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Schwab C.,ZAH Landessternwarte | Spronck J.F.P.,Yale University | Tokovinin A.,CTIO | Fischer D.A.,Yale University | Marcy G.W.,University of California at Berkeley
EPJ Web of Conferences | Year: 2011

Small telescopes can play an important role in the search for exoplanets because they offer an opportunity for high cadence observations that are not possible with large aperture telescopes. However, there is a shortage of high resolution spectrometers for precision Doppler planet searches. We report on an innovative design for CHIRON, an inexpensive spectrometer that we are building for the 1.5-m telescope at CTIO in Chile. The resolution will be R >80.000, the spectral format spanning 410 to 880nm. The total throughput of the telescope and spectrometer will be better than 12%, comparable with the efficiency of state-of-the-art spectrometers. The design is driven by the requirements for precision Doppler searches for exoplanets using an iodine cell. The optical layout is a classical echelle with 140mm beam size. The bench-mounted spectrometer will be fibre-fed followed by an image slicer. An apochromatic refractor is used as the camera. Image quality and throughput of the design are excellent over the full spectral range. Extensive use of commercially available components and avoidance of complicated custom optics are key for quick and resource-efficient implementation. © Owned by the authors, published by EDP Sciences, 2011. Source

Spronck J.F.P.,Yale University | Schwab C.,ZAH Landessternwarte | Fischer D.A.,Yale University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

The detection of Earth analogues requires extreme Doppler precision and long term stability in order to measure tiny reflex velocities in the host star. The PSF from the spectrometer should be slowly varying with temperature and pressure changes. However, variations in the illumination of the slit and of the spectrograph optics occur on time scales of seconds, primarily because of guiding errors, but also on timescales of minutes, because of changes in the focus or seeing. These variations yield differences in the PSF from observation to observation, which are currently limiting the Doppler precision. Here, we present the design of a low cost fiber optic feed, FINDS, used to stabilize the PSF of the Hamilton spectrograph of Lick observatory along with the first measurements that show dramatic improvement in stability. © 2010 Copyright SPIE - The International Society for Optical Engineering. Source

Schwab C.,Yale University | Gutcke T.,ZAH Landessternwarte | Spronck J.F.P.,Yale University | Fischer D.A.,Yale University | Szymkowiak A.,Yale University
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

The detection of earth-like exoplanets with the Doppler technique requires extreme precision spectrographs stable over timescales of years. The precision requirement of 10 cm/s is equivalent to a relative uncertainty of 3x10 -10, and, with the typical dispersion of the Echelle spectrographs used for this purpose, translates to a shift of a few nanometers of the spectrum on the detector. Consequently, the instrument must be well understood and optimized in every component and detail. We describe the Yale Doppler diagnostic facility (YDDF), a dedicated bench mounted Echelle spectrograph in our lab at Yale University, which will be used to systematically study the influence of different components at this precision level. The spectrograph bench allows for a flexible optical configuration, high resolution and sampling, and wide spectral coverage. Further, we incorporated a turbulence and guiding simulator to realistically reproduce the situation at the telescope, enabling end-to-end tests of important parameters. © 2012 SPIE. Source

Reffert S.,ZAH Landessternwarte | Quirrenbach A.,ZAH Landessternwarte
Astronomy and Astrophysics | Year: 2011

Context. The recently completed re-reduction of the Hipparcos data by van Leeuwen (2007a, Astrophysics and Space Science Library, 350) makes it possible to search for the astrometric signatures of planets and brown dwarfs known from radial velocity surveys in the improved Hipparcos intermediate astrometric data. Aims. Our aim is to put more significant constraints on the orbital parameters which cannot be derived from radial velocities alone, i.e. the inclination and the longitude of the ascending node, than was possible before. The determination of the inclination in particular allows to calculate an unambiguous companion mass, rather than the lower mass limit which can be obtained from radial velocity measurements. Methods. We fitted the astrometric orbits of 310 substellar companions around 258 stars, which were all discovered via the radial velocity method, to the Hipparcos intermediate astrometric data provided by van Leeuwen. Results. Even though the astrometric signatures of the companions cannot be detected in most cases, the Hipparcos data still provide lower limits on the inclination for all but 67 of the investigated companions, which translates into upper limits on the masses of the unseen companions. For nine companions the derived upper mass limit lies in the planetary and for 75 companions in the brown dwarf mass regime, proving the substellar nature of those objects. Two of those objects have minimum masses also in the brown dwarf regime and are thus proven to be brown dwarfs. The confirmed planets are the ones around Pollux (β Gem b), Ïμ Eri b, Ïμ Ret b, μ Ara b, υ And c and d, 47 UMa b, HD 10647 b and HD 147513 b. The confirmed brown dwarfs are HD 137510 b and HD 168443 c. In 20 cases, the astrometric signature of the substellar companion was detected in the Hipparcos data, resulting in reasonable constraints on inclination and ascending node. Of these 20 companions, three are confirmed as planets or lightweight brown dwarfs (HD 87833 b, ι Dra b, and γ Cep b), two as brown dwarfs (HD 106252 b and HD 168443 b), and four are low-mass stars (BD  -04 782 b, HD 112758 b, ρ CrB b, and HD169822 b). Of the others, many are either brown dwarfs or very low mass stars. For Ïμ Eri, we derive a solution which is very similar to the one obtained using Hubble Space Telescope data. © 2011 ESO. Source

Johnson J.A.,California Institute of Technology | Payne M.,University of Florida | Howard A.W.,University of California at Berkeley | Clubb K.I.,San Francisco State University | And 9 more authors.
Astronomical Journal | Year: 2011

We report radial velocity (RV) measurements of the G-type subgiants 24 Sextanis (= HD 90043) and HD 200964. Both are massive, evolved stars that exhibit periodic variations due to the presence of a pair of Jovian planets. Photometric monitoring with the T12 0.80 m APT at Fairborn Observatory demonstrates both stars to be constant in brightness to ≤0.002 mag, thus strengthening the planetary interpretation of the RV variations. Based on our dynamical analysis of the RVtime series, 24 Sex b, c have orbital periods of 452.8 days and 883.0 days, corresponding to semimajor axes 1.333 AU and 2.08 AU, and minimum masses 1.99 MJup and 0.86 MJup, assuming a stellar mass M* =1.54M⊙. HD 200964 b, c have orbital periods of 613.8 days and 825.0 days, corresponding to semimajor axes 1.601 AU and 1.95 AU, and minimum masses 1.99 MJup and 0.90 M Jup, assuming M* = 1.44M⊙. We also carry out dynamical simulations to properly account for gravitational interactions between the planets. Most, if not all, of the dynamically stable solutions include crossing orbits, suggesting that each system is locked in a mean-motion resonance that prevents close encounters and provides long-term stability. The planets in the 24 Sex system likely have a period ratio near 2:1, while the HD 200964 system is even more tightly packed with a period ratio close to 4:3. However, we caution that further RV observations and more detailed dynamical modeling will be required to provide definitive and unique orbital solutions for both cases, and to determine whether the two systems are truly resonant. © 2011 The American Astronomical Society. All rights reserved. Source

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