A Test of the Neutron Star Hypothesis for Fomalhaut b

Abstract

Fomalhaut b is a directly imaged object in the debris disk 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 disk. 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 nondetection corresponds to an upper limit on the X-ray flux of Fomalhaut b of F_X < 1.3e-14 erg/cm/s^2 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 < 2e25 erg/s 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 91000 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.

7 pages

References in corpus (8)

• Optical Images of an Exosolar Planet 25 Light Years from Earth
• The Magnificent Seven: Magnetic fields and surface temperature distributions
• X-ray Emission from T Tauri Stars and the Role of Accretion: Inferences from the XMM-Newton Extended Survey of the Taurus Molecular Cloud
• Modeling giant extrasolar ring systems in eclipse and the case of J1407b: sculpting by exomoons?
• High-contrast Imaging with Spitzer: Deep Observations of Vega, Fomalhaut, and epsilon Eridani
• Altair - the 'hottest' magnetically active star in X-rays
• Burn Out or Fade Away? On the X-ray and Magnetic Death of Intermediate Mass Stars
• The companion candidate near Fomalhaut - a background neutron star?

Cited by in corpus (2)

• Fomalhaut b could be massive and sculpting the narrow, eccentric debris disc, if in mean-motion resonance with it
• Understanding Fomalhaut as a Cooper pair