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Circumstellar disks around Herbig Be stars
Aims. Our goal is to investigate the properties of the circumstellardisks around intermediate mass stars to determine their occurrence,lifetime and evolution. Methods: We completed a search forcircumstellar disks around Herbig Be stars using the NRAO Very LargeArray (VLA) and the IRAM Plateau de Bure (PdB) interferometers. Thusfar, we have observed 6 objects with 4 successful detections. Theresults towards 3 of these stars (R Mon, MWC 1080, MWC 137) werepresented elsewhere. We present our new VLA and PdBI data for the threeobjects MWC 297, Z CMa, and LKHα 215. We constructed the SED fromnear-IR to centimeter wavelengths by adding our millimeter andcentimeter data to the available data at other wavelengths, mainlySpitzer images. The entire SED was fitted using a disk+envelope model.In addition, we compiled all the disk millimeter observations in theliterature and completed a statistical analysis of all the data. Results: We show that the disk mass is usually only a small percentage(less than 10%) of the mass of the entire envelope in HBe stars. For thedisks, there are large source-to-source variations. Two disks in oursample, R Mon and Z CMa, have similar sizes and masses to those found inT Tauri and Herbig Ae stars. The disks around MWC 1080 and MWC 297 are,however, smaller (r_out < 100 AU). We did not detect the diskstowards MWC 137 and LkHα 215 at millimeter wavelengths, whichlimits the mass and the size of the possible circumstellar disks. Conclusions: A comparison between our data and previous results for TTauri and Herbig Ae stars indicates that although massive disks (~0.1M_ȯ) are found in young objects (~104 yr), the masses ofthe disks around Herbig Be stars are usually 5-10 times lower than thosearound lower mass stars. We propose that disk photoevaporation isresponsible for this behavior. In Herbig Be stars, the UV radiationdisperses the gas in the outer disk on a timescale of a few105 yr. Once the outer part of the disk has vanished, theentire gaseous disk is photoevaporated on a very short timescale(~105 yr) and only a small, dusty disk consisting of largegrains remains.
| Extended shells around B[e] stars. Implications for B[e] star evolution
Aims.The position of B[e] stars in the upper left part of theHertzsprung-Russell diagram creates a quandary. Are these stars youngstars evolving onto the main sequence or old stars that are evolving offof it? Spectral characteristics suggest that B[e] stars can be placedinto five subclasses and are not a homogeneous set. Suchsub-classification is believed to coincide with varying origins anddifferent evolutions. However, the evolutionary connection of B[e] stars- and notably sgB[e] - to other stars is unclear, particularly toevolved massive stars. We attempt to provide insight into theevolutionary past of B[e] stars. Methods: We performed an Hαnarrow-band CCD imaging survey of B[e] stars, in the northernhemisphere. Prior to the current work, no emission-line survey of B[e]stars had yet been made, while only two B[e] stars appeared to have ashell nebula as seen in the Digital Sky Survey. Of nebulae around B[e]stars, only the ring nebula around MWC 137 has been previously observedextensively. Results: In this presentation we report the findings fromour narrow-band optical imaging survey of the environments of 25 B[e]stars. Of the objects surveyed, 7 show bipolar or uni- polar structuresup to 15 arcmin across; 5 show faint, large, or filamentary shells; and2 are compact planetary nebula-type systems. The most spectacular systemobserved is a large bipolar structure associated with MWC 314. Conclusions: The possible links between B[e] stars and other evolvedstars, implied by our observations, are investigated.
