120 research outputs found
Deep Photometry of GRB 041006 Afterglow: Hypernova Bump at Redshift z=0.716
We present deep optical photometry of the afterglow of gamma-ray burst (GRB)
041006 and its associated hypernova obtained over 65 days after detection (55
R-band epochs on 10 different nights). Our early data (t<4 days) joined with
published GCN data indicates a steepening decay, approaching F_nu ~t^{-0.6} at
early times (<<1 day) and F_nu ~t^{-1.3} at late times. The break at
t_b=0.16+-0.04 days is the earliest reported jet break among all GRB
afterglows. During our first night, we obtained 39 exposures spanning 2.15
hours from 0.62 to 0.71 days after the burst that reveal a smooth afterglow,
with an rms deviation of 0.024 mag from the local power-law fit, consistent
with photometric errors. After t~4 days, the decay slows considerably, and the
light curve remains approximately flat at R~24 mag for a month before decaying
by another magnitude to reach R~25 mag two months after the burst. This
``bump'' is well-fitted by a k-corrected light curve of SN1998bw, but only if
stretched by a factor of 1.38 in time. In comparison with the other GRB-related
SNe bumps, GRB 041006 stakes out new parameter space for GRB/SNe, with a very
bright and significantly stretched late-time SN light curve. Within a small
sample of fairly well observed GRB/SN bumps, we see a hint of a possible
correlation between their peak luminosity and their ``stretch factor'', broadly
similar to the well-studied Phillips relation for the type Ia supernovae.Comment: ApJ Letters, accepted. Additional material available at
ftp://cfa-ftp.harvard.edu/pub/kstanek/GRB041006
Detecting "Temperate" Jupiters: The Prospects of Searching for Transiting Gas Giants in Habitability Zones
This paper investigates the effects of observing windows on detecting
transiting planets by calculating the fraction of planets with a given period
that have zero, one (single), two (double), or 3 (multiple) transits
occurring while observations are being taken. We also investigate the effects
of collaboration by performing the same calculations with combined observing
times from two wide-field transit survey groups. For a representative field of
the 2004 observing season, both XO and SuperWASP experienced an increase in
single and double transit events by up to 20-40% for planets with periods 14 <
P < 150 days when collaborating by sharing data. For the XO Project using its
data alone, between 20-40% of planets with periods 14-150 days should have been
observed at least once. For the SuperWASP Project, 50-90% of planets with
periods between 14-150 days should have been observed at least once. If XO and
SuperWASP combined their observations, 50-100% of planets with periods less
than 20 days should be observed three or more times. We find that in general
wide-field transit surveys have selected appropriate observing strategies to
observe a significant fraction of transiting giant planets with semimajor axes
larger than the Hot Jupiter regime. The actual number of intermediate-period
transiting planets that are detected depends upon their true semimajor axis
distribution and the signal-to-noise of the data.Comment: 14 pages, 12 figures, 4 tables, accepted to MNRA
Searching for Gravitational Waves from Binary Inspirals with LIGO
We describe the current status of the search for gravitational waves from
inspiralling compact binary systems in LIGO data. We review the result from the
first scientific run of LIGO (S1). We present the goals of the search of data
taken in the second scientific run (S2) and describe the differences between
the methods used in S1 and S2.Comment: 9 pages, 2 figures. Published in proceedings of the 8th Gravitational
Wave Data Analysis Workshop, Milwaukee, WI, USA, 17-20 December 200
Spin-orbit misalignment in the HD80606 planetary system
We recently reported the photometric and spectroscopic detection of the
primary transit of the 111-day-period, eccentric extra-solar planet HD80606 b,
at Observatoire de Haute-Provence, France (Moutou et al. 2009). The whole
egress of the primary transit and a section of its central part were observed,
