225 research outputs found
Age differences in children's referential communication performance : an investigation of task effects
Social and motivational influences on reading
Pages numbered 1-70Bibliography: p. 47-69Supported in part by the National Institute of Education under contract no. NIE-400-81-003
Retired A Stars and Their Companions: Exoplanets Orbiting Three Intermediate-Mass Subgiants
We report precision Doppler measurements of three intermediate-mass subgiants
from Lick and Keck Observatories. All three stars show variability in their
radial velocities consistent with planet-mass companions in Keplerian orbits.
We find a planet with a minimum mass of 2.5 Mjup in a 351.5 day orbit around HD
192699, a planet with a minimum mass of 2.0 Mjup in a 341.1 day orbit around HD
210702, and a planet with a minimum mass of 0.61 Mjup in a 297.3 day orbit
around HD 175541. Stellar mass estimates from evolutionary models indicate that
all of these stars were formerly A-type dwarfs with masses ranging from 1.65 to
1.85 Msun. These three long-period planets would not have been detectable
during their stars' main-sequence phases due to the large rotational velocities
and stellar jitter exhibited by early-type dwarfs. There are now 9 "retired"
(evolved) A-type stars (Mstar > 1.6 Msun) with known planets. All 9 planets
orbit at distances a \geq 0.78 AU, which is significantly different than the
semimajor axis distribution of planets around lower-mass stars. We examine the
possibility that the observed lack of close-in planets is due to engulfment by
their expanding host stars, but we find that this explanation is inadequate
given the relatively small stellar radii of K giants (Rstar < 32 Rsun = 0.15
AU) and subgiants (Rstar < 7 Rsun = 0.03 AU). Instead, we conclude that planets
around intermediate-mass stars reside preferentially beyond ~0.8 AU, which may
be a reflection of different formation and migration histories of planets
around A-type stars.Comment: 31 pages, 9 figures, 6 tables, ApJ accepted, corrected minor typo
A New Planet Around an M Dwarf: Revealing a Correlation Between Exoplanets and Stellar Mass
We report precise Doppler measurements of GJ317 (M3.5V) that reveal the
presence of a planet with a minimum mass Msini = 1.2 Mjup in an eccentric,
692.9 day orbit. GJ317 is only the third M dwarf with a Doppler-detected Jovian
planet. The residuals to a single-Keplerian fit show evidence of a possible
second orbital companion. The inclusion of an additional Jupiter-mass planet (P
= 2700 days, Msini = 0.83 Mjup) improves the quality of fit significantly,
reducing the rms from 12.5 m/s to 6.32 m/s. A false-alarm test yields a 1.1%
probability that the curvature in the residuals of the single-planet fit is due
to random fluctuations, lending additional credibility to the two-planet model.
However, our data only marginally constrain a two-planet fit and further
monitoring is necessary to fully characterize the properties of the second
planet. To study the effect of stellar mass on Jovian planet occurrence we
combine our samples of M stars, Solar-mass dwarfs and intermediate-mass
subgiants. We find a positive correlation between stellar mass and the
occurrence rate of Jovian planets within 2.5 AU; the former A-type stars in our
sample are nearly 5 times more likely than the M dwarfs to harbor a giant
planet. Our analysis shows that the correlation between Jovian planet
occurrence and stellar mass remains even after accounting for the effects of
stellar metallicity.Comment: ApJ accepted, 27 pages, 6 figures, 3 table
The Prograde Orbit of Exoplanet TrES-2b
We monitored the Doppler shift of the G0V star TrES-2 throughout a transit of
its giant planet. The anomalous Doppler shift due to stellar rotation (the
Rossiter-McLaughlin effect) is discernible in the data, with a signal-to-noise
ratio of 2.9, even though the star is a slow rotator. By modeling this effect
we find that the planet's trajectory across the face of the star is tilted by
-9 +/- 12 degrees relative to the projected stellar equator. With 98%
confidence, the orbit is prograde.Comment: ApJ, in press [15 pages
A Long-Period Jupiter-Mass Planet Orbiting the Nearby M Dwarf GJ849
We report precise Doppler measurements of GJ849 (M3.5V) that reveal the
presence of a planet with a minimum mass of 0.82 Mjup in a 5.16 year orbit. At
a = 2.35 AU, GJ849b is the first Doppler-detected planet discovered around an M
