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Toward Understanding the B[e] Phenomenon. I. Definition of the Galactic FS CMa Stars
The B[e] phenomenon is defined as the simultaneous presence oflow-excitation forbidden line emission and strong infrared excess in thespectra of early-type stars. It was discovered in our Galaxy 30 yearsago in the course of the early exploration of the infrared sky andinitially identified in 65 Galactic objects, of which nearly halfremained unclassified. The phenomenon is associated with objects atdifferent evolutionary stages, ranging from the pre-main-sequence to theplanetary nebula stage. We review the studies of both the original 65and subsequently identified Galactic stars with the B[e] phenomenon. Anew classification is proposed for stars with the B[e] phenomenon basedon the time of dust formation in their environments. Properties of theunclassified Galactic B[e] stars are analyzed. We propose that theseobjects are binary systems that are currently undergoing or haverecently undergone a phase of rapid mass exchange, associated with astrong mass loss and dust formation. A new name, FS CMa stars, andclassification criteria are proposed for the unclassified B[e] stars.
| 3He in the Milky Way Interstellar Medium: Ionization Structure
The cosmic abundance of the 3He isotope has importantimplications for many fields of astrophysics. We are using the 8.665 GHzhyperfine transition of 3He+ to determine the3He/H abundance in Milky Way H II regions and planetarynebulae. This is one in a series of papers in which we discuss issuesinvolved in deriving accurate 3He/H abundance ratios from theavailable measurements. Here we describe the ionization correction weuse to convert the 3He+/H+ abundance,y+3, to the 3He/H abundance,y3. In principle the nebular ionization structure cansignificantly influence the y3 derived for individualsources. We find that in general there is insufficient informationavailable to make a detailed ionization correction. Here we make asimple correction and assess its validity. The correction is based onradio recombination line measurements of H+ and4He+, together with simple core-halo sourcemodels. We use these models to establish criteria that allow us toidentify sources that can be accurately corrected for ionization andthose that cannot. We argue that this effect cannot be very large formost of the sources in our observational sample. For a wide range ofmodels of nebular ionization structure we find that the ionizationcorrection factor varies from 1 to 1.8. Although larger corrections arepossible, there would have to be a conspiracy between the density andionization structure for us to underestimate the ionization correctionby a substantial amount.
| And in the Darkness Bind Them: Equatorial Rings, B[e] Supergiants, and the Waists of Bipolar Nebulae
We report the discovery of two new circumstellar ring nebulae in thewestern Carina Nebula, and we discuss their significance in stellarevolution. The brighter of the two new objects, SBW 1, resembles alidless staring eye and encircles a B1.5 Iab supergiant. Although seenin Carina, its luminosity class and radial velocity imply a largerdistance of ~7 kpc in the far Carina arm. At that distance its size andshape are nearly identical to the equatorial ring around SN 1987A, butSBW 1's low N abundance indicates that the ring was excreted without itsstar passing through a red supergiant phase. The fainter object, SBW 2,is a more distorted ring, is N-rich, and is peculiar in that its centralstar seems to be invisible. We discuss the implications of these two newnebulae in context with other circumstellar rings such as those aroundSN 1987A, Sher 25, HD 168625, RY Scuti, WeBo 1, SuWt 2, and others. Thering bearers fall into two groups: Five rings surround hot supergiants,and it is striking that all except for the one known binary are carboncopies of the ring around SN 1987A. We propose a link between these Bsupergiant rings and B[e] supergiants, where the large spatiallyresolved rings derive from the same material that would have given riseto emission lines during the earlier B[e] phase, when it was much closerto the star. The remaining four rings surround evolved intermediate-massstars; all members of this ring fellowship are close binaries, hintingthat binary interactions govern the forging of such rings. Two-thirds ofour sample are found in or near giant H II regions. We estimate thatthere may be several thousand more dark rings in the Galaxy, but we arescarcely aware of their existence-either because they are onlyilluminated in precious few circumstances or because of selectioneffects. For intermediate-mass stars, these rings might be thepreexisting equatorial density enhancements invoked to bind the waistsof bipolar nebulae.Based in part on observations made at the Clay Telescope of the MagellanObservatory, a joint facility of the Carnegie Observatories, HarvardUniversity, the Massachusetts Institute of Technology, the University ofArizona, and the University of Michigan.
| De-reddening of optical spectra Which extinction curve?
