Contenuti
Immagini
Carica la tua immagine
DSS Images Other Images
Articoli relazionati
Mid- and Far-Infrared Photometry of Galactic Planetary Nebulae with the AKARI All-Sky Survey
We provide mid- and far-infrared photometry of 857 Galactic planetarynebulae (PNe) using data derived from the AKARI All-Sky Survey. Theseinclude fluxes at 9 and 18 ?m obtained with the Infrared Camera(IRC), and at 65, 90, 140 and 160 ?m using the far-Infrared Surveyor(FIS). It is noted that the IR luminosities of the youngest PNe arecomparable to the total luminosities of the central stars, andsubsequently decline to 5×102 L&sun; whereD > 0.08 pc. This is consistent with an evolution of PNe dustopacities, and appreciable absorption in young and proto-PNe. We alsonote that there is little evidence for the evolution in IR/radio fluxratios suggested by previous authors. The fall-off of dust temperatureswith increasing nebular diameter is similar to that determined inprevious studies, whilst levels of Ly? heating are <0.5 of thetotal energy budget of the grains. There appears to be an evolution inthe infrared excess (IRE) as nebulae expand, with the largest valuesoccurring in the most compact PNe.
| Far-infrared Imaging of Post-asymptotic Giant Branch Stars and (Proto)-planetary Nebulae with the AKARI Far-Infrared Surveyor
By tracing the distribution of cool dust in the extended envelopes ofpost-asymptotic giant branch stars and (proto)-planetary nebulae((P)PNe), we aim to recover, or constrain, the mass-loss historyexperienced by these stars in their recent past. The Far-InfraredSurveyor (FIS) instrument on board the AKARI satellite was used toobtain far-infrared maps for a selected sample of post-AGB stars and(P)PNe. We derived flux densities (aperture photometry) for 13 post-AGBstars and (P)PNe at four far-infrared wavelengths (65, 90, 140, and 160?m). Radial (azimuthally averaged) profiles are used to investigatethe presence of extended emission from cool dust. No (detached) extendedemission is detected for any target in our sample at levels significantwith respect to background and cirrus emission. Only IRAS 21046+4739reveals tentative excess emission between 30'' and 130''. Estimates ofthe total dust and gas mass from the obtained maps indicate that theenvelope masses of these stars should be large in order to be detectedwith the AKARI FIS. Imaging with higher sensitivity and higher spatialresolution is needed to detect and resolve, if present, any cool compactor extended emission associated with these evolved stars.
| The influence of binarity on dust obscuration events in the planetary nebula M 2-29 and its analogues
The central star of the planetary nebula (CSPN) M 2-29 shows anextraordinary R Coronae Borealis-like fading event in its opticallightcurve. The only other CSPN to show these events are CPD-56°8032(Hen 3-1333) and V651 Mon (NGC 2346). Dust cloud formation in the lineof sight appears responsible but the exact triggering mechanism is notwell understood. Understanding how planetary nebulae (PNe) trigger dustobscuration events may help understand the same process in a wide rangeof objects including Population-I WC9 stars, symbiotic stars and perhapsasymptotic giant branch (AGB) stars with long secondary periods (LSPs).A binary scenario involving an eccentric, wide companion that triggersdust formation via interaction at periastron is a potential explanationthat has been suggested for LSP variables. Model fits to the lightcurvesof CPD-56°8032 and M 2-29 show the dust forms in excess of 70 AU atthe inner edge of a dust disk. In the case of CPD-56°8032 thisradius is far too large to coincide with a binary companion trigger,although a binary may have been responsible for the formation of thedust disk. We find no direct evidence to support previous claims ofbinarity in M 2-29 either from the OGLE lightcurve or deepmedium-resolution VLT FLAMES spectroscopy of the CSPN. We classify theCSPN as Of(H) with Teff = 50 ± 10 kK and log g = 4.0± 0.3. We find a mean distance of 7.4 ± 1.8 kpc to M 2-29at which the MV = -0.9 mag CSPN could potentially hide asubgiant luminosity or fainter companion. A companion would help explainthe multiple similarities with D'-type symbiotic stars whose outernebulae are thought to be bona-fide PNe. The 7.4 kpc distance, oxygenabundance of 8.3 dex and Galactic coordinates (? = 4.0, b = -3.0)prove that M 2-29 is a Galactic Bulge PN and not a Halo PN as commonlymisconceived.Based on observations made with the Very Large Telescope at ParanalObservatory under program ID 079.D-0764(A).
| An Optical-infrared Study of the Young Multipolar Planetary Nebula NGC 6644
High-resolution Hubble Space Telescope imaging of the compact planetarynebula NGC 6644 has revealed two pairs of bipolar lobes and a centralring lying close to the plane of the sky. From mid-infrared imagingobtained with the Gemini Telescope, we have found a dust torus which isoriented nearly perpendicular to one pair of the lobes. We suggest thatNGC 6644 is a multipolar nebula and construct a three-dimensional modelthat allows the visualization of the object from different lines ofsight. These results suggest that NGC 6644 may have similar intrinsicstructures as other multipolar nebulae and the phenomenon of multipolarnebulosity may be more common than previously believed.
