Abstract: We report high-precision, high-cadence photometric measurements of the star HD 209458, which is known from radial velocity measurements to have a planetary-mass companion in a close orbit. We detect two separate transit events at times that are consistent with the radial velocity measurements. In both cases, the detailed shape of the transit curve due to both the limb darkening of the star and the finite size of the planet is clearly evident. Assuming stellar parameters of 1.1 R⊙ and 1.1 M⊙, we find that the data are best interpreted as a gas giant with a radius of 1.27 ± 0.02 RJup in an orbit with an inclination of 871 ± 02. We present values for the planetary surface gravity, escape velocity, and average density and discuss the numerous observations that are warranted now that a planet is known to transit the disk of its parent star.

Abstract: Doppler measurements from Keck exhibit a sinusoidal periodicity in the velocities of the G0 dwarf HD 209458, having a semiamplitude of 81 m s 21 and a period of 3.5239 days, which is indicative of a “51 Peg‐like” planet with a minimum mass ( ) of 0.62 MJup and a semimajor axis of 0.046 AU. Follow-up photometry reveals M sin i a drop of 0.017 mag at the predicted time (within the errors) of transit by the companion based on the velocities. This is the first extrasolar planet observed to transit its star. The radius of the planet derived from the magnitude of the dimming is 1.42 RJup, which is consistent with models of irradiated Jupiter-mass planets. The transit implies that , leading to a true mass of 0.62 MJup for the planet. The resulting mean density of 0.27 g cm 23 sin i 1 0.993 implies that the companion is a gas giant. Subject headings: planetary systems — stars: individual (HD 209458)

Abstract: The recent transit observation of HD 209458 ban extrasolar planet orbiting a Sun-like star¨ con—rmed that it is a gas giant and determined that its orbital inclination is 85i. This inclination makes possible investigations of the planet atmosphere. In this paper we discuss the planet transmission spectra during a transit. The basic tenet of the method is that the planet atmosphere absorption features will be superimposed on the stellar —ux as the stellar —ux passes through the planet atmosphere above the limb. The ratio of the planets transparent atmosphere area to the star area is small (D10~3 to 10~4); for this method to work, very strong planet spectral features are necessary. We use our models of close-in extra- solar giant planets to estimate promising absorption signatures: the alkali metal lines; in particular, the Na I and K I resonance doublets; and the He I 2 3S¨2 3P triplet line at 1083.0 nm. If successful, obser- vations will constrain the line-of-sight temperature, pressure, and density. The most important point is that observations will constrain the cloud depth, which in turn will distinguish between diUerent atmo- sphere models. We also discuss the potential of this method for extrasolar giant planets at diUerent orbital distances and orbiting nonsolar-type stars. Subject headings: planetary systemsradiative transferstars: atmospheres

Abstract: ▪ Abstract Since the discovery of the first bona-fide brown dwarfs and extra-solar planets in 1995, the field of low-mass stars and substellar objects has progressed considerably, both from theoret...

Abstract: We have investigated the formation of gaseous envelopes of giant planets with wide ranges of parameters through quasi-static evolutionary simulations. In the nucleated instability model, rapid gas accretion is triggered when the solid core mass exceeds a critical mass. The gas accretion should be regulated essentially by core accretion rate and grain opacity in the outermost envelope. The conventional critical core mass ~5-20 M⊕ (M⊕: Earth's mass), however, is based on some nominal values of these quantities. The discovery of extrasolar giant planets requires investigation of the gas accretion processes under various circumstances. Furthermore, the current planetary accretion theory points out that the cores of Jupiter and Saturn would have been isolated from planetesimals and the core accretion would have almost stopped in their later stage of formation before their masses reached the conventional critical core mass. Through numerical simulations of quasi-static evolution of the gaseous envelope, we have investigated the characteristic growth times of the envelope mass for wide ranges of core accretion rate and grain opacity. We also studied the case where core accretion stops before onset of rapid gas accretion. Our main results are (1) the growth time of the envelope mass τg depends strongly on the core mass, moderately on the grain opacity, and weakly on the past core accretion process, and (2) τg is expressed approximately as τg ~ 108(Mcore /M⊕)-2.5(κ gr/1 cm 2 g-1) yr, where Mcore is the core mass and κgr is the grain opacity. Our results combined with the recent planetary accretion theory suggest surface density of solid materials twice as massive as that of the minimum-mass solar nebula model and the longer lifetime of the nebula than the 108 yr needed to form Jupiter and Saturn; otherwise migration of protoplanets may have to be considered. Our extensive parametric study not only confirms the difficulty in the formation of the giant planets quantitatively and rigorously, it also gives essential information in considering the problem of the formation, which is quite useful in applications.

