3,531 research outputs found
SkyDOT (Sky Database for Objects in the Time Domain): A Virtual Observatory for Variability Studies at LANL
The mining of Virtual Observatories (VOs) is becoming a powerful new method
for discovery in astronomy. Here we report on the development of SkyDOT (Sky
Database for Objects in the Time domain), a new Virtual Observatory, which is
dedicated to the study of sky variability. The site will confederate a number
of massive variability surveys and enable exploration of the time domain in
astronomy. We discuss the architecture of the database and the functionality of
the user interface. An important aspect of SkyDOT is that it is continuously
updated in near real time so that users can access new observations in a timely
manner. The site will also utilize high level machine learning tools that will
allow sophisticated mining of the archive. Another key feature is the real time
data stream provided by RAPTOR (RAPid Telescopes for Optical Response), a new
sky monitoring experiment under construction at Los Alamos National Laboratory
(LANL).Comment: to appear in SPIE proceedings vol. 4846, 11 pages, 5 figure
Limits on I-band microvariability of the Galactic Bulge Miras
We search for microvariability in a sample of 485 Mira variables with high
quality I-band light curves from the second generation Optical Gravitational
Lensing Experiment (OGLE-II). Rapid variations with amplitudes in the ~0.2-1.1
mag range lasting hours to days were discovered in Hipparcos data by de Laverny
et al. (1998). Our search is primarily sensitive to events with time-scales of
about 1 day, but retains a few percent efficiency (per object) for detecting
unresolved microvariability events as short as 2 hours. We do not detect any
candidate events. Assuming that the distribution of the event time profiles is
identical to that from the Hipparcos light curves we derive the 95% confidence
level upper limit of 0.038 per year per star for the rate of such events (1 per
26 years per average object of the ensemble). The high event rates of the order
of 1 per year per star implied by the Hipparcos study in the H_P band are
excluded with high confidence by the OGLE-II data in the I band. Our
non-detection could still be explained by much redder spectral response of the
I filter compared to the H_P band or by population differences between the
bulge and the solar neighborhood. In any case, the OGLE-II I-band data provide
the first limit on the rate of the postulated microvariability events in Mira
stars and offer new quantitative constraints on their properties. Similar
limits are obtained for other pulse shapes and a range of the assumed
time-scales and size-frequency distributions.Comment: Accepted for publication in Ap
Lupus-TR-3b: A Low-Mass Transiting Hot Jupiter in the Galactic Plane?
We present a strong case for a transiting Hot Jupiter planet identified
during a single-field transit survey towards the Lupus Galactic plane. The
object, Lupus-TR-3b, transits a V=17.4 K1V host star every 3.91405d.
Spectroscopy and stellar colors indicate a host star with effective temperature
5000 +/- 150K, with a stellar mass and radius of 0.87 +/- 0.04M_sun and 0.82
+/- 0.05R_sun, respectively. Limb-darkened transit fitting yields a companion
radius of 0.89 +/- 0.07R_J and an orbital inclination of 88.3 +1.3/-0.8 deg.
Magellan 6.5m MIKE radial velocity measurements reveal a 2.4 sigma K=114 +/-
25m/s sinusoidal variation in phase with the transit ephemeris. The resulting
mass is 0.81 +/- 0.18M_J and density 1.4 +/- 0.4g/cm^3. Y-band PANIC image
deconvolution reveal a V>=21 red neighbor 0.4'' away which, although highly
unlikely, we cannot conclusively rule out as a blended binary with current
data. However, blend simulations show that only the most unusual binary system
can reproduce our observations. This object is very likely a planet, detected
from a highly efficient observational strategy. Lupus-TR-3b constitutes the
faintest ground-based detection to date, and one of the lowest mass Hot
Jupiters known.Comment: 4 pages, 4 figures, accepted for publication in ApJ
Behavioral Consequences of NMDA Antagonist-Induced Neuroapoptosis in the Infant Mouse Brain
Background: Exposure to NMDA glutamate antagonists during the brain growth spurt period causes widespread neuroapoptosis in the rodent brain. This period in rodents occurs during the first two weeks after birth, and corresponds to the third trimester of pregnancy and several years after birth in humans. The developing human brain may be exposed to NMDA antagonists through drug-abusing mothers or through anesthesia. Methodology/Principal Findings: We evaluated the long-term neurobehavioral effects of mice exposed to a single dose of the NMDA antagonist, phencyclidine (PCP), or saline, on postnatal day 2 (P2) or P7, or on both P2 and P7. PCP treatment on P2 + P7 caused more severe cognitive impairments than either single treatment. Histological examination of acute neuroapoptosis resulting from exposure to PCP indicated that the regional pattern of degeneration induced by PCP in P2 pups was different from that in P7 pups. The extent of damage when evaluated quantitatively on P7 was greater for pups previously treated on P2 compared to pups treated only on P7. Conclusions: These findings signify that PCP induces different patterns of neuroapoptosis depending on the developmental age at the time of exposure, and that exposure at two separate developmental ages causes more severe neuropathological and neurobehavioral consequences than a single treatment
