We have obtained new detailed abundances of the Fe-group elements Sc through Zn (Z=21-30) in three very metal-poor ([Fe/H] $\approx -3$) stars: BD 03 740, BD -13 3442 and CD -33 1173. High-resolution ultraviolet HST/STIS spectra in the wavelength range 2300-3050Å were gathered, and complemented by an assortment of optical echelle spectra. The analysis featured recent laboratory atomic data for number of neutral and ionized species for all Fe-group elements except Cu and Zn. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys indicates that they are positively correlated in stars with [Fe/H]<-$2. The abundances of these elements in BD 03 740, BD -13 3442 and CD -33 1173 and HD 84937. (studied in a previous paper of this series) are in accord with these trends and lie at the high end of the correlations. Six elements have detectable neutral and ionized features, and generally their abundances are in reasonable agreement. For Cr we find only minimal abundance disagreement between the neutral (mean of [Cri/Fe]=+0.01) and ionized species (mean of [Crii/Fe]=+0.08), unlike most studies in the past. The prominent exception is Co, for which the neutral species indicates a significant overabundance (mean of [Co/H]=-2.53), while no such enhancement is seen for the ionized species (mean of [Coii/H]=-2.93). These new stellar abundances, especially the correlations among Sc, Ti, and V, suggest that models of element production in early high-mass metal-poor stars should be revisited.
We present a new iron abundance analysis of the hyper metal-poor star HE$~$1327-2326, based on Fe II lines detected in its UV spectral range for the first time. In a Cosmic Origins Spectrograph (COS) spectrum, five new Fe II lines could be measured. A Si I line was also detected for the first time. We determine a 1D Local Thermodynamic Equilibrium (LTE) Fe II abundance of [Fe II/H] = -5.99$\pm$0.25. We also investigate departures from LTE for both Fe I and Fe II lines. Guided by 3D Non-LTE (NLTE) analyses of other well-studied metal-poor stars, we identify potential "residual" 3D effects in HE…
We study the dust present in 56 Galactic planetary nebulae (PNe) through their iron depletion factors, their C/O abundance ratios (in 51 objects), and the dust features that appear in their infrared spectra (for 33 objects). Our sample objects have deep optical spectra of good quality, and most of them also have ultraviolet observations. We use these observations to derive the iron abundances and the C/O abundance ratios in a homogeneous way for all the objects. We compile detections of infrared dust features from the literature and we analyze the available Spitzer/IRS spectra. Most of the PNe…
Iron suffers from high levels of depletion in the highly ionized environments of planetary nebulae, making the direct determination of undepleted elemental iron abundances difficult. Zinc, which does not suffer from the same depletion effects as iron, may be used as a surrogate element to measure iron abundances as there is an approximately constant zinc-to-iron ratio across a wide range of metallicities. In this paper, we report zinc abundances of six Galactic Bulge planetary nebulae determined from new observations taken with ISAAC on the Very Large Telescope, Chile, prior to the instrument'…
In the aim of determining accurate iron abundances in stars, this work is meant to empirically calibrate H-collision cross-sections with iron, where no quantum mechanical calculations have been published yet. Thus, a new iron model atom has been developed, which includes hydrogen collisions for excitation, ionization and charge transfer processes. We show that collisions with hydrogen leading to charge transfer are important for an accurate non-LTE modeling. We apply our calculations on several benchmark stars including the Sun, the metal-rich star α Cen A and the metal-poor star HD140283.
