UCB Astro Theory seminar
The initial conditions in the process of star (and planet) formation
Paola Caselli (Leeds, UK)
* deuterated: describing a compound which has had some of its normal hydrogen (protium) replaced with the heavy isotope deuterium.
PSC: pre-stellar cores; dense regions within interstellar molecular clouds; provide initial conditions in the process of star and planet formation. Nearby PSC's show that they are cold (T<10K), quiescent (molecular lines near thermal), and have chemistry affected by molecular freeze-out onto dust grains. Under such conditions deuterated molecules "flourish" (?), and can be used to unveil the PSC physical and chemical structure. PSC puzzles: (1) what is happening to the gas and dust in their nuclei? (2) How do different environments and external conditions affect the PSC physical/chemical structure? (3) are PACs in high-mass star forming regions similar to the well-known low-mass PSCs (studied locally)? Observational and theoretical work on (nearby) PSCs reviewed; ongoing search and study of massive PSCs embedded in IR-dark clouds, which host the initial conditions for stellar cluster and high-mass star formation.
UCB Astro Theory seminar
The Orion Challenge
Jonathan C. Tan (U. Florida)
* Orion Kleinmann-Low (KL) nebula: cool (<600K), intense, extended infrared source that is the most active part of the Orion Complex. Appears to consist of a cluster of young and forming stars embedded in a dusty molecular cloud. Bright in IR (<20um), blocked by dust in visible light. Hot stellar winds, massive young stars heating surrounding gas. Center appears to host a ~30Msun star (IRc2). Water maser and concentrations of CO also detected.
KL nebula is the closest region of massive SF, but is one of the most poorly understood. Invoked in support of 3 different theoretical models of how high-mass stars form: Core accretion, competitive accretion, stellar collisions. Review these models and recent work on constraining core accretion; finding initial conditions of massive starless cores; expected observed properties of massive protostars. Orion KL can be understood within the Core Accretion paradigm, after allowing for the distrubance of a recent tidal perturbation from fly-by of the Becklin-Neugebauer runaway B star.
0902.1067
Reheating in tachyonic inflationary models: effects on the large scale curvature perturbations
* tachyon: a hypothetical subatomic particle that moves faster than light. A tachyon will be constrained to the space-like portion of the energy-momentum graph--it cannot slow down to subluminal speeds. In the framework of QFT, tachyons are understood as signifying an instability of the system, and dismissed through tachyon condensation (rather than being treated as real faster-than-light particles)--such instabilityes are described by tachyonic fields. According to the the widely accepted understanding of the concept of a particle, tachyon particles are too unstable to be treated as existent---hence faster than light information transmission and causality violations with tachyons are impossible. Conventional massive particles are sometimes called "bradyons" or "tardyons" in contrast (but only in the context of discussions about tachyons. Tachyons have imaginary masses. No experimental evidence for the existence of tachyon particles has been found.
0902.1067
Reheating in tachyonic inflationary models: effects on the large scale curvature perturbations
Jain, Chingangbam, Sriramkumar
Perterbative reheating and its effects on the evolution of the curvatures perturbations in tachyonic inflationary models. A system consisting of a tachyon and a perfect fluid (assumed to be radiation). Numerically solve the equation and study the evolution of the perturbations for all scales about Hubble. Study the effects of transition from tachyon-driven inflation to the radiaiton dominated epoch on the evolution of the large scale curvature and non-adiabatic pressure perturbations. Two possible types of decay of the tachyon into radiation. Plot spectrum of curvature perturbations at the end of inflation (primordial power spectrum) as well as the early stages of the radiation-dominated epoch. Reheating does not affect the amplitude of the curvature perturbations. Similar results are previous studies based on super-Hubble scales. Before the transition to the radiation dominated epoch, the relative non-adiabatic pressure perturbation between the tachyon and radiation decays in a fashion very similar to that of the intrinsic entropy perturbation associated with the tachyon. After the transition, the relative non-adiabatic perturbation dies down extremely rapidly during the early stages of the radiation dominated epoch. This is important because it ensures that the amplitude of the curvature perturbations remain unaffected during reheating. Discuss the corresponding results for the chaotic inflation model in the case of the canonical scalar field.
1108.1349
On the mass-to-light ratios of fossil groups. Are they simply dark clusers?
Proctor, ... Rykoff, et al
* Fossil groups: X-ray bright galaxy groups with large differences between the luminosities of their brightest and second brightest galaxies; believed to be some of the oldest galaxy systems in the universe.
* why is this consistent with an "old system"?
Study of 10 fossible group candidates (average 33 spectroscopically confirmed members per group); deepest study of its type to date. Analysis of luminosity function of fossil groups for this sample. Confirm the high masses previously reported for many of fossil systems (closer to clusters than groups). Also confirm high dynamical M/L ratios reported in many previous studies. Similar to previous results, but interpretation is not. Show luminosities of the BCGs in these systems are consistent with their high dynamical masses, their richnesses are extremely low. New interpretation of fossil systems: simly the result of the high BCG luminosities and low richnesses, while the high masses and low richnesses also explain the high M/L ratios. Fossil systems can be characterised as cluster-like in their masses and BCG luminosities, but posses the richness and optical luminosities of relatively poor groups. No theory for fossil group formation.
* this is interesting. The BCG luminosity corresponds to the DM halo mass, but the richness doesn't. What causes such a discrepancy?
* can we get DM mass from lensing of these fossil groups? has it been done already?
1108.1358
Exact extreme value statistics and the halo mass function
Harrison, Coles
Motivation: presence of extremely massive clusters at uncomfortably high redshifts for the standard cosmological model to explain. Develop framework for the study of the most massive halos, based on EVS (extreme value statistics). Start with the known distribution of extreme values from an underlying distribution, instead of asymptotic theory (which is independent of the underlying distribution). Illustrate that the former is more robust with a discussion of the use of EVS as a probe of primordial non-Gaussianity.
* interesting.
1108.1374
Wide-field infrared survey telescope (WFIRST) interim report
Green, Schechter, Baltay, Bean, Bennett, ..., Lauer, Perlmutter, Rauscher, Rhodes, ... Stern, ... Wright,...
SDT (science definition team) of WFIRST created by NASA on Dec., 2010. Produce an interim DRM (design reference mission). DRM will be completed in 2012.
* hmm, is it interesting enough to read this? Maybe for comparison with Euclid...
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