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Multigenerational Star Formation in L1551
The L1551 molecular cloud is undergoing a long and sustained period ofrelatively high efficiency star formation. It contains two smallclusters of Class 0 and I protostars, as well as a halo of more evolvedClass II and III YSOs, indicating a current and at least one past burstof star formation. We present here new, sensitive maps of 850 and 450μm dust emission covering most of the L1551 cloud; new CO J=2-1 dataof the molecular cloud; and a new, deep, optical image of [S II]emission (6730 Å). Compact submillimeter emitters are concentratedin two subclusters: L1551 IRS5 and L1551 NE, and the HL Tauri group.Both stellar groups show significant extended emission and outflow/jetactivity. A jet, terminating at HH 265 and with a very weak associatedmolecular outflow, may originate from LkHα 358 or from a binarycompanion to another member of the HL Tauri group. Several Herbig-Haroobjects associated with L1551 IRS5/L1551 NE were clearly detected in thesubmillimeter, as were faint ridges of emission tracing outflow cavitywalls. We confirm a large-scale molecular outflow originating from L1551NE, parallel to that from L1551 IRS5, and suggest that the ``hollowshell'' morphology is more likely due to two interacting outflows. Weconfirm the presence of a prestellar core (L1551 MC) of mass 2-3Msolar northwest of L1551 IRS5. The next-generation clustermay be forming in this core. The L1551 cloud appears cometary inmorphology and appears to be illuminated and eroded from the directionof Orion, perhaps explaining the multiple episodes of star formation.
| First sky validation of an optical polarimetric interferometer
Aims.We present the first lab and sky validation of spectro-polarimetricequipment put at the combined focus of an optical long-baselineinterferometer. We tested the polarimetric mode designed for the visibleGI2T Interferometer to offer spectropolarimetric diagnosis at themilliarcsecond scale. Methods.We first checked the wholeinstrumental polarization in the lab with a fringe simulator, and thenwe observed α Cep and α Lyr as stellar calibrators ofdifferent declinations to tabulate the polarization effects throughoutthe GI2T declination range. Results.The difference between bothlinear polarizations is within the error bars and the visibilitiesrecorded in natural light (i.e. without the polarimeter) for calibrationpurposes are the same order of magnitude as the polarized ones. Wefollowed the α Cep visibility for 2 h after the transit andα Lyr for 1.5 h and detected no decrease with hour angle due tothe fringe pattern smearing by instrumental polarization. Conclusions.Differential celestial rotation due to the dissymetricCoudé trains of the GI2T is well-compensated by the fieldrotators, so the instrumental polarization is controlled over arelatively wide hour angle range (±2 h around the transit atleast). Such a polarimetric mode opens new opportunities especially forstudies of circumstellar environments and significantly enhances boththe potential of an optical array and its ability for accuratecalibration.
| B-type supergiants in the Small Magellanic Cloud: rotational velocities and implications for evolutionary models
High-resolution spectra for 24 SMC and Galactic B-type supergiants havebeen analysed to estimate the contributions of both macroturbulence androtation to the broadening of their metal lines. Two differentmethodologies are considered, viz. goodness-of-fit comparisons betweenobserved and theoretical line profiles and identifying zeros in theFourier transforms of the observed profiles. The advantages andlimitations of the two methods are briefly discussed with the lattertechniques being adopted for estimating projected rotational velocities(v sin i) but the former being used to estimate macroturbulentvelocities. The projected rotational velocity estimates range fromapproximately 20 to 60 km s-1, apart from one SMC supergiant,Sk 191, with a v sin i ≃ 90 km s-1. Apart from Sk 191,the distribution of projected rotational velocities as a function ofspectral type are similar in both our Galactic and SMC samples withlarger values being found at earlier spectral types. There is marginalevidence for the projected rotational velocities in the SMC being higherthan those in the Galactic targets but any differences are only of theorder of 5-10 km s-1, whilst evolutionary models predictdifferences in this effective temperature range of typically 20 to 70 kms-1. The combined sample is consistent with a linearvariation of projected rotational velocity with effective temperature,which would imply rotational velocities for supergiants of 70 kms-1 at an effective temperature of 28 000 K (approximately B0spectral type) decreasing to 32 km s-1 at 12 000 K (B8spectral type). For all targets, the macroturbulent broadening wouldappear to be consistent with a Gaussian distribution (although otherdistributions cannot be discounted) with an 1/e half-width varying fromapproximately 20 km s-1 at B8 to 60 km s-1 at B0spectral types.
