תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Planetary nebula distances re-examined: an improved statistical scale
The distances of planetary nebulae (PNe) are still quite uncertain.Although observational estimates are available for a small proportion ofPNe, based on statistical parallax and the like, such distances are verypoorly determined for the majority of galactic PNe. In particular,estimates of so-called `statistical' distance appear to differ byfactors of ~2.7.We point out that there is a well-defined correlation between the 5-GHzluminosity of the sources, L5, and their brightnesstemperatures, TB. This represents a different trend to thoseinvestigated in previous statistical analyses, and permits us todetermine independent distances to a further 449 outflows. Thesedistances are shown to be closely comparable to those determined using aTB-R correlation, providing that the latter trend is taken tobe non-linear.This non-linearity in the TB-R plane has not been noted inprevious analyses, and is likely responsible for the broad (andconflicting) ranges of distance that have previously been published.Finally, we point out that there is a close accord between observedtrends within the L5-TB and TB-Rplanes, and the variation predicted through nebular evolutionarymodelling. This is used to suggest that observational biases areprobably modest, and that our revised distance scale is reasonablytrustworthy.
| The relation between Zanstra temperature and morphology in planetary nebulae
We have created a master list of Zanstra temperatures for 373 galacticplanetary nebulae based upon a compilation of 1575 values taken from thepublished literature. These are used to evaluate mean trends intemperature for differing nebular morphologies. Among the most prominentresults of this analysis is the tendency forη=TZ(HeII)/TZ(HeI) to increase with nebularradius, a trend which is taken to arise from the evolution of shelloptical depths. We find that as many as 87 per cent of nebulae may beoptically thin to H ionizing radiation where radii exceed ~0.16 pc. Wealso note that the distributions of values η and TZ(HeII)are quite different for circular, elliptical and bipolar nebulae. Acomparison of observed temperatures with theoretical H-burning trackssuggests that elliptical and circular sources arise from progenitorswith mean mass ≅ 1 Msolar(although the elliptical progenitors are probably more massive).Higher-temperature elliptical sources are likely to derive fromprogenitors with mass ≅2 Msolar, however, implying thatthese nebulae (at least) are associated with a broad swathe ofprogenitor masses. Such a conclusion is also supported by trends in meangalactic latitude. It is found that higher-temperature ellipticalsources have much lower mean latitudes than those with smallerTZ(HeII), a trend which is explicable where there is anincrease in with increasing TZ(HeII).This latitude-temperature variation also applies for most other sources.Bipolar nebulae appear to have mean progenitor masses ≅2.5Msolar, whilst jets, Brets and other highly collimatedoutflows are associated with progenitors at the other end of the massrange (~ 1 Msolar). Indeed it ispossible, given their large mean latitudes and low peak temperatures,that the latter nebulae are associated with the lowest-mass progenitorsof all.The present results appear fully consistent with earlier analyses basedupon nebular scale heights, shell abundances and the relativeproportions of differing morphologies, and offer further evidence for alink between progenitor mass and morphology.
