研究吸積流（Accretion flow）的動力學對於了解極早期恒星與其恆生盤如何形成有很重要的一步。這些吸積流常出現在磁流體動力學模擬中，然而，由於它們的亮度低而很少被觀察到。在篇論文中，我們使用阿塔卡馬大毫米/亞毫米陣列（ALMA）望遠鏡並通過一氧化碳分子譜線（C18O（2–1)）發現了巨大吸積流圍繞著一個具有開普勒盤 （Keplerian disk）的非常年輕的原恆星VLA1623A，而其尺寸約3600天文單位。我們使用樹狀圖演算法 （"Dendrogram''）從三維位置-位置-速度（Position-Position-Velocity）的原始數據中識別三組不同速度範圍的流狀結構。在這些流狀結構中，有的流狀結構可能是噴流（outflow）或被其他物質所撞擊。而另外，其中二個流狀結構的運動學與旋轉坍塌模型 (CMU model, Ulrich 1976; Cassen & Moosman 1981) 很好地匹配，旋轉坍塌模型描述其吸積流的速度結構具有恆定角動量。而我們的結果給出其離心半徑為150天文單位，與Murillo et al. (2013) 所估計的開普勒盤尺寸相同。而透過旋轉坍塌模型，我們能夠生成吸積流的三維—位置-位置-位置視圖 （Position-Position-Position），該視圖顯示其開普勒盤的厚度為30天文單位。

Studying the accretion flows surrounding extremely young protostars is an im- portant step toward understanding how protostellar disks are assembled in the early stage of star formation. The accretion flows are commonly seen in magnetohydro- dynamics (MHD) simulations; however, they are rarely observed due to their low intensity. Here we report our discovery of thousand-AU scale accretion flows around an extremely young protostar VLA1623A with a protostellar disk likely just formed, using Atacama Large Millimeter/submillimeter Array (ALMA) observations of C18O (2–1) emission. We identify three groups of stream-like structures at different velocity ranges from the three-dimensional Position-Position-Velocity (PPV) data cube using the “Dendrogram” algorithm. Some of these stream-like structures are likely to be outflows or the envelope material shocks by outflows, but we find that the kinematics of two identified streams are well matched with the CMU model (Ulrich, 1976; Cassen and Moosman, 1981) which describes the velocity structure of the accreting gas with constant angular momentum. Our results give a centrifugal radius of 150 AU, same as the Keplerian disk size estimated by Murillo et al. (2013). With the CMU model, we are able to produce a three dimensional (Position-Position-Position) view of the accretion flows which shows that the thickness of the Keplerian disk at r = 150 AU is < 30 AU.

Basu, S. (1998). Constraints on the Formation and Evolution of Circumstellar Disks in Rotating Magnetized Cloud Cores. The Astrophysical Journal, 509(1):229–237.
Boss, A. P. (1995). Gravitational Collapse and Binary Protostars. Revista Mexicana de Astronomia y Astrofisica Conference Series, 1:165.
Cassen, P. and Moosman, A. (1981). On the formation of protostellar disks. Icarus, 48(3):353–376.
Evans, N. J., Dunham, M. M., Jørgensen, J. K., Enoch, M. L., Merín, B., van Dishoeck, E. F., Alcalá, J. M., Myers, P. C., Stapelfeldt, K. R., Huard, T. L., Allen, L. E., Harvey, P. M., van Kempen, T. A., Blake, G. A., Koerner, D. W., Mundy, L. G., Padgett, D. L., and Sargent, A. I. (2009). THE SPITZERc2d LEGACY RE- SULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES. The Astrophysical Journal Supplement Series, 181(2):321–350.
Frerking, M. A., Langer, W. D., and Wilson, R. W. (1982). The relationship be- tween carbon monoxide abundance and visual extinction in interstellar clouds. The Astrophysical Journal, 262:590–605.
Goodman, A. A., Rosolowsky, E. W., Borkin, M. A., Foster, J. B., Halle, M., Kauff- mann, J., and Pineda, J. E. (2008). A role for self-gravity at multiple length scales in the process of star formation. Nature, 457(7225):63–66.
