181 research outputs found
Which Radial Velocity Exoplanets Have Undetected Outer Companions?
(Abridged) The observed radial velocity (RV) eccentricity distribution for
extrasolar planets in single-planet systems shows that a significant fraction
of planets are eccentric (). Here we investigate the effects on an RV
planet's eccentricity produced by undetected outer companions. We have carried
out Monte Carlo simulations of mock RV data to understand this effect and
predict its impact on the observed distribution. We first quantify the
statistical effect of undetected outer companions and show that this alone
cannot explain the observed distribution. We then modify the simulations to
consist of two populations, one of zero-eccentricity planets in double-planet
systems and the other of single planets drawn from an eccentric distribution.
Our simulations show that a good fit to the observed distribution is obtained
with 45% zero-eccentricity double-planets and 55% single eccentric planets.
Matching the observed distribution allows us to determine the probability that
a known RV planet's orbital eccentricity has been biased by an undetected
wide-separation companion. Our simulations show that moderately-eccentric
planets, with and , have a and probability, respectively, of having an undetected outer companion. We
encourage both high-contrast direct imaging and RV follow-up surveys of known
RV planets with moderate eccentricities to test our predictions and look for
previously undetected outer companions.Comment: 23 pages (12 text, 2 tables, 9 figures). Accepted to the
Astrophysical Journal 30 June 200
High-Contrast 3.8 Micron Imaging Of The Brown Dwarf/Planet-Mass Companion to GJ 758
We present L' band (3.8 ) MMT/Clio high-contrast imaging data for the
nearby star GJ 758, which was recently reported by Thalmann et al. (2009) to
have one -- possibly two-- faint comoving companions (GJ 758B and ``C",
respectively). GJ 758B is detected in two distinct datasets. Additionally, we
report a \textit{possible} detection of the object identified by Thalmann et al
as ``GJ 758C" in our more sensitive dataset, though it is likely a residual
speckle. However, if it is the same object as that reported by Thalmann et al.
it cannot be a companion in a bound orbit. GJ 758B has a H-L' color redder than
nearly all known L--T8 dwarfs. Based on comparisons with the COND evolutionary
models, GJ 758B has T 560 K and a mass
ranging from 10--20 M if it is 1 Gyr old to 25--40
M if it is 8.7 Gyr old. GJ 758B is likely in a highly eccentric orbit, e
0.73, with a semimajor axis of 44 AU. Though GJ 758B is sometimes discussed within the context of
exoplanet direct imaging, its mass is likely greater than the deuterium-burning
limit and its formation may resemble that of binary stars rather than that of
jovian-mass planets.Comment: 14 pages, 3 figures. Accepted for publication in The Astrophysical
Journal Letter
Wertigkeit der funktionellen MR-Urografie in der Beurteilung kongenitaler Anomalien von Niere und Harntrakt: retrospektive Datenanalyse zum Vergleich von funktioneller MR-Urografie und 99mTc-MAG3-Diureseszintigrafie bzw. Nierensonografie
Zur Funktionsdiagnostik bei Kindern mit kongenitalen Anomalien von Niere und Harntrakt (CAKUT) wird neben dem Goldstandard-Verfahren 99mTc-MAG3-Diureseszintigrafie derzeit die funktionelle MR-Urografie (fMRU) als kombiniert funktionell-morphologisches Untersuchungsverfahren etabliert. Ziel der Untersuchung ist die Evaluation der Wertigkeit der fMRU in der Beurteilung von CAKUT bezüglich seitengetrennter Nierenfunktion und Harnabfluss sowie Morphologie. Bei 112 pädiatrischen Patienten mit CAKUT des Universitätsklinikums Jena wurden die morphologischen Untersuchungsergebnisse von fMRU und Nierensonografie verglichen. In einer Untergruppe von 30 Patienten wurde ein Vergleich zwischen seitengetrennten Funktionsparametern von fMRU und Szintigrafie angestellt. Die fMRU ermöglichte bei allen 112 Patienten eine detaillierte anatomisch-morphologische Darstellung des gesamten Harntraktes, wobei sonografische Vorbefunde durch die fMRU bestätigt oder gar spezifiziert wurden. Bezüglich seitengetrennter Nierenfunktion und Harnabfluss ergaben sich zwischen fMRU und Szintigrafie statistisch noch Differenzen. In Übereinstimmung mit der aktuellen Studienlage konnte aufgezeigt werden, dass die fMRU eine adäquate Beurteilung von Funktion