Robert A. Wittenmyer - The University of Texas

Robert A. Wittenmyer
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Robert A. Wittenmyer
The University of Texas
United States

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Earth and Planetary Astrophysics (46)
Solar and Stellar Astrophysics (14)
Instrumentation and Methods for Astrophysics (5)

Publications Authored By Robert A. Wittenmyer

We report the discovery of a second long-period giant planet orbiting HD 30177, a star previously known to host a massive Jupiter analog (HD 30177b: a=3.8$\pm$0.1 au, m sin $i=9. Read More

We report the detection of two new planets orbiting the K giants HD 86950 and HD 222076, based on precise radial velocities obtained with three instruments: AAT/UCLES, FEROS, and CHIRON. HD 86950b has a period of 1270$\pm$57 days at $a=2.72\pm$0. Read More

The Weihai Echelle Spectrograph (WES) is the first fiber-fed echelle spectrograph for astronomical observation in China. It is primarily used for chemical abundance and asteroseismology studies of nearby bright stars, as well as radial velocity detections for exoplanets. The optical design of WES is based on the widely demonstrated and well-established white-pupil concept. Read More

We present the data reduction procedures being used by the GALAH survey, carried out with the HERMES fibre-fed, multi-object spectrograph on the 3.9~m Anglo-Australian Telescope. GALAH is a unique survey, targeting 1 million stars brighter than magnitude V=14 at a resolution of 28,000 with a goal to measure the abundances of 29 elements. Read More

We present spectroscopic stellar parameters for the complete target list of 164 evolved stars from the Pan-Pacific Planet Search, a five-year radial velocity campaign using the 3.9m Anglo-Australian Telescope. For 87 of these bright giants, our work represents the first determination of their fundamental parameters. Read More

In an effort to measure the masses of planets discovered by the NASA {\it K2} mission, we have conducted precise Doppler observations of five stars with transiting planets. We present the results of a joint analysis of these new data and previously published Doppler data. The first star, an M dwarf known as K2-3 or EPIC~201367065, has three transiting planets ("b", with radius $2. Read More

We present an analysis of the relative throughputs of the 3.9-metre Anglo-Australian Telescope's 2dF/HERMES system, based upon spectra acquired during the first two years of the GALAH survey. Averaged spectral fluxes of stars were compared to their photometry to determine the relative throughputs of fibres for a range of fibre position and atmospheric conditions. Read More

The Second Workshop on Extreme Precision Radial Velocities defined circa 2015 the state of the art Doppler precision and identified the critical path challenges for reaching 10 cm/s measurement precision. The presentations and discussion of key issues for instrumentation and data analysis and the workshop recommendations for achieving this precision are summarized here. Beginning with the HARPS spectrograph, technological advances for precision radial velocity measurements have focused on building extremely stable instruments. Read More

We present updated simulations of the detectability of Jupiter analogs by the 17-year Anglo-Australian Planet Search. The occurrence rate of Jupiter-like planets that have remained near their formation locations beyond the ice line is a critical datum necessary to constrain the details of planet formation. It is also vital in our quest to fully understand how common (or rare) planetary systems like our own are in the Galaxy. Read More

We report the detection of a double planetary system around the evolved intermediate-mass star HD 47366 from precise radial-velocity measurements at Okayama Astrophysical Observatory, Xinglong Station, and Australian Astronomical Observatory. The star is a K1 giant with a mass of 1.81+-0. Read More

We report the discovery of two giant planets orbiting the K giant HD 33844 based on radial velocity data from three independent campaigns. The planets move on nearly circular orbits with semimajor axes $a_b=1.60\pm$0. Read More

Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD~20782, with an orbital period of 597~days and an eccentricity of 0.96. Read More

White dwarfs are the end state of most stars, including the Sun, after they exhaust their nuclear fuel. Between 1/4 and 1/2 of white dwarfs have elements heavier than helium in their atmospheres, even though these elements should rapidly settle into the stellar interiors unless they are occasionally replenished. The abundance ratios of heavy elements in white dwarf atmospheres are similar to rocky bodies in the Solar system. Read More

We present multiwavelength, multi-telescope, ground-based follow-up photometry of the white dwarf WD 1145+017, that has recently been suggested to be orbited by up to six or more, short-period, low-mass, disintegrating planetesimals. We detect 9 significant dips in flux of between 10% and 30% of the stellar flux from our ground-based photometry. We observe transits deeper than 10% on average every ~3. Read More

We present precise Doppler observations of WASP-47, a transiting planetary system featuring a hot Jupiter with both inner and outer planetary companions. This system has an unusual architecture and also provides a rare opportunity to measure planet masses in two different ways: the Doppler method, and the analysis of transit-timing variations (TTV). Based on the new Doppler data, obtained with the Planet Finder Spectrograph on the Magellan/Clay 6. Read More

Planets are known to orbit giant stars, yet there is a shortage of planets orbiting within ~0.5 AU (P<100 days). First-ascent giants have not expanded enough to engulf such planets, but tidal forces can bring planets to the surface of the star far beyond the stellar radius. Read More

