1,126 research outputs found
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 T_(eff) = 6148 ± 48 K, log g = 4.030^(+0.015)_(–0.026) and [Fe/H] = 0.034 ± 0.78. The inferred stellar mass is M* = 1.314^(+0.063)_(–0.060) M☉ and the star has a relatively large radius of R* = 1.836^(+0.066)_(–0.046) R☉. The planet is a typical hot Jupiter with period 4.1137913 ± 0.00001 days and a mass of M_P = 1.524 ± 0.088 M J and radius of R_P = 1.290^(+0.064)_(–0.050) R_J. 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 V < 9 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^(–1)
Spitzer Phase Curves of KELT-1b and the Signatures of Nightside Clouds in Thermal Phase Observations
We observed two full orbital phase curves of the transiting brown dwarf
KELT-1b, at 3.6um and 4.5um, using the Spitzer Space Telescope. Combined with
previous eclipse data from Beatty et al. (2014), we strongly detect KELT-1b's
phase variation as a single sinusoid in both bands, with amplitudes of
ppm at 3.6um and ppm at 4.5um, and confirm the secondary
eclipse depths measured by Beatty et al. (2014). We also measure noticeable
Eastward hotspot offsets of degrees at 3.6um and
degrees at 4.5um. Both the day-night temperature contrasts and the hotspot
offsets we measure are in line with the trends seen in hot Jupiters (e.g.,
Crossfield 2015), though we disagree with the recent suggestion of an offset
trend by Zhang et al. (2018). Using an ensemble analysis of Spitzer phase
curves, we argue that nightside clouds are playing a noticeable role in
modulating the thermal emission from these objects, based on: 1) the lack of a
clear trend in phase offsets with equilibrium temperature, 2) the sharp
day-night transitions required to have non-negative intensity maps, which also
resolves the inversion issues raised by Keating & Cowan (2017), 3) the fact
that all the nightsides of these objects appear to be at roughly the same
temperature of 1000K, while the dayside temperatures increase linearly with
equilibrium temperature, and 4) the trajectories of these objects on a Spitzer
color-magnitude diagram, which suggest colors only explainable via nightside
clouds.Comment: AJ in press. Updated to reflect the accepted versio
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 T_(eff) = 6148 ± 48 K, log g = 4.030^(+0.015)_(–0.026) and [Fe/H] = 0.034 ± 0.78. The inferred stellar mass is M* = 1.314^(+0.063)_(–0.060) M☉ and the star has a relatively large radius of R* = 1.836^(+0.066)_(–0.046) R☉. The planet is a typical hot Jupiter with period 4.1137913 ± 0.00001 days and a mass of M_P = 1.524 ± 0.088 M J and radius of R_P = 1.290^(+0.064)_(–0.050) R_J. 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 V < 9 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^(–1)
Spitzer and z' Secondary Eclipse Observations of the Highly Irradiated Transiting Brown Dwarf KELT-1b
We present secondary eclipse observations of the highly irradiated transiting
brown dwarf KELT-1b. These observations represent the first constraints on the
atmospheric dynamics of a highly irradiated brown dwarf, and the atmospheres of
irradiated giant planets at high surface gravity. Using the Spitzer Space
Telescope, we measure secondary eclipse depths of 0.195+/-0.010% at 3.6um and
0.200+/-0.012% at 4.5um. We also find tentative evidence for the secondary
eclipse in the z' band with a depth of 0.049+/-0.023%. These measured eclipse
depths are most consistent with an atmosphere model in which there is a strong
substellar hotspot, implying that heat redistribution in the atmosphere of
KELT-1b is low. While models with a more mild hotspot or even with dayside heat
redistribution are only marginally disfavored, models with complete heat
redistribution are strongly ruled out. The eclipse depths also prefer an
atmosphere with no TiO inversion layer, although a model with TiO inversion is
permitted in the dayside heat redistribution case, and we consider the
possibility of a day-night TiO cold trap in this object. For the first time, we
compare the IRAC colors of brown dwarfs and hot Jupiters as a function of
effective temperature. Importantly, our measurements reveal that KELT-1b has a
[3.6]-[4.5] color of 0.07+/-0.11, identical to that of isolated brown dwarfs of
similarly high temperature. In contrast, hot Jupiters generally show redder
[3.6]-[4.5] colors of ~0.4, with a very large range from ~0 to ~1. Evidently,
despite being more similar to hot Jupiters than to isolated brown dwarfs in
terms of external forcing of the atmosphere by stellar insolation, KELT-1b has
an atmosphere most like that of other brown dwarfs. This suggests that surface
gravity is very important in controlling the atmospheric systems of substellar
mass bodies.Comment: 14 pages, 3 tables, 11 figures. Accepted by ApJ. Updated to reflect
the accepted versio
Photosynthetic activity and population dynamics of Amoebobacter purpureus in a meromictic saline lake
Abstract A dense population of the purple sulfur bacterium Amoebobacter purpureus in the chemocline of meromictic Mahoney Lake (British Columbia, Canada) underwent consistent changes in biomass over a two year study period. The integrated amount of bacteriochlorophyll reached maxima in August and declined markedly during early fall. Bacteriochlorophyll was only weakly correlated with the light intensity and water temperature in the chemocline. In the summer, bacterial photosynthesis was limited by sulfide availability. During this period the intracellular sulfur concentration of A. purpureus cells decreased. A minimum concentration was measured at the top of the bacterial layer in August, when specific photosynthetic rates of A. purpureus indicated that only 14% of the cells were photosynthetically active. With the exception of a time period between August and September, the specific growth rates calculated from CO2 fixation rates of A. purpureus were similar to growth rates calculated from actual biomass changes in the bacterial layer. Between August and September 86% of the A. purpureus biomass disappeared from the chemocline and were deposited on the littoral sediment of Mahoney Lake or degraded within the mixolimnion. This rise of cells to the lake surface was not mediated by an increase in the specific gas vesicle content which remained constant between April and November. The upwelling phenomenon was related to the low sulfur content of A. purpureus cells and a low resistance of surface water layers against vertical mixing by wind
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