arXiv subjects

P. Bonifacio

Publications and source records attributed to P. Bonifacio.

At least 127 records · Page 7Linked to original sources

arXiv2014

Clues on the Galactic evolution of sulphur from star clusters

(Abridged) The abundances of alpha-elements are a powerful diagnostic of the star formation history and chemical evolution of a galaxy. Sulphur, being moderately volatile, can be reliably measured in the interstellar medium (ISM) of damped Ly-alpha galaxies and extragalactic HII regions. Measurements in stars of different metallicity in our Galaxy can then be readily compared to the abundances in external galaxies. Such a comparison is not possible for Si or Ca that suffer depletion onto dust in the ISM. Furthermore, studying sulphur is interesting because it probes nucleosynthetic conditions that are very different from those of O or Mg. The measurements in star clusters are a reliable tracers of the Galactic evolution of sulphur. We find NLTE=6.11+/-0.04 for M 4, NLTE=7.17+/-0.02 for NGC 2477, and NLTE=7.13+/-0.06 for NGC 5822. For the only star studied in Trumpler 5 we find A(S)NLTE=6.43+/-0.03 and A(S)LTE=6.94+/-0.05. Our measurements show that, by and large, the S abundances in Galactic clusters trace reliably those in field stars. The only possible exception is Trumpler 5, for which the NLTE sulphur abundance implies an [S/Fe] ratio lower by roughly 0.4 dex than observed in field stars of comparable metallicity, even though its LTE sulphur abundance is in line with abundances of field stars. Moreover the LTE sulphur abundance is consistent only with the abundance of another alpha-element, Mg, in the same star, while the low NLTE value is consistent with Si and Ca. The S abundances in our sample of stars in clusters imply that the clusters are chemically homogeneous for S within 0.05 dex.

astro-ph.SR↗

arXiv2014

Science Case and Requirements for the MOSAIC Concept for a Multi-Object Spectrograph for the European Extremely Large Telescope

Over the past 18 months we have revisited the science requirements for a multi-object spectrograph (MOS) for the European Extremely Large Telescope (E-ELT). These efforts span the full range of E-ELT science and include input from a broad cross-section of astronomers across the ESO partner countries. In this contribution we summarise the key cases relating to studies of high-redshift galaxies, galaxy evolution, and stellar populations, with a more expansive presentation of a new case relating to detection of exoplanets in stellar clusters. A general requirement is the need for two observational modes to best exploit the large (>40 sq. arcmin) patrol field of the E-ELT. The first mode ('high multiplex') requires integrated-light (or coarsely resolved) optical/near-IR spectroscopy of >100 objects simultaneously. The second ('high definition'), enabled by wide-field adaptive optics, requires spatially-resolved, near-IR of >10 objects/sub-fields. Within the context of the conceptual study for an ELT-MOS called MOSAIC, we summarise the top-level requirements from each case and introduce the next steps in the design process.

astro-ph.IM↗

arXiv2014

Abundances of lithium, oxygen, and sodium in the turn-off stars of Galactic globular cluster 47 Tuc

We aim to determine abundances of Li, O and Na in a sample of of 110 turn-off (TO) stars, in order to study the evolution of light elements in this cluster and to put our results in perspective with observations of other globular and open clusters, as well as with field stars. We use medium resolution spectra obtained with the GIRAFFE spectrograph at the ESO 8.2m Kueyen VLT telescope and use state of the art 1D model atmospheres and NLTE line transfer to determine the abundances. We also employ CO5BOLD hydrodynamical simulations to assess the impact of stellar granulation on the line formation and inferred abundances. Our results confirm the existence of Na-O abundance anti-correlation and hint towards a possible Li-O anti-correlation in the TO stars of 47 Tuc. We find no convincing evidence supporting the existence of Li-Na correlation. The obtained 3D NLTE mean lithium abundance in a sample of 94 TO stars where Li lines were detected reliably, $\langle A({\rm Li})_{\rm 3D~NLTE}\rangle = 1.78 \pm 0.18$ dex, appears to be significantly lower than what is observed in other globular clusters. At the same time, star-to-star spread in Li abundance is also larger than seen in other clusters. The highest Li abundance observed in 47 Tuc is about 0.1 dex lower than the lowest Li abundance observed among the un-depleted stars of the metal-poor open cluster NGC 2243. The lithium abundances in 47 Tuc, when put into context with observations in other clusters and field stars, suggest that stars that are more metal-rich than [FeH] \sim -1.0 experience significant lithium depletion during their lifetime on the main sequence, while the more metal-poor stars do not. Rather strikingly, our results suggest that initial lithium abundance with which the star was created may only depend on its age (the younger the star, the higher its Li content) and not on its metallicity.

