Empirical relations for cluster RR Lyrae stars revisited

Our former study on the empirical relations between the Fourier parameters of the light curves of the fundamental mode RR Lyrae stars and their basic stellar parameters has been extended to considerably larger data sets. The most significant contribution to the absolute magnitude M_v comes from the period P and from the first Fourier amplitude A_1, but there are statistically significant contributions also from additional higher order components, most importantly from A_3 and in a lesser degree from the Fourier phase phi_51. When different colors are combined in reddening-free quantities, we obtain basically period-luminosity-color relations. Due to the log T_eff (B-V, log g, [Fe/H]) relation from stellar atmosphere models, we would expect some dependence also on phi_31. Unfortunately, the data are still not extensive and accurate enough to decipher clearly the small effect of this Fourier phase. However, with the aid of more accurate multicolor data on field variables, we show that this Fourier phase should be present either in V-I or in B-V or in both. From the standard deviations of the various regressions, an upper limit can be obtained on the overall inhomogeneity of the reddening in the individual clusters. This yields sigma_E(B-V)}< 0.012 mag, which also implies an average minimum observational error of sigma_V > 0.018 mag.Comment: 14 pages, 11 figures, 11 tables, accepted in Astronomy & Astrophysic

RR Lyrae stars in Galactic globular clusters. VI. The Period-Amplitude relation

We compare theory and observations for fundamental RR Lyrae in the solar neighborhood and in both Oosterhoff type I (OoI) and type II (OoII) Galactic globular clusters (GGCs). The distribution of cluster RR_ab in the PA_V plane depends not only on the metal abundance, but also on the cluster Horizontal Branch (HB) morphology. On average the observed k_puls parameter, connecting the period to the visual amplitude, increases when moving from metal-poor to metal-rich GGCs. However, this parameter shows marginal changes among OoI clusters with intermediate to red HB types and iron abundances -1.8<= [Fe/H] <=-1.1, whereas its value decreases in OoII clusters with the bluer HB morphology. Moreover, at [Fe/H]=-1.7+-0.1 the OoI clusters present redder HB types and larger values than the OoII clusters. The RR_ab variables in Omega Cen and in the solar neighborhood further support the evidence that the spread in [Fe/H], at fixed k_puls, is of the order of +-0.5 dex. Synthetic HB simulations show that the PA_V plane can provide accurate cluster distance estimates. The RR_ab variables in OoI and in OoII clusters with very blue HB types obey a well-defined M_V(RR)-k_puls relation, while those in OoII clusters with moderately blue HB types present a zero-point that is ~0.05 mag brighter. Regarding field variables, we show that with [Fe/H]=> -1.0 a unique M_V(RR)-k_puls relation can be adopted, independently of the parent HB morphology. Current findings suggest that the PA_V distribution does not seem to be a robust diagnostic for the metal abundance of RR_ab variables. However, the same observables can be used to estimate the absolute magnitude of globular cluster and field RR_ab variables. We show that over the metallicity range -2.4<= [Fe/H] <= 0.0 the M_V(RR)-[Fe/H] relation shows a parabolic behavior.Comment: Paper accepted on A&A, 13 pages, 18 figure

Programmable Oscillator

A programmable oscillator is a frequency synthesizer with an output phase that tracks an arbitrary function. An offset, phase-locked loop circuit is used in combination with an error control feedback loop to precisely control the output phase of the oscillator. To down-convert the received signal, several stages of mixing may be employed with the compensation for the time-base distortion of the carrier occurring at any one of those stages. In the Goldstone Solar System Radar (GSSR), the compensation occurs in the mixing from an intermediate frequency (IF), whose value is dependent on the station and band, to a common IF used in the final stage of down-conversion to baseband. The programmable oscillator (PO) is used in the final stage of down-conversion to generate the IF, along with a time-varying phase component that matches the time-base distortion of the carrier, thus removing it from the final down-converted signal

AdS Black Hole Solutions in the Extended New Massive Gravity

We have obtained (warped) AdS black hole solutions in the three dimensional extended new massive gravity. We investigate some properties of black holes and obtain central charges of the two dimensional dual CFT. To obtain the central charges, we use the relation between entropy and temperature according to the AdS/CFT dictionary. For AdS black holes, one can also use the central charge function formalism which leads to the same results.Comment: 24pages, some organization corrected, minor corrections, references added, final published versio

