Time-resolved Low-resolution Spectra of BLAP-009 and BLAP-014

Paul Ross Mcwhirter,Marco C Lam

doi:10.3847/2515-5172/ac0641

Abstract

Abstract We present time resolved low resolution spectra of BLAP-009 and BLAP-014 collected with SPRAT on the Liverpool Telescope. The spectra were median-stacked in four ranges of phase. It was intended to note the variation in the shape of the helium absorption lines as a function of phase, but they do not appear to vary with time in low resolution spectra. The lack of clear offsets in the absorption lines suggest that there can only be small radial velocity due to either unseen companion or rapid expansion/contraction of the envelope.

Highlights

Blue Large Amplitude Pulsators (BLAPs) are a new type of variable star reported by Pietrukowicz et al (2017, hereafter P17) that has a high effective temperature (∼30, 000 K) and exhibits large variability (0.2 − 0.4 mag) over a short timescale (20-40 min)
We present time resolved low resolution spectra of BLAP-009 and BLAP-014 collected with SPRAT on the Liverpool Telescope
It was intended to note the variation in the shape of the helium absorption lines as a function of phase, but they do not appear to vary with time in low resolution spectra

Summary

Introduction

Blue Large Amplitude Pulsators (BLAPs) are a new type of variable star reported by Pietrukowicz et al (2017, hereafter P17) that has a high effective temperature (∼30, 000 K) and exhibits large variability (0.2 − 0.4 mag) over a short timescale (20-40 min). They discovered 14 BLAPs from the Optical Gravitational Lensing Experiment (Udalski et al 2015, OGLE). They proposed that the large amplitude can arise from the oscillations within a thick hydrogenhelium atmosphere of low-mass stars. Stellar evolution models have shown three potential evolutionary scenarios: (1) progenitors of extremely low mass white dwarfs (Romero et al 2018) (2) post-common envelope stars (Byrne & Jeffery 2018, 2020); (3) mid/late stage of core helium burning stars (Wu & Li 2018). Ramsay (2018) applied interstellar reddening correction using data available from Gaia DR2 (Gaia Collaboration et al 2018) showing BLAPs occupying space near where hot subdwarfs and hot white dwarfs lie in the HR diagram

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Conclusion