Bibcode
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
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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