Download - C18O molecular emission of Cepheus A
Chin. Asrron. Astrophys. Vol. 21, No. 2, pp. 191-196, 1997 A translation of Acta Astron. Sin. Vol. 37, No. 4, pp. 396-403, 1996
0 1997 Elsevier Science B.V. All rights reserved
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PO molecular emission of Cepheus At
YU Zhi-yao Shanghai Observatory, Chinese Academy of Sciences, Shanghai 200030
Abstract We used the mm wave telescope of Nagoya University and observed
the molecular emission of C1sO(.7=1-O) in Cepheus A. The line profile, total and
partial intensity contour maps and velocity-position diagrams as well as relevant
parameters of the region are derived.
Key words: molecular cloud-region of star formation-molecular emission
1. INTRODUCTION
Since Sargent[ll in 1977 first observed Cepheus A as a CO hotspot, this object has attracted
continued interest and attention. Here, one can observe the radio continuum spectrum[“l,
OH and Hz0 maser emissions 1’1, infrared radiationf’l as well as high velocity blueshifted
and redshifted wings in the CO line profiles[51. The C180(J=1-O) molecular emission is
an extremely good tracer of compact cores of star forming regions L61. This paper report on
observations of this line (rest frequency 109.782182GHz) using the 4 mm wave telescope of
Nagoya University, Japan. The observations were made in the period 1993 December 20-26
and have yielded the line profile, total and partial intensity contour maps and position-
velocity diagram as well as the relevant parameters of the core region.
2. OBSERVATIONS AND RESULTS
The Nagoya telescope 11~ a half-power width of 2.7arcmin (at 110GHz) and a beam
efficiency of 0.7. At the front end is a 4K cooled NbSIS frequency mixer, at the rear end,
a 1024-channel, acousto-optic spectrograph (velocity resolution 0.1 km/s, velocity coverage
lOOkm/s). The system temperature was 300K[7], and measurements of the background
optical thickness and the calibration source S 140 were made once every 2 hours. The
C180(J=1-O) molecular line was observed at 74 points in a 24’~ 10’8’ area and maps were
constructed. The parameters of the centre of observation are given in Table 1.
t Supported by National Natural Science Foundation, Chinese Academy of Sciences Astronomy
Commission and Radio Astronomy Joint Laboratory
Received 1995-07-21; revised version 199645-10
191
192 YU Zhi-yao
Table 1 Parnmeters of the Centre of Observation
Y (19%) 6 (195oJ I h r, w AV (km s-‘) V, hl s-‘I
22hs4” 20.2 61”44 Sji8 108P87 ZPIO I.00 3.17 - 10.59
2.1 The Line Profile
1.5 I : CE 1224047 ;
I z , l.O-
I
, I I ’ I
- 15.0 - 10.0 -5.0
LSR Veloaty (kms _ ’ )
Fig. 1 The C’80(J=1-O) line profile
The observed line profile of C”O(J=l- 0) is shown in Fig. 1. We note the wide wings (the line at the peak position has
a zero-intensity width of 5.0 km/s). Such wide wings reflect molecular outflows that
exert such an important effect in the for- mation of protostars in the cores of molec-
ular clouds. For young solar-type stars of a few solar luminosities, typical outflow has a velocity of up to 10 km/s. Thus, it seems that the protostellar core associated with
Cepheus A may be of the solar type.
2.2 Total Intensity Contour Map
The molecular outflow can be more clearly seen in the total intensity contour map of
Fig. 2 (constructed from observations at 2’ intervals). We note the tendency of the contours
to elongate in the EW direction. The C’sO(.7=l-O) outflow in the core region of Cepheus
A is seen to be quite dense.
2.00 L ” ,I z. .a 0
1 : .! ,.. 11000 109.90 109 60
Garactic Longitude (Degree)
Fig. 2 The total intensity contour map
C”O in Cepheus A 193
The outflow dynamical timescale t can be estimated by the formula181
t = Do/AV
in terms of the distance D, the angular size 0 and full width at zero intensity AV. We
take D = 750 pc. From Figs. 1 and 2 we find 0 = 3.5 x 10m3, AV = 5.0 km/s. Hence we get
t = 5.0x lo4 yr.
2.3 Partial Intensity Contour Maps
Fig. 3 gives four partial intensity contour maps, integrated over four separate 0.5 km/s
7 j . .