Abstract: Since the discovery of the first bona-fide brown dwarfs and extra-solar planets in 1995, the field of low mass stars and substellar objects has considerably progressed, both from theoretical and observational viewpoints.Recent developments in the physics entering the modeling of these objects have led to significant improvements in the theory and to a better understanding of their mechanical and thermal properties. This theory can now be confronted with observations directly in various observational diagrams (color-color, color-magnitude, mass-magnitude, mass-spectral type), a stringent and unavoidable constraint which became possible only recently, with the generation of synthetic spectra. In this paper, we present the current state-of-the-art general theory of low-mass stars and sub-stellar objects, from one solar mass to one Jupiter mass, regarding primarily their interior structure and evolution. This review is a natural complement to the previous review on the atmosphere of low-mass stars and brown dwarfs (Allard et al 1997). Special attention is devoted to the comparison of the theory with various available observations. The contribution of low-mass stellar and sub-stellar objects to the Galactic mass budget is also analysed.

Abstract: The close-in extrasolar giant planets (CEGPs), AU from their parent stars, may have a large (0.05 component of optically re—ected light. We present theoretical optical photometric light curves and polar- ization curves for the CEGP systems from re—ected planetary light. DiUerent particle sizes of three con- densates are considered. In the most re—ective case, the variability is B100 kmag, which will be easily detectable by the upcoming satellite missions Microvariability and Oscillations of Stars (MOST ), COROT , and Measuring Oscillations in Nearby Stars (MONS), and possibly from the ground in the near future. The least re—ective case is caused by small, highly absorbing grains such as solid Fe, with variation of much less than 1 kmag. Polarization for all cases is lower than current detectability limits. We also discuss the temperature-pressure pro—les and resulting emergent spectra of the CEGP atmospheres. We discuss the observational results of q Boo b by Cameron et al. and Charbonneau et al. in context of our model results. The predictionsthe shape and magnitude of the light curves and polarization curves¨ are highly dependent on the sizes and types of condensates present in the planetary atmosphere. Subject headings: planetary systemsradiative transferstars: atmospheres

Abstract: ABSTRA C T We investigate the gravitational interaction of a Jovian-mass protoplanet with a gaseous disc with aspect ratio and kinematic viscosity expected for the protoplanetary disc from which it formed. Different disc surface density distributions are investigated. We focus on the tidal interaction with the disc with the consequent gap formation and orbital migration of the protoplanet. Non-linear two-dimensional hydrodynamic simulations are employed using three independent numerical codes. A principal result is that the direction of the orbital migration is always inwards and such that the protoplanet reaches the central star in a near-circular orbit after a characteristic viscous time-scale of ,10 4 initial orbital periods. This is found to be independent of whether the protoplanet is allowed to accrete mass or not. Inward migration is helped by the disappearance of the inner disc, and therefore the positive torque it would exert, because of accretion on to the central star. Maximally accreting protoplanets reach about 4 Jovian masses on reaching the neighbourhood of the central star. Our results indicate that a realistic upper limit for the masses of closely orbiting giant planets is ,5 Jupiter masses, if they originate in protoplanetary discs similar to the minimum-mass solar nebula. This is because of the reduced accretion rates obtained for planets of increasing mass. Assuming that some process such as termination of the inner disc through a magnetospheric cavity stops the migration, the range of masses estimated for a number of close orbiting giant planets as well as their inward orbital migration can be accounted for by consideration of disc‐protoplanet interactions during the late stages of giant planet formation.

