Grids of stellar models including second harmonic and colors:solar composition(Z = 0.0172,X = 0.7024)

Grids of stellar evolution are required in many fields of astronomy/astrophysics,such as planet hosting stars,binaries,clusters,chemically peculiar stars,etc.In this study,a grid of stellar evolution models with updated ingredients and recently determined solar abundances is presented.The solar values for the initial abundances of hydrogen,heavy elements and mixing-length parameter are 0.0172,0.7024 and 1.98,respectively.The mass step is small enough(0.01 M_⊙)that interpolation for a given star mass is not required.The range of stellar mass is 0.74 to10.00 M_⊙.We present results in different forms of tables for easy and general application.The second stellar harmonic,required for analysis of apsidal motion of eclipsing binaries,is also listed.We also construct rotating models to determine the effect of rotation on stellar structure and derive fitting formulae for luminosity,radius and the second harmonic as a function of rotational parameter.We also compute and list colors and bolometric corrections of models required for transformation between theoretical and observational results.The results are tested for the Sun,the Hyades cluster,the slowly rotating chemically peculiar Am stars and eclipsing binaries with apsidal motion.The theoretical and observational results along isochrones are in good agreement.The grids are also applicable to rotating stars provided that equatorial velocity is given.     

Chaos and Periodicities in Solar Flare Index from Kandilli Observatory during 1976–2014

The Solar Flare Index is regarded as one of the most important solar indices in the field of solarterrestrial research. It has the maximum effect on Earth of all other solar activity indices and is being considered for describing the short-lived dynamo action inside the Sun. This paper attempts to study the short as well as long-term temporal fluctuations in the chromosphere region of the Sun using the Solar Flare Index. The daily Solar Flare Index for Northern, Southern Hemisphere and Total Disk are considered for a period from January 1976 to December 2014(total 14 245 days) for chaotic as well as periodic analysis.The 0–1 test has been employed to investigate the chaotic behavior associated with the Solar Flare Index.This test revealed that the time series data is non-linear and multi-periodic in nature with deterministic chaotic features. For periodic analysis, the Raleigh Power Spectrum algorithm has been used for identifying the predominant periods within the data along with their confidence score. The well-known fundamental period of 27 days and 11 years along with their harmonics are well affirmed in our investigation with a period of 28 days and 10.77 years. The presence of 14 days and 7 days periods in this investigation states the short-lived action inside the Sun. Our investigation also demonstrates the presence of other mid-range periods including the famous Rieger type period which are very much confirming the results obtained by other authors using various solar activity indicators.     

Solar flare forecasting based on sequential sunspot data

It is widely believed that the evolution of solar active regions leads to solar flares. However, information about the evolution of solar active regions is not employed in most existing solar flare forecasting models. In the current work, a shortterm solar flare forecasting model is proposed, in which sequential sunspot data, including three days of information about evolution from active regions, are taken as one of the basic predictors. The sunspot area, the McIntosh classification, the magnetic classification and the radio flux are extracted and converted to a numerical format that is suitable for the current forecasting model. Based on these parameters, the sliding-window method is used to form the sequential data by adding three days of information about evolution. Then, multi-layer perceptron and learning vector quantization are employed to predict the flare level within 48 h. Experimental results indicate that the performance of the proposed flare forecasting model works better than previous models.     

非理想效应的冷密气体状态方程及其在天体物理中的应用

On the basis of the theory of the grand-canonical ensemble, we have developed a grand-canonical approach in the 'chemical picture" for the equation of state. The approach defines atomic configuration probabilities and gives a conservation equation for the electron number for calculating the occupation numbers of atoms and molecules. The approach also incorporates the perturbations caused by plasma interactions in cool-dense gases into the equation of state formulation and gives the resulting nonidca) terms of thcrmodynamic properties. The resulting formulae have been applied to the study of the properties of cool-dense plasmas and standard solar models. The phase transitions of high temperature plasmas and the influences of pressure ionization effects through solar interior opacities on solar models have been investigated.     

