Ve Sin Research Articles

The VLT-FLAMES Tarantula Survey

Context. The origin of massive runaway stars is an important unsolved problem in astrophysics. Two main scenarios have been proposed, namely: dynamical ejection or release from a binary at the first core collapse. However, their relative contribution remains heavily debated. Aims. Taking advantage of two large spectroscopic campaigns towards massive stars in 30 Doradus, we aim to provide observational constraints on the properties of the O-type runaway population in the most massive active star-forming region in the Local Group. Methods. We used radial velocity measurements of the O-type star populations in 30 Doradus obtained by the VLT-FLAMES Tarantula Survey and the Tarantula Massive Binary Monitoring to identify single and binary O-type runaways. Here, we discuss the rotational properties of the detected runaways and qualitatively compare the observations with expectations of ejection scenarios. Results. We identified 23 single and one binary O-type runaway objects, most of them located outside the main star-forming regions in 30 Doradus. We find an overabundance of rapid rotators (ve sin i > 200 km s−1) among the runaway population, thus providing an explanation for the observed overabundance of rapidly rotating stars in the 30 Doradus field. Considerations of the projected rotation rates and runaway line-of-sight velocities reveal a conspicuous absence of rapidly rotating (ve sin i > 210 km s−1), fast-moving (vlos > 60 km s−1) runaway stars in our sample, strongly suggesting the presence of two different populations of runaway stars: a population of rapidly spinning but slowly moving runaway stars and a population of fast-moving but slowly rotating ones. These are detected with a ratio close to 2:1 in our sample. Conclusions. We argue that slowly moving but rapidly spinning runaway stars result from binary ejections, while rapidly moving but slowly spinning runaways could result from dynamical ejections. Given that detection biases will more strongly impact the slow-moving runaway population, our results suggest that the binary evolution scenario dominates the current massive runaway star population in 30 Doradus.

The VLT-FLAMES survey of massive stars

Context. NGC 2004#115 was classified as a single lined Be spectroscopic binary in the Large Magellanic Cloud. Its Hα morphology is reminiscent of the Galactic systems LB-1 and HR 6819, both of which are proposed as either Be+BH or Be+stripped He-star systems. Aims. Multi-epoch optical spectra of NGC 2004#115 are used to determine if this binary can be explained by either of these two scenarios, and hence shed additional light on these interesting systems. Methods. VLT-FLAMES and SALT-HRS data covering a baseline of ∼20 years were analyzed to determine radial velocities and orbital parameters, while non-LTE model atmospheres were used to determine stellar parameters and the relative brightness of the system components. Archive MACHO, Gaia, and XMM-Newton data provide additional constraints on the system. Results. NGC 2004#115 is found to be a triple system consisting of an inner binary with a period P = 2.92 d, eccentricity e ∼ 0.0, and mass function f = 0.07 M⊙. The only firmly detected star in this inner binary is a B2 star, the primary, with a projected rotational velocity (ve sin i) of 10 km s−1 and a luminosity of log L/L⊙ = 3.87. It contributes ∼60% of the total V-band light, with the tertiary contributing the other ∼40% of the light, while the secondary is not detected in the optical spectrum. The possibility that the primary is a low mass inflated stripped star is excluded since its Roche radius would be smaller than its stellar radius in such a compact system. A main sequence star of mass 8.6 M⊙ is therefore inferred; however, the assumption of synchronous rotation leads to a secondary mass in excess of 25 M⊙, which would therefore be a black hole. The tertiary is detected as a fainter blended component to the hydrogen and helium lines, which is consistent with a slightly less massive B-type star, though with ve sin i ∼ 300 km s−1. The data do not permit the characterization of the outer period, though it likely exceeds 120 days and is therefore in a stable configuration. The disk-like emission is variable, but may be associated with the inner binary rather than the rapidly rotating tertiary. XMM-Newton provides an upper limit of 5 × 1033 ergs s−1 in the 0.2–12 keV band which is consistent with, though not constraining, the system hosting a quiescent B+BH binary. A number of caveats to this scenario are discussed.

