Limb darkening scan during 163 Erigone occultation of Regulus

ATel #5989; Costantino Sigismondi (ICRANet and Observatorio Nacional, Rio de Janeiro)
on 19 Mar 2014; 23:21 UT
Credential Certification: Luca Zampieri (luca.zampieri@oapd.inaf.it)

Tweet

The 1.3 mas prolate fast-rotating Be and first magnitude star Regulus is occulted on March 20, 2014 around 6.06 UT (reference for predictions: http://occultations.org/Regulus2014/ and http://www.asteroidoccultation.com/2014_03/0320_163_32317_Summary.txt and Atel#5917)on a totality path including New York City, by the 84 mas size asteroid 163 Erigone moving at 6 mas/s. Due to the distance of the asteroid, D=1.185 AU, the signature of the light curve of the star during the occultation will include Fresnel fringes convoluted with stellar diameter effect and, ultimately, with the Limb Darkening Function (LDF) of the star. The Fresnel scale sqrt(lambda*D/2) (Richichi and Glindemann A&A 538, A56 2012) is 326 m for 600 nm, corresponding to 0.45 mas. The duration of the diffraction pattern in the light curve of the occultation is [0.45/6]=0.075 s, both at disappearance and reappearance of the star. At the centerline the signal due to the stellar diameter effect has a maximum duration of [1.3/6.0]=0.217 s, both at disappearance and reappearance of the star, with a LDF modulation which deviates from the pure geometrical term depending on the u parameter of LDF (D. Heyrovský, ApJ, 656:483-492, 2007). The signature of the LDF, also known as gravity darkening – the star becomes brighter at its poles than at its equator - for such fast rotating star (McAlister, H.A.; et al. , Ap. J. 628, 439–452, 2005), under ideal observational conditions, can be appreciated starting with a 60 fps video and 40 cm telescope, to limit scintillation effects. Optical photometric observations are recommended for achieving the maximum time resolution.