Determining the fundamental parameters of F and G supergiants

A technique for determining the effective temperature T _eff and the acceleration of gravity log g of F and G supergiants is discussed using four bright stars as examples, specifically two F supergiants, α Lep(F0 Ib) and π Sgr (F2 II), and two G supergiants, β Aqr (G0 Ib) and α Aqr (G2 Ib). In all four cases the parameter log g was derived from the high precision parallaxes recently obtained by van Leeuwen in a new reduction of data from Hipparcos. Because of this, the accuracy of the determinations of log g is much greater than before. Estimates of the parameter T _eff were checked using accurate values of T _eff obtained previously by the infrared flux method (IRFM). In the case of the early F supergiants, this method confirms the good accuracy of the T _eff values derived from the Balmer lines and the β-index. Measurements of the Balmer lines for the G supergiants are difficult because of strong blending, so the indices [c ₁] and β serve as indicators of T _eff . It is shown that the indices [c ₁] and β yield a systematic difference in the values of T _eff ; the IRFM confirms that deriving T _eff from the index [c ₁] is more accurate. Based on the values of T _eff and log g that have been found here, with the aid of the evolutionary tracks, we estimate the mass M and age t of each star. The Fe II lines, which are insensitive to departures from LTE, have been used to determine the microturbulence parameter V _t and the iron abundance. The latter is close to the solar iron abundance. Some problems concerning the chemical composition of these stars are discussed using the supergiant α Lep as an example. Translated from Astrofizika, Vol. 52, No. 2, pp. 237–257 (May 2009).     

Origin of anomalous sodium abundances in yellow supergiants

Leningrad State University. Translated from Astrofizika, Vol. 31, No. 2, pp. 293–303, September–October, 1989.     

The solar system abundances of phosphorus and titanium and the nebular volatility of phosphorus

Abstract— The bulk chemical composition of Orgueil and 25 other carbonaceous chondrites was determined by x‐ray fluorescence analysis. The sample sizes of the analyzed meteorites were in all cases 120 mg. The abundances of P and Ti in Orgueil and Ivuna were precisely determined by the standard addition method. The new P CI abundance is 926 ± 65 ppm. Excluding the low P of Ivuna and one Orgueil sample with unusual chemistry gives a CI P content of 930 ± 23 ppm. A CI abundance of 926 ppm corresponds to a P/Si wt ratio of 8.66 times 10^?3 (atomic ratio 7.85 times 10^?3). For Ti a CI content of 458 ± 18 ppm and a Ti/Si wtratio of 4.28 times 10^?3 (atomic ratio 2.51 times 10^?3) were found. A Si content of 10.69% was obtained for average CI. The new P CI abundance is 20 to 30% below earlier estimates, while the Ti CI abundance is in agreement with earlier determinations. From the results of the analyses of bulk carbonaceous chondrites it is concluded: (1) Refractory element/Mg ratios increase from CI through CM and C3O to C3V, but ratios among Al, Ca and Ti are constant, except for low Ca/Al ratios in the reduced subgroup of C3V. (2) The Si/Mg ratios are constant in all groups of carbonaceous chondrites. (3) There is a volatility related depletion of Cr and Fe, but the Cr/Fe ratios are constant. (4) The sequence of volatility related depletions of the moderately volatile elements P, Au, As, Mn, and Zn follows condensation temperatures (except for As), if in condensation calculations non‐ideal solid solution in the host phase is considered.     

The abundances of ammonia in the atmospheres of Jupiter,Saturn, and Titan

An investigation of low-resolution ratio spectra of Jupiter, Saturn, and Titan in the region 5400–6500 Å has permitted new evaluations of ammonia absorption bands. The distribution of ammonia over the disk of Jupiter is very inhomogeneous. The carbon-to-nitrogen ratio is distinctly different from the solar value, but this is probably a result of uneven mixing of methane and ammonia, as suggested previously by Kuiper, rather than a compositional anomaly. The abundance of ammonia on Saturn also shows spatial variations, but appears constant in time over a 3-yr period. Two weak, unidentified absorptions were discovered in the red region of Titan's spectrum, in the absence of any detectable ammonia. The new upper limit is ηN < 120 cm-am.     

