A pilot study of the radio‐continuum emission from MASH planetary nebulae

We present a new planetary nebula, first identified in images from the Australia Telescope Compact Array, although not recognized at that time. Recent observations with the Spitzer Space Telescope during the GLIMPSE Legacy program have rediscovered the object. The high-resolution radio and infrared images enable the identification of the central star or its wind, the recognition of the radio emission as thermal, and the probable presence of polycyclic aromatic hydrocarbons in and around the source. These lead to the conclusion that G313.3+00.3 is a planetary nebula. This object is of particular interest because it was discovered solely through radio and mid-infrared imaging, without any optical (or near-infrared) confirmation, and acts as a proof of concept for the discovery of many more highly extinguished planetary nebulae. G313.3+00.3 is well resolved by both the instruments with which it was identified and suffers extreme reddening due to its location in the Scutum-Crux spiral arm.

Maser emission of SiO, H$_2$O, and OH is widespread in asymptotic giant branch (AGB) stars with oxygen- (O-) rich envelopes. This emission quickly disappears during the post-AGB phase and is extremely rare in planetary nebulae (PNe). So far, only eight PNe have been confirmed to show OH and/or H$_2$O maser emission, and none have ever been found to show SiO maser emission. We intend to obtain the first detection of a SiO maser from a PN. Such a detection would provide us with a useful tool to probe mass loss in PNe at a scales of a few AU from the central star, much shorter than the scales traced by H$_2$ or OH masers. We compiled two different samples. The first one comprises all known PNe with confirmed OH and/or H$_2$O maser emission, as well as two candidate PNe showing OH masers. For the second sample, we compiled single-dish SiO maser detections in the literature, and compared them with catalogs of PNe and radio continuum emission (which could trace photoionized gas in PNe). We identified five targets (either PN or radio continuum sources) within the beam of the single-dish SiO maser observations. We then carried out interferometric observations of both samples with the Australia Telescope Compact Array, to confirm the spatial association between continuum and SiO maser emission. We find no SiO maser emission associated with any confirmed or candidate PN. In all targets, except IRAS 17390$-$3014, there is no spatial coincidence between SiO masers and radio continuum emission. While in IRAS 17390$-$3014 we cannot completely rule out a possible association, it is unlikely that the radio continuum emission arises from a PN. The absence of SiO maser emission in PNe showing OH or H$_2$O masers is of special interest, since thermal SiO emission has been reported in at least one of these targets, indicating that SiO molecules can be present in the gas phase. Since some maser-emitting PNe show evidence of having O-rich outer envelopes, and carbon- (C-) rich central stars and inner envelopes, we speculate that SiO abundance could be very low in the central regions where physical conditions are optimal for maser pumping, and C-bearing molecules may be dominant in the gas phase at those locations.

We observed 64 newly identified galactic bulge planetary nebulae in the radio continuum at 3 and 6 cm with the Australia Telescope Compact Array. We present their radio images, positions, flux densities, and angular sizes. The survey appears to have detected a larger ratio of more extended planetary nebulae with low surface brightness than in previous surveys. We calculated their distances according to Van de Steene & Zijlstra (1995). We find that most of the new sample is located on the near side around the galactic center and closer in than the previously known bulge PNe. Based on H-alpha images and spectroscopic data, we calculated the total H-alpha flux. We compare this flux value with the radio flux density and derive the extinction. We confirm that the distribution of the extinction values around the galactic center rises toward the center, as expected.

We present polarimetric observations of the 4 ground-state transitions of OH, toward a sample of maser-emitting planetary nebulae (PNe) using the Australia Telescope Compact Array. This sample includes confirmed OH-emitting PNe, confirmed and candidate H2O-maser-emitting PNe. Polarimetric observations provide information related to the magnetic field of these sources. Maser-emitting PNe are very young PNe and magnetic fields are a key ingredient in the early evolution and shaping process of PNe. Our preliminary results suggest that magnetic field strengths may change very rapidly in young PNe.

