M. T. Ruiz

A reappraisal of the chemical composition of the Orion nebula based on Very Large Telescope echelle spectrophotometry

We present Very Large Telescope (VLT) UVES echelle spectrophotometry of the Orion nebula in the 3100-10 400 A range. We have measured the intensity of 555 emission lines, many of them corresponding to permitted lines of different heavy-element ions. This is the largest set of spectral emission lines ever obtained for a Galactic or extragalactic H II region. We have derived He + , C 2+ , O + , O 2+ and Ne 2+ abundances from pure recombination lines. This is the first time that O + and Ne 2+ abundances have been obtained from these kinds of lines in the nebula. We have also derived abundances from collisionally excited lines for a large number of ions of different elements. In all cases, ionic abundances obtained from recombination lines are larger than those derived from collisionally excited lines. We have obtained remarkably consistent independent estimations of the temperature fluctuation parameter, t 2 , from different methods, which are also similar to other estimates from the literature. This result strongly suggests that moderate temperature fluctuations (t 2 between 0.02 and 0.03) are present in the Orion nebula. We have compared the chemical composition of the nebula with those of the Sun and other representative objects. The heavy-element abundances in the Orion nebula are only slightly higher than the solar ones, a difference that can be explained by the chemical evolution of the solar neighbourhood.

Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager

An exoplanet extracted from the bright Direct imaging of Jupiter-like exoplanets around young stars provides a glimpse into how our solar system formed. The brightness of young stars requires the use of next-generation devices such as the Gemini Planet Imager (GPI). Using the GPI, Macintosh et al. discovered a Jupiter-like planet orbiting a young star, 51 Eridani (see the Perspective by Mawet). The planet, 51 Eri b, has a methane signature and is probably the smallest exoplanet that has been directly imaged. These findings open the door to understanding solar system origins and herald the dawn of a new era in next-generation planetary imaging. Science, this issue p. 64; see also p. 39 The Gemini Planet Imager detects a Jupiter-like exoplanet orbiting the young star 51 Eridani. [Also see Perspective by Mawet] Directly detecting thermal emission from young extrasolar planets allows measurement of their atmospheric compositions and luminosities, which are influenced by their formation mechanisms. Using the Gemini Planet Imager, we discovered a planet orbiting the ~20-million-year-old star 51 Eridani at a projected separation of 13 astronomical units. Near-infrared observations show a spectrum with strong methane and water-vapor absorption. Modeling of the spectra and photometry yields a luminosity (normalized by the luminosity of the Sun) of 1.6 to 4.0 × 10−6 and an effective temperature of 600 to 750 kelvin. For this age and luminosity, “hot-start” formation models indicate a mass twice that of Jupiter. This planet also has a sufficiently low luminosity to be consistent with the “cold-start” core-accretion process that may have formed Jupiter.

Chromospheric activities and kinematics for solar type dwarfs and subgiants: analysis of the activity distribution and the AVR

Aims. In this work we present chromospheric activity indices, kinematics, radial-velocities, and rotational velocities for more than 850 FGK-type dwarfs and subgiant stars in the southern hemisphere and test how best to calibrate and measure S-indices from echelle spectra. Methods. We measured our parameters using the high-resolution and high-S /N FEROS echelle spectra acquired for this purpose. Results. We confirm the bimodal distribution of chromospheric activities for such stars and highlight the role that the more active K-dwarfs play in biasing the number of active stars. We show that the age-activity relationship does appear to continue to ages older than the Sun if we simply compare main sequence stars and subgiant stars with an offset of around 2.5 Gyr between the peaks of both distributions. Also we show evidence of an increased spin-down timescale for cool K dwarfs compared with earlier F and G type stars. We highlight that activities drawn from low-resolution spectra (R < 2500) significantly increase the rms scatter when calibrating onto common systems of measurements like the Mt. Wilson system. Also we show that older and widely used catalogues —————‐ ‐ ‐ ‐

Faint emission lines in the Galactic H ii regions M16, M20 and NGC 3603★

We present deep echelle spectrophotometry of the Galactic H II regions M16, M20 and NGC 3603. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100‐10 400 A range. We have detected more than 200 emission lines in each region. Physical conditions have been derived using different continuum and line intensity ratios. We have derived He + ,C ++ and O ++ abundances from pure recombination lines as well as collisionally excited lines (CELs) for a large number of ions of different elements. We have obtained consistent estimations of the temperature fluctuation parameter, t 2 , using different methods. We also report the detection of deuterium Balmer lines up to Dδ (M16) and to Dγ (M20) in the blue wings of the hydrogen lines, which excitation mechanism seems to be continuum fluorescence. The temperature fluctuation paradigm agrees with the results obtained from optical CELs, and the more uncertain ones from far-infrared fine-structure CELs in NGC 3603, although, more observations covering the same volume of the nebula are necessary to obtain solid conclusions.

