1. The molecular gas associated with the Association Ara OB1
E.M.Arnal 1,2, G.A.Romero3, J.May4,
D.Minniti 5
Instituto Argentino de Radioastronomía, Argentina
Universidad Nacional de La Plata, FCAG, Argentina
Fellow from CONICET, Argentina
Universidad de Chile, Depto de Astronomía, Chile
Pontificia Universidad de Chile, Depto. Astronomía, Chile

2. objetos Overview of the Ara OB1 region Galactic Latitude
NGC 6167
(l,b)= (335.2, -1.4)
Distance = 1280± 180 pc
Age (1,2)~(4-5) x 107 yr
Vrad~ -36± 14 kms-1
Earliest Sp.Type =>B3V
Av~2.8±0.3 mag
objetos
-1.0
NGC 6193
(l,b)=(336.7, -1.6)
1100 < d < 1340 pc
Distance = 1320± 120 pc
Age ~5 x 106 yr
Vrad~ -30.6± 6.3 kms-1
Av~1.5 mag
HD (O7V)
HD (O5V: + O6:)
Galactic Latitude
-2.0
NGC 6188=> The Rim nebula
337.0
336.0
335.0
Galactic Longitude

3. Ara OB1: another example of sequential star forming ?
Herbst & Havlen (1977) have suggested that the star
formation in Ara OB1 may may have been triggered by a
supernova explosion.
Arnal et al. (1988) have found evidence for an expanding
shell of neutral (HI) and molecular (CO) gas coexisting
with the OB association.It is suggested that this thick
shell, possibly originated by the winds from the massive
stars of NGC6167, is genetically linked to AraOB1.
Rizzo & Bajaja (1994) also found evidence for an expanding
HI structure in the region.
A multicolor polarimetric study of the region (Waldhausen
et al., 1999) is also in line with the scenario of sequential
star formation suggested by Arnal et al. (1988).
NGC 6167
NGC 6193
RCW108-IR

4. RCW108-IR
RCW108
-26.9 (CO) < Vr < (H2CO) kms-Vr(H92α)=-24 kms-1(ATCA,HPBW=20”)
Vr(Hα)=-18.9±6.2 kms-1
Vr(H109α)= -24.9±2.2 kms-1 (HPBW=4’.4)
Vr(H166α)= -20.0±5.0 kms-1 (HPBW=34’.4)
NGC6193
15´ ~ 5.8pc
Vr(st) ~ -30.6±6.3 kms-1

5. Previous radio continuum and molecular line observations in the region
Mostly towards RCW108-IR.
OH GHz (Caswell & Robinson 1967, HPBW=12’, Vr= kms-1)
H2CO (4.8 GHz) (Whiteoak & Gardner 1974, HPBW=4’.2, Vr= kms-1)
CO (115 GHz) (Gillespie et al. 1977, HPBW= )
CO (115 GHz) (Whiteoak & Otrupcek 1982, HPBW=2’.8, Vr = kms-1
12CO,13CO,18CO of a small region (2’x 2’) centred on RCW108-IR, HPBW=30”(±10”),
Vr=-22.5 / kms-1. (Urquhart et al. 2003) [MOPRA]
Extensive 13CO (110 GHz) of this region were performed by Yamaguchi et al. (1999)
, as part of their molecular line studies of southern sky HII region “associated with
bright rimmed clouds”. Association of IRAS point sources with molecular clouds.[Nanten]
Radio Continuum
High resolution (HPBW=5’) 5 GHz Parkes (Goss & Shaver 1970) [Sυ= 8.6 Jy]
2.4 GHz Parkes (Duncan et al. 1995) (HPBW=10’) [Sυ=9.2±0.6 Jy]
Interferometric observations at 408 MHz (Shaver & Goss 1970) [Sυ= 2.2 Jy]
ATCA 4.8 (HPBW=20”) & 8.3 (HPBW=12”) GHz. Embedded source is a O8-O9 star

6. The region of Ara OB1 is an active high mass
Based on above...
The region of Ara OB1 is an active high mass
star forming region in the southern sky.
And...
Very little is known about the large scale spatial
distribution and properties of the molecular gas
that may be physically related to this stellar
complex.

