Discovery of a double Blue Straggler sequence in M15: new insight into the core-collapse process
| Autor: | Francesco R. Ferraro, Alison Sills, Giacomo Beccari, Jongsuk Hong, Enrico Vesperini, Barbara Lanzoni, Emanuele Dalessandro, Andrea Dieball, Silvia Raso, Christian Knigge, Livia Origlia |
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| Přispěvatelé: | Beccari G., Ferraro F.R., Dalessandro E., Lanzoni B., Raso S., Origlia L., Vesperini E., Hong J., Sills A., Dieball A., Knigge C., ITA, USA, DEU, CAN, TWN |
| Jazyk: | angličtina |
| Rok vydání: | 2019 |
| Předmět: |
Point spread function
010504 meteorology & atmospheric sciences Population stars: kinematics and dynamic Collapse (topology) FOS: Physical sciences Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Star (graph theory) 01 natural sciences Blue straggler globular clusters: individual (NGC 7078) 0103 physical sciences Cluster (physics) Astrophysics::Solar and Stellar Astrophysics education 010303 astronomy & astrophysics Solar and Stellar Astrophysics (astro-ph.SR) Astrophysics::Galaxy Astrophysics 0105 earth and related environmental sciences Physics education.field_of_study Sequence Oscillation Astronomy and Astrophysics stragglers Astrophysics - Astrophysics of Galaxies Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science Astrophysics of Galaxies (astro-ph.GA) |
| Popis: | In this paper we report on the discovery of a double blue straggler star (BSS) sequence in the core of the core-collapsed cluster M15 (NGC 7078). We performed a detailed photometric analysis of the extremely dense core of the cluster using a set of images secured with the Advanced Camera for Survey in the High Resolution Channel mode on-board the Hubble Space Telescope. The proper combination of the large number of single frames in the near-UV (F220W), and blue (F435W) filters allowed us to perform a superb modeling of the Point Spread Function and an accurate deblending procedure. The Color-Magnitude diagram revealed the presence of two distinct parallel sequences of blue stragglers. In particular, the blue BSS sequence is characterized by the intriguing presence of two different branches. The first branch appears extremely narrow, it extends up to 2.5 magnitudes brighter than the cluster main-sequence turnoff (MS-TO) point, and it is nicely reproduced by a 2 Gyr-old collisional isochrone. The second branch extends up to 1.5 magnitudes from the MS-TO and it is reproduced by a 5.5 Gyr-old collisional isochrone. Our observations suggest that each of these branches is mainly constituted by a population of nearly coeval collisional BSS of different masses generated during two episodes of high collisional activity. We discuss the possibility that the oldest episode corresponds to the core-collapse event (occurred about 5.5 Gyr ago), while the most recent one (occurred about 2 Gyr ago) is associated with a core oscillation in the post-core collapse evolution. The discovery of these features provides further strong evidence in support of the connection between the BSS properties and GC dynamical evolution, and it opens new perspectives on the study of core-collapse and post core-collapse evolution. Accepted for publication on ApJ |
| Databáze: | OpenAIRE |
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