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A new look at the long-period eclipsing binary V383 Scorpi
Context. The system V383 Sco was discovered to be an eclipsing binarystar at the beginning of the twentieth century. This system has one ofthe longest orbital periods known (13.5 yr) and was initially classifiedas a ζAur-type eclipsing variable. It was then forgotten about fordecades, with no progress made in understanding it. Aims: Thisstudy provides a detailed look at the system V383 Sco, using new dataobtained before, during, and after the last eclipse, which occurred in2007/8. There was a suspicion that this system could be similar toeclipsing systems with extensive dusty disks like EE Cep and ɛAur. This and other, alternative hypotheses are considered here. Methods: The All Sky Automated Survey (ASAS-3) V and I light curves havebeen used to examine apparent magnitude and colour changes. Low- andhigh-resolution spectra have been obtained and used for spectralclassification, to analyse spectral line profiles, as well as todetermine the reddening, radial velocities and the distance to thesystem. The spectral energy distribution (SED) was analysed using allavailable photometric and spectroscopic data. Using our own originalnumerical code, we performed a very simplified model of the eclipse,taking into account the pulsations of one of the components. Results: The low-resolution spectrum shows apparent traces of molecularbands, characteristic of an M-type supergiant. The presence of this starin the system is confirmed by the SED, by a strong dependence of theeclipse depth on the photometric bands, and by the nature of pulsationalchanges. The presence of a very low excitation nebula around the systemhas been inferred from [O i] 6300 Å emission in thehigh-resolution spectrum. Analysis of the radial velocities, reddening,and period-luminosity relation for Mira-type stars imply a distance tothe V383 Sco system of 8.4 ± 0.6 kpc. The distance to the nearbyV381 Sco is 6.4 ± 0.8 kpc. The very different and oppositelydirected radial velocities of these two systems (89.8 km s-1vs. - 178.8 km s-1) seem to be in agreement with a bulge/barkinematic model of the Galactic centre and inconsistent with purelycircular motion. Conclusions: We have found strong evidence forthe presence of a pulsating M-type supergiant in the V383 Sco system.This supergiant periodically obscures the much more luminous F0 I-typestar, causing the deep (possibly total) eclipses which vary in durationand shape.Based on data from the All Sky Automated Survey (ASAS-3) conducted bythe Warsaw University Observatory (Poland), at the Las CampanasObservatory, on observations collected at the La Silla ParanalObservatory, ESO (Chile), with the HARPS spectrograph at the 3.6 mtelescope (ESO run 084.D-0591(A)), and on a low-resolution spectrumobtained at the South African Astronomical Observatory (SAAO) with theGrating Spectrograph at the 1.9 m Radcliffe telescope. Appendix A isavailable in electronic form at http://www.aanda.orgAppendix B is onlyavailable at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/550/A93
| Atmospheric extinction properties above Mauna Kea from the Nearby SuperNova Factory spectro-photometric data set
We present a new atmospheric extinction curve for Mauna Kea spanning3200-9700 Å. It is the most comprehensive to date, being based onsome 4285 standard star spectra obtained on 478 nights spread over aperiod of 7 years obtained by the Nearby SuperNova Factory using theSuperNova Integral Field Spectrograph. This mean curve and itsdispersion can be used as an aid in calibrating spectroscopic or imagingdata from Mauna Kea, and in estimating the calibration uncertaintyassociated with the use of a mean extinction curve. Our method fordecomposing the extinction curve into physical components, and theability to determine the chromatic portion of the extinction even oncloudy nights, is described and verified over the wide range ofconditions sampled by our large dataset. We demonstrate good agreementwith atmospheric science data obtain at nearby Mauna Loa Observatory,and with previously published measurements of the extinction above MaunaKea.Extinction tables are only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/549/A8
| The Gaia spectrophotometric standard stars survey - I. Preliminary results
We describe two ground-based observing campaigns aimed at building agrid of approximately 200 spectrophotometric standard stars (SPSS), withan internal ≃1 per cent precision and tied to Vega within ≃3per cent, for the absolute flux calibration of data gathered by Gaia,the European Space Agency (ESA) astrometric mission. The criteria forthe selection and a list of candidates are presented, together with adescription of the survey strategy and the adopted data analysismethods. We also discuss a short list of notable rejected SPSScandidates and difficult cases, based on identification problems,literature discordant data, visual companions and variability. In fact,all candidates are also monitored for constancy (within ±5 mmag,approximately). In particular, we report on a CALSPEC standard, 1740346,that we found to be a δ Scuti variable during our short-termmonitoring (1-2 h) campaign. Based on data obtained within the Gaia DataProcessing and Analysis Consortium (DPAC) - and coordinated by theGround-based Observations for Gaia (GBOG) working group - at varioustelescopes; see acknowledgments.
| BAL Phosphorus Abundance and Evidence for Immense Ionic Column Densities in Quasar Outflows: VLT/X-Shooter Observations of Quasar SDSS J1512+1119
We present spectroscopic analysis of the broad absorption line (BAL)outflow in quasar SDSS J1512+1119. In particular, we focus our attentionon a kinematic component in which we identify P V and S IV/S IV*absorption troughs. The shape of the unblended phosphorus doublettroughs and the three S IV/S IV* troughs allow us to obtain reliablecolumn density measurements for these two ions. Photoionization modelingusing these column densities and those of He I* constrain the abundanceof phosphorus to the range of 0.5-4 times the solar value. The totalcolumn density, ionization parameter, and metallicity inferred from theP V and S IV column densities lead to large optical depth values for thecommon transition observed in BAL outflows. We show that the true C IVoptical depth is ~1000 times greater in the core of the absorptionprofile than the value deduced from its apparent optical depth.Based on observations collected at the European Southern Observatory,Chile, PID:87.B-0229.
