- ID:
- ivo://CDS.VizieR/J/A+A/616/A58
- Title:
- Variability of the adiabatic parameter
- Short Name:
- J/A+A/616/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Numerical models of the evolution of interstellar and intergalactic plasmas often assume that the adiabatic parameter {gamma} (the ratio of the specific heats) is constant (5/3 in monoatomic plasmas). However, {gamma} is determined by the total internal energy of the plasma, which depends on the ionic and excitation state of the plasma. Hence, the adiabatic parameter may not be constant across the range of temperatures available in the interstellar medium. We aim to carry out detailed simulations of the thermal evolution of plasmas with Maxwell-Boltzmann and non-thermal ({kappa} and n) electron distributions in order to determine the temperature variability of the total internal energy and of the adiabatic parameter. The plasma, composed of H, He, C, N, O, Ne, Mg, Si, S, and Fe atoms and ions, evolves under collisional ionization equilibrium conditions, from an initial temperature of 10^9^K. The calculations include electron impact ionization, radiative and dielectronic recombinations and line excitation. The ionization structure was calculated solving a system of 112 linear equations using the Gauss elimination method with scaled partial pivoting. Numerical integrations used in the calculation of ionization and excitation rates are carried out using the double-exponential over a semi-finite interval method. In both methods a precision of 10^-15^ is adopted. The total internal energy of the plasma is mainly dominated by the ionization energy for temperatures lower than 8x10^4^K with the excitation energy having a contribution of less than one percent. In thermal and non-thermal plasmas composed of H, He, and metals, the adiabatic parameter evolution is determined by the H and He ionizations leading to a profile in general having three transitions. However, for {kappa} distributed plasmas these three transitions are not observed for {kappa<15} and for {kappa<5} there are no transitions. In general, {gamma} varies from 1.01 to 5/3. Lookup tables of the {gamma} parameter are presented as supplementary material.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/698/895
- Title:
- Variations in QSOs optical flux
- Short Name:
- J/ApJ/698/895
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze a sample of optical light curves, compiled from the literature, for 100 quasars, 70 of which have black hole mass estimates. Our sample is the largest and broadest used yet for modeling quasar variability. The sources in our sample have z<2.8, 10^42^<~{lambda}L_{lambda}_(5100{AA})<~10^46^, and 10^6^<~M_BH_/M_{sun}_<~10^10^. We model the light curves as a continuous time stochastic process, providing a natural means of estimating the characteristic timescale and amplitude of quasar variations. We employ a Bayesian approach to estimate the characteristic timescale and amplitude of flux variations; our approach is not affected by biases introduced from discrete sampling effects.
- ID:
- ivo://CDS.VizieR/J/ApJ/664/1033
- Title:
- Variations in supernova yields
- Short Name:
- J/ApJ/664/1033
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Theoretical nucleosynthetic yields from supernovae are sensitive to both the details of the progenitor star and the explosion calculation. We attempt to comprehensively identify the sources of uncertainties in these yields. In this paper we concentrate on the variations in yields from a single progenitor arising from common 1D methods of approximating a supernova explosion. Subsequent papers will examine 3D effects in the explosion and the progenitor, and trends in mass and composition. For the 1D explosions we find that both elemental and isotopic yields for Si and heavier elements are a sensitive function of explosion energy. Also, piston-driven and thermal bomb-type explosions have different yields for the same explosion energy. Yields derived from 1D explosions are nonunique.
- ID:
- ivo://CDS.VizieR/J/ApJS/188/242
- Title:
- Variations on debris disks. II.
- Short Name:
- J/ApJS/188/242
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe comprehensive calculations of the formation of icy planets and debris disks at 30-150AU around 1-3M_{sun}_ stars. Disks composed of large, strong planetesimals produce more massive planets than disks composed of small, weak planetesimals. The maximum radius of icy planets ranges from ~1500km to 11500km. The formation rate of 1000km objects-"Plutos"-is a useful proxy for the efficiency of icy planet formation. Plutos form more efficiently in massive disks, in disks with small planetesimals, and in disks with a range of planetesimal sizes. Although Plutos form throughout massive disks, Pluto production is usually concentrated in the inner disk. Despite the large number of Plutos produced in many calculations, icy planet formation is inefficient. At the end of the main sequence lifetime of the central star, Plutos contain less than 10% of the initial mass in solid material. This conclusion is independent of the initial mass in the disk or the properties of the planetesimals. Debris disk formation coincides with the formation of planetary systems containing Plutos. As Plutos form, they stir leftover planetesimals to large velocities. A cascade of collisions then grinds the leftovers to dust, forming an observable debris disk. In disks with small (<~1-10km) planetesimals, collisional cascades produce luminous debris disks with maximum luminosity ~10-2 times the stellar luminosity. Disks with larger planetesimals produce debris disks with maximum luminosity ~5x10^-4^ (10km) to 5x10^-5^ (100km) times the stellar luminosity. Following peak luminosity, the evolution of the debris disk emission is roughly a power law, f{propto}t^-n^ with n~0.6-0.8. Observations of debris disks around A-type and G-type stars strongly favor models with small planetesimals. In these models, our predictions for the time evolution and detection frequency of debris disks agree with published observations. We suggest several critical observations that can test key features of our calculations.