Discovery of new mercury–manganese stars, including a fast rotator

ABSTRACT The origin of mercury–manganese (HgMn) stars is still poorly understood and the statistical analysis of an extensive sample of well characterized objects would be very valuable. Nevertheless, the compilation of a clean and reliable list of all known HgMn stars, and complete characterization of those objects, is still a pending issue. We report the identification of 13 new HgMn stars from our own spectroscopic observations and from publicly available spectral libraries. In addition, we perform a thorough literature search to give a list of 46 confirmed HgMn stars (plus a further nine suspected HgMn stars) discovered over the last years or neglected by other compilations. When required, we performed specific observations to confirm doubtful cases. For the 13 newly identified HgMn stars we derived photospheric chemical abundances by spectral synthesis. Besides Hg and Mn, which are overabundant in the whole sample, P, Ga, and Xe are overabundant in the hottest stars of the sample, and Sr, Zr, and Pt among the coolest; Y is present in most stars of the sample. Three of these new HgMn stars are members of open clusters: HD 93549 in IC 2602, HD 96473 in NGC 3532, and HD 322659 in NGC 6281. Furthermore, our sample includes HD 145842, an object remarkable for its high rotation. In fact, its projected rotational velocity of ve sin i = 124 km s−1 is the highest measured in any HgMn star and is more than 30 per cent above the theoretical limit predicted by the diffusion theory, which makes HD 145842 a challenging test case for the current models.

The spin rates of O stars in WR+O Magellanic Cloud binaries

ABSTRACT Some massive, merging black holes (BHs) may be descendants of binary O stars. The evolution and mass transfer between these O stars determine the spins of their progeny BH. These will be measurable with future gravitational wave detectors, incentivizing the measurement of the spins of O stars in binaries. We previously measured the spins of O stars in Galactic Wolf–Rayet (WR)+O binaries. Here we measure the ve sin i of four Large Magellanic Cloud (LMC) and two Small Magellanic Cloud (SMC) O stars in WR+O binaries to determine whether lower metallicity might affect the spin rates. We find that the O stars in Galactic and Magellanic WR+O binaries display average ve sin i = 258 ± 18 and 270 ± 15 km s−1, respectively. Two LMC O stars measured on successive nights show significant line width variability, possibly due to differing orbital phases exhibiting different parts of the O stars illuminated differently by their WR companions. Despite this variability, the ve sin i are highly supersynchronous but distinctly subcritical for the O stars in all these binaries; thus we conclude that an efficient mechanism for shedding angular momentum from O stars in WR+O binaries must exist. This mechanism, probably related to Roche lobe overflow (RLOF)-created dynamo magnetic fields, prevents nearly 100 per cent breakup spin rates, as expected when RLOF operates, as it must, in these stars. A Spruit–Tayler dynamo and O star wind might be that mechanism.

A census of massive stars in NGC 346

Spectroscopy for 247 stars towards the young cluster NGC 346 in the Small Magellanic Cloud has been combined with that for 116 targets from the VLT-FLAMES Survey of Massive Stars. Spectral classification yields a sample of 47 O-type and 287 B-type spectra, while radial-velocity variations and/or spectral multiplicity have been used to identify 45 candidate single-lined (SB1) systems, 17 double-lined (SB2) systems, and one triple-lined (SB3) system. Atmospheric parameters (Teff and log g) and projected rotational velocities (ve sin i) have been estimated using TLUSTY model atmospheres; independent estimates of ve sin i were also obtained using a Fourier Transform method. Luminosities have been inferred from stellar apparent magnitudes and used in conjunction with the Teff and ve sin i estimates to constrain stellar masses and ages using the BONNSAI package. We find that targets towards the inner region of NGC 346 have higher median masses and projected rotational velocities, together with smaller median ages than the rest of the sample. There appears to be a population of very young targets with ages of less than 2 Myr, which have presumably all formed within the cluster. The more massive targets are found to have lower projected rotational velocities consistent with previous studies. No significant evidence is found for differences with metallicity in the stellar rotational velocities of early-type stars, although the targets in the Small Magellanic Cloud may rotate faster than those in young Galactic clusters. The rotational velocity distribution for single non-supergiant B-type stars is inferred and implies that a significant number have low rotational velocity (≃10% with ve < 40 km s−1), together with a peak in the probability distribution at ve≃ 300 km s−1. Larger projected rotational velocity estimates have been found for our Be-type sample and imply that most have rotational velocities between 200–450 km s−1.

