1,966 research outputs found
Direct Imaging of Multiple Planets Orbiting the Star HR 8799
Direct imaging of exoplanetary systems is a powerful technique that can
reveal Jupiter-like planets in wide orbits, can enable detailed
characterization of planetary atmospheres, and is a key step towards imaging
Earth-like planets. Imaging detections are challenging due to the combined
effect of small angular separation and large luminosity contrast between a
planet and its host star. High-contrast observations with the Keck and Gemini
telescopes have revealed three planets orbiting the star HR 8799, with
projected separations of 24, 38, and 68 astronomical units. Multi-epoch data
show counter-clockwise orbital motion for all three imaged planets. The low
luminosity of the companions and the estimated age of the system imply
planetary masses between 5 and 13 times that of Jupiter. This system resembles
a scaled-up version of the outer portion of our Solar System.Comment: 30 pages, 5 figures, Research Article published online in Science
Express Nov 13th, 200
Astrometric Monitoring of the HR 8799 Planets: Orbit Constraints from Self-Consistent Measurements
We present new astrometric measurements from our ongoing monitoring campaign
of the HR 8799 directly imaged planetary system. These new data points were
obtained with NIRC2 on the W.M. Keck II 10 meter telescope between 2009 and
2014. In addition, we present updated astrometry from previously published
observations in 2007 and 2008. All data were reduced using the SOSIE algorithm,
which accounts for systematic biases present in previously published
observations. This allows us to construct a self-consistent data set derived
entirely from NIRC2 data alone. From this dataset, we detect acceleration for
two of the planets (HR 8799b and e) at 3. We also assess possible
orbital parameters for each of the four planets independently. We find no
statistically significant difference in the allowed inclinations of the
planets. Fitting the astrometry while forcing coplanarity also returns
consistent to within 1 of the best fit values, suggesting that if
inclination offsets of 20 are present, they are not detectable
with current data. Our orbital fits also favor low eccentricities, consistent
with predictions from dynamical modeling. We also find period distributions
consistent to within 1 with a 1:2:4:8 resonance between all planets.
This analysis demonstrates the importance of minimizing astrometric systematics
when fitting for solutions to highly undersampled orbits.Comment: 18 pages, 11 figures. Accepted for publication in A
Phase-Dependent Properties of Extrasolar Planet Atmospheres
Recently the Spitzer Space Telescope observed the transiting extrasolar
planets, TrES-1 and HD209458b. These observations have provided the first
estimates of the day side thermal flux from two extrasolar planets orbiting
Sun-like stars. In this paper, synthetic spectra from atmospheric models are
compared to these observations. The day-night temperature difference is
explored and phase-dependent flux densities are predicted for both planets. For
HD209458b and TrES-1, models with significant day-to-night energy
redistribution are required to reproduce the observations. However, the
observational error bars are large and a range of models remains viable.Comment: 8 pages, 7 figures, accepted for publication in the Astrophysical
Journa
A Redescription of the First Instar of Rhantus calidus (Fabricius) (Coleoptera: Dytiscidae) with Notes on its Biology
First instars of Rhantus calidus (Fabricius) representing a Georgia population are described and illustrated. Dimensions are provided along with an analysis of the primary chaetotaxy of legs, head, and last abdominal segment. The presence of first instars at the study site demonstrated that R. calidus either requires or is at least tolerant of warmer temperatures for completion of its life cycle. Habitats with temperatures comparable to this site were likely present in a warm Atlantic coastal enclave during the last glacial maximum (LGM), making it probable that the LGM dytiscid fauna of Georgia included R. calidus
Corrections for Identification of Mature Larvae of Rhantus calidus (Fabricius) and Hoperius planatus Fall (Coleoptera: Dytiscidae) in Georgia
