AN UNUSUAL T TAURI ABUNDANCE IN THE SOUTHERN HIGH MASS STAR FORMING REGION

RCW 34Lientjie de Villiers

M.Sc. PROJECT SUPERVISOR: Prof. D.J. van der Walt

CONTENTS

Star-formation

T Tauri star?

Results: Colour-colour diagram Two-point correlation

analysis Colour-magnitude diagram Colour Cut K-band luminosity function

Conclusions

Future prospects & Relavance to Meerkat

STAR FORMATION

Molecular cloud

Pre-stellar core

Infrared protostar

T Tauri Pre-main

sequence star

STAR FORMATION

CLASS 0:Main accretion phase

Age 104 yrM 0.5 Mo

CLASS I:Late accretion phase

Age ~105 yrM 0.1 Mo

CLASS II:Optically thick disk

Age ~106 yrMdisk 0.01 Mo

T TAURI STAR? PMS stars near Molecular Clouds

< 2 Mo; 1-4 Myr

RTTauri > RMS for same mass more luminous

No H-fusion; Powered by gravitational energy

Accretion Optical & UV excess emission

IR excess circumstellar disk

Magnetic field starspots & excess X-ray & Radio emission

Hartmann (1998); Appenzeller & Mundt (1989)

RESULTS: Two-colour diagram

“Clustering”

10 < Av < 15

Not MS – too massive

CTT locus lower boundary

RESULTS: Two-colour diagram

RESULTS: Two-colour diagram

Appears to be T Tauri stars on 2CD BUT background stars on coordinate plot.

VERIFY!!

Two-point correlation function

Colour-magnitude diagram

Slope of KLF

RESULTS: Two-point correlation analysis

Definition:

Two-point correlation function (r12): the probability that points appear in each of the volume elements dV1 and dV2 at separation r12,

Poisson process: = 0

Significant clustering: > 0

9Peebles (1976)

Numerical formula:

RESULTS: Two-point correlation analysis

Significant clustering until 260 pixels (~ 2’)

Clustering shows for T Tauri’s too spatial correlation

RESULTS: Two-point correlation analysis

As for galaxies, with highly non-linear clustering: TPCF ~ declining power-law for Taurus-Auriga

(Gomez et al., 1993)

(r0 = correlation length).

Fitted a power-law on TPCF of RCW 34 too. (5 pix binning i.s.o. 20 pix reveal trends on

small scales)

0

( )r

rr

RESULTS: Two-point correlation analysis Twice-broken power-

law for Taurus1

2 of the 3 parts seen for RCW 34

Correspondence between slopes & transitions (knees)

2nd “knee”: between random distribution of ass. members primordial structure

2nd knee indicate Jeans length for ~1Mo

core formation2 agree

with T Tauri distribution

TAURUS RCW 34

SLOPE – INTERM.

0.12 -0.95

SLOPE – LARGE 0.10 -0.84

2nd KNEE 0.18 pc 0.26 pc

1 Krauss & Hillenbrand (2008), 2Larson (1995)

RESULTS: Colour-Magnitude diagram

Similar to HR-diagram. Verify T Tauri location.

RESULTS: Colour-Magnitude diagram

Reddening too much for MS – must be PMO’s

T Tauri’s located where expected: M* < 2Mo

RESULTS: Color-Cut

No control fields observed – needed for KLF.

Different method: colorcut4

Take all stars bluer than a combined isochrone as a statistical “control field”

3 Harayama (2008)

RESULTS: K-band Luminosity Function

KLF is given by

Slope of logarithmic KLF for RCW 34: = 0.31

About 50% of the members of the young cluster NGC 2264 are CTTs.

KLF slope of NGC 2264 is 0.32 ± 0.04

Relation between CTT abundance and ? Need Spec.

4 Lada et al. (1993)

RESULTS: KLF and age

NGC 2264 ~ 5 Myr4 serve as an estimate for the age

of RCW 34, providing the apparent similar stellar populations in both clusters.

IC 348, showed a population of emission-line stars, with

an age representing a star formation duration of 3Myr, centered on the cluster core5,6.

Herbig (1998) suggested that this very young cluster is superimposed on a more broadly distributed non- emission-line population that permeates the region of IC 348, with an age representing star formation of 1 − 10 Myr ago.

4 Lada et al. (1993), 5Herbig (1998), 6Luhman (1998)

CONCLUSIONSTwo different stages of star formation in RCW 34:

1st stage: originated from a surrounding MC with dimensions > image frame that lower mass star formation the older population of T Tauri stars separated by Jeans length of dense cores. T Tauri ages are around 1 - 4 Myr parts of the cloud had already been destroyed leave the T Tauri’s exposed

2nd stage: H II region appears to be part of the remaining core of the larger MC star formation was triggered a 2nd time at a later stage formation of the central young massive star shock formed by this exciting, high mass star trigger for on-going star formation at the ionization front young stars sources that show a NIR excess on the 2CD.

It appears as if star formation in RCW 34 is not coeval.

FUTURE PROSPECTS

Confirm results with:

Spectroscopy.

Surrounding fields obtained from sky surveys (2MASS / VISTA?(deeper)): are cluster borders detected?

Analyze optical data multi wavelength info on RCW 34.

Construct IMF – number of low mass stars expected?

Collaboration with Dr. Lucas – use Synthetic Besançon Stellar Population Models to model this field. Preliminary result: T Tauri cluster on 2CD is indeed due to

a mixture of cluster members and field dwarfs.

RELEVANCE TO MEERKAT

Confirm the nature of the possible T Tauri stars with the deeper survey of MeerKAT.

Radio-mapping of RCW 34’s molecular cloud obtain its real shape and dimensions?

With better angular- & spatial resolution of SKA distinguish between binary & multiple systems at small spatial scales – fill in the missing first part of TPCF power law.

ROSAT discovered 91 T Tauri stars in the vicinity of the Taurus- Auriga star-forming region. 17-29 of them were also detected by an 8.4 GHz VLA survey with a sensitivity limit of ~ 0.15 mJy7.

7Mamajek et al. (1996)

THANK YOU!

Ps. 147:4

“He determines and counts the number of the stars;

He calls them all by their names”

RCW 34 (G264.29+1.47)

Ionization front with bright point source: 12th mag PMS O-star L = 5 x 105 L and R 23 R

2.

Large IR excess dust around exciting star.

1 Deharveng et al. (2005) & Heydari-Malayeri (1988); 2 Vittone et. Al. (1987)

Cometary shaped H II region

3 kpc in the region of Vela R2 with AV = 4.2 mag1.

METHOD

DATA REDUCTION

SIRIUS pipeline

10 ditherings of telescope

RESULTSCMD - COLORCUT

No control fields – needed for KLF.

Different method: colorcut (Harayama, 2008)

Combined isochrone: smooth turnover points between: 0.7 Myr PMS 1 Myr low-mass (1.2 Mo) PMS 2.5 Myr MS

Take all stars bluer than isochrone as “control field”