Spring Colloquium 2008 --- Astronomy Department

Many distinguished scientists (Halley, Celsius, Birkeland and others) have puzzled over the links between northern lights (more generally, the aurora) and disturbances of the earth’s magnetic field. Before the end of his career at the start of the 20th century, Birkeland had elucidated many features of the process through which electrons and ions interact with magnetic fields in near-Earth space to gain energy. They then stream along the magnetic field into the upper atmosphere where they excite particles whose glow we observe from the ground. Today we understand much better the mechanisms that produce aurora on Earth and we have begun to study auroral processes elsewhere in the solar system using telescopes of great resolving power to provide images. With additional in situ spacecraft measurements we attempt to account for the details. Although many features of planetary auroras have parallels on earth, some do not. This talk will consider similarities and differences among auroras and related phenomena observed at earth, Jupiter, Saturn, and the large moons of the latter two. The differing auroral structures arise because there are many different mechanisms for transferring energy from the magnetic field to charged particles but, in every case, the final step in the process excites atmospheric emissions, as Birkeland would have expected.

Do the Milky Way's Outskirts Live up to Cosmological Expectations?

The current galaxy formation paradigm implies that
galaxies, such as our own Milky Way, are
'baryon condensates' at the center of extensive dark matter halos,
and exhibit a wealth of detailed substructure
that reflects their hiearchical formation: numerous sub-halos and
tidally distrupted streams. Only in the local group can we
currently put galaxy formation to a test based on its fine-scale
predictions.
The Sloan Digital Survey, and its follow-on project SEGUE,
have just provided an unprecedented data set to study the Milky Way's
outskirts, and I will present recent quantitative comparisons between
model predictions and these new observations.

The fastest, largest, and least well-organized observatory in the world.

abstract: Historical plate archives, educational and outreach
observatories, and the hard drives of amateurs contain countless
images, many of which are uncalibrated as far as scientific uses are
concerned. Nonetheless, they contain enormous information about
asteroids, stellar proper motions, variability, and transients; indeed
many amateurs and educators make important discoveries and
measurements each year.

We have built a reliable and robust system that takes as input an
astronomical image, and returns as output the pointing, scale, and
orientation of that image (the astrometric calibration or WCS
information). The system requires no first guess, and works with the
information in the image pixels alone. The success rate is very high
(~99.9 percent for shallow UV and optical imaging survey data), with
essentially no false positives. With lower precision, it also
determines the date at which the image was taken, the filter or
bandpass, and the photometric zeropoint.

We are using this system to generate consistent and
standards-compliant calibration data for all digital and digitized
astronomical imaging, no matter what its origin or archival state.
This is the first step in a program of making all of the world's
heterogeneous astronomical data searchable and interoperable, and
organizing the world's amateurs and educators into the largest,
fastest, and most reliable observatory in the world.

Binary Black Hole Mergers

The collision of two black holes is thought to be
one of the most energetic events in the universe, emitting
in gravitational waves as much as 5-10% of the rest mass energy
of the system. An international effort is currently
underway to detect gravitational waves from black hole
collisions and other cataclysmic events in the universe.
The early success of the detectors will rely on the
matched filtering technique to extract what are, by the time the
waves reach earth, very weak distortions in the local geometry
of space and time. In the case of black hole mergers numerical
simulations are needed to obtain predictions of waveforms during
the final stages of coalescence. 2005 was a watershed year
for numerical simulations of black holes, and we are now beginning
to explore the fascinating landscape of black hole
collisions in the fully non-linear regime of Einstein's theory.
In this talk I will give an overview of the recent successes
and what we have learned about the merger process, for
astrophysically relevant binaries and, time permitting, more esoteric
configurations. The latter include hyperbolic encounters fine-tuned
to an approximate threshold of merger, exhibiting behavior
similar to "zoom-whirl" geodesics in a black hole background. These
types of orbits may have some relevance to speculative black hole
formation by parton collisions at the LHC in large extra dimension
scenarios.

