Spectroscopy of blue horizontal branch stars in NGC 6656 (M22)

Recent investigations revealed very peculiar properties of blue horizontal branch (HB) stars in \omega Centauri, which show anomalously low surface gravity and mass compared to other clusters and to theoretical models. \omega Centauri, however, is a very unusual object, hosting a complex mix of multiple stellar populations with different metallicity and chemical abundances. We measured the fundamental parameters (temperature, gravity, and surface helium abundance) of a sample of 71 blue HB stars in M22, with the aim of clarifying if the peculiar results found in \omega Cen are unique to this cluster. M22 also hosts multiple sub-populations of stars with a spread in metallicity, analogous to \omega Cen. The stellar parameters were measured on low-resolution spectra fitting the Balmer and helium lines with a grid of synthetic spectra. From these parameters, the mass and reddening were estimated. Our results on the gravities and masses agree well with theoretical expectations, matching the previous measurements in three "normal" clusters. The anomalies found in \omega Cen are not observed among our stars. A mild mass underestimate is found for stars hotter than 14\,000 K, but an exact analogy with \omega Cen cannot be drawn. We measured the reddening in the direction of M22 with two independent methods, finding E(B-V)=0.35 \pm 0.02 mag, with semi-amplitude of the maximum variation \Delta(E(B-V))=0.06 mag, and an rms intrinsic dispersion of \sigma(E(B-V))=0.03 mag.Comment: 11 pages, 9 Postscript figure

Temporal Oscillation of Conductances in Quantum Hall Effect of Bloch Electrons

We study a nonadiabatic effect on the conductances in the quantum Hall effect of two-dimensional electrons with a periodic potential. We found that the Hall and longitudinal conductances oscillate in time with a very large frequencies due to quantum fluctuation.Comment: 8 pages, 4 figure

A hot horizontal branch star with a close K-type main-sequence companion

Dynamical interactions in binary systems are thought to play a major role in the formation of extreme horizontal branch stars (EHBs) in the Galactic field. However, it is still unclear if the same mechanisms are at work in globular clusters, where EHBs are predominantly single stars. Here we report on the discovery of a unique close binary system (period ~1.61 days) in the globular cluster NGC6752, comprising an EHB and a main-sequence companion of 0.63+-0.05 Msun. Such a system has no counterpart among nearly two hundred known EHB binaries in the Galactic field. Its discovery suggests that either field studies are incomplete, missing this type of systems possibly because of selection effects, or that a particular EHB formation mechanism is active in clusters but not in the field

Contribution to a Carbon Consistent Database for Austria

Andreas Geisler participated in IIASA's 1999 Young Scientists Summer Program (YSSP) and this paper summarizes his research. He was supervised by Matthias Jonas, research scholar in IIASA's Forestry (FOR) Project. Geisler's YSSP research task contributes to IIASA's research on Full Carbon Accounting and to the "Database for Assessment of Carbon Balance Modeling in Austria" study, work that commenced in June, 1999. The boundary conditions in setting up the Austrian carbon database are that it: is carbon consistent; satisfies the needs of Austria's carbon modeling community; and is consistent with FOR's existing database on Russia. The objective of the three-month YSSP task were to: create a database framework; fill the database with national data sets; track down carbon inconsistensies; and discuss options on how these can be overcome. However, the first objective had to be slightly changed during the course of the work, since available data sources posed some problems in creating the database setting. Therefore, after discussions with the research institutions employed with building the "Austrian Carbon Balance Model" (which are: Austrian Research Centers Seibersdorf; Institute for Industrial Ecology, St. Poelten; and Joanneum Research, Graz), as well as with other Austrian research institutions and experts (see Acknowledgments) the objective was changed towards trying to obtain consistency of the relevant carbon flows on a national level. Therefore, as a first step, some Austrian wood related carbon flows were quantified with regard to consistency principles and the underlying options to overcome inconsistencies are very well reported. The carbon consistent database will be completed by mid 2001 and will put Austria a step forward in Full Carbon Accounting