astro-ph.SR↗

arXiv2014

High-resolution abundance analysis of very metal-poor r-I stars

Moderately r-process-enriched stars (r-I) are at least four times as common as those that are greatly enriched in r-process elements (r-II), and the abundances in their atmospheres are important tools for obtaining a better understanding of the nucleosynthesis processes responsible for the origin of the elements beyond the iron peak. The main aim of this work is to derive abundances for a sample of seven metal-poor stars with classified as r-I stars, to understand the role of these stars for constraining the astrophysical nucleosynthesis event(s) that is(are) responsible for the production of the r-process, and to investigate whether they differ, in any significant way, from the r-II stars. We carried out a detailed abundance analysis based on high-resolution spectra obtained with the VLT/UVES spectrograph. The OSMARCS LTE 1D model atmosphere grid was employed, along with the spectrum synthesis code Turbospectrum. We have derived abundances of light elements Li, C, and N, alpha-elements, odd-Z elements, iron-peak elements, and the trans-iron elements from the first peak, the second peak, the third peak, and the actinides regions. The results are compared with values for these elements for r-II and normal very and extremely metal-poor stars reported in the literature, ages based on radioactive chronometry are explored using different models, and a number of conclusions about the r-process and the r-I stars are presented. Hydrodynamical models were used for some elements, and general behaviors for the 3D corrections were presented.

astro-ph.SR↗

arXiv2014

A super lithium-rich red-clump star in the open cluster Trumpler 5

Context. The existence of lithium-rich low-mass red giant stars still represents a challenge for stellar evolution models. Stellar clusters are privileged environments for this kind of investigation. Aims. To investigate the chemical abundance pattern of the old open cluster Trumpler\,5, we observed a sample of four red-clump stars with high-resolution optical spectrographs. One of them (#3416) reveals extremely strong lithium lines in its spectrum. Methods. One-dimensional, local thermodynamic equilibrium analysis was performed on the spectra of the observed stars. A 3D-NLTE analysis was performed to derive the lithium abundance of star #3416. Results. Star #3416 is super Li-rich with A(Li)=3.75\,dex. The lack of $^6$Li enrichment ($^6$Li/$^7$Li$<$2%), the low carbon isotopic ratio ($^{12}$C/$^{13}$C=14$\pm$3), and the lack of evidence for radial velocity variation or enhanced rotational velocity ($v\sin i = 2.8\,$\kms) all suggest that lithium production has occurred in this star through the Cameron & Fowler mechanism. Conclusions. We identified a super Li-rich core helium-burning, red-clump star in an open cluster. Internal production is the most likely cause of the observed enrichment. Given the expected short duration of a star's Li-rich phase, enrichment is likely to have occurred at the red clump or in the immediately preceding phases, namely during the He-flash at the tip of the red giant branch (RGB) or while ascending the brightest portion of the RGB.

astro-ph.SR↗

arXiv2014

The Gaia-ESO Survey: processing of the FLAMES-UVES spectra

The Gaia-ESO Survey is a large public spectroscopic survey that aims to derive radial velocities and fundamental parameters of about 10^5 Milky Way stars in the field and in clusters. Observations are carried out with the multi-object optical spectrograph FLAMES, using simultaneously the medium resolution (R~20,000) GIRAFFE spectrograph and the high resolution (R~47,000) UVES spectrograph. In this paper, we describe the methods and the software used for the data reduction, the derivation of the radial velocities, and the quality control of the FLAMES-UVES spectra. Data reduction has been performed using a workflow specifically developed for this project. This workflow runs the ESO public pipeline optimizing the data reduction for the Gaia-ESO Survey, performs automatically sky subtraction, barycentric correction and normalisation, and calculates radial velocities and a first guess of the rotational velocities. The quality control is performed using the output parameters from the ESO pipeline, by a visual inspection of the spectra and by the analysis of the signal-to-noise ratio of the spectra. Using the observations of the first 18 months, specifically targets observed multiple times at different epochs, stars observed with both GIRAFFE and UVES, and observations of radial velocity standards, we estimated the precision and the accuracy of the radial velocities. The statistical error on the radial velocities is sigma~0.4 km s^-1 and is mainly due to uncertainties in the zero point of the wavelength calibration. However, we found a systematic bias with respect to the GIRAFFE spectra (~0.9 km s^-1) and to the radial velocities of the standard stars (~0.5 kms^-1) retrieved from the literature. This bias will be corrected in the future data releases, when a common zero point for all the setups and instruments used for the survey will be established.

