2,150 research outputs found
A multiwavelength analysis of planetary nebulae in the Large Magellanic Cloud
This paper examines, compares and plots optical, near- and mid-infrared (MIR)
photometric data for 605 planetary nebulae (PNe) in the Large Magellanic Cloud
(LMC). With the aid of multi-wavelength surveys such as the Spitzer legacy
programme Surveying the Agents of a Galaxy's Evolution, the Two Micron All Sky
Survey and the Magellanic Cloud Photometric Survey, plots have been constructed
to expose the relative contributions from molecular hydrogen, polycyclic
aromatic hydrocarbons, forbidden emission lines, warm dust continuum and
stellar emission at various bands. Besides identifying trends, these plots have
helped to reveal PN mimics including six previously known PNe in the outer LMC
which are re-classied as other object types. Together with continuing follow-up
optical observations, the data have enabled a substantial reduction in the
number of PNe previously tagged as `likely' and `possible'. The total number of
LMC PNe is adjusted to 715 but with a greater degree of confidence in regard to
classification.
In each colour-colour plot, the more highly evolved LMC PNe are highlighted
for comparison with younger, brighter PNe. The faintest and most evolved PNe
typically cluster in areas of colour-colour space occupied by ordinary stars.
Possible reasons for the wide disparity in infrared colour-colour ratios, such
as evolution and dust composition, are presented for evaluation. A correlation
is found between the optical luminosity of PNe, emission-line ratios and the
MIR dust luminosity at various bands. Luminosity functions using the four
Infrared Array Camera and Multiband Imaging Photometer of Spitzer (MIPS) [24]
bands are directly compared, revealing an increasing accumulation of PNe within
the brightest two magnitudes at longer wavelengths. A correlation is also found
between the MIPS [24] band and the [O III] 5007 and H-beta fluxes.Comment: 25 pages, 18 figures, accepted in MNRA
Extending the RP survey to the outer LMC
We are extending our search for faint PNe in the LMC to include the outer 56
deg2 area not covered in the original UKST survey of the central 25 deg2
region. Candidate PNe have been selected using the Magellanic Cloud Emission
Line Survey (MCELS) and the first round of observations has yielded 93 new LMC
PNe while confirming the 102 previously known PNe in the outer LMC. We plan to
continue our spectroscopic object identification program until we cover all our
remaining candidates in the survey area. These observations, providing medium
and high resolution spectra from 3650 Ang to 6900 Ang will additionally be used
to measure fluxes for a series of research projects including luminosity
functions, abundances and LMC kinematics.Comment: 2 pages, 1 figure, IAU283 poster contributio
A New Population of Planetary Nebulae Discovered in the Large Magellanic Cloud (I): Preliminary Sample
We report our initial discovery of 73 new planetary nebulae (PNe) in the
Large Magellanic Cloud (LMC) following confirmatory 2dF spectroscopy on the
Anglo-Australian Telescope (AAT). Preliminary candidate sources come from a 10
per cent sub-area of our new deep, high resolution H-alpha map of the central
25 deg. square of the LMC obtained with the UK Schmidt Telescope (UKST). The
depth of the high resolution map was extended to Requiv~22 for H-alpha (4.5 x
10-17 ergs cm-2 s-1 Ang-1) by a process of multi-exposure median co-addition of
a dozen 2-hour H-alpha exposures. The resulting map is at least 1-magnitude
deeper than the best wide-field narrow-band LMC images currently available.
This depth, combined with our selection technique, has also led to the
discovery of extended AGB halos around many new and previously known LMC PNe
for the first time. Once complete, our new survey is expected to triple the LMC
PN population and have significant implications for the LMC PN luminosity
function, kinematics, abundance gradients chemical evolution and, via study of
the AGB halos, the initial to final mass relation for low to intermediate mass
stars.Comment: 14 pages, 21 figures (zipped). Accepted for publication in Mmonthly
Notices of the Royal Astronomical Societ
H-alpha Stacked Images Reveal Large Numbers of PNe in the LMC
Our new, deep, high resolution H-alpha and matching R-band UKST
multi-exposure stack of the central 25 sq. degrees of the LMC promises to
provide an unprecedented homogeneous sample of >1,000 new PNe. Our preliminary
2dF spectroscopy on the AAT has vindicated our selection process and confirmed
136 new PNe and 57 emission-line stars out of a sample of 263 candidate sources
within an initial 2.5 sq. deg. area. To date approximately one third of the
entire LMC has been scanned for candidates (~7.5 sq.deg.). More than 750 new
emission sources have been catalogued so far along with independent
re-identification of all known and possible PNe found from other surveys. Once
our image analysis is complete, we plan comprehensive spectroscopic follow-up
of the whole sample, not only to confirm our PN candidates but also to derive
nebula temperatures and densities which, with the aid of photoionization
modeling, will yield stellar parameters which are vital for constructing H-R
diagrams for these objects. A prime objective of the survey is to produce a
Luminosity Function which will be the most accurate and comprehensive ever
derived in terms of numbers, magnitude range and evolutionary state; offering
significant new insights into the LMC's evolutionary history. The observation
and measurement of our newly discovered AGB halos around 60% of these PN will
also assist in determining the initial- to final-mass ratios for this phase of
stellar evolution.Comment: 6 pages, 3 figures, LaTeX, to be published in Proceedings of the ESO
