Evolution of the Dust/Gas Environment around Herbig Ae/Be Stars

Abstract

Using the KOSMA 3 m telescope, 54 Herbig Ae/Be (HAe/Be) stars were surveyed in CO and ¹³CO emission lines. The properties of the stars and their circumstellar environments were studied by fitting spectral energy distributions (SEDs). The mean line width of ¹³CO (2-1) lines of this sample is 1.87 km s^-1. The average column density of H₂ is found to be 4.9 × 10²¹ cm^-2 for stars younger than 10⁶ yr, while this drops to 2.5 × 10²¹ cm^-2 for those older than 10⁶ yr. No significant difference is found among the SEDs of HAe and HBe stars of the same age. Infrared excess decreases with age, envelope masses and envelope accretion rates decease with age after 10⁵ yr, the average disk mass of the sample is 3.3 × 10^-2 M _sun, the disk accretion rate decreases more slowly than the envelope accretion rate, and a strong correlation between the CO line intensity and the envelope mass is found.