Specific IC 2118 information

Brief philosophical note from Luisa

Real science vs. textbook science:

• Science (history) as presented in textbooks may seem a never-ending series of right answers. Real science has a lot of dead ends as we struggle to find out what the ‘right answer’ is.
• Science problems in textbooks have well-defined problems, specific methods you’re supposed to use to solve them, and right (exact) answers (1.2 can be wrong when 1.3 is right). Real science is not quite “made up as you go along” but it may feel that way in the coming days. Different people approach the same problem in different ways, and many answers can be right (1.2 and 1.3 can both be right). The only way you know it’s the right answer is if you believe that everything you did to get there is right.

Why should anyone care about young stars?

• Understanding star formation includes understanding how planets form, including planets like Earth.
• Star formation is the "happening field" right now! TONS of new discoveries happening all the time, many driven by Spitzer.
• A friend who is the author of a popular college textbook told me that the chapter that she revises most frequently (particularly recently) in response to new developments is the star formation chapter.
• By doing this project, you are participating in the revolution!

Young stars in general

Introduction to star formation

Cartoon from Greene, American Scientist, Jul-Aug 2001

Stars begin their life in a cloud of gas and dust called a nebula. Gravitational forces cause the nebula to start to condense (shrink). (a, b)

As the nebula shrinks, like a spinning skater pulling in her arms, it begins to spin more rapidly. The same physics ("conservation of angular momentum") means that the dust and gas in the nebula doesn't fall straight into the center; it falls onto a disk surrounding the central object, and from the disk, the matter falls onto the central object. The temperature at the center of the shrinking nebula rises due to increasing pressure and friction between the particles. The figure has this stage labeled as a "protostar", but for some astronomers, beginning at this stage, and until the star starts to turn H into He the object is still called a protostar. Since the protostar is still embedded in a thick cloud of gas and dust, it can only be detected in the infrared. (c)

When the protostar enters the next stage, labeled in the figure as the T Tauri stage, it’s still gaining mass and contracting slowly because material is still falling onto it, but it begins to eject gas in two giant gas jets, called bipolar flows. These jets and stellar winds eventually sweep away the envelope of gas still surrounding the protostar. In the surrounding disk protoplanets are beginning to form. (d)

Leftover material in the disk surrounding the star clumps together and undergoes many collisions until most of the material has been swept up by objects orbiting the star, such as planets, asteroids and comets. (e)

The star’s life so far has been governed by the continuous inward pressure of gravity. The gravitational pressure keeps compressing the gas into a smaller and smaller volume, making it hotter and hotter in the core. As soon as the temperature in the core of the protostar becomes great enough, nuclear fusion begins. When this nuclear fusion begins, finally the star has a way to "fight back" against gravity. So much energy is released in this reaction that it enables the star to "push back" with an outward radiation pressure that balances the inward push of gravity. The protostar is now a full-fledged star, fusing hydrogen into helium in its core. (f) The star will stay the same size until it runs out of nuclear fuel in the core (all of the hydrogen has been converted into helium). Then, the pressure from gravity takes over again, pushing in on the star.

Finding the cluster members

Spitzer is so sensitive that it easily sees things at the far reaches of the Universe with only a few seconds' integration. When studying clusters of stars, not just with Spitzer, one of the first major goals is to figure out which objects are truly cluster members and which are not. This pdf file has a discussion of how to find members of young clusters in general.

Working specifically with IC 2118

Many of the tools and techniques developed for IC 2118 will work in any other star-forming region observed with Spitzer. Here are some things pertaining specifically to the IC 2118 region. (to come when i have time!)