Fundamental parameters and intrinsic colors of F,G, and K supergiants and classical cepheids

We used high-resolution echelle spectra with high signal-to-noise ratio to determine with a high degree of accuracy some atmospheric parameters (T _eff, log g and [Fe/H]) for 68 non-variable supergiants of types F, G, and K and 26 classical Cepheids in 302 pulsation phases. Very accurate effective temperatures, with errors of only 10–30 K, were determined by the line-depth ratio method. We found that the observed intrinsic color indices (B ? V)₀ can be related to these parameters: (B ? V)₀ = 57.984? 10.3587(log T _eff)² + 1.67572(log T _eff)³ ? 3.356 log g+ 0.321 V _t + 0.2615[Fe/H] + 0.8833log g(log T _eff). With this empirical relation, the intrinsic colors of individual supergiants and classical Cepheids of spectral types F0-K0 and of luminosity classes I and II can be estimated with an accuracy as high as 0.05 ^m , which is comparable to the accuracy of the most elaborate photometric procedures. In view of large distances to supergiants, the method we propose here allows a large-scale mapping of interstellar extinction with an accuracy of 0.1–0.2 ^m in a quite large region of the Galaxy.     

Determination of abundances in the atmospheres of F-, G-, and K-dwarfs

The algorithm of the determination of abundances in atmospheres of stars of spectral classes F, G, and K using fits to the observed spectral lines or selected parts of the blended lines is discussed. The technique allows to determine the parameters of the atmosphere, i.e., gravity, microturbulent velocity, rotational velocity of the star, and abundance of elements, for a given effective temperature of the star. At each stage of the iterative process the model atmosphere is recalculated for a new set of input data. The results of applying the procedure for the analysis of the spectra of the Sun (G2 V) and HD 101348 (G3 V) are discussed.     

Abundances and absolute stellar magnitudes for F and G supergiants of Magellanic Clouds

Using high-resolution spectra, we study 31 yellow supergiants of the Large and Small Magellanic Clouds by the method of atmosphere models. Abundance values of 20 chemical elements are determined. It is shown that ??-elements are in a slight excess and neutron-capture elements have an excess up to 0.60 dex. Approbation of a new technique for the determination of absolute stellar magnitudes of late-type supergiants is performed. The technique is based on the use of the spectroscopic criterion, namely, depth-line ratios for iron. Absolute stellar magnitudes of nine supergiants of the Large Magellanic Cloud are calculated using this technique. A value of the distance modulus of the Large Magellanic Cloud is estimated: m ? M = 18.4 ± 0.3 ^m .     

Hydrogen and helium abundances in neutron-star atmospheres

An analysis is presented of the burning and diffusion of hydrogen and helium in a neutron-star atmosphere. An initial two-component atmosphere of hydrogen and carbon and of helium and carbon is examined utilizing various photospheric temperatures. The hydrogen burns through the proton-proton reaction and the CN-cycle and the helium by the triple-alpha process and alpha capture on carbon. It is found that only a negligible proportion of hydrogen or helium can exist after a few years in the neutron-star atmosphere.     

