1,093 research outputs found
A Proper Motion Survey for White Dwarfs with the Wide Field Planetary Camera 2
We have performed a search for halo white dwarfs as high proper motion
objects in a second epoch WFPC2 image of the Groth-Westphal strip. We identify
24 high proper motion objects with mu > 0.014 ''/yr. Five of these high proper
motion objects are identified as strong white dwarf candidates on the basis of
their position in a reduced proper motion diagram. We create a model of the
Milky Way thin disk, thick disk and stellar halo and find that this sample of
white dwarfs is clearly an excess above the < 2 detections expected from these
known stellar populations. The origin of the excess signal is less clear.
Possibly, the excess cannot be explained without invoking a fourth galactic
component: a white dwarf dark halo. We present a statistical separation of our
sample into the four components and estimate the corresponding local white
dwarf densities using only the directly observable variables, V, V-I, and mu.
For all Galactic models explored, our sample separates into about 3 disk white
dwarfs and 2 halo white dwarfs. However, the further subdivision into the thin
and thick disk and the stellar and dark halo, and the subsequent calculation of
the local densities are sensitive to the input parameters of our model for each
Galactic component. Using the lowest mean mass model for the dark halo we find
a 7% white dwarf halo and six times the canonical value for the thin disk white
dwarf density (at marginal statistical significance), but possible systematic
errors due to uncertainty in the model parameters likely dominate these
statistical error bars. The white dwarf halo can be reduced to around 1.5% of
the halo dark matter by changing the initial mass function slightly. The local
thin disk white dwarf density in our solution can be made consistent with the
canonical value by assuming a larger thin disk scaleheight of 500 pc.Comment: revised version, accepted by ApJ, results unchanged, discussion
expande
Optimal placement of a limited number of observations for period searches
Robotic telescopes present the opportunity for the sparse temporal placement
of observations when period searching. We address the best way to place a
limited number of observations to cover the dynamic range of frequencies
required by an observer. We show that an observation distribution geometrically
spaced in time can minimise aliasing effects arising from sparse sampling,
substantially improving signal detection quality. The base of the geometric
series is however a critical factor in the overall success of this strategy.
Further, we show that for such an optimal distribution observations may be
reordered, as long as the distribution of spacings is preserved, with almost no
loss of quality. This implies that optimal observing strategies can retain
significant flexibility in the face of scheduling constraints, by providing
scope for on-the-fly adaptation. Finally, we present optimal geometric
samplings for a wide range of common observing scenarios, with an emphasis on
practical application by the observer at the telescope. Such a sampling
represents the best practical empirical solution to the undersampling problem
that we are aware of. The technique has applications to robotic telescope and
satellite observing strategies, where target acquisition overheads mean that a
greater total target exposure time (and hence signal-to-noise) can often in
practice be achieved by limiting the number of observations.Comment: 8 pages with 16 figure
Cosmological Model Predictions for Weak Lensing: Linear and Nonlinear Regimes
Weak lensing by large scale structure induces correlated ellipticities in the
images of distant galaxies. The two-point correlation is determined by the
matter power spectrum along the line of sight. We use the fully nonlinear
evolution of the power spectrum to compute the predicted ellipticity
correlation. We present results for different measures of the second moment for
angular scales \theta \simeq 1'-3 degrees and for alternative normalizations of
the power spectrum, in order to explore the best strategy for constraining the
cosmological parameters. Normalizing to observed cluster abundance the rms
amplitude of ellipticity within a 15' radius is \simeq 0.01 z_s^{0.6}, almost
independent of the cosmological model, with z_s being the median redshift of
background galaxies.
Nonlinear effects in the evolution of the power spectrum significantly
enhance the ellipticity for \theta < 10' -- on 1' the rms ellipticity is \simeq
0.05, which is nearly twice the linear prediction. This enhancement means that
the signal to noise for the ellipticity is only weakly increasing with angle
for 2'< \theta < 2 degrees, unlike the expectation from linear theory that it
is strongly peaked on degree scales. The scaling with cosmological parameters
also changes due to nonlinear effects. By measuring the correlations on small
(nonlinear) and large (linear) angular scales, different cosmological
parameters can be independently constrained to obtain a model independent
estimate of both power spectrum amplitude and matter density \Omega_m.
Nonlinear effects also modify the probability distribution of the ellipticity.
Using second order perturbation theory we find that over most of the range of
interest there are significant deviations from a normal distribution.Comment: 38 pages, 11 figures included. Extended discussion of observational
prospects, matches accepted version to appear in Ap
Phase 1b/2a trial of the superoxide dismutase mimetic GC4419 to reduce chemoradiotherapy-induced oral mucositis in patients with oral cavity or oropharyngeal carcinoma
PURPOSE: To assess the safety of the superoxide dismutase mimetic GC4419 in combination with radiation and concurrent cisplatin for patients with oral cavity or oropharyngeal cancer (OCC) and to assess the potential of GC4419 to reduce severe oral mucositis (OM).
