Planetary Transit Candidates in the CSTAR Field: Analysis of the 2008 Data

The Chinese Small Telescope ARray (CSTAR) is a group of four identical, fully automated, static 14.5 cm telescopes. CSTAR is located at Dome A, Antarctica and covers 20 square degree of sky around the South Celestial Pole. The installation is designed to provide high-cadence photometry for the purpose of monitoring the quality of the astronomical observing conditions at Dome A and detecting transiting exoplanets. CSTAR has been operational since 2008, and has taken a rich and high-precision photometric data set of 10,690 stars. In the first observing season, we obtained 291,911 qualified science frames with 20-second integrations in the i-band. Photometric precision reaches about 4 mmag at 20-second cadence at i=7.5, and is about 20 mmag at i=12. Using robust detection methods, ten promising exoplanet candidates were found. Four of these were found to be giants using spectroscopic follow-up. All of these transit candidates are presented here along with the discussion of their detailed properties as well as the follow-up observations.

Gap formation in a self-gravitating disk and the associated migration of the embedded giant planet

We present the results of our recent study on the interactions between a giant planet and a self-gravitating gas disk. We investigate how the disks self-gravity affects the gap formation process and the migration of the giant planet. Two series of 1-D and 2-D hydrodynamic simulations are performed. We select several surface densities and focus on the gravitationally stable region. To obtain more reliable gravity torques exerted on the planet, a refined treatment of disks gravity is adopted in the vicinity of the planet. Our results indicate that the net effect of the disks self-gravity on the gap formation process depends on the surface density of the disk. We notice that there are two critical values, Sigma_I and Sigma_II. When the surface density of the disk is lower than the first one, Sigma_0 < Sigma_I, the effect of self-gravity suppresses the formation of a gap. When Sigma_0 > Sigma_I, the self-gravity of the gas tends to benefit the gap formation process and enlarge the width/depth of the gap. According to our 1-D and 2-D simulations, we estimate the first critical surface density Sigma_I approx 0.8MMSN. This effect increases until the surface density reaches the second critical value Sigma_II. When Sigma_0 > Sigma_II, the gravitational turbulence in the disk becomes dominant and the gap formation process is suppressed again. Our 2-D simulations show that this critical surface density is around 3.5MMSN. We also study the associated orbital evolution of a giant planet. Under the effect of the disks self-gravity, the migration rate of the giant planet increases when the disk is dominated by gravitational turbulence. We show that the migration timescale associates with the effective viscosity and can be up to 10^4 yr.

Modeling Planetary System Formation with N-Body Simulations: Role of Gas Disk and Statistics Comparing to Observations

During the late stage of planet formation when Mars-size cores appear, interactions among planetary cores can excite their orbital eccentricities, speed their merges and thus sculpture the final architecture of planet systems. This series of work contributes to the final assembling of planet systems with N-body simulations, including the type I and II migration of planets, gas accretion of massive cores in a viscous disk. In this paper, the standard formulations of type I and II migrations are adopted to investigate the formation of planet systems around solar mass stars. Statistics on the final distributions of planetary masses, semi-major axes and eccentricities are derived, which are comparable to those of the observed systems. Our simulations predict some orbital signatures of planet systems around solar mass stars: 36% of the survival planets are giant planets (Mp>10Me). Most of the massive giant planets (Mp>30Me) locate at 1-10AU. Terrestrial planets distribute more or less evenly at <1-2 AU. Planets in inner orbits (<1 AU) may accumulate at the inner edges of either the protostellar disk (3-5 days) or its MRI dead zone (30-50 days). There is a planet desert in the mass-eccecntricity diagram, i.e., lack of planets with masses 0.005 - 0.08 MJ in highly eccentric orbits (e > 0.3 - 0.4). The average eccentricity (~ 0.15) of the giant planets (Mp>10Me) are bigger than that (~ 0.05) of the terrestrial planets (Mp< 10Me). A planet system with more planets tends to have smaller planet masses and orbital eccentricities on average.