Spectral lines are used to determine a broad range of physicalproperties within HII regions and planetary nebulae (PNe). It istherefore important that we possess accurate intensities for thetransitions, and have the means by which observed results may beaccurately de-reddened. We point out that there are serious differencesbetween the “standard” extinction curves, and that these maylead to errors in line ratios of as high as ˜80%. It is noted thatthe variation in Balmer line ratios in planetary nebulae is mostconsistent with the extinction curves of Whitworth [Whitworth, A.E.,1958. AJ 63, 201] and Ardeberg and Virdefors [Ardeberg, A., Virdefors,B., 1982. A&A 115, 347], and that these are likely to represent themost reliable functions for spectral de-reddening.
| The IDV source J 1128+5925, a new candidate for annual modulation?
Context: Short time-scale radio variations of compact extragalacticradio sources, known as IntraDay Variability (IDV), can be explained inat least some sources by a source-extrinsic effect, in which thevariations are interpreted as scintillation of radio waves caused by theturbulent interstellar medium of the Milky Way. One of the mostconvincing observational arguments in favour of propagation-inducedvariability is the so-called “annual modulation” of thecharacteristic variability time-scale, which is due to the orbitalmotion of the Earth. So far there are only two sources known which showsuch a well-defined seasonal cycle, a few more sources with fewer datacan be regarded as possible candidates for this effect. However,source-intrinsic effects, such as structural variations, can also causethe observed changes of the variability time-scale. Data for the new,recently discovered, and highly variable IDV source J 1128+5925 arepresented. Aims: We study the frequency and time dependence of the IDVin this compact quasar. We measure the characteristic variabilitytime-scale of the IDV throughout the year, and analyze whether theobserved changes in the variability time-scale are consistent withannual modulation. Assuming a radio wave propagation effect as origin,we are able to constrain some physical properties (such as distance,scattering-strength, and possible anisotropy) of the“plasma” screen, which may cause the scintillation. Methods: We monitored the flux density variability of J 1128+5925 withdense time sampling between 2.7 and 10.45 GHz. We observed with the 100m Effelsberg radio telescope of the Max-Planck-Institut fürRadioastronomie (MPIfR) at 2.70 GHz, 4.85 GHz, and 10.45 GHz, as well aswith the 25 m Urumqi radio telescope (China) at 4.85 GHz. From tenobserving sessions, each of which lasted several days during the periodbetween 2004-2006, we determine the variability characteristics andtime-scales which we investigate in view of possible scintillation andannual modulation. Results: The observed pronounced changes of thevariability time-scale of J 1128+5925 are modelled with an anisotropicannual modulation model. The observed frequency dependence of thevariation is in good agreement with the prediction from interstellarscintillation. Adopting a simple model for the annual modulation modeland also using the frequency dependence of the IDV, we derive a lowerlimit to the distance the scattering screen and an upper limit for thescintillating source size. The latter is found to be consistent with themeasured core size from Very Long Baseline Interferometry (VLBI).
| The ISO LWS high-resolution spectral survey towards Sagittarius B2
A full spectral survey was carried out towards the giant molecular cloudcomplex, Sagittarius B2 (SgrB2), using the Infrared Space Observatory(ISO) Long Wavelength Spectrometer (LWS) Fabry-Pérot mode. Thisprovided complete wavelength coverage in the range 47-196μm(6.38-1.53THz) with a spectral resolution of 30-40kms-1. Thisis a unique data set covering wavelengths inaccessible from the ground.It is an extremely important region of the spectrum as it contains boththe peak of the thermal emission from dust, and crucial spectral linesof key atomic (OI, CII, OIII, NII and NIII) and molecular species(NH3, NH2, NH, H2O, OH,H3O+, CH, CH2, C3, HF andH2D+). In total, 95 spectral lines have beenidentified and 11 features with absorption depth greater than 3σremain unassigned. Most of the molecular lines are seen in absorptionagainst the strong continuum, whereas the atomic and ionic lines appearin emission (except for absorption in the OI 63μm and CII 158μmlines). SgrB2 is located close to the Galactic Centre and so many of thefeatures also show a broad absorption profile due to material locatedalong the line of sight. A full description of the survey data set isgiven with an overview of each detected species and final line lists forboth assigned and unassigned features.Based on observations with Infrared Space Observatory (ISO), an ESAproject with instruments funded by ESA Member States (especially the PIcountries: France, Germany, the Netherlands and the United Kingdom) withthe participation of ISAS and NASA.E-mail: e.t.polehampton@rl.ac.uk
