Young stars in the nearest solar neighbourhood

1. Young stars in the nearest solar neighbourhood David Fernández, Francesca Figueras, Jordi Torra Departament d’Astronomia i Meteorologia Universitat de Barcelona The Gould Belt and other large star forming complexes

2. Stellar trajectories Observations: Theory: The young stellar component Models Gas & diffuse X-ray distribution Work in progress, Fernández PhD thesis The Gould Belt and other large star forming complexes

3. The young stellar component in the solar neighbourhood • Individual objects (Hipparcos data): • T Tauri stars (Frink 1998) • O-B stars (Fernández 1998, Torra et al. 2000) • X-ray G5 V stars (age from Lx) • Groups: • Young local associations (compilation, several authors) • OB associations (de Zeeuw et al. 1999) • Moving groups (Asiain et al. 1999) The Gould Belt and other large star forming complexes

4. Gas & diffuse X-ray distribution in the solar neighbourhood (I) Local bubble (LB): Low density (~0.005 cm-3) region filled with hot gas (~106 K), responsible for an important fraction of the 1/4 keV emission (soft X-rays) Not completely filled? ð Local cavity + Local bubble Snowden et al. (1998), Egger (1998): Distribution of the diffuse soft X-ray background Sfeir et al. (1999): Distribution of the neutral gas in the LISM (X,Y), (X,Z), (Y,Z) maps ð Elongated to high galactic latitudes, and tilted perpendicular to the Gould Belt’s plane The Gould Belt and other large star forming complexes

5. Gas & diffuse X-ray distribution in the solar neighbourhood (II) Loop I & Local bubble: Loop I is still an active superbubble, hotter (2.5·106 K) and denser (0.015 cm-2) than the LB ð Pressure higher than in the LB HI “wall” (NH > 1020 cm-2) between both at R ~ 40 pc Breitschwerdt et al. (2000): Study of the hydromagnetic instability caused by the interaction between the LB and Loop I Schematic representation of the interaction Other bubbles: Heiles (1998): GSH 238+00+09 major superbubble toward l ~ 238o The Gould Belt and other large star forming complexes

6. Some models in the literature Olano (1982): Gould Belt as an expanding ring of gas Pöppel & Marronetti (2000): Explosive event 35 Myr ago at R ~ 120 pc, (l,b) ~ (140º,16º) (Olano’s model 1) consistent with kinematics of CNM Inclusion of three young disturbance centers in the model: Orion, Hercules and Loop I Olano (2001): The origin of the local system of gas and stars ð rotating supercloud ~2·107 M and ~400 pc Sirius supercluster (500 Myr ago) + Gould Belt + Local arm (after collision with a main spiral arm 100 Myr ago) The Gould Belt and other large star forming complexes

7. Stellar trajectories • Galactic potential: • General axisymmetric potential (Allen & Santillán 1991) • Bulge + disk + halo (Ro= 8.5 kpc, o= 220 km s-1) • Spiral arm perturbation (Fernández et al. 2001): • p= 30 km s-1 kpc-1 ; i = -6o, m = 2, = 330o • Central bar potential (triaxial ellipsoid, Palous et al. 1993): • b = 70 km s-1 kpc-1 • Method: • Integration of the equations of motion (fourth order Runge-Kutta) • Coordinates: • (x,h,z): Rotating Local Standard of Rest The Gould Belt and other large star forming complexes

8. OB associations in Scorpius-Centaurus Relation with Loop I superbubble (age ~ 10 Myr): stellar winds and supernovae Responsible for the origin of the Local Bubble? (Maíz-Apellániz 2001, Berghöfer & Breitschwerdt 2001) Data from de Zeeuw et al. (1999): The Gould Belt and other large star forming complexes

9. Evolution of the OB associations in Scorpius-Centaurus (I) (-15) -age < t < 0 Myr • Orbits very similar to Maíz-Apellániz (2001), although in our case they concentrate more in space • Expected number of past SNe: • LCC 6 • UCL 13 • US 1 • SNe of LCC responsible for the creation of the LB But there is a great spatial asymmetry (too much?) Olano’s model t = -31 Myr t = -20 Myr t= -10 Myr Present LCC UCL US The Gould Belt and other large star forming complexes

10. Evolution of the OB associations in Scorpius-Centaurus (II) (-15) -age < t < 0 Myr UCL • A little confusing projection since the associations are not placed on the (x,z) plane • UCL and US are not so distant from the LB! US LCC The Gould Belt and other large star forming complexes

11. Evolution of the Pleiades moving group The youngest moving group in the solar neighbourhood Substructures found in Asiain et al. (1999): Hipparcos data (O-B-A stars) + non parametric technics (U,V,W,age) B1: composed by Sco-Cen OB association members B2: seems to be the superposition of several OB associations from the Gould Belt B3 and B4:birthplace close to the minimum of the spiral arm potential The Gould Belt and other large star forming complexes