| Galactic Planetary Nebulae and their central stars. I. An accurate and homogeneous set of coordinates
We have used the 2nd generation of the Guide Star Catalogue (GSC-II) asa reference astrometric catalogue to compile the positions of 1086Galactic Planetary Nebulae (PNe) listed in the Strasbourg ESO Catalogue(SEC), its supplement and the version 2000 of the Catalogue of PlanetaryNebulae. This constitutes about 75% of all known PNe. For these PNe, theones with a known central star (CS) or with a small diameter, we havederived coordinates with an absolute accuracy of ~0\farcs35 in eachcoordinate, which is the intrinsic astrometric precision of the GSC-II.For another 226, mostly extended, objects without a GSC-II counterpartwe give coordinates based on the second epoch Digital Sky Survey(DSS-II). While these coordinates may have systematic offsets relativeto the GSC-II of up to 5 arcsecs, our new coordinates usually representa significant improvement over the previous catalogue values for theselarge objects. This is the first truly homogeneous compilation of PNepositions over the whole sky and the most accurate one available so far.The complete Table \ref{tab2} is only available in electronic form atthe CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/408/1029}
| GLIMPSE. I. An SIRTF Legacy Project to Map the Inner Galaxy
The Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE),a Space Infrared Telescope Facility (SIRTF) Legacy Science Program, willbe a fully sampled, confusion-limited infrared survey of 2/3 of theinner Galactic disk with a pixel resolution of ~1.2" using the InfraredArray Camera at 3.6, 4.5, 5.8, and 8.0 μm. The survey will coverGalactic latitudes |b|<=1deg and longitudes|l|=10deg-65° (both sides of the Galactic center). Thesurvey area contains the outer ends of the Galactic bar, the Galacticmolecular ring, and the inner spiral arms. The GLIMPSE team will processthese data to produce a point-source catalog, a point-source dataarchive, and a set of mosaicked images. We summarize our observingstrategy, give details of our data products, and summarize some of theprincipal science questions that will be addressed using GLIMPSE data.Up-to-date documentation, survey progress, and information oncomplementary data sets are available on the GLIMPSE Web site.
| The Correlations between Planetary Nebula Morphology and Central Star Evolution: Analysis of the Northern Galactic Sample
Northern Galactic planetary nebulae (PNs) are studied to disclosepossible correlations between the morphology of the nebulae and theevolution of the central stars (CSs). To this end, we have built thebest database available to date, accounting for homogeneity andcompleteness. We use updated statistical distances and an updatedmorphological classification scheme, and we calculate Zanstratemperatures for a large sample of PNs. With our study we confirm thatround, elliptical, and bipolar PNs have different spatial distributionswithin the Galaxy, with average absolute distances to the Galactic planeof 0.73, 0.38, and 0.21 kpc, respectively. We also find evidence thatthe distributions of the CS masses are different across thesemorphological groups, although we do not find that CSs hosted by bipolarPNs are hotter, on average, than CSs within round and elliptical PNs.Our results are in broad agreement with previous analyses, indicatingthat round, elliptical, and bipolar PNs evolve from progenitors indifferent mass ranges and might belong to different stellar populations,as also indicated by the helium and nitrogen abundances of PNs ofdifferent morphology.
| The dust content of planetary nebulae: a reappraisal
We have performed a statistical analysis using broad band IRAS data onabout 500 planetary nebulae with the aim of characterizing their dustcontent. Our approach is different from previous studies in that it usesan extensive grid of photoionization models to test the methods forderiving the dust temperature, the dust-to-gas mass ratio and theaverage grain size. In addition, we use only distance independentdiagrams. With our models, we show the effect of contamination by atomiclines in the broad band IRAS fluxes during planetary nebula evolution.We find that planetary nebulae with very different dust-to-gas massratios exist, so that the dust content is a primordial parameter for theinterpretation of far infrared data of planetary nebulae. In contrastwith previous studies, we find no evidence for a decrease in thedust-to-gas mass ratio as the planetary nebulae evolve. We also showthat the decrease in grain size advocated by Natta & Panagia(\cite{NattaPanagia}) and Lenzuni et al. (\cite{Lenzuni}) is an artefactof their method of analysis. Our results suggest that the timescale fordestruction of dust grains in planetary nebulae is larger than theirlifetime. Table~1 is only accessible 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
| The kinematics of 867 galactic planetary nebulae
We present a compilation of radial velocities of 867 galactic planetarynebulae. Almost 900 new measurements are included. Previously publishedkinematical data are compared with the new high-resolution data toassess their accuracies. One of the largest samples in the literatureshows evidence for a systematic velocity offset. We calculate weightedaverages between all available data. Of the final values in thecatalogue, 90% have accuracies better than 20 km s(-1) . We use thiscompilation to derive kinematical parameters of the galacticdifferential rotation obtained from least-square fitting and toestablish the Disk rotation curve; we find no significal trend for thepresence of an increasing external rotation curve. We examine also therotation of the bulge; the derived curve is consistent with a linearlyincreasing rotation velocity with l: we find V_b,r=(9.9+/-1.3)l -(6.7+/-8.5) km s(-1) . A possible steeper gradient in the innermostregion is indicated. Table 2 is available in electronic form only, viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Planetary Nebulae in the NRAO VLA Sky Survey
The 1.4 GHz NRAO VLA Sky Survey (NVSS) images and source catalog wereused to detect radio emission from the 885 planetary nebulae north ofJ2000 declination delta = -40 deg in the Strasbourg-ESO Catalogue ofGalactic Planetary Nebulae. We identified 680 radio sources brighterthan about S = 2.5 mJy beam-1 (equivalent to T ~ 0.8 K in the 45" FWHMNVSS beam) with planetary nebulae by coincidence with accurate opticalpositions measured from Digitized Sky Survey (DSS) images. Totalextinction coefficients c at lambda = 4861 Angstroms were calculated forthe 429 planetary nebulae with available H beta fluxes and low free-freeoptical depths at 1.4 GHz. The variation of c with Galactic latitude andlongitude is consistent with the extinction being primarily interstellarand not intrinsic.
