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Context. Most globular clusters are believed to host a single stellar population. They can thus be considered a good place to study the Spite plateau and to search for possible evolutionary modifications of the Li content.

Context. Solar-like oscillations have been observed in numerous red giants from ground and from space. An important question arises: could we expect to detect non-radial modes probing the internal structure of these stars?

Context. In recent years, the solar chemical abundances have been studied in considerable detail because of discrepant values of solar metallicity inferred from different indicators, i.e., on the one hand, the “sub-solar” photospheric abundances resulting from spectroscopic chemical composition analyses with the aid of 3D hydrodynamical models of the solar atmosphere, and, on the other hand, the high metallicity inferred by helioseismology.

Context. The solar oxygen abundance has undergone a major downward revision in the past decade, the most noticeable one being the update including 3D hydrodynamical simulations to model the solar photosphere. Up to now, such an analysis has only been carried out by one group using one radiation-hydrodynamics code.

Context. The stable element hafnium (Hf) and the radioactive element thorium (Th) were recently suggested as a suitable pair for radioactive dating of stars. The applicability of this elemental pair needs to be established for stellar spectroscopy.

Aims.We determine the solar abundance of phosphorus using CO5BOLD 3D hydrodynamic model atmospheres.

Context.Line asymmetries are generated by convective Doppler shifts in stellar atmospheres, especially in metal-poor stars, where convective motions penetrate to higher atmospheric levels. Such asymmetries are usually neglected in abundance analyses. The determination of the $\rm ^6Li/^7Li$isotopic ratio is prone to suffering from such asymmetries, as the contribution of 6Li is a slight blending reinforcement of the red wing of each component of the corresponding 7Li line, with respect to its blue wing.

Context.It seems that the recently identified class of pulsating stars, the γDor type-variables, includes objects with different metal abundances and a large percentage of binaries.

Context.Unlike silicon and calcium, sulphur is an α-element that does not form dust. Some of the available observations of the evolution of sulphur with metallicity indicate an increased scatter of sulphur-to-iron ratios at low metallicities or even a bimodal distribution, with some stars showing constant S/Fe at all metallicities and others showing an increasing S/Fe ratio with decreasing metallicity. In metal-poor stars S ilines of Multiplet 1 at 920 nm are not yet too weak to permit the measurement of the sulphur abundance A(S); however, in ground-based observations they are severely affected by telluric lines.

Context.Sulphur is an element which is formed in the α-process and is easily measured in the gaseous phase in external galaxies. Since it does not form dust, it is the preferred indicator for α-elements, rather than Si or Mg, for which dust corrections are necessary. The measurement of the sulphur abundance in stars is not an easy task, relying mainly on high excitation lines with non-negligible deviations from LTE. The 1082 nm sulphur forbidden transition is less sensitive to departures from LTE and is less dependent on temperature uncertainties than other sulphur lines usually employed as abundance indicators. Therefore it should provide a more robust abundance diagnostics.

We examine the large sample of λBoo candidates collected in Table 1 of Gerbaldi et al. ([CITE]) to see how many of them show composite spectra. Of the 132 λBoo candidates we identify 22 which definitely show composite spectra and 15 more for which there are good reasons to suspect a composite spectrum. The percentage of λBoo candidates with composite spectra is therefore >17% and possibly considerably higher. For such stars the λBoo classification should be reconsidered taking into account the fact that their spectra are composite. We argue that some of the underabundances reported in the literature may simply be the result of the failure to consider the composite nature of the spectra. This leads to the legitimate suspicion that some, if not all, the λBoo candidates are not chemically peculiar at all. A thorough analysis of even a single one of the λBoo candidates with composite spectra, in which the composite nature of the spectrum is duly considered, which would demonstrate that the chemical peculiarities persist, would clear the doubt we presently have that the stars with composite spectra may not be λBoo stars at all.

We describe an automatic procedure for determining abundances from high resolution spectra. Such procedures are becoming increasingly important as large amounts of data are delivered from 8 m telescopes and their high-multiplexing fiber facilities, such as FLAMES on ESO-VLT. The present procedure is specifically targeted for the analysis of spectra of giants in the Sgr dSph; however, the procedure may be, in principle, tailored to analyse stars of any type. Emphasis is placed on the algorithms and on the stability of the method; the external accuracy rests, ultimately, on the reliability of the theoretical models (model-atmospheres, synthetic spectra) used to interpret the data. Comparison of the results of the procedure with the results of a traditional analysis for 12 Sgr giants shows that abundances accurate at the level of 0.2 dex, comparable with that of traditional analysis of the same spectra, may be derived in a fast and efficient way. Such automatic procedures are not meant to replace the traditional abundance analysis, but as an aid to extract rapidly a good deal of the information contained in the spectra.