| Abundances of Galactic Anticenter Planetary Nebulae and the Oxygen Abundance Gradient in the Galactic Disk
We have obtained spectrophotometric observations of 41 anticenterplanetary nebulae (PNe) located in the disk of the Milky Way. Electrontemperatures and densities, as well as chemical abundances for He, N, O,Ne, S, Cl, and Ar were determined. Incorporating these results into ourexisting database of PN abundances yielded a sample of 124 well-observedobjects with homogeneously determined abundances extending from 0.9 to21 kpc in galactocentric distance. We performed a detailed regressionanalysis which accounted for uncertainties in both oxygen abundances andradial distances in order to establish the metallicity gradient acrossthe disk to be 12 + log(O/H) = (9.09 ± 0.05) - (0.058 ±0.006) × Rg , with Rg in kpc. While we seesome evidence that the gradient steepens at large galactocentricdistances, more objects toward the anticenter need to be observed inorder to confidently establish the true form of the metallicitygradient. We find no compelling evidence that the gradient differsbetween Peimbert Types I and II, nor is oxygen abundance related to thevertical distance from the galactic plane. Our gradient agrees well withanalogous results for H II regions but is steeper than the one recentlypublished by Stanghellini & Haywood over a similar range ingalactocentric distance. A second analysis using PN distances from adifferent source implied a flatter gradient, and we suggest that we havereached a confusion limit which can only be resolved with greatlyimproved distance measurements and an understanding of the naturalscatter in oxygen abundances.Partially based on observations obtained with the Apache PointObservatory 3.5 m telescope, which is owned and operated by theAstrophysical Research Consortium.
| Post-common-envelope binaries from SDSS. IX: Constraining the common-envelope efficiency
Context. Reconstructing the evolution of post-common-envelope binaries(PCEBs) consisting of a white dwarf and a main-sequence star canconstrain current prescriptions of common-envelope (CE) evolution. Thispotential could so far not be fully exploited due to the small number ofknown systems and the inhomogeneity of the sample. Recent extensivefollow-up observations of white dwarf/main-sequence binaries identifiedby the Sloan Digital Sky Survey (SDSS) paved the way for a betterunderstanding of CE evolution. Aims: Analyzing the new sample ofPCEBs we derive constraints on one of the most important parameters inthe field of close compact binary formation, i.e. the CE efficiency?. Methods: After reconstructing the post-CE evolution andbased on fits to stellar evolution calculations as well as aparametrized energy equation for CE evolution, we determine the possibleevolutionary histories of the observed PCEBs. In contrast to mostprevious attempts we incorporate realistic approximations of the bindingenergy parameter ?. Each reconstructed CE history corresponds toa certain value of the mass of the white dwarf progenitor and - moreimportantly - the CE efficiency ?. We also reconstruct CEevolution replacing the classical energy equation with a scaled angularmomentum equation and compare the results obtained with both algorithms. Results: We find that all PCEBs in our sample can bereconstructed with the energy equation if the internal energy of theenvelope is included. Although most individual systems have solutionsfor a broad range of values for ?, only for ? = 0.2-0.3 dowe find simultaneous solutions for all PCEBs in our sample. If we adjust? to this range of values, the values of the angular momentumparameter ? cluster in a small range of values. In contrast if wefix ? to a small range of values that allows us to reconstruct allour systems, the possible ranges of values for ? remains broad forindividual systems. Conclusions: The classical parametrizedenergy equation seems to be an appropriate prescription of CE evolutionand turns out to constrain the outcome of the CE evolution much morethan the alternative angular momentum equation. If there is a universalvalue of the CE efficiency, it should be in the range of ? =0.2-0.3. We do not find any indications for a dependence of ? onthe mass of the secondary star or the final orbital period.Appendix A and Figures 2-5 are only available in electronic form at http://www.aanda.org
| Three-dimensional Structure of the Central Region of NGC 7027: A Quest for Trails of High-velocity Jets
We report on the results of a radio interferometric observation of NGC7027 in the CO J = 2-1 and 13CO J = 2-1 lines. The resultsare analyzed with morpho-kinematic models developed from the softwaretool Shape. Our goal is to reveal the morpho-kinematic properties of thecentral region of the nebula, and to explore the nature of unseenhigh-velocity jets that may have created the characteristic structure ofthe central region consisting of molecular and ionized components. Asimple ellipsoidal shell model explains the intensity distributionaround the systemic velocity, but the high-velocity features deviatefrom the ellipsoidal model. Through the Shape automatic reconstructionmodel, we found a possible trail of a jet only in one direction, but noother possible holes were created by the passage of a jet.