| Quantitative spectroscopy of BA-type supergiants
Luminous BA-type supergiants have enormous potential for modernastrophysics. They allow topics ranging from non-LTE physics and theevolution of massive stars to the chemical evolution of galaxies andcosmology to be addressed. A hybrid non-LTE technique for thequantitative spectroscopy of these stars is discussed. Thorough testsand first applications of the spectrum synthesis method are presentedfor the bright Galactic objects η Leo (A0 Ib), HD 111613 (A2 Iabe),HD 92207 (A0 Iae) and β Ori (B8 Iae), based on high-resolution andhigh-S/N Echelle spectra. Stellar parameters are derived fromspectroscopic indicators, consistently from multiple non-LTE ionizationequilibria and Stark-broadened hydrogen line profiles, and they areverified by spectrophotometry. The internal accuracy of the methodallows the 1σ-uncertainties to be reduced to 1-2% in T_effand to 0.05-0.10 dex in log g. Elemental abundances are determined forover 20 chemical species, with many of the astrophysically mostinteresting in non-LTE (H, He, C, N, O, Mg, S, Ti, Fe). The non-LTEcomputations reduce random errors and remove systematic trends in theanalysis. Inappropriate LTE analyses tend to systematicallyunderestimate iron group abundances and overestimate the light andα-process element abundances by up to factors of two to three onthe mean. This is because of the different responses of these species toradiative and collisional processes in the microscopic picture, which isexplained by fundamental differences of their detailed atomic structure,and not taken into account in LTE. Contrary to common assumptions,significant non-LTE abundance corrections of ~0.3 dex can be found evenfor the weakest lines (Wλ 10 mÅ). Non-LTEabundance uncertainties amount to typically 0.05-0.10 dex (random) and~0.10 dex (systematic 1σ-errors). Near-solar abundances arederived for the heavier elements in the sample stars, and patternsindicative of mixing with nuclear-processed matter for the lightelements. These imply a blue-loop scenario for η Leo because offirst dredge-up abundance ratios, while the other three objects appearto have evolved directly from the main sequence. In the most ambitiouscomputations several ten-thousand spectral lines are accounted for inthe spectrum synthesis, permitting the accurate reproduction of theentire observed spectra from the visual to near-IR. This prerequisitefor the quantitative interpretation of intermediate-resolution spectraopens up BA-type supergiants as versatile tools for extragalacticstellar astronomy beyond the Local Group. The technique presented hereis also well suited to improve quantitative analyses of less extremestars of similar spectral types.
| Atlas and Catalog of Dark Clouds Based on Digitized Sky Survey I
We present a quantitative atlas and catalog of dark clouds derived byusing the optical database ``Digitized Sky Survey I''. Applying atraditional star-count technique to 1043 plates contained in thedatabase, we produced an AV map covering the entire region inthe galactic latitude range |b| ≤ 40°. The map was drawn at twodifferent angular resolutions of 6' and 18', and is shown in detail in aseries of figures in this paper. Based on the AV map, weidentified 2448 dark clouds and 2841 clumps located inside them. Somephysical parameters, such as the position, extent, and opticalextinction, were measured for each of the clouds and clumps. We alsosearched for counterparts among already known dark clouds in theliterature. The catalog of dark clouds presented in this paper lists thecloud parameters as well as the counterparts.
