- ID:
- ivo://CDS.VizieR/J/ApJ/719/996
- Title:
- Effects of binarity in SEGUE pipeline
- Short Name:
- J/ApJ/719/996
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We examine the effects that unresolved binaries have on the determination of various stellar atmospheric parameters for targets from the Sloan Extension for Galactic Understanding and Exploration (SEGUE) using numerical modeling, a grid of synthetic spectra, and the SEGUE Stellar Parameter Pipeline (SSPP). The SEGUE survey, a component of the Sloan Digital Sky Survey-II (SDSS-II) project focusing on Galactic structure, provides medium resolution spectroscopy for over 200000 stars of various spectral types over a large area on the sky. To model undetected binaries that may be in this sample, we use a variety of mass distributions for the primary and secondary stars in conjunction with empirically determined relationships for orbital parameters to determine the fraction of G-K dwarf stars, defined by SDSS color cuts as having 0.48<=(g-r)_0_<=0.75, that will be blended with a secondary companion. We focus on the G-K dwarf sample in SEGUE as it records the history of chemical enrichment in our galaxy. To determine the effect of the secondary on the spectroscopic parameters, specifically effective temperature, surface gravity, metallicity, and [{alpha}/Fe], we synthesize a grid of model spectra from 3275 to 7850K and [Fe/H]=-0.5 to -2.5 from MARCS model atmospheres using TurboSpectrum. These temperature and metallicity ranges roughly correspond to a stellar mass range of 0.1-1.0M_{sun}_. We assume that both stars in the pair have the same metallicity. We analyze both "infinite" signal-to-noise ratio (S/N) models and degraded versions of the spectra, at median S/N of 50, 25, and 10.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/650/A203
- Title:
- Effects of IMG on Galactic chemical enrichment
- Short Name:
- J/A+A/650/A203
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We have been seeing mounting evidence that the stellar initial mass function (IMF) might extend far beyond the canonical Mi~100M_{sun}_ limit, but the impact of such a hypothesis on the chemical enrichment of galaxies is yet to be clarified. We aim to address this question by analysing the observed abundances of thin- and thick-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair instability supernovae. We built new sets of chemical yields from massive and very massive stars up to Mi~350M_{sun}_ by combining the wind ejecta extracted from our hydrostatic stellar evolution models with explosion ejecta from the literature. Using a simple chemical evolution code, we analysed the effects of adopting different yield tables by comparing predictions against observations of stars in the solar vicinity. After several tests, we set our focus on the [O/Fe] ratio that best separates the chemical patterns of the two Milky Way components. We nd that with a standard IMF, truncated at Mi~100M_{sun}_, we can reproduce various observational constraints for thin-disc stars; however, the same IMF fails to account for the [O/Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi=350M_{sun}_; while including the chemical ejecta of very massive stars in the form of winds and pair instability supernova (PISN) explosions. Our study indicates that PISN may have played a significant role in shaping the chemical evolution of the thick disc of the Milky Way. Including their chemical yields makes it easier to reproduce not only the level of the a-enhancement, but also the observed slope of thick-disc stars in the [O/Fe] versus [Fe/H] diagram. The bottom line is that the contribution of very massive stars to the chemical enrichment of galaxies is potentially quite important and should not be neglected in models of chemical evolution.
