Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21915313r&link_type=abstract
American Astronomical Society, AAS Meeting #219, #153.13
Astronomy and Astrophysics
Astronomy
Scientific paper
V1408 Aql is a low-mass X-ray binary with an orbital period of 9.329 hrs. Its optical orbital light curve has previously been measured by Thorstensen (1987), who found a sinusoidal modulation that he attributed to the irradiated face of the secondary star; and it has been measured by Hakala et al. (1999), who, based on their much smaller but multicolor data set, attributed the modulation to partial eclipses of a thick accretion disk around the compact star. Their model implies an orbital inclination near 75o. Using this inclination, Nowak et al. (2008) modeled the X-ray spectrum of V1408 Aql and concluded that its compact star is a rapidly rotating black hole.
We have obtained extensive optical photometry of V1408 Aql. The average orbital light curve is nearly sinusoidal with a peak-to-peak amplitude of 23%. The RXTE/ASM X-ray light curve shows no periodicities at or near the orbital period. We show that a model in which the orbital modulation is caused by the varying aspect of the heated face of the secondary star yields excellent fits to the mean light curve. There is no eclipse, limiting the orbital inclination to less than 70o. The mass ratio M2/MX is unlikely to be small because: (1) the large amplitude of the sinusoidal variation favors a large secondary, which in turn favors a larger mass ratio, and (2) there is no evidence for superhumps, which are often present in light curves when the mass ratio is less than 0.25. The larger mass ratio means the compact star is more likely to be a neutron star than a black hole.
Bayless Amanda J.
Mason Paul A.
Robertson Paul
Robinson Edward L.
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