Harris, R. J., Cox, E. G., Looney, L. W., Li, Z.-Y., Yang, H., Fernández-López, M., Kwon, W., Sadavoy, S., Segura-Cox, D., Stephens, I., and Tobin, J. J. (2018). ALMA Observations of Polarized 872 μm Dust Emission from the Protostellar Systems VLA 1623 and L1527. eprint arXiv:1805.08792.
Hatchell, J., Fuller, G. A., Richer, J. S., Harries, T. J., and Ladd, E. F. (2007). Star formation in Perseus. II. SEDs, classification, and lifetimes. A&A, 468(3):1009– 1024.
28
Kratter, K. M., Matzner, C. D., Krumholz, M. R., and Klein, R. I. (2010). On the Role of Disks in the Formation of Stellar Systems: A Numerical Parameter Study of Rapid Accretion. The Astrophysical Journal, 708(2):1585–1597.
Lee, C.-F., Li, Z.-Y., Codella, C., Ho, P. T. P., Podio, L., Hirano, N., Shang, H., Turner, N. J., and Zhang, Q. (2018). A 100 au Wide Bipolar Rotating Shell Em- anating from the HH 212 Protostellar Disk: A Disk Wind? The Astrophysical Journal, 856(1):14.
Lee, C.-F., Li, Z.-Y., Ho, P. T. P., Hirano, N., Zhang, Q., and Shang, H. (2017). For- mation and Atmosphere of Complex Organic Molecules of the HH 212 Protostellar Disk. The Astrophysical Journal, 843(1):27.
Li, Z.-Y., Krasnopolsky, R., Shang, H., and Zhao, B. (2014). ON THE ROLE OF PSEUDODISK WARPING AND RECONNECTION IN PROTOSTELLAR DISK FORMATION IN TURBULENT MAGNETIZED CORES. The Astrophysi- cal Journal, 793(2):130–19.
Loinard, L., Torres, R. M., Mioduszewski, A. J., and Rodríguez, L. F. (2008). A Preliminary VLBA Distance to the Core of Ophiuchus, with an Accuracy of 4%. The Astrophysical Journal, 675(1):L29–L32.
Murillo, N. M. and Lai, S.-P. (2013). DISENTANGLING THE ENTANGLED: OB- SERVATIONS AND ANALYSIS OF THE TRIPLE NON-COEVAL PROTOSTEL- LAR SYSTEM VLA1623. The Astrophysical Journal, 764(1):L15–7.
Murillo, N. M., Lai, S.-P., Bruderer, S., Harsono, D., and van Dishoeck, E. F. (2013). A Keplerian disk around a Class 0 source: ALMA observations of VLA1623A. A&A, 560:A103–16.
Ossenkopf, V. and Henning, T. (1994). Dust opacities for protostellar cores. A&A, 291:943–959.
Pattle, K., Ward-Thompson, D., Kirk, J. M., White, G. J., Drabek-Maunder, E., Buckle, J., Beaulieu, S. F., Berry, D. S., Broekhoven-Fiene, H., Currie, M. J., Fich,
29

M., Hatchell, J., Kirk, H., Jenness, T., Johnstone, D., Mottram, J. C., Nutter, D., Pineda, J. E., Quinn, C., Salji, C., Tisi, S., Walker-Smith, S., Di Francesco, J., Hogerheijde, M. R., André, P., Bastien, P., Bresnahan, D., Butner, H., Chen, M., Chrysostomou, A., Coude, S., Davis, C. J., Duarte-Cabral, A., Fiege, J., Friberg, P., Friesen, R., Fuller, G. A., Graves, S., Greaves, J., Gregson, J., Griffin, M. J., Hol- land, W., Joncas, G., Knee, L. B. G., Könyves, V., Mairs, S., Marsh, K., Matthews, B. C., Moriarty-Schieven, G., Rawlings, J., Richer, J., Robertson, D., Rosolowsky, E., Rumble, D., Sadavoy, S., Spinoglio, L., Thomas, H., Tothill, N., Viti, S., Wouter- loot, J., Yates, J., and Zhu, M. (2015). The JCMT Gould Belt Survey: first results from the SCUBA-2 observations of the Ophiuchus molecular cloud and a virial anal- ysis of its prestellar core population. Mon. Not. R. Astron. Soc., 450(1):1094–1122.
