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We report high-resolution (R = 30\ 000, 45\ 000 and 75\ 000) echelle andmedium-resolution (R = 22\ 000 and 10\ 000) spectroscopic observations of thelong-period, eclipsing binary $\epsilon$ Aurigae during the 2009 - 2011eclipse. Low-excitation shell lines, viz, the K {\sevensize \rm I} line at 7699\AA\ (with 346 data points), Cr {\sevensize \rm I} lines at 5345.807 \AA\ and5348.326 \AA\ and Fe {\sevensize \rm I} line at 5110.435 \AA\ which originatedfrom the disk shaped secondary, H$\alpha$ and the shell components of the NaD$_{1}$ and D$_{2}$ lines show significant variation in their shapes and radialvelocities during the eclipse. The equivalent width curve shown by the K{\sevensize \rm I} line around the ingress and egress phases indicates that thegas density in the trailing edge is about a factor of two higher than thedensity in the leading edge. Using a geometrical model, in which a homogeneous,cylindrical Keplarian disk eclipses the F0Ia primary star and the shellabsorption lines originate from the gaseous atmosphere around an opaque disk,we fit the equivalent width and the radial velocity curves of the K {\sevensize\rm I} line covering the full eclipse. A reasonably good fit can be achieved bya low-mass binary model where the mass of the central star of the disk is 5.4M$_{\odot}$ and the mass of the primary is 2.5 M$_{\odot}$ and a disk size of8.9 AU. The low-mass of the primary, with enhanced $s$-process elements foundby Sadakane et al. (2010), supports that it is a post-AGB F supergiant. For thehigh-mass binary model, the modelled radial velocity curve deviatessignificantly from the observations.

K I 7699 {\AA} and related shell lines during the recent eclipse of $\epsilon$ Aurigae