The VLT-FLAMES Tarantula Survey

Previous analyses of the spectra of OB-type stars in the Magellanic Clouds have identified targets with low projected rotational velocities and relatively high nitrogen abundances; the evolutionary status of these objects remains unclear. The VLT-FLAMES Tarantula Survey obtained spectroscopy for over 800 early-type stars in 30 Doradus of which 434 stars were classified as B-type. We have estimated atmospheric parameters and nitrogen abundances using TLUSTY model atmospheres for 54 B-type targets that appear to be single, have projected rotational velocities, ve sin i ≤ 80 km s−1 and were not classified as supergiants. In addition, nitrogen abundances for 34 similar stars observed in a previous FLAMES survey of the Large Magellanic Cloud have been re-evaluated. For both samples, approximately 75–80% of the targets have nitrogen enhancements of less than 0.3 dex, consistent with them having experienced only small amounts of mixing. However, stars with low projected rotational velocities, ve sini ≤ 40 km s−1 and significant nitrogen enrichments are found in both our samples and simulations imply that these cannot all be rapidly rotating objects observed near pole-on. For example, adopting an enhancement threshold of 0.6 dex, we observed five and four stars in our VFTS and previous FLAMES survey samples, yet stellar evolution models with rotation predict only 1.25 ± 1.11 and 0.26 ± 0.51 based on our sample sizes and random stellar viewing inclinations. The excess of such objects is estimated to be 20–30% of all stars with current rotational velocities of less than 40 km s−1. This would correspond to ~2–4% of the total non-supergiant single B-type sample. Given the relatively large nitrogen enhancement adopted, these estimates constitute lower limits for stars that appear inconsistent with current grids of stellar evolutionary models. Including targets with smaller nitrogen enhancements of greater than 0.2 dex implies larger percentages of targets that are inconsistent with current evolutionary models, viz. ~70% of the stars with rotational velocities less than 40 km s−1 and ~6–8% of the total single stellar population. We consider possible explanations of which the most promising would appear to be breaking due to magnetic fields or stellar mergers with subsequent magnetic braking.

Pattern recognition in spectra

We present a new automated procedure that simultaneously derives the effective temperature Teff, surface gravity log g, metallicity [Fe/H], and equatorial projected rotational velocity ve sin i for stars. The procedure is inspired by the well-known PCA-based inversion of spectropolarimetric full-Stokes solar data, which was used both for Zeeman and Hanle effects. The efficiency and accuracy of this procedure have been proven for FGK, A, and late type dwarf stars of K and M spectral types. Learning databases are generated from the Elodie stellar spectra library using observed spectra for which fundamental parameters were already evaluated or with synthetic data. The synthetic spectra are calculated using ATLAS9 model atmospheres. This technique helped us to detect many peculiar stars such as Am, Ap, HgMn, SiEuCr and binaries. This fast and efficient technique could be used every time a pattern recognition is needed. One important application is the understanding of the physical properties of planetary surfaces by comparing aboard instrument data to synthetic ones.

Results of magnetic field measurements of CP-stars performed with the 6-m telescope. III. Observations in 2009

We present the results of measuring longitudinal magnetic fields (Be), rotation velocities (ve sin i), and radial velocities (Vr) of 44 stars observed with the Main Stellar Spectrograph (MSS) of the 6-m BTA telescope of the Special Astrophysical Observatory in 2009. For the first time, magnetic fields were detected for the stars HD5441, HD199180, HD225627, and BD+00° 4535. We show that for the same stars, the longitudinal fields Be measured from the Hβ hydrogen line core and from metal lines can differ by 10% and up to a factor of 2–3. Except in rare cases, magnetic fields measured from the metal lines are stronger. We believe that this phenomenon is of a physical nature and depends on the magnetic field topology and the physical conditions inside a specific star. Observations of standard stars without magnetic fields confirm the absence of systematic errors capable of introducing distortions into the longitudinal-field measurement results. In this work we comment on the results for each of the stars.

