Galactic PNe Research Articles

Radio-continuum detections of Galactic Planetary Nebulae - I. MASH PNe detected in large-scale radio surveys

We present an updated and newly compiled radio-continuum data-base for MASH PNe detected in the extant large scale "blind" radio-continuum surveys (NVSS, SUMSS/MGPS-2 and PMN) and, for a small number of MASH PNe, observed and detected in targeted radio-continuum observations. We found radio counterparts for approximately 250 MASH PNe. In comparison with the percentage of previously known Galactic PNe detected in the NVSS and MGPS-2 radio-continuum surveys and according to their position on the flux density-angular diameter and the radio brightness temperature evolutionary diagrams we conclude, unsurprisingly, that the MASH sample presents the radio-faint end of the known Galactic PNe population. Also, we present radio-continuum spectral properties of a small sub-sample of MASH PNe located in the strip between declinations -30arcdeg and -40arcdeg, that are detected in both the NVSS and MGPS-2 radio surveys.

Searching for Faint Planetary Nebulae Using the Digital Sky Survey

AbstractRecent Hα surveys such as SHS and IPHAS have improved the completeness of the Galactic planetary nebula (PN) census. We now know of ∼3000 PNe in the Galaxy, but this is far short of most estimates, typically ~25 000 or more for the total population. The size of the Galactic PN population is required to derive an accurate estimate of the chemical enrichment rates of nitrogen, carbon, and helium. In addition, a high PN count (>20 000) is strong evidence that most main-sequence stars of mass 1–8 M⊙ will go through a PN phase, while a low count (<10 000) argues that special conditions (e.g. close binary interactions) are required to form a PN. We describe a technique for finding hundreds more PNe using the existing data collections of the digital sky surveys, thereby improving the census of Galactic PNe.

Faint recombination lines in Galactic PNe with a [WC] nucleus

Aims. We present spatially resolved high-resolution spectrophotometric data for the planetary nebulae PB 8, NGC 2867, and PB 6. We have analyzed two knots in NGC 2867 and PB 6 and one in PB 8. The three nebulae are ionized by [WC] type nuclei: early [WO] for PB 6 and NGC 2867 and [WC 5-6] in the case of PB 8. Our aim is to study the behavior of the abundance discrepancy problem (ADF) in this type of planetary nebula. Methods. We measured a large number of optical recombination (ORL) and collisionally excited lines (CEL), from different ionization stages (many more than in any previous work), thus, we were able to derive physical conditions from many different diagnostic procedures. We determined ionic abundances from the available collisionally excited and recombination lines. Based on both sets of ionic abundances, we derived total chemical abundances in the nebulae using suitable ionization correction factors. Results. From CELs, we have found abundances typical of Galactic disk planetary nebulae. Moderate ADF(O ++ ) were found for PB 8 (2.57) and NGC 2867 (1.63). For NGC 2867, abundances from ORLs are higher but still consistent with Galactic disk planetary nebulae. On the contrary, PB 8 presents a very high O/H ratio from ORLs. A high C/O was obtained from ORLs for NGC 2867; this ratio is similar to C/O obtained from CELs and with the chemical composition of the wind of the central star, indicating that there was no further C-enrichment in the star, relative to O, after the nebular material ejection. On the contrary, we found C/O < 1 in PB 8. Interestingly, we obtain (C/O) ORLs /(C/O) CELs < 1 in PB 8 and NGC 2867; this added to the similarity between the heliocentric velocities measured in [O III] and O II lines for our three objects argue against the presence of H-deficient metal-rich knots coming from a late thermal pulse event.