| A Search for Formaldehyde 6 cm Emission toward Young Stellar Objects. II. H2CO and H110α Observations
We report the results of our second survey for Galactic H2COmaser emission toward young stellar objects. Using the GBT and the VLAin the A configuration we observed 58 star-forming regions anddiscovered the fifth H2CO 6 cm maser region in the Galaxy(G23.71-0.20). We have discussed the detection toward G23.71-0.20 in aprevious paper. Here we present all the other results from our survey,including detection of H2CO absorption features toward 48sources, detection of the H110α recombination line toward 29sources, detection (including tentative detections) of the carbonrecombination line C110α toward 14 sources, subarcsecond angularresolution images of 6 cm continuum emission toward five sources, andobservations of the H2CO masers in IRAS 18566+0408 and NGC7538. In the case of NGC 7538, we detected the two main H2COmaser components, and our observations confirm variability of theblueshifted component recently reported by Hoffman et al. Thevariability of both maser components in NGC 7538 could be caused by ashock wave that reached the redshifted component approximately 14 yrbefore reaching the blueshifted component. If that were the case, wewould expect to detect an increase in the flux density rate of change ofthe blueshifted component sometime after the year 2009. Our data alsosupport the use of H2CO/H110α observations as a tool toresolve the kinematic distance ambiguity of massive star-forming regionsin the Galaxy.
| Molecular Line Survey of CRL 618 from 80 to 276 GHz and Complete Model
We present the complete data set, model, and line identification of asurvey of the emission from the C-rich proto-planetary nebula CRL 618performed with the IRAM 30 m telescope in the frequency ranges80.25-115.75 GHz, 131.25-179.25 GHz, and 204.25-275.250 GHz. A selectionof lines from different species has been used in previous works toderive the structure of the source, its physical conditions, and thechemical abundances in the different gas regions. In this work, we haveused this information to run a global simulation of the spectrum inorder to check the consistency of the model and to ease the task of lineidentification. The total number of lines that have a correspondence inboth data and model is ~3100, although quite often in this object manylines blend into complex features, so that the model, which takes intoaccount line blending, is a key tool at this stage of the analysis. Ofall the lines that we have been able to label, ~55% of them belong tothe different forms of HC3N, and ~18% to HC5N. Thedensity of remaining unidentified features above the 3 σ limit isonly 1 per ~2.1 GHz (74 features), which is unprecedented in theanalysis of this type of large millimeter-wave line surveys.
| s-Process Abundances in Planetary Nebulae
The s-process should occur in all but the lower mass progenitor stars ofplanetary nebulae, and this should be reflected in the chemicalcomposition of the gas that is expelled to create the current planetarynebula shell. Weak forbidden emission lines are expected from severals-process elements in these shells and have been searched for and insome cases detected in previous investigations. Here we extend thesestudies by combining very high signal-to-noise ratio echelle spectra ofa sample of PNe with a critical analysis of the identification of theemission lines of Z>30 ions. Emission lines of Br, Kr, Xe, Rb, Ba,and Pb are detected with a reasonable degree of certainty in at leastsome of the objects studied here, and we also tentatively identify linesfrom Te and I, each in one object. The strengths of these lines indicateenhancement of s-process elements in the central star progenitors, andwe determine the abundances of Br, Kr, and Xe, elements for which atomicdata relevant for abundance determination have recently becomeavailable. As representative elements of the ``light'' and ``heavy''s-process peaks, Kr and Xe exhibit similar enhancements over solarvalues, suggesting that PN progenitors experience substantial neutronexposure.
