Wednesday, May 25, 2011, 11:40 AM - 12:30 PM

Astrophysics with Kepler II

Meeting-in-a-Meeting

America South

311.01

2:00 PM - 2:15 PM

The light curves produced by the Kepler photometer are unprecedented in their photometric precision, completeness, and contiguity. Moreover, although Kepler was designed to detect 100 ppm changes in brightness corresponding to transits of Earth-size planets crossing Sun-size stars, the Kepler light curves preserve intrinsic intensity variations across a large dynamic range, including those of RR Lyrae stars, which can increase their brightness by more than a factor of two over a few hours. The large dynamic range and phenomenal photometric precision of Kepler promises to revolutionize the study of intrinsic stellar variability and a wide variety of variable stars on timescales from minutes to several years.

311.02

2:15 PM - 2:30 PM

The Kepler mission is generating an unprecedented set of lightcurves for stars, with the best precision and coverage ever achieved. Not surprisingly, there have been many new phenomena seen. Some of these we think we understand, and some remain mysterious. We present a short sampler of some of these, both as individual cases, and also certain classes of variables. In addition to variability in the stars, there are substantial instrumental effects. We discuss our current understanding and ability to correct for these (which are different from quarter to quarter), and what sorts of stellar variability cannot currently be confidently measured.

311.03

The Kepler Cluster Study

Soren Meibom¹, Kepler Science Team
¹Harvard-Smithsonian,CfA.

2:30 PM - 2:45 PM

The Kepler Cluster Study is a program to search for transiting planets around members of 4 open star clusters in the Kepler field of view, and to study the dependencies of stellar rotation, differential rotation, and other activity and dynamo related observables, on stellar age and mass. This talk will describe the study and present its first results and near term goals. Kepler was selected as the 10th mission of the Discovery Program. Funding for this mission is provided by NASA, Science Mission Directorate.

311.04

2:45 PM - 3:00 PM

Open clusters in the Kepler field are becoming a test bed for all of the major methods of age determination for stars. We present preliminary results for Kepler observations and supporting ground-based observations of detached eclipsing binaries in the old open clusters NGC 6791 and NGC 6819. The goals of this program are to characterize an ensemble of multiple star systems that can 1) constrain the cluster ages more strongly than any other technique via mass and radius measurements of evolved stars, and 2) precisely determine the masses and radii of stars spanning the cluster color-magnitude diagrams in order to validate model predictions for photometry.

311.05

3:00 PM - 3:15 PM

The Kepler-9 planetary system contains three transiting planets, two of which have been confirmed via transit timing variations caused by their mutual gravitationally interaction. The host star is active, and the light curve shows starspot modulations that are comparable in size to the depths of the transits. If the planet transits over a starspot it will cause a change in the transit shape, and thus induce a shift in the measured mid-transit time that cannot be removed by simple detrending. We present a study of the effects of the starspots on the transit shapes, and specifically on the measured transit times.

311.06

A First Look at Galaxies with Kepler

Michael N. Fanelli¹, Kepler Team
¹NASA Ames Research Center.

3:15 PM - 3:30 PM

Kepler is principally an exoplanet and stellar astrophysics experiment. Late-type dwarf stars form the bulk of the ~170K sources in the target list. Although centered at low galactic latitude (13.5°), the continuously monitored field-of-view contains over 11K cataloged galaxies. During the early phase of the mission, a number of galaxies were observed, some serendipitously, and then dropped. Another set of galaxies was explicitly monitored for several observing quarters to assess their viability as “quiescent” photometric and astrometric sources. Normal galaxies are not expected to be variable on the timescales and amplitudes seen in stellar sources, and are not subject to centroid motions due to parallax, proper motion or binarity. We describe the light curves of the observed galaxies, their observed photometric and astrometric precision, and the potential for identifying variability due to active nuclei and episodic events. These data provide a first look at normal galaxies surveyed with Kepler, and complement observations of the few known active galaxies in the field.

312

The Panchromatic View of Star Formation and Protoplanetary Disks in Diverse Environments II

Meeting-in-a-Meeting

America Central

312.01

Star Formation and the Dynamical Evolution of Young Clusters

Nicholas James Wright^1
1Harvard-Smithsonian Center for Astrophysics.

