On the misalignment of the C18O molecular outflow in Cepheus E

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  • CHINESE ASTRONOMY AND ASTROPHYSICS

    PERGAMON Chinese Astronomy and Astrophysics 23 (1999) 174-178

    On the misalignment of the Cl80 molecular

    outflow in Cepheus Et* YU Zhi-yao

    Shanghai Observatory, Chinese Academy of Sciences, Shanghai 200090

    Abstract The contour diagram of the total intensity (integrated over all the

    whole velocity range) of the Cl*0 (J=l-0) line, in Cepheus E shows two unaligned

    extensions, one to the NW, one to the E. By considering the contour diagrams

    of the line intensity integrated over 5 separate velocity intervals, it is shown that the misalignment of the outflow is mainly in the blue shifted component with

    respect to the peak velocity.

    Key words: molecular cloud-molecular outflow-misalignment

    1. INTRODUCTION

    Sargent observed the giant molecular cloud Cepheus 0B3 in CO lines and studied their

    structure and distribution, and labelled their most prominent features as Cepheus A-F11y21.

    Yu Zhi-yao, et a1.131 first observed the Cl80 (J=l-2) line (rest frequency 109.782182GI-I~) in

    the giant molecular cloud Cepheus E and obtained its spectrum, an intensity contour map

    and the physical parameters of its core. The contour map shows a fairly symmetrical core

    with two extensions, one to the NW, one to the E. We surmised that this probably indicates

    an outflow that is not properly lined up. In this paper we shall consider further the question of misalignment using contour maps of intensities integrated over separate velocity intervals.

    2. OBSERVATIONS

    The observations were made using the 4-m millimetre radio telescope of Nagoya University,

    Japan, between 1993 December 20 and 26. The telescope parameters have been given in a

    t Supported by National Natural Science Foundation Received 1997-03-04; revised version 1997X)4-13

    * A translation of Acta Astmn. Sin. Vol. 39, No. 4, pp. 405-411, 1998

    0275-1062/99/$ - see front matter @ 1999 Elsevier Science B.V. All rights reserved.

    PII: SO2751062(99)00042-9

  • YU Zhi-yoo / Chinese Astronomy and Astrophysics 23 (1999) 174-178 175

    previous paper 11. Within an area of 24/x24, the CO line was observed at 93 points. The coordinates of the centre are a(1950) = 23hlm2.9s, 6(1950) = 6131 31.7, I = 110.50, b =

    1.57O. 1.5

    8 :CEI224073 i

    i ;

    !J 6UL i2.00

    I I _I - 15.0 - 10.0 - 5.0

    LSR velocity (km/s)

    Fig. 1 The spectrum of CO (J=l-0) 1 me at the observed centre of Cepheus E

    The data have a S/N ratio of 5. The spectrum at the central position is displayed in

    Fig. 1. From the figure we see that the noise in the profile is about 0.15 K and the peak antenna temperature is 0.85K. And the whole width at zero intensity is about 5 km/s.

    Emission lines like this one probably indicate molecular outflows in the core of molecular

    clouds important for the process of protostar formation.

    3. CONTOUR MAPS FOR DIFFERENT VELOCITY INTERVALS

    The main part of the line is in a 2.5 km/s velocity range, from -11.5 to -9.5. We divide

    this range into five 0.5 km/s intervals and the contour maps of intensities integrated over

    each of the 5 intervals are displayed as Figs.2 (a)-(e). F&.2(a) and 2(b), the blue shifted

    component with respect to the peak velocity, show clearly the asymmetrical extensions to

    the NW and E. Fig. 2(c) pertain to the core of the line, 60% from the blue shift side,

    and 40% from the red shifted side of the peak velocity (-10.2 km/s). Fig. 2(c) also show the asymmetrical extensions. In contrast, intensities over the two red shifted intervals (Figs. 2(d)

    and 2(e)) do not show the misaligned features. The E extension on Fig2(d) is relatively weak

    compared to the E extension on Figs. 2(a)-(c). Fig. 2( ) e over the most red shifted interval,

    does not show an outflow at all; what it shows is that the core distribution is displaced in a

    northwesterly direction with respect to the core position in the other figures.

    Fig. 2(a) VLSR = (-11.5, -11.0) 0 ver this velocity interval, the molecular density is com- paratively small. It is distributed roughly in two regions, one is an E extension from the

    core, size about 2.0x2.5 pc, the other is a 5x 1.5 pc region, at about 2.0 pc from the core of

    distribution to the NW.

    Fig. 2(b) VLsR = (-11.0, -10.5) The density is getting larger, and the misaligned extensions

    to the NW and E can clearly be seen. Size about 3.0~ 3.0 PC.

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  • YU Zhi-yao / Chinese Astronomy and Astrophysics 29 (1999) I 74-178 177

    110.70 110.64 ,IO._w 110.40

    Galactic Longitude ()

    Contour level Min. = 0.500 (K km/s) step. = 0.500 (K km/s)

    (e)

    Fig. 2(e) CO contour map. V&R = (-9.5, -9.0)

    Fig. 2(c) VL~R = (-10.5, -10.0) The peak intensity is getting larger still. The extensions and size as in Fig. 2(b).

    Fig. 2(d) V&R = (-10.0, -9.5) The density is again large. There is no clear sign of the asymmetrical extensions. The morphology shows a slight extension to the E. Size about

    2.0~2.4~~

    Fig.2(e) VLSR = (-9.5, -9.0) The density is getting smaller. No evidence for the NW and E extensions. The morphology is a northwesterly displacement of the core of distribution.

    Size about l.Oxl.5pc.

    The spectrum of the CO line of Cepheus E displayed in Fig. 1 shows that the flux density

    is clearly greater in the blue shifted component (relative to the peak velocity) than in

    the red shift component. We are still not clear about the relevance of this observation to

    the intensity distribution and the asymmetrical outflows. The contour maps for separated

    4. DISCUSSION

    velocity intervals given in Fig. 2 were intended for clarifying this question.

    From Fig. 2 we again notice the greater intensity in the blue shifted maps. The phe-

    nomenon that the blue shifted component is greater than the red shift component has been observed in many molecular clouds before, but it is the first time that it is observed in the

    CO outflow of Cepheus E.

  • 178 YU Zhi-yao / Chinese Astronomy and Aetrophyaics $3 (I 999) 174-l 78

    Comparing the different panels of Fig.2, we see that the misalignment of the two extensions seen in the total intensity map is mainly due to misalignment in the blue shifted component131, and is not evident in the red shifted component. There are three possibilities for this phenomenon of misalignment, partial obscuration of the red shifted component, nonuniformity of the ambient medium for the two components, and nonuniformity in the blue and redshiited components in the distribution of the outflow. The first possibility is the most likely.

    ACKNOWLEDGEMENT I thank Prof. Y. Fukui and Dr. Nagahama of Department of Astrophysics, Nagoya University, Japan for facility and support for the observation and data treatment.

    References

    1 Sargent A. I., ApJ, 1977, 218,736

    2 Sargent A. I., A$, 1979, 233, 163

    3 Yu Zhi-yao, Nagahama T., FWcui Y., Kexue Tongbao, 1996, 41, 622

    4 Kawabata K., Ogawa H., Fukui Y. et al., A&A, 1985,151, 1

    5 Yu Zhi-yao, CAA 1997, 21, 191 = AAnS 1996, 37, 396

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