Starless Cloud Core L1517b in Envelope Expansion With Core Collapse

Abstract

Various spectral emission lines from the star-forming molecular cloud core L1517B manifest red asymmetric double-peaked profiles with stronger red peaks and weaker blue peaks, in contrast to the oft-observed blue-skewed molecular spectral line profiles with blue peaks stronger than red peaks. Invoking a spherically symmetric general polytropic hydrodynamic shock model for the envelope expansion with a core collapse (EECC) phase, we show the radial flow velocity, mass density, and temperature structures of a self-similar evolution for L1517B in a dynamically consistent manner. By prescribing simple radial profiles of abundance distribution for pertinent molecules, we perform molecular excitation and radiative transfer calculations using the publicly available RATRAN code set for the spherically symmetric case. Emphatically, the spectral profiles of line emissions from the same molecules but for different line transitions as well as spectra of closely pertinent isotopologues strongly constrain the self-similar hydrodynamics of a cloud core with prescribed abundances. Our computational results show that the EECC model reproduces molecular spectral line profiles in sensible agreement with the observational data of the Institut de Radioastronomie Millimétrique (IRAM), Five College Radio Astronomical Observatory, and Effelsberg 100 m telescopes for L1517B. We also report the spatially resolved observations of the optically thick line HCO + (1 − 0) using the Purple Mountain Observatory 13.7 m telescope at Delingha in China and the relevant fitting results. Hyperfine line structures of NH 3 and N 2 H + transitions are also fitted to consistently reveal the dynamics of the central core collapse. As a consistent model check, radial profiles of 1.2 mm and 850 μm dust continua observed by the IRAM 30 m telescope and the Submillimeter Common-User Bolometer Array, respectively, are also fitted numerically using the same EECC model that produces the molecular line profiles. L1517B is likely undergoing an EECC shock phase. For future observational tests, we also predict several molecular line profiles with spatial distributions, the radial profile of the sub-millimeter continuum at wavelength 450 μm, as well as the radial profiles of the column density and visual extinction for L1517B.

A multiwavelength observation and investigation of six infrared dark clouds

“…Such coexistence of inward and outward motions in star-forming molecular clouds or cores may be the "envelope expansion with core collapse (EECC)" (Gao & Lou 2010;. The clouds or cores B68 (Lada et al 2003), SFO 11NE (Thompson & White 2004), L1495A-N, L1507A, L1512 (Lee et al 2001), L1517B (Fu et al 2011), and L1689-SMM16 (Chitsazzadeh et al 2014) were also shown relative to the reports.…”

Filament L1482 in the California molecular cloud

“…For quasi-spherical molecular clumps in hydrodynamic evolution, it is possible to use at least four major observational diagnostics to constrain self-consistent dynamic models coupled with radiative transfer calculations (e.g. Fu et al 2011), namely, extensive observations of various properties of molecular lines (e.g. line profiles), submillimeter continuum emissions from thermal dusts, and dust extinction observations as well as neutral hydrogen 21 cm absorption lines in MCs.…”

Why Do Some Cores Remain Starless?

“…As with other cores, estimates of its physical properties are subject to the molecular tracer. For instance, the mass and radius for this core varies between ~ 0.05 M ⊙ and ~ 0.06 pc(Benson & Myers 1989) to ~ 1.7 M ⊙ (Kirk et al 2005) and ~ 3.89 M ⊙ (Fu et al 2011). The gas temperature for this core has been reported to be ~ 9 K (Tafalla et al 2002; Keto & Field 2005).…”

“…A starless core that is probably experiencing a breathing mode, i.e. exhibiting signs of in-fall close to the centre, but has an expanding envelope (Keto & Field 2005; Fu, Gao, & Lou 2011). As with other cores, estimates of its physical properties are subject to the molecular tracer.…”