Spectroscopic follow-up of hot subdwarf variables found in ZTF -- Atmospheric and fundamental properties of radial-mode sdB pulsators

Abstract

Hot subdwarf variables (sdBVs) that display large-amplitude ($>$1%), short-period variability, as a result of radial-mode pulsations, have recently become objects of interest as they show unique properties among the sdBV classes. Since the discovery of objects such as Balloon 090100001 and CS 1246, twelve more have been discovered in the Zwicky Transient Facility (ZTF) survey that display similar characteristics. However, due to lack of broad spectroscopic investigations, it remains unclear whether these objects constitute a distinct class of radial-mode dominant sdBVs that share common atmospheric and fundamental properties. Here we aim to spectroscopically define these peculiar sdBVs as a population. We collected low-resolution spectroscopy on a sample of sdBVs discovered in the ZTF survey, including time-series observations. We fitted the spectra to a grid of theoretical models to determine their mean effective temperature, surface gravity and helium abundance and any corresponding variability. We then use these properties to estimate the mass, radius and luminosity using a spectral energy distribution fitting method. We show that the resulting properties are similar to the radial-mode dominant sdBVs, Balloon 090100001 and CS 1246, and that they are distinguishable from other similar radial-mode pulsators, such as blue large-amplitude pulsators. We find that these stars, on average, have mean effective temperatures of 28,300 K and surface gravity measurements of $\log g=5.56$, with changes in these parameters on the order of 1000 K and 0.10 dex, respectively. The location of these stars on the $T_{\text{eff}}$ -- $\log g$ plane places them on the boundary region between the low-amplitude, multi-periodic V361 Hya and V1093 Her stars, where the hybrid DW Lyn pulsators lie. The masses and radii of the majority of the sdBVs in our sample align with canonical-mass sdB properties.

Accepted for publication in A&A (Astronomy and Astrophysics)

References in corpus (21)

• The Gaia mission
• Gaia Data Release 3: Summary of the content and survey properties
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• The unWISE Catalog: Two Billion Infrared Sources from Five Years of WISE Imaging
• A catalogue of white dwarfs in Gaia EDR3
• The Zwicky Transient Facility: Observing System
• An Analysis of the Shapes of Interstellar Extinction Curves. VII. Milky Way Spectrophotometric Optical-through-Ultraviolet Extinction and Its R-Dependence
• Blue large-amplitude pulsators as a new class of variable stars
• Year 1 of the ZTF high-cadence Galactic Plane Survey: Strategy, goals, and early results on new single-mode hot subdwarf B-star pulsators
• A new class of pulsating hot subdwarfs
• Mode identification for Balloon 090100001 using combined multicolour photometry and spectroscopy
• Pulsation in faint blue stars
• Short-period pulsating hot-subdwarf stars observed by TESS I. Southern ecliptic hemisphere
• Identifying Blue Large Amplitude Pulsators from Gaia DR2 & ZTF DR3
• HD 133729: A blue large-amplitude pulsator in orbit around a main-sequence B-type star
• The OmegaWhite Survey for Short-Period Variable Stars VII: High amplitude, short period blue variables
• Discovery of new TESS pulsating hot subdwarfs
• The OmegaWhite survey for Short-Period Variable Stars III: Follow-up Photometric and Spectroscopic Observations
• Pulse Timing Discovery of a Three-Day Companion to the Hot Subdwarf BPM 36430
• Observational Parameters of Blue Large-amplitude Pulsators
• The oscillation properties of the Blue Large Amplitude Pulsators (BLAPs): relative change rate of periods, excitations, and period relations