Lithium and zirconium abundances in massive Galactic O-rich AGB stars

Lithium and zirconium abundances (the latter taken as representative for s-process enrichment) are determined for a large sample of massive Galactic O-rich AGB stars, for which high resolution optical spectroscopy has been obtained (R=40,000-50,000). This is done by computing synthetic spectra based on classical hydrostatic model atmospheres for cool stars using extensive line lists. The results obtained are discussed in the framework of hot bottom burning (HBB) and nucleosynthesis models. The complete sample is studied attending to various observational properties such as the position of the stars in the IRAS two-colour diagram ([12]-[25] vs [25]-[60]), Galactic distribution, expansion velocity (derived from the OH maser emission) and period of variability (when available). We conclude that a considerable fraction of the sources observed are actually massive AGB stars (M > 3-4 solar masses) experiencing HBB, as deduced from the strong Li overabundances found. A comparison of our results with similar studies carried out in the past for the Magellanic Clouds (MCs) reveals that, in contrast to MC AGB stars, our Galactic sample does not show any indication of s-process element enrichment. The differences observed are explained as a consequence of metallicity effects. Finally, we discuss the results obtained in the framework of stellar evolution by comparing our results with the data available in the literature for Galactic post-AGB stars and PNe.

Chemical composition of the Galactic bulge from deep spectroscopy of planetary nebulae

Previous abundance analyses for the Galactic bulge using giant stars, RR Lyrae variables and PNe (based on the traditional method by means of collisionally excited lines – CELs) as tracers yielded different results (c.f. the review by McWilliam (1997, ARAA, 35, 503 and references therein). We have obtained deep long-slit medium resolution spectra for a sample of 25 Galactic bulge PNe (GBPNe) and 6 Galactic disk PNe (GDPNe) with which we have carried out detailed extinction analyses, plasma diagnostics and elemental abundance determinations, using both CELs and optical recombinations lines (ORLs) from heavy elemental ions. Here we report the preliminary results and compare them with earlier work for both bulge and disk PNe.

Milky Way and Magellanic Cloud Surveys for Planetary Nebulae

The recent on-line availability of large-scale, wide-field surveys of the Galaxy and Magellanic Clouds in several optical and near/mid-infrared passbands has provided unprecedented opportunities to refine selection techniques and eliminate contaminants in PN surveys. This has been coupled with new surveys offering improved detection rates via higher sensitivity and resolution. This will permit more extreme ends of the PN luminosity function to be explored and enable studies of under represented PN evolutionary states. Known PNe in our Galaxy and LMC have thus been significantly increased over the last few years due primarily to the advent of narrow-band imaging in important nebula lines such as H $\alpha$ , [O iii] and [S iii]. These PNe are generally of lower surface brightness, larger angular extent, in more obscured regions and in later stages of evolution than those in most previous surveys. A more representative PN population for in-depth study is now available, particularly in the LMC where the known distance adds considerable utility for derived PN parameters. Future prospects for Galactic and LMC PNe research are briefly highlighted.

The double-dust chemistry phenomenon in PNe with [WC]-type central stars

We present preliminary conclusions derived from the analysis of a sample of galactic PNe with [WC]-type central stars (WCPNe) observed with Spitzer/IRS. We report the detection of double-dust (C-rich and O-rich) chemistry in all stars in the sample for which a good S/N spectrum was obtained. Our observations reveal that the simultaneous presence of oxygen and carbon-rich dust features in the infrared spectra of WCPNe is not restricted to late/cool [WC]-type stars, as previously suggested in the literature, but it is found to be a common feature associated to all WCPNe. In particular, mixed chemistry is observed in at least seven early/hot WCPNe in the sample. Various scenarios are proposed to interpret the results obtained in the framework of the chemical evolution of PNe.

Unravelling the chemical inhomogeneity of PNe with VLT FLAMES integral-field unit spectroscopy

Recent weak emission-line long-slit surveys and modelling studies of PNe have convincingly argued in favour of the existence of an unknown component in the planetary nebula plasma consisting of cold, hydrogen-deficient gas, as an explanation for the long-standing recombination-line versus forbidden-line temperature and abundance discrepancy problems. Here we describe the rationale and initial results from a detailed spectroscopic study of three Galactic PNe undertaken with the VLT FLAMES integral-field unit spectrograph, which advances our knowledge about the small-scale physical properties, chemical abundances and velocity structure of these objects across a two-dimensional field of view, and opens up for exploration an uncharted territory in the study and modelling of PNe and photoionized nebulae in general.