| The Role of Evolutionary Age and Metallicity in the Formation of Classical Be Circumstellar Disks. II. Assessing the Evolutionary Nature of Candidate Disk Systems
We present the first detailed imaging polarization observations of sixSMC and six LMC clusters, known to have large populations of B-typestars that exhibit excess Hα emission from 2-CD photometricstudies, to constrain the evolutionary status of these stars and hencebetter establish links between the onset of disk formation in classicalBe stars and cluster age and/or metallicity. We parameterize and removethe interstellar polarization (ISP) associated with each line of sight,thereby isolating the presence of any intrinsic polarization. We use thewavelength dependence of this intrinsic polarization to discriminatepure gas disk systems, i.e., classical Be stars, from compositegas-plus-dust disk systems, i.e., Herbig Ae/Be or B[e] stars. Ourintrinsic polarization results, along with available near-IR colorinformation, support the suggestion of Wisniewski et al. that classicalBe stars are present in clusters of age 5-8 Myr and contradictassertions that the Be phenomenon only develops in the second half of aB star's main-sequence lifetime, i.e., no earlier than 10 Myr. Theprevalence of polarimetric Balmer jump signatures decreases withmetallicity; we speculate that either it is more difficult to form largedisk systems in low-metallicity environments or that average disktemperatures are higher in low-metallicity environments. Thepolarimetric signatures of ~25% of our sample appear unlikely to arisefrom true classical Be star disk systems, suggesting one should proceedwith caution when attempting to determine the role of evolutionary ageand/or metallicity in the Be phenomenon purely via 2-CD results.
| Discovery of a New Dusty B[e] Star in the Small Magellanic Cloud
We present new optical spectroscopic and archival Spitzer IRACphotometric observations of a B-type star in the SMC cluster NGC 346,NGC 346:KWBBe 200. We detect numerous Fe II, [O I], and [Fe II] lines,as well as strong P Cygni profile H I emission lines in its opticalspectrum. The star's near-IR color and optical to IR spectral energydistribution clearly indicate the presence of an infrared excess,consistent with the presence of gas and warm, T~800 K, circumstellardust. Based on a crude estimate of the star's luminosity and theobserved spectroscopic line profile morphologies, we find that the staris likely to be a B-type supergiant. We suggest that NGC 346:KWBBe 200is a newly discovered B[e] supergiant star, and represents the fifthsuch object to be identified in the SMC.
| A Search for Low-Amplitude Variability in Six Open Clusters Using the Robust Median Statistic
We used point-spread function fitting and a differential ensembledetermined from a robust median statistic (RoMS) to examine stars in sixopen clusters in a search for δ Scuti variables. In the search fornew variable stars among hundreds or thousands of stars, the RoMS isproved more effective for finding low-amplitude variables than thetraditional error-curve approach. This high-precision differentialapproach was applied to the open clusters NGC 225, NGC 559, NGC 6811,NGC 6940, NGC 7142, and NGC 7160. Thirteen variables, 29 suspectedvariables, and 65 potential variables were found, and time-series dataof the variables are presented. Among the 13 variables we found nine newδ Scuti variables.
| Large-scale variability in the profiles of Hα and Hβ in the spectrum of the Herbig B8e star MWC 419 and a model interpretation of it
Spectroscopic data taken with a moderate resolution spectrograph in theregion of the Hα and Hβ lines are presented for the HerbigB8e star MWC 419. The spectroscopic observations were accompanied bybroad band BVR photometric measurements. The observations reveal avariability in the line profiles that is typical of Herbig Ae/Be starswith signs of a strong stellar wind. The greatest changes are observedin the region of the absorption components of the line profiles, whichconvert the profile from a type P CygII to P CygIII, as well as in theintensities of the central emission components. A model technique isused for quantitative interpretation of this variability and it showsthat the P Cyg profile conversion of the absorption component can beexplained in terms of a stellar wind model in which its distributionover latitude varies on a time scale of a few days.
| Relation between the Luminosity of Young Stellar Objects and Their Circumstellar Environment
We present a new model-independent method of comparison of NIRvisibility data of YSOs. The method is based on scaling the measuredbaseline with the YSO's distance and luminosity, which removes thedependence of visibility on these two variables. We use this method tocompare all available NIR visibility data and demonstrate that itdistinguishes YSOs of luminosity L*<~103Lsolar (low L) from YSOs of L*>~103Lsolar (high L). This confirms earlier suggestions, based onfits of image models to the visibility data, for the difference betweenthe NIR sizes of these two luminosity groups. When plotted against the``scaled'' baseline, the visibility creates the following data clusters:low-L Herbig Ae/Be stars, T Tauri stars, and high-L Herbig Be stars. Wemodel the shape and size of clusters with different image models andfind that low-L Herbig stars are best explained by the uniformbrightness ring and the halo model, T Tauri stars with the halo model,and high-L Herbig stars with the accretion disk model. However, theplausibility of each model is not well established. Therefore, we try tobuild a descriptive model of the circumstellar environment consistentwith various observed properties of YSOs. We argue that low-L YSOs haveoptically thick disks with the optically thin inner dust sublimationcavity and an optically thin dusty outflow above the inner disk regions.High-L YSOs have optically thick accretion disks with high accretionrates enabling gas to dominate the NIR emission over dust. Althoughobservations would favor such a description of YSOs, the required dustdistribution is not supported by our current understanding of dustdynamics.