2:00 PM - 2:22 PM

America Central

Dynamical evolution plays a key role in shaping the observable properties of star clusters and stellar associations. Observable properties such as mass segregation, clustering, and runaway stars are all products of complex N-body interactions in large stellar systems. I will discuss the implications for star cluster research of dynamical evolution, as well recent results and upcoming possibilities through missions such as GAIA.

312.02

Observations and theory on the externally induced photoevaporation of circumstellar disk

Mario G. Guarcello^1
1Harvard-Smithsonian CfA.

2:22 PM - 2:44 PM

America Central

Class II Pre-Main Sequence stars are characterized by the presence of the circumstellar disk in the equatorial plane, which is the site of the planets formation. The induced photoevaporation of disks is one of the key processes leading the evolution of these structures. Photoevaporation occurs when the disk is irradiated by UV and X-ray radiation: Far UltraViolet (FUV) photons (with energy ranging from 6eV to 13.6eV) dissociate H2 molecules, while Extreme UltraViolet (EUV, from 13.6eV to 100eV ) and X-ray photons ionize gas atoms. Since both processes heat the gas up to 1000K-10000K, the thermal pressure drives a photoevaporative flow of gas away from the disk. Photoevaporation is usually induced by the central star itself; however, direct images (taken with the Hubble Space Telescope) of the young stars surrounded by photoevaporating disks in the Orion Nebula Cluster showed that photoevaporation can be induced by the energetic radiation emitted by nearby massive stars. In these cases, the externally induced photoevaporation can dissipate the disks in short timescale (even smaller than 1 Myear in the more extreme situations). Besides, recent studies of the massive young clusters NGC2244 and NGC6611 confirmed that the evolution of circumstellar disks is affected by induced photoevaporation in the core of such massive clusters, but there is still some controversy about these results. In this talk I will review the main features of the photoevaporation process, its effects on disks evolution when it is induced by nearby ionizing sources, and the supporting observational evidences.

312.03

Protoplanetary disk chemistry

Karin Oberg^1
1Harvard-Smithsonian CfA.

2:44 PM - 3:06 PM

America Central

The accretion disks around pre-main-sequence stars provide the raw material and initial conditions for the formation of planetary systems. Disk chemistry is thus essential to predict the composition of planetesimals and eventually planets - comet compositions in our own solar system reveal that efficient astrophysical pathways to chemical complexity exists. The chemical evolution is predicted to depend on radiation fields, temperature and density structures. This can be exploited to develop molecular probes of otherwise inaccessible disk processes, and protoplanetary disk chemistry studies typically have the combined objective of constraining how the disk physics drives the disk chemistry, and how the disk chemistry traces the disk physics. Observationally, disk chemistry has been characterized by infrared spectroscopy of the innermost few AUs, far-infrared spectroscopy of the disk atmosphere, and millimeter spectroscopy of the outer disk. This has revealed strong emission from a range of common molecules and ions such as CO, CN, HCN, C2H2, H2O, OH, H2CO, HCO+, N2H+ and DCO+. As expected some lines are found to follow trends with respect to quiescent stellar heating, mass accretion rates, X-ray ionization, and the disk density structure. In response to these observations and in anticipation of more detailed data from especially ALMA, the physical-chemical modeling and theory of disks is the subject of intense efforts. A range of different model approaches have been developed that vary in their treatment of disk structure, radiation fields, and chemical networks. The results stress the importance of UV and X-ray fields as well as the treatment of grain surface chemistry and its relation to gas-phase processes. These recent advances in observations and models of disk chemistry will be reviewed together with current challenges, and the next generation of models, laboratory experiments and observations that will address them.

312.04

Protoplanetary disks to planets

Catherine Espaillat^1
1Harvard-Smithsonian Center for Astrophysics.

3:06 PM - 3:28 PM

America Central

In their initial stages of formation planets should interact with the

accretion disk surrounding the newborn star, clearing the material
around themselves and leaving behind an observational signature in the
form of clearings in the disk. Stars with inner holes in
their disks have been detected and are labeled as transitional objects.
A few years ago, Spitzer identified a new class of "pre-transitional
disks" which have gaps rather than holes - they have an inner disk, a
gap, and an outer disk. In several cases, millimeter imaging has
confirmed the cavities in (pre-)transitional disks previously inferred
from SED modeling. Infrared variability has also been found to be a
common phenomenon in such objects. Physical mechanisms that have been
presented to explain disk clearing can be tested with these
observations; forming planets emerge as the most likely explanation.

