Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
Discovery of a Luminous Blue Variable with an Ejection Nebula Near the Quintuplet Cluster
We report on the discovery of a luminous blue variable (LBV) lying ?7pc in projection from the Quintuplet cluster. This source, which we callLBV G0.120 - 0.048, was selected for spectroscopy owing to itsdetection as a strong source of Paschen-? (P?) excess in arecent narrowband imaging survey of the Galactic center region with theHubble Space Telescope/Near-Infrared Camera and Multi-ObjectSpectrometer. The K-band spectrum is similar to that of the Pistol Starand other known LBVs. The new LBV was previously cataloged as aphotometric variable star, exhibiting brightness fluctuations of up to?1 mag between 1994 and 1997, with significant variability alsooccurring on month-to-month timescales. The luminosity of LBV G0.120- 0.048, as derived from Two-Micron All Sky Survey photometry, isapproximately equivalent to that of the Pistol Star. However, thetime-averaged brightness of LBV G0.120 - 0.048 between 1994 and1997 exceeded that of the Pistol Star; LBV G0.120 - 0.048 alsosuffers more extinction, which suggests that it was intrinsically moreluminous in the infrared than the Pistol Star between 1994 and 1997.P? images reveal a thin circular nebula centered on LBV G0.120- 0.048 with a physical radius of ?0.8 pc. We suggest that thisnebula is a shell of ejected material launched from a discrete eruptionthat occurred between 5000 and 10,000 years ago. Because of the veryshort amount of time that evolved massive stars spend in the LBV phase,and the close proximity of LBV G0.120 - 0.048 to the Quintupletcluster, we suggest that this object might be coeval with the cluster,and may have once resided within it.
| The nature of stars with the B[e] phenomenon through interferometric eyes
Stars that present the B[e] phenomenon are known to form a heterogeneousgroup. This group is composed by objects in different evolutionarystages, like high- and low-mass evolved stars, intermediate-masspre-main sequence stars and symbiotic objects. However, for more than50% of the confirmed B[e] stars the evolutionary stage is still unknown,so that they are gathered in the group of the unclassified B[e] stars.High-angular resolution interferometry is certainly an important tool toanswer questions related to the circumstellar geometry of these objects.In this work, we present the results related to seven objects, based onobservations from VLTI/MIDI, VLTI/AMBER and CHARA/VEGA.
| Hα spectropolarimetry of the B[e] supergiant GG Carinae
Aims. We study the geometry of the circumstellar environment of the B[e]supergiant star GG Car. Methods: We present observations acquiredusing the IAGPOL imaging polarimeter in combination with theEucalyptus-IFU spectrograph to obtain spectropolarimetric measurementsof GG Car across Hα at two epochs. Polarization effects along theemission line are analysed using the Q-U diagram. In particular, thepolarization position angle (PA) obtained using the line effect is ableto constrain the symmetry axis of the disk/envelope. Results: Byanalysing the fluxes, GG Car shows an increase in its double-peakedHα line emission relative to the continuum within the interval ofour measurements (~43 days). The depolarization line effect aroundHα is evident in the Q-U diagram for both epochs, confirming thatlight from the system is intrinsically polarized. A rotation of the PAalong Hα is also observed, indicating a counter-clockwise rotatingdisk. The intrinsic PA calculated using the line effect (~85°) isconsistent between our two epochs, suggesting a clearly defined symmetryaxis of the disk.Based on observations obtained at the Observatório do Pico dosDias, LNA/MCT, Itajubá, Brazil.
