3,227 research outputs found
SPITZER SAGE Observations of Large Magellanic Cloud Planetary Nebulae
We present IRAC and MIPS images and photometry of a sample of previously
known planetary nebulae (PNe) from the SAGE survey of the Large Magellanic
Cloud (LMC) performed with the Spitzer Space Telescope. Of the 233 known PNe in
the survey field, 185 objects were detected in at least two of the IRAC bands,
and 161 detected in the MIPS 24 micron images. Color-color and color-magnitude
diagrams are presented using several combinations of IRAC, MIPS, and 2MASS
magnitudes. The location of an individual PN in the color-color diagrams is
seen to depend on the relative contributions of the spectral components which
include molecular hydrogen, polycyclic aromatic hydrocarbons (PAHs), infrared
forbidden line emission from the ionized gas, warm dust continuum, and emission
directly from the central star. The sample of LMC PNe is compared to a number
of Galactic PNe and found to not significantly differ in their position in
color-color space. We also explore the potential value of IR PNe luminosity
functions (LFs) in the LMC. IRAC LFs appear to follow the same functional form
as the well-established [O III] LFs although there are several PNe with
observed IR magnitudes brighter than the cut-offs in these LFs.Comment: 18 pages, 10 figures, 3 tables, to be published in the Astronomical
Journal. Additional online data available at
http://www.cfa.harvard.edu/irac/publications
The binary fraction of planetary nebula central stars I. A high-precision, I-band excess search
In an attempt to determine how many planetary nebulae derive from binary
interactions, we have started a project to measure their unbiased binary
fraction. This number, when compared to the binary fraction of the presumed
parent population can give a first handle on the origin of planetary nebulae.
By detecting 27 bona fide central stars in the I band we have found that 30% of
our sample have an I band excess between one and a few sigmas, possibly
denoting companions brighter than M3-4V and with separations smaller than
approximately 1000 AU. By accounting for the undetectable companions, we
determine a de-biased binary fraction of 67-78% for all companions at all
separations. We compare this number to a main sequence binary fraction of
(50+/-4)% determined for spectral types F6V-G2V, appropriate if the progenitors
of today's PN central star population is indeed the F6V-G2V stars. The error on
our estimate could be between 10 and 30%. We conclude that the central star
binary fraction may be larger than expected from the putative parent
population. Using the more sensitive J band of a subset of 11 central stars,
the binary fraction is 54% for companions brighter than approximately M5-6V and
with separations smaller than about 900 AU. De-biassing this number we obtain a
binary fraction of 100-107%. The two numbers should be the same and the
discrepancy is likely due to small number statistics.
We also present an accurately vetted compilation of observed main sequence
star magnitudes, colours and masses, which can serve as a reference for future
studies. We also present synthetic colours of hot stars as a function of
temperature (20-170kK) and gravity (log g= 6-8) for Solar and PG1159
compositions.Comment: 22 pages, 6 figures, 12 tables, accepted by MNRA
The Planetary Nebulae Luminosity Function and distances to Virgo, Hydra I and Coma clusters
The luminosity function of planetary nebulae populations in galaxies within
10-15 Mpc distance has a cut-off at bright magnitudes and a functional form
that is observed to be invariant in different galaxy morphological types. Thus
it is used as a secondary distance indicator in both early and late-type
galaxies. Recent deep surveys of planetary nebulae populations in brightest
cluster galaxies (BCGs) seem to indicate that their luminosity functions
deviate from those observed in the nearby galaxies. We discuss the evidence for
such deviations in Virgo, and indicate which physical mechanisms may alter the
evolution of a planetary nebula envelope and its central star in the halo of
BCGs. We then discuss preliminary results for distances for the Virgo, Hydra I
and Coma clusters based on the observed planetary nebulae luminosity functions.Comment: 5 pages, one figure. To appear on the Proceedings of the IAU Symp.
