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In this era of large-scale stellar spectroscopic surveys, measurements ofstellar attributes ("labels," i.e. parameters and abundances) must be madeprecise and consistent across surveys. Here, we demonstrate that this can beachieved by a data-driven approach to spectral modeling. With The Cannon, wetransfer information from the APOGEE survey to determine precise Teff, log g,[Fe/H], and [$\alpha$/M] from the spectra of 450,000 LAMOST giants. The Cannonfits a predictive model for LAMOST spectra using 9952 stars observed in commonbetween the two surveys, taking five labels from APOGEE DR12 as ground truth:Teff, log g, [Fe/H], [\alpha/M], and K-band extinction $A_k$. The model is thenused to infer Teff, log g, [Fe/H], and [$\alpha$/M] for 454,180 giants, 20% ofthe LAMOST DR2 stellar sample. These are the first [$\alpha$/M] values for thefull set of LAMOST giants, and the largest catalog of [$\alpha$/M] for giantstars to date. Furthermore, these labels are by construction on the APOGEElabel scale; for spectra with S/N > 50, cross-validation of the model yieldstypical uncertainties of 70K in Teff, 0.1 in log g, 0.1 in [Fe/H], and 0.04 in[$\alpha$/M], values comparable to the broadly stated, conservative APOGEE DR12uncertainties. Thus, by using "label transfer" to tie low-resolution (LAMOST R$\sim$ 1800) spectra to the label scale of a much higher-resolution (APOGEE R$\sim$ 22,500) survey, we substantially reduce the inconsistencies betweenlabels measured by the individual survey pipelines. This demonstrates thatlabel transfer with The Cannon can successfully bring different surveys ontothe same physical scale.

Label Transfer from APOGEE to LAMOST: Precise Stellar Parameters for 450,000 LAMOST Giants