| Forty Years of Spectroscopic Stellar Astrophysics in Japan
The development of Japanese spectroscopic stellar astrophysics in therecent 40 years is reviewed from an observational point of view. In thisarticle, the research activities are provisionally divided into fourfields: hot stars, hot emission-line (Be) stars, cool stars, and otherstars. Historical developments of the observational facilities atOkayama Astrophysical Observatory (spectrographs and detectors) are alsosummarized in connection with the progress in scientific researchactivities.
| Dust scattering in the Miras R Car and RR Sco resolved by optical interferometric polarimetry
We present optical interferometric polarimetry measurements of theMira-like variables R Car and RR Sco, using the Sydney UniversityStellar Interferometer. By making visibility measurements in twoperpendicular polarizations, the relatively low-surface brightness lightscattered by atmospheric dust could be spatially separated from thebright Mira photospheric flux. This is the first reported successful useof long-baseline optical interferometric polarimetry. Observations wereable to place constraints on the distribution of circumstellar materialin R Car and RR Sco. The inner radius of dust formation for both starswas found to be less than 3 stellar radii: much closer than the expectedinnermost stable location for commonly assumed astrophysical `dirtysilicate' dust in these systems (silicate dust with a significant ironcontent). A model with the dust distributed over a shell which isgeometrically thin compared to the stellar radius was preferred over anoutflow. We propose dust components whose chemistry and opacityproperties enable survival at these extreme inner radii.
| Le message de la lumiere.
Not Available
| Spectral Analysis of 4 Lacertae and ν Cephei
Elemental abundance analysis based on high S/N and high resolutionDominion Astrophysical Observatory spectrograms have been performed fortwo early type supergiants: 4 Lac (B9 Iab) and {\msf ν } Cep (A2 Ia).Lines as weak as of order 5 mÅ are employed in this study. Theprojected rotational velocities of these stars are 14 and 26 kms-1, respectively. Both stars show similar radial velocityamplitudes, macroturbulent velocities and the same general elementalabundance trends. Their He, CNO and light element abundances are solaror overabundant while the iron peak and heavy element abundances aresolar or underabundant. Detailed LTE model atmosphere abundance analysisshows that 4 Lac has nuclearly processed matter in its photosphere while{\msf ν } Cep does not.
| Variability of Stars in the Pulkovo Spectrophotometric Catalog
We present the results of a statistical study of brightness variabilityfor 693 stars of the Pulkovo spectrophotometric database in fivespectral bands in the range λλ 320 1080 nm. Significantbrightness variations were detected in at least one spectral bandagainst the background of the random noise for one-third of the starsnot earlier believed to be variable. A comparison of the distributionsof these variations in amplitude and spectral band for the normal andvariable stars shows that variability is inherent to most stars to someextent and is often wavelength dependent.
| The Orion Nebula in the Mid-Infrared
We present two wide-field (~5'×3&farcm;5),diffraction-limited (λ/D~=0.5" at 10 μm), broadband 10 and 20μm images of the Orion Nebula, plus six 7-13 μm narrowband(λ/Δλ~=1) images of the BN/KL complex taken at the3.8 m UKIRT telescope with the MPIA MAX camera. The wide-field images,centered on the Trapezium and BN/KL regions, are mosaics of35''×35'' frames obtained with standardchopping and nodding techniques and reconstructed using a newrestoration method developed for this project. They show the filamentarystructure of the dust emission from the walls of the H II region andreveal a new remarkable group of arclike structures ~1' to the south ofthe Trapezium. The morphology of the Ney-Allen Nebula, produced bywind-wind interaction in the vicinity of the Trapezium stars, suggests acomplex kinematical structure at the center of the cluster. We findindications that one of the most massive members of the cluster, theB0.5 V star θ1 Ori D, is surrounded by aphotoevaporated circumstellar disk. Among the four historic Trapezium OBstars, this is the only one without a binary companion, suggesting thatstellar multiplicity and the presence of massive circumstellar disks maybe mutually exclusive. In what concerns the BN/KL complex, we findevidence for extended optically thin silicate emission on top of thedeep 10 μm absorption feature. Assuming a simple two-component model,we map with ~=0.5" spatial resolution the foreground optical depth,color temperature, and mid-IR luminosity of the embedded sources. Weresolve a conspicuous point source at the location of the IRc2-A knot,approximately 0.5" north of the deeply embedded H II region ``I.'' Weanalyze the spectral profile of the 10 μm silicate absorption featureand find indication for grain crystallization in the harsh nebularenvironment. In the OMC-1 South region, we detect several point sourcesand discuss their association with the mass-loss phenomenology observedat optical and millimeter wavelengths. Finally, we list the position andphotometry of 177 point sources, the large majority of which aredetected for the first time in the mid-IR. Twenty-two of them lack acounterpart at shorter wavelengths and are therefore candidates fordeeply embedded protostars. The comparison of photometric data obtainedat two different epochs reveals that source variability at 10 μm ispresent up to a level of ~1 mag on a timescale of ~2 yr. With thepossible exception of a pair of OB stars, all point sources detected atshorter wavelengths display 10 μm emission well above thephotospheric level, which we attribute to disk circumstellar emission.The recent model of Robberto et al. provides the simplest explanationfor the observed mid-IR excess.
