Differential Radial Velocities and Stellar Parameters of Nearby Young Stars

Radial velocity searches for substellar mass companions have focused primarily on stars older than 1 Gyr. Increased levels of stellar activity in young stars hinders the detection of solar system analogs and therefore there has been a prejudice against inclusion of young stars in radial velocity surveys until recently. Adaptive optics surveys of young stars have given us insight into the multiplicity of young stars but only for massive, distant companions. Understanding the limit of the radial velocity technique, restricted to high-mass, close-orbiting planets and brown dwarfs, we began a survey of young stars of various ages. While the number of stars needed to carry out full analysis of the problems of planetary and brown dwarf population and evolution is large, the beginning of such a sample is included here. We report on 61 young stars ranging in age from beta Pic association (~12 Myr) to the Ursa Majoris association (~300 Myr). This initial search resulted in no stars showing evidence for companions greater than ~1-2 M_Jup in short period orbits at the 3 sigma-level. Additionally, we present derived stellar parameters, as most have unpublished values. The chemical homogeneity of a cluster, and presumably of an association, may help to constrain true membership. As such, we present [Fe/H] abundances for the stars in our sample.Comment: Accepted for publication in the PAS

Searching for Planets in the Hyades V: Limits on Planet Detection in the Presence of Stellar Activity

We present the results of a radial velocity survey of a sample of Hyades stars, and discuss the effects of stellar activity on radial velocity measurements. The level of radial velocity scatter due to rotational modulation of stellar surface features for the Hyades is in agreement with the predictions of Saar & Donahue (1997)- the maximum radial velocity rms of up to ~50 m/s, with an average rms of ~16 m/s. In this sample of 94 stars, we find 1 new binary, 2 stars with linear trends indicative of binary companions, and no close-in giant planets. We discuss the limits on extrasolar planet detection in the Hyades and the constraints imposed on radial velocity surveys of young stars.Comment: To appear in the June 2004 issue of A

Low-mass companions to Hyades stars

It is now well established that a large fraction of the low-mass stars are binaries or higher order multiples. Similarly a sizable fraction have giant planets. In contrast to these, the situation for brown dwarf companions is complicated: While close systems seem to be extremely rare, wide systems are possibly more common. In this paper, we present new results on a survey for low-mass companions in the Hyades. After measuring precisely the radial velocity of 98 Hyades dwarf stars for 5 years, we have selected all stars that show low-amplitude long-period trends. With AO-observations of these 14 stars we found companion candidates around nine of them, where one star has two companions. The two companions of HIP 16548 have masses between 0.07 to 0.08 Mo, and are thus either brown dwarfs or very low mass stars. In the case of HAN 172 we found a companion with a mass between 0.08 to 0.10 Mo, which is again between a star and a brown dwarf. The other seven stars all have stellar companions. In two additional cases, the RV-variations are presumably caused by stellar activity, and in another case the companion could be a short-period binary. The images of the remaining two stars are slightly elongated, which might imply that even these are binaries. Because at least 12 of the 14 stars showing low-amplitude RV trends turn out to have companions with a mass greater than 70 MJupiter, or are just active, we finally estimate the number of companions with masses between 10 MJupiter and 70 MJupiter within 8 AU of the host stars in the Hyades as less equal 2%.Comment: 10 pages, 10 figure

Growth and characterization of crystals for IR detectors and second harmonic gereration devices

Two types of materials, L-arginine phosphate (LAP) and doped triglycine sulfate (TGS), are examined for their growth characteristics and relevant properties for second harmonic generation and IR detector applications, respectively

Confirmation of the Planet Hypothesis for the Long-period Radial Velocity Variations of Beta Geminorum

We present precise stellar radial velocity measurements for the K giant star Beta Gem spanning over 25 years. These data show that the long period low amplitude radial velocity variations found by Hatzes & Cochran (1993) are long-lived and coherent. An examination of the Ca II K emission, spectral line shapes from high resolution data (R = 210,000), and Hipparcos photometry show no significant variations of these quantities with the RV period. These data confirm the planetary companion hypothesis suggested by Hatzes & Cochran (1993). An orbital solution assuming a stellar mass of 1.7 M_sun yields a period, P = 589.6 days, a minimum mass of 2.3 M_Jupiter, and a semi-major axis, and a = 1.6 AU. The orbit is nearly circular (e = 0.02). Beta Gem is the seventh intermediate mass star shown to host a sub-stellar companion and suggests that planet-formation around stars much more massive than the sun may common.Comment: 10 pages, 9 figures, Astronomy and Astrophysics, in pres

