Day 111

Thursday (already).  MNRAS referee report on the photoz paper was harsh in words, and off the mark.


Bonn AIfA Promotionskolloquium
Dynamical Evolution of massive Star Clusters
Andreas Kuepper


Results from high-performance computations of star clusters dissolving in the tidal field of their host galaxy.  Formation process of tidal tails and substructure within such tidal streams; compare with theoretical expectations.  Influence of tidal debris on the appearance of star clusters shown. Case study: Palomar 13.  Outlook on how to use this to study DM content of the MW.


* Palomar 13: one of the smallest, faintest globular clusters known.  Highly eccentric, retrograde, highly inclined galactic orbit that passes through relatively cose to the galactic center; gravitational tidal forces has stripped away the delicately bound stars.  A "young halo" globular cluster.  4 previously reported RR Lyrae variables, and a proportionally large group of blue straggler stars confirmed.


* Blue stragglers (BSS): main sequence stars in open or globular clusters that are more luminous and bluer than the main sequence turn-off point for the cluster.  Blue stragglers are off the H-R diagram of the cluster members, and centrally concentrated.  The small size of this cluster, combined with the shape of its light profile (a clear departure from a classical King function beyond the tidal radius) suggests that Pal 13 is in the final throes of destruction.  (destructive processes would preferentially strip less massive stars, hence the blue stragglers [?])  [Blue stragglers can be due to a secondary star formation in star clusters--from Charlie Conroy's talk...]


1110.4103
A new type of compact stellar population: dark star clusters
Banerjee, Kroupa


Retention of SNe remnants in dense stellar systems, especially that of massive stellar BHs, in star clusters.  Invoke a wide variety of physical phenomena: Gravitational waves, formation of X-ray binaries, modification of the dynamical evolution of the cluster.  Rapid removal of outer stars of a cluster by strong tidal field in the inner region of our Galaxy can unveil its BH sub-cluster, which appears as a star cluster that is gravitationally bound by an invisible mass.  Study the formation and properties of such systems through N-body computations, estimate they can be present in significant numbers in the inner region of the MW.  Call them "dark star clusters" (DSCs) as they appear dimmer than normal star clusters of similar mass.  Finding of DSCs will robustly cross-check BH retention; not only constrain the uncertain natal kicks of BHs, but sill also pinpoint star clusters as potential sites for GW emission.  Relevance for IRS 13E.


* GCIRS 13E: a potentially intermediate mass black hole (IMBH) with a mass of about 1300 solar masses orbiting Sgr A* at a distance of about 3 ly.  Orbital velocity = 280 km/s.  Associated with a small cluster of 7 massive (type O; Wolf-Rayet; luminous blue; 5-10 Msun) stars orbiting it.  Strong x-ray emission.  


1110.4104
New SPB stars in the field of the young open cluster NGC 2244 discovered by the MOST photometric satellite
Gruber, et al


SPB: slowly pulsating B-stars.  Frequency ranges consistent with g-modes of l<=2.  Could be the first known pre-main sequence (PMS) SPB stars.


MPIfR Special Colloquium (Oct. 26, 11pm, MPIfR Auditorium 0.02)
New methods and tools for specifying the MW's magnetic field structure, and some implications for very high energy CR propagation
Phil Kronberg


Two new RM [?] analyses for specifying the average magnetic field geometry in the MW.  (i) Within 1.5 kpc of the Galactic mid-plane near the Sun, a "grand magnetic design" clearly indicated in MR's.  The milky way disk's magnetic structure appears similar to other grand design spiral galaxies when seen with similar linear resolution.  (ii) same all-sky Faraday RM (l,b) data to generate mathematical model templates for the halo+disk magnetic field.  These two studies will help to define the environment for HE CR propagation, and to ultimately understand their energy-dependent anisotropies.