Dynamic Star Formation
A dynamic picture of star formation is emerging from recent observational and theoretical results. This picture implies that molecular cloud formation must be included as part of the story of star formation, setting the initial conditions for further collapse. Global effects of gravity are important; a combination of cloud geometry and gravity provides a simple mechanism for cluster formation. Using this new paradigm, numerical simulations now underway will be tested against detailed observations of young stellar populations, especially from Spitzer infrared surveys, with the aim of developing a more quantitive theory of star formation.
Oleg Gnedin, Ohio State Univ./Univ. Mich.
The Life and Death of Star Clusters
Globular star clusters are some of the easiest astronomical objects to observe and are ubiquitous in all galaxies. Yet we are only beginning to understand how they fit into the formation of structure in the Universe. I will describe our efforts to produce a consistent picture of how, when, and where globular clusters form, based on the combination of space and ground-based observations, supercomputer simulations, and analytical theory. I will also describe the evolution of star clusters over time, leading to the dissolution of many and the survival of the fittest.
The Cooling of Neutron Stars and Strange Quark Stars
Neutron stars are some of the most exotic objects in the universe with central pressures of 1036 dynes/cm2 and gravitational binding energies of 1053 ergs. Strange quark stars are more exotic, consisting almost entirely of deconfined quark matter rather than neutrons and protons. In this talk, I will discuss the relationship of the description of dense matter in these compact objects to observations of their surface temperature as a function of age. First, I will present our new description of the crusts of strange quark stars. These strange crusts imply that the cooling of strange quark stars will be qualitatively different from the usual scenario where a crust is not present. Second, I will describe the effect of a "quartic term" on the nuclear symmetry energy and show that models which predict neutron stars colder than the observational data, like the equation of state of Akmal, et. al. (APR), may be "repaired" with a quartic term.
Shear Flows Driven by the Lorentz Force During Flux Emergence: The Energy Source for Coronal Mass Ejections and Flares
Current mechanisms of coronal mass ejection (CME) initiation rely primarily on ad hoc assumptions to energize coronal magnetic fields to erupt. Most notably, artificial shearing of coronal magnetic arcades has been employed for nearly three decades to model flares and CMEs. This talk will focus on the recent discovery that such shearing motions are driven by the the Lorentz force that naturally arises when bipolar magnetic fields emerge from the photosphere into the corona. These spontaneous shearing motions will be shown to produce eruptions in a fully self-consistent manner in both magnetic arcades and flux ropes.The shearing motions transport axial flux and energy from the submerged portion of the field to the expanding portion, strongly coupling the solar interior to the corona. This physical mechanism explains the concentration of magnetic shear near polarity inversion lines where prominences form and also explains why these magnetic structures erupt in flares and CMEs.
Galaxy Evolution in Dense Environments: A Revised Outlook 4 years after ACS
The Advanced Camera for Surveys (ACS) has dramatically increased the quantity and quality of imaging of distant clusters of galaxies, especially in the redshift range beyond z = 0.8. I will summarize the ACS science team's contributions to revising our understanding of the formation and evolution of clusters, based on data spanning 92% of the Hubble time. Highlights will include new constraints on (i) the formation of massive, early-type galaxies, (ii) the origins of different galaxy morphologies, (iii) mergers in clusters, and (iv) the nature of protoclusters at z > 2.
The A-Type Supergiant Star Deneb: Tale of a Stellar Wind
The A-type supergiant star Deneb is an evolved, roughly 20-solar-mass star and one of the most interesting stars in the Galaxy. This presentation will place this star in the context of luminous, massive stars generally, including their potential as extragalactic distance indicators. Then it will review present knowledge of the fundamental properties of Deneb, including its poorly-determined mass-loss rate, and will review recent efforts to determine the variability properties of its photosphere and of its stellar wind, and possible relationships between the two.
The Nature of Short-Hard Gamma-Ray Bursts
I will discuss the revolution in our understanding of short-hard gamma-ray bursts that has been provoked by the discovery of the first afterglows of these elusive events. The existence of the short bursts as a distinct population was first suggested in 1974 and confirmed in 1993. Until 2005, however, the afterglow revolution that revealed the origins of long-duration gamma-ray bursts in the deaths of massive stars had passed the short bursts by. With eleven afterglows and multiple redshifts now in-hand, the short bursts are revealed as a cosmological phenomenon, like their long-duration counterparts. Compared to long bursts, however, short bursts are less energetic, lower-redshift explosions produced by a much longer-lived progenitor, and lack associated supernovae to very deep limits. I will review the viable models for these cosmic explosions, and derive quantitative constraints on the local rate and progenitor lifetimes of short bursts by placing the recent events in the context of the full BATSE burst catalog (1991-2000). If the short bursts are produced by compact object merger events, these constraints translate directly into event rate estimates for LIGO, VIRGO, and future ground-based gravitational-wave detectors.
Evolution of Hot Jupiters
In the last six years, a number of planets have been discovered which transit their parent star. Mass and radius measurements, as well as recent observations of radiation directly emitted by the planet place strong constraints on models for the structure and cooling of these objects. In this talk I will discuss the evolution of close-in gas giants, with an emphasis on the role of strong stellar irradiation and tidal heating.
Vicky Kalogera, Northwestern Univ.
Accreting Compact Objects in Nearby Galaxies
In the last few years Chandra observations have revolutionized the study of X-ray binaries with accreting neutron stars and black holes by reaching extragalactic distances and stellar environments of varied star formation history. In this colloquium I will summarize some of these recent observations of young star clusters and of elliptical galaxies, and I will discuss our current theoretical understanding pertinent to their interpretation.
Magnetic Fields, The HII Region / PDR Connection
The interstellar medium (ISM) is now known to have a pressure that is dominated by magnetic fields and turbulence. Thermal gas pressure hardly matters. Modern instrumentation can routinely detect the infrared spectrum emitted by interstellar gasses near star-forming regions. These regions are often heavily obscured by dust so that only the infrared can be seen. I will discuss the development of the theoretical tools needed to understand these observations. The Orion HII region and PDR are the nearest star forming region and extensive and tests any theory of the interaction between stars and nearby gas. I will discuss recent numerical simulations that reproduce the large-scale features of this region and discuss implications for understanding the spectra of far more distant, luminous, and obscured objects like starburst galaxies.
Deborah Haarsma, Calvin College/MSU
Distant Galaxy Clusters and Galaxy Evolution
Galaxy clusters at redshift 1 and greater are still rare and prized objects, critical for answering a range of cosmological and evolutionary questions. They give us a view of merger and star formation histories in the densest regions of the universe, and can be used to study hierarchical structure formation and feedback. I will review recent discoveries of distant clusters, current observational results for the evolution of galaxies in clusters, and the physical mechanisms that may cause the quenching of star formation and the formation of the "red sequence". More clusters are needed to address these questions. We recently identified ~5 new clusters of galaxies around redshift 1 from the ROSAT Optical X-ray Survey, using ground-based near infrared imaging. These significantly increase the sample of x-ray luminous clusters that can be used to study galaxy evolution.