I I II > 1 I I,
; I
110.00 109.90 109.80 110.00 109.90 109 80
230 :--
I a, I. II ‘1 c> Cc)’
t 2.00
t- ” ” ” ** .’ 1 ,I ,/,
110.00 109.90 109.80
Galactic Longthde (Degree)
110.00 i 09.90 10980
Galactic Longitude (Degree)
Fig. 3 Partial intensity contour maps integrated over 4 LSR velocity ranges (a) -11.5 N -11.0,
(b) -11.0 N -10.5, (c) -10.5 w -10.0, (d) -10.0 N -9.5
194 YU Zhi-yao
velocity ranges between -11.5 and -9.5 km/s. The aim is to see more clearly how the centre
of the distribution changes with the velocity. The maps show clearly the EW displacement
of the centre. Also, the contour lines in map 3(b) (for the velocity range -ll.O- -10.5) are
conspicuously aligned along the EW direction.
2.4 Position-Velocity diagrams
A position-velocity diagram shows how the velocity range varies with the longitude for
a given latitude or how it varies with the latitude at a given longitude. 6 such diagrams are
shown in Fig. 4. The form of the vertical tic labels indicates the type of diagram. For
example, Fig. 4(a) is a longitude-velocity diagram at latitude offset 6.0 arcmin, while Fig. 4(f)
is a latitude-velocity diagram at longitude offset 12.0 arcmin. These diagrams indicate that
the emission in the velocity range -12.5 - -9.5 km/s is mainly found near the central
position (I = 108.87”, b = 2.10’).
3. DISCUSSION
3.1 Properties of the Outflow
There are two schools of thought on the interpretation of the observations of Cepheus
A: molecular outflow and disk structure. Our work supports the former view, that is, there
is an outflow in the EW direction.
The outflow is confirmed by other observations including infrared polarizationI’Ol, radio
continuuml”] and NH3 molecular emission [ii]. There are some interesting correlations in
its CO, optical and infrared properties. The transverse width of the optical emission region
is comparable to the CO lobe. This implies that the outflow is ejected from young stars
deeply imbedded in the cloud. The filamentary structure of the H-II region was interpreted
in Refs. [12, 131 as striation caused by hot shocks and was taken to indicate outflows at
locations very close to the young stars.
3.2 Physical Parameters of the C180(J=1-O) Core
These are given in Table 2. They were calculated in a similar manner to Ref. [14].
Table 2 Physical Parameters of the Core of Cepheus A
Sue
(PC 1
1.1
Tex
(K)
IO
T (PO) N (PO) !V 0-L) II (HJ I~ (LTE) WV”)
(10’tm -? ) (I@‘cm -?) CIO’cm-‘) (M, 1 (M, )
0.070 13.2 7.8 , 2.2 120 1200
3.3 Velocity Range and Spatial Extent
From the diagrams of Fig.4 we extract the velocity ranges and spatial extents shown
in Tables 3 and 4. From these tables we see that the spatial extent is greater in longitude than in lati-
tude, again indicating an outflow along the EW direction. That we could only construct
2 longitude-velocity diagrams as opposed to 4 latitude-velocity diagrams is just another
manifestation of the same fact.
C”O in Cepheus A
--6.OU ‘: .c E
--8.OU : ‘r:
-1o.ou B E
+12.ou
I
- 20.0 -15.0 - 10.0 -5.0 0.0
velwitdkm/s)
t
I I !
I ,.,~.,,.I,, -20.0 -15.0 - 10.0 -5.0 0
velocity( km/s)
4.ou
6.OU
8.OU
’ lO.OU
I
12.ou
, I I 16.wJ -20.0 -15.0 -10.0 -5.0 0.0
Velocity(km/s)
6.OU ‘: .c i
E 8.OU :
‘= lO.OU 8
z /
12.ou t
0
(f)
! 4.ou
t 6.OU
--8.OU
-1o.ou
12.ou
1 ; I , 16.W -20.0 -15.0 -10.0 -5.0 0.0
Velocity (km/s)
Fig.4 (a)-(b) Longitude-velocity diagrams at constant latitude offsets. (c)-(f) Latitude-velocity
diagrams at constant longitude offsets
196 YU Zhi-yao
Table 3 Velocity Range and Longitude Range
Fixed Latitude Offset (arcmin) Velocity Rauge (km/s) Longitude Range (arcmin)
6.0 3.0 7.5
8.0 2.8 a.7
Table 4 Velocity Range and Latitude Range
Fixed Longitude Offset (arcmin) Velocity Rrrnge (km/s) Latitude Range (arcmin)
6.0 2.0 4.5
8.0 3.1 6.0
10.0 2.0 4.1
12.0 0.3 1.5
ACKNOWLEDGMENT I thank Professor Y. Fukui and Dr T. Nagahama of Nagoya Uni
versity for help and support for the observation and data treatment.
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