Friday. Is it really Friday already? I need to run a lot of things, and I need to prioritize. German class is fun. It's getting into the grammar: bestimmte Artikel der die das, unbestimmte Artikel ein eine, and Verneinung kein keine. Also Plurals. Everyone is so confused, because the rules are not presented in a straightforward manner in the textbook; the teacher explains the rules, but in German.
1111.2333
NSV 11749, an elder sibling of the born again stars V605 Aql and V4334 Sgr?
Bertolami, Rohrmann, Granada, Althaus
* born-again episode: about 25% of all post-AGB stars undergo this, where the carbon-oxygen core is now surrounded by helium with an outer shell of hydrogen. If the helium is re-ignited a thermal pulse occurs and the star quickly returns to the AGB, becoming a He burning, H-deficient stellar object. If the star still has H-burning shell when this thermal pulse occurs, it is termed a late thermal pulse. Otherwise it is called a very late thermal pulse [because the H is gone, presumably]. The outer atmosphere of the born-again star develops a stellar wind and the star once more follows an evolutionary track across the HR diagram. But this phase is very brief, lasting only about 200 years before the star again heads towards the WD stage. Observationally, the late thermal pulse phase appears almost identical to a Wolf-Rayet star in the midst of its own planetary nebula.
* Wolf-Rayet stars: eveolved, massive stars (>20 Msun initially), which are losing mass rapidly by means of very strong stellar wind (2000 km/s). Surface temperature very hot (25,000K to 50,000K). Fast mass loss (1e-5 Msun/yr, compared to 1e-14Msun/yr for the Sun).
* Asymptotic giant branch (AGB): region of the HR diagram populated by evolving low to medium-mass stars; 0.6-10 Msun stars @ late in their lives. Observationally, AGB stars appear as red giants. Interior structure is characterized by a central and inert core of carbon and oxygen, a shell where helium is undergoing fusion to form carbon (He burning), another shell where H is undergoing fusion forming He (H burning), and a very large envelope of material of composition similar to normal stars.
* stellar evolution: when a star exhausts the supply of H by nuclear fusion in the core, the core contracts and its temperature increases, causing outer layers of the star to expand and cool. The star's luminosity increases greatly, and it becomes a red giant, following a track leading into the upper-right hand corner of the HR diagram. Eventually, He burning begins. Onset of He burning in the core halts the star's cooling and increases luminosity, and the star instead moves down and leftwards in the HR diagram (this is the horizontal branch for pop II or red clump for pop I). After He burning completes in the core, the star again moves to the right and upwards of the HR diagram. Its path is almost aligned with the previous red giant track, hence the name "asymptotic giant branch". Stars at this stage of stellar evolution are known as AGB stars.
* red giant branch stars: shells are still fusing hydrogen into He, whiel the core is inactive helium. (AGB produce C from He--i.e., He burning is happening).
A post-discovery of a born again star, based on lightcurves. Lacks a planetary nebula. Born-again stars are rare (only 2 observed so far, this will be the 3rd one). Help understand violent reactive convective burning.
1111.2334
Detection of Pristine gas two billion years after the big bang
Fumagalli, O'Maera, Prochaska
Detected two gas clouds with no discernible elements heavier than H; the deuterium in one system detected at a level predicted by BBN. Implies transport of heavy elements from galaxies to their surroundings is highly inhomogeneous.
* where is the gas cloud located? At z~3 (age of universe, 2 Byr), in an SDSS quasar spectra, then confirmed with high-res spectra.
1111.2335
Exploring the effects of detailed chemical profiles on the adiabatic oscillation spectrum of sdB stars: first results
Bertolami, Corsico, Althaus
* sdB (sub-dwarf B) star: sub dwarf star with spectral type B. They are from the extreme horizontal branch stars of the HR diagram. Represents a late state in the evolution of some stars, when red giant loses its outer H layers before the core begins to fuse Helium. Unclear as to why the early mass loss occurs, but interaction of stars in a binary system is thought obe one of the main mechanisms. Single subdwarf may be the result of a merger of two white dwarf stars. Significant component (being more luminous) in the hot star population of old stellar systems; prominent on UV images. Possible cause of UV upturn in the light output of elliptical galaxies. Expected to become WD without going through any more giant stages. M~0.5Msun, contain 1% H, the rest He. R~0.15-0.25 Rsun, T~20000 to 40000K. Pulsates at few second to few minute periods.
* sub dwarf stars: produce energy from H fusion. Underluminous because of their low metallicity, which decreases the opacity of outer layers and decreases the radiation pressure, resulting in a smaller, hotter star for a given mass. This lower opacity allows them to emit a higher percentage of UV light for the same spectral type relative to Pop I star (UV excess). Usually members of the MW's halo, frequently have high space velocities relative to the Sun.
* hot subdwarfs (subdwarf B and subdwarf O): entirely different class of objects to cool subdwarfs. Represent a late stage in the evolution of some stars, cause when a red giant star loses its outer hydrogen layers before the core begins to fuse helium.
Diffusion at H-He transition and He-burning convective cores: is it affected by pulsation? Diffusion of He and H has a strong impact on the peroid spectrum of sdBVs stars, less efficient mode trapping [?]. Astroseismology of sdBVs stars offer good opportunity to constrain extramixing processes in the He-burning cores of horizontal branch stars.