workshop on Planetary Nebulae beyond the Milky Way held at ESO, Garching, May
19-21, 200
A New Population of Planetary Nebulae Discovered in the Large Magellanic Cloud (IV): The Outer LMC
We have extended our PNe survey to the outer ~64deg^2 of the LMC using maps
from the Magellanic Cloud Emission Line Survey (MCELS) and the UK Schmidt
Telescope (UKST) H-alpha survey. Although the MCELS survey has poorer ~5
arcsecond resolution than both the UKST H-alpha survey and the original H-alpha
median stacked map in the LMC's central 25deg^2, it has the advantage of
additional narrow-band filters at H-alpha, [OIII] and [SII] providing improved
diagnostic capabilities. Using these data to uncover new emission line
candidates we have so far spectroscopically confirmed an extra 61 LMC PNe which
we present here for the first time. We have also independently recovered and
spectroscopically confirmed 107 of the 109 (98%) PNe that were previously known
to exist in the outer LMC. The majority of our newly discovered and previously
known PNe were confirmed using the AAOmega, multi-object fibre spectroscopy
system on the 3.9-m Anglo-Australian Telescope (AAT) and the 6dF multi-object
spectrograph on the UKST. These newly identified PNe were cross-checked against
extant multi-wavelength imaging surveys in the near and mid-infrared in
particular and against the latest emission-line ratio diagnostic plots for
improved confidence in PNe identification.Comment: 24 pages, 22 figures, accepted MNRAS main journal stt 160
The Unusual Variability of the Large Magellanic Cloud Planetary Nebula RPJ 053059-683542
We present images and light curves of the bipolar Planetary Nebula RPJ
053059-683542 that was discovered in the Reid-Parker AAO/UKST H-alpha survey of
the Large Magellanic Cloud (LMC). The emission from this object appears
entirely nebular, with the central star apparently obscured by a central band
of absorption that bisects the nebula. The light curves, which were derived
from images from the SuperMACHO project at CTIO, showed significant, spatially
resolved variability over the period 2002 January through 2005 December.
Remarkably, the emission from the two bright lobes of the nebula vary either
independently, or similarly but with a phase lag of at least one year. The
optical spectra show a low level of nebular excitation, and only modest N
enrichment. Infrared photometry from the 2MASS and SAGE surveys indicates the
presence of a significant quantity of dust. The available data imply that the
central star has a close binary companion, and that the system has undergone
some kind of outburst event that caused the nebular emission to first brighten
and then fade. Further monitoring, high-resolution imaging, and detailed IR
polarimetry and spectroscopy would uncover the nature of this nebula and the
unseen ionizing source.Comment: Accepted for ApJ Letters; 6 page
An Evaluation of the Excitation Class Parameter for the Central Stars of Planetary Nebulae
The three main methods currently in use for estimating the excitation class
of planetary nebulae (PNe) central stars are compared and evaluated using 586
newly discovered and previously known PNe in the Large Magellanic Cloud (LMC).
In order to achieve this we ran a series of evaluation tests using line ratios
derived from de-reddened, flux calibrated spectra. Pronounced differences
between the methods are exposed. Diagrams were created by comparing excitation
classes with H-beta line fluxes. The best methods are then compared to
published temperatures using the Zanstra method and assessed for their ability
to reflect central star effective temperatures and evolution. As a result we
call for a clarification of the term `excitation class' according to the
different input parameters used. The first method, which we refer to as Exneb
relies purely on the ratios of certain key emission lines. The second method,
which we refer to as Ex* includes modeling to create a continuous variable and,
for optically thick PNe in the Magellanic Clouds, is designed to relate more
closely to intrinsic stellar parameters. The third method, we refer to as Ex
[OIII]/H-beta since the [OIII]/H-beta ratio is used in isolation to other
temperature diagnostics. Each of these methods is shown to have serious
drawbacks when used as an indicator for central star temperature. Finally, we
suggest a new method (Exrho) for estimating excitation class incorporating both
the [OIII]/H-beta and the HeII4686 /H-beta ratios. Although any attempt to
provide accurate central star temperatures using the excitation class derived
from nebula lines will always be limited, we show that this new method provides
a substantial improvement over previous methods with better agreement to
temperatures derived through the Zanstra method.Comment: 14 pages, 18 figure. This peer reviewed paper has been accepted for
publication in PAS
Confirmation of New Planetary Nebulae in the Large Magellanic Cloud
We present Hubble Space Telescope (HST) images of new planetary nebulae (PNe)
that were discovered in the Reid-Parker AAO/UKST H-alpha survey of the Large
Magellanic Cloud. These serendipitous observations from various HST programs
yield independent confirmations of 6 PNe; one other detected nebula may also be
a PN, and one appears to be a region of diffuse emission. The high resolution
HST archival images enable us to determine the physical sizes, the nebular
morphology, and related features of these new PNe in detail for the first time.
In a few cases we were also able to identify the central star, which was
impossible with the lower resolution, wide-field discovery data. The
confirmation of faint, extended halos surrounding many PNe in the RP catalog
must await the acquisition of new deep, high-resolution, narrow-band imagery.Comment: 6 figures. To appear in PASP, 2007 Januar
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