Star Formation Studies Using AST/RO

Student: Desika Narayanan

Mentor: Dr. Sung Kim

Center for Astrophysics

Cambridge, Massachusetts

Summer 2001

Objective

-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 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?

UV light!

COCO

CO

CO

CO

CI

CI

CI

CI

Rotational transitions in molecules

Observer

Radio light!

CO

CI

CI

CI

CI

Observations

Observations were made in a series of pointings. After data are reduced, and spectra obtained, these locations are used to make a contour map of emission.

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

IRAS 100 micron image

PPointings 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) = €f(x)e-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?

Fourier Transform

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

SMC Observations

Observations divided intoSMC-E and SMC-W

Each observation made in a seriesof 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-B

SMC Results

SMC-E had too low of a S/N to get any lines out. More observation time is needed.

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

NGC 6334 (460GHz)

Measured at:-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)

CO 809 Ghz (J=7-->6) The higher transitions map traces

the hotter and denser regions of the molecular cloud

12 CI (809 GHz)

.

Conclusions

Personal:

- 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

Scientific:

- The CO emission and 12CI emission occurs in relatively similar areas in NGC 6334

Ackowledgements

-Dr. Sung Kim

-AST/RO Group

-CARA