- ID:
- ivo://CDS.VizieR/J/A+A/492/277
- Title:
- Analysis of Collinder 69 stars with VOSA
- Short Name:
- J/A+A/492/277
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The physical properties of almost any kind of astronomical object can be derived by fitting synthetic spectra or photometry extracted from theoretical models to observational data. We want to develop an automatic procedure to perform this kind of fitting to a relatively large sample of members of a stellar association and apply this methodology to the case of Collinder 69. We combine the multiwavelength data of our sources and follow a work-flow to derive the physical parameters of the sources. The key step of the work-flow is performed by a new VO-tool, VOSA. All the steps in this process are done in a VO environment.
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- ID:
- ivo://CDS.VizieR/J/ApJ/733/L51
- Title:
- Dark matter densities in cluster isochrones
- Short Name:
- J/ApJ/733/L51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In order to characterize how dark matter (DM) annihilation inside stars changes the aspect of a stellar cluster, we computed the evolution until the ignition of the He burning of stars from 0.7M_{sun}_ to 3.5M_{sun}_ within halos of DM with different characteristics. We found that, when a cluster is surrounded by a dense DM halo, the positions of the cluster' stars in the H-R diagram have a brighter and hotter turnoff point than in the classical scenario without DM, therefore giving the cluster a younger appearance. The high DM densities required to produce these effects are expected only in very specific locations, such as near the center of our Galaxy. In particular, if DM is formed by the 8 GeV weakly interacting massive particles recently invoked to reconcile the results from direct detection experiments, then this signature is predicted for halos of DM with a density {rho}_{chi}_=3x10^5^GeV/cm^3^. A DM density gradient inside the stellar cluster would result in a broader main sequence, turnoff, and red giant branch regions. Moreover, we found that for very high DM halo densities the bottom of the isochrones in the H-R diagram rises to higher luminosities, leading to a characteristic signature on the stellar cluster. We argue that this signature could be used to indirectly probe the presence of DM particles in the location of a cluster.
- ID:
- ivo://CDS.VizieR/J/A+A/585/A5
- Title:
- Exoplanet hosts/field stars age consistency
- Short Name:
- J/A+A/585/A5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Transiting planets around stars are discovered mostly through photometric surveys. Unlike radial velocity surveys, photometric surveys do not tend to target slow rotators, inactive or metal-rich stars. Nevertheless, we suspect that observational biases could also impact transiting-planet hosts. This paper aims to evaluate how selection effects reflect on the evolutionary stage of both a limited sample of transiting-planet host stars (TPH) and a wider sample of planet-hosting stars detected through radial velocity analysis. Then, thanks to uniform derivation of stellar ages, a homogeneous comparison between exoplanet hosts and field star age distributions is developed. Stellar parameters have been computed through our custom-developed isochrone placement algorithm, according to Padova evolutionary models. The notable aspects of our algorithm include the treatment of element diffusion, activity checks in terms of logR'_HK_ and vsini, and the evaluation of the stellar evolutionary speed in the Hertzsprung-Russel diagram in order to better constrain age. Working with TPH, the observational stellar mean density {rho}_*_ allows us to compute stellar luminosity even if the distance is not available, by combining {rho}_* with the spectroscopic logg. The median value of the TPH ages is ~5Gyr. Even if this sample is not very large, however the result is very similar to what we found for the sample of spectroscopic hosts, whose modal and median values are [3, 3.5)Gyr and ~4.8Gyr, respectively. Thus, these stellar samples suffer almost the same selection effects. An analysis of MS stars of the solar neighbourhood belonging to the same spectral types bring to an age distribution similar to the previous ones and centered around solar age value. Therefore, the age of our Sun is consistent with the age distribution of solar neighbourhood stars with spectral types from late F to early K, regardless of whether they harbour planets or not. We considered the possibility that our selected samples are older than the average disc population.
- ID:
- ivo://CDS.VizieR/VI/54
- Title:
- Horizontal Branch Stellar Model Calculations
- Short Name:
- VI/54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This data set consists of evolutionary sequences from the Zero Age Horizontal Branch (ZAHB) to the point where log L/Lsun reaches 2.25 on the lower AGB. These calculations have enhanced oxygen abundance according to a relation used by VandenBerg (1992ApJ...391..685V) and Bergbusch and VandenBerg (1992ApJS...81..163B) for main sequence and red-giant branch models. Also, zero age sequences for oxygen enhanced and scaled-solar compositions are given.