| Star formation in the region of young open cluster - NGC 225
NGC 225 is believed to be a 120 Myr old open cluster located at tilda650 pc. Eight stars with H alphaemission are found to belocated around the cluster, of which two are probable Herbig Be stars,indicating a very young age for the cluster. To explore whether theHerbig Be stars, which are pre- main sequence (PMS) stars are part ofthis cluster, we re-estimated the cluster parameters using optical(UBV)pg and 2MASS JHK photometry. We combined the above data to detectthe presence of any possible PMS stars in the cluster region. Among theidentified 28 proper motion members, 15 stars were found to havenear-infrared (NIR) excess indicating that they are PMS stars. Also,most of the upper MS stars were found to show NIR excess suggesting thatthe brighter proper motion member stars have not yet reached the MS. PMSisochrones were used to estimate the age of stars with NIR excess and isfound to be between 0.5-10 Myr. Thus, the cluster NGC 225 is a veryyoung cluster, younger than 10 Myr and its age is not 120 Myr aspreviously believed. We propose that a recent star formation hasresulted in the formation of NGC 225, two Herbig Be stars, stars with Hemission, dust lanes and nebulosity in the vicinity of the cluster.
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| 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.
| 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
| Some implications of the introduction of scattered starlight in the spectrum of reddened stars
This paper presents new investigations on coherent scattering in theforward direction (orders of magnitude; conservation of energy;dependence of scattered light on geometry and wavelength), and on howscattered light contamination in the spectrum of reddened stars ispossibly related to as yet unexplained observations (the diminution ofthe 2200 Å bump when the obscuring material is close to the star,the difference between Hipparcos and photometric distances). This paperthen goes on to discuss the fit of the extinction curve, a possible roleof extinction by the gas in the far-UV, and the reasons of theinadequacy of the Fitzpatrick and Massa [ApJSS, 72 (1990) 163] fit.
| PAHs in circumstellar disks around Herbig Ae/Be stars
We investigate the presence and properties of PAHs on the surface ofcircumstellar disks around Herbig Ae/Be stars by comparing thepredictions of disk models with observations. We present results of aradiation transfer code for disks heated by the central star, inhydrostatic equilibrium in the vertical direction (flared disks). Thedust is a mixture of large grains in thermal equilibrium, transientlyheated small grains and PAHs. Special attention is given to theinfluence of the stellar, disk and PAH properties on the strength of thePAH emission lines and their spatial distribution. The models predict aninfrared SED showing PAH features at 3.3, 6.2, 7.7, and 11.3 μmclearly visible above the continuum, and with some of them very strong.The PAH emission, spatially extended, comes mostly from the outer diskregion (R100 AU) while the continuum emission at similarwavelengths, mostly due to warm large grains, is confined to theinnermost disk regions (R few AU). We compare the model results toinfrared observations from ISO and ground-based telescopes of somethirty Herbig Ae/Be stars. Most of the observed PAH features in objectswith spectral type later than B9 are well described by our disk modelsand we discuss in some detail the PAH characteristics one can derivefrom the existing data. Objects with strong radiation field (generallyearlier than about B9) have the 3.3 μm feature (often the only oneobserved) much weaker than predicted, and we discuss possibleexplanations (dissipation of the disk, photoevaporation or modificationof the PAH properties).Appendix is only available in electronic form athttp://www.edpsciences.org
| Spectral and Photoelectric Studies of the Herbig Ae/Be Star HD 259431
Spectral and photoelectric (ubvy, H, H) observations of the Herbig Ae/Bestar HD 259431 are reported. It is found that as its brightness fades,this star becomes bluer in the Paschen continuum and the intensity andequivalent width of the hydrogen emission lines increase. The spectralobservations reveal significant variations in the intensity of the Mg II4481 Å photospheric absorption line. A rise and fall in theluminosity by 0m.04 within a period of 5-7 minutes was recorded. Radicalvariations in the H lineshape ("double" "P Cyg") and flare activity arenot only observed in this star, but also in a number of HAEBE stars. Itis suggested that flare activity may initiate a change in the velocitygradient at the base of the wind and, thereby, induce "double P Cyg" or"P Cyg single" transitions. The nonradial pulsations of this star arealso discussed.
