Vibrational Instability of Metal-Poor Low-Mass Main-Sequence Stars

We find that low-degree low-order g-modes become unstable in metal-poor low-mass stars due to the $\varepsilon$-mechanism of the pp-chain. Since the outer convection zone of these stars is limited only to the very outer layers, the uncertainty in the treatment of convection does not affect the result significantly. The decrease in metallicity leads to decrease in opacity and hence increase in luminosity of a star. This makes the star compact and results in decrease in the density contrast, which is favorable to the $\varepsilon$-mechanism instability. We find also instability for high order g-modes of metal-poor low-mass stars by the convective blocking mechanism. Since the effective temperature and the luminosity of metal-poor stars are significantly higher than those of Pop I stars, the stars showing $\gamma$ Dor-type pulsation are substantially less massive than in the case of Pop I stars. We demonstrate that those modes are unstable for about $1\,M_\odot$ stars in the metal-poor case.Comment: 4 pages, 4 figures, To be published in Astrophysics and Space Science Proceedings series (ASSP). Proceedings of the "20th Stellar Pulsation Conference Series: Impact of new instrumentation and new insights in stellar pulsations", 5-9 September 2011, Granada, Spai

Tidal interactions of close-in extrasolar planets: the OGLE cases

Close-in extrasolar planets experience extreme tidal interactions with their host stars. This may lead to a reduction of the planetary orbit and a spin-up of stellar rotation. Tidal interactions have been computed for a number of extrasolar planets in circular orbits within 0.06 AU, namely for OGLE-TR-56 b. We compare our range of the tidal dissipation value with two dissipation models from Sasselov (2003) and conclude that our choices are equivalent to these models. However, applied to the planet OGLE-TR-56 b, we find in contrast to Sasselov (2003) that this planet will spiral-in toward the host star in a few billion years. We show that the average and maximum value of our range of dissipation are equivalent to the linear and quadratic dissipation models of Sasselov (2003). Due to limitations in the observational techniques, we do not see a possibility to distinguish between the two dissipation models as outlined by Sasselov (2003). OGLE-TR-56 b may therefore not serve as a test case for dissipation models. The probable existence of OGLE-TR-3 b at 0.02 AU and the discovery of OGLE-TR-113 b at 0.023 AU and OGLE-TR-132 b at 0.03 AU may also counter Sasselovs (2003) assumption of a pile-up stopping boundary at 0.04 AU.Comment: 7 pages, 4 figure

Sounding stellar cycles with Kepler - I. Strategy for selecting targets

The long-term monitoring and high photometric precision of the Kepler satellite will provide a unique opportunity to sound the stellar cycles of many solar-type stars using asteroseismology. This can be achieved by studying periodic changes in the amplitudes and frequencies of the oscillation modes observed in these stars. By comparing these measurements with conventional ground-based chromospheric activity indices, we can improve our understanding of the relationship between chromospheric changes and those taking place deep in the interior throughout the stellar activity cycle. In addition, asteroseismic measurements of the convection zone depth and differential rotation may help us determine whether stellar cycles are driven at the top or at the base of the convection zone. In this paper, we analyze the precision that will be possible using Kepler to measure stellar cycles, convection zone depths, and differential rotation. Based on this analysis, we describe a strategy for selecting specific targets to be observed by the Kepler Asteroseismic Investigation for the full length of the mission, to optimize their suitability for probing stellar cycles in a wide variety of solar-type stars.Comment: accepted for publication in MNRA

Pressure Dependence of Born Effective Charges, Dielectric Constant and Lattice Dynamics in SiC

The pressure dependence of the Born effective charge, dielectric constant and zone-center LO and TO phonons have been determined for $3C$-SiC by a linear response method based on the linearized augmented plane wave calculations within the local density approximation. The Born effective charges are found to increase nearly linearly with decreasing volume down to the smallest volume studied, $V/V_0=0.78$, corresponding to a pressure of about 0.8 Mbar. This seems to be in contradiction with the conclusion of the turnover behavior recently reported by Liu and Vohra [Phys.\ Rev.\ Lett.\ {\bf 72}, 4105 (1994)] for $6H$-SiC. Reanalyzing their procedure to extract the pressure dependence of the Born effective charges, we suggest that the turnover behavior they obtained is due to approximations in the assumed pressure dependence of the dielectric constant $\varepsilon_\infty$, the use of a singular set of experimental data for the equation of state, and the uncertainty in measured phonon frequencies, especially at high pressure.Comment: 25 pages, revtex, 5 postscript figures appended, to be published in Phys. Rev.

HD 46375: seismic and spectropolarimetric analysis of a young Sun hosting a Saturn-like planet