313

The Oort Cloud: How is it Filled? How is it Emptied?

Special Session

St. George AB

313.01

A Jovian Mass Object in the Oort Cloud?

Jack J. Lissauer¹, J. J. Matese², D. P. Whitmire^2
1NASA Ames Research Center, ²University of Louisiana.

2:05 PM - 2:30 PM

St. George AB

We discuss an updated dynamical and statistical analysis of cometary evidence suggesting that the Sun may have a Jovian mass companion orbiting in the outer regions of the Oort comet cloud. Such a companion could also have produced the detached Kuiper Belt object Sedna. If the object exists, evidence for it likely resides in the data collected by the recently completed Wide-field Infrared Survey Explorer (WISE) mission.

313.02

WISE and the Oort Cloud

Edward L. Wright^1
1UC, Los Angeles.

2:30 PM - 2:55 PM

St. George AB

Even at the inner edge of the Kuiper Belt, objects are too cold for WISE to see their thermal emission. Thus WISE is limited to reflected Sunlight, and this is brighter in the optical than at 3.4 microns. Hence WISE is only efficient for finding gas giants in the Oort cloud, with mass greater than Jupiter, whose internal heat produces a large flux at 4.6 microns. For Jupiter itself, DIRBE measured 6 kJy at 4.9 microns. Since the W2 band is more centered on the peak of the spectrum, WISE could see this at a distance 10000 times greater than the actual distance of Jupiter, or nearly one light-year. But if Jupiter were this far from the Sun, its bolometric flux would go down by nearly a factor of two, and the W2 flux would go down by a larger but model dependent factor. Thus WISE should be able to barely pick up the 1 Jupiter mass object at a distance of 30,000 AU that is at one corner of the Matese and Whitmire parameter space. But such an object would only be one source among thousands of band 2 only sources at the 5 sigma limit. Finding this needle in a haystack will require a reprocessing and co-addition of the post-cryogen data collected by WISE, an effort which is currently not funded by NASA.

313.03

Galalctic Tides & the Sinusoidal Potential

David F. Bartlett^1
1Univ. of Colorado.

2:55 PM - 3:30 PM

St. George AB

The sinusoidal potential is a nonNewtonian alternative to dark matter. Instead of φ = -GM/r we write φ = -(GM/r) cos k_or, where k_o= 2π/ λ_o and λ_o = R_o/20= 400 pc. Evidence for this choice for the “wavelength” λ_o has been given in one article and many previous meetings of the AAS & DDA. The solar system and nearby stars are trapped in a local groove of width Δr < 400 pc. The rapid alternation of attraction and repulsion within the groove gives very strong Galactic radial tides. The epicyclic period is only 7 Myr .

The Keplerian period for comets in the middle of the Oort cloud is also 7 Myr. The 1:1 resonance between material in the groove and the cloud provides a new mechanism for filling the Oort cloud.
The Oort cloud is emptied by the same strong radial tides. Evidence is found in the 499 comets with calculated 1/a_original in the latest Catalogue of Cometary Orbits (Marsden & Williams 2008).
^.
I separate the comets into 12 classes on the basis of Quality (4 types) and semi-major axis a_original . For 10 of the 12 classes radial tides dominate Z-tides. The classic Oort cloud comets (1851-1996) have a particularly strong modulation with galactic longitude. This modulation is exactly in those directions where a radial tide would be important. The equally numerous recent Oort comets (1996-2008) show a different evidence for strong radial tides. The recent comets generally have much larger perihelion distances q than the classic ones. Here the evidence is that a radial tide is removing angular momentum from the orbit and thus bringing the perihelion closer to the earth and to observers.

314

SPICA and the Promise of the Far-Infrared

Special Session

Gloucester

314.01

SPICA: The Space Infrared Telescope for Cosmology and Astrophysics

Takao Nakagawa^1
1Institute of Space and Astronautical Science, Japan.