Peek-A-Boo Pulsars: Transient radio emission from neutron stars

The first radio pulsar was discovered 40 years ago, with close to 2000
of these objects known today. However, these exotic neutron stars
continue to surprise us with newly observed phenomena. One example of
this is the recently discovered classes of "peek-a-boo" pulsars,
neutron stars whose radio emission is sporadic and not easily
detectable through standard searches. In this talk, I will describe
the properties of these mysterious neutron stars and discuss recent
radio and X-ray observations. I will explain some theories put forth
to explain their unusual emission properties and the implications of
these new classes of pulsars for estimates of the number of neutron
stars in the Galaxy.

		Speaker	Title	Host
January	24	Margareth Kivelson (UCLA; joint CIPS/EPS)	"Auroras and related phenomena at moons and planets" Many distinguished scientists (Halley, Celsius, Birkeland and others) have puzzled over the links between northern lights (more generally, the aurora) and disturbances of the earth’s magnetic field. Before the end of his career at the start of the 20th century, Birkeland had elucidated many features of the process through which electrons and ions interact with magnetic fields in near-Earth space to gain energy. They then stream along the magnetic field into the upper atmosphere where they excite particles whose glow we observe from the ground. Today we understand much better the mechanisms that produce aurora on Earth and we have begun to study auroral processes elsewhere in the solar system using telescopes of great resolving power to provide images. With additional in situ spacecraft measurements we attempt to account for the details. Although many features of planetary auroras have parallels on earth, some do not. This talk will consider similarities and differences among auroras and related phenomena observed at earth, Jupiter, Saturn, and the large moons of the latter two. The differing auroral structures arise because there are many different mechanisms for transferring energy from the magnetic field to charged particles but, in every case, the final step in the process excites atmospheric emissions, as Birkeland would have expected.	dePater
	31	George Rieke (joint IGPP?)	A Planet's Rocky Road to Success One of the largest coherent legacies of the Spitzer telescope will be studies of planetary debris disks, formed of collisional debris and analogous to the zodiacal cloud and Kuiper Belt in the Solar System. The Spitzer data have allowed us to study literally hundreds of nearby planetary systems, of ages from a few million years to a 5 - 10 Gyr. These observations let us compare hypotheses for the evolution of our system with the average behavior of many others. I will show how the data 1.) substantiate theories for a vigorous collisional growth of terrestrial planets around an age of 10-15Myr; 2.) suggest the presence of large impacts such as the one that formed the moon; 3.) but also indicate that they are relatively rare; and 4.) show that collisional activity within the terrestrial planet zones generally persists roughly to the time of corresponding to the Late Heavy Bombardment.	Chiang
February	7	Kartik Sheth (CIT)	The Redshift Evolution of Galactic Structures (Bars, Bulges & Disks) at z < 1 from COSMOS: Quantifying the Assembly of the Hubble Sequence We have analyzed the redshift-dependent fraction of galactic bars over 0.2<z<0.84 in 2,157 luminous face-on spiral galaxies from the COSMOS 2-square degree field. Our sample is an order of magnitude larger than that used in any previous investigation, and is based on substantially deeper imaging data than that available from earlier wide-area studies of high-redshift galaxy morphology. We find that the fraction of barred spirals declines rapidly with redshift. Whereas in the local Universe about 65% of luminous spiral galaxies contain bars (SB+SAB), at z 0.84 this fraction drops to about 20%. Over this redshift range the fraction of strong (SB) bars drops from about 30% to under 10%. It is clear that when the Universe was half its present age, the census of galaxies on the Hubble sequence was fundamentally different from that of the present day. A major clue to understanding this phenomenon has also emerged from our analysis, which shows that the bar fraction in spiral galaxies is a strong function of stellar mass, integrated color and bulge prominence. The bar fraction in very massive, luminous spirals is about constant out to z 0.84 whereas for the low mass, blue spirals it declines significantly with redshift beyond z=0.3. There is also a slight preference for bars in bulge dominated systems at high redshifts which may be an important clue towards the co-evolution of bars, bulges and black holes. Our results thus have important ramifications for the processes responsible for galactic downsizing, suggesting that massive galaxies matured early in a dynamical sense, and not just as a result of the regulation of their star formation rate.