Deep echelle spectrophotometry of S 311, a Galactic H ii region located outside the solar circle

We present echelle spectrophotometry of the Galactic H II region S 311. The data have been taken with the Very Large Telescope Ultraviolet-Visual Echelle Spectrograph in the 3100‐ 10 400 A range. We have measured the intensities of 263 emission lines; 178 are permitted lines of H 0 ,D 0 (deuterium), He 0 ,C 0 ,C + ,N 0 ,N + ,O 0 ,O + ,S + ,S i 0 ,S i + ,A r 0 and Fe 0 ; some of them are produced by recombination and others mainly by fluorescence. Physical conditions have been derived using different continuum- and line-intensity ratios. We have derived He + , C ++ and O ++ ionic abundances from pure recombination lines as well as abundances from collisionally excited lines for a large number of ions of different elements. We have obtained consistent estimations of t 2 applying different methods. We have found that the temperature fluctuations paradigm is consistent with the T e(He I )v ersus T e(H I) relation for H II regions, in contrast with what has been found for planetary nebulae. We report the detection of deuterium Balmer lines up to Dδ in the blue wings of the hydrogen lines, whose excitation mechanism seems to be continuum fluorescence. Ke yw ords: ISM: abundances ‐ H II regions ‐ ISM: individual: S 311.

SPECTROSCOPIC ANALYSIS OF HOT, HYDROGEN-RICH WHITE DWARFS: THE PRESENCE OF METALS AND THE BALMER-LINE PROBLEM

We present an analysis of optical spectra for 29 DAO white dwarfs. First, we present our new up-to-date model atmosphere grids computed without the assumption of local thermodynamic equilibrium in which we have included carbon, nitrogen, and oxygen at solar abundances. We demonstrate that the addition of these metals in the model atmospheres is essential in overcoming the Balmer-line problem, which manifests itself as an inability to fit all the Balmer lines simultaneously with consistent atmospheric parameters. We then present the spectroscopic analysis of our sample of DAO white dwarfs for which we determine the effective temperature, surface gravity, and helium abundance. We also present 18 hot DA white dwarfs that also suffer from the Balmer-line problem. We analyze these stars with models analogous to those for the DAO white dwarfs save for the presence of helium. Systematic differences between our newly determined atmospheric parameters with respect to previous determinations are explored. Far-ultraviolet spectra from the FUSE archive are then examined to demonstrate that there exists a correlation between higher metallic abundances and instances of the Balmer-line problem. The implications of these findings for all hot, hydrogen-rich white dwarfs are discussed. Specifically, the possible evolutionary scenario for DAO white dwarfs is revised and post-extreme horizontal branch evolution is no longer needed to explain the evolution for the majority of the DAO stars. Finally, we discuss how the presence of metals might drive a weak stellar wind which in turn could explain the presence of helium in DAO white dwarfs.

Hubble Space Telescope Observations of the Dusty Small Magellanic Cloud H II Region N88A

We present results from the analysis of Hubble Space Telescope Faint Object Spectrograph (FOS), WFPC1, IUE, and Cerro Tololo Inter-American Observatory 4 m observations of the morphology, physical conditions, and chemical abundances in the anomalous H II region N88A in the Small Magellanic Cloud. Not only is N88A unusual among SMC H II regions because it contains much dust, it also is found to have a high electron density and complex ionization structure. The derived reddening curve for the nebula is flatter in the UV than the general SMC extinction curve, suggesting the absence of small grains. A detailed abundance analysis, using both empirical emission-line diagnostics and photoionization model comparisons, indicates that carbon and silicon are enriched in the nebula, while He, O, N, Ne, and Ar are similar in abundance to other SMC H II regions. There is no evidence for the large fluctuations in temperature or density that are seen to occur in some comparably dense planetary nebulae, so we believe that our rather traditional analyses are well founded. We conclude that SMC N88A is a very young H II region forming out of a small dusty molecular cloud that is being disrupted by star formation in a larger OB association in the area. The high carbon and silicon abundances in N88A are attributed to photoevaporation of dust grains existing in the molecular cloud material—rather than being ejected from recent stellar mass loss from stars in N88A itself.

Three planetary companions around M 67 stars

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

Discovery of a T dwarf + white dwarf binary system

The definitive version is available at : www3.interscience.wiley.com Copyright Wiley-Blackwell and Royal Astronomical Society

A transiting planet among 23 new near-threshold candidates from the OGLE survey ⋆ - OGLE-TR-182

By re-processing the data of the second season of the OGLE survey for planetary transits and adding new mesurements on the same fields gathered in subsequent years with the OGLE telescope, we have identified 23 new transit candidates, recorded as OGLE-TR-178 to OGLE-TR-200. We studied the nature of these objects with the FLAMES/UVES multi-fiber spectrograph on the VLT. One of the candidates, OGLE-TR-182, was confirmed as a transiting gas giant planet on a 4-day orbit. We characterised it with further observations using the FORS1 camera and UVES spectrograph on the VLT. OGLE-TR-182b is a typical “hot Jupiter” with an orbital period of 3.98 days, a mass of