2:00 PM - 2:30 PM

Gloucester

We are presenting an overview of the SPICA (Space Infrared Telescope for Cosmology and Astrophysics) mission, which is a mission optimized for mid- and far-infrared astronomy with a cryogenically cooled 3-m class (3.2 m in the current design) telescope. Its high spatial resolution and unprecedented sensitivity in the mid- and far-infrared will enable us to address a number of key problems in present-day astronomy, ranging from the star-formation history of the universe to the formation of planets. To reduce the mass of the whole mission, SPICA will be launched at ambient temperature and cooled down on orbit by mechanical coolers on board with an efficient radiative cooling system. This combination allows us to have a 3-m class cooled (6 K) telescope in space with moderate total weight (3.7t). SPICA is proposed as a Japanese-led mission together with extensive international collaboration. ESA is a major partner and is supposed to take responsibility for the SPICA telescope assembly, a European ground segment, an European instrument systems engineering and management. The assessment study on the European contribution to the SPICA mission has been conducted under the framework of the ESA Cosmic Vision 2015-2025. US community also shows strong interest to participate in SPICA and to procure a sensitive far-infrared and sub-mm spectrometer. Assessment study of this type of spectrometers was conducted with NASA funding in 2010. Korean participation is also being discussed extensively. The target launch year of SPICA is late 2010s.

314.02

Far-IR Emission Lines from High-Redshift Cooling

J. Michael Shull^1
1Univ. of Colorado.

2:30 PM - 3:00 PM

Gloucester

Formation of the first stars and galaxies is initiated by radiative cooling of primordial gas clouds (Population III) and metal-contaminated gas (Population II) in dark-matter halos. The primary coolants are hydrogen (H I, H2, HD) and fine-structure transitions from [C II], [O I], [Si II], [Fe II], the heavy elements formed by nucleosynthesis in early massive stars and supernovae. Enriched by the first stars, metal lines control the high-redshift transition from Pop III to Pop II, once the metallicity rises above a critical value of approximately Z_crit = 0.0003 Z_solar. Direct emission-line detection would quantify the cooling that governs the transition in stellar initial mass function. Because early nucleosynthesis may be biased toward alpha-process (O, Si) and Fe-group elements, the fine-structure line ratios may not reflect solar abundances. Current models of primordial cooling suggest that line-detection sensitivities (BLISS, ALMA) could approach values, 10^-20 W / m^2, at which large cooling gas clouds could be seen. Limits on the integrated backgrounds at wavelengths of [C II] (157.74 microns), [O I] (63.18, 145.5 microns), [Si II] (34.8 microns); [Fe II] (25.99, 35.35 microns) redshifted into the far-IR and sub-mm, could constrain the high-redshift radiative cooling rates associated with early galaxies.

314.03

The Evolution of the Interstellar Medium as Traced by Mid and Far-IR Spectroscopy

Gordon Stacey^1
1Cornell.

3:00 PM - 3:30 PM

Gloucester

I will discuss how the mid and far-infrared fine structure lines of abundant atoms and ions can be used to trace the evolution of the interstellar medium in galaxies from earliest times to the present. These lines are of particular interest as they are both easily excited and suffer relatively little from extinction by dust. I plan a review of the current state of knowledge, followed by a discussion of the new science that will be enabled with the advent of SPICA and ALMA.

315

Using the Discoveries of Astronomy to Teach Physics

Special Session

Staffordshire

315.01

Using Cosmology to Teach Physics

Max Tegmark^1
1MIT.

2:00 PM - 2:20 PM

Staffordshire

I describe why I think cosmology is an excellent tool for teaching physics.

315.02

Using Exoplanets to Engage Students in Physics

David Charbonneau^1
1Harvard University.

2:20 PM - 2:40 PM

Staffordshire

A hundred planets transiting bright stars are now known, ensuring that at any particular site at least one transit is visible on any given night. Most of these worlds were discovered with 4-inch telescopes, and so the modest telescopes that nest atop the physics buildings of many college campuses are more than adequate to pursue the transit events. Fueled by results from the NASA Kepler Mission and the promise of Earth-like worlds, exoplanets offer an enormous opportunity to engage first-year college students in physics. The simple geometric nature of these systems permits the direct application of introductory mechanics to deduce the basic properties of some planets orbiting other stars. Moreover, by gathering and analyzing their own data, students can understand the fundamentals of experimental science and data analysis. I will discuss the opportunities to engage students in physics through transiting exoplanets, with specific examples drawn from a first-year undergraduate course at Harvard University. I will also review the practical aspects, including software and hardware, of establishing an exoplanet observing lab appropriate for college students.

