Detection of HCOOCH3 toward a Low-Mass Protostar, NGC 1333 IRAS 4B

The rotational spectral lines of methylformate (HCOOCH3) have been detected toward a low-mass protostar, NGC 1333 IRAS 4B, with the Nobeyama 45m radio telescope. The column density is derived to be (7–37)× 1015 cm−2, assuming a source size of 1′′ and the range of the excitation temperature to be from 50K to 200K. The column density is almost comparable to those found in other low-mass star-forming regions, NGC 1333 IRAS 4A and IRAS 16293−2422. The line width of HCOOCH3 is (1.0–1.2)kms−1, which is narrower than that of the highexcitation line of CH3OH (8−4–9−3). Since NGC 1333 IRAS 4B is likely to be a very young protostar, HCOOCH3 appears even in the early stage of protostellar evolution. The spectral lines of HCOOCH3 could be used as a novel tracer for detecting an onset of star formation.