S6-10

Optical Spectroscopic observations of the Be/X-Ray binary A0535+262/V725 Tau
during the giant outburst in 2009
Y. Moritani(1), D. Nogami(1), A. T. Okazaki(2), A. Imada(3), E. Kambe(3), S. Honda(1), O. Hashimoto(4) and K. Ichikawa(1)1) Kytoto Univ. 2) Hokkai-gakuen Univ. 3) OAO/NAOJ 4) GAO

Optical high dispersion spectroscopic observations of the Be/X-ray binary A0535+262/V725 Tau during the giant
outburst in November 2009 are reported. This giant outburst lasted approximately 30 days, and Swift/BAT teamreported that A0535+262 brightened up to more than 3 times of the Crab in the 15 - 50 keV band. We carried out
the spectroscopic monitoring at OAO and GAO from November 2009 to March 2010, before the giant outburst
to the rising phase of the normal outburst which occurred after the next periastron. Obtained H-alpha, H-beta
and He I emission line exhibited drastic profile variability during the observations.

2.A0535+262/ V725 Tau

1.Be/X-ray Binary
・Be star + compact object (NS)・Majority of HMXRBs
・3 states:Fig. 1: Be/X ray binaries
1. Quiescent LX≲1036 erg/s(Okazaki+ 2002, MNRAS, 337, 967)
36-37
2. Normal (type I) outburst LX～10erg/s・Orbital modulation
3. Giant (type II) outburst LX≳1037 erg/s・Less frequently than normal outbursts
・Be stars (B emission stars):
・B stars which have exhibited Balmer lines in emission
at least once (Luminosity class ; III-V)
・Equatorial region … weak outflow(≲ 1 km/s), balance
between the surface gravity and the centrifugal force
due to rapid rotation (≲several 100 km/s)⇒geometrically thin circumstellar envelope (Be disc)・O9.7IIIe + NS, mV ~ 8.9 mag (Giangrande+ 1980, A&AS, 40, 289)
・Porb = 110.24 days (Moritani+ 2010, MNRAS, 405,467)
・e ~ 0.47 (Finger+ 1994, AIPC, 308, 459)
・NS…103-sec. pulsar (Caballero+ 2007, A&A, 465, L21)
・6 giant outburst have been observed; in 1975, 1980, 1991,1996, 2005 and 2009
・Giant outburst in Nov./ Dec. 2009
・Gradual brightening from Oct. (Sugizaki+ 2009, Atel. #2277)
・Rapid brightening at 30 Nov. (JD 2455166)
・3.1 Crab at the peak in 15-50 keV(Krimm + 2009, Atel. #2336)
・Periastron passage in Mar. 2010… a normal outburst
giant outburst

normal outburst

Fig. 2: Light curve by Swift/BAT (15-50 keV)
Short black lines: date of our observations
Red lines: estimated periastron passage using
Moritani+ 2010, MNRAS, 405,467.
188cm tel. @OAO

3.Observations
・OAO/HIDES, GAO/GAOES …optical Echelle spectrograph
・R ~ 50,000, S/N ~ 100
・Wavelength and Lines;
・OAO/HIDES:3800 – 6700Å …Hα, Hβ, Hγ, He Iλ6678, He Iλ5876, He Iλ4471
・GAO/GAOES:4800 – 6700 Å … Hα, Hβ, He Iλ5876

4.Observed Line Profiles
Hα線

He Iλ6678線

Hβ線

He Iλ5875線

Hγ線

1.5m tel. @GAO

・Remarkable profile variability 5.Redshifted Enhanced Component… correlation between
Q. The enhanced component is emitted from the Be
Balmer lines and He I lines.
disc or from the accretion disc around the NS?
・Redshifted (～100km/s) red
・The radial velocity of the component...
enhanced component
1) varies in a range several tens km/s… double peaked in Hα line2) decrease around the periastron passage
・This component had⇒It is possible that the source is Be disc.
weakened before the normaloutburst.
・Peak Separation of the enhanced component inHα line profile increased from the apastron.
⇒Be disc shrank due to… The tidal interaction with the NS?
… The gas transferred to the NS?

He Iλ4471線

Fig. 4 : The geometry of A0535+262(Coe + 2006, MNRAS, 368,447)
Fig. 3: Representative spectral lines.
Top: from left, Hα lines, Hβ lines and Hγ lines.
Bottom: from left, He Iλ6678 lines, He Iλ5875 lines and He Iλ4471 lines.
IAU Symposium 272 – Active OB stars

Fig. 5: Radial velocity (left) and peak separation (right) of the redshifted,enhanced component in Hα line profiles along with the orbital phase.
19-23 July 2010
in Paris, France