Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars III. Detection of lithium in the metal-poor bulge dwarf MOA-2010-BLG-285S

Context. To study the evolution of Li in the Galaxy it is necessary to observe dwarf or subgiant stars. These are the only long-lived stars whose present-day atmospheric chemical composition reflects their natal Li abundances according to standard models of stellar evolution. Although Li has been extensively studied in the Galactic disk and halo, to date there has only been one uncertain detection of Li in an unevolved bulge star. Aims. Our aim with this study is to provide the first clear detection of Li in the Galactic bulge, based on an analysis of a dwarf star that has largely retained its initial Li abundance. Methods. We performed a detailed elemental abundance analysis of the bulge dwarf star MOA-2010-BLG-285S using a high-resolution and high signal-to-noise spectrum obtained with the UVES spectrograph at the VLT when the object was optically magnified during a gravitational microlensing event (visual magnification A similar to 550 during observation). The Li abundance was determined through synthetic line profile fitting of the (7)Li resonance doublet line at 670.8 nm. The results have been corrected for departures from LTE. Results. MOA-2010-BLG-285S is, at [Fe/H] = -1.23, the most metal-poor dwarf star detected so far in the Galactic bulge. Its old age (12.5 Gyr) and enhanced [alpha/Fe] ratios agree well with stars in the thick disk at similar metallicities. This star represents the first unambiguous detection of Li in a metal-poor dwarf star in the Galactic bulge. We find an NLTE corrected Li abundance of log epsilon(Li) = 2.16, which is consistent with values derived for Galactic disk and halo dwarf stars at similar metallicities and temperatures. Conclusions. Our results show that there are no signs of Li enrichment or production in the Galactic bulge during its earliest phases. Observations of Li in other galaxies (omega Cen) and other components of the Galaxy suggest further that the Spite plateau is universal.

THE GEMINI NICI PLANET-FINDING CAMPAIGN: DISCOVERY OF A CLOSE SUBSTELLAR COMPANION TO THE YOUNG DEBRIS DISK STAR PZ Tel

We report the discovery of a tight substellar companion to the young solar analog PZ Tel, a member of the beta Pic moving group observed with high-contrast adaptive optics imaging as part of the Gemini Near-Infrared Coronagraphic Imager Planet-Finding Campaign. The companion was detected at a projected separation of 16.4 +/- 1.0 AU (0.'' 33 +/- 0.'' 01) in 2009 April. Second-epoch observations in 2010 May demonstrate that the companion is physically associated and shows significant orbital motion. Monte Carlo modeling constrains the orbit of PZ Tel B to eccentricities >0.6. The near-IR colors of PZ Tel B indicate a spectral type of M7 +/- 2 and thus this object will be a new benchmark companion for studies of ultracool, low-gravity photospheres. Adopting an age of 12(-4)(+8) Myr for the system, we estimate a mass of 36 +/- 6 M(Jup) based on the Lyon/DUSTY evolutionary models. PZ Tel B is one of the few young substellar companions directly imaged at orbital separations similar to those of giant planets in our own solar system. Additionally, the primary star PZ Tel A shows a 70 mu m emission excess, evidence for a significant quantity of circumstellar dust that has not been disrupted by the orbital motion of the companion.

Self-bound models of compact stars and recent mass-radius measurements

The exact composition of a specific class of compact stars, historically referred to as ""neutron stars,'' is still quite unknown. Possibilities ranging from hadronic to quark degrees of freedom, including self-bound versions of the latter, have been proposed. We specifically address the suitability of strange star models (including pairing interactions) in this work, in the light of new measurements available for four compact stars. The analysis shows that these data might be explained by such an exotic equation of state, actually selecting a small window in parameter space, but still new precise measurements and also further theoretical developments are needed to settle the subject.

Transiting exoplanets from the CoRoT space mission IX. CoRoT-6b: a transiting ""hot Jupiter"" planet in an 8.9d orbit around a low-metallicity star

The CoRoT satellite exoplanetary team announces its sixth transiting planet in this paper. We describe and discuss the satellite observations as well as the complementary ground-based observations - photometric and spectroscopic - carried out to assess the planetary nature of the object and determine its specific physical parameters. The discovery reported here is a ""hot Jupiter"" planet in an 8.9d orbit, 18 stellar radii, or 0.08 AU, away from its primary star, which is a solar-type star (F9V) with an estimated age of 3.0 Gyr. The planet mass is close to 3 times that of Jupiter. The star has a metallicity of 0.2 dex lower than the Sun, and a relatively high (7)Li abundance. While the light curve indicates a much higher level of activity than, e. g., the Sun, there is no sign of activity spectroscopically in e. g., the [Ca II] H&K lines.

