- ID:
- ivo://CDS.VizieR/J/MNRAS/403/2012
- Title:
- PopStar II. Giant HII regions models
- Short Name:
- J/MNRAS/403/2012
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper of a series reporting the results from the popstar evolutionary synthesis models. Here, we present synthetic emission-line spectra of HII regions photoionized by young star clusters, for seven values of cluster masses and for ages between 0.1 and 5.2Myr. The ionizing spectral energy distributions (SEDs) are those obtained by the popstar code for six different metallicities, with a very low-metallicity set, Z=0.0001 , not included in previous similar works. We assume that the radius of the HII region is the distance at which the ionized gas is deposited by the action of the mechanical energy of the winds and supernovae from the central ionizing young cluster.
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Search Results
- ID:
- ivo://CDS.VizieR/J/MNRAS/432/2746
- Title:
- POPSTAR models. III. Young star clusters
- Short Name:
- J/MNRAS/432/2746
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the third paper of a series reporting the results from the POPSTAR evolutionary synthesis models. The main goal of this work is to present and discuss the synthetic photometric properties of single stellar populations resulting from our POPSTAR code. Colours in the Johnson and Sloan Digital Sky Survey (SDSS) systems, H{alpha} and H{beta} luminosities and equivalent widths, and ionizing region size, have been computed for a wide range of metallicity (Z=0.0001-0.05) and age (0.1Myr to 20Gyr). We calculate the evolution of the cluster and the region geometry in a consistent manner. We demonstrate the importance of the contribution of emission lines to broader band photometry when characterizing stellar populations, through the presentation of both contaminated and non-contaminated colours (in both the Johnson and SDSS systems). The tabulated colours include stellar and nebular components, in addition to line emission. The main application of these models is the determination of physical properties of a given young ionizing cluster, when only photometric observations are available; for an isolated star-forming region, the young star cluster models can be used, free from the contamination of any underlying background stellar population. In most cases, however, the ionizing population is usually embedded in a large and complex system, and the observed photometric properties result from the combination of a young star-forming burst and the underlying older population of the host. Therefore, the second objective of this paper is to provide a grid of models useful in the interpretation of mixed regions where the separation of young and old populations is not sufficiently reliable. We describe the set of popstar spectral energy distributions (SEDs), and the derived colours for mixed populations where an underlying host population is combined in different mass-ratios with a recent ionizing burst. These colours, together with other common photometric parameters, such as the H{alpha} radius of the ionized region, and Balmer line equivalent widths and luminosities, allow one to infer the physical properties of star-forming regions even in the absence of spectroscopic information.
- ID:
- ivo://CDS.VizieR/J/AZh/79/738
- Title:
- Population model of binary stars in the Galaxy
- Short Name:
- J/AZh/79/738
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A comparative study of the population of the galactic binary stars is performed for two modes of star formation: star formation at a constant rate over 10^+10^yrs, and a burst of star formation that reprocesses the same mass of gas into stars over 10^+9^yrs. Estimates are presented for the star formation rates and populations of about 100 types of binaries and the products of their evolution.
- ID:
- ivo://CDS.VizieR/J/ApJS/171/146
- Title:
- Population synthesis in the blue. IV
- Short Name:
- J/ApJS/171/146
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new set of model predictions for 16 Lick absorption line indices from H{delta} through Fe5335 and UBV colors for single stellar populations with ages ranging between 1 and 15Gyr, [Fe/H] ranging from -1.3 to +0.3, and variable abundance ratios. The models are based on accurate stellar parameters for the Jones library stars and a new set of fitting functions describing the behavior of line indices as a function of effective temperature, surface gravity, and iron abundance. The abundances of several key elements in the library stars have been obtained from the literature in order to characterize the abundance pattern of the stellar library, thus allowing us to produce model predictions for any set of abundance ratios desired. We develop a method to estimate mean ages and abundances of iron, carbon, nitrogen, magnesium, and calcium that explores the sensitivity of the various indices modeled to those parameters. The models are compared to high-S/N data for Galactic clusters spanning the range of ages, metallicities, and abundance patterns of interest. Essentially all line indices are matched when the known cluster parameters are adopted as input. Comparing the models to high-quality data for galaxies in the nearby universe, we reproduce previous results regarding the enhancement of light elements and the spread in the mean luminosity-weighted ages of early-type galaxies.