Intrinsic iron abundance spreads in globular clusters
INAF–Osservatorio Astrofisico di Arcetri（意大利国家天体物理研究所阿切特里天文台）；INAF–Osservatorio Astronomico di Padova（意大利国家天体物理研究所帕多瓦天文台）；INAF-Osservatorio di Astrofisica e Scienza dello Spazio（意大利国家天体物理研究所天体物理学与空间科学观测站）
We performed an iron abundance determination of the hot, hydrogen deficient post-AGB star PG1159-035, which is the prototype of the PG1159 spectral class and the GW Vir pulsators, and of two related objects (PG1520+525, PG1144+005), based on the first detection of Fe VIII lines in stellar photospheres. In another PG1159 star, PG1424+535, we detect Fe VII lines. In all four stars, each within Teff = 110,000 - 150,000 K, we find a solar iron abundance. This result agrees with our recent abundance analysis of the hottest PG1159 stars (Teff = 150,000 - 200,000 K) that exhibit Fe X lines. On the wh…
Abundance of iron in the atmosphere of Arcturus has been determined from the profiles or regions of the profiles of the weak lines sensitive to iron abundance. The selected lines of Fe I and Fe II were synthesized with the MARCS theoretical models of the atmosphere. From the observed profiles of lines available with a high spectral resolution in the atlas by Hinkle and Wallace (2005), the values of the iron abundance $A = 6.95 \pm 0.03$ and the radial-tangential macroturbulent velocity $5.6 \pm 0.2$ km/s were obtained for Arcturus. The same physical quantities were found for the Sun as a star;…
The abundance of iron is measured from emission line complexes at 6.65 keV (Fe line) and 8 keV (Fe/Ni line) in {\em RHESSI} X-ray spectra during solar flares. Spectra during long-duration flares with steady declines were selected, with an isothermal assumption and improved data analysis methods over previous work. Two spectral fitting models give comparable results, viz. an iron abundance that is lower than previous coronal values but higher than photospheric values. In the preferred method, the estimated Fe abundance is $A({\rm Fe}) = 7.91 \pm 0.10$ (on a logarithmic scale, with $A({\rm H}) =…
AIMS. In this paper we present the chemical abundance analysis from high resolution UVES spectra of seventeen bright giant stars of the Globular Cluster M~22. RESULTS. We obtained an average iron abundance of [Fe/H]=-1.76\pm0.02 (internal errors only) and an αenhancement of 0.36\pm0.04 (internal errors only). Na and O, and Al and O follow the well known anti-correlation found in many other GCs. We identified two groups of stars with significantly different abundances of the s-process elements Y, Zr and Ba. The relative numbers of the two group members are very similar to the ratio of the stars…
We present CN and CH indices and CaII triplet metallicities for 34 giant stars and chemical abundances for 33 elements in 14 giants in the globular cluster M2. Assuming the program stars are cluster members, our analysis reveals (i) an extreme variation in CN and CH line strengths, (ii) a metallicity dispersion with a dominant peak at [Fe/H] = -1.7 and smaller peaks at -1.5 and -1.0, (iii) star-to-star abundance variations and correlations for the light elements O, Na, Al and Si and (iv) a large (and possibly bimodal) distribution in the abundances of all elements produced mainly via the s-pro…
We have been exploring large spectroscopic databases such as SDSS to search for unique stars with extremely low iron content with the goal of extracting detailed information from the early phases of the Galaxy. We recently identified two extremely iron-poor dwarf stars J0815+4729 (Aguado et al. 2018a) and J0023+0307 (Aguado et al. 2018b) from SDSS/BOSS database and confirmed from high-quality spectra taken with ISIS and OSIRIS spectrographs at the 4.2m WHT and 10.4m GTC telescopes, respectively, located in La Palma (Canary Islands, Spain). We have also acquired high-resolution spectroscopy wit…
We investigate the origin of the most iron-poor stars including SMSS J031300.36-670839.3 with [Fe/H] < -7.52. We compute the change of surface metallicity of stars with the accretion of interstellar matter (ISM) after their birth using the chemical evolution model within the framework of the hierarchical galaxy formation. The predicted metallicity distribution function agrees very well with that observed from extremely metal-poor stars. In particular, the lowest metallicity tail is well reproduced by the Population III stars whose surfaces are polluted with metals through ISM accretion. This s…
