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

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

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  1. 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

  2. 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

  3. T Tauri Pre-main sequence star Pre-stellar core Molecular cloud Infrared protostar STAR FORMATION

  4. 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

  5. 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)

  6. RESULTS: Two-colour diagram • “Clustering” • 10 < Av < 15 • Not MS – too massive • CTT locus  lower boundary

  7. RESULTS: Two-colour diagram

  8. 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

  9. 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)

  10. RESULTS: Two-point correlation analysis • Significant clustering until 260 pixels (~ 2’) • Clustering shows for T Tauri’s too  spatial correlation

  11. 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)

  12. 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)

  13. RESULTS: Colour-Magnitude diagram • Similar to HR-diagram. Verify • T Tauri location.

  14. RESULTS: Colour-Magnitude diagram • Reddening too much for MS – must be PMO’s • T Tauri’s located where expected: M* < 2Mo

  15. 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)

  16. 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)

  17. 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)

  18. 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.

  19. 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.

  20. 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)

  21. THANK YOU! Ps. 147:4 “He determines and counts the number of the stars; He calls them all by their names”

  22. 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)

  23. 10 ditherings of telescope METHOD DATA REDUCTION SIRIUS pipeline

  24. 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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