IRAS 20000+4954 (Z Cyg):
One of the most striking properties of this star is its very high radial
velocity (
).
It is a Mira variable with a relatively short period (
days, GCVS).
For this type of miras,
it has been suggested (see e.g.
Habing et al. 1994) that radiation
pressure on dust is less effective. If this is the case in Z Cyg, either dust
condensation is relatively low or the star might have a low luminosity.
Yet this is not consistent with the high (
) value of 
.
The expansion velocity measured in OH is very small:
(Sivagnanam
et al. 1989), and slightly greater in CO
(
). This may indicate
an asymmetric envelope.
Groenewegen et al. (1996) estimated the
mass-loss rate from CO(2-1) emission
to be 
/yr.
IRAS 20194+3646 (BI Cyg):
This object is a known binary with irregular variability (Lc) and supergiant
luminosity (Proust et al. 1981).
It displays one of the highest value of : 
.
Binarity may be at least partially responsible for this high value,
since the
geometry of the envelope is probably affected by the companion. Also, if the
companion is hot, it
could photodissociate CO in the external regions of the shell.
IRAS 20547+0247 (U Equ):
OH and H2O masers have been been found to vary in velocity
and character in this unusual star over short timescales
(Barnbaum
et al. 1996). The outflow velocities are small in OH and H2O
(
and 
, respectively), and double peaked profiles
are not always present. We recently detected a weak CO(2-1) line
at IRAM (3 sigma) (
;
integrated intensity: 0.403 K 
)
with an expansion velocity of 
, which,
unlike the masers, is in the normal range for an evolved star.
U Equ has a number of interesting characteristics that
point to an unusual circumstellar environment. Its optical spectrum
shows anomalously deep, yet narrow
molecular absorption lines of TiO, AlO and VO and bright
molecular emission lines of the same compounds.
Its 
colour indicates optically thin dust, yet the LRS
spectrum shows strong silicate
absorption and a strong 
excess,
consistent with a thick, dusty envelope. It is possible, then, that this star
has a cold Keplerian disk viewed edge on, with axial
nebulosity from which the optical emission arises
(Barnbaum et al. 1996).
The spectral type of the central star is difficult to identify
with certainty. The presence of H
, H
and
H
absorption and an absence of photospheric molecular bands indicate
an early-K spectral type, yet the presence
of the Paschen series points to a warmer type, early to mid-G. Luminosity
sensitive absorption lines in the blue indicate a giant luminosity.
Neither object is detected in CO, with 
and 157,
respectively. In these cases, the origin of the low CO emission
is probably related to photodissociation by strong UV radiation from the
Be stars. The case of 06259-1301 is well studied, and
Brown et al. (1995) find that the star is surrounded by
an inhomogeneous disk of dust and gas and has a circumstellar extinction
in the
FUV that could be characteristic of PAHs. H2 is photodissociated and CO
has disappeared. Other observations suggest a
bipolar object (a Herbig Ae/Be star, surrounded by a disk, according to
Sitko et al. 1994). In 06491-0654, two components in the wind have been
identified (Hutsemekers 1985), probably due to an outburst. This object
would be in a transition state between Be and B[e] stars
(Jaschek et al. 1992).
05132+5331, 07120-4433, 09076+3110, 16235+1900, 19510-5919 and 21088+6817 (Tables 14 (click here) and 17 (click here)):
All these objects are located in region II in the
van der Veen & Habing
(1988) diagram. This indicates that
they are surrounded by small amounts of circumstellar material. Indeed
their LRS is of class 1n or 2n with 
, which, for such low opacity,
indicates no silicates or very little.
Then, the flux could be more photospheric than circumstellar
and so, the 
would be less meaningful.