[vsnet-alert 3637] XTE J1859+226

[Rob Hynes <rih@astro.soton.ac.uk>]

Dear colleagues,

We would like to thank all those who have contributed ground-based 
support for the HST/XTE campaign on XTE J1859+226.  The following 
circular has been submitted.

Regards,
	R.I. Hynes, on behalf of the team listed below


R.I. Hynes, Southampton University and C.A. Haswell, A.J. Norton,
S. Chaty, D.J. Rolfe, D.A. Lott, Open University, J.E. Solheim,
R. Ostensen, Tromso University, R.A. Garcia, CEA Saclay, R. Fried,
Flagstaff, K. O'Brien, K. Horne, St Andrews University, Z. Ioannou,
Keele, A. Shafter, San Diego State University, T.M.C. Abbott, Nordic
Optical Telescope, K. Krisciunas, University of Washington,
R. J. Ivison, University College London, Y. Sano, Nayoro, Hokkaido,
Japan, W. Chen, C. Shrader, Goddard Space Flight Center, M. Livio,
STScI, E.L. Robinson, University of Texas, R.M. Wagner, Ohio State
University, report:

"Following optical and near-infrared monitoring of XTE J1859+226
(IAUC 7279, 7284), HST/STIS observations were performed on Oct
18.10-18.38 spanning 112-1026nm.  The UV spectrum shows broad
(12000km/s FWZI) and deep Lyman alpha absorption, strong CIV 155nm
emission (EW 1.1nm, 4000km/s FWZI) and weaker emission lines of CIII,
NV, OIII, OIV, OV, SiIV and HeII.  Sharp absorption lines of SiII,
SiIII, MgII and other species also appear with possible interstellar
origin.  Preliminary analysis of the 220nm interstellar feature
suggests E(B-V)=0.58 +/- 0.07.  The dereddened optical-UV spectral
energy distribution (SED) is a steep blue power-law (spectral index
+1.2) in the optical, flattening in the UV.  This SED resembles those
of other short period SXTs, suggesting that XTE J1859+226 has a binary
period < 1d.  A 20% decline in 110-170nm fluxes during the observation
coincides with an X-ray decline seen in RXTE/ASM lightcurves.  Shorter
timescale variations are present but no persistent coherent modulation
was detected.  Preliminary analyses of 33 hours of optical time-series
data collected between October 13.86 and October 20.24 at Nordic
Optical Telescope, Braeside, Jacobus Kapteyn Telescope, Keele,
Mt. Laguna, St. Andrews and Manastash Ridge Observatory, and also 2.5
hours infrared time-series data at UKIRT on Oct. 18.19-18.31 UT
suggests a 1% modulation with period 22-23 minutes.  Further HST
observations are scheduled for Nov 6.82-6.93, Nov 19.43-19.55;
coordinated ground based observations are encouraged."

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