178 research outputs found
Extrasolar Planets in the Classroom
The field of extrasolar planets is still, in comparison with other
astrophysical topics, in its infancy. There have been about 300 or so
extrasolar planets detected and their detection has been accomplished by
various different techniques. Here we present a simple laboratory experiment to
show how planets are detected using the transit technique. Following the simple
analysis procedure describe we are able to determine the planetary radius to be
1.27 +/- 0.20 R_{J} which, within errors agrees with the establish value of
1.32 +/- 0.25 R_{J}.Comment: 7 pages, 2 figures, published in Physics Educatio
The high-energy spectrum of the nearby planet-hosting inactive mid-M dwarf LHS 3844
To fully characterize the atmospheres, or lack thereof, of terrestrial
exoplanets we must include the high-energy environments provided by their host
stars. The nearby mid-M dwarf LHS 3844 hosts a terrestrial world which lacks a
substantial atmosphere. We present a time series UV spectrum of LHS 3844 from
1131-3215A captured by HST/COS. We detect one flare in the FUV, which has an
absolute energy of 8.96+/-0.79e28 erg and an equivalent duration of 355+/-31 s.
We extract the flare and quiescent UV spectra separately. For each spectrum we
estimate the Ly-alpha flux using correlations between UV line strengths. We use
Swift-XRT to place an upper limit on the soft X-ray flux and construct a
differential emission model (DEM) to estimate flux that is obscured by the
interstellar medium. We compare the DEM flux estimates in the XUV to other
methods that rely on scaling from the Ly-alpha, Si IV, and N V lines in the UV.
The XUV, FUV, and NUV flux of LHS 3844 relative to its bolometric luminosity is
log10(Lband/LBol) = -3.65, -4.16, and -4.56, respectively, for the quiescent
state. These values agree with trends in high-energy flux as a function of
stellar effective temperature found by the MUSCLES survey for a sample of
early-M dwarfs. Many of the most spectroscopically accessible terrestrial
exoplanets orbit inactive mid- to late-M dwarfs like LHS 3844. Measurements of
M dwarf high-energy spectra are preferable for exoplanet characterization, but
are not always possible. The spectrum of LHS 3844 is a useful proxy for the
current radiation environment for these worlds.Comment: Published in AJ; HLSPs now availabl
Triple Reassortant H3N2 Influenza A Viruses, Canada, 2005
Since January 2005, H3N2 influenza viruses have been isolated from pigs and turkeys throughout Canada and from a swine farmer and pigs on the same farm in Ontario. These are human/classical swine/avian reassortants similar to viruses that emerged in US pigs in 1998 but with a distinct human-lineage neuraminidase gene
Hot Jupiter Magnetospheres
(Abridged) The upper atmospheres of close-in gas giant exoplanets are
subjected to intense heating/tidal forces from their parent stars.
Atomic/ionized hydrogen (H) layers are sufficiently rarefied that magnetic
pressure may dominate gas pressure for expected planetary magnetic field
strength. We examine the magnetospheric structure using a 3D isothermal
magnetohydrodynamic model that includes: a static "dead zone" near the magnetic
equator containing magnetically confined gas; a "wind zone" outside the
magnetic equator in which thermal pressure gradients and the
magneto-centrifugal-tidal effect give rise to transonic outflow; and a region
near the poles where sufficiently strong tidal forces may suppress transonic
outflow. Using dipole field geometry, we estimate the size of the dead zone to
be ~1-10 planetary radii for a range of parameters. To understand appropriate
base conditions for the 3D isothermal model, we compute a 1D thermal model in
which photoelectric heating from the stellar Lyman continuum is balanced by
collisionally-excited Lyman {\alpha} cooling. This 1D model exhibits a H layer
with temperatures T=5000-10000K down to pressures of 10-100 nbar. Using the 3D
isothermal model, we compute H column densities and Lyman {\alpha} transmission
spectra for parameters appropriate to HD 209458b. Line-integrated transit
depths of 5-10% can be achieved for the above base conditions. Strong magnetic
fields increase the transit signal while decreasing the mass loss, due to
higher covering fraction and density of the dead zone. In our model, most of
the transit signal arises from magnetically confined gas, some of which may be
outside the L1 equipotential. Hence the presence of gas outside the L1
equipotential does not directly imply mass loss. Lastly, we discuss the domain
of applicability for the magnetic wind model described in this paper and in the
Roche-lobe overflow model.Comment: 26 pages, 17 figures (5 color), 2 appendices; submitted to ApJ;
higher resolution version available at
http://www.astro.virginia.edu/~gbt8f/HotJupMag_fullres_astroph.pd
GMRT radio observations of the transiting extrasolar planet HD189733b at 244 and 614 MHz
We report a sensitive search for meter-wavelength emission at 244 and 614 MHz
