臺灣博碩士論文加值系統

In this thesis, I present the results using two methods to model the magnetic fields in protostellar cores with interferometric polarimetry. I compare high angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A with empirical models of density profiles and magnetic fields in protostellar core. With the assumptions of uniform temperature distribution, constant dust property, and small dust alignment efficiency, the simulations of Stokes I, Q, and U maps are computed with integrals along the line-of-sight. The Stokes I, Q, and U maps are then convolved into visibilities of Stokes parameters to be compared with observations using two methods. The first method of modeling magnetic fields is based on the comparisons of modeled polarization angle and observed polarization angle. The second method is a direct analysis of Stokes parameter visibilities from models and observations. Three types of magnetic field configurations, poloidal magnetic fields, inclined poloidal magnetic fields, and polodial and toroidal magnetic fields, are used to model the polarization distribution in IRAS 4A. The results show that hourglass structures alone cannot reproduce the depolarization effect in IRAS 4A if the inclination angle is indeed as small as what have been inferred from the outflow line-of-sight velocity and proper motions. My analysis favors a morphology of inclined magnetic fields with an hourglass structure at scales of few hundred AU and a toroidal component with a maximum in a middle section of the disk around the protostars. Applications of the modeling magnetic fields in the visibility space to high quality interferometric polarization measurements and detail studies with magnetohydrodynamics (MHD) simulations would be feasible in the future.

Contents

1 Introduction 1

2 Observations and Data Analysis 6

3 Methods 10
3.1 Density Distribution 11
3.2 Magnetic Field Structure 11
3.3 Stokes Parameters 13
3.4 Fitting Density Models 15
3.5 Fitting Magnetic Field Models 17
3.5.1 Method A 18
3.5.2 Method B 20

4 Results 21
4.1 Plummer-like Density Models 21
4.2 Magnetic Field Models from Method A 22
4.2.1 Poloidal Magnetic Fields 22
4.2.2 Poloidal and Toroidal Magnetic Fields 23
4.3 Magnetic Field Models from Method B 24
4.3.1 Poloidal Magnetic Fields 24
4.3.2 Poloidal Magnetic Fields with Inclination 25

5 Discussion 27
5.1 Hourglass Structure 27
5.2 Polarization Hole 28
5.3 The Magnetic Field Structure in IRAS 4A 29
6 Conclusion 31
 

