The Historical X-ray Transient KY TrA in quiescence

Zurita, C.; Corral-Santana, J. M.; Casares, J.
Bibliographical reference

Monthly Notices of the Royal Astronomical Society, Volume 454, Issue 3, p.3351-3356

Advertised on:
12
2015
Number of authors
3
IAC number of authors
2
Citations
7
Refereed citations
7
Description
We present deep optical images of the historical X-ray Transient KY TrA in quiescence from which we confirm the identification of the counterpart reported by Murdin et al. and derive an improved position of α = 15:28:16.97 and δ = -61:52:57.8. In 2007 June we obtained I, R and V images, where the counterpart seems to be double indicating the presence of an interloper at ˜1.4 arcsec NW. After separating the contribution of KY TrA we calculate I = 21.47 ± 0.09, R = 22.3 ± 0.1 and V = 23.6 ± 0.1. Similar brightness in the I-band was measured in 2004 May and 2010 June. Variability was analysed from series of images taken in 2004, spanning 0.6 h, and in two blocks of 6 h during 2007. We find that the target is not variable in any data set above the error levels ˜0.07 mags. The presence of the interloper might explain the non-detection of the classic ellipsoidal modulation; our data indicates that it contributes around half of the total flux, which would make a variation <0.15 mag not detectable. A single spectrum obtained in 2004 May shows the H α emission characteristic of X-ray transients in quiescence with a full width at half-maximum FWHM = 2700 ± 280 km s-1. If the system follows the FWHM-K2 correlation found by Casares, this would correspond to a velocity semi-amplitude of the donor star of K2 = 630 ± 74 km s-1. Based on the outburst amplitude and colours of the optical counterpart in quiescence we derive a crude estimate of the orbital period of 8 h and an upper limit of 15 h which would lead to mass function estimates of ≈9 M⊙ and <16 M⊙, respectively.
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