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מאמרים קשורים
Spectroscopic survey of post-AGB star candidates
Aims.Our goal is to establish the true nature of post-AGB starcandidates and to identify new post-AGB stars. Methods: We used lowresolution optical spectroscopy and we compared the spectra of thecandidate post-AGB stars with those of stars in the library spectaavailable in the literature and with spectra of "standard" post-AGBstars, and direct imaging in narrow-band filters. Results: Spectra wereobtained for 16 objects: 14 objects have not been observed previouslyand 2 objects are already known post-AGB stars used as "standards" foridentification. From the spectra we identify: six new post-AGB starswith spectral types between G5 and F5, two H ii regions the morphologyof which is revealed in the direct images for the first time, a G giantwith infrared emission, a young stellar object, a probable post-AGB starwith emission lines and three objects for which the classification isstill unclear. As a whole, our results provide new, reliableidentifications for 10 objects among listed post-AGB star candidates.Based on observations collected at the Centro Astronómico HispanoAlemán (CAHA) at Calar Alto, operated jointly by the Max-PlanckInstitut für Astronomie and the Instituto de Astrofísica deAndalucía (CSIC), and at the Observatorio de Sierra Nevada, whichis operated by the Consejo Superior de InvestigacionesCientíficas through the Instituto de Astrofísica deAndalucía (Granada, Spain). Appendices A-D are only available inelectronic form at http://www.aanda.org
| Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
The availability of the Hipparcos Catalogue has triggered many kinematicand dynamical studies of the solar neighbourhood. Nevertheless, thosestudies generally lacked the third component of the space velocities,i.e., the radial velocities. This work presents the kinematic analysisof 5952 K and 739 M giants in the solar neighbourhood which includes forthe first time radial velocity data from a large survey performed withthe CORAVEL spectrovelocimeter. It also uses proper motions from theTycho-2 catalogue, which are expected to be more accurate than theHipparcos ones. An important by-product of this study is the observedfraction of only 5.7% of spectroscopic binaries among M giants ascompared to 13.7% for K giants. After excluding the binaries for whichno center-of-mass velocity could be estimated, 5311 K and 719 M giantsremain in the final sample. The UV-plane constructed from these datafor the stars with precise parallaxes (σπ/π≤20%) reveals a rich small-scale structure, with several clumpscorresponding to the Hercules stream, the Sirius moving group, and theHyades and Pleiades superclusters. A maximum-likelihood method, based ona Bayesian approach, has been applied to the data, in order to make fulluse of all the available stars (not only those with precise parallaxes)and to derive the kinematic properties of these subgroups. Isochrones inthe Hertzsprung-Russell diagram reveal a very wide range of ages forstars belonging to these groups. These groups are most probably relatedto the dynamical perturbation by transient spiral waves (as recentlymodelled by De Simone et al. \cite{Simone2004}) rather than to clusterremnants. A possible explanation for the presence of younggroup/clusters in the same area of the UV-plane is that they have beenput there by the spiral wave associated with their formation, while thekinematics of the older stars of our sample has also been disturbed bythe same wave. The emerging picture is thus one of dynamical streamspervading the solar neighbourhood and travelling in the Galaxy withsimilar space velocities. The term dynamical stream is more appropriatethan the traditional term supercluster since it involves stars ofdifferent ages, not born at the same place nor at the same time. Theposition of those streams in the UV-plane is responsible for the vertexdeviation of 16.2o ± 5.6o for the wholesample. Our study suggests that the vertex deviation for youngerpopulations could have the same dynamical origin. The underlyingvelocity ellipsoid, extracted by the maximum-likelihood method afterremoval of the streams, is not centered on the value commonly acceptedfor the radial antisolar motion: it is centered on < U > =-2.78±1.07 km s-1. However, the full data set(including the various streams) does yield the usual value for theradial solar motion, when properly accounting for the biases inherent tothis kind of analysis (namely, < U > = -10.25±0.15 kms-1). This discrepancy clearly raises the essential questionof how to derive the solar motion in the presence of dynamicalperturbations altering the kinematics of the solar neighbourhood: doesthere exist in the solar neighbourhood a subset of stars having no netradial motion which can be used as a reference against which to measurethe solar motion?Based on observations performed at the Swiss 1m-telescope at OHP,France, and on data from the ESA Hipparcos astrometry satellite.Full Table \ref{taba1} is only available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/430/165}
| Near-Infrared Interferometric Images of the Hot Inner Disk surrounding the Massive Young Star MWC 349A
We present images of the massive young star MWC 349A at 1.65, 2.16, and2.27, and 3.08 μm, reconstructed from complex visibility dataobtained with an aperture-masking interferometric technique on the KeckI telescope. These images have an approximately elliptical appearanceand are consistent with the expected shape of a nearly edge-on disk.Visibility data at 1.65, 2.27, and 3.08 μm were fitted with uniformellipses with major axes 36+/-2, 47+/-2, and 62+/-1 mas in length,respectively. The major axis is at a position angle of100°+/-3°, consistent with the position angle of the dark laneobserved previously in VLA radio continuum maps at 8 and 22 GHz. Thisaxis is also perpendicular to the symmetry axis of the bipolar lobes ofH66α recombination line emission and is consistent with positionsof the recombination line maser spots at 1.3 mm. At an assumed distanceof 1.2 kpc, the linear sizes of the disk are 44 and 57 AU at 1.65 and2.27 μm, respectively. These images are consistent with a dust diskhaving an angle between the symmetry axis of the disk and the plane ofthe sky of 15° and thickness of 6 AU, or an angle of 20° andthickness of 1.4 AU, giving an upper bound to the mass of the disk ofMd<5.7 Msolar or Md<1.3Msolar, respectively.