References

Aitken, D. K., Efstathiou, A., McCall, A., & Hough, J. H. 2002, MNRAS, 329, 647A
Allen, A., Li, Z.-Y., & Shu, F. H. 2003, ApJ, 599, 363A
Alves, F. O., Girart, J. M., Lai, S.-P., Rao, R., & Zhang, Q. 2011, ApJ,726, 63A
Attard, M., Houde, M., Novak, G., Li, H.-b., Vaillancourt, J. E., Dowell, C. D., Davidson, J., & Shinnaga, H. 2009, ApJ, 702, 1584A
Chandrasekhar, S., & Fermi, E. 1953, ApJ, 118, 116C
Ching, T-C, Lai, S-P, Girart, J. M., & Rao, R., in preparation
Choi, M. 2005, ApJ, 630, 976C
Choi, M., Hodapp, K. W., Hayashi, M., Motohara, K., Pak, S., & Pyo, T.-S. 2006, ApJ, 646, 1050C
Crutcher, R. M. 1999, ApJ, 520, 706C
Di Francesco, J., Myers, P. C., Wilner, D. J., Ohashi, N., & Mardones, D. 2001, ApJ, 562, 770D
Fiege, J. D., & Pudritz, R. E. 2000, ApJ, 544, 830
Galli, D., Lizano, S., Shu, F. H., & Allen, A. 2006, ApJ, 647, 374G
Galli, D., & Shu, F. H. 1993, Ap, .417, 220G
Girart, J. M., Crutcher, R. M., & Rao, R. 1999, ApJ, 525L, 109G
Girart, J. M., Rao, R., & Marrone, D. P. 2006, Science, 313, 812G
Goncalves, J., Galli, D., & Walmsley, M. 2005, A&A, 40, 979G
Harvey, D. W. A., Wilner, D. J., Lada, C. J., Myers, P. C., & Alves, J. F. 2003b, ApJ, 598, 1112H
Harvey, D. W. A., Wilner, D. J., Myers, P. C., & Tafalla, M. 2003a, ApJ, 597, 424H
Jorgensen, J. K., Schoier, F. L., & van Dishoeck, E. F. 2002, A&A, 389, 908J
Krasnopolsky, R., Li, Z.-Y., & Shang, H. 2011, ApJ, 733, 54K
Lai, S-P, Ching, T-C, Girart, J. M., & Rao, R., in preparation
Lai, S.-P., Crutcher, R. M., Girart, J. M., & Rao, R. 2002, ApJ, 566, 925L
Lazarian, A. 2007, JQSRT, 106, 225L
Leahy, P., & Fernini, I. 1989,VLA Scientific Memorandum No. 161, Correction Schemes for Polarized Intensity
Lee, H. M., & Draine, B. T. 1985, ApJ, 290, 211
Lucas, P. W., Fukagawa, M., Tamura, M., Beckford, A. F., Itoh, Y., Murakawa, K., Suto, H., Hayashi, S. S., Oasa, Y., Naoi, T., Doi, Y., Ebizuka, N., & Kaifu, N. 2004, MNRAS, 352, 1347L
Marrone, D. P., & Rao, R. 2008, Proc. SPIE, 7020, 60
Mouschovias, T. C., & Ciolek, G. E. 1999, in The Origin of Stars and Planetary Systems, ed. C. J. Lada, & N. D. Kylafis (Dordrecht: Kluwer), 305
Nutter, D., Stamatellos, D., & Ward-Thompson, D. 2009, MNRAS, 396, 1851N
Padoan, P., Goodman, A., Draine, B. T., Juvela, M., Nordlund, A., & Rognvaldsson, O. E. 2001, ApJ, 559, 1005P
Plummer, H. C. 1911, MNRAS, 71, 460
Press, W. H., Teukolsky, S. A., Vetterling, W. T., & Flannery, B. P. 1992, Numerical Recipes in C (2ed.; New York: Cambridge Univ. Press)
Rao, R., Girart, J. M., Marrone, D. P., Lai, S.-P., & Schnee, S. 2009, ApJ, 707, 921R
Reipurth, B., Lindgren, H., Mayor, M., Mermilliod, J.-C., & Cramer, N. 2002, AJ, 124, 2813R
Ridge, N. A., Schnee, S. L., Goodman, A. A., & Foster, J. B. 2006, ApJ, 643, 932
Sandell, G., Aspin, C., Duncan, W. D., Russell, A. P. G., & Robson, E. I. 1991, ApJ, 376L, 17S
Sault, R. J., Teuben, P. J., & Wright, M. C. H. 1995, in ASP Conf. Ser. 77, Astronomical Data Analysis Software and Systems IV, ed. R. A. Shaw, H. E. Payne, & J. J. E. Hayes (San Francisco: ASP), 433
Shu, F. H., Allen, A., Shang, H., Ostriker, E. C., & Li, Z.-Y. 1999, in NATO ASIC Proc. 540: The Origin of Stars and Planetary Systems, ed. C. J. Lada, & N. D. Kylafis (Dordrecht: Kluwer), 193
Shu, F. H., Galli, D., Lizano, S., & Cai, M. 2006, ApJ, 647, 382S
Thompson, A. R., Moran, J. M., & Swenson, G. W., Jr. 2001, Interferometry and Synthesis in Radio Astronomy (2nd ed.; New York: Wiley)
Weber, E. J., & Davis, Jr., L. 1967, ApJ, 148, 217W
Whitworth, A. P., & Ward-Thompson, D. 2001, ApJ, 547, 317