289 "Advancing the physics of cosmic distances
Planetary Nebulae and their parent stellar populations. Tracing the mass assembly of M87 and Intracluster light in the Virgo cluster core
The diffuse extended outer regions of galaxies are hard to study because they
are faint, with typical surface brightness of 1% of the dark night sky. We can
tackle this problem by using resolved star tracers which remain visible at
large distances from the galaxy centres. This article describes the use of
Planetary Nebulae as tracers and the calibration of their properties as
indicators of the star formation history, mean age and metallicity of the
parent stars in the Milky Way and Local Group galaxies . We then report on the
results from a deep, extended, planetary nebulae survey in a 0.5 sqdeg region
centred on the brightest cluster galaxy NGC 4486 (M87) in the Virgo cluster
core, carried out with SuprimeCam@Subaru and FLAMES-GIRAFFE@VLT. Two PN
populations are identified out to 150 kpc distance from the centre of M87. One
population is associated with the M87 halo and the second one with the
intracluster light in the Virgo cluster core. They have different line-of-sight
velocity and spatial distributions, as well as different planetary nebulae
specific frequencies and luminosity functions. The intracluster planetary
nebulae in the surveyed region correspond to a luminosity of four times the
luminosity of the Large Magellanic Cloud. The M87 halo planetary nebulae trace
an older, more metal-rich, parent stellar population. A substructure detected
in the projected phase-space of the line-of-sight velocity vs. major axis
distance for the M87 halo planetary nebulae provides evidence for the recent
accretion event of a satellite galaxy with luminosity twice that of M33. The
satellite stars were tidally stripped about 1 Gyr ago, and reached apocenter at
a major axis distance of 60-90 kpc from the centre of M87. The M87 halo is
still growing significantly at the distances where the substructure is
detected.Comment: 8 pages, 3 figures, To appear in the proceedings of the IAU Symposium
317 "The General Assembly of Galaxy Halos: Structure, Origin and Evolution'',
A. Bragaglia, M. Arnaboldi, M. Rejkuba & D. Romano, ed
Intracluster stars in the Virgo cluster core
We have investigated the properties of the diffuse light in the Virgo cluster
core region, based on the detection of intracluster planetary nebulae (PNe) in
four fields. We eliminate the bias from misclassified faint continuum objects,
using improved Monte Carlo simulations, and the contaminations by high redshift
Ly galaxies, using the Ly luminosity function in blank fields.
Recent spectroscopic observations confirm that our photometric PN samples are
well-understood. We find that the diffuse stellar population in the Virgo core
region is inhomogeneous on scales of 30'-90': there exist significant
field-to-field variations in the number density of PNe and the inferred amount
of intracluster light, with some empty fields, some fields dominated by
extended Virgo galaxy halos, and some fields dominated by the true intracluster
component. There is no clear trend with distance from M87. The mean surface
luminosity density, its rms variation, and the mean surface brightness of
diffuse light in our 4 fields are L
arcmin, L arcmin, and
mag arcsec respectively. Our results indicate that
the Virgo cluster is a dynamically young environment, and that the intracluster
component is associated at least partially with local physical processes like
galaxy interactions or harassment. We also argue, based on kinematic evidence,
that the so-called 'over-luminous' PNe in the halo of M84 are dynamically
associated with this galaxy, and must thus be brighter than and part of a
different stellar population from the normal PN population in elliptical
galaxies.Comment: 31 pages, 6 figure. In press on the Astronomical Journa
Diffuse Light in Hickson Compact Groups: The Dynamically Young System HCG 44
Compact groups are associations of a few galaxies in which the environment
plays an important role in galaxy evolution. The low group velocity dispersion
favors tidal interactions and mergers, which may bring stars from galaxies to
the diffuse intragroup light. Numerical simulations of galaxy clusters in
hierarchical cosmologies show that the amount of the diffuse light increases
with the dynamical evolution of the cluster. We search for diffuse light in the
galaxy group HCG 44 in order to determine its luminosity and luminosity
fraction. Combining with literature data, we aim to constrain the dynamical
status of Hickson compact groups. We use Intra Group planetary nebulae (IGPNe)
as tracers of diffuse light. These are detected by the so-called on band-off
band technique. We found 12 emission line objects in HCG 44, none of them
associated with the galaxies of the group. 6/12 emission line objects are
consistent with being IGPNe in HCG 44, but are also consistent with being
Ly background galaxies. Thus we derive an upper limit to the diffuse
light fraction in HCG 44 of 4.7%. We find a correlation between the fraction of
elliptical galaxies and the amount of diffuse light in Hickson compact groups.
Those with large fraction of diffuse light are those with large fractions in
number and luminosity of E/S0 galaxies. We propose an evolutionary sequence for
Hickson compact groups in which the amount of diffuse light increases with the
dynamical evolution of the group.Comment: 9 pages, 4 figures, accepted for publication at A&
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