allowing the measurement of the planetary radius, and evidence for a spin-orbit
misalignment through the observation of the Rossiter-McLaughlin anomaly. The
ingress having not been observed for this long-duration transit, uncertainties
remained in the parameters of the system. We present here a refined, combined
analysis of our photometric and spectroscopic data, together with further
published radial velocities, ground-based photometry, and Spitzer photometry
around the secondary eclipse, as well as new photometric measurements of HD
80606 acquired at Mount Hopkins, Arizona, just before the beginning of the
primary transit. Although the transit is not detected in those new data, they
provide an upper limit for the transit duration, which narrows down the
possible behaviour of the Rossiter-McLaughlin anomaly in the unobserved part of
the transit. We analyse the whole data with a Bayesian approach using a
Markov-chain Monte Carlo integration on all available information. We find R_p
= 0.98 +- 0.03 R_Jup for the planetary radius, and a total primary transit
duration of 11.9 +- 1.3 hours from first to fourth contact. Our analysis
reinforces the hypothesis of spin-orbit misalignment in this system (alignment
excluded at >95 % level), with a positive projected angle between the planetary
orbital axis and the stellar rotation (median solution lambda ~ 50 degrees). As
HD80606 is a component of a binary system, the peculiar orbit of its planet
could result from a Kozai mechanism.Comment: accepted for Publication in Astronomy & Astrophysics, submitted 11
May 200
NICMOS Observations of the Transiting Hot Jupiter XO-1b
We refine the physical parameters of the transiting hot Jupiter planet XO-1b
and its stellar host XO-1 using HST NICMOS observations. XO-1b has a radius
Rp=1.21+/-0.03 RJup, and XO-1 has a radius Rs=0.94+/-0.02 RSun, where the
uncertainty in the mass of XO-1 dominates the uncertainty of Rp and Rs. There
are no significant differences in the XO-1 system properties between these
broad-band NIR observations and previous determinations based upon ground-based
optical observations. We measure two transit timings from these observations
with 9 s and 15 s precision. As a residual to a linear ephemeris model, there
is a 2.0 sigma timing difference between the two HST visits that are separated
by 3 transit events (11.8 days). These two transit timings and additional
timings from the literature are sufficient to rule out the presence of an Earth
mass planet orbiting in 2:1 mean motion resonance coplanar with XO-1b. We
identify and correct for poorly understood gain-like variations present in
NICMOS time series data. This correction reduces the effective noise in time
series photometry by a factor of two, for the case of XO-1.Comment: 13 pages, 8 figures, submitted to Ap
HAT-P-12b: A Low-Density Sub-Saturn Mass Planet Transiting a Metal-Poor K Dwarf
We report on the discovery of HAT-P-12b, a transiting extrasolar planet
orbiting the moderately bright V=12.8 K4 dwarf GSC 03033-00706, with a period P
= 3.2130598 +- 0.0000021 d, transit epoch Tc = 2454419.19556 +- 0.00020 (BJD)
and transit duration 0.0974 +- 0.0006 d. The host star has a mass of 0.73 +-
0.02 Msun, radius of 0.70 +- ^0.02_0.01 Rsun, effective temperature 4650 +- 60
K and metallicity [Fe/H] = -0.29 +- 0.05. We find a slight correlation between
the observed spectral line bisector spans and the radial velocity, so we
consider, and rule out, various blend configurations including a blend with a
background eclipsing binary, and hierarchical triple systems where the
eclipsing body is a star or a planet. We conclude that a model consisting of a
single star with a transiting planet best fits the observations, and show that
a likely explanation for the apparent correlation is contamination from
scattered moonlight. Based on this model, the planetary companion has a mass of
0.211 +- 0.012 MJup, and a radius of 0.959 +- ^0.029_0.021 RJup yielding a mean
density of 0.295 +- 0.025 g cm^-3. Comparing these observations with recent
theoretical models we find that HAT-P-12b is consistent with a ~ 1-4.5 Gyr,
mildly irradiated, H/He dominated planet with a core mass Mc <~ 10 Mearth.
