The Stellar Activity - Rotation Relationship

Using a new catalog of 824 solar and late-type stars with X-ray luminosities and rotation periods we have studied the relationship between rotation and stellar activity. From an unbiased subset of this sample the power law slope of the unsaturated regime, $L_X/L_{bol}\propto Ro^\beta$, is fit as $\beta=-2.70\pm0.13$. This is inconsistent with the canonical $\beta=-2$ slope to a confidence of 5$\sigma$ and argues for an interface-type dynamo. Super-saturation is observed for the fastest rotators in our sample and its parametric dependencies are explored. Significant correlations are found with both the corotation radius and the excess polar updraft, the latter theory being supported by other observations. We also present a new X-ray population synthesis model of the mature stellar component of our Galaxy and use it to reproduce deep observations of a high Galactic latitude field. The model, XStar, can be used to test models of stellar spin-down and dynamo decay, as well as for estimating stellar X-ray contamination rates for non-stellar studies.Comment: 4 pages, 4 figures. To appear in the proceedings of Cool Stars 17: 17th Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, AN 334, 1-2, Eds Klaus Strassmeier and Mercedes Lopez-Morale

A Third Planet Orbiting HIP 14810

We present new precision radial velocities and a three-planet Keplerian orbit fit for the V = 8.5, G5 V star HIP 14810. We began observing this star at Keck Observatory as part of the N2K Planet Search Project. Wright et al. (2007) announced the inner two planets to this system, and subsequent observations have revealed the outer planet planet and the proper orbital solution for the middle planet. The planets have minimum masses of 3.9, 1.3, and 0.6 M_Jup and orbital periods of 6.67, 147.7, and 952 d, respectively. We have numerically integrated the family of orbital solutions consistent with the data and find that they are stable for at least 10^6 yr. Our photometric search shows that the inner planet does not transit.Comment: ApJL, accepte

A Super-Earth Orbiting the Nearby Sun-like Star HD 1461

We present precision radial velocity data that reveal a Super-Earth mass planet and two probable additional planets orbiting the bright nearby G0V star HD 1461. Our 12.8 years of Keck HIRES precision radial velocities indicate the presence of a 7.4M_Earth planet on a 5.77-day orbit. The data also suggest, but cannot yet confirm, the presence of outer planets on low-eccentricity orbits with periods of 446.1 and 5017 days, and projected masses (M sin i) of 27.9 and 87.1M_Earth, respectively. Test integrations of systems consistent with the radial velocity data suggest that the configuration is dynamically stable. We present a 12.2-year time series of photometric observations of HD 1461, which comprise 799 individual measurements, and indicate that it has excellent long-term photometric stability. However, there are small amplitude variations with periods comparable to those of the suspected 2nd and 3rd signals in the radial velocities near 5000 and 446 days, thus casting some suspicion on those periodicities as Keplerian signals. If the 5.77-day companion has a Neptune-like composition, then its expected transit depth is of order ~0.5 millimags. The geometric a priori probability of transits is ~8%. Phase-folding of the ground-based photometry shows no indication that transits of the 5.77-day companion are occurring, but high-precision follow-up of HD 1461 during upcoming transit phase windows will be required to definitively rule out or confirm transits. This new system joins a growing list of solar-type stars in the immediate galactic neighborhood that are accompanied by at least one Neptune- (or lower) mass planets having orbital periods of 50 days or less.Comment: 33 pages, 7 figure

Rotation periods of exoplanet host stars

The stellar rotation periods of ten exoplanet host stars have been determined using newly analysed Ca II H & K flux records from Mount Wilson Observatory and Stromgren b, y photometric measurements from Tennessee State University's automatic photometric telescopes (APTs) at Fairborn Observatory. Five of the rotation periods have not previously been reported, with that of HD 130322 very strongly detected at Prot = 26.1 \pm 3.5 d. The rotation periods of five other stars have been updated using new data. We use the rotation periods to derive the line-of-sight inclinations of the stellar rotation axes, which may be used to probe theories of planet formation and evolution when combined with the planetary orbital inclination found from other methods. Finally, we estimate the masses of fourteen exoplanets under the assumption that the stellar rotation axis is aligned with the orbital axis. We calculate the mass of HD 92788 b (28 MJ) to be within the low-mass brown dwarf regime and suggest that this object warrants further investigation to confirm its true nature.Comment: Accepted for publication in MNRAS. 15 pages, 11 figure

Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search

We present time series measurements of chromospheric activity for more than 2600 main sequence and subgiant stars on the California Planet Search (CPS) program with spectral types ranging from about F5V to M4V for main sequence stars and from G0IV to about K5IV for subgiants. The large data set of more than 44,000 spectra allows us to identify an empirical baseline floor for chromospheric activity as a function of color and height above the main sequence. We define $\Delta S$ as an excess in emission in the Ca II H\&K lines above the baseline activity floor and define radial velocity jitter as a function of $\Delta S$ and \bv\ for main sequence and subgiant stars. Although the jitter for any individual star can always exceed the baseline level, we find that K dwarfs have the lowest level of jitter. The lack of correlation between observed jitter and chromospheric activity in K dwarfs suggests that the observed jitter is dominated by instrumental or analysis errors and not astrophysical noise sources. Thus, given the long-term precision for the CPS program, radial velocities are not correlated with astrophysical noise for chromospherically quiet K dwarf stars, making these stars particularly well-suited for the highest precision Doppler surveys. Chromospherically quiet F and G dwarfs and subgiants exhibit higher baseline levels of astrophysical jitter than K dwarfs. Despite the fact that the \rms\ in Doppler velocities is correlated with the mean chromospheric activity, it is rare to see one-to-one correlations between the individual time series activity and Doppler measurements, diminishing the prospects for correcting activity-induced velocity variations.Comment: 17 figures, two large tex tables, accepted Ap

ARE STATE CONSUMER PROTECTION ACTS REALLY LITTLE-FTC ACTS?

ABSTRACT: State Consumer Protection Acts (CPAs) were designed to supplement the Federal Trade Commission\u27s mission of protecting consumers and are often referred to as little-FTC Acts. There is growing concern that enforcement under these acts is not only qualitatively different than FTC enforcement, but may be counterproductive for consumers. This article examines a sample of CPA claims and compares them to the FTC standard. It identifies qualitative differences between CPA and FTC claims by commissioning a Shadow Federal Trade Commission of experts in consumer protection. The study finds that many CPA claims include conduct that would not be illegal under the FTC standards and that most of the cases with illegal conduct would not warrant FTC enforcement. Even among CPA cases where the plaintiff prevailed, nearly half do not include illegal conduct under the FTC standard and most of the cases with illegal conduct would not invoke FTC enforcement. The results clearly suggest private litigation under little-FTC Acts tends to pursue a different consumer protection mission than the Bureau of Consumer Protection at the Federal Trade Commission