We derive a self-consistent set of atmospheric parameters and abundances of 17 elements for the red giant star Arcturus: T eff = 4286 ? 30 K, log g = 1.66 ? 0.05, and Fe/H = --0.52 ? 0.04. The ...effective temperature was determined using model atmosphere fits to the observed spectral energy distribution from the blue to the mid-infrared (0.44 to 10 Delta *mm). The surface gravity was calculated using the trigonometric parallax of the star and stellar evolution models. A differential abundance analysis relative to the solar spectrum allowed us to derive iron abundances from equivalent width measurements of 37 Fe I and 9 Fe II lines, unblended in the spectra of both Arcturus and the Sun; the Fe/H value adopted is derived from Fe I lines. We also determine the mass, radius, and age of Arcturus: M = 1.08 ? 0.06 M , R = 25.4 ? 0.2 R , and Delta *t = 7.1+1.5 -- 1.2 Gyr. Finally, abundances of the following elements are measured from an equivalent width analysis of atomic features: C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, and Zn. We find the chemical composition of Arcturus typical of that of a local thick-disk star, consistent with its kinematics.
ABSTRACT
The Pristine survey uses narrow-band photometry to derive precise metallicities down to the extremely metal-poor regime ($ \rm Fe/H \lt -3$), and currently consists of over 4 million ...FGK-type stars over a sky area of $\sim 2500\, \mathrm{deg}^2$. We focus our analysis on a subsample of ∼80 000 main-sequence turn-off stars with heliocentric distances between 6 and 20 kpc, which we take to be a representative sample of the inner halo. The resulting metallicity distribution function (MDF) has a peak at $ \rm Fe/H =-1.6$, and a slope of Δ(LogN)/$\Delta \rm Fe/H = 1.0 \pm 0.1$ in the metallicity range of $-3.4\; \lt\; \rm Fe/H\; \lt -2.5$. This agrees well with a simple closed-box chemical enrichment model in this range, but is shallower than previous spectroscopic MDFs presented in the literature, suggesting that there may be a larger proportion of metal-poor stars in the inner halo than previously reported. We identify the Monoceros/TriAnd/ACS/EBS/A13 structure in metallicity space in a low-latitude field in the anticentre direction, and also discuss the possibility that the inner halo is dominated by a single, large merger event, but cannot strongly support or refute this idea with the current data. Finally, based on the MDF of field stars, we estimate the number of expected metal-poor globular clusters in the Milky Way halo to be 5.4 for $ \rm Fe/H\; \lt\; -2.5$ and 1.5 for $ \rm Fe/H\; \lt\; -3$, suggesting that the lack of low-metallicity globular clusters in the Milky Way is not due simply to statistical undersampling.
We present a joint analysis of the four most prominent sodium-sensitive features (Na D, Na i ...8190A, Na i ...1.14 ...m, and Na i ...2.21 ...m), in the optical and near-infrared spectral ranges, of ...two nearby, massive (... ~ 300 km s super( -1)), early-type galaxies (named XSG1 and XSG2). Our analysis relies on deep Very Large Telescope/X-Shooter long-slit spectra, along with newly developed stellar population models, allowing for Na/Fe variations, up to ~1.2 dex, over a wide range of age, total metallicity, and initial mass function (IMF) slope. The new models show that the response of the Na-dependent spectral indices to Na/Fe is stronger when the IMF is bottom heavier. For the first time, we are able to match all four Na features in the central regions of massive early-type galaxies finding an overabundance of Na/Fe in the range 0.5-0.7 dex and a bottom-heavy IMF. Therefore, individual abundance variations cannot be fully responsible for the trends of gravity-sensitive indices, strengthening the case towards a non-universal IMF. Given current limitations of theoretical atmosphere models, our Na/Fe estimates should be taken as upper limits. For XSG1, where line strengths are measured out to ~0.8 R sub( e), the radial trend of Na/Fe is similar to .../Fe and C/Fe, being constant out to ~0.5 R sub( e), and decreasing by ~0.2-0.3 dex at ~0.8 R sub( e), without any clear correlation with local metallicity. Such a result seems to be in contrast to the predicted increase of Na nucleosynthetic yields from asymptotic giant branch stars and Type II supernovae. For XSG1, the Na-inferred IMF radial profile is consistent, within the errors, with that derived from TiO features and the Wing-Ford band presented in a recent paper. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
Using new long-slit spectroscopy obtained with X-Shooter at ESO-VLT, we study, for the first time, radial gradients of optical and near-infrared initial mass function (IMF)-sensitive ...features in a representative sample of galaxies at the very high mass end of the galaxy population. The sample consists of seven early-type galaxies (ETGs) at z ∼ 0.05, with central velocity dispersion in the range 300 ≲ σ ≲ 350 km s−1. Using state-of-the-art stellar population synthesis models, we fit a number of spectral indices, from different chemical species (including TiO and Na indices), to constrain the IMF slope (i.e. the fraction of low-mass stars), as a function of galactocentric distance, over a radial range out to ∼4 kpc. ETGs in our sample show a significant correlation of IMF slope and surface mass density. The bottom-heavy population (i.e. an excess of low-mass stars in the IMF) is confined to central galaxy regions with surface mass density above $\rm \sim 10^{10}\, M_\odot \, kpc^{-2}$, or, alternatively, within a characteristic radius of ∼2 kpc. Radial distance, in physical units, and surface mass density are the best correlators to IMF variations, with respect to other dynamical (e.g. velocity dispersion) and stellar population (e.g. metallicity) properties. Our results for the most massive galaxies suggest that there is no single parameter that fully explains variations in the stellar IMF, but IMF radial profiles at z ∼ 0 rather result from the complex formation and mass accretion history of galaxy inner and outer regions.