This work describes a study of elemental abundances for 30 metal-poor stars whose chemical abundances provide excellent information for setting constraints on models of neutron-capture processes. Based on the abundances of main r- and weak r-process stars, the abundance patterns of main r-process and weak r-process are obtained. The two r-process component coefficients are defined to determine the relative contributions from individual neutron-capture process to abundances of metal-poor stars. Based on the component coefficients, we find that metal-poor stars BD+4 2621 and HD 4306 are also wea…
The Milky Way bulge is an important tracer of the early formation and chemical enrichment of the Galaxy. The abundances of different iron-peak elements in field bulge stars can give information on the nucleosynthesis processes that took place in the earliest supernovae. Cobalt (Z=27) and copper (Z=29) are particularly interesting.We aim to identify the nucleosynthesis processes responsible for the formation of the iron-peak elements Co and Cu. Methods. We derived abundances of the iron-peak elements cobalt and copper in 56 bulge giants, 13 of which were red clump stars. High-resolution spectra…
The progenitor systems and explosion mechanisms responsible for the thermonuclear events observationally classified as Type Ia supernovae are uncertain and difficult to uniquely constrain using traditional observations of Type Ia supernova host galaxies, progenitors, light curves, and remnants. For the subset of thermonuclear events that are prolific producers of iron, we use published theoretical nucleosynthetic yields to identify a set of elemental abundance ratios infrequently observed in metal-poor stars but shared across a range of progenitor systems and explosion mechanisms: [Na,Mg,Co/Fe…
PENELLOPE: IX. Lithium, iron and barium elemental abundances in eight nearby young clusters
INAF-Osservatorio Astronomico di Roma（罗马天文台）；INAF-Osservatorio Astrofisico di Catania（卡塔尼亚天文台）；European Southern Observatory（欧洲南方天文台）；INAF-Osservatorio Astronomico di Capodimonte（卡波迪蒙特天文台）；Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences（孔科利天文台，匈牙利研究网络天文学与地球科学研究中心）；Institute of Physics and Astronomy, ELTE Eötvös Loránd University（罗兰大学物理与天文学研究所）；Institute for Astronomy (IfA), University of Vienna（维也纳大学天体物理研究所）；Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台）；ASI, Italian Space Agency（意大利航天局）
Terzan 5 is a complex stellar system in the Galactic bulge, harboring stellar populations with very different iron content (Δ[Fe/H] ~1 dex) and with ages differing by several Gyrs. Here we present an investigation of its variable stars. We report on the discovery and characterization of three RR Lyrae stars. For these newly discovered RR Lyrae and for six Miras of known periods we provide radial velocity and chemical abundances from spectra acquired with X-SHOOTER at the VLT. We find that the three RR Lyrae and the three short period Miras (P<300 d) have radial velocity consistent with being T…
Spectra of unevolved metal-poor halo stars uniquely reflect the elemental abundances incorporated during the earliest Galactic epoch. Their heavy-element content is well understood as the products of neutron capture on iron-peak elements. However, the lightest elements just past the iron peak, with atomic number 30<Z<52, show striking abundance patterns open to several interpretations. Understanding their nature may illuminate the diverse halo, thick disk, or extragalactic origins of metal-poor stars. For five metal-poor dwarfs, we analyzed high-resolution echelle UV spectra from the Hubble Sp…
One of the primary objectives of the TOPoS survey is to search for the most metal-poor stars. Our search has led to the discovery of one of the most iron-poor objects known, SDSS\,J092912.32+023817.0. This object is a multiple system, in which two components are clearly detected in the spectrum. We have analysed 16 high-resolution spectra obtained using the UVES spectrograph at the ESO 8.2m VLT telescope to measure radial velocities and determine the chemical composition of the system. Cross correlation of the spectra with a synthetic template yields a double-peaked cross-correlation function …
We present $\gtrsim 15,000$ metal-rich (${\rm [Fe/H]}>-0.2$dex) A and F stars whose surface abundances deviate strongly from Solar abundance ratios and cannot plausibly reflect their birth material composition. These stars are identified by their high [Ba/Fe] abundance ratios (${\rm [Ba/Fe]}>1.0$dex) in the LAMOST DR5 spectra analyzed by Xiang et al. (2019). They are almost exclusively main sequence and subgiant stars with $T_{\rm eff}\gtrsim6300$K. Their distribution in the Kiel diagram ($T_{\rm eff}$--$\log g$) traces a sharp border at low temperatures along a roughly fixed-mass trajectory (…
