904 research outputs found
Defending Daubert: It\u27s Time to Amend Federal Rule of Evidence 702
The 2000 amendments to Rule 702 sought to resolve the debate that had emerged in the courts in the 1990s over the proper meaning of Daubert by codifying the rigorous and structured approach to expert admissibility announced in the Daubert trilogy. Fifteen years later, however, the amendments have only partially accomplished this objective. Many courts continue to resist the judiciary’s proper gatekeeping role, either by ignoring Rule 702’s mandate altogether or by aggressively reinterpreting the Rule’s provisions.
Informed by this additional history of recalcitrance, the time has come for the Judicial Conference to return to the drafting table and finish the job it began in 2000. Rule 702 should be amended to secure the promise of Daubert and effectively protect future litigants and juries from the powerful and quite misleading impact of unreliable expert testimony
CCD BV survey of 42 open clusters
We present results of a photometric survey whose aim was to derive structural
and astrophysical parameters for 42 open clusters. While our sample is
definitively not representative of the total open cluster sample in the Galaxy,
it does cover a wide range of cluster parameters and is uniform enough to allow
for simple statistical considerations. BV wide-field CCD photometry was
obtained for open clusters for which photometric, structural, and dynamical
evolution parameters were determined. The limiting and core radii were
determined by analyzing radial density profiles. The ages, reddenings, and
distances were obtained from the solar metallicity isochrone fitting. The mass
function was used to study the dynamical state of the systems, mass segregation
effect and to estimate the total mass and number of cluster members. This study
reports on the first determination of basic parameters for 11 out of 42
observed open clusters. The angular sizes for the majority of the observed
clusters appear to be several times larger than the catalogue data indicate.
The core and limiting cluster radii are correlated and the latter parameter is
3.2 times larger on average. The limiting radius increases with the cluster's
mass, and both the limiting and core radii decrease in the course of dynamical
evolution. For dynamically not advanced clusters, the mass function slope is
similar to the universal IMF slope. For more evolved systems, the effect of
evaporation of low-mass members is clearly visible. The initial mass
segregation is present in all the observed young clusters, whereas the
dynamical mass segregation appears in clusters older than about log(age)=8.
Low-mass stars are deficient in the cores of clusters older than log(age)=8.5
and not younger than one relaxation time.Comment: 13 pages, 8 figure
The Second-Generation Guide Star Catalog: Description and Properties
The GSC-II is an all-sky database of objects derived from the uncompressed
DSS that the STScI has created from the Palomar and UK Schmidt survey plates
and made available to the community. Like its predecessor (GSC-I), the GSC-II
was primarily created to provide guide star information and observation
planning support for HST. This version, however, is already employed at some of
the ground-based new-technology telescopes such as GEMINI, VLT, and TNG, and
will also be used to provide support for the JWST and Gaia space missions as
well as LAMOST, one of the major ongoing scientific projects in China. Two
catalogs have already been extracted from the GSC-II database and released to
the astronomical community. A magnitude-limited (R=18.0) version, GSC2.2, was
distributed soon after its production in 2001, while the GSC2.3 release has
been available for general access since 2007.
The GSC2.3 catalog described in this paper contains astrometry, photometry,
and classification for 945,592,683 objects down to the magnitude limit of the
plates. Positions are tied to the ICRS; for stellar sources, the all-sky
average absolute error per coordinate ranges from 0.2" to 0.28" depending on
magnitude. When dealing with extended objects, astrometric errors are 20% worse
in the case of galaxies and approximately a factor of 2 worse for blended
images. Stellar photometry is determined to 0.13-0.22 mag as a function of
magnitude and photographic passbands (B,R,I). Outside of the galactic plane,
stellar classification is reliable to at least 90% confidence for magnitudes
brighter than R=19.5, and the catalog is complete to R=20.Comment: 52 pages, 33 figures, to be published in AJ August 200
New X-ray observations of the Geminga pulsar wind nebula
Previous observations of the middle-aged pulsar Geminga with XMM-Newton and
Chandra have shown an unusual pulsar wind nebula (PWN), with a 20" long central
(axial) tail directed opposite to the pulsar's proper motion and two 2' long,
bent lateral (outer) tails. Here we report on a deeper (78 ks) Chandra
observation and a few additional XMM-Newton observations of the Geminga PWN.