| A systematic study of variability among OB-stars based on HIPPARCOS photometry
Context: Variability is a key factor for understanding the nature of themost massive stars, the OB stars. Such stars lie closest to the unstableupper limit of star formation. Aims: In terms of statistics, thedata from the HIPPARCOS satellite are unique because of time coverageand uniformity. They are ideal to study variability in this large,uniform sample of OB stars. Methods: We used statisticaltechniques to determine an independant threshold of variabilitycorresponding to our sample of OB stars, and then applied an automaticalgorithm to search for periods in the data of stars that are locatedabove this threshold. We separated the sample stars into 4 maincategories of variability: 3 intrinsic and 1 extrinsic. The intrinsiccategories are: OB main sequence stars (~2/3 of the sample), OBe stars(~10%) and OB Supergiant stars (~1/4).The extrinsic category refers toeclipsing binaries. Results: We classified about 30% of the wholesample as variable, although the fraction depends on magnitude level dueto instrumental limitations. OBe stars tend to be much more variable(≈80%) than the average sample star, while OBMS stars are belowaverage and OBSG stars are average. Types of variables include αCyg, β Cep, slowly pulsating stars and other types from the generalcatalog of variable stars. As for eclipsing binaries, there arerelatively more contact than detached systems among the OBMS and OBestars, and about equal numbers among OBSG stars.
| The pre- versus post-main sequence evolutionary phase of B[e] stars. Constraints from 13CO band emission
Context: Many galactic B[e] stars suffer from improper distancedeterminations, which make it difficult to distinguish between a pre-and post-main sequence evolutionary phase on the basis of luminosityarguments. In addition, these stars have opaque circumstellar material,obscuring the central star, so that no detailed surface abundancestudies can be performed. Aims: Instead of studying the surfaceabundances as a tracer of the evolutionary phase, we propose a differentindicator for the supergiant status of a B[e] star, based on theenrichment of its circumstellar matter by 13C, and detectablevia its 13CO band emission in the K band spectra. Methods: Based on stellar evolution models, we calculate the variationof the 12C/13C isotopic surface abundance ratioduring the evolution of non-rotating stars with different initialmasses. For different values of the 12C/13C ratiowe then compute synthetic first-overtone vibration-rotational bandspectra from both the 12CO and 13CO molecule atdifferent spectral resolutions. We further discuss the influence ofstellar rotation on the variation of the surface12C/13C ratio and on the possibility of13CO band detection. Results: The surface12C/13C isotope ratio is found to decreasestrongly during the post-main sequence evolution of non-rotating stars,from its interstellar value of about 70 to a value of about 15-20 forstars with initial masses higher than 7 Mȯ, and to avalue of less than 5 for stars with initial masses higher than 25Mȯ. We find that detectable 13CO band heademission is produced for isotope ratios12C/13{C}⪉ 20, and can most easily be detectedwith a spectral resolution of R˜ 1500 ldots 3000. For the rotatingstellar models, the drop in 12C/13C already occursfor all stars with M_in ⪆ 9 Mȯ during themain-sequence evolution. The detection of 13CO band heademission in such mid-resolution K band spectra of a B[e] star thusfavours an evolved rather than a young nature of the object.
| Toward Understanding the B[e] Phenomenon. I. Definition of the Galactic FS CMa Stars
The B[e] phenomenon is defined as the simultaneous presence oflow-excitation forbidden line emission and strong infrared excess in thespectra of early-type stars. It was discovered in our Galaxy 30 yearsago in the course of the early exploration of the infrared sky andinitially identified in 65 Galactic objects, of which nearly halfremained unclassified. The phenomenon is associated with objects atdifferent evolutionary stages, ranging from the pre-main-sequence to theplanetary nebula stage. We review the studies of both the original 65and subsequently identified Galactic stars with the B[e] phenomenon. Anew classification is proposed for stars with the B[e] phenomenon basedon the time of dust formation in their environments. Properties of theunclassified Galactic B[e] stars are analyzed. We propose that theseobjects are binary systems that are currently undergoing or haverecently undergone a phase of rapid mass exchange, associated with astrong mass loss and dust formation. A new name, FS CMa stars, andclassification criteria are proposed for the unclassified B[e] stars.
| Galactic distributions and statistics of the HD stars in the michigan spectral catalogue.
