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تسجيل مستخدم جديدProbing the Outer Galactic halo with RR Lyrae from the Catalina Surveys
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We present the analysis of 12227 type-ab RR Lyrae found among the 200 million public lightcurves in the Catalina Surveys Data Release 1 (CSDR1). These stars span the largest volume of the Milky Way ever surveyed with RR Lyrae, covering ~20,000 square degrees of the sky (0 < RA < 360, -22 < Dec < 65 deg) to heliocentric distances of up to 60kpc. Each of the RR Lyrae are observed between 60 and 419 times over a six-year period. Using period finding and Fourier fitting techniques we determine periods and apparent magnitudes for each source. We find that the periods at generally accurate to sigma = 0.002% by comparison with 2842 previously known RR Lyrae and 100 RR Lyrae observed in overlapping survey fields. We photometrically calibrate the light curves using 445 Landolt standard stars and show that the resulting magnitudes are accurate to ~0.05 mags using SDSS data for ~1000 blue horizontal branch stars and 7788 of the RR Lyrae. By combining Catalina photometry with SDSS spectroscopy, we analyze the radial velocity and metallicity distributions for > 1500 of the RR Lyrae. Using the accurate distances derived for the RR Lyrae, we show the paths of the Sagittarius tidal streams crossing the sky at heliocentric distances from 20 to 60 kpc. By selecting samples of Galactic halo RR Lyrae, we compare their velocity, metallicity, and distance with predictions from a recent detailed N-body model of the Sagittarius system. We find that there are some significant differences between the distances and structures predicted and our observations.
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eq R_{mathrm{gc}} leq 141 ; mathrm{kpc}$ with a distance precision of 3% and thus is able to trace the halo out to larger distances than most previous studies. After excising stars that are attributed to dense regions such as stellar streams, the Galactic disc and bulge as well as halo globular clusters, the sample contains ${sim}11,000$ sources within $20 ; mathrm{kpc} leq R_{mathrm{gc}} leq 131 ; mathrm{kpc}$. We then apply forward modeling using ellipsoidal stellar density models $rho(l,b,R_{mathrm{gc}})$ both with a constant and a radius-dependent halo flattening $q(R_{mathrm{gc}})$. Assuming constant flattening $q$, the distribution of the sources is reasonably well fit from $20 ; mathrm{kpc}$ to $131 ; mathrm{kpc}$ by a single power law with $n=4.40^{+0.05}_{-0.04}$ and $q=0.918^{+0.016}_{-0.014}$. The distance distribution is fit comparably well by an Einasto profile with $n=9.53^{+0.27}_{-0.28}$, an effective radius $r_{mathrm{eff}}=1.07 pm 0.10 ; mathrm{kpc}$ and a halo flattening of $q=0.923 pm 0.007$. If we allow for a radius-dependent flattening $q(R_{mathrm{gc}})$, we find evidence for a distinct flattening of $q{sim}0.8$ of the inner halo at ${sim} 25 ; mathrm{kpc}$. Additionally, we find that the south Galactic hemisphere is more flattened than the north Galactic hemisphere. The results of our work are largely consistent with many earlier results, e.g. cite{Watkins2009}, cite{Iorio2017}. We find that the stellar halo, as traced in RR Lyrae stars, exhibits a substantial number of further significant over- and underdensities, even after all known overdensities have been masked.
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