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Issue A&A
Volume 420, Number 2, June III 2004
Page(s) 533 - 546
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20035611



A&A 420, 533-546 (2004)
DOI: 10.1051/0004-6361:20035611

Very cold cores in the Taurus Molecular Ring as seen by ISO

L. V. Tóth1, 2, M. Haas1, D. Lemke1, K. Mattila3 and T. Onishi4

1  Max-Planck-Instutute für Astronomie, Königstuhl, 17, 69117, Heidelberg, Germany
2  Department of Astronomy of the Loránd Eötvös University, Pázmány Péter sétány 1, 1117 Budapest, Hungary
3  Helsinki University Observatory, PO Box 14 Tähtitorninmäki, 00014 University of Helsinki, Finland
4  Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan

(Received 1 November 2003 / Accepted 19 February 2004)

Abstract
Three prominent cold objects of the Taurus Molecular Ring ( TMR ) were revealed by our ISOPHOT 200  $\mu$m map of the south-eastern part of the Heiles Cloud 2 ( HCL 2 ) cloud complex. One corresponds to the cyanopolyyne peak region of the TMC-1 ridge, ( TMC-1 CP ), one is the HCL2-E cloud, and one which we call HCL2-ES lies south of TMC-1. The 200/100  $\mu$m colour temperatures and column densities of the three ISOPHOT cold clouds are $\approx$ 12 K, and 1.2  $\pm$ 0.7  $\times$ 1022 cm -2 respectively, as calculated from ISO/IRAS surface brightnesses. As Nagoya-4 m C $^{\rm 18}$O (1-0) spectra show, these are dense molecular clouds with $N({\rm H})> 10^{21}$ cm -2 column density peaks. The ISOPHOT 200  $\mu$m surface brightness is well correlated with the C $^{\rm 18}$O line intensity ( $corr.~coef.\approx 70$%). The large dust particle emissivity is found to be increased in the prototypical very dense core TMC-1 CP. As the low linewidths ( $\Delta v=0.8$  $\pm$ 0.2 km s -1) indicate, the level of turbulent energy density is 50% lower in these three clouds than in other clouds of HCL2. Dense cores were identified inside the C $^{\rm 18}$O clouds by NH 3 measurements with the Effelsberg-100 m telescope and Nobeyama-45 m H 13CO + data. The density of the dense cores is $n\ge 1.1$  $\times$ 105 cm -3, and their kinetic temperatures are $\la$ 10 K, in good agreement with the FIR results. The total molecular gas mass in the gravitationally bound cloud cores of TMC-1 CP and HCL2-E is about 21  $M_{\odot}$ and 8  $M_{\odot}$ respectively. The cores, TMC-1 CPb and HCL2-Eab are associated with 3 low mass YSO candidate 2MASS point sources, while 35 other low mass YSO candidates are seen elsewhere in TMR south, which we consider as evidence for ongoing low mass star formation.


Key words: ISM: clouds -- dust, extinction -- ISM: individual objects: Taurus clouds -- ISM: molecules -- ISM: structure -- stars: formation

Offprint request: L. V. Tóth, lvtoth@mpia-hd.mpg.de

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© ESO 2004


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