Detection of superhumps in XTE J1118+480 approaching quiescence期刊界 All Journals 搜尽天下杂志传播学术成果专业期刊搜索期刊信息化学术搜索

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Detection of superhumps in XTE J1118+480 approaching quiescence

Authors:	C Zurita J Casares T Shahbaz R M Wagner C B Foltz P Rodríguez-Gil R I Hynes P A Charles E Ryan G Schwarz S G Starrfield

Institution:	Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain; Large Binocular Telescope Observatory, University of Arizona, Tucson, Arizona, USA; MMT Observatory, University of Arizona, Tucson, Arizona, USA; Department of Physics &Astronomy, University of Southampton, Southampton SO17 1BJ; Steward Observatory, University of Arizona, Tucson, Arizona, USA; Department of Physics &Astronomy, Arizona State University, Tempe, Arizona, USA

Abstract:	We present the results of our monitoring of the halo black hole soft X-ray transient (SXT) XTE J1118+480 during its decline to quiescence. The system has decayed 0.5 mag from 2000 December to its present near-quiescent level at R ≃18.65 (2001 June). The ellipsoidal light curve is distorted by an additional modulation that we interpret as a superhump of P _sh=0.17049(1) d i.e. 0.3 per cent longer than the orbital period. This implies a disc precession period P _prec∼52 d . After correcting the average phase-folded light curve for veiling, the amplitude difference between the minima suggests that the binary inclination angle lies in the range i =71–82° . However, we urge caution in the interpretation of these values because of residual systematic contamination of the ellipsoidal light curve by the complex form of the superhump modulation. The orbital-mean H α profiles exhibit clear velocity variations with ∼500 km s⁻¹ amplitude. We interpret this as the first spectroscopic evidence of an eccentric precessing disc.

Keywords:	accretion accretion discs binaries: close stars: individual: XTE J1118+480 X-rays: stars

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