We report the discovery of a substellar-mass companion to the K0-giant HD 17092 with the Hobby-Eberly Telescope. In the absence of any correlation of the observed 360-day periodicity with the standard indicators of stellar activity, the observed radial velocity variations are most plausibly explained in terms of a Keplerian motion of a planetary-mass body around the star. With the estimated stellar mass of 2.3Msun, the minimum mass of the planet is 4.6MJ. The planet's orbit is characterized by a mild eccentricity of e=0.17 and a semi-major axis of 1.3 AU. This is the tenth published detection of a planetary companion around a red giant star. Such discoveries add to our understanding of planet formation around intermediate-mass stars and they provide dynamical information on the evolution of planetary systems around post-main sequence stars.
We report new VLT/NACO imaging observations of the young, nearby brown dwarf 2MASSW J1207334-393254 and its suggested planetary mass companion (2M1207 b). Three epochs of VLT/NACO measurements obtained over nearly one year show that the planetary mass companion candidate shares the same proper motion and, with a high confidence level, is not a stationary background object. This result confirms the status of 2M1207 b as of planetary mass (5 times the mass of Jupiter) and the first image of a planetary mass companion in a different system than our own. This discovery offers new perspectives for …
We present Gemini near-infrared adaptive optics imaging and spectroscopy of a planetary mass candidate companion to 1RXS J160929.1-210524, a roughly solar-mass member of the 5 Myr-old Upper Scorpius association. The object, separated by 2.22" or 330 AU at ~150 pc, has infrared colors and spectra suggesting a temperature of 1800(-100/+200) K, and spectral type of L4(-2/+1). The H- and K-band spectra provide clear evidence of low surface gravity, and thus youth. Based on the widely used DUSTY models, we infer a mass of 8(-2/+4)Mjupiter. If gravitationally bound, this would be the lowest mass com…
(abridged) There is considerable interest in the possible interaction between parent stars and giant planetary companions in 51 Peg-type systems. We demonstrate from MOST satellite photometry and Ca II K line emission that there has been a persistent, variable region on the surface of tau Boo A which tracked its giant planetary companion for some 440 planetary revolutions and lies ~68deg (phi=0.8) in advance of the sub-planetary point. The light curves are folded on a range of periods centered on the planetary orbital period and phase dependent variability is quantified by Fourier methods and …
The determinations of element abundances in red-giant stars and in particular in AGB stars are reviewed and the resulting abundances are compared with those obtained for planetary nebulae in the Galaxy and in nearby galaxies. The problems, possibilities and implications of such comparisons when estimating yields from low-mass and intermediate-mass stars are illustrated and commented on.
Upcoming space-based photometric satellites offer the possibility of detecting continuum flux variability at the micro-magnitude level. We show that the Doppler flux variability induced by the reflex motion of stars due to planetary companions has an amplitude of (3-alpha)K/c, where K is the reflex radial velocity amplitude and alpha is the logarithmic slope of source spectral flux in the observed frequency band. For many of the known close-in planetary systems with periods less than ~0.2 years, the periodic Doppler variability is of order a micromagnitude, and is significant relative to the v…
Self-gravitating protostellar discs are unstable to fragmentation if the gas can cool on a time scale that is short compared to the orbital period. We use a combination of hydrodynamic simulations and N-body orbit integrations to study the long term evolution of a fragmenting disc with an initial mass ratio to the star of M_disc/M_star = 0.1. For a disc which is initially unstable across a range of radii, a combination of collapse and subsequent accretion yields substellar objects with a spectrum of masses extending (for a Solar mass star) up to ~0.01 M_sun. Subsequent gravitational evolution …
I argue that cool giant companions in most symbiotic binary systems possess magnetic activity on a much higher level than isolated, or in wide binary systems, cool giants. Based on the behavior of main sequence stars, I assume that magnetic activity and X-ray luminosity increase with rotation velocity. I then show that the cool companions in symbiotic systems are likely to rotate much faster than isolated, or in wide binary systems, cool giants. The magnetic activity of the cool giant may be observed as a global axisymmetrical mass loss geometry from the cool giant (before the hot companion in…
High precision radial velocity observations of the solar-type star 16 Cygni B taken at McDonald Observatory and at Lick Observatory, have each independently discovered periodic radial-velocity variations indicating the presence of a Jovian-mass companion to this star. The orbital fit to the combined data gives a period of 800.8 days, a velocity amplitude of 43.9 m/s, and an eccentricity of 0.63. This is the largest eccentricity of any planetary system discovered so far. Assuming that 16 Cygni B has a mass of 1.0 Msun, this implies a mass for the companion of 1.5 sin i Jupiter masses. While the…
We have investigated the possibility that radiation pressure might trigger planetary nebula (PN) ejection during helium-shell flashes in asymptotic- giant-branch (AGB) stars. We find that the outward flux at the base of the hydrogen envelope during a flash will reach the Eddington limit when the envelope mass falls below a critical value that depends on the core mass and composition. These results may help to explain the helium-burning PN nuclei found in the Magellanic Clouds.