| Chemical composition of evolved stars of high galactic latitude
We have carried out abundance analysis for a sample of high galacticlatitude supergiants in search of evolved stars.We find that HD 27381 has atmospheric parameters and an abundancepatternvery similar to that of the post-AGB star HD 107369.HD 10285 and HD 25291 are moderately metal-poor andshow the influence of mixing that has brought the productsof NeNa cycle to the surface.The high galactic latitude B supergiant HD 137569 shows selectivedepletion of refractory elements normally seen in post-AGB stars.We find that the high velocity B typestar HD 172324 shows moderate deficiency of Fe group elements butthe CNO abundances are verysimilar to that of disk B supergiants. The observed variations inthe radial velocities, transient appearance of emission componentsin hydrogen line profiles and doublingof O I lines at 7774 Å support the possibility of this star beinga pulsating variable or a binary star.
| First results from the ESO VLTI calibrators program
The ESO Very Large Telescope Interferometer (VLTI) is one of the leadinginterferometric facilities. It is equipped with several 8.2 and 1.8 mtelescopes, a large number of baselines up to 200 m, and with severalsubsystems designed to enable high quality measurements and to improvesignificantly the limits of sensitivities currently available tolong-baseline interferometry. The full scientific potential of the VLTIcan be exploited only if a consistent set of good quality calibrators isavailable. For this, a large number of observations of potentialcalibrators have been obtained during the commissioning phase of theVLTI. These data are publicly available. We briefly describe theinterferometer, the VINCI instrument used for the observations, the dataflow from acquisition to processed results, and we present and commenton the volume of observations gathered and scrutinized. The result is alist of 191 calibrator candidates, for which a total of 12 066observations can be deemed of satisfactory quality. We present a generalstatistical analysis of this sample, using as a starting point theangular diameters previously available in the literature. We derive thegeneral characteristics of the VLTI transfer function, and its trendwith time in the period 2001 through mid-2004. A second paper will bedevoted to a detailed investigation of a selected sample, aimed atestablishing a VLTI-based homogeneous system of calibrators.
| On the massive stellar population of the super star cluster Westerlund 1
We present new spectroscopic and photometric observations of the youngGalactic open cluster Westerlund 1 (Wd 1) that reveala unique population of massive evolved stars. We identify ~200 clustermembers and present spectroscopic classifications for ~25% of these. Wefind that all stars so classified are unambiguously post-Main Sequenceobjects, consistent with an apparent lack of an identifiable MainSequence in our photometric data to V 20. We are able to identifyrich populations of Wolf Rayet stars, OB supergiants and short livedtransitional objects. Of these, the latter group consists of both hot(Luminous Blue Variable and extreme B supergiant) and cool (YellowHypergiant and Red Supergiant) objects - we find that half the knownGalactic population of YHGs resides within Wd 1. We obtain a meanV-MV ~ 25 mag from the cluster Yellow Hypergiants, implying aMain Sequence turnoff at or below MV =-5 (O7 V or later).Based solely on the masses inferred for the 53 spectroscopicallyclassified stars, we determine an absolute minimum mass of ~1.5 ×10^3~Mȯ for Wd 1. However, considering the completephotometrically and spectroscopically selected cluster population andadopting a Kroupa IMF we infer a likely mass for Wd 1 of~10^5~Mȯ, noting that inevitable source confusion andincompleteness are likely to render this an underestimate. As such, Wd 1is the most massive compact young cluster yet identified in the LocalGroup, with a mass exceeding that of Galactic Centre clusters such asthe Arches and Quintuplet. Indeed, the luminosity, inferred mass andcompact nature of Wd 1 are comparable with those of Super Star Clusters- previously identified only in external galaxies - and is consistentwith expectations for a Globular Cluster progenitor.
| CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular ResolutionMeasurements (CHARM, Richichi & Percheron \cite{CHARM}, A&A,386, 492), which includes results available until July 2004. CHARM2 is acompilation of direct measurements by high angular resolution methods,as well as indirect estimates of stellar diameters. Its main goal is toprovide a reference list of sources which can be used for calibrationand verification observations with long-baseline optical and near-IRinterferometers. Single and binary stars are included, as are complexobjects from circumstellar shells to extragalactic sources. The presentupdate provides an increase of almost a factor of two over the previousedition. Additionally, it includes several corrections and improvements,as well as a cross-check with the valuable public release observationsof the ESO Very Large Telescope Interferometer (VLTI). A total of 8231entries for 3238 unique sources are now present in CHARM2. Thisrepresents an increase of a factor of 3.4 and 2.0, respectively, overthe contents of the previous version of CHARM.The catalog is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/431/773
| Improved Baade-Wesselink surface brightness relations
Recent, and older accurate, data on (limb-darkened) angular diameters iscompiled for 221 stars, as well as BVRIJK[12][25] magnitudes for thoseobjects, when available. Nine stars (all M-giants or supergiants)showing excess in the [12-25] colour are excluded from the analysis asthis may indicate the presence of dust influencing the optical andnear-infrared colours as well. Based on this large sample,Baade-Wesselink surface brightness (SB) relations are presented fordwarfs, giants, supergiants and dwarfs in the optical and near-infrared.M-giants are found to follow different SB relations from non-M-giants,in particular in V versus V-R. The preferred relation for non-M-giantsis compared to the earlier relation by Fouqué and Gieren (basedon 10 stars) and Nordgren et al. (based on 57 stars). Increasing thesample size does not lead to a lower rms value. It is shown that theresiduals do not correlate with metallicity at a significant level. Thefinally adopted observed angular diameters are compared to thosepredicted by Cohen et al. for 45 stars in common, and there isreasonable overall, and good agreement when θ < 6 mas.Finally, I comment on the common practice in the literature to average,and then fix, the zero-point of the V versus V-K, V versus V-R and Kversus J-K relations, and then rederive the slopes. Such a commonzero-point at zero colour is not expected from model atmospheres for theV-R colour and depends on gravity. Relations derived in this way may bebiased.
| Video observation of meteors at Yunnan Observatory
In the last 20 years, with the development of the CCD and imageintensifiers, the use of small flexible video meteor observation systemshas gradually increased, with the prospect that one day videoobservation will replace the visual observation and ordinaryphotographic observations. In this paper we report on the research anddevelopment of the No.1 meteor-comet video camera system of YunnanObservatory and some preliminary observed results. The system consistsof 5 changeable modules; it has a 36° large-field camera dedicatedto the observation of meteors, with which a magnitude 6 star can berecorded on a single frame with an accuracy of about 0.2 mag. We alsopresent a comparison of the video camera system with the traditionalphotographic system, and outline the merits, possible improvements andfuture development of the video system.
| HD 183143: A Hypergiant
We present spectroscopic evidence that the luminosity of HD 183143 ishigher by one magnitude than thought previously. The star is yet anotherB6-8 Ia-0 white hypergiant of the Galaxy. Its absolute visual magnitudeis close to -8 mag, and its distance is close to 2 kpc. We describespectroscopic manifestations of the nonstationary behavior of itsatmosphere and wind.
