Rotation velocities of red and blue field horizontal-branch stars

We present measurements of the projected stellar rotation velocities (upsilon sin i) of a sample of 45 candidate field horizontal-branch (HB) stars spanning a wide range of effective temperatures, from red HB stars with T-eff similar or equal to 5000 K to blue HB stars with T-eff of 17,000 K. Among the cooler blue HB stars (T-eff = 7500-11500 K), we confirm prior studies showing that, although a majority of stars rotate at upsilon sin i < 15 km s(-1), there exists a subset of "fast rotators '' with upsilon sin i as high as 30-35 km s(-1). All but one of the red HB stars in our sample have upsilon sin i < 10 km s(-1), and no analogous rotation bimodality is evident. We also identify a narrow-lined hot star (T-eff similar or equal to 16,000 K) with enhanced photospheric metal abundances and helium depletion, similar to the abundance patterns found among hot BHB stars in globular clusters, and four other stars that may also belong in this category. We discuss details of the spectral line fitting procedure that we use to deduce upsilon sin i and explore how measurements of field HB star rotation may shed light on the issue of HB star rotation in globular clusters.