Podio, L., Codella, C., Gueth, F., Cabrit, S., Bachiller, R., Gusdorf, A., Lee, C.-F., Lefloch, B., Leurini, S., Nisini, B., and Tafalla, M. (2015). The jet and the disk of the HH 212 low-mass protostar imaged by ALMA: SO and SO2 emission. A&A, 581:A85.
Rosolowsky, E. W., Pineda, J. E., Kauffmann, J., and Goodman, A. A. (2008). Struc- tural Analysis of Molecular Clouds: Dendrograms. The Astrophysical Journal, 679(2):1338–1351.
Sakai, N., Oya, Y., Higuchi, A. E., Aikawa, Y., Hanawa, T., Ceccarelli, C., Lefloch, B., López-Sepulcre, A., Watanabe, Y., Sakai, T., Hirota, T., Caux, E., Vastel, C., Kahane, C., and Yamamoto, S. (2017). Vertical structure of the transition zone from infalling rotating envelope to disc in the Class 0 protostar, IRAS 04368+2557. Monthly Notices of the Royal Astronomical Society: Letters, 467(1):L76–L80.
Seifried, D., Banerjee, R., Pudritz, R. E., and Klessen, R. S. (2014). Accretion and magnetic field morphology around Class 0 stage protostellar discs. Mon. Not. R. Astron. Soc., 446(3):2776–2788.
Takakuwa, S., Saito, M., Saigo, K., Matsumoto, T., Lim, J., Hanawa, T., and Ho, P. T. P. (2014). Angular Momentum Exchange by Gravitational Torques and Infall
30

in the Circumbinary Disk of the Protostellar System L1551 NE. The Astrophysical Journal, 796(1):1.
Terebey, S., Shu, F. H., and Cassen, P. (1984). The collapse of the cores of slowly rotating isothermal clouds. Astrophysical Journal, 286:529–551.
Tokuda, K., Onishi, T., Saigo, K., Kawamura, A., Fukui, Y., Matsumoto, T., Inut- suka, S.-i., Machida, M. N., Tomida, K., and Tachihara, K. (2014). ALMA OB- SERVATIONS OF A HIGH-DENSITY CORE IN TAURUS: DYNAMICAL GAS INTERACTION AT THE POSSIBLE SITE OF A MULTIPLE STAR FORMA- TION. The Astrophysical Journal, 789(1):L4–6.
Ulrich, R. K. (1976). An infall model for the T Tauri phenomenon. Astrophysical Journal, 210:377–391.
van Dishoeck, E. F. and Blake, G. A. (1998). Chemical Evolution of Star-Forming Regions. Annual Review of Astronomy and Astrophysics, 36(1):317–368.
Yen, H.-W., Takakuwa, S., Ohashi, N., Aikawa, Y., Aso, Y., Koyamatsu, S., Machida, M. N., Saigo, K., Saito, M., Tomida, K., and Tomisaka, K. (2014). ALMA OBSERVATIONS OF INFALLING FLOWS TOWARD THE KEPLERIAN DISK AROUND THE CLASS I PROTOSTAR L1489 IRS. The Astrophysical Journal, 793(1):1–20.
Yorke, H. W., Bodenheimer, P., and Laughlin, G. (1993). The formation of protostellar disks. I - 1 M(solar). The Astrophysical Journal, 411:274.
Yu, T. and Chernin, L. M. (1997). BIMA Observations of the VLA 1623 Molecular Outflow. The Astrophysical Journal Letters, 479(1):L63–L66.
Zhu, Z., Hartmann, L., and Gammie, C. (2010). Long-term Evolution of Protostellar and Protoplanetary Disks. II. Layered Accretion with Infall. The Astrophysical Journal, 713(2):1143–1158.
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