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AN UNUSUAL T TAURI ABUNDANCE IN THE SOUTHERN HIGH MASS STAR FORMING REGION RCW 34

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AN UNUSUAL T TAURI ABUNDANCE IN THE SOUTHERN HIGH MASS STAR FORMING REGION RCW 34. Lientjie 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

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AN UNUSUAL T TAURI ABUNDANCE IN THE SOUTHERN HIGH MASS STAR FORMING REGION RCW 34

Lientjie de Villiers

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

slide2

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
slide3

T Tauri Pre-main sequence star

Pre-stellar core

Molecular cloud

Infrared protostar

STAR FORMATION

slide4

CLASS 0:

Main accretion phase

Age 104 yr

M  0.5 Mo

CLASS I:

Late accretion phase

Age ~105 yr

M  0.1 Mo

CLASS II:

Optically thick disk

Age ~106 yr

Mdisk  0.01 Mo

STAR FORMATION

slide5

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)

slide6

RESULTS: Two-colour diagram

  • “Clustering”
  • 10 < Av < 15
  • Not MS – too massive
  • CTT locus  lower boundary
slide8

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
slide9

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

Numerical formula:

9Peebles (1976)

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RESULTS: Two-point correlation analysis

  • Significant clustering until 260 pixels (~ 2’)
  • Clustering shows for T Tauri’s too  spatial correlation
slide11

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)
slide12

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

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

slide13

RESULTS: Colour-Magnitude diagram

  • Similar to HR-diagram. Verify
  • T Tauri location.
slide14

RESULTS: Colour-Magnitude diagram

  • Reddening too much for MS – must be PMO’s
  • T Tauri’s located where expected: M* < 2Mo
slide15

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)

slide16

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)

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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)

slide18

CONCLUSIONS

  • Two 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.

slide19

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.
slide20

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)

slide21

THANK YOU!

Ps. 147:4

“He determines and counts the number of the stars;

He calls them all by their names”

slide23

RCW 34

(G264.29+1.47)

  • Cometary shaped H II region3 kpc in the region of Vela R2 with AV = 4.2 mag1.
  • Ionization front with bright point source: 12th mag PMS O-starL = 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)

slide24

10 ditherings

of telescope

METHOD

DATA REDUCTION

SIRIUS pipeline

slide25

RESULTS

CMD - 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”
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