The spectral type of the optical counterpart to the high-mass X-ray binary IGR J06074+2205
ATel #2085; Pablo Reig & Andreas Zezas (FORTH/University of Crete)
on 15 Jun 2009; 15:38 UT
Credential Certification: Pablo Reig (pablo.reig@uv.es)
Subjects: Optical, Binary, Neutron Star
Spectroscopic observations of the optical
counterpart to the high-mass X-ray binary IGR J06074+2205 were obtained
from the 1.3m telescope of the Skinakas observatory in Crete (Greece) and
from the 1.5m telescope of the Fred Lawrence Whipple Observatory at Mt.
Hopkins (Arizona) on several occasions throughout 2006-2008.These
observations allowed us to identify the spectral type of this source and
study its long-term spectral variability.
The blue-end spectrum (4000-5000 A) of IGR J06074+2205 is dominated by
hydrogen and neutral helium, clearly indicating an early-type star (O or
B). The Balmer series lines from Hbeta up to Heta are seen in
absorption. No or very weak HeII lines (at 4541 A and 4686 A) are present,
which implies a type later than B0. The weak MgII 4481 indicates
a type earlier than B2, whereas the strong CIII+OII blend indicates a
type earlier than B1.5. SiIII 4552-68-75 is also present. On the main
sequence SiIII have their maximum strength at type B0.5.
As for the luminosity class, the fact that the relative strength of the
SiIII 4552-68-75 complex and the CIII+OII blends are comparable to that of
nearby HeI lines favours a main sequence classification. Likewise, the
relative weak strength of OII lines also indicates a luminosity class V
star.
In summary, we assign a spectral type B0.5V to IGR J06074+2205, although a
slightly later type, i.e. B1V, cannot be ruled out.
Our monitoring of IGR J06074+2205 also reveals that the Halpha line is highly
variable, both in strength and shape. V/R variability on timescales of
months is clearly seen, indicating global changes in the structure of the
equatorial disc.
