New Luminous Variable Star in M33
A new bright LBV (Luminous Blue Variable) star was detected in M33 galaxy.
LBV stars are the most massive stars in the final stages of evolution
before exploding in of supernovae. The masses of such stars are more
than 50 solar masses. It is exactly after the explosions of these stars
that the black holes appear. The new LBV star (Fig.1) is the seventh in
M33. Five previous stars (VarA, VarB, VarC, Var2, Var83) were detected
by Hubble and Sandage in the middle of last century; the sixth, V532,
was identified in SAO RAS 10 years ago. Luminosity of new LBV is 2 million
solar luminosities, its mass is about 100 solar masses. It is one of the
brightest LBV stars of the M33 galaxy. The star's temperature, measured
on the spectra obtained on the 6-m BTA telescope (Fig.2), is 16000 K.
In the infrared spectral range (the data by Spitzer Space Telescope)
the star is surrounded by two dust envelopes. The temperature of these
dust components is 900 and 420K.
Fig.1. The map of the centre of the M33 galaxy. The brightest object is the core of the galaxy, - a compact star cluster comprising a supermassive black hole. The new LBV star N93351 is located down and to the left from the core. The white line shows the way the spectrograph slit was located during the observations. The star is located at the distance of 400 light years from the galactic core and it is in the zone of its gravitational effect.
Fig.2. The spectrum of the new LBV obtained on the 6-m BTA telescope, on the basis of which the temperature and mass of the star were determined. The brightest lines in the spectrum are the hydrogen lines in the stellar atmosphere, however, the most numerous lines are the lines of ionized iron. Apart from them, one can see the absorption lines of titanium, magnesium and helium. The stellar atmosphere flows out (via the stellar wind) with the velocity of 200km/s.