| An IRAS survey of star-forming regions toward Cygnus
The distribution of young stellar objects (YSOs) toward the Cygnus Xregion obtained from the Infrared Astronomical Satellite (IRAS) iscombined with a recent (C-12)O (J = 2-1) survey. The most luminous YSOsare examined for membership in the Local arm and the Perseus arm. Thefar-infrared, radio, and molecular emission is also analyzed from aglobal perspective. Seventy YSOs have been identified, corresponding tostars earlier than about B7 ZAMS, primarily associated with molecularclouds in the Local arm. The (C-12)O (J = 2-1) emission associated withthese YSOs reveals 23 instances of broad-line wings including 10 withspatially complex, extended high-velocity molecular emission. We haveidentified a new Perseus arm star-forming region, IRAS 20144+3726, andhave also identified 20264+4042 and 20321+4112 near the H II regions DR7 and 18P61 as broad-wing outflow sources also located in the Perseusarm. We conclude that no more than three YSOs earlier than approximatelyB0 ZAMS currently exist in the Perseus arm region located behind CygnusX.
| Interstellar extinction in the vicinity of the North America and Pelican Nebulae. II
The results of photoelectric photometry of 564 stars in the Vilniusseven-color system in three areas near the North America and PelicanNebulae are given. Photometric spectral types, absolute magnitudes,color excesses, interstellar extinction,s and distances to the stars aredetermined. We find that the dark cloud separating both nebulae is at580 pc distance. A number of stars immersed in the dark cloud have beenfound. It seems that the dark cloud extends south down to 40 degdeclination. The area southwest of alpha Cygni in the declination zones42 deg and 43 deg is comparatively transparent at least up to 1 kpc.
| Possible young stellar objects in the region of the Cygnus OB2 (VI Cygni) association from IRAS observations
Several massive young stellar objects are found from an analysis of the12- to 100-micron flux data of IRAS sources in the region of the Cyg OB2association. Sixty-four sources with positive spectral indices andsteeply increasing FIR flux distribution similar to that found in knownyoung stellar objects are identified. Some of these sources have massivecold dust shells with FIR luminosities of the order of 1000 to 10,000solar luminosities and are most likely massive young stellar objectswhich may show bipolar structure and molecular outflows. The luminosityfunction for the IRAS sources in the Cyg OB2 suggests that most of thesources with positive spectral indices are most likely members of theCyg OB2 association. It is suggested that there may be a few hundredlow-mass young stellar objects in the Cyg OB2 association.
| Not Available
Not Available
| E. W. Fick Observatory stellar radial velocity measurements. I - 1976-1984
Stellar radial velocity observations made with the large vacuumhigh-dispersion photoelectric radial velocity spectrometer at FickObservatory are reported. This includes nearly 2000 late-type starsobserved during 585 nights. Gradual modifications to this instrumentover its first eight years of operation have reduced the observationalerror for high-quality dip observations to + or - 0.8 km/s.
| Narrow-band photometry of late-type stars
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1970A&AS....1..199H&db_key=AST
| The Cygnus II Association.
Not Available
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הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
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תצפית ומידע אסטרומטרי
| קבוצת-כוכבים: | ברבור |
| התרוממות ימנית: | 20h34m36.00s |
| סירוב: | +41°05'54.3" |
| גודל גלוי: | 6.668 |
| מרחק: | 268.097 פארסק |
| תנועה נכונה: | 0.3 |
| תנועה נכונה: | 18.4 |
| B-T magnitude: | 8.603 |
| V-T magnitude: | 6.828 |
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