| The metal-enriched host of an energetic γ-ray burst at z ≈ 1.6
Context. The star-forming nature of long γ-ray burst (GRB) hostgalaxies provides invaluable constraints on the progenitors of GRBs andmight open a short-cut to the characteristics of typical star-forminggalaxies throughout the history of the Universe. Due to the absence ofnear-infrared (NIR) spectroscopy, however, detailed investigations,specifically a determination of the gas-phase metallicity of gamma-rayburst hosts, was largely limited to redshifts z < 1 to date. Aims: We observed the galaxy hosting GRB 080605 at z = 1.64 usingoptical/NIR spectroscopy and high-resolution HST/WFC3 imaging in therest-frame wavelength range between 1150 and 8700 Å. These dataallow us to study a z > 1 GRB host in unprecedented detail andinvestigate the relation between GRB hosts and field galaxies. Methods: We availed of VLT/X-shooter optical/NIR spectroscopy to measurethe metallicity, electron density, star-formation rate (SFR), andreddening of the host of GRB 080605. Specifically, we used differentstrong-line diagnostics to robustly measure the gas-phase metallicitywithin the interstellar medium (ISM) for the first time based on [N ii]at this redshift. Results: The host of the energetic(Eγ,iso ~ 2 × 1053 erg) GRB 080605 atz ~ 1.64 is a morphologically complex, vigorously star-forming galaxywith an Hα-derived SFR of 31-6+12M&sun; yr-1. Its ISM is significantly enrichedwith metals. Specifically, [N ii]/Hα = 0.14 ± 0.02, whichyields an oxygen abundance 12 + log (O/H) between 8.3 and 8.6 dependingon the adopted strong-line calibrator. This corresponds to values in therange of 0.4 - 0.8 Z&sun;. For its measured stellar massM* = 8.0-1.6+1.3 × 109M&sun; and SFR, this value is consistent with the fundamentalmetallicity relation defined by star-forming field galaxies. The absenceof strong Lyα emission constrains the escape fraction ofresonantly-scattered Lyα photons to fesc ≲ 0.08. Conclusions: Our observations provide a detailed picture of theconditions in the ISM of a highly star-forming galaxy with irregularmorphology at z ~ 1.6. They include the first robust metallicitymeasurement based on [N ii] for a GRB host at z > 1 and directlyillustrate that GRB hosts are not necessarily metal-poor, both onabsolute scales as well as relative to their stellar mass and SFR. GRBhosts could thus be fair tracers of the population of ordinarystar-forming galaxies at high redshift.Based on observations made with telescopes at the European SouthernObservatory at La Silla/Paranal, Chile under program 087.B-0737(C).
| On the incidence of weak magnetic fields in DA white dwarfs
Context. About 10% of white dwarfs have magnetic fields with strength inthe range between about 105 and 5 × 108 G.It is not known whether the remaining white dwarfs are not magnetic, orif they have magnetic fields too weak to be detected with the techniquesadopted in the large surveys. Information is particularly lacking forthe cooler (and generally fainter) white dwarfs. Aims: Wedescribe the results of the first survey specifically devised to clarifythe detection frequency of kG-level magnetic fields in cool DA whitedwarfs. Methods: Using the FORS1 instrument of the ESO VLT, wehave obtained Balmer line circular spectropolarimetric measurements of asmall sample of cool (DA6 - DA8) white dwarfs. Using FORS and UVESarchive data, we have also revised numerous white dwarf fieldmeasurements previously published in the literature. Results: Wehave discovered an apparently constant longitudinal magnetic field of~9.5 kG in the DA6 white dwarf WD 2105-820. This staris the first weak-field white dwarf that has been observed sufficientlyto roughly determine the characteristics of its field. The availabledata are consistent with a simple dipolar morphology with magnetic axisnearly parallel to the rotation axis, and a polar strength of ≃ 56kG. Our re-evaluation of the FORS archive data for white dwarfsindicates that longitudinal magnetic fields weaker than 10 kG havepreviously been correctly identified in at least three white dwarfs.However, for one of these three weak-field stars (WD2359-434), UVES archive data show a ~100 kG mean fieldmodulus. Either at the time of the FORS observations the star's magneticfield axis was nearly perpendicular to the line of sight, or the star'smagnetic field has rather complex structure. Conclusions: We findthat the probability of detecting a field of kG strength in a DA whitedwarf is of the order of 10% for each of the cool and hot DA stars. Ifthere is a lower cutoff to field strength in white dwarfs, or a fieldbelow which all white dwarfs are magnetic, the current precision ofmeasurements is not yet sufficient to reveal it.Based on observations collected at the European Organisation forAstronomical Research in the Southern Hemisphere, Chile, under observingprogramme 073.D-0516, and obtained from the ESO/ST-ECF Science ArchiveFacility.Table 3 is available in electronic form at http://www.aanda.org
| Two compact H ii regions at the remote outskirts of the Magellanic Clouds
Aims: The H ii regions LMC N191 and SMC N77 are among theoutermost massive star-forming regions in the Magellanic Clouds. So far,few works have dealt with these objects despite their interestingcharacteristics. We aim at studying various physical properties of theseobjects regarding their morphology (in the optical and Spitzer IRACwavelengths), ionized gas emission, nebular chemical abundances,exciting sources, stellar content, age, presence or absence of youngstellar objects, etc. Methods: This study is based mainly onoptical ESO NTT observations, both imaging and spectroscopy, coupledwith other archive data, notably Spitzer images (IRAC 3.6, 4.5, 5.8, and8.0 μm) and 2MASS observations. Results: We show the presenceof two compact H ii regions, a low-excitation blob (LEB) named LMC N191Aand a high-excitation blob (HEB) named SMC N77A, and study theirproperties and those of their exciting massive stars as far as spectraltype and mass are concerned. We also analyze the environmental stellarpopulations and determine their evolutionary stages. Based on SpitzerIRAC data, we characterize the YSO candidates detected in the directionof these regions. Massive star formation is going on in these youngregions with protostars of mass ~10 and 20 M&sun; in theprocess of formation.Based on observations obtained at the European Southern Observatory, LaSilla, Chile, Program 69.C-0286(A) and 69.C-0286(B).
