119168880
Two Distinct Red Giant Branches in the Globular Cluster NGC 288
We report the presence of two distinct red giant branches (RGBs) in the globular cluster NGC 288 from the narrowband calcium and Stroemgren b and y photometry obtained at the CTIO 4 m Blanco telescope. The RGB of NGC 288 is clearly split into two in the hk [=(Ca - b) - (b - y)] index, while the split is not shown in the b - y color. Unlike other globular clusters with multiple populations reported thus far, the horizontal branch of NGC 288 is only mildly extended. Our stellar population models show that this and the presence of two distinct RGBs in NGC 288 can be reproduced if slightly metal-rich ({Delta}[m/H] {approx} 0.16) second generation stars are also enhanced in helium by small amount ({Delta}Y {approx} 0.03) and younger by {approx}1.5 Gyr. The RGB split in the hk index is most likely indicating that the second generation stars were affected by supernovae enrichment, together with the pollution of lighter elements by intermediate-mass asymptotic giant branch stars or fast-rotating massive stars. In order to confirm this, however, spectroscopy of stars in the two distinct RGB groups is urgently required.
11936862
Bootes II: Not a Dwarf Galaxy but Possibly Shed by One
We present moderately deep V I C photometry of Boötes II, obtained using the SOAR Telescope. While identified initially as an old, metal-poor, dwarf galaxy, Boötes II appears to be a moderately metal-rich globular cluster with [Fe/H] ≈ −0.7. The slope of the red giant branch suggests that [α/Fe] ≈ 0.0, and the turn-off indicates an age of 7 to 9 Gyrs, considerably younger than most globular clusters, but similar to Palomar 12. Like that object, Boötes II lies in the direction of the Sagittarius dwarf galaxy tidal stream, and, with a distance of almost 50 kpc, is probably associated with the more distant portion of the stream, as defined by Belokurov et al. (2006a).
205218920
Enrichment by supernovae in globular clusters with multiple populations
The most massive globular cluster in the Milky Way, ω Centauri, is thought to be the remaining core of a disrupted dwarf galaxy, as expected within the model of hierarchical merging. It contains several stellar populations having different heavy elemental abundances supplied by supernovae—a process known as metal enrichment. Although M 22 appears to be similar to ω Cen, other peculiar globular clusters do not. Therefore ω Cen and M 22 are viewed as exceptional, and the presence of chemical inhomogeneities in other clusters is seen as ‘pollution’ from the intermediate-mass asymptotic-giant-branch stars expected in normal globular clusters. Here we report Ca abundances for seven globular clusters and compare them to ω Cen. Calcium and other heavy elements can only be supplied through numerous supernovae explosions of massive stars in these stellar systems, but the gravitational potentials of the present-day clusters cannot preserve most of the ejecta from such explosions. We conclude that these globular clusters, like ω Cen, are most probably the relics of more massive primeval dwarf galaxies that merged and disrupted to form the proto-Galaxy.
118885035
INFRARED PHOTOMETRY OF NGC 6791
We present deep JHK photometry of the old and metal-rich open cluster NGC 6791. The photometry reaches below the main-sequence turnoff to K ≈ 16.5 mag. We combine our photometry with that from Stetson et al. to provide color-magnitude diagrams showing K versus J - K, K versus V - K, and V versus V - K. We study the slope of the red giant branch in the infrared but find that it is not a useful metallicity indicator for the cluster, nor any metal-rich cluster that lacks a well-populated red giant branch, because it is not linear, as has often been assumed, in K versus J - K. The mean color of the red horizontal-branch/red clump stars provide an estimate of the cluster reddening, E(B - V) = 0.14 ± 0.04 mag for [Fe/H] = +0.4 ± 0.1. The mean magnitudes of these stars also provide a good distance estimate, (m - M)0 = 13.07 ± 0.04. Finally, we find that the isochrones of Yi et al. provide optimal fits in V versus B - V and V - K and K versus J - K and V - K for such values if [Fe/H] lies between +0.3 and +0.5 (with a slight preference for +0.5) and ages between 9 Gyr ([Fe/H] = +0.3) and 7.5 Gyr ([Fe/H] = +0.5).
