- ID:
- ivo://CDS.VizieR/J/A+A/635/A161
- Title:
- Measured atmospheric parameters of NGC6397 stars
- Short Name:
- J/A+A/635/A161
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent work has used spectra of ~5000 stars in NGC 6397 that were extracted from a MUSE mosaic to determine the atmospheric parameters for these stars by fitting the spectra against the Goettingen Spectral Library. A significant change in metallicity between the turn off and the red giant branch was found and was discussed as a possible manifestation of predicted effects of atomic diffusion. However, the small amplitude of the effect and inconsistency with earlier measurements call for more attention before this result is interpreted. Systematic effects due to the interpolation or to the synthetic spectra cannot be ruled out at this level of precision. We reanalyze the data with : the ELODIE and MILES reference libraries in order to assess the robustness of the result. These empirical libraries have a finer metallicity coverage down to approximately the cluster metallicity turn-off. Methods. We used the ULySS full-spectrum fitting package, together with the library interpolators to remeasure the three atmospheric parameters effective temperature, surface gravity, and [Fe/H] metallicity. We find a very low [Fe/H] dispersion along the isochrone (0.07dex), consistent with our error estimate (0.05dex). However, the [Fe/H] trend is not reproducible. This shows that the data have the potential to reveal patterns of the magnitude of the expected physical effects, but the analysis methods need to be refined to cull systematic effects that currently dominate the patterns.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/817/128
- Title:
- Megamaser Cosmology Project. VIII. NGC5765B
- Short Name:
- J/ApJ/817/128
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As part of the Megamaser Cosmology Project, here we present a new geometric distance measurement to the megamaser galaxy NGC 5765b. Through a series of very long baseline interferometry observations, we have confirmed the water masers trace a thin, sub-parsec Keplerian disk around the nucleus, implying an enclosed mass of 4.55+/-0.40x10^7^M_{sun}_. Meanwhile, from single-dish monitoring of the maser spectra over two years, we measured the secular drifts of maser features near the systemic velocity of the galaxy with rates between 0.5 and 1.2km/s/yr. Fitting a warped, thin-disk model to these measurements, we determine a Hubble Constant H_0_ of 66.0+/-6.0km/s/Mpc with an angular-diameter distance to NGC 5765b of 126.3+/-11.6Mpc. Apart from the distance measurement, we also investigate some physical properties related to the maser disk in NGC 5765b. The high-velocity features are spatially distributed into several clumps, which may indicate the existence of a spiral density wave associated with the accretion disk. For the redshifted features, the envelope defined by the peak maser intensities increases with radius. The profile of the systemic masers in NGC 5765b is smooth and shows almost no structural changes over the two years of monitoring time, which differs from the more variable case of NGC 4258.
- ID:
- ivo://CDS.VizieR/J/A+A/581/A83
- Title:
- Metal enriched X-ray bursting neutron star atmos.
- Short Name:
- J/A+A/581/A83
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Low-mass X-ray binaries hosting neutron stars (NS) exhibit thermonuclear (type-I) X-ray bursts, which are powered by unstable nuclear burning of helium and/or hydrogen into heavier elements deep in the NS "ocean". In some cases the burning ashes may rise from the burning depths up to the NS photosphere by convection, leading to the appearance of the metal absorption edges in the spectra, which then force the emergent X-ray burst spectra to shift toward lower energies. These effects may have a substantial impact on the color correction factor fc and the dilution factor w, the parameters of the diluted blackbody model F_E_=wB_E_(f_c_T_eff_) that is commonly used to describe the emergent spectra from NSs. The aim of this paper is to quantify how much the metal enrichment can change these factors. We have developed a new NS atmosphere modeling code, which has a few important improvements compared to our previous code required by inclusion of the metals. The opacities and the internal partition functions (used in the ionization fraction calculations) are now taken into account for all atomic species. In addition, the code is now parallelized to counter the increased computational load.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A109
- Title:
- Metal enrichment in semi-analytical model
- Short Name:
- J/A+A/589/A109
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Gas flows play a fundamental role in galaxy formation and evolution, providing the fuel for the star formation process. These mechanisms leave an imprint in the amount of heavy elements that enrich the interstellar medium (ISM). Thus, the analysis of this metallicity signature provides additional constraint on the galaxy formation scenario. We aim to discriminate between four different galaxy formation models based on two accretion scenarios and two different star formation recipes. We address the impact of a bimodal accretion scenario and a strongly regulated star formation recipe on the metal enrichment process of galaxies. We present a new extension of the eGalICS model, which allows us to track the metal enrichment process in both stellar populations and in the gas phase. Based on stellar metallicity bins from 0 to 2.5Z_{sun}_, our new chemodynamical model is applicable for situations ranging from metal-free primordial accretion to very enriched interstellar gas contents. We use this new tool to predict the metallicity evolution of both the stellar populations and gas phase. We compare these predictions with recent observational measurements. We also address the evolution of the gas metallicity with the star formation rate (SFR). We then focus on a sub-sample of Milky Way-like galaxies. We compare both the cosmic stellar mass assembly and the metal enrichment process of such galaxies with observations and detailed chemical evolution models.