Abstract: We report results from a large Hubble Space Telescope project to observe a significant (~34,000) ensemble of main-sequence stars in the globular cluster 47 Tucanae with a goal of defining the frequency of inner orbit, gas giant planets. Simulations based on the characteristics of the 8.3 days of time series data in the F555W and F814W Wide Field Planetary Camera 2 (WFPC2) filters show that ~17 planets should be detected by photometric transit signals if the frequency of hot Jupiters found in the solar neighborhood is assumed to hold for 47 Tuc. The experiment provided high-quality data sufficient to detect planets. A full analysis of these WFPC2 data reveals ~75 variables, but no light curves resulted for which a convincing interpretation as a planet could be made. The planet frequency in 47 Tuc is at least an order of magnitude below that for the solar neighborhood. The cause of the absence of close-in planets in 47 Tuc is not yet known; presumably the low metallicity and/or crowding of 47 Tuc interfered with planet formation, with orbital evolution to close-in positions, or with planet survival.

Abstract: We report a spectroscopic orbit with period P = 3.52433 +/- 0.00027 days for the planetary companion that transits the solar-type star HD209458. For the metallicity, mass, and radius of the star we derive [Fe/H] = 0.00 +/- 0.02, M = 1.1 +/- 0.1 solar masses, and R = 1.3 +/- 0.1 solar radii. This is based on a new analysis of the iron lines in our HIRES template spectrum, and also on the absolute magnitude and color of the star, and uses isochrones from four different sets of stellar evolution models. Using these values for the stellar parameters we reanalyze the transit data and derive an orbital inclination of i = 85.2 +/- 1.4 degrees. For the planet we derive a mass of Mp = 0.69 +/- 0.05 Jupiter masses, a radius of Rp = 1.54 +/- 0.18 Jupiter radii, and a density of 0.23 +/- 0.08 grams per cubic cm.

Abstract: We report results of a search for planets around 530 main-sequence stars using the Keck HIRES spectrometer, which has provided Doppler precision of 3 m s-1 during the past 3 yr. We report six new strong planet candidates having complete Keplerian orbits, with periods ranging from 24 days to 3 yr. These are HD 10697, HD 37124, HD 134987, HD 177830, HD 192263, and HD 222582. We also provide updated orbital parameters for the previously announced planets around HD 187123, HD 195019, HD 201277, and HD 217107. Four of the six newly discovered planets have minimum M sin i masses less than 2 MJUP, while the remaining two have M sin i ~ 5 MJUP. The distribution of planetary masses continues to exhibit a rise toward lower masses. The orbital eccentricities of the new planets range from 0.12 to 0.71, which also continues the ubiquity of high eccentricities. All 17 known extrasolar planets orbiting beyond 0.2 AU have eccentricities greater than ~0.1. The current limiting Doppler precision of the Keck Doppler survey is 3 m s-1 per observation as determined from observations of both stable stars and residuals to Keplerian fits.

Abstract: Magma oceans, plate tectonics, and stagnant-lid convection have transferred heat out of the terrestrial planets at various times in their histories. The implications of the existence of multiple branches are graphically illustrated by approximating the globally averaged mantle heat flow as a function of the interior potential temperature. For this assumption to be valid, the mantle heat flow needs to be able to change rapidly relative to the potential temperature, or, equivalently, lithosphere needs to be a small fraction of the mass planet. This criterion is satisfied by the Earth, Venus, and Mars, but not the Moon. At a given potential temperature the function may be multivalued with a separate branch representing each mode of convection. The heat flow evolves along a branch as the potential temperature changes depending on whether the heat flow is greater or less than the global radioactive heat generation. When the end of a branch is reached, the state of the system jumps to another branch, quickly changing the global heat flow. Examples include transitions from a magma ocean to plate tectonics, probably on the Earth and Mars, and conceivably Venus; and the transition from a stagnant-lid planet to a magma ocean on Venus and the eventual return to a stagnant-lid planet.

Abstract: We revisit the idea that density-wave wakes of planets drive accretion in protostellar disks. The effects of many small planets can be represented as a viscosity if the wakes damp locally, but the viscosity is proportional to the damping length. Damping occurs mainly by shocks even for earth-mass planets. The excitation of the wake follows from standard linear theory including the torque cutoff. We use this as input to an approximate but quantitative nonlinear theory based on Burger's equation for the subsequent propagation and shock. Shock damping is indeed local but weakly so. If all metals in a minimum-mass solar nebula are invested in planets of a few earth masses each, dimensionless viscosities [alpha] of order dex(-4) to dex(-3) result. We compare this with observational constraints. Such small planets would have escaped detection in radial-velocity surveys and could be ubiquitous. If so, then the similarity of the observed lifetime of T Tauri disks to the theoretical timescale for assembling a rocky planet may be fate rather than coincidence.

