A test of the neutron star hypothesis for Fomalhaut b

作者：Poppenhaeger K; Auchettl K; Wolk S J

来源：Monthly Notices of the Royal Astronomical Society, 2017, 468(4): 4018-4024.

DOI：10.1093/mnras/stx565

• stars: individual: Fomalhaut
• stars: neutron
• planetary systems
• X-rays: individual: Fomalhaut b

Fomalhaut b is a directly imaged object in the debris disc of the star Fomalhaut. It has been hypothesized to be a planet; however, there are issues with the observed colours of the object that do not fit planetary models. An alternative hypothesis is that the object is a neutron star in the near fore- or background of Fomalhaut's disc. We test if Fomalhaut b could be a neutron star using X-ray observations with Chandra's HRC-I instrument in the energy range of 0.08-10 keV. We do not detect X-ray emission from either Fomalhaut b or the star Fomalhaut itself. Our non-detection corresponds to an upper limit on the X-ray flux of Fomalhaut b of F-X < 1.3 x 10(-14) erg cm(-2) s(-1) in the energy range 0.08-10 keV. For the A-type central star Fomalhaut, we derive an X-ray upper limit of L-X < 2.0 x 10(25) erg s(-1) in the energy range 0.08-10 keV. Fomalhaut b's X-ray non-detection constrains the parameter space for a possible neutron star significantly, implying surface temperatures lower than 91 000 K and distances closer than 13.3 pc to the Solar system. In addition, we find that reflected starlight from the central star fits the available optical detections of Fomalhaut b; a smaller planet with a large ring system might explain such a scenario.

• 出版日期2017-7