| Properties That Cannot Be Explained by the Progenitors of Planetary Nebulae
I classify a large number of planetary nebulae (458) according to theprocess that caused their progenitors to blow axisymmetrical winds. Theclassification is based primarily on the morphologies of the differentplanetary nebulae, assuming that binary companions, stellar orsubstellar, are necessary in order to have axisymmetrical mass loss onthe asymptotic giant branch. I propose four evolutionary classes,according to the binary-model hypothesis: (1) Progenitors of planetarynebula that did not interact with any companion. These amount to ~10% ofall planetary nebulae. (2) Progenitors that interact with stellarcompanions that avoided a common envelope, 11^{+2}_{-3}% of all nebulae.(3) Progenitors that interact with stellar companions via a commonenvelope phase, 23^{+11}_{-5}% of all nebulae. (4) Progenitors thatinteract with substellar (i.e., planets and brown dwarfs) companions viaa common envelope phase, 56^{+5}_{-8}% of all nebulae. In order todefine and build the different classes, I start with clarifying somerelevant terms and processes related to binary evolution. I then discusskinematical and morphological properties of planetary nebulae thatappear to require the interaction of the planetary nebula progenitorsand/or their winds with companions, stellar or substellar.
| Planetary nebulae morphologies, central star masses and nebular properties.
We have constituted a sample of about 80 PN with defined morphologiesand well observed basic parameters (fluxes, angular radii, expansionvelocities and magnitudes of the central stars). For these PN, we havederived the central star masses by comparing the observed set ofparameters with those predicted by a simple evolutionary model of a PN,expanding at the same velocity as the observed one. We have thenexamined the relations between the PN morphological types and otherproperties, linked to the central star mass. Bipolar PN are shown tohave a wider distribution of central star masses than the rest of PN,and shifted towards higher values. They lie closer to the Galactic planeand tend to have larger N/O ratios. Point symmetric PN, which have notbeen much studied so far, are found to constitute an outstanding class.They show an almost perfect M_*_-v_exp_ correlation. They correspond toa rather short evolutionary stage of PN. They lie, on average, furtherfrom the Galactic plane than bipolar PN and tend to have lower N/O.Globally, PN with higher central star masses are found closer to theGalactic plane, and the observed relation between N/O and M_*_ isroughly consistent with the predictions from evolutionary models for AGBstars.