| The light element abundance distribution in NGC 5128 from planetary nebulae
Context. Planetary nebulae in the nearest large elliptical galaxyprovide light element abundances difficult or impossible to measure byother means in a stellar system very different from the galaxies in theLocal Group. Aims: The light element abundance pattern from manyplanetary nebulae (PNe) at a range of radial distances was measured fromoptical spectroscopy in the elliptical galaxy NGC 5128, which hosts theradio source Centaurus A. The PN abundances, in particular for oxygen,and the PN progenitor properties are related to the galaxy stellarproperties. Methods: PNe in NGC 5128 covering the upper 4 mag ofthe luminosity function were selected from a catalogue. VLT FORS1multi-slit spectra in blue and red ranges were obtained over threefields at 3, 9 and 15' projected radii (4, 8 and 17 kpc, for an adopteddistance of 3.8 Mpc) and spectra were extracted for 51 PNe. Accurateelectron temperature and density diagnostics are usually required forabundance determination, but were not available for most of the PNe.Cloudy photoionization models were run to match the spectra by aspherical, constant density nebula ionized by a black body central star.He, N, O and Ne abundances with respect to H were determined and, forbrighter PN, S and Ar; central star luminosities and temperatures arealso derived. Results: Emission line ratios for the 51 PNe areentirely typical of PN such as in the Milky Way. The temperaturesensitive [O III]4363 Å line was weakly detected in 10 PNe, both[O II] and [O III] lines were detected in 30 PNe, and only the bright [OIII]5007 Å line was detected in 7 PN. For 40 PNe with Cloudymodels, from the upper 2 mag of the [O III] luminosity function, themost reliably estimated element, oxygen, has a mean 12 + log(O/H) of8.52 with a narrow distribution. No obvious radial gradient is apparentin O/H over a range 2-20 kpc. Comparison of the PN abundances with thestellar population, from the spectra of the integrated stellar light onthe multi-slits and existing photometric studies, suggests an averagemetallicity of [Fe/H] = -0.4 and [O/Fe] = 0.25. Conclusions: Themasses of the PN central stars in NGC 5128 deduced from model tracksimply an epoch of formation even more recent than found for the minorityyoung population from colour magnitude studies. The PN may belong to theyoung tail of a recent, minor, star formation episode or derive fromother evolutionary channels, perhaps involving binary stars.Based on observations collected at the European Organisation forAstronomical Research in the Southern Hemisphere, Chile in observingproposals 64.N-0219, 66.B-0134, 67.B-0111 and 71.B-0134.Tables 5, 6 and8-12 are available in electronic form at http://www.aanda.org
| A Classification of H II Regions Based on Oxygen and Helium Lines: The Cases of TOL 2146-391 and TOL 0357-3915
We present long-slit spectrophotometry of two H II galaxies: TOL2146-391 and TOL 0357-3915. We performed a detailed analysisthat involves abundance determinations relaxing the assumption ofhomogeneous temperature. The temperature inhomogeneity values, t2, were obtained through two methods: (1) comparingabundances from oxygen recombination lines to abundances fromcollisionally excited lines and (2) by using the line intensity ratiosof a set of He I lines together with the HELIO10 program. We find thatthe HELIO10 program is a good alternative to obtain a t 2value in photoionized regions where recombination lines of heavyelements are not available. We have plotted 27 high- and low-metallicityH II regions in an oxygen degree of ionization versus t 2diagram; we find areas populated by H II regions and areas void of them;the physical characteristics of each area are discussed. In addition, anaverage t 2 value can be determined for the objects in eacharea. We propose to use this langt 2rang value for the caseswhere a direct measurement of t 2 cannot be determined.Based on observations collected at the European Southern Observatory,Chile, proposal number ESO 69.C-0203(A).
| Know Your Neighborhood: A Detailed Model Atmosphere Analysis of Nearby White Dwarfs
We present improved atmospheric parameters of nearby white dwarfs lyingwithin 20 pc of the Sun. The aim of the current study is to obtain thebest statistical model of the least-biased sample of the white dwarfpopulation. A homogeneous analysis of the local population is performedcombining detailed spectroscopic and photometric analyses based onimproved model atmosphere calculations for various spectral typesincluding DA, DB, DC, DQ, and DZ stars. The spectroscopic technique isapplied to all stars in our sample for which optical spectra areavailable. Photometric energy distributions, when available, are alsocombined to trigonometric parallax measurements to derive effectivetemperatures, stellar radii, as well as atmospheric compositions. Arevised catalog of white dwarfs in the solar neighborhood is presented.We provide, for the first time, a comprehensive analysis of the massdistribution and the chemical distribution of white dwarf stars in avolume-limited sample.
| The Wolf-Rayet population of the nearby barred spiral galaxy NGC 5068 uncovered by the Very Large Telescope and Gemini
We present a narrow-band Very Large Telescope/Focal ReducedLow-dispersion Spectrograph #1 imaging survey of the SAB(rs)cd spiralgalaxy NGC 5068, located at a distance of 5.45 Mpc, from which 160candidate Wolf-Rayet sources have been identified, of which 59 casespossess statistically significant λ4686 excesses. Follow-upGemini Multi-Object Spectrograph spectroscopy of 64 candidates,representing 40 per cent of the complete photometric catalogue, confirmsWolf-Rayet signatures in 30 instances, corresponding to a 47 per centsuccess rate. 21 out of 22 statistically significant photometric sourcesare spectroscopically confirmed. Nebular emission detected in 30 percent of the Wolf-Rayet candidates spectrally observed, which enable are-assessment of the metallicity gradient in NGC 5068. A centralmetallicity of log (O/H) + 12 ˜ 8.74 is obtained, declining to8.23 at R25. We combine our spectroscopy with archivalHα images of NGC 5068 to estimate a current star formation rate of?, and provide a catalogue of the 28 brightest H II regions from our owncontinuum subtracted Hα images, of which ˜17 qualify asgiant H II regions. Spectroscopically, we identify 24 WC- and 18 WN-typeWolf-Rayet stars within 30 sources since emission-line fluxes indicatemultiple Wolf-Rayet stars in several cases. We estimate an additional˜66 Wolf-Rayet stars from the remaining photometric candidates,although sensitivity limits will lead to an incomplete census ofvisually faint WN stars, from which we estimate a global population of˜170 Wolf-Rayet stars. Based on the Hα-derived O starpopulation of NGC 5068 and N(WR)/N(O) ˜ 0.03, representative ofthe Large Magellanic Cloud, we would expect a larger Wolf-Rayetpopulation of 270 stars. Finally, we have compared the spatialdistribution of spectroscopically confirmed WN and WC stars with SloanDigital Sky Survey derived supernovae, and find both WN and WC stars tobe most consistent with the parent population of Type Ib supernovae.
