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Title: Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey

Abstract

We present 838 ab-type RR Lyrae stars from the Lowell Observatory Near Earth Objects Survey Phase I (LONEOS-I). These objects cover 1430 deg{sup 2} and span distances ranging from 3-30kpc from the Galactic Center. Object selection is based on phased, photometric data with 28-50 epochs. We use this large sample to explore the bulk properties of the stellar halo, including the spatial distribution. The period-amplitude distribution of this sample shows that the majority of these RR Lyrae stars resemble Oosterhoff type I, but there is a significant fraction (26%) which have longer periods and appear to be Oosterhoff type II. We find that the radial distributions of these two populations have significantly different profiles ({rho}{sub OoI} {approx} R{sup -2.26{+-}0.07} and {rho}{sub OoII} {approx} R{sup -2.88{+-}0.11}). This suggests that the stellar halo was formed by at least two distinct accretion processes and supports dual-halo models.

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
940509
Report Number(s):
UCRL-JRNL-228444
Journal ID: ISSN 0004-637X; ASJOAB; TRN: US200824%%72
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, vol. 678, no. 2, May 1, 2008, pp. 865-887; Journal Volume: 678; Journal Issue: 2
Country of Publication:
United States
Language:
English
Subject:
99 GENERAL AND MISCELLANEOUS; DISTRIBUTION; SPATIAL DISTRIBUTION; STARS

Citation Formats

Miceli, A, Rest, A, Stubbs, C W, Hawley, S L, Cook, K H, Magnier, E A, Krisciunas, K, Bowell, E, and Koehn, B. Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey. United States: N. p., 2007. Web.
Miceli, A, Rest, A, Stubbs, C W, Hawley, S L, Cook, K H, Magnier, E A, Krisciunas, K, Bowell, E, & Koehn, B. Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey. United States.
Miceli, A, Rest, A, Stubbs, C W, Hawley, S L, Cook, K H, Magnier, E A, Krisciunas, K, Bowell, E, and Koehn, B. Fri . "Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey". United States. doi:. https://www.osti.gov/servlets/purl/940509.
@article{osti_940509,
title = {Evidence for Distinct Components of the Galactic Stellar Halo from 838 RR Lyrae Stars Discovered in the LONEOS-I Survey},
author = {Miceli, A and Rest, A and Stubbs, C W and Hawley, S L and Cook, K H and Magnier, E A and Krisciunas, K and Bowell, E and Koehn, B},
abstractNote = {We present 838 ab-type RR Lyrae stars from the Lowell Observatory Near Earth Objects Survey Phase I (LONEOS-I). These objects cover 1430 deg{sup 2} and span distances ranging from 3-30kpc from the Galactic Center. Object selection is based on phased, photometric data with 28-50 epochs. We use this large sample to explore the bulk properties of the stellar halo, including the spatial distribution. The period-amplitude distribution of this sample shows that the majority of these RR Lyrae stars resemble Oosterhoff type I, but there is a significant fraction (26%) which have longer periods and appear to be Oosterhoff type II. We find that the radial distributions of these two populations have significantly different profiles ({rho}{sub OoI} {approx} R{sup -2.26{+-}0.07} and {rho}{sub OoII} {approx} R{sup -2.88{+-}0.11}). This suggests that the stellar halo was formed by at least two distinct accretion processes and supports dual-halo models.},
doi = {},
journal = {Astrophysical Journal, vol. 678, no. 2, May 1, 2008, pp. 865-887},
number = 2,
volume = 678,
place = {United States},
year = {Fri Feb 23 00:00:00 EST 2007},
month = {Fri Feb 23 00:00:00 EST 2007}
}
  • We discuss the role that dwarf galaxies may have played in the formation of the Galactic halo (Halo) using RR Lyrae stars (RRL) as tracers of their ancient stellar component. The comparison is performed using two observables (periods, luminosity amplitudes) that are reddening and distance independent. Fundamental mode RRL in 6 dwarf spheroidals (dSphs) and 11 ultra faint dwarf galaxies (∼1300) show a Gaussian period distribution well peaked around a mean period of (Pab) = 0.610 ± 0.001 days (σ = 0.03). The Halo RRL (∼15,000) are characterized by a broader period distribution. The fundamental mode RRL in all the dSphs apart from Sagittariusmore » are completely lacking in High Amplitude Short Period (HASP) variables, defined as those having P ≲ 0.48 days and A{sub V} ≥ 0.75 mag. Such variables are not uncommon in the Halo and among the globular clusters and massive dwarf irregulars. To further interpret this evidence, we considered 18 globulars covering a broad range in metallicity (–2.3 ≲ [Fe/H] ≲ –1.1) and hosting more than 35 RRL each. The metallicity turns out to be the main parameter, since only globulars more metal-rich than [Fe/H] ∼ –1.5 host RRL in the HASP region. This finding suggests that dSphs similar to the surviving ones do not appear to be the major building-blocks of the Halo. Leading physical arguments suggest an extreme upper limit of ∼50% to their contribution. On the other hand, massive dwarfs hosting an old population with a broad metallicity distribution (Large Magellanic Cloud, Sagittarius) may have played a primary role in the formation of the Halo.« less
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