Wayne M. Schlingman

Formation and Evolution of Planetary Systems: Upper Limits to the Gas Mass in Disks Around Sun-like Stars

We have carried out a sensitive search for gas emission lines at IR and millimeter wavelengths for a sample of 15 young Sun-like stars selected from our dust disk survey with Spitzer. We have used mid-IR lines to trace the warm (300-100 K) gas in the inner disk and millimeter transitions of ^(12)CO to probe the cold (~20 K) outer disk. We report no gas line detections from our sample. Line flux upper limits are first converted to warm and cold gas mass limits using simple approximations allowing a direct comparison with values from the literature. We also present results from more sophisticated models following Gorti & Hollenbach that confirm and extend our simple analysis. These models show that the [S I] 25.23 μm line can set constraining limits on the gas surface density at the disk inner radius and traces disk regions up to a few AU. We find that none of the 15 systems have more than 0.04M_J of gas within a few AU from the disk inner radius for disk radii from 1 to ~40 AU. These gas mass upper limits even in the eight systems younger than ~30 Myr suggest that most of the gas is dispersed early. The gas mass upper limits in the 10-40 AU region, which is mainly traced by our CO data, are <2 M_⊕. If these systems are analogs of the solar system, they either have already formed Uranus- and Neptune-like planets or will not form them beyond 100 Myr. Finally, the gas surface density upper limits at 1 AU are smaller than 0.01% of the minimum mass solar nebula for most of the sources. If terrestrial planets form frequently and their orbits are circularized by gas, then circularization occurs early.

The formation and evolution of planetary systems: Placing our solar system in context with Spitzer

We provide an overview of the Spitzer Legacy Program, Formation and Evolution of Planetary Systems, that was proposed in 2000, begun in 2001, and executed aboard the Spitzer Space Telescope between 2003 and 2006. This program exploits the sensitivity of Spitzer to carry out mid-infrared spectrophotometric observations of solar-type stars. With a sample of ~328 stars ranging in age from ~3 Myr to ~3 Gyr, we trace the evolution of circumstellar gas and dust from primordial planet-building stages in young circumstellar disks through to older collisionally generated debris disks. When completed, our program will help define the timescales over which terrestrial and gas giant planets are built, constrain the frequency of planetesimal collisions as a function of time, and establish the diversity of mature planetary architectures. In addition to the observational program, we have coordinated a concomitant theoretical effort aimed at understanding the dynamics of circumstellar dust with and without the effects of embedded planets, dust spectral energy distributions, and atomic and molecular gas line emission. Together with the observations, these efforts will provide an astronomical context for understanding whether our solar system—and its habitable planet—is a common or a rare circumstance. Additional information about the FEPS project can be found on the team Web site.

A national study assessing the teaching and learning of introductory astronomy. Part I. The effect of interactive instruction

We present the results of a national study on the teaching and learning of astronomy as taught in general education, non-science-major, introductory astronomy courses. Nearly 4000 students enrolled in 69 sections of courses taught by 36 different instructors at 31 institutions completed (pre- and post-instruction) the Light and Spectroscopy Concept Inventory (LSCI) from Fall 2006 to Fall 2007. The classes varied in size and were from all types of institutions, including 2- and 4-year colleges and universities. Normalized gain scores for each class were calculated. Pre-instruction LSCI scores were clustered around ∼25%, independent of class size and institution type, and normalized gain scores varied from about −0.07 to 0.50. To estimate the fraction of classroom time spent on learner-centered, active-engagement instruction we developed and administered an Interactivity Assessment Instrument (IAI). Our results suggest that the differences in gains were due to instruction in the classroom, not the type of c...

THE BOLOCAM GALACTIC PLANE SURVEY. X. A COMPLETE SPECTROSCOPIC CATALOG OF DENSE MOLECULAR GAS OBSERVED TOWARD 1.1 mm DUST CONTINUUM SOURCES WITH 7.°5 ⩽ l ⩽ 194°

The Bolocam Galactic Plane Survey (BGPS) is a 1.1 mm continuum survey of dense clumps of dust throughout the Galaxy covering 170 deg2. We present spectroscopic observations using the Heinrich Hertz Submillimeter Telescope of the dense gas tracers, HCO+ and N2H+ 3-2, for all 6194 sources in the BGPS v1.0.1 catalog between 7.?5 ? l ? 194?. This is the largest targeted spectroscopic survey of dense molecular gas in the Milky Way to date. We find unique velocities for 3126 (50.5%) of the BGPS v1.0.1 sources observed. Strong N2H+ 3-2 emission (T mb > 0.5 K) without HCO+ 3-2 emission does not occur in this catalog. We characterize the properties of the dense molecular gas emission toward the entire sample. HCO+ is very sub-thermally populated and the 3-2 transitions are optically thick toward most BGPS clumps. The median observed line width is 3.3?km?s?1 consistent with supersonic turbulence within BGPS clumps. We find strong correlations between dense molecular gas integrated intensities and 1.1 mm peak flux and the gas kinetic temperature derived from previously published NH3 observations. These intensity correlations are driven by the sensitivity of the 3-2 transitions to excitation conditions rather than by variations in molecular column density or abundance. We identify a subset of 113 sources with stronger N2H+ than HCO+ integrated intensity, but we find no correlations between the N2H+/HCO+ ratio and 1.1 mm continuum flux density, gas kinetic temperature, or line width. Self-absorbed profiles are rare (1.3%).

A Classical Test Theory Analysis of the Light and Spectroscopy Concept Inventory National Study Data Set.

This paper is the first in a series of investigations into the data from the recent national study using the Light and Spectroscopy Concept Inventory (LSCI). In this paper, we use classical test theory to form a framework of results that will be used to evaluate individual item difficulties, item discriminations, and the overall reliability of the LSCI. We perform an analysis of individual students’ normalized gains, providing further insight into the prior results from this data set. This investigation allows us to better understand the efficacy of measuring student achievement using the LSCI. Future papers will discuss our investigation of the data from the recent national study using item response theory (IRT).