Abstract: C. Hayashi prescribed a "minimum-mass solar nebula," which contained just enough material to make the planets. This prescription, which has been widely used in constructing scenarios for planet formation, proposed that ice will condense when the temperature falls below 170 K (the "snow line"). In Hayashi's model, that occurred at 2.7 AU. It is usually assumed that the cores of the giant planets (e.g., Jupiter) form beyond the snow line. The snow line, in Hayashi's model, is where the temperature of a black body that absorbed direct sunlight and reradiated as much as it absorbed would be 170 K. Since Hayashi, there have been a series of more detailed models of the absorption by dust of the stellar radiation and of accretional heating, which alter the location of the snow line. We have attempted a "self-consistent" model of a T Tauri disk in the sense that we used dust properties and calculated surface temperatures that matched observed disks. We then calculated the midplane temperature for those disks, with no accretional heating or with small (≤10-8 M☉ yr-1) accretion rates. (Larger accretion rates can push the snow line out to beyond 4 AU but do not match the observed disks.) Our models bring the snow line in to the neighborhood of 1 AU—not far enough to explain the close planetary companions to other stars, but much closer than in recent starting lines for orbit migration scenarios.

Abstract: All magnetized planets in the solar system emit intense cyclotron maser radiation. Like Jupiter, extrasolar giant planets are probably magnetized. If, in addition, there is a source of energetic (keV) electrons in their magnetospheres, from auroral processes or as a result of magnetic coupling between the planet and a satellite, it is likely that extrasolar planets are cyclotron-maser emitters. Detection and follow-up observations of cyclotron maser radiation from an exoplanet would reveal the presence, strength, and complexity of the planetary magnetic field, the planet's rotation rate, and possibly the presence of an Io-like moon within the planet's magnetosphere. Magnetic fields may be necessary for life to exist on the surface of planets because they provide protection from the nefarious effects of energetic particles of stellar winds, stellar flares, and cosmic rays. We have conducted a search for radio emission from extrasolar planets and brown dwarfs at decimeter and meter wavelengths using the Very Large Array (VLA). We have observed seven extrasolar planets and two brown dwarfs at 333 and 1465 MHz, and one extrasolar planet and one brown dwarf at 74 MHz. Typical (1 σ) sensitivities were 0.02-0.07 mJy at 1465 MHz, 1-10 mJy at 333 MHz, and ~50 mJy at 74 MHz. To date, no detections have been made.

Abstract: We use numerical N-body simulations of the Orion Nebula Cluster (ONC) to investigate the destruction of protoplanetary disks by close stellar encounters and UV radiation from massive stars. The simulations model a cluster of 4000 stars, and we consider separately cases in which the disks have fixed radii of 100 AU and 10 AU. In the former case, depending on a star's position and orbit in the cluster over 10^7 years, UV photoevaporation removes at least 0.01 Msol from its disk, and can remove up to 1 Msol. We find no dynamical models of the ONC consistent with the suggestion of Storzer and Hollenbach that the observed distribution and abundance of proplyds could be explained by a population of stars on radial orbits which spend relatively little time near Theta 1C Ori (the most massive star in the ONC). Instead the observations require either massive disks (e.g. a typical initial disk mass of 0.4 Msol) or a very recent birth for Theta 1C Ori. When we consider the photoevaporation of the inner 10 AU of disks in the ONC, we find that planet formation would be hardly affected. Outside that region, planets would be prevented from forming in about half the systems, unless either the initial disk masses were very high or they formed in less than ~ 2 Myr and Theta 1C Ori has only very recently appeared. We also present statistics on the distribution of minimum stellar encounter separations. This peaks at 1000 AU, with less than 10% of stars having had an encounter closer than 100 AU after 10^7 years. We conclude that stellar encounters are unlikely to play a significant role in destroying protoplanetary disks. In the absence of any disruption mechanism other than those considered here, we would thus predict planetary systems like our own to be common amongst stars forming in ONC-like environments.

