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Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 1 Structure and kinematics.

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Presentation on theme: "Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 1 Structure and kinematics."— Presentation transcript:

1 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 1 Structure and kinematics of the Gould Belt from Hipparcos Data Francesca Figueras, Jordi Torra, David Fernández Universitat de Barcelona

2 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 2 Barcelona work Praga (97)  Garching (01) Kinematics of young stars. I. Local Irregularities (GB structure and kinematics) Torra, J., Fernández, D., Figueras, F., A&A 359, 82 (2000) On the evolution of moving groups: an aplication to Pleiades moving group Asiain, R., Figueras, F., Torra, J., A&A 350, 434 (1999) Kinematics of young stars. II. Galactic Spiral Structure Fernández, D., Figueras, F., Torra, J., A&A 372, 833 (2001) Young stars in the nearest solar neighbourhood Fernández, D., Figueras, F., Torra, J. (Garching, tomorrow)

3 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 3 Before Hipparcos data Poppel review 1997 The stellar component of the Gould’s belt from Hipparcos data: GB: Venice’s 97, Palous (98), Torra et al. (99), Lindblad (00), Alfaro et al. (00) OC and Assocciations: De Zeeuw et al (99), Robichon et al. (99), Brown (01) X-ray & RASS-Tycho data: Guillout, Sterzik, Neuhauser,.. High energy sources Gehrels, Grenier The stellar component of the Gould’s belt

4 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 4 Working sample : 6922 O and B stars Data compilation: Astrometric Data (Hipparcos) photometric data (H&M,98) radial velocities (Grenier, 1997 + Barbier-Brossat, 2000) Careful treatement of: Stellar distances Radial velocities Stellar ages

5 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 5 Stellar distances Trigonometric and/or Photometric (individual error evaluation)  the one with smallest error Trigonometric distances accepted only if  /  < 25 %: Photometric distances (Crawford,75) : nos systematic trends for   /  < 15 % “For distances estimated as R = 1/ , a symmetric error law for parrallaxes results in a non-symmetric, biased distribution for distances” The bias is: always less than 5.5 % Smaller than 3 % for 88 % of the stars Distance bias smaller than 5 pc for 82 % of the stars

6 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 6 Stellar radial velocities (for 3397 stars) Possible kinematic bias: Binney & Merrifield (1998): “Due to observational programmes: radial velocity availability is higher for high proper motion stars” Higher degree of completeness for distant stars The fraction is not a flat function kinematic bias present in our sample  Needs for evaluation through numerical simulations

7 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 7 Stellar ages (for 2864 stars) Individual ages from photometry, using evolutionary models of Bressan et al (1993) Bias (F&B,98): over-estimation on 30-50 % due to stellar rotation (not taken into account in the models) Careful treatement with the aim of retaining as many as possible of the very young stars To be considered when deriving GB age

8 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 8 Initial Sample 6922 Hipparcos stars. Vlim ~ 8 Stroemgren Photometry 3031 stars Radial Velocity 3397 stars Sample 1 3915 stars r,  Completeness V lim ~ 6.5 = 0.60 mas = 0.16 = 0.83 mas /yr = 0.70 mas/yr 2468 if ages are considered Sample 2 2272 stars r, , vr Completeness V lim ~ 6.5 = 0.57 mas = 0.16 = 0.81 mas/yr = 0.67 mas/yr = 3.44 km/s 1789 if ages are considered Working samples

9 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 9 Structural parameters of the Gould Belt Method: Comerón et al. (1994) + iteration until convergence Requirement: homogeneous completeness of the sample over the celestial sphere Numerical simulations to evaluate biases and to estimate errors on parameters Critical questions to answer: Older stars have a small limiting distance: Can our method be able to detect an inclined structure if present? For which scale heigh of the belts our method looses its statistical capability? Are the available number of stars enough to undertake this study? Realistic error estimation from simulations.

10 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 10 Simulations for the structure analysis > 30 Myr 30 – 60 Myr > 60 Myr Z o = 40 pcZ o = 80 pc Conclusions: The angular halfwidths correctly reflect the growth of the scale heigh of the simulated belts (  2-5 o ) q is well recovered though with  0.13-0.17 There is a presence of a small systematic trend in (i G,  G ) when increasing Z o (always smaller that the errors) For old stars, when forcing and inclination of 20 o, there is a probability less than 5 % to obtain a null inclination ( i G,  4 o, as in the real sample)

11 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 11 Structural parameters of the Gould Belt GB extended up to 600 pc GB orientation i G = 16-22 o,  p = 275-295 o, depending on age GB is narrow than the Galactic Belt For R < 600pc : 60 % of stars younger than 60 Myr belong to the GB The inclination i = 27.5 o +/- 1 o (Guillot et al., 1998, RASS- Tycho) is not compatible with our results (very nearby sample possible influenced by the Sco-Cen)

12 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 12 Kinematic model & resolution procedure Model: First order development of the systematic velocity field (A,B,C,K) Palous (98): “the second-order terms have low significance” No systematic motion perpendicular to the galactic plane Solutions for V , (  l +  b ), (V  +  l +  b ) Resolution procedure: Weighted least squares Weights: (  2 i, obs +  2 i, cos ) -1 : individual observational errors (considering correlations) cosmic residual velocity dispersion ellipsoid Iterative process: simultaneous determination of model parameters and cosmic dispersion obtained  cos increasing with age, close to Wielen (77) values  cos effects in solar motion and Oort Constants are  0.5 km/s/kpc