- ID:
- ivo://CDS.VizieR/J/ApJS/167/177
- Title:
- Emission lines of evolving HII regions
- Short Name:
- J/ApJS/167/177
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We build, as far as theory will permit, self-consistent model HII regions around central clusters of aging stars. These produce strong emission line diagnostics applicable to either individual HII regions in galaxies or to the integrated emission line spectra of disk or starburst galaxies. The models assume that the expansion and internal pressure of individual HII regions is driven by the net input of mechanical energy from the central cluster, be it through winds or supernova events. This eliminates the ionization parameter as a free variable, replacing it with a parameter that depends on the ratio of the cluster mass to the pressure in the surrounding interstellar medium. These models explain why HII regions with low abundances have high excitation and demonstrate that at least part of the warm ionized medium is the result of overlapping faint, old, large, and low-pressure HII regions. We present line ratios (at both optical and IR wavelengths) that provide reliable abundance diagnostics for both single HII regions or for integrated galaxy spectra, and we find a number that can be used to estimate the mean age of the cluster stars exciting individual HII regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/774/6
- Title:
- Empirical scaling laws for shell dynamos
- Short Name:
- J/ApJ/774/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Numerical dynamo models always employ parameter values that differ by orders of magnitude from the values expected in natural objects. However, such models have been successful in qualitatively reproducing properties of planetary and stellar dynamos. This qualitative agreement fuels the idea that both numerical models and astrophysical objects may operate in the same asymptotic regime of dynamics. This can be tested by exploring the scaling behavior of the models. For convection-driven incompressible spherical shell dynamos with constant material properties, scaling laws had been established previously that relate flow velocity and magnetic field strength to the available power. Here we analyze 273 direct numerical simulations using the anelastic approximation, involving also cases with radius-dependent magnetic, thermal, and viscous diffusivities. These better represent conditions in gas giant planets and low-mass stars compared to Boussinesq models. Our study provides strong support for the hypothesis that both mean velocity and mean magnetic field strength scale as a function of the power generated by buoyancy forces in the same way for a wide range of conditions.
- ID:
- ivo://CDS.VizieR/J/ApJ/776/L31
- Title:
- Energy feedback from XRB from z=0 to z=19.92
- Short Name:
- J/ApJ/776/L31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray photons, because of their long mean-free paths, can easily escape the galactic environments where they are produced, and interact at long distances with the intergalactic medium, potentially having a significant contribution to the heating and reionization of the early universe. The two most important sources of X-ray photons in the universe are active galactic nuclei (AGNs) and X-ray binaries (XRBs). In this Letter we use results from detailed, large scale population synthesis simulations to study the energy feedback of XRBs, from the first galaxies (z~20) until today. We estimate that X-ray emission from XRBs dominates over AGN at z>~6-8. The shape of the spectral energy distribution of the emission from XRBs shows little change with redshift, in contrast to its normalization which evolves by ~4 orders of magnitude, primarily due to the evolution of the cosmic star-formation rate. However, the metallicity and the mean stellar age of a given XRB population affect significantly its X-ray output. Specifically, the X-ray luminosity from high-mass XRBs per unit of star-formation rate varies an order of magnitude going from solar metallicity to less than 10% solar, and the X-ray luminosity from low-mass XRBs per unit of stellar mass peaks at an age of ~300Myr and then decreases gradually at later times, showing little variation for mean stellar ages >~3Gyr. Finally, we provide analytical and tabulated prescriptions for the energy output of XRBs, that can be directly incorporated in cosmological simulations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/2471
- Title:
- Enhanced momentum feedback from clustered SN
- Short Name:
- J/MNRAS/465/2471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Young stars typically form in star clusters, so the supernovae (SNe) they produce are clustered in space and time. This clustering of SNe may alter the momentum per SN deposited in the interstellar medium (ISM) by affecting the local ISM density, which in turn affects the cooling rate. We study the effect of multiple SNe using idealized 1D hydrodynamic simulations which explore a large parameter space of the number of SNe, and the background gas density and metallicity. The results are provided as a table and an analytic fitting formula. We find that for clusters with up to ~100 SNe, the asymptotic momentum scales superlinearly with the number of SNe, resulting in a momentum per SN which can be an order of magnitude larger than for a single SN, with a maximum efficiency for clusters with 10-100 SNe. We argue that additional physical processes not included in our simulations - self-gravity, breakout from a galactic disc, and galactic shear - can slightly reduce the momentum enhancement from clustering, but the average momentum per SN still remains a factor of 4 larger than the isolated SN value when averaged over a realistic cluster mass function for a star-forming galaxy. We conclude with a discussion of the possible role of mixing between hot and cold gas, induced by multidimensional instabilities or pre-existing density variations, as a limiting factor in the build-up of momentum by clustered SNe, and suggest future numerical experiments to explore these effects.
