Two formation channels of ultra-compact dwarf galaxies in Hickson compact groups

Context. The formation of ultra-compact dwarf galaxies (UCDs) is believed to be driven by interaction, and UCDs are abundant in the cores of galaxy clusters, environments that mark the end-point of galaxy evolution. Nothing is known about the properties of UCDs in compact groups of galaxies, environments where most of galaxy evolution and interaction is believed to occur and where UCDs in an intermediate stage in their evolution may be expected. Aims. The main goal of this study is to detect and characterize, for the first time, the UCD population of compact groups of galaxies. For that, two nearby groups in different evolutionary stages, HCG22 and HCG90, were targeted. Methods. We selected about 40 UCD candidates from pre-existing photometry of both groups, and obtained spectra of these candidates using the VLT FORS2 instrument in MXU mode. Archival HST/ACS imaging was used to measure their structural parameters. Results. We detect 16 and 5 objects belonging to HCG22 and HCG90, respectively, covering the magnitude range -10.0 > M(R) > -11.5 mag. Their integrated colours are consistent with old ages covering a broad range in metallicities (metallicities confirmed by the spectroscopic measurements). Photometric mass estimates put 4 objects in HCG90 and 9 in HCG22 in the mass range of UCDs (> 2 x 10(6) M(circle dot)) for an assumed age of 12Gyr. These UCDs are on average 2-3 times larger than the typical size of Galactic GCs, covering a range of 2 less than or similar to r(h) less than or similar to 21 pc. The UCDs in HCG22 are more concentrated around the central galaxy than in HCG90, at the 99% confidence level. They cover a broad range in [alpha/Fe] abundances from sub-to super-solar. The spectra of 3 UCDs (2 in HCG22, 1 in HCG90) show tentative evidence of intermediate age stellar populations. The clearest example is the largest and most massive UCD (similar to 10(7) M(circle dot)) in our sample, which is detected in HCG22. Its properties are most consistent with a stripped dwarf galaxy nucleus. We calculate the specific frequency (S(N)) of UCDs for both groups, finding that HCG22 has about three times higher S(N) than HCG90. Conclusions. The ensemble properties of the detected UCDs supports two co-existing formation channels: a star cluster origin (low-luminosity, compact sizes, old ages, super-solar alpha/Fe), and an origin as tidally stripped dwarf nuclei (more extended and younger stellar populations). Our results imply that the UCDs detected in both groups do not, in their majority, originate from relatively recent galaxy interactions. Most of the detected UCDs have likely been brought into the group along with their host galaxies.

Transiting exoplanets from the CoRoT space mission XIV. CoRoT-11b: a transiting massive ""hot-Jupiter"" in a prograde orbit around a rapidly rotating F-type star

The CoRoT exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V = 12.9 mag F6 dwarf star (M(*) = 1.27 +/- 0.05 M(circle dot), R(*) = 1.37 +/- 0.03 R(circle dot), T(eff) = 6440 +/- 120 K), with an orbital period of P = 2.994329 +/- 0.000011 days and semi-major axis a = 0.0436 +/- 0.005 AU. The detection of part of the radial velocity anomaly caused by the Rossiter-McLaughlin effect shows that the transit-like events detected by CoRoT are caused by a planet-sized transiting object in a prograde orbit. The relatively high projected rotational velocity of the star (upsilon sin i(star) = 40 +/- 5 km s(-1)) places CoRoT-11 among the most rapidly rotating planet host stars discovered so far. With a planetary mass of M(p) = 2.33 +/- 0.34 M(Jup) and radius R(p) = 1.43 +/- 0.03 R(Jup), the resulting mean density of CoRoT-11b (rho(p) = 0.99 +/- 0.15 g/cm(3)) can be explained with a model for an inflated hydrogen-planet with a solar composition and a high level of energy dissipation in its interior.

Transiting exoplanets from the CoRoT space mission XIII. CoRoT-13b: a dense hot Jupiter in transit around a star with solar metallicity and super-solar lithium content

We announce the discovery of the transiting planet CoRoT-13b. Ground-based follow-up in CFHT and IAC80 confirmed CoRoT's observations. The mass of the planet was measured with the HARPS spectrograph and the properties of the host star were obtained analyzing HIRES spectra from the Keck telescope. It is a hot Jupiter-like planet with an orbital period of 4.04 days, 1.3 Jupiter masses, 0.9 Jupiter radii, and a density of 2.34 g cm(-3). It orbits a G0V star with T(eff) = 5 945 K, M(*) = 1.09 M(circle dot), R(*) = 1.01 R(circle dot), solar metallicity, a lithium content of +1.45 dex, and an estimated age of between 0.12 and 3.15 Gyr. The lithium abundance of the star is consistent with its effective temperature, activity level, and age range derived from the stellar analysis. The density of the planet is extreme for its mass, implies that heavy elements are present with a mass of between about 140 and 300 M(circle plus).

