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.

Abstract......i
1 Introduction......1
2 Observational data......4
2.1 ObservationswiththeSMA......4
2.1.1 1.3mmand870μmobservationswiththeSMA......4
2.1.2 1.3mmand1.1mmobservationswiththeSMA......5
2.2 ALMA870μm(Band7)observations......5
3 Method and Modeling......11
3.1 Procedureofmakingsynthesizedimages......11
3.1.1 Step1:ModelSetup......11
3.1.2 Step2:CalculatingTemperature......12
3.1.3 Step3:RadiativeTransfer......12
3.1.4 Step4:SimulatingObservations......13
3.1.5 Step5:Imaging.......13
3.2 Model1:Singlepower-lawenvelope......13
3.3 Model 2: Broken power-law envelope with outflow cones......13
4 Results and Analyses......18
4.1 Theinitialparametersearchrangesandgrids......18
4.2 Thenarroweddownparameterrangesandgrids......19
4.2.1 Thebestmodel......27
5 Discussion......35
5.1 Thepresenceofthecentralpointsources......35
5.2 LuminosityofB1-bN&B1-bS......35
5.2.1 TheintrinsicluminosityoftheFHC......35
5.2.2 Thebolometricluminosityofthesource......36
5.3 MassofB1-bN&B1-bS......36
5.4 The density and temperature profiles of B1-bN&B1-bS......37
5.5 TheenvelopestructureofB1-bN&B1-bS......38
5.6 EvolutionarystageofB1-bN&B1-bS......39
6 Conclusion......40
Bibliography......43

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