A BAYESIAN ANALYSIS OF THE AGES OF FOUR OPEN CLUSTERS

In this paper we apply a Bayesian technique to determine the best fit of stellar evolution models to find the main sequence turn off age and other cluster parameters of four intermediate-age open clusters: NGC 2360, NGC 2477, NGC 2660, and NGC 3960. Our algorithm utilizes a Markov chain Monte Carlo technique to fit these various parameters, objectively finding the best fit isochrone for each cluster. The result is a high precision isochrone fit. We compare these results with the those of traditional “by eye” isochrone fitting methods. By applying this Bayesian technique to NGC 2360, NGC 2477, NGC 2660, and NGC 3960 we determine the ages of these clusters to be 1.35 ± 0.05, 1.02 ± 0.02, 1.64 ± 0.04, and 0.860 ± 0.04 Gyr, respectively. The results of this paper continue our effort to determine cluster ages to higher precision than that offered by these traditional methods of isochrone fitting

Spin-glass behavior in KxRu4-yNiyO8 hollandite materials

We report the synthesis and comprehensive ac and dc susceptibility measurements of KxRu4−yNiyO8 hollandite. The value of the relative frequency shift, δTf , has been determined as 0.025 which is within the range expected for spin-glass systems (0.005–0.06). Additionally, the characteristic flipping time of a single spin flip, τ0, and the dynamical critical exponent, −zv, were determined to have values of 5.82×10−8 s and 6.1(3), respectively from the power law. While the value of τ0 is comparatively very large, −zv is consistent with what is expected for spin-glass systems. Field-cooled hysteresis behavior demonstrates a small increase in the remnant magnetization (at 2 K) on increasing the strength of the cooling field, suggesting that the degree of short-range correlations increases consistent with the formation of larger spin clusters. Thermoremnant magnetization data indicate an exponential-like decay of the magnetization as a function of time with the remnant magnetization remaining nonzero. However, it is clear from these data that multiple components contribute to the decay behavior. Collectively, these data confirm spin-glass character for K0.73(3)Ni1.9(5)Ru2.1(5)O8 and clearly demonstrate that the magnetic behavior of this material is far from simplistic

Improving white dwarfs as chronometers with gaia parallaxes and spectroscopic metallicities

White dwarfs (WDs) offer unrealized potential in solving two problems in astrophysics: stellar age accuracy and precision. WD cooling ages can be inferred from surface temperatures and radii, which can be constrained with precision by high-quality photometry and parallaxes. Accurate and precise Gaia parallaxes along with photometric surveys provide information to derive cooling and total ages for vast numbers of WDs. Here we analyze 1372 WDs found in wide binaries with main-sequence (MS) companions and report on the cooling and total age precision attainable in these WD+MS systems. The total age of a WD can be further constrained if its original metallicity is known because the MS lifetime depends on metallicity at fixed mass, yet metallicity is unavailable via spectroscopy of the WD. We show that incorporating spectroscopic metallicity constraints from 38 wide binary MS companions substantially decreases internal uncertainties in WD total ages compared to a uniform constraint. Averaged over the 38 stars in our sample, the total (internal) age uncertainty improves from 21.04% to 16.77% when incorporating the spectroscopic constraint. Higher mass WDs yield better total age precision; for eight WDs with zero-age MS masses ≥2.0 M⊙, the mean uncertainty in total ages improves from 8.61% to 4.54% when incorporating spectroscopic metallicities. We find that it is often possible to achieve 5% total age precision for WDs with progenitor masses above 2.0 M⊙ if parallaxes with ≤1% precision and Pan-STARRS g, r, and i photometry with ≤0.01 mag precision are available

Effect of Systematic Uncertainties on Density and Temperature Estimates in Coronae of Capella

