arXiv subjects

Artie P. Hatzes

Publications and source records attributed to Artie P. Hatzes.

At least 73 records · Page 4Linked to original sources

arXiv2012

Doppler tomography of transiting exoplanets: A prograde, low-inclined orbit for the hot Jupiter CoRoT-11b

We report the detection of the Doppler shadow of the transiting hot Jupiter CoRoT-11b. Our analysis is based on line-profile tomography of time-series, Keck/HIRES high-resolution spectra acquired during the transit of the planet. We measured a sky-projected, spin-orbit angle of 0.1 +/- 2.6 degrees, which is consistent with a very low-inclined orbit with respect to the stellar rotation axis. We refined the physical parameters of the system using a Markov chain Monte Carlo simultaneous fitting of the available photometric and spectroscopic data. An analysis of the tidal evolution of the system shows how the currently measured obliquity and its uncertainty translate into an initial absolute value of less than about 10 degrees on the zero-age main sequence, for an expected average modified tidal quality factor of the star Q'* > 4 x 10^6. This is indicative of an inward migration scenario that would not have perturbed the primordial low obliquity of CoRoT-11b. Taking into account the effective temperature and mass of the planet host star (Teff=6440 K, M*=1.23 MSun), the system can be considered a new telling exception to the recently proposed trend, according to which relatively hot and massive stars (Teff>6250 K, M*>1.2 MSun) seem to be preferentially orbited by hot Jupiters with high obliquity.

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arXiv2011

KIC 1571511B: A Benchmark Low-Mass Star In An Eclipsing Binary System In The Kepler Field

KIC 1571511 is a 14d eclipsing binary (EB) in the Kepler dataset. The secondary of this EB is a very low mass star with a mass of 0.14136 +/- 0.00036 M_sun and a radius of 0.17831 +0.00051/-0.00062 R_sun (statistical errors only). The overall system parameters make KIC 1571511B an ideal "benchmark object": among the smallest, lightest and best-described stars known, smaller even than some known exoplanet. Currently available photometry encompasses only a small part of the total: future Kepler data releases promise to constrain many of the properties of KIC 1571511B to unprecedented level. However, as in many spectroscopic single-lined systems, the current error budget is dominated by the modeling errors of the primary and not by the above statistical errors. We conclude that detecting the RV signal of the secondary component is crucial to achieving the full potential of this possible benchmark object for the study of low mass stars.

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arXiv2011

On the Mass of CoRoT-7b

The mass of CoRoT-7b, the first transiting superearth exoplanet, is still a subject of debate. A wide range of masses have been reported in the literature ranging from as high as 8 M_Earth to as low as 2.3 M_Earth. Although most mass determinations give a density consistent with a rocky planet, the lower value permits a bulk composition that can be up to 50% water. We present an analysis of the CoRoT-7b radial velocity measurements that uses very few and simple assumptions in treating the activity signal. By only analyzing those radial velocity data for which multiple measurements were made in a given night we remove the activity related radial velocity contribution without any a priori model. We demonstrate that the contribution of activity to the final radial velocity curve is negligible and that the K-amplitude due to the planet is well constrained. This yields a mass of 7.42 +/- 1.21 M_Earth and a mean density of rho = 10.4 +/- 1.8 gm cm^-3. CoRoT-7b is similar in mass and radius to the second rocky planet to be discovered, Kepler-10b, and within the errors they have identical bulk densities - they are virtual twins. These bulk densities lie close to the density - radius relationship for terrestrial planets similar to what is seen for Mercury. CoRoT-7b and Kepler-10b may have an internal structure more like Mercury than the Earth.

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arXiv2011

News From The Gamma Cephei Planetary System

The Gamma Cephei planetary system is one of the most interesting systems due to several reasons: 1.) it is the first planet candidate detected by precise radial velocity (RV) measurements that was discussed in the literature (Campbell et al. 1988); 2.) it is a tight binary system with a ~ 20AU; and 3.) the planet host star is an evolved K-type star. In Hatzes et al. (2003) we confirmed the presence of the planetary companion with a minimum mass of 1.7 M_Jup at 2 AU. In this paper we present additional eight years of precise RV data from the Harlan J. Smith 2.7 m Telescope and its Tull Coude spectrograph at McDonald Observatory. The 900 d signal, that is interpreted as the presence of the giant planetary companion, is strongly confirmed by adding the new data. We present an updated orbital solution for the planet, which shows that the planet is slightly more massive and the orbit more circular than previous results have suggested. An intensive high-cadence week of RV observations in 2007 revealed that Gamma Cep A is a multi-periodic pulsator. We discuss this issue within the context of searching for additional planets in this system.