We report the detection of a planetary companion with a minimum mass of m sin i = 0.0771 M_Jup = 24.5 M_Earth to the nearby (d = 9.4 pc) M2.5V star GJ 176. The star was observed as part of our M dwarf planet search at the Hobby-Eberly Telescope (HET). The detection is based on 5 years of high-precision differential radial velocity (RV) measurements using the High-Resolution-Spectrograph (HRS). The orbital period of the planet is 10.24 d. GJ 176 thus joins the small (but increasing) sample of M dwarfs hosting short-periodic planets with minimum masses in the Neptune-mass range. Low mass planets…
Multi-band (0.9 to 1.6 um) images of the TW Hydrae Association (TWA) brown dwarf, 2MASS J1207334-393254 (also known as 2M1207), and its candidate planetary mass companion (2M1207b) were obtained on 2004 Aug 28 and 2005 Apr 26 with HST/NICMOS. The images from these two epochs unequivocally confirm the two objects as a common proper motion pair (16.0 sigma confidence). A new measurement of the proper motion of 2M1207 implies a distance to the system of 59+-7 pc and a projected separation of 46+-5 AU. The NICMOS and previously published VLT photometry of 2M1207b, extending overall from 0.9 to 3.8…
Microlensing light curves are now being monitored with the precision required to detect small perturbations due to planetary companions of the primary lens. Microlensing is complementary to other planetary search techniques in its potential for measuring the statistical frequency of planets beyond the solar neighborhood. We present an algorithm to analyze the efficiency with which the presence of binaries can be detected in real microlensing datasets. Such an analysis is required in order to draw statistical inferences about lensing companions. We apply the method to artificial (but realistic)…
The ensemble of now more than 250 discovered planetary systems displays a wide range of masses, orbits and, in multiple systems, dynamical interactions. These represent the end point of a complex sequence of events, wherein an entire protostellar disk converts itself into a small number of planetary bodies. Here, we present self-consistent numerical simulations of this process, which produce results in agreement with some of the key trends observed in the properties of the exoplanets. Analogs to our own solar system do not appear to be common, originating from disks near the boundary between b…
In this paper we discuss the nature and the possible formation scenarios of the companion of the brown dwarf 2MASS 1207334-393254. We initially discuss the basic physical properties of this object and conclude that, although from its absolute mass ($5M_{\rm Jup}$), it is a planetary object, in terms of its mass ratio $q$ and of its separation $a$ with respect to the primary brown dwarf, it is consistent with the statistical properties of binaries with higher primary mass. We then explore the possible formation mechanism for this object. We show that the standard planet formation mechanism of c…
We examine the relationship between the frequency of close companions (stellar and planetary companions with orbital periods < 5 years) and the metallicity of their Sun-like (~ FGK) hosts. We confirm and quantify a ~4 sigma positive correlation between host metallicity and planetary companions. We find little or no dependence on spectral type or distance in this correlation. In contrast to the metallicity dependence of planetary companions, stellar companions tend to be more abundant around low metallicity hosts. At the ~2 sigma level we find an anti-correlation between host metallicity and th…
We present the results of a deep imaging survey of stars surrounded by planets detected with the radial velocity technique. The purpose is to search for and to characterize long-period stellar and substellar companions. The sample contains a total of 26 stars, among which 6 exhibit additional radial velocity drifts. We used NACO, at the ESO Very Large Telescope, and PUEO-KIR, at the Candian French Hawaiian Telescope, to conduct a near-infrared coronographic survey with adaptive optics of the faint circumstellar environment of the planetary hosts. The domain investigated ranges between 0.1 to 1…