astro-ph.IM↗

arXiv2014

Light element abundances in the Galactic globular cluster 47 Tuc

It is very likely that most (perhaps all) Galactic globular clusters (GGCs) have experienced two or even more star-formation episodes. This is indicated, in particular, by peculiar chemical composition of the cluster stars which show large variation in the abundances of light elements, such as Li, C, N, O, Na, Mg, and Al. We studied the abundances of Na, Mg, and Al in the atmospheres of 103 red giant branch stars located below (49 stars) and above (54 stars) the RGB bump in the GGC 47 Tuc. Our results show that the spread of [Na/Fe] abundance ratios is about three times larger than that of [Mg/Fe]. Our data also confirm the existence of weak Na-Al correlation, similar to the one observed in other GGCs. At the same time, we find no evidence for the existence of three populations of stars characterized with different abundances of aluminum, as reported recently by Carretta et al. (2013).

astro-ph.SR↗

arXiv2014

The Be-test in the Li-rich star \#1657 of NGC 6397: evidence for Li-flash in RGB stars?

The Li-rich turn-off star in the globular cluster NGC 6397 could represent the smoking gun for some very rare episode of Li enrichment in globular clusters. We aim to understand the nature of the Li enrichment by performing a spectroscopic analysis of the star, in particular of its beryllium (Be) abundance, and by investigating its binary nature. We observe the near UV region where the Beii resonance doublet and the NH bands are located. We could not detect the Beii lines and derive an upper limit of log (Be/H)< -12.2, that is consistent with the Be observed in other stars of the cluster. We could detect a weak G-band, which implies a mild carbon enhancement [C/Fe]$+0.4\pm0.2$. We could not detect the UV NH band, and we derive an upper limit [N/Fe]$< 0.0$. For oxygen we could notdetect any of the near UV OH lines, which implies that oxygen cannot be strongly enhanced in this star. This is consistent with the detection of the Oi triplet at 777nm, which is consistent with [O/Fe]~0.5. Combining the UVES and Mike data, we could not detect any variation in the radial velocity greater than 0.95 kms$^{-1}$ over 8 years. The chemical composition of the star strongly resembles that of `first generation' NGC6397 stars, with the huge Li as the only deviating abundance. Not detecting Be rules out two possible explanations of the Li overabundance: capture of a substellar body and spallation caused by a nearby type II SNe. Discrepancies are also found with respect to other accretion scenarios,except for contamination by the ejecta of a star that has undergone the RGB Li-flash.

astro-ph.SR↗

arXiv2014

Three planetary companions around M67 stars

For the past six years we have carried out a search for massive planets around main sequence and evolved stars in the open cluster (OC) M67, using radial velocity (RV) measurements obtained with HARPS at ESO (La Silla), SOPHIE at OHP and HRS at HET. Additional RV data come from CORALIE at the Euler Swiss Telescope. We aim to perform a long-term study on giant planet formation in open clusters and determine how it depends on stellar mass and chemical composition. We report the detection of three new extrasolar planets: two in orbit around the two G dwarfs YBP1194 and YBP1514, and one around the evolved star S364. The orbital solution for YBP1194 yields a period of 6.9 days, an eccentricity of 0.24, and a minimum mass of 0.34 Mj. YBP1514 shows periodic RV variations of 5.1 days, a minimum mass of 0.40 Mj, and an eccentricity of 0.39. The best Keplerian solution for S364 yields a period of 121.7 days, an eccentricity of 0.35 and a minimum mass of 1.54 Mj. An analysis of H_alpha core flux measurements as well as of the line bisectors spans revealed no correlation with the RV periods, indicating that the RV variations are best explained by the presence of a planetary companion. Remarkably, YBP1194 is one of the best solar twins identified so far, and YBP1194b is the first planet found around a solar twin that belongs to a stellar cluster. In contrast with early reports and in agreement with recent findings, our results show that massive planets around stars of open clusters are as frequent as those around field stars.