Not Available
| Spectral atlas of massive stars around He I 10 830 Å
We present a digital atlas of peculiar, high-luminosity massive stars inthe near-infrared region (10 470-11 000 Å) at medium resolution(R≃7000). The spectra are centered around He I 10 830 Å,which is formed in the wind of those stars, and is a crucial line toobtain their physical parameters. The instrumental configuration alsosampled a rich variety of emission lines of Fe II, Mg II, C I, N I, andPa γ. Secure identifications for most spectral lines are given,based on synthetic atmosphere models calculated by our group. We alsopropose that two unidentified absorption features have interstellarand/or circumstellar origin. For the strongest one (10 780 Å) anempirical calibration between E(B-V) and equivalent width is provided.The atlas displays the spectra of massive stars organized in fourcategories, namely Be stars, OBA Iape (or luminous blue variables, LBVcandidates and ex/dormant LBVs), OB supergiants and Wolf-Rayet stars.For comparison, the photospheric spectra of non emission-line stars arepresented. Selected LBVs were observed in different epochs from 2001 to2004, and their spectral variability reveals that some stars, such asη Car, AG Car and HR Car, suffered dramatic spectroscopic changesduring this time interval.Based on observations made at Observatório do Pico dos Dias/LNA(Brazil). Figures 5 to 18 are only available in electronic form athttp://www.aanda.org Electronic version of the spectra (fichiers FITS)is only available in electronic form at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/465/993
| Spectral Analysis of the Pre-WN Candidate HD 326823
We present a spectral analysis of the peculiar emission-line star HD326823. As has been reported in the literature, this object seems to bea rare, massive star entering the Wolf-Rayet (W-R) phase. In order toconfirm its evolutionary status, we used the radiative transfer codeCMFGEN to obtain its physical parameters and chemical abundances for thefirst time. By analyzing ultraviolet to optical observations of HD326823, we were able to obtain the following parameters:L=2×105 Lsolar, R*=30Rsolar, T*=22,280 K,M˙=5.2×10-6 Msolar yr-1, andv∞=200 km s-1. In addition, we demonstratedthat this star is severely hydrogen-depleted and helium-rich, withXH~3% and XHe~96% (mass fractions), confirmingprevious qualitative claims of a hydrogen deficiency. From the N IIλ5754 transition, we estimated an upper limit for the nitrogenabundance that is compatible with the idea that HD 326823 is a pre-WNstar (XN<~1%). Our models indicate that the Fe II linespresent in the optical spectrum are not formed in a sphericallysymmetric wind. We found that the iron ionization structure is dominatedby Fe III and Fe IV, and that these ions dominate the UV. By comparingour results with WNE and WNL stars in the H-R diagram, we suggest thatHD 326823 is a pre-WN8 star. The use of the transformedradius-temperature diagram also confirms a pre-WNL status. The idea thatstars may enter the W-R stage with a very low hydrogen mass fraction issupported by our results.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| A catalogue of eclipsing variables
A new catalogue of 6330 eclipsing variable stars is presented. Thecatalogue was developed from the General Catalogue of Variable Stars(GCVS) and its textual remarks by including recently publishedinformation about classification of 843 systems and making correspondingcorrections of GCVS data. The catalogue1 represents thelargest list of eclipsing binaries classified from observations.
| New Estimates of the Solar-Neighborhood Massive Star Birthrate and the Galactic Supernova Rate
The birthrate of stars of masses >=10 Msolar is estimatedfrom a sample of just over 400 O3-B2 dwarfs within 1.5 kpc of the Sunand the result extrapolated to estimate the Galactic supernova ratecontributed by such stars. The solar-neighborhood Galactic-plane massivestar birthrate is estimated at ~176 stars kpc-3Myr-1. On the basis of a model in which the Galactic stellardensity distribution comprises a ``disk+central hole'' like that of thedust infrared emission (as proposed by Drimmel and Spergel), theGalactic supernova rate is estimated at probably not less than ~1 normore than ~2 per century and the number of O3-B2 dwarfs within the solarcircle at ~200,000.
