Day 507

Thursday.

1309.2629
Two estimates of the distance to the Galactic centre
Francis, Anderson

Use updated globular cluster distances to estimate the distance to the Galactic center, finding 7.3 pm 0.4 kpc, from symmetry considerations.

1309.2631
Exploring the Milky Way stellar disk.  A detailed elemental abundance study of 703 F and G dwarf stars in the Solar neighbourhood
Bensby, Feltzing, Oey

Detailed elemental abundances for O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y and Ba; data show there is an old and alpha-enhanced disk population, and then a younger and less alpha-enhanced disk population.  They show a bimodal distribution in [alpha/Fe], clearer if more uncertain data are discarded.  Find that the alpha-enhanced population have orbital parameters placing their birthplaces in the inner Galactic disk while the low-alpha stars mainly come from the outer Galactic disk.

1309.2642
Do gravitational lens galaxies have an excess of luminous substructure?
Nierenberg, Oldenburg, Treu

SL can be used to directly measure the mass function of their satellites, thus testing one of the fundamental predictions of CDM cosmological models.  Given the importance of this test it is essential to ensure that galaxies acting as SL have dark and luminous satellites which are representative of the overall galaxy population.  Address this issue by measuring the number and spatial distribution of luminous satellites in ACS imaging around lens galaxies from the SLACS lenses, and comparing them with the satellite population in ACS imaging of non lens galaxies selected from COSMOS, which has similar depth and resolution to the ACS images of SLACS lenses.  In order to compare the samples of lens and non lens galaxies, which have intrinsically different stellar mass distributions, measure the number of satellites per host as a continuous function of host stellar mass for both populations.  Find that the number of satellites as a function of host stellar mass, as well as the spatial distribution are consistent between the samples.  Using these results, predict the number of satellites we would expect to find around a subset of the CLASS lenses, and find a result consistent with the number observed by Jackson+ 2010.  Thus conclude that within measurement uncertainties, there is no significant difference in the satellite populations of lens and non lens galaxies.

1309.2790
Dynamical models and galaxy surveys
Binney, Sanders

Equilibrium dynamical models are essential tools for extracting science from surveys of our Galaxy.  Show how models can be tested with data from a survey before the survey's selection function has been determined.  Illustrate the application of this method by presenting some results for the RAVE survey.  Extend published analytic distribution functions to include chemistry and fit the chosen functional form to a combination of the GCS and sample of G-dwarfs observed at z~1.75 kpc by the SEGUE survey.  By including solid dynamics, able to predict the contribution that the thick disk/halo stars surveyed by SEGUE should make to the GCS survey.  Show that the measured [Fe/H] distribution from the GCS includes many fewer stars at [Fe/H]<-0.6 than are predicted.  The problem is more likely to lie in discordant abundance scales than with incorrect dynamics.

1309.2794
Dynamics for galactic archeology
Binney

Our Galaxy is a complex machine in which several processes operate simultaneously: metal-poor gas is accreted, is chemically enriched by dying stars, and then drifts inwards, surrendering its angular momentum to stars; new stars are formed on nearly circular orbits in the equatorial plane and then diffuse through orbit space to eccentric and inclined orbits; the central stellar bar surrenders angular momentum to the surrounding disc and dark halo while acquiring angular momentum from inspiralling gas; the outer parts of the disc are constantly disturbed by satellite objects, both luminous and dark, as they sweep through pericenter.  Review the conceptual tools required to bring these complex happenings into focus.  First concern must be the construction of equilibrium models of the Galaxy, for upon these hang the hopes of determining the Galaxy's mean gravitational field, which is required for every subsequent step.  Ideally the equilibrium model should be formulated so that the secular evolution of the system can be modeled with perturbation theory.  Such theory can be used to understand how stars diffuse through orbit space from either the thin gas disc in which presumably disc stars formed, or the debris of an accreted object, the presumed origin of many halo stars.  Coupling this understanding to the still very uncertain predictions of the theory of stellar evolution and nucleosynthesis, can extract a complete model of the chemodynamic evolution of our reasonably generic Galaxy.  Discuss the relation of such a model to cosmological simulations of galaxy formation, which provide general guidance but cannot be relied on for quantitative detail.

1309.2826
Discovery of a Quadruple lens in CANDELS with a record lens redshift z=1.53
van der Wel et al

High-z lens of z=1.53, spectroscopically confirmed source at z=3.417, Einstein radius of 0.35"; source magnification 40x.

1309.2899
Mapping a star with transits: orbit precession effects in the Kepler-13 system
Szabó, Simon, Kiss

Kepler-13b is an intriguing exoplanet system due to the rapid precession rate, exhibiting several exotic phenomena.  Analyze Kepler Short Cadence data with a total time-span of 928 days to reveal changes in transit duration, depth, asymmetry, and identify the possible signals of stellar rotation and low-level activity.  Investigate long-term variations of transit light curves, testing for duration, peak depth and asymmetry.  Also performed cluster analysis on Kepler quarters.  Compute the autocorrelation function of the out-of-transit light variations.  Transit duration, peak depth, and asymmetry evolve slowly, due to the slowly drifting transit path through the stellar disk.  The detected transit shapes will map the stellar surface on the time scale of decades.  Find a very significant clustering pattern with 3-orbit period.  Source is very probably the rotating stellar surface, in 5:3 spin-orbit resonance reported in a previous study.  The autocorrelation function of the out-of-transit light variations, filtered to 25.4 hours and harmonics, shows slow variations and a peak around 300-360 day period, which could be related to the activity cycle of the host star.

1309.2917
Higher order non-inear parameters with PLANCK
Gong, Takahashi

Investigate how higher order NL parameters affect lower order ones through loop effects.  Calculate the loop corrections up to two-loops and explicitly show that the tree contribution is stable against loop terms in most cases.  Argue that, nevertheless, observational constraints on NL parameters such as fNL and tauNL can also give a limit even for higher order ones due to the loop contribution.  Discuss these issues both for single-source and multi-source cases.