astro-ph.SR↗

arXiv2013

MyGIsFOS: an automated code for parameter determination and detailed abundance analysis in cool stars

The current and planned high-resolution, high-multiplexity stellar spectroscopic surveys, as well as the swelling amount of under-utilized data present in public archives have led to an increasing number of efforts to automate the crucial but slow process to retrieve stellar parameters and chemical abundances from spectra. We present MyGIsFOS, a code designed to derive atmospheric parameters and detailed stellar abundances from medium - high resolution spectra of cool (FGK) stars. We describe the general structure and workings of the code, present analyses of a number of well studied stars representative of the parameter space MyGIsFOS is designed to cover, and examples of the exploitation of MyGIsFOS very fast analysis to assess uncertainties through Montecarlo tests. MyGIsFOS aims to reproduce a ``traditional'' manual analysis by fitting spectral features for different elements against a precomputed grid of synthetic spectra. Fe I and Fe II lines can be employed to determine temperature, gravity, microturbulence, and metallicity by iteratively minimizing the dependence of Fe I abundance from line lower energy and equivalent width, and imposing Fe I - Fe II ionization equilibrium. Once parameters are retrieved, detailed chemical abundances are measured from lines of other elements. MyGIsFOS replicates closely the results obtained in similar analyses on a set of well known stars. It is also quite fast, performing a full parameter determination and detailed abundance analysis in about two minutes per star on a mainstream desktop computer. Currently, its preferred field of application are high-resolution and/or large spectral coverage data (e.g UVES, X-Shooter, HARPS, Sophie).

astro-ph.IM↗

arXiv2013

Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars. III. Line formation in the atmospheres of giants located close to the base of RGB

We utilize state-of-the-art 3D hydrodynamical and classical 1D stellar model atmospheres to study the influence of convection on the formation properties of various atomic and molecular spectral lines in the atmospheres of four red giant stars, located close to the base of the red giant branch, RGB ($T_{\mathrm eff}\approx5000$ K, $\log g=2.5$), and characterized by four different metallicities, [M/H] = 0.0, -1.0, -2.0, -3.0. The role of convection in the spectral line formation is assessed with the aid of abundance corrections, i.e., the differences in abundances predicted for a given equivalent width of a particular spectral line with the 3D and 1D model atmospheres. We find that for lines of certain neutral atoms the abundance corrections strongly depend both on metallicity of a given model atmosphere and the line excitation potential. While abundance corrections for all lines of both neutral and ionized elements tend to be small at solar metallicity, for lines of neutral elements with low ionization potential and low-to-intermediate $χ$ they quickly increase with decreasing metallicity, reaching in their extremes to -0.6...-0.8 dex. In all such cases the large abundance corrections are due to horizontal temperature fluctuations in the 3D hydrodynamical models. Abundance corrections of molecular lines are very sensitive to metallicity of the underlying model atmosphere and may be larger (in absolute value) than -0.5 dex at [M/H] = -3.0 (-1.5 dex in the case of CO). We also find that an approximate treatment of scattering in the 3D model calculations leads to the abundance corrections that are altered by less than ~0.1 dex, both for atomic and molecular (CO) lines, with respect to the model where scattering is treated as true absorption throughout the entire atmosphere, with the largest differences for the resonance and low-excitation lines.

astro-ph.SR↗

arXiv2013

TOPoS: I. Survey design and analysis of the first sample

The metal-weak tail of the metallicity distribution function (MDF) of the Galactic Halo stars contains crucial information on the formation mode of the first generation of stars. To determine this observationally, it is necessary to observe large numbers of extremely metal-poor stars. We present here the Turn-Off Primordial Stars survey (TOPoS) that is conducted as an ESO Large Programme at the VLT. This project has {four} main goals: (i) to understand the formation of low-mass stars in a low-metallicity gas: determine the metal-weak tail of the halo MDF below [M/H]=-3.5. In particular, we aim at determining the critical metallicity, that is the lowest metallicity sufficient for the formation of low-mass stars; (ii) to determine the relative abundance of the elements in extremely metal-poor stars, which are the signature of the massive first stars; (iii) to determine the trend of the lithium abundance at the time when the Galaxy formed; and (iv) to derive the fraction of C-enhanced extremely metal-poor stars with respect to normal extremely metal-poor stars. The large number of stars observed in the SDSS provides a good sample of candidates of stars at extremely low metallicity. Candidates with turn-off colours down to magnitude g=20 were selected from the low-resolution spectra of SDSS by means of an automated procedure. X-Shooter has the potential of performing the necessary follow-up spectroscopy, providing accurate metallicities and abundance ratios for several key elements for these stars. We here present the stellar parameters of the first set of stars. The nineteen stars range in iron abundance between -4.1 and -2.9 dex relative to the Sun. Two stars have a high radial velocity and, according to our estimate of their kinematics, appear to be marginally bound to the Galaxy and are possibly accreted from another galaxy.