2150926
A Chemical Abundance Study of three RHB and two RGB stars in NGC6637 (M69)
We present a detailed chemical abundance study of three red horizontal branch and two red giant branch stars in the metal-rich globular cluster NGC 6637 (M69). The value of [Fe/H] derived from LTE calculations is $-$0.77 $\pm$ 0.02 dex. We also discuss the anticorrelation between oxygen and sodium abundances in the program stars and compare the [Si/Ti] ratio of NGC 6637 with those of other globular clusters.
119279392
THE RR LYRAE VARIABLES AND HORIZONTAL BRANCH OF NGC 6656 (M22)
The first calibrated broadband UBVI time-series photometry is presented for the RR Lyrae variable stars in NGC 6656 (M22), with observations spanning a range of 22 years. We have also redetermined the variability types and periods for the RR Lyrae stars identified previously by photographic observations, revising the number of fundamental-mode RR Lyrae variables (RR0) to 10 and the number of first-overtone variables (RR1) to 16. The mean periods of the RR0 and RR1 variables are (P) {sub RR0} = 0.66 ± 0.02 days and (P) {sub RR1} = 0.33 ± 0.01 days, respectively, supporting an Oosterhoff II classification for the cluster. The number ratio of RR1-type to all RR-type variables is N {sub 1}/N{sub RR} = 0.61, also consistent with an Oosterhoff II designation. Both the RR Lyrae stars' minimum light colors and the blue edge of the RR Lyrae instability strip suggest E( B – – V) = 0.36 ± 0.02 mag toward M22. Regarding the HB morphology of M22, we find (B-R)/(B+V+R) = +0.97 ± 0.1 and at least one ''gap'' located in an unusual part of the blue HB, in the middle of the so-called hot HB stars.
14997681
NEW LIMITS FOR NEUTRINOLESS TAU DECAYS
Neutrinoless 3-prong tau lepton decays into a charged lepton and either two charged particles or one neutral meson have been searched for using 4.79fb^(-1) of data collected with the CLEO II detector at Cornell Electron Storage Ring. This analysis represents an update of a previous study and the addition of six decay channels. In all channels the numbers of events found are compatible with background estimates and branching fraction upper limits are set for 28 different decay modes. These limits are either more stringent than those set previously or represent the first attempt to find these decays.
14107601
Cosmological Imprint of the Second Law of Thermodynamics
We study the evolution of the universe in the presence of inflaton, matter, radiation and holographic dark energy. The time evolution of the scale factor is obtained by solving the Friedmann equation of the universe with a good approximation. We present two independent ways which determine the value of the dark energy constant d~1 from the observational data. The two ways are measuring the deceleration parameter and measuring a universal constant depending only on d. The universal constant is given by a dimensionless combination of three scale factors at the equipartition times of radiation–matter, radiation–dark energy and matter–dark energy. We also discuss that the second law of thermodynamics determines the point of time when the dark-energy-dominated era begins in the universe.
119299991
Classification of Hypercylindrical Spacetimes with Momentum Flow
For the five-dimensional spacetimes whose four-dimensional sections are static, spherically symmetric ($SO(3)$), and flat asymptotically, we study the behavior of Arnowitt-Deser-Misner mass, tension, and momentum densities characterizing such asymptotically hypercylindrical metrics under boosts along the cylindrical axis. For such stringlike metrics two boost-invariant quantities are found, which are a sort of ``string rest mass squared'' and the sum of mass and tension densities. Analogous to the case of a moving point particle, we show that the asymptotically hypercylindrical geometries can be classified into three types depending on the value of the string rest mass squared, namely, ``ordinary string'', ``null string'' and ``tachyonlike string'' geometries. This asymptotic analysis shows that the extraordinary metrics reported recently by some of the authors belong to the tachyonlike string. Consequently, it is likely that such extraordinary solutions are the final states of tachyonic matter collapse. We also report two new vacuum solutions which belong to the null string and the tachyonlike string, respectively.
126168504
Neutrino Masses, Lepton Flavor Violations, and Flavor Changing Neutral Currents in the Composite Little Higgs Model
209834712
Search for anomalous production of prompt like-sign muon pairs and constraints on physics beyond the standard model with the ATLAS detector
An inclusive search for anomalous production of two prompt, isolated muons with the same electric charge is presented. The search is performed in a data sample corresponding to 1.6 fb(-1) of integr ...