| Spectroscopic Follow-up of X-Ray Sources in the ChaMPlane Survey: Identification of a New Cataclysmic Variable
We present a multi-object optical spectroscopy follow-up study of X-raysources in a field along the Galactic plane (l = 327fdg42, b = 2fdg26)which is part of the Chandra Multi-wavelength Plane survey (ChaMPlane).We obtained spectra for 46 stars, including 15 likely counterparts toX-ray sources, and sources showing an Hα color excess. This hasled to the identification of a new cataclysmic variable (CV), CXOPSJ154305.5-522709, also named ChaMPlane Bright Source 7 (CBS 7), and weidentified eight X-ray sources in the field as active late-type stars.CBS 7 was previously studied in X-rays and showed a hard spectrum andtwo periods: 1.22 ± 0.08 hr and 2.43 ± 0.26 hr. We presenthere clear evidence that the source is a CV through the detection of H,He I, and He II emission lines in its optical spectrum. The hard X-rayspectrum and the presence of the He II λ4686 in emission with alarge equivalent width suggest a magnetic CV. The near-infraredcounterpart is significantly variable, and we found a period consistentwith the longest X-ray period at 2.39 ± 0.05 hr but not theshortest X-ray period. If this period is the orbital period, this wouldplace the system in the CV period gap. The possible orbital periodsuggests a dM4 ± 1 companion star. The distance is then estimatedto be ~1 kpc. The system could be a relatively hard and X-ray luminouspolar or an intermediate polar, possibly nearly synchronous.
| Analysis of Two Small Magellanic Cloud H II Regions Considering Thermal Inhomogeneities: Implications for the Determinations of Extragalactic Chemical Abundances
We present long-slit spectrophotometry considering the presence ofthermal inhomogeneities (t 2) of two H II regions in theSmall Magellanic Cloud (SMC): NGC 456 and NGC 460. Physical conditionsand chemical abundances were determined for three positions in NGC 456and one position in NGC 460, first under the assumption of uniformtemperature and then allowing for the possibility of thermalinhomogeneities. We determined t 2 values based on threedifferent methods: (1) by comparing the temperature derived using oxygenforbidden lines with the temperature derived using helium recombinationlines (RLs), (2) by comparing the abundances derived from oxygenforbidden lines with those derived from oxygen RLs, and (3) by comparingthe abundances derived from ultraviolet carbon forbidden lines withthose derived from optical carbon RLs. The first two methods averaged t2 = 0.067 ± 0.013 for NGC 456 and t 2 =0.036 ± 0.027 for NGC 460. These values of t 2 implythat when gaseous abundances are determined with collisionally excitedlines they are underestimated by a factor of nearly two. From theseobjects and others in the literature, we find that in order to accountfor thermal inhomogeneities and dust depletion, the O/H ratio inlow-metallicity H II regions should be corrected by 0.25-0.45 dexdepending on the thermal structure of the nebula or by 0.35 dex if suchinformation is not available.Based on observations collected at the European Southern Observatory,Chile, proposal number ESO 69.C-0203(A).
| Magnetic field measurements and their uncertainties: the FORS1 legacy
Context. During the last decade, the FORS1 instrument of the ESO VeryLarge Telescope has been extensively used to study stellar magnetism. Anumber of interesting discoveries of magnetic fields in several classesof stars have been announced, many of which obtained at a ~3σlevel; some of the discoveries are confirmed by measurements obtainedwith other instruments, some are not. Aims: We investigate thereasons for the discrepancies between the results obtained with FORS1and those obtained with other instruments. Methods: Using the ESOFORS pipeline, we have developed a semi-automatic procedure for magneticfield determination. We have applied this procedure to the full contentof circular spectropolarimetric measurements of the FORS1 archive(except for most of the observations obtained in multi-objectspectropolarimetric mode). We have devised and applied a number ofconsistency checks to our field determinations, and we have compared ourresults to those previously published in the literature. Results:We find that for high signal-to-noise ratio measurements, photon noisedoes not account for the full error bars. We discuss how fieldmeasurements depend on the specific algorithm adopted for datareduction, and we show that very small instrument flexures, negligiblein most of the instrument applications, may be responsible for somespurious field detections in the null profiles. Finally, we find that weare unable to reproduce some results previously published in theliterature. Consequently, we do not confirm some important discoveriesof magnetic fields obtained with FORS1 and reported in previouspublications. Conclusions: Our revised field measurements showthat there is no contradiction between the results obtained with thelow-resolution spectropolarimeter FORS1 and those obtained withhigh-resolution spectropolarimeters. FORS1 is an instrument capable ofperforming reliable magnetic field measurements, provided that thevarious sources of uncertainties are properly taken into account.Table 5 is available in electronic form at http://www.aanda.org
| Physical studies of 81P/Wild 2 from the last two apparitions
Context. We downloaded data for the comet 81P/Wild 2 for May and June2004 from the ESO archive and monitored this comet from January toAugust 2010 during its 6th perihelion passage since its discovery in1978. Photometric data were used to monitor the comet's gas and dustactivity as a function of heliocentric distance. Non-photometric datawere used for an analysis of the evolution of the dust coma morphology. Aims: The goal of the analysis of the observational data was tocharacterize the evolution of the cometary activity as the nucleusapproaches the Sun. We also aimed to assess the gas and dust productionrates for the last two apparitions and investigated the evolution of thedust coma morphology during the last passage in 2010. Methods:The long-slit spectra data were acquired with the EFOSC2 instrumentmounted at the 3.6. m ESO telescope in Chile, while narrowband andbroadband images were obtained using the 1-m telescope at the LulinObservatory in Taiwan. Image enhancing techniques were used toinvestigate the evolution of the dust coma morphology in the R-broadbandimages, and we modeled the evolution of these dust jets. Where possible,we studied the dust and gas production rate, and the radial profiles ofthe dust brightness in the Sun-anti-sunward directions. Results:The morphological analysis helped us to detect the jet structures in thedust coma by using the Larson-Sekanian filter. In May 2004, only onefeature had been found on the sunward side. In 2010, one of the jetfeatures had been switched-off after January, and at least four new jetswere found from April to May. The physical properties show an averagereddening between 4420 Å and 6840 Å of 8.4% per 1000 Åand the average resulting log of the C2-to-CN production rateratio is -0.454 ± 0.13, which would place Wild 2 in the"depleted" category according to the taxonomic classification. The slopeof the radial dependence of the gas production rates for CN andC2 is very consistent with observations of many otherJupiter-family comets. The slopes of the surface brightness lie between0.98 and 1.38 in the images taken at the Lulin observatory, whose therange interval from 2000 km to 30 000 km is roughly consistent with theρ-1 law. However, the gradient of the radial profile inthe sunward direction in the outer region (4.0 ≤ log ρ(km) ≤4.5) is slightly steeper than that in the inner region (3.3 ≤ logρ(km) ≤ 4.0).Based on observations made with the European Southern Observatorytelescopes obtained from the ESO/ST-ECF Science Archive Facility.