dwarf to orbit beyond 0.21 AU, and is only the second Jupiter mass planet
discovered around a star less massive than 0.5 Msun. This detection brings to 4
the number of M stars known to harbor planets. Based on the results of our
survey of 1300 FGKM main--sequence stars we find that giant planets within 2.5
AU are ~3 times more common around GK stars than around M stars. Due to the
GJ849's proximity of 8.8 pc, the planet's angular separation is 0."27, making
this system a prime target for high--resolution imaging using adaptive optics
and future space--borne missions such as the Space Interferometry Mission. We
also find evidence of a linear trend in the velocity time series, which may be
indicative of an additional planetary companion.Comment: 12 pages, 3 figues, 2 tables, PASP Accepte
Measurement of the Spin-Orbit Alignment in the Exoplanetary System HD 189733
We present spectroscopy of a transit of the exoplanet HD 189733b. By modeling
the Rossiter-McLaughlin effect (the anomalous Doppler shift due to the partial
eclipse of the rotating stellar surface), we find the angle between the sky
projections of the stellar spin axis and orbit normal to be lambda = -1.4 +/-
1.1 deg. This is the third case of a ``hot Jupiter'' for which lambda has been
measured. In all three cases lambda is small, ruling out random orientations
with 99.96% confidence, and suggesting that the inward migration of hot
Jupiters generally preserves spin-orbit alignment.Comment: ApJ Letters, in pres
Stellar Spin-Orbit Misalignment in a Multiplanet System
Stars hosting hot Jupiters are often observed to have high obliquities,
whereas stars with multiple co-planar planets have been seen to have low
obliquities. This has been interpreted as evidence that hot-Jupiter formation
is linked to dynamical disruption, as opposed to planet migration through a
protoplanetary disk. We used asteroseismology to measure a large obliquity for
Kepler-56, a red giant star hosting two transiting co-planar planets. These
observations show that spin-orbit misalignments are not confined to hot-Jupiter
systems. Misalignments in a broader class of systems had been predicted as a
consequence of torques from wide-orbiting companions, and indeed
radial-velocity measurements revealed a third companion in a wide orbit in the
Kepler-56 system.Comment: Accepted for publication in Science, published online on October 17
2013; PDF includes main article and supplementary materials (65 pages, 27
figures, 7 tables); v2: small correction to author lis
First radial velocity results from the MINiature Exoplanet Radial Velocity Array (MINERVA)
The MINiature Exoplanet Radial Velocity Array (MINERVA) is a dedicated
observatory of four 0.7m robotic telescopes fiber-fed to a KiwiSpec
spectrograph. The MINERVA mission is to discover super-Earths in the habitable
zones of nearby stars. This can be accomplished with MINERVA's unique
combination of high precision and high cadence over long time periods. In this
work, we detail changes to the MINERVA facility that have occurred since our
previous paper. We then describe MINERVA's robotic control software, the
process by which we perform 1D spectral extraction, and our forward modeling
Doppler pipeline. In the process of improving our forward modeling procedure,
we found that our spectrograph's intrinsic instrumental profile is stable for
at least nine months. Because of that, we characterized our instrumental
profile with a time-independent, cubic spline function based on the profile in
the cross dispersion direction, with which we achieved a radial velocity
precision similar to using a conventional "sum-of-Gaussians" instrumental
profile: 1.8 m s over 1.5 months on the RV standard star HD 122064.
Therefore, we conclude that the instrumental profile need not be perfectly
accurate as long as it is stable. In addition, we observed 51 Peg and our
results are consistent with the literature, confirming our spectrograph and
Doppler pipeline are producing accurate and precise radial velocities.Comment: 22 pages, 9 figures, submitted to PASP, Peer-Reviewed and Accepte
The genomes of two key bumblebee species with primitive eusocial organization
Background: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. Results: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. Conclusions: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation
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