Energy input and response from prompt and early optical afterglow emission in gamma-ray bursts
The taxonomy of optical emission detected during the critical first few
minutes after the onset of a gamma-ray burst (GRB) defines two broad classes:
prompt optical emission correlated with prompt gamma-ray emission, and early
optical afterglow emission uncorrelated with the gamma-ray emission. The
standard theoretical interpretation attributes prompt emission to internal
shocks in the ultra-relativistic outflow generated by the internal engine;
early afterglow emission is attributed to shocks generated by interaction with
the surrounding medium. Here we report on observations of a bright GRB that,
for the first time, clearly show the temporal relationship and relative
strength of the two optical components. The observations indicate that early
afterglow emission can be understood as reverberation of the energy input
measured by prompt emission. Measurements of the early afterglow reverberations
therefore probe the structure of the environment around the burst, whereas the
subsequent response to late-time impulsive energy releases reveals how earlier
flaring episodes have altered the jet and environment parameters. Many GRBs are
generated by the death of massive stars that were born and died before the
Universe was ten per cent of its current age, so GRB afterglow reverberations
provide clues about the environments around some of the first stars.Comment: 13 pages, 4 figures, 1 table. Note: This paper has been accepted for
publication in Nature, but is embargoed for discussion in the popular press
until formal publication in Natur
Optical monitoring of the gravitationally lensed quasar Q2237+0305 from APO between June 1995 and January 1998
We present a data set of images of the gravitationally lensed quasar
Q2237+0305, that was obtained at the Apache Point Observatory (APO) between
June 1995 and January 1998. Although the images were taken under variable,
often poor seeing conditions and with coarse pixel sampling, photometry is
possible for the two brighter quasar images A and B with the help of exact
quasar image positions from HST observations. We obtain a light curve with 73
data points for each of the images A and B. There is evidence for a long (>~
100 day) brightness peak in image A in 1996 with an amplitude of about 0.4 to
0.5 mag (relative to 1995), which indicates that microlensing has been taking
place in the lensing galaxy. Image B does not vary much over the course of the
observation period. The long, smooth variation of the light curve is similar to
the results from the OGLE monitoring of the system (Wozniak et al. 2000a).Comment: 8 pages, 5 figures; accepted for publication in A&
Optical afterglows of Gamma-Ray Bursts: peaks, plateaus, and possibilities
The optical light-curves of GRB afterglows display either peaks or plateaus.
We identify 16 afterglows of the former type, 17 of the latter, and 4 with
broad peaks, that could be of either type. The optical energy release of these
two classes is similar and is correlated with the GRB output, the correlation
being stronger for peaky afterglows, which suggests that the burst and
afterglow emissions of peaky afterglows are from the same relativistic ejecta
and that the optical emission of afterglows with plateaus arises more often
from ejecta that did not produce the burst emission.
Consequently, we propose that peaky optical afterglows are from impulsive
ejecta releases and that plateau optical afterglows originate from long-lived
engines, the break in the optical light-curve (peak or plateau end) marking the
onset of the entire outflow deceleration.
In the peak luminosity--peak time plane, the distribution of peaky afterglows
displays an edge with L_p \propto t_p^{-3}, which we attribute to variations
(among afterglows) in the ambient medium density. The fluxes and epochs of
optical plateau breaks follow a L_b \propto t_b^{-1} anticorrelation.
Sixty percent of 25 afterglows that were well-monitored in the optical and
X-rays show light-curves with comparable power-law decays indices and
achromatic breaks. The other 40 percent display three types of decoupled
behaviours: i) chromatic optical light-curve breaks (perhaps due to the peak of
the synchrotron spectrum crossing the optical), ii) X-ray flux decays faster
than in the optical (suggesting that the X-ray emission is from local
inverse-Compton scattering), and iii) chromatic X-ray light-curve breaks
(indicating that the X-ray emission is from external up-scattering).Comment: 11 pages, table with afterglows added, to appear in MNRA
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