We report the results of a Hubble Space Telescope snapshot survey aimed at finding resolved binary companions of the central stars of Galactic planetary nebulae (PNe). Using the the Wide Field and Planetary Camera and Wide Field Planetary Camera 2, we searched the fields of 113 PNe for stars whose close proximity to the central star suggests a physical association. In all, we find 10 binary nuclei that are very likely to be physically associated and another six that are possible binary associations. By correcting for interstellar extinction and placing the central stars' companions on the main sequence (or, in one case, on the white dwarf cooling curve), we derive distances to the objects, and thereby significantly increase the number of PNe with reliable distances. Comparison of our derived distances with those obtained from various statistical methods shows that all of the latter have systematically overestimated the distances, by factors ranging up to a factor of 2 or more. We show that this error is most likely due to the fact that the properties of our PNe with binary nuclei are systematically different from those of PNe used heretofore to calibrate statistical methods. Specifically, our PNe tend to have lower surface brightnesses at the same physical radius than the traditional calibration objects. This difference may arise from a selection effect: the PNe in our survey are typically nearby, old nebulae, whereas most of the objects that calibrate statistical techniques are low-latitude, high surface brightness, and more distant nebulae. As a result, the statistical methods that seem to work well with samples of distant PNe, for example, those in the Galactic bulge or external galaxies, may not be applicable to the more diverse population of local PNe. Our distance determinations could be improved with better knowledge of the metallicities of the individual nebulae and central stars, measurements of proper motions and radial velocities for additional candidate companions, and deeper HST images of several of our new binary nuclei.

We report on OH maser emission toward G336.644−0.695 (IRAS 16333−4807), which is a H2O maser-emitting Planetary Nebula (PN). We have detected 1612, 1667, and 1720 MHz OH masers at two epochs using the Australia Telescope Compact Array, hereby confirming it as the seventh known case of an OH-maser-emitting PN. This is only the second known PN showing 1720 MHz OH masers after K 3−35 and the only evolved stellar object with 1720 MHz OH masers as the strongest transition. This PN is one of a group of very young PNe. The 1612 MHz and 1667 MHz masers are at a similar velocity to the 22 GHz H2O masers, whereas the 1720 MHz masers show a variable spectrum, with several components spread over a higher velocity range (up to 36 km s−1). We also detect Zeeman splitting in the 1720 MHz transition at two epochs (with field strengths of ∼2 to ∼10 mG), which suggests the OH emission at 1720 MHz is formed in a magnetized environment. These 1720 MHz OH masers may trace short-lived equatorial ejections during the formation of the PN.

We present simultaneous observations of H$_2$O maser emission and radio\ncontinuum at 1.3 cm carried out with the Australia Telescope Compact Array\ntowards two sources, IRAS 16333$-$4807 and IRAS 12405$-$6219, catalogued as\nplanetary nebula (PN) candidates, and where single-dish detections of H$_2$O\nmasers have been previously reported. Our goal was to unambiguously confirm the\nspatial association of the H$_2$O masers with these two PN candidates. We\ndetected and mapped H$_2$O maser emission in both fields, but only in IRAS\n16333$-$4807 the maser emission is spatially associated with the radio\ncontinuum emission. The properties of IRAS 16333$-$4807 provide strong support\nfor the PN nature of the object, hereby confirming it as the fifth known case\nof a H$_2$O maser-emitting PN. This source is bipolar, like the other four\nknown H$_2$O maser-emitting PNe, indicating that these sources might pertain to\na usual, but short phase in the evolution of bipolar PNe. In IRAS 12405$-$6219,\nthe H$_2$O maser and radio continuum emission are not associated with each\nother and, in addition, the available data indicate that this source is an H II\nregion rather than a PN.\n

We present a catalogue of a large sample of extended radio sources in the SCORPIO field, observed and resolved by the Australia Telescope Compact Array. SCORPIO, a pathfinder project for addressing the early operations of the Australia SKA Pathfinder, is a survey of ∼5 square degrees between 1.4 and 3.1 GHz, centered at l = 343.5○, b = 0.75○ and with an angular resolution of about 10 arcsec. It is aimed at understanding the scientific and technical challenges to be faced by future Galactic surveys. With a mean sensitivity around $100\ \mu \mathrm{Jy\ beam}^{-1}$ and the possibility to recover angular scales at least up to 4 arcmin, we extracted 99 extended sources, 35 of them detected for the first time. Among the 64 known sources 55 had at least a tentative classification in literature. Studying the radio morphology and comparing the radio emission with infrared we propose as candidates 6 new H ii regions, 2 new planetary nebulae, 2 new luminous blue variable or Wolf–Rayet stars and 3 new supernova remnants. This study provides an overview of the potentiality of future radio surveys in terms of Galactic source extraction and characterization and a discussion on the difficulty to reduce and analyze interferometric data on the Galactic plane.