We show that the low ratios of $α$ elements (Mg, Si, and Ca) to Fe recently found for a small fraction of extremely metal-poor stars can be naturally explained with the nucleosynthesis yields of core-collapse supernovae, i.e., $13-25M_\odot$ supernovae, or hypernovae. For the case without carbon enhancement, the ejected iron mass is normal, consistent with observed light curves and spectra of nearby supernovae. On the other hand, the carbon enhancement requires much smaller iron production, and the low [$α$/Fe] of carbon enhanced metal-poor stars can also be reproduced with $13-25M_\odot$ fain…
We report the discovery of SDSS J131326.89-001941.4, an ultra iron-poor red giant star ([Fe/H] ~ -4.3) with a very high carbon abundance ([C/Fe]~ +2.5). This object is the fifth star in this rare class, and the combination of a fairly low effective temperature (Teff ~ 5300 K), which enhances line absorption, with its brightness (g=16.9), makes it possible to measure the abundances of calcium, carbon and iron using a low-resolution spectrum from the Sloan Digital Sky Survey. We examine the carbon and iron abundance ratios in this star and other similar objects in the light of predicted yields f…
We present an analysis of high-resolution Keck/HIRES spectroscopic observations of J0815+4729, an extremely carbon-enhanced, iron-poor dwarf star. These high-quality data allow us to derive a metallicity of [Fe/H]$=-5.49{\pm}0.14$ from the three strongest \ion{Fe}{1} lines and to measure a high [Ca/Fe]~$=0.75{\pm}0.14$. The large carbon abundance of A(C)~$=7.43{\pm}0.17$ (or [C/Fe]~$\sim 4.49{\pm}0.11$) places this star in the upper boundary of the low-carbon band in the A(C)-[Fe/H] diagram, suggesting no contamination from a binary AGB companion. We detect the oxygen triplet at 777nm for the …
Abundances of planetary nebulae and evolved stars: Iron and sulfur depletion, and carbon and nitrogen enrichment, in low- and intermediate-mass stellar populations in the Milky Way
We have derived new abundances of the rare-earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally-consistent Ba, rare-earth, and Hf (56<= Z <= 72) element distributions. These have been used in a critical comparison bet…
We present new ultra-metal-poor (UMP) stars parameters with [Fe/H]<-4.0 based on line-by-line non-local thermodynamic equilibrium (NLTE) abundances using an up-to-date iron model atom with a new recipe for non-elastic hydrogen collision rates. We study the departures from LTE in their atmospheric parameter and show that they can grow up to ~1.0 dex in [Fe/H], 150K in Teff and 0.5 dex in log g toward the lowest metallicities. Accurate NLTE atmospheric stellar parameters, in particular [Fe/H] being signifcantly higher, are the first step to eventually providing full NLTE abundance patterns that …
We present and discuss the strong correspondence between evolution of the emission length scale in the lower transition region and in situ measurements of the fast solar wind composition during this most recent solar minimum. We combine recent analyses demonstrating the variance in the (supergranular) network emission length scale measured by SOHO (and STEREO) with that of the Helium abundance (from WIND) and the degree of Iron fractionation in the solar wind (from the ACE and Ulysses). The net picture developing is one where a decrease in the Helium abundance and the degree of Iron fractionat…
The chemical abundances of metal-poor stars provide a great deal of information regarding the individual nucleosynthetic processes that created the observed elements and the overall process of chemical enrichment of the galaxy since the formation of the first stars. Here we review the abundance patterns of the neutron-capture elements (Z > 38) in those metal-poor stars and our current understanding of the conditions and sites of their production at early times. We also review the relative contributions of these different processes to the build-up of these elements within the galaxy over time, …
We present homogeneous and accurate iron abundances for almost four dozen (47) of Galactic Cepheids using high-spectral resolution (R$\sim$40,000) high signal-to-noise ratio (S/N $\ge$ 100) optical spectra collected with UVES at VLT. A significant fraction of the sample (32) is located in the inner disk (RG $le$ 6.9 kpc) and for half of them we provide new iron abundances. Current findings indicate a steady increase in iron abundance when approaching the innermost regions of the thin disk. The metallicity is super-solar and ranges from 0.2 dex for RG $\sim$ 6.5 kpc to 0.4 dex for RG $\sim$ 5.5…
Detailed non-LTE calculations for red supergiant stars are presented to investigate the influence of NLTE on the formation of atomic iron and titanium lines in the J-band. With their enormous brightness at J-band red supergiant stars are ideal probes of cosmic abundances. Recent LTE studies have found that metallicities accurate to 0.15 dex can be determined from medium resolution spectroscopy of individual red supergiants in galaxies as distant as 10 Mpc. The non-LTE results obtained in this investigation support these findings. Non-LTE abundance corrections for iron are smaller than 0.05 dex…
