IJAA  Vol.4 No.3 , September 2014
Inferring the Structure of the Pre-Protostellar Core L1498
ABSTRACT
We present a study of the pre-protostellar core (PPC) L1498. A series of self-consistent, three-dimensional continuum radiative transfer models are constructed. The outputs of these models are convolved with appropriate telescope beam responses, including the effect of beam chopping to simulate SCUBA observations. The simulated observations are compared with existing observational data. An automated search is conducted in the multi-dimensional parameter space to identify the best-fit model. Grids of models are constructed in the vicinity of the best fit in order to understand the sensitivity/uncertainty of the results. We find that the source is well fit by a prolate spheroid of cutoff (and thus approximately outer) radius rcut = 0.073 ± 0.005 pc, axis ratio q = 2.0 ± 0.2, a central luminosity L* < 10-3 Lsun, and an optical depth in the visible of τv = 20 ± 5. We find that the PPC is illuminated by two external radiation fields: a uniform ISRF of strength sISRF= 0.5 ± 0.25 and a local plane-parallel radiation field sPPRF = 1.0 ± 0.5. Both of these radiation fields are locally attenuated, with τISRF = 1.0 ± 0.25, and τPPRF = 1.25 ± 0.75, consistent with the fact that L1498 is embedded in a larger cloud. Most interestingly, the density fall-off at the outer edge is extremely steep, having a power law of m > 10. This is effectively a “sharp edge” to the PPC, and together with the constant density interior, is interpreted as potential signs of a pressure-confined core.

Cite this paper
Doty, S. , Doty, S. and Perkett, M. (2014) Inferring the Structure of the Pre-Protostellar Core L1498. International Journal of Astronomy and Astrophysics, 4, 519-529. doi: 10.4236/ijaa.2014.43048.
References
[1]   Willacy, K., Langer, W.D. and Velusamy, T. (1998) Dust Emission and Molecular Depletion in L1498. The Astrophysical Journal Letters, 507, L171, http://dx.doi.org/10.1086/311695

[2]   Zhou, S., Evans, N.J., Wang, Y., Peng, R. and Lo, K.Y. (1994) A C(18)O Survey of Dense Cores in the Taurus Molecular Cloud: Signatures of Evolution and Protostellar Collapse. Astrophysical Journal, 433, 131-148. http://dx.doi.org/10.1086/174630

[3]   Hogerheijde, M.R. and Sandell, G. (2000) Testing Envelope Models of Young Stellar Objects with Submillimeter Continuum and Molecular-Line Observations. The Astrophysical Journal, 534, 880. http://dx.doi.org/10.1086/308795

[4]   Bergin, E.A., Alves, J., Huard, T. and Lada, C.J. (2002) N2H+ and C18O Depletion in a Cold Dark Cloud. The Astrophysical Journal Letters, 570, L101. http://dx.doi.org/10.1086/340950

[5]   Hily-Blant, P., Pineau des Forets, G., Faure, A., Le Gal, R. and Padovani, M. (2013) The CN/C15N Isotopic Ratio towards Dark Clouds. A&A, 557, A65.
http://dx.doi.org/10.1051/0004-6361/201321364

[6]   Maret, S., Bergin, E.A. and Tafalla, M. (2013) Chemical Modeling of the L1498 and L1517B Prestellar Cores: CO and HCO+ Depletion. A&A, 559, A53. http://dx.doi.org/10.1051/0004-6361/201322089

[7]   Langer, W.D. and Willacy, K. (2001) Preprotostellar Core Properties from Far-Infrared Observations. The Astrophysical Journal, 557, 714-726. http://dx.doi.org/10.1086/322257

[8]   Tafalla, M., Myers, P.C., Caselli, P. and Walmsley, C.M. (2004) On the Internal Structure of Starless Cores. A&A, 416, 191-212. http://dx.doi.org/10.1051/0004-6361:20031704

[9]   Tafalla, M., Santiago-Garcia, J., Myers, P.C., Caselli, P., Walmsley, C.M. and Crapsi, A. (2006) On the Internal Structure of Starless Cores. A&A, 455, 577-593.
http://dx.doi.org/10.1051/0004-6361:20065311

[10]   Shirley, Y.L., Nordhaus, M.K., Grcevich, J.M., Evans, N.J.E., Rawlings, J.M.C. and Tatematsu, K. (2005) Modeling the Physical Structure of the Low-Density Pre-Protostellar Core Lynds 1498. The Astrophysical Journal, 632, 982-1000. http://dx.doi.org/10.1086/431963

[11]   Mathis, J.S., Mezger, P.G. and Panagia, N. (1983) Interstellar Radiation Field and Dust Temperatures in the Diffuse Interstellar Matter and in Giant Molecular Clouds. Astronomy & Astrophysics, 128, 212-229.

[12]   Doty, S.D., Everett, S.E., Shirley, Y.L., Evans, N.J.E. and Palotti, M.L. (2005) Constraining the Structure of the NonSpherical Pre-Protostellar Core L1544. Monthly Notices of the Royal Astronomical Society, 359, 228. http://dx.doi.org/10.1111/j.1365-2966.2005.08893.x

[13]   Cambesy, L. (1999) Mapping of the Extinction in Giant Molecular Clouds Using Optical Star Counts. Astronomy & Astrophysics, 345, 965.

