Resolving the Controversy Over the Core Radius of 47 Tucanae (NGC 104)

This paper investigates the discrepancy between recent measurements of the density profile of the globular cluster 47 Tuc that have used HST data sets. Guhathakurta et al. (1992) used pre-refurbishment WFPC1 V-band images to derive r_c = 23" +/- 2". Calzetti et al. (1993) suggested that the density profile is a superposition of two King profiles (r_c = 8" and r_c = 25") based on U-band FOC images. De Marchi et al. (1996) used deep WFPC1 U-band images to derive r_c = 12" +/- 2". Differences in the adopted cluster centers are not the cause of the discrepancy. Our independent analysis of the data used by De Marchi et al. reaches the following conclusions: (1) De Marchi et al.'s r_c ~ 12" value is spuriously low, a result of radially-varying bias in the star counts in a magnitude limited sample -- photometric errors and a steeply rising stellar luminosity function cause more stars to scatter across the limiting magnitude into the sample than out of it, especially near the cluster center where crowding effects are most severe. (2) Changing the limiting magnitude to the main sequence turnoff, away from the steep part of the luminosity function, partially alleviates the problem and results in r_c = 18". (3) Combining such a limiting magnitude with accurate photometry derived from PSF fitting, instead of the less accurate aperture photometry employed by De Marchi et al., results in a reliable measurement of the density profile which is well fit by r_c = 22" +/- 2". Archival WFPC2 data are used to derive a star list with a higher degree of completeness, greater photometric accuracy, and wider areal coverage than the WFPC1 and FOC data sets; the WFPC2-based density profile supports the above conclusions, yielding r_c = 24" +/- 1.9".Comment: 22 pages, 5 figures, 1 table; accepted for publication in PASP; see http://www.ucolick.org/~raja/hgg.tar.gz for full-resolution figure

The Evolutionary Status of SS433

We consider possible evolutionary models for SS 433. We assume that common-envelope evolution is avoided if radiation pressure is able to expel most of a super-Eddington accretion flow from a region smaller than the accretor's Roche lobe. This condition is satisfied, at least initially, for largely radiative donors with masses in the range 4-12 solar masses. For donors more massive than about 5 solar masses, moderate mass ratios q = M_2/M_1 > 1 are indicated, thus tending to favor black-hole accretors. For lower mass donors, evolutionary considerations do not distinguish between a neutron star or black hole accretor. In all cases the mass transfer (and mass loss) rates are much larger than the likely mass-loss rate in the precessing jets. Almost all of the transferred mass is expelled at radii considerably larger than the jet acceleration region, producing the "stationary" H-alpha line, the infrared luminosity, and accounting for the low X-ray luminosity.Comment: 13 pages, Astrophysical Journal Letters, accepte

Laboratory experiments simulating electron cyclotron masers in space

[Abstract unavailable

Piracy off the Horn of Africa

This report discusses recent (2010) pirate attacks on vessels, including United States vessels, in the waters off the Horn of Africa. The Horn of Africa is sometimes called the Somali Peninsula and includes the nations of Eritrea, Djibouti, Ethiopia, and Somalia. This report explores reasons behind the increased number of pirate attacks in recent years, as well as what efforts are being taken to combat said attacks, including those by the 111th Congress and President Obama and his Administration

Piracy off the Horn of Africa

This report discusses recent (2008-2009) pirate attacks on vessels, including United States vessels, in the waters off the Horn of Africa. The Horn of Africa is sometimes called the Somali Peninsula and includes the nations of Eritrea, Djibouti, Ethiopia, and Somalia. This report explores reasons behind the increased number of pirate attacks in recent years, as well as what efforts are being taken to combat said attacks, including those by the 111th Congress and President Obama and his Administration

The nonlinear anomalous lattice elasticity associated with the high-pressure phase transition in spodumene: A high precission static compression study

The high-pressure behavior of the lattice elasticity of spodumene, LiAlSi2O6, was studied by static compression in a diamond-anvil cell up to 9.3 GPa. Investigations by means of single-crystal XRD and Raman spectroscopy within the hydrostatic limits of the pressure medium focus on the pressure ranges around similar to 3.2 and similar to 7.7 GPa, which have been reported previously to comprise two independent structural phase transitions. While our measurements confirm the well-established first-order C2/c-P2(1)/c transformation at 3.19 GPa (with 1.2% volume discontinuity and a hysteresis between 0.02 and 0.06 GPa), both unit-cell dimensions and the spectral changes observed in high-pressure Raman spectra give no evidence for structural changes related to a second phase transition. Monoclinic lattice parameters and unit-cell volumes at in total 59 different pressure points have been used to re-calculate the lattice-related properties of spontaneous strain, volume strain, and the bulk moduli as a function of pressure across the transition. A modified Landau free energy expansion in terms of a one component order parameter has been developed and tested against these experimentally determined data. The Landau solution provides a much better reproduction of the observed anomalies than any equation-of-state fit to data sets truncated below and above P (tr), thus giving Landau parameters of K (0) = 138.3(2) GPa, K' = 7.46(5), lambda (V) = 33.6(2) GPa, a = 0.486(3), b = -29.4(6) GPa and c = 551(11) GPa

Variation in Suicide Risk among Subgroups of Sexual and Gender Minority College Students

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163395/2/sltb12637_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163395/1/sltb12637.pd

Confrontation and the Utility of Rules

There is a good reason why evidence scholars continue to be fascinated and perplexed, and some courts continue at least to be perplexed, by the types of evidence that tend to be lumped together misleadingly under the headings nonassertive conduct or implied assertions. Evidence of this sort highlights a paradox of the prevailing law of hearsay. I believe that this paradox cannot be resolved without fundamentally transforming the structure of that law. Thus, while I agree - within the current framework - with many of the insights so ably stated in this Symposium, I think evidence scholars must devote their efforts to construction of a better structure

On a Theoretical Interpretation of the Period Gap in Binary Millisecond Pulsars

We reexamine evolutionary channels for the formation of binary millisecond pulsars in order to understand their observed orbital period distribution. The available paths provide a natural division into systems characterized by long orbital periods (> 60 d) and short orbital periods (< 30 d). Systems with initial periods 1 - 2 d ultimately produce low mass He white dwarfs with short orbital periods ( few days), early massive Case B evolution produces CO white dwarfs with orbital periods < 20 d. Common envelope evolution result in short period systems (P < 1 d) from unstable low mass Case B evolution producing He white dwarfs, and from unstable Case C evolution leading to CO white dwarfs. On the other hand, the long orbital period group arises from stable low mass Case B evolution with initial periods > few days producing low mass He white dwarfs and periods > 30 d, and from stable Case C evolution producing CO white dwarfs. The lack of observed systems between 23 and 56 days probably reflects the fact that for comparable initial orbital periods (< few days) low mass Case B and early massive Case B evolution lead to very discrepant final periods. We show in particular that the lower limit (~ 23 d) cannot result from common-envelope evolution.Comment: 20 pages, one encapsulated figure, LaTeX, accepted by Ap