Jovian-mass Planets Research Articles

The Use of Transit Timing to Detect Terrestrial-Mass Extrasolar Planets

Future surveys for transiting extrasolar planets are expected to detect hundreds of jovian-mass planets and tens of terrestrial-mass planets. For many of these newly discovered planets, the intervals between successive transits will be measured with an accuracy of 0.1 to 100 minutes. We show that these timing measurements will allow for the detection of additional planets in the system (not necessarily transiting) by their gravitational interaction with the transiting planet. The transit-time variations depend on the mass of the additional planet, and in some cases terrestrial-mass planets will produce a measurable effect. In systems where two planets are seen to transit, the density of both planets can be determined without radial-velocity observations.

Radio Emission from Extrasolar Planets

By virtue of their planetary-scale magnetic fields, the Earth and all of the gas giants in our solar system possess solar-wind deformed magnetospheres. The magnetic polar regions of these “magnetic planets” produce intense, aurora-related radio emission from solar-wind powered electron currents. Simple scaling laws suggest that Jovian-mass planets close to their host stars should produce radio emission; detecting such emission would be the first direct detection of many of these planets. We describe searches using the Very Large Array (VLA) for radio emission from the planets orbiting HD 114762, 70 Vir, and τ Boo. Our limits are just above those predicted for the planetary emissions. We discuss the possibilities for more stringent limits and the implications that the existing observations have for the planets' radio emissions, and hence on the planetary magnetic fields and stellar wind environments.

Survival of Terrestrial Planets in the Presence of Giant Planet Migration

The presence of ``Hot Jupiters'', Jovian mass planets with very short orbital periods orbiting nearby main sequence stars, has been proposed to be primarily due to the orbital migration of planets formed in orbits initially much further from the parent star. The migration of giant planets would have profound effects on the evolution of inner terrestrial planets in these systems, and previous analyses have assumed that no terrestrial planets survive after migration has occurred. We present numerical simulations showing that a significant fraction of terrestrial planets could survive the migration process, eventually returning to circular orbits relatively close to their original positions. A fraction of the final orbits are in the Habitable Zone, suggesting that planetary systems with close-in giant planets are viable targets for searches for Earth-like habitable planets around other stars.

A NEW CHANNEL TO SEARCH FOR EXTRA-SOLAR SYSTEMS WITH MULTIPLE PLANETS VIA GRAVITATIONAL MICROLENSING

Gaudi, Naber & Sackett pointed out that if an event is caused by a lens system containing more than two planets, all planets will affect the central region of the magnification pattern, and thus the existence of the multiple planets can be inferred by detecting additionally deformed anomalies from intensive monitoring of high magnification events. Unfortunately, this method has important limitations in identifying the existence of multiple planets and determining their parameters due to the degeneracy of the resulting light curve anomalies from those induced by a single planet and the complexity of multiple planet lensing models. In this paper, we propose a new channel to search for multiple planets via microlensing. The method is based on the fact that the anomalies induced by multiple planets are well approximated by the superposition of those of the single planet systems where the individual planet-primary pairs act as independent lens systems. Then, if the source trajectory passes both of the outer deviation regions induced by the individual planets, one can unambiguously identify the existence of the multiple planets. We illustrate that the probability of successively detecting light curve anomalies induced by two Jovian-mass planets located in the lensing zone through this channel will be substantial. Since the individual anomalies can be well modeled by much simpler single planet lensing models, the proposed method has an important advantage of allowing one to accurately determine the parameters of the individual planets.

Ground-based photometric detection of extrasolar planets

The discovery of terrestrial-sized extrasolar planets around main-sequences stars is currently possible from the ground for several sub-solar, small-radii eclipsing binary systems. Terrestrial planets in these systems should form in the binary orbital plane, and are likely to have periods significantly smaller than those of the terrestrial planets in the Solar System, and hence, should be more easily detectable. Our observations of the CM Draconis system indicate that such detections are indeed possible, especially when the photometric data (differential light curve) can be correlated with possible planetary orbital models of the quasi-periodic signal expected (i.e. a matched-filter implementation). The importance of the discovery of the first habitable planets, and follow-up observations for the detection of exobiology are outlined. In addition, non-transiting jovian-mass planets in such systems can also be detected by precisely timing the binary eclipse minima. Our preliminary observations of ten such systems have demonstrated the feasibility of this detection method. Over two hundred such systems could be surveyed for jovian-mass planets, providing a statistically meaningful sample for understanding the formation of giant planets around close double stars, thus complimenting our main objective: the detection of habitable-sized planets.

Parent Stars of Extrasolar Planets. V. HD 75289

The results of a new spectroscopic analysis of HD 75289, recently reported to harbor a Jovian-mass planet, are presented. From high-resolution, high signal-to-noise ratio spectra, we derive [Fe/H] = +0.28 ± 0.05 for this star, in agreement with the spectroscopic study of Gratton et al. published 10 years ago. In addition, we present a reanalysis of the spectra of υ And and τ Boo; our new parameters for these two stars are now in better agreement with photometrically derived values and with the recent spectroscopic analyses of Fuhrmann et al. We also report on extended abundance analyses of 14 Her, HD 187123, HD 210277, and ρ1 Cnc. If we include the recent spectroscopic analyses of HD 217107 by Randich et al. and Sadakane et al., who both reported [Fe/H] ~ +0.30 for this star, we can state that all the hot-Jupiter systems studied to date have metal-rich parent stars. We find that the mean [C/Fe] and [Na/Fe] values among the sample of stars with planets are smaller than the corresponding quantities among field stars of the same [Fe/H].