| H2O Maser Observations of Candidate Post-AGB Stars and Discovery of Three High-Velocity Water Sources
We present the results of 22 GHz H2O maser observations of asample of 85 post-asymptotic giant branch (post-AGB) candidate stars,selected on the basis of their OH 1612 MHz maser and far-infraredproperties. All sources were observed with the Tidbinbilla 70 m radiotelescope, and 21 detections were made; 86 GHz SiO Mopra observations ofa subset of the sample are also presented. Of the 21 H2Odetections, 15 are from sources that are likely to be massive AGB starsand most of these show typical, regular H2O maser profiles.In contrast, nearly all the detections of more evolved stars exhibitedhigh-velocity H2O maser emission. Of the five sources seen,v223 (W43A, IRAS 18450-0148) is a well-known ``water-fountain'' sourcethat belongs to a small group of post-AGB stars with highly collimated,high-velocity H2O maser emission. A second source in oursample, v270 (IRAS 18596+0315), is also known to have high-velocityemission. We report the discovery of similar emission from a furtherthree sources, d46 (IRAS 15445-5449), d62 (IRAS 15544-5332), and b292(IRAS 18043-2116). The source d46 is an evolved post-AGB star withhighly unusual maser properties. The H2O maser emission fromd62 is probably associated with a massive star. The source b292 is ayoung post-AGB star that is highly likely to be a water-fountain source,with masers detected over a velocity range of 210 km s-1.
| Methanol as a diagnostic tool of interstellar clouds. II. Modelling high-mass protostellar objects
Context: Fundamental properties of interstellar clouds must be known toinvestigate the initial conditions of star formation within them and theinteraction of newly formed stars with their environment. Methanol hasproven to be useful to probe densities and temperatures of variousenvironments within interstellar clouds. Aims: We aim to explore thepotential of methanol as a tracer molecule for regions in whichhigh-mass stars are forming or have recently formed, in particularso-called high-mass protostellar objects (HMPOs) and infrared darkclouds (IRDCs). Methods: We present and analyse multi-frequencycentimetre and (sub)millimetre single-dish observations of methanoltoward a sample of 13 sources that are in the poorly understood earliestphases of evolution of high-mass stars (HMPOs and IRDCs). For eachsource in our sample, we derive physical parameters such as the kinetictemperature, the spatial density. and the methanol column density. Weapply our large velocity gradient modelling and fitting technique thatinvolves fitting a synthetic spectrum to all the measured linessimultaneously. Results: In several sources, we find that more than onephysical component is necessary to fit the spectra; moreover, broadnon-Gaussian linewidths suggest outflows in many sources from both theIRDC and the HMPO subsamples. Kinetic temperatures are found to bebetween 10 and 60 K and spatial densities in the range105-106 cm-3. Hotter, denser cores arefound in a few HMPOs, indicating that these sources already harbour hotcores heated by protostars.Based on observations with the 100-m telescope of the MPIfR(Max-Planck-Institut für Radioastronomie) at Effelsberg, with theCaltech Submillimeter Observatory and with the IRAM 30 m telescope. IRAMis supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain).Tables 7, 8 and Figs. 7 to 29 are only available in electronic formhttp://www.aanda.org
| Magnetic fields in planetary nebulae and post-AGB nebulae
Magnetic fields are an important but largely unknown ingredient ofplanetary nebulae. They have been detected in oxygen-rich asymptoticgiant branch (AGB) and post-AGB stars, and may play a role in theshaping of their nebulae. Here we present SCUBA submillimetrepolarimetric observations of four bipolar planetary nebulae and post-AGBstars, including two oxygen-rich and two carbon-rich nebulae, todetermine the geometry of the magnetic field by dust alignment. Three ofthe four sources (NGC 7027, 6537 and 6302) present a well-definedtoroidal magnetic field oriented along their equatorial torus or disc.NGC 6302 may also show field lines along the bipolar outflow. CRL 2688shows a complex field structure, where part of the field aligns with thetorus, whilst an other part approximately aligns with the polar outflow.It also presents marked asymmetries in its magnetic structure. NGC 7027shows evidence for a disorganized field in the south-west corner, wherethe SCUBA shows an indication for an outflow. The findings show a clearcorrelation between field orientation and nebular structure.