- ID:
- ivo://CDS.VizieR/J/ApJ/683/321
- Title:
- Metallicities of GRB, DLA, and Ly{alpha} galaxies
- Short Name:
- J/ApJ/683/321
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We test the hypothesis that the host galaxies of long-duration gamma-ray bursts (GRBs) as well as quasar-selected damped Ly{alpha} (DLA) systems are drawn from the population of UV-selected star-forming, high-z galaxies (generally referred to as Lyman break galaxies). Specifically, we compare the metallicity distributions of the GRB and DLA populations against simple models where these galaxies are drawn randomly from the distribution of star-forming galaxies according to their star formation rate and HI cross section, respectively. We find that it is possible to match both observational distributions assuming very simple and constrained relations between luminosity, metallicity, and HI sizes. The simple model can be tested by observing the luminosity distribution of GRB host galaxies and by measuring the luminosity and impact parameters of DLA-selected galaxies as a function of metallicity. Our results support the expectation that GRB and DLA samples, in contrast with magnitude-limited surveys, provide an almost complete census of z~3 star-forming galaxies that are not heavily obscured.
- ID:
- ivo://CDS.VizieR/J/ApJ/737/L20
- Title:
- Metallicity dependent star formation rates
- Short Name:
- J/ApJ/737/L20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive a metallicity-dependent relation between the surface density of the star formation rate ({Sigma}_SFR_) and the gas surface density ({Sigma}_g_) in a feedback-regulated model of star formation in galactic disks. In this model, star formation occurs in gravitationally bound protocluster clumps embedded in larger giant molecular clouds with the protocluster clump mass function following a power-law function with a slope of -2. Metallicity-dependent feedback is generated by the winds of OB stars (M>~5M_{sun}_) that form in the clumps. The quenching of star formation in clumps of decreasing metallicity occurs at later epochs due to weaker wind luminosities, thus resulting in higher final star formation efficiencies (SFE_exp_). By combining SFE_exp_ with the timescales on which gas expulsion occurs, we derive the metallicity-dependent SFR per unit time in this model as a function of {Sigma}_g_. This is combined with the molecular gas fraction in order to derive the global dependence of {Sigma}_SFR_ on {Sigma}_g_. The model reproduces very well the observed star formation laws extending from low gas surface densities up to the starburst regime. Furthermore, our results show a dependence of {Sigma}_SFR_ on metallicity over the entire range of gas surface densities in contrast to other models and can also explain part of the scatter in the observations. We provide a tabulated form of the star formation laws that can easily be incorporated into numerical simulations or semi-analytical models of galaxy formation and evolution.
- ID:
- ivo://CDS.VizieR/J/ApJ/775/125
- Title:
- Metallicity of galaxies from colors
- Short Name:
- J/ApJ/775/125
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There is a well known correlation between the mass and metallicity of star-forming galaxies. Because mass is correlated with luminosity, this relation is often exploited, when spectroscopy is not available, to estimate galaxy metallicities based on single band photometry. However, we show that galaxy color is typically more effective than luminosity as a predictor of metallicity. This is a consequence of the correlation between color and the galaxy mass-to-light ratio and the recently discovered correlation between star formation rate (SFR) and residuals from the mass-metallicity relation. Using Sloan Digital Sky Survey spectroscopy of ~180000 nearby galaxies, we derive "LZC relations," empirical relations between metallicity (in seven common strong line diagnostics), luminosity, and color (in 10 filter pairs and four methods of photometry). We show that these relations allow photometric metallicity estimates, based on luminosity and a single optical color, that are ~50% more precise than those made based on luminosity alone; galaxy metallicity can be estimated to within ~0.05-0.1 dex of the spectroscopically derived value depending on the diagnostic used. Including color information in photometric metallicity estimates also reduces systematic biases for populations skewed toward high or low SFR environments, as we illustrate using the host galaxy of the supernova SN 2010ay. This new tool will lend more statistical power to studies of galaxy populations, such as supernova and gamma-ray burst host environments, in ongoing and future wide-field imaging surveys.