astro-ph.SR↗

arXiv2013

Fundamental constants and high resolution spectroscopy

Absorption-line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine-structure constant, alpha, and the proton-to-electron mass ratio, mu = m_p/m_e, as measured in remote regions of the Universe to their value today on Earth. In recent years, some evidence has emerged of small temporal and also spatial variations in alpha on cosmological scales which may reach a fractional level of 10 ppm . We are conducting a Large Programme of observations with VLT UVES to explore these variations. We here provide a general overview of the Large Programme and report on the first results for these two constants, discussed in detail in Molaro et al. and Rahmani et al. A stringent bound for Delta(alpha)/Alpha is obtained for the absorber at_abs = 1.6919 towards HE 2217-2818. The absorption profile is complex with several very narrow features, and is modeled with 32 velocity components. The relative variation in alpha in this system is +1.3+-2.4_{stat}+-1.0_{sys} ppm if Al II lambda 1670AA and three Fe II transitions are used, and +1.1+-2.6_{stat} ppm in a lightly different analysis with only Fe II transitions used. The expectation at this sky position of the recently-reported dipolar variation of alpha is (3.2--5.4)+-1.7 ppm depending on dipole model. This constraint of Delta(alpha)/alpha at face value is not supporting this expectation but is not inconsistent with it at the 3 sigma level. For the proton-to-electron mass ratio the analysis of the H_2 absorption lines of the z_{abs}~2.4018 damped Ly alpha system towards HE 0027- 1836 provides Delta(mu)/mu = (-7.6 +- 8.1_{stat} +- 6.3_{sys}) ppm which is also consistent with a null variation. (abridged)

astro-ph.CO↗

arXiv2013

Isotope Spectroscopy

The measurement of isotopic ratios provides a privileged insight both into nucleosynthesis and into the mechanisms operating in stellar envelopes, such as gravitational settling. In this article, we give a few examples of how isotopic ratios can be determined from high-resolution, high-quality stellar spectra. We consider examples of the lightest elements, H and He, for which the isotopic shifts are very large and easily measurable, and examples of heavier elements for which the determination of isotopic ratios is more difficult. The presence of 6Li in the stellar atmospheres causes a subtle extra depression in the red wing of the 7Li 670.7 nm doublet which can only be detected in spectra of the highest quality. But even with the best spectra, the derived $^6$Li abundance can only be as good as the synthetic spectra used for their interpretation. It is now known that 3D non-LTE modelling of the lithium spectral line profiles is necessary to account properly for the intrinsic line asymmetry, which is produced by convective flows in the atmospheres of cool stars, and can mimic the presence of 6Li. We also discuss briefly the case of the carbon isotopic ratio in metal-poor stars, and provide a new determination of the nickel isotopic ratios in the solar atmosphere.

astro-ph.SR↗

arXiv2013

X-Shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars

The extremely metal-poor stars are the direct descendants of the first generation stars. They carry the chemical signature of the pristine Universe at the time they formed, shortly after the Big Bang. We aim to derive information about extremely metal-poor stars from their observed spectra. Four extremely metal-poor stars were selected from the Sloan Digital Sky Survey (SDSS) and observed during the guaranteed observing time of X-Shooter. The X-Shooter spectra were analysed using an automatic code, MyGIsFOS, which is based on a traditional analysis method. It makes use of a synthetic grid computed from one-dimensional, plane-parallel, hydrostatic model atmospheres. The low metallicity derived from the SDSS spectra is confirmed here. Two kinds of stars are found. Two stars are confirmed to be extremely metal-poor, with no evidence of any enhancement in carbon. The two other stars are strongly enhanced in carbon. We could not derive iron abundance for one of them, while [Ca/H] is below -4.5. Two of the stars are members of the rare population of extremely metal-poor stars low in alpha elements.