Red supergiants in the LMC – III: luminous F and G stars

New BVRI observations for 40 and spectrophotometric measurements for 3 F to G LMC supergiant candidates (and 3 galactic F to G supergiants) are presented. The errors of the BVRI data are 0.01 to 0.03 mag in most cases. The wavelength range of the spectra is 3400 to 6400 Å, their resolution 10 Å. The mean error of the fluxes is 0.03 mag. Spectral indices measuring the strengths of the Hβ, Hγ, Hδ, NaD and CaII H+K lines, the CHα₀ and CNβ₀ bands, of the Balmer jump and the slope of the continuum redwards are discussed as measures of effective temperature and luminosity on the basis of galactic stars with accurate MK types and parallaxes. The Hγ line and the continuum gradient are very good temperature criteria, the CHα₀ band and especially the Balmer jump for luminosity. The luminosity classification given for F to G supergiant candidates in the LMC in the literature is often doubtful. 5 of the 3 stars observed spectrophotometrically turn out to be probably galactic foreground dwarfs on the basis both of the Balmer jump and the comparison of their flux distributions with synthetic ones based on the Kurucz model atmospheres. Surface gravities derived purely on the basis of flux distributions and such ones given by models of stellar evolution agree with each other for dwarfs and giants only. For supergiants the former are about 1.0 dex higher than the latter. As a consequence effective temperatures and metallicities given by these two methods deviate from each other for such stars, too. The intrinsic colours and temperatures of galactic and LMC supergiants do not differ. With absolute magnitudes up to -9.6 mag the upper luminosity limit in the LMC does not exceed that in the Galaxy, where Ia-0 supergiants have M_V of up to -9.5 mag. The metallicities of the supergiants show a rather large scatter. Nevertheless the mean metallicities of 0.0 ± 0.09 dex for the Galaxy and -0.6 ± 0.10 dex for the LMC agree well with other observations.     

A study of the H-alpha line in late G and K supergiants

A spectroscopic study of H_α has been carried out to investigate the properties of expanding chromospheres of late G and K supergiants. Spectra of 23 stars brighter thanV = 6.0 have been obtained at dispersions of 4–10 å mm^-1 using the coude and the coudé-echelle spectrographs at the 102-cm telescope of Kavalur Observatory. The H_α profiles are all asymmetric in the sense that the absorption core is shifted to the blue by amounts ranging between -4 and -24 km s^-1. H_α profiles were theoretically computed using radiative transfer in spherically symmetric expanding atmospheres covering a large range of integrated optical depths. These were compared with the characteristics of the observed line in the programme stars. The analysis shows that the H_α line is formed in a region with velocity increasing outward. The computed equivalent widths and line core displacements were matched with those observed to obtain hydrogen column densities and expansion velocities. From these, the rates of mass loss in these stars were determined to be in the range of 10⁶10^-7 M_⊙ yr^-1.     

Red supergiants in the LMC — II. Spectrophotometry and model atmospheres

We have analysed polarization data for a large number of isolated pulsars to investigate the evolution of pulsar radio beams. Assuming that a circular beam is directed along the axis of a dipolar magnetic field, we demonstrate that the distribution of magnetic inclination angles for the parent population of all pulsars is not flat but highly concentrated towards small inclination angles and that, consequently, the average beaming fraction is only ∼ 10 per cent. Furthermore, we find that there is a tendency for the beam axis to align with the rotational axis on a time-scale of ∼ 10⁷ yr. This has interesting consequences for statistical studies of the pulsar population. Finally, the luminosity of pulsars is shown to be independent of the impact parameter, which indicates that pulsar beams are sharp-edged and have a relatively flat integrated intensity distribution.     

Temperature behavior of elemental abundances in the atmospheres of magnetic peculiar stars

We analyze the temperature dependence of the abundances of the chemical elements Si, Ca, Cr, and Fe in the atmospheres of normal, metallic-line (Am), magnetic peculiar (Ap), and pulsating magnetic peculiar (roAp) stars in the range 6000–15000 K. The Cr and Fe abundances in the atmospheres of Ap stars increase rapidly as the temperature rises from 6000 to 9000–10000 K. Subsequently, the Cr abundance decreases to values that exceed the solar abundance by an order of magnitude, while the Fe abundance remains enhanced by approximately +1.0 dex compared to the solar value. The temperature dependence of the abundances of these elements in the atmospheres of normal and Am stars is similar in shape, but its maximum is several orders of magnitude lower than that observed for Ap stars. In the range 6000–9500 K, the observed temperature dependences for Ap stars are satisfactorily described in terms of element diffusion under the combined action of gravitational settling and radiative acceleration. It may well be that diffusion also takes place in the atmospheres of normal stars, but its efficiency is very low due to the presence of microturbulence. We show that the magnetic field has virtually no effect on the Cr and Fe diffusion in Ap stars in the range of effective temperatures 6000–9500 K. The Ca abundance and its variation in the atmospheres of Ap stars can also be explained in terms of the diffusion model if we assume the existence of a stellar wind with a variable moderate rate of ～(2–4) × 10^{? 15}M_⊙ yr^?1.     