| Spectral Analysis and Classification of Herbig Ae/Be Stars
We present an analysis of the optical spectra of 75 early-typeemission-line stars, many of which have been classified previously asHerbig Ae/Be (HAeBe) stars. Accurate spectral types were derived for 58members of the sample; high continuum veiling, contamination bynonphotospheric absorption features, or a composite binary spectrumprevented accurate spectral typing for the rest. Approximately half ofour sample exhibited [O I] λ6300 forbidden-line emission down toour detection limit of 0.1 Å equivalent width; a third of thesample exhibited Fe II emission (multiplet 42). A subset of 11 of theHAeBe sample showed abnormally strong Fe II absorption; 75% of thissubset are confirmed UX Ori objects. Combining our spectral typingresults with photometry from the literature, we confirm previousfindings of high values of total-to-selective extinction(RV~5) in our larger sample, suggesting significant graingrowth in the environments of HAeBe stars. With this high value ofRV, the vast majority of HAeBe stars appear younger than withthe standard RV=3.1 extinction law and are more consistentwith being pre-main-sequence objects.
| 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.
| Optical interferometry in astronomy
Here I review the current state of the field of optical stellarinterferometry, concentrating on ground-based work although a briefreport of space interferometry missions is included. We pause both toreflect on decades of immense progress in the field as well as toprepare for a new generation of large interferometers just now beingcommissioned (most notably, the CHARA, Keck and VLT Interferometers).First, this review summarizes the basic principles behind stellarinterferometry needed by the lay-physicist and general astronomer tounderstand the scientific potential as well as technical challenges ofinterferometry. Next, the basic design principles of practicalinterferometers are discussed, using the experience of past and existingfacilities to illustrate important points. Here there is significantdiscussion of current trends in the field, including the new facilitiesunder construction and advanced technologies being debuted. This decadehas seen the influence of stellar interferometry extend beyond classicalregimes of stellar diameters and binary orbits to new areas such asmapping the accretion discs around young stars, novel calibration of thecepheid period-luminosity relation, and imaging of stellar surfaces. Thethird section is devoted to the major scientific results frominterferometry, grouped into natural categories reflecting these currentdevelopments. Lastly, I consider the future of interferometry,highlighting the kinds of new science promised by the interferometerscoming on-line in the next few years. I also discuss the longer-termfuture of optical interferometry, including the prospects for spaceinterferometry and the possibilities of large-scale ground-basedprojects. Critical technological developments are still needed to makethese projects attractive and affordable.
| Large-Scale Structure and Dynamics of Cassiopeia OB7
A large region (9°×9°) surrounding the OB associationCassiopeia OB7 has been studied for signs of interaction between thestars and the ambient gas. A large half-shell has been detected in H Iaround Cas OB7, as well as in the infrared and partially in CO. Thishalf-shell covers a range of 20 km s-1 but could reach 40 kms-1 when extrapolating to the whole shell. The structure is120 pc across if located at 2 kpc, the distance to Cas OB7. At thisdistance, we estimate the mass of the shell to be approximately 30,000Msolar. Interestingly, all Cas OB7 members are located wellwithin the edge of this shell. We believe that there is a strong hint ofinteraction between the gas and the stars based on morphologicalevidence. The velocity of both objects (association and shell) and theirrespective distance are also in agreement. We explain the missing halfby an expansion into the interarm region.
