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A NEAR-INFRARED STUDY OF THE SOUTHERN
STAR FORMING REGION RCW 34
Lientjie de Villiers
M.Sc. PROJECT SUPERVISOR: Prof. D.J. van der Walt
CONTENTS
Star-formation
The region RCW 34
M.Sc. Objectives
Method
Preliminary results
Future objectives
Relevance to SKA
STAR-FORMATION
From the Virial theorem, if U  2K  gravitational
collapse of molecular cloud.
From above the Jeans criterion can be derived as
M c  M J where the Jeans mass MJ is given by the
RHS of
3
2
 5kT   3 
Mc  

 
 G mH   40 
Molecular cloud
T Tauri 
Pre-main
sequence star
1
2
(1).
Pre-stellar core
Infrared protostar
RCW 34
~ 3 kpc
L = 5 x 105 L and R  23 R.
Cometary shaped H II region.
Bright point source in front of
ionization front.
Large IR excess  dust around
exciting star.
Near-IR observations  star formation at
border of ionization front (Zavagno et al.)
Source
OBJECTIVES
Study stars associated with high mass star in NIR
Ks band (extinction less at 2.2 m)
Stack images  Long integration times  obtain deep
(~18th –19th mag) JHKs images  sub-solar – solar mass
stars.
Error vs magnitude graphs (reliability of data)
Magnitude distribution histograms
2-Color diagram, dereddening
2-point correlation analysis of spatial clustering
Ks luminosity function (KLF)
Initial Mass Function (IMF)
METHOD
OBSERVATIONS
& DATA REDUCTION
JHKs-bands on 1.4 m IRSF.
30s exposure
Reduction with the SIRIUS pipeline in IRAF
(Image Reduction & Analysis facility)
Stacked images  ~ 60min integration times.
METHOD
SELECTION OF STARS
Crowded field
Initially: Source Extractor
Problem: fixed apertures in crowded field – wrong
photometry.
Solution 1: Aperture corrected photometry – no
optimal aperture radius (graph of mag. vs. aperture radius)
Solution 2: PSF photometry:
In IRAF
Perform PSF fitting
photometry using
ALLSTAR
Extract stars with
DAOFIND in Daophot
(5 detection)
Compute PSF with PSF
task, using 20 stars
selected by PSTSELECT
18.500
J band
METHOD
Chart Title
18.000
y = 0.948x + 4.7947
R2 = 0.9967
17.500
IRSF magnitude
18.000
17.000
PHOTOMETRY
Ks band
16.500
17.500
2
15.500
17.000
15.000
17.400
16.500
14.500
17.200
14.000
17.000
10.000
y = 0.9691x + 4.396
R2 = 0.9968
10.500
11.000
11.500
12.000
16.000
16.800
IRSF magnitude
IRSF magnitude
y = 1.0299x + 4.7561
Calibrate by
subtracting
R = 0.9973
Used 2MASS (2 Micron All Sky
Stacked all images ofthe
one night
obtained constant
Survey) all-sky point source
 no specific airmass  need
Avg:
4.121
catalog
 40
of brightest stars
from
magnitudes
of
different calibration
method
H-band
Stddev: 0.066
with
coordinates
corresponding
than standard stars all IRSF stars
with results of Daofind
found by Daofind 
Apparent magnitude.
16.000
12.500
13.000
13.500
14.000
14.500
2MASS magnitude
16.600
Avg: 5.102
Stddev:
0.035
Get average
offset
between
16.400
15.500
16.200
EXTREMELY close linear
15.000correlation between
10.000
10.500
2MASS and
IRSF 11.000
magnitudes – confirmed
by a very small standard
deviation on the offsets.
16.000
15.800
15.600
15.400
15.200
11.000
11.500
2MASS and IRSF for each of the
12.000
12.500
13.000
Avg:
4.010 standard
40 stars &
calculate
2MASS magnitude
Stddev:
0.036
deviation.
11.500
12.000
12.500
2MASS magnitude
13.000
13.500
PRELIMINARY RESULTS
RELIABILITY OF DATA
Relative error for N counts =
N
1

