- ID:
- ivo://CDS.VizieR/J/A+A/582/A97
- Title:
- SSP in NIR. II. Synthesis models
- Short Name:
- J/A+A/582/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present unresolved single stellar population synthesis models in the near-infrared (NIR) range. The extension to the NIR is important for the study of early-type galaxies, since these galaxies are predominantly old and therefore emit most of their light in this wavelength range. The models are based on a library of empirical stellar spectra, the NASA infrared telescope facility (IRTF) spectral library. Integrating these spectra along theoretical isochrones, while assuming an initial mass function (IMF), we have produced model spectra of single age-metallicity stellar populations at a resolution R~2000. These models can be used to fit observed spectral of globular clusters and galaxies, to derive their age distribution, chemical abundances and IMF. The models have been tested by comparing them to observed colours of elliptical galaxies and clusters in the Magellanic Clouds. Predicted absorption line indices have been compared to published indices of other elliptical galaxies. The comparisons show that our models are well suited for studying stellar populations in unresolved galaxies. They are particularly useful for studying the old and intermediate-age stellar populations in galaxies, relatively free from contamination of young stars and extinction by dust. These models will be indispensable for the study of the upcoming data from JWST and extremely large telescopes, such as the E-ELT.
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- ID:
- ivo://CDS.VizieR/J/A+A/502/817
- Title:
- SSP models for star clusters in tidal fields
- Short Name:
- J/A+A/502/817
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Evolutionary synthesis models are the primary means of constructing spectrophotometric models of stellar populations, and deriving physical parameters from observations compared with these models. One of the basic assumptions of evolutionary synthesis models has been the time-independence of the stellar mass function, apart from the successive removal of high-mass stars by stellar evolution. However, dynamical simulations of star clusters in tidal fields have demonstrated that the mass function can be changed by the preferential removal of low-mass stars from clusters. We combine the results of dynamical simulations of star clusters in tidal fields with our evolutionary synthesis code GALEV. We extend the models to consider the total cluster disruption time as additional parameter.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A109
- Title:
- Ssynthetic spectra of supernovae models
- Short Name:
- J/A+A/621/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observational surveys are now able to detect an increasing number of transients, such as core-collapse supernovae (SN) and powerful non-terminal outbursts (SN impostors). Dedicated spectroscopic facilities can follow up these events shortly after detection. Here we investigate the properties of these explosions at early times.We use the radiative transfer code CMFGEN to build an extensive library of spectra simulating the interaction of supernovae and their progenitor's winds/circumstellar medium (CSM).We consider a range of progenitor mass-loss rates (dM/dt=5x10^-4^ to 10^-2^ M_{sun}/yr), abundances (solar, CNO-processed, and He-rich), and SN luminosities (L=1.9x10^8^ to 2.5x10^10^L_{sun}_). The models simulate events ~=1-day after explosion, and we assume a fixed location of the shock front as R_in_=8.6x10^13^cm. We show that the large range of massive star properties at the pre-SN stage causes a diversity of early-time interacting SN and impostors. We identify three main classes of early-time spectra consisting of relatively high-ionisation (e.g. HeII and OVI), medium-ionisation (e.g. CIII and NIII), and low-ionisation lines (e.g. HeI and FeII/III). They are regulated by L and the CSM density. Given a progenitor wind velocity v_inf_, our models also place a lower limit of dM/dt>~5x10^-4^(v_inf_=150km/s)M_{sun}_/yr for detection of CSM interaction signatures in observed spectra. Early-time SN spectra should provide clear constraints on progenitors by measuring H, He, and CNO abundances if the progenitors come from single stars. The connections are less clear considering the effects of binary evolution. Nevertheless, our models provide a clear path for linking the final stages of massive stars to their post-explosion spectra at early times, and guiding future observational follow-up of transients with facilities such as the Zwicky Transient Facility.
- ID:
- ivo://CDS.VizieR/J/A+A/557/A26
- Title:
- STAGGER-grid of 3D stellar models. I.
- Short Name:
- J/A+A/557/A26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the STAGGER-grid, a comprehensive grid of time-dependent, three-dimensional (3D), hydrodynamic model atmospheres for late-type stars with realistic treatment of radiative transfer, covering a wide range in stellar parameters. All our models were generated with the Stagger-code, using realistic input physics for the equation of state (EOS) and for continuous and line opacities. Our ~220 grid models range in effective temperature, Teff, from 4000 to 7000K in steps of 500K, in surface gravity, logg, from 1.5 to 5.0 in steps of 0.5dex, and metallicity, [Fe/H], from -4.0 to +0.5 in steps of 0.5 and 1.0dex.
- ID:
- ivo://CDS.VizieR/J/A+A/560/A8
- Title:
- STAGGER-grid of 3D stellar models. II.
