Small Loose Young Associations
The SACY Project
Search for Associations
Containing Young stars
Carlos A. O. Torres & Germano R. Quast (LNA / MCT/BRAZIL)
Claudio H. F. Melo & Michael Sterzik (ESO)
Ramiro de la Reza & Licio da Silva (ON / MCT/BRAZIL)
80’s - Isolated T Tauri stars?
89 - New T Tauri stars found around TW Hya
90’s - PDS (IRAS)
2000 - Horologium Association (ROSAT) & Tucana Association
Both nearby (~50 pc), adjacent, with similar kinematics and ages a unique and large association? Others?
Background
Sample definition
ROSAT All-Sky Bright Source Catalogue
Proper motions from Hipparcos or Tycho-2 Catalogues
(B-V) 0.6 (later than G0)
Excluding known RS CVn, W UMa, giants, etc (SIMBAD)
Excluding Mv < 2.0 (or L < 10 Lʘ ages > 5 Myr)
Goals
Li abundance
Metallicity
Radial and Rotational Velocities
Duplicity
Evolutionary stage
Instruments
FEROS (ESO - 1.52 m & 2.2m)
Coudé (OPD/LNA - 1.60m)
CORALIE (ESO - Swiss Euler Telescope)
Statistics
Southern ROSAT Sources
SACY [Hip + TYC & (B-V)0.6]
Observed objects (not sources)
Data from literature
9574
1953
1750
150
-70
+10
-10
-50
-30
=18
=6
=12
=0
-70
+10
-10
-50
-30
=18
=6
=12
=0
RESULTS Giants 17%
Dwarfs (IV & V) 83%
Young stars (*) 39%
Pleiades age 22%
Old stars 39%
SB
10%
16%
38%
(*) Includes dwarf stars later than M0
UVW from stars with
parallaxes
UVW from6D clustering
analysis
UVW taken from
literature
Concentration detected
around U0V0W0
Group/Association?
Age from Li strength or
Isochrone fitting
1st s
tep
– lo
ok f
or c
once
ntra
tion
in t
he U
VW
spa
ce
? 3.5 F
? km/s 30
VV
σ=
Out of ad-hoc XYZ constraints to the
member list?
Loop over all young objectsin the catalogue
Minimize:2)0(2)0(2)0(2),( WWVVUUisoVMVMpF
Starrejected
Yes
Add star toMember list
No
Compute newU0V0W0 using
new member list
2nd s
tep
- L
oo
p o
ver
cata
log
ue
un
til
con
verg
ence
is
reac
hed
Probabilities?New ad-hoc
XYZ constraints?New limits: F or σ?
COMPARISON OF THE AD-HOC CURVESTO BARAFFE MODELS
5 Myr
10 Myr
50 Myr100 Myr
Expansion of the Associations in X direction
Within β PicA
Concentration in the UVW space:
U=-10.1 V=-15.9 W=-9.1
The β Pic Association
46 Members
ʘ
ʘʘ
5 Myr
10 myr
70 myr
β Pic Association
β Pic AssociationN S
Concentration in the UVW space:U=- 9.6 V=-20.9 W=-1.3
U=-12.7 V=-21.9 W=-5.6
U=-10.5 V=-23.2 W=-4.3
The GAYA Complex:
Tuc-HorA: 36 Members
ColA: 27 Members
CarA: 21 Members
ʘ
ʘ
ʘ
5 Myr
10 Myr
30 Myr70 Myr
GAYA ComplexGreen Tuc-HorAWhite ColARed CarA
Concentration in the UVW space:
U=-10.5 V=-18.0 W=-4.9
The TW Hya Association
22 Members
ʘ
ʘ ʘ
TWA 20
5 Myr8 Myr
70 Myr
TW Hya Association
Concentration in the UVW space:
U=-11.0 V=-19.9 W=-10.4
The ε Cha Association
24 Members (4 from η Cha)
ʘ
ʘ ʘ
5 Myr
10 Myr
70 Myr
ε Cha AssociationRed Field MembersGreen η Cha C. MembersBlank Others η Cha Cluster
Concentration in the UVW space:
U=-13.6 V=-2.7 W=-9.4
The Octantis Association
11 Members
ʘ
ʘ ʘ
5 Myr
10 Myr
70 Myr
Oct Association
Concentration in the UVW space:
U=-22.0 V=-14.4 W=-5.0
The Argus Association
63 Members (35 from IC 2391)
ʘ
ʘ ʘ
Argus Association
5 Myr10 Myr
30 Myr70 Myr
Red Field MembersGreen IC 2391 Members
Concentration in the UVW space:
U=-6.8 V=-27.2 W=-13.3
The AB Dor Association
75 Members
ʘ
ʘ ʘ
AB Dor Association
5 Myr
10 Myr
70 Myr
AB Dor Association
N S
Association N Age U σ V σ W σ EXP
β Pic 46 10 -10.1 2.1 -15.9 0.8 -9.1 0.9 Y
Tuc- Hor 36 30 -9.6 0.9 -20.9 0.8 -1.3 0.9 Y
Col 27 30 -12.7 1.1 -21.9 0.8 -5.6 0.9 Y
Car 21 30 -10.5 0.4 -23.2 0.8 -4.3 1.6 Y?
TW Hya 22 8 -10.5 0.9 -18.0 1.5 -4.0 0.9 Y
ε Cha 24 6 -11.0 1.2 -19.9 1.2 -10.4 1.6 N?
Oct 11 10 -13.6 2.5 -2.7 1.4 -9.4 1.0 Y
Argus 63 40 -22.0 0.3 -14.4 1.3 -5.0 1.3 N
AB Dor 75 70 -6.8 1.3 -27.2 1.1 -13.3 1.5 N
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
LCC
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
E C ha
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
TWA
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
TW E
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
UC L
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
US
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
Rho Oph
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
CrA
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
B Pic
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
GAYA 1
Y p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
GAYA 2
Y p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
LCC
Z p
c
X pc
-50 0 50 100 150 200
-200
-150
-100
-50
0
50
E C ha
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
TWA
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
TW E
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
UC L
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
US
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
Rho Oph
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
CrA
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
B Pic
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
GAYA 1
Z p
c
X pc
-50 0 50 100 150 200
-150
-100
-50
0
50
100
GAYA 2
Z p
c
X pc
-2 5 -2 0 -1 5 -1 0 -5 0 5
-3 0
-2 5
-2 0
-1 5
-1 0
-5
0
SACY
GAYA 1 OctA GAYA 2 AnA TW A ArgA YS SA US E Cha LC C B Pic TW A E
V k
m/s
U km /s
-2 5 -2 0 -1 5 -1 0 -5 0 5
-2 0
-1 5
-1 0
-5
0
5
1 0
SACY
GAYA 1 OctA GAYA 2 AnA TW A ArgA YS SA US E Cha LC C B Pic TW A E
W k
m/s
U km /s
-3 0 -2 5 -2 0 -1 5 -1 0 -5 0
-2 0
-1 5
-1 0
-5
0
5
1 0
SACY
GAYA 1 OctA GAYA 2 AnA TW A ArgA YS SA US E Cha LC C B Pic TW A E
W
km/s
V km /s
Insights
The distribution of young stars in the solar neighborhood is patchy, forming huge kinematical associations.
We recognize at least 14 young associations in the SACY database (there are five more possible associations to verify) .
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