123 research outputs found
Planets in Stellar Clusters Extensive Search. I. Discovery of 47 Low-amplitude Variables in the Metal-rich Cluster NGC 6791 with Millimagnitude Image Subtraction Photometry
We have undertaken a long-term project, Planets in Stellar Clusters Extensive
Search (PISCES), to search for transiting planets in open clusters. As our
first target we have chosen NGC 6791 -- a very old, populous, metal rich
cluster. In this paper we present the results of a test observing run at the
FLWO 1.2 m telescope. Our primary goal is to demonstrate the feasibility of
obtaining the accuracy required for planetary transit detection using image
subtraction photometry on data collected with a 1 m class telescope. We present
a catalog of 62 variable stars, 47 of them newly discovered, most with low
amplitude variability. Among those there are several BY Dra type variables. We
have also observed outbursts in the cataclysmic variables B7 and B8 (Kaluzny et
al. 1997).Comment: 15 pages LaTeX, including 8 PostScript figures and 3 tables. More
discussion added on the implications for transit detection. Accepted for
publication in the Astronomical Journal. Version with full resolution figures
available through ftp at
ftp://cfa-ftp.harvard.edu/pub/bmochejs/PISCES/papers/1_N6791
RJK Observations of the Optical Afterglow of GRB 991216
We present near-infrared and optical observations of the afterglow to the
Gamma-Ray Burst (GRB) 991216 obtained with the F. L. Whipple Observatory 1.2-m
telescope and the University of Hawaii 2.2-m telescope. The observations range
from 15 hours to 3.8 days after the burst. The temporal behavior of the data is
well described by a single power-law decay with index -1.36 +/-0.04,
independent of wavelength. The optical spectral energy distribution, corrected
for significant Galactic reddening of E(B-V)=0.626, is well fitted by a single
power-law with index -0.58 +/- 0.08. Combining the IR/optical observations with
a Chandra X-ray measurement gives a spectral index of -0.8 +/- 0.1 in the
synchrotron cooling regime. A comparison between the spectral and temporal
power-law indices suggest that a jet is a better match to the observations than
a simple spherical shock.Comment: Accepted to the Astrophysical Journal, 12 pages, 4 postscript figure
BVI Photometric Variability Survey of M3
We have conducted a three band (BVI) variability survey of the globular
cluster M3. This is the first three band survey of the cluster using modern
image subtraction techniques. Observations were made over 9 nights in 1998 on
the 1.2m telescope at the F.L. Whipple Observatory in Arizona. We present
photometry for 180 variable stars in the M3 field, of which 12 are newly
discovered. New discoveries include six SX Phe type variables which all lie in
the blue straggler region of the color magnitude diagram, two new first
overtone RR Lyrae, a candidate multi-mode RR Lyrae, a detached eclipsing
binary, and two unclassified variables. We also provide revised periods for 52
of the 168 previously known variables that we observe. The catalog and
photometry for the variable stars are available via anonymous ftp at
ftp://cfa-ftp.harvard.edu/pub/kstanek/M3/Comment: 35 pages, 11 figures. Movies associated with this paper at
http://www-cfa.harvard.edu/~jhartman/M3_movies.html Accepted for publication
in the Astronomical Journal. This replacement contains a few minor revision
The Transit Light Curve Project. IX. Evidence for a Smaller Radius of the Exoplanet XO-3b
We present photometry of 13 transits of XO-3b, a massive transiting planet on
an eccentric orbit. Previous data led to two inconsistent estimates of the
planetary radius. Our data strongly favor the smaller radius, with increased
precision: R_p = 1.217 +/- 0.073 R_Jup. A conflict remains between the mean
stellar density determined from the light curve, and the stellar surface
gravity determined from the shapes of spectral lines. We argue the light curve
should take precedence, and revise the system parameters accordingly. The
planetary radius is about 1 sigma larger than the theoretical radius for a
hydrogen-helium planet of the given mass and insolation. To help in planning
future observations, we provide refined transit and occultation ephemerides.Comment: To appear in ApJ [22 pages
Two 'b's in the Beehive: The Discovery of the First Hot Jupiters in an Open Cluster
We present the discovery of two giant planets orbiting stars in Praesepe
(also known as the Beehive Cluster). These are the first known hot Jupiters in
an open cluster and the only planets known to orbit Sun-like, main-sequence
stars in a cluster. The planets are detected from Doppler shifted radial
velocities; line bisector spans and activity indices show no correlation with
orbital phase, confirming the variations are caused by planetary companions.
Pr0201b orbits a V=10.52 late F dwarf with a period of 4.4264 +/- 0.0070 days
and has a minimum mass of 0.540 +/- 0.039 Mjup, and Pr0211b orbits a V=12.06
late G dwarf with a period of 2.1451 +/- 0.0012 days and has a minimum mass of
1.844 +/- 0.064 Mjup. The detection of 2 planets among 53 single members
surveyed establishes a lower limit on the hot Jupiter frequency of 3.8
(+5.0)(-2.4) % in this metal-rich open cluster. Given the precisely known age
of the cluster, this discovery also demonstrates that, in at least 2 cases,
giant planet migration occurred within 600 Myr after formation. As we endeavor
to learn more about the frequency and formation history of planets,
environments with well-determined properties -- such as open clusters like
Praesepe -- may provide essential clues to this end.Comment: 5 pages, 3 tables, 2 figures. Published in ApJ Letter
A Putative Early-Type Host Galaxy for GRB 060502B: Implications for the Progenitors of Short-Duration Hard-Spectrum Bursts
Starting with the first detection of an afterglow from a short-duration
hard-spectrum gamma-ray burst (SHB) by Swift last year, a growing body of
evidence has suggested that SHBs are associated with an older and
lower-redshift galactic population than long-soft GRBs and, in a few cases,
with large (>~ 10 kpc) projected offsets from the centers of their putative
host galaxies. Here we present observations of the field of GRB 060502B, a SHB
detected by Swift and localized by the X-ray Telescope (XRT). We find a massive
red galaxy at a redshift of z=0.287 at an angular distance of 17.1 arcsec from
our revised XRT position. Using associative and probabilistic arguments we
suggest that this galaxy hosted the progenitor of GRB 060502B. If true, this
offset would correspond to a physical displacement of 73 +- 19 kpc in
projection, about twice the largest offset inferred for any SHB to date and
almost an order of magnitude larger than a typical long-soft burst offset.
Spectra and modeling of the star-formation history of this possible host show
it to have undergone a large ancient starburst. If the progenitor of GRB
060502B was formed in this starburst episode, the time of the GRB explosion
since birth is tau = 1.3 +- 0.2 Gyr and the minimum kick velocity of the SHB
progenitor is v_kick = 55 +- 15 km/s.Comment: Accepted to the Astrophysical Journal. 18 pages, 3 figures; expanded
discussion of alternative host possibilitie
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