Towards a New Distance Scale and Luminosity Function for Nearby Planetary Nebulae

The local planetary nebula (PN) census is dominated by extremely evolved examples, and until recently, was incomplete. New discoveries from the AAO/UKST Hα Survey and SHASSA, have partially remedied this problem. In addition, we find that some currently accepted nearby PNe are in fact Stromgren spheres in the ISM ionised by a hot white dwarf. Distance estimates for a robust sample of calibrating PNe from the literature, plus new distances for a number of highly evolved PNe, have allowed a new Hα surface brightness – radius relationship to be devised as a useful distance indicator. It covers >6 dex in SB, and while the spread in SB is ∼1 dex at a given radius, optically thick (mainly bipolar and bipolar-core) PNe tend to populate the upper bound of the trend, while common-envelope PNe and very high-excitation PNe form a sharp lower boundary. Hence, distances can be estimated for all remaining local PNe, allowing the definition of a relatively complete census of PNe in the solar neighbourhood within 1.0 kpc. This provides a first look at the faint end of the PN luminosity function, and new estimates of the space density, scale height, total number, and birth rate of Galactic PNe.

3D Spectroscopy — a powerful new tool for PN research

Historically, technological progress with detectors and instrumentation has been essential for advances in any field of observational astronomy, e.g. the advent of CCDs being crucial for high dynamic range imaging and quantitative spectroscopy of galactic PNe, faint object spectrophotometry for the discovery of extragalactic PNe to distances as far as 100 Mpc, etc. The emerging technique of integral field (“3D”) spectroscopy, which is being applied quite successfully to extragalactic astronomy, has unfortunately hardly been used so far for the study of PNe. However, 3D spectroscopy has an enormous potential for various observational problems, ranging from high spatial resolution emission line mapping in different wavelengths simultaneously, over extremely high sensitivity spectroscopy of low surface brightness objects like e.g. PN haloes, to accurate 3D spectrophotometry of extragalactic PNe, and many others. As an attempt to encourage PN researchers to make better use of these new opportunities, the presently existing suite of 3D instruments on 4–8m class telescopes is reviewed, highlighting some examples of successful 3D observations for the study of PNe.

The abundance distributions of Galactic bulge and disc planetary nebulae

We present an abundance analysis of a sample of Galactic bulge planetary nebulae (GBPNe). The observational data set consists of spectra of 88 nebulae obtained with the FLAIR II multiobject spectrograph on the UK Schmidt Telescope, together with spectra of 42 nebulae obtained with the RGO Spectrograph on the Anglo-Australian Telescope. After selecting those for which reliable nebular electron temperatures could be derived, collisionally excited line abundances were derived for 45 GBPNe. These were then compared with similarly derived abundances for 54 Galactic disc PNe (GDPNe), taken from the work of Kingsburgh & Barlow. We find that within the errors the abundances have the same average values, essentially the same distributions – including that for the mass-sensitive N/O ratio – and show the same relationships. The width of the nitrogen distribution exceeds that arising from errors, which could be a consequence of the range of precursor masses. The ratio of Type-I to non-Type-I PNe in the bulge and disc samples is similar, 18 and 25 per cent respectively. For the GDPNe, we find larger N/H and N/O ratios for the small number of those with He/H > 0.14, compared with those with He/H < 0.14. For neither disc nor bulge sample is there any strong evidence for a depletion of oxygen for the higher-mass precursor stars (Type I PNe). We find no correlation between O/H and N/O or He/H. On the N/O to He/H plane, the bulge and disc PNe show a distribution whereby the low N/O values only occur for low He/H values, but at N/O > 0.25 the whole range of He/H values were sampled. The theoretical tracks to which we compare our data do not explain the PNe with low He/H abundance and high N/O ratio. Realistic uncertainties in collisionally excited lines (CEL) abundances for individual PNe are quite large, of the order of 40 per cent for oxygen. Large samples are therefore required to get good statistical accuracy. This is usually achieved by combining many studies, and so we have compared the results of a number of published studies with our own, to search for any systematic differences. The average abundances are found to be the same within the errors except for cases where the abundance derivation methods are dissimilar, where systematic differences can occur. The N/O ratio is especially sensitive to the details of the abundance derivations. Our bulge PN sample shows no evidence for either very-low-metallicity objects or for super-metal-rich objects – the implied mass and age distributions of the bulge PN precursor stars are indistinguishable within the observational errors from those in the local Galactic disc.

