narayanan by cuiliqing


									Star Formation Studies Using

     Student: Desika Narayanan
       Mentor: Dr. Sung Kim
       Center for Astrophysics
      Cambridge, Massachusetts
           Summer 2001

-Stars are born in the pockets of Giant Molecular Clouds.
- Photodissociation regions (PDRs) are areas in the clouds where
the Far Ultraviolet light of newborn stars play an integral role in
the chemistry of molecular clouds

  - Why study these PDRs? They regulate star formation.
-Objective of scientific study: to better understand the role of
PDRs in GMCs.
"       Mapping Regions of Emission in:
    "     CO (7-->6)      809 GHz
    "     12CI                   809GHz
    "     CO (4-->3)     460 GHz
    "     CO (2-->1)     230 Ghz

          Clouds Studied:
    "     Small Magallenic Cloud (East and West)
    "     Large Magallenic Cloud
    "     NGC 6334 (Galactic)

          Good mapping will hopefully indicate where star formation might be going on.
          Further inspection of the spectra taken at different locations will help define physical
          parameters such as temperature, density and elemental abundance.
How do we study the PDRs?

                                                           Radio light!


   UV light!                 CO      CO
                                                     CI                    Observer


                               CI                                     CI


                     Rotational transitions in molecules

                               "       Observations were made in a series of
       IRAS 100 micron image           pointings. After data are reduced, and
                                       spectra obtained, these locations are
                                       used to make a contour map of
                               "       All observations were made with the
                                       Antarctic Submillimeter Telescope and
                                       Remote Observatory (AST/RO)

                                   "      Has the ability to observe 230, 460,
                                          490, 806 and 809 Ghz windows
                                   "      Utilizes the high and dry atmosphere
                                          of the pole's environment to improve
                                          quality of data
Pointings in SMC-E
Spectra: Temperature versus Frequency

                   Baseline Ripple
" Baseline ripples caused by:
     -Rapid changes in atmosphere
     -Gain instabilities in mixer
     -Impedance mismatch in instrumentation (causes standing waves)
" Removed by polynomial fit and subtraction in Comb
" Removed by Fourier transform algorithm

" Problems with polynomial fitting:
     -Want to fit around line to avoid removing signal (line not always clear)
     -Best to subtract over whole line rather than pieces to avoid rms problems
   down the road (difficult then to get a good fit)
     -High order fitting can introduce artificial features
Before Linear Baseline Subtraction

Subtraction around the line

                  Fourier Transforms

" Used for a more serious form of sinusoidal ripple

" F(s) = € -i2xspdx
    -Picks out sinusoidal functions with certain amplitudes and phases.

" Comb plots F(s) versus frequency and allows you to remove certain components
Messy spectra with obvious emission lines
                        "   Possible line at -40 km/s?
                    "   The ripple is the spike off the chart.
                        If we remove bright components,
Fourier Transform
                        we can get rid of some of ripple.
4 components were removed, after the first 5
                        "   Note the recovery of the third line
SMC Observations

               "   Observations divided into
                   SMC-E and SMC-W
               "   Each observation made in a
                   of pointings 1.7' apart (distance
                   varies for different obs. Runs).
               "   SMC-E and SMC-W both
                   studied at 230 Ghz
                   (CO J=2-->1)

 SMC          SMC-E had too low of a S/N to get any lines out. More
              observation time is needed.
Results        SMC-W had bad baseline problems that I couldn't get out

              SMC-W Raw Data:
SMC-W emission   " Many of the pointings ended up
                    showing nice emission
SMC-W map

            "   Measured at:
NGC 6334        -460 GHz (CO J=4-->3)
                -809 GHz (CO J=7-->6)

 (460GHz)   "
                -809 GHz (12CI)

                Raw data was Excellent

            "   Reductions only involved linear baseline subtraction
460 Ghz (CO J=4-->3)
                       " The higher transitions map traces
CO 809 Ghz (J=7-->6)      the hotter and denser regions of the
                          molecular cloud
                  "   .

12 CI (809 GHz)

- I Learned about mathematical data reduction processes (ie Fourier transform,
   baseline fitting)
- I was able to learn some of the science behind studying Star Forming regions
- Mapping Techniques
- Sampling Theorem
- The CO emission and 12CI emission occurs in relatively similar areas in NGC 6334

-Dr. Sung Kim
-AST/RO Group

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