C18O molecular emission of Cepheus A

Download C18O molecular emission of Cepheus A

Post on 03-Jul-2016

219 views

Category:

Documents

3 download

TRANSCRIPT

  • 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. R., Gee G., Huang Y.-L., ApJ, 1988, 327, 350

    Ellis H. B. Jr., Lester D. F., Harvey P. M. et al., ApJ, 1990, 365, 287

    Sato S., Nagata T., Nakajima T. et al., ApJ, 1985, 291, 708

    TomelIes J. M., Ho P. T. P., ApJ, 1985, 288, 595

    Leuzen R., Hodapp K.-W., Solf J., A&A, 1984, 137, 202

    Joyce R. R., Simon T., AJ, 1986, 91, 113

    Sato F., Mizuno A., Nagahama T. et al., ApJ, 1994, 435, 279