COMMON LYMAN-ALPHA ABSORPTION TOWARD THE QUASAR PAIR Q1343- EVIDENCE FOR LARGE AND QUIESCENT CLOUDS(2640A, Q1343+266B )

We present observations of the Ly alpha forest of the close quasar pai r Q1343+2640A (z(em) = 2.029) and B (z(em) = 2.031). We detect eight a bsorption lines of Ly alpha common to both spectra and not attributabl e to metalline systems in the redshift range 1.7 < z < 2.1 and four li nes which are seen in one spectrum but not the other. At the 9''.5 sep aration of the two quasars, this implies a firm lower limit on the cha racteristic size of the Ly alpha clouds of 40 h(100)(-1) kpc (where h( 100) H-0/100 km s(-1) Mpc(-1), q(0) = 0.5) at a redshift z similar or equal to 1.8. The upper -1 limit on the cloud size is much more uncert ain owing to the small number of observed lines, but taking the observ ed fraction of common lines at face value in the context of a simple m odel, the absorbers are shown to have radii smaller than about 310 h(1 00)(-1) kpc. Significant velocity and equivalent width variations are seen with an rms velocity difference of similar to 65 km s(-1) between the common absorption lines along the two lines of sight.