216 research outputs found
Searching for binary central stars of planetary nebulae with Kepler
The Kepler Observatory offers unprecedented photometric precision (<1 mmag)
and cadence for monitoring the central stars of planetary nebulae, allowing the
detection of tiny periodic light curve variations, a possible signature of
binarity. With this precision free from the observational gaps dictated by
weather and lunar cycles, we are able to detect companions at much larger
separations and with much smaller radii than ever before. We have been awarded
observing time to obtain light-curves of the central stars of the six confirmed
and possible planetary nebulae in the Kepler field, including the newly
discovered object Kn 61, at cadences of both 30 min and 1 min. Of these six
objects, we could confirm for three a periodic variability consistent with
binarity. Two others are variables, but the initial data set presents only weak
periodicities. For the central star of Kn 61, Kepler data will be available in
the near future
Searching for Faint Planetary Nebulae Using the Digital Sky Survey
Recent Halpha surveys such as SHS and IPHAS have improved the completeness of
the Galactic planetary nebula (PN) census. We now know of ~3,000 PNe in the
Galaxy, but this is far short of most estimates, typically ~25,000 or more for
the total population. The size of the Galactic PN population is required to
derive an accurate estimate of the chemical enrichment rates of nitrogen,
carbon, and helium. In addition, a high PN count (~20,000) is strong evidence
that most 1-8 Msun main sequence stars will go through a PN phase, while a low
count (<10,000) argues that special conditions (e.g., a close binary
interaction) are required to form a PN. We describe a technique for finding
hundreds more PNe using the existing data collections of the digital sky
surveys, thereby improving the census of Galactic PNe.Comment: 11 pages, 7 figures, accepted for publication in the Publications of
the Astronomical Society of Australia (PASA), full resolution paper available
at http://www.wiyn.org/jacoby_pasa.pd
A New Approach to Non-Commutative U(N) Gauge Fields
Based on the recently introduced model of arXiv:0912.2634 for non-commutative
U(1) gauge fields, a generalized version of that action for U(N) gauge fields
is put forward. In this approach to non-commutative gauge field theories, UV/IR
mixing effects are circumvented by introducing additional 'soft breaking' terms
in the action which implement an IR damping mechanism. The techniques used are
similar to those of the well-known Gribov-Zwanziger approach to QCD.Comment: 11 pages; v2 minor correction
A SINFONI view of flies in the Spiderweb: a galaxy cluster in the making
The environment of the high-z radio galaxy PKS 1138-262 at z~2.2 is a prime
example of a forming galaxy cluster. We use deep SINFONI data to perform a
detailed study of the kinematics of the galaxies within 60 kpc of the radio
core and we link this to the kinematics of the protocluster on the megaparsec
scale. Identification of optical emission lines shows that 11 galaxies are at
the redshift of the protocluster. The density of line emitters is more than an
order of magnitude higher in the core of the protocluster than the larger scale
environment. This implies a matter overdensity in the core of delta_m~70 which
is similar to the outskirts of local galaxy clusters. The velocity distribution
of the confirmed satellite galaxies shows a broad, double-peaked velocity
structure with sigma=1360+/-206 km/s. A similar broad, double-peaked
distribution was found in a previous study targeting the large scale
protocluster structure, indicating that a common process is acting on both
small and large scales. Including all spectroscopically confirmed protocluster
galaxies, a velocity dispersion of 1013+/-87 km/s is found. We show that the
protocluster has likely decoupled from the Hubble flow and is a dynamically
evolved structure. Comparison to the Millenium simulation indicates that the
protocluster velocity distribution is consistent with that of the most massive
haloes at z~2, but we rule out that the protocluster is a fully virialized
structure based on dynamical arguments and its X-ray luminosity. Comparison to
merging haloes in the Millennium simulation shows that the structure as
observed in and around the Spiderweb galaxy is best interpreted as being the
result of a merger between two massive haloes. We propose that this merger can
result in an increase in star formation and AGN activity in the protocluster
core and is possibly an important stage in the evolution of massive cD
galaxies.Comment: 12 pages, 7 figures. Accepted for publication in MNRA
Commutative limit of a renormalizable noncommutative model
Renormalizable models on Moyal space have been obtained by
modifying the commutative propagator. But these models have a divergent "naive"
commutative limit. We explain here how to obtain a coherent such commutative
limit for a recently proposed translation-invariant model. The mechanism relies
on the analysis of the uv/ir mixing in general Feynman graphs.Comment: 11 pages, 3 figures, minor misprints being correcte
Globules and pillars seen in the [CII] 158 micron line with SOFIA
Molecular globules and pillars are spectacular features, found only in the
interface region between a molecular cloud and an HII-region. Impacting
Far-ultraviolet (FUV) radiation creates photon dominated regions (PDRs) on
their surfaces that can be traced by typical cooling lines. With the GREAT
receiver onboard SOFIA we mapped and spectrally resolved the [CII] 158 micron
atomic fine-structure line and the highly excited 12CO J=11-10 molecular line
from three objects in Cygnus X (a pillar, a globule, and a strong IRAS source).
