491 research outputs found
Moduli Spaces of Parabolic Higgs Bundles and Parabolic K(D) Pairs over Smooth Curves: I
This paper concerns the moduli spaces of rank two parabolic Higgs bundles and
parabolic K(D) pairs over a smooth curve. Precisely which parabolic bundles
occur in stable K(D), pairs and stable Higgs bundles is determined. Using Morse
theory, the moduli space of parabolic Higgs bundles is shown to be a
non-compact, connected, simply connected manifold, and a computation of its
Poincar\'e polynomial is given.Comment: 25 pages, figure correcte
Rationality of Moduli Spaces of Parabolic Bundles
The moduli space of parabolic bundles with fixed determinant over a smooth
curve of genus greater than one is proved to be rational whenever one of the
multiplicities associated to the quasi-parabolic structure is equal to one. It
follows that if rank and degree are coprime, the moduli space of vector bundles
is stably rational, and the bound obtained on the level is strong enough to
conclude rationality in many cases.Comment: latex2
High Angular Resolution, Sensitive CS J=2-1 and J=3-2 Imaging of the Protostar L1551 NE: Evidence for Outflow-Triggered Star Formation ?
High angular resolution and sensitive aperture synthesis observations of CS
() and CS () emissions toward L1551 NE, the second brightest
protostar in the Taurus Molecular Cloud, made with the Nobeyama Millimeter
Array are presented. L1551 NE is categorized as a class 0 object deeply
embedded in the red-shifted outflow lobe of L1551 IRS 5. Previous studies of
the L1551 NE region in CS emission revealed the presence of shell-like
components open toward L1551 IRS 5, which seem to trace low-velocity shocks in
the swept-up shell driven by the outflow from L1551 IRS 5. In this study,
significant CS emission around L1551 NE was detected at the eastern tip of the
swept-up shell from = 5.3 km s to 10.1 km s, and
the total mass of the dense gas is estimated to be 0.18 0.02 .
Additionally, the following new structures were successfully revealed: a
compact disklike component with a size of 1000 AU just at L1551 NE,
an arc-shaped structure around L1551 NE, open toward L1551 NE, with a size of
AU, i.e., a bow shock, and a distinct velocity gradient of the
dense gas, i.e., deceleration along the outflow axis of L1551 IRS 5. These
features suggest that the CS emission traces the post-shocked region where the
dense gas associated with L1551 NE and the swept-up shell of the outflow from
L1551 IRS 5 interact. Since the age of L1551 NE is comparable to the timescale
of the interaction, it is plausible that the formation of L1551 NE was induced
by the outflow impact. The compact structure of L1551 NE with a tiny envelope
was also revealed, suggesting that the outer envelope of L1551 NE has been
blown off by the outflow from L1551 IRS 5.Comment: 29 pages, 12 figures, Accepted for Publication in the Astrophysical
Journa
Study of a Threshold Cherenkov Counter Based on Silica Aerogels with Low Refractive Indices
To identify and in the region of GeV/c, a
threshold Cherenkov counter equipped with silica aerogels has been
investigated. Silica aerogels with a low refractive index of 1.013 have been
successfully produced using a new technique. By making use of these aerogels as
radiators, we have constructed a Cherenkov counter and have checked its
properties in a test beam. The obtained results have demonstrated that our
aerogel was transparent enough to make up for loss of the Cherenkov photon
yield due to a low refractive index. Various configurations for the photon
collection system and some types of photomultipliers, such as the fine-mesh
type, for a read out were also tested. From these studies, our design of a
Cherenkov counter dedicated to separation up to a few GeV/c %in the
momentum range of GeV/c with an efficiency greater than \%
was considered.Comment: 21 pages, latex format (article), figures included, to be published
in Nucl. Instrm. Meth.