und Obstruktion ermöglicht. In der morphologischen Beurteilung ist sie sowohl der Sonografie als auch der Szintigrafie überlegen. Obwohl fMRU und Szintigrafie ähnliche funktionelle Parameter untersuchen, ist ein unmittelbarer statistischer Vergleich der ermittelten Werte nur begrenzt möglich, da methodisch grundlegende Unterschiede bestehen. Wenngleich die fMRU Nierensonografie und Szintigrafie in naher Zukunft nicht ersetzen wird, zeigt sie dennoch großes Potential als komplementäre Untersuchungsmethode. Vor allem in der Diagnostik komplexer kongenitaler Harntraktanomalien, bei uneindeutigen Sonografiebefunden und in der präoperativen Planung sollte sie perspektivisch in spezialisierten Zentren vermehrt eingesetzt werden
Direct Imaging Confirmation and Characterization of a Dust-Enshrouded Candidate Exoplanet Orbiting Fomalhaut
We present Subaru/IRCS J band data for Fomalhaut and a (re)reduction of
archival 2004--2006 HST/ACS data first presented by Kalas et al. (2008). We
confirm the existence of a candidate exoplanet, Fomalhaut b, in both the 2004
and 2006 F606W data sets at a high signal-to-noise. Additionally, we confirm
the detection at F814W and present a new detection in F435W. Fomalhaut b's
space motion may be consistent with it being in an apsidally-aligned, non
debris ring-crossing orbit, although new astrometry is required for firmer
conclusions. We cannot confirm that Fomalhaut b exhibits 0.7-0.8 mag
variability cited as evidence for planet accretion or a semi-transient dust
cloud. The new, combined optical SED and IR upper limits confirm that emission
identifying Fomalhaut b originates from starlight scattered by small dust, but
this dust is most likely associated with a massive body. The Subaru and
IRAC/4.5 micron upper limits imply M < 2 Mj, still consistent with the range of
Fomalhaut b masses needed to sculpt the disk. Fomalhaut b is very plausibly "a
planet identified from direct imaging" even if current images of it do not,
strictly speaking, show thermal emission from a directly imaged planet.Comment: 13 pages, 3 figures; ApJ Letters in press. Fixed one outdated
reference and a few typo
Direct Detection and Orbit Analysis of the Exoplanets HR 8799 bcd from Archival 2005 Keck/NIRC2 Data
We present previously unpublished July 2005 -band coronagraphic data of
the young, planet-hosting star HR 8799 from the newly-released Keck/NIRC2
archive. Despite poor observing conditions, we detect three of the planetary
companions (HR 8799 bcd), two of them (HR 8799 bc) without advanced image
processing. Comparing these data with previously published 1998-2011 astrometry
and that from re-reduced October 2010 Keck data constrains the orbits of the
planets. Analyzing the planets' astrometry separately, HR 8799 d's orbit is
likely inclined at least 25 from face-on and the others may be on in
inclined orbits. For semimajor axis ratios consistent with a 4:2:1 mean-motion
resonance, our analysis yields precise values for HR 8799 bcd's orbital
parameters and strictly constrains the planets' eccentricities to be less than
0.18--0.3. However, we find no acceptable orbital solutions with this resonance
that place the planets in face-on orbits; HR 8799 d shows the largest deviation
from such orbits. Moreover, few orbits make HR 8799 d coplanar with b and c,
whereas dynamical stability analyses used to constrain the planets' masses
typically assume coplanar and/or face-on orbits. This paper illustrates the
significant science gain enabled with the release of the NIRC2 archive.Comment: 7 pages, 3 figures, ApJ Letters in pres
New Extinction and Mass Estimates of the Low-mass Companion 1RXS 1609 B with the Magellan AO System: Evidence of an Inclined Dust Disk
We used the Magellan adaptive optics system to image the 11 Myr substellar
companion 1RXS 1609 B at the bluest wavelengths to date (z' and Ys). Comparison
with synthetic spectra yields a higher temperature than previous studies of
and significant dust extinction of
mag. Mass estimates based on the DUSTY tracks gives
0.012-0.015 Msun, making the companion likely a low-mass brown dwarf surrounded
by a dusty disk. Our study suggests that 1RXS 1609 B is one of the 25% of Upper
Scorpius low-mass members harboring disks, and it may have formed like a star
and not a planet out at 320 AU.Comment: 5 pages, 4 figures; accepted to ApJ
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