| Chemical abundances in the protoplanetary disc LV 2 (Orion) - II. High-dispersion VLT observations and microjet properties
Integral field spectroscopy of the LV 2 proplyd is presented taken withthe Very Large Telescope (VLT)/FLAMES Argus array at an angularresolution of 0.31 × 0.31 arcsec2 and velocityresolutions down to 2 km s-1 pixel-1. Followingsubtraction of the local M42 emission, the spectrum of LV 2 is isolatedfrom the surrounding nebula. We measured the heliocentric velocities andwidths of a number of lines detected in the intrinsic spectrum of theproplyd, as well as in the adjacent Orion nebula falling within a 6.6× 4.2 arcsec2 field of view. It is found thatfar-ultraviolet to optical collisional lines with critical densities,Ncr, ranging from 103 to 109cm-3 suffer collisional de-excitation near the rest velocityof the proplyd correlating tightly with their critical densities. Linesof low Ncr are suppressed the most. The bipolar jet arisingfrom LV 2 is spectrally and spatially well detected in several emissionlines. We compute the [O III] electron temperature profile across LV 2in velocity space and measure steep temperature variations associatedwith the red-shifted lobe of the jet, possibly being due to a shockdiscontinuity. From the velocity-resolved analysis the ionized gas nearthe rest frame of LV 2 has Te= 9200 ± 800 K andNe˜ 106 cm-3, while thered-shifted jet lobe has Te≈ 9000-104 K andNe˜ 106-107 cm-3. Thejet flow is highly ionized but contains dense semineutral clumpsemitting neutral oxygen lines. The abundances of N+, O2+, Ne2 +, Fe2 +, S+and S2+are measured for the strong red-shifted jet lobe. Iron in thecore of LV 2 is depleted by 2.54 dex with respect to solar as a resultof sedimentation on dust, whereas the efficient destruction of dustgrains in the fast microjet raises its Fe abundance to at least 30 percent solar. Sulphur does not show evidence of significant depletion ondust, but its abundance both in the core and the jet is only about halfsolar. Based on observations made with ESO telescopes at the ParanalObservatory under programme 078.C-0247(A).
| Accretion in the detached post-common-envelope binary LTT 560
In a previous study, we found that the detached post-common-envelopebinary LTT 560 displays an Hα emission line consisting of twoanti-phased components. While one of them was clearly caused by stellaractivity from the secondary late-type main-sequence star, our analysisindicated that the white dwarf primary star is potentially the origin ofthe second component. However, the low resolution of the data means thatour interpretation remains ambiguous. We here use time-series UVES datato compare the radial velocities of the Hα emission components tothose of metal absorption lines from the primary and secondary stars. Wefind that the weaker component most certainly originates in the whitedwarf and is probably caused by accretion. An abundance analysis of thewhite dwarf spectrum yields accretion rates that are consistent withmass loss from the secondary due to a stellar wind. The second andstronger Hα component is attributed to stellar activity on thesecondary star. An active secondary is likely to be present because ofthe occurrence of a flare in our time-resolved spectroscopy.Furthermore, Roche tomography indicates that a significant area of thesecondary star on its leading side and close to the first Lagrange pointis covered by star spots. Finally, we derive the parameters for thesystem and place it in an evolutionary context. We find that the whitedwarf is a very slow rotator, suggesting that it has had anangular-momentum evolution similar to that of field white dwarfs. Wepredict that LTT 560 will begin mass transfer via Roche-lobe overflow in~3.5 Gyr, and conclude that the system is representative of theprogenitors of the current population of cataclysmic variables. It willmost likely evolve to become an SU UMa type dwarf nova.Based on observations made at ESO telescopes (079.D-0276).
| Cool White Dwarfs Found in the UKIRT Infrared Deep Sky Survey
We present the results of a search for cool white dwarfs in the UnitedKingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS)Large Area Survey (LAS). The UKIDSS LAS photometry was paired with theSloan Digital Sky Survey to identify cool hydrogen-rich white dwarfcandidates by their neutral optical colors and blue near-infraredcolors, as well as faint reduced proper motion magnitudes. Opticalspectroscopy was obtained at Gemini Observatory and showed the majorityof the candidates to be newly identified cool degenerates, with a smallnumber of G- to K-type (sub)dwarf contaminants. Our initial search of280 deg2 of sky resulted in seven new white dwarfs witheffective temperature T eff ≈ 6000 K. The currentfollow-up of 1400 deg2 of sky has produced 13 new whitedwarfs. Model fits to the photometry show that seven of the newlyidentified white dwarfs have 4120 K <=T eff <= 4480 K,and cooling ages between 7.3 Gyr and 8.7 Gyr; they have 40 kms-1 <= v tan <= 85 km s-1 and arelikely to be thick disk 10-11 Gyr-old objects. The other half of thesample has 4610 K <=T eff <= 5260 K, cooling agesbetween 4.3 Gyr and 6.9 Gyr, and 60 km s-1 <= vtan <= 100 km s-1. These are either thin diskremnants with unusually high velocities, or lower-mass remnants of thickdisk or halo late-F or G stars.
