摘要：6478 Gault, a main-belt asteroid, was detected of cometary activity recently and has been recognized as an active asteroid since 2018 December. We present imaging and spectroscopic observations of 6478 Gault, to probe its properties since activation and to shed light on the how Gault became an active asteroid. We obtain V-band imaging and optical spectra using the Alhambra Faint Object Spectrograph and Camera on board the 2.5m Nordic Optical Telescope. Our V-band imaging shows a long tail spanning more than 3′, but there is no trace of possible fragmentation or debris in our imaging. A close look at the asteroid also shows a precursor of a second tail. Our spectrum shows that Gault is a C-type asteroid, indicating it belongs to the carbonaceous Tamara family in the Phocaea family region. In addition, we also investigate possible emission lines of CN and C2 that are commonly seen in comets. However, they are not detected in our optical spectrum. As CN and C2 are strong emission lines and can be used as alternate indicators of water, the nondetection of CN and C2 evinces no trace of water production from ice sublimation.
