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Delta Scuti (δ Set) (1) stars are opacity-driven pulsators with masses of 1.5-2.5[M.sub.[dot encircle]], their pulsations resulting from the varying ionization of helium. In less massive stars (2) such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar example, with no firm theoretical basis, models predict that the convective envelope in δ Sct stars extends only about 1 per cent of the radius (3), but with sufficient energy to excite solar-like oscillations (4,5). This was not observed before the Kepler mission (6), so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the δ Sct star HD 187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted., Thirty days of continuous observations of HD 187547 (KIC 7548479) by the Kepler mission with a cadence of 1 min led to its identification as a δ Sct pulsator (Fig. [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.01.011 Byline: J.P. Emery (a), D.P. Cruikshank (b), J. Van Cleve (c) Keywords: Asteroids; Asteroids; composition; Infrared observations; Spectroscopy; Surfaces; asteroids Abstract: We present thermal emission spectra (5.2-38 [mu]m) of the Trojan asteroids 624 Hektor, 911 Agamemnon, and 1172 Aneas. The observations used the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. Emissivity spectra are created by dividing the measured Spectral Energy Distribution (SED) by a model of the thermal continuum. We employ the Standard Thermal Model (STM), allowing physical parameters (e.g., radius and albedo) to vary in order to find the best thermal continuum fit to the SED. The best-fit effective radius (R) and visible geometric albedo (p.sub.v) for Hektor (R=110.0[+ or -]7.3, p.sub.v= 0.038.sub.-0.017.sup.+0.028) and Aneas (R=69.1[+ or -]5.1, p.sub.v= 0.044.sub.-0.014.sup.+0.020) agree very well with previous estimates, and for Agamemnon (R=71.5[+ or -]5.2, p.sub.v= 0.062.sub.-0.019.sup.+0.024) we find slightly a smaller size and higher albedo than previously derived. Other thermal models (e.g., thermophysical) result in estimates of R and p.sub.v that vary a few percent from the STM, but the resulting emissivity spectra are identical. The emissivity spectra of all three asteroids display an emissivity plateau near 10-[mu]m and another broader rise from [approximately equal to]18 to 28 [mu]m. We interpret these as indications of fine-grained silicates on the surfaces of these asteroids. The emissivity spectra more closely resemble emission spectra from cometary comae than those from solid surfaces and measured in the laboratory for powdered meteorites and regolith analogs. We hypothesize that the coma-like emission from the solid surfaces of trojans may be due to small silicate grains being imbedded in a relatively transparent matrix, or to a very under-dense (fairy-castle) surface structure. These hypotheses need to be tested by further laboratory and theoretical scattering work as well as continued thermal emission observations of asteroids. Author Affiliation: (a) NASA Ames Research Center/SETI Institute, Moffett Field, CA 94035, USA (b) NASA Ames Research Center, Moffett Field, CA 94035, USA (c) Ball Aerospace and Technologies Corp., Boulder, CO 80301, USA Article History: Received 20 July 2005; Revised 15 December 2005

Using the SpectroCam-10 instrument on the Hale 200' telescope at Palomar Observatory, we obtained an extensive set of images and spectra of Mars in the thermal infrared during the 1993 and 1995 oppositions. Images were taken using a set of seven wide-band filters centered at 7.9, 8.8, 9.8, 10.3, 11.7, 12.5, and 17.9 [[micro]meter]. Spatially resolved slit spectra with a spectral resolving power of [Lambda]/[Delta][Lambda] = 100 between 7.5 and 13.5 [[micro]meter] were also obtained. Initial analysis of data from the 1993 opposition led to the identification of an absorption feature at 9.2 [[micro]meter] in the Acidalia region. At the time the feature was first identified, it was impossible to determine whether it was caused by a local enhancement of atmospheric dust over Acidalia, or by nonunit emissivity of surface materials in that region. Subsequent observations taken during the 1995 opposition showed that the feature in Acidalia persisted, indicating that it was of surficial origin. Because of its spectral position and shape, we interpret the feature to be the result of the emissivity spectrum of coarse (sand-sized or greater) silicate materials on the surface in Acidalia. While the spectral range available in our data is probably insufficient to make a specific mineralogical interpretation, we find it to be consistent with the emissivity spectrum of a terrestrial basalt sample measured in the laboratory.