| Central stars of planetary nebulae. II. New OB-type and emission-line stars
Context. There are more than 3000 confirmed and probably known Galacticplanetary nebulae (PNe), but central star spectroscopic information isavailable for only 13% of them. Aims: We have undertaken aspectroscopic survey of the central stars in PNe to identify theirspectral types. Methods: We performed spectroscopic observationsat low resolution with the 2-m telescope at CASLEO, Argentina. Results: We present the spectra of 46 central stars of PNe, most of themare OB-type and emission-line stars.Based on data collected at the Complejo Astronómico El Leoncito(CASLEO), which is operated under agreement between the Consejo Nacionalde Investigaciones Científicas y Técnicas de laRepública Argentina y Universidades Nacionales de La Plata,Córdoba y San Juan, Argentina.The reduced spectra (FITS files)are available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A172
| The inverse problem of the theory of degenerate dwarfs
Based on the radii and masses of degenerate dwarfs derived fromHIPPARCOS and other observations, we estimate the microscopic parametersof a Chandrasekhar model (the relativistic parameter at the stellarcenter x 0, and the chemical-composition parameterµ e = A/Z, where A is the mass number and Z is thenuclear charge). We have obtained analytical expressions for themacroscopic characteristics (mass, radius, energy) as functions of x0 and µ e . From the calculated dependenceof the energy on these parameters, we have found constraints on therange of variability of x 0, which are in good agreement withthe observed radius distribution of dwarfs. The critical value of x0 at which stability breaks down due to general-relativisitceffects is found more accurately than previously. We propose ageneralized model with an inhomogeneous (coordinate-dependent) chemicalcomposition, with µ e = µ e ( r).
| The Relation between Dynamics and Star Formation in Barred Galaxies
We analyze optical and near-infrared data of a sample of 11 barredspiral galaxies, in order to establish a connection between starformation and bar/spiral dynamics. We find that 22 regions located inthe bars and 20 regions in the spiral arms beyond the end of the barpresent azimuthal color/age gradients that may be attributed to starformation triggering. Assuming a circular motion dynamic model, wecompare the observed age gradient candidates with stellar populationsynthesis models. A link can then be established with the disk dynamicsthat allows us to obtain parameters like the pattern speed of the bar orspiral as well as the positions of resonance radii. We subsequentlycompare the derived pattern speeds with those expected from theoreticaland observational results in the literature (e.g., bars ending nearcorotation). We find a tendency to overestimate bar pattern speedsderived from color gradients in the bar at small radii, away fromcorotation; this trend can be attributed to non-circular motions of theyoung stars born in the bar region. In spiral regions, we find that ~50%of the color gradient candidates are "inverse," i.e., with the directionof stellar aging contrary to that of rotation. The other half of thegradients found in spiral arms have stellar ages that increase in thesame sense as rotation. Of the nine objects with gradients in both barsand spirals, six (67%) appear to have a bar and a spiral with similar? p , while three (33%) do not.
| An interesting candidate for isolated massive-star formation in the Small Magellanic Cloud
Context. The region of the Small Magellanic Cloud (SMC) with which thispaper is concerned contains the highest concentration of IRAS/Spitzersources, H i emission, and molecular clouds in this neighboring galaxy.However, it has been the target of very few studies, despite thisevidence of star formation. Aims: We present the first detailedstudy of the compact H ii region N33 in the SMC by placing it in a widercontext of massive star formation. Moreover, we show that N33 is aparticularly interesting candidate for isolated massive star formation. Methods: This analysis is based mainly on optical ESO NTTobservations, both imaging and spectroscopy, coupled with other archivedata, notably Spitzer images (IRAC 3.6, 4.5, 5.8, and 8.0 μm) and2MASS observations. Results: We derive a number of physicalcharacteristics of the compact H ii region N33 for the first time. Thisgas and dust formation of 7.4 arcsec (2.2 pc) in diameter is powered bya massive star of spectral type O6.5-O7 V. The compact H ii regionbelongs to a rare class of H ii regions in the Magellanic Clouds, calledhigh-excitation blobs (HEBs). We show that this H ii region is notrelated to any star cluster. Specifically, we do not find any traces ofclustering around N33 on scales larger than 10'' (~3 pc). On smallerscales, there is a marginal stellar concentration, the low density ofwhich, below the 3σ level, does not classify it as a real cluster.We also verify that N33 is not a member of any large stellarassociation. Under these circumstances, N33 is also therefore attractivebecause it represents a remarkable case of isolated massive-starformation in the SMC. Various aspects of the relevance of N33 to thetopic of massive-star formation in isolation are discussed.Based on observations obtained at the European Southern Observatory, LaSilla, Chile, Program 69.C-0286(A) and 69.C-0286(B).
| Dust and Chemical Abundances of the Sagittarius Dwarf Galaxy Planetary Nebula Hen2-436
We have estimated elemental abundances of the planetary nebula (PN)Hen2-436 in the Sagittarius (Sgr) spheroidal dwarf galaxy using ESO/VLTFORS2, Magellan/MMIRS, and Spitzer/IRS spectra. We have detectedcandidates of fluorine [F II] λ4790, krypton [Kr III]λ6826, and phosphorus [P II] λ7875 lines and successfullyestimated the abundances of these elements ([F/H] = +1.23, [Kr/H] =+0.26, [P/H] = +0.26) for the first time. These elements are known to besynthesized by the neutron capture process in the He-rich intershellduring the thermally pulsing asymptotic giant branch (AGB) phase. Wepresent a relation between C, F, P, and Kr abundances among PNe andC-rich stars. The detections of these elements in Hen2-436 support theidea that F, P, Kr together with C are synthesized in the same layer andbrought to the surface by the third dredge-up. We have detected N II andO II optical recombination lines (ORLs) and derived the N2+and O2+ abundances. The discrepancy between the abundancederived from the oxygen ORL and that derived from the collisionallyexcited line is >1 dex. To investigate the status of the central starof the PN, nebula condition, and dust properties, we construct atheoretical spectral energy distribution (SED) model to match theobserved SED with CLOUDY. By comparing the derived luminosity andtemperature of the central star with theoretical evolutionary tracks, weconclude that the initial mass of the progenitor is likely to be~1.5-2.0 M sun and the age is ~3000 yr after the AGB phase.The observed elemental abundances of Hen2-436 can be explained by atheoretical nucleosynthesis model with a star of initial mass 2.25 Msun, Z = 0.008, and LMC compositions. We have estimated thedust mass to be 2.9×10-4 M sun (amorphouscarbon only) or 4.0×10-4 M sun (amorphouscarbon and polycyclic aromatic hydrocarbon). Based on the assumptionthat most of the observed dust is formed during the last two thermalpulses and the dust-to-gas mass ratio is 5.58 × 10-3,the dust mass-loss rate and the total mass-loss rate are<3.1×10-8 M sun yr-1and<5.5×10-6 M sun yr-1,respectively. Our estimated dust mass-loss rate is comparable to a Sgrdwarf galaxy AGB star with similar metallicity and luminosity.
