The BOSS Lyman-alpha Forest Sample from SDSS Data Release 9

We present the BOSS Lyman-alpha (Lya) Forest Sample from SDSS DataRelease 9, comprising 54,468 quasar spectra with zqso > 2.15 suitablefor Lya forest analysis. This data set probes the intergalactic mediumwith absorption redshifts 2.0 z_alpha 5.7 over an area of 3275square degrees, and encompasses an approximate comoving volume of 20h^-3 Gpc^3. With each spectrum, we have included several productsdesigned to aid in Lya forest analysis: improved sky masks that flagpixels where data may be unreliable, corrections for known biases in thepipeline estimated noise, masks for the cores of damped Lya systems andcorrections for their wings, and estimates of the unabsorbed continua sothat the observed flux can be converted to a fractional transmission.The continua are derived using a principal component fit to the quasarspectrum redwards of restframe Lya (lambda > 1216 Ang), extrapolatedinto the forest region and normalized by a linear function to fit theexpected evolution of the Lya forest mean-flux. The estimated continuum