a near-infrared study of the southern star forming region rcw 34 lientjie de villiers m.sc. project...
TRANSCRIPT
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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
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CONTENTS
Star-formation
The region RCW 34
M.Sc. Objectives
Method
Preliminary results
Future objectives
Relevance to SKA
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From above the Jeans criterion can be derived as where the Jeans mass MJ is given by the
RHS of (1).
STAR-FORMATION
13
22
0
5 3
4cH
kTM
G m
c JM M
Molecular cloudPre-stellar core
Infrared protostar
T Tauri Pre-main
sequence star
From the Virial theorem, if gravitational collapse of molecular cloud.
2U K
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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
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OBJECTIVESStudy 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)
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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.
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METHOD
SELECTION OF STARS
Crowded field
Initially: Source Extractor
Problem: fixed apertures in crowded field – wrong photometry.
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Solution 1: Aperture corrected photometry – no optimal aperture radius (graph of mag. vs. aperture radius)
Solution 2: PSF photometry:
In IRAFExtract stars with
DAOFIND in Daophot (5 detection)
Compute PSF with PSF task, using 20 stars
selected by PSTSELECT
Perform PSF fitting photometry using
ALLSTAR
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METHOD
PHOTOMETRY
Stacked all images of one night no specific airmass need
different calibration method than standard stars
Used 2MASS (2 Micron All Sky Survey) all-sky point source
catalog 40 of brightest stars with coordinates corresponding
with results of Daofind
Get average offset between 2MASS and IRSF for each of the
40 stars & calculate standard deviation.
EXTREMELY close linear correlation between
2MASS and IRSF magnitudes – confirmed by a very small standard deviation on the offsets.
Calibrate by subtracting the obtained constant from magnitudes of
all IRSF stars found by Daofind Apparent magnitude.
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PRELIMINARY RESULTSRELIABILITY OF DATA
Relative error for N counts =
Therefore as N , the relative error
Magnitude = thus
Error on magnitude
Plot of magnitude-error vs magnitude vs. N with inverse x-axis (minus sign).
1N
N N
2.5log N N
1
N 1
N
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PRELIMINARY RESULTSRELIABILITY OF DATA
J-BAND
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PRELIMINARY RESULTSRELIABILITY OF DATA
H-BAND
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PRELIMINARY RESULTSRELIABILITY OF DATA
Ks-BAND
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18.0
20
PRELIMINARY RESULTSAPPARENT MAGNITUDE DISTRIBUTIONS
Out of deep images & with the detection of stars on 5 level Succeeded to detected very faint (low mass) stars
20.0
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PRELIMINARY RESULTSAPPARENT MAGNITUDE DISTRIBUTIONS
17.0
19.5
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PRELIMINARY RESULTSAPPARENT MAGNITUDE DISTRIBUTIONS
17.0
18.5
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(2)
PRELIMINARY RESULTSINTERSTELLAR 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
[J - H] = [J – H]0 + 0.107 AV Rieke &
LebofskyE(H - K) = 0.063Av
[H - K] = [H – K]0 + 0.063 AV
Slope of reddening lines: E(J-H) / E(H-K)
(3)
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PRELIMINARY RESULTSTWO-COLOR DIAGRAMS
T Tauri: (J-H) = 0.580.11 (H-K) + 0.52 0.06
MS & Giant branches
from Koorneef.
T Tauri Locus
(Meyer et. Al)
Reddening:
|| to reddening vector
(T Tauri due to disk)
5 Av
Left – photometric err.
Problem: 5 vs 15 2CD
Suggestions:• Maybe some stars are real: MS not infinitely narrow; Lada et al. (1993) found ~50% 20% of cluster shows NIR excess.• New calibration constant for 5 detection level.• Remove “bad-pixels” detected as “faint stars”• Investigate errors on color terms – indication of accuracy.• Two point correlation – field stars > 1-2 correlation lengths from center.
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PRELIMINARY RESULTSTWO-COLOR DIAGRAMS
Infrared excess
Embedded stars –
accretion disk / dust shell
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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
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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.
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THANK YOU!!
Ps. 19:1 “The heavens declare the glory of God; And the firament shows His
handiwork.”
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STAR-FORMATION Virial theorem: (1)
condition for stable, gravitationally bound system.
2 0K U
/c HN M m Ug, K and Rc into (1) with gives: ( = mean molecular weight)
(5)
1
32 03 43
5 3c
cH c
M kTGM
m M
2U K23
~5
cg
c
GMU
R
3
2K NkT
1
3
0
3
4c
c
MR
If gravitational collapse of molecular cloud
Gravitational potential energy: (2) Kinetic energy (monatomic gas): (3)
Radius i.t.o. density: (4)
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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.
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RCW 34
~ 3 kpc L = 5 x 105 L and R 23 R. Cometary shaped H II region.
Near-IR observations star formation at
border of ionization front (Zavagno et al.)
Source
Molecular bar divided region into 3 regions: Dense, less dense & diffuse.
Bright MSX & IRAS point source (O 9.5 Ib) in front of ionization front excites H II region.
Large IR excess dust around exciting star
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RCW 34 Bright MSX (Midcourse Space Experiment) & IRAS point
source in front of bright ionization front (Deharveng et al.).
Near-IR observations star formation at border of ionization front (Zavagno et al.)
Source
Large IR excess dust around exciting star
Molecular bar divided into 3
regions:
Dense, heated post shock
Cold less dense besides
Diffuse in front of dense parts (~102 per cm3 & 30-60K)
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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.
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METHOD
DATA REDUCTION
SIRIUS pipeline
10 ditherings of telescope
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Got “weird” stars with high error value at bright magnitudes
Extracted “weird” stars’ coordinates
Plot on image
Bad pixels / dust explanation
PRELIMINARY RESULTSRELIABILITY OF DATA
Relative error for N counts =
Therefore as N , the relative error
Magnitude = thus
Error on magnitude
Plot of magnitude-error vs magnitude vs. N with inverse x-axis (minus sign).
1N
N N
2.5log N N
1
N 1
N
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PRELIMINARY RESULTSINTERSTELLAR REDDENING
Difference in magnitude due to dust: m(0) = m - A (1) change in intrinsic color due to reddening:
1 21 2 1 2(0) (0) ( ) V
V V
A Am m m m A
A A
E(J – H) = 0.107Av
[J - H] = [J – H]0 + 0.107 AV
Known ratio: Rieke &
Lebofsky
[H - K] = [H – K]0 + 0.063 AV
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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.
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