Below the Lyman Edge: UV Polarimetry of Quasars

The Lyman edge at 912 \AA is an important diagnostic region for studying quasi-stellar objects (QSOs). In particular, it reveals a great deal about the physical conditions within the atmospheres of accretion disks, a ubiquitous component of QSO theories. A robust prediction of accretion disk models is a significant polarization due to electron scattering just longward (in wavelength) of the Lyman edge because of the wavelength dependence of the Hydrogen absorption opacity. Observations of the Lyman edge regions of QSOs have shown scant evidence for the predicted features-few QSOs show the broad, partial Lyman edges expected to be common according to most theories, and none show the high polarizations expected longward of the Lyman edge. Still, polarization spectra of a small number of QSOs have shown a rising polarization (up to 20%) at wavelengths shortward of the Lyman edge. We have now doubled our sample of intermediate-redshift QSOs observed with the HST/FOS spectropolarimeter to determine the amount of polarization on both sides of the Lyman limit. For this new sample of six objects, polarizations are low and mostly consistent with zero below the Lyman edge. Another important result of the new data is that it strengthens the conclusion that quasars are generally not polarized significantly just longward of the Lyman edge at $\sim 1000 \AA. There is no significant statistical wavelength dependence to the polarization longward of the Lyman edge indicating that simple plane-parallel atmospheres with scattering-dominated opacity are not significant sources of UV flux in quasars.Comment: Accepted to Ap.J., 30 pages, 8 figure

Comets - Teacher Page: Lesson Plan

The purpose of this lesson is for students to explore the nature and composition of a comet. The student will select ingredients to create a comet and will learn to identify ingredients responsible for a comet nucleus, and how changes in the nucleus when the comet approaches the Sun cause two different kinds of tails to form. Students can explore some facts, myths, and legends linked to the appearance of comets throughout history. The site also contains a section on evaluation and assessment that is based upon what the students observed about comets in the "Make A Comet" activity. It challenges students to observe images of different comets and asks them to identify what type of tail or tails the comets are showing. There is also an extensive vocabulary list of associated terms. Educational levels: Intermediate elementary, Middle school

Climate change and the humanities

This volume of essays fills a lacunae in the current climate change debate by bringing new perspectives on the role of humanities scholars within this debate. The humanities have historically played an important role in the various debates on environment, climate and society. The past two decades especially have seen a resurfacing of these environmental concerns across humanities disciplines in the wake of what has been termed climate change. This book argues that these disciplines should be more confident and vocal in responding to climate change while questioning the way in which the climate change debate is currently being conducted in academic, political and social arenas. Addressing climate change through the varied approaches of the humanities means re-thinking and re-evaluating its fundamental assumptions and responses to perceived crisis through the lens of history, philosophy and literature. The volume aims thus to be a catalyst for emerging scholarship in this field and to appeal to an academic and popular readership