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3D global MHD simulations of magneto-driven turbulence are performed for the disk of 100 AU with reduced amount of 10μm fluffy dust grains. We use X-ray and cosmic ray ionization, as well as simplified treatment of recombination on dust grains. The ionization of gas and charging of dust grains are dynamically evolving during the simulation, making the zone of high magnetic dissipation (’dead’ zone) variable. In our simulations, the jump in MRI-driven turbulent viscosity inside and outside of dead zone is insignificant. We find no hard edge, but rather a smooth transition between active and dead zone. Subsequently, there is no visible pressure bump at outer edge of the dead zone.
There have recently been a flood of ground-based detections of the near-infrared thermal emission of a number of hot Jupiters. Although these near-infrared detections have revealed a great deal about the atmospheric characteristics of individual hot Jupiters, the question is: what information does this ensemble of near-infrared detections reveal about the atmospheric dynamics and reradiation of all hot Jupiters? I explore whether there is any correlation between how brightly these planets shine in the near-infrared compared to their incident stellar flux, as was theoretically predicted to be the case. Secondly, I look for whether there is any correlation between the host star's activity and the planet's near-infrared emission, like there is in the mid-infrared, where Spitzer observations have revealed a correlation between the host star activity with the presence, or lack thereof, of a temperature inversion and a hot stratosphere.
The equilibrium tide model in the weak friction approximation is used by the binary star and exoplanet communities to study the tidal evolution of short-period systems, however, each uses a slightly different approach which potentially leads to different conclusions about the timescales on which various processes occur. Here we present an overview of these two approaches, and show that for short-period planets the circularization timescales they predict differ by at most a factor of a few. A discussion of the timescales for orbital decay, spin-orbit synchronization and spin-orbit alignment is also presented.
We present new photometric and astrometric data available for S Ori 70 and 73, the two T-type planetary-mass member candidates in the σ Orionis cluster (~3 ± 2 Myr, d~360 pc). S Ori 70 (J ~ 19.9 mag) has a spectral type of T5.5 ± 1.0 measured from published near-infrared spectra, while no spectroscopic data are available for S Ori 73 (J ~ 21 mag). We estimate the spectral type of S Ori 73 by using J, H, and CH4off (λc=1.575 μm, Δλ=0.112 μm) photometry and comparing the H-CH4off index of S Ori 73 with the colors of field stars and brown dwarfs of spectral types in the range F to late T. The locations of S Ori 70 and 73 in the J-H vs H-CH4off color-color diagram are consistent with spectral types T8 ± 1 and T4 ± 1, respectively. Proper motion measurements of the two sources are larger than the motion of the central σ Ori star, making their cluster membership somehow uncertain.
The β Pic disk of dust and gas has been regarded as the prototype of young planetary systems since the 1980s and has revealed over the years an impressive amount of indirect signs pointing toward the presence of at least one giant planet. We present here the recently detected first giant planet around this star. We show how this planet could explain some very peculiar features of the star environment (disk, spectroscopic variability), and how it constrains the scenarios of planetary system formation (timescales, mechanisms).
Microlensing searches for planets are sensitive to small, cold exoplanets from 1–6 AU from their host stars and therefore probe an important part of parameter space. Other techniques would require many years of observations, often from space, to detect similar systems. Microlensing events can be characterised from only ground-based observations over a relatively short (≤100d) timescales. LCOGT and SUPA/St Andrews are building a robotic global network of telescopes that will be well suited to follow these events. Here we present preliminary results of the Galactic Bulge observing season 2010 March–October.
Small ground-based telescopes can effectively be used to look for transiting rocky planets around nearby low-mass M stars, as recently demonstrated for example by the MEarth project. Since December 2009 at the Astronomical Observatory of the Autonomous Region of Aosta Valley (OAVdA) we are monitoring photometrically a sample of red dwarfs with accurate parallax measurements. The primary goal of this ‘pilot study’ is the characterization of the photometric microvariability of each target over a typical period of approximately 2 months. This is the preparatory step to long-term survey with an array of identical small telescopes, with kick-off in early 2011. Here we discuss the present status of the study, describing the stellar sample, and presenting the most interesting results obtained so far, including the aggressive data analysis devoted to the characterization of the variability properties of the sample and the search for transit-like signals.
We present high resolution computer simulations of dust dynamics and planetesimal formation in turbulence triggered by the magnetorotational instability. Particles representing approximately meter-sized boulders clump in large scale overpressure regions in the simulation box. These overdensities readily contract due to the combined gravity of the particles to form gravitationally bound clusters with masses ranging from a few to several ten times the mass of the dwarf planet Ceres. Gravitationally bound clumps are observed to collide and merge at both moderate and high resolution. The collisional products form the top end of a distribution of planetesimal masses ranging from less than one Ceres mass to 35 Ceres masses. It remains uncertain whether collisions are driven by dynamical friction or underresolution of clumps.
