observations of c18o (j = 1 − 0) emission spectrum in the dark cloud l 1211
TRANSCRIPT
Pergamon Chin. Astron. Astrophys. Vol. 20. No.1, pp. 38-44, 1996
A translation of Acrn Asfron. Sin. Vol. 36, No.% PP. 261-278, 1995 Copyright 0 1996 Elsevier Science Ltd
Printed in Great Britain. All rights reserved
SO2751062(96)00006-9 02751062/96 $24.00+0.00
Observations of Cl80 (J = 1 - 0) emission
spectrum in the dark cloud L12d
YU Zhi-yaol Yasuo Fukui2 Tomoo Nagahama2 ‘Shanghai Observatory, Chinese Academy of Sciences, Shanghai 200030
2 Department of Astrophysics, Nagoya University, Japan
Abstract We observed, for the first time, the C’s0 (J = 1 - 0) emission line
in the dark cloud L 1211 and found broad wings in the line in the compact core
of the dark. We present a two-dimensional atlas of the spectral profile and maps
of integrated and partially integrated intensities.’
Key words: dark cloud - molecular spectra
1. INTRODUCTION
L 1211 is a dark molecular cloud, its distance is 75Opc tlJ. It is an attractive target of
observation and study. Schwartz et a1.i21 have observed it using the CO (J = 1 - 0) line
and did not find broad wind emission. To explore the compact core of the dark cloud we
observed it using the C’s0 (J = 1 - 0) 1 ine (rest frequency 109.782182GHz) and found for
the first time, the broad wings and structure of the line in the compact core.
2. OBSERVATION AND RESULTS
The observation was carried out between December 20-26, 1993, using the 4m mm-wave
radio telescope of Department of Astrophysics, Nagoya University. The half-power width is
2.7’ at llOGHz, and the beaming efficiency is 0.7. The front end of the receiver is fitted
with a 4 K-cooled NbSIS frequency mixer, and the rear end, an acousto-optic spectrograph.
The velocity resolution of the spectrograph is 0.1 km/s, its velocity coverage is 100 km/s and
it comprises 1024 channels[31. Measurement of optical thickness and the calibration source
S 140 was made once every two hours. Over a 24/x18’ area, the C’s0 line was observed
at 74 points and various maps were constructed. The central position of observation was
t Supported by Chinese Academy of Sciences Joint Laboratory of Observatories Received 1994-03-25; revised version 1994-0910
’ 13 velocity-longitude and velocity-latitude diagrams are also given in the original article. These, and some partially integrated intensity maps are not included in this translation to save space
38
40 YU Zhi-yao et al.
L = 108.9333’, B = 2.6667’, the velocity of local standard of rest, VL~R = -10.5 km/s, and
the antenna temperature was 0.84 K.
Our observed data are presented in a number of maps.
2.1 An Atlas of Spectral Profiles the C’“0 (J = 1 - 0) line profiles at various points
of the dark cloud are given in Fig. 1. Here, we can ses broad emission wings, in contrast
to Schwartz et al.‘s observation of the CO line. These authors found their line had two
components with VR at -11.7 and -8.6km/s (and corresponding T); of 11 and 5 K. The C’s0
line we observed showed a single peak and broad wings, the red and blue wings having widths
of 3 and 2 km/s, respectively. The broad wing emissions originate in molecular outflows in
the molecular core that are so important in the formation of proto-stars. The outflows can
be more clearly seen in the intensity maps of Figs. 2 and 3. Generally speaking, bright
objects like Orion BN usually have CO wings with widths greater than 100 km/s, while for
young objects with solar type stars of a few solar luminosities, the most typical molecular
flow velocities are below 10 km/s121. Thus, apparently, the protostellar cores associated with
L 1211 are probably solar type objects.
2.2 Integrated Intensity Map
Fig. 2 gives the integrated intensity map of C’s0 (J = 1 - 0) emission of the dark cloud
L 1211. This is a complete map. We first observed at intervals of 4’, then we increased the
observed points to one every 2’. We see that the intensity contour lines are shaped like a
T, with extensions in the east-west direction and to the south. The C’s0 molecules show
a considerable concentration towards the centre, and most are located within a 3.0 x3.0
pc2 range. It is thus indicated that the molecular outflow from the core of L 1211 is in the
east-west direction. Further indication is shown by the partially integrated intensity maps.
2.3 Maps of Intensities Integrated over Different Velocity Intervals
Maps of C’s0 (J = 1 - 0) intensities over five 0.8km/s velocity intervals between -11.5
and -9.0 km/s, are shown in Fig. 3. 1 These 5 intervals contain most of the intensity. Greater
or lesser degrees of central condensation and the predominantly east-west extension can be
seen in these maps.
2.4 Velocity-Position Diagrams
Six velocity-longitude diagrams at six fixed latitude offsets, and seven velocity-latitude
diagrams at seven fixed longitude offsets were constructed. 2 The velocity scatter ranges
from 1.1 to 2.2 km/s in the velocity-longitude diagrams and from 0.5 to 2.0 km/s in the
velocity-latitude diagrams, this indicates again that the molecular outflow is mainly in the
east-west direction, and is bipolar.
