The NASA-UC Eta-Earth Program: III. A Super-Earth orbiting HD 97658 and a Neptune-mass planet orbiting Gl 785

We report the discovery of planets orbiting two bright, nearby early K dwarf stars, HD 97658 and Gl 785. These planets were detected by Keplerian modelling of radial velocities measured with Keck-HIRES for the NASA-UC Eta-Earth Survey. HD 97658 b is a close-in super-Earth with minimum mass Msini = 8.2 +/- 1.2 M_Earth, orbital period P = 9.494 +/- 0.005 d, and an orbit that is consistent with circular. Gl 785 b is a Neptune-mass planet with Msini = 21.6 +/- 2.0 M_Earth, P = 74.39 +/- 0.12 d, and orbital eccentricity 0.30 +/- 0.09. Photometric observations with the T12 0.8 m automatic photometric telescope at Fairborn Observatory show that HD 97658 is photometrically constant at the radial velocity period to 0.09 mmag, supporting the existence of the planet.Comment: Submitted to ApJ, 7 pages, 6 figures, 5 table

Five planets and an independent confirmation of HD 196885Ab from Lick Observatory

We present time series Doppler data from Lick Observatory that reveal the presence of long-period planetary companions orbiting nearby stars. The typical eccentricity of these massive planets are greater than the mean eccentricity of known exoplanets. HD30562b has Msini = 1.29 Mjup, with semi-major axis of 2.3 AU and eccentricity 0.76. The host star has a spectral type F8V and is metal rich. HD86264b has Msini = 7.0 Mjup, arel = 2.86 AU, an eccentricity, e = 0.7 and orbits a metal-rich, F7V star. HD87883b has Msini = 1.78 Mjup, arel = 3.6 AU, e = 0.53 and orbits a metal-rich K0V star. HD89307b has Msini = 1.78 Mjup, arel = 3.3 AU, e = 0.24 and orbits a G0V star with slightly subsolar metallicity. HD148427b has Msini = 0.96 Mjup, arel = 0.93 AU, eccentricity of 0.16 and orbits a metal rich K0 subgiant. We also present velocities for a planet orbiting the F8V metal-rich binary star, HD196885A. The planet has Msini = 2.58 Mjup, arel = 2.37 AU, and orbital eccentricity of 0.48, in agreement with the independent discovery by Correia et al. 2008.Comment: 12 figures, 8 tables, accepted Ap

The NASA-UC Eta-Earth Program: II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses

We report the discovery of HD 156668b, an extrasolar planet with a minimum mass of M_P sin i = 4.15 M_Earth. This planet was discovered through Keplerian modeling of precise radial velocities from Keck-HIRES and is the second super-Earth to emerge from the NASA-UC Eta-Earth Survey. The best-fit orbit is consistent with circular and has a period of P = 4.6455 d. The Doppler semi-amplitude of this planet, K = 1.89 m/s, is among the lowest ever detected, on par with the detection of GJ 581e using HARPS. A longer period (P ~ 2.3 yr), low-amplitude signal of unknown origin was also detected in the radial velocities and was filtered out of the data while fitting the short-period planet. Additional data are required to determine if the long-period signal is due to a second planet, stellar activity, or another source. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 156668 (an old, quiet K3 dwarf) is photometrically constant over the radial velocity period to 0.1 mmag, supporting the existence of the planet. No transits were detected down to a photometric limit of ~3 mmag, ruling out transiting planets dominated by extremely bloated atmospheres, but not precluding a transiting solid/liquid planet with a modest atmosphere.Comment: This planet was announced at the 2010 AAS meeting in Wash. DC; 12 pages, 8 figures, 3 tables, submitted to Ap

Two Exoplanets Discovered at Keck Observatory

We present two exoplanets detected at Keck Observatory. HD 179079 is a G5 subgiant that hosts a hot Neptune planet with Msini = 27.5 M_earth in a 14.48 d, low-eccentricity orbit. The stellar reflex velocity induced by this planet has a semiamplitude of K = 6.6 m/s. HD 73534 is a G5 subgiant with a Jupiter-like planet of Msini = 1.1 M_jup and K = 16 m/s in a nearly circular 4.85 yr orbit. Both stars are chromospherically inactive and metal-rich. We discuss a known, classical bias in measuring eccentricities for orbits with velocity semiamplitudes, K, comparable to the radial velocity uncertainties. For exoplanets with periods longer than 10 days, the observed exoplanet eccentricity distribution is nearly flat for large amplitude systems (K > 80 m/s), but rises linearly toward low eccentricity for lower amplitude systems (K > 20 m/s).Comment: 8 figures, 6 tables, accepted, Ap

A High Eccentricity Component in the Double Planet System Around HD 163607 and a Planet Around HD 164509

