References

 
• Cesarsky, D., Jones, A. P., Lequeux, J., & Verstraete, L. 2000, A&A, 358, 708 NASA ADS  
• Dufton, P. L., & Kingston, A. E. 1991, MNRAS, 248, 827 NASA ADS  
• Ehrenfreund P., d'Hendecourt L., Dartois E., et al. 1997, Icarus, 130, 1 NASA ADS  
• Esteban, C., Peimbert, M., Torres-Peimbert, S., & Escalante, V. 1998, MNRAS, 295, 40  
• Fuente, A., Martín-Pintado, J., Cernicharo, J., & Bachiller, R. 1990, A&A, 237, 471 NASA ADS  
• Fuente, A., Martín-Pintado, J., Cernicharo, J., & Bachiller, R. 1993, A&A, 276, 473 NASA ADS  
• Fuente, A., Martín-Pintado, J., & Gaume, R. 1995, ApJ, 442, L33 NASA ADS  
• Fuente, A., Martín-Pintado, J., Rodriguez-Fernándo, N. J., Cernicharo, J., & Gerin, M. 2000, A&A, in press  
• Gibb, E. L., et al. 2000, ApJ, 535, 347  
• Goldsmith, P. F., et al. 2000, ApJ, 539, L123 NASA ADS  
• Hébrard, G., Péquignot, D., Vidal-Madjar, A., Walsh, J. R., & Ferlet, R. 2000, A&A, 354, L79 NASA ADS  
• Hogerheijde, M. R., Jansen, D. J., & van Dishoeck, E. F. 1995, A&A, 294, 792 NASA ADS  
• Jansen, D. J., van Dishoeck, E. F., & Black, J. H. 1994, A&A, 282, 605 NASA ADS  
• Jansen, D. J., Spaans, M., Hogerheijde, M. R., & van Dishoeck, E. F. 1995, A&A, 303, 541 NASA ADS  
• Kaler, J. B., Aller, L. H., & Bowen, I. S. 1965, ApJ, 141, 912 NASA ADS  
• Lis, D. C., Schilke, P., & Keene, J. 1997, in CO: Twenty-five years of Millimeter-Wave Spectroscopy, ed. W. B. Latter, S. J. E. Radford, P. R. Jewell, J. G. Mangum, & J. Bally (Kluwer), IAU Symp., 170, 128  
• Lis, D. C., Serabyn, E., Keene, J., et al. 1998, ApJ, 509, 299 NASA ADS  
• Marconi, A., Testi, L., Natta, A., & Walmsley, C. M. 1998, A&A, 330, 696 NASA ADS  
• Minchin, N., White, G. J., Stutzki, J., & Krause, D. 1994, A&A, 291, 250 NASA ADS  
• Rubin, R. H., Dufour, R. J., & Walter, D. K. 1993, ApJ, 413, 242 NASA ADS  
• Schenewerk, M. S., Snyder, L. E., Hollis, J. M., Jewell, P. R., & Ziurys, L. M. 1988, ApJ, 328, 785 NASA ADS  
• Schilke, P., Walmsley, C. M., Pineau des Forêts, G., & Flower, D. R. 1997, A&A, 321, 293 NASA ADS  
• Steiman-Cameron, T. Y., Haas, M. R., Tielens, A. G. G. M., & Burton, M. G. 1997, ApJ, 478, 261 NASA ADS  
• Snyder, L. E., Hollis, J. M., & Ulich, B. L. 1976, ApJ, 208, L91 NASA ADS  
• Snyder, L. E., Schenewerk, M. S., & Hollis, J. M. 1985, ApJ, 298, 360 NASA ADS  
• Timmermann, R., Bertoldi, F., Wright, C. M., et al. 1996, A&A, 315, L281 NASA ADS  
• Turner, B. E., Chan, K.-W., Green, S., & Lubowich, D. A. 1992, ApJ, 399, 114 NASA ADS  
• Turner, B. E. 1998, ApJ, 495, 804 NASA ADS  
• Ungerechts, H., Walmsley, C. M., & Winnewisser, G. 1986, A&A, 157, 207 NASA ADS  
• van Dishoeck, E. F. 1988, in Rate Coefficients in Astrochemistry, ed. T. J. Millar, & D. A. Williams (Kluwer, Astrophys. Space Science Library), 146, 49  
• Walmsley, C. M., Natta, A., Oliva, E., & Testi, L. 2000, A&A, 364, 301 NASA ADS  
• Walmsley, C. M., & Ungerechts, H. 1983, A&A, 122, 164 NASA ADS  
• Walmsley, C. M., Pineau des Forêts, G., & Flower, D. R. 1999, A&A, 342, 542 (WPF) NASA ADS  
• Westley, M. S., Baragiola, R. A., Johnson, R. E., & Baratta, G. A. 1995, Nature, 373, 405 NASA ADS  
• Wilson, T. L., & Rood, R. T. 1994, ARA&A, 32, 191 NASA ADS  
• Wyrowski, F., Walmsley, C. M., Natta, A., & Tielens, A. G. G. M. 1997, A&A, 324, 1135 NASA ADS  
• Wyrowski, F., Schilke, P., Hofner, P., & Walmsley, C. M. 1997, ApJ, 487, L171 NASA ADS  
• Yusef-Zadeh, F. 1990, ApJ, 361, L19 NASA ADS

• If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
• You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
• You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.