| The association of IRAS sources and 12CO emission in the outer Galaxy
We have revisited the question of the association of CO emission withIRAS sources in the outer Galaxy using data from the FCRAO Outer GalaxySurvey (OGS). The availability of a large-scale high-resolution COsurvey allows us to approach the question of IRAS-CO associations from anew direction - namely we examined all of the IRAS sources within theOGS region for associated molecular material. By investigating theassociation of molecular material with random lines of sight in the OGSregion we were able to construct a quantitative means to judge thelikelihood that any given IRAS-CO association is valid and todisentangle multiple emission components along the line of sight. Thepaper presents a list of all of the IRAS-CO associations in the OGSregion. We show that, within the OGS region, there is a significantincrease ( ~ 22%) in the number of probable star forming regions overprevious targeted CO surveys towards IRAS sources. As a demonstration ofthe utility of the IRAS-CO association table we present the results ofthree brief studies on candidate zone-of-avoidance galaxies with IRAScounterparts, far outer Galaxy CO clouds, and very bright CO clouds withno associated IRAS sources. We find that ~ 25% of such candidate ZOAGsare Galactic objects. We have discovered two new far outer Galaxystar-forming regions, and have discovered six bright molecular cloudsthat we believe are ideal targets for the investigation of the earlieststages of sequential star formation around HII regions. Finally, thispaper provides readers with the necessary data to compare othercatalogued data sets with the OGS data.Tables 1, 2 and A1 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/399/1083
| Merged catalogue of reflection nebulae
Several catalogues of reflection nebulae are merged to create a uniformcatalogue of 913 objects. It contains revised coordinates,cross-identifications of nebulae and stars, as well as identificationswith IRAS point sources.The catalogue 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/cgi-bin/qcat?J/A+A/399/141
| On the Interferometric Sizes of Young Stellar Objects
Long-baseline optical interferometers can now detect and resolve hotdust emission thought to arise at the inner edge of circumstellar disksaround young stellar objects (YSOs). We argue that the near-infraredsizes being measured are closely related to the radius at which dust issublimated by the stellar radiation field. We consider how realisticdust optical properties and gas opacity dramatically affect thepredicted location of this dust destruction radius, an exerciseroutinely done in other contexts but so far neglected in the analysis ofnear-infrared sizes of YSOs. We also present the accumulated literatureof near-infrared YSO sizes in the form of a size-luminosity diagram andcompare with theoretical expectations. We find evidence that large(>~1.0 μm) dust grains predominate in the inner disks of T Tauriand Herbig Ae/Be stars, under the assumption that the innermost gaseousdisks are optically thin at visible wavelengths.
| Photoelectric Investigation of the Herbig Ae/Be Star MWC 1080
The results of photoelectric observations of the Herbig Ae/Be star MWC1080 in the Strömgren system are given. It was found that MWC 1080undergoes rapid rises and falls in brightness with an amplitude of up to0 m .25, occurring in a time interval of from several minutes to severalhours. It is shown that MWC 1080 is similar to MWC 342 and MWC 419. Itis suggested that there is a fundamental difference between themechanisms of brightness variation of these three objects and of HerbigAe/Be stars.