Spectroscopic study on the beryllium abundances of red giant stars

Abstract An extensive spectroscopic study was carried out for the beryllium abundances of 200 red giants (mostly of late G- and early K-type), which were determined from the near-UV Be ii 3131.066 line based on high-dispersion spectra obtained by Subaru/High Dispersion Spectrograph, with an aim of investigating the nature of surface Be contents in these evolved giants; e.g., dependence upon stellar parameters, degree of peculiarity along with its origin and build-up timing. We found that Be is considerably deficient (to widely different degrees from star to star) in the photosphere of these evolved giants by ∼ 1–3 dex (or more) compared to the initial abundance. While the resulting Be abundances [A(Be)] appear to depend weakly upon Teff, log g, [Fe/H], M, age, and ve sin i, this may be attributed to the metallicity dependence of A(Be) coupled with the mutual correlation between these stellar parameters, since such tendencies almost disappear in the metallicity-scaled Be abundance ([Be/Fe]). By comparing the Be abundances (as well as their correlations with Li and C) to the recent theoretical predictions based on sophisticated stellar evolution calculations, we concluded that such a considerable extent/diversity of Be deficit is difficult to explain only by the standard theory of first dredge-up in the envelope of red giants, and that some extra mixing process (such as rotational or thermohaline mixing) must be responsible, which presumably starts to operate already in the main-sequence phase. This view is supported by the fact that appreciable Be depletion is seen in less evolved intermediate-mass B–A type stars near to the main sequence.

Application of Redlich-Kister Model to Measure and Predict Thermo Physical Properties of Binary Liquid Mixtures at Various Temperatures

Study conducts in this research are Viscosities,ŋ, and densities, of 1, 4-dioxane with Benzene at different mole fractions and various temperatures in the atmospheric pressure condition. From experimentations excess volumes, Vᴱ, and deviation sin viscosities,Δŋ, of mixtures at infinite dilutions have been obtained. The measured systems exhibited positive values of Vᶆᴱ and negative values of Δŋ. The binary mixture 1, 4 dioxane + Benzene show positive Vᴱ and negative Δŋ with increasing temperatures. The outcomes clearly indicate that weak interactions present in mixture. It is mainly because of number and position of methyl groups exist in these aromatic hydrocarbons. These measured data tailored to the non-linear models to derive the binary coefficients. Standard deviations are considered between the fitted outcomes and the calculated data is helpful deliberate mixing behavior of the binary mixtures. It can conclude that in our cases, the data found with the values correlated by the corresponding models very well. The molecular interactions existing between the components and comparison of liquid mixtures also discussed.

Atmospheric velocity fields in tepid main sequence stars

Context. The line profiles of the stars with ve sin i below a few km s −1 can reveal direct signatures of local velocity fields such as convection in stellar atmospheres. This effect is well established in cool main sequence stars, and has been detected and studied in three A stars. Aims. This paper reports observations of main sequence B, A and F stars (1) to identify additional stars with suffi ciently low values of ve sin i to search for spectral line profile signatures of local veloc ity fields, and (2) to explore how the signatures of the local v elocity fields in the atmosphere depend on stellar parameters such as effective temperature and peculiarity type. Methods. We have carried out a spectroscopic survey of B and A stars of low ve sin i at high resolution. Comparison of model spectra with those observed allows us to detect signatures of the loc al velocity fields such as asymmetric excess line wing absorp tion, best-fit ve sin i parameter values that are found to be larger for strong lines than for weak lines, and discrepancies between observed and modelled line profile shapes. Results. Symptoms of local atmospheric velocity fields are always det ected through a non-zero microturbulence parameter for main sequence stars having Te below about 10000 K, but not for hotter stars. Direct line profile tracers of the atmospheric velocity field are found in six very sharp-lined stars in addition to the three r eported earlier. Direct signatures of velocity fields are fo und to occur in A stars with and without the Am chemical peculiarities, although the amplitude of the effects seems larger in Am stars. Velocity fields are also directly detected in spectral line profiles of A and e arly F supergiants, but without significant line asymmetrie s. Conclusions. We confirm that several atmospheric velocity field signature s, particularly excess line wing absorption which is strong er in the blue line wing than in the red, are detectable in the spe ctral lines of main sequence A stars of suffi ciently low ve sin i. We triple the sample of A stars known to show these effects, which are found both in Am and normal A stars. We argue that the observed line distortions are probably due to convective motions reachin g the atmosphere. These data still have not been satisfactor ily explained by models of atmospheric convection, including numerical simulations.

