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Hubble Space Telescope NICMOS Imaging Polarimetry of Proto-Planetary Nebulae. II. Macromorphology of the Dust Shell Structure via Polarized Light
The structure of the dusty circumstellar envelopes (CSEs) ofproto-planetary nebulae (PPNs) reveals the mass-loss history of thesesources and how such histories may differ for elliptical (SOLE) andbipolar (DUPLEX) PPNs. To study the PPN structures via dust-scatteredlinearly polarized starlight, we have compiled the imaging-polarimetricdata for all 18 evolved stars that have been obtained to date withNICMOS on board the Hubble Space Telescope. This alternative imagingtechnique provides a unique way to probe the distribution of dust grainsthat scatter light around evolved stars. The new perspective gained fromthe imaging-polarimetric data has revealed several new aspects to thestructures of PPNs. Point symmetry is a prevalent imaging-polarimetriccharacteristic resulting from the azimuthal density gradient in theCSEs. Among these point-symmetric nebulae, three detailed morphologicaltypes can be differentiated by their polarized intensity, Ip,and polarization strength, P. While the azimuthal density gradient isreversed above and below the equatorial plane in optically thickerbipolar nebulae, there is no gradient reversal in optically thinnerelliptical nebulae. The equatorial plane of the system defined by theintegrated angle of polarization is not necessarily orthogonal to theaxis of the apparent bipolar structure in the total intensity data.
| H I Absorption of Polarized Emission: A New Technique for Determining Kinematic Distances to Galactic Supernova Remnants
We present a new method of determining the systemic velocity of Galacticsupernova remnants (SNRs) based on H I absorption of their linearlypolarized radio continuum emission. Conventional H I observations oftotal power emission are limited by H I emission and self-absorptionalong the line of sight, but since H I emission is unpolarized, the onlylimits on measurements of absorption of the polarized emission are noiseand velocity resolution. This leads to lower uncertainties and makes itpossible to obtain absorption profiles for virtually all Galactic SNRswith very precise H I column densities. To demonstrate the newtechnique, we have obtained H I absorption profiles from Tycho'ssupernova remnant (G120.1+1.4). Absorption profiles of the polarizedemission are very similar to those of the total power emission. Opticaldepths from the polarization profiles are slightly larger because ofsmall-scale emission features. We also observed polarization absorptionprofiles of the Boomerang pulsar wind nebula (part of G106.3+2.7) andthe plerionic SNR DA 495 (G65.7+1.2), remnants that are so faint thatabsorption profiles cannot be obtained in total power.
| 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
| A catalogue of galaxies behind the southern Milky Way. II. The Crux and Great Attractor regions (l~ 289o to 338o)
In this second paper of the catalogue series of galaxies behind thesouthern Milky Way, we report on the deep optical galaxy search in theCrux region (289o <= l <= 318o and-10o <= b <= 10o) and the Great Attractorregion (316o <= l <= 338o and-10o <= b <= 10o}). The galaxy cataloguesare presented, a brief description of the galaxy search given, as wellas a discussion on the distribution and characteristics of the uncoveredgalaxies. A total of 8182 galaxies with major diameters D >~ 0.2arcmin were identified in this ~ 850 square degree area: 3759 galaxiesin the Crux region and 4423 galaxies in the Great Attractor region. Ofthe 8182 galaxies, 229 (2.8%) were catalogued before in the optical (3in radio) and 251 galaxies have a reliable (159), or likely (92)cross-identification in the IRAS Point Source Catalogue (3.1%). A numberof prominent overdensities and filaments of galaxies are identified.They are not correlated with the Galactic foreground extinction andhence indicative of extragalactic large-scale structures. Redshiftsobtained at the South African Astronomical Observatory (SAAO) for 518 ofthe newly catalogued galaxies in the Crux and Great Attractor regions(Fairall et al. \cite{Fairall98}; Woudt et al. \cite{Woudt99}) confirmdistinct voids and clusters in the area here surveyed. With this opticalgalaxy search, we have reduced the width of the optical ``Zone ofAvoidance'' for galaxies with extinction-corrected diameters larger than1.3 arcmin from extinction levels AB >= 1.0m toAB >= 3.0m: the remaining optical Zone of Avoidance is nowlimited by | b | <~ 3o (see Fig. \ref{cruxf1new}). The twooptical catalogues and their respective listings of IRAScross-identifications are available in electronic format 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/380/441