| Spitzer mid-infrared observations of seven bipolar planetary nebulae
We have investigated the mid-infrared (MIR) and visual structures ofseven bipolar planetary nebulae (BPNe), using imaging and spectroscopyacquired using the Spitzer Space Telescope (SST), and the ObservatorioAstronomico Nacional in Mexico. The results show that the sources aremore extended towards longer MIR wavelengths, as well as having higherlevels of surface brightness in the 5.8- and 8.0-?m bands. It is alsonoted that the 5.8?m/4.5?m and 8.0?m/4.5?m flux ratiosincrease with increasing distance from the nuclei of the sources. All ofthese latter trends may be attributable to emission by polycyclicaromatic hydrocarbons (PAHs) and/or warm dust continua withincircumnebular photodissociation regions (PDRs). A corresponding decreasein the flux ratios 8.0?m/5.8?m may, by contrast, arise due tochanges in the properties of the PAH emitting grains. We note evidencefor 8.0?m ring-like structures in the envelope of NGC 2346, locatedin a region beyond the minor axis limits of the ionized envelope. Ananalysis of the inner two rings shows that whilst they have highersurface brightnesses at longer MIR wavelengths, they are relativelystronger (compared to underlying emission) at 3.6 and 4.5?m. There isalso evidence for point-reflection symmetry along the major axis of theoutflow. Finally, the fall-off in surface brightness along the nebularminor axis suggests that progenitor mass-loss rates were more-or-lessconstant. NGC 6905 shows evidence for a centrally located and unresolvedMIR emission excess. We show that whilst flux ratios are inconsistentwith stellar and ionized gas components of emission, the emission can beexplained in terms of shock-excited H2, or grain continuumand PAH emission bands. We provide the deepest image so far published ofthe outer visual structure of NGC 6445, and compare these results withSpitzer imaging at 8.0?m. The distributions are quite distinct, andmay indicate collimation of the outer ionized emission by a cylindricalPDR. We finally note that the MIR colours of the lobes and nuclei of thesources are radically different. It is also shown that 3.6-?memission in BPNe differs from that for the generality of planetarynebulae. We discuss various mechanisms which may contribute to thesedifferences of colour.
| Disk evaporation in a planetary nebula
Aims: Binary interactions are believed to be importantcontributors to the structures seen in planetary nebulae (PN), and thesole cause of the newly discovered compact dust disks. The evolution ofthese disks is not clear, nor are the binary parameters required fortheir creation. Methods: Using HST imaging and VLT spectroscopy,both long-slit and integral field, we study the Galactic bulge planetarynebula M 2-29 for which a 3-year eclipse event of the central star hasbeen attributed to a dust disk. Results: The central PN cavity ofM 2-29 is being filled with a decreasingly, slow wind. An inner highdensity core is detected, of radius smaller than 250 AU, interpreted asa rotating gas/dust disk with a bipolar disk wind. The evaporating diskis argued to be the source of the slow wind. The central star is thesource of a very fast wind (~103 km s-1). Anouter, partial ring is seen in the equatorial plane, expanding at 12 kms-1. The azimuthal asymmetry is attributed to mass-lossmodulation by an eccentric binary. A crucial point in disk evolution isrepresented by M 2-29 where ionization causes the gas to be lost,leaving a low-mass dust disk behind.Based on observations collected at the European Organisation forAstronomical Research in the Southern Hemisphere, Chile (proposals075.D-0104, 077.D-0652, 081.D-0130) and HST (program 9356).
| A comprehensive population synthesis study of post-common envelope binaries
We apply population synthesis techniques to calculate the present-daypopulation of post-common envelope binaries (PCEBs) for a range oftheoretical models describing the common envelope (CE) phase. Adoptingthe canonical energy budget approach, we consider models where theejection efficiency ?CE is either a constant or afunction of the secondary mass. We obtain the envelope binding energyfrom detailed stellar models of the progenitor primary, with and withoutthe thermal and ionization energy, but we also test a commonly usedanalytical scaling. We also employ the alternative angular momentumbudget approach, known as the ?-algorithm. We find that aconstant, global value of ?CE >~ 0.1 can adequatelyaccount for the observed population of PCEBs with late spectral-typesecondaries. However, this prescription fails to reproduce IK Pegasi (IKPeg), which has a secondary with spectral type A8. We can account for IKPeg if we include thermal and ionization energy of the giant's envelope,or if we use the ?-algorithm. However, the ?-algorithmpredicts local space densities that are 1 to 2 orders of magnitudegreater than estimates from observations. In contrast, the canonicalenergy budget prescription with an initial mass ratio distribution thatfavours unequal initial mass ratios (n(qi) ~q-0.99i) gives a local space density which is ingood agreement with observations, and best reproduces the observeddistribution of PCEBs. Finally, all models fail to reproduce the sharpdecline for orbital periods, Porb >~ 1 d in the orbitalperiod distribution of observed PCEBs, even if we take into accountselection effects against systems with long orbital periods and earlyspectral-type secondaries.