	14	Roger Chevalier (UVa)	The Death and Afterlife of Massive Stars Observations of supernovae and gamma-ray bursts show that massive stars end their lives with wide variety of properties. For supernovae, mass loss plays a crucial role in that variety. The circumstellar interaction and explosion characteristics provide diagnostics for the stellar evolution leading up to the explosion.	Klein
	21	Bill Bottke (bottke@boulder.swri.edu joint EPS/ASTRO.CIPS; joint IGPP)	An Asteroid Breakup 160 My Ago as the Probable Source of the K-T Impactor The terrestrial and lunar cratering rate is often assumed to have been nearly constant over the last 3 Gy. Different lines of evidence, however, suggest the impact flux from kilometer-sized bodies increased by at least a factor of 2 over the last ~100 My. Here we report that this apparent surge was triggered by the catastrophic disruption of the Baptistina parent body, a ~170 km diameter carbonaceous chondrite-like asteroid that broke up 160 +30 -20 My ago in the inner main belt. Numerous fragments produced by the collision were slowly delivered by dynamical processes to orbits where they could strike the terrestrial planets. Using numerical simulations to model this asteroid shower, we find it is the most likely source (>90% probability) of the Chicxulub impactor that produced the Cretaceous-Tertiary (K/T) mass extinction event 65 My ago.
	28	Judd Bowman (CIT)	"First Light" from New Probes of the Dark Ages and Reionization The application of redshifted 21 cm emission from neutral hydrogen in the high-redshift intergalactic medium (IGM) to probe reionization and the early universe is transitioning rapidly from the realm of theory to practice. The Murchison Widefield Array (MWA) deployed its first 32 antenna tiles in November, 2007, followed by a "first light" demonstration in December. By the end of 2008, all 512 antenna tiles will be deployed and primary science observations will follow in 2009 and 2010. Another, very different, approach to extracting information from the redshifted 21 cm signal is to directly constrain the global (mean) brightness temperature as a function of redshift. The Experiment to Detect the Global EOR Signature (EDGES) has been designed for this purpose (and is small enough to fit in your suitcase!). EDGES saw its "first light" at the end of the 2006. In this talk, I will report on the status and preliminary findings of the initial MWA and EDGES deployments. These efforts, combined with recent developments in theoretical modeling and analysis techniques, are establishing a robust prediction of the reionization science possible with radio experiments. I will review the latest expectations -- now grounded with real hardware experiences -- and highlight the implications for the coming years.	Backer
March	6	Hans Walter-Rix (MPG)	Do the Milky Way's Outskirts Live up to Cosmological Expectations? The current galaxy formation paradigm implies that galaxies, such as our own Milky Way, are 'baryon condensates' at the center of extensive dark matter halos, and exhibit a wealth of detailed substructure that reflects their hiearchical formation: numerous sub-halos and tidally distrupted streams. Only in the local group can we currently put galaxy formation to a test based on its fine-scale predictions. The Sloan Digital Survey, and its follow-on project SEGUE, have just provided an unprecedented data set to study the Milky Way's outskirts, and I will present recent quantitative comparisons between model predictions and these new observations.	Davis/Croton
	13	Ed Prather (and Gina Brissenden): coll. + education workshop	Are you really teaching if no one is learning? Insights from nearly a decade of research on the teaching and learning of astronomy. When we think about how we were socialized into the world of teaching and learning as university science students, it is not surprising that we tend to practice traditional lecture methods with our students once we start teaching our own courses. Acknowledging that traditional lecture-based instruction is insufficient at promoting significant conceptual gains for our students in introductory science courses is only the first step. But what can we do in the traditional lecture setting that really works? We typically receive little to no training or professional development on instructional strategies that are explicitly designed to challenge students' naï ideas and intellectually engage their thinking at a level deeper than what is fostered during traditional lecture, and which leads to more significant conceptual gains. Members of the Center for Astronomy Education (CAE) at the University of Arizona have been developing and conducting research on the effectiveness of learner-centered instructional strategies and materials that put students in