We report the detection of sixteen binary systems from the Anglo-Australian Planet Search. Solutions to the radial velocity data indicate that the stars have companions orbiting with a wide range of masses, eccentricities and periods. Three of the systems potentially contain brown-dwarf companions while another two have eccentricities that place them in the extreme upper tail of the eccentricity distribution for binaries with periods less than 1000 d. Read More

Solid material in protoplanetary discs will suffer one of two fates after the epoch of planet formation; either being bound up into planetary bodies, or remaining in smaller planetesimals to be ground into dust. These end states are identified through detection of sub-stellar companions by periodic radial velocity (or transit) variations of the star, and excess emission at mid- and far-infrared wavelengths, respectively. Since the material that goes into producing the observable outcomes of planet formation is the same, we might expect these components to be related both to each other and their host star. Read More

Precise radial velocities from the Anglo-Australian Telescope confirm the presence of a rare short-period planet around the K0 giant HD 121056. An independent two-planet solution using the AAT data shows that the inner planet has P=89.1+/-0. Read More

The MINiature Exoplanet Radial Velocity Array (MINERVA) is a US-based observational facility dedicated to the discovery and characterization of exoplanets around a nearby sample of bright stars. MINERVA employs a robotic array of four 0.7 m telescopes outfitted for both high-resolution spectroscopy and photometry, and is designed for completely autonomous operation. Read More

We have investigated the dynamical stability of the proposed companions orbiting the Algol type short-period eclipsing binary SW Lyncis (Kim et al. 2010). The two candidate companions are of stellar to sub-stellar nature, and were inferred from timing measurements of the system's primary and secondary eclipses. Read More

This work is part of an ongoing project which aims to detect terrestrial planets in our neighbouring star system $\alpha$ Centauri using the Doppler method. Owing to the small angular separation between the two components of the $\alpha$ Cen AB binary system, the observations will to some extent be contaminated with light coming from the other star. We are accurately determining the amount of contamination for every observation by measuring the relative strengths of the H-$\alpha$ and NaD lines. Read More

In this work we revisit the proposed multi-circumbinary system RZ Dra. We find the proposed system to be highly unstable. We attempt to find a best-fit light-travel time model rendering the orbits to follow stable orbits. Read More

In the last few years, a number of planets have been proposed to orbit several post main-sequence binary star systems on the basis of observed variations in the timing of eclipses between the binary components. A common feature of these planet candidates is that the best-fit orbits are often highly eccentric, such that the multiple planet systems proposed regularly feature mutually crossing orbits - a scenario that almost always leads to unstable planetary systems. In this work, we present the results of dynamical studies of all multiple-planet systems proposed to orbit these highly evolved binary stars, finding that most do not stand up to dynamical scrutiny. Read More

We report the discovery of two long-period giant planets from the Anglo-Australian Planet Search. HD 154857c is in a multiple-planet system, while HD 114613b appears to be solitary. HD 114613b has an orbital period P=10. Read More

We present a detailed dynamical analysis of the orbital stability of the BD +20 2457 system, which features planets or brown dwarfs moving on relatively eccentric orbits. We find that the system exhibits strong dynamical instability on astronomically short timescales across a wide range of plausible orbital eccentricities, semi-major axes, and inclinations. If the system truly hosts massive planets or brown dwarfs, our results suggest that they must move on orbits significantly different to those proposed in the discovery work. Read More

We present six years of new radial-velocity data from the Anglo-Australian and Magellan Telescopes on the HD 73526 2:1 resonant planetary system. We investigate both Keplerian and dynamical (interacting) fits to these data, yielding four possible configurations for the system. The new data now show that both resonance angles are librating, with amplitudes of 40 degrees and 60 degrees, respectively. Read More

We present the results of our recent study on the interactions between a giant planet and a self-gravitating gas disk. We investigate how the disk's self-gravity affects the gap formation process and the migration of the giant planet. Two series of 1-D and 2-D hydrodynamic simulations are performed. Read More

In this work we carry out an analysis of the observed times of primary and secondary eclipses of the post-common envelope binary NSVS14256825. Recently, \cite{Almeida2013} proposed that two circumbinary companions orbit this short-period eclipsing binary, in order to explain observed variations in the timing of mutual eclipses between the two binary components. Using a standard weighted least-squares minimisation technique, we have extensively explored the topology of $\chi^2$ parameter space of a single planet model. Read More

Recent observations of the NN Serpentis post-common envelope binary system have revealed eclipse timing variations that have been attributed to the presence of two Jovian-mass exoplanets. Under the assumption that these planets are real and survived from the binary's Main Sequence state, we reconstruct initial binaries that give rise to the present NN Ser configuration and test the dynamical stability of the original system. Under standard assumptions about binary evolution, we find that survival of the planets through the entire Main Sequence life-time is very unlikely. Read More

Dynamical studies of new exoplanet systems are a critical component of the discovery and characterisation process. Such studies can provide firmer constraints on the parameters of the newly discovered planets, and may even reveal that the proposed planets do not stand up to dynamical scrutiny. Here, we demonstrate how dynamical studies can assist the characterisation of such systems through two examples: QS Virginis and HD 73526. Read More