Abstract: Auroras are (generally) high-latitude atmospheric emissions that result from the precipitation of energetic charged particles from a planet's magnetosphere. Auroral emissions from the giant planets have been observed from ground-based observatories, Earth-orbiting satellites (e.g., International Ultraviolet Explorer (IUE), Hubble Space Telescope (HST), and Roentgensatellit (ROSAT)), flyby spacecraft (e.g., Voyager 1 and 2), and orbiting spacecraft platforms (e.g., Galileo) at X-ray, ultraviolet (UV), visible, infrared (IR), and radio wavelengths. UV, visible, and IR auroras are atmospheric emissions, produced or initiated when ambient atmospheric species are excited through collisions with the precipitating particles, while radio and X-ray auroras are beam emissions, produced by the precipitating species themselves. The emissions at different wavelengths provide unique and complementary information, accessible to remote sensing, about the key physical processes operating in the atmospheric and magnetospheric regions where they originate. This paper reviews the development of our current understanding of auroral emissions from Jupiter, Saturn, Uranus, and Neptune, as revealed through multispectral observations and supplemented by plasma measurements.

Abstract: We report results from the Anglo-Australian Planet Search -- a survey for planets around 200 solar-type stars in the southern hemisphere, which is being carried out on the 3.9m Anglo-Australian Telescope. Limiting Doppler precisions of 3m/s have been demonstrated from the first 2.5 years of operation, making this the highest precision planet search in the southern hemisphere. From these data we report results for two new sub-stellar detections. The first is a "51 Peg"-like planet around the star HD179949 with Msin i = 0.84 Mjup. Photometric study reveals this is not a transiting system. The second is a brown dwarf or very low-mass star companion to HD164427 in an eccentric orbit with Msin i = 46Mjup. Hipparcos data indicate this latter object is unlikely to have a mass greater than 0.18 Msol.

Abstract: We present the results of an analysis of time-series photometry, Ca II H and K spectrophotometry, and high-dispersion visible spectra of nine nearby Sun-like stars recently identified as having planets. For the six stars whose presumed planets have orbital periods of less than 4 months (? Boo, 51 Peg, ? And, ?1 Cnc, ? CrB, and 70 Vir), sine-curve fits to the photometric data show no variations with semiamplitude greater than 1 or 2 parts in 104. Photometric variations in 47 UMa are similarly small, although our photometric data of this star are slightly affected by variability of the comparison star. Nonvariability at this level of precision is sufficient to rule out surface magnetic activity as the cause of the observed radial-velocity variations in these seven stars and makes nonradial pulsations unlikely as well. Thus, our photometry provides indirect but strong support for true reflex motions?planets?in these seven stars, but cannot yet so support the planetary hypothesis for the two additional stars, 16 Cyg B and Gl 411. Continued photometric monitoring of the short-period systems may soon result in the direct detection of these planets in reflected light. We have used our photometric fluxes to search for possible transits of the extrasolar planets. Transits definitely do not occur in ? Boo, 51 Peg, ? And, and ?1 Cnc, and probably do not occur in ? CrB and 70 Vir. Our transit-search results are inconclusive for 47 UMa, and we cannot address the issue for 16 Cyg B and Gl 411. The precision of our photometry is sufficient to detect transits of planets even if they are not gas giants, as currently assumed, but much smaller objects with rocky compositions. The chance of finding at least one transit in the six stars is ~40%. We find significant year-to-year photometric variability only in ? Boo, which is not only the youngest star in the sample but also the star with the shallowest convective zone. The interseasonal range in its yearly mean photometric flux is ~0.002 mag, roughly twice the 0.0008 mag decadal variation in the Sun's total irradiance. Monitoring of the relative Ca II H and K fluxes began between 1966 and 1968 for 51 Peg, ? Boo, ? CrB, and Gl 411, between 1990 and 1993 for 47 UMa, 70 Vir, 16 Cyg B, and ?1 Cnc, and in 1996 for ? And. The data have been newly recalibrated for improved long-term instrumental stability, resulting in better precision of the Ca II records. Five of the nine stars in this study have little or no detectable year-to-year variation in Ca II flux. The remaining four show moderate or pronounced variability: ? Boo, whose radial-velocity and photometric variations have comparatively high amplitudes; Gl 411, whose planetary companion was inferred astrometrically, not spectroscopically; ?1 Cnc, which may undergo decadal cyclic activity; and ? And, which shows moderate year-to-year variability. Except for 47 UMa, intraseasonal variability consistent with rotation was detected in the Ca II records of all stars. However, the rotation periods determined for ? And, 70 Vir, and 16 Cyg B are of low confidence. An examination of the recalibrated Ca II records for 51 Peg finds a rotation period of 22 days, in contrast to our previous result of 37 days. Ages have been estimated from the mean Ca II flux and, where possible, the rotation period. We find general consistency with the ages determined by others comparing properties determined from high-resolution spectroscopy to evolutionary models, although the uncertainties are, in general, large.