Properties of filaments in solar cycle 20-23 from McIntosh Archive

A filament is a cool, dense structure suspended in the solar corona. The eruption of a filament is often associated with a coronal mass ejection(CME), which has an adverse effect on space weather. Hence,research on filaments has attracted much attention in the recent past. The tilt angle of active region(AR)magnetic bipoles is a crucial parameter in the context of the solar dynamo, which governs the conversion efficiency of the toroidal magnetic field to poloidal magnetic field. Filaments always form over polarity inversion lines(PILs), so the study of tilt angles for these filaments can provide valuable information about generation of a magnetic field in the Sun. We investigate the tilt angles of filaments and other properties using McIntosh Archive data. We fit a straight line to each filament to estimate its tilt angle. We examine the variation of mean tilt angle with time. The latitude distribution of positive tilt angle filaments and negative tilt angle filaments reveals that there is a dominance of positive tilt angle filaments in the southern hemisphere and negative tilt angle filaments dominate in the northern hemisphere. We study the variation of the mean tilt angle for low and high latitudes separately. Investigations of temporal variation with filament number indicate that total filament number and low latitude filament number vary cyclically, in phase with the solar cycle. There are fewer filaments at high latitudes and they also show a cyclic pattern in temporal variation. We also study the north-south asymmetry of filaments with different latitude criteria.     

Measurement of Hubble constant: were differences in secondary distance indicators apparent as early as the HST Key Project?

Different measurements of the Hubble constant(H₀)are not consistent,and a tension between the CMB based methods and cosmic distance ladder based methods has been observed.Measurements from various distance based methods are also inconsistent.To aggravate the problem,the same cosmological probe(TypeⅠa SNe for instance)calibrated through different methods also provides different values of H₀.We compare various distance ladder based methods through the already available unique data obtained from the Hubble Space Telescope(HST).Our analysis is based on parametric(t-test)as well as non-parametric statistical methods such as the Mann-Whitney U test and Kolmogorov-Smirnov test.Our results show that different methods provide different values of H₀ and the differences are statistically significant.The biases in the calibration would not account for these differences as the data have been taken from a single telescope with a common calibration scheme.The unknown physical effects or issues with the empirical relations of distance measurement from different probes could give rise to these differences.     

The Lyman-alpha Solar Telescope(LST) for the ASO-S mission——Ⅲ. data and potential diagnostics

The Lyman-alpha Solar Telescope(LST) is one of the three payloads onboard the Advanced Space-based Solar Observatory(ASO-S) mission. It aims at imaging the Sun from the disk center up to 2.5 R_⊙ targeting solar eruptions, particularly coronal mass ejections(CMEs), solar flares, prominences/filaments and related phenomena, as well as the fast and slow solar wind. The most prominent speciality of LST is the simultaneous observation of the solar atmosphere in both Lyα and white light(WL)with high temporospatial resolution both on the solar disk and the inner corona. New observations in the Lyα line together with traditional WL observations will provide us with many new insights into solar eruptions and solar wind. LST consists of a Solar Corona Imager(SCI) with a field of view(FOV) of 1.1 –2.5 R_⊙, a Solar Disk Imager(SDI) and a full-disk White-light Solar Telescope(WST) with an identical FOV up to 1.2 R_⊙. SCI has a dual waveband in Lyα(121.6 ± 10 nm) and in WL(700 ± 40 nm), while SDI works in the Lyα waveband of 121.6 ± 7.5 nm and WST works in the violet narrow-band continuum of 360 ± 2.0 nm. To produce high quality science data, careful ground and in-flight calibrations are required.We present our methods for different calibrations including dark field correction, flat field correction, radiometry, instrumental polarization and optical geometry. Based on the data calibration, definitions of the data levels and processing procedures for the defined levels from raw data are described. Plasma physical diagnostics offer key ingredients to understand ejecta and plasma flows in the inner corona, as well as different features on the solar disk including flares, filaments, etc. Therefore, we are making efforts to develop various tools to detect the different features observed by LST, and then to derive their physical parameters,for example, the electron density and temperature of CMEs, the outflow velocity of the solar wind, and the hydrogen density and mass flows of prominences. Coordinated observations and data analyses with the coronagraphs onboard Solar Orbiter, PROBA-3, and Aditya are also briefly discussed.     

