41 research outputs found
SMC SMP 24: A newly radio-detected planetary nebula in the small magellanic cloud
In this paper we report new radio-continuum detection of an extragalactic PN:
SMC SMP 24. We show the radio-continuum image of this PN and present the
measured radio data. The newly reduced radio observations are consistent with
the multi-wavelength data and derived parameters found in the literature. SMC
SMP 24 appear to be a young and compact PN, optically thick at frequencies
below 2 GHz.Comment: accepted for publication in Serbian Astronomical Journa
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 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 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
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
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
A search for candidate radio supernova remnants in the nearby irregular starburst galaxies NGC 4214 and NGC 4395
We present the results of a search for new candidate radio supernova remnants (SNRs) in the nearby starburst irregular galaxies NGC 4214 and NGC 4395 using archived radio observations made with the Very Large Array (VLA) at the wavelengths of 3.5 cm, 6 cm and 20 cm for NGC 4214 and 6 cm and 20 cm for NGC 4395. These observations were analyzed as part of our ongoing search for candidate radio SNRs in nearby galaxies: the goal of this search is to prepare a large sample of candidate radio SNRs for the purpose of a robust statistical study of the properties of these sources. Based on our analysis, we have confirmed the nonthermal nature of the discrete radio sources α and β in NGC 4214 and classify these sources as candidate radio SNRs based on their positional coincidences with HII regions in that galaxy. We have measured the flux densities of the two candidate radio SNRs at each wavelength and calculated corresponding spectral indices: we have also measured flux densities of two other discrete radio sources in these galaxies - ρ in NGC 4214 and #3 in NGC 4395 which we suspect to be additional candidate radio SNRs based on their positional coincidences with other HII regions in these galaxies. However, the radio data presently available for these sources cannot confirm such a classification and additional observations are needed. We have also calculated the radio luminosities Lradio at the wavelength of 20 cm for these two candidate radio SNRs as well as the corresponding values for the minimum total energy Emin required to power these radio sources via synchrotron emission and the corresponding magnetic field strength Bmin. We have compared our mean calculated values for these properties with the mean values for populations of candidate radio SNRs in other starburst galaxies: while the values for Lradio and Bmin are roughly comparable to the values seen in other starburst galaxies, the mean value for Emin is higher than the mean value of any other starburst galaxy. Finally, we include these two candidate radio SNRs in a discussion of the Σ − D relation for extragalactic candidate radio SNRs and find that these sources are located on the shallower end of the master Σ − D relation for all extragalactic SNRs as derived by Urošević et al.(2005).published_or_final_versio
A catalogue of integrated H\alpha\ fluxes for ~1100 Galactic planetary nebulae
We present new determinations of the integrated H\alpha\ flux for ~1100
Galactic planetary nebulae measured from the Southern H-Alpha Sky Survey Atlas
(SHASSA) and its northern counterpart, the Virginia Tech Spectral-Line Survey
(VTSS). This catalogue is the largest homogeneous database of its kind,
tripling the number of currently available measurements.Comment: 2 pages, 2 figures, presented at the IAU Symposium "Planetary
Nebulae: an Eye to the Future" No. 283, 201
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
Testing the binary hypothesis for the formation and shaping of planetary nebulae
There is no quantitative theory to explain why a high 80% of all planetary
nebulae are non-spherical. The Binary Hypothesis states that a companion to the
progenitor of a central star of 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
nebulae and to compare it with that of the main sequence population.
Preliminary results from photometric variability and the infrared excess
techniques indicate that the binary fraction of central stars of planetary
nebulae is higher than that of the main sequence, implying that PNe could
preferentially form via a binary channel. This article briefly reviews these
results and current studies aiming to refine the binary fraction.Comment: EUROWD12 Proceeding
XSHOOTER spectroscopy of the enigmatic planetary nebula Lin49 in the Small Magellanic Cloud
We performed a detailed spectroscopic analysis of the fullerene C60-containing planetary nebula (PN) Lin49 in the Small Magellanic Cloud (SMC) using XSHOOTER at the European Southern Observatory Very Large Telescope and the Spitzer/Infrared Spectrograph instruments. We derived nebular abundances for nine elements. We used TLUSTY to derive photospheric parameters for the central star. Lin49 is C-rich and metal-deficient PN (Z ∼ 0.0006). The nebular abundances are in good agreement with asymptotic giant branch nucleosynthesis models for stars with initial mass 1.25 M⊙ and metallicity Z = 0.001. Using the TLUSTY synthetic spectrum of the central star to define the heating and ionizing source, we constructed the photoionization model with CLOUDY that matches the observed spectral energy distribution (SED) and the line fluxes in the UV to far-IR wavelength ranges simultaneously. We could not fit the ∼1–5 μm SED using a model with 0.005–0.1-μm-sized graphite grains and a constant hydrogen density shell owing to the prominent near-IR excess, while at other wavelengths the model fits the observed values reasonably well. We argue that the near-IR excess might indicate either (1) the presence of very small particles in the form of small carbon clusters, small graphite sheets, or fullerene precursors, or (2) the presence of a high-density structure surrounding the central star. We found that SMC C60 PNe show a near-IR excess component to lesser or greater degree. This suggests that these C60 PNe might maintain a structure nearby their central star