| A Westerbork Synthesis Radio Telescope 327 MHz Survey of the Galactic Plane
The Westerbork Synthesis Radio Telescope (WSRT) has been used to surveythe Galactic plane region 42^deg^ < l < 92^deg^ at a frequency of327 MHz. We present images of the emission within |b| < 1.6^deg^ atresolution of 1' x 1' csc δ and detection level as low as 10 mJybeam^-1^. Inspection of the survey image has produced a catalog ofnearly 4000 discrete sources with sizes less than about ~3'. The catalogof these sources and FITS files of seven images covering the survey areaare available on the World Wide Web athttp://www.ras.ucalgary.ca/wsrt_survey.html. Approximately 15% of thesources are resolved, with dimensions of 1'- 3'. The spatialdistribution of resolved sources shows concentrations toward the spiralarms and follows the warping of the Galactic disk over the length of thesurvey region, indicating that a sizable fraction is Galactic. Spectralindices are calculated for 1313 sources detected in other radio surveysat frequencies greater than 408 MHz. The resolved sources exhibit abimodal spectral index distribution, with distinct nonthermal andthermal populations. Comparison with the IRAS Point Source Catalogueresults in 118 identifications between WSRT and IRAS sources. Most ofthese are thermal radio sources associated with compact Galactic objectssuch as H II regions and planetary nebulae. A search for variabilityamong 2148 of the compact sources has resulted in 29 candidatelow-frequency variable sources.
| A CS(2-1) survey of IRAS point sources with color characteristics of ultra-compact HII regions.
We have made a complete survey of the CS(2-1) emission toward IRAS pointsources in the galactic plane. The sources observed were selectedaccording to their far infrared (FIR) colors, which are characteristicof UC HII regions. They have 25μm/12μm flux ratios larger than 3.7and 60μm/12μm flux ratios larger than 19.3. The survey covered aregion from b=-2deg to b=2deg from l=300deg to l=0deg and from l=0deg tol=60deg, and from b=-4deg to b=4deg elsewhere. We detected 843 sourcesout of 1427 sources observed. The distributions of detected andundetected sources in a FIR color-color diagram show some differences,suggesting that more than one type of object is present in our observedsample.
| A statistical distance scale for Galactic planetary nebulae
A statistical distance scale is proposed. It is based on the correlationbetween the ionized mass and the radius and the correlation between theradio continuum surface brightness temperature and the nebular radius.The proposed statistical distance scale is an average of the twodistances obtained while using the correlation. These correlations,calibrated based on the 1`32 planetary nebulae with well-determinedindividual distances by Zhang, can reproduce not only the averagedistance of a sample of Galactic Bulge planetary nebulae exactly at thedistance to the Galactic center, but also the expected Gaussiandistribution of their distances around the Galactic center. This newdistance scale is applied to 647 Galactic planetary nebulae. It isestimated that this distance scale can be accurate on average to35%-50%. Our statistical distance scale is in good agreement with theone recently proposed by Van de Steene and Zijlstra. The correlationsfound in this study can be attributed to the fact that the core mass ofthe central stars has a very sharp distribution, strongly peaked atapprox. 0.6 solar mass. We stress that the scatter seen in thestatistical distance scale is likely to be real. The scatter is causedby the fact that the core mass distribution, although narrow andstrongly peaked, has a finite width.
| A catalogue HeII 4686 line intensities in Galactic planetary nebulae.
We have compiled the intensities of the HeII 4686 lines measured inGalactic planetary nebulae. We present a few observational diagramsrelated to this parameter, and discuss them with the help of theoreticaldiagrams obtained from simple model planetary nebulae surroundingevolving central stars of various masses. We determine the hydrogen andhelium Zanstra temperature for all the objects with accurate enoughdata. We argue that, for Galactic planetary nebulae as a whole, the maincause for the Zanstra discrepancy is leakage of stellar ionizing photonsfrom the nebulae.
| Confrontation of theoretical tracks for post-AGB stars with observations of planetary nebulae
We have constructed a distance-independent diagram to test publishedtheoretical tracks for the evolution of post-AGB stars by comparing themwith the Galactic planetary nebulae data base. We have found noinconsistency between observations and the set of tracks computed bySchoenberner (1981, 1983) and Bloecker & Schoenberner (1990). On theother hand, observations do not seem support the large transition timesbetween the end of the AGB superwind and the beginning of the planetarynebula ionization phase adopted in the models of Vassiliadis & Wood(1994).
