A study of clumping in the Cepheus giant molecular cloud complex OB3

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  • Pergamon

    Chin Asrron. Asfrophys. Vol. 21. No. 1. 45-49. 1997 pp A translation of Acre AstruphTs. Sin. Vol. 16. No 4. 377-382, 1996 pp.

    0 1997 Elsevier Science Ltd Printed in Great Britain. All rtehts reserved

    SO2751062(97)00006-4 0275-1062/97 f332.00 + 0 00

    A study of clumping in the Cepheus

    molecular cloud complex OB3t


    YU Zhi-yao

    Shanghai Observatory, Chinese Academy of Sciences, Shanghai 200030

    Abstract From the Cl80 line profiles given in a previous paper total and

    partial intensity maps for two cores of the Cepheus 0B3 Complex, Cep B and

    Cep F, have been constructed. An analysis of the maps shows that the complex

    is clustered and that the different cores are not gravitationally bound. The

    dynamical timescale of the outflows in these cores was also obtained.

    Key words: giant molecular cloud-Cep B-Cep F-cloud complex


    When mapping is made of the radio lines of interstellar molecules we often find evidence

    for clumping in giant molecular cloud complexes of the Milky Way, such as Cepheus 0B3.

    A typical complex is composed of a large number of individual clouds of various scales and

    masse&l. The clumping process of the gas in such complexes is related to their formation

    and evolution. A better understanding of the distribution of the gas and its kinematics in

    the complexes is a necessary condition for a good theory of their origin and evolution.

    The giant complex Cepheus OB3 was observed and mapped by Sargent121 using the

    CO lines, and the designations Cep A-F came from this author. Harju, Walmsley and

    Wouterloot131 using ammonia maps studied the clumping properties of the Cepheus complex.

    Cepheus 0B3 was also partly observed by Carrll using 13C0 lines.

    The present author using the new 4 m radio telescope of Nagoya University observed

    the OB3 complex in the Cl80 (J = 1-O) line and found the LSR velocities of the Cep B and

    Cep F differed appreciably from the other clouds of the complex (see Table 1 of Ref. [4]).

    To investigate the clumping of the entire complex and the question of gravitational

    bounding we particularly observed and mapped Cep B and Cep F in the Cl80 line and

    derived the physical parameters of the Cl80 cores 141. We found that the complex to be

    clumped and that the individual clouds to be not gravitationally bound.

    t Supported by National Natural Science Foundation and Joint Laboratory for Astronomy and Radio


    Received 1995-08-30: revised vemion 1996-07-16


  • 46 YU Zhi-yao

    Baaed on the maps l(a) and l(b) of our previous paper 141, we applied imaging treatment

    and obtained total and partially integrated intensity contour maps for Cep B and Cep F. We found that the OB3 complex to be clumped and obtained the important conclusion that

    the clumps are not gravitationally bound. We also derived the dynamical timescales of their



    2.1 The Total Intensity Maps

    Figs. 1 and 2 give, respectively, the integrated intensity maps of Cep B and Cep F in

    the Cl80 (J =1-O) 1 ine, integrated over the whole velocity range. Both maps are complete,

    with observations at 2 intervals. The lowest contour value is 3.0 K km/s and the contours

    are at intervals of 1.0 K km/s. If we use a lower minimum level, then we shall be able to

    see features that are in the partial intensity maps of Figs. 3 and 4, integrated over finite

    intervals of the velocity range.

    r I --e-r I

    l.Opc ;l

    110.35 110.30 110.25 110.20

    Galactic Longitude (Degree) HPW

    tn3s .

    1 I


    2.30 a 3 1 tiP8W

    j a 3 1 / 109.90 109.80 109.70 109.60

    Galactic Longitude (Degree)

    Fig. 1 The integrated intensity map of Cep B Fig. 2 The integrated intensity map of Cep F

    For Cep B, the contours are in the shape of a smooth flow that extends to the east. For Cep F, the contours are more symmetrical, with an elongation in the north-south direction.

    From the line maps of Ref. [4] and Figs. 1 and 2 here we can derive the dynamical

    timescale of the outflow, t, according to the formulall,

    t = DO/AV(FWZI)

    where D is the di: tsnce, taken to be 75Opq 0 is the angular size, and the denominator is the full width of the line at zero intensity 11. Note that t here is different from the T in Ref. [4], which is optical thickness. From the maps, we find, for Cep B, 0 = 8.7x lo- rad

    and AV = 2.0 km/s, hence t = 3.03x 1Oyr. For Cep F, we find 0 = 2.6x10m3rad, AV =

    4.0 km/s, hence t = 4.37x lo6 yr.

