Ýçindekiler
Görüntüler
Resim Yükleyin
DSS Images Other Images
Ýlgili Makaleler
A search for diffuse bands in the circumstellar envelopes of post-AGB stars
In this work we present the results of a systematic search for diffusebands (DBs, hereafter) in the circumstellar envelopes of a carefullyselected sample of post-AGB stars. We concentrated on analyzing 9 of theDBs most commonly found in the interstellar medium. The strength ofthese features is determined using high-resolution optical spectroscopy,and the results obtained are compared with literature data on fieldstars affected only by interstellar reddening. Based on the weakfeatures observed in the subsample of post-AGB stars dominated bycircumstellar reddening, we conclude that the carrier(s) of these DBsmust not be present in the circumstellar environment of these sources,or at least not under the excitation conditions in which DBs are formed.This conclusion is applicable to all the post-AGB stars studied,irrespective of the dominant chemistry or the spectral type of the starconsidered. A detailed radial velocity analysis of the features observedin individual sources confirms this result, as the Doppler shiftsmeasured are found to be consistent with an interstellar origin.
| Evolution from AGB to planetary nebula in the MSX survey
We investigate the evolution of oxygen- and carbon-rich AGB stars,post-AGB objects, and planetary nebulae using data collected mainly fromthe MSX catalogue. Magnitudes and colour indices are compared with thosecalculated from a grid of synthetic spectra that describe the post-AGBevolution beginning at the onset of the superwind. We find that carbonstars and OH/IR objects form two distinct sequences in the (K-[8.3])×([8.3]-[14.7]) MSX colour diagram. OH/IR objects are distributedin two groups: the bluest ones are crowded near [14.7]-[21.3]≃ 1and [8.3]-[14.7]≃ 2, and a second, redder group is spread over alarge area in the diagram, where post-AGB objects and planetary nebulaeare also found. High mass-loss rate OH/IR objects, post-AGB stars, andplanetary nebulae share the same region in the (K-[8.3])×([8.3]-[14.7]) and [14.7]-[21.3]×([8.3]-[14.7]) colour-colourdiagrams. This region in the diagram is clearly separated from a bluerone where most OH/IR stars are found. We use a grid of models ofpost-AGB evolution, which are compared with the data. The gap in thecolour-colour diagrams is interpreted as the result of the rapidtrajectory in the diagram of the stars that have just left the AGB.Based on results obtained by the MSX survey.Tables 1 to 3 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/431/565
| A search for circumstellar dust disks with ADONIS
We present results of a coronographic imaging search for circumstellardust disks with the Adaptive Optics Near Infrared System (ADONIS) at theESO 3.6 m telescope in La Silla (Chile). 22 candidate stars, known to beorbited by a planet or to show infrared excess radiation, were examinedfor circumstellar material. In the PSF-subtracted images no clear diskwas found. We further determine the detection sensitivities and outlinehow remaining atmospheric fluctuations still can hamper adaptive opticsobservations.Based on observations collected at the European Southern Observatory, LaSilla, Chile (65.I-0098, 67.C-0240, 68.C-0070).
| Version 2000 of the Catalogue of Galactic Planetary Nebulae
The ``Catalogue of Galactic Planetary Nebulae (Version 2000)'' appearsin Abhandlungen aus der Hamburger Sternwarte, Band XII in the year 2001.It is a continuation of CGPN(1967) and contains 1510 objects classifiedas galactic PNe up to the end of 1999. The lists of possible pre-PNe andpossible post-PNe are also given. The catalogue is restricted only tothe data belonging to the location and identification of the objects. Itgives identification charts of PNe discovered since 1965 (published inthe supplements to CGPN) and those charts of objects discovered earlier,which have wrong or uncertain identification. The question ``what is aplanetary nebula'' is discussed and the typical values of PNe and oftheir central stars are summarized. Short statistics about thediscoveries of PNe are given. The catalogue is also available in theCentre de Données, Strasbourg and at Hamburg Observatory viainternet. The Catalogue 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/378/843
| An ultraviolet, optical and infrared study of Herbig Ae/Be stars
We have selected a list of 45 Herbig Ae/Be-type candidates on the baseof their IRAS colors and their spectral types. We propose the presenceof a broad infrared excess as a defining criterion for these stars,rather than the detection of circumstellar nebulosity. In this way, ourselection also includes more evolved young stars, that are no longerembedded in their star-forming region. A few objects in our sample arewell-known Herbig Ae/Be stars, others are new. New optical andnear-infrared photometric observations, as well as ultraviolet ones, arepresented. The position of the objects in several color-color diagrams,as well as their de-reddened energy distributions, permit a reliableclassification. Three objects probably are binaries with a coolsecondary, 9 appear to be related to the Vega-type stars and 33 objectscan be classified as genuine Herbig Ae/Be stars. The majority of theHerbig Ae/Be stars have a dusty environment consisting of a distinct hotand cool component. These isolated Herbig Ae/Be stars suggest anevolution from embedded Herbig Ae/Be stars to beta Pictoris-likemain-sequence stars, an evolution in which planet formation may play animportant role. Based on observations obtained at the European SouthernObservatory, La Silla, Chile; and at the Swiss Telescope, La Silla,Chile; and at the Swiss Telescope, Hochalpine ForschungsstationJungfraujoch, Switzerland, and with the International UltravioletExplorer (IUE)