Abstract We estimate the coronal density of Capella using the O vii and Fe xvii line systems in the soft X-ray regime that have been observed over the course of the Chandra mission. Our analysis combines measures of error due to uncertainty in the underlying atomic data with statistical errors in the Chandra data to derive meaningful overall uncertainties on the plasma density of the coronae of Capella. We consider two Bayesian frameworks. First, the so-called pragmatic Bayesian approach considers the atomic data and their uncertainties as fully specified and uncorrectable. The fully Bayesian approach, on the other hand, allows the observed spectral data to update the atomic data and their uncertainties, thereby reducing the overall errors on the inferred parameters. To incorporate atomic data uncertainties, we obtain a set of atomic data replicates, the distribution of which captures their uncertainty. A principal component analysis of these replicates allows us to represent the atomic uncertainty with a lower-dimensional multivariate Gaussian distribution. A t-distribution approximation of the uncertainties of a subset of plasma parameters including a priori temperature information, obtained from the temperature-sensitive-only Fe xvii spectral line analysis, is carried forward into the density- and temperature-sensitive O vii spectral line analysis. Markov Chain Monte Carlo based model fitting is implemented including Multi-step Monte Carlo Gibbs Sampler and Hamiltonian Monte Carlo. Our analysis recovers an isothermally approximated coronal plasma temperature of ≈5 MK and a coronal plasma density of ≈1010 cm−3, with uncertainties of 0.1 and 0.2 dex, respectively.</jats:p

Defining a New Prognostic Index for Stage I Nonseminomatous Germ Cell Tumors Using CXCL12 Expression and Proportion of Embryonal Carcinoma.

PURPOSE: Up to 50% of patients diagnosed with stage I nonseminomatous germ cell tumors (NSGCTs) harbor occult metastases. Patients are managed by surveillance with chemotherapy at relapse or adjuvant treatment up front. Late toxicities from chemotherapy are increasingly recognized. Based on a potential biologic role in germ cells/tumors and pilot data, our aim was to evaluate tumor expression of the chemokine CXCL12 alongside previously proposed markers as clinically useful biomarkers of relapse. EXPERIMENTAL DESIGN: Immunohistochemistry for tumor expression of CXCL12 was assessed as a biomarker of relapse alongside vascular invasion, histology (percentage embryonal carcinoma), and MIB1 staining for proliferation in formalin-fixed paraffin-embedded orchidectomy samples from patients enrolled in the Medical Research Council's TE08/22 prospective trials of surveillance in stage I NSGCTs. RESULTS: TE08/TE22 trial patients had a 76.4% 2-year relapse-free rate, and both CXCL12 expression and percentage embryonal carcinoma provided prognostic value independently of vascular invasion (stratified log rank test P = 0.006 for both). There was no additional prognostic value for MIB1 staining. A model using CXCL12, percentage embryonal carcinoma, and VI defines three prognostic groups that were independently validated. CONCLUSIONS: CXCL12 and percentage embryonal carcinoma both stratify patients' relapse risk over and above vascular invasion alone. This is anticipated to improve the stratification of patients and identify high-risk cases to be considered for adjuvant therapy

The ACS Survey of Galactic Globular Clusters XIV: Bayesian Single-Population Analysis of 69 Globular Clusters

We use Hubble Space Telescope (HST) imaging from the ACS Treasury Survey to determine fits for single population isochrones of 69 Galactic globular clusters. Using robust Bayesian analysis techniques, we simultaneously determine ages, distances, absorptions and helium values for each cluster under the scenario of a ‘single’ stellar population on model grids with solar ratio heavy element abundances. The set of cluster parameters is determined in a consistent and reproducible manner for all clusters using the Bayesian analysis suite BASE-9. Our results are used to re-visit the age–metallicity relation. We find correlations with helium and several other parameters such as metallicity, binary fraction and proxies for cluster mass. The helium abundances of the clusters are also considered in the context of carbon, nitrogen, and oxygen abundances and the multiple population scenario

Les Discamphiceratinae (Psiloceratidae), une nouvelle sous-famille d'ammonites (Cephalopoda) du Jurassique inférieur

The main reason for using visual languages is that they are often far more convenientto the user than traditional textual languages. Therefore, visual languages intended for use by both computers and humans ought to be designed and analyzed not only from the perspective of computational resource requirements, but equally importantly, also from the perspectiveof languages that are cognitively usable and useful. Theoretical and practical research on visual languages need to takeinto account the full context of a coupled human-computer system in which the visual language facilitates interactions between the computational and the cognitive parts. This implies that theoretical analyses ought to address issues of comprehension, reasoning and interaction in the cognitive realm as well as issues of visual program parsing, execution and feedback in the computational realm. The human aspect is crucial to visual languages, and therefore weadvocate a correspondingly broadened scope of in..