| The Optical Spectrum of an LBV Candidate in the Cyg OB2 Association
We have obtained the first high-spectral-resolution (R=15000 and 60000)optical spectra for the extremely luminous star No. 12, identified withthe IR source IRAS 20308+4104 in the Cyg OB2 association. We haveidentified about 200 spectral features at 4552 7939 Å, includingthe interstellar NaI, KI lines and numerous DIBs, which are thestrongest absorption lines in the spectrum, along with the HeI, CII, andSiII lines. A two-dimensional spectral classification indicates that thestar's spectral type is B5±0.5 Ia+. Our analysis of theradial-velocity pattern shows the presence of a radial-velocity gradientin the stellar atmosphere, due to the infall of matter onto the star.The strong Hα emission line displays broad Thompson wings andtime-variable core absorption, providing evidence that the stellar windis inhomogeneous, and a slightly blue-shifted P Cygni absorptionprofile. We conclude that the wind is time-variable.
| Mid-Infrared and Submillimeter Observations of the Illuminating Source of MCNeil's Variable Nebula
We present post-outburst observations of the mid-infrared spectrum andsubmillimeter continuum of the illuminating source of the newlydiscovered McNeil's Nebula in the L1630 region of Orion. The 12 μmflux of this source has increased by a factor of ~25 after the outburst,whereas the submillimeter continuum remains at its pre-outburst level.The bolometric luminosity has increased by at least an order ofmagnitude, to ~34 Lsolar, and is likely less than 90Lsolar. The mid-infrared spectrum exhibits a strong and redcontinuum with no emission or absorption features. The infrared slope ofthe spectral energy distribution identifies the illuminating source as aflat-spectrum protostar, in both its active and quiescent states. New COspectral line observations show no evidence of a molecular outflow.
| Non-LTE Line Formation for Hydrogen Revisited
We discuss aspects of non-LTE line formation for hydrogen in early-typestars. We evaluate the effect of variations in the electron-impactexcitation cross sections in model atoms of differing complexity bycomparison with observation. While the Balmer lines are basicallyunaffected by the choice of atomic data, the Paschen, Brackett, andPfund series members allow us to discriminate between the differentmodels. Non-LTE calculations based on the widely used approximationformulae of Mihalas, Heasley, & Auer and of Johnson fail tosimultaneously reproduce the optical and IR spectra over the entireparameter range. The use of data from ab initio calculations up toprincipal quantum number n<=7 largely solves the problem. Werecommend a reference model using the available data. This model is ofgeneral interest because of the ubiquity of the hydrogen spectrum.
| The Origins and Evolutionary Status of B Stars Found Far from the Galactic Plane. I. Composition and Spectral Features
The existence of faint blue stars far above the Galactic plane that havespectra that are similar to nearby Population I B stars presents severalinteresting questions. Among them are the following: Can a Population IB star travel from the disk to a position many kiloparsecs above theplane in a relatively short main-sequence lifetime? Is it possible thatsingle massive star formation is occurring far from the Galactic plane?Are these objects something else masquerading as main-sequence B stars?This paper (the first of two) analyzes the abundances of a sample ofthese stars and reveals several that are chemically similar to nearbyPopulation I B stars, whereas others clearly have abundance patternsmore like those expected in blue horizontal-branch (BHB) orpost-asymptotic giant branch stars. Several of those with old evolvedstar abundances also have interesting features of note in their spectra.We also consider why this sample does not have any classical Be starsand identify at least two nearby solar-metallicity BHB stars.Based on observations made at the 2.1 m Otto Struve Telescope ofMcDonald Observatory operated by the University of Texas at Austin.
