Summer Research Projects - 2005

Presented at the Dog and Pony Show*, Feb. 3, 2005

Research themes of David's group

We do x-ray spectroscopy and numerical (mostly spectral) modeling of hot plasmas in both laboratory and astrophysical settings. General information is available on David's webpage.

  1. Spectral modeling of soft-x-ray emission from SSX experiments (low-resolution SXR), using PrismSpect (maybe post-processing of MHD simulations using Spect3D), to diagnose plasma temperature, density (emission measure), impurity level. Also high-resolution (IDS) UV spectral modeling (C III line at 229.7 nm), to diagnose flow via line shape. Work closely with SSX team; mostly numerical modeling using well-established codes.

    This project is related to Prof. Michael Brown's work on self-organization in plasmas, and applications to magnetic acitivity on the Sun.

    Background and initial simulations at:

    Modeling codes: PrismSpect, Spect3D and others written by colleagues at Prism Computational Sciences

  2. Magnetic reconnection in Bp stars, which are hot stars with very strong, large-scale magnetic fields. MHD simulations by collaborators show periodic magnetospheric breakout events that may lead to reconnection heating. Need to (a) gather x-ray datasets from astronomical archives; (b) post-process MDH simulations to produce light-curves and spectra to be compared to data.

    Recent short review of theoretical work: "Magnetic Channeling of Radiatively Driven Hot-Star Winds" by Owocki, Townsend, & ud-Doula (from Magnetic Fields in the Universe conference, Brazil, 2004) - we will collaborate closely with these authors on this project.

    Early, seminal paper on magnetospheres of hot stars (Shore & Brown 1990): This is the one with the cartoon of the rotating magnetosphere.

    Overview with links to relevant papers and simulations, by Rich Townsend. Included there is the simulation of the rotating magnetized hot star that I showed in my presentation.

  3. Other hot stars with large-scale magnetic fields have stronger winds. Fields channel the wind flow, leading to shock-heating. Continuation of project (Stephanie Tonnesen, honors thesis, 2003) to post-process MHD simulations in order to produce x-ray diagnostics (spectral and time-variability) to be compared to data.

    See same links as for project (2), above, also Stephanie's poster from the 2003 AAS meeting.

    And my page with more information about the application to one particular star, theta-1 Ori C.

    A typical MHD simulation result for theta-1 Ori C, showing a temperature map of the magnetically confined, shock-heated plasma. We will be working with simualtions like this one.

    Note that the difference between this project and the previous one is that these stars have stronger winds and weaker fields, do not rotate as rapidly, and seem to produce x-rays via shock heating rather than magnetic reconnection.

  4. Non-magnetized hot stars have massive, highly supersonic stellar winds, which are subject to instabilities that lead to embedded radiation-hydrodynamic shocks, producing x-rays. Our group has developed spectral diagnostics of the plasma dynamics. Continuation of project (Roban Kramer, honors thesis, 2003) to model and fit Doppler broadened x-ray emission line profiles to Chandra X-ray Telescope spectra. Modeling needs to be refined and line profiles from roughly a half-dozen stars fit.

    Roban's poster from the 2003 AAS meeting.

    Our refereed papers on the development of the line profile model and on its application to the massive star zeta Pupis.

  5. X-ray emission line ratio diagnostics of plasma density are a powerful tool in astrophysics. For hot stars, there's added complexity because the most important diagnostic is sensitive also to the local UV field properties. We have codes for modeling the atomic physics, radiation transport, and spectral synthesis. This summer we will be studying the diagnostic sensitivity of these line ratios to various physical parameters and applying the diagnostic schemes we develop to data from the Chandra X-ray telescope.

    One of the important original papers (Blumenthal et al. 1972).

    Application of this diagnostic in one of my papers, on tau Sco.

    We will be comparing the Blumenthal et al. model to our own custom-computed modeling, done with PrismSpect.

updated February 6, 2005