skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: RR Lyrae in XSTPS: The halo density profile in the north galactic cap

Abstract

We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ≈376.75 deg{sup 2} at α ≈ 150° and δ ≈ 27° down to a magnitude limit of i ≈ 19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more than 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. and Sesar et al. RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We considermore » non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.« less

Authors:
; ; ;  [1];  [2]; ;  [3]
  1. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871 (China)
  2. Department of Astronomy, Peking University, Beijing 100871 (China)
  3. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
Publication Date:
OSTI Identifier:
22356624
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 788; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCOUNTING; CATALOGS; COLOR; COVERINGS; CURRENTS; DETECTION; DISTANCE; EFFICIENCY; ESA; GALAXIES; LIMITING VALUES; MINES; PROBES; SKY; SPHERICAL CONFIGURATION; STARS; STREAMS; TELESCOPES

Citation Formats

Faccioli, L., Smith, M. C., Yuan, H.-B., Liu, X.-W., Zhang, H.-H., Zhao, H.-B., and Yao, J.-S., E-mail: lorenzo.faccioli@cea.fr, E-mail: msmith@shao.ac.cn. RR Lyrae in XSTPS: The halo density profile in the north galactic cap. United States: N. p., 2014. Web. doi:10.1088/0004-637X/788/2/105.
Faccioli, L., Smith, M. C., Yuan, H.-B., Liu, X.-W., Zhang, H.-H., Zhao, H.-B., & Yao, J.-S., E-mail: lorenzo.faccioli@cea.fr, E-mail: msmith@shao.ac.cn. RR Lyrae in XSTPS: The halo density profile in the north galactic cap. United States. doi:10.1088/0004-637X/788/2/105.
Faccioli, L., Smith, M. C., Yuan, H.-B., Liu, X.-W., Zhang, H.-H., Zhao, H.-B., and Yao, J.-S., E-mail: lorenzo.faccioli@cea.fr, E-mail: msmith@shao.ac.cn. 2014. "RR Lyrae in XSTPS: The halo density profile in the north galactic cap". United States. doi:10.1088/0004-637X/788/2/105.
@article{osti_22356624,
title = {RR Lyrae in XSTPS: The halo density profile in the north galactic cap},
author = {Faccioli, L. and Smith, M. C. and Yuan, H.-B. and Liu, X.-W. and Zhang, H.-H. and Zhao, H.-B. and Yao, J.-S., E-mail: lorenzo.faccioli@cea.fr, E-mail: msmith@shao.ac.cn},
abstractNote = {We present a catalog of RR Lyrae stars (RRLs) observed by the Xuyi Schmidt Telescope Photometric Survey (XSTPS). The area we consider is located in the north Galactic cap, covering ≈376.75 deg{sup 2} at α ≈ 150° and δ ≈ 27° down to a magnitude limit of i ≈ 19. Using the variability information afforded by the multi-epoch nature of our XSTPS data, combined with colors from the Sloan Digital Sky Survey, we are able to identify candidate RRLs. We find 318 candidates, derive distances to them, and estimate the detection efficiency. The majority of our candidates have more than 12 observations, and for these we are able to calculate periods. These also allow us to estimate our contamination level, which we predict is between 30% and 40%. Finally, we use the sample to probe the halo density profile in the 9-49 kpc range and find that it can be well fitted by a double power law. We find good agreement between this model and the models derived for the south Galactic cap using the Watkins et al. and Sesar et al. RRL data sets, after accounting for possible contamination in our data set from Sagittarius stream members. We consider non-spherical double power-law models of the halo density profile and again find agreement with literature data sets, although we have limited power to constrain the flattening due to our small survey area. Much tighter constraints will be placed by current and future wide-area surveys, most notably ESA's astrometric Gaia mission. Our analysis demonstrates that surveys with a limited number of epochs can effectively be mined for RRLs. Our complete sample is provided as accompanying online material; as an example the first few entries of each electronic table are shown in the text.},
doi = {10.1088/0004-637X/788/2/105},
journal = {Astrophysical Journal},
number = 2,
volume = 788,
place = {United States},
year = 2014,
month = 6
}
  • Revised periods, light curves, and metal abundances (Preston ..delta..s's and corresponding (Fe/H) values) are given for nearly 40 RR Lyrae variables of the Lick North Galactic Pole survey. The most distant stars lie at a height z above the galactic plane of 20--25 kpc. The data give no evidence for composition gradients in the RR Lyraes apart from the composition difference between the variables in the halo (<..delta..s>=7.7, <(Fe/H)>=-1.5) and the disk (<..delta..s>=5.0, <(Fe/H)>=-1.0). We show from a statistical argument that the sample of stars is too small to detect an abundance gradient over the 20-kpc interval in z unlessmore » the space density of RR Lyraes in Oosterhoff group I falls off about four times faster than the RR Lyraes of group II. Difficulties in inferring the halo abundance gradient for common subdwarfs, based on studies of halo RR Lyraes, are cited. It is not clear whether the paucity of RR Lyraes with (Fe/H)< or approx. =-2.2 is related to a corresponding lack of extremely metal-poor subdwarfs or due to an effect of stellar evolution.« less
  • 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.more » 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.« less
  • We present analysis of 12,227 type-ab RR Lyraes (RRLs) found among the 200 million public light curves in Catalina Surveys Data Release 1. These stars span the largest volume of the Milky Way ever surveyed with RRLs, covering {approx}20,000 deg{sup 2} of the sky (0 Degree-Sign < {alpha} < 360 Degree-Sign , -22 Degree-Sign < {delta} < 65 Degree-Sign ) to heliocentric distances of up to 60 kpc. Each of the RRLs is 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. Wemore » find that the periods are generally accurate to {sigma} = 0.002% in comparison to 2842 previously known RRLs and 100 RRLs 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 {approx}0.05 mag using Sloan Digital Sky Survey (SDSS) data for {approx}1000 blue horizontal branch stars and 7788 RRLs. By combining Catalina photometry with SDSS spectroscopy, we analyze the radial velocity and metallicity distributions for >1500 of the RRLs. Using the accurate distances derived for the RRLs, 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 RRLs, 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.« less
  • 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
  • While N-body simulations testify to a cuspy profile of the central region of dark matter halos, observations favor a shallow, cored density profile of the central region of at least some spiral galaxies and dwarf spheroidals. We show that a central profile, very close to the observed one, inevitably forms in the center of dark matter halos if we make a supposition about a moderate energy relaxation of the system during the halo formation. If we assume the energy exchange between dark matter particles during the halo collapse is not too intensive, the profile is universal: it depends almost notmore » at all on the properties of the initial perturbation and is very akin, but not identical, to the Einasto profile with a small Einasto index n ∼ 0.5. We estimate the size of the 'central core' of the distribution, i.e., the extent of the very central region with a respectively gentle profile, and show that the cusp formation is unlikely, even if the dark matter is cold. The obtained profile is in good agreement with observational data for at least some types of galaxies but clearly disagrees with N-body simulations.« less