Observing and Modelling Stellar Magnetic Fields

In this chapter, we examine the question of how spectropo- larimetric observations of magnetic stars may be modelled, and how modelling techniques may be used to extract much detailed informa- tion about the stellar magnetic field and other characteristics of the magnetized stellar atmosphere. In the preceding chapter, we discussed how the energy levels of atoms are split by a magnetic field, and how this leads in turn to splitting of spectral lines in to multiple components, an effect called the Zeeman or Paschen-Back effect depending on the field strength. We saw that the polarisation characteristics of these components provide valuable tools for detection and measurement of stellar magnetic fields, and that polarisation measurements allow one to obtain, in a straight-forward way, an estimate of the mean line-of-sight field component averaged over the visible hemisphere (the mean longitudinal field h Bzi ). We also saw that, if the field is large enough and ve sin i small enough, observation of splitting of spectral lines into discrete components makes it possible to estimate the mean field modulus h Bi , again averaged over the visible hemisphere. Finally, we looked at some simple multipole models of stellar field structure that can reproduce simple data-sets such as observed values of h Bzi , or of h Bzi and h Bi , over a stellar rotation, and how these models lead to the fundamental conceptual model known as the oblique rotator. Determination of mean field values directly from the spectra (in the same way as radial velocities and projected rotation velocities are derived), and the modelling of such integral or moment data with simple geometric field structures, provide a useful and valuable source of information about global characteristics of the stellar field. However, such models are based on data-sets that are often

Abundances of a sample of A and F-type dwarf members of the Ursa Major Group

Abundances of 11 chemical elements have been determined for 10 F and 12 A dwarfs (“normal” and chemically peculiar) bona-fide and probable members of the Ursa Major Group (age about 500 Myr). The abundances were determined in a uniform manner using a model atmosphere analysis by minimising the chi-square of grids of synthetic spectra to observed high resolution high S/ N( R � 25 000 and R � 70 000) spectra obtained in three narrow spectral regions centered around 5075 A, 5525 A and 6160 A. Specifically, Takeda’s (1995) semiautomated procedure was used to derive the abundances of C, O, Na, Mg, Si, Ca, Sc, Fe, Ni, Y, and Ba, the projected rotational velocity ve sin i and the microturbulent velocity for each star analysed. In graphs [X/H] versus Teff, the A stars exhibit larger star-to-star variations in [Fe/H], [Ni/H], and [Si/H] than the F dwarfs do. The abundance of nickel is the only one that appears to be correlated with that of iron.

Abundances and chemical stratification analysis in the atmosphere of Cr-type Ap star HD 204411