| Near infrared photometry of IRAS sources with colours like planetary nebulae. III
We present the near infrared photometry of a new sample of 225 IRASsources, many of them previously unidentified in the literature,selected because their far infrared colours are similar to those shownby known planetary nebulae. The results obtained are used to establishthe main source of near infrared emission. Combining this informationwith the far infrared IRAS data and a few additional criteria wedetermine the nature and evolutionary stage of all the sources observedso far, including those for which near infrared photometry waspreviously reported in Papers I and II. Among the unidentified IRASsources in our sample we find only a small percentage of planetarynebulae, many of them very young and dusty, showing peculiar nearinfrared colours. Most of the new objects observed in the near infraredare identified as transition objects in the previous stages of thestellar evolution. Among them, we find heavily obscured late-AGB stars,early post-AGB stars still obscured by thick circumstellar envelopeswhich are probably the true progenitors of planetary nebulae, and asignificant fraction of stars with bright optical counterparts showinglittle or no near infrared excess, which we associate with highlyevolved post-AGB stars with low mass progenitors, which may never becomeplanetary nebulae. In addition, we also find a small percentage of youngstellar objects, as well as a few Seyfert galaxies. We conclude that, inmost cases, based on near infrared data alone, it is not possible togive a confident classification of the unidentified IRAS source.However, the near infrared is shown to be a powerful tool, speciallywhen dealing with objects which are heavily obscured in the optical. Inthis case, the detection of the near infrared counterpart is the onlyway in which we can extend the study of these sources to other spectralranges and may be crucial to understand the short-lived phase whichprecedes the formation of a new planetary nebula. Based on observationscollected at the European Southern Observatory, La Silla (Chile) and atthe Spanish Observatorio del Teide, Tenerife, Spain. Table 6 is onlyavailable electronically at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| New and misclassified Planetary Nebulae
Altogether 86 objects discovered in the period 1991-1994 have beenaccepted by the author as new PN (Table 1). In Appendices A and B tothis table the lists of possible pre-PN as well as of possible post-PN,respectively, are given. Table 2 presents 6 misclassified objects whichwe suggest removing from CGPN.
| SAO stars with infrared excess in the IRAS Point Source Catalog
We have undertaken a search for SAO stars with infrared excess in theIRAS Point Source Catalog. In contrast to previous searches, the entireIRAS (12)-(25)-(60) color-color diagram was used. This selection yieldeda sample of 462 stars, of which a significant number are stars withcircumstellar material. The stars selected can be identified aspre-main-sequence stars, Be stars, protoplanetary systems, post-AGBstars, etc. A number of objects are (visual) binary stars.Characteristic temperatures and IR excesses are calculated and theirrelations to spectral type are investigated.
| 1612 MHz OH survey of IRAS point sources. I - Observations made at Dwingeloo, Effelsberg and Parkes
The data from a large sky survey are presented including a northernpilot study and a detailed southern study in which detections are biasedtoward the most evolved sources and distant sources. Both areinvestigated at the 1612-MHz transition of OH to take advantage of thestrongest line for AGB stars with optically thick dust shells. The IRASsources are chosen by considering their IR colors related to fluxes at12, 25, and 60 microns. Observations are reported for 2703 IRAS pointsources at the 1612-MHz transition, and 738 OH/IR stars are detected.The survey identifies 597 of the sources as previously unidentified, and95 percent of the OH profiles observed have twin-peak masercharacteristics which are related to emission from expandingcircumstellar shells. The other 5 percent of the sources are concludedto be transition objects between OH/IR stars and planetary nebulae.
| Objects in transition from the AGB to the planetary nebula stage - New visual and infrared observations
Results are presented of visual and IR observations of 42 IRAS pointsources that are candidates for objects in transition from the AGB tothe planetary nebula stage. Evidence is presented that most of thesesources are very different from mass-losing AGB stars. One of thecandidate transition objects was found to be a possible young planetarynebula on the basis of its hydrogen recombination lines observed in theNIR. Based on the shapes of their spectra, the sources were found tofall into five classes (which do not form an evolutionary sequence fromthe AGB to the planetary nebula), each containing at least 10 percent ofthe whole sample. The differences between the classes are caused bytheir history and by the present-day mass loss rate.
| Four-colour and H-beta photometry for early type stars in three southern galactic regions
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1980A&AS...41...85L&db_key=AST
|
Yeni bir Makale Öner
Ýlgili Baðlantýlar
Yeni Bir Baðlantý Öner
sonraki gruplarýn üyesi:
|
Gözlemler ve gökölçümü verileri
| Takýmyýldýz: | Akrep |
| Sað Açýklýk: | 17h12m58.77s |
| Yükselim: | -32°14'33.6" |
| Görünürdeki Parlaklýk: | 8.751 |
| Uzaklýk: | 606.061 parsek |
| özdevim Sað Açýklýk: | 5.5 |
| özdevim Yükselim: | -4.5 |
| B-T magnitude: | 8.809 |
| V-T magnitude: | 8.756 |
Kataloglar ve belirtme:
|
INHABITED SKY