Characters for identification of mature larvae of Rhantus calidus and Hoperius planatus in Georgia are evaluated and critiqued. MaÂture larvae of R. calidus have only eight cereal sensilla (setae) while those of Hoperius have numerous medial and lateral sensilla. This is presented as an obvious and reliable character set for identification of R. calidus and H. planatus in Georgia
At Physiological Temperatures the ATPase Rates of Shortening Soleus and Psoas Myofibrils Are Similar
AbstractWe obtained the temperature dependences of the adenosine triphosphatase (ATPase) activities (calcium-activated and relaxed) of myofibrils from a slow muscle, which we compared with those from a fast muscle. We chose rabbit soleus and psoas because their myosin heavy chains are almost pure: isoforms I and IIX, respectively. The Arrhenius plots of the ATPases are linear (4–35°C) with energies of activation for soleus myofibrils 155kJmol−1 (activated) and 78kJmol−1 (relaxed). With psoas myofibrils, the energies of activation were 71kJmol−1 (activated) and 60kJmol−1 (relaxed). When extrapolated to 42°C the ATPase rates of the two types of myofibril were identical: 50s−1 (activated) and 0.23s−1 (relaxed). Whereas with psoas myofibrils the Km for adenosine triphosphate (activated ATPase) is relatively insensitive to temperature, that for soleus myofibrils increased from 0.3μM at 4°C to 66.5μM at 35°C. Our results illustrate the importance of temperature when comparing the mechanochemical coupling in different types of muscle. We discuss the problem of how to reconcile the similarity of the myofibrillar ATPase rates at physiological temperatures with their different mechanical properties
Magnetoresistance behavior of a ferromagnetic shape memory alloy: Ni_1.75Mn_1.25Ga
A negative-positive-negative switching behavior of magnetoresistance (MR)
with temperature is observed in a ferromagnetic shape memory alloy
Ni_1.75Mn_1.25Ga. In the austenitic phase between 300 and 120 K, MR is negative
due to s-d scattering. Curiously, below 120K MR is positive, while at still
lower temperatures in the martensitic phase, MR is negative again. The positive
MR cannot be explained by Lorentz contribution and is related to a magnetic
transition. Evidence for this is obtained from ab initio density functional
theory, a decrease in magnetization and resistivity upturn at 120 K. Theory
shows that a ferrimagnetic state with anti-ferromagnetic alignment between the
local magnetic moments of the Mn atoms is the energetically favoured ground
state. In the martensitic phase, there are two competing factors that govern
the MR behavior: a dominant negative trend up to the saturation field due to
the decrease of electron scattering at twin and domain boundaries; and a weaker
positive trend due to the ferrimagnetic nature of the magnetic state. MR
exhibits a hysteresis between heating and cooling that is related to the first
order nature of the martensitic phase transition.Comment: 17 pages, 5 figures. Accepted in Phys. Rev.
A Description of the Third Instar of Platambus flavovittaus (Larson and Wolfe, 1998) with Comments on the Larval Morphology of Platambus stagninus (Say, 1823) and a Key to the Agabini (Coleoptera: Dytiscidae) of Georgia
Mature Agabini larvae collected from a small temporary road-side habitat were reared to the adult stage and identified as Platambus flavovittattus (Larson and Wolfe, 1998). The mature larva is described and illustrated with an emphasis on leg morphology. Important differences between cranial temporal curvatures of P. flavovittatus and P. stagninus (Say, 1823) are described. A larval key is constructed to facilitate identification of Georgia agabine genera and species
Theoretical prediction and experimental study of a ferromagnetic shape memory alloy: Ga_2MnNi
We predict the existence of a new ferromagnetic shape memory alloy Ga_2MnNi
using density functional theory. The martensitic start temperature (T_M) is
found to be approximately proportional to the stabilization energy of the
martensitic phase (deltaE_tot) for different shape memory alloys. Experimental
studies performed to verify the theoretical results show that Ga_2MnNi is
ferromagnetic at room temperature and the T_M and T_C are 780K and 330K,
respectively. Both from theory and experiment, the martensitic transition is
found to be volume conserving that is indicative of shape memory behavior.Comment: 11 pages, 3 figure
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