Space-based measurements of elemental abundances and their relation to solar abundances

The solar wind provides a source of solar abundance data that only recently is being fully exploited. The Ion Composition Instrument (ICI) aboard the ISEE-3/ICE spacecraft was in the solar wind continuously from August 1978 to December 1982. The results have allowed us to establish long-term average solar wind abundance values for helium, oxygen, neon, silicon, and iron. The Charge-Energy-Mass (CHEM) instrument aboard the CCE spacecraft of the AMPTE mission has measured the abundance of these elements in the magnetosheath and has also added carbon, nitrogen, magnesium, and sulfur to the list. There is strong evidence that these magnetosheath abundances are representative of the solar wind. Other sources of solar wind abundances are Solar Energetic Particle (SEP) experiments and Apollo lunar foils. When comparing the abundances from all of these sources with photospheric abundances, it is clear that helium is depleted in the solar wind while silicon and iron are enhanced. Solar wind abundances for carbon, nitrogen, oxygen, and neon correlate well with the photospheric values. The incorporation of minor ions into the solar wind appears to depend upon both the ionization times for the elements and the Coulomb drag exerted by the outflowing proton flux.     

On the abundances of carbon dioxide isotopologues in the atmospheres of mars and earth

The isotopic composition of carbon dioxide in the Martian atmosphere from the measurements of Mars Science Laboratory have been used to estimate the relative abundances of CO₂ isotopologues in the Martian atmosphere. Concurrently, this study has revealed long-standing errors in the amounts of some of low-abundance CO₂ isotopologues in the Earth’s atmosphere in the databases of spectroscopic parameters of gases (HITRAN, etc.).     

Integrated colors in the solar neighborhood

The bivariate spectral type-luminosity class distribution combined with thez-distribution and broad-band photometric data have been used in order to derive integrated colors in Johnson's UBVRIJKL system for the solar neighborhood.The frequency distribution of white dwarfs is also taken into account for theU-B, B-V colors.     

Hidden mass in the solar neighborhood

It is suggested that the minimum mass of a star at the time of its formation is approximately 0.01M . Making use of this fact and the stellar mass functionF(M) M ^–, it is found that the hidden mass (or the missing mass) in the solar neighborhood may be explained by the presence of a large number of invisible stars of very low mass (0.01M M<0.07M ).     

Halo streams in the solar neighborhood

The phase-space structure of our Galaxy holds the key to understand and reconstruct its formation. The ΛCDM model predicts a richly structured phase-space distribution of dark matter and (halo) stars, consisting of streams of particles torn from their progenitors during the process of hierarchical merging. While such streams quickly loose their spatial coherence in the process of phase mixing, the individual stars keep their common origin imprinted into their kinematic and chemical properties, allowing the recovery of the Galaxy’s individual “building blocks”. The field of Galactic Archeology has witnessed a dramatic boost over the last decade, thanks to the increasing quality and size of available data sets. This is especially true for the solar neighborhood, a volume of 1–2 kpc around the sun, where large scale surveys like SDSS/SEGUE continue to reveal the full 6D phase-space information of thousands of halo stars. In this review, I summarize the discoveries of stellar halo streams made so far and give a theoretical overview over the search strategies imployed. This article is intended as an introduction to researchers new to the field, but also as a reference illustrating the achievements made so far. I conclude that disentangling the individual fragments from which the Milky Way was built requires more precise data that will ultimately be delivered by the Gaia mission.