A catalogue of integrated H-alpha fluxes for 1,258 Galactic planetary nebulae

We present a catalogue of new integrated H-alpha fluxes for 1258 Galactic planetary nebulae (PNe), with the majority, totalling 1234, measured from the Southern H-Alpha Sky Survey Atlas (SHASSA) and/or the Virginia Tech Spectral-line Survey (VTSS). Aperture photometry on the continuum-subtracted digital images was performed to extract H-alpha + [NII] fluxes in the case of SHASSA, and H-alpha fluxes from VTSS. The [NII] contribution was then deconvolved from the SHASSA flux using spectrophotometric data taken from the literature or derived by us. Comparison with previous work shows that the flux scale presented here has no significant zero-point error. Our catalogue is the largest compilation of homogeneously derived PN fluxes in any waveband yet measured, and will be an important legacy and fresh benchmark for the community. Amongst its many applications, it can be used to determine statistical distances for these PNe, determine new absolute magnitudes for delineating the faint end of the PN luminosity function, provide baseline data for photoionization and hydrodynamical modelling, and allow better estimates of Zanstra temperatures for PN central stars with accurate optical photometry. We also provide total H-alpha fluxes for another 75 objects which were formerly classified as PNe, as well as independent reddening determinations for ~270 PNe, derived from a comparison of our H-alpha data with the best literature H-beta fluxes. In an appendix, we list corrected H-alpha fluxes for 49 PNe taken from the literature, including 24 PNe not detected on SHASSA or VTSS, re-calibrated to a common zero-point.Comment: 49 pages, 7 figures, 10 tables, to appear in MNRAS. This version includes full-length tables 1 and

The H\alpha\ surface brightness - radius relation: a robust statistical distance indicator for planetary nebulae

Measuring the distances to Galactic planetary nebulae (PNe) has been an intractable problem for many decades. We have now established a robust optical statistical distance indicator, the H$\alpha$ surface brightness- radius or S-r relation, which addresses this problem. We developed this relation from a critically evaluated sample of primary calibrating PNe. The robust nature of the method results from our revised calibrating distances with significantly reduced systematic uncertainties, and the recent availability of high-quality data, including updated nebular diameters and integrated H$\alpha$ fluxes. The S-r technique is simple in its application, requiring only an angular size, an integrated H\alpha\ flux, and the reddening to the PN. From these quantities, an intrinsic radius is calculated, which when combined with the angular size, yields the distance directly. Furthermore, we have found that optically thick PNe tend to populate the upper bound of the trend, while optically-thin PNe fall along the lower boundary in the S-r plane. This enables sub-trends to be developed which offer even better precision in the determination of distances, as good as 18 per cent in the case of optically-thin, high-excitation PNe. This is significantly better than any previous statistical indicator. We use this technique to create a catalogue of statistical distances for over 1100 Galactic PNe, the largest such compilation in the literature to date. Finally, in an appendix, we investigate both a set of transitional PNe and a range of PN mimics in the S-r plane, to demonstrate its use as a diagnostic tool. Interestingly, stellar ejecta around massive stars plot on a tight locus in S-r space with the potential to act as a separate distance indicator for these objects.Comment: 49 pages, 17 tables, 8 figures. Published in MNRAS; supplementary tables are included at end of this manuscrip

Planetary nebulae and their mimics: the MASH-MEN Project

The total number of true, likely and possible planetary nebulae (PN) now known in the Milky Way is about 3000, approximately twice the number known a decade ago. The new discoveries are a legacy of the recent availability of wide-field, narrowband imaging surveys, primarily in the light of H-alpha. The two most important are the AAO/UKST SuperCOSMOS H-alpha survey - SHS and the Isaac Newton photometric H-alpha survey - IPHAS, which are responsible for most of the new discoveries. A serious problem with previous PN catalogues is that several different kinds of astrophysical objects are able to mimic PN in some of their observed properties leading to significant contamination. These objects include H II regions and Stromgren zones around young O/B stars, reflection nebulae, Wolf-Rayet ejecta, supernova remnants, Herbig-Haro objects, young stellar objects, B[e] stars, symbiotic stars and outflows, late-type stars, cataclysmic variables, low redshift emission-line galaxies, and even image/detector flaws. PN catalogues such as the Macquarie/AAO/Strasbourg H-alpha Planetary Nebula catalogue (MASH) have been carefully vetted to remove these mimics using the wealth of new wide-field multi-wavelength data and our 100% follow-up spectroscopy to produce a compilation of new PN discoveries of high purity. During this process significant numbers of PN mimics have been identified. The aim of this project is to compile these MASH rejects into a catalogue of Miscellaneous Emission Nebulae (MEN) and to highlight the most unusual and interesting examples. A new global analysis of these MEN objects is underway before publishing the MEN catalogue online categorizing objects by type together with their spectra and multi-wavelength images.Comment: 2 pages, IAU 283: An Eye To The Future proceeding