- ID:
- ivo://CDS.VizieR/J/MNRAS/387/105
- Title:
- Isochrone database for single- and binary-star SSPs
- Short Name:
- J/MNRAS/387/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We first presented an isochrone data base that can be widely used for stellar population synthesis studies and colour-magnitude diagram (CMD) fitting. The data base consists of the isochrones of both single-star and binary-star simple stellar populations (ss-SSPs and bs-SSPs). The ranges for the age and metallicity of populations are 0-15Gyr and 0.0001-0.03, respectively. All data are available for populations with two widely used initial mass functions (IMFs), that is, Salpeter IMF and Chabrier IMF. The uncertainty caused by the data base (about 0.81 per cent) is designed to be smaller than those caused by the Hurley code and widely used stellar spectra libraries (e.g. BaSeL 3.1) when it is used for stellar population synthesis. Based on the isochrone data base, we then built a rapid stellar population synthesis (RPS) model and calculated the high-resolution (0.03nm) integrated spectral energy distributions, Lick indices and colour indices for bs-SSPs and ss-SSPs. In particular, we calculated the UBVRIJHKLM colours, ugriz colours and some composite colours that consist of magnitudes on different systems. These colours are useful for disentangling the well-known stellar age-metallicity degeneracy according to our previous work. As an example for applying the isochrone data base for CMD fitting, we fitted the CMDs of two star clusters (M67 and NGC1868) and obtained their distance moduli, colour excesses, stellar metallicities and ages. The results showed that the isochrones of bs-SSPs are closer to those of real star clusters. It suggests that we should take the effects of binary interactions into account in stellar population synthesis. We also discussed on the limitations of the application of the isochrone data base and the results of the RPS model.
- ID:
- ivo://CDS.VizieR/J/A+A/631/A77
- Title:
- Low-mass stellar models and isochrones
- Short Name:
- J/A+A/631/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an extended grid of state-of-the art stellar models for low-mass stars including updated physics (nuclear reaction rates, surface boundary condition, mass-loss rate, angular momentum transport, rotation-induced mixing, and torque prescriptions). We evaluate the impact of wind braking, realistic atmospheric treatment, rotation, and rotation-induced mixing on the structural and rotational evolution from the pre-main sequence (PMS) to the turn-off. Using the STAREVOL code, we provide an updated PMS grid. We computed stellar models for seven different metallicities, from [Fe/H]=-1dex to [Fe/H]=+0.3dex with a solar composition corresponding to Z=0.0134. The initial stellar mass ranges from 0.2 to 1.5M_{sun}_ with extra grid refinement around one solar mass. We also provide rotating models for three different initial rotation rates (slow, median, and fast) with prescriptions for the wind braking and disc-coupling timescale calibrated on observed properties of young open clusters. The rotational mixing includes the most recent description of the turbulence anisotropy in stably stratified regions. The overall behaviour of our models at solar metallicity, and their constitutive physics, are validated through a detailed comparison with a variety of distributed evolutionary tracks. The main differences arise from the choice of surface boundary conditions and initial solar composition. The models including rotation with our prescription for angular momentum extraction and self-consistent formalism for angular momentum transport are able to reproduce the rotation period distribution observed in young open clusters over a wide range of mass values. These models are publicly available and can be used to analyse data coming from present and forthcoming asteroseismic and spectroscopic surveys such as Gaia, TESS, and PLATO.The overall behaviour of our models at solar metallicity, and their constitutive physics, are validated through a detailed comparison with a variety of distributed evolutionary tracks. The main differences arise from the choice of surface boundary conditions and initial solar composition. The models including rotation with our prescription for angular momentum extraction and self-consistent formalism for angular momentum transport are able to reproduce the rotation period distribution observed in young open clusters over a wide range of mass values. These models are publicly available and can be used to analyse data coming from present and forthcoming asteroseismic and spectroscopic surveys such as Gaia, TESS, and PLATO.
- ID:
- ivo://CDS.VizieR/J/A+A/533/A109
- Title:
- Pisa pre-main sequence tracks and isochrones
- Short Name:
- J/A+A/533/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In recent years new observations of pre-main sequence stars (pre-MS) with Z<Z_{sun}_ have been made available. To take full advantage of the continuously growing amount of data of pre-MS stars in different environments, we need to develop updated pre-MS models for a wide range of metallicity to assign reliable ages and masses to the observed stars. We present updated evolutionary pre-MS models and isochrones for a fine grid of mass, age, metallicity, and helium values. We use a standard and well-tested stellar evolutionary code (i.e. FRANEC), that adopts outer boundary conditions from detailed and realistic atmosphere models. In this code, we incorporate additional improvements to the physical inputs related to the equation of state and the low temperature radiative opacities essential to computing low-mass stellar models. We make available via internet a large database of pre-MS tracks and isochrones for a wide range of chemical compositions (Z=0.0002-0.03), masses (M=0.2-7.0M_{sun}_), and ages (1-100Myr) for a solar-calibrated mixing length parameter alpha (i.e. 1.68). For each chemical composition, additional models were computed with two different mixing length values, namely alpha=1.2 and 1.9. Moreover, for Z>=0.008, we also provided models with two different initial deuterium abundances. The characteristics of the models have been discussed in detail and compared with other work in the literature. The main uncertainties affecting theoretical predictions have been critically discussed. Comparisons with selected data indicate that there is close agreement between theory and observation.