| The Abundances of Light Neutron-Capture Elements in Planetary Nebulae. I. Photoionization Modeling and Ionization Corrections
We have conducted a large-scale survey of 120 planetary nebulae (PNe) tosearch for the near-infrared emission lines [Kr III] 2.199 μm and [SeIV] 2.287 μm. The neutron (n)-capture elements Se and Kr may beenriched in a PN if its progenitor star experienced s-processnucleosynthesis and third dredge-up. In order to determine Se and Krabundances, we have added these elements to the atomic databases of thephotoionization codes Cloudy and XSTAR, which we use to deriveionization correction factors (ICFs) to account for the abundances ofunobserved Se and Kr ions. However, much of the atomic data governingthe ionization balance of these two elements are unknown, and have beenapproximated from general principles. We find that uncertainties in theatomic data can lead to errors approaching 0.3 dex in the derived Seabundances and up to 0.2-0.25 dex for Kr. To reduce the uncertainties inthe Kr ionization balance stemming from the approximate atomic data, wehave modeled 10 bright PNe in our sample, selected because they exhibitemission lines from multiple Kr ions in their optical and near-infraredspectra. We have empirically adjusted the uncertain Kr atomic data untilthe observed line intensities of the various Kr ions are adequatelyreproduced by our models. Using the adjusted Kr atomic data, we havecomputed a grid of models over a wide range of physical parameters(central star temperature, nebular density, and ionization parameter)and derived formulae that can be used to compute Se and Kr ICFs. In thesecond paper of this series, we will apply these ICFs to our full sampleof 120 PNe, which comprises the first large-scale survey of n-captureelements in PNe.This paper includes data taken at the McDonald Observatory of theUniversity of Texas at Austin.
| Infrared Emission from Interstellar Dust. IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era
IR emission spectra are calculated for dust heated by starlight, formixtures of amorphous silicate and graphitic grains, including varyingamounts of PAH particles. The models are constrained to reproduce theaverage Milky Way extinction curve. The calculations include the effectsof single-photon heating. Updated IR absorption properties for the PAHsare presented that are consistent with observed emission spectra,including those newly obtained by Spitzer. We find a size distributionfor the PAHs giving emission band ratios consistent with the observedspectra of the Milky Way and other galaxies. Emission spectra arepresented for a wide range of starlight intensities. We calculate howthe efficiency of emission into different IR bands depends on PAH size;the strong 7.7 μm emission feature is produced mainly by PAHparticles containing <103 C atoms. We also calculate howthe emission spectrum depends on U, the starlight intensity relative tothe local interstellar radiation field. The submillimeter andfar-infrared emission is compared to the observed emission from thelocal interstellar medium. Using a simple distribution function, wecalculate the emission spectrum for dust heated by a distribution ofstarlight intensities, such as occurs within galaxies. The models areparameterized by the PAH mass fraction qPAH, the lower cutoffUmin of the starlight intensity distribution, and thefraction γ of the dust heated by starlight withU>Umin. We present graphical procedures using Spitzer IRACand MIPS photometry to estimate the parameters qPAH,Umin, and γ, the fraction fPDR of the dustluminosity coming from photodissociation regions with U>100, and thetotal dust mass Mdust.
| Laboratory detection of the negative molecular ion CCH^-
Aims.This paper reports the laboratory detection of the rotationalspectrum of the acetylide anion, CCH^-. Methods: Five successiverotational transitions have been measured to high accuracy in a dcdischarge with a free space millimeter-wave spectrometer in thefrequency range 83-417 GHz. Results: Precise spectroscopic constantshave been obtained for CCH- and transition rest frequenciescan now be calculated to better than 1 km s-1 in equivalentradial velocity far into the terahertz region, allowing for deepastronomical searches for this anion in space. The highly stable andfairly polar CCH- anion is a likely candidate for radioastronomical detection, its neutral analogue CCH being among one of themost abundant molecules in a wide variety of astrophysical sources.
| Multi-frequency monitoring of γ-ray loud blazars. I. Light curves and spectral energy distributions
Context: Being dominated by non-thermal emission from alignedrelativistic jets, blazars allow us to elucidate the physics ofextragalactic jets, and, ultimately, how the energy is extracted fromthe central black hole in radio-loud active galactic nuclei. Aims:Crucial information is provided by broad-band spectral energydistributions (SEDs), their trends with luminosity and correlatedmulti-frequency variability. With this study we plan to obtain adatabase of contemporaneous radio-to-optical spectra of a sample ofblazars, which are and will be observed by current and futurehigh-energy satellites. Methods: Since December 2004 we are performinga monthly multi-frequency radio monitoring of a sample of 35 blazars atthe antennas in Medicina and Noto. Contemporaneous near-IR and opticalobservations for all our observing epochs are organised. Results: UntilJune 2006 about 4000 radio measurements and 5500 near-IR and opticalmeasurements were obtained. Most of the sources show significantvariability in all observing bands. Here we present the multi-frequencydata acquired during the first eighteen months of the project, andconstruct the SEDs for the best-sampled sources.