| Discovery of a Multipolar Structure with an Equatorial disk in NGC 6072
From near-infrared and molecular hydrogen imaging observations, we havediscovered that the planetary nebula NGC 6072 has a multipolar structurewith a prominent equatorial ring. We have modeled the object by a doublebipolar system, each with an equatorial ring and a pair of bipolarlobes. The bipolar axes of the two systems are estimated to be separatedby 47°. The existence of such a double bipolar system suggests thatthe object has undergone separate fast outflow episodes separated byseveral thousand years.
| High- and low-resolution spectroscopic observations of the peculiar planetary-nebula HD 149427 (=PC 11)
Aims: We discuss the status of the A-type component of the binarycentral star in the peculiar planetary nebula HD 149427. Methods:We acquired low and high spectral resolution optical spectroscopy forthe range 4500-9000 Å. Results: The analysis of the highresolution spectrum shows that the A-type star has an effectivetemperature of Teff = 8700 ± 150 K and a surfacegravity of log g = 2.3 ± 0.4, corresponding to a spectral typeA3-A4 II. These parameters infer a luminosity estimate oflog(L/L?) = 3.69 ± 0.32, implying a distance of10 ± 0.6 kpc. The A-type star is slightly metal-poor; barium andstrontium, two key elements for monitoring the s-processnucleosynthesis, are not enriched; nitrogen is enriched relative to Sun;while carbon and oxygen are underabundant. The photospheric abundance ofthe A-type giant star in HD 149427 is compared with the abundance inother types of stars at different evolutionary stages.ARRAY(0x382e430)
| Planetary Nebulae Detected in the Spitzer Space Telescope GLIMPSE II Legacy Survey
We report the result of a search for the infrared counterparts of 37planetary nebulae (PNs) and PN candidates in the Spitzer Galactic LegacyInfrared Mid-Plane Survey Extraordinaire II (GLIMPSE II) survey. Thephotometry and images of these PNs at 3.6, 4.5, 5.8, 8.0, and 24 ?m,taken through the Infrared Array Camera (IRAC) and the Multiband ImagingPhotometer for Spitzer (MIPS), are presented. Most of these nebulae arevery red and compact in the IRAC bands, and are found to be bright andextended in the 24 ?m band. The infrared morphology of these objectsare compared with H? images of the Macquarie-AAO-Strasbourg (MASH)and MASH II PNs. The implications for morphological difference indifferent wavelengths are discussed. The IRAC data allow us todifferentiate between PNs and H II regions and be able to reject non-PNsfrom the optical catalog (e.g., PNG 352.1 - 00.0). Spectral energydistributions are constructed by combing the IRAC and MIPS data withexisting near-, mid-, and far-IR photometry measurements. The anomalouscolors of some objects allow us to infer the presence of aromaticemission bands. These multi-wavelength data provide useful insights intothe nature of different nebular components contributing to the infraredemission of PNs.
| Binary planetary nebulae nuclei towards the Galactic bulge. II. A penchant for bipolarity and low-ionisation structures
Considerable effort has been applied towards understanding the preciseshaping mechanisms responsible for the diverse range of morphologiesexhibited by planetary nebulae (PNe).At least 10-20% of PNe have central stars (CSPN) with a close binarycompanion thought responsible for heavily shaping the ejected PN duringcommon-envelope (CE) evolution, however morphological studies of the fewavailable examples found no clear distinction between PNe and post-CEPNe.The discovery of several new binary central stars (CSPN) from theOGLE-III photometric variability survey has significantly increased thenumber of post-CE PNe available for morphological analysis to 30 PNe.High quality Gemini South narrow-band images are presented for most ofthe OGLE sample, while some previously known post-CE PNe are reanalysedwith images from the literature.Nearly 30% of nebulae have canonical bipolar morphologies, however thiscould be as high as 60% once inclination effects are incorporated withthe aid of geometric models. This is the strongest observationalevidence yet linking CE evolution to bipolar morphologies. A higher thanaverage proportion of the sample shows low-ionisation knots, filamentsor jets suggesting they have a binary origin. These features are alsocommon in nebulae around emission-line nuclei which may be explained byspeculative binary formation scenarios for H-deficient CSPN.Based on observations made with Gemini South under programsGS-2008B-Q-65 and GS-2009A-Q-35.
