We have investigated a group of 18 Algol-type binaries to determine the gen
eral morphologies and physical properties of the accretion regions in these
systems. The systems studied were V505 Sgr, RZ Cas, AI Dra, TV Cas, TW Cas
, delta Lib, RW Tau, TW Dra, beta Per, TX UMa, U Sge, S Equ, U CrB, RS Vul,
SW Cyg, CX Dra, TT Hya, and AU Mon, in order of increasing orbital period
P = 1.18-11.11 days. In addition, the RS CVn-type binary HR 1099 (V711 Tau)
was observed to illustrate the appearance of chromospheric H alpha emissio
n. Nearly 2200 time-resolved H alpha spectra were collected from 1992 March
to 1994 December with the McMath-Pierce Solar Telescope at NSO and mostly
with the Coude Feed Telescope at KPNO. The spectra were obtained at phases
around the entire orbit of each binary and were closely spaced to permit th
e detection of transitions in the profiles. Moreover, the spectra were obta
ined typically within three orbital cycles to reduce the influence of secul
ar variations. Difference profiles were calculated by subtracting a composi
te theoretical photospheric spectrum from the observed spectrum.
The analysis of the H alpha difference profiles demonstrates that the accre
tion structures in Algol binaries have four basic morphological types: (1)
double-peaked emission systems in which the accretion structure is a transi
ent or classical accretion disk; (2) single-peaked emission systems in whic
h the accreted gas was found along the trajectory of the gas stream and als
o between the two stars in an accretion annulus; (3) alternating single- an
d double-peaked emission systems, which can change between a single-peaked
and a double-peaked type within an orbital cycle; and (4) weak spectrum sys
tems in which there was little evidence of any accretion structure since th
e difference spectra are weak at all phases. The first two types are the do
minant morphologies. The first type can be interpreted physically as a disk
like distribution, while the second is a gas stream-like distribution.
The most common type in short-period Algols with 2.7 days < P < 4.5 days is
a predominantly single-peaked emission feature in the H alpha difference p
rofiles (Type 2). This feature is redshifted during the phase interval phi
similar to 0.15-0.45 and blueshifted from phi similar to 0.55-0.85. This si
ngle-peaked emission is often composed of two closely spaced emission peaks
where one peak is at the H alpha rest wavelength. The other peak is bluesh
ifted at phi similar to 0.65, where the line of sight is along the length o
f the approaching gas stream. Systems which display this morphology include
RZ Cas, RW Tau, TW Dra, beta Per, TX UMa, S Equ, and RS Vul. The orbital v
ariation of the Ha observed profiles of HR 1099 was similar to that seen in
the difference spectra of this group and suggests that chromospheric emiss
ion may play a significant role in these binaries. A less common morphologi
cal type in the group of short-period Algols was a widely separated double-
peaked disk-like distribution (Type 1) where the gas is in a transient or c
lassical accretion disk. All of the long-period systems (P > 6 days) were f
ound to have slightly variable but permanent accretion disks at all epochs
(i.e., CX Dra, TT Hya, and AU Mon), similar to those found in cataclysmic v
ariables. SW Cyg (P = 4.57 days) was found to be an intermediate case betwe
en the shorter period systems with P < 4.5 days and the longer period group
with P > 6 days. Two systems, U Sge and U CrB, displayed alternating singl
e- and double-peaked emission at different epochs (Type 3), and changes fro
m one type to another were detected within a 12 hour time interval. Observa
tions at multiple epochs suggest that four members of the single-peaked emi
ssion group, namely RW Tau, TX UMa, S Equ, and RS Vul, may actually belong
to the alternating group. So, the complete group of alternating systems cov
ers periods of 2.7 days < P < 4.5 days. Finally, the systems V505 Sgr, 6 Li
b, AI Dra, TW Cas, and TV Cas had weak difference spectra or uninteresting
observed spectra at most phases (Type 4). All of these systems have orbital
periods P < 2.4 days and are high in the r-q diagram. In these cases, the
mass-gaining star is very large relative to the binary separation, and the
path of the gas stream path is very short, so there is very little room to
form any substantial accretion structures as found in the other systems.