- ID:
- ivo://CDS.VizieR/VI/109
- Title:
- Population Synthesis Models at very low metallicities
- Short Name:
- VI/109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Using new sets of stellar evolution models at very low metallicities (Z=10^-7^; 10^-5^) and previously published grids we examine spectral properties of the ionising continua, the Lyman-break, and the Ly{alpha} and He1640 recombination lines in starbursts. The metallicity dependence of these properties, especially the transition from primordial galaxies (Population III) to currently observed metallicities, is examined for various IMFs and star formation histories.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A25
- Title:
- Post-AGB and CSPNe evolutionary models
- Short Name:
- J/A+A/588/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The post-asymptotic giant branch (AGB) phase is arguably one of the least understood phases of the evolution of low- and intermediate- mass stars. The two grids of models presently available are based on outdated micro- and macrophysics and do not agree with each other. Studies of the central stars of planetary nebulae (CSPNe) and post-AGB stars in different stellar populations point to significant discrepancies with the theoretical predictions of post-AGB models. We study the timescales of post-AGB and CSPNe in the context of our present understanding of the micro- and macrophysics of stars. We want to assess whether new post-AGB models, based on the latter improvements in TP-AGB modeling, can help us to understand the discrepancies between observation and theory and within theory itself. In addition, we aim to understand the impact of the previous AGB evolution for post-AGB phases. We computed a grid of post-AGB full evolutionary sequences that include all previous evolutionary stages from the zero age main sequence to the white dwarf phase. We computed models for initial masses between 0.8 and 4M_{sun}_ and for a wide range of initial metallicities (Z_0_= 0.02, 0.01, 0.001, 0.0001). This allowed us to provide post-AGB timescales and properties for H-burning post-AGB objects with masses in the relevant range for the formation of planetary nebulae (~0,5-0,8M_{sun}_). We included an updated treatment of the constitutive microphysics and included an updated description of the mixing processes and winds that play a key role during the thermal pulses (TP) on the AGB phase.
487. Post-AGB evolution
- ID:
- ivo://CDS.VizieR/J/ApJS/92/125
- Title:
- Post-AGB evolution
- Short Name:
- J/ApJS/92/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we present the results for the post-AGB phases of stellar evolutionary sequences, complete from the main-sequence phase, through the AGB phase, and on into the planetary nebula and white dwarf regimes. Mass loss has been included using an empirical formalism derived from observed mass-loss rates of planetary nebula nuclei available in the literature and from radiation-pressure-driven stellar wind theory. Models are calculated for initial masses 0.89, 0.95, 1.0, 1.5, 2.0, 2.5, 3.5, and 5.0M_{sun}_, and metallicities 0.016, 0.008, 0.004, and 0.001. These abundance and mass values were chosen to allow comparison with Galactic, and Magellanic Cloud planetary nebulae and their nuclei. The post-AGB evolutionary sequences fall into two distinct groups depending on when the planetary nebula nuclei leave the AGB: one group where helium-shell burning is dominant, and the other group where hydrogen-shell burning is dominant. Of the 27 computed sequences: 17 are hydrogen-burners, and 10 are helium-burners. In only five cases was any effort made to control the phase of departure from the AGB. Lower mass models are more likely to leave the AGB burning helium, as the preceding AGB evolution has a mass-loss rate which is greatest immediately prior to a helium-shell flash. The calculations are compared with the large observational database that has developed over recent years for the Large Magellanic Cloud. These calculations will be useful for determining the planetary nebula luminosity function, and for the study of the ultraviolet excess observed in elliptical galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/747/106
- Title:
- Potential of the finite Mestel disk
- Short Name:
- J/ApJ/747/106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Mestel determined the surface mass distribution of the finite disk for which the circular velocity is constant in the disk and found the gravitational field for points in the z=0 plane. Here we find the exact closed form solutions for the potential and the gravitational field of this disk in cylindrical coordinates over all the space. The finite Mestel disk (FMD) is characterized by a cuspy mass distribution in the inner disk region and by an exponential distribution in the outer region of the disk. The FMD is quite different from the better known exponential disk or the untruncated Mestel disk which, being infinite in extent, are not realistic models of real spiral galaxies. In particular, the FMD requires significantly less mass to explain a measured velocity curve.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A39
- Title:
- Power-2 limb-darkening law from STAGGER-grid
- Short Name:
- J/A+A/616/A39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Inaccurate limb-darkening models can be a significant source of error in the analysis of the light curves for transiting exoplanet and eclipsing binary star systems, particularly for high-precision light curves at optical wavelengths. The power-2 limb-darkening law, I_{lambda}_({mu})=1-c(1-{mu}^{alpha}^), has recently been proposed as a good compromise between complexity and precision in the treatment of limb-darkening. My aim is to develop a practical implementation of the power-2 limb-darkening law and to quantify the accuracy of this implementation. I have used synthetic spectra based on the 3D stellar atmosphere models from the Stagger-grid to compute the limb- darkening for several passbands (UBVRI, CHEOPS, TESS, Kepler, etc.). The parameters of the power-2 limb-darkening laws are optimized using a least-squares fit to a simulated light curve computed directly from the tabulated I_{lambda}_({mu}) values. I use the transformed parameters h_1_=1-c(1-2^(-{alpha})^) and h_2_=c2^(-{alpha}^) to directly compare these optimized limb-darkening parameters to the limb darkening measured from Kepler light curves of 16 transiting exoplanet systems. The posterior probability distributions (PPDs) of the transformed parameters h_1_ and h_2_ resulting from the light curve analysis are found to be much less strongly correlated than the PPDs for c and {alpha}. The agreement between the computed and observed values of (h_1_, h_2_) is generally very good but there are significant differences between the observed and computed values for Kepler-17, the only star in the sample that shows significant variability between the eclipses due to magnetic activity (star spots). The tabulation of h_1_ and h_2_ provided here can be used to accurately model the light curves of transiting exoplanets. I also provide estimates of the priors that should be applied to transformed parameters h_1_ and h_2_ based on my analysis of the Kepler light curves of 16 stars transiting exoplanets.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A32
- Title:
- Precipitable water vapour at Cerro Armazones
- Short Name:
- J/A+A/588/A32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We studied the precipitable water vapour (PWV) content near Cerro Armazones and discuss the potential use of our technique of modelling the telluric absorption lines for the investigation of other molecular layers. The site is designated for the European Extremely Large Telescope (E-ELT) and the nearby planned site for the Cherenkov Telescope Array (CTA). Spectroscopic data from the Bochum Echelle Spectroscopic Observer (BESO) instrument were investigated by using line-by-line radiative transfer model (LBLRTM) radiative transfer models for the Earths atmosphere with the telluric absorption correction tool molecfit. All observations from the archive in the period from December 2008 to the end of 2014 were investigated. The dataset completely covers the El Nino event registered in the period 2009-2010. Models of the 3D Global Data Assimilation System (GDAS) were used for further comparison. Moreover, for those days with coincidence of data from a similar study with VLT/X-shooter and microwave radiometer LHATPRO data at Cerro Paranal, a direct comparison is presented. This analysis shows that the site has systematically lower PWV values, even after accounting for the decrease in PWV expected from the higher altitude of the site with respect to Cerro Paranal, using the average atmosphere found with radiosondes. We found that GDAS data are not a suitable method for predicting of local atmospheric conditions - they usually systematically overestimate the PWV values. Due to the large sample, we were furthermore able to characterize the site with respect to symmetry across the sky and variation with the years and within the seasons. This kind of technique of studying the atmospheric conditions is shown to be a promising step into a possible monitoring equipment for CTA.
