224 research outputs found
X-RED: A Satellite Mission Concept To Detect Early Universe Gamma Ray Bursts
Gamma ray bursts (GRBs) are the most energetic eruptions known in the
Universe. Instruments such as Compton-GRO/BATSE and the GRB monitor on BeppoSAX
have detected more than 2700 GRBs and, although observational confirmation is
still required, it is now generally accepted that many of these bursts are
associated with the collapse of rapidly spinning massive stars to form black
holes. Consequently, since first generation stars are expected to be very
massive, GRBs are likely to have occurred in significant numbers at early
epochs. X-red is a space mission concept designed to detect these extremely
high redshifted GRBs, in order to probe the nature of the first generation of
stars and hence the time of reionisation of the early Universe. We demonstrate
that the gamma and x-ray luminosities of typical GRBs render them detectable up
to extremely high redshifts (z~10-30), but that current missions such as HETE2
and SWIFT operate outside the observational range for detection of high
redshift GRB afterglows. Therefore, to redress this, we present a complete
mission design from the science case to the mission architecture and payload,
the latter comprising three instruments, namely wide field x-ray cameras to
detect high redshift gamma-rays, an x-ray focussing telescope to determine
accurate coordinates and extract spectra, and an infrared spectrograph to
observe the high redshift optical afterglow. The mission is expected to detect
and identify for the first time GRBs with z > 10, thereby providing constraints
on properties of the first generation of stars and the history of the early
Universe.Comment: 14 pages, 10 figures, spie.cls neede
Does the ICU experience predict psychological symptoms in relatives of patients with severe sepsis and end-of-life decisions?
EPIC 219388192 b - an inhabitant of the brown dwarf desert in the Ruprecht 147 open cluster
We report the discovery of EPIC 219388192 b, a transiting brown dwarf in a
5.3-day orbit around a member star of Ruprecht-147, the oldest nearby open
cluster association, which was photometrically monitored by K2 during its
Campaign 7. We combine the K2 time-series data with ground-based adaptive
optics imaging and high resolution spectroscopy to rule out false positive
scenarios and determine the main parameters of the system. EPIC 219388192 b has
a radius of =~ and mass of
=~, yielding a mean density of
~. The host star is nearly a Solar twin with
mass =~, radius
=~, effective temperature
=~K and iron abundance [Fe/H]=~dex.
Its age, spectroscopic distance, and reddening are consistent with those of
Ruprecht-147, corroborating its cluster membership. EPIC 219388192 b is the
first brown dwarf with precise determinations of mass, radius and age, and
serves as benchmark for evolutionary models in the sub-stellar regime.Comment: 13 pages, 11 figures, 4 tables, submitted to AAS Journal
K2-137 b: an Earth-sized planet in a 4.3-hour orbit around an M-dwarf
We report the discovery from K2 of a transiting terrestrial planet in an
ultra-short-period orbit around an M3-dwarf. K2-137 b completes an orbit in
only 4.3 hours, the second-shortest orbital period of any known planet, just 4
minutes longer than that of KOI 1843.03, which also orbits an M-dwarf. Using a
combination of archival images, AO imaging, RV measurements, and light curve
modelling, we show that no plausible eclipsing binary scenario can explain the
K2 light curve, and thus confirm the planetary nature of the system. The
planet, whose radius we determine to be 0.89 +/- 0.09 Earth radii, and which
must have a iron mass fraction greater than 0.45, orbits a star of mass 0.463
+/- 0.052 Msol and radius 0.442 +/- 0.044 Rsol.Comment: 12 pages, 9 figures, accepted for publication in MNRA
Three Small Planets Transiting a Hyades Star
We present the discovery of three small planets transiting K2-136 (LP 358
348, EPIC 247589423), a late K dwarf in the Hyades. The planets have orbital
periods of , , and
days, and radii of , , and , respectively. With an age of
600-800 Myr, these planets are some of the smallest and youngest transiting
planets known. Due to the relatively bright (J=9.1) host star, the planets are
compelling targets for future characterization via radial velocity mass
measurements and transmission spectroscopy. As the first known star with
multiple transiting planets in a cluster, the system should be helpful for
testing theories of planet formation and migration.Comment: Accepted to The Astronomical Journa
Exoplanets around Low-mass Stars Unveiled by K2
We present the detection and follow-up observations of planetary candidates
around low-mass stars observed by the K2 mission. Based on light-curve
analysis, adaptive-optics imaging, and optical spectroscopy at low and high
resolution (including radial velocity measurements), we validate 16 planets
around 12 low-mass stars observed during K2 campaigns 5-10. Among the 16
planets, 12 are newly validated, with orbital periods ranging from 0.96-33
days. For one of the planets (K2-151b) we present ground-based transit
photometry, allowing us to refine the ephemerides. Combining our K2 M-dwarf
planets together with the validated or confirmed planets found previously, we
investigate the dependence of planet radius on stellar insolation and
metallicity [Fe/H]. We confirm that for periods days, planets
with a radius are less common than planets with a
radius between 1-2. We also see a hint of the "radius valley"
between 1.5 and 2 that has been seen for close-in planets around
FGK stars. These features in the radius/period distribution could be attributed
to photoevaporation of planetary envelopes by high-energy photons from the host
star, as they have for FGK stars. For the M dwarfs, though, the features are
not as well defined, and we cannot rule out other explanations such as
atmospheric loss from internal planetary heat sources, or truncation of the