Version 2000 of the Catalogue of Galactic Planetary Nebulae

The "Catalogue of Galactic Planetary Nebulae (Version 2000)" appears in Abhandlungen aus der Hamburger Sternwarte, Band XII in the year 2001. It is a continuation of CGPN(1967) and contains 1510 objects classified as galactic PNe up to the end of 1999. The lists of possible pre-PNe and possible post-PNe are also given. The catalogue is restricted only to the data belonging to the location and identification of the objects. It gives identification charts of PNe discovered since 1965 (published in the supplements to CGPN) and those charts of objects discovered earlier, which have wrong or uncertain identification. The question "what is a planetary nebula" is discussed and the typical values of PNe and of their central stars are summarized. Short statistics about the discoveries of PNe are given. The catalogue is also available in the Centre de Données, Strasbourg and at Hamburg Observatory via internet.

The distance scale of planetary nebulae

By collecting distances from the literature, a set of 73 planetary nebulae with mean distances of high accuracy is derived. This sample is used for recalibration of the mass-radius relationship, used by many statistical distance methods. An attempt to correct for a statistical peculiarity, where errors in the distances influences the mass{radius relationship by increasing its slope, has been made for the rst time. Distances to PNe in the Galactic Bulge, derived by this new method as well as other statistical methods from the last decade, are then used for the evaluation of these methods as distance indicators. In order of achieving a Bulge sample that is free from outliers we derive new criteria for Bulge membership. These criteria are much more stringent than those used hitherto, in the sense that they also discriminate against background objects. By splitting our Bulge sample in two, one with optically thick (small) PNe and one with optically thin (large) PNe, we nd that our calibration is of higher accuracy than most other calibrations. Dierences between the two subsamples, we believe, are due to the incompleteness of the Bulge sample, as well as the dominance of optical diameters in the \thin sample and radio diameters in the \thick sample. Our nal conclusion is that statistical methods give distances that are at least as accurate as the ones obtained from many individual methods. Also, the \long distance scale of Galactic PNe is conrmed.

The Galactic disc distribution of planetary nebulae with warm dust emission features — I

We investigate the Galactic disc distribution of a sample of planetary nebulae characterized in terms of their mid-infrared spectral features. The total number of Galactic disc PNe with 8–13 μm spectra is brought up to 74 with the inclusion of 24 new objects, the spectra of which we present for the first time. 54 PNe have clearly identified warm dust emission features, and form a sample that we use to construct the distribution of the C/O chemical balance in Galactic disc PNe. The dust emission features complement the information on the progenitor masses brought by the gas-phase N/O ratios: PNe with unidentified infrared emission bands have the highest N/O ratios, while PNe with the silicate signature have either very high N enrichment or close to none. We find a trend for a decreasing proportion of O-rich PNe towards the third and fourth Galactic quadrants. Two independent distance scales confirm that the proportion of O-rich PNe decreases from per cent inside the solar circle to per cent outside. PNe with warm dust are also the youngest. PNe with no warm dust are uniformly distributed in C/O and N/O ratios, and do not appear to be confined to They also have higher 6-cm fluxes, as expected from more evolved PNe. We show that the IRAS fluxes are a good representation of the bolometric flux for compact and IR-bright PNe, which are probably optically thick. Selection of objects with should probe a good portion of the Galactic disc for these young, dense and compact nebulae, and the dominant selection effects are rooted in the PN catalogues.