The abundance of beryllium in the oldest, most metal-poor stars acts as a probe of early star formation and Galactic chemical evolution. We have analyzed high-resolution, high signal-to-noise Keck/HIRES spectra of 24 stars with [Fe/H] from -2.3 to -3.5 in order to determine the history of Be abundances and explore the possibility of a Be plateau. We have determined stellar parameters spectroscopically. Oxygen abundances have been derived from three OH features which occur in the same spectral region. We have supplemented this sample with reanalyzed spectra of 25 stars from previous observation…
Non-local thermodynamic equilibrium (non-LTE) line formation for Ca I-Ca II, Ti I-Ti II, and Fe I-Fe II is considered in model atmospheres of giant stars with an effective temperature of 4000 K $\le$ Teff $\le$ 5000 K and a metal abundance of -4 $\le$ [Fe/H] $\le$ 0. The departures from LTE are analyzed depending on atmospheric parameters. We present the non-LTE abundance corrections for 28 lines of Ca I, 42 lines of Ti I, 54 lines of Ti II, and 262 lines of Fe I and a three-dimensional interpolation code to obtain the non-LTE correction online (http://spectrum.inasan.ru/nLTE/) for an individu…
[Abridged] Investigations of neutron(n)-capture element nucleosynthesis and chemical evolution have largely been based on stellar spectroscopy. However, the recent detection of these elements in several planetary nebulae (PNe) indicates that nebular spectroscopy is a promising new tool for such studies. In PNe, n-capture element abundance determinations reveal details of s-process nucleosynthesis and convective mixing in evolved low-mass stars, as well as the chemical evolution of elements that cannot be detected in stellar spectra. Only one or two ions of a given trans-iron element can typica…
We present the study of the metallicity dependence of the Fourier amplitude ratios R_21 and R_31 for the light curves of short-period Galactic classical Cepheids in B, V, R_C and I_C bands. Based on the available photometric and spectroscopic data we determined the relations between the atmospheric iron abundance, [Fe/H], and the Fourier parameters. Using these relations we calculated the photometric [Fe/H] values of all program Cepheids with an average accuracy of 0.15 dex. No spectroscopic iron abundance was known before for 14 of these stars. These empirical results provide an alternate met…
Neutral Fe lines in metal-poor stars yield conflicting abundances depending on whether and how deviations from local thermodynamic equilibrium (LTE) are considered. We have collected new high resolution and high signal-to-noise ultraviolet (UV) spectra of three warm dwarf stars with [Fe/H] = -2.9 with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. We locate archival UV spectra for three other warm dwarfs with [Fe/H] = -3.3, -2.2, and -1.6, supplemented with optical spectra for all six stars. We calculate stellar parameters using methods that are largely independent of …
We have performed accurate iron abundance measurements for 44 red giants (RGs) in the Carina dwarf spheroidal (dSph) galaxy. We used archival, high-resolution spectra (R~38,000) collected with UVES at ESO/VLT either in slit mode (5) or in fiber mode (39, FLAMES/GIRAFFE-UVES). The sample is more than a factor of four larger than any previous spectroscopic investigation of stars in dSphs based on high-resolution (R>38,000) spectra. We did not impose the ionization equilibrium between neutral and singly-ionized iron lines. The effective temperatures and the surface gravities were estimated by fit…
Spectroscopic measurements of iron abundances are prone to systematic modelling errors. We present 3D non-LTE calculations across 32 STAGGER-grid models with effective temperatures from 5000 K to 6500 K, surface gravities of 4.0 dex and 4.5 dex, and metallicities from $-$3 dex to 0 dex, and study the effects on 171 Fe I and 12 Fe II optical lines. In warm metal-poor stars, the 3D non-LTE abundances are up to 0.5 dex larger than 1D LTE abundances inferred from Fe I lines of intermediate excitation potential. In contrast, the 3D non-LTE abundances can be 0.2 dex smaller in cool metal-poor stars …
