Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 1 Young stars in the nearest solar neighbourhood David Fernández, Francesca Figueras, Jordi Torra Departament d’Astronomia i Meteorologia Universitat de Barcelona

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 2 The young stellar component Gas & diffuse X-ray distribution Models Work in progress, Fernández PhD thesis Observations:Theory: Stellar trajectories

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 3 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 L x ) Groups: Young local associations (compilation, several authors) OB associations (de Zeeuw et al. 1999) Moving groups (Asiain et al. 1999) The young stellar component in the solar neighbourhood

Young stars in the nearest solar neighbourhood Oct 24, 2001 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 (~10 6 K), responsible for an important fraction of the 1/4 keV emission (soft X-rays) Not completely filled?  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  Elongated to high galactic latitudes, and tilted perpendicular to the Gould Belt’s plane

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 5 Loop I & Local bubble: Loop I is still an active superbubble, hotter (2.5·10 6 K) and denser (0.015 cm -2 ) than the LB  Pressure higher than in the LB HI “wall” (N H > 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 major superbubble toward l ~ 238 o Gas & diffuse X-ray distribution in the solar neighbourhood (II)

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 6 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  rotating supercloud ~2·10 7 M  and ~400 pc Sirius supercluster (500 Myr ago) + Gould Belt + Local arm (after collision with a main spiral arm 100 Myr ago) Some models in the literature

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 7 Galactic potential: General axisymmetric potential (Allen & Santillán 1991) Bulge + disk + halo (R o = 8.5 kpc,  o = 220 km s -1 ) Spiral arm perturbation (Fernández et al. 2001):  p = 30 km s -1 kpc -1 ; i = -6 o, m = 2,   = 330 o 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: (  ): Rotating Local Standard of Rest Stellar trajectories

Young stars in the nearest solar neighbourhood Oct 24, 2001 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): AssociacióPositionNumber of members Age(U,V,W) hel Upper Scorpius (US) R ~ 145 pc (l,b) ~ (350º,20º) 120 ST:B-M ~5 Myr(-4.7,-16.8,-6.7) Upper Centaurus Lupus (UCL) R ~ 140 pc (l,b) ~ (330º,15º) 221 ST: B-M ~13 Myr(-3.9,-20.3,-3.4) Lower Centaurus Crux (LCC) R ~ 118 pc (l,b) ~ (300º,5º) 180 ST: B-M ~10 Myr(-8.8,-20.0,-6.2)

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 9 Evolution of the OB associations in Scorpius-Centaurus (I) (-15) -age < t < 0 Myr LCC UCL US Orbits very similar to Maíz-Apellániz (2001), although in our case they concentrate more in space Expected number of past SNe: LCC 6 UCL13 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

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 10 Evolution of the OB associations in Scorpius-Centaurus (II) (-15) -age < t < 0 Myr LCC UCL US A little confusing projection since the associations are not placed on the (  ) plane  UCL and US are not so distant from the LB!

Young stars in the nearest solar neighbourhood Oct 24, 2001 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) U (km/s)V(km/s)W(km/s)Age (Myr)Number of objects B (4.7) (3.3) -5.5 (1.9) 20 (10) 34 B (5.3) (3.7) -5.6 (2.2) 60 (20) 75 B (5.1) (2.7) -5.6 (4.6) 300 (120) 50 B (4.8) (3.3) -8.5 (4.7) 150 (50) 53 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

Young stars in the nearest solar neighbourhood Oct 24, 2001 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)

Young stars in the nearest solar neighbourhood Oct 24, 2001 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)

Young stars in the nearest solar neighbourhood Oct 24, 2001 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)

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 15 Evolution of the B2 substructure - Pleiades MG (IV) Olano’s model (t = -31 Myr) t = -30 Myr

Young stars in the nearest solar neighbourhood Oct 24, 2001 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 = 10 o 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) GC GR

Young stars in the nearest solar neighbourhood Oct 24, 2001 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 M cloud > 2·10 5 M 

Young stars in the nearest solar neighbourhood Oct 24, 2001 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

Young stars in the nearest solar neighbourhood Oct 24, 2001 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

Young stars in the nearest solar neighbourhood Oct 24, 2001 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)  Stellar velocities should have a common origin Star formation in dispersed cloudlets which disappear after the formation process (Feigelson 1996)  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?

Young stars in the nearest solar neighbourhood Oct 24, 2001 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

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 22 New young associations near the Sun (I) AssociationPositionNumber of members Age(U,V,W) hel ReferencesComments TW HydraeR ~ 55 pc (l,b) ~ (278º,23º) ~20 ST: F-M ~10 Myr(-11,-18,-7) (-10.2,-17.4,-4.6) (-12.7,-20.6,-6.2) Webb et al. (1999) Jayawardhana et al. (1999) Sterzik et al. (1999) Mamajek et al. (2000) Makarov & Fabricius (2001) Originated near the Sco-Cen molecular complex TucanaeR ~ 45 pc (l,b) ~ (121º,18º) ~20 ST:B7-M ~20 Myr(-10.5,-20.8,0.3)Zuckerman & Webb (2000)Half of them ROSAT sources  Cha cluster R ~ 100 pc (l,b) ~ (292º,-21º) ~13 ST: B8-M ~8 Myr(-11.8,-19.1,-10.5)Mamajek et al. (1999a, 1999b, 2000) Lawson et al. (2001) Lawson (2001) Mamajek & Fiegelson (2001) Related to Sco- Cen  Cha R ~ 110 pc (l,b) ~ (300º,15º) ~7~10 Myr(-5,-21,-10) (-10.2,-18.6,-8.8) Frink et al. (1998) Terranegra et al. (1999) Mamajek et al. (2000) Originated near the GMC that formed the GB

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 23 New young associations near the Sun (II) AssociationPositionNumber of members Age(U,V,W) hel ReferencesComments Extended R CrA R ~ 130 pc (l,b) ~ (359º,-37º) ~21 ST: B8-M ~10 Myr (-3.8,-14.3,-8.3) Neuhäuser et al. (2000) Quast et al. (2001) No GB Horologium A R ~ 60 pc (l,b) ~ (285º,-61º) ~16 ST:F-M ~30 Myr(-9.5,-20.9,-2.1)Torres et al. (2000)Members are not IRAS sources CapricornusR ~ 48 pc (l,b) ~ (31º,-35º) 6 ST: F-M ~10 Myr(-10,-13,--13)van der Ancker et al. (2000, 2001)  Pic R ~ 20 pc (l,b) ~ (258º,-30º) 3 ST: A,M ~20 Myr(-12.5,-17.0,-9.8)Barrado y Navascués et al. (1999) HD R ~ 100 pc (l,b) = (4º36º) 3 ST: B9.5,M ~5 Myr(-3.0,-13.0,-3.0)Weinberger et al. (2000)  Pic-like star

Young stars in the nearest solar neighbourhood Oct 24, 2001 The Gould Belt and other large star forming complexes 24 Evolution of the new young associations (I) -age < t < 0 Myr

Young stars in the nearest solar neighbourhood Oct 24, 2001 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

Young stars in the nearest solar neighbourhood Oct 24, 2001 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  hundreds 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 <  < 200 pc, 0 <  < 100 pc  Common origin for all of them?  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  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)