VLA observations of the 9(2)-10(1)A+ methanol masers toward W3(OH)

Measurements at 2-arcsec resolution of the 9(2)-10(1)A+ emission line of methanol toward W3(OH) are presented. The frequency resolution was 12.2 kHz, or 0.16 km/s at the line rest frequency 23121.01 MHz. The two velocity components seen in single-dish spectra are separated by about 1-arcsec, but each is unresolved. This implies intrinsic source sizes of less than 1-arcsec. For the masing spike feature at -43.3 km/s, the line brightness temperature is greater than 20,000 K. For the broader emission at -43.9 km/s, it is greater than 5000 K, showing that this emission is also caused by masing. The spike is 0.5-arcsec southwest and the broader feature is 1.5 arcsec northwest of the continuum peak. An absorption-line spectrum of the 10(1)-9(2)A- line taken with the 100 m telescope is also presented, and it is concluded that this absorption and the 9(2)-10(1)A+ maser emission are both formed in the same cloud where OH masers and ammonia absorption are present.