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arXiv2009

Angular Diameters and Effective Temperatures of Twenty-five K Giant Stars from the CHARA Array

Using Georgia State University's CHARA Array interferometer, we measured angular diameters for 25 giant stars, six of which host exoplanets. The combination of these measurements and Hipparcos parallaxes produce physical linear radii for the sample. Except for two outliers, our values match angular diameters and physical radii estimated using photometric methods to within the associated errors with the advantage that our uncertainties are significantly lower. We also calculated the effective temperatures for the stars using the newly-measured diameters. Our values do not match those derived from spectroscopic observations as well, perhaps due to the inherent properties of the methods used or because of a missing source of extinction in the stellar models that would affect the spectroscopic temperatures.

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arXiv2008

The Discovery of Stellar Oscillations in the K Giant $ι$ Dra

$ι$ Dra (HIP 75458) is a well-known example for a K giant hosting a substellar companion since its discovery by Frink et al. (2002). We present radial velocity measurements of this star from observations taken with three different instruments spanning nearly 8 years. They show more clearly that the RV period is long-lived and coherent thus supporting the companion hypothesis. The longer time baseline now allows for a more accurate determination of the orbit with a revised period of P=511 d and an additional small linear trend, indicative of another companion in a wide orbit. Moreover we show that the star exhibits low amplitude, solar like oscillations with frequencies around 3-4 d$^{-1}$ (34.7-46.3 $μ$Hz).

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arXiv2007

The Discovery of Stellar Oscillations in the Planet Hosting Giant Star Beta Geminorum

We present the results of a long time series of precise stellar radial velocity measurements of the planet hosting K giant star Beta Geminorum. A total of 20 hours of observations spanning three nights were obtained and the radial velocity variations show the presence of solar-like stellar oscillations. Our period analysis yields six significant pulsation modes that have frequencies in the range of 30 - 150 microHz. The dominant mode is at a frequency of 86.9 microHz and has an amplitude of 5.3 m/s. These values are consistent with stellar oscillations for a giant star with a stellar mass of approximately 2 solar masses. This stellar mass implies a companion minimum mass of 2.6 Jupiter masses. Beta Gem is the first planet hosting giant star in which multi-periodic stellar oscillations have been detected. The study of stellar oscillations in planet hosting giant stars may provide an independent, and more accurate determination of the stellar mass.

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arXiv2006

Results from the Exoplanet Search Programmes with BEST and TEST

Thueringer Landessternwarte Tautenburg (TLS) has started to operate a small dedicated telescope - the Tautenburg Exoplanet Search Telescope (TEST) - searching for transits of extrasolar planets in photometric time series observations. In a joint effort with the Berlin Exoplanet Search Telescope (BEST) operated by the Institut fuer Planetenforschung of the "Deutsches Zentrum fuer Luft- und Raumfahrt (DLR)" at the Observatoire de Haute-Provence (OHP), France, two observing sites are used to optimise transit search. Here, we give a short overview of these systems and the data analysis. We describe a software pipeline that we have set up to identify transit events of extrasolar planets and variable stars in time series data from these and other telescopes, and report on some first results.

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arXiv2006

Detection Limits from the McDonald Observatory Planet Search Program

Based on the long-term radial-velocity surveys carried out with the McDonald Observatory 2.7m Harlan J. Smith Telescope from 1988 to the present, we derive upper limits to long-period giant planet companions for 31 nearby stars. Data from three phases of the McDonald Observatory 2.7m planet-search program have been merged together and for 17 objects, data from the pioneering Canada-France-Hawaii Telescope (CFHT) radial-velocity program have also been included in the companion-limits determination. For those 17 objects, the baseline of observations is in excess of 23 years, enabling the detection or exclusion of giant planets in orbits beyond 8 AU. We also consider the possibility of eccentric orbits in our computations. At an orbital separation of 5.2 AU, we can exclude on average planets of M sin i > 2.0+/-1.1 Mjup (e=0) and M sin i > 4.0+/-2.8 Mjup (e=0.6) for 25 of the 31 stars in this survey. However, we are not yet able to rule out "true Jupiters," i.e. planets of M sin i ~ 1 Mjup in 5.2 AU orbits. These limits are of interest for the Space Interferometry Mission (SIM), Terrestrial Planet Finder (TPF), and Darwin missions which will search for terrestrial planets orbiting nearby stars, many of which are included in this work.

