509 research outputs found
On the Frequency of Potential Venus Analogs from Kepler Data
The field of exoplanetary science has seen a dramatic improvement in
sensitivity to terrestrial planets over recent years. Such discoveries have
been a key feature of results from the {\it Kepler} mission which utilizes the
transit method to determine the size of the planet. These discoveries have
resulted in a corresponding interest in the topic of the Habitable Zone (HZ)
and the search for potential Earth analogs. Within the Solar System, there is a
clear dichotomy between Venus and Earth in terms of atmospheric evolution,
likely the result of the large difference ( factor of two) in incident
flux from the Sun. Since Venus is 95\% of the Earth's radius in size, it is
impossible to distinguish between these two planets based only on size. In this
paper we discuss planetary insolation in the context of atmospheric erosion and
runaway greenhouse limits for planets similar to Venus. We define a ``Venus
Zone'' (VZ) in which the planet is more likely to be a Venus analog rather than
an Earth analog. We identify 43 potential Venus analogs with an occurrence rate
(\eta_{\venus}) of and for M
dwarfs and GK dwarfs respectively.Comment: 6 pages, 3 figures, 2 tables. Accepted for publication in the
Astrophysical Journal Letters. More information and graphics can be found at
the Habitable Zone Gallery (http://hzgallery.org
Host Galaxies Catalog Used in LIGO Searches for Compact Binary Coalescence Events
An up-to-date catalog of nearby galaxies considered as hosts of binary
compact objects is provided with complete information about sky position,
distance, extinction-corrected blue luminosity and error estimates. With our
current understanding of binary evolution, rates of formation and coalescence
for binary compact objects scale with massive-star formation and hence the
(extinction-corrected) blue luminosity of host galaxies. Coalescence events in
binary compact objects are among the most promising gravitational-wave sources
for ground-based gravitational-wave detectors such as LIGO. Our catalog and
associated error estimates are important for the interpretation of analyses,
carried out for LIGO, to constrain the rates of compact binary coalescence,
given an astrophysical population model for the sources considered. We discuss
how the notion of effective distance, created to account for the antenna
pattern of a gravitational-wave detector, must be used in conjunction with our
catalog. We note that the catalog provided can be used on other astronomical
analysis of populations that scale with galaxy blue luminosity.Comment: 29 pages, 7 figures, Accepted to Astrophysical Journal. To appear in
March 20 2008 Astrophysical Journa
Demarcating circulation regimes of synchronously rotating terrestrial planets within the habitable zone
We investigate the atmospheric dynamics of terrestrial planets in synchronous rotation within the habitable zone of low-mass stars using the Community Atmosphere Model (CAM). The surface temperature contrast between day and night hemispheres decreases with an increase in incident stellar flux, which is opposite the trend seen on gas giants. We define three dynamical regimes in terms of the equatorial Rossby deformation radius and the Rhines length. The slow rotation regime has a mean zonal circulation that spans from day to night side, with both the Rossby deformation radius and the Rhines length exceeding planetary radius, which occurs for planets around stars with effective temperatures of 3300 K to 4500 K (rotation period > 20 days). Rapid rotators have a mean zonal circulation that partially spans a hemisphere and with banded cloud formation beneath the substellar point, with the Rossby deformation radius is less than planetary radius, which occurs for planets orbiting stars with effective temperatures of less than 3000 K (rotation period < 5 days). In between is the Rhines rotation regime, which retains a thermally-direct circulation from day to night side but also features midlatitude turbulence-driven zonal jets. Rhines rotators occur for planets around stars in the range of 3000 K to 3300 K (rotation period ∼ 5 to 20 days), where the Rhines length is greater than planetary radius but the Rossby deformation radius is less than planetary radius. The dynamical state can be observationally inferred from comparing the morphology of the thermal emission phase curves of synchronously rotating planets
Optimal Location of Sources in Transportation Networks
We consider the problem of optimizing the locations of source nodes in
transportation networks. A reduction of the fraction of surplus nodes induces a
glassy transition. In contrast to most constraint satisfaction problems
involving discrete variables, our problem involves continuous variables which
lead to cavity fields in the form of functions. The one-step replica symmetry
breaking (1RSB) solution involves solving a stable distribution of functionals,
which is in general infeasible. In this paper, we obtain small closed sets of
functional cavity fields and demonstrate how functional recursions are
converted to simple recursions of probabilities, which make the 1RSB solution
feasible. The physical results in the replica symmetric (RS) and the 1RSB
frameworks are thus derived and the stability of the RS and 1RSB solutions are
examined.Comment: 38 pages, 18 figure
Exploring Kepler Giant Planets in the Habitable Zone
The Kepler mission found hundreds of planet candidates within the habitable
zones (HZ) of their host star, including over 70 candidates with radii larger
than 3 Earth radii () within the optimistic habitable zone (OHZ)
(Kane et al. 2016). These giant planets are potential hosts to large
terrestrial satellites (or exomoons) which would also exist in the HZ. We
calculate the occurrence rates of giant planets (~3.0--25~) in
the OHZ and find a frequency of for G stars, for K stars, and for M stars. We compare this with
previously estimated occurrence rates of terrestrial planets in the HZ of G, K
and M stars and find that if each giant planet has one large terrestrial moon
then these moons are less likely to exist in the HZ than terrestrial planets.
However, if each giant planet holds more than one moon, then the occurrence
rates of moons in the HZ would be comparable to that of terrestrial planets,
and could potentially exceed them. We estimate the mass of each planet
candidate using the mass-radius relationship developed by Chen & Kipping
(2016). We calculate the Hill radius of each planet to determine the area of
influence of the planet in which any attached moon may reside, then calculate
the estimated angular separation of the moon and planet for future imaging
missions. Finally, we estimate the radial velocity semi-amplitudes of each
planet for use in follow up observations.Comment: 19 Pages, 16 Figures, 5 Table
A List of Galaxies for Gravitational Wave Searches
We present a list of galaxies within 100 Mpc, which we call the Gravitational
Wave Galaxy Catalogue (GWGC), that is currently being used in follow-up
searches of electromagnetic counterparts from gravitational wave searches. Due
to the time constraints of rapid follow-up, a locally available catalogue of
reduced, homogenized data is required. To achieve this we used four existing
catalogues: an updated version of the Tully Nearby Galaxy Catalog, the Catalog
of Neighboring Galaxies, the V8k catalogue and HyperLEDA. The GWGC contains
information on sky position, distance, blue magnitude, major and minor
diameters, position angle, and galaxy type for 53,255 galaxies. Errors on these
quantities are either taken directly from the literature or estimated based on
our understanding of the uncertainties associated with the measurement method.
By using the PGC numbering system developed for HyperLEDA, the catalogue has a
reduced level of degeneracies compared to catalogues with a similar purpose and
is easily updated. We also include 150 Milky Way globular clusters. Finally, we
compare the GWGC to previously used catalogues, and find the GWGC to be more
complete within 100 Mpc due to our use of more up-to-date input catalogues and
the fact that we have not made a blue luminosity cut.Comment: Accepted for publication in Classical and Quantum Gravity, 13 pages,
7 figure
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