7. Carbon Monoxide databases
12CO (J=1 => 0), n0 = GHz
Radiotelescope m m
Columbia University - CTIO NANTEN - Las Campanas
Covered area o.75 x 3o o.8 x 0º.4 & 0º.5 x 0º.6
HPBW (arcmin)
Spatial sampling & 2.7
Vel. Res. (kms-1)
Vel. Cov. (kms-1) ~ ~112
Observing shift Nov April – May 2001

8. Ta* Integrated CO emission between –30 and –15 kms-1 CTIO results -1.0
Galactic Latitude
(FWHM=8’.7)
-2.0
337.0
336.0
335.0
Galactic Longitude

9. CO channel images Channel width= 2.1 kms-1 -28.0 -25.9 -23.8
-1.0
-2.0
-28.0
-25.9
-23.8
337.0
336.0
335.0
Galactic Latitude
-21.7
-19.6
-17.5
Galactic Longitude

10. CTIO results [-27,-23]kms-1 (Arnal et al. 2003) B D C E F -48 00 -24
-24.6
-23.5
-21.8
-23.8 20
Declination 40
-49 00
16h39m
16h33m
Right Ascension

11. Ara OB1 (l,b)=(336o.5,-1o.5) 12CO (λ~ 2.6mm) Composite image
Red ([SII] 6716,6731), Green (Hα), Blue([OIII])

12. Features E, F & C (NANTEN)
Declination F C E
Right ascension
Right ascension
[-28,-18] kms-1
[-27,-19] kms-1

13. NGC 6188 (The Rim nebula) and Features E, F & C (NANTEN)
-24.2
-25.2
-21.4
-22
-23.7
-23.8
-25
-25.7
-26
-26.3
-26.3
-23.3 E
-23.4
-27 C
-29
-23.7 F

14. NGC 6188 – Position-velocity
– –
[Kms-1]
Declination
Declination RA
Velocity gradients along NGC 6188

15. Velocity vs position diagram for feature E (NANTEN data)
-48 15
declination 30 45
RCW 108_IR
IRAS
S12= Jy
S25= Jy
S60= Jy
S100=18700 Jy
-49 00
Vel (kms-1)

16. Velocity vs position diagram for feature F (NANTEN data)
-48 40
IRAS
Declination
-49 00
S12= Jy
S25= Jy
S60= Jy
S100=4080 Jy
Rad. Vel. (kms-1)

17. Summing up
Based on morphological and kinematical arguments, nine molecular
concentrations are likely to be associated with the absorbing material
observed in the vicinity of NGC 6193
Most of the CO structures associated with Ara OB1 fall in the
narrow velocity range –24 to –20 kms-1.But... There is also CO gas
(projected close to NGC 6193) that depicts the highest negative
(-28.5 kms-1) and positive (-17.5 kms-1) velocities
The total amount of molecular gas is ~ 1.5 x 104 Mо.
Three concentrations (labeled E, F and H, respectively) are the
dominant features.
The above features have a strong correlation with infrared emission
(IRAS+MSX)
Peak of emission of feature E almost coincident with RCW108-IR
(IRAS )
Velocity gradient along NGC On average, its radial velocity is
a few kms-1 more negative than those of structures C, E, F & H.
Possible molecular outflows in features E and F?

18. Coming soon ... Infrared spectroscopy of the open cluster
associated with IRAS (R.Barbá)
Revisiting the HI ( Parkes λ~21-cm)
N. McClure-Griffiths.
Narrow band filter images ==> Ionization
structure (R. Barbá + F. Comeron)
New molecular line observations
(Structures C, E, F, H plus NGC 6188
(PDR edge-on?))

19. Acknowledgements Dr. M. Roth, Director of Las Campanas Observatory
Prof. Y. Fukui and Dr. A. Mizuno for allocating observing
time to this project
NANTEN crew during the observing shift: Dr. Toshikazu
Onishi, and Yoshiaki Moriguchi and Hiro Saito.

20. Ara OB1 (l,b)=(336o.5,-1o.5) 12CO (λ~ 2.6mm) Composite image
Red ([SII] 6716,6731), Green (Hα), Blue([OIII])

21. S2.41 (Jy) Continuum emission at 2.417 GHz (HPBW=10’ ) -1.00
Galactic Latitude
-2.00
-3.00
Galactic Longitude

22. CTIO & NANTEN [-27,-23] kms-1
Declination
Right ascension

23. IRAS point sources -1.00 Galactic Latitude -2.00 337.0 336.0 335.0
Galactic Longitude
Yamaguchi et al 1999 (Y)
Arnal et al 2003 (J)