| X-ray emission from planetary nebulae calculated by 1D spherical numerical simulations
We calculate the X-ray emission from both constant and time-evolvingshocked fast winds blown by the central stars of planetary nebulae (PNe)and compare our calculations with observations. Using sphericallysymmetric numerical simulations with radiative cooling, we calculate theflow structure and the X-ray temperature and luminosity of the hotbubble formed by the shocked fast wind. We find that a constant fastwind gives results that are very close to those obtained from theself-similar solution. We show that in order for a fast shocked wind toexplain the observed X-ray properties of PNe, rapid evolution of thewind is essential. More specifically, the mass-loss rate of the fastwind should be high early on when the speed is ~300-700 kms-1, and then it needs to drop drastically by the time the PNage reaches ~1000 yr. This implies that the central star has a veryshort pre-PN (post-asymptotic giant branch) phase.
| First Detection of an H2CO 6 cm Maser Flare: A Burst in IRAS 18566+0408
We report the discovery of a short-duration (less than 3 months)outburst of the H2CO 6 cm maser in IRAS 18566+0408(G37.55+0.20). During the flare, the peak flux density of the maserincreased by a factor of 4; after less than a month, it decayed to thepreflare value. This is the first detection of a short, burstlikevariability of an H2CO 6 cm maser. The maser shows anasymmetric line profile that is consistent with the superposition of twoGaussian components. We did not detect a change in the velocity or theline width of the Gaussian components during the flare. If the twoGaussian components trace two separate maser regions, then very likelyan event outside the maser gas triggered simultaneous flares at twodifferent locations.
| Infrared Mapping of Four Interesting Planetary Nebulae
We present Two Micron All Sky Survey near-infrared (NIR) photometricmapping of the planetary nebulae A30, A78, NGC 7027, and BD +30 3639. Itis shown that the NIR envelopes of both NGC 7027 and BD +30 3639 extendto much greater distances than has previously been supposed. It alsoappears that the dust in NGC 7027 has extinction properties similar tothose of interstellar grains, and that the radii of the particles mustbe reasonably large. An analysis of emission in A78 and A30 shows theinfrared indices to be reasonably large and implies grain temperaturesTgr of order ~950 K. Similarly, the angular extensions of thecontinua (>18" and >22", respectively) suggest that they may arisefrom very small grains indeed. By contrast, while BD +30 3639 is alsocharacterized by a high-temperature continuum, much of this emissionappears to be confined to the core. This may imply that grain heatingarises through direct stellar irradiation.
| Radio-continuum spectrum, brightness temperature, and planetary nebulae properties
Context: .Radio-continuum spectra are frequently used to infer thedensity distribution of ionized gaseous regions, while observedcorrelations between the brightness temperature and otherdistance-independent parameters are used to test evolutionary models ofplanetary nebulae. Aims: .We check empirical correlations amongfeatures derived from the observed radio data and the inferredconclusions available in the literature, using self-consistentphotoionization models. Methods: .Photoionization models arecomputed for the physical conditions of planetary nebulae in order toderive self-consistent radio-continuum spectra, as well as thebrightness temperature. Results: .The temperature and ionizationdistributions throughout the nebulae explain the observed range ofspectral indexes in the thick region of the spectrum, even for a uniformdensity distribution, usually challenged in the literature. The obtainedmodels fit the observed radio spectra for planetary nebulae in a largerange of spectral indexes. Our calculations show a correlation betweenthe spectral index obtained in a given frequency range and the nebulasize, as well as reproduce the observed relations between the brightnesstemperature and other distance-independent parameters. Such diagrams arefrequently used to check evolutionary models of the central star and/orof the nebula. Conclusions: .Since PNe images clearly show thatthe density is not constant inside the nebulae, and models with uniformand non-uniform density distributions can both reproduce the observedradio spectra, we conclude that it is not possible to favour one of themfrom the radio data, or to infer a particular density distribution forplanetary nebulae.
| Chemical abundances in planetary nebulae and stellar evolution.
I will review basic aspects of galactic Planetary Nebulae focussing onstatus of art on their chemical abundances and relationship with thestellar evolution theory.
| The research of some statistical and spectral characteristics of the radio sources from the RADIOASTRON catalogue at wavelengths of the order of 1mm.
