Pulsation in faint blue stars

Abstract

Following the discovery of blue large-amplitude pulsators (BLAPs) by the OGLE survey, additional hot, high-amplitude pulsating stars have been discovered by the Zwicky Transient Facility. It has been proposed that all of these objects are low-mass pre-white dwarfs and that their pulsations are driven by the opacity of iron-group elements. With this expanded population of pulsating objects, it was decided to compute a sequence of post-common-envelope stellar models using the MESA stellar evolution code and to examine the pulsation properties of low-mass pre-white dwarfs using non-adiabatic analysis with the GYRE stellar oscillation code. By including the effects of atomic diffusion and radiative levitation, it is shown that a large region of instability exists from effective temperatures of 30,000 K up to temperatures of at least 50,000 K and at a wide range of surface gravities. This encompasses both groups of pulsator observed so far, and confirms that the driving mechanism is through iron group element opacity. We make some conservative estimates about the range of periods, masses, temperatures and gravities in which further such pulsators might be observed.

14 pages, 12 figures, accepted for publication in MNRAS

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• The OmegaWhite Survey for Short-Period Variable Stars VII: High amplitude, short period blue variables
• Tidally Tilted Pulsations in HD 265435, a subdwarf B Star with a Close White Dwarf Companion
• Minute-Cadence Observations of the LAMOST Fields with the TMTS: II. Catalogues of Short-Period Variable Stars from the First Two-Year Surveys
• Confirmation of Monoperiodicity Above 20 Seconds for Two Blue Large-Amplitude Pulsators
• Understanding the rotational variability of K2 targets. HgMn star KIC 250152017 and blue horizontal branch star KIC 249660366
• The oscillation properties of the Blue Large Amplitude Pulsators (BLAPs): relative change rate of periods, excitations, and period relations
• Improved hydrodynamic pulsation models for the pulsating extreme helium star V652 Herculis
• A Minute-Cadence Deep Bulge Survey: First Data Release of DREAMS
• Spectroscopic follow-up of hot subdwarf variables found in ZTF -- Atmospheric and fundamental properties of radial-mode sdB pulsators