January 2016 – title page.%%%%The Academic Senate of Macquarie University granted this degree in 2015, but the date 2016 appears on the title page, the verso of the title page and the spine.%%%%%%%%%%%%1. Planetary nebulas - history and overview – 2. The planetary nebula luminosity function – 3. New bulge PNs – 4. Duplicate objects – 5. Other observations – 6. New bulge PNLF – 7. Results and discussion – A. Spectral features – B. Galactic bulge mosaic II survey fields – C. Galactic bulge PNs – D. Publications – References.%%%%A new population of Galactic bulge planetary nebulas is presented. Nebula candidates were discovered by systematically reviewing archival [OIII] on/off band survey imaging of the central -5⁰ ≤ l ≤ 5⁰, -5⁰ ≤ b ≤ 5⁰ region around the Galactic centre. An image segmentation and interleaving scheme was developed to facilitate this review. The resultant candidates (> 200) were then double checked against complementary archival Hα sky survey data to screen for obvious planetary nebula (PN) mimics or spurious image artefacts.%%%%Confirmatory spectroscopy of the PN candidates was pursued with thin slit, fibre multiobject and wide field spectrographs. Custom software was built to streamline interfacing with third-party spectroscopic management tools and a parallel greedy set cover algorithm implemented for efficient field selection in constrained multi-object observations.%%%%The combined imaging and spectroscopic evidence yielded true (4), probable (31) and possible (83) PNs toward the bulge. Secondary discoveries such as new PN mimics and late type stars were by-products of the confirmatory spectroscopy. Instances of literature PN duplication encountered during the investigation were noticed and documented.%%%%Spectral analysis of new PNs, including those obtained with a new optimised sky subtraction technique devised and demonstrated here, provided diagnostic data allowing radial velocity and Balmer decrement determination. Using a combined diameter and radial velocity criterion, bona fide bulge PNs were distinguished from new foreground PNs. Where Balmer decrements were available for new bulge PNs, differential aperture photometry was used to provide a modest data increment to Galactic bulge planetary nebula luminosity function (PNLF).%%%%The PNLF was revised with data from some new bulge PNs, but more significantly, by a series of corrections to the data derived from previously known bulge PNs (~225), such as improved filter transmission effects, statistically justified binning and application of a uniform bulge-relevant extinction law. The result was the most rigorous bulge PNLF to date. An improvement on the legacy PNLF, the revised PNLF exhibited a form inconsistent with typical extragalactic examples, an expected result of the unusual extinction correction method used to address bulge-specific observational limitations. Issues restricting the accuracy of the bulge PNLF were identified. Until those restrictions are ameliorated, the utility of the PNLF in aiding physical understanding…

Eight planetary nebulae (PNe) are known to emit OH and/or H2O masers, but there is no report of an SiO maser in this type of objects. We present a search for SiO masers in 16 confirmed and candidate PNe, carried out with the Australia Telescope Compact Array. We found no evidence of association between SiO masers and PNe in our data. Previous detections of thermal SiO emission in PNe show that these molecules can be present in gas phase in this type of objects, but it is not yet clear whether they can be found where the physical conditions are appropriate for maser pumping. We suggest that the best candidates for a new search would be PNe showing high-velocity outflows.

We report 11 new radio continuum measurements of established planetary nebulae (PNe) in the Small Magellanic Cloud (SMC) that we observed at 5.5 and 9 GHz with the Australia Telescope Compact Array (ATCA). These new radio detections are PNe with catalogued names: SMP SMC 2, SMP SMC 3, SMP SMC 5, SMP SMC 8, SMP SMC 13, SMP SMC 14, SMP SMC 19, MGPN SMC 8, SMP SMC 22, SMP SMC 26 and SMP SMC 27. We supplement our data with available high-resolution radio observations from MeerKAT and construct the spectral energy distribution (SED) in the radio regime for each PN. We determine the angular diameters of four of the eleven PNe from radio flux density alone using SED modelling, which are compared to the corresponding Hubble Space Telescope (HST) optical diameters. Our results are in good agreement with the optically-derived angular diameters from independent HST observations. We plot our new diameter estimates against a larger sample of Galactic PNe and compare diameters obtained via the SED method to those found in the literature. Our sample diameters, when compared to the Galactic PNe, suggest that the angular diameter measurement methods are comparable independent of the distance.

