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

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