Photometric variability of the Be star CoRoT-ID 102761769

Context. Classical Be stars are rapid rotators of spectral type late O to early A and luminosity class V-III, which exhibit Balmer emission lines and often a near infrared excess originating in an equatorially concentrated circumstellar envelope, both produced by sporadic mass ejection episodes. The causes of the abnormal mass loss (the so-called Be phenomenon) are as yet unknown. Aims. For the first time, we can now study in detail Be stars outside the Earth's atmosphere with sufficient temporal resolution. We investigate the variability of the Be Star CoRoT-ID 102761769 observed with the CoRoT satellite in the exoplanet field during the initial run. Methods. One low-resolution spectrum of the star was obtained with the INT telescope at the Observatorio del Roque de los Muchachos. A time series analysis was performed using both cleanest and singular spectrum analysis algorithms to the CoRoT light curve. To identify the pulsation modes of the observed frequencies, we computed a set of models representative of CoRoT-ID 102761769 by varying its main physical parameters inside the uncertainties discussed. Results. We found two close frequencies related to the star. They are 2.465 c d(-1) (28.5 mu Hz) and 2.441 c d(-1) (28.2 mu Hz). The precision to which those frequencies were found is 0.018 c d(-1) (0.2 mu Hz). The projected stellar rotation was estimated to be 120 km s(-1) from the Fourier transform of spectral lines. If CoRoT-ID 102761769 is a typical Galactic Be star it rotates near the critical velocity. The critical rotation frequency of a typical B5-6 star is about 3.5 c d(-1) (40.5 mu Hz), which implies that the above frequencies are really caused by stellar pulsations rather than star's rotation.

uvby-beta photometry of solar twins The solar colors, model atmospheres, and the T(eff) and metallicity scales

Aims. Solar colors have been determined on the uvby-beta photometric system to test absolute solar fluxes, to examine colors predicted by model atmospheres as a function of stellar parameters (T(eff), log g, [Fe/H]), and to probe zero-points of T(eff) and metallicity scales. Methods. New uvby-beta photometry is presented for 73 solar-twin candidates. Most stars of our sample have also been observed spectroscopically to obtain accurate stellar parameters. Using the stars that most closely resemble the Sun, and complementing our data with photometry available in the literature, the solar colors on the uvby-beta system have been inferred. Our solar colors are compared with synthetic solar colors computed from absolute solar spectra and from the latest Kurucz (ATLAS9) and MARCS model atmospheres. The zero-points of different T(eff) and metallicity scales are verified and corrections are proposed. Results. Our solar colors are (b - y)(circle dot) = 0.4105 +/- 0.0015, m(1,circle dot) = 0.2122 +/- 0.0018, c(1,circle dot) = 0.3319 +/- 0.0054, and beta(circle dot) = 2.5915 +/- 0.0024. The (b - y)(circle dot) and m(1,circle dot) colors obtained from absolute spectrophotometry of the Sun agree within 3-sigma with the solar colors derived here when the photometric zero-points are determined from either the STIS HST observations of Vega or an ATLAS9 Vega model, but the c(1,circle dot) and beta(circle dot) synthetic colors inferred from absolute solar spectra agree with our solar colors only when the zero-points based on the ATLAS9 model are adopted. The Kurucz solar model provides a better fit to our observations than the MARCS model. For photometric values computed from the Kurucz models, (b - y)(circle dot) and m(1,circle dot) are in excellent agreement with our solar colors independently of the adopted zero-points, but for c(1,circle dot) and beta circle dot agreement is found only when adopting the ATLAS9 zero-points. The c(1,circle dot) color computed from both the Kurucz and MARCS models is the most discrepant, probably revealing problems either with the models or observations in the u band. The T(eff) calibration of Alonso and collaborators has the poorest performance (similar to 140 K off), while the relation of Casagrande and collaborators is the most accurate (within 10 K). We confirm that the Ramirez & Melendez uvby metallicity calibration, recommended by Arnadottir and collaborators to obtain [Fe/H] in F, G, and K dwarfs, needs a small (similar to 10%) zero-point correction to place the stars and the Sun on the same metallicity scale. Finally, we confirm that the c(1) index in solar analogs has a strong metallicity sensitivity.

