29 research outputs found
First release of the IPHAS catalogue of new extended planetary nebulae
Date of Acceptance: 30/06/2014We present the first results of our search for new, extended planetary nebulae (PNe) based on careful, systematic, visual scrutiny of the imaging data from the Isaac Newton Telescope Photometric Ha Survey of the Northern Galactic plane (IPHAS). The newly uncovered PNe will help to improve the census of this important population of Galactic objects that serve as key windows into the late-stage evolution of low- to intermediate-mass stars. They will also facilitate study of the faint end of the ensemble Galactic PN luminosity function. The sensitivity and coverage of IPHAS allows PNe to be found in regions of greater extinction in the Galactic plane and/or those PNe in a more advanced evolutionary state and at larger distances compared to the general Galactic PN population. Using a set of newly revised optical diagnostic diagrams in combination with access to a powerful, new, multiwavelength imaging data base, we have identified 159 true, likely and possible PNe for this first catalogue release. The ability of IPHAS to unveil PNe at low Galactic latitudes and towards the Galactic Anticentre, compared to previous surveys, makes this survey an ideal tool to contribute to the improvement of our knowledge of the whole Galactic PN population.Peer reviewe
Multi-frequency Study of the LMC Supernova Remnant (SNR) B0513-692 and New SNR Candidate J051327-6911
We present a new multi-wavelength study of supernova remnant (SNR) B0513-692
in the Large Magellanic Cloud (LMC). The remnant also has a strong, superposed,
essentially unresolved, but unrelated radio source at its north-western edge,
J051324-691049. This is identified as a likely compact HII region based on
related optical imaging and spectroscopy. We use the Australia Telescope
Compact Array (ATCA) at 4790 and 8640 MHz to determine the large scale
morphology, spectral index and polarization characteristics of B0513-692 for
the first time. We detect a strongly polarized region (49%) in the remnant's
southern edge. Interestingly we also detect a small (~40 arcsec) moderately
bright, but distinct optical, circular shell in our Halpha imagery which is
adjacent to the compact HII region and just within the borders of the NE edge
of B0513-692. We suggest this is a separate new SNR candidate based on its
apparently distinct character in terms of optical morphology in 3 imaged
emission lines and indicative SNR optical spectroscopy (including enhanced
optical [SII] emission relative to Halpha).Comment: 12 page
Murchison Widefield Array and XMM-Newton observations of the Galactic supernova remnant G5.9+3.1
In this paper we discuss the radio continuum and X-ray properties of the
so-far poorly studied Galactic supernova remnant (SNR) G5.9+3.1. We present the
radio spectral energy distribution (SED) of the Galactic SNR G5.9+3.1 obtained
with the Murchison Widefield Array (MWA). Combining these new observations with
the surveys at other radio continuum frequencies, we discuss the integrated
radio continuum spectrum of this particular remnant. We have also analyzed an
archival XMM-Newton observation, which represents the first detection of X-ray
emission from this remnant. The SNR SED is very well explained by a simple
power-law relation. The synchrotron radio spectral index of G5.9+3.1, is
estimated to be 0.420.03 and the integrated flux density at 1GHz to be
around 2.7Jy. Furthermore, we propose that the identified point radio source,
located centrally inside the SNR shell, is most probably a compact remnant of
the supernova explosion. The shell-like X-ray morphology of G5.9+3.1 as
revealed by XMM-Newton broadly matches the spatial distribution of the radio
emission, where the radio-bright eastern and western rims are also readily
detected in the X-ray while the radio-weak northern and southern rims are weak
or absent in the X-ray. Extracted MOS1+MOS2+PN spectra from the whole SNR as
well as the north, east, and west rims of the SNR are fit successfully with an
optically thin thermal plasma model in collisional ionization equilibrium with
a column density N_H~0.80x cm and fitted temperatures spanning
the range kT~0.14-0.23keV for all of the regions. The derived electron number
densities n_e for the whole SNR and the rims are also roughly comparable
(ranging from ~ cm to ~ cm, where f
is the volume filling factor). We also estimate the swept-up mass of the X-ray
emitting plasma associated with G5.9+3.1 to be ~.Comment: Accepted for publication in A&
The Sigma - D relation for planetary nebulae
We present an extended analysis of the relation between radio surface
brightness and diameter -- the so-called relation for planetary
nebulae (PNe). We revise our previous derivation of the theoretical
relation for the evolution of bremsstrahlung surface brightness in order to
include the influence of the fast wind from the central star. Different
theoretical forms are derived: for the first and second
phases of evolution and for the final stage of
evolution. Also, we analyzed several different Galactic PN samples. All samples
are influenced by severe selection effects, but Malmquist bias seems to be less
influential here than in the supernova remnant (SNR) samples. We derived
empirical relations for 27 sample sets using 6 updated PN papers
from which an additional 21 new sets were extracted. Twenty four of these have
a trivial form of . However, we obtain one empirical
relation that may be useful for determining distances to PNe. This
