36 research outputs found

    Newly-Discovered Planets Orbiting HD~5319, HD~11506, HD~75784 and HD~10442 from the N2K Consortium

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    Initially designed to discover short-period planets, the N2K campaign has since evolved to discover new worlds at large separations from their host stars. Detecting such worlds will help determine the giant planet occurrence at semi-major axes beyond the ice line, where gas giants are thought to mostly form. Here we report four newly-discovered gas giant planets (with minimum masses ranging from 0.4 to 2.1 MJup) orbiting stars monitored as part of the N2K program. Two of these planets orbit stars already known to host planets: HD 5319 and HD 11506. The remaining discoveries reside in previously-unknown planetary systems: HD 10442 and HD 75784. The refined orbital period of the inner planet orbiting HD 5319 is 641 days. The newly-discovered outer planet orbits in 886 days. The large masses combined with the proximity to a 4:3 mean motion resonance make this system a challenge to explain with current formation and migration theories. HD 11506 has one confirmed planet, and here we confirm a second. The outer planet has an orbital period of 1627.5 days, and the newly-discovered inner planet orbits in 223.6 days. A planet has also been discovered orbiting HD 75784 with an orbital period of 341.7 days. There is evidence for a longer period signal; however, several more years of observations are needed to put tight constraints on the Keplerian parameters for the outer planet. Lastly, an additional planet has been detected orbiting HD 10442 with a period of 1043 days.Comment: Accepted for publication in Ap

    Star formation histories of dwarf galaxies in the FIRE simulations: dependence on mass and Local Group environment

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    We study star formation histories (SFHs) of 500\simeq500 dwarf galaxies (stellar mass M=105109MM_\ast = 10^5 - 10^9\,M_\odot) from FIRE-2 cosmological zoom-in simulations. We compare dwarfs around individual Milky Way (MW)-mass galaxies, dwarfs in Local Group (LG)-like environments, and true field (i.e. isolated) dwarf galaxies. We reproduce observed trends wherein higher-mass dwarfs quench later (if at all), regardless of environment. We also identify differences between the environments, both in terms of "satellite vs. central" and "LG vs. individual MWvs. isolated dwarf central." Around the individual MW-mass hosts, we recover the result expected from environmental quenching: central galaxies in the "near field" have more extended SFHs than their satellite counterparts, with the former more closely resemble isolated ("true field") dwarfs (though near-field centrals are still somewhat earlier forming). However, this difference is muted in the LG-like environments, where both near-field centrals and satellites have similar SFHs, which resemble satellites of single MW-mass hosts. This distinction is strongest for M=106107MM_\ast = 10^6 - 10^7\,M_\odot but exists at other masses. Our results suggest that the paired halo nature of the LG may regulate star formation in dwarf galaxies even beyond the virial radii of the MW and Andromeda. Caution is needed when comparing zoom-in simulations targeting isolated dwarf galaxies against observed dwarf galaxies in the LG.Comment: Main text: 11 pages, 8 figures; appendices: 4 pages, 4 figures. Submitted to MNRAS; comments welcom

    Two Exoplanets Discovered at Keck Observatory

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    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

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

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    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

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

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    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

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    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

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

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    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

    M2K: II. A Triple-Planet System Orbiting HIP 57274

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    Doppler observations from Keck Observatory have revealed a triple planet system orbiting the nearby mid-type K dwarf, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with \msini\ = 11.6 \mearth (0.036 \mjup), an orbital period of 8.135 ±\pm 0.004 d, and slightly eccentric orbit e=0.19±0.1e=0.19 \pm 0.1. We calculate a transit probability of 6.5% for the inner planet. The second planet has \msini\ = 0.4 \mjup\ with an orbital period of 32.0 ±0.02\pm 0.02 d in a nearly circular orbit, and e=0.05±0.03e = 0.05 \pm 0.03. The third planet has \msini\ = 0.53 \mjup\ with an orbital period of 432 ±8\pm 8 d (1.18 years) and an eccentricity e=0.23±0.03e = 0.23 \pm 0.03. This discovery adds to the number of super Earth mass planets with \msini < 12 \mearth\ that have been detected with Doppler surveys. We find that 56 ±18\pm 18% super-Earths are members of multi-planet systems. This is certainly a lower limit because of observational detectability limits, yet significantly higher than the fraction of Jupiter mass exoplanets, 20±820 \pm 8%, that are members of Doppler-detected, multi-planet systems.Comment: 11 figures, submitte to ApJ on Sept 10, 201
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