A RAY-TRACING ALGORITHM FOR SPINNING COMPACT OBJECT SPACETIMES WITH ARBITRARY QUADRUPOLE MOMENTS. II. NEUTRON STARS

Journal Article · Tue Jul 10 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/753/2/175· OSTI ID:22039361

Bauboeck, Michi; Psaltis, Dimitrios; Oezel, Feryal; Johannsen, Tim ^[1]

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1. Astronomy Department, University of Arizona, 933 N. Cherry Avenue, Tucson, AZ 85721 (United States)

A moderately spinning neutron star acquires an oblate shape and a spacetime with a significant quadrupole moment. These two properties affect its apparent surface area for an observer at infinity, as well as the light curve arising from a hot spot on its surface. In this paper, we develop a ray-tracing algorithm to calculate the apparent surface areas of moderately spinning neutron stars making use of the Hartle-Thorne metric. This analytic metric allows us to calculate various observables of the neutron star in a way that depends only on its macroscopic properties and not on the details of its equation of state. We use this algorithm to calculate the changes in the apparent surface area, which could play a role in measurements of neutron-star radii and, therefore, in constraining their equation of state. We show that whether a spinning neutron star appears larger or smaller than its non-rotating counterpart depends primarily on its equatorial radius. For neutron stars with radii {approx}10 km, the corrections to the Schwarzschild spacetime cause the apparent surface area to increase with spin frequency. In contrast, for neutron stars with radii {approx}15 km, the oblateness of the star dominates the spacetime corrections and causes the apparent surface area to decrease with increasing spin frequency. In all cases, the change in the apparent geometric surface area for the range of observed spin frequencies is {approx}<5% and hence only a small source of error in the measurement of neutron-star radii.

• OSTI ID: 22039361
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 753; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ALGORITHMS
ASTRONOMY
ASTROPHYSICS
CORRECTIONS
EQUATIONS OF STATE
GRAVITATION
HOT SPOTS
NEUTRON STARS
QUADRUPOLE MOMENTS
RELATIVISTIC RANGE
SCHWARZSCHILD METRIC
SPACE-TIME
SPIN
SURFACE AREA
VISIBLE RADIATION