale surface convection on resonant-mode frequencies in the Sun. We show that the full oscillation equations, in the presence of temporally stationary 3D flows, can be reduced to an effective “quiet-Sun” wave equation with altered sound speed, Brünt–Väisäla frequency, and Lamb frequency. We derive the modified equation and relations for the appropriate averaging of 3D flows and thermal quantities to obtain the properties of this effective medium. Using flows obtained from 3D numerical simulations of near-surface convection, we quantify their effect on solar oscillation frequencies and find that they are shifted systematically and substantially. We argue therefore that consistent interpretations of resonant frequencies must include modifications to the wave equation that effectively capture the impact of vigorous hydrodynamic convection.

scholarly journals Influence of metallicity on the near-surface effect on oscillation frequencies

2018 ◽  
Vol 620 ◽  
pp. A107 ◽  
Author(s):  
L. Manchon ◽  
K. Belkacem ◽  
R. Samadi ◽  
T. Sonoi ◽  
J. P. C. Marques ◽  
...  
Keyword(s):  
Surface Effect ◽  
Strong Impact ◽  
Surface Layers ◽  
Frequency Spectra ◽  
Near Surface ◽  
Empirical Correction ◽  
Hydrodynamical Simulations ◽  
Oscillation Frequencies ◽  
High Degree ◽  
The Impact

Context. The CoRoT and Kepler missions have provided high-quality measurements of the frequency spectra of solar-like pulsators, enabling us to probe stellar interiors with a very high degree of accuracy by comparing the observed and modelled frequencies. However, the frequencies computed with 1D models suffer from systematic errors related to the poor modelling of the uppermost layers of stars. These biases are what is commonly named the near-surface effect. The dominant effect is thought to be related to the turbulent pressure that modifies the hydrostatic equilibrium and thus the frequencies. This has already been investigated using grids of 3D hydrodynamical simulations, which also were used to constrain the parameters of the empirical correction models. However, the effect of metallicity has not been considered so far. Aims. We aim to study the impact of metallicity on the surface effect, investigating its influence across the Hertzsprung-Russell diagram, and providing a method for accounting for it when using the empirical correction models. Methods. We computed a grid of patched 1D stellar models with the stellar evolution code CESTAM in which poorly modelled surface layers have been replaced by averaged stratification computed with the 3D hydrodynamical code CO5BOLD. It allowed us to investigate the dependence of both the surface effect and the empirical correction functions on the metallicity. Results. We found that metallicity has a strong impact on the surface effect: keeping Teff and log g constant, the frequency residuals can vary by up to a factor of two (for instance from [Fe/H] = + 0.0 to [Fe/H] = + 0.5). Therefore, the influence of metallicity cannot be neglected. We found that the correct way of accounting for it is to consider the surface Rosseland mean opacity. It allowed us to give a physically grounded justification as well as a scaling relation for the frequency differences at νmax as a function of Teff, log g and κ. Finally, we provide prescriptions for the fitting parameters of the most commonly used correction functions. Conclusions. We show that the impact of metallicity through the Rosseland mean opacity must be taken into account when studying and correcting the surface effect.

scholarly journals The impact and cost‐effectiveness of community‐basedHIVself‐testing in sub‐Saharan Africa: a health economic and modelling analysis

2019 ◽  
Vol 22 (S1) ◽  
pp. e25243 ◽  
Author(s):  
Valentina Cambiano ◽  
Cheryl C Johnson ◽  
Karin Hatzold ◽  
Fern Terris‐Prestholt ◽  
Hendy Maheswaran ◽  
...  
Keyword(s):  
Health Economic ◽  
Cost Effectiveness ◽  
Sub Saharan Africa ◽  
Modelling Analysis ◽  
Sub Saharan ◽  
The Impact

scholarly journals A quantitative description of the spatial–temporal distribution and evolution pattern of world cultural heritage

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Liang Yongqi ◽  
Yang Ruixia ◽  
Wang Pu ◽  
Yang Anlin ◽  
Chen Guolong
Keyword(s):  
Cultural Heritage ◽  
World Heritage ◽  
World Heritage Site ◽  
Heritage Sites ◽  
Evolution Pattern ◽  
Modelling Analysis ◽  
Time Series Modelling ◽  
World Cultural Heritage ◽  
The Impact ◽  
Peak Value

