- ID:
- ivo://CDS.VizieR/J/MNRAS/399/432
- Title:
- Fitted UBV magnitude for MS stars
- Short Name:
- J/MNRAS/399/432
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We fit the colour-magnitude diagrams of stars between the zero-age main-sequence and terminal-age main sequence in young clusters and associations. The ages we derive are a factor of 1.5-2 longer than the commonly used ages for these regions, which are derived from the positions of pre-main-sequence stars in colour-magnitude diagrams. From an examination of the uncertainties in the main-sequence and pre-main-sequence models, we conclude that the longer age scale is probably the correct one, which implies that we must revise upwards the commonly used ages for young clusters and associations. Such a revision would explain the discrepancy between the observational lifetimes of protoplanetary discs and theoretical calculations of the time to form planets. It would also explain the absence of clusters with ages between 5 and 30Myr.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/604/A129
- Title:
- Formation of MW halo and its dwarf satellites
- Short Name:
- J/A+A/604/A129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a homogeneous set of accurate atmospheric parameters for a complete sample of very and extremely metal-poor stars in the dwarf spheroidal galaxies (dSphs) Sculptor, Ursa Minor, Sextans, Fornax, Bootes I, Ursa Major II, and Leo IV. We also deliver a Milky Way (MW) comparison sample of giant stars covering the -4<[Fe/H]<-1.7 metallicity range. We show that, in the [Fe/H]=>-3.7 regime, the non-local thermodynamic equilibrium (NLTE) calculations with non-spectroscopic effective temperature (Teff) and surface gravity (log g) based on the photometric methods and known distance provide consistent abundances of the FeI and FeII lines. This justifies the FeI/FeII ionisation equilibrium method to determine log g for the MW halo giants with unknown distance. The atmospheric parameters of the dSphs and MW stars were checked with independent methods. In the [Fe/H]>-3.5 regime, the TiI/TiII ionisation equilibrium is fulfilled in the NLTE calculations. In the logg-Teff plane, all the stars sit on the giant branch of the evolutionary tracks corresponding to [Fe/H]=-2 to -4, in line with their metallicities. For some of the most metal-poor stars of our sample, we hardly achieve consistent NLTE abundances from the two ionisation stages for both iron and titanium. We suggest that this is a consequence of the uncertainty in the Teff-colour relation at those metallicities. The results of these work provide the base for a detailed abundance analysis presented in a companion paper.
- ID:
- ivo://CDS.VizieR/J/ApJS/255/22
- Title:
- FRII radio sources dynamical models
- Short Name:
- J/ApJS/255/22
- Date:
- 03 Dec 2021 13:25:10
- Publisher:
- CDS
- Description:
- Dynamical evolution models of 361 extragalactic Fanaroff-Riley type II radio sources selected from the Cambridge 3CRR, 6CE, 5C6, and 5C7 Sky Surveys, as well as the Bologna B2, Green Bank GB, and GB2 Surveys, are presented. Their spectra, compiled mostly from the recent catalogs of radio sources and the available NASA/IPAC and Astrophysical Catalogs Support System databases, along with morphological characteristics of the sources determined from their radio maps, have been modeled using the DYNAGE algorithm and/or its extension (KDA EXT) for the hypothetical case of further evolution after the jet's termination. The best-fit models provide estimates of a number of important physical parameters of the sources, as (i) the jet power, (ii) the density distribution of the external gaseous medium surrounding the radio core and the jet propagating through it, (iii) the initial energy distribution of the relativistic particles accelerated at the shock fronts, and (iv) the age of the observed radio structure. Additionally, estimates of some derivative parameters are provided, e.g., the radio lobes' pressure, their longitudinal expansion velocity, the magnetic field strength, and the total energy deposited in the lobes. The observed spectra and their best-fit models are included. Finally, one of the useful applications of the above models is presented, namely a strong correlation between the ambient medium density and the rest-frame two-point spectral index available directly from the observed spectra.
- ID:
- ivo://CDS.VizieR/J/MNRAS/480/1547
- Title:
- Full Evolutionary Sequences of Massive WDs
- Short Name:
- J/MNRAS/480/1547
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We explore the evolution of hydrogen-rich and hydrogen-deficient white dwarf stars with masses between 1.012 and 1.307M_{sun}, and initial metallicity of Z=0.02. These sequences are the result of main-sequence stars with masses between 8.8 and 11.8M_{sun}. The simulations were performed with MESA (Modules for Experiments in Stellar Astrophysics), starting at the zero-age main sequence, through thermally pulsing and mass-loss phases, ending at the white dwarf cooling sequence. We present reliable chemical profiles for the whole mass range considered, covering the different expected central compositions (i.e. C/O, O/Ne and Ne/O/Mg) and its dependence on the stellar mass. In addition, we present detailed chemical profiles of hybrid C/O-O/Ne core white dwarfs, found in the mass range between 1.024 and 1.15M_{sun}. We present the initial-to-final mass relation, the mass-radius relation and cooling times considering the effects of atmosphere and core composition.
- ID:
- ivo://CDS.VizieR/VI/157
- Title:
- Full-spectrum fitting of simple stellar pop.
