1204.6037
The same, but different: Stochasticity in binary destruction
Parker, Goodwin
Investigate the stochasticity of the destruction of binaries in clusters with 10-100s AU separation (intermediates, visual binaries); should depend on the individual dynamical history. In statistically identical clusters, the number of intermediate binaries that are destroyed after 1Myr can vary by a factor of >2, with resulting distribution completely different statistically. The mass radio distributions are altered (more low mass ration systems destroyed). Conclude: finding different intermediate (visual) binary populations in different clusters does not provide evidence that the initial populations were different.
1204.6044
Astrophysical tests of modified gravity: constraints from distance indicators in the nearby universe
Jain, Vikram, Sakstein
* tip of the red giant branch (TRGB): distance indicator in astronomy, uses the luminosity of the brightest RGB stars in a galaxy to gauge the distance to that galaxy. HR diagram is a plot of stellar luminosity versus surface temperature; once H is exhausted in core, fusion continues in a shell around the core--surface temperature decrease while the overall luminosity of the star will increase. When He burning stars (with the triple-alpha process), the surface temperature starts in increase, resulting in a sharp discontinuity in the evolutionary track of the star on the HR diagram---the TRGB. Use I-band measurement, where magnitude insensitive to their metallicity and their mass, making it a useful distance indicator. TRGB indicator uses stars in the old stellar populations (Pop II).
* Cepheids: variable stars, with strong direct relationship between it's luminosity and pulsation period. Classical Cepheids are Pop I variable stars which are 4-20 teams more massive than the sun, and 1e5 times more luminous; are yellow supergiants of spectral class F6-K2, and their radii change by ~25% during a pulsation cycle. The accepted explanation for the pulsation of Cepheids is called the Eddington valve, or kappa-mechanism (kappa=gas opacity). HeIII is more opaque than HeII; the heating causes more ionization, making the star opaque; the opaque star accumulates heat and expands; the expanded star cools and recombines HeIII with electron to HeII; the star loses radiation and starts to shrink.
* water masers: Analysis of the motion of masers (masers in SF region are known to move across the sky along the material that is flowing out from forming stars) in the BH disk can dynamically determine the distance to a galaxy. [wiki still doesn't fully explain here]
Distance measurements to test gravity (chameleon theories). Three nearby distance indicators, cepheids, TRGB, and water masers, operate in gravitational fields of widely different strengths, enabling tests of scalar-tensor gravity theories because they are screened from enhanced forces to different extents. Inferred distances from cepheids and TRGB stars altered in opposite directions. Use published data, compare cepheid and TRGB distances in a sample of unscreened dwarf galaxies within 10 Mpc. Contro sample: use a comparable set of screened galaxies. Find no evidence for the order unity force enhancements expected in these theories. Constraints on chameleon theories, as well as symmetron and dilation screening scenarios; in f(R) model, rule out fR0 > 5e-7 at 2sigma. Compare TRGB and maser distances to NGC 4258 to test larger field values (with approximations and caveats).
1204.6046
Astrophysical tests of modified gravity: a screening map of the nearby universe
Cabre, Vikram, Zhao, Jain, Koyama
Astrophysical tests of modified gravity in nearby universe: key element is the screening mechanism, where GR is restored in massive haloes or high density environments like the MW. In chameleon theories of gravity, including all f(R) models, field dwarf galaxies may be unscreened and therefore feel and extra force, as opposed to screened galaxies. The first step to study differences between screened and unscreened galaxies is to create a 3d screening map. Use N-body simulations to test and calibrate simple approximations to determine the level of screening in galaxy catalogs. Sources of systematic errors in the screening map due to observational inaccuracies are modeled and their contamination is estimated. Apply methods to create a map out to 200 Mpc in the SDSS footprint using published data. In companion papers, use this map to carry out new test of gravity using distance indicators and the disks of dwarf galaxies. Screening map available.
1204.6108
Do we have a theory of early universe cosmology?
Brandenberger
Speculations about in "inflationary multiverse": from phenomenological point of view, the inflationary universe is very successful, but it suffers from conceptual problems, and this it does not (yet) have the status of a solid theory. Alternative ideas w/o inflation but agrees with observation: "matter bounce" and "string gas cosmology"; mention predictions for future observations which the 3 scenarios can be observationally distinguished.
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