13 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 13 Detailed treatement Possible biases in the fitting parameters induced by: observational constraints - irregular spatial distribution of the stars - incompleteness effects - biases in the availability of radial velocities the presence of observational errors in the right hand side of equations, not considered in a WLS fit) Correlation among variables Numerical experiments to globally evaluate all these effects

14 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 14 Simulations for kinematic analysis Case 1: Pseudostars with real spatial and Vr distribution + errors in Vr and  Case 2: Case 1 + error in distances Case 3: Case 2 + rejection criteria Expected biases in the combined solution: 100 < R < 600 pc: biases of A  + 0.5 on B,  - 0.8 on B. C & K negligible Solar motion  0.3, 0.4 km/s 600 < R < 2000 pc : A,C,K negligible, B  + 0.9 Solar motion  + 0.3, 0.4 km/s No bias from the rejection criteria Lack of radial velocity data: bias  0.2 km/s/kpc

15 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 15 Results A long standing problem: Discrepances in the A Oort contant between solutions from radial velocities and from proper motions: Real Data:  A  2-3 km/s/kpc Crézé(1970): error in distance  underestimation in A from radial velocity equations Our simulations  this effect is less important than the distance cut Feast et al. (1998): no bias was present with the new distance scale From our simulations: A bias of  1,1.5 km/s/kpc is present in the opposite sense  even enlarge the difference An overestimation in our photometric distances by 20 % (rotation effects)  account only for a difference of 1-2 km/s/kpc The discrepance is not due to the irregular spatial distribution of the stars Atributted to the departure of some stellar groups from the adopted linear model (removing stars 200 < l<250 o the discrepance in A  vanishes,  2 statistics improve)

16 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 16 Results Discrepances in V o (   4 km/s between Vr & proper motion solution:: It remains when eliminating some particular regions From our simulations  No effect from irregular distribution of stars Again, Atributted to local departure from the linear model (MG?) Correlations: Are small in all cases (vr,  + , vr +  +  ) Not the cause of differences in vr,  +  The combined solution presents the smallest correlations The largest  2 value comes from radial velocity (not in the simulations), due to underestimation of errors in vr or to  cos determination.

17 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 17 Kinematics of young stars: the global behaviour 600 < R < 2000 pc U o = 9.0 +/- 0.8 V o = 13.4 +/- 0.7 W o = 8.3 +/- 0.5 A = 13.0 +/- 0.7 B = -12.1 +/- 0.7 C = 0.5 +/- 0.8 K = -2.9 +/- 0.6 Bias expected from simulations: (U,V,W) underestimated in  0.4 km/s B underestimated in  0.8 km/s/kpc Our resuts indicate a tendency to obtain lower values of A when the distance horizon of the sample is approached. The same for: Feast et al. (1998), Cepheids: A = 15.1 +/- 0.3 Hanson (1987), nearby stars: A = 11.3 +/- 1.1 Explanation: Oling & Merrifield (1998): variation of Oort constants as a function of galactocentric distance Our resuts indicate near null values for C & K: pure differential rotation, in good agreeement with Lindblad et al. (1997): C = 0.8 +/- 1.1, K = -1.1 +/- 0.8

18 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 18 Variations of Oort parameters with age A increase of A,B with age A decrease of C,K with age GB age from kinematic behaviour = GB age from spatial distribution GB age = (30-60) Myr 100 < R < 600 pc

19 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 19 Oort constants when excluding Sco-Cen and Ori OB1 These associations are not the only responsible for the peculiar kinematics observed for the youngest stars and attributed to the Gould Belt The GB is not a casual arrangement of these two associations Excluded:ABCK None 5.7 (1.4) -20.7 (1.4) 5.2 (1.4) 7.1 (1.4) Sco-Cen 6.9 (1.6) -19.7 (1.6) 4.7 (1.6) 5.8 (1.6) Ori OB1 6.1 (1.6) -20.7 (1.6) 5.3 (1.6) 6.3 (1.6) Both Complexes7.2 (1.8) -19.7 (1.8) 4.9 (1.9) 6.0 (1.9) The two main complexes in the GB Stars selected from Brown et al. (1994; Ori OB1), de Zeeuw et al. (1999; Sco-Cen) 100 < R < 600 pc, age < 30 Myr

20 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 20 Expansion of the system as a function of distance Variation of KR as a function of heliocentric distance (stars with  < 60 Myr) The expansion diminish rapidly with increasing distance for R < 250 pc At R > 300 pc only Per OB2 has a mean residual motion away from the Sun Ori OB1 has an almost null radial residual motion (U,V,W) res = (-1.2, -2.8, 2.1) km/s

21 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 21 Residuals, local irregularities OB stars  < 60 Myr: residual space velocity vectors  < 150 pc 150 <  < 300 pc Olano’s ring (t=0) Breitschwerdt et al. (2000) Loop I + LB A well defined concentration of OB stars in 225 o a large number of field OB spread in a large area

22 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 22 Residuals, local irregularities OB stars  < 60 Myr: residual space velocity vectors  < 150 pc 150 <  < 300 pc Olano’s ring (t=0) A well defined concentration of OB stars in 225 o a large number of field OB spread in a large area

23 Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 23 Residuals, local irregularities Distribution of OB stars in 225 o { "@context": "http://schema.org", "@type": "ImageObject", "contentUrl": "http://images.slideplayer.com/2519481/9/slides/slide_22.jpg", "name": "Structure and kinematics of the Gould Belt from Hipparcos Data Oct 24, 2001 The Gould Belt and other large star forming complexes 23 Residuals, local irregularities Distribution of OB stars in 225 o


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