| The Supernova Remnant G106.3+2.7 and Its Pulsar-Wind Nebula: Relics of Triggered Star Formation in a Complex Environment
We propose that the pulsar nebula associated with the pulsar J2229+6114and the supernova remnant (SNR) G106.3+2.7 are the result of the samesupernova explosion. The whole structure is located at the edge of an HI bubble with extended regions of molecular gas inside. The radialvelocities of both the atomic hydrogen and the molecular materialsuggest a distance of 800 pc. At this distance, the SNR is 14 pc longand 6 pc wide. Apparently, the bubble was created by the stellar windand supernova explosions of a group of stars in its center, which alsotriggered the formation of the progenitor star of G106.3+2.7. Theprogenitor star exploded at or close to the current position of thepulsar, which is at one end of the SNR rather than at its center. Theexpanding shock wave of the supernova explosion created a comet-shapedsupernova remnant by running into dense material and then breaking outinto the inner part of the H I bubble. A synchrotron nebula with ashell-like structure (the ``Boomerang'') of length 0.8 pc was created bythe pulsar wind interacting with the dense ambient medium. The expandingshock wave created an H I shell of mass 0.4 Msolar aroundthis nebula by ionizing the atomic hydrogen in its vicinity.
| Mass, linear momentum and kinetic energy of bipolar flows in protoplanetary nebulae
We have studied the CO emission from protoplanetary nebulae (PPNe). Oursample is composed of 37 objects and includes, we think, all wellidentified PPNe detected in CO, together with the two yellow hypergiantsemitting in CO and one young PN. We present a summary of the existing COdata, including accurate new observations of the 12CO and13CO J=1-0 and J=2-1 lines in 16 objects. We identify in thenebulae a slowly expanding shell (represented in the spectra by acentral core) and a fast outflow (corresponding to the line wings), thatin the well studied PPNe is known to be bipolar. Excluding poor data, weend up with a sample of 32 sources (including the 16 observed by us);fast flows are detected in 28 of these nebulae, being absent in only 4.We present a method to estimate from these data the mass, ``scalar''momentum and kinetic energy of the different components of the molecularoutflows. We argue that the uncertainties of our method can hardly leadto significant overestimates of these parameters, althoughunderestimates may be present in not well studied objects. The totalnebular mass is often as high as ~1 Msun, and the mass-lossrate, that (presumably during the last stages of the AGB phase)originated the nebula, had typical values ~10-4Msun yr-1. The momentum corresponding to this massejection process in most studied nebulae is accurately coincident withthe maximum momentum that radiation pressure, acting through absorptionby dust grains, is able to supply (under expected conditions). Weestimate that this high-efficiency process lasts about 1000-10 000 yr,after which the star has ejected a good fraction of its mass and the AGBphase ends. On the other hand, the fast molecular outflows, that haveprobably been accelerated by shock interaction with axial post-AGB jets,carry a significant fraction of the nebular mass, with a very highmomentum (in most cases between 1037 and 1040 g cms-1) and very high kinetic energy (usually between1044 and 1047 erg). In general, yellow hypergiantsand post-AGB objects with low initial mass show nebular masses andmomenta that are, respectively, higher and lower than these values. Wecompare the momenta of the fast outflows with those that can be suppliedby radiation pressure, taking into account the expected shortacceleration times and some effects that can increase the momentumtransfer. We find that in about 80% of PPNe, the fast molecular flowshave too high momenta to be powered by radiation pressure. In some casesthe momentum of the outflow is ~1000 larger than that carried byradiation pressure; such high factors are difficult to explain evenunder exceptional conditions. Wind interaction is the basic phenomenonin the PN shaping from the former AGB envelopes; we conclude that thisinteraction systematically takes place along a dominant direction andthat this process is not powered by radiation pressure. Due to the lackof theoretical studies, the possible momentum source remains a matter ofspeculation.