N
N
Therefore as N , the relative error 
Magnitude = 2.5log  N  N  thus
Trend of relative error in counts v.s. counts
1
N
Error on magnitude 
1.2
Plot of magnitude-error vs magnitude 
inverse x-axis (minus sign).
1
1
N
vs. N with
1/sqrt(N)
0.8
0.6
0.4
0.2
0
0
50
100
150
N counts
200
250
300
PRELIMINARY RESULTS
RELIABILITY OF DATA
J-BAND
PRELIMINARY RESULTS
RELIABILITY OF DATA
H-BAND
PRELIMINARY RESULTS
RELIABILITY OF DATA
Ks-BAND
PRELIMINARY RESULTS
APPARENT MAGNITUDE DISTRIBUTIONS
Out of deep images & with the detection 20
of stars on 5  level
 Succeeded to detected very faint (low mass) stars
18.0
20.0
PRELIMINARY RESULTS
APPARENT MAGNITUDE DISTRIBUTIONS
17.0
19.5
PRELIMINARY RESULTS
APPARENT MAGNITUDE DISTRIBUTIONS
17.0
18.5
PRELIMINARY RESULTS
INTERSTELLAR REDDENING
Difference in magnitude due to dust: m(0) = m - A (1)
Reddening law (difference in intrinsic color due to reddening)
E(J - H) = 0.107Av
(2)
 [J - H] = [J – H]0 + 0.107 AV
Rieke &
Lebofsky
E(H - K) = 0.063Av
[H - K] = [H – K]0 + 0.063 AV
(3)
Slope of reddening lines: E(J-H) / E(H-K)
PRELIMINARY RESULTS
TWO-COLOR DIAGRAMS
MS & Giant branches
from Koorneef.
T Tauri Locus
(Meyer et. Al)
Reddening:
|| to reddening vector
(T Tauri due to disk)
Suggestions:
5 Av
• Maybe some stars are real: MS not infinitely narrow;
Lada et al. (1993) found ~50%  20% of cluster
shows
NIR excess.
Left
– photometric
err.
• New calibration constant for 5  detection level.
Problem:
• Remove “bad-pixels” detected as “faint stars”
5accuracy.
vs 15 2CD
• Investigate errors on color terms – indication of
Tauri:
(J-H)
= 0.580.11
 (H-K)
+ 0.52
 0.06lengths from center.
•T Two
point
correlation
– field stars
> 1-2
correlation
PRELIMINARY RESULTS
TWO-COLOR DIAGRAMS
Infrared excess
Embedded stars –
accretion disk / dust shell
FUTURE OBJECTIVES
Investigate strange T Tauri clustering on 2CD.
Determine location of T Tauri’s and IR excess stars
on image (dusty regions ?).
Two-point correlation.
Characterize population of stars:
KLS
IMF
RELEVANCE TO SKA
YSO & T Tauris still embedded  circumstellar
matter radiate in IR – distinguish b.m.o. IR excess in 2CD
Need to investigate star formation in IR at first to characterize
population
Expand to multi-wavelength
Radio complements IR:
Mapping
Some stars with IR excess have hotspots of ~ 7000K  can
get information about their rotation.
With better angular- & spatial resolution of SKA  distinct
between binary systems & stars currently indistinguishable
 get thermal radiation of individual T Tauris.
THANK YOU!!
Ps. 19:1 “The heavens declare the glory of
God; And the firament shows His
handiwork.”
STAR-FORMATION
Virial theorem: 2K  U  0
(1)
 condition for stable, gravitationally bound system.
If U  2K  gravitational collapse of molecular cloud
Gravitational potential energy:
Kinetic energy (monatomic gas):
Radius i.t.o. density:
 3M c 
Rc  

4

0 

1
3
3 GM c2
Ug ~ 
5 Rc
(2)
3
K  NkT
2
(3)
(4)
Ug, K and Rc into (1) with N  M c /  mH gives:
( = mean molecular weight)
 40 
3M c kT 3
 GM c2 

 mH
5
3
M
c 

1
3
(5)
RCW 34
Cometary shaped H II region
G264.29+1.47
3.1 kpc
Excited by O 9.5 Ib (O 8.5V) star (Vittone et al. & Heydari-Malayeri)
L = 5 x 105 L and R  23 R.
RCW 34
~ 3 kpc
L = 5 x 105 L and R  23 R.
Cometary shaped H II region.
Bright MSX & IRAS point source
(O 9.5 Ib) in front of ionization
front  excites H II region.
Molecular bar divided region into
3 regions: Dense, less dense &
diffuse.
Large IR excess  dust around
exciting star
Near-IR observations  star formation at
border of ionization front (Zavagno et al.)
Source
RCW 34
Bright MSX (Midcourse Space Experiment) & IRAS point
source in front of bright ionization front (Deharveng et al.).
Large IR excess 
dust around exciting star
Molecular bar divided into 3
regions:
Source
Dense, heated  post shock
Cold less dense  besides
Diffuse  in front of dense
parts (~102 per cm3 & 30-60K)
Near-IR observations  star formation at border of
ionization front (Zavagno et al.)
METHOD
TELESCOPE
1.4 m Infrared telescope at Sutherland
NIR camera  SIRIUS
Designed for deep & wide JHKs-bands simultaneous
surveys (1.25, 1.65, 2.2 m).
Images with 30s exposure time & total of 60 min
integration time per night.
METHOD
DATA REDUCTION
10 ditherings
of telescope
PRELIMINARY RESULTS
RELIABILITY OF DATA
of relative errorNin counts
Relative error for N Trend
counts
= N  1 v.s. counts
1.2
N
Therefore as N , the relative error 
1
Magnitude = 2.5log  N  N  thus
1/sqrt(N)
0.8
0.6
Error on magnitude 
0.4
1
N
Plot of magnitude-error vs magnitude 
inverse x-axis (minus sign).
0.2
1
N
vs. N with
0
0
50
100
150
200
250
300
N counts
Got “weird” stars with high error value at bright magnitudes
Extracted “weird” stars’ coordinates
Plot on image
Bad pixels / dust  explanation
PRELIMINARY RESULTS
INTERSTELLAR REDDENING
Difference in magnitude due to dust: m(0) = m - A (1)
change in intrinsic color due to reddening:
 A1 A 2 
m1 (0)  m 2 (0)  (m1  m 2 )  AV 


A
A
V 
 V
E(J – H) = 0.107Av
Known ratio:
Rieke &
Lebofsky
 [J - H] = [J – H]0 + 0.107 [H - K] = [H – K]0 + 0.063 AV
AV
FUTURE OBJECTIVES
Stellar clusters important in determination
of IMF  equidistant & co-eval populations of
stars  instantaneous sampling of IMF at
different epochs in Galactic history.