Most short period transiting exoplanets have circular orbits, as expected from an estimation of the circularisation timescale using classical tidal theory. Interestingly, a small number of short period transiting exoplanets seem to have orbits with a small eccentricity. Such systems are valuable as they may indicate that some key physics is missing from formation and evolution models. We have analysed the results of a campaign of radial velocity measurements of known transiting planets with the SOPHIE and HARPS spectrographs using Bayesian methods and obtained new constraints on the orbital elements of 12 known transiting exoplanets. We also reanalysed the radial velocity data for another 42 transiting systems and show that some of the eccentric orbits reported in the Literature are compatible with a circular orbit. As a result, we show that the systems with circular and eccentric orbits are clearly separated on a plot of the planetary mass versus orbital period. We also show that planets following the trend where heavier hot Jupiters have shorter orbital periods (the “mass-period relation” of hot Jupiters), also tend to have circular orbits, with no confirmed exception to this rule so far.
QS Vir is an eclipsing cataclysmic variable with 3.618 hrs orbital period. This system has the interesting characteristics that it does not show mass transfer between the components through the L1 Lagrangian point and shows a complex orbital period variation history. Qian et al. (2010) associated the orbital period variations to the presence of a giant planet in the system plus angular momentum loss via magnetic braking. Parsons et al. (2010) obtained new eclipse timings and observed that the orbital period variations associated to a hypothetical giant planet disagree with their measurements and concluded that the decrease in orbital period is part of a cyclic variation with period ~16 yrs. In this work, we present 28 new eclipse timings of QS Vir and suggest that the orbital period variations can be explained by a model with two circumbinary bodies. The best fitting gives the lower limit to the masses M1 sin(i) ~ 0.0086 M⊙ and M2 sin(i) ~ 0.054 M⊙; orbital periods P1 ~ 14.4 yrs and P2 ~ 16.99 yrs, and eccentricities e1 ~ 0.62 and e2~0.92 for the two external bodies. Under the assumption of coplanarity among the two external bodies and the inner binary, we obtain a giant planet with ~0.009 M⊙ and a brown dwarf with ~ 0.056 M⊙ around the eclipsing binary QS Vir.
CARMENES (Calar Alto high-Resolution search for M dwarfs with Exo-earths with Near-infrared and optical Echelle Spectrographs) is a next-generation instrument for the 3.5 m telescope at the Calar Alto Observatory. CARMENES will conduct a five-year exoplanet survey targeting ~300 M stars. The CARMENES instrument consists of two separate fiber-fed spectrographs covering the wavelength range from 0.52 to 1.7 μm at a spectral resolution of R = 85,000. The spectrographs are housed in a temperature-stabilized environment in vacuum tanks, to enable a 1 m/s radial velocity precision employing a simultaneous emission-line calibration.
The migration of protoplanets in discs not only depends on the thermodynamics of the ambient disc but also on the orbital parameters of the embedded planet. In the fully radiative regime, planets can migrate outward if their orbital parameters fit in a very small range. We simulate planets in fully radiative discs (and isothermal discs - for reference) and determine the influence of the orbital parameters (a, e and i) and the planetary mass on the migration time scale and direction.
Studies of the structure and evolution of protoplanetary disks are important for understanding star and planet formation. Here, we present the direct image of an interacting binary protoplanetary system. Both circumprimary and circumsecondary disks are resolved in the near-infrared. There is a bridge of infrared emission connecting the two disks and a long spiral arm extending from the circumprimary disk. Numerical simulations show that the bridge corresponds to gas flow and a shock wave caused by the collision of gas rotating around the primary and secondary stars. Fresh material streams along the spiral arm, consistent with the theoretical scenarios where gas is replenished from a circummultiple reservoir.
Indirect and direct spectroscopic studies of exoplanets are beginning to probe the most prominent chemical constituents and processes in their atmospheres. However, studies of equivalently low-temperature brown dwarfs have been taking place for over a decade. In this review, I summarize some of the results of detailed spectroscopic, photometric and polarimetric studies of brown dwarfs of various effective temperatures, surface gravities and metallicities, highlighting the insight gained into the chemistry and cloud formation of planetary-like atmospheres. Nonequilibrium chemistry and variations in cloud properties are singled out as critical ingredients for interpreting exoplanet spectra. I also discuss recent direct spectroscopic studies of exoplanet atmospheres, both close to and widely-separated from their host star, and propose that the latter are better analogs to isolated brown dwarfs.