  • Clumping in Cepheus OB3 47

    c.,....,.... ,,,, .,

    2.60 - .I _ Y -

    I "



    0 . . I _ 2.54 - I "

    " .a r

    2.45 L. 110.35 110.30 110.25 11O.P

    Galactic Longitude (Degree)


    L-,1., ., ,,c

    2.80 - u .# . -

    110.35 110.30 i10.25 110.20

    Galactic Longitude (Degree)


    Fig. 3 Partial intensity maps of Cep B, integrated over velocity intervals (-12.5, -12.0) (a) and

    (-12.0, -11.5) (b). Minimum contour 0.5 K km/s, contour interval 0.5K km/s

    2.2 Partial Intensity Maps

    To look into the velocity structure in the cores Cep B and Cep F, we give the partial

    intensity maps, integrated over different finite intervals of the velocity range. Fig. 3 refers to

    Cep B, the two maps a and b refer to the velocity intervals (-12.5, -12.0) and (-12.0, -11.5).

    (All velocities in units of km/s). Fig. 4 refers to Cep F and the four maps a, b, c, d refer to

    the velocity intervals, (-9.5, -9.O), (-9.0, -8.5), (-8.5, -8.0) and (-8.0, -7.5). In both figures,

    the lowest contour value is 0.5 K km/s, and the contours are at intervals of 0.5 K km/s.

    Fig. 3 shows clearly that, for Cep B, the main contribution of the intensity is in the two

    velocity ranges shown, and that the centres of the intensity distribution in the two ranges are

    separated in the E-W direction. Fig. 4 shows clearly that, for Cep F, the contribution comes

    mainly from the four velocity intervals shown and that, while the centres of distribution in

    maps (c) and (d) roughly agree in position, the centre of map (b) is displaced in the SE-NW

    direction, and the centres of (a) and (b) are relatively displaced in the N-S direction.


    (1) The morphology of the intensity maps suggests that the Cepheus 0B3 Complex

    is clustered and that the clusters are not gravitationally bound, for there are considerable

    differences between Cep B and Cep F. The former is elongated in the East-West direction,

    while the latter, in the North-South direction. There are other differences of detail.

    (2) The same conclusion is also suggested by the partial intensity maps. The core

    intensities are distributed differently in Cep B and Cep F, and also differently from other

    components of the complex.

    (3) The East-West elongation of the (total) intensity map of Cep B is consistent with the

    East-West displacement of the centres its partial intensity maps. Likewise, the North-South

    elongation and displacement in the case of Cep F.

    (4) Both this paper and Ref. [4] d ea with the question of clustering in the Cepheus 1 OB3 Complex, but the methods are different. In Ref. [4], the starting point was the rather

  • 48 YU Zhi-yao

    I l.Opc

    Galaclic Longitude (Degree)


    Galactic Longitude (Degree)


    2.30 -

    I- I 1.0 pc 109.90 lc9.90 10970 109.60

    Galactic Longitude (Degree)


    I 0 . .

    2.M .,I 1 d . . . . 1 . . . .I (l? - I.OPC 250 I Y . ., Galactic Longitude (Degree)


    Fig.4 Partial intensity maps of Cep F, integrated over velocity intervals (-9.5, -9.0) (a), (-9.0,

    -8.5) (b), (-8.5, -8.0) (c) and (-8.0, -7.5) (d). S ame contour minimum and interval as in Fig. 3

  • Clumping in Cepheus OB3 49

    large differences between the LSR velocities of the CO line peak Cep B and Cep F and

    the other components of the Complex, and hence differences in the physical parameters and their distributions. Here, we first construct the total and partial intensity maps of Cep B

    and Cep F, which we then analyse.

    (5) One of the reasons for our conclusion that the clusters are not gravitationally

    bound could be that the cloud had never been in equilibrium and that the individual cores

    are merely transitory objects. Another reason could be input of certain mechanical energy leading to expansion of the cloud. The energy of the OB association is entirely sufficient for

    the breakup of the cloudll.

    ACKNOWLEDGMENT I thank Professor Y. Fukui and Dr. T. Nagahama of the Depart-

    ment of Astrophysics, Nagoya University, Japan, for help and support in the observation

    and data treatment of the present project.


    [l] Carr J. S., ApJ, 1987, 323, 170

    [2] Sargent A. I., ApJ, 1977, 218, 736

    [ 3) Harju J., W&n&y C. M., Wouterloot J. G. A., In: Falgarone E., Boulanger F., Duvert G.

    eds., IAU Symp., No.147, Frugmenttstion of Molecular Clouds and Star Formation, 1991,


    [4] Yu Zhi-yea, T. Nagahama and T. Fukui, CAA 1996, 20, 38 = AAnS 1995, 36, 261

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