The donor of Aquila X-1 revealed by high angular resolution near-infrared spectroscopy
D. Mata S\'anchez (1,2), T. Mu\~noz-Darias (1,2), J. Casares (1,2,3),, F. Jim\'enez-Ibarra (1,2) ((1) Instituto de Astrof\'isica de Canarias,, Tenerife, Spain, (2) Universidad de La Laguna, Tenerife, Spain, (3), University of Oxford, Oxford, UK)
TL;DR
This study used high-resolution near-infrared spectroscopy to identify and analyze the companion star of Aquila X-1, providing the first dynamical measurements and fundamental parameters for this neutron star binary.
Contribution
It presents the first direct detection and dynamical analysis of the companion star in Aquila X-1 using high angular resolution spectroscopy.
Findings
Identified the companion as a K4 ± 2 star
Measured the orbital velocity as 136 ± 4 km/s
Estimated the distance to Aquila X-1 as 6 ± 2 kpc
Abstract
The low mass X-ray binary Aquila X-1 is one of the most active neutron star X-ray transients. Despite it has a relatively bright quiescent optical counterpart, the detection of its companion has been hampered by the presence of a nearby interloper star. Using the infrared integral field spectrograph SINFONI on the VLT-8.2m telescope, we unambiguously single out Aquila X-1 from the interloper. Phase-resolved near infrared spectroscopy reveals absorption features from a K4 +- 2 companion star moving at a projected velocity of K_2= 136 +- 4 km/s. We here present the first dynamical solution and associated fundamental parameters of Aquila X-1, imposing new constraints to the orbital inclination (36 deg < i < 47 deg) and the distance (d = 6 +- 2 kpc) to this prototypical neutron star transient.
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