an active role in the traditional lecture classroom. The results of this work have been incorporated into a series of "Teaching Excellence Workshops" that members of CAE have been conducting around the nation as part of the NASA Spitzer and JPL Navigator Education and Public Outreach programs. As a part of continuing efforts to determine the effectiveness of these workshops, CAE is conducting a national research project using the Light and Spectroscopy Concept Inventory administered by faculty who were on the CAE mailing list and listserv (Astrolrner@CAE). Similar to the Force Concept Inventory used in physics, the Light and Spectroscopy Concept Inventory (LSCI) was developed to measure student gains over the course of a semester on a core concept in astronomy-the nature of light and spectroscopy (Bardar et al 2006). Our preliminary findings support that astronomy courses taught using learner-centered methods, that is, Interactive-Engagement-do improve student learning significantly over more traditional methods. In addition to measuring student learning gains, we have developed an instructor survey to measure the perceived level of Interactive-Engagement instructors believe occurs in their courses which we are cross-correlating with an additional survey to be taken by students in these courses. Results of this research will be presented along with several of these learner-centered instructional strategies.	Heiles
	20	David Hogg (NYU)	The fastest, largest, and least well-organized observatory in the world. abstract: Historical plate archives, educational and outreach observatories, and the hard drives of amateurs contain countless images, many of which are uncalibrated as far as scientific uses are concerned. Nonetheless, they contain enormous information about asteroids, stellar proper motions, variability, and transients; indeed many amateurs and educators make important discoveries and measurements each year. We have built a reliable and robust system that takes as input an astronomical image, and returns as output the pointing, scale, and orientation of that image (the astrometric calibration or WCS information). The system requires no first guess, and works with the information in the image pixels alone. The success rate is very high (~99.9 percent for shallow UV and optical imaging survey data), with essentially no false positives. With lower precision, it also determines the date at which the image was taken, the filter or bandpass, and the photometric zeropoint. We are using this system to generate consistent and standards-compliant calibration data for all digital and digitized astronomical imaging, no matter what its origin or archival state. This is the first step in a program of making all of the world's heterogeneous astronomical data searchable and interoperable, and organizing the world's amateurs and educators into the largest, fastest, and most reliable observatory in the world.	Bloom
	27	Spring Break
April	3	Marc Kuchner (Goddard)	Debris Disks and Hidden Planets When a planet orbits inside a debris disk like the disk around Vega or Beta Pictoris, the planet may be invisible, but the patterns it creates in the disk may give it away. Observing and decoding these patterns may be the only way we can detect exo-Neptunes orbiting more than 20 AU from their stars, and the only way we can spot planets in systems undergoing the late stages of planet formation. Fortunately, every few months, a new image of a debris disk appears with curious structures begging for explanation. I'll describe some new ideas in the theory of these planet-disk interactions and provide a buyers guide to the latest models (and the planets they predict).	Kalas
	10	Steve Allen (Stanford)	New cosmological constraints from X-ray studies of galaxy clusters The natures of dark matter and dark energy - the dominant mass-energy components of the Universe - are among the most profound questions in physics. X-ray observations of galaxy clusters provide one of our most powerful tools to investigate these mysteries. I will present new results from two experiments that employ X-ray observations. The first uses Chandra X-ray Observatory measurements of the baryonic mass fraction in the largest, dynamically relaxed clusters. This method, like type Ia supernovae studies, measures distance as a function of redshift and traces the acceleration of the Universe directly. It leads to comparably tight, though entirely independent, constraints to supernovae studies, and measures the mean matter and dark energy densities and the dark energy equation of state. The second experiment uses observations of the growth of cosmic structure, as manifested in the evolution of the X-ray luminosity function of galaxy clusters. It leads to tight constraints on the amplitude of mass fluctuations in the Universe, and entirely new constraints on dark energy. The analysis of both experiments includes a rigorous treatment of systematic uncertainties. I will place our new X-ray results in the context of the best other current cosmological data. In combination with cosmic microwave background and supernovae studies, we obtain improved insight to date into the nature of dark energy, measuring the equation of state to a precision of 5-6 per cent. I will comment on the prospects for improving these results over the next few years.	Quataert
