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Register a new userThe donor of Aquila X-1 revealed by high angular resolution near-infrared spectroscopy
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Added by
Daniel Mata S\\'anchez
Publication date
2016
fields
Physics
and research's language is
English
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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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Studies of transiting extrasolar planets are of key importance for understanding the nature of planets outside our solar system because their masses, diameters, and bulk densities can be measured. An important part of transit-search programmes is the removal of false-positives. The critical question is how many of the candidates that passed all previous tests are false positives. For our study we selected 25 CoRoT candidates that have already been screened against false-positives using detailed analysis of the light curves and seeing-limited imaging, which has transits that are between 0.7 and 0.05% deep. We observed 20 candidates with the adaptive optics imager NaCo and 18 with the high-resolution infrared spectrograph CRIRES. We found previously unknown stars within 2 arcsec of the targets in seven of the candidates. All of these are too faint and too close to the targets to have been previously detected with seeing-limited telescopes in the optical. Our study thus leads to the surprising results that if we remove all candidates excluded by the sophisticated analysis of the light-curve, as well as carrying out deep imaging with seeing-limited telescopes, still 28-35% of the remaining candidates are found to possess companions that are bright enough to be false-positives. Given that the companion-candidates cluster around the targets and that the J-K colours are consistent with physical companions, we conclude that the companion-candidates are more likely to be physical companions rather than unrelated field stars.
We present results from a near infrared survey of the He I line (10830 Angstrom) in cool dwarf stars taken with the PHOENIX spectrograph at the 4-m Mayall telescope at Kitt Peak National Observatory. Spectral synthesis of this region reproduces some but not all atomic and molecular features. The equivalent width of the He line appears directly correlated with the soft X-ray stellar surface flux except among the coolest M dwarf stars, where the helium is surprisingly weak.
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