We have investigated a highly energetic H-ingestion event during shell He burning leading to H-burning luminosities of $\log(L_\mathrm{H}/\mathrm{\Lsun}) \sim 13$ in a $45 \Msun$ Pop III massive stellar model. In order to track the nucleosynthesis which may occur in such an event, we run a series of single-zone nucleosynthesis models for typical conditions found in the stellar evolution model. Such nucleosynthesis conditions may lead to $\textit{i}-$process neutron densities of up to $ \sim 10^{13} \mathrm{cm}^{-3}$. The resulting simulation abundance pattern, where Mg comes from He burning an…
The abundances of carbon, oxygen, and iron in late-type stars are important parameters in exoplanetary and stellar physics, as well as key tracers of stellar populations and Galactic chemical evolution. We carried out three-dimensional (3D) non-LTE radiative transfer calculations for CI and OI, and 3D LTE radiative transfer calculations for FeII, across the STAGGER-grid of 3D hydrodynamic model atmospheres. The absolute 3D non-LTE versus 1D LTE abundance corrections can be as severe as $-0.3$ dex for CI lines in low-metallicity F dwarfs, and $-0.6$ dex for OI lines in high-metallicity F dwarfs…
We have derived new very accurate abundances of the Fe-group elements Sc through Zn (Z = 21-30) in the bright main-sequence turnoff star HD 84937, based on high-resolution spectra covering the visible and ultraviolet spectral regions. New or recent laboratory transition data for 14 species of seven elements have been used. Abundances from more than 600 lines of non-Fe species have been combined with about 550 Fe lines in HD 84937 to yield abundance ratios of high precision. The abundances have been determined from both neutral and ionized transitions, which generally are in agreement with each…
In the current era of large spectroscopic surveys of the Milky Way, reference stars for calibrating astrophysical parameters and chemical abundances are of paramount importance. We determine elemental abundances of Mg, Si, Ca, Sc, Ti, V, Cr, Mn, Co and Ni for our predefined set of Gaia FGK benchmark stars. By analysing high-resolution and high-signal to noise spectra taken from several archive datasets, we combined results of eight different methods to determine abundances on a line-by-line basis. We perform a detailed homogeneous analysis of the systematic uncertainties, such as differential …
Transit observations in the helium triplet around 10830 Angstrom are a successful tool to study exoplanetary atmospheres and their mass loss. Forming those lines requires ionisation and recombination of helium in the exoplanetary atmosphere. This ionisation is caused by stellar photons at extreme ultra-violet (EUV) wavelengths; however, no currently active telescopes can observe this part of the stellar spectrum. The relevant part of the stellar EUV spectrum consists of individual emission lines, many of them being formed by iron at coronal temperatures. The stellar iron abundance in the coron…
We analyze a sample of 3,944 low-resolution (R ~ 2000) optical spectra from the Sloan Digital Sky Survey (SDSS), focusing on stars with effective temperatures 5800 < Teff < 6300 K, and distances from the Milky Way plane in excess of 5 kpc, and determine their abundances of Fe, Ca, and Mg. We followed the same methodology as in the previous paper in this series, deriving atmospheric parameters by chi2 minimization, but this time we obtained the abundances of individual elements by fitting their associated spectral lines. Distances were calculated from absolute magnitudes obtained by a statistic…
Heavy element abundances in extremely metal-poor stars provide strong constraints on the processes of forming these elements in the first stars. We attempt to determine precise abundances of strontium in a homogeneous sample of extremely metal-poor stars. The abundances of strontium in 54 very or extremely metal-poor stars, was redetermined by abandoning the local thermodynamic equilibrium (LTE) hypothesis, and fitting non-LTE (NLTE) profiles to the observed spectral lines. The corrected Sr abundances and previously obtained NLTE Ba abundances are compared to the predictions of several hypothe…
The presence of elements heavier than helium in white dwarf atmospheres is often a signpost for the existence of rocky objects that currently or previously orbited these stars. We have measured the abundances of various elements in the hydrogen-atmosphere white dwarfs G149-28 and NLTT 43806. In comparison with other white dwarfs with atmospheres polluted by heavy elements, NLTT 43806 is substantially enriched in aluminum but relatively poor in iron. We compare the relative abundances of Al and eight other heavy elements seen in NLTT 43806 with the elemental composition of bulk Earth, with simu…
Based on high-resolution spectral observations for a sample of very metal-poor stars, we investigate how well stellar chemical abundances can be derived with available theoretical methods and computational tools.