- ID:
- ivo://CDS.VizieR/J/ApJ/713/615
- Title:
- Very metal-poor Cepheid models
- Short Name:
- J/ApJ/713/615
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Classical Cepheids are primary distance indicators playing a fundamental role in the calibration of the extragalactic distance scale. The possible dependence of their characteristic period-luminosity (PL) relation on chemical composition is still debated in the literature, and the behavior of these pulsators at very low metallicity regimes is almost unexplored. In order to derive constraints on the application of the PL relation at low metal abundances, we investigate the properties of the few ultra-low metallicity (Z~0.0004) Cepheids recently discovered in the Blue Compact Dwarf galaxy IZw18. To this purpose, we have computed an updated and extended set of nonlinear convective models for Z=0.0004 and Y=0.24, spanning a wide range of stellar masses, and taking into account the evolutionary constraints for selected luminosity levels. As a result, we are able to predict the topology of the instability strip, the variations of all the relevant quantities along the pulsation cycle, including the morphology of the light curves, the theoretical period-luminosity-color, period-Wesenheit, and PL relations at such a low metallicity.
- ID:
- ivo://CDS.VizieR/J/A+A/608/A89
- Title:
- Very metal poor stars in MW halo
- Short Name:
- J/A+A/608/A89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the non-local thermodynamic equilibrium (NLTE) abundances of up to 10 chemical species in a sample of 59 very metal-poor (VMP, -4<=[Fe/H]<~-2) stars in seven dwarf spheroidal galaxies (dSphs) and in the Milky Way (MW) halo. Our results are based on high-resolution spectroscopic datasets and homogeneous and accurate atmospheric parameters determined in Paper I. We show that once the NLTE effects are properly taken into account, all massive galaxies in our sample, that is, the MW halo and the classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax, reveal a similar plateau at [alpha/Fe]=0.3 for each of the alpha-process elements: Mg, Ca, and Ti. We put on a firm ground the evidence for a decline in alpha/Fe with increasing metallicity in the Bootes I ultra-faint dwarf galaxy (UFD), that is most probably due to the ejecta of type Ia supernovae. For Na/Fe, Na/Mg, and Al/Mg, the MW halo and all dSphs reveal indistinguishable trends with metallicity, suggesting that the processes of Na and Al synthesis are identical in all systems, independent of their mass. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. We show that Sr in the massive galaxies is better correlated with Mg than Fe and that its origin is essentially independent of Ba, for most of the [Ba/H] range. Our three UFDs, that is Bootes I, UMa II, and Leo IV, are depleted in Sr and Ba relative to Fe and Mg, with very similar ratios of [Sr/Mg]=-1.3 and [Ba/Mg]=-1 on the entire range of their Mg abundances. The subsolar Sr/Ba ratios of Bootes I and UMa II indicate a common r-process origin of their neutron-capture elements. Sculptor remains the classical dSph, in which the evidence for inhomogeneous mixing in the early evolution stage, at [Fe/H]<-2, is the strongest.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A124
- Title:
- Visibilities of stellar oscillation modes
- Short Name:
- J/A+A/531/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Kepler produces a large amount of data used for asteroseismological analyses, particularly of solar-like stars and red giants. The mode amplitudes observed in the Kepler spectral band have to be converted into bolometric amplitudes to be compared to models. We give a simple bolometric correction for the amplitudes of radial modes observed with Kepler, as well as the relative visibilities of non-radial modes. We numerically compute the bolometric correction c_K-bol_ and mode visibilities, for different effective temperatures Teff within the range 4000-7500K, using a similar approach to a recent one from the literature. We derive a law for the correction to bolometric values: c_K-bol_=1+a_1_(Teff-To)+a_2_(Teff-To)^2^, with To=5934K, a_1_=1.349e-4K^-1^, and a_2_=-3.120e-9K^-2^ or, alternatively, as the power law c_K-bol_=(Teff/To)^alpha^ with alpha=0.80. We give tabulated values for the mode visibilities based on limb-darkening, computed from ATLAS9 model atmospheres for Teff in [4000,7500]K, logg in [2.5,4.5], and [M/H] in [-1.0,+1.0]. We show that using LD profiles already integrated over the spectral band provides quick and good approximations for visibilities. We point out the limits of these classical visibility estimations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/440/2036
- Title:
- VPHAS+ survey synthetic colours
- Short Name:
- J/MNRAS/440/2036
