a near-infrared study of the southern star forming region rcw 34 lientjie de villiers m.sc. project...

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.