Strong RR Lyrae excess in the Hercules-Aquila Cloud
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Abstract:
We map the large-scale sub-structure in the Galactic stellar halo using accurate 3D positions of ∼14 000 RR Lyrae reported by the Catalina Sky Survey. In the heliocentric distance range of 10–25 kpc, in the region of the sky approximately bounded by 30° < l < 55° and −45° < b < −25°, there appears to be a strong excess of RRab stars. This overdensity, peaking at 18 kpc, is most likely associated with the so-called Hercules-Aquila Cloud (HAC), previously detected using main-sequence tracers at similar distances in the Sloan Digital Sky Survey data. Our analysis of the period–amplitude distribution of RR Lyrae in this region indicates that the HAC is dominated by the Oosterhoff I type population. By comparing the measured RR Lyrae number density to models of a smooth stellar halo, we estimate the significance of the observed excess and provide an updated estimate of the total luminosity of the Cloud's progenitor.Keywords:
RR Lyrae variable
Instability strip
We present some applications of our Synthetic Horizontal Branches (SHB) simulations, aimed to reproduce the peculiar period distributions of RR Lyrae belonging to the Galactic Globular Clusters M3 and M5. We show some evidence, supporting the importance of SHBs in obtaining parameters such as the mass distribution inside the instability strip.
RR Lyrae variable
Instability strip
Mass distribution
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RR Lyrae variable
Horizontal branch
Instability strip
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A survey of 380 sq. deg. of the sky with the 1m Schmidt telescope at the Observatorio Nacional de Llano del Halo and the QUEST camera has found 498 RR Lyrae variables lying from 4 to 60 kpc from the Sun. We describe the halo substructure revealed by these data and the results of measuring some of the stars' radial velocities and metal abundances.
RR Lyrae variable
Substructure
Variable star
Schmidt camera
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Paper I: "RR Lyrae Variables in Globular Clusters and the Second-Parameter Phenomenon" Authors: M. Catelan, A. V. Sweigart, J. Borissova Abstract: We propose to use RR Lyrae variables in globular clusters to probe the origin of the second-parameter phenomenon. Paper II: "New Possible Variables in the Outer-Halo Globular Cluster Palomar 3" Authors: J. Borissova, N. Spassova, M. Catelan, V. D. Ivanov Abstract: We present a list of ten possible variable stars in the globular cluster Pal 3. Seven are new suspected variables. The variability of the RR Lyr candidate reported by Burbidge & Sandage (1958), as well as of the Pop. II Cepheid and RR Lyr from Gratton & Ortolani (1984), are confirmed. Paper III: "On the Production of Bright RR Lyrae Variables in Metal-Rich Globular Clusters" Authors: A. V. Sweigart, M. Catelan Abstract: See astro-ph/9708174.
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Phenomenon
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On the Interpretation of RR Lyrae Properties in Globular Clusters and in Other Population II Systems
Abstract The differences in observational parameters of the RR Lyrae variables and horizontal branch stars of globular clusters and other population II systems are considered. A discontinuous behaviour of some parameters is outlined. The Oosterhoff dichotomy and the HB morphology are discussed with regard to a conjecture of mass loss in the pre-HB phase.
RR Lyrae variable
Horizontal branch
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A survey of 380 sq. deg. of the sky with the 1m Schmidt telescope at the Observatorio Nacional de Llano del Halo and the QUEST camera has found 498 RR Lyrae variables lying from 4 to 60 kpc from the Sun. We describe the halo substructure revealed by these data and the results of measuring some of the stars' radial velocities and metal abundances.
RR Lyrae variable
Substructure
Schmidt camera
Variable star
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RR Lyrae variables play a prominent role in many of the problems of globular clusters, and from several points of view. In the first place they can be considered as pretty good indicators of population and distance; although they do not form a completely homogeneous set of stars, the knowledge of their mean absolute magnitude gives a powerful means of establishing distances within and outside the Galaxy, and hence of determining the form and size of the Galaxy itself. Moreover, the number of RR Lyrae stars in clusters, the relative frequency of RR c and RR ab , types, the length of the transition periods, the array of colors, when correctly interpreted, give important information on the degree of evolution, age and chemical composition of the clusters. Placed as they are in a peculiar region of the H — R diagram of Population II, the RR Lyr variables can be used as a good test of the theories of advanced evolution or the models of pulsating stars.
RR Lyrae variable
Horizontal branch
Absolute magnitude
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RR Lyrae variable
Blue straggler
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RR Lyrae variable
Distance modulus
Variable star
Apparent magnitude
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Blue straggler
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