316 research outputs found
Single cell preparations of Mycobacterium tuberculosis damage the mycobacterial envelope and disrupt macrophage interactions
For decades, investigators have studied the interaction o
Multiwavelength Transit Observations of the Candidate Disintegrating Planetesimals Orbiting WD 1145+017
We present multiwavelength, multi-telescope, ground-based follow-up
photometry of the white dwarf WD 1145+017, that has recently been suggested to
be orbited by up to six or more, short-period, low-mass, disintegrating
planetesimals. We detect 9 significant dips in flux of between 10% and 30% of
the stellar flux from our ground-based photometry. We observe transits deeper
than 10% on average every ~3.6 hr in our photometry. This suggests that WD
1145+017 is indeed being orbited by multiple, short-period objects. Through
fits to the multiple asymmetric transits that we observe, we confirm that the
transit egress timescale is usually longer than the ingress timescale, and that
the transit duration is longer than expected for a solid body at these short
periods, all suggesting that these objects have cometary tails streaming behind
them. The precise orbital periods of the planetesimals in this system are
unclear from the transit-times, but at least one object, and likely more, have
orbital periods of ~4.5 hours. We are otherwise unable to confirm the specific
periods that have been reported, bringing into question the long-term stability
of these periods. Our high precision photometry also displays low amplitude
variations suggesting that dusty material is consistently passing in front of
the white dwarf, either from discarded material from these disintegrating
planetesimals or from the detected dusty debris disk. For the significant
transits we observe, we compare the transit depths in the V- and R-bands of our
multiwavelength photometry, and find no significant difference; therefore, for
likely compositions the radius of single-size particles in the cometary tails
streaming behind the planetesimals in this system must be ~0.15 microns or
larger, or ~0.06 microns or smaller, with 2-sigma confidence.Comment: 16 pages, 12 figures, submitted to ApJ on October 8th, 201
KELT-1b: A Strongly Irradiated, Highly Inflated, Short Period, 27 Jupiter-mass Companion Transiting a mid-F Star
We present the discovery of KELT-1b, the first transiting low-mass companion
from the wide-field Kilodegree Extremely Little Telescope-North (KELT-North)
survey. The V=10.7 primary is a mildly evolved, solar-metallicity, mid-F star.
The companion is a low-mass brown dwarf or super-massive planet with mass of
27.23+/-0.50 MJ and radius of 1.110+0.037-0.024 RJ, on a very short period
(P=1.21750007) circular orbit. KELT-1b receives a large amount of stellar
insolation, with an equilibrium temperature assuming zero albedo and perfect
redistribution of 2422 K. Upper limits on the secondary eclipse depth indicate
that either the companion must have a non-zero albedo, or it must experience
some energy redistribution. Comparison with standard evolutionary models for
brown dwarfs suggests that the radius of KELT-1b is significantly inflated.
Adaptive optics imaging reveals a candidate stellar companion to KELT-1, which
is consistent with an M dwarf if bound. The projected spin-orbit alignment
angle is consistent with zero stellar obliquity, and the vsini of the primary
is consistent with tidal synchronization. Given the extreme parameters of the
KELT-1 system, we expect it to provide an important testbed for theories of the
emplacement and evolution of short-period companions, and theories of tidal
dissipation and irradiated brown dwarf atmospheres.Comment: 30 pages, 19 figures. Submitted to Ap
KELT-2Ab: A Hot Jupiter Transiting the Bright (V=8.77) Primary Star of a Binary System
We report the discovery of KELT-2Ab, a hot Jupiter transiting the bright
(V=8.77) primary star of the HD 42176 binary system. The host is a slightly
evolved late F-star likely in the very short-lived "blue-hook" stage of
evolution, with \teff=6148\pm48{\rm K}, and
\feh=0.034\pm0.78. The inferred stellar mass is
\msun\ and the star has a relatively large radius
of \rsun. The planet is a typical hot Jupiter with
period days and a mass of \mj\ and
radius of \rj. This is mildly inflated as compared
to models of irradiated giant planets at the 4 Gyr age of the system.