AbstractDepicting the temporal and spatial evolution pattern of global world cultural heritage systematically and finely is the basis of heritage recognition and protection. In this study, 869 world cultural heritage inscriptions (through 2019) were selected as the research objects, and the times and types of each World Heritage site were manually annotated from more than 5000 pieces of data. Through time series modelling, the advantages of and changes in heritage declarations in different regions and periods were analysed, and the impact of heritage strategy on the number of heritage sites included in each region was evaluated. The results showed that the implementation of heritage policy greatly impacted each region, especially on the number of heritage sites in Asia and the Pacific region. Using the heritage era to carry out modelling analysis, from the perspective of the integrity of historical heritage cultural types, it is considered that there may be cultural heritage sites in the Caribbean and Latin America that have not been given enough attention. The modelling analysis results of era attributes can support the fairness of heritage determination. By calculating the frequency and peak value of heritage sites at the national scale, the frequency and peak value of each country in the top 10 list are used to characterize the ability of national declarations of cultural heritage and reveal the differences in the ability of each member country to declare heritage sites and the heritage era. By calculating the distribution density of the heritage era, this study finds that the world’s cultural heritage is not concentrated in the Middle Ages (600–1450) but the periods of Reformation and Exploration (1450–1700) and Progress and Empire (1850–1914). The above analysis shows that there are imbalances and strategic adjustment effects concerning regions, countries, eras and types in World Heritage list development. The composition types of heritage are complex, and the combination types have obvious changes in different periods. It is suggested that the strategy of world cultural heritage collection should be further optimized to fully guarantee the balance of regions, countries and types, and the heritage value should be fully considered in heritage protection with more diversity and complexity of types.

A Method for Evaluating Intensity of Water Cavitation Peening Processing

2011 ◽  
Vol 675-677 ◽  
pp. 747-750
Author(s):  
B. Han ◽  
Dong Ying Ju ◽  
Xiao Guang Yu
Keyword(s):  
Residual Stress ◽  
Process Capability ◽  
Diffraction Method ◽  
Spring Steel ◽  
Bubble Collapse ◽  
Plastic Layer ◽  
Process Conditions ◽  
X Ray Diffraction ◽  
Near Surface ◽  
The Impact

Water cavitation peening (WCP) with aeration, namely, a new ventilation nozzle with aeration is adopted to improve the process capability of WCP by increasing the impact pressure induced by the bubble collapse on the surface of components. In this study, in order to investigate the process capability of the WCP with aeration a standard N-type almen strips of spring steel SAE 1070 was treated byWCP with various process conditions, and the arc height value and the residual stress in the superficial layers were measured by means of the Almen-scale and X-ray diffraction method, respectively. The optimal fluxes of aeration and the optimal standoff distances were achieved. The maximum of arc height value reach around 150μm. The depth of plastic layer observed from the results of residual stresses is up to 150μm. The results verify the existence of macro-plastic strain in WCP processing. The distributions of residual stress in near-surface under different peening intensity can provide a reference for engineers to decide the optimal process conditions of WCP processing.

scholarly journals Assessing the regional impacts of Mexico City emissions on air quality and chemistry

2009 ◽  
Vol 9 (11) ◽  
pp. 3731-3743 ◽  
Author(s):  
M. Mena-Carrasco ◽  
G. R. Carmichael ◽  
J. E. Campbell ◽  
D. Zimmerman ◽  
Y. Tang ◽  
...  
Keyword(s):  
Air Quality ◽  
Mexico City ◽  
Ozone Production ◽  
Anthropogenic Aerosol ◽  
Near Surface ◽  
Mixing Ratios ◽  
Regional Impacts ◽  
Photolysis Rates ◽  
Regional Air Quality ◽  
The Impact