We derive an intrinsic colour calibration for F–K stars using broad band Johnson colours and line indices KPand $HP2$. Through this calibration we can determine $E(B-V)$of an individual star within 0.03 mag. The $E(B-V)$values thus derived are in excellent agreement with those derived from Strömgren photometry through the Schuster & Nissen (1989) calibration. The agreement is also good with the reddening maps of Burstein & Heiles (1982) and Schlegel et al. (1998), although in this case there exists a small offset of about 0.01 mag. This calibration may be applied to the large body of data of the HK survey extension which will be published in the near future.

Some insight on the first generation of stars can be obtained from the chemical composition of their direct descendants, extremely metal‐poor stars (EMP), with metallicity less than or equal to 1/1000 of the solar metallicity. Such stars are exceedingly rare, the most successful surveys, for this purpose, have so far provided only about 100 stars with 1/1000 the solar metallicity and 4 stars with about 1/10000 of the solar metallicity. The Sloan Digital Sky Survey has the potential to provide a large number of candidates of extremely low metallicity. X‐shooter has the unique capability of performing the necessary follow‐up spectroscopy providing accurate metallicities and abundance ratios for several elements (Mg, Al, Ca, Ti, Cr, Sr,...) for EMP candidates. We here report on the results for the first two stars observed in the course of our Franco‐Italian X‐shooter GTO. The two stars were targeted to be of metallicity around –3.0, the analysis of the X‐shooter spectra showed them to be of metallicity around –2.0, but with a low αto iron ratio, which explains the underestimate of the metallicity from the SDSS spectra. The efficiency of X‐shooter allows an in situstudy of the outer halo, for the two stars studied here we estimate distances of 3.9 and 9.1 kpc, these are likely the most distant dwarf stars studied in detail to date (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Zirconium (Zr), together with strontium and yttrium, is an important element in the understanding of the Galactic nucleosynthesis. In fact, the triad Sr‐Y‐Zr constitutes the first peak of s‐process elements. Despite its general relevance not many studies of the solar abundance of Zr were conducted. We derive the zirconium abundance in the solar photosphere with the same CO5BOLD hydrodynamical model of the solar atmosphere that we previously used to investigate the abundances of C‐N‐O. We review the zirconium lines available in the observed solar spectra and select a sample of lines to determine the zirconium abundance, considering lines of neutral and singly ionised zirconium. We apply different line profile fitting strategies for a reliable analysis of Zr lines that are blended by lines of other elements. The abundance obtained from lines of neutral zirconium is very uncertain because these lines are commonly blended and weak in the solar spectrum. However, we believe that some lines of ionised zirconium are reliable abundance indicators. Restricting the set to Zr II lines, from the CO5BOLD 3D model atmosphere we derive A(Zr) = 2.62 ± 0.06, where the quoted error is the RMS line‐to‐line scatter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Sulphur is a volatile αelement which is not locked into dust grains in the interstellar medium ISM. Hence, its abundance does not need to be corrected for dust depletion when comparing the ISM to the stellar atmospheres. The abundance of sulphur in the photosphere of metalpoor stars is a matter of debate: according to some authors, [SFe] versus [FeH] forms a plateau at low metallicity, while, according to other studies, there is a large scatter or perhaps a bimodal distribution. In metalpoor stars sulphur is detectable by its lines of multiplet 1 at 920 nm, but this range is heavily contaminated by telluric absorptions, and one line of the multiplet is blended by the hydrogen Paschen ζline. We study the possibility of using multiplet 3 at 1045 nm for deriving the sulphur abundance because this range, now observable at the VLT with the infrared spectrograph CRIRES, is little contaminated by telluric absorption and not affected by blends at least in metalpoor stars. We compare the abundances derived from multiplets 1 and 3, taking into account NLTE corrections and 3D effects. Here we present the results for a sample of four stars, although the scatter is less pronounced than in previous analysis, we cannot find a plateau in [SFe], and confirm the scatter of the sulphur abundance at low metallicity © 2010 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim

Context. The detailed chemical abundances of extremely metal-poor (EMP) stars are key guides to understanding the early chemical evolution of the Galaxy. Most existing data, however, treat giant stars that may have experienced internal mixing later.Aims. We aim to compare the results for giants with new, accurate abundances for all observable elements in 18?EMP turnoff stars.Methods. VLT/UVES spectra at R ~ 45?000 and S/N ~ 130?per?pixel (???330-1000?nm) are analysed with OSMARCS model atmospheres and the TURBOSPECTRUM code to derive abundances for C, Mg, Si, Ca, Sc, Ti, Cr, Mn, Co, Ni, Zn, Sr, and?Ba.Results. For Ca, Ni, Sr, and Ba, we find excellent consistency with our earlier sample of EMP?giants, at all metallicities. However, our abundances of C, Sc, Ti, Cr, Mn and Co are ~0.2?dex larger than in giants of similar metallicity. Mg and Si?abundances are ~0.2?dex lower (the giant [Mg/Fe]?values are slightly revised), while Zn is again ~0.4?dex higher than in giants of similar?[Fe/H] (6?stars only).Conclusions. For C, the dwarf/giant discrepancy could possibly have an astrophysical cause, but for the other elements it must arise from shortcomings in the analysis. Approximate computations of granulation (3D)?effects yield smaller corrections for giants than for dwarfs, but suggest that this is an unlikely explanation, except perhaps for C, Cr, and Mn. NLTE?computations for Na and Al provide consistent abundances between dwarfs and giants, unlike the LTE?results, and would be highly desirable for the other discrepant elements as well. Meanwhile, we recommend using the giant abundances as reference data for Galactic chemical evolution models.

Context. The light elements Li, O, Na, Al, and Mg are known to show star-to-star variations in the globular clusters 47?Tuc and NGC?6752. Such variations are interpreted as coming from processing in a previous generation of stars. Aims. In this paper we investigate the abundances of the ?-element sulfur, for which no previous measurements exist. In fact this element has not been investigated in any Galactic globular cluster so far. The only globular cluster for which such measurements are available is Terzan 7, which belongs to the Sgr dSph. Methods. We use high-resolution spectra of the S?i Mult.?1, acquired with the UVES spectrograph at the 8.2?m VLT-Kueyen telescope, for turn-off and giant stars in the two globular clusters. The spectra were analysed making use of ATLAS static plane parallel model atmospheres and SYNTHE spectrum synthesis. We also compute 3D corrections from CO5BOLD?hydrodynamic models and apply corrections due to NLTE effects taken from the literature. Results. In the cluster NGC?6752 sulfur has been measured only in four subgiant stars. We find no significant star-to-star scatter and a mean ?[S/Fe]? = +0.49 ? 0.15, consistent with what is observed in field stars of the same metallicity. In the cluster 47?Tuc we measured S in 4 turn-off and 5 subgiant stars with a mean ?[S/Fe]? = +0.18 ? 0.14. While this result is compatible with no star-to-star scatter we notice a statistically significant correlation of the sulfur abundance with the sodium abundance and a tentative correlation with the silicon abundance. Conclusions. The sulfur-sodium correlation is not easily explained in terms of nucleosynthesis. An origin due to atomic diffusion can be easily dismissed. The correlation cannot be easily dismissed either, in view of its statistical significance, until better data for more stars is available.

Context. Europium is an almost pure r-process element, which may be useful as a reference in nucleocosmochronology.Aims. Determine the photospheric solar abundance using CO5BOLD? 3D?hydrodynamical model atmospheres.Methods. Disc-centre and integrated-flux observed solar spectra are used. The europium abundance is derived using equivalent-width measurements. As a reference, one-dimensional model atmospheres are in addition used.Results. The europium photospheric solar abundance (0.52 ? 0.02) agrees with previous determinations. We determine the photospheric isotopic fraction of 151Eu?to be 49% ? 2.3% using the intensity spectra, and 50% ? 2.3% using the flux spectra. This compares well to the meteoritic isotopic fraction 47.8%. We explore 3D?corrections for dwarfs and sub-giants in the temperature range ~5000?K to ~6500?K and solar and 1/10-solar metallicities and find them to be negligible for all models investigated.Conclusions. Our photospheric Eu?abundance agrees well with previous determinations based on 1D?models. This is in line with our conclusion that 3D?effects for this element are negligible in the case of the Sun.