We report precise Doppler measurements of HD 142022 obtained during the past six years with the CORALIE echelle spectrograph at La Silla Observatory together with a few additional observations made recently with the HARPS echelle spectrograph. Our radial velocities reveal evidence of a planetary companion with an orbital period P = 1928 +53-39 days, an eccentricity e = 0.53 +0.23-0.18, and a velocity semiamplitude K = 92 +102-29 m/s. The inferred companion minimum mass is M2sini = 5.1 +2.6-1.5 MJup and the semimajor axis a = 3.03+/-0.05 AU. Only one full orbital revolution has been monitored y…
In a recent work Ciardullo et al. (1999) list 19 planetary nebulae surveyed by the Hubble Space Telescope for the presence of resolved visual binary companions of their central stars. For ten planetary nebulae they argue for probable physical association of the resolved stars with the central stars, while for nine the association is less likely. Such stellar companions, at orbital separations of hundreds to thousands of astronomical units, will cause the structures of these planetary nebulae to possess a non-axisymmetrical signatures. By using images from the literature of these 19 planetary n…
We report limits in the planetary-mass regime for companions around the nearest single white dwarf to the Sun, van Maanen's star (vMa 2), from deep J-band imaging with Gemini North and Spitzer IRAC mid-IR photometry. We find no resolved common proper motion companions to vMa 2 at separations from 3" - 45", at a limiting magnitude of J~23. Assuming a total age for the system of 4.1 +/-1 Gyr, and utilising the latest evolutionary models for substellar objects, this limit is equivalent to companion masses >7 +/-1 Mjup (T~300K). Taking into account the likely orbital evolution of very low mass com…
From optical high-resolution spectra the nature of the unseen companion of HW Vir is determined without detection of any spectral features originating from the secondary itself. Using radial velocity measurements from the primary hot subdwarf B star and from weak additional absorption lines detected close to the secondary eclipse, probably caused by reflected light off the surface of the secondary, the mass and radius of the companion is determined. The values are consistent with those of a M type main sequence star.
We report the detection of a extrasolar planet candidate orbiting the G1 V star HD 39091. The orbital period is 2083 d and the eccentricity is 0.62. With a minimum (M sin $i$) mass of 10.3 M$_{\rm JUP}$ this object falls near the high mass end of the observed planet mass function, and may plausibly be a brown dwarf. Other characteristics of this system, including orbital eccentricity and metallicity, are typical of the well populated class of radial velocity planets in eccentric orbits around metal-rich stars.
We present an analysis of Hipparcos astrometric measurements of Upsilon Andromedae, a nearby main-sequence star around which three planet candidates have recently been discovered by means of radial-velocity measurements. The stellar orbit associated with the outermost candidate has a period of 1269 +/- 9 days and a minimum semi-major axis of 0.6 milli-arc-sec (mas). Using the Hipparcos data together with the spectroscopic elements we found a semi-major axis of 1.4 +/- 0.6 mas. This implies a mass of 10.1 (+4.7, -4.6) Jupiter masses for that planet of Upsilon Andromedae.
Starting from a previously stated hypothesis concerning the discretization of the orbits for periodic celestial motions, the mass of ups-Andromedae and the periods of its b- and d- companions are estimated using the accurately known period of the massive c-companion. Moreover, the periods and the orbital major semiaxes of other hypotetically existing and not yet discovered smaller planets of ups-Andromedae are guessed.
