Category Archives: Milky Way

FSR 584: Another new nearby globular cluster candidate

Bica et.al. have announced another nearby globular cluster candidate in the Milky Way:

http://arxiv.org/abs/0709.3315

Author: E. Bica, C. Bonatto, S. Ortolani, B. Barbuy
Title: FSR584 – a new globular cluster in the Galaxy?
Comments: Astronomy and Astrophysics, accepted. 6 pages and 6 figures

Abstract: We investigate the nature of the recently catalogued star cluster candidate FSR584, which is projected in the direction of the molecular cloud W3 and may be the nearest globular cluster to the Sun. 2MASS CMDs, the stellar radial density profile, and proper motions are employed to derive fundamental and structural parameters. The CMD morphology and the radial density profile show that FSR584 is an old star cluster. With proper motions, the properties of FSR584 are consistent with a metal-poor globular cluster with a well-defined turnoff and evidence of a blue horizontal-branch. FSR584 might be a Palomar-like halo globular cluster that is moving towards the Galactic plane. The distance from the Sun is approx 1.4kpc, and it is located at approx 1kpc outside the Solar circle. The radial density profile is characterized by a core radius of rc=0.3+/-0.1 pc. However, we cannot exclude the possibility of an old open cluster. Near-infrared photometry coupled to proper motions support the scenario where FSR584 is a new globular cluster in the Galaxy. The absorption is A_V=9.2+/-0.6$, which makes it a limiting object in the optical and explains why it has so far been overlooked

This one is apparently projected over starforming region W3, and at a distance of only 1.4 kpc (4,600 ly). It would probably even beat the recently discovered record holder, FSR 1767. However, as of this time, the authors cannot exclude that this may be an old open cluster.

A preliminary webpage for this probable globular has been created at

http://www.seds.org/~spider/spider/MWGC/fsr0584.html

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FSR 1767: New Milky Way Globular Cluster, No. 158

A new globular cluster in the Milky Way has just been announced: FSR 1767.

This one is particular in being the closest known globular to us at only about 4,900 light-years, thus beating M4 and NGC 6397 at about 6,500 to 7,500 ly. It is a low-mass globular with perhaps 1/10 of the stars in M4, and estimated as of absolute magnitude -4.7 Mv, diameter 6.5 ly.

According to my counting, this is currently Milky Way Globular Cluster No. 158 to be recognized. [- Hartmut]

Reference:
Charles Bonatto, Eduardo Bica, Sergio Ortolani, Beatriz Barbuy, 2007. FSR1767 – a new globular cluster in the Galaxy. To be published in MNRAS.

Abstract:
The globular cluster (GC) nature of the recently catalogued candidate FSR 1767 is established in the present work. It results as the closest GC so far detected in the Galaxy. The nature of this object is investigated by means of 2MASS colour-magnitude diagrams (CMDs), the stellar radial density profile (RDP) and proper-motions (PM). The properties are consistent with an intermediate metallicity ($\feh\approx-1.2$) GC with a well-defined turnoff (TO), red-giant branch (RGB) and blue horizontal-branch (HB). The distance of FSR 1767 from the Sun is $\ds\approx1.5$ kpc, and it is located at the Galactocentric distance $\rgc\approx5.7$ kpc. With the space velocity components $(V,W)=(184\pm14,-43\pm14)\rm km s^{-1}$, FSR 1767 appears to be a Palomar-like GC with $\mv\approx-4.7$, that currently lies $\approx57$ pc below the Galactic plane. The RDP is well represented by a King profile with the core and tidal radii $\rc=0.24\pm0.08$ pc and $\rt=3.1\pm1.0$ pc, respectively, with a small half-light radius $\rh=0.60\pm0.15$ pc. The optical absorption is moderate for an infrared GC, $A_V=6.2\pm0.3$, which together with its central direction and enhanced contamination explains why it has so far been overlooked.

Preprint:
http://www.arxiv.org/abs/0708.0501

SEDS webpage:
http://www.seds.org/~spider/spider/MWGC/fsr1767.html

The discovery of two extremely low luminosity Milky Way GCs


[0706.0019] The discovery of two extremely low luminosity Milky Way globular clusters:

Authors: S. Koposov (1,2), J. T. A. de Jong (1), V. Belokurov (2), H.-W. Rix (1), D.B. Zucker (2), N.W. Evans (2), G. Gilmore (2), M.J. Irwin (2), E. F. Bell (1) ((1) Max Planck Institute for Astronomy, (2) Institute of Astronomy, University of Cambridge)

(Submitted on 31 May 2007)

We report the discovery of two extremely low luminosity globular clusters in the Milky Way Halo. These objects were detected in the Sloan Digital Sky Survey Data Release 5 and confirmed with deeper imaging at the Calar Alto Observatory. The clusters, Koposov 1 and Koposov 2, are located at about 40-50 kpc and appear to have old stellar populations and luminosities of only Mv around -1. Their observed sizes of about 3 pc are well within the expected tidal limit of about 10 pc at that distance. Together with Palomar 1, AM 4 and Whiting 1, these new clusters are the lowest luminosity globulars orbiting the Milky Way (…)