| Pre-main sequence star Proper Motion Catalogue
We measured the proper motions of 1250 pre-main sequence (PMS) stars andof 104 PMS candidates spread over all-sky major star-forming regions.This work is the continuation of a previous effort where we obtainedproper motions for 213 PMS stars located in the major southernstar-forming regions. These stars are now included in this present workwith refined astrometry. The major upgrade presented here is theextension of proper motion measurements to other northern and southernstar-forming regions including the well-studied Orion and Taurus-Aurigaregions for objects as faint as V≤16.5. We improve the precision ofthe proper motions which benefited from the inclusion of newobservational material. In the PMS proper motion catalogue presentedhere, we provide for each star the mean position and proper motion aswell as important photometric information when available. We providealso the most common identifier. The rms of proper motions vary from 2to 5 mas/yr depending on the available sources of ancient positions anddepending also on the embedding and binarity of the source. With thiswork, we present the first all-sky catalogue of proper motions of PMSstars.
| Using High Resolution Data to Investigate the Variability of GG Carinae System
GG Carinae is a peculiar emission line object classified as a B[e] star.Using high resolution data we confirm that GG Carinae is at same time abinary system and a variable star.
| Misidentified and Missing Southern Eclipsing Binaries
Analysis of ASAS-3 data for 442 southern eclipsing binaries yielded 7stars with incorrect classifications, 3 with incorrect positions, and 20for which no counterpart could be located
| The peculiar circumstellar environment of NGC 2024 IRS2
We re-examine the nature of NGC 2024 IRS2 in light of the recentdiscovery of the late O-type star, IRS2b, located 5 arcsec from IRS2.Using L-band spectroscopy, we set a lower limit of AV = 27.0mag on the visual extinction towards IRS2. Arguments based on the natureof the circumstellar material, favor an AV of 31.5 mag. IRS2is associated with the UCHII region G206.543-16.347 and the infraredsource IRAS 05393-0156. We show that much of the mid-infrared emissiontowards IRS2, as well as the far infrared emission peaking at 100μm, do not originate in the direct surroundings of IRS2, but insteadfrom an extended molecular cloud. Using new K-, L- and L'-bandspectroscopy and a comprehensive set of infrared and radio continuummeasurements from the literature, we apply diagnostics based on theradio slope, the strength of the infrared hydrogen recombination lines,and the presence of CO band-heads to constrain the nature and spatialdistribution of the circumstellar material of IRS2. Using simple gaseousand/or dust models of prescribed geometry, we find strong indicationsthat the infrared flux originating in the circumstellar material of IRS2is dominated by emission from a dense gaseous disk with a radius ofabout 0.6 AU. At radio wavelengths the flux density distribution is bestdescribed by a stellar wind recombining at a radius of about 100 AU.Although NGC 2024 IRS2 shares many similarities with BN-like objects, wedo not find evidence for the presence of a dust shell surrounding thisobject. Therefore, IRS2 is likely more evolved.