Atmospheric parameters and oxygen abundances of 825 nearby FGK stars are derived using high-quality spectra and a non-local thermodynamic equilibrium analysis of the 777 nm OI triplet lines. We ...assign a kinematic probability for the stars to be thin-disk (P sub(1)), thick-disk (P sub(2)), and halo (P sub(3)) members. We confirm previous findings of enhanced O/Fe in thick-disk (P sub(2) > 0.5) relative to thin-disk (P sub(1) > 0.5) stars with Fe/H lap -0.2, as well as a "knee" that connects the mean O/Fe-Fe/H trend of thick-disk stars with that of thin-disk members at Fe/H gap -0.2. Nevertheless, we find that the kinematic membership criterion fails at separating perfectly the stars in the O/Fe-Fe/H plane, even when a very restrictive kinematic separation is employed. Stars with "intermediate" kinematics (P sub(1) < 0.7, P sub(2) < 0.7) do not all populate the region of the O/Fe-Fe/H plane intermediate between the mean thin-disk and thick-disk trends, but their distribution is not necessarily bimodal. Halo stars (P sub(3) > 0.5) show a large star-to-star scatter in O/Fe-Fe/H, but most of it is due to stars with Galactocentric rotational velocity V < -200 km s super(-1); halo stars with V > -200 km s super(-1) follow an O/Fe-Fe/H relation with almost no star-to-star scatter. Early mergers with satellite galaxies explain most of our observations, but the significant fraction of disk stars with "ambiguous" kinematics and abundances suggests that scattering by molecular clouds and radial migration have both played an important role in determining the kinematic and chemical properties of solar neighborhood stars.
Type Ia supernovae are key tools for measuring distances on a cosmic scale. They are generally thought to be the thermonuclear explosion of an accreting white dwarf in a close binary system. The ...nature of the mass donor is still uncertain. In the single-degenerate model it is a main-sequence star or an evolved star, whereas in the double-degenerate model it is another white dwarf. We show that the velocity structure of absorbing material along the line of sight to 35 type Ia supernovae tends to be blueshifted. These structures are likely signatures of gas outflows from the supernova progenitor systems. Thus, many type Ia supernovae in nearby spiral galaxies may originate in single-degenerate systems.
We examine closely the solar center-to-limb variation of continua and lines and compare observations with predictions from both a three-dimensional (3D) hydrodynamic simulation of the solar surface ...(provided by M. Asplund and collaborators) and one-dimensional (1D) model atmospheres. Intensities from the 3D time series are derived by means of the new synthesis code ASS epsilon T, which overcomes limitations of previously available codes by including a consistent treatment of scattering and allowing for arbitrarily complex line and continuum opacities. In the continuum, we find very similar discrepancies between synthesis and observation for both types of model atmospheres. This is in contrast to previous studies that used a 'horizontal' and time-averaged representation of the 3D model and found a significantly larger disagreement with observations. The presence of temperature and velocity fields in the 3D simulation provides a significant advantage when it comes to reproducing solar spectral line shapes. Nonetheless, a comparison of observed and synthetic equivalent widths reveals that the 3D model also predicts more uniform abundances as a function of position angle on the disk. We conclude that the 3D simulation provides not only a more realistic description of the gas dynamics, but despite its simplified treatment of the radiation transport, it also predicts reasonably well the observed center-to-limb variation, which is indicative of a thermal structure free from significant systematic errors.