We develop a new method of modeling microlensing events based on a Monte Carlo simulation that incorporates both a Galactic model and the constraints imposed by the observed characteristics of the event. The method provides an unbiased way to analyze the event especially when parameters are poorly constrained by the observed lightcurve. We apply this method to search for planetary companions of the lens in OGLE-2003-BLG-423, whose maximum magnification A_max=256+-43 (or A_max=400+-115 from the lightcurve data alone) is the highest among single-lens events ever recorded. The method permits us, …
Planetary nebulae are thought to be formed when a slow wind from the progenitor giant star is overtaken by a subsequent fast wind generated as the star enters its white dwarf stage$^{1}$. A shock forms near the boundary between the winds, which creates a relatively dense shell that provides the characteristic appearance of a planetary nebula. A spherically symmetric wind will produce a spherically symmetric shell, yet over half of known planetary nebulae are not spherical; rather, they are elliptical or bipolar in shape$^{2}$. While a magnetic field could launch and collimate a bipolar outflow…
We present near-IR interferometric measurements of the K1.5 giant Arcturus (alpha Bootis), obtained at the IOTA interferometer with the FLUOR instrument, in four narrow filters with central wavelengths ranging from 2.03 to 2.39 micron. These observations were expected to allow us to quantify the wavelength dependence of the diameter of a typical K giant. They are compared to predictions from both plane-parallel and spherical model atmospheres. Unexpectedly, neither can explain the observed visibilities. We show how these data suggest the presence of a companion, in accordance with the Hipparco…
Doppler measurements of the M4 dwarf star, Gliese 876, taken at both Lick and Keck Observatory reveal periodic, Keplerian velocity variations with a period of 61 days. The orbital fit implies that the companion has a mass of, M = 2.1 MJUP /sin i, an orbital eccentricity of, e = 0.27+-0.03, and a semimajor axis of, a = 0.21 AU. The planet is the first found around an M dwarf, and was drawn from a survey of 24 such stars at Lick Observatory. It is the closest extrasolar planet yet found, providing opportunities for follow--up detection. The presence of a giant planet on a non-circular orbit, 0.2…
It has long been speculated that the observed periodic radial velocity pattern for the K giant Pollux might be explained in terms of an orbiting planetary companion. We have collected 80 high-resolution spectra for Pollux at Lick Observatory yielding precise radial velocities with a mean error of 3.8 m/s, providing the most comprehensive and precise data set available for this star. Our data confirm the periodicity previously seen in the radial velocities. We derive a period of 589.7+/-3.5 days and, assuming a primary mass of 1.86 M_Sun, a minimum companion mass of 2.9+/-0.3 M_Jup, consistent …
The recent HST optical images, and the optical and ultraviolet spectra, of Magellanic planetary nebulae (PNe), together with the large data-base that has been collected in the past decade, allows unprecedented insight in the evolution of PNe and their central stars. In this paper we present a selection of recent results: The analysis of PN morphology, both in the optical and ultra-violet emission lines; the relation between nebular morphology and the chemistry produced by stellar evolution; the direct determination of the transition time from observations; and the study of the nature and evolu…
Since 1999, we have been conducting a radial velocity survey of 179 K giants using the CAT at UCO/Lick observatory. At present ~20-100 measurements have been collected per star with a precision of 5 to 8 m/s. Of the stars monitored, 145 (80%) show radial velocity (RV) variations at a level >20 m/s, of which 43 exhibit significant periodicities. Our aim is to investigate possible mechanism(s) that cause these observed RV variations. We intend to test whether these variations are intrinsic in nature, or possibly induced by companions, or both. In addition, we aim to characterise the parameters o…
I propose that the relatively high eccentricity found in some tidally strongly interacting binary systems, where the mass-losing star is an evolved giant star, e.g., an asymptotic giant branch star, is caused by an enhanced mass loss rate during periastron passages. Tidal interaction by itself will circularize the orbits of these systems in a relatively short time, hence a mechanism which increases the eccentricity on a shorter time scale is required. The proposed scenario predicts that the nebula formed by the mass loss process possesses a prominent departure from axisymmetrical structure. Su…
In the current strategy of microlensing planet searches focusing on high-magnification events, wide and close binaries pose important sources of contamination that imitates planetary signals. For the purpose of finding systematic differences, we compare the patterns of central perturbations induced by a planet and a binary companion under severe finite-source effect. We find that the most prominent difference shows up in the morphology of the edge features with negative excess that appear at the edge of the circle with its center located at the caustic center and a radius equivalent to the sou…
Current detection methods of planetary companions do not allow retrieving their spectral information properties. The method of Differential Interferometry has the potential to complement such information by comparing interferometric observables in various spectral channels. We outline the basic aspects of this method and how it can soon be realised by the Mid-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) observatory. A set of possible candidates for such direct observation has been selected among currently identified planetary companions. Differen…