- ID:
- ivo://CDS.VizieR/J/A+AS/107/445
- Title:
- Envelopes of oxygen-rich AGB stars
- Short Name:
- J/A+AS/107/445
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/ApJ/416/276
- Title:
- Eq. of State in Magnetic Neutron Stars
- Short Name:
- J/ApJ/416/276
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This catalog is based on the calculated equation of state in cold dense matter. Each table in the catalog lists bulk properties of Fe-56 in a magnetic field ranging from one million to 1000 million Tesla.
- ID:
- ivo://CDS.VizieR/J/A+A/550/A43
- Title:
- Equation of state for magnetized plasmas
- Short Name:
- J/A+A/550/A43
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have developed an analytical equation of state (EOS) for magnetized fully-ionized plasmas that cover a wide range of temperatures and densities, from low-density classical plasmas to relativistic, quantum plasma conditions. This EOS directly applies to calculations of structure and evolution of strongly magnetized white dwarfs and neutron stars. We review available analytical and numerical results for thermodynamic functions of the nonmagnetized and magnetized Coulomb gases, liquids, and solids. We propose a new analytical expression for the free energy of solid Coulomb mixtures. Based on recent numerical results, we have constructed analytical approximations for the thermodynamic functions of harmonic Coulomb crystals in quantizing magnetic fields. The analytical description ensures a consistent evaluation of all astrophysically important thermodynamic functions based on the first, second, and mixed derivatives of the free energy. Our numerical code for calculation of thermodynamic functions based on these approximations has been made publicly available. Using this code, we calculate and discuss the effects of electron screening and magnetic quantization on the position of the melting point in a range of densities and magnetic fields relevant to white dwarfs and outer envelopes of neutron stars. We consider also the thermal and mechanical structure of a magnetar envelope and argue that it can have a frozen surface which covers the liquid ocean above the solid crust.
- ID:
- ivo://CDS.VizieR/J/A+A/603/A57
- Title:
- 51 Eri b SPHERE/IFS spectra & atmosphere models
- Short Name:
- J/A+A/603/A57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- 51 Eridani b is an exoplanet around a young (20Myr) nearby (29.4pc) F0-type star, which was recently discovered by direct imaging. It is one of the closest direct imaging planets in angular and physical separation (~0.5", ~13AU) and is well suited for spectroscopic analysis using integral field spectrographs. We aim to refine the atmospheric properties of the known giant planet and to constrain the architecture of the system further by searching for additional companions. We used the extreme adaptive optics instrument SPHERE at the Very Large Telescope (VLT) to obtain simultaneous dual-band imaging with IRDIS and integral field spectra with IFS, extending the spectral coverage of the planet to the complete Y- to H-band range and providing additional photometry in the K12-bands (2.11, 2.25 micron). We present the first spectrophotometric measurements in the Y and K bands for the planet and revise its J-band flux to values 40% fainter than previous measurements. Cloudy models with uniform cloud coverage provide a good match to the data. We derive the temperature, radius, surface gravity, metallicity, and cloud sedimentation parameter fsed. We find that the atmosphere is highly super-solar ([Fe/H]~1.0), and the low fsed~1.26 value is indicative of a vertically extended, optically thick cloud cover with small sized particles. The model radius and surface gravity estimates suggest higher planetary masses of M_gravity_=9.1^+4.9^_-3.3_. The evolutionary model only provides a lower mass limit of >2M_jupiter_ (for pure hot-start). The cold-start model cannot explain the luminosity of the planet. The SPHERE and NACO/SAM detection limits probe the 51 Eri system at solar system scales and exclude brown-dwarf companions more massive than 20M_jupiter_ beyond separations of ~2.5AU and giant planets more massive than 2M_jupiter_ beyond 9 au.