Abstract: We apply our recently elaborated, powerful numerical approach to the high-resolution modeling of the structure and emission of circumstellar dust disks, incorporating all relevant physical processes. Specifically, we examine the resonant structure of a dusty disk induced by the presence of one planet. It is shown that the planet, via resonances and gravitational scattering, produces (1) an asymmetric resonant dust belt with one or more clumps intermittent with one or a few off-center cavities; and (2) a central cavity void of dust. These features can serve as indicators of a planet embedded in the circumstellar dust disk and, moreover, can be used to determine its major orbital parameters and even the mass of the planet. The results of our study reveal a remarkable similarity with various types of highly asymmetric circumstellar disks observed with the James Clerk Maxwell Telescope around Epsilon Eridani and Vega. The proposed interpretation of the clumps in those disks as being resonant patterns is testable -- it predicts the asymmetric design around the star to revolve, viz., by 1.2--1.6 deg/yr about Vega and 0.6--0.8 deg/yr about Epsilon Eri.

Abstract: We show that a space-based gravitational microlensing survey for terrestrial extra-solar planets is feasible in the near future, and could provide a nearly complete picture of the properties of planetary systems in our Galaxy. We present simulations of such a survey using a 1-2m aperture space telescope with a ~2 square degree field-of-view which is used to continuously monitor ~10^8 Galactic bulge main sequence stars. The microlensing techniques allows the discovery of low mass planets with high signal-to-noise, and the space mission that we have studied are sensitive to planets with masses as low as that of Mars. By targeting main sequence source stars, which can only be resolved from space, the space-based microlensing survey is able to detect enough light from the lens stars to determine the spectral type of one third of the lens stars with detected planets, including virtually all of the F, G, and K stars which comprise one quarter of the event sample. This enables the determination of the planetary masses and separations in physical units, as well as the abundance of planets as a function of stellar type and distance from the Galactic center. We show that a space-based microlensing planet search program has its highest sensitivity to planets at orbital separations of 0.7-10 AU, but it will also have significant sensitivity at larger separations and will be able to detect free-floating planets in significant numbers. This complements the planned terrestrial planet transit missions which are sensitive to terrestrial planets at separations of =< 1 AU. Such a mission also detect ~50,000 giant planets via transits, and it is, therefore, the only proposed planet detection method that is sensitive to planets at all orbital radii.

Abstract: The population of the Kuiper Belt within 50 AU of the Sun has likely been severely depleted by gravitational perturbations from the giant planets, particularly Neptune. The density of Kuiper Belt objects is expected to be two orders of magnitude higher just beyond 50 AU, where planetary perturbations are insignificant. In 1998 and 1999, we surveyed for Kuiper Belt Objects (KBOs) in 6 fields of the ecliptic (total sky area 1.5 deg^2) to limiting magnitudes between R=24.9 and R=25.9. This is deep enough to detect KBOs of diameter >~ 160 km at a distance of 65 AU. We detected 24 objects. None of these objects, however, is beyond 53 AU. Our survey places a 95% CL upper limit of Sigma 160 km KBOs in the 55--65 AU region is, at >95% confidence, less than the mean density in the 30--50 AU region, and at most twothirds of the mean density from 40--50 AU. Thus, a substantial density increase beyond 50 AU is excluded in this model-independent estimate, implying that some process or event in the history of the Solar System has truncated the distribution of 160-km planetesimals at ~50 AU. A dense primordial disk could be present beyond 50 AU if it contains only smaller objects, or is sufficiently thin and inclined to have escaped detection in our 6 survey fields.

Abstract: Spectroscopic studies of the upper atmospheres of the giant planets using infrared wavelengths sensitive to the H3+ molecular ion show that this species plays a critical role in determining the phy...