The new Chandra observation has shown that the axial tail, which includes up to
three brighter blobs, extends at least 50" (i.e., 0.06 d_{250} pc) from the
pulsar. It also allowed us to image the patchy outer tails and the emission in
the immediate vicinity of the pulsar with high resolution. The PWN luminosity,
L_{0.3-8 keV} ~ 3\times 10^{29} d_{250}^2 erg/s, is lower than the pulsar's
magnetospheric luminosity by a factor of 10. The spectra of the PWN elements
are rather hard (photon index ~ 1). Comparing the two Chandra images, we found
evidence of PWN variability, including possible motion of the blobs along the
axial tail. The X-ray PWN is the synchrotron radiation from relativistic
particles of the pulsar wind; its morphology is connected with the supersonic
motion of Geminga. We speculate that the outer tails are either (1) a sky
projection of the limb-brightened boundary of a shell formed in the region of
contact discontinuity, where the wind bulk flow is decelerated by shear
instability, or (2) polar outflows from the pulsar bent by the ram pressure
from the ISM. In the former case, the axial tail may be a jet emanating along
the pulsar's spin axis, perhaps aligned with the direction of motion. In the
latter case, the axial tail may be the shocked pulsar wind collimated by the
ram pressure.Comment: 16 pages, including 6 figures; minor changes in the text; typos
corrected; published in Ap
Automated optical identification of a large complete northern hemisphere sample of flat spectrum radio sources with S_6cm > 200 mJy
This paper describes the automated optical APM identification of radio
sources from the Jodrell Bank - VLA Astrometric Survey (JVAS), as used for the
search for distant radio-loud quasars. The sample has been used to investigate
possible relations between optical and radio properties of flat spectrum radio
sources. From the 915 sources in the sample, 756 have an optical APM
identification at a red (e) and/or blue (o) plate,resulting in an
identification fraction of 83% with a completeness and reliability of 98% and
99% respectively. About 20% are optically identified with extended APM objects
on the red plates, e.g. galaxies. However the distinction between galaxies and
quasars can not be done properly near the magnitude limit of the POSS-I plates.
The identification fraction appears to decrease from >90% for sources with a 5
GHz flux density of >1 Jy, to <80% for sources at 0.2 Jy. The identification
fraction, in particular that for unresolved quasars, is found to be lower for
sources with steeper radio spectra. In agreement with previous studies, we find
that the quasars at low radio flux density levels also tend to have fainter
optical magnitudes, although there is a large spread. In addition, objects with
a steep radio-to-optical spectral index are found to be mainly highly polarised
quasars, supporting the idea that in these objects the polarised synchrotron
component is more prominent. It is shown that the large spread in
radio-to-optical spectral index is possibly caused by source to source
variations in the Doppler boosting of the synchrotron component [Abridged].Comment: LaTex, 17 pages, 5 gif figures, 4 tables. Accepted for publication in
MNRAS. High resolution figures can be found at http://www.roe.ac.uk/~ignas
Memberships and CM Diagrams of the Open Cluster NGC 7243
The results of astrometric and photometric investigations of the open cluster
NGC 7243 are presented. Proper motions of 2165 stars with root-mean-square
error of 1.1 mas/yr were obtained by means of PDS scanning of astrometric
plates covering the time interval of 97 years. A total of 211 cluster members
down to V=15.5 mag have been identified. V and B magnitudes have been
determined for 2118 and 2110 stars respectively. Estimations of mass (348Mo < M
< 522Mo), age (t=2.5x10^8 yr), distance (r=698 pc) and reddening (E(B-V)=0.24)
of the cluster NGC 7243 have been made.Comment: 24 pages, 15 figures. Submitted to Astronomy and Astrophysic
HST/WFPC2 observations of the LMC pulsar PSR B0540-69
The study of the younger, and brighter, pulsars is important to understand
the optical emission properties of isolated neutron stars. PSRB0540-69, the
second brightest (V~22) optical pulsar, is obviously a very interesting target
for these investigations. The aim of this work is threefold: constraining the
pulsar proper motion and its velocity on the plane of the sky through optical
astrometry, obtaining a more precise characterisation of the pulsar optical
spectral energy distribution (SED) through a consistent set of multi-band,
high-resolution, imaging photometry observations, measuring the pulsar optical
phase-averaged linear polarisation, for which only a preliminary and uncertain
measurement was obtained so far from ground-based observations. We performed
high-resolution observations of PSRB0540-69 with the WFPC2 aboard the HST, in
both direct imaging and polarimetry modes. From multi-epoch astrometry we set a
3sigma upper limit of 1 mas/yr on the pulsar proper motion, implying a
transverse velocity <250 km/s at the 50 kpc LMC distance. Moreover, we
determined the pulsar absolute position with an unprecedented accuracy of 70
mas. From multi-band photometry we characterised the pulsar power-law spectrum
