Line Shift and Broadening Caused by the Gravity Bending of the Cassegrain Spectrograph

The effects of the gravity bending of both the collimator and camera of the Cassegrain spcctrograph of the 1-m telescope at the Yunnan Observatory are analysed theoretically, Forty-five photographs with the comparison spectrum at as many pointings of the telescope are taken to measure the line shift caused by the gravity bending. The measured results show that the effects of the gravity bending surely exist and the line lift is of the order of magnitude of a micron. The measured data are in accordance with the theoretical calculations. Some methods are also discussed for offsetting the effects of the gravity bending on the mea surcment of wavelengths, line profiles and spectral resolving powers.