- Short Name:
- J/A+A/560/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the implications of averaging methods with different reference depth scales for 3D hydrodynamical model atmospheres computed with the Stagger-code. The temporally and spatially averaged (hereafter denoted as <3D>) models are explored in the light of local thermodynamic equilibrium (LTE) spectral line formation by comparing spectrum calculations using full 3D atmosphere structures with those from <3D> averages. We explored methods for computing mean <3D> stratifications from the Stagger-grid time-dependent 3D radiative hydrodynamical atmosphere models by considering four different reference depth scales (geometrical depth, column-mass density, and two optical depth scales). Furthermore, we investigated the influence of alternative averages (logarithmic, enforced hydrostatic equilibrium, flux-weighted temperatures). For the line formation we computed curves of growth for FeI and FeII lines in LTE.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A89
- Title:
- STAGGER-grid of 3D stellar models. III.
- Short Name:
- J/A+A/573/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relation between 1D atmosphere models that rely on the mixing length theory and models based on full 3D radiative hydrodynamic (RHD) calculations to describe convection in the envelopes of late-type stars. The adiabatic entropy value of the deep convection zone, s_bot_, and the entropy jump, {Delta}s, determined from the 3D RHD models, are matched with the mixing length parameter, {alpha}_MLT_, from 1D hydrostatic atmosphere models with identical microphysics (opacities and equation-of-state). We also derive the mass mixing length, {alpha}_m_, and the vertical correlation length of the vertical velocity, C[V_z_,V_z_], directly from the 3D hydrodynamical simulations of stellar subsurface convection.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A90
- Title:
- STAGGER-grid of 3D stellar models. IV.
- Short Name:
- J/A+A/573/A90
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We compute the emergent stellar spectra from the UV to far infrared for different viewing angles using realistic 3D model atmospheres for a large range in stellar parameters to predict the stellar limb darkening. We have computed full 3D LTE synthetic spectra based on 3D radiative hydrodynamic atmosphere models from the Stagger-grid in the ranges: Teff from 4000 to 7000K, logg from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. From the resulting intensities at different wavelength, we derived coefficients for the standard limb darkening laws considering a number of often-used photometric filters. Furthermore, we calculated theoretical transit light curves, in order to quantify the differences between predictions by the widely used 1D model atmosphere and our 3D models.
- ID:
- ivo://CDS.VizieR/J/A+A/611/A11
- Title:
- STAGGER-grid of 3D stellar models. V.
- Short Name:
- J/A+A/611/A11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have calculated spectra from 1000 to 200000{AA} with a constant resolving power of {lambda}/{Delta}{lambda}=20000 and from 8470 and 8710{AA} (Gaia Radial Velocity Spectrometer - RVS - spectral range) with a constant resolving power of {lambda}/{Delta}{lambda}=300000. This for the Stagger-grid 3D stellar atmosphere models in the ranges: Teff from 4000 to 7000K, logg from 1.5 to 5.0, and [Fe/H], from -4.0 to +0.5. We used synthetic spectra to compute theoretical colours in the Johnson-Cousins UBV(RI)C, SDSS, 2MASS, Gaia, SkyMap- per, Stroemgren systems, and HST-WFC3.
- ID:
- ivo://CDS.VizieR/J/A+A/321/29
- Title:
- Star cluster evolution
- Short Name:
- J/A+A/321/29
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A model of spectral evolution of star forming galaxies of various metallicity has been used to study the relation between the optical emission line ratio R_23_=([OII]{lambda}3727+[OIII]{lambda}{lambda}4959,5007)/H{beta} and the nebular oxygen abundance. It is shown that the scatter in an empirical comparison sample could be due to various upper stellar mass limits or different slopes of the stellar initial mass function in these objects.
- ID:
- ivo://CDS.VizieR/J/ApJ/789/147
- Title:
- Star formation histories of LG dwarf galaxies
- Short Name:
- J/ApJ/789/147
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present uniformly measured star formation histories (SFHs) of 40 Local Group (LG) dwarf galaxies based on color-magnitude diagram (CMD) analysis from archival Hubble Space Telescope imaging. We demonstrate that accurate SFHs can be recovered from CMDs that do not reach the oldest main sequence turn-off (MSTO), but emphasize that the oldest MSTO is critical for precisely constraining the earliest epochs of star formation. We find that: (1) the average lifetime SFHs of dwarf spheroidals (dSphs) can be approximated by an exponentially declining SFH with {tau} ~ 5 Gyr; (2) lower luminosity dSphs are less likely to have extended SFHs than more luminous dSphs; (3) the average SFHs of dwarf irregulars (dIrrs), transition dwarfs, and dwarf ellipticals can be approximated by the combination of an exponentially declining SFH ({tau} ~ 3-4 Gyr) for lookback ages >10-12 Gyr ago and a constant SFH thereafter; (4) the observed fraction of stellar mass formed prior to z = 2 ranges considerably (80% for galaxies with M < 10^5^ M_{sun}_ to 30% for galaxies with M > 10^7^ M_{sun}_) and is largely explained by environment; (5) the distinction between "ultra-faint" and "classical" dSphs is arbitrary; (6) LG dIrrs formed a significantly higher fraction of stellar mass prior to z = 2 than the Sloan Digital Sky Survey galaxies from Leitner and the SFHs from the abundance matching models of Behroozi et al. This may indicate higher than expected star formation efficiencies at early times in low mass galaxies. Finally, we provide all the SFHs in tabulated electronic format for use by the community.
