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GEP I: A globular cluster in the center of the dwarf spheroidal galaxy Andromeda XXV?

Published online by Cambridge University Press:  11 March 2020

Felice Cusano Open the ORCID record for Felice Cusano [Opens in a new window] ,
Alessia Garofalo  and
Gisella Clementini
Felice Cusano
Affiliation:
INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3 - 40129 Bologna – Italy email: [email protected]
Alessia Garofalo
Affiliation:
INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3 - 40129 Bologna – Italy email: [email protected]
Gisella Clementini
Affiliation:
INAF - Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, via Gobetti 93/3 - 40129 Bologna – Italy email: [email protected]
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Abstract

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Looking for variable stars in the M31 dwarf spheroidal satellite Andromeda XXV (And XXV), which we have observed with the LBC at the LBT, we serendipitously discovered a clustering of stars (Gep I) of 12 arcsec in diameter, near the center of And XXV. This is one of the very few clusters known to be associated with a dwarf spheroidal galaxy. The half light radius (rh) of Gep I at the distance of And XXV corresponds to 25 pc in linear extension. Radius and absolute V (MV∼ −4.9 mag) magnitude place Gep I in the region of the MV-rh plane that seems to be forbidden to ordinary globular clusters (GCs). The seeing-limited resolution of our photometry could resolve only a few bright stars in Gep I. The CMD of these sources is compatible with an old stellar population placed at a heliocentric distance of ∼750–800 kpc, thus confirming a real concentration of old stars. The ground-based CMD of Gep I is severely incomplete. Future high resolution imaging and spectroscopy of the brightest stars will permit to disentangle the puzzle on the real nature of Gep I.

Keywords

galaxies: star clusters: generalgalaxies: star clusters: individual: Gep I
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 14 , Symposium S351: Star Clusters: From the Milky Way to the Early Universe , May 2019 , pp. 64 - 67
Copyright
© International Astronomical Union 2020

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