Detection of superhumps in XTE J1118+480 approaching quiescence

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, Sumner Starrfield

Research output: Contribution to journalArticlepeer-review

59 Scopus citations

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 Psh = 0.17049(1) d i.e. 0.3 per cent longer than the orbital period. This implies a disc precession period Pprec ∼ 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 Hα profiles exhibit clear velocity variations with ∼ 500 km s-1 amplitude. We interpret this as the first spectroscopic evidence of an eccentric precessing disc.

Original languageEnglish (US)
Pages (from-to)791-799
Number of pages9
JournalMonthly Notices of the Royal Astronomical Society
Volume333
Issue number4
DOIs
StatePublished - Jul 11 2002

Keywords

  • Accretion, accretion discs
  • Binaries: close
  • Stars: individual: XTE J1118+480
  • X-rays: stars

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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