- Short Name:
- VI/157
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this second paper of a series on the accuracy and precision of the determination of age and metallicity of simple stellar populations (SSPs) by means of the full spectrum fitting technique, we study the influence of star cluster mass through stochastic fluctuations of the number of stars near the top of the stellar mass function, which dominate the flux in certain wavelength regimes depending on the age.We consider SSP models based on the Padova isochrones, spanning the age range 7.0<=log(age/yr)<=10.1. Simulated spectra of star clusters in the mass range 10^4^<=M/M_{sun}_<10^6^ are compared with SSP model spectra to determine best-fit ages and metallicities using a full-spectrum fitting routine in four wavelength regimes: the blue optical (0.35-0.70um), the red optical (0.6-1.0um), the near-IR (1.0-2.5um), and the mid-IR (2.5-5.0um). We compare the power of each wavelength regime in terms of both the overall precision of age and metallicity determination, and of its dependence on cluster mass. We also study the relevance of spectral resolution in this context by utilizing two different spectral libraries (BaSeL and BT-Settl). We highlight the power of the mid-IR regime in terms of identifying young massive clusters in dusty star forming regions in distant galaxies. The spectra of the simulated star clusters and SSPs are made available online to enable follow-up studies by the community.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A58
- Title:
- Full spectrum of Proxima Centauri
- Short Name:
- J/A+A/603/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of Proxima b, a terrestrial temperate planet, presents the opportunity of studying a potentially habitable world in optimal conditions. A key aspect to model its habitability is to understand the radiation environment of the planet in the full spectral domain. We characterize the X-rays to mid-IR radiative properties of Proxima with the goal of providing the top-of-atmosphere fluxes on the planet. We also aim at constraining the fundamental properties of the star, namely its mass, radius, effective temperature and luminosity. We employ observations from a large number of facilities and make use of different methodologies to piece together the full spectral energy distribution of Proxima. In the high-energy domain, we pay particular attention to the contribution by rotational modulation, activity cycle, and flares so that the data provided are representative of the overall radiation dose received by the atmosphere of the planet.
- ID:
- ivo://CDS.VizieR/J/ApJ/638/725
- Title:
- Fundamental manifold of spheroids
- Short Name:
- J/ApJ/638/725
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a unifying empirical description of the structural and kinematic properties of all spheroids embedded in dark matter halos. We find that the intracluster stellar spheroidal components of galaxy clusters, which we call cluster spheroids (CSphs) and which are typically 100 times the size of normal elliptical galaxies, lie on a fundamental plane as tight as that defined by elliptical galaxies (rms in effective radius of 0.07) but having a different slope.
- ID:
- ivo://CDS.VizieR/J/other/AstBu/74.62
- Title:
- Fundamental parameters of CP stars
- Short Name:
- J/other/AstBu/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The paper presents the results of determination of fundamental parameters (effective temperature, surface gravity, luminosity, mass, radius, rotation velocity, and radial velocity) for 146 stars observed at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences with the Main Stellar Spectrograph during 2009-2011; 124 of the stars are magnetic or potentially magnetic objects. We obtained and analyzed at least 500 pairs of circularly-polarized-emission spectra. Various methods and approaches were used in estimating the fundamental parameters.
- ID:
- ivo://CDS.VizieR/J/A+A/440/305
- Title:
- Fundamental parameters of fast-rotating B stars
- Short Name:
- J/A+A/440/305
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we develop a calculation code to account for the effects carried by fast rotation on the observed spectra of early-type stars. Stars are assumed to be in rigid rotation, and the grid of plane-parallel model atmospheres used to represent the gravitational darkening are calculated by means of a non-LTE approach. Attention is paid to the relation between the apparent and parent non-rotating counterpart stellar fundamental parameters and apparent, and true Vsini parameters as a function of the rotation rate Omega/Omega_c_, stellar mass, and inclination angle. It is shown that omitting of gravitational darkening in the analysis of chemical abundances of CNO elements can produce systematic overestimation or underestimation, depending on the lines used, rotational rate, and inclination angle.
- ID:
- ivo://CDS.VizieR/J/A+A/565/A11
- Title:
- Gaia photometry for white dwarfs
- Short Name:
- J/A+A/565/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Gaia space mission, through its 5-6 years survey of the whole sky up to magnitude V=20-25, will drastically increase the sample of known white dwarfs allowing to address new science questions. In this paper we provide a characterisation of Gaia photometry for the case of white dwarfs to better prepare for the analysis of the scientific output of the mission including relationships among colours involving Gaia magnitudes (white light G, blue GBP, red GRP and GRVS passbands) and colours from other commonly used photometric systems (Johnson-Cousins, SDSS and 2MASS). We also present numbers of white dwarfs predicted by the Gaia Universe Model Snapshot and compare them with an alternative simulation calibrated with the local white dwarfs sample. In these online tables we provide the values used to fit the relationships in the paper, especially useful for those cases where the deviation from the established relationships is large. The most recent Gaia transmission curves and three different compositions for white dwarfs were considered here (pure hydrogen, pure helium and mixed composition with H/He=0.1).