Context.Unevolved metal-poor stars constitute a fossil record of the early Galaxy, and can provide invaluable information on the properties of the first generations of stars.?Binary systems also provide direct information on the stellar masses of their member stars.Aims.The purpose of this investigation is a detailed abundance study of the double-lined spectroscopic binary CS?22876-032, which comprises the two most metal-poor dwarfs known. Methods.We used high-resolution, high-S/N ratio spectra from the UVES spectrograph at the ESO VLT telescope. Long-term radial-velocity measurements and broad-band photometry allowed us to determine improved orbital elements and stellar parameters for both components. We used OSMARCS 1D?models and the turbospectrum spectral synthesis code to determine the abundances of Li, O, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co and Ni. We also used the CO5BOLD?model atmosphere code to compute the 3D?abundance corrections, notably for Li?and O.Results.We find a metallicity of [Fe/H] ~ -3.6 for both stars, using 1D?models with 3D?corrections of ~-0.1?dex from averaged 3D?models. We determine the oxygen abundance from the near-UV OH bands; the 3D?corrections are large, -1 and -1.5?dex for the secondary and primary respectively, and yield [O/Fe] ~ 0.8, close to the high-quality results obtained from the [OI]?630?nm line in metal-poor giants. Other [ ?/Fe] ratios are consistent with those measured in other dwarfs and giants with similar [Fe/H], although Ca and Si are somewhat low ([X/Fe] ? 0). Other element ratios follow those of other halo stars. The Li?abundance of the primary star is consistent with the Spite plateau, but the secondary shows a lower abundance; 3D?corrections are small. Conclusions.The Li?abundance in the primary star supports the extension of the Spite Plateau value at the lowest metallicities, without any decrease. The low abundance in the secondary star could be explained by endogenic Li?depletion, due to its cooler temperature. If this is not the case, another, yet unknown mechanism may be causing increased scatter in A(Li) at the lowest metallicities.

We derive an intrinsic colour calibration for F-K stars using broad band Johnson colours and line indices $KP$ and $HP2$ . Through this calibration we can determine $E(B-V)$ of an individual star within 0.03 mag. The $E(B-V)$ values thus derived are in excellent agreement with those derived from Strömgren photometry through the Schuster & Nissen ([CITE]) calibration. The agreement is also good with the reddening maps of Burstein & Heiles ([CITE]) and Schlegel et al. ([CITE]), although in this case there exists a small offset of about 0.01 mag. This calibration may be applied to the large body of data of the HK survey extension which will be published in the near future.

Sulphur (S) is a non-refractory α-element that is not locked into dust grains in the interstellar medium. Thus no correction to the measured, interstellar sulphur abundance is needed and it can be readily compared to the S content in stellar photospheres. Here we present the first measurement of sulphur in the metal poor globular cluster (GC) NGC 6397, as detected in a MIKE/Magellan high signal-to-noise, high-resolution spectrum of one red giant star. While abundance ratios of sulphur are available for a larger number of Galactic stars down to an [Fe/H] of  ~  −3.5 dex, no measurements in globular clusters more metal poor than  −1.5 dex have been reported so far. We find aNLTE, 3-D abundance ratio of [S/Fe] = +0.52  ±  0.20 (stat.)  ± 0.08 (sys.), based on theS I, Multiplet 1 line at 9212.8 Å. This value is consistent with a Galactic halo plateau as typical of other α-elements in GCs and field stars, but we cannot rule out its membership with a second branch of increasing [S/Fe] with decreasing [Fe/H], claimed in the literature, which leads to a large scatter at metallicities around  − 2 dex. The [S/Mg] and [S/Ca] ratios in this star are compatible with a Solar value to within the (large) uncertainties. Despite the very large scatter in these ratios across Galactic stars between literature samples, this indicates that sulphur traces the chemical imprints of the other α-elements in metal poor GCs. Combined with its moderate sodium abundance ([S/Na]NLTE= 0.48), the [S/Fe] ratio in this GC extends a global, positive S-Na correlation that is not seen in field stars and might indicate that proton-capture reactions contributed to the production of sulphur in the (metal poor) early GC environments.

Context.Extremely metal-poor stars (EMP) are very rare objects that hold in their atmospheres the fossil record of the chemical composition of the early phases of Galactic evolution. Finding these objects and determining their chemical composition provides important constraints on these early phases.