The Galactic disc distribution of planetary nebulae with warm dust emission features -- II

We address the question of whether the distribution of warm-dust compositions in IR-bright Galactic disc PNe (Paper I, Casassus et al.) can be linked to the underlying stellar population. The PNe with warm dust emission represent a homogeneous population, which is presumably young and minimally affected by a possible dependence of PN lifetime on progenitor mass. The sample in Paper I thus allows testing of the predictions of single-star evolution, through a comparison with synthetic distributions and under the assumption that tip-of-the-AGB and PN statistics are similar. We construct a schematic model for AGB evolution (adapted from Groenewegen & de Jong), the free parameters of which are calibrated with the luminosity function (LF) of C stars in the LMC, the initial-final mass relation and the range of PN compositions. The observed metallicity gradient and distribution of star-forming regions with Galactocentric radius (Bronfman et al.) allow us to synthesize the Galactic disc PN progenitor population. We find that the fraction of O-rich PNe, is a tight constraint on AGB parameters. For our best model, a minimum PN progenitor mass predicts that about 50 per cent of all young PNe should be O-rich, compared with an observed fraction of 22 per cent; thus at a 2σ confidence level at 1σ). By contrast, current AGB models for single stars can account neither for the continuous range of N enrichment (Leisy & Dennefeld) nor for the observation that the majority of very C-rich PNe have Peimbert type I (Paper I). is thus an observable quantity much easier to model. The decrease in with Galactocentric radius, as reported in Paper I, is a strong property of the synthetic distribution, independent of Mmin. This trend reflects the sensitivity of the surface temperature of AGB stars and of the core mass at the first thermal pulse to the Galactic metallicity gradient.

Search and preliminary analysis of new Galactic PNe

In general, the methods for searching new PNe exploit one of their characteristics and typically introduce a bias in the sample extracted. It is therefore important to perform PN searches based on different selection criteria. Some years ago we started a new search for PN candidates on the plates of the Palomar Near Infrared Photographic Survey of the Galactic Plane. The selection criterion is based on the consideration that PNe have I(R) &gt; I(NIR) up to AV ∼ 10, whereas normal field stars have I(R) &lt; I(NIR). First the plates are examined directly using a binocular, with a medium magnification, searching for faint diffuse nebulosity. Hereafter the comparison between R and NIR images is used both to detect new compact PN candidate and to discard, among diffuse objects, reflection nebulae. Spectra and imaging of the new objects were obtained in dedicated program both at the ESO and Asiago Observatories. From a preliminary analysis of the data for the new PNe it appears that the sample contains objects with very different characteristics. They have different morphologies and spectral features, but in general only few of the new PNe have an IRAS counterpart and these show a small flux in the IR. In particular, in the IRAS color-color plot they do not seem confined to the area of the bona-fide PNe; this still preliminary evidence may indicate that our selection criteria is pointing to PNe which remain undiscovered using other methods.

On the distance to Galactic planetary nebulae

view Abstract Citations (46) References (60) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS On the Distance to Galactic Planetary Nebulae Zhang, C. Y. Abstract The distances are determined for 145 Galactic PNe using two methods. The distances for a sample of 131 PNe are determined using method A, based on the stellar mass and surface gravity. Method B, making use of the stellar luminosity, is applied to another sample of 61 PNe, of which 47 are in common with those in the sample for method A. The properties of the central star, such as the core mass, luminosity, and surface gravity, are inferred from the modeling of the distance-independent parameters. The results from the two methods used in this paper are consistent with each other. A distance of 11.3 kpc is found for K648 using method A of this work. This is in good agreement with the distance of 10 kpc of its hosting globular cluster M15. Publication: The Astrophysical Journal Pub Date: June 1993 DOI: 10.1086/172740 Bibcode: 1993ApJ...410..239Z Keywords: Milky Way Galaxy; Planetary Nebulae; Computational Astrophysics; Distance; Globular Clusters; Stellar Mass; Astrophysics; ISM: PLANETARY NEBULAE: GENERAL full text sources ADS | data products SIMBAD (131)

High-resolution imaging and the H-R diagram of Galactic bulge planetary nebulae

Images of six Galactic PNe in the forbidden O III 5007 line obtained with unprecedented resolution are compared here with those obtained at radio wavelengths. A self-consistent photoionization model obtained using optical spectrophotometry is used to derive chemical abundances and to place the central stars on the H-R diagram. The results are similar to those obtained with the classical Zanstra technique, but with the advantage that objects with high or low temperature central stars can be studied with equal ease. A wide range of metallicity is found which shows that the objects currently passing through the PN phase in the Galactic bulge were born both during and after the collapse of the Galaxy.