[vsnet-alert 5861] XTE J1118+480: IAUC 7617 tells superhumps still exist

[Makoto Uemura <uemura@kusastro.kyoto-u.ac.jp>]

XTE J1118+480: IAUC 7617 tells superhumps still exist

    In IAU Circular 7617, J. Casares et al. reports that the 
possible halo black hole X-ray nova, XTE J1118+480 is still 
in the gradually fading phase to quiescence.  They reported 
the object is now at R=18.6mag and fading at 0.003mag/day during 
Dec. 2000 - Apr 2001.  They furthermore detected small amplitude 
modulations on the normal orbital (ellipsoidal) modulation.  
Their PDM period analysis yields a period of 0.17049(1) day and  
they interpret them as superhumps since the period is slightly longer 
than a reported orbital period.

    On XTE J1118+480, the VSNET collaboration team performed the 
extensive photometric campaign during the 2000 outburst and 
revealed that superhumps exist throughout the outburst. 
Our data set shows the mean superhump period during the outburst
is slightly longer than that reported in IAUC 7617, which may 
imply a continuous period changing.  In the case of SU UMa-type 
dwarf nova, the "late superhump" is sometimes obvserved after 
superoutburst which correspond to the main outburst of XTE J1118+480.  
It is known that phases of the superhump and the late-superhump 
are different and their mechanisms are also probably different.  
To determine the peak time of the current superhumps are essential 
to study the nature of them and accretion discs in low-mass X-ray 
binaries.  Further time-series photometry is encouraged.

Regards,
Makoto Uemura

VSNET Home Page

Return to Daisaku Nogami

---

vsnet-adm@kusastro.kyoto-u.ac.jp