astro-ph.GA↗

arXiv2013

The influence of convection on the atmospheric structures and observable properties of red giant stars

During the recent years significant progress has been made in the modeling of red giant atmospheres with the aid of 3D hydrodynamical model atmosphere codes. In this contribution we provide an overview of selected results obtained in this context by utilizing 3D hydrodynamical CO5BOLD stellar model atmospheres. Hydrodynamical simulations show that convective motions lead to significant differences in the atmospheric structures of red giants with respect to those predicted by the classical 1D model atmospheres. Results of these simulations also show that in certain cases 1D models fail to reproduce even the average properties of the 3D hydrodynamical models, such as P-T profiles. Large horizontal temperature fluctuations in the 3D model atmospheres, as well as differences between the temperature profiles of the average <3D> and 1D models, lead to large discrepancies in the strengths of spectral lines predicted by the 3D and 1D model atmospheres. This is especially important in models at lowest metallicities ([M/H]<-2.0) where the 3D-1D abundance differences may reach (or even exceed) -0.6 dex for lines of neutral atoms and molecules. We also discuss several simplifications and numerical aspects involved in the present 3D hydrodynamical modeling of red giant atmospheres, and briefly address several issues where urgent progress may be needed.

astro-ph.SR↗

arXiv2013

The UVES Large Program for Testing Fundamental Physics: I Bounds on a change in alpha towards quasar HE 2217-2818

Absorption line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, α, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations of α on cosmological scales which may reach a fractional level of ~ 10 ppm (parts per million). To test these claims we are conducting a Large Program with the VLT UVES . We are obtaining high-resolution (R ~ 60000 and high signal-to-noise ratio (S/N ~ 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this Program, that of HE 2217-2818. We apply the Many Multiplet method to measure α in 5 absorption systems towards this quasar: zabs = 0.7866, 0.9424, 1.5558, 1.6279 and 1.6919. The most precise result is obtained for the absorber at zabs = 1.6919 where 3 Fe II transitions and Al II λ1670 have high S/N and provide a wide range of sensitivities to α. The absorption profile is complex, with several very narrow features, and requires 32 velocity components to be fitted to the data. Our final result for the relative variation in α in this system is Deltaα/α = +1.3 +/- 2.4stat +/- 1.0sys ppm. This is one of the tightest current bounds on α variation from an individual absorber. The absorbers towards quasar HE 2217-2818 reveal no evidence for variation in α at the 3 ppm precision level (1σ confidence). If the recently reported 10 ppm dipolar variation of α across the sky were correct, the expectation at this sky position is (3.2-5.4) +/-1.7 ppm depending on dipole model used . Our constraint of Deltaα/α=+1.3+/-2.4stat +/-1.0sys ppm is not inconsistent with this expectation.

astro-ph.CO↗

arXiv2013

Spectral line asymmetries in the metal-poor red giant HD 122563: CO5BOLD predictions versus observations

We study the influence of convection on the asymmetries and Doppler shifts of Fe I spectral lines in the metal-poor red giant HD 122563. To this end, we compute theoretical Fe I line shifts and line bisectors using 3D hydrodynamical model atmosphere of HD 122563 calculated with the CO5BOLD code. We then make a detailed comparison of the theoretical line shifts and bisectors with those derived from the high quality HARPS spectrum of HD 122563 taken from the ESO Science Archive Facility (R = 115 000, average signal-to-noise ratio, S/N = 310). In general, we find a good agreement between the theoretically predicted and observed Doppler shifts of Fe I line cores, with somewhat larger discrepancies seen in the case of weaker (equivalent width W < 5 pm) and stronger lines (W > 11 pm). Both observed and theoretical coreshifts cover a range between 0 and -1 km/s, with increasingly stronger blueshifts for weaker lines and slight hints of a coreshift dependence on wavelength. Theoretical bisectors reproduce the observed ones reasonably well too, however, theoretical bisectors of the weak red (lambda > 600 nm) Fe I lines have blueshifts that are by up to 200 m/s larger than observed. The obtained results therefore suggest that the current CO5BOLD models are capable of reproducing the large-scale velocity fields in the atmosphere of HD 122563 suficiently well. Nevertheless, further efforts are needed in order to understand the physical reasons behind the discrepancies in theoretical predictions and observed properties of the weakest and strongest Fe I lines.

astro-ph.SR↗