| The Carina Spiral Feature: Strömgren-Hβ photometry approach. I. The photometric data-base
A data-base collating all uvbybeta photometry available at present forO-B9 stars brighter than 10th visual magnitude in the field of theCarina Spiral Feature is presented. The completeness and homogeneity ofthe data-base are discussed.Based on CDS data.Table 1 is only available in electronic form at the CDS via anonymousftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/410/523
| An IUE Atlas of Pre-Main-Sequence Stars. III. Co-added Final Archive Spectra from the Long-Wavelength Cameras
We identified 137 T Tauri stars (TTS) and 97 Herbig Ae/Be (HAEBE) starsobserved by IUE in the wavelength interval 1900-3200 Å. Eachlow-resolution (R~6 Å) spectrum was visually inspected for sourcecontamination and data quality, and then all usable spectra werecombined to form a single time averaged spectrum for each star. Forsources with multiple observations, we characterized variability andcompared with previously published amplitudes at shorter wavelengths. Wecombined several co-added spectra of diskless TTS to produce a pair ofintrinsic stellar spectra unaffected by accretion. We then fittedspectra of TTS with the reddened sum of an intrinsic spectrum and aschematic veiling continuum, measuring emission line fluxes from theresiduals. We used extinction and distance estimates from the literatureto convert measured Mg II line fluxes into intrinsic line luminosities,noting that the IUE detection limit introduces a sample bias such thatintrinsic line luminosity is correlated with extinction. This samplebias complicates any physical interpretation of TTS intrinsicluminosities. We measured extinction toward HAEBE stars by fitting ourco-added IUE spectra with reddened spectra of main-sequence stars andalso from V band minus 3000 Å color excess. We measured excessline emission and absorption in spectra of HAEBE stars divided by fittedspectra of main-sequence stars, noting that HAEBE stars with an infraredexcess indicating circumstellar material typically also have anomalousUV line strengths. In the latter situation, Mg II is usually shallowerthan in a main-sequence star of the same spectral class, whereas Fe IIlines are equally likely to be deeper or shallower. Our co-added spectraof TTS, HAEBE stars, and main-sequence templates are availableelectronically.
| Formation scenarios for the young stellar associations between galactic longitudes l = 280degr - 360degr
We investigate the spatial distribution, the space velocities and agedistribution of the pre-main sequence (PMS) stars belonging toOphiuchus, Lupus and Chamaeleon star-forming regions (SFRs), and of theyoung early-type star members of the Scorpius-Centaurus OB association.These young stellar associations extend over the galactic longituderange from 280degr to 360degr , and are at a distance interval ofaround 100 and 200 pc. This study is based on a compilation ofdistances, proper motions and radial velocities from the literature forthe kinematic properties, and of basic stellar data for the constructionof Hertzsprung-Russel diagrams. Although there was no well-known OBassociation in Chamaeleon, the distances and the proper motions of agroup of 21 B- and A-type stars, taken from the Hipparcos Catalogue,lead us to propose that they form a young association. We show that theyoung early-type stars of the OB associations and the PMS stars of theSFRs follow a similar spatial distribution, i.e., there is no separationbetween the low and the high-mass young stars. We find no difference inthe kinematics nor in the ages of these two populations studied.Considering not only the stars selected by kinematic criteria but thewhole sample of young early-type stars, the scattering of their propermotions is similar to that of the PMS stars and all the young starsexhibit a common direction of motion. The space velocities of theHipparcos PMS stars of each SFR are compatible with the mean values ofthe OB associations. The PMS stars in each SFR span a wide range of ages(from 1 to 20 Myr). The ages of the OB subgroups are 8-10 Myr for UpperScorpius (US), and 16-20 Myr for Upper Centaurus Lupus (UCL) and forLower Centaurus Crux (LCC). Thus, our results do not confirm that UCL isolder than the LCC association. Based on these results and theuncertainties associated with the age determination, we cannot say thatthere is indeed a difference in the age of the two populations. Weanalyze the different scenarios for the triggering of large-scalestar-formation that have been proposed up to now, and argue that mostprobably we are observing a spiral arm that passes close to the Sun. Thealignment of young stars and molecular clouds and the average velocityof the stars in the opposite direction to the Galactic rotation agreewith the expected behavior of star formation in nearby spiral arms.Tables 1 to 4 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/404/913
| Catalog of Galactic OB Stars
An all-sky catalog of Galactic OB stars has been created by extendingthe Case-Hamburg Galactic plane luminous-stars surveys to include 5500additional objects drawn from the literature. This work brings the totalnumber of known or reasonably suspected OB stars to over 16,000.Companion databases of UBVβ photometry and MK classifications forthese objects include nearly 30,000 and 20,000 entries, respectively.