and we derived the most accurate measurement of the spectral index
(0.70+/-0.07) which indicates a spectral turnover between the optical and X-ray
bands. Finally, from polarimetry we obtained a new measurement of the pulsar
phase-averaged polarisation degree (16+/-4%),consistent with magnetosphere
models depending on the actual intrinsic polarisation degree and depolarisation
factor, and we found that the polarisation vector (22+/-12deg position angle)
is possibly aligned with the semi-major axis of the pulsar-wind nebula and with
the apparent proper motion direction of its bright emission knot.Comment: 14 pages, 12 figures, accepted for publication in Astronomy &
Astrophysic
Optical-uv spectrum and proper motion of the middle-aged pulsar b1055-52
PSRB1055-52 is a middle-aged (~535 kyr) radio, X-ray, and gamma-ray pulsar
showing X-ray thermal emission from the neutron star (NS) surface. A candidate
optical counterpart to PSRB1055-52 was proposed by Mignani and coworkers based
on Hubble Space Telescope (HST) observations performed in 1996, in one spectral
band only. We report on HST observations of this field carried out in 2008, in
four spectral bands. The astrometric and photometric analyses of these data
confirm the identification of the proposed candidate as the pulsar's optical
counterpart. Similarly to other middle-aged pulsars, its optical-UV spectrum
can be described by the sum of a power-law (PLO) component, presumably emitted
from the pulsar magnetosphere, and a Rayleigh-Jeans (RJ) component emitted from
the NS surface. The spectral index of the PLO component, alpha_O=1.05+/-0.34,
is larger than for other pulsars with optical counterparts. The RJ component,
with the brightness temperature TO=(0.66+/-0.10) d_350**2 R_O,13**-2 MK (where
d_350 and R_O,13 are the distance to the pulsar in units of 350 pc and the
radius of the emitting area in units of 13 km), shows a factor of 4 excess with
respect to the extrapolation of the X-ray thermal component into the
UV-optical. This hints that the RJ component is emitted from a larger, colder
area, and suggests that the distance to the pulsar is smaller than previously
thought. From the absolute astrometry of the HST images we measured the pulsar
coordinates with a position accuracy of 0.15". From the comparison with
previous observations we measured the pulsar proper motion, mu = 42+/-5 mas/yr,
which corresponds to a transverse velocity V_t = (70+/-8) d_350 km/s.Comment: 12 pages, 5 figures, accepted for publication on Astrophysical
Journal, (Fig1a available at http://www.mssl.ucl.ac.uk/~rm2/
The 3D Structure of N132D in the LMC: A Late-Stage Young Supernova Remnant
We have used the Wide Field Spectrograph (WiFeS) on the 2.3m telescope at
Siding Spring Observatory to map the [O III] 5007{\AA} dynamics of the young
oxygen-rich supernova remnant N132D in the Large Magellanic Cloud. From the
resultant data cube, we have been able to reconstruct the full 3D structure of
the system of [O III] filaments. The majority of the ejecta form a ring of
~12pc in diameter inclined at an angle of 25 degrees to the line of sight. We
conclude that SNR N132D is approaching the end of the reverse shock phase
before entering the fully thermalized Sedov phase of evolution. We speculate
that the ring of oxygen-rich material comes from ejecta in the equatorial plane
of a bipolar explosion, and that the overall shape of the SNR is strongly
influenced by the pre-supernova mass loss from the progenitor star. We find
tantalizing evidence of a polar jet associated with a very fast oxygen-rich
knot, and clear evidence that the central star has interacted with one or more
dense clouds in the surrounding ISM.Comment: Accepted for Publication in Astrophysics & Space Science, 18pp, 8
figure
The Physical Parameters of the Micro-quasar S26 in the Sculptor Group Galaxy NGC 7793
NGC 7793 - S26 is an extended source (350 pc 185 pc) previously
studied in the radio, optical and x-ray domains. It has been identified as a
micro-quasar which has inflated a super bubble. We used Integral Field Spectra
from the Wide Field Spectrograph on the ANU 2.3 m telescope to analyse spectra
between 3600--7000 \AA. This allowed us to derive fluxes and line ratios for
selected nebular lines. Applying radiative shock model diagnostics, we estimate
shock velocities, densities, radiative ages and pressures across the object. We
show that S26 is just entering its radiative phase, and that the northern and
western regions are dominated by partially-radiative shocks due to a lower
density ISM in these directions. We determine a velocity of expansion along the
jet of 330 km s, and a velocity of expansion of the bubble in the minor
axis direction of 132 km s. We determine the age of the structure to be
yr, and the jet energy flux to be erg
s The jet appears to be collimated within deg, and to undergo
very little precession. If the relativistic , then some 4
M of relativistic matter has already been processed through the jet.
We conclude that the central object in S26 is probably a Black Hole with a mass
typical of the ultra-luminous X-ray source population which is currently
consuming a fairly massive companion through Roche Lobe accretion.Comment: Accepted for publication in MNRAS; 12 pages, 7 figures and 3 table
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