RR Lyrae stars in four globular clusters in the Fornax dwarf galaxy

(Abridged) We have surveyed four globular clusters in the Fornax dwarf galaxy for RR Lyrae stars, using archival HST observations. We identify 197 new RR Lyrae stars in these four clusters. Despite the short observational baseline, we derive periods, light-curves, and photometric parameters for each. The Fornax clusters have exceptionally large RR Lyrae specific frequencies compared with the Galactic globular clusters. Furthermore, the Fornax cluster RR Lyrae stars are unusual in that their characteristics are intermediate between the two Galactic Oosterhoff groups. In this respect the Fornax clusters are similar to the field populations in several dwarf galaxies. We revise previous measurements of the HB morphology in each cluster. The Fornax clusters closely resemble the ``young'' Galactic halo population defined by Zinn. The existence of the second parameter effect among the Fornax clusters is also confirmed. Finally, we determine foreground reddening and distance estimates for each cluster. We find a mean distance modulus to Fornax of (m-M)_0 = 20.66 +/- 0.03 (random) +/- 0.15 (systematic). Our measurements are consistent with a line of sight depth of 8-10 kpc for this galaxy, matching its projected dimensions, and incompatible with tidal model explanations for the observed high velocity dispersions in many dSph galaxies. Dark matter dominance is suggested.Comment: 26 pages, 6 figures. Accepted for publication in MNRAS. Table 2 and Figure 2 will only be available in the electronic version. On-line data will soon be available at http://www.ast.cam.ac.uk/STELLARPOPS/Fornax_RRlyr

Long-term photometric monitoring of RR Lyr stars in M3

The period-change behaviour of 134 RR Lyrae stars in the globular cluster Messier 3 (M3) is investigated on the ~120-year time base of the photometric observations. The mean period-change rates (\beta \approx 0.01 d Myr^-1) of the subsamples of variables exhibiting the most regular behaviour are in good agreement with theoretical expectations based on Horizontal-Branch stellar evolution models. However, a large fraction of variables show period changes that contradict the evolutionary expectations. Among the 134 stars studied, the period-change behaviour of only 54 variables is regular (constant or linearly changing), slight irregularities are superimposed on the regular variations in 23 cases and the remaining 57 stars display irregular period variations. The light curve of ~50 per cent of the RRab stars is not stable, i.e., these variables exhibit Blazhko modulation. The large fraction of variables with peculiar behaviour (showing light-curve modulation and/or irregular O-C variation) indicate that, probably, variables with regular period changes incompatible with their evolutionary stages also could display some kind of instability of the pulsation light curve and/or period, but the available observations have not disclosed it yet. The temporal appearence of the Blazhko effect in some stars, and the 70-90 years long regular changes preceded or followed by irregular, rapid changes of the pulsation period in some cases support this hypothesis. [...] Abstract truncated due to the limitations of astroph. See full abstract in the paper.Comment: 22 pages, 14 figures, accepted for publication in MNRA

Gravitating σ\sigma Model Solitons

We study axially symmetric static solitons of O(3) nonlinear $\sigma$ model coupled to (2+1)-dimensional anti-de Sitter gravity. The obtained solutions are not self-dual under static metric. The usual regular topological lump solution cannot form a black hole even though the scale of symmetry breaking is increased. There exist nontopological solitons of half integral winding in a given model, and the corresponding spacetimes involve charged Ba$\tilde n$ados-Teitelboim-Zanelli black holes without non-Abelian scalar hair.Comment: 35 pages, RevTe

Angle of Repose and Angle of Marginal Stability: Molecular Dyanmics of Granular Particles

