N/A

The First Hydrostatic Core (FHC) is proposed to form after the initial col-
lapse of a prestellar core, as a seed of a Class 0 protostar. FHCs are difficult
to be observed because they are small, compact, embedded, and short lived. In
this work, we explored the physical properties of two well-known FHC candi-
dates, B1-bN & B1-bS, by comparing interferometric data from SMA 1.1 &
1.3 mm and ALMA 870 μm observations with simulated synthesis images of
the two sources. The simulated images are based on a simple model containing
a single, hot compact first core-like component at the center surrounded by a
large-scale, cold and dusty envelope described by a broken power-law density
distribution with an index α. Our results show that the hot compact components
of B1-bN & B1-bS can be described by temperatures of ∼ 500 K with a size
of ∼ 4 au, which are in agree with theoretical predictions of an FHC. If alpha
inside the broken radii is fixed to −1.5, we find α ∼ −2.9 and ∼ −3.3 outside
the broken radii for B1-bN and B1-bS, respectively, consistent with theoreti-
cal calculations of a collapsing, bounded envelope and previous observations.
Comparing the density and temperature profiles of the two sources with radi-
ation hydrodynamic simulations of an FHC, we find both sources lie close to,
but before the second collapse stage. We suggest that B1-bS may have started
the collapsing process earlier compared to B1-bN, since a larger discontinuity
point is found in its density profile.

Andre, P., Ward-Thompson, D., and Barsony, M. (1993). Submillimeter continuum obser- vations of Rho Ophiuchi A - The candidate protostar VLA 1623 and prestellar clumps. Astrophys. J., 406:122–141.
Belloche, A., Parise, B., van der Tak, F. F. S., Schilke, P., Leurini, S., Gu ̈sten, R., and Nyman,L.-A ̊.(2006).TheevolutionarystateofthesoutherndensecoreChamaeleon- MMS1. Astron. Astrophys., 454:L51–L54.
Bhandare, A., Kuiper, R., Henning, T., Fendt, C., Marleau, G.-D., and Ko ̈lligan, A. (2018). First core properties: from low- to high-mass star formation. Astron. Astrophys., 618:A95.
Boss, A. P. and Yorke, H. W. (1995). Spectral energy of first protostellar cores: Detecting ’class -I’ protostars with ISO and SIRTF. Astrophys. J., 439:L55–L58.
Chen, X., Arce, H. G., Zhang, Q., Bourke, T. L., Launhardt, R., Schmalzl, M., and Henning, T. (2010). L1448 IRS2E: A Candidate First Hydrostatic Core. Astrophys. J., 715:1344– 1351.
Dullemond, C. P., Juhasz, A., Pohl, A., Sereshti, F., Shetty, R., Peters, T., Commercon, B., and Flock, M. (2012). RADMC-3D: A multi-purpose radiative transfer tool. Astro- physics Source Code Library.
Dunham, M. M., Chen, X., Arce, H. G., Bourke, T. L., Schnee, S., and Enoch, M. L. (2011). Detection of a Bipolar Molecular Outflow Driven by a Candidate First Hydrostatic Core. Astrophys. J., 742:1.
Enoch, M. L., Lee, J.-E., Harvey, P., Dunham, M. M., and Schnee, S. (2010). A Candidate Detection of the First Hydrostatic Core. Astrophys. J., 722:L33–L38.
Friesen, R. K., Pon, A., Bourke, T. L., Caselli, P., Di Francesco, J., Jørgensen, J. K., and Pineda, J. E. (2018). ALMA Detections of the Youngest Protostars in Ophiuchus. Astro- phys. J., 869(2):158.
Fuente, A., Gerin, M., Pety, J., Commerc ̧on, B., Agu ́ndez, M., Cernicharo, J., Marcelino, N., Roueff, E., Lis, D. C., and Wootten, H. A. (2017). Chemical segregation in the young protostars Barnard 1b-N and S. Evidence of pseudo-disk rotation in Barnard 1b-S. Astron. Astrophys., 606:L3.
