Stellar limb darkening scan during 163 Erigone asteroidal occultation of Regulus on March 20, 2014 at 6:06 UT
ATel #5987; C. Sigismondi (ICRANet, UFRJ and Observatorio Nacional, Rio de Janeiro), T. Flatres (IOTA/ES), T. George (IOTA/US), F. Braga-Ribas (Observatorio Nacional, Rio de Janeiro)
on 19 Mar 2014; 19:03 UT
Credential Certification: Costantino Sigismondi (sigismondi@icra.it)
Subjects: Infra-Red, Optical, Request for Observations, Asteroid, Star, Asteroid (Binary)
The 1.3 mas fast-rotating, first magnitude Be star
Regulus, Alpha Leonis, is occulted on March 20, 2014 around 6 UT
(reference for predictions: http://occultations.org/Regulus2014/
and http://www.asteroidoccultation.com/2014_03/0320_163_32317_Summary.txt )
on a totality path including New York City,
by the 84 mas-sized 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 diffraction pattern in the light curve of the occultation
lasts [0.45/6]=0.075 s either at the disapparition and at the reapparition of the star.
Similarly the light of the star does not disappear/reappear suddendly because
of the stellar diameter effect (geometrical) which has a
maximum duration of [1.3/6.0]=0.217 s on the path's centerline.
Moreover the light curve is modulated by the LDF of the star
J(i)=Jo*[(1-x + x*cos(i)]
where i is the angle between the line of sight and the normal and x the darkening coefficient
(H. N. Russel and H. Shapley, Ap. J. 36, 240, 1912), and by a possible dwarf companion (ATel#5917).
Nonlinear LDF may fit better the observed data (J. W. Barnes, Astrophys. J. 705, 683 2009).
The LDF of such fast rotating star it is also known as gravity darkening: the star becomes brighter at its poles than at its equator (McAlister, et al. , Ap. J. 628, 439, 2005).
Under ideal observational conditions, the signature of Regulus LDF
can be appreciated starting with a 50 fps video and a 20 cm telescope,
to limitate scintillation effects;
photometric observations are encouraged for achieving the maximum time resolution.
High quality photometry will also show, or put an upper limit, on the presence of dust
or satellites around the occulting asteroid.
Data analysis of 2005 Regulus occultation and simulation of the 2014 occultation