[14]   Ward-Thompson, D., Scott, P.F., Hills, R.E. and Andre, P. (1994) A Submillimetre Continuum Survey of Pre-Protostellar Cores. Monthly Notices of the Royal Astronomical Society, 268, 276-290.
http://dx.doi.org/10.1093/mnras/268.1.276

[15]   Ward-Thompson, D., Andre, P. and Kirk, J.M. (2002) The Initial Conditions of Isolated Star Formation—V. ISOPHOT Imaging and the Temperature and Energy Balance of Pre Stellar Cores. Monthly Notices of the Royal Astronomical Society, 329, 257-276.
http://dx.doi.org/10.1046/j.1365-8711.2002.04969.x

[16]   Men’shcikov, A.B. and Henning, T (1997) Radiation Transfer in Circumstellar Disks. Astronomy & Astrophysics, 318, 879-907.

[17]   Lis, D.C., Serabyn, E., Zylka, R. and Li, Y. (2001) Quiescent Giant Molecular Cloud Cores in the Galactic Center. The Astrophysical Journal, 550, 761. http://dx.doi.org/10.1086/319815

[18]   Doty, S.D. and Palotti, M.L. (2002) A Study of Some Current Methods of Analysing Observations of Star-Forming Regions. Monthly Notices of the Royal Astronomical Society, 335, 993-1004.
http://dx.doi.org/10.1046/j.1365-8711.2002.05681.x

[19]   Egan, M.P., Leung, C.M. and Spangna, G.F. (1988) CSDUST3: A Radiation Transport Code for a Dusty Medium with 1-d Planar, Spherical or Cylindrical Geometry. Computer Physics Communications, 48, 271-292. http://dx.doi.org/10.1016/0010-4655(88)90047-1

[20]   Spagna, G.F., Leung, C.M. and Egan, M.P. (1991) Radiation Transport in Dust in Disk Geometry. I. Application to Externally Heated Interstellar Clouds. Astrophysical Journal, 379, 232-244.
http://dx.doi.org/10.1086/170497

[21]   Shirley, Y.L., Evans, N.J., Rawlings, J.C. and Gregersen, E.M. (2000) Tracing the Mass during Low-Mass Star Formation. I. Submillimeter Continuum Observations. The Astrophysical Journal Supplement Series, 131, 249. http://dx.doi.org/10.1086/317358

[22]   Ossenkopf, V. and Henning, T. (1994) Dust Opacities for Protostellar Cores. Astronomy & Astrophysics, 291, 943-959.

[23]   Press, W.H., Teukolsky, S.A., Vetterling, W.T. and Flannery, B.P. (2007) Numerical Recipes: The Art of Scientific Computing. 3rd Edition, Cambridge University Press, New York.

[24]   Doty, S.D. and Lueng, C.M. (1994) A Critical Evaluation of Semianalytic Methods in the Study of Centrally Heated, Unresolved, Infrared Sources. The Astrophysical Journal, 424, 729-747.
http://dx.doi.org/10.1086/173926

[25]   Bonner, W. (1956) Boyle’s Law and Gravitational Instability. Monthly Notices of the Royal Astronomical Society, 116, 351-359. http://dx.doi.org/10.1093/mnras/116.3.351

[26]   Keto, E. and Myers, P. (1986) CO Observations of Southern High-Latitude Clouds. The Astrophysical Journal, 304, 466-480. http://dx.doi.org/10.1086/164181

[27]   Elmegreen, B. (1989) A Pressure and Metallicity Dependence for Molecular Cloud Correlations and the Calibration of Mass. The Astrophysical Journal, 338, 178-196. http://dx.doi.org/10.1086/167192

[28]   Bertoldi, F. and McKee, C.F. (1992) Pressure-Confined Clumps in Magnetized Molecular Clouds. The Astrophysical Journal, 395, 140-157. http://dx.doi.org/10.1086/171638

[29]   Heyer, M. and Brunt, C.M. (2004) The Universality of Turbulence in Galactic Molecular Clouds. The Astrophysical Journal, 615, L45.

[30]   Field, G.B., Blackman, E.G. and Keto, E.R. (2011) Does External Pressure Explain Recent Results for Molecular Clouds. Monthly Notices of the Royal Astronomical Society, 416, 710-714.
http://dx.doi.org/10.1111/j.1365-2966.2011.19091.x

[31]   Indebetouw, R., et al. (2013) ALMA Resolves 30 Doradus: Sub-Parsec Molecular Cloud Structure near the Closest Super Star Cluster. The Astrophysical Journal, 774, 73.

[32]   Huang, X., Zhou, T. and Lin, D.N.C. (2013) On the Coagulation and Size Distribution of Pressure Confined Cores. The Astrophysical Journal, 769, 23.

[33]   Lada, C., Muench, A., Rathborne, J., Alves, J. and Lombardi, M. (2008) The Nature of the Dense Core Population in the Pipe Nebula: Thermal Cores Under Pressure. The Astrophysical Journal, 672, 410.

[34]   Pitann, J., et al. (2013) G048.66-0.29: Physical State of an Isolated Site of Massive Star Formation. The Astrophysical Journal, 766, 68.

[35]   Padoan, P., Federrath, C., Chabrier, G., et al. (2014) Protostars and Planets VI. University of Arizona Space Science Series, In Press.

[36]   Kuiper, T.B.H., Langer, W.D. and Velusamy, T. (1996) Evolutionary Status of the Pre-Protostellar Core L1498. The Astrophysical Journal, 468, 761. http://dx.doi.org/10.1086/177732

 
 
Top