Fujishiro, K., Tokuda, K., Tachihara, K., Takashima, T., Fukui, Y., Zahorecz, S., Saigo, K., Matsumoto, T., Tomida, K., Machida, M. N., Inutsuka, S.-i., Andre ́, P., Kawamura, A., and Onishi, T. (2020). A Low-velocity Bipolar Outflow from a Deeply Embedded Object in Taurus Revealed by the Atacama Compact Array. Astrophys. J., 899(1):L10.
Gerin, M., Pety, J., Commerc ̧on, B., Fuente, A., Cernicharo, J., Marcelino, N., Ciardi, A., Lis, D. C., Roueff, E., Wootten, H. A., and Chapillon, E. (2017). Evidence for disks at an early stage in class 0 protostars? Astron. Astrophys., 606:A35.
Gerin, M., Pety, J., Fuente, A., Cernicharo, J., Commerc ̧on, B., and Marcelino, N. (2015). Nascent bipolar outflows associated with the first hydrostatic core candidates Barnard 1b-N and 1b-S. Astron. Astrophys., 577:L2.
Hirano, N., Kamazaki, T., Mikami, H., Ohashi, N., and Umemoto, T. (1999). Discovery of Two Extreme Young Protostars in Barnard 1. In Nakamoto, T., editor, Star Formation 1999, pages 181–182.
Hirano, N. and Liu, F.-c. (2014). Two Extreme Young Objects in Barnard 1-b. Astrophys. J., 789:50.
Ho, P. T. P., Moran, J. M., and Lo, K. Y. (2004). The Submillimeter Array. Astrophys. J., 616(1):L1–L6.
Huang, Y.-H. and Hirano, N. (2013). Probing the Earliest Stage of Protostellar Evolu- tion—Barnard 1-bN and Barnard 1-bS. Astrophys. J., 766(2):131.
Hung, C.-L., Lai, S.-P., and Yan, C.-H. (2010). The Evolution of Density Structure of Starless and Protostellar Cores. Astrophys. J., 710(1):207–211.
Inutsuka, S.-i. (2012). Present-day star formation: From molecular cloud cores to pro- tostars and protoplanetary disks. Progress of Theoretical and Experimental Physics, 2012(1):01A307.
Larson, R. B. (1969). Numerical calculations of the dynamics of collapsing proto-star. MNRAS, 145:271.
Machida, M. N., Inutsuka, S.-i., and Matsumoto, T. (2008). High- and Low-Velocity Mag- netized Outflows in the Star Formation Process in a Gravitationally Collapsing Cloud. Astrophys. J., 676:1088–1108.
Marcelino, N., Gerin, M., Cernicharo, J., Fuente, A., Wootten, H. A., Chapillon, E., Pety, J., Lis, D. C., Roueff, E., Commerc ̧on, B., and Ciardi, A. (2018). ALMA observations of the young protostellar system Barnard 1b: Signatures of an incipient hot corino in B1b-S. Astron. Astrophys., 620:A80.
Masunaga, H. and Inutsuka, S.-i. (2000). A Radiation Hydrodynamic Model for Protostellar Collapse. II. The Second Collapse and the Birth of a Protostar. Astrophys. J., 531:350– 365.
Masunaga, H., Miyama, S. M., and Inutsuka, S.-i. (1998). A Radiation Hydrodynamic Model for Protostellar Collapse. I. The First Collapse. Astrophys. J., 495:346–369.
Maureira, M. J., Arce, H. G., Dunham, M. M., Pineda, J. E., Ferna ́ndez-Lo ́pez, M., Chen, X., and Mardones, D. (2017). Kinematics of a Young Low-mass Star-forming Core: Un- derstanding the Evolutionary State of the First-core Candidate L1451-mm. Astrophys. J., 838:60.
Ossenkopf, V. and Henning, T. (1994). Dust opacities for protostellar cores. Astron. Astro- phys., 291:943–959.
Penston, M. V. (1969). Dynamics of self-gravitating gaseous spheres-III. Analytical results in the free-fall of isothermal cases. MNRAS, 144:425.