Estimations of cosmological parameters from the observational variation of the fine structure constant

We present constraints on the quintessence scalar field model from observational data of the variation of the fine structure constant obtained from the Keck telescope and VLT. Within the theoretical frame proposed by Bekenstein, the constraints on the parameters of the quintessence scalar field model are obtained. Considering the prior of Ωm0 as WMAP 7 suggests, we obtain various results from different sam- ples. Based on these results, we also calculate the probability density function of the coupling constant ζ. The best-fit values show a consistent relationship between ζ and the different experimental results. In our work, we test two different potential models, namely, the inverse power law potential and the exponential potential. The results show that both the large value of the parameters in the potential and the strong coupling can cause a variation in the fine structure constant.     

Measurements of spectral lines observed with Hinode/EIS as implications for coronal heating

We have measured the line widths and nonthermal velocities in 12 solar regions using high resolution EUV data taken by Hinode/EIS. We find that there exists a positive correlation between the intensity and nonthermal velocity for the Fe xII emission line as well as some other lines. The correlation coefficients decrease from the disk center to the limb. However, the nonthermal velocities of a particular spectral line do not vary much in different regions, so they are considered isotropic. In particular, we find that for a coronal loop structure, the largest widths and nonthermal velocities occur at the footpoints, where outflows appear. Based on these observational results, we discuss several physical processes responsible for coronal heating.     

Resolved SZE Cluster Count

We study the counts of resolved SZE(Sunyaev-Zel‘dovich effect)clusters expected from an interferometric survey in different cosmological models under different conditions.The self-similar universal gas model and Press-Schechter mass function are used.We take the observing frequency to be 90GHz,and consider two dish diameters,1.2m and 2.5m.We calculate the number density of the galaxy clusters dN/(dΩdz)at a high flux limit Sv^lim=100mJy and at a relative low Sv^lim=10mJy.The total numbers of SZE clusters N in two low-Ω0 models are compared.The results show that the inθuence of the resolved effect depends not only on D,but also on Sv^lim;at a given D,the effect is more significant for a high than for a low Sv^lim.Also,the resolved effect for a flat universe is more impressive than tnat for an open universe.ForD=1.2m and Sv^lim=10mJy,the resolved effect is very weak.Considering the designed interferometers which will be used to survey SZE clusters,we find that the resolved effect is insignificant when estimating the expected yield of the SZE cluster surveys.     

The influence of ionospheric thin shell height on TEC retrieval from GPS observation

We investigate the influence of assumed height for the thin shell ionosphere model on the Total Electron Content(TEC) derived from a small scale Global Positioning System(GPS) network. TEC and instrumental bias are determined by applying a grid-based algorithm to the data on several geomagnetically quiet days covering a 10 month period in 2006. Comparisons of TEC and instrumental bias are made among assumed heights from 250 km to 700 km with an interval of 10 km. While the TEC variations with time follow the same trend, TEC tends to increase with the height of the thin shell. The difference in TEC between heights 250 km and 700 km can be as large as～8 TECU in both daytime and nighttime. The times at which the TEC reaches its peak or valley do not vary much with the assumed heights. The instrumental biases, especially bias from the satellite, can vary irregularly with assumed height. Several satellites show a large deviation of～3 ns for heights larger than 550 km. The goodness of fit for different assumed heights is also examined. The data can be generally well-fitted for heights from 350 km to 700 km. A large deviation happens at heights lower than 350 km. Using the grid-based algorithm, there is no consensus on assumed height as related to data fitting. A thin shell height in the range 350-500 km can be a reasonable compromise between data fitting and peak height of the ionosphere.     

