High signal-to-noise spectra with spectral resolution of more than 10(
5) have been obtained of one normal B9.5V, one normal A1V, two Am star
s, and two HgMn B stars having v sin i less than 6 km s(-1). These spe
ctra are modeled with LTE line profile synthesis to test the extent to
which the spectrum of each star can be modeled correctly with a singl
e set of parameters T-e, log g, chemical abundances, v sin i, and (dep
th-independent) microturbulent velocity xi. The answer to this questio
n is important for abundance analysis of A and B stars; if conventiona
l line synthesis does not reproduce the line profiles observed in star
s of small v sin i, results obtained from such analysis are not likely
to be very precise. The comparison of models with observations is the
n used to search for direct evidence of atmospheric motions, including
line-strength dependent broadening, line core shape, and line asymmet
ries, in order to study how the microturbulence derived from abundance
analysis is related to more direct evidence of atmospheric velocity f
ields. It is found for the three stars with 12,000 greater than or equ
al to T-e greater than or equal to 10,200 K (the normal star 21 Peg an
d the two HgMn stars 53 Tau and HD 193452) that xi is less than 1 km s
(-1), and line profiles are reproduced accurately by the synthesis wit
h a single set of parameters. The slightly cooler (T-e approximate to
9800 K) star HD 72660 has only a slightly stronger surface convective
layer than the hotter stars, but for this star xi approximate to 2.2 k
m s(-1). Strong spectral lines all show significant asymmetry, with th
e blue line wing deeper than the red wing, and have line bisectors whi
ch have curvature towards the blue with a span of about 0.5 to 1.0 km
s(-1). A single model fits all lines satisfactorily. The two Am stars
(HD 108642 and 32 Aqr), with T-e approximate to 8000 K, are found to h
ave much larger values of xi (4 to 5 km s(-1)). The strong spectral li
nes of these two stars are extremely asymmetric, with depressed blue w
ings, and the bisectors have spans of order 3 km s(-1). No consistent
fit to all lines can be found with a single model of the type used her
e. It is concluded (a) that classical LTE line synthesis is able to re
produce with considerable accuracy the line profiles of late B and ear
ly A stars with T-e above about 9500 K, but that the LTE model with de
pth-independent microturbulence provides a very poor approximation for
cooler A stars, (b) that curve-of-growth microturbulent velocities in
A stars are related to directly detectable atmospheric velocity field
s, and (c) that the discrepancies between calculated and observed line
profiles in stars with temperatures in the vicinity of 8000 K are so
large that abundances derived mainly from saturated lines may well con
tain significant errors. As a by-product, laboratory gf values for Fe
II between 3800 and 5300 Angstrom have been combined to form a set of
data optimized for internal consistency of the g f values.