Pezzuto, S., Elia, D., Schisano, E., Strafella, F., Di Francesco, J., Sadavoy, S., Andre ́, P., Benedettini, M., Bernard, J. P., di Giorgio, A. M., Facchini, A., Hennemann, M., Hill, T., Ko ̈nyves, V., Molinari, S., Motte, F., Nguyen-Luong, Q., Peretto, N., Pestalozzi, M., Polychroni, D., Rygl, K. L. J., Saraceno, P., Schneider, N., Spinoglio, L., Testi, L., Ward- Thompson, D., and White, G. J. (2012). Herschel observations of B1-bS and B1-bN: two first hydrostatic core candidates in the Perseus star-forming cloud. Astron. Astrophys., 547:A54.
Pineda, J. E., Arce, H. G., Schnee, S., Goodman, A. A., Bourke, T., Foster, J. B., Robitaille, T., Tanner, J., Kauffmann, J., Tafalla, M., Caselli, P., and Anglada, G. (2011). The Enig- matic Core L1451-mm: A First Hydrostatic Core? Or a Hidden VeLLO? Astrophys. J., 743:201.
Price, D. J., Tricco, T. S., and Bate, M. R. (2012). Collimated jets from the first core. MNRAS, 423:L45–L49.
Saigo, K., Tomisaka, K., and Matsumoto, T. (2008). Evolution of First Cores and Formation of Stellar Cores in Rotating Molecular Cloud Cores. Astrophys. J., 674(2):997–1014.
Shu, F. H. (1977). Self-similar collapse of isothermal spheres and star formation. Astro- phys. J., 214:488–497.
Tobin, J. J., Looney, L. W., Li, Z.-Y., Chandler, C. J., Dunham, M. M., Segura-Cox, D., Sadavoy, S. I., Melis, C., Harris, R. J., Kratter, K., and Perez, L. (2016). The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). II. Multiplicity of Protostars in the Perseus Molecular Cloud. Astrophys. J., 818:73.
Cˇernis,K.andStraizˇys,V.(2003).InterstellarExtinctionintheDirectionoftheBarnard1 Dark Cloud in Perseus. Baltic Astronomy, 12:301–321.
Va ̈isa ̈la ̈, M. S., Harju, J., Mantere, M. J., Miettinen, O., Sault, R. S., Walmsley, C. M., and Whiteoak, J. B. (2014). High-resolution ammonia mapping of the very young protostellar core Chamaeleon-MMS1. Astron. Astrophys., 564:A99.
van Gelder, M. L., Tabone, B., Tychoniec, Ł., van Dishoeck, E. F., Beuther, H., Boogert, A. C. A., Caratti o Garatti, A., Klaassen, P. D., Linnartz, H., Mu ̈ller, H. S. P., and Taquet, V. (2020). Complex organic molecules in low-mass protostars on Solar System scales. I. Oxygen-bearing species. Astron. Astrophys., 639:A87.
Vorobyov, E. I. and Basu, S. (2005). The effect of a finite mass reservoir on the col- lapse of spherical isothermal clouds and the evolution of protostellar accretion. MNRAS, 360(2):675–684.
Weingartner, J. C. and Draine, B. T. (2001). Dust Grain-Size Distributions and Extinction in the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud. Astrophys. J., 548:296–309.
Ysard, N., Koehler, M., Jimenez-Serra, I., Jones, A. P., and Verstraete, L. (2019). From grains to pebbles: the influence of size distribution and chemical composition on dust emission properties. Astron. Astrophys., 631:A88.
Zari, E., Lombardi, M., Alves, J., Lada, C. J., and Bouy, H. (2016). Herschel-Planck dust optical depth and column density maps. II. Perseus. Astron. Astrophys., 587:A106.
Zucker, C., Schlafly, E. F., Speagle, J. S., Green, G. M., Portillo, S. K. N., Finkbeiner, D. P., and Goodman, A. A. (2018). Mapping Distances across the Perseus Molecular Cloud Using CO Observations, Stellar Photometry, and Gaia DR2 Parallax Measure- ments. Astrophys. J., 869(1):83.