We present an implementation of realistic static friction in molecular dynamics (MD) simulations of granular particles. In our model, to break contacts between two particles, one has to apply a finite amount of force, determined by the Coulomb criterion. Using a two dimensional model, we show that piles generated by avalanches have a {\it finite} angle of repose $\theta_R$ (finite slopes). Furthermore, these piles are stable under tilting by an angle smaller than a non-zero tilting angle $\theta_T$, showing that $\theta_R$ is different from the angle of marginal stability $\theta_{MS}$, which is the maximum angle of stable piles. These measured angles are compared to a theoretical approximation. We also measure $\theta_{MS}$ by continuously adding particles on the top of a stable pile.Comment: 14 pages, Plain Te

Study of Globular Cluster M53: new variables, distance, metallicity

We study the variable star content of the globular cluster M53 to compute the physical parameters of the constituting stars and the distance of the cluster. Covering two adjacent seasons in 2007 and 2008, new photometric data are gathered for 3048 objects in the field of M53. By using the OIS method and subsequently TFA, we search for variables in the full sample by using DFT and BLS methods. We select variables based on the statistics related to these methods combined with visual inspections. We identified 12 new variables (2 RR Lyrae stars, 7 short periodic stars - 3 of them are SX Phe stars - and 3 long-period variables). No eclipsing binaries were found in the present sample. Except for the 3 (hitherto unknown) Blazhko RR Lyrae stars, no multiperiodic variables were found. We showed that after proper period shift, the PLC relation for the first overtone RR Lyrae sample tightly follows the one spanned by the fundamental stars. Furthermore, the slope is in agreement with the one derived from other clusters. Based on the earlier Baade-Wesselink calibration of the PLC relations, the derived reddening-free distance modulus of M53 is 16.31 +/- 0.04 mag, corresponding to a distance modulus of 18.5 mag for the Large Magellanic Cloud. From the Fourier parameters of the RRab stars we obtained an average iron abundance of -1.58 +/- 0.03. This is ~0.5 dex higher than the overall abundance of the giants as given in the literature and derived in this paper from the three-color photometry of giants. We suspect that the source of this discrepancy (observable also in other, low-metallicity clusters) is the want of sufficient number of low-metallicity objects in the calibrating sample of the Fourier method.Comment: Accepted for publication in Astronomy & Astrophysics. The paper contains 5 tables and 13 figure

A matched-pair cluster design study protocol to evaluate implementation of the Canadian C-spine rule in hospital emergency departments: Phase III

BACKGROUND: Physicians in Canadian emergency departments (EDs) annually treat 185,000 alert and stable trauma victims who are at risk for cervical spine (C-spine) injury. However, only 0.9% of these patients have suffered a cervical spine fracture. Current use of radiography is not efficient. The Canadian C-Spine Rule is designed to allow physicians to be more selective and accurate in ordering C-spine radiography, and to rapidly clear the C-spine without the need for radiography in many patients. The goal of this phase III study is to evaluate the effectiveness of an active strategy to implement the Canadian C-Spine Rule into physician practice. Specific objectives are to: 1) determine clinical impact, 2) determine sustainability, 3) evaluate performance, and 4) conduct an economic evaluation. METHODS: We propose a matched-pair cluster design study that compares outcomes during three consecutive 12-months "before," "after," and "decay" periods at six pairs of "intervention" and "control" sites. These 12 hospital ED sites will be stratified as "teaching" or "community" hospitals, matched according to baseline C-spine radiography ordering rates, and then allocated within each pair to either intervention or control groups. During the "after" period at the intervention sites, simple and inexpensive strategies will be employed to actively implement the Canadian C-Spine Rule. The following outcomes will be assessed: 1) measures of clinical impact, 2) performance of the Canadian C-Spine Rule, and 3) economic measures. During the 12-month "decay" period, implementation strategies will continue, allowing us to evaluate the sustainability of the effect. We estimate a sample size of 4,800 patients in each period in order to have adequate power to evaluate the main outcomes. DISCUSSION: Phase I successfully derived the Canadian C-Spine Rule and phase II confirmed the accuracy and safety of the rule, hence, the potential for physicians to improve care. What remains unknown is the actual change in clinical behaviors that can be affected by implementation of the Canadian C-Spine Rule, and whether implementation can be achieved with simple and inexpensive measures. We believe that the Canadian C-Spine Rule has the potential to significantly reduce health care costs and improve the efficiency of patient flow in busy Canadian EDs