Abstract. The impact of Mexico City (MCMA) emissions is examined by studying its effects on air quality, photochemistry, and on ozone production regimes by combining model products and aircraft observations from the MILAGRO experiment during March 2006. The modeled influence of MCMA emissions to enhancements in surface level NOx, CO, and O3 concentrations (10–30% increase) are confined to distances <200 km, near surface. However, the extent of the influence is significantly larger at higher altitudes. Broader MCMA impacts (some 900 km Northeast of the city) are shown for specific outflow conditions in which enhanced ozone, NOy, and MTBE mixing ratios over the Gulf of Mexico are linked to MCMA by source tagged tracers and sensitivity runs. This study shows that the "footprint" of MCMA on average is fairly local, with exception to reactive nitrogen, which can be transported long range in the form of PAN, acting as a reservoir and source of NOx with important regional ozone formation implications. The simulated effect of MCMA emissions of anthropogenic aerosol on photochemistry showed a maximum regional decrease of 40% in J[NO2→NO+O], and resulting in the reduction of ozone production by 5–10%. Observed ozone production efficiencies are evaluated as a function of distance from MCMA, and by modeled influence from MCMA. These tend to be much lower closer to MCMA, or in those points where modeled contribution from MCMA is large. This research shows that MCMA emissions do effect on regional air quality and photochemistry, both contributing large amounts of ozone and its precursors, but with caveat that aerosol concentrations hinder formation of ozone to its potential due to its reduction in photolysis rates.

scholarly journals The Impact of Finer-Resolution Air–Sea Coupling on the Intraseasonal Oscillation of the Indian Monsoon

2011 ◽  
Vol 24 (10) ◽  
pp. 2451-2468 ◽  
Author(s):  
Nicholas P. Klingaman ◽  
Steven J. Woolnough ◽  
Hilary Weller ◽  
Julia M. Slingo
Keyword(s):  
Atmospheric Stability ◽  
Intraseasonal Oscillation ◽  
Boreal Summer ◽  
Upper Ocean ◽  
Vertical Resolution ◽  
Coupled Models ◽  
Diurnal Variability ◽  
Near Surface ◽  
The Impact ◽  
Coupling Frequency

Abstract A newly assembled atmosphere–ocean coupled model, called HadKPP, is described and then used to determine the effects of subdaily air–sea coupling and fine near-surface ocean vertical resolution on the representation of the Northern Hemisphere summer intraseasonal oscillation. HadKPP comprises the Hadley Centre atmospheric model coupled to the K-Profile Parameterization ocean boundary layer model. Four 30-member ensembles were performed that vary in ocean vertical resolution between 1 and 10 m and in coupling frequency between 3 and 24 h. The 10-m, 24-h ensemble exhibited roughly 60% of the observed 30–50-day variability in sea surface temperatures and rainfall and very weak northward propagation. Enhancing only the vertical resolution or only the coupling frequency produced modest improvements in variability and just a standing intraseasonal oscillation. Only the 1-m, 3-h configuration generated organized, northward-propagating convection similar to observations. Subdaily surface forcing produced stronger upper-ocean temperature anomalies in quadrature with anomalous convection, which likely affected lower-atmospheric stability ahead of the convection, causing propagation. Well-resolved air–sea coupling did not improve the eastward propagation of the boreal summer intraseasonal oscillation in this model. Upper-ocean vertical mixing and diurnal variability in coupled models must be improved to accurately resolve and simulate tropical subseasonal variability. In HadKPP, the mere presence of air–sea coupling was not sufficient to generate an intraseasonal oscillation resembling observations.

scholarly journals Nature-based cooling potential: a multi-type green infrastructure evaluation in Toronto, Ontario, Canada

2021 ◽  
Author(s):  
Vidya Anderson ◽  
William A. Gough
Keyword(s):  
Urban Agriculture ◽  
Air Temperature ◽  
Green Infrastructure ◽  
Urban Climate ◽  
Surface Air Temperature ◽  
Green Roofs ◽  
Near Surface ◽  
Green Walls ◽  
The Impact ◽  
Agriculture Systems

AbstractThe application of green infrastructure presents an opportunity to mitigate rising temperatures using a multi-faceted ecosystems-based approach. A controlled field study in Toronto, Ontario, Canada, evaluates the impact of nature-based solutions on near surface air temperature regulation focusing on different applications of green infrastructure. A field campaign was undertaken over the course of two summers to measure the impact of green roofs, green walls, urban vegetation and forestry systems, and urban agriculture systems on near surface air temperature. This study demonstrates that multiple types of green infrastructure applications are beneficial in regulating near surface air temperature and are not limited to specific treatments. Widespread usage of green infrastructure could be a viable strategy to cool cities and improve urban climate.

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