a near-infrared study of the southern star forming region rcw 34 lientjie de villiers m.sc. project...
TRANSCRIPT
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
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
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
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)
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 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
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.
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
PRELIMINARY RESULTSRELIABILITY OF DATA
J-BAND
PRELIMINARY RESULTSRELIABILITY OF DATA
H-BAND
PRELIMINARY RESULTSRELIABILITY OF DATA
Ks-BAND
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
PRELIMINARY RESULTSAPPARENT MAGNITUDE DISTRIBUTIONS
17.0
19.5
PRELIMINARY RESULTSAPPARENT MAGNITUDE DISTRIBUTIONS
17.0
18.5
(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)
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.
PRELIMINARY RESULTSTWO-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: (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)
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.
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
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)
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
SIRIUS pipeline
10 ditherings of telescope
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
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
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.