| The history of mass dispersal around Herbig Ae/Be stars
We present a systematic study of the material surroundingintermediate-mass stars. Our sample includes 34 Herbig Ae/Be (HAEBE)stars of different ages and luminosities. This is a quite completerepresentation of the whole class of HAEBE stars and consequently, ourconclusions should have a solid statistical meaning. In addition, wehave observed 2 intermediate-mass protostars and included published dataon 15 protostellar objects in order to determine the evolution of thecircumstellar material in the early stages of stellar evolution. All theHAEBE stars have been classified according with the three Types alreadydefined in Fuente et al. (\cite{fuen98}): Type I stars are immersed in adense clump and have associated bipolar outflows, their ages are ~ 0.1Myr; Type II stars are still immersed in the molecular cloud though notin a dense clump, their ages are between ~ a few 0.1 to ~ a few Myr;Type III stars have completely dispersed the surrounding material andare located in a cavity of the molecular cloud, their ages are >1Myr. Our observations are used to reconstruct the evolution of thecircumstellar material around intermediate-mass stars and investigatethe mass dispersal mechanisms at the different stages of the stellarevolution. Our results can be summarized as follows: intermediate-massstars disperse >=90% of the mass of the parent clump during theprotostellar phase. During this phase, the energetic outflows sweep outthe gas and dust forming a biconical cavity while the equatorialmaterial is infalling to feed the circumstellar disk and eventually theprotostar. In this way, the density structure of the parent clumpremains well described by a density law n~ r\beta with -2=1 Myr. Since the outflowdeclines and the stars are still too cold to generate UV photons,stellar winds are expected to be the only dispersal mechanism at work.In 1 Myr an early-type star (B0-B5) and in >=1 to 10 Myr a late-typestar (later than B6) meets the ZAMS. Now the star is hot enough toproduce UV photons and starts excavating the molecular cloud.Significant differences exist between early-type and late-type stars atthis evolutionary stage. Only early-type stars are able to create large(R>0.08 pc) cavities in the molecular cloud, producing a dramaticchange in the morphology of the region. This difference is easilyunderstood if photodissociation plays an important role in the massdispersal around these objects.
| CHARM: A Catalog of High Angular Resolution Measurements
The Catalog of High Angular Resolution Measurements (CHARM) includesmost of the measurements obtained by the techniques of lunaroccultations and long-baseline interferometry at visual and infraredwavelengths, which have appeared in the literature or have otherwisebeen made public until mid-2001. A total of 2432 measurements of 1625sources are included, along with extensive auxiliary information. Inparticular, visual and infrared photometry is included for almost allthe sources. This has been partly extracted from currently availablecatalogs, and partly obtained specifically for CHARM. The main aim is toprovide a compilation of sources which could be used as calibrators orfor science verification purposes by the new generation of largeground-based facilities such as the ESO Very Large Interferometer andthe Keck Interferometer. The Catalog is 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/386/492, and from theauthors on CD-Rom.
| Empirical calibration of the near-infrared Ca II triplet - III. Fitting functions
Using a near-infrared stellar library of 706 stars with a wide coverageof atmospheric parameters, we study the behaviour of the CaII tripletstrength in terms of effective temperature, surface gravity andmetallicity. Empirical fitting functions for recently definedline-strength indices, namely CaT*, CaT and PaT, are provided. Thesefunctions can be easily implemented into stellar population models toprovide accurate predictions for integrated CaII strengths. We alsopresent a thorough study of the various error sources and their relationto the residuals of the derived fitting functions. Finally, the derivedfunctional forms and the behaviour of the predicted CaII are comparedwith those of previous works in the field.
| A multi-epoch spectrophotometric atlas of symbiotic stars
A multi-epoch, absolute-fluxed spectral atlas extending from about 3200to 9000 Å is presented for 130 symbiotic stars, including membersof the LMC, SMC and Draco dwarf galaxies. The fluxes are accurate tobetter than 5% as shown by comparison with Tycho and ground-basedphotometric data. The spectra of 40 reference objects (MKK cool giantstandards, Mira and Carbon stars, planetary nebulae, white dwarfs, hotsub-dwarfs, Wolf-Rayet stars, classical novae, VV Cep and Herbig Ae/Beobjects) are provided to assist the interpretation of symbiotic starspectra. Astrometric positions and counterparts in astrometriccatalogues are derived for all program symbiotic stars. The spectra areavailable in electronic form from the authors. Based on observationscollected with the telescopes of the European Southern Observatory (ESO,Chile) and of the Padova & Asiago Astronomical Observatories(Italy). Tables 2 and 3 are only available in electronic form (a) 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/383/188, and (b) from thepersonal home page http://ulisse.pd.astro.it/symbio_atlas/ Figures 4-256are only available in electronic form (a) at http://www.edpsciences.organd (b) from the personal home pagehttp://ulisse.pd.astro.it/symbio_atlas/
| Halos around Herbig Ae/Be stars - more common than for the less massive T Tauri stars
We present sub-arcsec observations of a sample of 31 Herbig Ae/Be andrelated stars obtained with the technique of near-infrared speckleinterferometry. In 18 of the 31 stars we find evidence for circumstellarhalos. These halos have a typical size of 1.1'', corresponding to ~1000AU at the distances of the objects. Most of the halos have blue colours,hence are seen in scattered light. The incidence of observablecircumstellar matter is significantly higher than in a larger sample ofT Tauri stars observed with the same technique (Leinert et al.\cite{leinert93a}). We suggest that this difference results as aconsequence of a faster initial evolution of the more massive HerbigAe/Be stars. The near-infrared halos found in our study appear tocorrespond to the ``envelopes'' invoked to model the strong mid-infraredexcesses of Herbig Ae/Be stars.