KELT-2A is the third brightest star with a transiting planet identified by
ground-based transit surveys, and the ninth brightest star overall with a
transiting planet. KELT-2Ab's mass and radius are unique among the subset of
planets with host stars, and therefore increases the diversity of bright
benchmark systems. We also measure the relative motion of KELT-2A and -2B over
a baseline of 38 years, robustly demonstrating for the first time that the
stars are bound. This allows us to infer that KELT-2B is an early K-dwarf. We
hypothesize that through the eccentric Kozai mechanism KELT-2B may have
emplaced KELT-2Ab in its current orbit. This scenario is potentially testable
with Rossiter-McLaughlin measurements, which should have an amplitude of
44 m s.Comment: 9 pages, 2 tables, 4 figures. A short video describing this paper is
available at http://www.youtube.com/watch?v=wVS8lnkXXlE. Revised to reflect
the ApJL version. Note that figure 4 is not in the ApJL versio
Miniature exoplanet radial velocity array I: design, commissioning, and early photometric results
The MINiature Exoplanet Radial Velocity Array (MINERVA) is a US-based observational facility dedicated to the discovery and characterization of exoplanets around a nearby sample of bright stars. MINERVA employs a robotic array of four 0.7 m telescopes outfitted for both high-resolution spec- troscopy and photometry, and is designed for completely autonomous operation. The primary science program is a dedicated radial velocity survey and the secondary science objective is to obtain high precision transit light curves. The modular design of the facility and the flexibility of our hardware allows for both science programs to be pursued simultaneously, while the robotic control software provides a robust and efficient means to carry out nightly observations. In this article, we describe the design of MINERVA including major hardware components, software, and science goals. The telescopes and photometry cameras are characterized at our test facility on the Caltech campus in Pasadena, CA, and their on-sky performance is validated. New observations from our test facility demonstrate sub-mmag photometric precision of one of our radial velocity survey targets, and we present new transit observations and fits of WASP-52b—a known hot-Jupiter with an inflated radius and misaligned orbit. The process of relocating the MINERVA hardware to its final destination at the Fred Lawrence Whipple Observatory in southern Arizona has begun, and science operations are expected to commence within 2015
Cosmic-Ray Positrons: Are There Primary Sources?
Cosmic rays at the Earth include a secondary component originating in
collisions of primary particles with the diffuse interstellar gas. The
secondary cosmic rays are relatively rare but carry important information on
the Galactic propagation of the primary particles. The secondary component
includes a small fraction of antimatter particles, positrons and antiprotons.
In addition, positrons and antiprotons may also come from unusual sources and
possibly provide insight into new physics. For instance, the annihilation of
heavy supersymmetric dark matter particles within the Galactic halo could lead
to positrons or antiprotons with distinctive energy signatures. With the
High-Energy Antimatter Telescope (HEAT) balloon-borne instrument, we have
measured the abundances of positrons and electrons at energies between 1 and 50
GeV. The data suggest that indeed a small additional antimatter component may
be present that cannot be explained by a purely secondary production mechanism.
Here we describe the signature of the effect and discuss its possible origin.Comment: 15 pages, Latex, epsfig and aasms4 macros required, to appear in
Astroparticle Physics (1999
Multiwavelength Transit Observations of the Candidate Disintegrating Planetesimals Orbiting WD 1145+017
We present multiwavelength, ground-based follow-up photometry of the white dwarf WD 1145+017, which has recently been suggested to be orbited by up to six or more short-period, low-mass, disintegrating planetesimals. We detect nine significant dips in flux of between 10% and 30% of the stellar flux in our ~32 hr of photometry, suggesting that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the asymmetric transits that we observe, we confirm that the transit egress is usually longer than the ingress, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals are unclear, but at least one object, and likely more, have orbital periods of ~4.5 hr. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high-precision photometry also displays low-amplitude variations, suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. We compare the transit depths in the V- and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions, the radius of single-size particles in the cometary tails streaming behind the planetesimals must be ~0.15 μm or larger, or ~0.06 μm or smaller, with 2σ confidence
KELT-6b: A P~7.9 d Hot Saturn Transiting a Metal-Poor Star with a Long-Period Companion
We report the discovery of KELT-6b, a mildly-inflated Saturn-mass planet
transiting a metal-poor host. The initial transit signal was identified in
KELT-North survey data, and the planetary nature of the occulter was
established using a combination of follow-up photometry, high-resolution
imaging, high-resolution spectroscopy, and precise radial velocity
measurements. The fiducial model from a global analysis including constraints
from isochrones indicates that the V=10.38 host star (BD+31 2447) is a mildly
evolved, late-F star with T_eff=6102 \pm 43 K, log(g_*)=4.07_{-0.07}^{+0.04}
and [Fe/H]=-0.28 \pm 0.04, with an inferred mass M_*=1.09 \pm 0.04 M_sun and
radius R_star=1.58_{-0.09}^{+0.16} R_sun. The planetary companion has mass
M_P=0.43 \pm 0.05 M_J, radius R_P=1.19_{-0.08}^{+0.13} R_J, surface gravity
log(g_P)=2.86_{-0.08}^{+0.06}, and density rho_P=0.31_{-0.08}^{+0.07}
g~cm^{-3}. The planet is on an orbit with semimajor axis a=0.079 \pm 0.001 AU
and eccentricity e=0.22_{-0.10}^{+0.12}, which is roughly consistent with
circular, and has ephemeris of T_c(BJD_TDB)=2456347.79679 \pm 0.00036 and
P=7.845631 \pm 0.000046 d. Equally plausible fits that employ empirical
constraints on the host star parameters rather than isochrones yield a larger
planet mass and radius by ~4-7%. KELT-6b has surface gravity and incident flux
similar to HD209458b, but orbits a host that is more metal poor than HD209458
by ~0.3 dex. Thus, the KELT-6 system offers an opportunity to perform a
comparative measurement of two similar planets in similar environments around
stars of very different metallicities. The precise radial velocity data also
reveal an acceleration indicative of a longer-period third body in the system,
although the companion is not detected in Keck adaptive optics images.Comment: Published in AJ, 17 pages, 15 figures, 6 table
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