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



The young stellar component

Gas & diffuse X-ray distribution

Models

Work in progress, Fernández PhD thesis

Observations: Theory:

Stellar trajectories



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



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



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)



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



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



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)



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



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!



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



Evolution of the B2 substructure - Pleiades MG (I)

t = 0 (at present)

Olano’s model

(t = 0)



Evolution of the B2 substructure - Pleiades MG (II)

t = -10 Myr

Olano’s model

(t = -10 Myr)



Evolution of the B2 substructure - Pleiades MG (III)

t = -20 Myr

Olano’s model

(t = -20 Myr)



Evolution of the B2 substructure - Pleiades MG (IV)

Olano’s model

(t = -31 Myr)

t = -30 Myr



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



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



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



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



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?



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



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



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



Evolution of the new young associations (I)

-age < t < 0 Myr



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



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)

young stars in the nearest solar neighbourhood

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