Spectroscopic variabilities in lambda Pavonis

Aims. We investigate the time-varying patterns in line profiles, V/R, and radial velocity of the Be star HD 173948 (lambda Pavonis). Methods. Time series analyses of radial velocity, V/R, and line profiles of He I, Fe II, and Si II were performed with the Cleanest algorithm. An estimate of the stellar rotation frequency was derived from the stellar mass and radius in the Roche limit by adopting an aspect angle i derived from the fittings of non-LTE model spectra affected by rotation. The projected rotation velocity, necessary as input for the spectral synthesis procedure, was evaluated from the Fourier transform of the rotation profiles of all neutral helium lines in the optical range. Results. Emission episodes in Balmer and He i lines, as well as V/R cyclic variations, are reported for spectra observed in year 1999, followed by a relatively quiescent phase (2000) and then again a new active epoch (2001). From time series analyses of line profiles, radial velocities, and V/R ratios, four signals with high confidence levels are detected: nu(1) = 0.17 +/- 0.02, nu(2) = 0.49 +/- 0.05, nu(3) = 0.82 +/- 0.03, and nu(4) = 1.63 +/- 0.04 c/d. We interpret nu 4 as a non-radial pulsation g-mode, nu 3 as a signal related to the orbital timescale of ejected material, which is near the theoretical rotation frequency 0.81 c/d inferred from the fitting of the models taken into account for gravity darkening. The signals nu(1) and nu(2) are viewed as aliases of nu(3) and nu(4).

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.

Kinematics of galaxies in compact groups Studying the B-band Tully-Fischer relation

We obtained new Fabry-Perot data cubes and derived velocity fields, monochromatic, and velocity dispersion maps for 28 galaxies in the Hickson compact groups 37, 40, 47, 49, 54, 56, 68, 79, and 93. We also derived rotation curves for 9 of the studied galaxies, 6 of which are strongly asymmetric. Combining these new data with previously published 2D kinematic maps of compact group galaxies, we investigated the differences between the kinematic and morphological position angles for a sample of 46 galaxies. We find that one third of the unbarred compact group galaxies have position angle misalignments between the stellar and gaseous components. This and the asymmetric rotation curves are clear signatures of kinematic perturbations, probably because of interactions among compact group galaxies. A comparison between the B-band Tully-Fisher relation for compact group galaxies and for the GHASP field-galaxy sample shows that, despite the high fraction of compact group galaxies with asymmetric rotation curves, these lay on the TF relation defined by galaxies in less dense environments, although with more scatter. This agrees with previous results, but now confirmed for a larger sample of 41 galaxies. We confirm the tendency for compact group galaxies at the low-mass end of the Tully-Fisher relation (HCG 49b, 89d, 96c, 96d, and 100c) to have either a magnitude that is too bright for its mass (suggesting brightening by star formation) and/or a low maximum rotational velocity for its luminosity (suggesting tidal stripping). These galaxies are outside the Tully Fisher relation at the 1 sigma level, even when the minimum acceptable values of inclinations are used to compute their maximum velocities. Including such galaxies with nu < 100 km s(-1) in the determination of the zero point and slope of the compact group B-band Tully-Fisher relation would strongly change the fit, making it different from the relation for field galaxies, which has to be kept in mind when studying scaling relations of interacting galaxies, especially at high redshifts.

Transiting exoplanets from the CoRoT space mission X. CoRoT-10b: a giant planet in a 13.24 day eccentric orbit

Context. The space telescope CoRoT searches for transiting extrasolar planets by continuously monitoring the optical flux of thousands of stars in several fields of view. Aims. We report the discovery of CoRoT-10b, a giant planet on a highly eccentric orbit (e = 0.53 +/- 0.04) revolving in 13.24 days around a faint (V = 15.22) metal-rich K1V star. Methods. We used CoRoT photometry, radial velocity observations taken with the HARPS spectrograph, and UVES spectra of the parent star to derive the orbital, stellar, and planetary parameters. Results. We derive a radius of the planet of 0.97 +/- 0.07 R(Jup) and a mass of 2.75 +/- 0.16 M(Jup). The bulk density,rho(p) = 3.70 +/- 0.83 g cm(-3), is similar to 2.8 that of Jupiter. The core of CoRoT-10b could contain up to 240 M(circle plus) of heavy elements. Moving along its eccentric orbit, the planet experiences a 10.6-fold variation in insolation. Owing to the long circularisation time, tau(circ) > 7 Gyr, a resonant perturber is not required to excite and maintain the high eccentricity of CoRoT-10b.