| The circumstellar molecular envelope of HD 101584
CO radio line observations reveal a molecular gas envelope around thepeculiar star HD101584 with characteristics very similar to those ofwellknown young post-AGB objects. We estimate that there is at least 0.1M_sun of molecular gas, very likely remnant gas from a formerAGB-envelope. This gas has been efficiently accelerated to very highvelocities (>50 {km s(-1) , and a significant fraction to >100 {kms(-1) ). There is evidence for an expanding disk-like structure seenclose to edge-on, and a high-velocity bipolar outflow. In the latter theexpansion velocity increases linearly with distance from the star,suggesting either a brief period of ejection or a fast wind interactingwith a slower wind. A significant fraction of the high-velocity gas hasreached a welldefined terminal velocity. Momentum well above theavailable radiation momentum has been transferred to the gas. There arealso indications of high-density, low-velocity molecular gas, possiblyin a disk close to the star. The (12) CO/(13) CO-ratio in the envelopeis uncertain, but probably quite low ( ~ 10). The systemic heliocentricvelocity is 50+/-2 {km s(-1) .
| The Boomerang Nebula: The Coldest Region of the Universe?
We have discovered absorption of the 3 K microwave background radiationby ultracold CO gas in the Boomerang Nebula, a bipolar reflection nebulailluminated by a star that has recently evolved off the asymptotic giantbranch (AGB). During the AGB phase, stars with main-sequence masses of1--8 Msolar eject large amounts of matter, affecting their subsequentevolution as well as the chemical and dynamical evolution of the Galaxy.Our new observations of CO and 13CO millimeter-wave lines toward theBoomerang Nebula show it to be quite extreme and perhaps unique in itsmass-ejection properties. We find that it has been losing mass through afast (164 km s-1) molecular wind at a prodigious rate of 10-3 Msolaryr-1 (a factor of about 10 larger than the highest rates seen inAGB/post-AGB objects until now) for at least approximately 1500 yr. Thiswind contains ultracold gas at temperatures below the microwavebackground temperature, making the Boomerang Nebula the coldest place inthe universe found so far (excluding laboratories), and confirming anearlier prediction of the existence of such envelopes. The 12C/13C ratiois rather low (5), close to the lowest value attainable (3) throughequilibrium CNO-cycle nucleosynthesis. The mechanical wind momentum(dM/dt x Vexp) in the Boomerang Nebula exceeds the total radiativemomentum (L*/c) by a factor greater than 104. The data also show thepresence of an inner shell, expanding at 35 km s-1, which may haveresulted from the ejection of a common envelope by a central binarystar.
| Multiple outflows in the bipolar planetary nebula M1-16: A molecular line study
Extensive observations of the molecular gas in the young, compactplanetary nebula M1-16 have been made, using theSwedish-ESO-Submillimeter Telescope. A map of the CO J = 2-1 emissionshows that the molecular envelope contains both a slow and a fastoutflow with expansion velocities of 19 km/s and greater than 34 km/s,respectively. The slow outflow is mildly elliptical, while the fastmolecular outflow is bipolar. This fast outflow is roughly aligned withthe very fast outflows recently found in the optical, while the longaxis of the slow elliptical outflow is roughly orthogonal to the opticaloutflow axis. The kinematic timescales for the CO fast outflow and theoptical very fast outflow agree closely, supporting the view that theformer represents material in the slow outflow accelerated by the veryfast outflow. The kinematic signature of a disk expanding with about15.5 km/s can also be seen in the CO J = 2-1 data. The mass-loss rate(a) for the slow outflow is greater than or equal to 2.8 x10-5 solar mass/yr and possibly as large as 9 x10-5 solar mass/yr, (b) for the fast outflow is greater thanor equal to 5 x 10-6 solar mass/yr, and (c) for the very fastoptically visible outflow is approximately equal 5 x 10-7solar mass/yr. The disk mass is approximately equal 6 x 10-3solar mass. Grain photoelectric heating results in temperatures of 20-70K in molecular gas of the slow outflow. The (13)C/(12)C abundance ratioin M1-16 is found to be 0.33, quite possibly the highest found for anyevolved object. Upper limits for the (18)O/(16)O and (17)O/(16)O ratioswere found to be consistent with the values found in AGB stars. A searchfor