Dr. Steven Doty: Research Description

Modeling: General

Astrophysics concerns itself with the Universe: where it came from, how it works, and where it is going to. Unlike experiments in which we can choose to set up any situation we desire, the all of the experiments we study as astronomers/astrophysicists have already been set up for us. As a result, we have to work backwards: we must take the light from the stars (the experimental output) and infer the situation that produced it (the experimental conditions).

This work is done by constructing detailed models of the physics involved in regions around stars to predict the light we would observe. By comparing the observations with the models, we can see which models best fit the data -- and thus get a good idea about the environments around stars.

Star Formation: 1-D

In my work, I am primarily interested in how and where stars are born. This is called Star Formation. A region of recent and massive star formation is in Orion's belt. Orion (the Hunter) is easily visible to the naked eye in the fall sky. It is one of the closest (~ 500 pc) and most studied star-forming regions in our galaxy.	.
Most of the information we receive is in the form of infrared (heat) radiation emitted by small, solid particles called dust grains. These particles are about 1 micron or less in radius -- about the size and composition of the particles in cigarette smoke. They are heated by absorbing starlight, warm up, and emit infrared radiation that we receive at the Earth. We can observe this radiation by using both ground and space-based observatories (green symbols to the right). By fitting the data with models (solid line to the right) we can infer the properties of the source. In this case, a fit to AFGL 2591 shows tells us how strong the star is, how must material surrounds it, and how centrally condensed the region is.	.
Aside from dust grains, there are also molecules in these regions in which stars form. One important question is where is the galactic oxygen? One potential place is water, since it is stable, and since hydrogen is the most abundant cosmic element. We can study the potential existence of water by seeing how much emission there is around a star-forming region. In the panel to the right we shown the observed emission by water masing (maser = laser that emits microwaves instead of visible light) in Orion as a function of position in the source. The observed data are given by the symbols (dots), and the models are given by the solid lines. Note that by observing one line we may be able to say something about the amount of water -- namely that there is about 1 water molecule for every million hydrogen molecules (x = 10^-6).	.
We can also get a better fit by including more data. In the panel at the right, we show results from observations by the Infrared Space Observatory (ISO) toward AFGL 2591. The lines here are thousands of absorption lines of water, absorbing light emitted by a hot source in the background (blue line). We fit all of these lines simultaneously (red line). This model confirms the results for total mass, luminosity, and density structure inferred by the dust modeling above.	.

Star Formation: 3-Dimensions

Given the above results, it appears that we have a basic understanding of the processes and principles involved in the formation of stars. Recent data, however, show significant irregularity in star-forming regions (consider the orion case above). As a result, we are now considering the effects of a three-dimensional source structure -- including clumps, holes, disks, etc., on the emitted radiation. To the right is an example -- HH30.	.
One recent piece of work has been the construction of a fully three-dimensional simulation of the transfer of radiation through irregular regions. As an example, a simple "off the cuff" model to somewhat mimic HH30 is shown to the right.	.
What good is this? Well, in clumpy regions, the clumpy material may block light, while the "holes" may let light through. As a result, the temperature structure is not uniform. Instead, hotspots may occur further into the region than might otherwise be expected. Working with Matt Palotti ('02) we showed that this may occur -- see the panel at the right.	.

TO CONTACT ME

Dr. Steven Doty
Department of Physics and Astronomy
Olin 109
Denison University
Granville, OH  43023

You can also e-mail me at doty@cc.denison.edu.