On the extended stellar structure around NGC 288

Abstract

We report on observational evidence of an extra-tidal clumpy structure around NGC 288 from an homogeneous coverage of a large area with the Pan-STARRS PS1 database. The extra-tidal star population has been disentangled from that of the Milky Way field by using a cleaning technique that successfully reproduced the stellar density, luminosity function and colour distributions of MW field stars. We have produced the cluster stellar density radial profile and a stellar density map from independent approaches, from which we found results in excellent agreement : the feature extends up to 3.5 times the cluster tidal radius. Previous works based on shallower photometric data sets have speculated on the existence of several long tidal tails, similar to that found in Pal 5. The present outcome shows that NGC 288 could hardly have such tails, but favours the notion that interactions with the MW tidal field has been a relatively inefficient process for stripping stars off the cluster. These results point to the need of a renewed overall study of the external regions of Galactic globular clusters (GGCs) in order to reliably characterise them. Hence, it will be possible to investigate whether there is any connection between detected tidal tails, extra-tidal stellar populations, extent diffuse halo-like structures with the GGCs' dynamical histories in the Galaxy.

Stellar Streams Discovered in the Dark Energy Survey

“…8) from the cluster center. The DES Y3A2 data are deeper than the Pan-STARRS data analyzed by Piatti (2018) and support previous reports of clumpy extratidal structure extending~ 1 . 5 from the core of NGC 288.…”

“…Since we are primarily interested in main-sequence (MS) and red giant branch (RGB) stars associated with old, metal-poor stellar populations, we constrain our sample to the color range < -< g r 0.0 1.0. In contrast to previous DES photometric calibration techniques , 2018, no stellar locus regression adjustment was applied to the DES Y3A2 zeropoints derived by the FGCM. Instead, we followed the procedure described in DES Collaboration (2018) to account for interstellar dust extinction.…”

“…The analysis of NGC 288 was extended to a larger field by Leon et al (2000), who reported evidence of two sets of tidal tails, extended along the direction of motion and in the direction of the Galactic center. Subsequently, Grillmair et al (2004) used Two Micron All Sky Survey data to suggest a~ 17 tidal tail; however, this claim was later refuted by Piatti (2018) using deeper data from Pan-STARRS PS1. In contrast, Piatti (2018) found evidence for clumpy extratidal structure extending 120 pc (  0 .…”

“…Subsequently, Grillmair et al (2004) used Two Micron All Sky Survey data to suggest a~ 17 tidal tail; however, this claim was later refuted by Piatti (2018) using deeper data from Pan-STARRS PS1. In contrast, Piatti (2018) found evidence for clumpy extratidal structure extending 120 pc (  0 . 8) from the cluster center.…”

Pal 13: its moderately extended low-density halo and its accretion history

“…Hence, they are candidates to cross the Jacobi radius and thus to populate the cluster extra-tidal regions (Carballo-Bello et al 2012). In previous studies of the external regions of the globular cluster NGC 288 (Piatti 2018a) and NGC 6779 (Piatti & Carballo-Bello 2019), we used a strip along the cluster Main Sequence (MS), from underneath its MS turnoff down to 2 mag, to map the distribution of their stellar populations beyond their tidal radii. Those stars are low mass enough as to have been subject of tidal effects, so that we expect that their counterparts in Pal 13 should also be, particularly because Pal 13 is less massive than NGC 288 and NGC 6779 (Baumgardt et al 2019).…”