[vsnet-chat 2777] Of transients in UMa

[Joe Patterson <jop@astro.columbia.edu>]

             THE NEW X-RAY TRANSIENT IN UMA (XTE J1118+480)

     We have extended the set of photometric observations earlier
described by Lew Cook (vsnet-alert 4554), and see that the variation
appears to be quite stable in period and amplitude.  To within
measurement error, the waveform is sinusoidal and described by

Maximum light = 2451634.835 +  0.1706 E,
                    +-0.002  +-0.0009

with a full amplitude of 0.061+-0.005 mag in (approximately) V light.  
The smooth and sinusoidal waveform suggests an "orbital reprocessing" 
effect, in which the variation arises from X-ray heating of the 
secondary star's surface.  Efforts to verify this as Porb from 
spectroscopy are warmly recommended.  But the (likely) Lx and the 
(certain) Lx/Lopt are surprisingly low for an accreting neutron star.  
There are no eclipses, so it is unlikely that geometry can explain 
this.  Let's keep tracking this interesting star!


The CBA cabal

Joe Patterson (CBA-Big Apple)  jop@astro.columbia.edu
Lew Cook (CBA-California)
Bob Fried (CBA-Flagstaff, Braeside Observatory)
Denis Buczynski (CBO - Condor Brow Observatory)

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