| The evolutionary stage of five southern Galactic unclassified B[e] stars
The spectra of stars with the B[e] phenomenon are dominated by featuresthat are related to physical conditions of circumstellar material aroundthese objects and are not intrinsic to the stars. Because of this, theyform a very heterogeneous group. This group contains objects withdifferent evolutionary stages. Lamers et al. (1998) have suggested anew designation with five sub-groups, which indicate the evolutionarystage. They are: supergiants, pre-main sequence or Herbig Ae/Be, compactplanetary nebulae, symbiotic and unclassified. The unclassified grouphas many objects that need a better study to resolve their evolutionarystatus. Forbidden lines can be a useful tool to solve this problem. They can give informations about chemical composition, ionization anddensity of the circunstellar medium and probably the evolutionary phaseof these objects. We analize spectra of some galactic objects, obtainedwith the FEROS and B&c} spectrographs at the 1.52m telescope in ESO (LaSilla-Chile), with a special focus on the forbidden lines. We havestudied the spectra of five B[e] stars of uncertain evolutionary stage. We find that one of them is a pre-WN star, the other four are supergiantB[e] stars.
| Hydrogen infrared recombination lines as a diagnostic tool for the geometry of the circumstellar material of hot stars
We have analysed the infrared hydrogen recombination lines of a sampleof well studied hot massive stars observed with the Infrared SpaceObservatory. Our sample contains stars from several classes of objects,whose circumstellar environment is believed to be dominated by anionized stellar wind (the Luminous Blue Variables) or by a densedisk-like geometry (Be stars and B[e] stars). We show that hydrogeninfrared recombination lines can be used as a diagnostic tool toconstrain the geometry of the ionized circumstellar material. The linestrengths are sensitive to the density of the emitting gas. Highdensities result in optically thick lines for which line strengths areonly dependent on the emitting surface. Low density gas producesoptically thin lines which may be characterized by Menzel case Brecombination. The ISO observations show that stellar winds aredominated by optically thin H I recombination lines, while disks aredominated by optically thick lines. Disks and winds are well separatedin a diagnostic diagram using the Hu(14-6)/Bralpha and theHu(14-6)/Pfgamma line flux ratios. This diagnostic tool is useful toconstrain the nature of hot star environments in case they are highlyobscured, for instance while they are still embedded in their natalmolecular cloud. Based on observations with ISO, an ESA project withinstruments funded by ESA Member States (especially the PI countries:France, Germany, The Netherlands and the UK) and with the participationof ISAS and NASA.
| A photometric catalogue of southern emission-line stars
We present a catalogue of previously unpublished optical and infraredphotometry for a sample of 162 emission-line objects and shell starsvisible from the southern hemisphere. The data were obtained between1978 and 1997 in the Walraven (WULBV), Johnson/Cousins(UBV(RI)c) and ESO and SAAO near-infrared (JHKLM) photometricsystems. Most of the observed objects are Herbig Ae/Be (HAeBe) stars orHAeBe candidates appearing in the list of HAeBe candidates of Théet al. (1994), although several B[e] stars, LBVs and T Tauri stars arealso included in our sample. For many of the stars the data presentedhere are the first photo-electric measurements in the literature. Theresulting catalogue consists of 1809 photometric measurements. Opticalvariability was detected in 66 out of the 116 sources that were observedmore than once. 15 out of the 50 stars observed multiple times in theinfrared showed variability at 2.2 mu m (K band). Based on observationscollected at the European Southern Observatory, La Silla, Chile and onobservations collected at the South African Astronomical Observatory.Tables 2-4 are 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/380/609
| K-Band Spectroscopy of Luminous Young Stellar Objects
We present spectroscopy from 2.0 to 2.33 μm of 32 luminous youngstellar objects (YSOs), which are presumed to be precursors of HerbigAe/Be stars. From these stars, Brγ, H2, CO, He I, andFe II were found in emission with detection rates of 97%, 34%, 22%, 9%,and 3%, respectively. We compare the spectral features with those ofHerbig Ae/Be stars in the literature to investigate the spectralbehavior of intermediate- to high-mass YSOs and to search for theirrelations to the spectral energy distributions (SEDs). H2emission is detected only in Class I SEDs with particularly largespectral indices. The detection of H2 emission is related tothe degree of the dispersal of circumstellar envelopes, whereH2 molecules are probably excited by shocks from outflows. Onthe other hand, Brγ emission, which is generally thought to occurin stellar winds close to the stars, does not depend on the SEDs. Thisindicates that stellar wind from luminous YSOs does not change much fromthe embedded phase to the optically visible phase. CO emission is alsoindependent of the SEDs, but the detection rate is much lower than thatof Brγ emission. Probably, more specific physical conditionsregarding circumstellar disks and stellar radiation are necessary for COemission to take place.