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arXiv2006

Determination Of The Orbit Of The Planetary Companion To The Metal Rich Star HD 45350

We present the precise radial velocity (RV) data for the metal-rich star HD 45350 collected with the Harlan J. Smith (HJS) 2.7 m telescope and the Hobby-Eberly Telescope (HET) at McDonald Observatory. This star was noticed by us as a candidate for having a giant planetary companion in a highly eccentric orbit, but the lack of data close to periastron left the amplitude and thus mass of the planet poorly constrained. Marcy et al. (2005) announced the presence of the planet based on their Keck/HIRES data, but those authors also cautioned that the remaining uncertainties in the orbital solution might be large due to insufficient data near periastron passage. In order to close this phase gap we exploited the flexible queue scheduled observing mode of the HET to obtain intensive coverage of the most recent periastron passage of the planet. In combination with the long term data from the HJS 2.7 m telescope we determine a Keplerian orbital solution for this system with a period of 962 days, an eccentricity of e=0.76 and a velocity semi-amplitude K of 57.4 m/s. The planet has a minimum mass of m sin i = 1.82 +- 0.14 M_Jup and an orbital semi-major axis of a = 1.92 +-0.07 AU.

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arXiv2005

High-Resolution Spectroscopy of the Planetary Host HD 13189: Highly-Evolved and Metal-Poor

We report on the abundances of 13 elements in the planetary host HD 13189, a massive giant star. Abundances are found to be sub-solar, with [Fe/H] = -0.58 +/- 0.04$; HD 13189 is one of the most metal-poor planetary hosts yet discovered. Abundance ratios relative to Fe show no peculiarities with respect to random field stars. A census of metallicities of the seven currently known planet-harboring giants results in a distribution that is more metal-poor than the well-known metal-rich distribution of main sequence (MS) planetary hosts. This finding is discussed in terms of accretion of H-depleted material, one of the possible mechanisms responsible for the high-metallicity distribution of MS stars with planets. We estimate the mass of the HD 13189 progenitor to be 3.5 M_sun but cannot constrain this value to better than 2-6 M_sun. A stellar mass of 3.5 M_sun implies a planetary mass of m sin i = 14.0 +/- 0.8 M_J, placing the companion at the planet/brown dwarf boundary. Given its physical characteristics, the HD 13189 system is potentially unique among planetary systems, and its continued investigation should provide invaluable data to extrasolar planetary research.

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arXiv2004

HD 137510: An Oasis in the Brown Dwarf Desert

Since the beginning of precise Doppler surveys, which have had stunning success in detecting extrasolar planetary companions, one surprising enigma has emerged: the relative paucity of spectroscopic binaries where the secondary mass lies in between the stellar and planetary mass regime. This gap in the mass function for close-in (a < 3 - 4 AU) companions to solar-type stars is generally referred to as the ``Brown Dwarf Desert''. Here we report the detection of a companion to HD 137510 (G0IV), with a minimum mass of 26 M_Jupiter, moving in an eccentric orbit (e=0.4) with a period of 798 days and an orbital semimajor axis of 1.85 AU. The detection is based on precise differential radial velocity (RV) data obtained by the McDonald Observatory and Thueringer Landessternwarte Tautenburg planet search programs.

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arXiv2004

Radial Velocity Variations in Pulsating Ap Stars III. The Discovery of 16.21 min Oscillations in Beta CrB

We present the analysis of 3 hrs of a rapid time series of precise stellar radial velocity (RV) measurements (sigma = 4.5 m/s) of the cool Ap star Beta CrB. The integrated RV measurements spanning the wavelength interval 5000-6000 Ang. show significant variations (false alarm probability = 10^-5) with a period of 16.21 min (nu = 1028.17 micro Hz) and an amplitude of 3.54 +/- 0.56 m/s. The RV measured over a much narrower wavelength interval reveals one spectral feature at 6272 Ang. pulsating with the same 16.21 min period and an amplitude of 138 +/- 23 m/s. These observations establish Beta CrB to be a low-amplitude rapidly oscillating Ap star.