Context.As a galaxy evolves, its chemical composition changes and the abundance ratios of different elements are powerful probes of the underlying evolutionary processes. Phosphorous is an element whose evolution has remained quite elusive until now, because it is difficult to detect in cool stars. The infrared weak P ilines of the multiplet 1, at 1050−1082 nm, are the most reliable indicators of the presence of phosphorus. The availability of CRIRES at VLT has permitted access to this wavelength range in stellar spectra.

Context.Precise S abundances are important in the study of the early chemical evolution of the Galaxy. In particular the site of the formation remains uncertain because, at low metallicity, the trend of this α-element versus [Fe/H] remains unclear. Moreover, although sulfur is not bound significantly in dust grains in the ISM, it seems to behave differently in DLAs and old metal-poor stars.

Context.Copper is an element whose interesting evolution with metallicity is not fully understood. Observations of copper abundances rely on a very limited number of lines, the strongest are the Cu i lines of Mult. 1 at 324.7 nm and 327.3 nm which can be measured even at extremely low metallicities.

Context.The primordial nature of the Spite plateau is at odds with the WMAP satellite measurements, implying a primordial Li production at least three times higher than observed. It has also been suggested that A(Li) might exhibit a positive correlation with metallicity below [Fe/H]  ~  −2.5. Previous samples studied comprised few stars below [Fe/H] =  −3.

Context. Oxygen is the third most common element in the Universe. The measurement of oxygen lines in metal-poor unevolved stars, in particular near-UV OH lines, can provide invaluable information about the properties of the Early Galaxy.Aims. Near-UV OH lines constitute an important tool to derive oxygen abundances in metal-poor dwarf stars. Therefore, it is important to correctly model the line formation of OH lines, especially in metal-poor stars, where 3D hydrodynamical models commonly predict cooler temperatures than plane-parallel hydrostatic models in the upper photosphere.Methods. We have made use of a grid of 52 3D hydrodynamical model atmospheres for dwarf stars computed with the code CO5BOLD, extracted from the more extended CIFIST grid. The 52 models cover the effective temperature range 5000–6500 K, the surface gravity range 3.5–4.5 and the metallicity range -3 <[Fe/H] <0.Results. We determine 3D-LTE abundance corrections in all 52 3D models for several OH lines and $\ion{Fe}{i}$lines of different excitation potentials. These 3D-LTE corrections are generally negative and reach values of roughly –1 dex (for the OH 3167 with excitation potential of approximately 1 eV) for the higher temperatures and surface gravities.Conclusions. We apply these 3D-LTE corrections to the individual O abundances derived from OH lines of a sample the metal-poor dwarf stars reported in Israelian et al. (1998, ApJ, 507, 805), Israelian et al. (2001, ApJ, 551, 833) and Boesgaard et al. (1999, AJ, 117, 492) by interpolating the stellar parameters of the dwarfs in the grid of 3D-LTE corrections. The new 3D-LTE [O/Fe] ratio still keeps a similar trend as the 1D-LTE, i.e., increasing towards lower [Fe/H] values. We applied 1D-NLTE corrections to 3D $\ion{Fe}{i}$abundances and still see an increasing [O/Fe] ratio towards lower metallicites. However, the Galactic [O/Fe] ratio must be revisited once 3D-NLTE corrections become available for OH and Fe lines for a grid of 3D hydrodynamical model atmospheres.

Context. Oxygen is the third most common element in the Universe. The measurement of oxygen lines in metal-poor unevolved stars, in particular near-UV OH lines, can provide invaluable information about the properties of the Early Galaxy.

Context. The analysis of the solar spectra using hydrodynamical simulations, with a specific selection of lines, atomic data, and method for computing deviations from local thermodynamical equilibrium, has led to a downward revision of the solar metallicity, Z. We are using the latest simulations computed with the CO5BOLD code to reassess the solar chemical composition. Our previous analyses of the key elements, oxygen and nitrogen, have not confirmed any extreme downward revision of Z, as derived in other works based on hydrodynamical models.Aims. We determine the solar photospheric carbon abundance with a radiation-hydrodynamical CO5BOLD model and compute the departures from local thermodynamical equilibrium by using the Kiel code.Methods. We measured equivalent widths of atomic $\ion{C}{i}$lines on high-resolution, high signal-to-noise ratio solar atlases of disc-centre intensity and integrated disc flux. These equivalent widths were analysed with our latest solar 3D hydrodynamical simulation computed with CO5BOLD. Deviations from local thermodynamic equilibrium we computed in 1D with the Kiel code, using the average temperature structure of the hydrodynamical simulation as a background model.Results. Our recommended value for the solar carbon abundance relies on 98 independent measurements of observed lines and is A(C)=8.50 ±0.06. The quoted error is the sum of statistical and systematic errors. Combined with our recent results for the solar oxygen and nitrogen abundances, this implies a solar metallicity of Z= 0.0154 and Z/X= 0.0211.Conclusions. Our analysis implies a solar carbon abundance that is about 0.1 dex higher than what was found in previous analyses based on different 3D hydrodynamical computations. The difference is partly driven by our equivalent width measurements (we measure, on average, larger equivalent widths than the other work based on a 3D model), in part because of the different properties of the hydrodynamical simulations and the spectrum synthesis code. The solar metallicity we obtain from the CO5BOLD analyses is in slightly better agreement with the constraints of helioseismology than the previous 3D abundance results.