315.03

A Calculus-Level Introductory Physics Course with an Astronomy Theme

Joseph Amato^1
1Colgate University.

2:40 PM - 3:00 PM

Staffordshire

Physics from Planet Earth (PPE) is a one-semester, calculus-based introductory course in classical mechanics intended for first year students of physics, chemistry, astronomy and engineering. Most of the core topics in mechanics are included, but many of the examples and applications are drawn from astronomy, space science, and astrophysics. The laws of physics are assigned the task of exploring the heavens - the same task addressed by Newton over 300 years ago at the birth of classical mechanics. How do we know the distance to the Moon, Sun, or other galaxies? How do we know the masses of the Earth, Sun, and other planets and stars, and why do we believe in “missing” mass? As a physics course, PPE concentrates on how we know rather than what we know. Examples and applications include those of historical importance (the Earth-Moon distance, the Earth-Sun distance, Ptolemaic vs. Copernican models, weighing the Earth) as well as those of contemporary interest (Hubble’s Law, rocket propulsion, spacecraft gravity boosts, the Roche limit, search for extrasolar planets, orbital mechanics, pulsars, galactic rotation curves). The course has been taught successfully at Colgate for over a decade, using materials that have been developed and refined during the past 15 years. Developers of PPE are eager to enrich the course by identifying other topics in contemporary astronomy that can be adapted for the first year physics audience.

315.04

Using Planetary Nebulae to Teach Physics

Karen B. Kwitter^1
1Williams College.

3:00 PM - 3:10 PM

Staffordshire

We have developed an interactive website, "Gallery of Planetary Nebula Spectra," (www.williams.edu/Astronomy/research/PN/nebulae/) that contains high-quality optical-to-near-infrared spectra, atlas information, and bibliographic references for more than 160 planetary nebulae that we have observed in the Milky Way Galaxy. To make the material more accessible to students, I have created three undergraduate-level exercises that explore physics-related aspects of planetary nebulae. “Emission Lines and Central Star Temperature” uses the presence or absence of emission lines from species with different ionization potentials to rank the temperatures of the exciting stars in a selection of nebulae. “Interstellar Reddening” uses the observed Balmer decrement in a sample of planetary nebulae at different Galactic latitudes to infer the distribution of interstellar dust in the Milky Way. Finally, “Determining the Gas Density in Planetary Nebulae,” which I will focus on here, uses the observed intensity ratio of the 6717 Å and 6731 Å emission lines from singly ionized sulfur to determine the electron density in the nebular gas. These exercises demonstrate that planetary nebula spectra are useful real-world examples illustrating a variety of physical principles, including the behavior of blackbodies, wavelength-dependent particle scattering, recombination-line ratios, atomic physics, and statistical mechanics.

315.05

Lessons from Outreach: What works; what doesn’t

Philip M. Sadler^1
1Harvard-Smithsonian, CfA.

3:10 PM - 3:20 PM

Staffordshire

Outreach to teachers in the form of professional development can help to inform college instructors as to the effectiveness of methods aimed at increasing subject matter and pedagogical content knowledge. College faculty employ a wide range of activities in summer institute programs, often in all-day, residential programs. Comparing such immersion experiences can tell us quite a bit about learning using a variety of systematic approaches to teaching physics and astronomy under ideal conditions.

315.06

Excitement, Instruction, Engagement, and Learning

Chris David Impey^1
1Univ. of Arizona.

3:20 PM - 3:30 PM

Staffordshire

The universe is the largest and most impressive possible arena for the exploration of physical principles. Educational research shows that the act of learning requires active engagement rather than passive transmission of information. Modern astronomy provides several unique advantages for the teaching of physics. It shows a small set of physical laws operating over a wide range of scales in very different cosmic contexts. It is driven by very rapid research advances and iconic telescopes and space missions. It is connected to a pervasive desire to understand our place in the universe. Although study of the universe is not like lab science, it illustrates the strengths and limitations of the scientific method. This talk will cover the best pedagogical practice for teaching astronomy and physics, and give examples of topics that provide the potential for a rich learning experience.

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