Difference between revisions of "Specific IC 2118 information"

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=Brief philosophical note from Luisa=
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=The cloud=
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Real science vs. textbook science:
 
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*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.
 
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*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.'''
 
  
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Why should anyone care about young stars?
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[[Image:ic2118iras.jpg|right]]IC 2118, the Witch Head Nebula is a small cloud near the supergiant star Rigel in the constellation Orion.  In the image at the right (taken by IRAS at 25 microns), IC 2118 is the structure at the bottom right corner. Rigel appears to be at least partially responsible for exciting and blowing off a significant portion of the nebula in this region.  This cloud is about 210 parsecs away, similar in distance to the Orion Nebula Cluster (a.k.a. the ONC, or the sword of Orion).  The ONC is a cluster of stars that are so bright that they too may be pushing around the gas and dust in the Witch Head Nebula.  The ONC is sort of the "downtown", the "urban" area of star formation - lots of stars close together, lots of things going on all the time. There are so many stars here, so close together, that if we lived there, there would never be night.  There are a ''lot'' of stars in the ONC!!  Our cloud, the Witch Head Nebula, is sort of the "country."  There are some things going on here, not a whole lot (especially in comparison to the ONC), but still interesting.
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*Understanding star formation includes understanding how planets form, including planets like Earth.
 
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*Star formation is the "happening field" right now!  TONS of new discoveries happening all the time, many driven by Spitzer.
 
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*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.  
 
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*By doing this project, you are participating in the revolution!
 
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=Young stars in general=
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What we are trying to do is characterize the process of pre-main sequence stellar evolution in this cluster. We want to (a) find the young stars, and (b) compare star formation in this cluster with others from different environments (such as the much denser ONC) to see if there are similarities or differences.
  
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==Introduction to star formation==
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Previous all-sky surveys, including both IRAS and 2MASS, have included this region, but not to the resolution or the wavelengths that Spitzer can provide, and there are few studies of this particular region in the literature.
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{| cellpadding="1"
 
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| [[Image:starformationcartoon.png]]
 
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|''Cartoon from Greene, American Scientist, Jul-Aug 2001''
 
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|}
 
  
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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)
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''Need to continue here with more information on a literature review''
  
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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) 
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=The observations=
  
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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) 
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In our first observation of this region, we selected for observation by IRAC and MIPS a target area based on the IRAS survey and recent work conducted by Kun et al. (2004).  Our Spitzer time was limited so we selected an area of the cloud near the "head" of the nebula that had a known IRAS source and 3 possible new classical T Tauri stars that were identified by Kun et al.  In our second observation of this region, we were granted 11.5 hrs to go as far down the cloud as we could. We were able to go about 2.5 degrees down the cloud with both IRAC and MIPS.
  
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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)
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[[Image:Ic2118_coverage.png]]
  
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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.
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On the left, previous objects in this region are indicated on top of a grayscale image in IRAS-25 (25 microns). In the center, the first year's coverage using IRAC is indicated.  On the right, you can see the second year's coverage using IRAC (cyan and magenta) and MIPS (pink, blue, and green).
  
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The observations we have cover a ''very'' large area.  For comparison, the full moon is about half a degree across.  Our mosaics are 2.5 degrees long, so 5 full moons long.  Because these mosaics are so large, it takes a lot of computing power to create them.  Luisa created our mosaics using a high-powered linux machine.  It took about 45 hours to generate the IRAC mosaics, about 9 hours to generate the MIPS-1 (24 micron) mosaic, and about 3 hours to generate the MIPS-2 (70 micron) mosaics. 
  
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=Examining the mosaics=
  
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==Finding the cluster members==
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to come.  include  warning that You may need to have a lot of RAM in your computer if you want to load in 3 or 4 of our mosaics all at the same time.
  
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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.  [[Media:findingclustermembers.pdf| This pdf file]] has a discussion of how to find members of young clusters in general.
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=A first look at the catalog with color-color plots=
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this discussion will center on using color-color plots with the catalog.  Need to emphasize here (and earlier) that many of the tools and techniques developed for IC 2118 will work in any other star-forming region observed with Spitzer.
  
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=Working specifically with IC 2118=
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=Examining special sources more in depth using SEDs=
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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.
 
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''(to come when i have time!)''
 

Latest revision as of 18:57, 23 February 2007

The cloud

Ic2118iras.jpg

IC 2118, the Witch Head Nebula is a small cloud near the supergiant star Rigel in the constellation Orion. In the image at the right (taken by IRAS at 25 microns), IC 2118 is the structure at the bottom right corner. Rigel appears to be at least partially responsible for exciting and blowing off a significant portion of the nebula in this region. This cloud is about 210 parsecs away, similar in distance to the Orion Nebula Cluster (a.k.a. the ONC, or the sword of Orion). The ONC is a cluster of stars that are so bright that they too may be pushing around the gas and dust in the Witch Head Nebula. The ONC is sort of the "downtown", the "urban" area of star formation - lots of stars close together, lots of things going on all the time. There are so many stars here, so close together, that if we lived there, there would never be night. There are a lot of stars in the ONC!! Our cloud, the Witch Head Nebula, is sort of the "country." There are some things going on here, not a whole lot (especially in comparison to the ONC), but still interesting.

What we are trying to do is characterize the process of pre-main sequence stellar evolution in this cluster. We want to (a) find the young stars, and (b) compare star formation in this cluster with others from different environments (such as the much denser ONC) to see if there are similarities or differences.

Previous all-sky surveys, including both IRAS and 2MASS, have included this region, but not to the resolution or the wavelengths that Spitzer can provide, and there are few studies of this particular region in the literature.

Need to continue here with more information on a literature review

The observations

In our first observation of this region, we selected for observation by IRAC and MIPS a target area based on the IRAS survey and recent work conducted by Kun et al. (2004). Our Spitzer time was limited so we selected an area of the cloud near the "head" of the nebula that had a known IRAS source and 3 possible new classical T Tauri stars that were identified by Kun et al. In our second observation of this region, we were granted 11.5 hrs to go as far down the cloud as we could. We were able to go about 2.5 degrees down the cloud with both IRAC and MIPS.

Ic2118 coverage.png

On the left, previous objects in this region are indicated on top of a grayscale image in IRAS-25 (25 microns). In the center, the first year's coverage using IRAC is indicated. On the right, you can see the second year's coverage using IRAC (cyan and magenta) and MIPS (pink, blue, and green).

The observations we have cover a very large area. For comparison, the full moon is about half a degree across. Our mosaics are 2.5 degrees long, so 5 full moons long. Because these mosaics are so large, it takes a lot of computing power to create them. Luisa created our mosaics using a high-powered linux machine. It took about 45 hours to generate the IRAC mosaics, about 9 hours to generate the MIPS-1 (24 micron) mosaic, and about 3 hours to generate the MIPS-2 (70 micron) mosaics.

Examining the mosaics

to come. include warning that You may need to have a lot of RAM in your computer if you want to load in 3 or 4 of our mosaics all at the same time.

A first look at the catalog with color-color plots

this discussion will center on using color-color plots with the catalog. Need to emphasize here (and earlier) that many of the tools and techniques developed for IC 2118 will work in any other star-forming region observed with Spitzer.

Examining special sources more in depth using SEDs

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