As a part of the “ Dust , Ice , and Gas In Time ” ( DIGIT ) key program on Herschel , we observed GSS30-IRS1 , a Class I protostar located in Ophiuchus ( d = 120 pc ) , with Herschel /Photodetector Array Camera and Spectrometer ( PACS ) .
More than 70 lines were detected within a wavelength range from 50 \mu m to 200 \mu m , including CO , H _ { 2 } O , OH , and two atomic [ O I ] lines at 63 and 145 \mu m. The [ C II ] line , known as a tracer of externally heated gas by the interstellar radiation field , is also detected at 158 \mu m. All lines , except [ O I ] and [ C II ] , are detected only at the central spaxel of 9 \arcsec .4 \times 9 \arcsec .4 .
The [ O I ] emissions are extended along a NE-SW orientation , and the [ C II ] line is detected over all spaxels , indicative of external PDR .
The total [ C II ] intensity around GSS30 reveals that the far-ultraviolet radiation field is in the range of 3 to 20 \textit { G } _ { \textrm { 0 } } , where \textit { G } _ { \textrm { 0 } } is in units of the Habing Field , 1.6 \times 10 ^ { -3 } erg cm ^ { -2 } s ^ { -1 } .
This enhanced external radiation field heats the envelope of GSS30-IRS1 , causing the continuum emission to be extended , unlike the molecular emission .
The best-fit continuum model of GSS30-IRS1 with the physical structure including flared disk , envelope , and outflow shows that the internal luminosity is 10 \textit { L } _ { \odot } , and the region is externally heated by a radiation field enhanced by a factor of 130 compared to the standard local interstellar radiation field .