From the analysis of more than 92 ks of data obtained with the laxpc instrument on board Astrosat we have detected a clear high-frequency QPO whose frequency varies between 67.4 and 72.3 Hz .
In the classification of variability classes of GRS 1915+105 , at the start of the observation period the source was in class \omega and at the end the variability was that of class \mu : both classes are characterized by the absence of hard intervals and correspond to disk-dominated spectra .
After normalization to take into account time variations of the spectral properties as measured by X-ray hardness , the QPO centroid frequency is observed to vary along the hardness-intensity diagram , increasing with hardness .
We also measure phase lags that indicate that HFQPO variability at high energies lags that at lower energies and detect systematic variations with the position on the hardness-intensity diagram .
This is the first time that ( small ) variations of the HFQPO frequency and lags are observed to correlate with other properties of the source .
We discuss the results in the framework of existing models , although the small ( 7 % ) variability observed is too small to draw firm conclusions .