| First observations with an H-band integrated optics beam combiner at the VLTI
This paper reports results obtained with the Very Large TelescopeInterferometer Commissioning Instrument (VLTI-VINCI) where the fiberinterferometric coupler MONA was temporarily replaced by an integratedoptics beam combiner (IONIC). The two-beam combiner operating in the Hatmospheric band was tested at Paranal during two weeks in July 2002.Fringes were recorded on several stars with the siderostats and the UnitTelescopes (UT). We demonstrate that integrated optics allows beamcombination with a high interferometric efficiency, stability andspatial filtering. The instrumental visibility of VLTI+IONIC is betterthan 85%, which is just 5% under the visibility of the IONIC devicealone. During this run, the flux injection in the IONIC combiner was notoptimized since we used the K-band MONA optics. However, we obtainfringes with the 35 cm siderostats on a star of magnitude mH=2.47(κ2 Scl). It allows us to extrapolate a magnitudearound mH6 with 8 m telescopes without adaptive optics and in thesame poor injection conditions.Based on observations collected at the European Southern Observatory,Paranal, Chile (public commissioning data).
| High-resolution spectroscopy of globular cluster post-Asymptotic Giant Branch stars
We present model atmosphere analyses of high resolution Keck and VLToptical spectra for three evolved stars in globular clusters, viz. ZNG-1in M 10, ZNG-1 in M 15 and ZNG-1 in NGC 6712. The derived atmosphericparameters and chemical compositions confirm the programme stars to bein the post-Asymptotic Giant Branch (post-AGB) evolutionary phase.Differential abundance analyses reveal CNO abundance patterns in M 10ZNG-1, and possibly M 15 ZNG-1, which suggest that both objects may haveevolved off the AGB before the third dredge-up occurred. The abundancepattern of these stars is similar to the third class of optically,bright post-AGB objects discussed by van Winckel (\cite{van97}).Furthermore, M 10 ZNG-1 exhibits a large C underabundance (with\bigtriangleup[C/O] -1.6 dex), typical of other hot post-AGBobjects. Differential \bigtriangleup[α/Fe] abundance ratios inboth M 10 ZNG-1 and NGC 6712 ZNG-1 are found to be approximately 0.0dex, with the Fe abundance of the former being in disagreement with thecluster metallicity of M 10. Given that the Fe absorption features inboth M 10 ZNG-1 and NGC 6712 ZNG-1 are well observed and reliablymodelled, we believe that these differential Fe abundance estimates tobe secure. However, our Fe abundance is difficult to explain in terms ofprevious evolutionary processes that occur on both the Horizontal Branchand the AGB.Equivalent width data table is only available in electronic form at theCDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/419/1123
| 400 years of Uranometria.
Not Available
| Quantitative Spectroscopy of Supergiants
Blue supergiants of spectral types B and A are the visually brighteststars in spiral and irregular galaxies, with their most luminous members(at M_V=-10) outshining entire dwarf galaxies. This characteristicallows us to use them as probes to study the Local Universe in greatdetail. In principle, already the existing large telescopes andinstrumentation facilitate quantitative spectroscopy of these objects asfar as the Virgo and Fornax clusters of galaxies. Beyond theirchallenging stellar atmospheres and opportunities for testingsophisticated non-LTE physics they offer numerous applications to modernastrophysics. Quantitative spectroscopy of supergiants can contribute toimprove our understanding of massive star evolution. Galactic abundancegradients and abundance patterns, as can be obtained from studies oflarge ensembles of supergiants in our own and other galaxies, willfoster the understanding of galactochemical evolution. Finally, they arepromising independent indicators for calibrating the extragalacticdistance scale, by application of the wind momentum-luminosity and theflux-weighted gravity-luminosity relationships. In view of this largepotential, the objective of this thesis is to improve the status ofquantitative spectroscopy of BA-type supergiants and to provide firstapplications on a sample of Galactic and extragalactic targets, withinthe Local Group and beyond.