Age distribution of the central stars of galactic disk planetary nebulae

Context. Determination of the ages of central stars of planetary nebulae (CSPN) is a complex problem, and there is presently no single method that can be generally applied. We have developed several methods of estimating the ages of CSPN, based on both the observed nebular properties and some properties of the stars themselves. Aims. Our aim is to estimate the ages and the age distribution of CSPN and to compare the derived results with mass and age determinations of CSPN and white dwarfs based on empirical determinations of these quantities. Methods. We considered a sample of planetary nebulae in the galactic disk, most of which (similar to 69%) are located in the solar neighbourhood, within 3 kpc from the Sun. We discuss several methods of deriving the age distribution of CSPN, namely; (i) the use of an age-metallicity relation that also depends on the galactocentric distance; (ii) the use of an age-metallicity relation obtained for the galactic disk; and (iii) the determination of ages from the central star masses obtained from the observed nitrogen abundances. Results. We estimated the age distribution of CSPN with average uncertainties of 1-2 Gyr, and compared our results with the expected distribution based both on the observed mass distribution of white dwarfs and on the age distribution derived from available mass distributions of CSPN. Based on our derived age distributions, we conclude that most CSPN in the galactic disk have ages under 6 Gyr, and that the age distribution is peaked around 2-4 Gyr.

A SEARCH FOR UNRECOGNIZED CARBON-ENHANCED METAL-POOR STARS IN THE GALAXY

We have developed a new procedure to search for carbon-enhanced metal-poor (CEMP) stars from the Hamburg/ESO (HES) prism-survey plates. This method employs an extended line index for the CH G band, which we demonstrate to have superior performance when compared to the narrower G-band index formerly employed to estimate G-band strengths for these spectra. Although CEMP stars have been found previously among candidate metal-poor stars selected from the HES, the selection on metallicity undersamples the population of intermediate-metallicity CEMP stars (-2.5 <= [Fe/H] <= -1.0); such stars are of importance for constraining the onset of the s-process in metal-deficient asymptotic giant branch stars (thought to be associated with the origin of carbon for roughly 80% of CEMP stars). The new candidates also include substantial numbers of warmer carbon-enhanced stars, which were missed in previous HES searches for carbon stars due to selection criteria that emphasized cooler stars. A first subsample, biased toward brighter stars (B < 15.5), has been extracted from the scanned HES plates. After visual inspection (to eliminate spectra compromised by plate defects, overlapping spectra, etc., and to carry out rough spectral classifications), a list of 669 previously unidentified candidate CEMP stars was compiled. Follow-up spectroscopy for a pilot sample of 132 candidates was obtained with the Goodman spectrograph on the SOAR 4.1 m telescope. Our results show that most of the observed stars lie in the targeted metallicity range, and possess prominent carbon absorption features at 4300 angstrom. The success rate for the identification of new CEMP stars is 43% (13 out of 30) for [Fe/H] < -2.0. For stars with [Fe/H] < -2.5, the ratio increases to 80% (four out of five objects), including one star with [Fe/H] < -3.0.

H alpha spectropolarimetry of the B[e] supergiant GG Carinae

Aims. We study the geometry of the circumstellar environment of the B[e] supergiant star GG Car. Methods. We present observations acquired using the IAGPOL imaging polarimeter in combination with the Eucalyptus-IFU spectrograph to obtain spectropolarimetric measurements of GG Car across Ha at two epochs. Polarization effects along the emission line are analysed using the Q-U diagram. In particular, the polarization position angle (PA) obtained using the line effect is able to constrain the symmetry axis of the disk/envelope. Results. By analysing the fluxes, GG Car shows an increase in its double-peaked Ha line emission relative to the continuum within the interval of our measurements (similar to 43 days). The depolarization line effect around Ha is evident in the Q-U diagram for both epochs, confirming that light from the system is intrinsically polarized. A rotation of the PA along Ha is also observed, indicating a counter-clockwise rotating disk. The intrinsic PA calculated using the line effect (similar to 85 degrees.) is consistent between our two epochs, suggesting a clearly defined symmetry axis of the disk.

The young, tight, and low-mass binary TWA22AB: a new calibrator for evolutionary models? Orbit, spectral types, and temperature