We present results of an abundance and stratification analysis of the weakly magnetic chemically peculiar star HD 204411 based on the echelle spectrum obtained with the high resolution spectrograph at the 3.55-m Telescopio Nazionale Galileo at the Observatorio del Roque de los Muchachos (La Palma, Spain). Atmospheric parameters obtained from the spec- troscopy and spectrophotometry together with the Hipparcos parallax show that this star has already left the Main Sequence band. The upper limit for the surface magnetic field derived from the differential broadening of the spectral lines with different magnetic sensitivity is 750 G, which agrees with the recent detection of the weak effective magnetic field in this star. The best fit to the observed spectral line profiles was obtained with a combination of the rotational velocity ve sin i = 5.4 km s −1 and the radial-tangential macroturbulence of 4.8 km s −1 . The average abundances of HD 204411 are typical for an Ap star of the Cr-type: C and O are deficient, Cr and Fe are strongly overabundant. Sr, Y, Zr and the rare-earths, which usually have large overabundances in cool Ap stars with strong magnetic fields, are either normal (Y, Ce) or only +0.5 dex overabundant in the weakly magnetic star HD 204411. The chemical stratification analysis was performed for 5 elements, Mg, Si, Ca, Cr and Fe. Si, Ca and Fe show a tendency to be concentrated below log τ5000 = −1, while for Mg we found marginal evidence for concentration in the upper atmosphere. This behaviour of Mg may be an artifact caused by the limited sample of spectral lines and poor atomic data available for the Mg  lines used in our analysis. Chromium, the most anomalous Fe-peak element, does not show significant abundance gradients in the line-forming region.

Magnetic field and chemical composition of the peculiar star HD 10221

We analyzed the chemical composition of the chemically peculiar (CP) star HD 0221=43 Cas using spectra taken with the NES spectrograph of the 6-m telescope with a spectral resolution of 45 000. The Hβ line profile corresponds most closely to Teff = 11 900 K and log g = 3.9. The rotational velocity is ve sin i = 27 ± 2 km s−1, and the microturbulence is ξt = 1 km s−1. The results of our abundance determination by the method of synthetic spectra show that the star has chemical anomalies typical of SrCrEu stars, although its effective magnetic field is weak, Be < 100 G. For silicon, we obtained an abundance distribution in atmospheric depth with a sharp jump of 1.5 dex at an optical depth of log τ5000 = −0.3 and with silicon concentration in deep atmospheric layers. Similar distributions were found in the atmospheres of cooler stars with strong and weak magnetic fields. A comparison of the chemical peculiarities in HD 10221 with known CP stars with magnetic fields of various strengths leads us to conclude that a low rotational velocity rather than amagnetic field is the determining factor in the formation mechanism of chemical anomalies in the atmospheres of CP stars.

Balmer lines as T$\mathsf{_{eff}}$ and log g indicators for non-solar composition atmospheres

Although the importance of a correct abundance assumption in the determination of effective temperature and surface gravity of a star has been demonstrated in the literature, this determination is often still extremely simplified, neglecting the effects of non-solar chemical abundances. In this paper we show how the modeling of the profiles of Hδ and Hγ, commonly used as Teff and log g indicators, is affected when the chemical composition is far from the standard one. As a target for our study we selected the chemically peculiar star HR 6000. Comparing the observed and synthetic profiles of Hδ and Hγ we obtained Teff = 12 950 K and log g = 4.05; the atmospheric model has been computed with a metal opacity scale evaluated for (M/H) = −0.5 and He/H = 0. A number of FeII lines have been used to infer the rotational velocity (ve sini = 0k m s −1 )a nd the heliocentric radial velocity (RV = 0.67 km s −1 ). By requiring that the abundance of iron is independent of the 96 measured equivalent widths, we determined the microturubulence velocity (ξ = 0k m s −1 ). The abundance pattern coming from our study is similar to the one inferred from UV lines by Castelli et al. (1985), with the exception of O, Al, Si, Sc and Ni. Possible causes for these descrepancies are discussed. With respect to the Sun, we found the iron peak elements to be normal or overabundant and the light elements, with the exception of Na and P, to be extremely underabundant. We find that HR 6000 is one of the most He-underabundant among the chemically peculiar stars.

Be-star rotation: how close to critical?

We argue that, in general, observational studies of Be‐star rotation have paid insufficient attention to the effects of equatorial gravity darkening. We present new line‐profile calculations that emphasize the insensitivity of line width to rotation for fast rotators. Coupled with a critical review of observational procedures, these calculations suggest that the observational parameter v sin i may systematically underestimate the true projected equatorial rotation velocity, ve sin i, by some tens of per cent for rapid rotators. A crucial implication of this work is that Be stars may be rotating much closer to their critical velocities than is generally supposed, bringing a range of new processes into contention for the elusive physical mechanism responsible for the circumstellar disc thought to be central to the Be phenomenon.