We present the prospects of observing extrasolar planets with the Stratospheric Observatory for Infrared Astronomy (SOFIA). Our analysis shows that optical and near-infrared photometric and spectrophotometric follow-up observations during planetary transits and\break eclipses will be feasible with SOFIA's instrumentation, especially with the HIPO-FLITECAM optical/NIR instruments. SOFIA has unique advantages in comparison to ground- and space-based observatories in this field of research which will be outlined.
Radial velocity surveys have discovered over 400 exoplanets. While measuring eccentricities of low-mass planets remains a challenge, giant exoplanets display a broad range of orbital eccentricities. Recently, spectroscopic measurements during transit have demonstrated that the short-period giant planets (“hot-Jupiters”) also display a broad range of orbital inclinations (relative to the rotation axis of the host star). Both properties pose a challenge for simple disk migration models and suggest that late-stage orbital evolution can play an important role in determining the final architecture of planetary systems. One possible formation mechanism for the inclined hot-Jupiters is some form of eccentricity excitation (e.g., planet scattering, secular perturbations due to a distant planet or wide binary) followed tidal circularization. The planet scattering hypothesis also makes predictions for the population of planets at large separations. Recent discoveries of planets on wide orbits via direct imaging and highly anticipated results from upcoming direct imaging campaigns are poised to provide a new type of constraint on planet formation. This proceedings describes recent progress in understanding the formation of giant exoplanets.
Searches for planets around giants represent an essential complement to ’traditional’ surveys, because they furnish information about properties of planetary systems around stars that are the descendants of the A-F main sequence (MS) stars with masses as high as ~5 M⊙. As the stars evolve off the MS, their effective temperatures and rotation rates decrease to the point that their radial velocity variations can be measured with a few ms−1 precision. This offers an excellent opportunity to improve our understanding of the population of planets around stars that are significantly more massive than the Sun, without which it would be difficult to produce abroad, integrated picture of planet formation and evolution. Since 2001, about 30 such objects have been identified, including our five published HET detections (Niedzielski et al. 2007; Niedzielski et al. 2009a; Niedzielski et al. 2009b). Our work has produced the tightest orbit of a planet orbiting a K-giant identified so far (0.6 AU), and the first convincing evidence for a multiplanet system around such as star (Niedzielski et al. 2009a). Our most recent discoveries (Niedzielski et al. 2009b) have identified new multiplanet systems, including a very intriguing one of two brown dwarf-mass bodies orbiting a 2.8M⊙, K2 giant. This particular detection challenges the standard interpretation of the so-called brown dwarf desert known to exist in the case of solar-mass stars. Along with discoveries supplied by other groups, our work has substantially added to the emerging evidence that stellar mass positively correlates with masses of substellar companions, all the way from red dwarfs to intermediate-mass stars. We present current status and forthcoming results from the Pennsylvania-Toruń Search for Planets performed with the Hobby-Eberly Telescope (HET) since 2004.
The four new transit light curves of WASP-12b are analyzed by using MCMC simulation so as to derive the system parameters. If the apsidal precession exists in the orbit of WASP-12b, according to the theory of Gimenez & Bastero (1995), the rate of precession is estimated as 0.0076 degrees per cycle in the case of orbit with an inclination of 90°.
For the solar sytem giant planets the measurement of the gravitational moments J2 and J4 provided valuable information about the interior structure. However, for extrasolar planets the gravitational moments are not accessible. Nevertheless, an additional constraint for extrasolar planets can be obtained from the tidal Love number k2, which, to first order, is equivalent to J2. k2 quantifies the quadrupolic gravity field deformation at the surface of the planet in response to an external perturbing body and depends solely on the planet's internal density distribution. On the other hand, the inverse deduction of the density distribution of the planet from k2 is non-unique. The Love number k2 is a potentially observable parameter that can be obtained from tidally induced apsidal precession of close-in planets (Ragozzine & Wolf 2009) or from the orbital parameters of specific two-planet systems in apsidal alignment (Mardling 2007). We find that for a given k2, a precise value for the core mass cannot be derived. However, a maximum core mass can be inferred which equals the core mass predicted by homogeneous zero metallicity envelope models. Using the example of the extrasolar transiting planet HAT-P-13b we show to what extend planetary models can be constrained by taking into account the tidal Love number k2.
We present the photometric analysis of 4 transits of the exoplanet WASP-4b, obtained with the Baade 6.5m telescope, one of the two Magellan telescopes at Las Campanas. The light curves have a photometric precision of 0.5 mmag and a time sampling of 30s. This high precision has allowed us to detect several “spot anomalies”: temporary brightenings due to the occultation of a starspot on the transit chord. By analyzing these anomalies we find the sky-projected stellar obliquity to be λ = 1°+12°−14°. The small value suggests that the planet migration mechanism preserved the initially low obliquity, or that tidal evolution has realigned the system.