protoplanetary disk. There also appears to be a relation between planet size
and metallicity: those few planets larger than about 3 are found
around the most metal-rich M dwarfs.Comment: 29 pages, 21 figures, 6 tables, Accepted in Astronomical Journa
The K2-ESPRINT Project II: Spectroscopic follow-up of three exoplanet systems from Campaign 1 of K2
We report on Doppler observations of three transiting planet candidates that were detected during Campaign 1 of the K2 mission. The Doppler observations were conducted with FIES, HARPS-N, and HARPS. We measure the mass of EPIC 201546283b, and provide constraints and upper limits for EPIC 201295312b and EPIC 201577035b. EPIC 201546283b is a warm Neptune orbiting its host star in 6.77 days and has a radius of 4.45_(-0.33)^(+0.33)R_â and a mass of 29.1_(-7.4)^(+7.5)M_â, which leads to a mean density of 1.80_(-0.55)^(+0.70) cm^(-3). EPIC 201295312b is smaller than Neptune with an orbital period of 5.66 days, a radius of 2.75_(-0.22^)(0.24)R_â, and we constrain the mass to be below 12 M_â at 95% confidence. We also find a long-term trend indicative of another body in the system. EPIC 201577035b, which was previously confirmed as the planet K2-10b, is smaller than Neptune, orbiting its host star in 19.3 days, with a radius of 3.84_(-0.34)^(+0.35)R_â. We determine its mass to be 27_(-16)^(+17)M_â, with a 95% confidence upper limit at 57M_â, and a mean density of 2.6_(-1.6)^(+2.1)g cm^(-3). These measurements join the relatively small collection of planets smaller than Neptune with measurements or constraints of the mean density. Our code for performing K2 photometry and detecting planetary transits is now publicly available
Global impacts of aerosols from particular source regions and sectors
We study the impacts of present-day aerosols emitted from particular regions and from particular sectors, as predicted by the Goddard Institute for Space Studies GCM, We track the distribution and direct radiative forcing of aerosols, including sulfate and black and organic carbon, emitted from major source regions (North America, Europe, south Asia, Southeast Asia, South America, and Africa). We also partition the emissions by sector, including industrial, power, residential, transport, biomass burning, and natural. Southeast Asia produces 15% and 10% of the world's black carbon and sulfate and exports over 2/3 of this burden over the Northern Hemisphere. About 1/2 of the SO<inf>2</inf> emitted by Southeast Asia and Europe is not converted to sulfate because of oxidant limitation. Although Africa has the largest biomass burning emissions, South America generates a larger (about 20% of the global carbonaceous) aerosol burden; about 1/2 of this burden is exported and dominates the carbonaceous aerosol load in the Southern Hemisphere. Calculated direct anthropogenic radiative forcings are -0.29, -0.06, and 0.24 W m-2 for sulfate, organic, and black carbon, respectively. The largest BC radiative forcings are from residential (0.09 W m-2) and transport (0.06 W m-2) sectors, making these potential targets to counter global warming. However, scattering components within these sectors reduce these to 0.04 and 0.03 W m-2, respectively. Most anthropogenic sulfate comes from power and industry sectors, and these sectors are responsible for the large negative aerosol forcings over the central Northern Hemisphere. Copyright 2007 by the American Geophysical Union
Company for the Ultra-high Density, Ultra-short Period Sub-Earth GJ 367 b: Discovery of Two Additional Low-mass Planets at 11.5 and 34 Days
GJ 367 is a bright (V â 10.2) M1 V star that has been recently found to host a transiting ultra-short period sub-Earth on a 7.7 hr orbit. With the aim of improving the planetary mass and radius and unveiling the inner architecture of the system, we performed an intensive radial velocity follow-up campaign with the HARPS spectrographâcollecting 371 high-precision measurements over a baseline of nearly 3 yrâand combined our Doppler measurements with new TESS observations from sectors 35 and 36. We found that GJ 367 b has a mass of M b = 0.633 ± 0.050 M â and a radius of R b = 0.699 ± 0.024 R â, corresponding to precisions of 8% and 3.4%, respectively. This implies a planetary bulk density of Ï b = 10.2 ± 1.3 g cmâ3, i.e., 85% higher than Earthâs density. We revealed the presence of two additional non-transiting low-mass companions with orbital periods of âŒ11.5 and 34 days and minimum masses of M c sin i c = 4.13 ± 0.36 M â and M d sin i d = 6.03 ± 0.49 M â, respectively, which lie close to the 3:1 mean motion commensurability. GJ 367 b joins the small class of high-density planets, namely the class of super-Mercuries, being the densest ultra-short period small planet known to date. Thanks to our precise mass and radius estimates, we explored the potential internal composition and structure of GJ 367 b, and found that it is expected to have an iron core with a mass fraction of 0.91 â 0.23 + 0.07 . How this iron core is formed and how such a high density is reached is still not clear, and we discuss the possible pathways of formation of such a small ultra-dense planet
Upper limits on the strength of periodic gravitational waves from PSR J1939+2134
The first science run of the LIGO and GEO gravitational wave detectors
presented the opportunity to test methods of searching for gravitational waves
from known pulsars. Here we present new direct upper limits on the strength of
waves from the pulsar PSR J1939+2134 using two independent analysis methods,
one in the frequency domain using frequentist statistics and one in the time
domain using Bayesian inference. Both methods show that the strain amplitude at
Earth from this pulsar is less than a few times .Comment: 7 pages, 1 figure, to appear in the Proceedings of the 5th Edoardo
Amaldi Conference on Gravitational Waves, Tirrenia, Pisa, Italy, 6-11 July
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