The group of B[e] stars, to which HD 45677 belongs, is not very homogeneous. It contains young stellar objects, such as Herbig Be stars, but also evolved objects, such as post-AGB stars, Luminous Blue Variables (LBVs) and planetary nebulae (Thé et al. 1994). Some of these stellar groups even occupy overlapping regions in the HR-diagram, which makes it even more difficult to classify such objects. To obtain a star's position in the HR-diagram we must know its distance, which is very uncertain for HD 45677. Sitko et al. (1994) argued that the UV extinction curve of HD 45677 in 1992 is compatible with interstellar extinction over a distance of 900 pc. At this distance HD 45677 would be at approximately the same distance as the outer ridge of a large molecular complex that stretches from the Mon R2 cloud to the CMa OB1 complex (Maddalena et al. 1986).
However, since our line of sight towards parts of Canis Majoris is known to
be almost devoid of interstellar extinction (e.g.
Bruhweiler 1994), the
use of an average distance-interstellar extinction relation by
Sitko et al. (1994)
may yield erroneous results. Therefore, we constructed a graph of
E(B-V) versus photometric stellar distance for stars from the Hipparcos
Input Catalogue, located within an 1
circle around HD 45677. This plot
is shown in Fig. 12 (click here). From this plot we derive a maximum distance of
1.5 kpc towards HD 45677, by assuming that its E(B-V) of 0
30 is
completely due to interstellar extinction.
Furthermore, we can compute a photometric distance towards HD 45677 by
assuming that it is located on the zero-age main-sequence (ZAMS) and by
assuming that there is no circumstellar obscuration present at the maximum
recorded brightness of HD 45677 by Swings & Swings (1972).
If we also
assume that its B-V at that time was not very different from the minimum of
the range shown in Fig. 2 (click here), and use the appropriate parameters for a B2 V
star from Schmidt-Kaler (1982), the resulting ZAMS distance is 550 pc.
Under the same assumptions we computed the maximum intrinsic luminosity of
HD 45677 by adopting the maximum distance of 1.5 kpc, resulting in
.
A HR-diagram with the position of HD 45677, computed using the ZAMS distance
of 550 pc, the distance of 900 pc by Sitko et al. (1994),
and the maximum
distance of 1.5 kpc is shown in Fig. 13 (click here). In Fig. 13 (click here)a the pre main-sequence
evolutionary tracks and the birthline by
Palla & Stahler (1993)
for a proto-stellar accretion rate of 
are
also plotted, whereas in Fig. 13 (click here)b we plotted the post main-sequence
evolutionary tracks by Maeder & Meynet (1988).
As can be seen from Fig. 13 (click here)a,
of the three positions of HD 45677 in the HR diagram, the one computed using
the ZAMS distance of 550 pc is the only one which falls below the birthline.
This implies that if HD 45677 is a young object, as suggested by
Grady et al. (1993),
its distance will be close to its ZAMS distance of 550 pc. In that
case the star cannot be formed in the molecular cloud suggested by
Sitko et al. (1994), leaving us with the question where the star formation
region is. However, as shown by
Palla & Stahler (1993) a higher proto-stellar
accretion rate will result in a birthline which will intersect the ZAMS
at considerably higher masses. But for masses like for HD 45677 still not more
than 10
yr is needed to reach the ZAMS.
If we assume that HD 45677 is in fact an evolved object, we do not have these
problems. In that case the star might very well have formed in the molecular
complex suggested by Sitko et al. (1994),
but a few times 
years ago.
Let us first consider several options of evolved objects.
Eruptive behaviour is known for massive stars close to the Humphrey-Davidson (HD) limit, such as LBVs (Humphreys et al. 1989). In the case of HD 45677 the temperature did not change as much as seen for LBVs in such a situation, and would be too high to fit a position close to the HD limit within a reasonable distance. Note here that indications of the luminosity class of HD 45677 are III or IV #P&(Pérez et al. 1993). However, the existence of the AG Car ring nebula is also not well explained by instabilities close to the HD limit as its luminosity class is still not exactly known (Humphreys et al. 1989). Other evolved objects that undergo phases of mass ejections leading to the formation of dusty disks as visible in the near- and far-IR are post-AGB stars and Symbiotics. HD 45677 is too hot to be a post-AGB star, but it could be in a certain transition phase of PNs. The presence of a companion could be the origin of the perturbations as detected. At the moment there are not even traces of such a companion.
