The Hubble Space Telescope Advanced Camera for Surveys Emission Line Survey of Andromeda. I. Classical Be Stars

We present results from a two epoch Hubble Space Telescope H emission line survey of the Andromeda galaxy that overlaps the footprint of the Panchromatic Hubble Andromeda Treasury (PHAT) survey. We found 552 (542) classical Be stars and 8429 (8556) normal B-type stars in epoch # 1 (epoch # 2), yield...

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Veröffentlicht in:The Astronomical journal 2020-03, Vol.159 (3), p.119
Hauptverfasser: Peters, M., Wisniewski, J. P., Williams, B. F., Lomax, J. R., Choi, Y., Durbin, M., Johnson, L. C., Lewis, A. R., Lutz, J., Sigut, T. A. A., Wallach, A., Dalcanton, J. J.
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Sprache:eng
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Zusammenfassung:We present results from a two epoch Hubble Space Telescope H emission line survey of the Andromeda galaxy that overlaps the footprint of the Panchromatic Hubble Andromeda Treasury (PHAT) survey. We found 552 (542) classical Be stars and 8429 (8556) normal B-type stars in epoch # 1 (epoch # 2), yielding an overall fractional Be content of 6.15% 0.26% (5.96% 0.25%). The fractional Be content decreased with spectral subtype from ∼23.6% 2.0% (∼23.9% 2.0%) for B0-type stars to ∼3.1% 0.34% (∼3.4% 0.35%) for B8-type stars in epoch # 1 (epoch # 2). We observed a clear population of cluster Be stars at early fractional main-sequence lifetimes, indicating that a subset of Be stars emerge onto the zero-age main sequence as rapid rotators. Be stars are 2.8× rarer in M31 for the earliest subtypes compared to the Small Magellanic Cloud, confirming that the fractional Be content decreases in significantly more metal-rich environments (like the Milky Way and M31). However, M31 does not follow a clear trend of Be fraction decreasing with metallicity compared to the Milky Way, which may reflect that the Be phenomenon is enhanced with evolutionary age. The rate of disk-loss or disk-regeneration episodes we observed, 22% 2% yr−1, is similar to that observed for seven other Galactic clusters reported in the literature, assuming these latter transient fractions scale by a linear rate. The similar number of disk-loss events (57) as disk-renewal events (43) was unexpected since disk dissipation timescales can be ∼2× the typical timescales for disk build-up phases.
ISSN:0004-6256
1538-3881
DOI:10.3847/1538-3881/ab6d74