other molecular species in M1-16 resulted in the detection of thehigh-excitation species HCN, CN, (13)CN, HCO(+), and H(13)CO(+) andpossibly N2H(+). Both the HCO(+)/HCN and CN/HCN line-intensity ratiosare enhanced, the former by a very large factor, over the values foundin the envelopes of AGB stars, probably as a result of enhancement ofthe CN and HCO(+) abundances due to photochemistry induced by thestellar UV. The CS J = 2-1, SiO J = 2-1 (v = 0), and SiS J = 6-5 lineswere not detected to low levels. For the high-excitation molecules,adequate collisional excitation of rotational levels and survivalagainst photodissociation by the UV radiation requires significantclumping of the molecular gas into clumps with H2 densitiesapproximately 105/cu cm. The IRAS fluxes of M1-16, assumingnegligible contribution from line emission, imply the presence of about(1.7-0.4) x 10-3 solar mass of cool dust (temperature around50 K) and a smaller quantity, (2.7-3.1) x 10-6 solar mass, ofwarmer dust (temperature around 125 K) for a power-law emissivity indexp = 1-2. The evolutionary nature of M1-16 cannot be explained byexisting single-star models of post-AGB evolution. The very high(13)C/(12)C abundance ratio in M1-16 suggests a possible evolutionaryconnection between M1-16 and the rare class of J-type silicate-carbonstars which also have high (13)C/(12)C ratios and are thought to bebinary systems with accretion disks.
| A new catalogue of members and candidate members of the Herbig Ae/Be (HAEBE) stellar group
A new up-to-date catalogue of Herbig Ae/Be (HAEBE) stars and relatedobjects is certainly needed, for both well-seasoned researchers and, inparticular, for new investigators starting to study the many interestingastrophysical properties of these very young objects. We present a briefdiscussion of the current observational characteristics that distinguishthis class from their main sequence counterparts. The HAEBE and relatedstars are listed in five tables, containing 287 objects. Table 1contains all Ae and Be stars which historically are recognized as trueHAEBE stars or potential candidate members. Table 2 gives the stars ofspectral type Fe, and emission line stars with very uncertain or unknownspectral type. In Table 3 are given all known Extreme Emission LineObjects (EELOs), of which most have not been identified to belong to anyspecific group. Table 4a and b list other Bep or B[e] stars with strongIR-excess and unknown spectral type. Table 5 contains the non-emissionline possible young objects. Furthermore, Table 6 contains 35 starsrejected from former published lists of HAEBE stars. In these tables weare including coordinates, spectral types, visual magnitudes, ranges inphotometric variability and references of several key publicationsrelated to each object. Relevant remarks, such as the presence of anebula in the vicinity of an object, are also given.
| Young bipolar nebulae
Young bipolar nebulae are those rather rare exceptions among deeplyembedded pre-main sequence objects driving bipolar outflows, which areamenable to detailed optical studies - by that means they provide uniqueinformation about this whole class of objects. The aim of this review isto work out, what their observations have told us about their structureand about the winds of young stars and their interaction withcircumstellar matter. While the emphasis lies on the discussion of theoptical observations, the large body of infrared and radio data is alsoconsidered. First, four of the best studied examples, S 106, Cep A, RMon, and L 1551 IRS 5, are analyzed in depth. Then, recent observationalresults about disks and winds of T Tauri stars are considered, whichshed new light also on the essential structural elements of youngbipolar nebulae. After the description of some peculiar cases, thecommon properties characterizing the whole class of young bipolarnebulae are worked out. We are led to a unified picture of the bipolarwinds causing both, the broad optically bright reflection lobes andmolecular outflows, as well as the highly collimated optical jetsobserved in some cases on their polar axes; structure and dynamics ofthe bipolar winds are determined by the close interaction between thecentral stars and their massive circumstellar disks. Finally, currenttheoretical concepts about the mechanisms driving the winds arediscussed, and present ideas about the evolution of bipolar nebulae aredescribed. The Appendix includes a catalog of young bipolar nebulae.