relation is obtained by extracting a recent nearby (< 1 kpc) Galactic PN
sample.Comment: 12 pages, 3 tables, 4 figures. Accepted for publication in Astronomy
& Astrophysic
The MeerKAT 1.3 GHz Survey of the Small Magellanic Cloud
We present new radio continuum images and a source catalogue from the MeerKAT survey in the direction of the Small Magellanic Cloud (SMC). The observations, at a central frequency of 1.3 GHz across a bandwidth of 0.8 GHz, encompass a field of view ā¼7āĆ7ā and result in images with resolution of 8 arcsec. The median broad-band Stokes I image Root Mean Squared noise value is ā¼11 Ī¼Jy beamā1. The catalogue produced from these images contains 108,330 point sources and 517 compact extended sources. We also describe a UHF (544ā1088 MHz) single pointing observation. We report the detection of a new confirmed Supernova Remnant (SNR) (MCSNR J0100ā7211) with an X-ray magnetar at its centre and 10 new SNR candidates. This is in addition to the detection of 21 previously confirmed SNRs and two previously noted SNR candidates. Our new SNR candidates have typical surface brightness an order of magnitude below those previously known, and on the whole they are larger. The high sensitivity of the MeerKAT survey also enabled us to detect the bright end of the SMC Planetary Nebulae (PNe) sample ā point-like radio emission is associated with 38 of 102 optically known PNe, of which 19 are new detections. Lastly, we present the detection of three foreground radio stars amidst 11 circularly polarised sources, and a few examples of morphologically interesting background radio galaxies from which the radio ring galaxy ESO 029āG034 may represent a new type of radio object
Radio continuum sources behind the Large Magellanic Cloud
We present a comprehensive multifrequency catalogue of radio sources behind the Large Magellanic Cloud (LMC) between 0.2 and 20Ā GHz, gathered from a combination of new and legacy radio continuum surveys. This catalogue covers an area of ā¼144Ā deg2 at angular resolutions from 45Ā arcsec to ā¼3Ā arcmin. We find 6434 discrete radio sources in total, of which 3789 are detected at two or more radio frequencies. We estimate the median spectral index (Ī±; where Sv ā¼ Ī½Ī±) of Ī±Ā =Ā ā0.89 and mean of ā0.88Ā Ā±Ā 0.48 for 3636 sources detected exclusively at two frequencies (0.843 and 1.384Ā GHz) with similar resolution [full width at half-maximum (FWHM) ā¼40ā45Ā arcsec]. The large frequency range of the surveys makes it an effective tool to investigate Gigahertz Peak Spectrum (GPS), Compact Steep Spectrum (CSS), and Infrared Faint Radio Source (IFRS) populations within our sample. We find 10 GPS candidates with peak frequencies near 5Ā GHz, from which we estimate their linear size. 1866 sources from our catalogue are CSS candidates with Ī±Ā &lt; ā0.8. We found six candidates for High Frequency Peaker (HFP) sources, whose radio fluxes peak above 5Ā GHz and no sources with unconstrained peaks and Ī±Ā &gt; 0.5. We found optical counterparts for 343 of the radio continuum sources, of which 128 have a redshift measurement. Finally, we investigate the population of 123 IFRSs found in this study
The ASKAP-EMU Early Science Project: Radio Continuum Survey of the Small Magellanic Cloud
We present two new radio continuum images from the Australian Square Kilometre Array Pathfinder (ASKAP) survey in the direction of the Small Magellanic Cloud (SMC). These images are part of the Evolutionary Map of the Universe (EMU) Early Science Project (ESP) survey of the Small and Large Magellanic Clouds. The two new source lists produced from these images contain radio continuum sources observed at 960 MHz (4489 sources) and 1320 MHz (5954 sources) with a bandwidth of 192 MHz and beam sizes of 30.0āĆ30.0ā and 16.3āĆ15.1ā, respectively. The median Root Mean Squared (RMS) noise values are 186 Ī¼Jy beamā1 (960 MHz) and 165 Ī¼Jy beamā1 (1320 MHz). To create point source catalogues, we use these two source lists, together with the previously published Molonglo Observatory Synthesis Telescope (MOST) and the Australia Telescope Compact Array (ATCA) point source catalogues to estimate spectral indices for the whole population of radio point sources found in the survey region. Combining our ASKAP catalogues with these radio continuum surveys, we found 7736 point-like sources in common over an area of 30 deg2. In addition, we report the detection of two new, low surface brightness supernova remnant candidates in the SMC. The high sensitivity of the new ASKAP ESP survey also enabled us to detect the bright end of the SMC planetary nebula sample, with 22 out of 102 optically known planetary nebulae showing point-like radio continuum emission. Lastly, we present several morphologically interesting background radio galaxies
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 Lā, 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.4 page(s
A Contribution of Carrier Transport Processes to the Photoacoustic Effects in Doped Narrow Gap Semiconductors
The contribution of free carrier transport processes to the photoacoustic effect in doped AIVBVI compounds was investigated using the photoacoustic (PA) frequency modulated transmission technique as a valuable tool in the study of thermal and carrier transport processes in semiconductors. The PA signals were measured and analyzed as a function of the modulation frequency in a specially constructed PA cell. The multiparametric fitting procedure was used to obtain some thermal and electronic transport parameters of doped and pure AIVBVI compounds