Evolutionary status of the pre-protostellar core L1498

Area of Science:

• Astronomy and Astrophysics
• Star Formation
• Astrochemistry

Background:

• L1498 serves as a key example of a dense, cold pre-protostellar core.
• Understanding its evolutionary status requires detailed study of its structure, dynamics, and chemistry.

Purpose of the Study:

• To investigate the evolutionary status, structure, dynamics, and chemical properties of the L1498 pre-protostellar core.
• To map molecular emissions at high spatial and spectral resolution.

Main Methods:

• High spatial and spectral resolution observations of molecules (CCS, NH3, C3H2, HC7N, C18O, 13CO, CS) using NASA's DSN 70 m antennas, AT&T 7 m antenna, VLA, and OVRO MMA.
• Analysis of molecular emission distributions and line profiles to infer density, structure, and chemical differentiation.
• Combining data from multiple telescopes to achieve high angular resolution (9"-12").

Main Results:

• Identified a dense core (n(H2) > 10^4 cm^-3) traced by CCS emission, elongated SE-NW.
• Observed an 'onion-shell' chemical structure with NH3 in the inner core and CCS in the outer shell, supported by limb brightening.
• Detected small-scale dense condensations within the CCS and CS emitting regions.

Conclusions:

• The observed chemical differentiation suggests a time-dependent evolution in a quasi-static or slowly contracting core.
• L1498's outer envelope is actively accreting low-density gas, driving the core's growth.
• The core may become unstable and collapse to form a protostar within the next 5 million years.