| Spitzer 24 ?m Images of Planetary Nebulae
Spitzer MIPS 24 ?m images were obtained for 36 Galactic planetarynebulae (PNe) whose central stars are hot white dwarfs (WDs) or pre-WDswith effective temperatures of ~100,000 K or higher. Diffuse 24 ?memission is detected in 28 of these PNe. The eight nondetections areangularly large PNe with very low H? surface brightnesses. We findthree types of correspondence between the 24 ?m emission and H?line emission of these PNe: six show 24 ?m emission more extendedthan H? emission, nine have a similar extent at 24 ?m andH?, and 13 show diffuse 24 ?m emission near the center of theH? shell. The sizes and surface brightnesses of these three groupsof PNe and the nondetections suggest an evolutionary sequence, with theyoungest ones being brightest and the most evolved ones undetected. The24 ?m band emission from these PNe is attributed to [O IV] 25.9?m and [Ne V] 24.3 ?m line emission and dust continuum emission,but the relative contributions of these three components depend on thetemperature of the central star and the distribution of gas and dust inthe nebula.
| The Origin and Shaping of Planetary Nebulae: Putting the Binary Hypothesis to the Test
Planetary nebulae (PNs) are circumstellar gas ejected during an intensemass-losing phase in the lives of asymptotic giant branch stars. PNshave a stunning variety of shapes, most of which are not sphericallysymmetric. The debate over what makes and shapes the circumstellar gasof these evolved, intermediate mass stars has raged for two decades.Today the community is reaching a consensus that single stars cannottrivially manufacture PNs and impart to them nonspherical shapes andthat a binary companion, possibly even a substellar one, might be neededin a majority of cases. This theoretical conjecture has, however, notbeen tested observationally. In this review we discuss the problem fromboth the theoretical and observational standpoints, explaining theobstacles that stand in the way of a clean observational test and waysto ameliorate the situation. We also discuss indirect tests of thishypothesis and its implications for stellar and galactic astrophysics.
| The True Shapes of the Dumbbell and the Ring
Using images centered around the 2.12 ?m line of molecular hydrogenobtained with the Wide Field Infrared Camera on the Canada-France-HawaiiTelescope, we show that in spite of the different apparent morphologies,the Dumbbell Nebula and the Ring Nebula share the same intrinsicthree-dimensional triple biconic structure.
| The Magellanic Cloud Calibration of the Galactic Planetary Nebula Distance Scale
Galactic planetary nebula (PN) distances are derived, except in a smallnumber of cases, through the calibration of statistical properties ofPNs. Such calibrations are limited by the accuracy of individual PNdistances, which are obtained with several nonhomogeneous methods, eachcarrying its own set of liabilities. In this paper we use the physicalproperties of the PNs in the Magellanic Clouds and their accuratelyknown distances to recalibrate the Shklovsky/Daub distance technique.Our new calibration is very similar (within 1%) to the commonly useddistance scale by Cahn et al., although there are important differences.We find that neither distance scale works well for PNs with classic(``butterfly'') bipolar morphology, and while the radiation-bounded PNsequences in both the Galactic and the Magellanic Cloud calibration havesimilar slopes, the transition from optically thick to optically thinappears to occur at higher surface brightness and smaller size than inthat adopted by Cahn et al. The dispersion in the determination of thescale factor suggests that PN distances derived by this method areuncertain by at least 30%, and that this dispersion cannot be reducedsignificantly by using better calibrators. We present a catalog ofGalactic PN distances using our recalibration, which can be used forfuture applications, and compare the best individual Galactic PNdistances to our new and several other distance scales, both in theliterature and newly recalibrated by us, finding that our scale is themost reliable to date.
| The visual and mid-infrared properties of the bipolar planetary nebula NGC 650-1
The bipolar planetary nebula NGC 650-1 has been imaged in H?,H?, [NII] ?6583Å and [SII]??6717+6731Å. These results are used to map thevariation of extinction over the interior regions of the shell, where wefind evidence for a gradual increase in AV between the SW andNE limits of the central emission bar. It is argued that this is likelyto arise from dust associated with the nebular envelope itself. We havealso produced a map of electron densities over this region, and findevidence for marked variations in ne over a scale of~5arcsec, a variation which is probably related to the clumpy emissionstructure observed in low-excitation images. We finally present contourmapping of mid-infrared Spitzer images of the source at 3.6,4.5,5.8and8?m. These show that the central bar has a more or less uniformemission structure, although with evidence for condensations which aresimilar to, and in most cases coincidental with, comparablelow-excitation structures noted in [NII]. There is also evidence for anincrease in 8/4.5?m and 5.8/4.5?m emission ratios with distancefrom the nucleus, and for an extension of 8 and 5.8?m emission beyondthe ionized regime; a trend which is attributed to strong polycyclicaromatic hydrocarbon band emission within the nebular photodissociativeregime.