Joint fit of Warm Absorbers in COS and HETG spectra of NGC 3783

Warm Absorbers(WAs), as an important form of AGN outflows, show absorption in both the UV and X-ray bands. Using XSTAR generated photoionization models, for the first time we present a joint fit to the simultaneous observations of HST/COS and Chandra/HETG on NGC 3783. A total of five WAs explain well all absorption features from the AGN outflows, which are spread over a wide range of parameters: ionization parameter logξ from 0.6 to 3.8, column density log NHfrom 19.5 to 22.3 cm~(-2), velocity v from 380 to 1060 km s~(-1), and covering factor from 0.33 to 0.75. Not all the five WAs are consistent in pressure. Two of them are likely different parts of the same absorbing gas, and two of the other WAs may be smaller discrete clouds that are blown out from the inner region of the torus at different periods. The five WAs suggest a total mass outflowing rate within the range of 0.22–4.1 solar mass per year.     

A new parametrization of dark energy equation of state leading to double exponential potential

We show that a phenomenological form of energy density for the scalar field can provide the required transition from decelerated(q 0) to accelerated expansion(q 0) phase of the universe.We have used the latest type Ia supernova(SNIa) and Hubble parameter datasets to constrain the model parameters. The best fit values obtained from those datasets are then applied to reconstruct ωφ(z), the equation of state parameter for the scalar field. The results show that the reconstructed forms of q(z) and ω_φ(z) do not differ much from the standard ΛCDM value at the current epoch. Finally, the functional form of the relevant potential V(φ) is derived by a parametric reconstruction. The corresponding V(φ)comes out to be a double exponential potential, which has a number of cosmological implications.Additionally, we have also studied the effect of this particular scalar field dark energy sector on the evolution of matter overdensities.     

Relations between stellar mass and electron temperature-based metallicity for star-forming galaxies in a wide mass range

We select 947 star-forming galaxies from SDSS-DR7 with [O III]λ4363emission lines detected at a signal-to-noise ratio larger than 5σ. Their electron temperatures and direct oxygen abundances are then determined. We compare the results from different methods. t2, the electron temperature in the low ionization region, estimated from t3, that in the high ionization region, is compared using three analysis relations between t2- t3. These show obvious differences, which result in some different ionic oxygen abundances. The results of t3, t2, O++/H+and O+/H+derived by using methods from IRAF and literature are also compared. The ionic abundances O++/H+are higher than O+/H+for most cases. The different oxygen abundances derived from Teand the strong-line ratios show a clear discrepancy, which is more obvious following increasing stellar mass and strong-line ratio R23. The sample of galaxies from SDSS with detected [O III]λ4363 have lower metallicites and higher star formation rates, so they may not be typical representatives of the whole population of galaxies. Adopting data objects from Andrews Martini, Liang et al. and Lee et al. data, we derive new relations of stellar mass and metallicity for star-forming galaxies in a much wider stellar mass range: from 106 M to 1011 M.     

Searching for exoplanets by HEPS II. detecting earth-like planets in habitable zone around planet hosts within 30 pc

HEPS(Habitable ExoPlanet Survey) is a planning astrometry satellite that aims to find Earth-like planets in the solar neighbourhood. In this paper, we selected 140 planet harboring stars within 30 pc of the solar system to be potential targets for HEPS. We calculate the detection probability of the planet in habitable zone(HZ) for each system using the simulated data of astrometry measurements. For those host stars without planets in HZ, we inject an additional planet of 10 M⊕ in their HZs and check the stability of the systems. Considering five observation modes of different sampling cadence and total observation time, we obtain a table containing the total detection probability of the planets in HZs for all of the 140 selected systems. This paper provides a potential ranked list of target stars for HEPS, or other astrometric mission to detect Earth-like planets in the future. We also calculate an empirical fitted expression of the detection probability as a function of both sampling cadence and total observation time. We conclude a quantitative method to estimate the detection probability for certain planet hosts and observation modes via the empirical expression. We show the minimum requirements of both sampling cadence and observation time for Proxima Centauri, HD 189733 and HD 102365, if the detection probability of habitable-zone planets of these three systems needs to be 90%.     

