Stephanie,


I promised I'd write about research projects. I'll try to keep it short (ha! You've heard that before).  

So, I'm giving you a brief description/reminder of each of the 4 1/2 projects we talked about in my office. As you're well aware, I can always be induced to provide more information -- just ask. I've tried to include some information about what role you'd be playing in each of these projects, about what you'd be doing on a day-to-day basis, what the prospects are for publication, and, generally, what the pros and cons are of each project.  There are papers (some of which have been written by me) and supporting information available for all of these projects.  I haven't collected references and links here, but some exist on my website, and more will soon.  Especially for the Chandra projects, you can see what I and other people have been doing with similar data. 



1. A project primarily related to Chandra or XMM spectral data. 

	a. A normal hot star (epsilon CMa - that star in the direction of lowest interstellar column density; theta1 Ori C - illuminates the Orion Nebula; beta Cru - pulsating hot star).  Each of these stars has its own individual peculiarities.  They are three of the very few hot stars observed with Chandra (or XMM, the European X-ray telescope).  
	We could do some (numerical) modeling of in conjunction with the data analysis and model fitting for any of these three stars. In terms of the data analysis, we'd look at line widths and ratios, and time variability (we're in the process of publishing some papers applying these diagnostic techniques to other Chandra datasets). 
	A project based on one of these stars would almost certainly lead to a refereed publication and a meeting presentation.  The data are good and rare.  We have the Chandra software installed and running (and other students know how to use it).  You'd learn a lot about hot stars and their winds, which is what I know the most about. There's lots of interesting physics in these objects, and you would not be simply doing data reduction and analysis. We'd have plenty of opportunity to study basic and advanced astrophysical phenomena. 

	b. The unusual Be star -- possible white dwarf X-ray binary -- gamma Cassiopeia.  We'd concentrate on the spectral properties, while the principle investigator (PI), Myron Smith, would concentrate on the time variability analysis.  The spectrum for this star is pretty amazing -- unlike normal hot stars, it's got primarily a continuum spectrum.  But there are some lines. It's possible there are even absorption lines, which would be very unusual. 
	You'd probably learn a lot about spectral formation, X-ray binaries, and get to work on a very bright, very unusual and controversial object.   We'd be doing  a lot of the same line identification, analysis, and model-fitting that are needed for the normal hot stars too. Doing real theory/modeling is probably beyond the scope of a thesis, but we'll be trying to discriminate between these two interesting models (accretion onto a white dwarf vs. magneto-coronal process involving the disk).  So you'll learn and write some background information about these two scenarios and interpret your data-fitting results in light of them.
	The possible pitfall with this project is that I'm not the PI, so we have to rely on Myron Smith more than we, perhaps, would like.  This may prevent us from publishing a paper that contains your thesis work primarily.  Myron may want to wait until we can include more stuff.  However, you can present your results at a meeting, I'm sure.  Finally, I know less about gamma Cas and about megnetic processes.  -- don't want to sound too negative; this is a great project, but kind of difficult.  Definitely doable, though. 


2. Magnetically Confined Wind Shock modeling (and application to X-ray datasets).  Zeus MHD modeling, in collaboration with Stan Owocki and Asif ud-Doula, of a hybrid magnetic-wind model: a radiation-driven wind from a star with a large-scale dipole magnetic field. We would most likely figure out how to model some aspect of X-ray production.  
	Asif and Stan have this modeling going pretty well.  Zeus is a big numerical code (we looked at some Zeus simulations in seminar the week we talked about shock modeling).  It took Asif the better part of a year to really get it running.   But now the boundary conditions are implemented (which is generally the hard part of numerical hydro), and the radiation force has been included (not generally a standard part of hydro codes).  It's not exactly trivial to modify the parameters of a run, but apparently this code is pretty usable now. 
 	This project may come the closest to being a pure theory project (well, along with the next one).  We'd be biting off a relatively small, but important part of it.  You'd be doing a lot of coding, trying out different schemes to accurately calculate the temperature and X-ray production within the hydro code.  You'd have to work somewhat closely with Stan and Asif (which I think is good, but not necessarily easy).  We'd be looking at things like how the passage of the emitted X-rays through the wind affects the emergent spectrum; and how the viewing angle effects the observed X-rays (and thus we'd be able to make some predictions about observables as a function of rotation phase). And of course, you'd get to make pretty pictures and movies of your calculations. 
	Ultimately, we could compare the predictions of these calculations to Chandra observations, so there may be a bit of a data analysis angle to this project too.  (The Orion nebula star, theta1 Ori C, is a prime candidate for the MCWS model, so this project could, to some extent, be combined with (1a).) 
	Stan's a perfectionist who only publishes once his papers are great, so this project will not necessarily lead to a refereed publication immediately.  But again, we will be able to present the results at a meeting (The Canary Islands next summer?).  


3. Rad.-hydro modeling of the line-force instability.  The line-force instability is the leading mechanism for explaining X-ray production in hot stars.  Stan is the main person in the field of modeling the line-force instability.  He and I have done a lot of calculations of wind structure (i.e. time-dependent density, velocity, temperature as a function of position in the wind.)  We'd like to characterize the structure as a function of radius and as a function of the input physics and stellar properties.  
	This project would give you an opportunity to learn a lot about the basics of radiation-driven winds, shocks, and X-rays.  We'd be running hydro simulations, again, working on techniques for making predictions about X-ray emission from hydro simulations, and also employing statistical techniques to describe, succintly, the overall properties of the wind in these simulations with just a few numbers. 
	Stan and I have thought for a while that we're pretty close to having something publishable here.  And again, you'd be able to present your results at a meeting.  And also, like the previous project, you'd be making pretty pictures and movies of these simulations.  But you wouldn't have to worry about magnetic fields. And we'd also be comparing the hydro simulation results to data.  There's some information about the line-force instability and our models of it on the "hot star winds" section of my webpage. 
	I know more about this project and the physics involved than I do about the previous one. 


4. Laboratory astrophysics: Creating and characterizing an X-ray photoionized nebula in the laboratory.  Modeling (and experimental?) involvement in SANDIA Z-machine gas cell experiments.  The idea is to characterize the properties of a gas exposed to X-rays and observe its spectral properties, effectively benchmarking "X-ray photoionization" codes that people use to model X-ray binaries, quasars, etc.  
	This is probably my most innovative project.  It's also the most physicsy one.  But since we're working closely with Jim Bailey, who's an excellent experimentalist, we wouldn't have to get our hands too dirty with experimental physics if we didn't want to.  Because it's innovative, it's not clear to me that people will pay that much attention to our results and it may be a while before we publish much.  (But, as with all the other projects, we definitely could present results at a meeting within the next year.) 
	We'd be using various codes (including radiation hydrodynamics codes) to model the interaction of the X-rays with the neon gas.  This would include "view factor" modeling (like the movie I showed you) as well as hydro, and also spectral synthesis.  All these codes are up and running on our computers. We will be using these calculations to design a new generation of experiments, as well as to model results from ongoing experiments.  
	If you're thinking that you might want to go to graduate school in physics, as opposed to astronomy, or if you like blowing things up (the Z-machine is the most powerful X-ray source on the planet -- 1.8 MJ of X-rays in 10 ns) then this may be the project for you. 



OK, I've tried to describe the gist of each project.  I think that all of these projects are important, and all of them will get done, one way or another.  It will be great to have you involved in one of them.  Let me know (there's no big rush though) what your thoughts are.  Does the gamma Cas project still intrigue you?  This project would start out as a mostly observational one, but we could move in theory directions as we got into it. 


David