We report the detection of three new exoplanets from Keck Observatory. HD 163607 is a metal-rich G5IV star with two planets. The inner planet has an observed orbital period of 75.29 $\pm$ 0.02 days, a semi-amplitude of 51.1 $\pm$ 1.4 \ms, an eccentricity of 0.73 $\pm$ 0.02 and a derived minimum mass of \msini = 0.77 $\pm$ 0.02 \mjup. This is the largest eccentricity of any known planet in a multi-planet system. The argument of periastron passage is 78.7 $\pm$ 2.0$^{\circ}$; consequently, the planet's closest approach to its parent star is very near the line of sight, leading to a relatively high transit probability of 8%. The outer planet has an orbital period of 3.60 $\pm$ 0.02 years, an orbital eccentricity of 0.12 $\pm$ 0.06 and a semi-amplitude of 40.4 $\pm$ 1.3 \ms. The minimum mass is \msini = 2.29 $\pm$ 0.16 \mjup. HD 164509 is a metal-rich G5V star with a planet in an orbital period of 282.4 $\pm$ 3.8 days and an eccentricity of 0.26 $\pm$ 0.14. The semi-amplitude of 14.2 $\pm$ 2.7 \ms\ implies a minimum mass of 0.48 $\pm$ 0.09 \mjup. The radial velocities of HD 164509 also exhibit a residual linear trend of -5.1 $\pm$ 0.7 \ms\ per year, indicating the presence of an additional longer period companion in the system. Photometric observations demonstrate that HD 163607 and HD 164509 are constant in brightness to sub-millimag levels on their radial velocity periods. This provides strong support for planetary reflex motion as the cause of the radial velocity variations.Comment: 10 pages, 8 figures, accepted to Ap

The NASA-UC Eta-Earth Program: I. A Super-Earth Orbiting HD 7924

We report the discovery of the first low-mass planet to emerge from the NASA-UC Eta-Earth Program, a super-Earth orbiting the K0 dwarf HD 7924. Keplerian modeling of precise Doppler radial velocities reveals a planet with minimum mass M_P sin i = 9.26 M_Earth in a P = 5.398 d orbit. Based on Keck-HIRES measurements from 2001 to 2008, the planet is robustly detected with an estimated false alarm probability of less than 0.001. Photometric observations using the Automated Photometric Telescopes at Fairborn Observatory show that HD 7924 is photometrically constant over the radial velocity period to 0.19 mmag, supporting the existence of the planetary companion. No transits were detected down to a photometric limit of ~0.5 mmag, eliminating transiting planets with a variety of compositions. HD 7924b is one of only eight planets known with M_P sin i < 10 M_Earth and as such is a member of an emerging family of low-mass planets that together constrain theories of planet formation.Comment: ApJ accepted, 10 pages, 10 figures, 4 table

Effects of Two Energy Scales in Weakly Dimerized Antiferromagnetic Quantum Spin Chains

By means of thermal expansion and specific heat measurements on the high-pressure phase of (VO)$_2$P$_2$O$_7$, the effects of two energy scales of the weakly dimerized antiferromagnetic $S$ = 1/2 Heisenberg chain are explored. The low energy scale, given by the spin gap $\Delta$, is found to manifest itself in a pronounced thermal expansion anomaly. A quantitative analysis, employing T-DMRG calculations, shows that this feature originates from changes in the magnetic entropy with respect to $\Delta$, $\partial S^{m}/ \partial \Delta$. This term, inaccessible by specific heat, is visible only in the weak-dimerization limit where it reflects peculiarities of the excitation spectrum and its sensitivity to variations in $\Delta$.Comment: 4 pages, 4 figures now identical with finally published versio

Radio Observations of HD 80606 Near Planetary Periastron

This paper reports Very Large Array observations at 325 and 1425 MHz (90cm and 20cm) during and near the periastron passage of HD 80606b on 2007 November 20. We obtain flux density limits (3-sigma) of 1.7 mJy and 48 microJy at 325 and 1425 MHz, respectively, equivalent to planetary luminosity limits of 2.3 x 10^{24} erg/s and 2.7 x 10^{23} erg/s. These are well above the Jovian value (at 40 MHz) of 2 x 10^{18} erg/s. The motivation for these observations was that the planetary magnetospheric emission is driven by a stellar wind-planetary magnetosphere interaction so that the planetary luminosity would be elevated. Near periastron, HD 80606b might be as much as 3000 times more luminous than Jupiter. Recent transit observations of HD 80606b provide stringent constraints on the planetary mass and radius, and, because of the planet's highly eccentric orbit, its rotation period is likely to be "pseudo-synchronized" to its orbital period, allowing a robust estimate of the former. We are able to make robust estimates of the emission frequency of the planetary magnetospheric emission and find it to be around 60--90 MHz. We compare HD 80606b to other high-eccentricity systems and assess the detection possibilities for both near-term and more distant future systems. Of the known high eccentricity planets, only HD 80606b is likely to be detectable, as HD 20782B b and HD 4113b are both likely to have weaker magnetic field strengths. Both the forthcoming "EVLA low band" system and the Low Frequency Array may be able to improve upon our limits for HD 80606b, and do so at a more optimum frequency. If the low-frequency component of the Square Kilometre Array (SKA-lo) and a future lunar radio array are able to approach their thermal noise limits, they should be able to detect an HD 80606b-like planet, unless the planet's luminosity increases by substantially less than a factor of 3000.Comment: 9 pages; accepted for publication in A

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

Improved Orbital Parameters and Transit Monitoring for HD 156846b

HD 156846b is a Jovian planet in a highly eccentric orbit (e = 0.85) with a period of 359.55 days. The pericenter passage at a distance of 0.16 AU is nearly aligned to our line of sight, offering an enhanced transit probability of 5.4% and a potentially rich probe of the dynamics of a cool planetary atmosphere impulsively heated during close approach to a bright star (V = 6.5). We present new radial velocity (RV) and photometric measurements of this star as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). The RV measurements from Keck-HIRES reduce the predicted transit time uncertainty to 20 minutes, an order of magnitude improvement over the ephemeris from the discovery paper. We photometrically monitored a predicted transit window under relatively poor photometric conditions, from which our non-detection does not rule out a transiting geometry. We also present photometry that demonstrates stability at the millimag level over its rotational timescale.Comment: 7 pages, 4 figures, accepted for publication in Ap