Taking advantage of the now available Gaia EDR3 parallaxes, we carry out an archival {\it Hubble Space Telescope} (HST) far ultraviolet spectroscopic analysis of 10 cataclysmic variable systems, including 5 carefully selected eclipsing systems. We obtain accurate white dwarf (WD) masses and temperatures, in excellent agreement with the masses for 4 of the eclipsing systems. For three systems in our sample, BD Pav, HS 2214, and TT Crt, we report the first robust masses for their WDs. We modeled the absorption lines to derive the WD chemical abundances and rotational velocities for each of the t…
Whether the higher occurrence of giant planets being hosted by metal-rich versus metal-poor stars results from formation or from "pollution" has been a question of intense debate. We present new patterns that emerge when planet/star systems are separated by stellar [Fe/H], and when systems with stellar companions are separated out. These differences can best be explained if the onset of high eccentricity planet migration is also a time when planet are sent into merge with the star. Planet migration into the star is likely a complementary explanation to the view that systems with higher initial…
High-resolution optical spectroscopy was conducted for the metal-poor post-AGB star CC Lyr to determine its chemical abundances and spectral line profiles. Our standard abundance analysis confirms its extremely low metallicity ([Fe/H]<-3.5) and a clear correlation between abundance ratios and the condensation temperature for 11 elements, indicating that dust depletion is the cause of the abundance anomaly of this object. The very low abundances of Sr and Ba, which are detected for the first time for this object, suggest that heavy neutron-capture elements are not significantly enhanced in this…
With the purpose of performing a homogeneous determination of elemental abundances for members of the Lupus T association, we analyzed three chemical elements: lithium, iron, and barium. The aims were: to derive the Li abundance for ~90% of known class II stars in the Lupus I, II, III, IV clouds; to perform chemical tagging of a region where few Fe abundance measurements have been obtained in the past, and no determination of the Ba content has been done up to now. We also investigated possible Ba enhancement, as this element has become increasingly interesting in the last years following the …
The aim of this study is to search for observational evidence of vertical iron stratification in the atmosphere of fourteen blue horizontal-branch (BHB) stars. We have found from our numerical simulations that five BHB stars: B22, B186 in the globular cluster NGC 288, WF2-820, WF2-2692 in M13 and B203 in M15 show clear signatures of the vertical stratification of iron whose abundance increases toward the lower atmosphere. Two other BHB stars (B334 in M15 and B176 in M92) also show possible iron stratification in their atmosphere. A dependence of the slope of iron stratification on the effectiv…
Abundances of Fe, Si, Ni, Ti, Na, Mg, Cu, Zn, Mn, Cr and Ca in the atmosphere of the K-dwarf HD 77338 are determined and discussed. HD 77338 hosts a hot Uranus-like planet and is currently the most metal-rich single star to host any planet. Determination of abundances was carried out in the framework of a self-consistent approach developed by Pavlenko et al. (2012). Abundances were computed iteratively by the program ABEL8, and the process converged after 4 iterations. We find that most elements follow the iron abundance, however some of the iron peak elements are found to be over-abundant in …
Using standard 1D-LTE model atmosphere analysis, we provide an in-depth investigation of iron abundance as derived from neutral and singly ionization iron lines (Fe {\scriptsize{I, II}}) in nearby star clusters. Specifically, we replicate the discrepancy regarding $Δ$[Fe/H], wherein the difference of Fe {\scriptsize{II}} - Fe {\scriptsize{I}} increases for stars of the same cluster with decreasing $T_\mathrm{eff}$, reaching an astonishing 1.0 dex at $T_\mathrm{eff}$ $\thicksim$ 4000 K. Previous studies have investigated this anomaly in the Pleiades and Hyades clusters with no concrete solution…
(abridged) The three most iron poor stars presently known ([Fe/H] equal to -5.96, -5.4 and -4.75) are carbon-rich, they are called C-Rich Ultra-Metal Poor Stars (CRUMPS). The origin of their peculiar surface abundances is not understood. We propose a synthetic view of the different models so far proposed to explain the peculiar abundances observed at the surface of the CRUMP stars. We deduce some expected trends based on nucleosynthetic arguments and look for signatures allowing to discriminate among models. We discuss the conditions for having CRUMP stars which are He-rich, i.e. with a mass f…
We explored the occurrence rate of small close-in planets among $\textit{Kepler}$ target stars as a function of the iron abundance and the stellar total velocity $V_\mathrm{tot}$. We estimated the occurrence rate of those planets by combining information from LAMOST and the California-$\textit{Kepler}$ Survey (CKS) and found that iron-poor stars exhibit an increase in the occurrence with $V_\mathrm{tot}$ from $f < 0.2$ planets per star at $ V_\mathrm{tot} < 30\ \mathrm{km~s}^{-1}$ to $f \sim 1.2$ at $V_\mathrm{tot} > 90\ \mathrm{km~s}^{-1}$. We suggest this planetary profusion may be a result …