Context. Tight binaries discovered in young, nearby associations are ideal targets for providing dynamical mass measurements to test the physics of evolutionary models at young ages and very low masses. Aims. We report the binarity of TWA22 for the first time. We aim at monitoring the orbit of this young and tight system to determine its total dynamical mass using an accurate distance determination. We also intend to characterize the physical properties (luminosity, effective temperature, and surface gravity) of each component based on near-infrared photometric and spectroscopic observations. Methods. We used the adaptive-optics assisted imager NACO to resolve the components, to monitor the complete orbit and to obtain the relative near-infrared photometry of TWA22 AB. The adaptive-optics assisted integral field spectrometer SINFONI was also used to obtain medium-resolution (R(lambda) = 1500-2000) spectra in JHK bands. Comparison with empirical and synthetic librairies were necessary for deriving the spectral type, the effective temperature, and the surface gravity for each component of the system. Results. Based on an accurate trigonometric distance (17.5 +/- 0.2 pc) determination, we infer a total dynamical mass of 220 +/- 21 M(Jup) for the system. From the complete set of spectra, we find an effective temperature T(eff) = 2900(-200)(+200) K for TWA22A and T(eff) = 2900(-100)(+200) for TWA22 B and surface gravities between 4.0 and 5.5 dex. From our photometry and an M6 +/- 1 spectral type for both components, we find luminosities of log(L/L(circle dot)) = -2.11 +/- 0.13 dex and log(L/L(circle dot)) = -2.30 +/- 0.16 dex for TWA22 A and B, respectively. By comparing these parameters with evolutionary models, we question the age and the multiplicity of this system. We also discuss a possible underestimation of the mass predicted by evolutionary models for young stars close to the substellar boundary.

Automated supervised classification of variable stars in the CoRoT programme Method and application to the first four exoplanet fields

Aims. In this work, we describe the pipeline for the fast supervised classification of light curves observed by the CoRoT exoplanet CCDs. We present the classification results obtained for the first four measured fields, which represent a one-year in-orbit operation. Methods. The basis of the adopted supervised classification methodology has been described in detail in a previous paper, as is its application to the OGLE database. Here, we present the modifications of the algorithms and of the training set to optimize the performance when applied to the CoRoT data. Results. Classification results are presented for the observed fields IRa01, SRc01, LRc01, and LRa01 of the CoRoT mission. Statistics on the number of variables and the number of objects per class are given and typical light curves of high-probability candidates are shown. We also report on new stellar variability types discovered in the CoRoT data. The full classification results are publicly available.

A search for thermally emitting isolated neutron stars in the 2XMMp catalogue

The relatively large number of nearby radio-quiet and thermally emitting isolated neutron stars (INSs) discovered in the ROSAT All-Sky Survey, dubbed the ""Magnificent Seven"", suggests that they belong to a formerly neglected major component of the overall INS population. So far, attempts to discover similar INSs beyond the solar vicinity failed to confirm any reliable candidate. The good positional accuracy and soft X-ray sensitivity of the EPIC cameras onboard the XMM-Newton satellite allow us to efficiently search for new thermally emitting INSs. We used the 2XMMp catalogue to select sources with no catalogued candidate counterparts and with X-ray spectra similar to those of the Magnificent Seven, but seen at greater distances and thus undergoing higher interstellar absorptions. Identifications in more than 170 astronomical catalogues and visual screening allowed us to select fewer than 30 good INS candidates. In order to rule out alternative identifications, we obtained deep ESO-VLT and SOAR optical imaging for the X-ray brightest candidates. We report here on the optical follow-up results of our search and discuss the possible nature of 8 of our candidates. A high X-ray-to-optical flux ratio together with a stable flux and soft X-ray spectrum make the brightest source of our sample, 2XMM J104608.7-594306, a newly discovered thermally emitting INS. The X-ray source 2XMM J010642.3+005032 has no evident optical counterpart and should be further investigated. The remaining X-ray sources are most probably identified with cataclysmic variables and active galactic nuclei, as inferred from the colours and flux ratios of their likely optical counterparts. Beyond the finding of new thermally emitting INSs, our study aims at constraining the space density of this Galactic population at great distances and at determining whether their apparently high density is a local anomaly or not.

Transiting exoplanets from the CoRoT space mission XVII. The hot Jupiter CoRoT-17b: a very old planet

We report on the discovery of a hot Jupiter-type exoplanet, CoRoT-17b, detected by the CoRoT satellite. It has a mass of 2.43 +/- 0.30 M(Jup) and a radius of 1.02 +/- 0.07 R(Jup), while its mean density is 2.82 +/- 0.38 g/cm(3). CoRoT-17b is in a circular orbit with a period of 3.7681 +/- 0.0003 days. The host star is an old (10.7 +/- 1.0 Gyr) main-sequence star, which makes it an intriguing object for planetary evolution studies. The planet's internal composition is not well constrained and can range from pure H/He to one that can contain similar to 380 earth masses of heavier elements.

First stars XII. Abundances in extremely metal-poor turnoff stars, and comparison with the giants

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 turno. stars. Methods. VLT/UVES spectra at R similar to 45 000 and S/N similar to 130 per pixel (lambda lambda 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 similar to 0.2 dex larger than in giants of similar metallicity. Mg and Si abundances are similar to 0.2 dex lower (the giant [Mg/Fe] values are slightly revised), while Zn is again similar to 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.