| G25.5+0.2: a possible symbiotic bipolar outflow
The nature of the source G25.5+0.2 is open to considerable uncertainty,and it has variously been identified as being a young stellar outflow,an HII region, a young supernova remnant and a planetary nebula. Wepresent further Two-Micron All-Sky Survey (2MASS), Mid-course SpaceExperiment (MSX) and Spitzer near- (NIR) and mid-infrared (MIR)photometry and mapping in an attempt to clarify the properties of thesource. It is apparent that the morphology varies appreciably with MIRwavelength and indicates the presence of a bipolar structure andprobable circum-nebular torus. It is also noted that the 2MASS stellarphotometry is quite disparate from that of earlier NIR measures andimplies an appreciable variation in the brightness and colour of thecentral star. These two factors, the nuclear variability and bipolarity,combine to suggest the G25.5+0.2 may be identifiable as a symbioticoutflow. The nebular continuum peaks at wavelengths ? ~ 40?m,and may be fitted using a ?-2 fall-off in grainemissivity, together with a model in which the grains have temperaturesTGR = 65 and 130K. An analysis of dust/gas mass ratios alsoimplies that md/mg ~ 1.2 × 10-2(ne/104cm-3) -> 1.27 ×10-1 (ne/104cm-3), dependingupon the types of grains and temperatures involved. Such a range istypical of what is observed in planetary nebulae and symbiotic outflows.
| An occultation event in the nucleus of the planetary nebula M 2-29
Aims: Eclipses and occultations of post-AGB stars provide a powerfulmethod of exploring the near-stellar environment, including closecompanions and circumstellar debris disks. Only six eclipsing systemsand one dust-occultation system are currently known. New cases areimportant for our understanding of binary evolution during the AGBmass-loss phase. Methods: We study the post-AGB central star ofthe (bipolar) Galactic bulge planetary nebula M 2-29. We have obtainedadditional HST imaging and SAAO spectroscopy of the object. Results: The star showed a pronounced, long-lasting occultation withsubsequent recovery. The event lasted almost 3 years, with a secondaryminimum 9 years later. The photometric behavior of M 2-29 resembles thedust-occultation events seen in NGC 2346, and is modeled as anoccultation by a circumbinary disk, where the binary period is 18 yr.Modulation during the decline shows evidence of another companion with aperiod of 23 days. Conclusions: M 2-29 is the first eclipsingdisk system among post-AGB stars. Close binaries with periods of around1 month, as found in M 2-29, have been proposed to supply the energyneeded to create the tori of bipolar planetary nebulae.
| Discovery of eclipsing binary central stars in the planetary nebulae M 3-16, H 2-29, and M 2-19
Progress in understanding the formation and evolution of planetarynebulae (PN) has been restricted by a paucity of well-determined centralstar masses.To address this deficiency we aim to (i) increase significantly thenumber of known eclipsing binary central stars of PN (CSPN); andsubsequently (ii) measure directly their masses and absolute dimensionsby combining their light curve parameters with planned radial velocitydata.Using photometric data from the third phase of the Optical GravitationalLensing Experiment (OGLE), we searched for periodic variability in alarge sample of PN towards the Galactic Bulge using Fourier andphase-dispersion minimisation techniques.Among some dozen periodically variable CSPN found, we report on threenew eclipsing binaries: M 3-16, H 2-29 and M 2-19.We present images, confirmatory spectroscopy and light curves of thesystems.
| Binary Central Stars of Planetary Nebulae Discovered Through Photometric Variability. I. What we Know and what we would like to Find Out
Shaping axisymmetric planetary nebulae is easier if a companioninteracts with a primary at the top of the asymptotic giant branch. Todetermine the impact of binarity on planetary nebula formation andshaping, we need to determine the central star of planetary nebulabinary fraction and period distribution. The short-period binaryfraction has been known to be 10-15% from a survey of ~100 central starsfor photometric variability indicative of irradiation effects,ellipsoidal variability, or eclipses. This survey technique is known tobe biased against binaries with long periods and this fact is used toexplain why the periods of all the binaries discovered by this surveyare smaller than 3 days. In this paper we assess the status of knowledgeof binary central stars discovered because of irradiation effects. Wedetermine that, for average parameters, this technique should be biasedagainst periods longer than 1-2 weeks, so it is surprising that nobinaries were found with periods longer than 3 days. Even more puzzlingis the fact that 9 out of 12 of the irradiated binaries have periodssmaller than 1 day, a fact that is starkly at odds with post-commonenvelope predictions. We suggest that either all common envelope modelstend to overestimate post-common envelope periods or this binary surveymight have suffered from additional, unquantified biases. If the latterhypothesis is true, the currently known short-period binary fraction isput in serious doubt. We also introduce a new survey for binary-relatedvariability, which will enable us to better quantify biases anddetermine an independent value for the short-period binary fraction.