Age and metallicity of star clusters in the Small Magellanic Cloud from integrated spectroscopy

Context. Analysis of ages and metallicities of star clusters in the Magellanic Clouds provide information for studies on the chemical evolution of the Clouds and other dwarf irregular galaxies. Aims. The aim is to derive ages and metallicities from integrated spectra of 14 star clusters in the Small Magellanic Cloud, including a few intermediate/old age star clusters. Methods. Making use of a full-spectrum fitting technique, we compared the integrated spectra of the sample clusters to three different sets of single stellar population models, using two fitting codes available in the literature. Results. We derive the ages and metallicities of 9 intermediate/old age clusters, some of them previously unstudied, and 5 young clusters. Conclusions. We point out the interest of the newly identified as intermediate/old age clusters HW1, NGC 152, Lindsay 3, Lindsay 11, and Lindsay 113. We also confirm the old ages of NGC 361, NGC 419, Kron 3, and of the very well-known oldest SMC cluster, NGC 121.

Transiting exoplanets from the CoRoT space mission XII. CoRoT-12b: a short-period low-density planet transiting a solar analog star

We report the discovery by the CoRoT satellite of a new transiting giant planet in a 2.83 days orbit about a V = 15.5 solar analog star (M(*) = 1.08 +/- 0.08 M(circle dot), R(*) = 1.1 +/- 0.1 R(circle dot), T(eff) = 5675 +/- 80 K). This new planet, CoRoT-12b, has a mass of 0.92 +/- 0.07 M(Jup) and a radius of 1.44 +/- 0.13 R(Jup). Its low density can be explained by standard models for irradiated planets.

Chemical evolution models for spiral disks: the Milky Way, M31, and M33

Context. The distribution of chemical abundances and their variation with time are important tools for understanding the chemical evolution of galaxies. In particular, the study of chemical evolution models can improve our understanding of the basic assumptions made when modelling our Galaxy and other spirals. Aims. We test a standard chemical evolution model for spiral disks in the Local Universe and study the influence of a threshold gas density and different efficiencies in the star formation rate (SFR) law on radial gradients of abundance, gas, and SFR. The model is then applied to specific galaxies. Methods. We adopt a one-infall chemical evolution model where the Galactic disk forms inside-out by means of infall of gas, and we test different thresholds and efficiencies in the SFR. The model is scaled to the disk properties of three Local Group galaxies (the Milky Way, M31 and M33) by varying its dependence on the star formation efficiency and the timescale for the infall of gas onto the disk. Results. Using this simple model, we are able to reproduce most of the observed constraints available in the literature for the studied galaxies. The radial oxygen abundance gradients and their time evolution are studied in detail. The present day abundance gradients are more sensitive to the threshold than to other parameters, while their temporal evolutions are more dependent on the chosen SFR efficiency. A variable efficiency along the galaxy radius can reproduce the present day gas distribution in the disk of spirals with prominent arms. The steepness in the distribution of stellar surface density differs from massive to lower mass disks, owing to the different star formation histories. Conclusions. The most massive disks seem to have evolved faster (i.e., with more efficient star formation) than the less massive ones, thus suggesting a downsizing in star formation for spirals. The threshold and the efficiency of star formation play a very important role in the chemical evolution of spiral disks. For instance, an efficiency varying with radius can be used to regulate the star formation. The oxygen abundance gradient can steepen or flatten in time depending on the choice of this parameter.

Insights on the Milky Way bulge formation from the correlations between kinematics and metallicity

Context. Two main scenarios for the formation of the Galactic bulge are invoked, the first one through gravitational collapse or hierarchical merging of subclumps, the second through secular evolution of the Galactic disc. Aims. We aim to constrain the formation of the Galactic bulge through studies of the correlation between kinematics and metallicities in Baade's Window (l = 1 degrees, b = -4 degrees) and two other fields along the bulge minor axis (l = 0 degrees, b = -6 degrees and b = -12 degrees). Methods. We combine the radial velocity and the [Fe/H] measurements obtained with FLAMES/GIRAFFE at the VLT with a spectral resolution of R = 20 000, plus for the Baade's Window field the OGLE-II proper motions, and compare these with published N-body simulations of the Galactic bulge. Results. We confirm the presence of two distinct populations in Baade's Window found in Hill et al. (2010, A&A, submitted): the metal-rich population presents bar-like kinematics while the metal-poor population shows kinematics corresponding to an old spheroid or a thick disc. In this context the metallicity gradient along the bulge minor axis observed by Zoccali et al. (2008, A&A, 486, 177), visible also in the kinematics, can be related to a varying mix of these two populations as one moves away from the Galactic plane, alleviating the apparent contradiction between the kinematic evidence of a bar and the existence of a metallicity gradient. Conclusions. We show evidence that the two main scenarios for the bulge formation co-exist within the Milky Way bulge.