HD 46375 is known to host a Saturn-like exoplanet orbiting at 0.04 AU from its host star. Stellar light reflected by the planet was tentatively identified in the 34-day CoRoT run acquired in October-November 2008. We constrain the properties of the magnetic field of HD 46375 based on spectropolarimetric observations with the NARVAL spectrograph at the Pic du Midi observatory. In addition, we use a high-resolution NARVAL flux spectrum to contrain the atmospheric parameters. With these constraints, we perform an asteroseismic analysis and modelling of HD 46375 using the frequencies extracted from the CoRoT light curve. We used Zeeman Doppler imaging to reconstruct the magnetic map of the stellar surface. In the spectroscopic analysis we fitted isolated lines using 1D LTE atmosphere models. This analysis was used to constrain the effective temperature, surface gravity, and chemical composition of the star. To extract information about the p-mode oscillations, we used a technique based on the envelope autocorrelation function (EACF). From the Zeeman Doppler imaging observations, we observe a magnetic field of ~5 gauss. From the spectral analysis, HD 46375 is inferred to be an unevolved K0 type star with high metallicity [Fe/H]=+0.39. Owing to the relative faintness of the star (m_hip=8.05), the signal-to-noise ratio is too low to identify individual modes. However, we measure the p-mode excess power and large separation Delta nu_0=153.0 +/- 0.7 muHz. We are able do constrain the fundamental parameters of the star thanks to spectrometric and seismic analyses. We conclude that HD 46375 is similar to a young version of Alpha-CenB. This work is of special interest because of its combination of exoplanetary science and asteroseismology, which are the subjects of the current Kepler mission and the proposed PLATO mission.Comment: Accepted in Astronomy & Astrophysics. 8 pages, 9 figure

How to select a chiropractor for the management of athletic conditions

<p>Abstract</p> <p>Background</p> <p>Chiropractors are an integral part of the management of musculoskeletal injuries. A considerable communication gap between the chiropractic and medical professions exists. Subsequently referring allopathic practitioners lack confidence in picking a chiropractic practitioner with appropriate management strategies to adequately resolve sporting injuries. Subsequently, the question is often raised: "how do you find a good chiropractor?".</p> <p>Discussion</p> <p>Best practice guidelines are increasingly suggesting that musculoskeletal injuries should be managed with multimodal active and passive care strategies. Broadly speaking chiropractors may be subdivided into "modern multimodal" or "classical" (unimodal) in nature. The modern multimodal practitioner is better suited to managing sporting injuries by incorporating passive and active care management strategies to address three important phases of care in the continuum of injury from the acute inflammation/pain phase to the chronic/rehabilitation phase to the injury prevention phase. In contrast, the unimodal, manipulation only and typically spine only approach of the classical practitioner seems less suited to the challenges of the injured athlete. Identifying what part of the philosophical management spectrum a chiropractor falls is important as it is clearly not easily evident in most published material such as Yellow Pages advertisements.</p> <p>Summary</p> <p>Identifying a chiropractic practitioner who uses multimodal treatment of adequate duration, who incorporates active and passive components of therapy including exercise prescription whilst using medical terminology and diagnosis without mandatory x-rays or predetermined treatment schedules or prepaid contracts of care will likely result in selection of a chiropractor with the approach and philosophy suited to appropriately managing athletic conditions. Sporting organizations and associations should consider using similar criteria as a minimum standard to allow participation in health care team selections.</p

TESS Discovery of an ultra-short-period planet around the nearby M dwarf LHS 3844

Data from the newly-commissioned \textit{Transiting Exoplanet Survey Satellite} (TESS) has revealed a "hot Earth" around LHS 3844, an M dwarf located 15 pc away. The planet has a radius of $1.32\pm 0.02$ $R_\oplus$ and orbits the star every 11 hours. Although the existence of an atmosphere around such a strongly irradiated planet is questionable, the star is bright enough ($I=11.9$, $K=9.1$) for this possibility to be investigated with transit and occultation spectroscopy. The star's brightness and the planet's short period will also facilitate the measurement of the planet's mass through Doppler spectroscopy.Comment: 10 pages, 4 figures. Submitted to ApJ Letters. This letter makes use of the TESS Alert data, which is currently in a beta test phase, using data from the pipelines at the TESS Science Office and at the TESS Science Processing Operations Cente

Gas Accretion and Galactic Chemical Evolution: Theory and Observations

This chapter reviews how galactic inflows influence galaxy metallicity. The goal is to discuss predictions from theoretical models, but particular emphasis is placed on the insights that result from using models to interpret observations. Even as the classical G-dwarf problem endures in the latest round of observational confirmation, a rich and tantalizing new phenomenology of relationships between $M_*$, $Z$, SFR, and gas fraction is emerging both in observations and in theoretical models. A consensus interpretation is emerging in which star-forming galaxies do most of their growing in a quiescent way that balances gas inflows and gas processing, and metal dilution with enrichment. Models that explicitly invoke this idea via equilibrium conditions can be used to infer inflow rates from observations, while models that do not assume equilibrium growth tend to recover it self-consistently. Mergers are an overall subdominant mechanism for delivering fresh gas to galaxies, but they trigger radial flows of previously-accreted gas that flatten radial gas-phase metallicity gradients and temporarily suppress central metallicities. Radial gradients are generically expected to be steep at early times and then flattened by mergers and enriched inflows of recycled gas at late times. However, further theoretical work is required in order to understand how to interpret observations. Likewise, more observational work is needed in order to understand how metallicity gradients evolve to high redshifts.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springer. 29 pages, 2 figure

Brief report on the effect of providing single versus assorted brand name condoms to hospital patients: a descriptive study

OBJECTIVES: This study examined condom acquisition by persons in a hospital setting when single versus assorted brand name condoms were provided. METHODS: Condom receptacles were placed in exam rooms of two clinics. During Phase 1, a single brand name was provided; for Phase 2, assorted brand names were added. Number of condoms taken was recorded for each phase. RESULTS: For one clinic there was nearly a two-fold increase in number of condoms taken (Phase 1 to Phase 2); for the second clinic there was negligible difference in number of condoms taken. CONCLUSIONS: The provision of assorted brand name condoms, over a single brand name, can serve to increase condom acquisition. Locations of condoms and target population characteristics are related factors