Monday.
1408.3407
Massive star archeology in globular clusters
Chantereau, Charbonnel, Meynet
Globular clusters are among the oldest structures in the Universe and they host today low-mass stars and no gas. However, there has been a time when they formed as gaseous objects hosting a large number of short-lived, massive stars. Many details on this early epoch have been depicted recently through unprecedented dissection of low-mass globular cluster stars via spectroscopy and photometry. In particular, multiple populations have been identified, which bear the nucleosynthetic fingerprints of the massive hot stars long disappeared. Discuss here how massive star archeology can be done through the lens of these multiple populations.
1408.3408
Hubble space telescope proper motions along the Sagittarius Stream: I. Observations and results for stars in four fields
Sohn, van der Marel, ... Kallivayalil, et al
Present HST study of stellar proper motions (PMs) for four fields spanning 200 degrees along the Sgr stream: one field in the trailing arm, one field near the Sgr dSph tidal radius, and two fields in the leading arm. From data with 6-9 year time baselines, determine absolute PMs of dozens of individual stars per field, using established techniques that use distant background galaxies to define a stationary reference frame. Stream stars are identified based on combined color-magnitude diagram (CMD) and PM information. The results are broadly consistent with the few existing PM measurements for the Sgr dSph and the trailing arm. However, new results provide the highest PM accuracy for the stream to date, the first PM measurements for the leading arm, and the first PM measurements for individual stream stars [also serendipitously determine the PM of the globular cluster NGC 6652 to be (5.6,-4.5) mas/yr]. In the trailing-arm field, the individual PMs allow kinematical separation of the trailing-arm stars from leading-arm stars that are 360 degrees further ahead in their orbit around the MW. Also, in three of the fields, find indications that two distinct kinematical components may exist within the same arm and wrap of the stream. Qualitative comparison of the HST data to the predictions of the Law& Majewski N-body model of the stream show that the PM measurements closely follow the predicted trend with Sgr longitude. While this does not necessarily indicate that the triaxial MW dark halo shape inferred from the N-body model is correct, it does provide a successful consistency check using PM data that the model was not tailored to reproduce. Quantitative data-model comparisons will be presented in a companion paper.
1408.3409
BONNSAI: a Bayesian tool for comparing stars with stellar evolution models
Schneider, Langer, ... Izzard, Lau
Powerful telescopes equipped with multi-fibre or IFS combined with detailed models of stellar atmospheres and automated fitting techniques allow for the analysis for large number of stars. These datasets contain a wealth of information that require new analysis techniques to bridge the gap between observations and stellar evolution models. To that end, develop BONNSAI (BONN Stsellar Astrophyscis Interface), a Bayesian statistical method, that is capable of comparing all available observables simultaneously to stellar models while taking observed uncertainties and prior knowledge such as IMF and distributions of stellar rotational velocities into account. BONNSAI can be used to (1) determine probability distributions of fundamental stellar parameters such as initial mass and stellar ages from complex datasets, (2) predict stellar parameters that were not yet observationally determined and (3) test stellar models to further advance the understanding of stellar evolution. An important aspect of BONNSAI is that it singles out stars that cannot be reproduced by stellar models through chi^2 hypothesis tests and posterior predictive checks. BONNSAI can be used with any set of stellar models and currently supports massive main-sequence single star models of MW and LMC and SMC composition. Apply new method to mock stars to demonstrate its functionality and capabilities. In a first application, use BONNSAI to test the stellar models of Brott+2011 by comparing the stellar ages inferred for the primary and secondary stars of eclipsing MW binaries. Ages are determined from dynamical masses and radii that are known to better than 3%. Find that the stellar models reproduce the MW binaries well. BONNSAI is available through a web-interface.
1408.3524
Cosmic-ray exposure ages of fossil micrometeorites from mid-Ordovician sediments at Lynna River, Russia
Measure the He and Ne concentrations of 50 individual extraterrestrial chromite grains recovered from mid-Ordovician (lower Darriwilian) sediments from the Lynna River section near St. Petersburg, Russia. High concentrations of solar wind-like He and Ne found in most grains indicate that they were delivered to Earth as micrometeoritic dust, while their abundance, stratigraphic position and major element composition indicate an origin related to the L chondrite parent body (LCPB) break-up even, 470 Ma ago. Compared to sediment-dispersed extraterrestrial chromite (SEC) grains extracted from coeval sediments at other localities, the grains from Lynna River are both highly concentrated and well preserved. As in previous work, in most grains from Lynna River, high concentrations of solar wind-derived He and Ne impede a clear quantification of cosmic-ray produced He and Ne. However, we have found several SEC grains poor in solar wind Ne, showing a resolvable contribution of cosmogenic 21Ne. This makes it possible, for the first time, to determine robust CR exposure (CRE) ages in these fossil micrometeorites, on the order of a few hundred-thousand years. These ages are similar to the CRE ages measured in chromite grains from cm-sized fossil meteorites recovered from coeval sediments in Sweden. As the CRE ages are shorted than the orbital decay time of grains of this size by Poynting-Robertson drag [solar radiation causing a dust grain orbiting a star to lose angular momentum, causing dusts that are small enough to be affected by this drag, but too large to be blown away from the star, to spiral into the star], this suggests that the grains were delivered to Earth through direct injection into an orbital resonance. Demonstrate how CRE ages of fossil micrometeorites can be used, in principle, to determine sedimentation rates, and to correlate the sediments at Lynna River with the fossil meteorite-bearing sediment layers in Sweden.
1408.3531
Constraints on 3.55 keV line emission from stacked observations of dwarf spheroidal galaxies
Malyshev, Neronov, Eckert
Analysis shows no evidence for the presence of the line in the stacked spectra of the dwarf galaxies.
1408.3578
Unveiling the secrets of metallicity and massive star formation using DLAs along gamma-ray bursts
Cucchiara, Fumagalli, ... Prochaska, et al
GRB hosts are star-forming, and have, on average, higher metallicity than the general QSO-DLA population.
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