1111.2337
Spiral flows in cool core galaxy clusters
Keshet
Spiral flows are ubiquitous in the cool cores of clusters and groups of galaxies, seen in multi-phase properties of cores, and "cold fronts" of X-ray edges. Analytically show spiral fronts impose strong constraints on the core: cold, fast flow below a hot, slow inflow, separated by slowly rotating, trailing, quasi spiral tangential discontinuity surface. Leads to a spiral pattern and two-phase plasma. Such flows can eliminate the cooling problem, provided that a feedback mechanism regulates the flow. Quasi stead-state model for an accretion-quenched, composite flow: fast phase is AGN bubble-regulated outflow, reproduce observed low star formation rates, explain bubble size. Simplest two-component model reproduces several key properties of cool cores; propose all such cores harbor a spiral flow. Can be tested in e.g., ASTRO-H.
1111.2354
The faint-end slope of the redshift 5.7 Lyman alpha luminosity function
Henry, Martin, Dressler, Sawicki, McCarthy
Use 6 LAEs to revise previous estimate of the number of faint LAEs; combine with the density of bright LAEs in Cosmic Origins survey and Subaru Deep Field to best constrain the redshift 5.7 LAE luminosity function. Most of the estimated faint LAEs would not be detectable with HST at this redshift.
* scary--using literally a handful of objects to re-write the luminosity function.
1111.2366
The cosmic web, multi-stream flows, and tessellations
Shandarin, Habib, Heitmann
Using that the initial CDM state can be described by a 3d manifold (in a 6d phase space) that remains continuous under evolution, apply a tessellation method on N-body sims to compute multi-stream and [NL] density fields. Uses the full phase space information and has no free parameters. Study correlation between multi-streaming and density, identification of structures such as Zeldovich pancakes and voids, and statistical measurements of e.g., volume fraction as a function of the number of streams [??], where a scaling relation is found.
* not sure exactly what this is for.
1111.2371
Reconstruction of gravitational lensing using WMAP7 data
Feng, Keating, Paar, Zahn
* Hi Oliver.
CMB non-Gaussianity due to lensing by LSS, used as a probe. WMAP7 cannot detect CMB lensing.
1111.2393
Binary asteroid encounters with terrestrial planets: timescales and effects
Fang, Margot
Many asteroids that make close encounters with terrestrial planets are in a binary configuration. Find: close approaches (<10 earth radii) occur for almost all binaries (of various separation) on 1-10 Myr timescales. Results suggest substantial modifications to a binary's semi-major axis, eccentricity, and inclination. Encounters can happen frequently, and will significantly affect the wider binaries. Tidal and radiative evolution can be altered or stopped by planetary encounters.
1111.2396
X-ray/optical classification of cluster mergers and the evolution of the cluster merger fraction
Mann, Ebeling
Present robust morphological classification of a statistically complete sample of 108 of the most X-ray luminous clusters at 0.15<z<0.7 observed with Chandra. Aims: (a) identify most disturbed massive clusters to be used as gravitational lenses and as probes of particle acceleration mechanisms (non-thermal radio emission), (b) find cluster mergers featuring subcluster trajectories for cluster collision studies, (c) constrain redshift evolution of cluster merger fraction, and (d) the 3rd public release of MACS sample, adding 24 to the previous 46. Relaxation classified by use of projected offset of BCG from x-ray peak (or global centroid) emission as segregation between gas and DM. Identify 10 complex systems with merger in recent past, 11 systems likely to be post-collision, binary, head-on mergers, and another 6 that are similar but harder to interpret. Find significant increase with redshift in the fraction of morphologically disturbed clusters starting at z~0.4, in spite of a detection bias in our sample against very disturbed systems at high redshift. Need a larger sample of clusters with high quality x-ray data at high z to trace the evolutionary history of cluster growth and relaxation close to the primary epoch of cluster formation at z~1.
1111.2487
First spectro-interferometric survey of Be stars I. Observations and constraints on the disks geometry and kinematics
Meilland, Millour, Kanaan, Stee, Petrov
No detection of correlation between stellar parameters and structure of the circumstellar environment (Be stars are surrounded by gaseous ciccumstellar disk, responsible for the observed IR excess and emission lines, process of disk formation debated). A simple model of geometrically thin Keplerian disk can explain most of spectrally-resolved K-band data. Some small departures from this model detected for 2 objects. Observations suggest rotation alone cannot explain the origin of the Be phenomenon, and that other mechanisms are playing a non-negligible role in the ejection of matter.
1111.2529
Principles of SNe-driven winds
Stringer, Bower, Cole, Frenk, Theuns
Assuming that a fixed fraction of the SNe energy drives the galactic winds (traditional analytical treatment), the derived scaling of the wind with circular velocity leads to a relationship between baryon content and galaxy circular velocity that matches observational data well. Test this simple model on a set of gasdynamical simulations of idealised galaxies in DM haloes of different mass. Find: although mass outflow in the simulations broadly follows the scaling implied by the model, the model is in fact quite inadequate as the description of the overall behaviour of the simulations. Isolate dominant physical processes at work in limiting cases, and motivate a more comprehensive model that incorporates both momentum-conserving and energy-conserving constraints on the outflow. This formulation provides the physical basis for a more realistic analytical model and can be used to extrapolate simulation results beyond the highest resolution.
1111.2544
Calibrating the BAO scale using the CMB: lifting the degeneracy between geometric and dynamic distortions using the sound horizon from the CMB
Hawken, Abdalla, Hütsi, Lahav
Geometric (Alcock-Paczynski) and dynamic (redshift space) distortions in the pattern of galaxy distribution: examine the possibility of lifting this degeneracy and constraining cosmological parameters by using the BAO scale as a feature of known physical size (r_s~150Mpc). Add sound horizon scale prior to toy model of power spectrum with BAO + geometric and dynamic distortions, and the error ellipses for LoS and tangential distortion parameters shrink by a factor of two for a DESpec/BigBOSS-like galaxy survey (20 (Gpc/h)^3) including shot noise.
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