| Spatially Resolved Circumstellar Structure of Herbig AE/BE Stars in the Near-Infrared
We have conducted the first systematic study of Herbig Ae/Be stars usingthe technique of long baseline stellar interferometry in thenear-infrared, with the objective of characterizing the distribution andproperties of the circumstellar dust responsible for the excessnear-infrared fluxes from these systems. The observations for this workhave been conducted at the Infrared Optical Telescope Array (IOTA). Theprincipal result of this paper is that the interferometer resolves thesource of infrared excess in 11 of the 15 systems surveyed. A newbinary, MWC 361-A, has been detected interferometrically for the firsttime. The visibility data for all the sources has been interpretedwithin the context of four simple models which represent a range ofplausible representations for the brightness distribution of the sourceof excess emission: a Gaussian, a narrow uniform ring, a flat blackbodydisk with a single temperature power law, and an infrared companion. Wefind that the characteristic sizes of the near-infrared emitting regionsare larger than previously thought (0.5-5.9 AU, as given by the FWHM ofthe Gaussian intensity). A further major result of this paper is thatthe sizes measured, when combined with the observed spectral energydistributions, essentially rule out accretion disk models represented byblackbody disks with the canonical T(r)~r-3/4 law. We alsofind that, within the range observed in this study, none of the sources(except the new binary) shows varying visibilities as the orientation ofthe interferometer baseline changes. This is the expected behavior forsources which appear circularly symmetric on the sky, and for thesources with the largest baseline position angle coverage (AB Aur, MWC1080-A) asymmetric brightness distributions (such as inclined disks orbinaries) become highly unlikely. Taken as an ensemble, with no clearevidence in favor of axisymmetric structure, the observations favor theinterpretation that the circumstellar dust is distributed in sphericalenvelopes (the Gaussian model) or thin shells (the ring model). Thisinterpretation is also supported by the result that the measured sizes,combined with the excess near-infrared fluxes, imply emission of finiteoptical depth, as required by the fact that the central stars areoptically visible. The measured sizes and brightnesses do not correlatestrongly with the luminosity of the central star. Moreover, in twocases, the same excess is observed from circumstellar structures thatdiffer in size by more than a factor of 2 and surround essentiallyidentical stars. Therefore, different physical mechanisms for thenear-infrared emission may be at work in different cases, oralternatively, a single underlying mechanism with the property that thesame infrared excess is produced on very different physical scales.
| EXPORT: Near-IR observations of Vega-type and pre-main sequence stars
We present near-IR JHK photometric data of a sample of 58 main-sequence,mainly Vega-type, and pre-main sequence stars. The data were takenduring four observing runs in the period May 1998 to January 1999 andform part of a coordinated effort with simultaneous optical spectroscopyand photo-polarimetry. The near-IR colors of the MS stars correspond inmost cases to photospheric colors, although noticeable reddening ispresent towards a few objects, and these stars show no brightnessvariability within the observational errors. On the other hand, the PMSstars show near-IR excesses and variability consistent with previousdata. Tables 1 and 2 are only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strastg.fr/cgi-bin/qcat?J/A+A/365/110
| 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.
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| Сазвежђа: | Касиопеја |
| Ректацензија: | 00h43m18.25s |
| Deклинација: | +61°54'40.1" |
| Apparent магнитуда: | 10.608 |
| Proper motion RA: | 1.3 |
| Proper motion Dec: | -4.1 |
| B-T magnitude: | 11.224 |
| V-T magnitude: | 10.659 |
Каталог и designations:
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