| Orientation Effects in Bipolar Planetary Nebulae
We show that the inclination to the line of sight of bipolar planetarynebulae strongly affects some of their observed properties. We modelthese objects as having a dusty equatorial density enhancement thatproduces extinction that varies with the viewing angle. Our sample of 29nebulae taken from the literature shows a clear correlation between theinclination angle and the near-infrared and optical photometricproperties as well as the detected luminosity of the objects. As theinclination angle increases (the viewing angle is closer to theequatorial plane) the objects become redder, their apparent luminositydecreases, and their projected expansion velocity becomes smaller. Wecompute two-dimensional models of stars embedded in dusty disklikestructures of various shapes and compositions and show that the observeddata can be reproduced by disk-star combinations with reasonableparameters. To compare with the observational data, we generate sets ofmodel data by randomly varying the star and disklike structureparameters within a physically meaningful range. We conclude that a onlya smooth pole to equator density gradient agrees with the observedphenomena.
| Spitzer Sage Observations of Large Magellanic Cloud Planetary Nebulae
We present IRAC and MIPS images and photometry of a sample of previouslyknown planetary nebulae (PNe) from the Surveying the Agents of aGalaxy's Evolution (SAGE) survey of the Large Magellanic Cloud (LMC)performed with the Spitzer Space Telescope. Of the 233 known PNe in thesurvey field, 185 objects were detected in at least two of the IRACbands, and 161 detected in the MIPS 24 ?m images. Color-color andcolor-magnitude diagrams are presented using several combinations ofIRAC, MIPS, and Two Micron All Sky Survey magnitudes. The location of anindividual PN in the color-color diagrams is seen to depend on therelative contributions of the spectral components which includemolecular hydrogen, polycyclic aromatic hydrocarbons (PAHs), infraredforbidden line emission from the ionized gas, warm dust continuum, andemission directly from the central star. The sample of LMC PNe iscompared to a number of Galactic PNe and found not to significantlydiffer in their position in color-color space. We also explore thepotential value of IR PNe luminosity functions (LFs) in the LMC. IRACLFs appear to follow the same functional form as the well-established [OIII] LFs although there are several PNe with observed IR magnitudesbrighter than the cut-offs in these LFs.
| Mid-infrared imaging of 18 planetary nebulae using the Spitzer Space Telescope
We present 3.6-, 4.5-, 5.8- and 8.0-?m photometric mapping of 18galactic planetary nebulae, based on observations taken with the SpitzerSpace Telescope. These are shown to have morphologies which aresometimes quite different from those observed in the visible, with muchof the emission arising outside the ionized shells. There is alsoevidence for a change in nebular sizes between the differing photometricbands. An analysis of mid-infrared (MIR) colours suggests that manynebulae have dust/polycyclic aromatic hydrocarbon (PAH) emissioncomponents, and it seems likely that longer wave MIR fluxes (inparticular) are associated with PAH emission features. Such features arelikely to be associated, in addition, with photodissociative regimes,where shock fragmentation of dust may lead to the replenishment ofsmaller PAH grains.Finally, we note that the source Ap 2-1 possesses a particularlyinteresting structure, and may represent a case in which the nebularshell is ploughing through an enveloping HII region. Similarly, itappears that central emission in M 2-48 may arise from a warm and dustycollimating disc.
| The Unusual Variability of the Large Magellanic Cloud Planetary Nebula RPJ 053059-683542
We present images and light curves of the bipolar planetary nebula RPJ053059-683542 that was discovered in the Reid-Parker AAO UKST H?survey of the Large Magellanic Cloud. The emission from this objectappears entirely nebular, with the central star apparently obscured by acentral band of absorption that bisects the nebula. The light curves,which were derived from images from the SuperMACHO project at CTIO,showed significant, spatially resolved variability over the period 2002January through 2005 December. Remarkably, the emission from the twobright lobes of the nebula vary either independently or similarly butwith a phase lag of at least 1 yr. The optical spectra show a low levelof nebular excitation, and only modest N enrichment. Infrared photometryfrom the 2MASS and SAGE surveys indicates the presence of a significantquantity of dust. The available data imply that the central star has aclose binary companion and that the system has undergone some kind ofoutburst event that caused the nebular emission to first brighten andthen fade. Further monitoring, high-resolution imaging, and detailed IRpolarimetry and spectroscopy would uncover the nature of this nebula andthe unseen ionizing source.