This paper presents a sensitive and comprehensive IRAC 3-8 $μ$m photometric survey of white dwarfs for companions in the planetary mass regime with temperatures cooler than the known T dwarfs. The search focuses on descendents of intermediate mass stars with $M\ga3$ $M_{\odot}$ whose inner, few hundred AU regions cannot be probed effectively for massive planets and brown dwarfs by any alternative existing method. Furthermore, examination for mid-infrared excess explores an extensive range of orbital semimajor axes, including the intermediate 5-50 AU range poorly covered and incompletely access…
Many extra-solar planets and a few planetary systems have been found indirectly by small periodic radial velocity variations around old nearby stars. The orbital characteristics of most of them are different from the planets in our solar system. Hence, planet formation theories have to be revised. Therefore, observational constraints regarding young planets would be very valuable. We have started a ground-based direct imaging search for giant planets in orbit around young nearby stars. Here, we will motivate the sample selection and will present our direct imaging observation of the very low-m…
We report the detection of a substellar companion orbiting the intermediate-mass giant star 11 Com (G8 III). Precise Doppler measurements of the star from Xinglong station and Okayama Astrophysical Observatory (OAO) revealed Keplerian velocity variations with an orbital period of 326.03 +/- 0.32 days, a semiamplitude of 302.8 +/- 2.6 m/s, and an eccentricity of 0.231 +/- 0.005. Adopting a stellar mass of 2.7 +/- 0.3 M_solar, the minimum mass of the companion is 19.4 +/- 1.5 M_Jup, well above the deuterium burning limit, and the semimajor axis is 1.29 +/- 0.05 AU. This is the first result from …
From adaptive optics observations with the Palomar 5-meter telescope we place upper limits on the masses of any planetary companions located between ~30-230 AU away from Vega, where our data are sensitive to depths ranging from H=12.5 mag to H=19.0 mag fainter than Vega itself. Our observations cover a plus-shaped area with two 25"x57" elements, excluding 7"x7" centered on the star. We have identified 2 double and 4 single point sources. These projected companions are 14.9-18.9 mag fainter than Vega, and if physically associated would have masses ranging from 4 to 35 Mjup and orbital radii 170…
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 orbi…
Binary population synthesis shows that mass transfer from a giant star to a main-sequence (MS) companion may account for some observed long-orbital period blue stragglers. However, little attention {\bf is paid to this blue straggler formation scenario} as dynamical instability often happens when the mass donor is a giant star. In this paper, we have studied the critical mass ratio, $q_{\rm c}$, for dynamically stable mass transfer from a giant star to a MS companion using detailed evolution calculations. The results show that a more evolved star is generally less stable for Roche lobe overflo…
Instabilities and strong dynamical interactions between several giant planets have been proposed as a possible explanation for the surprising orbital properties of extrasolar planetary systems. In particular, dynamical instabilities would seem to provide a natural mechanism for producing the highly eccentric orbits seen in many systems. Here we present results from numerical integrations for the dynamical evolution of planetary systems containing two identical giant planets in nearly circular orbits very close to the dynamical stability limit. We determine the statistical properties of the thr…
A hydrodynamic model involving cooling gas in the stagnation region of a collimated outflow is proposed for the formation of the giant parsec-scale bipolar envelope that surrounds the planetary nebula KjPn 8. Analytical calculations and numerical simulations are presented to evaluate the model. The envelope is considered to consist mainly of environmental gas swept-up by shocks driven by an episodic, collimated, bipolar outflow. In this model, which we call the ``free stagnation knot'' mechanism, the swept-up ambient gas located in the stagnation region of the bow-shock cools to produce a high…
We present the PLANET photometric data set for \ob14, a high magnification ($A_{\rm max}\sim 16$) event alerted by the OGLE collaboration toward the Galactic bulge in 1998. The PLANET data set consists a total of 461 I-band and 139 $V-$band points, the majority of which was taken over a three month period. The median sampling interval during this period is about 1 hour, and the $1σ$ scatter over the peak of the event is 1.5%. The excellent data quality and high maximum magnification of this event make it a prime candidate to search for the short duration, low amplitude perturbations that are s…
We report first results from our ground-based infrared imaging search for sub-stellar companions (brown dwarfs and giant planets) of young (up to 100 Myrs) nearby (up to 75 pc) stars, where companions should be well separated from the central stars and still relatively bright due to ongoing accretion and/or contraction. Among our targets are all members of the TW Hya association, as well as other binary and single young stars either discovered recently among ROSAT sources (some of which as yet unpublished) or known before. Our observations are performed mainly with SOFI and SHARP at the ESO 3.…
We present first results of our NAOS-CONICA search for close substellar companions around young nearby stars. This program was started only a few months ago. We have obtained 1st epoch images of several targets which are unpublished young stars (age<100 Myrs), hence ideal targets to look for planetary companions. For one target star we could even take a 2nd epoch image. By comparing both images we could look for co-moving companions of the target star. Those data show clearly that the detection of planetary companions m <13 Mjup inward a saturn-like orbit (r<10 AU) is feasible with NAOS-CONICA…