	17	Josh Simon (CIT)	Dark Matter in Dwarf Galaxies Over the last several years, three crucial shortcomings of the Cold Dark Matter (CDM) model have been discovered on galaxy-size scales. I present new observations addressing two of these problems: the missing satellite problem and the central density problem. I describe results from a Keck spectroscopic survey of the ultra-faint dwarf galaxies orbiting the Milky Way that were recently discovered by the Sloan Digital Sky Survey. We measure the masses of these galaxies based on their stellar kinematics and investigate whether they can account for the missing CDM satellites. I also present a rotation curve analysis of eight nearby low mass disk galaxies, based on high-resolution 2D velocity fields in Halpha and CO. This observing program has been designed to overcome some of the limitations of other rotation curve studies that rely mostly on long-slit spectra or low-resolution HI observations. We find that these objects exhibit the full range of dark matter density profiles between constant density and NFW halos, in contrast to the single universal density profile seen in CDM simulations. We consider possible explanations for the differences between observed and expected density profiles and argue that they are consistent with being caused by halo triaxiality.	Blitz
	24	Paul Martini (OSU)	The Evolution of AGN in Clusters of Galaxies Galaxies in clusters have undergone profoundly different evolution relative to their counterparts in the field. I will present new results that show the same holds true for the supermassive black holes at the centers of cluster galaxies. Comparision of low-redshift and high-redshift clusters shows that luminous AGN are substantially more common in high-redshift clusters, and that the population increases more rapidly than the field AGN population over the same redshift range. This substantial difference in AGN evolution between the field and clusters is indicative of an environmental dependence to AGN downsizing. As AGN feedback appears to lead to substantial heating of the intracluster medium, the evolution of the AGN population may also have implications for the use of the intracluster medium as a cosmological tool.	White
May	1	Frans Pretorius (Princeton)	Binary Black Hole Mergers The collision of two black holes is thought to be one of the most energetic events in the universe, emitting in gravitational waves as much as 5-10% of the rest mass energy of the system. An international effort is currently underway to detect gravitational waves from black hole collisions and other cataclysmic events in the universe. The early success of the detectors will rely on the matched filtering technique to extract what are, by the time the waves reach earth, very weak distortions in the local geometry of space and time. In the case of black hole mergers numerical simulations are needed to obtain predictions of waveforms during the final stages of coalescence. 2005 was a watershed year for numerical simulations of black holes, and we are now beginning to explore the fascinating landscape of black hole collisions in the fully non-linear regime of Einstein's theory. In this talk I will give an overview of the recent successes and what we have learned about the merger process, for astrophysically relevant binaries and, time permitting, more esoteric configurations. The latter include hyperbolic encounters fine-tuned to an approximate threshold of merger, exhibiting behavior similar to "zoom-whirl" geodesics in a black hole background. These types of orbits may have some relevance to speculative black hole formation by parton collisions at the LHC in large extra dimension scenarios.	Arons
	8	Maura McLaughlin (WVU)	Peek-A-Boo Pulsars: Transient radio emission from neutron stars The first radio pulsar was discovered 40 years ago, with close to 2000 of these objects known today. However, these exotic neutron stars continue to surprise us with newly observed phenomena. One example of this is the recently discovered classes of "peek-a-boo" pulsars, neutron stars whose radio emission is sporadic and not easily detectable through standard searches. In this talk, I will describe the properties of these mysterious neutron stars and discuss recent radio and X-ray observations. I will explain some theories put forth to explain their unusual emission properties and the implications of these new classes of pulsars for estimates of the number of neutron stars in the Galaxy.	Bower