12. Evolution of the B2 substructure - Pleiades MG (I) t = 0 (at present) Olano’s model (t = 0) The Gould Belt and other large star forming complexes

13. Evolution of the B2 substructure - Pleiades MG (II) t = -10 Myr Olano’s model (t = -10 Myr) The Gould Belt and other large star forming complexes

14. Evolution of the B2 substructure - Pleiades MG (III) t = -20 Myr Olano’s model (t = -20 Myr) The Gould Belt and other large star forming complexes

15. Evolution of the B2 substructure - Pleiades MG (IV) t = -30 Myr Olano’s model (t = -31 Myr) The Gould Belt and other large star forming complexes

16. Evolution of the B1 + B2 substructures (Pleiades MG) • Kernel function of the superposition of orbits B1 + B2 individual members back on time • Center at (x,y) = (60,10) • R = 61 pc, l = 10o • Pöppel’s model (2001): • Single isotropic disturbance centers: • Orion (R,l,b) = (200, 195,-40) • Hercules (R,l,b) = (145, 45, 35) • Loop I (R,l,b) = (210, 330, 35) GR GC The Gould Belt and other large star forming complexes

17. T Tau stars in Taurus-Auriga and Chamaeleon • Data from Frink (1999): • Only Hipparcos stars • Proper motions from Hipparcos / PPM / ACT/TRC / STARNET catalogues • Radial velocities from several sources • Taurus-Auriga: • ~150 pre-ROSAT + 86 new members • Two regions with different spatial distribution and proper motions • At present the south group is moving towards the central region, but it is possible an scenario with a common origin if Mcloud > 2·105 M The Gould Belt and other large star forming complexes

18. Evolution of the T Tau stars in Taurus-Auriga -15 < t < 0 Myr Olano’s model t = -31 Myr t = -20 Myr t= -10 Myr Present The Gould Belt and other large star forming complexes

19. Evolution of the T Tau stars and clouds in Taurus-Auriga -15 < t < 0 Myr Olano’s model t = -31 Myr t = -20 Myr t= -10 Myr Present The Gould Belt and other large star forming complexes

20. T Tau stars in Taurus-Auriga and Chamaeleon • Chamaeleon: • 178 ROSAT sources • Age ~ 5 Myr (Cha I) • Stars around the Chamaeleon cloud complex, although there are many weak-line T Tau stars up to 50 pc away the cores of SFR • Two proposed scenarios: • Star formation at cloud cores, with a later ejection (Sterzik & Durisen 1995) • ð Stellar velocities should have a common origin • Star formation in dispersed cloudlets which disappear after the formation process (Feigelson 1996) • ð Relative velocities between groups can be large • It seems there are at least two subgroups, at 170 pc and 90 pc (Frink 1999) • A third subgroup at 130 pc? The Gould Belt and other large star forming complexes

21. Evolution of the T Tau stars in Chamaeleon -15 < t < 0 Myr Olano’s model t = -31 Myr t = -20 Myr t= -10 Myr Present The Gould Belt and other large star forming complexes

22. New young associations near the Sun (I) The Gould Belt and other large star forming complexes

23. New young associations near the Sun (II) The Gould Belt and other large star forming complexes

24. Evolution of the new young associations (I) -age < t < 0 Myr The Gould Belt and other large star forming complexes

25. Evolution of the new young associations (II) • From these orbits back in time... • May be these local associations the responsible (at least in part) for the origin of the Local bubble? • Smith & Cox (2001): Origin of the LB from 2-3 SNe in the diffuse interstellar medium • At present no stars earlier than B2.5V (~ 9 M), but there are some B7-B9.5 (~ 3-4 M) • May more massive stars be exploded as SNe in the last few Myr? • In this way some explosions would took place in a nearly central region of the LB • This could be a more realistic description of the present spatial geometry of the LB The Gould Belt and other large star forming complexes

26. Conclusions: First results and work in progress • Compilation of data for young stars • New young stars: • Local associations ðhundreds of young stars very near the Sun, inside the Local bubble • G5V stars, ROSAT sources, with good ages (future work) • Stellar trajectories: • Most of the orbits for stars in the nearest solar neighbourhood concentrate back in time in the first galactic quadrant: 100 < x < 200 pc, 0 < h < 100 pc • ð Common origin for all of them? • ð Comparison with Olano’s model: origin from a rotating supercloud (future work) • T Tau stars: A subgroup in Tau-Aur follows Taurus cloud motion (from l ~ 270º) • Local associations might be (partial) responsible for the origin of the Local bubble • ð Spatial geometry of the Local bubble could be explained in a more natural way • Galactic potential: • Implementation of bracking forces for specific scenarios (future work) The Gould Belt and other large star forming complexes