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| Millimeter Wave Survey of the Protoplanetary Nebula CRL 618 and its Complete Model
This contribution presents a survey of the emission from the C-richprotoplanetary nebula CRL 618, performed with the IRAM 30 mradiotelescope from 80.25 GHz to 275.25 GHz. The analysis of the datahas resulted in a complete picture of the structure of the source, itsphysical conditions and the chemical abundances in different gasregions. More than 3000 molecular lines have been successfully labeledand modeled and only 74 features in the spectrum remain unidentified.
| Photoluminescence and cathodoluminescence by cosmic dust
Not Available
| The Excitation of SO in Cold Molecular Clouds: TMC-1
We have performed calculations on the excitation of SO using theaccurate collisional rate coefficients at low temperatures for thesystem SO-He recently published by Lique et al. Compared with theresults of Green, the new excitation rates show significant differencesfor transitions involving the low energy levels. We present a set ofradiative transfer models for different cloud geometries and physicalconditions, using the new rate coefficients for SO, and show that theyprovide a more correct diagnostic of the physical conditions of colddark clouds. We have applied these results to observations of mappingresults in TMC-1 done in the 23-12,34-23, and 22-11 transitions(using the IRAM 30 m telescope) and the 01-10transition (using the 100 m Effelsberg radio telescope). The intensitymaxima for all these lines is found around the so-called ammonia peak.The structure of TMC-1 is well represented by a cylindric filament withseveral cores [TK=8 K,n(H2)~3×104 cm-3] surrounded byan envelope [TK=10 K,n(H2)~(6-8)×103 cm-3] showing acomplex velocity structure. The abundance of SO in TMC-1 is nearlyconstant along the filament, X(SO)~=10-8, except at theammonia peak, where a higher SO abundance,X(SO)~=2.5×10-8, is required.
| XMM-Newton Observations of the Bipolar Planetary Nebulae NGC 2346 and NGC 7026
We have obtained X-ray observations of the bipolar planetary nebulae(PNe) NGC 2346 and NGC 7026 with XMM-Newton. These observations detecteddiffuse X-ray emission from NGC 7026 but not from NGC 2346. The X-rayemission from NGC 7026 appears to be confined within the bipolar lobesof the PN and has spectral properties suggesting a thermal plasmaemitting at a temperature of1.1+0.5-0.2×106 K. The X-rayspectrum of NGC 7026 is modeled using nebular and stellar abundances toassess whether a significant amount of nebular material has been mixedinto the shocked wind, but the results of this comparison are notconclusive owing to the small number of counts detected. Observations ofbipolar PNe indicate that diffuse X-ray emission is much less likelydetected in open-lobed nebulae than closed-lobed nebulae, possiblybecause open-lobed nebulae do not have strong fast winds or are unableto retain hot gas.
| Shock Processing of Interstellar Dust and Polycyclic Aromatic Hydrocarbons in the Supernova Remnant N132D
We observed the oxygen-rich Large Magellanic Cloud (LMC) supernovaremnant N132D (SNR 0525-69.6), using all instruments on board the Spitzer Space Telescope, IRS, IRAC, and MIPS (Infrared Spectrograph,Infrared Array Camera, and Multiband Imaging Photometer for Spitzer).The 5-40 μm IRS spectra toward the southeastern shell of the remnantshow a steeply rising continuum with [Ne III] and [O IV], as well as PAHemission. We also present the spectrum of a fast moving ejecta knot,previously detected at optical wavelengths, which is dominated by strong[Ne III] and [O IV] emission lines. We interpret the continuum asthermal emission from swept-up, shock-heated dust grains in theexpanding shell of N132D, which is clearly visible in the MIPS 24 μmimage. A 15-20 μm emission hump appears superposed on the dustcontinuum, and we attribute this to PAH CCC bending modes. We alsodetect the well-known 11.3 μm PAH CH bending feature, and find theintegrated strength of the 15-20 μm hump about a factor of 7 strongerthan the 11.3 μm band in the shell of the remnant. IRAC 3-9 μmimages do not show clear evidence of large-scale, shell-like emissionfrom the remnant, partly due to confusion with the ambient ISM material.However, we identified several knots of shocked interstellar gas basedon their distinct infrared colors. We discuss the bright infraredcontinuum and the polycyclic aromatic hydrocarbon features with respectto dust processing in young supernova remnants.
