53 research outputs found
A Large Brightness Enhancement of the QSO 0957+561 A Component
We report an increase of more than 0.2 mag in the optical brightness of the
leading image (A) of the gravitational lens Q0957+561, detected during the
09/2000 -- 06/2001 monitoring campaign (2001 observing season). The brightening
is similar to or even greater than the largest change ever detected during the
20 years of monitoring of this system. We discuss two different provisional
explanations to this event: intrinsic source variability or microlensing
(either short timescale microlensing or cessation of the historical
microlensing). An exhaustive photometric monitoring of Q0957+561 is needed
until summer of 2002 and during 2003 to discriminate between these
possibilities.Comment: 13 pages including 3 figures and 1 table. Accepted for publication in
ApJ Let
Brorfelde Schmidt CCD Catalog (BSCC)
The Brorfelde Schmidt CCD Catalog (BSCC) contains about 13.7 million stars,
north of +49 deg Declination with precise positions and V, R photometry. The
catalog has been constructed from the reductions of 18,667 CCD frames observed
with the Brorfelde Schmidt Telescope between 2000 and 2007. The Tycho-2 catalog
was used for astrometric and photometric reference stars. Errors of individual
positions are about 20 to 200 mas for stars in the R = 10 to 18 mag range.
External comparisons with 2MASS and SDSS reveal possible small systematic
errors in the BSCC of up to about 30 mas. The catalog is supplemented with J,
H, and K_s magnitudes from the 2MASS catalog. The catalog data file (about 550
MB ASCII, compressed) will be made available at the Strasbourg Data Center
(CDS).Comment: 16 pages, 22 figures, 2 tables, accepted by A
Further Investigation of the Time Delay, Magnification Ratios, and Variability in the Gravitational Lens 0218+357
High precision VLA flux density measurements for the lensed images of
0218+357 yield a time delay of 10.1(+1.5-1.6)days (95% confidence). This is
consistent with independent measurements carried out at the same epoch (Biggs
et al. 1999), lending confidence in the robustness of the time delay
measurement. However, since both measurements make use of the same features in
the light curves, it is possible that the effects of unmodelled processes, such
as scintillation or microlensing, are biasing both time delay measurements in
the same way. Our time delay estimates result in confidence intervals that are
somewhat larger than those of Biggs et al., probably because we adopt a more
general model of the source variability, allowing for constant and variable
components. When considered in relation to the lens mass model of Biggs et al.,
our best-fit time delay implies a Hubble constant of H_o = 71(+17-23) km/s-Mpc
for Omega_o=1 and lambda_o=0 (95% confidence; filled beam). This confidence
interval for H_o does not reflect systematic error, which may be substantial,
due to uncertainty in the position of the lens galaxy. We also measure the flux
ratio of the variable components of 0218+357, a measurement of a small region
that should more closely represent the true lens magnification ratio. We find
ratios of 3.2(+0.3-0.4) (95% confidence; 8 GHz) and 4.3(+0.5-0.8) (15 GHz).
Unlike the reported flux ratios on scales of 0.1", these ratios are not
strongly significantly different. We investigate the significance of apparent
differences in the variability properties of the two images of the background
active galactic nucleus. We conclude that the differences are not significant,
and that time series much longer than our 100-day time series will be required
to investigate propagation effects in this way.Comment: 33 pages, 9 figures. Accepted for publication in ApJ. Light curve
data may be found at http://space.mit.edu/RADIO/papers.htm
A Robust Determination of the Time Delay in 0957+561A,B and a Measurement of the Global Value of Hubble's Constant
Photometric monitoring of the gravitational lens system 0957+561A,B in the g
and r bands with the Apache Point Observatory (APO) 3.5 m telescope during 1996
shows a sharp g band event in the trailing (B) image light curve at the precise
time predicted from the observation of an event during 1995 in the leading (A)
image with a delay of 415 days. This success confirms the "short delay," and
the lack of any feature at a delay near 540 days rejects the "long delay" for
this system, resolving a long-standing controversy. A series of statistical
analyses of our light curve data yield a best fit delay of 417 +/- 3 days (95%
confidence interval). Recent improvements in the modeling of the lens system
(consisting of a galaxy and cluster) allow us to derive a value of the global
(at z = 0.36) value of Hubble's constant H_0 using Refsdal's method, a simple
and direct distance determination based on securely understood physics and
geometry. The result is H_0 = 63 +/- 12 km/s/Mpc (for Omega = 1) where this 95%
confidence interval is dominated by remaining lens model uncertainties.Comment: accepted by ApJ, AASTeX 4.0 preprint, 4 PostScript figure
Open video data sharing in developmental and behavioural science
Video recording is a widely used method for documenting infant and child
behaviours in research and clinical practice. Video data has rarely been shared
due to ethical concerns of confidentiality, although the need of shared
large-scaled datasets remains increasing. This demand is even more imperative
when data-driven computer-based approaches are involved, such as screening
tools to complement clinical assessments. To share data while abiding by
privacy protection rules, a critical question arises whether efforts at data
de-identification reduce data utility? We addressed this question by showcasing
the Prechtl's general movements assessment (GMA), an established and globally
practised video-based diagnostic tool in early infancy for detecting
neurological deficits, such as cerebral palsy. To date, no shared
expert-annotated large data repositories for infant movement analyses exist.
