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تسجيل مستخدم جديدBinary evolution pathways of Blue Large-Amplitude Pulsators
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Blue Large-Amplitude Pulsators (BLAPs) are a recently discovered class of pulsating star, believed to be proto-white dwarfs, produced by mass stripping of a red giant when it has a small helium core. An outstanding question is why the stars in this class of pulsator seem to form two distinct groups by surface gravity, despite predictions that stars in the gap between them should also pulsate. We use a binary population synthesis model to identify potential evolutionary pathways that a star can take to become a BLAP. We find that BLAPs can be produced either through common envelope evolution or Roche lobe overflow, with a Main Sequence star or an evolved compact object being responsible for the envelope stripping. The mass distribution of the inferred population indicates that fewer stars would be expected in the range of masses intermediate to the two known groups of pulsators, suggesting that the lack of observational discoveries in this region may be a result of the underlying population of pre-white dwarf stars. We also consider metallicity variation and find evidence that BLAPs at $Z = 0.010$ (half-Solar) would be pulsationally unstable and may also be more common. Based on this analysis, we expect the Milky Way to host around 12000 BLAPs and we predict the number density of sources expected in future observations such as the Legacy Survey of Space and Time at the Vera Rubin Observatory.
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Following the discovery of blue large-amplitude pulsators (BLAPs), single star evolu- tion models of post red giant branch stars that have undergone a common envelope (CE) ejection in the form of a high mass loss rate have been constructed and analys
ed for pulsation stability. The effects of atomic diffusion, particularly radiative levitation, have been examined. Two principal models were considered, being post-CE stars of 0.31 and 0.46 M$_{odot}$. Such stars are likely, in turn, to become either low-mass helium white dwarfs or core helium-burning extreme horizontal-branch stars. The inclusion of radiative levitation leads to opacity driven pulsations in both types of post-CE object when their effective temperatures are comparable to those of BLAPs, with similar periods. The extent of the instability region for models in these simulations, which are not in thermal balance, is larger than that found for static models, in agreement with previous theory. By comparing to observations, and making some simple evolutionary assumptions, we conclude the 0.31 M$_{odot}$ star is the more likely candidate for BLAPs. The rate of period change is negative for both cases, so the origin of BLAPs with positive rates of period change remain uncertain.
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Blue Large Amplitude Pulsators (BLAPs) are blue stars showing high amplitude (>0.2 mag) pulsations on a timescale of a few tens of mins. They form a new class of variable star recently discovered using OGLE data. It has lead to a number of investigat
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