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arXiv2003

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 $γ$ 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 $λ$8662 Å 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 $λ$8662 Å 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 $γ$ Cep first suggested by Walker et al. (1992). With an estimated binary orbital period of 57 years $γ$ 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.

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arXiv2003

Radial Velocity Variations in Pulsating Ap Stars. II. 33 Librae

We present precise relative radial velocity (RV) measurements for the rapidly oscillating Ap (roAp) star 33 Librae measured from high resolution data spanning the wavelength interval 5000--6200 A. We find that pulsational radial velocity amplitude determined over a broad wavelength range (~100 A) depends on the spectral region that is examined and can be as high as 60 m/s at 5600 A and as low as 7 m/s in the 5900 A region. RV measurements of individual spectral lines can show even higher RV amplitudes. The acoustic cross-sections of the atmosphere, i.e. the phase and amplitude of the pulsations, as a function of optical depth is found for spectral lines of Ca, Cr, Fe, La, Ce, Gd, Er and Nd. This analysis shows that pulsation phase is variable through the atmosphere and that Nd III lines pulsate almost 180 degrees out-of-phase with those of Nd II features and are formed significantly higher in the stellar atmosphere. This conclusively establishes the presence of at least one radial node to the pulsations in the upper stellar atmosphere. The histogram of pulsational phases for all individual spectral feature shows a bi-modal Gaussian distribution with 17% of the lines having a pulsational phase approximatels 165 degrees out-of-phase with most other spectral lines. This is also consistent with the presence of a radial node in the stellar atmosphere. The accumulation of phase due to a running wave component can explain the 165 degree phase difference as well as the broader width (by a factor of two) of one of the Gaussian components of the phase distribution.

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arXiv2002

Extrasolar Terrestrial Planets: Can We Detect Them Already?

With the example of Proxima Centauri we discuss the feasibility of detecting terrestrial planets (1 to a few M_Earth) using the high precision radial velocity (RV) technique. If a very high RV precision for M stars is achieved even planets with these extremely low masses become detectable. For Proxima Cen (M5V), one of the prime targets of our M-stars planet search program using the UVES spectrograph & iodine cell at the ESO VLT UT2, we obtain a long term RV precision of 2.5 m/s. Based on numerical simulations we determine that this level of precision would have already allowed us to detect planets with m sin i = 4 to 6 M_Earth inside the habitable zone of Proxima Cen.

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arXiv2002

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.

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arXiv2002

Searching for Planets in the Hyades II: Some Implications of Stellar Magnetic Activity

The Hyades constitute a homogeneous sample of stars ideal for investigating the dependence of planet formation on the mass of the central star. Due to their youth, Hyades members are much more chromospherically active than stars traditionally surveyed for planets using high precision radial velocity (RV) techniques. Therefore, we have conducted a detailed investigation of whether magnetic activity of our Hyades target stars will interfere with our ability to make precise RV searches for substellar companions. We measure chromospheric activity (which we take as a proxy for magnetic activity) by computing the equivalent of the R'HK activity index from the Ca II K line. is not constant in the Hyades: we confirm that it decreases with increasing temperature in the F stars, and also find it decreases for stars cooler than mid-K. We examine correlations between simultaneously measured R'HK and RV using both a classical statistical test and a Bayesian odds ratio test. We find that there is a significant correlation between R'HK and the RV in only 5 of the 82 stars in this sample. Thus, simple Rprime HK-RV correlations will generally not be effective in correcting the measured RV values for the effects of magnetic activity in the Hyades. We argue that this implies long timescale activity variations (of order a few years; i.e., magnetic cycles or growth and decay of plage regions) will not significantly hinder our search for planets in the Hyades if the stars are closely monitored for chromospheric activity. The trends in the RV scatter (sigma'_v) with , vsini, and P_rot for our stars is generally consistent with those found in field stars in the Lick planet search data, with the notable exception of a shallower dependence of sigma'_v on for F stars.

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