The Magnetic Field Geometry of Small Solar Wind Flux Ropes Inferred from their Twist Distribution

This work extends recent efforts on the force-free modeling of large flux rope-type structures (magnetic clouds, MCs) to much smaller spatial scales. We first select small flux ropes (SFRs) by eye whose duration is unambiguous and which were observed by the Solar Terrestrial Relations Observatory (STEREO) or Wind spacecraft during solar maximum years. We inquire into which analytical technique is physically most appropriate. We consider three models: (i) linear force-free field ($\bigtriangledown\times$ B = $\alpha (r)$ B) with a specific, prescribed constant $\alpha$ (Lundquist solution), and (ii) with $\alpha$ as a free constant parameter (Lundquist-alpha solution), (iii) uniform twist field (Gold-Hoyle solution). We retain only those cases where the impact parameter is less than one-half the FR radius, $R$, so the results should be robust (29 cases). The SFR radii lie in the range [$\sim$ 0.003, 0.059] AU. Comparing results, we find that the Lundquist-alpha and uniform twist solutions yielded comparable and small normalized $\chi^2$ values in most cases. We then use Grad-Shafranov (GS) reconstruction to analyze these events further. We then considered the twist per unit length, $\tau$, both its profile through the FR and its absolute value. We find $\tau$ to lie in the range [5.6, 34] turns/AU. The GH model-derived $\tau$ values are comparable to those obtained from GS reconstruction. We find that twist unit length ($L$) is inversely proportional to $R$, as $\tau \sim 0.17/R$. We combine MC and SFR results on $\tau (R)$ and give a relation which is approximately valid for both sets. The axial and azimuthal fluxes, $F_z$ and $F_\phi$, vary as $\approx 2.1 B_0 R^2 \times10^{21}$ Mx and $F_{\phi}/L \approx 0.36 B_0 R \times10^{21}$Mx/AU. The relative helicity per unit length, $H/L \approx 0.75 B_0^2 R^3$$\times 10^{42}$ Mx$^2$/AU.Comment: abstract shortened for arxiv, 31 pages, 15 Figures, in press at Solar Physic

A Planetary Companion to gamma Cephei A

We report on the detection of a planetary companion in orbit around the primary star of the binary system $\gamma$ Cephei. High precision radial velocity measurements using 4 independent data sets spanning the time interval 1981--2002 reveal long-lived residual radial velocity variations superimposed on the binary orbit that are coherent in phase and amplitude with a period or 2.48 years (906 days) and a semi-amplitude of 27.5 m s$^{-1}$. We performed a careful analysis of our Ca II H & K S-index measurements, spectral line bisectors, and {\it Hipparcos} photometry. We found no significant variations in these quantities with the 906-d period. We also re-analyzed the Ca II $\lambda$8662 {\AA} measurements of Walker et al. (1992) which showed possible periodic variations with the ``planet'' period when first published. This analysis shows that periodic Ca II equivalent width variations were only present during 1986.5 -- 1992 and absent during 1981--1986.5. Furthermore, a refined period for the Ca II $\lambda$8662 {\AA} variations is 2.14 yrs, significantly less than residual radial velocity period. The most likely explanation of the residual radial velocity variations is a planetary mass companion with $M$ sin $i$ = 1.7 $M_{Jupiter}$ and an orbital semi-major axis of $a_2$ $=$ 2.13 AU. This supports the planet hypothesis for the residual radial velocity variations for $\gamma$ Cep first suggested by Walker et al. (1992). With an estimated binary orbital period of 57 years $\gamma$ Cep is the shortest period binary system in which an extrasolar planet has been found. This system may provide insights into the relationship between planetary and binary star formation.Comment: 19 pages, 15 figures, accepted in Ap. J. Includes additional data and improved orbital solutio

Searching for Planets in the Hyades. I. The Keck Radial Velocity Survey

We describe a high-precision radial velocity search for jovian-mass companions to main sequence stars in the Hyades star cluster. The Hyades provides an extremely well controlled sample of stars of the same age, the same metallicity, and a common birth and early dynamical environment. This sample allows us to explore the dependence of the process of planet formation on only a single independent variable: the stellar mass. In this paper we describe the survey and summarize results for the first five years.Comment: 8 pages, 3 figures; To appear in the July 2002 issue of The Astronomical Journa

Acute Cardiorespiratory and Kinematic Adjustments upon Early Exposure to Barefoot Running

Please view abstract in the attached PDF file