We focus here on the globule and compare our data with existing Spitzer data
and recent Herschel Open-Time PACS data. Extended [CII] emission and more
compact CO-emission was found in the globule. We ascribe this emission mainly
to an internal PDR, created by a possibly embedded star-cluster with at least
one early B-star. However, external PDR emission caused by the excitation by
the Cyg OB2 association cannot be fully excluded. The velocity-resolved [CII]
emission traces the emission of PDR surfaces, possible rotation of the globule,
and high-velocity outflowing gas. The globule shows a velocity shift of ~2 km/s
with respect to the expanding HII-region, which can be understood as the
residual turbulence of the molecular cloud from which the globule arose. This
scenario is compatible with recent numerical simulations that emphazise the
effect of turbulence. It is remarkable that an isolated globule shows these
strong dynamical features traced by the [CII]-line, but it demands more
observational studies to verify if there is indeed an embedded cluster of
B-stars.Comment: Letter accepted by A&A (SOFIA special issue
The impact of a major cluster merger on galaxy evolution in MACS\,J0025.4-1225
We present results of an extensive morphological, spectroscopic, and
photometric study of the galaxy population of MACS J0025.41225 (z=0.586), a
major cluster merger with clear segregation of dark and luminous matter, to
examine the impact of mergers on galaxy evolution. Based on 436 galaxy spectra
obtained with Keck DEIMOS, we identified 212 cluster members within 4 Mpc of
the cluster centre, and classified them using three spectroscopic types; we
find 111 absorption-line, 90 emission-line (including 23 e(a) and 11 e(b)), and
6 E+A galaxies. The fraction of absorption(emission)-line galaxies is a
monotonically increasing(decreasing) function of both projected galaxy density
and radial distance to the cluster center. More importantly, the 6 observed E+A
cluster members are all located between the dark-matter peaks of the cluster
and within ~0.3Mpc radius of the X-ray flux peak, unlike the E+A galaxies in
other intermediate-redshift clusters which are usually found to avoid the core
region. In addition, we use Hubble Space Telescope imaging to classify cluster
members according to morphological type. We find the global fraction of spiral
and lenticular galaxies in MACS J0025 to be among the highest observed to date
in clusters at z>0.5. The observed E+A galaxies are found to be of lenticular
type with Sersic indices of ~2, boosting the local fraction of S0 to 70 per
cent between the dark-matter peaks. Combing the results of our analysis of the
spatial distribution, morphology, and spectroscopic features of the galaxy
population, we propose that the starburst phase of these E+A galaxies was both
initiated and terminated during the first core-passage about 0.5--1Gyr ago, and
that their morphology has already been transformed into S0 due to ram pressure
and/or tidal forces near the cluster core. By contrast, ongoing starbursts are
observed predominantly in infalling galaxies, and thus appears to be unrelated
to the cluster merger.Comment: 18 pages, 17 figures, accepted by MNRA
NTT follow-up observations of star cluster candidates from the FSR catalogue
We are conducting a large program to classify newly discovered Milky Way star
cluster candidates from the list of Froebrich, Scholz & Raftery (2007). Here we
present deep NIR follow-up observations from ESO/NTT of 14 star cluster
candidates. We show that the combined analysis of star density maps and
colour-colour/magnitude diagrams derived from deep near-infrared imaging is a
viable tool to reliably classify new stellar clusters. This allowed us to
identify two young clusters with massive stars, three intermediate age open
clusters, and two globular cluster candidates among our targets. The remaining
seven objects are unlikely to be stellar clusters. Among them is the object
FSR1767 which has previously been identified as a globular cluster using 2MASS
data by Bonatto et al. (2007). Our new analysis shows that FSR1767 is not a
star cluster. We also summarise the currently available follow-up analysis of
the FSR candidates and conclude that this catalogue may contain a large number
of new stellar clusters, probably dominated by old open clusters.Comment: 24pages, 3tables, 40figures, Accepted for publication by MNRAS, A
version with higher resolution figures can be found at
http://astro.kent.ac.uk/~df
Translation-invariant models for non-commutative gauge fields
Motivated by the recent construction of a translation-invariant
renormalizable non-commutative model for a scalar field (see arXiv:0802.0791
[math-ph]), we introduce models for non-commutative U(1) gauge fields along the
same lines. More precisely, we include some extra terms into the action with
the aim of getting rid of the UV/IR mixing.Comment: 9 page
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