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The VST Photometric H{alpha} Survey of the Southern Galactic Plane and Bulge (VPHAS+) is surveying the southern Milky Way in u, g, r, i and H{alpha} at ~1arcsec angular resolution. Its footprint spans the Galactic latitude range -5{deg}<b<+5{deg} at all longitudes south of the celestial equator. Extensions around the Galactic Centre to Galactic latitudes +/-10{deg} bring in much of the Galactic bulge. This European Southern Observatory public survey, begun on 2011 December 28, reaches down to ~20th magnitude (10{sigma}) and will provide single-epoch digital optical photometry for ~300 million stars. The observing strategy and data pipelining are described, and an appraisal of the segmented narrow-band H{alpha} filter in use is presented. Using model atmospheres and library spectra, we compute main-sequence (u-g), (g-r), (r-i) and (r-H{alpha}) stellar colours in the Vega system. We report on a preliminary validation of the photometry using test data obtained from two pointings overlapping the Sloan Digital Sky Survey. An example of the (u-g, g-r) and (r-H{alpha}, r-i) diagrams for a full VPHAS+ survey field is given. Attention is drawn to the opportunities for studies of compact nebulae and nebular morphologies that arise from the image quality being achieved. The value of the u band as the means to identify planetary-nebula central stars is demonstrated by the discovery of the central star of NGC 2899 in survey data. Thanks to its excellent imaging performance, the VLT Survey Telescope (VST)/OmegaCam combination used by this survey is a perfect vehicle for automated searches for reddened early-type stars, and will allow the discovery and analysis of compact binaries, white dwarfs and transient sources.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/2428
- Title:
- WASP-31b:HST/Spitzer transmission spectral survey
- Short Name:
- J/MNRAS/446/2428
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Hubble Space Telescope optical and near-IR transmission spectra of the transiting hot-Jupiter WASP-31b. The spectrum covers 0.3-1.7 {mu}m at a resolution R~70, which we combine with Spitzer photometry to cover the full-optical to IR. The spectrum is dominated by a cloud deck with a flat transmission spectrum which is apparent at wavelengths >0.52{mu}m. The cloud deck is present at high altitudes and low pressures, as it covers the majority of the expected optical Na line and near-IR H_2_O features. While Na I absorption is not clearly identified, the resulting spectrum does show a very strong potassium feature detected at the 4.2{sigma} confidence level. Broadened alkali wings are not detected, indicating pressures below ~10 mbar. The lack of Na and strong K is the first indication of a sub-solar Na/K abundance ratio in a planetary atmosphere (ln[Na/K]=-3.3+/-2.8), which could potentially be explained by Na condensation on the planet's night side, or primordial abundance variations. A strong Rayleigh scattering signature is detected at short wavelengths, with a 4{sigma} significant slope. Two distinct aerosol size populations can explain the spectra, with a smaller sub-micron size grain population reaching high altitudes producing a blue Rayleigh scattering signature on top of a larger, lower lying population responsible for the flat cloud deck at longer wavelengths. We estimate that the atmospheric circulation is sufficiently strong to mix micron size particles upwards to the required 1-10 mbar pressures, necessary to explain the cloud deck. These results further confirm the importance of clouds in hot Jupiters, which can potentially dominate the overall spectra and may alter the abundances of key gaseous species.
- ID:
- ivo://CDS.VizieR/J/A+A/543/A67
- Title:
- WDA and WDB apsidal-motion constants
- Short Name:
- J/A+A/543/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The internal structure constants k_j_ and the radius of gyration are useful tools for investigating the apsidal motion and tidal evolution of close binaries and planetary systems. These parameters are available for various evolutionary phases but they are scarce for the late stages of stellar evolution. To cover this gap, we present here the calculations of the apsidal-motion constants, the fractional radius of gyration, and the gravitational potential energy for two grids of cooling evolutionary sequences of white dwarfs and for neutron star models. The cooling sequences of white dwarfs were computed with LPCODE. An additional alternative to the white dwarf models was also adopted with the MESA code which allows non-stop calculations from the pre main-sequence (PMS) to the white dwarf cooling sequences. Neutron star models were acquired from the NSCool/TOV subroutines. The apsidal-motion constants, the moment of inertia and the gravitational potential energy were computed with a fourth-order Runge-Kutta method. The parameters are made available for four cooling sequences of white dwarfs (DA and DB types): 0.52, 0.57, 0.837 and 1.0M_{sun}_ and for neutron star models covering a mass range from 1.0 up to 2.183M_{sun}_, in 0.1 mass step. We show that, contrary to previously established opinion, the product of the form-factors {beta} and {alpha}, which are related to the moment of inertia, and gravitational potential energy, is not constant during some evolutionary phases. Regardless of the final products of stellar evolution (white dwarfs, neutron stars and perhaps black holes), we found that they recover the initial value of product {alpha}{beta} at the pre main-sequence phase (~0.4). These results may have important consequences for the investigation of the Jacobi virial equation.