| Comparison of two methods for determining the interstellar extinction of planetary nebulae
A comparison of the planetary nebulae as derived from the Balmerdecrement and from the ratio of radio and H-beta fluxes is presented onthe basis of a compilation of all the relevant radio and opticalmeasurements and a serious selection of the best data. It is shown thatthe extinction determined from the Balmer decrement is systematicallylarger than the one derived from the radio data, the slope of the (Copt,Crad) relation being about 1.2. It is argued that, for most distantplanetary nebulae, the total to selection extinction is significantlylower than 3, the value corresponding to the standard extinction law forthe interstellar medium.
| The extinction constants for galactic planetary nebulae
The extinction constants are determined from Balmer decrementmeasurements for over 900 planetary nebulae. Comparison with publishedextinction constants shows that the results from ESO are fairlyreliable. An analysis of the extinction constants derived from theBalmer decrement and from the radio/Hβ flux ratio indicates thatthe latter tends to be systematically smaller than the former forincreasing extinction. We suggest that the radio measurements ofPottasch's group probably underestimate the radio fluxes, at least forsome (faintest) objects.
| A catalogue of absolute fluxes and distances of planetary nebulae
The paper presents a complete list of averaged recalibrated absoluteH-beta fluxes, global (where possible) relative He II lambda 4686fluxes, 5 GHz radio flux densities, and H-alpha/H-beta interstellarextinction constants for 778 Galactic planetary nebulae. The catalogprovides much of the fundamental data required to generate Zanstratemperatures. When data with the lowest errors are selected, the opticaland radio/optical extinctions show a peculiar correlation, with theradio values slightly high at low extinction and notably low at highextinction. The data are used, along with the best estimates of angulardiameters, to calculate Shklovsky distances according to the Daub schemeon the scale used earlier by Cahn and Kaler (1971). Use of this distancescale shows approximate equality of the death rates of optically thickand optically thin planetary nebulae. The method gives the correctdistances to the Magellanic Clouds.
| Strasbourg - ESO catalogue of galactic planetary nebulae. Part 1; Part 2
Not Available
| The absolute H-beta fluxes for galactic planetary nebulae
The absolute H-beta flux measurements from spectrophotometricobservations of about 880 galactic planetary nebulae are presented. Thegalactic coordinates of PNe and the adopted diameters for the nebulae inarcsec are given. The final values of the H-beta flux, corrected for thenebular extension, are presented and compared to the results of othermeasurements.
| The B and V magnitudes of the central stars of planetary nebulae
The B and V magnitudes are determined for about 350 central stars ofplanetary nebulae, 190 of which are being given for the first time. Thestellar continuum was measured on spectra taken at ESO, Chile, and atOHP, France, in range of 400-740 nm, with a resolution of about 1 nm.
| Large planetary nebulae and their significance to the late stages of stellar evolution
Spectrophotometry of 75 large PNe with Shklovsky radii greater than 0.15pc is presented and used to calculate nebular parameters andcompositions, stellar Zanstra temperatures and luminosities, and coremasses. Nine new Peimbert type I nebulae are identified. About 40percent of the stars that are on cooling tracks are above 0.7 solarmass, and over 15 percent are above 0.8 solar mass. The largeplanetaries demonstrate a clear positive correlation between nitrogenenrichment and core mass. N/O is anticorrelated with O/H. The radii ofthe nebulae whose stars lie along specific cooling tracks increasemonotonically with decreasing central star temperature. For a givencentral temperature, the nebular radii also increase with increasingcore mass, showing that in this part of the log L-log T plane the highermass cores evolve more slowly in agreement with theoretical prediction.However, theoretical evolutionary rates for the large nebulae starsappear to be much too slow.
| Properties and evolution of dust grains in planetary nebulae
The IRAS data of 233 planetary nebulae (PNs) determining the propertiesof the dust contained in their envelopes have been analyzed. The mainresult is that the dust grains undergo substantial evolution during thelifetime of a PN. In particular, the grain size and the total dust massdecrease systematically with the nebular radius whereas the number ofemitting grains increases. Two scenarios which can explain these resultsare discussed. A first possibility is that grains undergo processeswhich both 'erode' and 'shatter' them. It is argued that sputtering byfast atoms of a stellar wind and grain-grain collisions may plausiblyproduce such effects. Alernatively, the dust present in PNs may have asize distribution since the very beginning and large grains may beselectively destroyed during the PN evolution.