| Evolution of the Circumstellar Molecular Envelope. I. A BIMA CO Survey of Evolved Stars
This paper reports the results of a small imaging survey of eightevolved stars including two AGB stars (IRC +10216 and Mira), fiveproto-planetary nebula (PPN) candidates (AFGL 2688, IRAS 22272+5435, HD161796, 89 Her, and HD 179821), and a planetary nebula (PN, NGC 7027).We present high-resolution 12CO J=1-->0 maps of their fullmolecular envelopes made by combining BIMA Millimeter Array and NRAO 12m telescope observations. For the PPNe and PN, the neutral molecularenvelopes are compared with images taken at optical, near-IR, and mid-IRwavelengths. Drawing from the literature, we augmented our BIMA surveysample to 38 well-studied sources with CO emission maps. We classifiedthis sample of sources based on the kinematics and morphologies of theCO emission into three types: spherical/elliptical/shell sources, disksources, and structured outflow sources. Confirming previous studies, wefind strong evidence for the photodissociation of the molecular envelopeas an object evolves from the AGB to PN stages. While the spherical AGBstars follow theoretical expectations for mass-loss rate versus envelopesize, the post-AGB structured outflow sources have significantly highermass-loss rates than expected probably because of their recentsuperwinds. We find evidence that the structured outflows are clearlyyounger than the AGB wind. The disk sources have little correlationbetween mass-loss rate and envelope size because their properties aredetermined more by the properties of the central stars and diskevolution than by the mass-loss rate history that shapes the sphericaland structured-outflow sources.
| The Chemical Evolution of Helium
We report on measurements of the 4He abundance toward theouter Galaxy H II region S206 with the NRAO Green Bank Telescope.Observations of hydrogen and helium radio recombination lines between 8and 10 GHz were made toward the peak radio continuum position in S206.We derive 4He/H=0.08459+/-0.00088 (random)+/-0.0010 (knownsystematic), 20% lower than optical recombination line results. It isdifficult to reconcile the large discrepancy between the optical andradio values even when accounting for temperature, density, andionization structure or for optical extinction by dust. Using only M17and S206 we determine ΔY/ΔZ=1.41+/-0.62 in the Galaxy,consistent with standard chemical evolution models. High heliumabundances in the old stellar population of elliptical galaxies can helpexplain the increase in UV emission with shorter wavelength between 2000and 1200 Å, called the ``UV upturn'' or UVX. Our lower values ofΔY/ΔZ are consistent with a normal helium abundance athigher metallicity and suggest that other factors, such as a variablered giant branch mass loss with metallicity, may be important. Whencombined with 4He abundances in metal-poor galaxy H IIregions, Magellanic Cloud H II regions, and M17 that have beendetermined from optical recombination lines, including the effects oftemperature fluctuations, our radio 4He/H abundance ratio forS206 is consistent with a helium evolution of ΔY/ΔZ=1.6. Alinear extrapolation to zero metallicity predicts a 4He/Hprimordial abundance ratio about 5% lower than that given by theWilkinson Microwave Anisotropy Probe and standard big bangnucleosynthesis. The measured 4He abundances may besystematically underestimated by a few percent if clumping exists inthese H II regions.
| The detection of the (J, K) = (18, 18) line of NH3
Aims.A study of the metastable (J,K)=(18, 18) line of ammonia (NH3) ispresented aiming at better defining the physical properties of moleculargas in extreme environments. Methods: .The spectra were collectedwith the Effelsberg 100-m telescope and are analyzed in combination withother data using a rotation diagram (Boltzmann plot). Results:.The first astronomical detection of the metastable (J,K) = (18, 18)line of NH3 is reported. This is the NH3 line with by far the highestenergy, 3130 K above the ground state, detected in interstellar space.It is observed in absorption toward the galactic center star formingregion Sgr B2. There is a clear detection toward Sgr B2 (M) and a likelyone toward Sgr B2 (N). An upper limit for emission is determined forOrion KL. If we combine the (18, 18) line results from Sgr B2 (M) withthe previously measured (12, 12) absorption line, we find a rotationtemperature, T_rot, of >1300 K for the absorbing cloud. This is atleast a factor of two higher than previously derived values from lesshighly excited ammonia lines. T_rot gives a lower limit to the kinetictemperature. There is a hot low density gas component in the envelope ofSgr B2. It is possible that the (18, 18) line arises in this region. Theradial velocity of the low density, hot envelope is the same as that ofthe dense hot cores, so the (18, 18) line could also arise in the densehot cores where non-metastable (J>K) absorption lines from energylevels of up to ~1350 K above the ground state have been observed. Adiscussion of scenarios is presented.
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