Abstracts

 
  1. 1.How many and which targets do exoplanet searches need? Xavier Bonfils (UJF-Grenoble)

Detections and non-detections from Doppler, photometric, astrometric, imaging and micro-lensing searches have sampled the outcome of the planetary formation in a large parameter space (planetary mass, radius, period, and eccentricity, stellar mass, metallicity, etc ...). We shall review the domain that has been explored so far and report on the current measurements for the occurrence of planets as a function of selected parameters. Extrapolating from these numbers, we shall estimate the sample size one must target to achieve some fiducial goals. In particular, we shall consider the appealing objective of detecting habitable Earth-like planets transiting M dwarfs which, aided by transmission and occultation spectroscopy, are contemplated as the shortest route to peek into an exo-Life laboratory.

  1. 2.The Solar Neighborhood: Who Are the Stars? Where Are the Planets? Todd Henry (Georgia State)

Since 1994, RECONS (www.recons.org, REsearch Consortium On Nearby Stars) has been discovering and characterizing the Sun's neighbors. Because of their proximity, nearby stars are natural locations to search for other solar systems --- they provide increased fluxes, larger astrometric perturbations, and higher probabilities for eventual resolution and detailed study of planets than similar stars at larger distances. As we continue to build a three-dimensional map of stars near the Sun, we are now beginning to add planetary companions orbiting the stars. Examination of the nearby stellar sample will reveal the prevalence and structure of solar systems in unprecedented detail, as well as the balance of Jovian and terrestrial worlds. The M dwarfs comprise roughly three-quarters of the stellar population, so will undoubtedly play leading roles in the search for other worlds, and will ultimately be key in our search for life elsewhere.


Here we outline what we know ... and what we don't know ... about the population of the nearest stars. We concentrate on two horizons, the classic 10 parsec sample of a few hundred stellar systems studied by RECONS since its inception, and the expanded 25 parsec sample that includes more than 2000 systems. Roughly two-thirds of the stellar systems within 25 parsecs do not yet have trigonometric parallaxes, so we don't know precisely which systems are members of the nearby stellar sample. Recent efforts in both hemispheres have identified many of the systems via photometry and/or spectroscopy, but continued work is required to hone the list to our true neighbors. Eventually, Gaia and LSST should provide parallaxes for many of the faint M dwarf members of the solar neighborhood, although there will still be a need to measure parallaxes for M dwarfs in the northern hemisphere. In the meantime, we have a great deal of work to do to construct the map of the solar neighborhood, and to characterize the stars that will yield the nearest planets.


In one effort particularly relevant to this session, RECONS has been using astrometric techniques to search for massive planets orbiting more than 100 of the nearest red dwarfs. Unlike radial velocity searches, our astrometric effort is most sensitive to Jovian planets in Jovian orbits, i.e. those that span decades. We have now been monitoring stars for up to 12 years with positional accuracies of a few milliarcseconds per night. We have detected companion stars and brown dwarfs, as well as enigmatic, unseen companions, and are currently pushing into the realm of Jovian planets. As a result, we are now able to assess the populations of stellar, brown dwarf, and Jovian companions orbiting the nearest red dwarfs that dominate the Galaxy.

  1. 3.How precise do we need radii, masses, Teff of M dwarfs to properly characterize planets? Leslie Rogers (MIT)

  2. 4.Direct Measurements of M Dwarf Radii with an Eye on Exoplanets Kaspar von Braun (Caltech)

M dwarfs are very attractive targets for many kinds of exoplanet science. Characterization of the exoplanets and their environment is dependent on knowledge of the stellar astrophysical parameters. The two methods for direct determination of M dwarf radii are interferometric measurements and studies of elipsing binary systems. In this talk, I will give an overview of M dwarf radii calculated with the above methods and how they compare with theoretically predicted values. Finally, I will elaborate on a few M dwarf exoplanetary systems that were recently studied using long-baseline interferometry.

  1. 5.What properties of M dwarfs can we reliably infer from models? Christiane Helling (St. Andrews)

  2. 6.Planet formation theory and metallicity: what we need to know? Andrew Youdin (CfA)

I will describe the complex interplay between planet formation theory and exoplanet observations, with an emphasis on the critical variables of stellar metallicity and mass. I will consider in turn the starting and ending points in the growth of planets. Planetesimal formation is the essential first step for the formation of rocky planets, or of any planets with a solid core. Most planetesimal formation models, including those based on the streaming instability, predict a strong dependence on disk metallicity and mass. Later in the disk's lifetime, the accretion of atmospheres sets a planet's ultimate mass and composition. The onset of the core accretion instability likely determines the abundance of giant planets. I will briefly describe ongoing work to determine how the critical core mass varies about the canonical value of 10 Earth masses. The yields of (present and future) exoplanet searches about a diversity of hosts is needed to test and refine these theories.

  1. 7.Techniques for determining metallicity: Barbara Rojas-Ayala (AMNH)