ABSTRACT We present our analyses of 15 months of Kepler data on KIC 10139564. We detected 57 periodicities with a variety of properties not previously observed all together in one pulsating subdwarf B (sdB) star. Ten of the periodicities were found in the low-frequency region, and we associate them with nonradial g modes. The other periodicities were found in the high-frequency region, which are likely p modes. We discovered that most of the periodicities are components of multiplets with a common spacing. Assuming that multiplets are caused by rotation, we derive a rotation period of 25.6 ± 1.8 d. The multiplets also allow us to identify the pulsations to an unprecedented extent for this class of pulsator. We also detect l ≥ 2 multiplets, which are sensitive to the pulsation inclination and can constrain limb darkening via geometric cancellation factors. While most periodicities are stable, we detected several regions that show complex patterns. Detailed analyses showed that these regions are complicated by several factors. Two are combination frequencies that originate in the super-Nyquist region and were found to be reflected below the Nyquist frequency. The Fourier peaks are clear in the super-Nyquist region, but the orbital motion of Kepler smears the Nyquist frequency in the barycentric reference frame and this effect is passed on to the sub-Nyquist reflections. Others are likely multiplets but unstable in amplitudes and/or frequencies. The density of periodicities also makes KIC 10139564 challenging to explain using published models. This menagerie of properties should provide tight constraints on structural models, making this sdB star the most promising for applying asteroseismology. To support our photometric analysis, we have obtained spectroscopic radial-velocity measurements of KIC 10139564 using low-resolution spectra in the Balmer-line region. We did not find any radial-velocity variation. We used our high signal-to-noise average spectrum to improve the atmospheric parameters of the sdB star, deriving Teff = 31 859 K and log g = 5.673 dex. [ABSTRACT FROM AUTHOR]

Context. Solar-like oscillations have been observed by Kepler and CoRoT in several solar-type stars. Aims. We study the variations in the stellar p-mode linewidth as a function of effective temperature. Methods. We study a time series of nine months of Kepler data. We analyse the power spectra of 42 cool main-sequence stars and subgiants using both maximum likelihood estimators and Bayesian estimators to recover individual mode characteristics such as frequencies, linewidths, and mode heights. Results. We report on the mode linewidth at both maximum power and maximum mode height for these 42 stars as a function of effective temperature. Conclusions. We show that the mode linewidth at either maximum mode height or maximum amplitude follows a scaling relation with effective temperature, which is a combination of a power law and a lower bound. The typical power-law index is about 13 for the linewidth derived from the maximum mode height, and about 16 for the linewidth derived from the maximum amplitude, while the lower bound is about 0.3 μHz and 0.7 μHz, respectively. We stress that this scaling relation is only valid for cool main-sequence stars and subgiants, and does not have any predictive power outside the temperature range of these stars. [ABSTRACT FROM AUTHOR]

We present an analysis of high-resolution spectra for two pulsating Am stars in the Kepler field. The stellar parameters derived in this way are important because parameters derived from narrow-band photometry may be affected by the strong metal lines in these stars. We analyse the Kepler time series of ten known Am stars and find that six of them clearly show δ Scuti pulsations. The other four appear to be non-pulsating. We derive fundamental parameters for all known pulsating Am stars from ground-based observations and also for the Kepler Am stars to investigate the location of the instability strip for pulsating Am stars. We find that there is not much difference between the Am-star instability strip and the δ Scuti instability strip. We find that the observed location of pulsating Am stars in the HR diagram does not agree with the location predicted from diffusion calculations. [ABSTRACT FROM AUTHOR]

Assesses the arguments presented by Jorge Luis Borges in his essay 'A New Refutation of Time,' in which he offers two proofs of the unreality of time based on the idealism of Berkeley, and the other on Leibniz's Principle of the Identity of Indiscernibles. Three axioms of the time order; Three premises of the berkeleian argument.

We describe a method for measuring the internal friction of solids at low temperatures. Our design uses a composite oscillator vibrating in torsion at 100 kHz. The oscillator makes good thermal contact to the cryostat while maintaining a iow background loss of Q[sup -1] ... 2 × 10[sup -6] at 2 K. The usefulness of the design is demonstrated by data for BaF[sub 2] and a-SiO[sub 2] from 2 to 300 K. [ABSTRACT FROM AUTHOR]

Abstract: We present thermal emission spectra (5.2–38 μm) of the Trojan asteroids 624 Hektor, 911 Agamemnon, and 1172 Aneas. The observations used the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. Emissivity spectra are created by dividing the measured Spectral Energy Distribution (SED) by a model of the thermal continuum. We employ the Standard Thermal Model (STM), allowing physical parameters (e.g., radius and albedo) to vary in order to find the best thermal continuum fit to the SED. The best-fit effective radius (R) and visible geometric albedo () for Hektor (, ) and Aneas (, ) agree very well with previous estimates, and for Agamemnon (, ) we find slightly a smaller size and higher albedo than previously derived. Other thermal models (e.g., thermophysical) result in estimates of R and that vary a few percent from the STM, but the resulting emissivity spectra are identical. The emissivity spectra of all three asteroids display an emissivity plateau near 10-μm and another broader rise from ∼18 to 28 μm. We interpret these as indications of fine-grained silicates on the surfaces of these asteroids. The emissivity spectra more closely resemble emission spectra from cometary comae than those from solid surfaces and measured in the laboratory for powdered meteorites and regolith analogs. We hypothesize that the coma-like emission from the solid surfaces of trojans may be due to small silicate grains being imbedded in a relatively transparent matrix, or to a very under-dense (fairy-castle) surface structure. These hypotheses need to be tested by further laboratory and theoretical scattering work as well as continued thermal emission observations of asteroids. [Copyright &y& Elsevier]