We derive atmospheric parameters and lithium abundances for 671 stars and include our measurements in a literature compilation of 1381 dwarf and subgiant stars. First, a "lithium desert" in the ...effective temperature (T sub(eff)) versus lithium abundance (A sub(Li)) plane is observed such that no stars with T sub(eff) Asymptotically = to 6075 K and A sub(Li) Asymptotically = to 1.8 are found. We speculate that most of the stars on the low A sub(Li) side of the desert have experienced a short-lived period of severe surface lithium destruction as main-sequence or subgiant stars. Next, we search for differences in the lithium content of thin-disk and thick-disk stars, but we find that internal processes have erased from the stellar photospheres their possibly different histories of lithium enrichment. Nevertheless, we note that the maximum lithium abundance of thick-disk stars is nearly constant from Fe/H = -1.0 to -0.1, at a value that is similar to that measured in very metal-poor halo stars (A sub(Li) Asymptotically = to 2.2). Finally, differences in the lithium abundance distribution of known planet-host stars relative to otherwise ordinary stars appear when restricting the samples to narrow ranges of T sub(eff) or mass, but they are fully explained by age and metallicity biases. We confirm the lack of a connection between low lithium abundance and planets. However, we find that no low A sub(Li) planet-hosts are found in the desert T sub(eff) window. Provided that subtle sample biases are not responsible for this observation, this suggests that the presence of gas giant planets inhibit the mechanism responsible for the lithium desert.
ABSTRACT
We present a new library of semi-empirical stellar population models that are based on the empirical MILES and semi-empirical sMILES stellar libraries. The models span a large range of age ...and metallicity, in addition to an α/Fe coverage from −0.2 to +0.6 dex, at MILES resolution (FWHM = $2.5\,$ Å) and wavelength coverage ($3540.5-7409.6\,$ Å). These models are aimed at exploring abundance ratios in the integrated light from stellar populations in star clusters and galaxies. Our approach is to build SSPs from semi-empirical stars at particular α/Fe values, thus producing new SSPs at a range of α/Fe values from sub-solar to super-solar. We compare these new SSPs with previously published and well-used models and find similar abundance pattern predictions, but with some differences in age indicators. We illustrate a potential application of our new SSPs, by fitting them to the high signal-to-noise data of stacked SDSS galaxy spectra. Age, metallicity, and α/Fe trends were measured for galaxy stacks with different stellar velocity dispersions and show systematic changes, in agreement with previous analyses of subsets of those data. These new SSPs are made publicly available.
Hydrological signatures are now used for a wide range of purposes, including catchment classification, process exploration, and hydrological model calibration. The recent boost in the popularity and ...number of signatures has however not been accompanied by the development of clear guidance on signature selection. Here we propose that exploring the predictability of signatures in space provides important insights into their drivers and their sensitivity to data uncertainties and is hence useful for signature selection. We use three complementary approaches to compare and rank 15 commonly used signatures, which we evaluate in 600+ U.S. catchments from the Catchment Attributes and MEteorology for Large‐sample Studies (CAMELS) data set. First, we employ machine learning (random forests) to explore how attributes characterizing the climatic conditions, topography, land cover, soil, and geology influence (or not) the signatures. Second, we use simulations of the Sacramento Soil Moisture Accounting model to benchmark the random forest predictions. Third, we take advantage of the large sample of CAMELS catchments to characterize the spatial autocorrelation (using Moran's I) of the signature field. These three approaches lead to remarkably similar rankings of the signatures. We show (i) that signatures with the noisiest spatial pattern tend to be poorly captured by hydrological simulations, (ii) that their relationship to catchments attributes are elusive (in particular they are not well explained by climatic indices), and (iii) that they are particularly sensitive to discharge uncertainties. We suggest that a better understanding of the drivers of hydrological signatures and a better characterization of their uncertainties would increase their value in hydrological studies.
Key Points
We used machine learning and a hydrological model to simulate 15 hydrological signatures over 600+ catchments in the United States
The predictability of the signatures is highly correlated with the smoothness of their spatial pattern, which we quantified using Moran's I
Poorly predicted signatures vary abruptly in space, they are particularly sensitive to streamflow errors, and their links to catchment attributes are elusive
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