Category Archives: NGC5139

The globular cluster Omega Cen.

Omega Centauri with WFC3

A wonderful panoramic view of the globular cluster Omega Centauri, taken by the new Wide Field Camera 3 installed aboard Hubble in May 2009… enjoy ! 😉

Image Credit: NASA


PoW for Sept. 21 :: Omega Cen, WD kicks…

Hello, welcome to the third issue of “Paper of the week”,covering publications and preprint
related to the world of Galactic Globular Clusters. This week I managed to find only a few preprints related to GGCs, and as you can see, it is Omega Centaury that continues to attract mostly the attenction of astronomers…

As always, any feedback on PoW will be much appreciated 😉


== General ==

§ “RR Lyrae stars in Galactic globular clusters. VI. The Period-Amplitude relation”
Authors: G. Bono, F. Caputo, M. Di Criscienzo

§ Constraining white-dwarf kicks in globular clusters : II. Observational Significance
Authors: Jeremy S. Heyl

== Omega Centauri ==

§ “A spectral atlas of post-main-sequence stars in omega Centauri:
kinematics, evolution, enrichment and interstellar medium”
(Revised version)
Authors: Jacco Th. van Loon, Floor van Leeuwen, Barry Smalley, Andrew W. Smith, Nicola A. Lyons,
Iain McDonald, Martha L. Boyer

§ “The Hottest Horizontal-Branch Stars in omega Centauri –
Late Hot Flasher vs. Helium Enrichment”
Authors: S. Moehler, S. Dreizler, T. Lanz, G. Bono, A.V. Sweigar, A. Calamida, M.Monelli, M. Nonino

* A “quick list” of PoW papers is also available at (under construction)

Papers on Omega Cen, NGC6440, NGC6388, NGC6441, M4…

Hello, here is a brief list (not sure if complete…) with the latest preprints regarding Galactic Globular Clusters, which appeared this month on astro-ph:

Star Counts in Omega Cen, Part I

Omega Centauri (NGC 5139) :: New Preprint

Star Counts in the Globular Cluster Omega Centauri.

I. Bright Stellar Components

Authors: V. Castellani, A.Calamida, G. Bono, P.B. Stetson, L.M. Freyhammer, S. Degl’Innocenti,
P. Prada Moroni, M. Monelli, C.E. Corsi, M. Nonino, R. Buonanno, F. Caputo, M. Castellani,
M. Dall’Ora, M. Del Principe, I. Ferraro, G. Iannicola, A.M. Piersimoni, L.Pulone, C. Vuerli

Comments: 54 pages, 17 figures,to be published in ApJ, see link at this http URL



We present an extensive photometric investigation on Horizontal Branch (HB), Red Giant Branch (RGB), and Main-Sequence Turn-Off (MSTO) stars in the Galactic globular cluster Omega Centauri = NGC 5139. The central regions of the cluster were covered with a mosaic of F435W, F625W, and F658N-band data collected with the Advanced Camera for Surveys on board the Hubble Space Telescope. The outer reaches were covered with a large set of U,B,V,I-band data collected with the mosaic CCD camera available at the 2.2m ESO/MPI telescope. The final catalogue includes ~ 1.7 million stars. We identified more than 3,200 likely HB stars, the largest sample ever collected in a globular cluster, and more than 12,500 stars brighter than the subgiant branch and fainter than the RGB bumps (15 < B < 18). We found that the HB morphology changes with the radial distance from the cluster center. The relative number of extreme HB stars decreases from ~ 30% to ~ 21% when moving from the center toward the outer reaches of the cluster, while the fraction of less hot HB stars increases from ~ 62% to ~ 72%. Current findings seem to support the evidence brought forward by Castellani et al. (2006a) that the Blue Tails, if affected by cluster dynamics, should be considered more a transient phenomenon rather than an intrinsic feature of GCs (…)

The chemical evolution of Omega Centauri’s progenitor system

The chemical evolution of Omega Centauri’s progenitor system

Authors: D. Romano (1), F. Matteucci (2), M. Tosi (1), E. Pancino (1), M. Bellazzini (1), F. R. Ferraro (3), M. Limongi (4), A. Sollima (3) ((1) INAF, Osservatorio Astronomico di Bologna; (2) Dipartimento di Astronomia, Univ. di Trieste; (3) Dipartimento di Astronomia, Univ. di Bologna; (4) INAF, Osservatorio Astronomico di Roma)

Comments: 11 pages, 9 figures; accepted for publication in MNRAS

Chemical evolution models are presented for the anomalous globular cluster Omega Centauri. After demonstrating that the chemical features of Omega Cen can not be reproduced in the framework of the closed-box self-enrichment scenario, we discuss a model in which this cluster is the remnant of a dwarf spheroidal galaxy evolved in isolation and then swallowed by the Milky Way. Both infall of primordial matter and metal-enriched gas outflows have to be considered in order to reproduce the stellar metallicity distribution function, the age-metallicity relation and several abundance ratios. Yet, as long as an ordinary stellar mass function and standard stellar yields are assumed, we fail by far to get the enormous helium enhancement required to explain the blue main sequence (and, perhaps, the extreme horizontal branch) stellar data. Rotating models of massive stars producing stellar winds with large helium excesses at low metallicities have been put forward as promising candidates to solve the `helium enigma’ of Omega Cen (Maeder & Meynet, 2006, A&A, 448, L37). However, we show that for any reasonable choice of the initial mass function the helium-to-metal enrichment of the integrated stellar population is unavoidably much lower than 70 and conclude that the issue of the helium enhancement in Omega Cen still waits for a satisfactory explanation. We briefly speculate upon possible solutions.


Searching for Planetary Transits in GCs…

NGC104 :: NGC5139 :: new preprint

Searching for Planetary Transits in Globular Clusters – 47 Tucanae and omega Centauri

Authors: David T.F Weldrake, Penny D Sackett, Terry J Bridges
Comments: 6 pages, 2 figures. To appear in the PASP proceedings of “Transiting Extrasolar Planets Workshop” MPIA Heidelberg Germany, 25th-28th September 2006. Eds: Cristina Afonso, David Weldrake & Thomas Henning

We have performed a large ground-based search for transiting Hot Jupiter planets in the outer regions of the globular clusters 47 Tucanae and omega Centauri. The aim was to help understand the role that environmental effects play on Hot Jupiter formation and survivability in globular clusters. Using the ANU 1m telescope and a 52′ X 52′ field, a total of 54,000 solar-type stars were searched for transits in both clusters with fully tested transit-finding algorithms. Detailed Monte Carlo simulations were performed to model the datasets and calculate the expected planet yields. Seven planets were expected in 47 Tuc, and five in omega Cen. Despite a detailed search, no planet-like candidates were identified in either cluster. Combined with previous theoretical studies of planet survivability, and the HST null result in the core of 47 Tuc, the lack of detections in the uncrowded outer regions of both clusters indicates that stellar metallicity is the dominant factor inhibiting Hot Jupiter formation in the cluster environment.