| CO and HCN observations of circumstellar envelopes. A catalogue - Mass loss rates and distributions
We have searched the literature for all observations of the (C-12)O(1-0), (C-12)O (2-1), and HCN (1-0) lines in circumstellar envelopes oflate type stars published between January 1985 and September 1992. Wereport data for 1361 observations (stellar velocity, expansion velocity,peak intensity, integrated area, noise level). This CO-HCN sample nowcontains 444 sources; 184 are identified as O-rich, 205 as C-rich, andthere are 9 S stars. About 85 percent of the sources are AGB stars.There are 32 planetary nebulae and about thirty post-AGB starscandidates. Besides results of mm-observations, we also listidentifications, coordinates, IRAS data, and chemical and spectral typesfor every source. For AGB stars, we have estimated (or compiled)bolometric fluxes and distances for 349 sources, and mass loss ratesdeduced from CO results for 324 sources, taking into account theinfluence of the CO photodissociation radius. We also list mass lossrates derived from detailed models of CO emission in the literature.
| IRAS LRS spectroscopy of galaxies
The study presents IRAS LRS data for 350 galaxies with pointlike IRASsources having either S(12) or S(25) not less than 1.5 Jy. Techniquesare presented which form the mean of an ensemble of LRS spectra, ll ofwhich are only of low signal-to-noise ratio, by quantitative evaluationof the significance of the individual spectra for each object ratherthan mere acceptance of the 'average spectrum' present in the completeLRS data base. Average LRS spectra for groups of galaxies with distinctoptical nuclear properties are formed. Average LRS spectra for severalcategories of objects are presented and interpreted. H II regiongalaxies show the polycyclic aromatic hydrocarbon spectrum of bands inemissions; type 2 Seyferts present a broad emission feature parking near16 microns; LINERs and galaxies without optical emission lines have LRSspectra that decline with wavelength, whereas type 1 Seyferts and WRgalaxies have red spectra suggestive of nonthermal emission processes.
| The molecular emission of young preplanetary nebulae
Molecular observations are presented of several preplanetary nebulae(PPNe) identified from their peculiar IR spectrum. Detections of (C-12)Oand (C-13)O J = 2-1, 1-0 emission in four subjects are reported: IRAS07134 + 1005, IRAS 17436 + 5003, IRAS 19114 + 0002, and IRAS 19500 -1709. SiO J = 3-2, 2-1 was detected in IRAS 19114 + 0002; HCN J = 1-0 inIRAS 07134 + 1005, IRAS 17436 + 5003, and IRAS 19500- 1709. Evidentsigns of a bipolar structure were found in IRAS 19114 + 0002 and IRAS19500 - 1709. In IRAS 19500 - 1709, wide and relatively intense wingswere found in (C-12)O and (C-13)O, which are considered to be producedby a high-velocity bipolar outflow that involves a significant fractionof the total molecular envelope.
| A catalog of co-added IRAS fluxes of Orion population stars
A catalog of co-added IRAS fluxes for the pre-main-sequence objects inthe Herbig-Bell catalog (HBC) is presented. This catalog doubles thenumber of HBC stars with detected IRAS fluxes and provides improved fluxvalues for the previously known sources. Noise level are given for allHBC fields in each band, permitting upper limits to be estimated for allundetected sources.
| CO observations of southern protoplanetary nebulae with optical counterparts
Millimeter wave emission observations of (C-12)O and (C-13)O in foursouthern protoplanetary nebulae (PPN), the Boomerang Nebula, Hen 401,Mz3, and Roberts 22, are reported. (C-12)O is detected for the firsttime in all four sources, and (C-13)O is detected in the BoomerangNebula. The data are analyzed using a molecular excitation and emissionmodel, and the results indicate that objects with higher stellartemperature tend to present a smaller CO abundance, probably due to thephotodissociation of molecules by stellar UV. The total molecular massof the PPN is found to range from 0.2 to 0.5 solar mass. The mass lossrates responsible for nebula formation are therefore high enough toexplain the post-AGB evolution of the objects.