RR Lyrae Variables in M33. I. Evidence For a Field Halo Population

We present observations of RR Lyrae variables in the Local Group late-type spiral galaxy M33. Using the Advanced Camera for Surveys on the Hubble Space Telescope, we have identified 64 ab-type RR Lyraes in M33. We have estimated reddenings for these stars based on their minimum light V-I colors and metallicities based on their periods. From the distributions of these properties, we conclude that the RR Lyraes belong to two populations - one associated with the halo of M33 and the other with its disk. Given that RR Lyraes are produced by populations older than ~10 Gyr, this suggests that not only does the field halo of M33 contain an old component, but so does its disk. This is one of the best pieces of evidence for the existence of a halo field component in M33. Using a relation between RR Lyrae absolute magnitude and metallicity (Mv(RR) = 0.23[Fe/H] + 0.93), we estimate a mean distance modulus of = 24.67 +/- 0.08 for M33. This places M33 approximately 70 kpc beyond M31 in line-of-sight distance.Comment: 20 pages, 17 figures, accepted for publication in The Astronomical Journa

The Importance of Reading with Children

This project looks at how many people are actually reading with their children outside of school and deeply assesses the benefits that reading brings to a child’s life that carry into adulthood. Durham’s Partnership for Children (2016) conducted a study that shows only 46% of parents are reading with their child every day at home. More than half of families are not receiving the benefits of reading with their child that include decreases in behavioral outbursts, increases in fluency, vocabulary, and comprehension. Researchers have done many in depth studies that isolate and look for specific variables that show the benefits of reading, such as brain scans while viewing books or animations, or measuring the amount of words children know by the time they get to kindergarten, or analysing how intervention with good reading and parenting practices helps children thrive in the aforementioned areas. This project synthesized information from multiple sources and research projects into a brochure for parents to gain a more holistic view of the benefits of reading at home with their children. Taking multiple research papers and translating them from scientific language into everyday language helps parents to quickly read and understand the plethora of benefits their child would receive from being read to and with throughout their adolescence

Metal insulator transition in modulated quantum Hall systems

The quantum Hall effect is studied numerically in modulated two-dimensional electron systems in the presence of disorder. Based on the scaling property of the Hall conductivity as well as the localization length, the critical energies where the states are extended are identified. We find that the critical energies, which are distributed to each of the subbands, combine into one when the disorder becomes strong, in the way depending on the symmetry of the disorder and/or the periodic potential.Comment: 4 pages, 4 figures, to appear in Physica

Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality

We present new deep photometry of the rich globular cluster (GC) systems around the Brightest Cluster Galaxies UGC 9799 (Abell 2052) and UGC 10143 (Abell 2147), obtained with the HST ACS and WFC3 cameras. For comparison, we also present new reductions of similar HST/ACS data for the Coma supergiants NGC 4874 and 4889. All four of these galaxies have huge cluster populations (to the radial limits of our data, comprising from 12000 to 23000 clusters per galaxy). The metallicity distribution functions (MDFs) of the GCs can still be matched by a bimodal-Gaussian form where the metal-rich and metal-poor modes are separated by ~0.8 dex, but the internal dispersions of each mode are so large that the total MDF becomes very broad and nearly continuous from [Fe/H] = -2.4 to Solar. There are, however, significant differences between galaxies in the relative numbers of \emph{metal-rich} clusters, suggesting that they underwent significantly different histories of mergers with massive, gas-rich halos. Lastly, the proportion of metal-poor GCs rises especially rapidly outside projected radii R > 4 R_eff, suggesting the importance of accreted dwarf satellites in the outer halo. Comprehensive models for the formation of GCs as part of the hierarchical formation of their parent galaxies will be needed to trace the systematic change in structure of the MDF with galaxy mass, from the distinctly bimodal form in smaller galaxies up to the broad continuum that we see in the very largest systems.Comment: In press for Astrophysical Journa