- 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.
1 - 6 of 6
Number of results to display per page
Search Results
- 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/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.
- ID:
- ivo://CDS.VizieR/J/ApJ/794/60
- Title:
- SDSS RGB stars distances
- Short Name:
- J/ApJ/794/60
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present distance determinations for a large and clean sample of red giant branch stars selected from the ninth data release of the Sloan Digital Sky Survey (Adelman-McCarthy et al. 2012ApJS..203...21A, Cat. V/139). The distances are calculated based on both observational cluster fiducials and theoretical isochrones. Distributions of distances from the two methods are very similar with peaks at about 10 kpc and tails extending to more than 70 kpc. We find that distances from the two methods agree well for the majority of the sample stars; though, on average, distances based on isochrones are 10% higher than those based on fiducials. We test the accuracy of our distance determinations using 332 stars from 10 Galactic globular and open clusters. The average relative deviation from the literature cluster distances is 4% for the fiducial-based distances and 8% for the isochrone-based distances, both of which are within the uncertainties. We find that the effective temperature and surface gravity derived from low-resolution spectra are not accurate enough to essentially improve the performance of distance determinations. However, for stars with significant extinction, effective temperature may help to better constrain their distances to some extent. We make our sample stars and their distances available from an online catalog. The catalog comprises 17941 stars with reasonable distance estimations reaching to more than 70 kpc, which is suitable for the investigation of the formation and evolution of the Galaxy, especially the Galactic halo.