| Interstellar scattering at a frequency of 102 MHz
The angular dimensions of compact radio sources at a frequency of 102MHz are measured by the interplanetary scintillation method. An estimateis obtained for interstellar scattering in the direction perpendicularto the Galactic plane. The possibility of measuring the angulardimensions of pulses using the interplanetary scintillation method isstudied.
| A catalogue of VLA radio continuum observations of planetary nebulae with the Very Large Array
An extended VLA survey of about 300 planetary nebulae, ranging in sizefrom 4 arcsec to 8 arcmin, has been completed. The maps and the measuredparameters, such as radio flux density, diameter, and position, arepresented. The brightness temperatures, total far-infrared flux, andinfrared excess are derived. Newly measured optical positions are givenfor a few sources. A compilation of all published VLA data of planetarynebulae is also included. High-resolution radio synthesis observationsare now available for approximately 400 nebulae.
| Thick radio shell in supernova remnant DA 495 (G65.7+1.2)?
High-resolution multifrequency radio observations of DA 495 (G65.7+1.2)at 20, 49, and 92 cm wavelengths are discussed, along with IRobservations. Although the remnant is shown to have a minimum near thecenter, its brightness distribution does not display limb brightening,giving it the characteristics of both shell-type SNRs and Crab-typeSNRs. An unusually thick shell with an inner radius of 125 arcsec and anouter radius of 500 arcsec is observed. Also discussed are the role ofthe reverse shock in the formation of the thick shell and theassociation of the open cluster NGC 6834 with DA 495.
| A catalogue of expansion velocities of Galactic planetary nebulae
Published observational data on 288 Galactic PN are compiled in tables,graphs, and sketches based on spatiokinematical models and brieflycharacterized. The criteria used in selecting the data are discussed,and particular attention is given to the accuracies of the distanceestimates and their implications for theoretical models of PN or stellarevolution.
| Planetary nebulae in the Galaxy
It is shown that the planetary nebulae can be divided into three typesaccording to the values of the mass of shell and a central star. Thecriteria are given using which one can determine the mass type of thenebula. The distance scale of each mass-type planetary nebulae is given.The distribution of planetary nebulae in the Galaxy, their formationrate, scale-height and other physical and kinematic characteristics areinvestigated. A catalogue of planetary nebulae emitting in the ratiorange is given.
| Photometry and spectroscopy of stars in northern H II regions
New UBV photometry of 60 candidates for the exciting stars of a sampleof optical H II regions between Galactic longitudes 30 and 70 deg ispresented, together with MK spectral types for a smaller number ofstars. These data allow the identification of 11 possible new excitingstars in 7 nebulae. A catalog of basic data on the 36 Sharpless (1959) HII regions in this longitude range has been compiled from the presentobservations and from a reanalysis of existing data and is alsopresented, with notes on individual nebulae.
| Radio patrol of the northern Milky Way - A catalog of sources. II
The paper presents a catalog of 1274 discrete sources detected during a5 yr, 6 cm, radio-patrol survey of the Galactic plane for variablesources. Approximately 20 percent of the volume of the Galactic disk wasrepeatedly observed on 16 occasions. The survey is capable of detectingboth short-term (few days) and long-term variability. Seventy-fivepercent of the sources are weaker than 75 mJy, and as a consequence,reliable detection of variability generally required luminosityvariations greater than or equal to 50 percent. Thirty-two variablesources and 27 possible variables were detected, of which 64 percentexhibited short-term variability. Two new identifications are proposedfor the short-term variables GT 0116 + 622 and GT 2318 + 620, with thetransient gamma-ray source Cas gamma-1 and the X-ray source 4U 2316 +61, respectively. The absence of giant outbursts leads to an upper limitof three on the number of objects in the survey area with radioproperties like Cyg X-3. A comparison with previous centimetervariability studies suggest the possible existence of two distinctvariability components.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
קטלוגים וכינוים:
|