| A selection of hot subluminous stars in the GALEX survey - I. Correlation with the Guide Star Catalog
We assembled a catalogue of bright, hot subdwarf and white dwarf starsextracted from a joint ultraviolet, optical and infrared source list.The selection is secured using colour criteria that correlate well witheffective temperatures Teff? 12 000 K. We built aNUV- V versus V - J diagram for ?60 000 bright sourcesusing the Galaxy Evolution Explorer (GALEX) NUV magnitude(NUV < 14), the associated Guide Star Catalog (GSC2.3.2)photographic quick-V magnitude and the Two-Micron All-Sky Survey J and Hmagnitudes. This distillation process delivered a catalogue of ?700sources with NUV- V < 0.5 comprising ˜160 known hotsubdwarf stars and another ˜60 known white dwarf stars. A reducedproper-motion diagram built using the proper-motion measurementsextracted from the Naval Observatory Merged Astrometric Dataset allowedus to identify an additional ˜120 new hot subdwarf candidates and˜10 hot white dwarf candidates. We present a spectroscopic studyof a subset of 52 subdwarfs, 48 of them analysed here for the firsttime, and with nine objects brighter than V ˜ 12. Our sample ofspectroscopically confirmed hot subdwarfs comprises 10 sdO-type starsand 42 sdB-type stars suitable for pulsation and binary studies. We alsopresent a study of 50 known white dwarfs selected in the GALEX surveyand six new white dwarfs from our catalogue of subluminous candidates.Ultraviolet, optical and infrared synthetic magnitudes employed in theselection and analysis of white dwarf stars are listed in appendix.Based on observations made with ESO telescopes at the La Silla ParanalObservatory under programmes 82.D-0750, 83.D-0540 and085.D-0866.Visiting Astronomer, Kitt Peak National Observatory, NationalOptical Astronomy Observatory, which is operated by the Association ofUniversities for Research in Astronomy (AURA) under cooperativeagreement with the National Science Foundation.
| Shocks and Cavities from Multiple Outbursts in the Galaxy Group NGC 5813: A Window to Active Galactic Nucleus Feedback
We present results from new Chandra, GMRT, and SOAR observations of NGC5813, the dominant central galaxy in a nearby galaxy group. The systemshows three pairs of collinear cavities at 1 kpc, 8 kpc, and 20 kpc fromthe central source, from three distinct outbursts of the central activegalactic nucleus (AGN), which occurred 3 × 106, 2× 107, and 9 × 107 yr ago. TheHα and X-ray observations reveal filaments of cool gas that hasbeen uplifted by the X-ray cavities. The inner two cavity pairs arefilled with radio-emitting plasma, and each pair is associated with anelliptical surface brightness edge, which we unambiguously identify asshocks (with measured temperature jumps) with Mach numbers of M ≈ 1.7and M ≈ 1.5 for the inner and outer shocks, respectively. Such clearsignatures from three distinct AGN outbursts in an otherwise dynamicallyrelaxed system provide a unique opportunity to study AGN feedback andoutburst history. The mean power of the two most recent outburstsdiffers by a factor of six, from (1.5-10)×1042 ergs-1, indicating that the mean jet power changes significantlyover long (~107 yr) timescales. The total energy output ofthe most recent outburst is also more than an order of magnitude lessthan the total energy of the previous outburst (1.5 ×1056 erg versus 4 × 1057 erg), which may bea result of the lower mean power, or may indicate that the most recentoutburst is ongoing. The outburst interval implied by both the shock andcavity ages (~107 yr) indicates that, in this system, shockheating alone is sufficient to balance radiative cooling close to thecentral AGN, which is the relevant region for regulating feedbackbetween the intracluster medium and the central supermassive black hole.
| Rapid optical and X-ray timing observations of GX339-4: multicomponent optical variability in the low/hard state
A rapid timing analysis of Very Large Telescope (VLT)/ULTRACAM (optical)and RXTE (X-ray) observations of the Galactic black hole binary GX339-4in the low/hard, post-outburst state of 2007 June is presented. Theoptical light curves in the r',g' and u' filters show slow (~20s)quasi-periodic variability. Upon this is superposed fast flaringactivity on times approaching the best time resolution probed (~50ms inr' and g') and with maximum strengths of more than twice the local mean.Power spectral analysis over ~0.004-10Hz is presented, and shows thatalthough the average optical variability amplitude is lower than that inX-rays, the peak variability power emerges at a higher Fourier frequencyin the optical. Energetically, we measure a large optical versus X-rayflux ratio, higher than that seen on previous occasions when the sourcewas fully jet dominated. Such a large ratio cannot be easily explainedwith a disc alone. Studying the optical-X-ray cross-spectrum in Fourierspace shows a markedly different behaviour above and below ~0.2Hz. Thepeak of the coherence function above this threshold is associated with ashort optical time lag with respect to X-rays, also seen as the dominantfeature in the time-domain cross-correlation at ~150ms. The rms energyspectrum of these fast variations is best described by distinct physicalcomponents over the optical and X-ray regimes, and also suggests amaximal irradiated disc fraction of 20 per cent around 5000Å. Ifthe constant time delay is due to propagation of fluctuations to (orwithin) the jet, this is the clearest optical evidence to date of thelocation of this component. The low-frequency quasi-periodic oscillationis seen in the optical but not in X-rays, and is associated with a lowcoherence. Evidence of reprocessing emerges at the lowest Fourierfrequencies, with optical lags at ~10s and strong coherence in the blueu' filter. Consistent with this, simultaneous optical spectroscopy alsoshows the Bowen fluorescence blend, though its emission location isunclear. However, canonical disc reprocessing cannot dominate theoptical power easily, nor explain the fast variability.
