2,520 research outputs found
A Spitzer/IRAC Search for Substellar Companions of the Debris Disk Star epsilon Eridani
We have used the InfraRed Array Camera (IRAC) onboard the Spitzer Space
telescope to search for low mass companions of the nearby debris disk star
epsilon Eridani. The star was observed in two epochs 39 days apart, with
different focal plane rotation to allow the subtraction of the instrumental
Point Spread Function, achieving a maximum sensitivity of 0.01 MJy/sr at 3.6
and 4.5 um, and 0.05 MJy/sr at 5.8 and 8.0 um. This sensitivity is not
sufficient to directly detect scattered or thermal radiation from the epsilon
Eridani debris disk. It is however sufficient to allow the detection of Jovian
planets with mass as low as 1 MJ in the IRAC 4.5 um band. In this band, we
detected over 460 sources within the 5.70 arcmin field of view of our images.
To test if any of these sources could be a low mass companion to epsilon
Eridani, we have compared their colors and magnitudes with models and
photometry of low mass objects. Of the sources detected in at least two IRAC
bands, none fall into the range of mid-IR color and luminosity expected for
cool, 1 Gyr substellar and planetary mass companions of epsilon Eridani, as
determined by both models and observations of field M, L and T dwarf. We
identify three new sources which have detections at 4.5 um only, the lower
limit placed on their [3.6]-[4.5] color consistent with models of planetary
mass objects. Their nature cannot be established with the currently available
data and a new observation at a later epoch will be needed to measure their
proper motion, in order to determine if they are physically associated to
epsilon Eridani.Comment: 36 pages, to be published on The Astrophysical Journal, vol. 647,
August 200
Magnetostrictive energy harvesting: materials and design study
In recent years, vibrational energy harvesting has established itself as a promising alternative to the use of batteries for powering microelectromechanical systems for large wireless sensor networks used in aerospace and building infrastructures. This paper has focused on the design and materials used in magnetostrictive cantilever energy harvesters. The study involved using both finite-element modeling to predict the resonance frequencies for different cantilever designs and magnetostrictive materials, followed by experimental measurements for validation. Two different magnetostrictive ribbons were investigated, FeâââGaâ with four different compositions (x = 17.5; 19.5; 21; 28 at.%) and amorphous metallic glass Metglas 2605SC (Fe81B13.5Si3.5C2). From the modeling, it was determined that the resonance frequency was strongly dependent on the cantilever length, thickness, and density. Changing the cantilever design to a ``T'' shape was found to decrease the resonance frequency. The experimental results found that the output voltage measured depended on the cantilever dimensions, especially the thickness, the Ga concentration, and the cantilever design. The output voltages for Fe80.5Ga19.5 cantilevers were comparable with the same dimension Metglas cantilevers. The results of the finite-element modeling were validated by good agreement between the computational and experimental resonance frequencies measured
History of Plio-Pleistocene Climate in the Northeastern Atlantic, Deep Sea Drilling Project Hole 552A
DSDP Hole 552A, cored with the HPC on Hatton Drift, represents an almost complete and undisturbed sediment section spanning the late Neogene and Quaternary. Lithologic, faunal, isotopic, and paleomagnetic analyses indicate that the section represents the most complete deep sea record of climatic evolution hitherto recovered at high latitudes in the northern hemisphere. A glacial record of remarkable resolution for the late Pliocene and Pleistocene is provided by oxygen and carbon isotope ratios in benthic foraminifers. In the upper part of the section, the whole of the standard oxygen isotope record of the past million years is well preserved. The onset of ice-rafting and glacial-interglacial alternations occurs at about 2.4 m.y. ago
Discovery of Two T Dwarf Companions with the Spitzer Space Telescope
We report the discovery of T dwarf companions to the nearby stars HN Peg
(G0V, 18.4 pc, ~0.3 Gyr) and HD 3651 (K0V, 11.1 pc, ~7 Gyr). During an ongoing
survey of 5'x5' fields surrounding stars in the solar neighborhood with IRAC
aboard the Spitzer Space Telescope, we identified these companions as candidate
T dwarfs based on their mid-IR colors. Using near-IR spectra obtained with SpeX
at the NASA IRTF, we confirm the presence of methane absorption that
characterizes T dwarfs and measure spectral types of T2.5+/-0.5 and T7.5+/-0.5
for HN Peg B and HD 3651 B, respectively. By comparing our Spitzer data to
images from 2MASS obtained several years earlier, we find that the proper
motions of HN Peg B and HD 3651 B are consistent with those of the primaries,
confirming their companionship. HN Peg B and HD 3651 B have angular separations
of 43.2" and 42.9" from their primaries, which correspond to projected physical
separations of 795 and 476 AU, respectively. A comparison of their luminosities
to the values predicted by theoretical evolutionary models implies masses of
0.021+/-0.009 and 0.051+/-0.014 Msun for HN Peg B and HD 3651 B. In addition,
the models imply an effective temperature for HN Peg B that is significantly
lower than the values derived for other T dwarfs at similar spectral types,
which is the same behavior reported by Metchev & Hillenbrand for the young
late-L dwarf HD 203030 B. Thus, the temperature of the L/T transition appears
to depend on surface gravity. Meanwhile, HD 3651 B is the first substellar
companion directly imaged around a star that is known to harbor a close-in
planet from RV surveys. The discovery of this companion supports the notion
that the high eccentricities of close-in planets like the one near HD 3651 may
be the result of perturbations by low-mass companions at wide separations.Comment: Astrophysical Journal, in pres
Investigation of Zero-Sound Dispersion Equation in the Complex Plane of Frequency
The known solutions to the zero-sound dispersion equation are considered as
placed on the physical and unphysical sheets in the complex plane of frequency.Comment: 15 pages, 7 figure
Femoral stiffness and strength critically depend on loading angle: a parametric study in a mouse-inbred strain
Ten-Micron Observations of Nearby Young Stars
(abridged) We present new 10-micron photometry of 21 nearby young stars
obtained at the Palomar 5-meter and at the Keck I 10-meter telescopes as part
of a program to search for dust in the habitable zone of young stars. Thirteen
of the stars are in the F-K spectral type range ("solar analogs"), 4 have B or
A spectral types, and 4 have spectral type M. We confirm existing IRAS
12-micron and ground-based 10-micron photometry for 10 of the stars, and
present new insight into this spectral regime for the rest. Excess emission at
10 micron is not found in any of the young solar analogs, except for a possible
2.4-sigma detection in the G5V star HD 88638. The G2V star HD 107146, which
does not display a 10-micron excess, is identified as a new Vega-like
candidate, based on our 10-micron photospheric detection, combined with
previously unidentified 60-micron and 100-micron IRAS excesses. Among the
early-type stars, a 10-micron excess is detected only in HD 109573A (HR 4796A),
confirming prior observations; among the M dwarfs, excesses are confirmed in AA
Tau, CD -40 8434, and Hen 3-600A. A previously suggested N band excess in the
M3 dwarf CD -33 7795 is shown to be consistent with photospheric emission.Comment: 40 pages, 4 figures, 5 tables. To appear in the January 1, 2004 issue
of Ap
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