The Red MSX Source (RMS) survey (Hoare et al. 2005) is a multi-wavelength programme of follow-up observations designed to distinguish between genuine massive young stellar objects (MYSOs) and other embedded or dusty objects, such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe). We have identified nearly 2000 MYSOs candidates by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. There are several other types of embedded or dust enshrouded objects that have similar colours as MYSOs and contaminate our sample. Two sources of contamination are from UCHII regions and PNe, both of which can be identified from the radio emission emitted by their ionised nebulae. In order to identify UCHII regions and PNe that contaminate our sample we have conducted high resolution radio continuum observations at 3.6 and 6 cm of all southern MYSOs candidates (235° < l < 350°) using the Australia Telescope Compact Array (ATCA).

Context.The Red MSX Source (RMS) survey is a multi-wavelength programme of follow-up observations designed to distinguish between genuine massive young stellar objects (MYSOs) and other embedded or dusty objects, such as ultra compact (UC) HII regions, evolved stars and planetary nebulae (PNe). We have identified nearly 2000 MYSOs candidates by comparing the colours of MSX and 2MASS point sources to those of known MYSOs. Aims.There are several other types of embedded or dust enshrouded objects that have similar colours as MYSOs and contaminate our sample. Two sources of contamination are from UCHII regions and PNe, both of which can be identified from the radio emission emitted by their ionised nebulae. Methods.In order to identify UCHII regions and PNe that contaminate our sample we have conducted high resolution radio continuum observations at 3.6 and 6 cm of all southern MYSOs candidates ( $235\degr< l < 350\degr$) using the Australia Telescope Compact Array (ATCA). These observations have a spatial resolution of ~1-2´´ and typical image rms noise values of ~0.3 mJy - sensitive enough to detect a HII region powered by B0.5 star at the far side of the Galaxy. Results.Of the 826 RMS sources observed we found 199 to be associated with radio emission, ~25% of the sample. The Galactic distribution, morphologies and spectral indices of the radio sources associated with the RMS sources are consistent with these sources being UCHII regions. Importantly, the 627 RMS sources for which no radio emission was detected are still potential MYSOs. In addition to the 802 RMS fields observed we present observations of a further 190 fields. These observations were made towards MSX sources that passed cuts in earlier versions of the survey, but were later excluded.

We present 11 spectra from 12 candidate radio sources co-identified with known planetary nebulae (PNe) in the Large Magellanic Cloud (LMC). Originally found in Australia Telescope Compact Array (ATCA) LMC surveys at 1.4, 4.8 and 8.64 GHz and confirmed by new high resolution ATCA images at 6 and 3 cm (4' /2' ), these complement data recently presented for candidate radio PNe in the Small Magellanic Cloud (SMC). Their spectra were obtained using the Radcliff 1.9-meter telescope in Sutherland (South Africa). All of the optical PNe and radio candidates are within 2' and may represent a population of selected radio bright sample only. Nebular ionized masses of these objects are estimated to be as high as 1.8 Mfi, supporting the idea that massive PNe progenitor central stars lose much of their mass in the asymptotic giant branch (AGB) phase or prior. We also identify a sub-population (33%) of radio PNe candidates with prominent ionized iron emission lines.

We present preliminary results from spectral observations of four (4) candidate radio sources co-identified with known planetary nebulae (PNe) in the Small Magellanic Cloud (SMC). These were made using the Radcliffe 1.9-meter telescope in Sutherland, South Africa. These radio PNe were originally found in Australia Telescope Compact Array (ATCA) surveys of the SMC at 1.42 and 2.37 GHz, and were further confirmed by new high resolution ATCA images at 6 and 3 cm (400 /200 ). Optical PNe and radio candidates are within 200 and may represent a sub- population of selected radio bright objects. Nebular ionized masses of these objects may be 2.6 Mo or greater, supporting the existence of PNe progenitor central stars with masses up to 8 Mo.