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2012MNRAS.422.2116K - Mon. Not. R. Astron. Soc., 422, 2116-2144 (2012/May-3)

The kinematic properties of BHB and RR Lyrae stars towards the anticentre and the North Galactic Pole: the transition between the inner and the outer halo.


Abstract (from CDS):

We identify 51 blue horizontal branch (BHB) stars, 12 possible BHB stars and 58 RR Lyrae stars in Anticentre fields. Their selection does not depend on their kinematics. Light curves and ephemerides are given for seven previously unknown RR Lyrae stars. All but four of the RR Lyrae stars are of Oosterhoff type I.

Our selection criteria for BHB stars give results that agree with those used by Smith et al. and Ruhland et al. We use five methods to determine distances for the BHB stars and three methods for the RR Lyrae stars to get distances on a uniform scale. Absolute proper motions [largely derived from the Second Guide Star Catalogue (GSCII) and Sloan Digital Sky Survey (Seventh Data Release) data bases] are given for these stars; radial velocities are given for 31 of the BHB stars and 37 of the RR Lyrae stars.

Combining these data for BHB and RR Lyrae stars with those previously found in fields at the North Galactic Pole, we find that retrograde orbits dominate for galactocentric distances greater than 12.5 kpc. The majority of metal-poor stars in the solar neighbourhood are known to be concentrated in a L versus Lzangular momentum plot. We show that the ratio of the number of outliers to the number in the main concentration increases with galactocentric distance. The location of these outliers with L and Lzshows that the halo BHB and RR Lyrae stars have more retrograde orbits and a more spherical distribution with increasing galactocentric distance. Six RR Lyrae stars are identified in the H99 group of outliers; the small spread in their [Fe/H] suggests that they could have come from a single globular cluster. Another group of outliers contains two pairs of RR Lyrae stars; the stars in each pair have similar properties.

Abstract Copyright: 2012 The Authors Monthly Notices of the Royal Astronomical Society2012 RAS

Journal keyword(s): stars: horizontal branch - stars: kinematics and dynamics - stars: variables: general - stars: variables: RR Lyrae - Galaxy: halo - Galaxy: structure

VizieR on-line data: <Available at CDS (J/MNRAS/422/2116): table4.dat table5.dat table6.dat table7.dat tablea1.dat tableb2.dat tabled1.dat tablee1.dat tablee2.dat tablee3.dat tablee4.dat>

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