In recent years, a number of planetary systems have been proposed to orbit evolved binary star systems. The presence of planets is invoked to explain observed variations in the timing of mutual eclipses between the primary and secondary components of the binary star system. The planets recently proposed orbiting the cataclysmic variable system QS Virginis are the latest in this on-going series of "extreme planets". Read More

Determining the orbital eccentricity of an extrasolar planet is critically important for understanding the system's dynamical environment and history. However, eccentricity is often poorly determined or entirely mischaracterized due to poor observational sampling, low signal-to-noise, and/or degeneracies with other planetary signals. Some systems previously thought to contain a single, moderate-eccentricity planet have been shown, after further monitoring, to host two planets on nearly-circular orbits. Read More

To understand the frequency, and thus the formation and evolution, of planetary systems like our own solar system, it is critical to detect Jupiter-like planets in Jupiter-like orbits. For long-term radial-velocity monitoring, it is useful to estimate the observational effort required to reliably detect such objects, particularly in light of severe competition for limited telescope time. We perform detailed simulations of observational campaigns, maximizing the realism of the sampling of a set of simulated observations. Read More

As a direct result of ongoing efforts to detect more exoplanetary systems, an ever-increasing number of multiple-planet systems are being announced. But how many of these systems are truly what they seem? In many cases, such systems are announced solely on the basis of orbital fits to observational data, and no attempt is made to see whether the proposed orbits are actually dynamically feasible. As a result, it is certain that planetary systems are being announced that involve planets moving on orbits that would be dynamically unstable on timescales of just a few hundred years. Read More

We present a detailed dynamical analysis of the orbital stability of the two circumbinary planets recently proposed to orbit the evolved eclipsing binary star system NSVS 14256825. As is the case for other recently proposed circumbinary planetary systems detected through the timing of mutual eclipses between the central binary stars, the proposed planets do not stand up to dynamical scrutiny. The proposed orbits for the two planets are extremely unstable on timescales of less than a thousand years, regardless of the mutual inclination between the planetary orbits. Read More

The abilities of radial velocity exoplanet surveys to detect the lowest-mass extra-solar planets are currently limited by a combination of instrument precision, lack of data, and "jitter". Jitter is a general term for any unknown features in the noise, and reflects a lack of detailed knowledge of stellar physics (asteroseismology, starspots, magnetic cycles, granulation, and other stellar surface phenomena), as well as the possible underestimation of instrument noise. We study an extensive set of radial velocities for the star HD 10700 ($\tau$ Ceti) to determine the properties of the jitter arising from stellar surface inhomogeneities, activity, and telescope-instrument systems, and perform a comprehensive search for planetary signals in the radial velocities. Read More

We perform several suites of highly detailed dynamical simulations to investigate the architectures of the 24 Sextantis and HD 200964 planetary systems. The best fit orbital solution for the two planets in the 24 Sex system places them on orbits with periods that lie very close to 2:1 commensurability, while that for the HD 200964 system places the two planets therein in orbits whose periods lie close to a 4:3 commensurability. In both cases, the proposed best-fit orbits are mutually crossing - a scenario that is only dynamically feasible if the planets are protected from close encounters by the effects of mutual mean motion resonance. Read More

We report the detection of a double planetary system orbiting around the evolved intermediate-mass star HD 4732 from precise Doppler measurements at Okayama Astrophysical Observatory (OAO) and Anglo-Australian Observatory (AAO). The star is a K0 subgiant with a mass of 1.7 M_sun and solar metallicity. Read More

We present a mass determination for the transiting super-Earth rho 1 Cancri e based on nearly 700 precise radial velocity (RV) measurements. This extensive RV data set consists of data collected by the McDonald Observatory planet search and published data from Lick and Keck observatories (Fischer et al. 2008). Read More

The post-main sequence eclipsing binary NN Serpentis was recently announced as the potential host of at least two massive planetary companions. In that work, the authors put forward two potential architectures that fit the observations of the eclipsing binary with almost identical precision. In this work, we present the results of a dynamical investigation of the orbital stability of both proposed system architectures, finding that they are only stable for scenarios in which the planets are locked in mutual mean motion resonance. Read More

We report the detection of two new planets from the Anglo-Australian Planet Search. These planets orbit two stars each previously known to host one planet. The new planet orbiting HD 142 has a period of 6005\pm427 days, and a minimum mass of 5. Read More

We re-analyze 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the ESO public archive. The new radial velocity (RV) measurements were obtained using a new data analysis technique that derives the Doppler measurement and other instrumental effects using a least-squares approach. Read More

We present high-precision radial velocity (RV) observations of four solar-type (F7-G5) stars - HD 79498, HD 155358, HD 197037, and HD 220773 - taken as part of the McDonald Observatory Planet Search Program. For each of these stars, we see evidence of Keplerian motion caused by the presence of one or more gas giant planets in long-period orbits. We derive orbital parameters for each system, and note the properties (composition, activity, etc. Read More