| Stars with the Largest Hipparcos Photometric Amplitudes
A list of the 2027 stars that have the largest photometric amplitudes inHipparcos Photometry shows that most variable stars are all Miras. Thepercentage of variable types change as a function of amplitude. Thiscompilation should also be of value to photometrists looking forrelatively unstudied, but large amplitude stars.
| Spectroscopy and photometry of the emission-line B-type stars AS 78 and MWC 657
We present the results of low- and high-resolution spectroscopic andmulticolour photometric observations of two early-type emission-linestars, AS 78 and MWC 657. Theywere identified by Dong & Hu (\cite{dong}) with the IRAS sources03549+5602 and 22407+6008, respectively, among many other sourcesdisplaying a very strong infrared excess, V-[25] >= 8 mag AS 78 isrecognized as a photometric variable for the first time. A large near-IRexcess radiation is detected in AS 78 and confirmed by new,higher-quality, data for MWC 657. Significant variations in the Balmerline profiles are detected for both objects. Modelling of the Balmerline profiles of AS 78 obtained in 1994 yields the following parametersof the star and its wind: Teff ~ 17 000 K, logLbol/Lsun ~ 4.0, dot M ~ 10-6Msun yr-1. The photometric and new spectroscopicdata indicate that the star's Teff increases with time, whilethe stellar wind changes its structure. Distances towards both objectsare estimated on the basis of their radial velocities and the galacticrotation curve. Consideration of different options about the nature andevolutionary state of both objects leads us to suggest that they arebinary systems containing a B-type intermediate-luminosity star and agaseous disk around the less luminous component. Table 9 is onlyavailable in electronic form at the CDS via anonymous ftp (130.79.128.5)or via http://cdsweb.u-strasbg.fr/Abstract.html
| Strömgren and Hβ photometry of O and B type stars in star-forming regions. III. Carina Spiral Feature
Strömgren and Hβ photometry of O and B type stars, generallybrighter than 9.5 mag is reported for the field of the Carina SpiralFeature. The observations are based on the PPM catalogue identificationsand are designed to improve the completeness of the existing uvbybetadata for the bright early-type stars in the field. We present new uvbyphotometry for 283 stars and Hβ photometry for 225 of them. Theseobservations are part of an ongoing effort to study the structure ofselected star-forming regions in the Milky Way by means of uvbybetaphotometry. A comparison of the new data to other uvbybeta data sets forthis field is presented. Based on data from the Strömgren AutomaticTelescope of the Copenhagen University Observatory, La Silla. Tables 1and 2 are only available in electronic form at the CDS via anonymous ftpto 130.79.128.5 or via http://cdsweb.u-strasbg.fr/Abstract.html
| Dust Grains and Circumstellar Motion: The Problem of the Hen and the Egg
In the last ten years, the number of models of circumstellar envelopeshas exponentially increased, both concerning evolved stars and formingstars with their planetary systems. The main progress was intoduction ofchemistry and coupling with dynamics. However, paradoxically, thenucleation theories did not evolve at the same rate; moreover, dynamicsand nucleation are rarely analysed at the same degree of accuracy: oneis of them is always mostly drawing attention. At the same timeobservations showed the presence of dust grains at a lot of sites whereit could not be expected from usual quasi equilibrium theories. Selfconsistent systems are omnipresent. Thus, it is important to distinguishcauses and effects, even if the phenomena are are strongly coupled.
