C18O molecular emission of Cepheus A

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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 Printed in Great Britain PII: SO2751062(97)00026-X 0275.1062/97 $32.00 + 0.00 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 11, infrared radiationfl 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~ 108 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 6144 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 C80(J=1-O) line profile The observed line profile of CO(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 CsO(.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 CO 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 polarizationIOl, 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) (10tm -? ) (I@cm -?) CIOcm-) (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. CO 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. References [II 121 1:; [51 [61 171 [81 191 DO1 PI PI P31 P41 Sargent A. I., ApJ, 1977, 218, 736 Hughes V. A., ApJ, 1985, 298, 830 Cohen R. J., Rowland P. R., Blair M. M., MNRAS, 1984, 210, 425 B&&man C. A., Becklin E. E., Wynn-Williams C. G., ApJ, 1979, 231, L47 Ho P. T. P., Moran J. M., Rodriguez L. F., ApJ, 1982, 262, 619 Mizuno A., O&hi T., Hayashi M. et al., Nature, 1994, 368, 719 Kawabata K., Ogawa H., Fukui Y. et al., A&A, 1985, 151, 1 Schwartz P. 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