The role of magnetic reconnection on jet/accretion disk systems

Context. It was proposed earlier that the relativistic ejections observed in microquasars could be produced by violent magnetic reconnection episodes at the inner disk coronal region (de Gouveia Dal Pino & Lazarian 2005). Aims. Here we revisit this model, which employs a standard accretion disk description and fast magnetic reconnection theory, and discuss the role of magnetic reconnection and associated heating and particle acceleration in different jet/disk accretion systems, namely young stellar objects (YSOs), microquasars, and active galactic nuclei (AGNs). Methods. In microquasars and AGNs, violent reconnection episodes between the magnetic field lines of the inner disk region and those that are anchored in the black hole are able to heat the coronal/disk gas and accelerate the plasma to relativistic velocities through a diffusive first-order Fermi-like process within the reconnection site that will produce intermittent relativistic ejections or plasmons. Results. The resulting power-law electron distribution is compatible with the synchrotron radio spectrum observed during the outbursts of these sources. A diagram of the magnetic energy rate released by violent reconnection as a function of the black hole (BH) mass spanning 10(9) orders of magnitude shows that the magnetic reconnection power is more than sufficient to explain the observed radio luminosities of the outbursts from microquasars to low luminous AGNs. In addition, the magnetic reconnection events cause the heating of the coronal gas, which can be conducted back to the disk to enhance its thermal soft X-ray emission as observed during outbursts in microquasars. The decay of the hard X-ray emission right after a radio flare could also be explained in this model due to the escape of relativistic electrons with the evolving jet outburst. In the case of YSOs a similar magnetic configuration can be reached that could possibly produce observed X-ray flares in some sources and provide the heating at the jet launching base, but only if violent magnetic reconnection events occur with episodic, very short-duration accretion rates which are similar to 100-1000 times larger than the typical average accretion rates expected for more evolved (T Tauri) YSOs.

Detection of high-velocity material from the wind-wind collision zone of Eta Carinae across the 2009.0 periastron passage

We report near-infrared spectroscopic observations of the Eta Carinae massive binary system during 2008-2009 using the CRIRES spectrograph mounted on the 8m UT 1 Very Large Telescope (VLT Antu). We detect a strong, broad absorption wing in He I lambda 10833 extending up to -1900 km s(-1) across the 2009.0 spectroscopic event. Analysis of archival Hubble Space Telescope/Space Telescope Imaging Spectrograph ultraviolet and optical data identifies a similar high-velocity absorption (up to -2100 km s(-1)) in the ultraviolet resonance lines of Si IV lambda lambda 1394, 1403 across the 2003.5 event. Ultraviolet resonance lines from low-ionization species, such as Si II lambda lambda 1527, 1533 and CII lambda lambda 1334, 1335, show absorption only up to -1200 km s(-1), indicating that the absorption with velocities -1200 to -2100 km s(-1) originates in a region markedly more rapidly moving and more ionized than the nominal wind of the primary star. Seeing-limited observations obtained at the 1.6m OPD/LNA telescope during the last four spectroscopic cycles of Eta Carinae (1989-2009) also show high-velocity absorption in He I lambda 10833 during periastron. Based on the large OPD/LNA dataset, we determine that material with velocities more negative than -900 km s(-1) is present in the phase range 0.976 <= phi <= 1.023 of the spectroscopic cycle, but absent in spectra taken at phi <= 0.947 and phi >= 1.049. Therefore, we constrain the duration of the high-velocity absorption to be 95 to 206 days (or 0.047 to 0.102 in phase). We propose that the high-velocity absorption component originates in shocked gas in the wind-wind collision zone, at distances of 15 to 45 AU in the line-of-sight to the primary star. With the aid of three-dimensional hydrodynamical simulations of the wind-wind collision zone, we find that the dense high-velocity gas is along the line-of-sight to the primary star only if the binary system is oriented in the sky such that the companion is behind the primary star during periastron, corresponding to a longitude of periastron of omega similar to 240 degrees-270 degrees. We study a possible tilt of the orbital plane relative to the Homunculus equatorial plane and conclude that our data are broadly consistent with orbital inclinations in the range i = 40 degrees-60 degrees.