HAT-P-12b is thus the least massive H/He dominated gas giant planet found to
date. This record was previously held by Saturn.Comment: Accepted for publication in ApJ, 13 pages, 9 figures, 5 table
Parameters and Predictions for the Long-Period Transiting Planet HD 17156b
We report high-cadence time-series photometry of the recently-discovered
transiting exoplanet system HD 17156, spanning the time of transit on UT 2007
October 1, from three separate observatories. We present a joint analysis of
our photometry, previously published radial velocity measurements, and times of
transit center for 3 additional events. Adopting the
spectroscopically-determined values and uncertainties for the stellar mass and
radius, we estimate a planet radius of Rp = 1.01 +/- 0.09 RJup and an
inclination of i = 86.5 +1.1 -0.7 degrees. We find a time of transit center of
Tc = 2454374.8338 +/- 0.0020 HJD and an orbital period of P = 21.21691 +/-
0.00071 days, and note that the 4 transits reported to date show no sign of
timing variations that would indicate the presence of a third body in the
system. Our results do not preclude the existence of a secondary eclipse, but
imply there is only a 9.2% chance for this to be present, and an even lower
probability (6.9%) that the secondary eclipse would be a non-grazing event. Due
to its eccentric orbit and long period, HD 17156b is a fascinating object for
the study of the dynamics of exoplanet atmospheres. To aid such future studies,
we present theoretical light curves for the variable infrared emission from the
visible hemisphere of the planet throughout its orbit.Comment: 8 pages, 4 figures, 1 table, emulateapj format. v2: accepted for
publication in ApJ, minor changes. Changed to emulateapj to save the
rainforest
Transiting Exoplanets with JWST
The era of exoplanet characterization is upon us. For a subset of exoplanets
-- the transiting planets -- physical properties can be measured, including
mass, radius, and atmosphere characteristics. Indeed, measuring the atmospheres
of a further subset of transiting planets, the hot Jupiters, is now routine
with the Spitzer Space Telescope. The James Webb Space Telescope (JWST) will
continue Spitzer's legacy with its large mirror size and precise thermal
stability. JWST is poised for the significant achievement of identifying
habitable planets around bright M through G stars--rocky planets lacking
extensive gas envelopes, with water vapor and signs of chemical disequilibrium
in their atmospheres. Favorable transiting planet systems, are, however,
anticipated to be rare and their atmosphere observations will require tens to
hundreds of hours of JWST time per planet. We review what is known about the
physical characteristics of transiting planets, summarize lessons learned from
Spitzer high-contrast exoplanet measurements, and give several examples of
potential JWST observations.Comment: 22 pages, 11 figures. In press in "Astrophysics in the Next Decade:
JWST and Concurrent Facilities, Astrophysics & Space Science Library,
Thronson, H. A., Tielens, A., Stiavelli, M., eds., Springer: Dordrecht
(2008)." The original publication will be available at
http://www.springerlink.co
A super-Earth transiting a nearby low-mass star
A decade ago, the detection of the first transiting extrasolar planet
provided a direct constraint on its composition and opened the door to
spectroscopic investigations of extrasolar planetary atmospheres. As such
characterization studies are feasible only for transiting systems that are both
nearby and for which the planet-to-star radius ratio is relatively large,
nearby small stars have been surveyed intensively. Doppler studies and
microlensing have uncovered a population of planets with minimum masses of
1.9-10 times the Earth's mass (M_Earth), called super-Earths. The first
constraint on the bulk composition of this novel class of planets was afforded
by CoRoT-7b, but the distance and size of its star preclude atmospheric studies
in the foreseeable future. Here we report observations of the transiting planet
GJ 1214b, which has a mass of 6.55 M_Earth and a radius 2.68 times Earth's
radius (R_Earth), indicating that it is intermediate in stature between Earth
and the ice giants of the Solar System. We find that the planetary mass and
radius are consistent with a composition of primarily water enshrouded by a
hydrogen-helium envelope that is only 0.05% of the mass of the planet. The
atmosphere is probably escaping hydrodynamically, indicating that it has
undergone significant evolution during its history. As the star is small and
only 13 parsecs away, the planetary atmosphere is amenable to study with
current observatories.Comment: 13 pages, 3 figures, published in Natur
Searches for Gravitational Waves from Binary Neutron Stars: A Review
A new generation of observatories is looking for gravitational waves. These
waves, emitted by highly relativistic systems, will open a new window for ob-
servation of the cosmos when they are detected. Among the most promising
sources of gravitational waves for these observatories are compact binaries in
the final min- utes before coalescence. In this article, we review in brief
interferometric searches for gravitational waves emitted by neutron star
binaries, including the theory, instru- mentation and methods. No detections
have been made to date. However, the best direct observational limits on
coalescence rates have been set, and instrumentation and analysis methods
continue to be refined toward the ultimate goal of defining the new field of
gravitational wave astronomy.Comment: 30 pages, 5 Figures, to appear in "Short-Period Binary Stars:
Observations, Analyses, and Results", Ed.s Eugene F. Milone, Denis A. Leahy,
David W. Hobil
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