Model-Synthesized Rate of Type Ia Supernovae and its Influence on the Chemical Enrichment of the ISM

Using Hurley＇s rapid binary stellar evolution code, we have studied the model-synthesized rate of Type Ia Supernovae （SNe Ia） and its influence on the chemical enrichment of the interstellar medium ejected by stellar populations. We adopt two popular scenarios, i.e., single degenerate scenario （SD） and double degenerate scenario （DD）, for the progenitors of SNe Ia to calculate the rates of SNe Ia. Rates calculated in this work agree with that of Hachisu et al. and Han ＆ Podsiadlowski, but are different from that usually adopted in chemical evolution models of galaxies. We apply the rates of SNe Ia to the chemical enrichment （especially Fe enrichment）, then compare the results with previous studies. As known SNe Ia slightly affect the enrichment of C, N, O and Mg elements, while significantly affect the enrichment of Fe. We find that the occurrence and the value of the Fe enrichment in our models are earlier and smaller than that commonly adopted in chemical evolution models. We also study the evolution of [Mg/Fe] ratios, which are almost reciprocals of the Fe enrichment. The study may provide constraints on the free parameters of chemical evolution models of galaxies and evolutionary population synthesis.     

Ionospheric inversion of the Venus Express radio occultation data observed by Shanghai 25m and New Norcia 35m antennas

Electron density profiles of Venus' ionosphere are inverted from the Venus Express(VEX) one-way open-loop radio occultation experiments carried out by the Shanghai 25 m antenna from November 2011 to January 2012 at solar maximum conditions and by the New Norcia 35 m antenna from August 2006 to June 2008 at solar intermediate conditions. The electron density profile(from 110 km to 400 km), retrieved from the X-band egress observation at the Shanghai station, shows a single peak near 147 km with a peak density of about 2 × 104cm-3at a solar zenith angle of 94?. As a comparison, the VEX radio science(Ve Ra) observations at the New Norcia station were also examined, including S- and X-band and dual-frequency data in the ingress mode. The results show that the electron density profiles retrieved from the S-band data are more analogous to the dual-frequency data in terms of the profile shape, compared with the X-band data. Generally, the S-band results slightly underestimate the magnitude of the peak density, while the X-band results overestimate it.The discrepancy in the X-band profile is probably due to the relatively larger unmodeled orbital errors. It is also expected that the ionopause height is sensitive to the solar wind dynamical pressure in high and intermediate solar activities, usually in the range of 200–1000 km on the dayside and much higher on the nightside. Structural variations("bulges" and fluctuations) can be found in the electron density profiles during intermediate solar activity, which may be caused by the interaction of the solar wind with the ionosphere. Considerable ionizations can be observed in Venus' nightside ionosphere, which are unexpected for the Martian nightside ionosphere in most cases.     

Frequency drift rate of solar decameter “drift pair” bursts

This paper deals with the detailed analysis of frequency drift rates of solar"drift pair"(DP)bursts observed from 2015 July 10 to 12 during a type Ⅲ burst storm.The observations were conducted by the UTR-2 radio telescope at 9–33 MHz with high frequency and time resolution.DPs were recorded drifting from higher to lower frequencies(forward DPs)as well as from lower to higher ones(reverse DPs).Patterns on their dynamic spectrum had various inclines and occupied different bandwidths.The frequency drift rate versus frequency dependence of these bursts has been studied.The fitting model to describe the peak evolution of these bursts in the frequency-time plane is presented.The relationship between DPs and type Ⅲ solar bursts is discussed.