Forbidden lines of [OI], [NII], [SII] and
[FeII] indicate the existence of a low density region. The electron
density of this region, 
cm
,
is determined by the ratio of the [SII]
lines and is high compared to most nebulae
(Osterbrock 1974). Because
HD 45677 is too ``cool'' to ionize gas that emits lines of [OIII], we
derived the electron temperature by the [NII] lines and determine
K, which is very high. The 
value of 30 is not far from those of some
planetary nebulae (Osterbrock 1974).
Since the temperature of HD 45677 is relatively low, these values should
indicate that an extended region should be visible. However, on our images
HD 45677 appears unresolved, so it seems unlikely that HD 45677 is
such a planetary nebula. The values also agree with the conclusion of
Swings (1973) who mentioned this region as being of considerable density, but with
a low temperature based on the absence of some forbidden lines like [SII].
Swings (1973) reported the occurrence of [NII] lines, now the [SII]
are also detected, clearly indicating the ongoing evolution of this region.
However, one of the most peculiar lines is the very strong and narrow blueshifted
H
absorption component at 9 km s
relative to the systemic velocity.
If we propose that this concentration of considerable density of gas is
distributed in a ring-like structure, indicated by its low velocity-dispersion, it might originate from
the 1950 event. At a minimum distance of 500 pc, the angular size of
this ring will be about 0
2 and indeed not yet visible.
As the evolved status of HD 45677 is also not clear we return to the
hypothesis that HD 45677 is still in a pre-main sequence phase.
This option
has some support by the new 
value of 70 km s
(Israelian et al. 1996),
a value similar to several comparable PMS objects,
and the detection of blueshifted HeI emission
as is reported for several HAeBe stars by
#B&Böhm & Catala (1995).
These findings are probably not unique for HAeBes.
Furthermore, the evaporation of cometary-like bodies in the vicinity of some Herbig Ae
type stars, the UXOR-group, has recently been discovered
(Grinin et al. 1994
and 1996, de , Winter et al. 1995 and
de Winter 1996) and show some typical
behaviour in colour and variation in line profiles. A colour behaviour due to
pure extinction, in the minima, or the so-called ``blueing effect'', during
the deep minima, as due to revolving dust clouds in a proto-planetary disk,
are not seen for HD 45677. Also the UXOR-group shows clear evidence
for infalling evaporating comet-like bodies by redshifted absorption
components in the NaID lines with co-variations in the
HeI and H
profiles on a daily time scale. The suggested
evaporation of a large cometary-like body around 1950 should have produced
similar line profiles. However, no dramatic changes in the mentioned lines
have been noticed, although the resolution could be a limiting factor.
Also, the time scale and amplitude of the minimum is comparable to those for
objects in the UXOR-group.
Figure 13: HR-diagram with the position of HD 45677 assuming a distance
of 550 pc (bottom), 900 pc (center), and 1.5 kpc (top). a) With the
pre main-sequence evolutionary tracks and birthline by Palla & Stahler
(1993), b) With the post main-sequence evolutionary tracks by Maeder &
Meynet (1988)
Finally, when HD 45677 is indeed a product of a molecular complex related to
the Mon R2 cloud and the CMa OB1 complex
(Maddalena et al. 1986), it would be
interesting to know whether it is still young enough for post-natal
circumstellar material to be the origin for the dynamical properties
observed. HD 45677 would then be an isolated young object being only
some 10
yrs old, similar to isolated HAe objects, such as HD 104237,
HR 5999 and HD 163296. But, in these cases evidences of their relative
youth, up to several times 10
yrs, are still seen in their near
surroundings such as T Tauri stars.
To give the final answer to the question of the evolutionary statues of HD 45677, a more accurate distance determination than the one presented here is necessary. If all goes well, this will become available soon, since this object is one of the primary targets for the Hipparcos astrometric satellite.