Star Formation Studies Using
Student: Desika Narayanan
Mentor: Dr. Sung Kim
Center for Astrophysics
-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
" 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?
UV light! CO CO
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 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
" 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,
we can get rid of some of ripple.
4 components were removed, after the first 5
" Note the recovery of the third line
" 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
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
" Measured at:
NGC 6334 -460 GHz (CO J=4-->3)
-809 GHz (CO J=7-->6)
-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
12 CI (809 GHz)
- I Learned about mathematical data reduction processes (ie Fourier transform,
- 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