An Investigation of Be/X-ray Pulsars with OGLE-III Data
We have studied five seasons of OGLE-III data for eight SMC Be/X-ray pulsars
for which no other survey data were available. We have determined orbital
periods for four of these binary systems, one of which also shows nonradial
pulsations. Optical identification of SMC X-2 is reconsidered, but no periods
were found for either of the two possible candidates
Old and Young X-ray Point Source Populations in Nearby Galaxies
We analyzed 1441 Chandra X-ray point sources in 32 nearby galaxies. The total
point-source X-ray luminosity L_XP is well correlated with B, K, and FIR+UV
luminosities of spiral host galaxies, and with the B and K luminosities for
ellipticals. This suggests an intimate connection between L_XP and both the old
and young stellar populations, for which K and FIR+UV luminosities are proxies
for the galaxy mass M and star-formation rate SFR. We derive proportionality
constants 1.3E29 erg/s/Msol and 0.7E39 erg/s/(Msol/yr), which can be used to
estimate the old and young components from M and SFR, respectively. The
cumulative X-ray luminosity functions for the point sources have quite
different slopes for the spirals (gamma ~= 0.5-0.8) and ellipticals (gamma ~=
1.4), implying *the most luminous point sources dominate L_XP* for the spirals.
Most of the point sources have X-ray colors that are consistent with either
LMXBs or Ultraluminous X-ray sources (ULXs a.k.a. IXOs) and we rule out
classical HMXBs (e.g. neutron-star X-ray pulsars) as contributing much to L_XP.
Thus, for spirals, the ULXs dominate L_XP. We estimate that >~20% of all ULXs
found in spirals originate from the older (pop II) stellar populations,
indicating that many of the ULXs that have been found in spiral galaxies are in
fact pop II ULXs, like those in elliptical galaxies. The linear dependence of
L_XP on the SFR argues for either a steepening in the X-ray luminosity function
of the young (pop I) X-ray source population at L_X >~10^(38.5-39) erg/s, or a
decreasing efficiency for producing all types of young X-ray point sources as
the galaxy SFR increases.Comment: 33 pages AASTEX, ApJ accepted. Please download full version with
figures from http://www.pha.jhu.edu/~colbert/chps_accepted.p
Timing and spectral studies of the transient X-ray pulsar EXO 053109-6609.2 with ASCA and Beppo-SAX
We report timing and spectral properties of the transient Be X-ray pulsar EXO
053109--6609.2 studied using observations made with the ASCA and BeppoSAX
observatories. Though there must have been at least one spin-down episode of
the pulsar since its discovery, the new pulse period measurements show a
monotonic spin-up trend since 1996. The pulse profile is found to have marginal
energy dependence. There is also evidence for strong luminosity dependence of
the pulse profile, a single peaked profile at low luminosity that changes to a
double peaked profile at high luminosity. This suggests a change in the
accretion pattern at certain luminosity level. The X-ray spectrum is found to
consist of a simple power-law with photon index in the range of 0.4--0.8. At
high intensity level the spectrum also shows presence of weak iron emission
line.Comment: 12 pages, 8 figures, Accepted for publication in Ap
Discovery of a new pulsating X-ray source with a 1549.1-s period, AX J183220-0840
A new pulsating X-ray source, AX J183220-0840, with a 1549.1-s period was
discovered at R.A.= 18h32m20s and Dec.=-8d40'30'' (J2000,
uncertainty=0.6degree) during an ASCA observation on the Galactic plane. The
source was observed two times, in 1997 and in 1999. A phase-averaged X-ray flux
of 1.1E-11 ergs cm-2 s-1 and pulsation period of 1549.1+/-0.4 s were
consistently obtained from these two observations. The X-ray spectrum was
represented by a flat absorbed power-law with a photon-index of =~0.8 and an
absorption column density of =~1.3E22 cm-2. Also, a signature of iron K-shell
line emission with a centroid of 6.7 keV and an equivalent width of
approximately 450 eV was detected. From the pulsation period and the iron-line
feature, AX J183220-0840 is likely to be a magnetic white dwarf binary with a
complexly absorbed thermal spectrum with a temperature of about 10 keV.Comment: 13 pages, 4 figures, accepted for publication in ApJ Letter
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