from HD189733b, the nearest known extrasolar transiting planet of `hot-Jupiter'
type. To discriminate any planetary emission from possible stellar or
background contributions, we observed the system for 7.7 hours encompassing the
planet's eclipse behind the host star. These GMRT observations provide very low
(3 sigma) upper limits of 2 mJy at 244 MHz and 160 micro-Jy at 614 MHz. These
limits are, respectively, about 40 and 500 times deeper than those reported
recently at a nearby frequency of 340 MHz. Possible explanations of our
non-detection include: (1) the Earth being outside the planet's emission beam;
(2) its highly variable emission with more rapid flaring than the temporal
sampling in our observations; (3) the planetary emission being intrinsically
too weak; or more likely, (4) the emission being predominantly at lower
frequencies because of a weak planetary magnetic field. We briefly discuss
these possibilities and the constraints on this exo-planetary system
environment.Comment: Accepted for publication in A&A letter
The Revised TESS Input Catalog and Candidate Target List
We describe the catalogs assembled and the algorithms used to populate the
revised TESS Input Catalog (TIC), based on the incorporation of the Gaia second
data release. We also describe a revised ranking system for prioritizing stars
for 2-minute cadence observations, and assemble a revised Candidate Target List
(CTL) using that ranking. The TIC is available on the Mikulski Archive for
Space Telescopes (MAST) server, and an enhanced CTL is available through the
Filtergraph data visualization portal system at the URL
http://filtergraph.vanderbilt.edu/tess_ctl.Comment: 30 pages, 16 figures, submitted to AAS Journals; provided to the
community in advance of publication in conjunction with public release of the
TIC/CTL on 28 May 201
Multilevel Governance and Security: Security Sector Reform in the Central African Republic
This article analyses how the security sector reform (SSR) process in the Central African Republic was defined and implemented between 2008 and 2010, putting emphasis on the interactions between national and international actors. It advocates an approach which consists of expanding the agenda of the traditional multilevel governance approach and which seeks to seize both the top?down and the bottom?up dynamics of decision?making processes. The first objective is to capture the sets of actors and procedures which drove the reform process, and to map out the various levels of government at which decisions are made. Secondly – and more fundamentally – the article aims to capture the intermingling of domestic and international decision?making processes, which increasingly overlap and interfere with each other in Southern countries
GMRT search for 150 MHz radio emission from the transiting extrasolar planets HD189733b and HD209458b
We report a sensitive search for meter-wavelength emission at 150 MHz from
two prominent transiting extrasolar planets, HD189733b and HD209458b. To
distinguish any planetary emission from possible stellar or background
contributions, we monitored these systems just prior to, during, and after the
planet's eclipse behind the host star. No emission was detected from HD209458b
with a 3-sigma upper limit of 3.6 mJy. For HD189733b we obtain a 3-sigma upper
limit of 2.1 mJy and a marginal 2.7-sigma detection of about 1.9+/-0.7 mJy from
a direction just 13" from the star's coordinates (i.e., within the beam), but
its association with the planet remains unconfirmed. Thus, the present GMRT
observations provide unprecedentedly tight upper limits for meter wavelengths
emissions from these nearest two transiting type exoplanets. We point out
possible explanations of the non-detections and briefly discuss the resulting
constraints on these systems.Comment: To be published in Astronomy & Astrophysic
Three red suns in the sky: A transiting, terrestrial planet in a triple M-dwarf system at 6.9 pc
We present the discovery from Transiting Exoplanet Survey Satellite (TESS) data of LTT 1445Ab. At a distance of 6.9 pc, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use MEarth data and results from the Science Processing Operations Center data validation report to determine that the planet transits the primary star in the system. The planet has a radius of , an orbital period of days, and an equilibrium temperature of K. With radial velocities from the High Accuracy Radial Velocity Planet Searcher, we place a 3σ upper mass limit of 8.4 on the planet. LTT 1445Ab provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. We also present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicate a moderate amount of variability, in agreement with that observed in the TESS light-curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system hints that the entire system may be co-planar, implying that the system may have formed from the early fragmentation of an individual protostellar core.Accepted manuscrip
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