Context. The analysis of the solar spectra using hydrodynamical simulations, with a specific selection of lines, atomic data, and method for computing deviations from local thermodynamical equilibrium, has led to a downward revision of the solar metallicity, Z. We are using the latest simulations computed with the CO5BOLD code to reassess the solar chemical composition. Our previous analyses of the key elements, oxygen and nitrogen, have not confirmed any extreme downward revision of Z, as derived in other works based on hydrodynamical models.

Context. The origin of carbon-enhanced metal-poor stars enriched with both sand relements is highly debated. Detailed abundances of these types of stars are crucial to understand the nature of their progenitors. Aims. The aim of this investigation is to study in detail the abundances of SDSS J1349-0229, SDSS J0912+0216 and SDSS J1036+1212, three dwarf CEMP stars, selected from the Sloan Digital Sky Survey.Methods. Using high resolution VLT/UVES spectra (R~ 30 000) we determine abundances for Li, C, N, O, Na, Mg, Al, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni and 21 neutron-capture elements. We made use of CO5BOLD 3D hydrodynamical model atmospheres in the analysis of the carbon, nitrogen and oxygen abundances. NLTE corrections for Ciand Oilines were computed using the Kiel code. Results. We classify SDSS J1349-0229 and SDSS J0912+0216 as CEMP-r+s stars. SDSS J1036+1212 belongs to the class CEMP-no/s, with enhanced Ba, but deficient Sr, of which it is the third member discovered to date. Radial-velocity variations have been observed in SDSS J1349-0229, providing evidence that it is a member of a binary system.Conclusions. The chemical composition of the three stars is generally compatible with mass transfer from an AGB companion. However, many details remain difficult to explain. Most notably of those are the abundance of Li at the level of the Spite plateau in SDSS J1036+1212 and the large over-abundance of the pure r-process element Eu in all three stars.

Context. The origin of carbon-enhanced metal-poor stars enriched with both sand relements is highly debated. Detailed abundances of these types of stars are crucial to understand the nature of their progenitors.

Context. Combined spectroscopic abundance analyses of stable and radioactive elements can be applied for deriving stellar ages. The achievable precision depends on factors related to spectroscopy, nucleosynthesis, and chemical evolution.Aims. We quantify the uncertainties arising from the spectroscopic analysis, and compare these to the other error sources.Methods. We derive formulae for the age uncertainties arising from the spectroscopic abundance analysis, and apply them to spectroscopic and nucleosynthetic data compiled from the literature for the Sun and metal-poor stars.Results. We obtained ready-to-use analytic formulae of the age uncertainty for the cases of stable+unstable and unstable+unstable chronometer pairs, and discuss the optimal relation between to-be-measured age and mean lifetime of a radioactive species. Application to the literature data indicates that, for a single star, the achievable spectroscopic accuracy is limited to about ±20% for the foreseeable future. At present, theoretical uncertainties in nucleosynthesis and chemical evolution models form the precision bottleneck. For stellar clusters, isochrone fitting provides a higher accuracy than radioactive dating, but radioactive dating becomes competitive when applied to many cluster members simultaneously, reducing the statistical errors by a factor $\sqrt{N}$.Conclusions. Spectroscopy-based radioactive stellar dating would benefit from improvements in the theoretical understanding of nucleosynthesis and chemical evolution. Its application to clusters can provide strong constraints for nucleosynthetic models.

Context. Combined spectroscopic abundance analyses of stable and radioactive elements can be applied for deriving stellar ages. The achievable precision depends on factors related to spectroscopy, nucleosynthesis, and chemical evolution.