Microlensing by Multiple Planets in High-Magnification Events

Microlensing is increasingly gaining recognition as a powerful method for the detection and characterization of extrasolar planetary systems. Naively, one might expect that the probability of detecting the influence of more than one planet on any single microlensing light curve would be small. Recently, however, Griest & Safizadeh have shown that, for a subset of events, those with minimum-impact parameter umin 0.1 (high-magnification events), the detection probability is nearly 100% for Jovian-mass planets with projected separations in the range 0.6-1.6 of the primary Einstein ring radius RE and remains substantial outside this zone. In this Letter, we point out that this result implies that, regardless of orientation, all Jovian-mass planets with separations near 0.6-1.6RE dramatically affect the central region of the magnification pattern and thus have a significant probability of being detected (or ruled out) in high-magnification events. The joint probability, averaged over all inclinations and phases, of two planets having projected separations within 0.6-1.6RE is substantial: 1%-15% for two planets with the intrinsic separations of Jupiter and Saturn orbiting around 0.3-1.0 M parent stars. We illustrate by example the complicated magnification patterns and light curves that can result when two planets are present, and we discuss the possible implications of our result on detection efficiencies and the ability to discriminate between multiple and single planets in high-magnification events.

Ground-based detectability of terrestrial and Jovian extrasolar planets: observations of CM Draconis at Lick Observatory.

The detection of terrestrial-sized extrasolar planets from the ground has been thought to be virtually impossible due to atmospheric scintillation limits. However, we show that this is not the case especially selected (but nevertheless main sequence) stars, namely small eclipsing binaries. For the smallest of these systems, CM Draconis, several months to a few years of photometric observations with 1-m-class telescopes will be sufficient to detect the transits of any short-period planets of sizes > or = 1.5 Earth radii (RE), using cross-correlation analysis with moderately good photometry. Somewhat larger telescopes will be needed to extend this detectability to terrestrial planets in larger eclipsing binary systems. (We arbitrarily define "terrestrial planets" herein as those whose disc areas are closer to that of Earth's than Neptune's i.e., less than about 2.78 RE.) As a "spin-off" of such observations, we will also be able to detect the presence of Jovian-mass planets without transits using the timing of the eclipse minima. Eclipse minima will drift in time as the binary system is offset by a sufficiently massive planet (i.e., one Jupiter mass) about the binary/giant-planet barycenter, causing a periodic variation in the light travel time to the observer. We present here an outline of present observations taking place at the University of California Lick Observatory using the Crossley 0.9-m telescope in collaboration with other observatories (in South Korea, Crete, France, Canary Islands, and New York) to detect or constrain the existence of terrestrial planets around main sequence eclipsing binary star systems, starting with CM Draconis. We demonstrate the applicability of photometric data to the general detection of gas giant planets via eclipse minima timings in many other small-mass eclipsing binary systems as well.

Radial velocity searches for other planetary systems:Current status and future prospects

Measurement of variations in the radial velocities of stars due to the reflex orbital motion of the star around the planetary-system barycenter constitutes a powerful method of searching for substellar or planetary mass companions. After several years of patient data acquisition, radial-velocity searches for planetary systems around other stars are now beginning to bear fruit. In late 1995 and early 1996, three candidate systems were announced with Jovian-mass planets around solar-type stars. The current paradigm for low-mass star formation suggests that planetary systems should be able to form in the circumstellar disks surrounding young stellar objects. These newly discovered systems, and other discoveries which will soon follow them, will test critically our understanding of the processes of star- and planet-formation. We review the techniques used in these radial-velocity searches and their results to date. We then discuss planned improvements in the surveys, and the prospects for the next 20 years.

On the astrometric detection of neighboring planetary systems

The range of masses detectable by the astrometric technique in a given hypothetical planetary system is a function of the primary's mass, the system's distance, the orbital periods of its major planets, and the external precision of the positional data. Recent advances in astrometric measuring and reduction procedures could be used to detect possible Jovian-mass planets in the vicinity of more than a dozen of the Sun's nearest stellar neighbors. The sample of stars which at present could be subjected to a meaningful, intensive astrometric study is large enough to give a statistical indication of the frequency of companion objects with masses of about one Jupiter, with a reasonable opportunity of detecting even smaller masses. To date, in the opinion of the author, no suggested extrasolar substellar mass (mass<0.01 M ⊙) has been confirmed, although some proposed systems still await further study. A compilation of positions of Barnard's star determined with the Allegheny and Van Vleck refractors and corrected positions determined with the Sproul refractor is suggestive of a gravitational interaction of the star and one or more Jovian-mass planets. Unfortunately, systematic errors may still exist in the major body of data. The construction of a highly stable astrometric instrument would augment recent advances in measuring and reduction procedures, significantly increasing the ability to survey our stellar neighbors for evidence of planetary companions.