| Bayesian posterior classification of planetary nebulae according to the Peimbert types
Context: Galactic planetary nebulae are observed with a wide variety ofkinematic properties, spatial distribution, chemical composition andmorphologies, comprising members of the dominant stellar populations ofour Galaxy. Due to their broad astrophysical interest, a propercharacterization of these populations is of major importance. Aims: Inthis paper we present a re-analysis of the criteria used to characterizethe Peimbert classes I, IIa, IIb, III and IV, through a statisticalstudy of a large sample of planetary nebulae previously classifiedaccording to these groups. In the original classification, it is usualto find planetary nebulae that cannot be associated with a single type;these most likely have dubious classifications into two or three types.Statistical methods can greatly contribute in providing a bettercharacterization of planetary nebulae groups. Methods: We use the BayesTheorem to calculate the posterior probabilities for an object to bemember of each of the types I, IIa, IIb, III and IV. This calculation isparticularly important for planetary nebulae that are ambiguouslyclassified in the traditional method. The posterior probabilities aredefined from the probability density function of classificatoryparameters of a well-defined sample, composed only by planetary nebulaeunambiguously fitted into the Peimbert types. Because the probabilitiesdepend on the available observational data, they are conditionalprobabilities, and, as new observational data are added to the sample,the classification of the nebula can be improved, to take into accountthis new information. Results: This method differs from the originalclassificatory scheme, because it provides a quantitative result of therepresentativity of the object within its group. Also, through the useof marginal distributions it is possible to extend the Peimbertclassification even to those objects for which only a few classificatoryparameters are known. Conclusions: We found that ambiguities in theclassification of planetary nebulae into the Peimbert types, should beassociated to difficulties in defining sharp boundaries for theprogenitor star mass for each of these types. Those can be at leastpartially explained by real overlaps of some of the parameters thatcharacterize the different stellar populations. Those results suggestthe need of a larger number of classificatory parameters for a reliablephysical classification of planetary nebulae.Tables [see full textsee full text] and [see full textsee full text] areonly available in electronic form at http://www.aanda.org
| The massive expanding molecular torus in the planetary nebula NGC 6302
Aims:We measure the mass and kinematics of the massive molecular torusin the the proto-typical butterfly planetary nebula NGC 6302.Determining the mass-loss history of the source is an important step inunderstanding the origin and formation of the wing-like morphology. Methods: Using the SMA interferometer we have imaged both thecontinuum emission and the J=2-1 transitions of 12CO and13CO at arcsecond resolution. These data are analysed incombination with observations of both the J=2-1 and J=3-2 transitions of12CO and 13CO made with JCMT. Results: The12CO and 13CO emission match the dark lane seen inabsorption in the H? image of the object and trace an expandingtorus of material. The CO indicates a mass of the torus of ~ 2 M_&sun;± 1 M_&sun;. The torus is expanding with a velocity of ~8 kms-1, centred at V_lsr=-31.5 km s-1. The size andexpansion velocity of the torus indicates that it was ejected from ~7500yr to 2900 yr ago, with a mass-loss rate of 5×10-4M_&sun; yr-1. In addition we detect a ballistic component inthe CO images which has a velocity gradient of 140 km s-1pc-1. Conclusions: The derived mass-loss history ofthe torus favours binary interaction as the cause of the ejection of thetorus and we predict the existence of a companion with an orbital periodP? 1 month.
| Absolute Calibration and Characterization of the Multiband Imaging Photometer for Spitzer. III. An Asteroid-based Calibration of MIPS at 160 ?m
We describe the absolute calibration of the Multiband Imaging Photometerfor Spitzer (MIPS) 160 ?m channel. After the on-orbit discovery of anear-IR ghost image that dominates the signal for sources hotter thanabout 2000 K, we adopted a strategy utilizing asteroids to transfer theabsolute calibrations of the MIPS 24 and 70 ?m channels to the 160?m channel. Near-simultaneous observations at all three wavelengthsare taken, and photometry at the two shorter wavelengths is fit usingthe standard thermal model. The 160 ?m flux density is predicted fromthose fits and compared with the observed 160 ?m signal to derive theconversion from instrumental units to surface brightness. Thecalibration factor we derive is 41.7 MJy sr-1MIPS160-1 (MIPS160 being the instrumental units). The scatterin the individual measurements of the calibration factor, as well as anassessment of the external uncertainties inherent in the calibration,lead us to adopt an uncertainty of 5.0 MJy sr-1MIPS160-1 (12%) for the absolute uncertainty on the 160 ?mflux density of a particular source as determined from a singlemeasurement. For sources brighter than about 2 Jy, nonlinearity in theresponse of the 160 ?m detectors produces an underestimate of theflux density: for objects as bright as 4 Jy, measured flux densities arelikely to be ~=20% too low. This calibration has been checked againstthat of the ISO (using ULIRGs) and IRAS (using IRAS-derived diameters),and is consistent with those at the 5% level.
|
Sottometti un nuovo articolo
Link relazionati
Sottometti un nuovo link
Membro dei seguenti gruppi:
|
Osservazione e dati astrometrici
| Costellazione: | Unicorno |
| Ascensione retta: | 07h09m22.52s |
| Declinazione: | -00°48'23.6" |
| Magnitudine apparente: | 11.588 |
| Moto proprio RA: | -2.7 |
| Moto proprio Dec: | -1 |
| B-T magnitude: | 11.804 |
| V-T magnitude: | 11.606 |
Cataloghi e designazioni:
|
INHABITED SKY