H alpha spectropolarimetry of RY Tauri and PX Vulpeculae (Research Note)

Aims. To detect line effects using spectropolarimetry in order to find evidence of rotating disks and their respective symmetry axes in T Tauri stars. Methods. We used the IAGPOL imaging polarimeter along with the Eucalyptus-IFU to obtain spectropolarimetric measurements of the T Tauri stars RY Tau (two epochs) and PX Vul (one epoch). Evidence of line effects showing a loop in the Q-U diagram favors a compact rather than an extended source for the line photons in a rotating disk. In addition, the polarization position angle (PA) obtained using the line effect can constrain the symmetry axis of the disk. Results. RY Tau shows a variable H alpha double peak in 2004-2005 data. A polarization line effect is evident in the Q-U diagram for both epochs confirming a clockwise rotating disk. A single loop is evident in 2004 changing to a linear excursion plus a loop in 2005. Interestingly, the intrinsic PA calculated using the line effect is consistent between our two epochs (similar to 167 degrees). An alternative intrinsic PA computed from the interstellar polarization-corrected continuum and averaged between 2001-2005 yielded a PA similar to 137 degrees. This last value is closer to perpendicular to the observed disk direction (similar to 25 degrees), as expected from single scattering in an optically thin disk. For PX Vul, we detected spectral variability in H alpha along with non-variable continuum polarization when compared with previous data. The Q-U diagram shows a well-defined loop in H alpha associated with a counter-clockwise rotating disk. The symmetry axis inferred from the line effect has a PA similar to 91 degrees (with an ambiguity of 90 degrees). Our results confirm previous evidence that the emission line in T Tauri stars has its origin in a compact source scattered off a rotating accretion disk.

DERIVING METALLICITIES FROM THE INTEGRATED SPECTRA OF EXTRAGALACTIC GLOBULAR CLUSTERS USING THE NEAR-INFRARED CALCIUM TRIPLET

The Ca II triplet (CaT) feature in the near-infrared has been employed as a metallicity indicator for individual stars as well as integrated light of Galactic globular clusters (GCs) and galaxies with varying degrees of success, and sometimes puzzling results. Using the DEIMOS multi-object spectrograph on Keck we obtain a sample of 144 integrated light spectra of GCs around the brightest group galaxy NGC 1407 to test whether the CaT index can be used as ametallicity indicator for extragalactic GCs. Different sets of single stellar population models make different predictions for the behavior of the CaT as a function of metallicity. In this work, the metallicities of the GCs around NGC 1407 are obtained from CaT index values using an empirical conversion. The measured CaT/metallicity distributions show unexpected features, the most remarkable being that the brightest red and blue GCs have similar CaT values despite their large difference in mean color. Suggested explanations for this behavior in the NGC 1407 GC system are (1) the CaT may be affected by a population of hot blue stars, (2) the CaT may saturate earlier than predicted by the models, and/or (3) color may not trace metallicity linearly. Until these possibilities are understood, the use of the CaT as a metallicity indicator for the integrated spectra of extragalactic GCs will remain problematic.

Beryllium abundances along the evolutionary sequence of the open cluster IC 4651-A new test for hydrodynamical stellar models

Context. Previous analyses of lithium abundances in main sequence and red giant stars have revealed the action of mixing mechanisms other than convection in stellar interiors. Beryllium abundances in stars with Li abundance determinations can offer valuable complementary information on the nature of these mechanisms. Aims. Our aim is to derive Be abundances along the whole evolutionary sequence of an open cluster. We focus on the well-studied open cluster IC 4651. These Be abundances are used with previously determined Li abundances, in the same sample stars, to investigate the mixing mechanisms in a range of stellar masses and evolutionary stages. Methods. Atmospheric parameters were adopted from a previous abundance analysis by the same authors. New Be abundances have been determined from high-resolution, high signal-to-noise UVES spectra using spectrum synthesis and model atmospheres. The careful synthetic modeling of the Be lines region is used to calculate reliable abundances in rapidly rotating stars. The observed behavior of Be and Li is compared to theoretical predictions from stellar models including rotation-induced mixing, internal gravity waves, atomic diffusion, and thermohaline mixing. Results. Beryllium is detected in all the main sequence and turn-off sample stars, both slow- and fast-rotating stars, including the Li-dip stars, but is not detected in the red giants. Confirming previous results, we find that the Li dip is also a Be dip, although the depletion of Be is more modest than for Li in the corresponding effective temperature range. For post-main-sequence stars, the Be dilution starts earlier within the Hertzsprung gap than expected from classical predictions, as does the Li dilution. A clear dispersion in the Be abundances is also observed. Theoretical stellar models including the hydrodynamical transport processes mentioned above are able to reproduce all the observed features well. These results show a good theoretical understanding of the Li and Be behavior along the color-magnitude diagram of this intermediate-age cluster for stars more massive than 1.2 M(circle dot).