2.5 Dynamical Time Scale of the Outflow
Molecular outflows are classified according to the luminosity of the central engine and
the energetics and morphology of the outflow. In the relevant calculations, distance D is
an important parameter. and the dynamical time scale of the outflow is proportional to D.
‘The original paper gives 5 further such maps (3 between -13.0 and -ll.(ikm/s, 2 between
-9.0 and -8.Okm/s) which are not reproduced here 2These diagrdma are given in the original paper and are not reproduced here
CT”0 in L 1211 41
Integrated Intensity (K km/s)
Ll”l1 c IX0 , , 1 8 1 1 6 1 I , , I 1 I 1
‘2. 8”
3.80
“. 78
3.76
’ 74 f -*
!? 2.72
s 2.7n
5 3.68 .% : 2.66 ,! .‘-’ 2.64 ‘, 2 2.62 m 0 2.60
2.58
2.56
i. 54
2.52
03 .e -0.2 2. I 0.6 -0.3
0.1 -1.3 -0.6 0.9 1.2
- i! l.c)Pc
2.4
2.50’.’ * ’ ’ ’ * I ’ I ’ ’ ’ ’ ’ ’ ’ ’ ’ * ’ ’ 109.10 109.00 108.90 101. HO
JHPLW Galactioc Longitude (Uegree)
Contour level Min.=s.ooo(K km/s) SteP.=l.OOO(K km/s)
Fig. 2 The integrated intensity map of C”O (J = 1 - 0)emission of dark cloud L 1‘211
Chanel map Ll”11 CM0 -ii.5--ii.okm/s
2 2.74 - b ” e 2.70 -
4 .z 2.86.
3
y 2.62.
a 9 258.
2.54-
2.!+ ’ ‘ ’ l ’ ’ * ’ ’ ’ ’ 109. IO lOS.00 rnHPBW . .
Gabctic Longitude (Degree) Contour kvel Min. =o.soo(K km/s) Step.=o.soo(K km/s)
42 YU Zhi-yao et al.
z 2.74
E B 2.70
4 2 2.66 I
.; 2.62
.a
Chanel map L1211 Cl80 -11.0--10.5km;s
. 2.82 - 1” “I” @ n I m r ’ II 6 I’
9 2.58
Galactic Longitude (Degree)
Contour kvel Min. =0.5OO(K km/s) Step. =o.‘Joo(K km/@
Chanel map I.1211 Cl80
-io.5--l’.okm/s * .
2.62.
2.78 -
c f 2.74 -
2 CI - 2.70 - -%
j 2.66 -
Galactic Longitude (Degree)
Contour. level Min. =o.!joo’(K km/s) Step. =o.s~(K km/s)
PO in L 1211
Chanel map L1211 cl80
-lO.o--9.jkm ‘:;
I”” I’, ” I ” “I’ ’ 1 2.82 -’
2.78 -
c z 2.14.
if P, 2.?0-
+l
.z 2.66 -
cl
.Y 2.62 - z S
; 2.58-
2.54 - .I ., .* .I
- 2.50 It I I 1 1 I * I I ti I t a 1 1 I 1 I I I I ,I
109.10 109.00 108.9O 108.80 HPB It:
Galactic Longitude (Degree)
Contour level Min. = o.wo(K km/s) Step. =o.wo(K km/s)
2.82 --
2.78-
s $j 2.74-
F
e 2.70-
-s
-2 2.66.
3
-2 : 2.62-
0” 2.58-
2.64 -
Chanel map L1211 Cl80 -9.s--9.okm/s
I ““1”“1”1
.a U .a
-I T
1 l.OPC
2.50L c I, I ,,I * ,,,I,,,, I,, ,J 109.10 109. oo 1~8.90 108.80
HPB W
Galactic Longitude (Degree) Contour levl Min. = 0.500 (K km/s) Step. = o. x~o(K km/s)
43
Fig. 3 Maps of partially integrated C’s0 (J = 1 - 0) 1’ lne intensity over different velocity intervals
44 YU Zhi-yao et al.
Here, we take the distance for L 1211 to be 750, according to Ref. [l].
The dynamical time scale of the outflow is estimated by the following formulaf2]:
1= D~/AVFWZI
where 0 is the angular size, and AVFWZI is the full width at zero intensity. From our
observations we take 0 = 4.4~ 10m3, AVFWZI = 5.0 km/s, and so we get t = 6.3~ lo5 yr.
References
[l] Fukti Y., In: Low Mass Star Formation and Pm-main Sequence Objects, ed. b. Reipurth, 95
[Z] Schwartz P. R., Gee Graham, Huang Y.-L., ApJ, 1988,32T, 350
[3] Kawabata K., Ogawa II., Fukui Y. et al., A&A, 1985, 151, 1