Rotation and Line Broadening in OBA Stars

Observational v sin i line-width measurements for OBA stars are summarized, and the relationship of these measurements to ve sin i, the true projected equatorial rotation velocity, reviewed. In general, ve sin i ≥ v sin i for Be Stars, while ve sin i ≤ v sin i for O-type stars. The implications are that (i) it is probable that Be Stars are closer to their critical rotation velocities than is generally supposed (rendering plausible a range of new physical mechanisms for the Be phenomenon); and (ii) some non-rotational macroscopic line broadening (‘turbulence’) occurs in the atmospheres of O stars (and BA supergiants). Physical interpretations of this ‘turbulence’ are considered.

High resolution spectroscopy of HD 207538 from Far-UV (FUSE) to Visible (SARG-TNG)

We present a detailed study of the suspected Chemically Peculiar star HD 207538 based on high resolution spec- troscopy in the far Ultraviolet (1000-3350 A) and visible (4600-7000 A) ranges. The stellar abundance synthesis analysis was performed by using Kurucz's codes ATLAS9 and SYNTHE to compute the atmospheric model and the synthetic spectrum respectively. Observations were obtained with the Far Ultraviolet Spectroscopic Explorer ,t heInternational Ultraviolet Explorersatellites whereas the optical spectrum was collected with the ground-based Telescopio Nazionale Galileotelescope. With our analysis we refine the value of the rotational velocity to ve sin i = 42 3k m s 1 and the microturbulence velocity to = 8 1k m s 1 . The stellar abundances inferred in this study show that C, N, O, Al, Si, P, S and Mn are compatible with the standard solar abundances, within the experimental errors. On the other hand, Fe, Ni and Zn are definitively underabundant. We also show that the helium content is comparable to the typical abundance of B-type stars. Because this spectrum is rich in stellar and interstellar features, we computed simultaneously a synthetic spectrum of the stellar and interstellar lines in order to disentangle the dierent absorption contributions. We thus also determined the column densi- ties of several interstellar elements (Feii ,N i ,P ii ,H i ,H 2, HD, CO, Cli and Ari) present in the gas in front of the star. Although several components are present along this sightline, our results suggest the presence of some translucent interstellar gas among the diuse components. With this work, we demonstrate that it is possible to perform a stellar spectroscopic analysis from the far-UV to visible spectral range, with consistent results in both ranges within errors, based on one single atmosphere model.

Rotation and lithium in the late-type stars of NGC 2516

We present CCD photometry and high-resolution spectroscopy of low-mass stars in the open cluster NGC 2516, which has an age of about 150Myr and may have a much lower metallicity than the Pleiades. 24 probable F to early K type, single cluster members have been identified from their photometry and radial velocities, along with three possible spectroscopic binaries. The projected equatorial velocities are measured and compared with younger and older clusters. Several fast rotating late G /early K stars are seen, but all hotter stars have ve sini < 20kms ¹1 . The data are consistent with angular momentum loss models with spindowntime-scales thatincreasefromtensofMyrforGstarstohundredsofMyrforKstars.The observed X-ray activity is consistent with the currently accepted rotation–activity paradigm. Lithium abundances are derived from the Li I 6708-Au line. The pattern of Li depletion is indistinguishablefromthatinthePleiades,including aspreadinthe,K0stars,wherethemost rapid rotators suffer the least Li depletion. The observations argue in favour of either a metallicity in the range ¹0:1 <[Fe/H]< 0:0 for NGC 2516, or a lower metallicity and extra Li depletion through non-standard mixing modes which occurs on time-scales of only ,50Myr. Neither our low signal-to-noise ratio spectroscopy nor our photometry can constrain [Fe/H] sufficiently to decide between these possibilities. A detailed spectroscopic chemical abundance analysis is urgently required.