Magnetic blue large-amplitude pulsators (BLAPs)
Pigulski, Andrzej; Kołaczek-Szymański, Piotr A.; Święch, Marta; Łojko, Piotr; Kowalski, Kacper J.
- Publisher
- Zenodo
- Language
- en
Abstract
With the discovery of blue large-amplitude pulsators (BLAPs), one of the most important questions to be resolved was to answer the question in which evolutionary channel(s) these radially pulsating stars can be formed. Situated on the H-R diagram between hot subdwarfs and the main sequence, they cannot be products of the evolution of single stars. Therefore, virtually all the scenarios that have been proposed to explain their origin, assumed binarity at some stage of their evolution. Among the scenarios that have emerged are those that assume that some BLAPs may have formed as the result of the merger of two low-mass white dwarfs or a white dwarf and a main-sequence star. The merger scenario may result in the formation of a magnetic field in the product of the merger, as is for example, postulated for magnetic white dwarfs. Pulsations in a star with a strong mognetic field can manifest in the way we know from rapidly oscillating Ap stars, that is, in the form of equidistant frequencies in the frequency spectrum, explained by the oblique pulsator model. We have shown that the three equidistant modes discovered in the first BLAP, OGLE-BLAP-001, can be explained in this way. Using all existing photometric data, including TESS observations, we found another BLAP with a similar frequency spectrum. Thus, at least these two stars seem to be good candidates for magnetic BLAPs, presumably the products of an evolution via merger. In our talk, we will summarize their properties and the current state of our work on magnetic BLAPs.
Full text
Magnetic blue large-amplitude pulsators (BLAPs) Andrzej Pigulski 1, Piotr A. Kołaczek-Szymański 1,2, Marta Święch 1, Piotr Łojko 1, Kacper J. Kowalski 1 1 Uniwersytet Wrocławski, Instytut Astronomiczny, Wrocław, Poland 2 STAR Institute, Université de Liège, Liège, Belgium Work supported by 9th TESS/16th Kepler Asteroseismic Science Consortium Workshop Legacy for future missions: unifying stellar voices across the HR diagram 7 –11 July 2025, ISTA, Klosterneuburg, Austria grant no. 2022/45/B/ST9/03862
Introducing BLAPs ▪Discovered about decade ago (Pietrukowicz et al. 2017) ▪They are hot: effective temperatures on the order of ~30 000 K. ▪Pulsation periods range between 4 and 75 minutes. ▪Full amplitudes can reach 0.5 mag in V. ▪Fundamental radial pulsations (one double-mode known). ▪About 100 presently known – they are rare. ▪Masses: 0.3 – 1.2 M⊙ (from models). ▪Their origin is under debate. Pietrukowicz et al. (2017) light curve colour-magnitude diagram
Known BLAPs https://www.astrouw.edu.pl/~jskowron/ogle4-sky/
Known BLAPs OGLE (86) remaining (24) https://www.astrouw.edu.pl/~jskowron/ogle4-sky/
Evolutionary scenarios leading to BLAPs B L A P s Core He burning star (binary origin) (Pietrukowicz et al. 2017, Wu & Li 2018) Surviving companion of type Ia SN (Meng et al. 2020) Shell H burning star (stripped pre-He flash RGB star) (Pietrukowicz et al. 2017, Romero et al. 2018, Byrne & Jeffery 2020) Evolved hot subdwarf (shell He burning) (Xiong et al. 2022)
Evolutionary scenarios leading to BLAPs B L A P s Core He burning star (binary origin) (Pietrukowicz et al. 2017, Wu & Li 2018) Surviving companion of type Ia SN (Meng et al. 2020) Shell H burning star (stripped pre-He flash RGB star) (Pietrukowicz et al. 2017, Romero et al. 2018, Byrne & Jeffery 2020) Evolved hot subdwarf (shell He burning) (Xiong et al. 2022) MS star + He WD merger (Zhang et al. 2023)
Evolutionary scenarios leading to BLAPs B L A P s Core He burning star (binary origin) (Pietrukowicz et al. 2017, Wu & Li 2018) Surviving companion of type Ia SN (Meng et al. 2020) Shell H burning star (stripped pre-He flash RGB star) (Pietrukowicz et al. 2017, Romero et al. 2018, Byrne & Jeffery 2020) Evolved hot subdwarf (shell He burning) (Xiong et al. 2022) MS star + He WD merger (Zhang et al. 2023) He WD + He WD merger (Kołaczek-Szymański et al. 2024) Poster #106 (Kołaczek-Szymański+) Poster #107 (Łojko+)
Magnetic BLAPs? If magnetic BLAPs exist, they can be oblique pulsators rotation axis magnetic (pulsation) axis
Magnetic BLAPs? If magnetic BLAPs exist, they can be oblique pulsators rotation axis magnetic (pulsation) axis Observationally: equally-spaced multiplets in frequency spectra
Δ1= f2 − f1 = 1.902964(11)/d Δ2= f1 − f3 = 1.902928(13)/d 2(Δ1 − Δ2)/(Δ1 + Δ2) ~ 4×10−5 Equidistant triplet! OGLE-BLAP-001: combined photometry Pigulski et al. (2024)
OGLE-BLAP-001: combined photometry Average light curve The amplitudes and phases of the dominant term and its harmonic
OBSERVATIONS: ZTF ( gri ): 2018 –2024 ATLAS ( co ): 2015 –2024 OGLE-IV ( I ): 2019 TESS : 2022 Sector: 54 (200 s) Gaia (DR3): 2014 –2017 P= 34.137 min Tmax = BJDTDB 2458294.62233 + 0.024400817 × E ZGP-BLAP-08: O – C diagram Pigulski et al. (2024)
OGLE 1’ ×1’ Scale: 0.26”/pixel ATLAS 2.5’ ×2.5’ Scale: 1.86”/pixel TESS 10.5’ ×10.5’ Scale: 21”/pixel ZGP-BLAP-08: images
ZGP-BLAP-08: combined photometry Pigulski et al. (2024)
Δ1= f2 − f1 = 0.657407(21)/d Δ2= f1 − f3 = 0.657474(24)/d 2(Δ1 − Δ2)/(Δ1 + Δ2) ~ 1.0×10−4 Equidistant triplet! ZGP-BLAP-08: combined photometry Pigulski et al. (2024)
ZGP-BLAP-08: combined photometry Average light curve The amplitudes and phases of the dominant term and its harmonic Pigulski et al. (2024)
ZGP-BLAP-08: combined photometry Average light curve at two rotational phases The amplitudes and phases of the dominant term and its harmonic Pigulski et al. (2024)
OGLE-BLAP-006 OGLE KMTNet P= 38.02 min Kim et al. (2025) OGLE finding chart OGLE-BLAP-006
OGLE-BLAP-006 Δ1= f2 − f1 = 0.365387(5)/d Δ2= f1 − f3 = 0.365410(10)/d 2(Δ1 − Δ2)/(Δ1 + Δ2) ~ 6×10−5 Equidistant triplet! Kim et al. (2025)