- ID:
- ivo://CDS.VizieR/J/A+A/640/A25
- Title:
- Metal-poor stars limb-darkening coefficients
- Short Name:
- J/A+A/640/A25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Benchmark stars are crucial as validating standards for current as well as future large stellar surveys of the Milky Way. However, the number of suitable metal-poor benchmark stars is currently limited, owing to the difficulty in determining reliable effective temperatures (Teff) in this regime. We aim to construct a new set of metal-poor benchmark stars, based on reliable interferometric effective temperature determinations and a homogeneous analysis. The aim is to reach a precision of 1% in Teff, as is crucial for sufficiently accurate determinations of the full set of fundamental parameters and abundances for the survey sources. We observed ten late type metal-poor dwarf and giants: HD 2665, HD 6755, HD 6833, HD 103095, HD 122563, HD 127243, HD 140283, HD 175305, HD 221170 and HD 224930. Only three of the ten stars (HD 103095, HD 122563 and HD 140283) have previously been used as benchmark stars. For the observations, we used the high angular resolution optical interferometric instrument PAVO at the CHARA array. We modelled angular diameters using 3D limb darkening models and determined effective temperatures directly from the Stefan-Boltzmann relation, with an iterative procedure to interpolate over tables of bolometric corrections. Surface gravities (log(g)) were estimated from comparisons to Dartmouth stellar evolution model tracks. We collected spectroscopic observations from the ELODIE and FIES spectrographs and estimated metallicities ([Fe/H]) from a 1D non-LTE abundance analysis of unblended lines of neutral and singly ionized iron. We inferred Teff to better than 1% for five of the stars (HD 103095, HD 122563, HD 127243, HD 140283 and HD 224930). The effective temperatures of the other five stars are reliable to between 2-3%; the higher uncertainty on the Teff for those stars is mainly due to their having a larger uncertainty in the bolometric fluxes. We also determined log(g) and [Fe/H] with median uncertainties of 0.03dex and 0.09dex, respectively. This study presents reliable and homogeneous fundamental stellar parameters for ten metal-poor stars that can be adopted as a new set of benchmarks. The parameters are based on our consistent approach of combining interferometric observations, 3D limb darkening modelling and spectroscopic observations. The next paper in this series will extend this approach to dwarfs and giants in the metal-rich regime.
- ID:
- ivo://CDS.VizieR/J/A+A/622/A84
- Title:
- Meteor showers new parent bodies
- Short Name:
- J/A+A/622/A84
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several new meteor showers are added to the International Astronomical Union (IAU) list of meteor showers every year. Given the multiplication of video meteor measurements new parent bodies are to be found in addition to new showers. Such an endeavor is usually performed by comparing orbital elements, using a high threshold single-linking Dsh-criterion. However, questions remain about the accuracy of the method and the veracity of the newly associated parent bodies. Our goal is to find the presence of new parent bodies in a statistical meaningful way. A search for parent bodies was performed among SonotaCo and EDMOND databases. The association of asteroids with meteors was based on different methods, discussed and compared below. In addition, a thorough statistical test was performed in order to investigate the possible random associations. A list of potential new parent bodies associated with at least 50 meteors is found. A statistical test was used to show whether the group of meteor orbits and the asteroid is a random coincidence or not. Out of 54 potential new parent bodies, only three new parent bodies are not excluded by the statistical test: 2014 BN14, 2015 TX24 and 2015 QT3, with a probability of chance occurrence of 37, 10 and 13%, respectively. This shows the need for rigorous method when searching for the existence of meteor showers and parent bodies. Ideally, such a test (or even better, tests) should be conducted in order to confirm (or not) the current IAU list of meteor showers. Similarly, all meteor orbit data in our databases should ideally be revisited using the latest methods providing a better estimate of the real uncertainty and accuracy of the derived orbits.
- ID:
- ivo://CDS.VizieR/J/MNRAS/403/1625
- Title:
- Method for orientation angles of galaxies
- Short Name:
- J/MNRAS/403/1625
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A method is proposed for the determination of the position and inclination angles of the plane of a spiral galaxy based on the assumption that every spiral arm is a monotonic function of the radius against azimuthal angle. This method may yield more accurate results than the more commonly employed isophote method, which is subject to a number of drawbacks. Analytical study, calibration against other methods and examples of application of the proposed method to real galaxies are presented.