PATIENTS AND METHODS: Patients with locally advanced OCC treated with definitive or postoperative intensity modulated radiation therapy (IMRT) plus cisplatin received GC4419 by 60-minute intravenous infusion, ending \u3c60 minutes before IMRT, Monday through Friday for 3 to 7 weeks, in a dose and duration escalation study. Oral mucositis was assessed twice weekly during and weekly after IMRT.
RESULTS: A total of 46 patients received GC4419 in 11 separate dosing and duration cohorts: dose escalation occurred in 5 cohorts receiving 15 to 112 mg/d over 3 weeks (n=20), duration escalation in 3 cohorts receiving 112 mg/d over 4 to 6 weeks (n=12), and then 3 additional cohorts receiving 30 or 90 mg/d over 6 to 7 weeks (n=14). A maximum tolerated dose was not reached. One dose-limiting toxicity (grade 3 gastroenteritis and vomiting with hyponatremia) occurred in each of 2 separate cohorts at 112 mg. Nausea/vomiting and facial paresthesia during infusion seemed to be GC4419 dose-related. Severe OM occurred through 60 Gy in 4 of 14 patients (29%) dosed for 6 to 7 weeks, with median duration of only 2.5 days.
CONCLUSIONS: The safety of GC4419 concurrently with chemoradiation for OCC was acceptable. Toxicities included nausea/vomiting and paresthesia. Doses of 30 and 90 mg/d administered for 7 weeks were selected for further study. In an exploratory analysis, severe OM seemed less frequent and briefer than expected
MIPS: The Multiband Imaging Photometer for SIRTF
The Multiband Imaging Photometer for SIRTF (MIPS) is to be designed to reach as closely as possible the fundamental sensitivity and angular resolution limits for SIRTF over the 3 to 700μm spectral region. It will use high performance photoconductive detectors from 3 to 200μm with integrating JFET amplifiers. From 200 to 700μm, the MIPS will use a bolometer cooled by an adiabatic demagnetization refrigerator. Over much of its operating range, the MIPS will make possible observations at and beyond the conventional Rayleigh diffraction limit of angular resolution
Outcome of patients with advanced ovarian cancer who do not undergo debulking surgery: A single institution retrospective review
OBJECTIVE: To assess the outcome of patients with advanced ovarian cancer (OC) who were treated without surgery, having received upfront chemotherapy and no interval debulking surgery (IDS). METHODS: Retrospective analysis of medical and chemotherapy records of consecutive patients with OC between 2005 and 2013 at UCL Hospitals London, UK who received neoadjuvant chemotherapy (NACT) was then found to be unsuitable for IDS following review by the multidisciplinary team. RESULTS: Eighty-three patients (18%) out of 467 receiving NACT did not undergo IDS. Median age was 70years (range 33-88); out of these 83 patients, 43 (51.8%) presented with stage IV disease. Forty-three of these 83 patients received carboplatin and paclitaxel (CP) (51.8%) and 37 received carboplatin alone (C) (44.6%); 3 patients (3.6%) received other platinum-based combinations. Reasons for not proceeding to surgery were: poor response to chemotherapy after 3-4 cycles of NACT (61/83, 73.5%); comorbidities (12/83, 14.5%); patient decision (4/83, 4.8%). Six patients (7.2%) received 2 lines of chemotherapy. In a univariate analysis CP, age <70years, and absence of comorbidities were factors influencing OS. In a multivariate analysis only having received CP remained independently associated with OS (HR 0.49, 95% CI 0.29-0.84). CONCLUSIONS: Chemotherapy alone can provide reasonable disease control in patients unsuitable for IDS and CP should be used if possible
Dust in the Photospheric Environment: Unified Cloudy Models of M, L, and T Dwarfs
We address the problem of how dust forms and how it could be sustained in the
static photospheres of cool dwarfs for a long time. In the cool and dense gas,
dust forms easily at the condensation temperature, T_cond, and the dust can be
in detailed balance with the ambient gas so long as it remains smaller than the
critical radius, r_cr. However, dust will grow larger and segregate from the
gas when it will be larger than r_cr somewhere at the lower temperature, which
we refer to as the critical temperature, T_cr. Then, the large dust grains will
precipitate below the photosphere and only the small dust grains in the region
of T_cr < T < T_cond can be sustained in the photosphere. Thus a dust cloud is
formed. Incorporating the dust cloud, non-grey model photo- spheres in
radiative-convective equilibrium are extended to T_eff as low as 800K. Observed
colors and spectra of cool dwarfs can consistently be accounted for by a single
grid of our cloudy models. This fact in turn can be regarded as supporting
evidence for our basic assumption on the cloud formation.Comment: 50 pages with 14 postscript figures, to be published in Astrophys.
- …