| Accurate Coordinates and 2MASS Cross Identifications for (Almost) All Gliese Catalog Star
We provide precise J2000, epoch 2000 coordinates, andcross-identifications to sources in the 2MASS Point Source Catalog fornearly all stars in the Gliese, Gliese-Jahreiss, and Woolley catalogs ofnearby stars. The only Gliese objects where we were not successful aretwo Gliese sources that are actually QSOs; two proposed companions tobrighter stars, which we believe do not exist; four stars included inone of the catalogs but identified there as only optical companions; oneprobable plate flaw; and two stars that simply remain unrecovered. Forthe 4251 recovered stars, 2693 have coordinates based on Hipparcospositions, 1549 have coordinates based on 2MASS data, and 9 havepositions from other astrometric sources. All positions have beencalculated at epoch 2000 using proper motions from the literature, whichare also given here.
| A very young component in the pre-eminent starburst region of the Small Magellanic Cloud
Context. Despite extensive research on various components of the N66/NGC346 complex, few studies have so far focused on N66A, which is a specialobject in the whole complex and therefore deserves scrutiny. The studyof this compact H ii region and its fellow objects seems important inthe framework of massive star formation in the Magellanic Clouds. Aims: We present a study of the compact H ii region N66A in the SMCpre-eminent starburst region N66/NGC 346. Methods: This analysisis based mainly on our optical ESO NTT observations, both imaging andspectroscopy, coupled with archive HST ACS data and Spitzer infraredimages (IRAC 3.6, 4.5, 5.8, and 8.0 μm). Results: We derive anumber of physical characteristics of the compact H ii region N66A. Forthe first time using spectroscopy, we present the spectralclassification of the main exciting star of N66A. Its spectral featuresindicate that it is a main-sequence massive star of type O8. We comparethis result with that based on the stellar Lyman continuum fluxestimated from the ionized gas Hβ flux. The compact H ii regionbelongs to a rare class of H ii regions in the Magellanic Clouds, calledhigh-excitation blobs (HEBs). We propose that N66A probably represents avery young massive star formation event in the N66 complex that has arange of ages.
| A new population of planetary nebulae discovered in the Large Magellanic Cloud - III. The luminosity function
Our previous identification and spectroscopic confirmation of 431 faint,new planetary nebulae (PNe) in the central 25 deg2 region ofthe Large Magellanic Cloud (LMC) permit us to now examine the shape ofthe LMC planetary nebula luminosity function (PNLF) through anunprecedented 10 mag range. The majority of our newly discovered andpreviously known PNe were observed using the 2dF, multi-object fibrespectroscopy system on the 3.9-m Anglo-Australian Telescope and theFLAMES multi-object spectrograph on the 8-m Very Large Telescope. Wepresent reliable [OIII]5007Å and H? flux estimates based oncalibrations to well-established PN fluxes from previous surveys andspectroscopic standard stars. The bright cut-off (M*) of the PNLF isfound by fitting a cumulative function to the bright end of the PNLFover a 3.4 mag range. This cut-off is used to estimate a new distancemodulus of 18.46 to the LMC, in close agreement with previous PNLFstudies and the best estimates by other indicators. The bright-endcut-off is robust to small samples of bright PNe since significantlyincreased PN samples do not change this fiducial. We then fit atruncated exponential curve directly to the bright end of the functionover a 6 mag range and test the curve's ability to indicate the positionof M*. Because of the significant increase in the number of LMC PNe, theshape of the PNLF is now examined in greater detail than has previouslybeen possible. Newly discovered features include a small increase in thenumber of PNe over the brightest 4 mag followed by a steep rise over 2mag, a peak at 6 mag below the bright cut-off and an almost lineardrop-off to the faint end. Dips at the bright end of the PNLF areexamined in relation to the overall shape of the PNLF and theexponential increase in the number of PNe. Through cumulative functions,the new LMC PNLF is compared to those from the Small Magellanic Cloudand a new deep local Galactic sample revealing the effects ofincompleteness. The new [OIII]5007Å LMC PNLF is then compared toour new H? LMC PNLF using calibrated and measured fluxes for thesame objects, revealing the effects of metallicity on the[OIII]5007Å line.
| A ~ 40 Year Variability Cycle in the Luminous Blue Variable/Wolf-Rayet Binary System HD 5980?
The massive Wolf-Rayet stellar system HD 5980 in the Small MagellanicCloud entered a sudden and brief ~ 1-3 mag eruptive state in themid-1990s. The cause of the instability is not yet understood, butmechanisms similar to those in luminous blue variables are suspected.Using a previously unreported set of spectroscopic data obtained in1955-1967 and recently acquired optical and HST/STIS spectra, we findthat (1) the brief eruptions of 1993 and 1994 occurred at the beginningof an extended (~ decades) high state of activity characterized by largeemission-line intensities; (2) the level of activity is currentlysubsiding; and (3) another strong emission-line episode appears to haveoccurred between 1960 and 1965, suggesting the possibility that thelong-term cyclical variability may be recurrent on a ~ 40 yeartimescale. These characteristics suggest the possible classification ofHD 5980 as an S Doradus-type variable. The effects due to binaryinteractions in the system are discussed, and we tentatively suggestthat the short duration and relatively hot spectral type (WN11/B1.5I)observed during maximum in the visual light curve may be attributed tothese interactions.
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Membre dels grups següents:
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Dades d'Observació i Astrometria
| Constel·lació: | Sagittarius |
| Ascensió Recta: | 20h10m56.84s |
| Declinació: | -30°13'06.6" |
| Magnitud Aparent: | 12.984 |
| Distancia: | 15.37 parsecs |
| Moviment propi RA: | -343.7 |
| Moviment propi Dec: | -254.4 |
| B-T magnitude: | 12.101 |
| V-T magnitude: | 12.912 |
Catàlegs i designacions:
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