Abstract: We present observations of the microlensing event MACHO 98-BLG-35, which reached a peak mag- ni—cation factor of almost 80. These observations by the Microlensing Planet Search (MPS) and MOA collaborations place strong constraints on the possible planetary system of the lens star and show intriguing evidence for a low-mass planet with a mass fraction 4 ) 10~5 " v " 2 ) 10~4. A giant planet with v \ 10~3 is excluded from 95% of the region between 0.4 and 2.5 from the lens star, where is R E R E the Einstein ring radius of the lens. This exclusion region is more extensive than the generic ii lensing zone,ˇˇ which is 0.6¨1.6 For smaller mass planets, we can exclude 57% of the ii lensing zone ˇˇ for R E. v \ 10~4 and 14% of the lensing zone for v \ 10~5. The mass fraction v \ 10~5 corresponds to an Earth-mass planet for a lensing star of mass D0.3 A number of similar events will provide sta- M _ . tistically signi—cant constraints on the prevalence of Earth-mass planets. In order to put our limits in more familiar terms, we have compared our results to those expected for a solar system clone, averaging over possible lens system distances and orientations. We —nd that such a system is ruled out at the 90% con—dence level. A copy of the solar system with Jupiter replaced by a second Saturn-mass planet can be ruled out at 70% con—dence. Our low-mass planetary signal (few Earth masses to Neptune mass) is sig- ni—cant at the 4.5 p con—dence level. If this planetary interpretation is correct, the MACHO 98-BLG-35 lens system constitutes the —rst detection of a low-mass planet orbiting an ordinary star without gas giant planets.20 Subject headings: gravitational lensingplanetary systemsstars: low-mass, brown dwarfs

Abstract: We examine the correlation between stellar metallicity and short period planets It appears that approximately 1% of dwarf stars in the solar neighborhood harbor short-period planets characterized by near-circular orbits and orbital periods P 02 dex), it appears that the fraction increases to 10% Using the Hipparcos database and the Hauck & Mermilliod (1998) compilation of Stromgren uvby photometry, we identify a sample of 206 metal-rich stars of spectral type K, G, and F which have an enhanced probability of harboring short-period planets Many of these stars would be excellent candidates for addition to radial velocity surveys We have searched the Hipparcos epoch photometry for transiting planets within our 206 star catalog We find that the quality of the Hipparcos data is not high enough to permit unambiguous transit detections It is, however, possible to identify candidate transit periods We then discuss various ramifications of the stellar metallicity - planet connection First, we show that there is preliminary evidence for increasing metallicity with increasing stellar mass among known planet-bearing stars This trend can be explained by a scenario in which planet-bearing stars accrete an average of 30 Earth Masses of rocky material after the gaseous protoplanetary disk phase has ended We present dynamical calculation which suggest that a survey of metallicities of spectroscopic binary stars can be used to understand the root cause of the stellar metallicity - planet connection

Abstract: We examine the correlation between stellar metallicity and the presence of short-period planets. It appears that approximately 1% of dwarf stars in the solar neighborhood harbor short-period planets characterized by near-circular orbits and orbital periods P 0.2 dex), it appears that the fraction increases to 10%. Using the Hipparcos database and the Hauck & Mermilliod compilation of Stromgren uvby photometry, we identify a sample of 206 metal-rich stars of spectral type K, G and F which have an enhanced probability of harboring short-period planets. Many of these stars would be excellent candidates for addition to radial velocity surveys. We have searched the Hipparcos epoch photometry for transiting planets within our 206 star catalog. We find that the quality of the Hipparcos data is not high enough to permit unambiguous transit detections. It is, however, possible to identify candidate transit periods. We then discuss various ramifications of the stellar metallicity-planet connection. First, we show that there is preliminary evidence for increasing metallicity with increasing stellar mass among known planet-bearing stars. This trend can be explained by a scenario in which planet-bearing stars accrete an average of 30 M⊕ of rocky material after the gaseous protoplanetary disk phase has ended. We present dynamical calculations which suggest that a survey of metallicities of spectroscopic binary stars can be used to understand the root cause of the stellar metallicity-planet connection.

Abstract: Part 1 The general background: The structure of the solar system. Observations and theories of star formation. What should a theory explain? Part 2 Setting the theoretical scene: Theories up to 1960. Part 3 Current theories: A brief survey of modern theories. The Sun, planets and satellites. Planetary orbits and angular momentum. A planetary collision. The Moon. Smaller planets and irregular satellites. Asteroids, meteorites and comets. Part 4 The current state of theories: Comparisons of the main theories. Appendices.