  Given their location on the Hertzsprung-Russell (HR) diagram, thoroughly
characterized subgiant stars can place stringent constraints on a wide range of
astrophysical problems. Accordingly, they are prime asteroseismic targets for
the Transiting Exoplanet Survey Satellite (TESS) mission. In this work, we
infer stellar properties for a sample of 347 subgiants located in the TESS
Continuous Viewing Zones (CVZs), which we select based on their likelihood of
showing asteroseismic oscillations. We investigate how well they can be
characterized using classical constraints (photometry, astrometry), and
validate our results using spectroscopic values. We derive luminosities,
effective temperatures, and radii with mean 1$\sigma$ random (systematic)
uncertainties of 4.5% (2%), 33 K (60 K), and 2.2% (2%), as well as more
model-dependent quantities such as surface gravities, masses, and ages. We use
our sample to demonstrate that subgiants are ideal targets for mass and age
determination based on HR diagram location alone, discuss the advantages of
stellar parameters derived from a detailed characterization over widely
available catalogs, show that the generally used 3D extinction maps tend to
overestimate the extinction for nearby stars (distance $\lesssim$ 500 pc), and
find a correlation that supports the rotation-activity connection in post main
sequence stars. The complementary roles played by classical and asteroseismic
data sets will open a window to unprecedented astrophysical studies using
subgiant stars.