| A catalog of pre-main-sequence emission-line stars with IRAS source associations
To aid in finding premain-sequence (PMS) emission-line stars that mighthave dusty circumstellar environments, 361 PMS stars that are associatedwith 304 separate IRAS sources were identified. These stars include 200classical T Tauri stars, 25 weak-lined (naked) T Tauri stars, 56 HerbigAe/Be stars, six FU Orionis stars, and two SU Aurigae stars. All six ofthe FU Orionis stars surveyed by IRAS were detected. Of the PMS-IRASPoint Source Catalog (PSC) associations, 90 are new and are not noted inthe PSC. The other 271 entries include 104 that are correctly identifiedin the PSC but have not yet appeared in the literature, 56 more that canbe found in both the PSC and in the published and unpublished iterature,and 111 that are in the literature but not in the PSC. Spectral slopediagrams constructed from the 12-, 25-, and 60-micron flux densitiesreveal unique distributions for the different PMS subclasses; thesediagrams may help identify the best candidate PMS stars for observationsof circumstellar dust.
| Proto-planetary nebulae - The case of CRL 618
The mm-wave emission observed from different molecules in theprotoplanetary nebulae CRL 618 and CRL 2688 includes lines whoseexcitation characteristics indicate that the gas and dust in CRL 618 aresignificantly hotter than in CRL 2688, OH 231.8+4.2, and IRC+10216.These differences, together with others seen in molecular abundances,are explainable on the assumption that photodissociation by the stellarUV emission is involved in CRL 618; this nebula's age is probably of theorder of 200 years, which compares with a transit time of about 1000years from AGB star to planetary nebula.
| Catalog of emission line stars of the orion population : 3 : 1988
Not Available
| Herbig-Haro emission in two bipolar reflection nebulae
CCD images and spectroscopic observations of the bipolar reflectionnebula called the Boomerang Nebula, whose central star is probablydouble, and of the nebula associated with PV Cephei, which is shown tobe bipolar, are presented. In both cases, line emission characteristicof low excited Herbig-Haro objects and indications for collimated highvelocity flows along the polar axis of the nebulae are found.
| Herbig-Haro emission in two bipolar reflection nebulae.
Not Available
| Granulare Overshoot-Schichten als Randbedingungen
Not Available
| Electronographic polarimetry - The Durham polarimeter
The present investigation is concerned with an instrument for mappingthe linear polarization of extended astronomical objects at opticalwavelengths. The first important studies of this type were based uponthe use of photographic techniques and photoelectric observations.Later, improvements in detector technology have made it possible toobserve fainter objects at higher spatial resolution. A description ispresented of the principles of operation of the Durham Universitypolarimeter which has been extensively used in the observations. Thepolarimeter uses a 40-mm McMullan electronographic camera to providesimultaneous detection at all the image points. The selected approachprovides advantages of increased speed, linearity, resolution, dynamicrange, and storage capacity in comparison to photographic detection.
| Models for the structure and origin of bipolar nebulae
Consideration of structural models for bipolar nebulae leads to aninvestigation of how such a geometry may arise. Although nonradialpulsation, rotationally forced mass ejection by a single star, and massloss from a common envelope binary are discussed, emphasis is put on abipolar nebulae origin from a binary star system in which the primary isevolving up the red giant branch to the point at which its radiusapproaches its tidal radius. Numerical models of this phenomenon showthat gravitational ejection from an asynchronous binary system leads toterminal outflow velocities in the observed 20-50 km/sec range, and thatthe rate of mass loss and the time scale over which the mass ejectiontakes place are consistent with observations if the particle density inthe outer layers of the primary star's atmosphere, from which thematerial is extracted, is in the range of 10 to the 14th to 10 to the15th/cu cm.
| A new bipolar nebula in Centaurus
A new bipolar or butterfly-shaped nebula has been discovered and shownto have an infrared excess. The spectra of the central object and wingsare of similar type, around G0. No emission lines are apparent. Theinfrared excess appears to be due to thermal emission from dust.
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