| Low-Mass Star Formation Induced by the Orion-Eridanus Bubble
During a spectroscopic survey performed with the Nordic OpticalTelescope in La Palma we found five classical T Tauri stars in thesmall, high latitude molecular clouds associated with the reflectionnebula IC2118. The star-forming clouds are located at the outer boundaryof the Orion star forming region, at a mean galactic latitude of-28°. Their positions in space and cometary shapes suggest theirinteraction with the Orion SFR. Using spectroscopic and near-infraredphotometric data we determined the positions of the newly discoveredpre-main sequence stars in the HRD. Comparison of the results withevolutionary models has shown that the masses of these stars are between0.3-0.8Msun and their ages are close to 106 yrs.They are roughly coeval and significantly younger than the known WTTS ofthe same region. We conclude that the birth of the molecular clouds andthe stars was probably induced by the interaction of the Orion -Eridanus Bubble with some small, diffuse high-latitude HI clouds.
| Infrared L'band (lambda-cen- ~3.9 mu-m) observations with TIFR near-infrared camera (TIRCAM).
TIRCAM is based on the SBRC InSb Focal Plane Array (58 x 62 pixels)sensitive between 1- 5 μm. TIRCAM system is described in Ojha et al.(2002). TIRCAM had its first light observations during March-April 2001from Gurusikhar 1.2m PRL telescope at Mt. Abu. After having thesuccessful first run in 2001, the TIRCAM was used for the L bandobservations of a few scientific targets in combination with freshtelescope mirrors in Nov. 2002 &Jan. 2003 (the aluminising operationof the primary &secondary mirrors of 1.2m telescope was carried outin mid 2002). Several at 3.9 μm. We could detect the stars upto ~ 7mag in L band from the Gurusikhar site. The TIRCAM L mag of detectedstars in Trapezium cluster were compared with the L band (3.5 μm)data of Muench et al. (2002). These measurements are in good agreementwith each other considering the two different center wavelengths. Weplan to explore TIRCAM's performance in the broad L (3.5 μm) &M(4.5 μm) bands from Hanle site in near future.
| Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars
This paper presents the catalogue and the method of determination ofaveraged quadratic effective magnetic fields < B_e > for 596 mainsequence and giant stars. The catalogue is based on measurements of thestellar effective (or mean longitudinal) magnetic field strengths B_e,which were compiled from the existing literature.We analysed the properties of 352 chemically peculiar A and B stars inthe catalogue, including Am, ApSi, He-weak, He-rich, HgMn, ApSrCrEu, andall ApSr type stars. We have found that the number distribution of allchemically peculiar (CP) stars vs. averaged magnetic field strength isdescribed by a decreasing exponential function. Relations of this typehold also for stars of all the analysed subclasses of chemicalpeculiarity. The exponential form of the above distribution function canbreak down below about 100 G, the latter value representingapproximately the resolution of our analysis for A type stars.Table A.1 and its references are only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/407/631 and Tables 3 to 9are only available in electronic form at http://www.edpsciences.org
| Long-term spectroscopic monitoring of the Luminous Blue Variable HD 160529
We have spectroscopically monitored the galactic Luminous Blue VariableHD 160529 and obtained an extensive high-resolution data set that coversthe years 1991 to 2002. During this period, the star evolved from anextended photometric minimum phase towards a new visual maximum. Inseveral observing seasons, we covered up to four months with almostdaily spectra. Our spectra typically cover most of the visual spectralrange with a high spectral resolution (lambda /Delta lambda ~ 20 000 ormore). This allows us to investigate the variability in many lines andon many time scales from days to years. We find a correlation betweenthe photospheric HeI lines and the brightness of the star, both on atime scale of months and on a time scale of years. The short-termvariations are smaller and do not follow the long-term trend, stronglysuggesting different physical mechanisms. Metal lines also show bothshort-term and long-term variations in strength and also a long-termtrend in radial velocity. Most of the line-profile variations can beattributed to changing strengths of lines. Propagating features in theline profiles are rarely observed. We find that the mass-loss rate of HD160529 is almost independent of temperature, i.e. visual brightness.Based on observations collected at the European Southern Observatory atLa Silla, Chile (proposals 69.D-0378, 269.D-5038).
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Membre dels grups següents:
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Dades d'Observació i Astrometria
Catàlegs i designacions:
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INHABITED SKY