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.Comment: 13 figures and 7 tables, accepted for publication in MNRA

New light on Galactic post-asymptotic giant branch stars. I. First distance catalogue

We have commenced a detailed analysis of the known sample of Galactic post-asymptotic giant branch (PAGB) objects compiled in the Toru\'n catalogue of Szczerba et al., and present, for the first time, homogeneously derived distance determinations for the 209 likely and 87 possible catalogued PAGB stars from that compilation. Knowing distances are essential in determining meaningful physical characteristics for these sources and this has been difficult to determine for most objects previously. The distances were determined by modelling their spectral energy distributions (SED) with multiple black-body curves, and integrating under the overall fit to determine the total distance-dependent flux. This method works because the luminosity of these central stars is very nearly constant from the tip of the AGB phase to the beginning of the white-dwarf cooling track. This then enables us to use a standard-candle luminosity to estimate the SED distances. For Galactic thin disk PAGB objects, we use three luminosity bins based on typical observational characteristics, ranging between 3500 and 12000 L_sun. We further adopt a default luminosity of 1700 L_sun for all halo PAGB objects. We have also applied the above technique to a further sample of 69 related nebulae not in the current edition of the Toru\'n catalogue. In a follow-up paper we will estimate distances to the subset of RV Tauri variables using empirical period-luminosity relations, and to the R\,CrB stars, allowing a population comparison of these objects with the other subclasses of PAGB stars for the first time.Comment: 24 pages, 8 tables, 4 figures. Submitted to MNRAS. Appendix B containing full list of SED figures excluded in this versio

The planetary nebula Abell 48 and its [WN4] central star

We have conducted a multi-wavelength study of the planetary nebula Abell 48 and give a revised classification of its nucleus as a hydrogen-deficient star of type [WN4]. The surrounding nebula has a morphology typical of PNe and importantly, is not enriched in nitrogen, and thus not the 'peeled atmosphere' of a massive star. Indeed, no WN4 star is known to be surrounded by such a compact nebula. The ionized mass of the nebula is also a powerful discriminant between the low-mass PN and high-mass WR ejecta interpretations. The ionized mass would be impossibly high if a distance corresponding to a Pop I star was adopted, but at a distance of 2 kpc, the mass is quite typical of moderately evolved PNe. At this distance, the ionizing star then has a luminosity of ~5000 Lsolar, again rather typical for a PN central star. We give a brief discussion of the implications of this discovery for the late-stage evolution of intermediate-mass stars.Comment: EUROWD12 Proceeding

Flux calibration of the AAO/UKST SuperCOSMOS H-alpha Survey

The AAO/UKST SuperCOSMOS H$\alpha$ Survey (SHS) was, when completed in 2003, a powerful addition to extant wide-field surveys. The combination of areal coverage, spatial resolution and sensitivity in a narrow imaging band, still marks it out today as an excellent resource for the astronomical community. The 233 separate fields are available online in digital form, with each field covering 25 square degrees. The SHS has been the motivation for equivalent surveys in the north, and new digital H$\alpha$ surveys now beginning in the south such as VPHAS+. It has been the foundation of many important discovery projects with the Macquarie/AAO/Strasbourg H$\alpha$ planetary nebula project being a particularly successful example. However, the full potential of the SHS has been hampered by lack of a clear route to acceptable flux calibration from the base photographic data. We have determined the calibration factors for 170 individual SHS fields, and present a direct pathway to the measurement of integrated H$\alpha$ fluxes and surface brightnesses for resolved nebulae detected in the SHS. We also include a catalogue of integrated H$\alpha$ fluxes for $>$100 planetary and other nebulae measured from the SHS, and use these data to show that fluxes, accurate to $\pm$ 0.10 - 0.14 dex ($\sim$25-35 per cent), can be obtained from these fields. For the remaining 63 fields, a mean calibration factor of 12.0 counts pix$^{-1}$ R$^{-1}$ can be used, allowing the determination of reasonable integrated fluxes accurate to better than $\pm$0.2 dex ($\sim$50 per cent). We outline the procedures involved and the caveats that need to be appreciated in achieving such flux measurements. This paper forms a handy reference source that will significantly increase the scientific utility of the SHS.Comment: 14 pages, 12 figures, 2 tables (plus 7 pp. of supplementary online information). Version to appear in MNRA