Such datasets would massively benefit training and recalibration of human
assessors and the development of computer-based approaches. In the current
study, sequences from a prospective longitudinal infant cohort with a total of
19451 available general movements video snippets were randomly selected for
human clinical reasoning and computer-based analysis. We demonstrated for the
first time that pseudonymisation by face-blurring video recordings is a viable
approach. The video redaction did not affect classification accuracy for either
human assessors or computer vision methods, suggesting an adequate and
easy-to-apply solution for sharing movement video data. We call for further
explorations into efficient and privacy rule-conforming approaches for
deidentifying video data in scientific and clinical fields beyond movement
assessments. These approaches shall enable sharing and merging stand-alone
video datasets into large data pools to advance science and public health
Theoretical Aspects of Gravitational Lensing in TeVeS
Since Bekenstein's (2004) creation of his Tensor-Vector-Scalar theory
(TeVeS), the Modified Newtonian dynamics (MOND) paradigm has been redeemed from
the embarrassment of lacking a relativistic version. One primary success of
TeVeS is that it provides an enhancement of gravitational lensing, which could
not be achieved by other MONDian theories. Following Bekenstein's work, we
investigate the phenomena of gravitational lensing including deflection angles,
lens equations and time delay. We find that the deflection angle would maintain
its value while the distance of closest approach vary in the MOND regime, this
coincides with the conclusion of Mortlock and Turner's (2001) intuitional
approach. Moreover, the scalar field, which is introduced to enhance the
deflection angle in TeVeS, contributes a negative effect on the potential time
delay. Unfortunately this phenomenon is unmeasurable in lensing systems where
we can only observe the time delay between two images for a given source.
However, this measurable time delay offers another constraint on the mass ratio
of the DM and MOND scenarios, which in general differs from that given by the
deflection angle. In other words, for a lensing system, if two masses, m_gN and
m_gM, are mutually alternatives for the deflection angles in their own
paradigm, regarding the time delay they are in general in an exclusive
relation.Comment: 15 pages, 7 figure
A Sharp Event in the Image a Light Curve of the Double Quasar 0957+561 and Prediction of the 1996 Image B Light Curve
CCD photometry of the gravitational lens system 0957+561A,B in the g and r
bands was obtained on alternate nights, weather permitting, from December 1994
through May 1995 using the Double Imaging Spectrograph (DIS) on the Apache
Point Observatory (APO) 3.5-meter telescope. The remote observing and fast
instrument change capabilities of this facility allowed accumulation of light
curves sampled frequently and consistently. The Honeycutt ensemble photometry
algorithm was applied to the data set and yielded typical relative photometric
errors of approximately 0.01 magnitudes. Image A exhibited a sharp drop of
about 0.1 magnitudes in late December 1994; no other strong features were
recorded in either image. This event displays none of the expected generic
features of a microlensing-induced flux variation and is likely to be intrinsic
to the quasar; if so, it should also be seen in the B image with the lensing
differential time delay. We give the expected 1996 image B light curves based
on two values of the time delay and brightness ratio which have been proposed
and debated in the literature. Continued monitoring of the system in the first
half of 1996 should easily detect the image B event and thus resolve the
time-delay controversy.Comment: submitted to ApJ Letters, 15 pages, uuencoded PostScript with figures
included; also available through WWW at
http://www.astro.princeton.edu/~library/prep.htm
Reducing Amyloid Plaque Burden via Ex Vivo Gene Delivery of an Aβ-Degrading Protease: A Novel Therapeutic Approach to Alzheimer Disease
Matthew Hemming and colleagues describe the ex vivo gene delivery of an Aβ-degrading protease that reduces amyloid plaque burden in transgenic mice expressing human amyloid precursor protein
- …