- ID:
- ivo://CDS.VizieR/J/MNRAS/434/806
- Title:
- Pre-main-sequence isochrones. II. SFR
- Short Name:
- J/MNRAS/434/806
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have derived ages for 13 young (<30Myr) star-forming regions and find that they are up to a factor of 2 older than the ages typically adopted in the literature. This result has wide-ranging implications, including that circumstellar discs survive longer (=~10-12Myr) and that the average Class I lifetime is greater (=~1Myr) than currently believed. For each star-forming region, we derived two ages from colour-magnitude diagrams. First, we fitted models of the evolution between the zero-age main sequence and terminal-age main sequence to derive a homogeneous set of main-sequence ages, distances and reddenings with statistically meaningful uncertainties. Our second age for each star-forming region was derived by fitting pre-main-sequence stars to new semi-empirical model isochrones. For the first time (for a set of clusters younger than 50Myr), we find broad agreement between these two ages, and since these are derived from two distinct mass regimes that rely on different aspects of stellar physics, it gives us confidence in the new age scale. This agreement is largely due to our adoption of empirical colour-T_eff_ relations and bolometric corrections for pre-main-sequence stars cooler than 4000K. The revised ages for the star-forming regions in our sample are: ~2Myr for NGC 6611 (Eagle Nebula; M 16), IC 5146 (Cocoon Nebula), NGC 6530 (Lagoon Nebula; M 8) and NGC 2244 (Rosette Nebula); ~6Myr for {sigma} Ori, Cep OB3b and IC 348; ~10Myr for {lambda} Ori (Collinder 69); ~11Myr for NGC 2169; ~12Myr for NGC 2362; ~13Myr for NGC 7160; ~14Myr for {chi}Per (NGC 884); and ~20Myr for NGC 1960 (M 36).
- ID:
- ivo://CDS.VizieR/J/MNRAS/424/3178
- Title:
- Pre-main-sequence isochrones. Pleiades benchmark
- Short Name:
- J/MNRAS/424/3178
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a critical assessment of commonly used pre-main-sequence isochrones by comparing their predictions to a set of well-calibrated colour-magnitude diagrams of the Pleiades in the wavelength range 0.4-2.5um. Our analysis shows that for temperatures less than 4000K, the models systematically overestimate the flux by a factor of 2 at 0.5um, though this decreases with wavelength, becoming negligible at 2.2um. In optical colours this will result in the ages for stars younger than 10Myr being underestimated by factors of between 2 and 3. We show that using observations of standard stars to transform the data into a standard system can introduce significant errors in the positioning of pre-main sequences in colour-magnitude diagrams. Therefore, we have compared the models to the data in the natural photometric system in which the observations were taken. Thus we have constructed and tested a model of the system responses for the Wide-Field Camera on the Isaac Newton Telescope. As a benchmark test for the development of pre-main-sequence models, we provide both our system responses and the Pleiades sequence.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A18
- Title:
- Revising the ages of planet-hosting stars
- Short Name:
- J/A+A/575/A18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This article aims to measure the age of stars with planets (SWP) through stellar tracks and isochrones computed with the Padova & Trieste Stellar Evolutionary Code (PARSEC). We developed algorithms based on two different techniques for determining the ages of field stars: isochrone placement and Bayesian estimation. Their application to a synthetic sample of coeval stars shows the intrinsic limits of each method. For instance, the Bayesian computation of the modal age tends to select the extreme age values in the isochrones grid. Therefore, we used the isochrone placement technique to measure the ages of 317 SWP. We found that ~6% of SWP have ages lower than 0.5Gyr. The age distribution peaks in the interval [1.5, 2]Gyr, then it decreases. However, ~7% of the stars are older than 11Gyr. The Sun turns out to be a common star that hosts planets, when considering its evolutionary stage. Our SWP age distribution is less peaked and slightly shifted towards lower ages if compared with ages in the literature and based on the isochrone fit. In particular, there are no ages below 0.5Gyr in the literature.