Kathryns Wheel: A spectacular galaxy collision discovered in the Galactic neighbourhood

We report the discovery of the closest collisional ring galaxy to the Milky Way. Such rare systems occur due to "bulls-eye" encounters between two reasonably matched galaxies. The recessional velocity of about 840 km/s is low enough that it was detected in the AAO/UKST Survey for Galactic H$\alpha$ emission. The distance is only 10.0 Mpc and the main galaxy shows a full ring of star forming knots, 6.1 kpc in diameter surrounding a quiescent disk. The smaller assumed "bullet" galaxy also shows vigorous star formation. The spectacular nature of the object had been overlooked because of its location in the Galactic plane and proximity to a bright star and even though it is the 60$^{\rm th}$ brightest galaxy in the HI Parkes All Sky Survey (HIPASS) HI survey. The overall system has a physical size of $\sim$15 kpc, a total mass of $M_\ast = 6.6\times 10^9$ M$_\odot$ (stars + HI), a metallicity of [O/H]$\sim-0.4$, and a star formation rate of 0.2-0.5 M$_\odot$\,yr$^{-1}$, making it a Magellanic-type system. Collisional ring galaxies therefore extend to much lower galaxy masses than commonly assumed. We derive a space density for such systems of $7 \times 10^{-5}\,\rm Mpc^{-3}$, an order of magnitude higher than previously estimated. This suggests Kathryn's Wheel is the nearest such system. We present discovery images, CTIO 4-m telescope narrow-band follow-up images and spectroscopy for selected emission components. Given its proximity and modest extinction along the line of sight, this spectacular system provides an ideal target for future high spatial resolution studies of such systems and for direct detection of its stellar populations.Comment: 18 pages, 12 figures, accepted for publication in MNRA

Discovery of planetary nebulae using predictive mid-infrared diagnostics

We demonstrate a newly developed mid-infrared planetary nebula (PN) selection technique. It is designed to enable efficient searches for obscured, previously unknown, PN candidates present in the photometric source catalogues of Galactic plane MIR sky surveys. Such selection is now possible via new, sensitive, high-to-medium resolution, MIR satellite surveys such as those from the Spitzer Space Telescope and the all-sky Wide-Field Infrared Survey Explorer (WISE) satellite missions. MIR selection is based on how different colour-colour planes isolate zones (sometimes overlapping) that are predominately occupied by different astrophysical object types. These techniques depend on the reliability of the available MIR source photometry. In this pilot study we concentrate on MIR point source detections and show that it is dangerous to take the MIR GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) photometry from Spitzer for each candidate at face value without examining the actual MIR image data. About half of our selected sources are spurious detections due to the applied source detection algorithms being affected by complex MIR backgrounds and the de-blending of diffraction spikes around bright MIR point sources into point sources themselves. Nevertheless, once this additional visual diagnostic checking is performed, valuable MIR selected PN candidates are uncovered. Four turned out to have faint, compact, optical counterparts in our H-alpha survey data missed in previous optical searches. We confirm all of these as true PNe via our follow-up optical spectroscopy. This lends weight to the veracity of our MIR technique. It demonstrates sufficient robustness that high-confidence samples of new Galactic PN candidates can be extracted from these MIR surveys without confirmatory optical spectroscopy and imaging. This is problematic or impossible when the extinction is large.Comment: 14 pages, 7 figures, 7 tables; accepted for publication in MNRA

Planetary nebulae : getting closer to an unbiased binary fraction

Why 80% of planetary nebulae are not spherical is not yet understood. The Binary Hypothesis states that a companion to the progenitor of the central star of a planetary nebula is required to shape the nebula and even for a planetary nebula to be formed at all. A way to test this hypothesis is to estimate the binary fraction of central stars of planetary nebula and to compare it with the main sequence population. Preliminary results from photometric variability and infrared excess techniques indicate that the binary fraction of central stars of planetary nebulae is higher than that of the putative main sequence progenitor population, implying that PNe could be preferentially formed via a binary channel. This article briefly reviews these results and future studies aiming to refine the binary fraction.Comment: SF2A 2012 proceeding