In addition to WR stars, the upper part of the HR diagram
contains many post-main sequence
stars whose evolutionary connections are not understood.
To unravel the relationships of these stars, more examples need to
be identified and studied in detail. LBVs are characterized by irregular
photometric and spectral variations over decades and evolve
from a hot (OB-type) visual minimum phase to
a cooler (A-type), visual maximum.
We have recently analysed HST
observations of an LBV in the giant HII region NGC2363 (left) - located
10,000,000 light years away in an external galaxy named NGC2366.
Drissen et al. (1997) ApJ 474 L35 discovered that the star, named
V1, has visually brightened by at least 4 magnitudes in the past 6 years
- see right panel. V1
is currently undergoing a giant eruption, such that one solar mass
of material is being ejected only every thousand years
( Crowther et al.
see here)!
One such star which has
received little previous attention, is the LBV candidate
He 3-519. We have conducted a study of He 3-519 and its surrounding
nebula. We find that He 3-519 is a highly evolved
massive star with a very dense, unstable slow wind, as
evidenced by dramatic line profile
variability. The parameters of the surrounding nebula are
consistent with the idea that it was ejected during an eruption in
the past, indicating that He 3-519 has all the characteristics of an LBV
and so should be considered as the 8th member of this class in our Galaxy.
(Smith et al. 1994 A&A 281 833) .
Following on this work, another poorly studied emission line object,
HDE316285, has been analysed by Hillier et al. 1998 A&A 340 483
(ps file).
We carry out a spectral analysis using our non-LTE atmosphere code.
The mass-loss from HDE316285 is prodigious. In less than 100,000
years it will lose over 20M(sun). Due to the low degree of ionization,
the derived H/He abundance ratio (1.5 by number) and mass-loss rate are
strongly coupled. The stellar wind from HDE316285 is more
extreme than P Cygni with an performance number (= ratio of wind
momentum to radiative momentum) 30 times greater. The low H/He
abundance ratio and a high N/He abundance ratio
confirms that HDE316285 is evolved. Although we find no evidence in
the literature for photometric variability,
we find strong evidence for significant spectral variability.
Because of the spectral variability, and because the stellar properties and
chemical content of HDE316285 are similar to known luminous blue
variables (LBVs), we suggest that it is a LBV.
Support for this contention comes from the detection by McGregor etal. of
a cold circumstellar dust shell associated with HDE316285.
However HDE316285, like P Cygni, could currently be in a relatively
quiescent phase of its LBV life, exhibiting significant spectral variations
but not undergoing major photometric outbursts similar to AG Car.
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02-Dec-99 zuserver2.star.ucl.ac.uk