| Proper motions of pre-main sequence stars { } in southern star-forming regions
We present proper motion measurements of pre-main sequence (PMS) starsassociated with major star-forming regions of the southern hemisphere(Chamaeleon, Lupus, Upper Scorpius - Ophiuchus, Corona Australis),situated in the galactic longitude range l = 290degr to l = 360degr . Alist of PMS stars as complete as possible was established based on theHerbig and Bell catalogue and many new catalogues like the PDS survey,the catalogue of Herbig Ae/Be stars by Thé et al. (\cite{the}),X-rays surveys, etc. The measurements made use of public material(mainly AC2000 and USNO-A2.0 catalogues) as well as scans of SERC-JSchmidt plates with the MAMA measuring machine (Paris) and Valinhos CCDmeridian circle observations (Brazil). We derived proper motions for 213stars, with an accuracy of 5 to 10 mas/yr depending mainly on thedifference of epochs between the position sources. The maincharacteristics of the sample are discussed. We show that systematicmotions of groups of stars exist, which are not explained by the reflexsolar motion. Based on observations made at Valinhos CCD MeridianCircle. Based on measurements made with MAMA automatic measuringmachine. Table 4 is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| An IUE Atlas of Pre-Main-Sequence Stars. I. Co-added Final Archive Spectra from the SWP Camera
We have identified 50 T Tauri stars (TTS) and 74 Herbig Ae/Be (HAEBE)stars observed in the IUE short-wavelength bandpass (1150-1980 Å).Each low-resolution (R~6 Å) spectrum was visually inspected forsource contamination and data quality, and then all good spectra werecombined to form a single time-averaged spectrum for each star. Use ofIUE Final Archive spectra processed with NEWSIPS reduces fixed patternnoise in individual spectra, allowing significant signal-to-noise ratiogains in our co-added spectra. For the TTS observed by IUE, we measuredfluxes and uncertainties for 17 spectral features, including twocontinuum windows and four fluoresced H2 complexes. Thirteenof the 32 accreting TTS observed by IUE have detectable H2emission, which until now had been reported only for T Tau. Using anempirical correlation between H2 and C IV line flux, we showthat lack of sensitivity can account for practically all nondetections,suggesting that H2 fluorescence may be intrinsically strongin all accreting TTS systems. Comparison of IUE and GHRS spectra of TTau show extended emission primarily, but not exclusively, in lines ofH2. We also fit reddened main-sequence templates to 72 HAEBEstars, determining extinction and checking spectral types. Several ofthe HAEBE stars could not be fitted well or yielded implausibly lowextinctions, suggesting the presence of a minority emission componenthotter than the stellar photosphere, perhaps caused by white dwarfcompanions or heating in accretion shocks. We identified broadwavelength intervals in the far-UV that contain circumstellar absorptionfeatures ubiquitous in B5-A4 HAEBE stars, declining in prominence forearlier spectral types, perhaps caused by increasing ionization of metalresonance lines. For 61 HAEBE stars, we measured or set upper limits ona depth index that characterizes the strength of circumstellarabsorption and compared this depth index with published IR properties.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Киль |
| Прямое восхождение: | 10h55m58.91s |
| Склонение: | -60°23'33.4" |
| Видимая звёздная величина: | 8.758 |
| Расстояние: | 10000000 парсек |
| Собственное движение RA: | -5.5 |
| Собственное движение Dec: | 2.2 |
| B-T magnitude: | 9.372 |
| V-T magnitude: | 8.809 |
Каталоги и обозначения:
|
INHABITED SKY
