Oct 24, 2001 The Gould Belt and other large star forming complexes 1
Young stars in the nearest solar neighbourhood
Young stars in the nearest solar neighbourhood
David Fernández, Francesca Figueras, Jordi Torra
Departament d’Astronomia i Meteorologia
Universitat de Barcelona
Oct 24, 2001 The Gould Belt and other large star forming complexes 2
Young stars in the nearest solar neighbourhood
The young stellar component
Gas & diffuse X-ray distribution
Models
Work in progress, Fernández PhD thesis
Observations: Theory:
Stellar trajectories
Oct 24, 2001 The Gould Belt and other large star forming complexes 3
Young stars in the nearest 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 young stellar component in the solar neighbourhood
Oct 24, 2001 The Gould Belt and other large star forming complexes 4
Young stars in the nearest solar neighbourhood
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? 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
Oct 24, 2001 The Gould Belt and other large star forming complexes 5
Young stars in the nearest solar neighbourhood
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 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
Gas & diffuse X-ray distribution in the solar neighbourhood (II)
Oct 24, 2001 The Gould Belt and other large star forming complexes 6
Young stars in the nearest solar neighbourhood
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 ~2·107 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
Oct 24, 2001 The Gould Belt and other large star forming complexes 7
Young stars in the nearest solar neighbourhood
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:
(): Rotating Local Standard of Rest
Stellar trajectories
Oct 24, 2001 The Gould Belt and other large star forming complexes 8
Young stars in the nearest solar neighbourhood
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):
Associació Position Number 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)
Oct 24, 2001 The Gould Belt and other large star forming complexes 9
Young stars in the nearest solar neighbourhood
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
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
Oct 24, 2001 The Gould Belt and other large star forming complexes 10
Young stars in the nearest solar neighbourhood
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!
Oct 24, 2001 The Gould Belt and other large star forming complexes 11
Young stars in the nearest solar neighbourhood
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
B1 -4.5(4.7) -20.1(3.3) -5.5(1.9) 20 (10) 34
B2 -10.7(5.3) -18.8(3.7) -5.6(2.2) 60 (20) 75
B3 -16.8(5.1) -21.7(2.7) -5.6(4.6) 300(120) 50
B4 -8.7(4.8) -26.4(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
Oct 24, 2001 The Gould Belt and other large star forming complexes 12
Young stars in the nearest solar neighbourhood
Evolution of the B2 substructure - Pleiades MG (I)
t = 0 (at present)
Olano’s model
(t = 0)
Oct 24, 2001 The Gould Belt and other large star forming complexes 13
Young stars in the nearest solar neighbourhood
Evolution of the B2 substructure - Pleiades MG (II)
t = -10 Myr
Olano’s model
(t = -10 Myr)
Oct 24, 2001 The Gould Belt and other large star forming complexes 14
Young stars in the nearest solar neighbourhood
Evolution of the B2 substructure - Pleiades MG (III)
t = -20 Myr
Olano’s model
(t = -20 Myr)
Oct 24, 2001 The Gould Belt and other large star forming complexes 15
Young stars in the nearest solar neighbourhood
Evolution of the B2 substructure - Pleiades MG (IV)
Olano’s model
(t = -31 Myr)
t = -30 Myr
Oct 24, 2001 The Gould Belt and other large star forming complexes 16
Young stars in the nearest solar neighbourhood
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)
GC
GR
Oct 24, 2001 The Gould Belt and other large star forming complexes 17
Young stars in the nearest solar neighbourhood
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
Oct 24, 2001 The Gould Belt and other large star forming complexes 18
Young stars in the nearest solar neighbourhood
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
Oct 24, 2001 The Gould Belt and other large star forming complexes 19
Young stars in the nearest solar neighbourhood
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
Oct 24, 2001 The Gould Belt and other large star forming complexes 20
Young stars in the nearest solar neighbourhood
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?
Oct 24, 2001 The Gould Belt and other large star forming complexes 21
Young stars in the nearest solar neighbourhood
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
Oct 24, 2001 The Gould Belt and other large star forming complexes 22
Young stars in the nearest solar neighbourhood
New young associations near the Sun (I)
Association Position Number of members
Age (U,V,W)hel References Comments
TW Hydrae R ~ 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
Tucanae R ~ 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
Oct 24, 2001 The Gould Belt and other large star forming complexes 23
Young stars in the nearest solar neighbourhood
New young associations near the Sun (II)
Association Position Number of members
Age (U,V,W)hel References Comments
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
Capricornus R ~ 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 141569 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
Oct 24, 2001 The Gould Belt and other large star forming complexes 24
Young stars in the nearest solar neighbourhood
Evolution of the new young associations (I)
-age < t < 0 Myr
Oct 24, 2001 The Gould Belt and other large star forming complexes 25
Young stars in the nearest solar neighbourhood
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
Oct 24, 2001 The Gould Belt and other large star forming complexes 26
Young stars in the nearest solar neighbourhood
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)