Updates on the Pulsating SdB Star Feige 48 through Spectroscopy

TL;DR

This study refines the atmospheric parameters of the pulsating sdB star Feige 48 using a self-consistent, metal-inclusive spectral modeling approach, and investigates its binary nature through spectroscopy and photometry.

Contribution

It introduces a detailed, metal-inclusive NLTE model atmosphere grid for Feige 48 and confirms the star's atmospheric parameters with high precision, also revealing the binary companion's nature.

Findings

Atmospheric parameters: Teff = 29,890 K, log g = 5.46, log N(He)/N(H) = -2.88.

The star's metal content does not significantly alter its bulk atmospheric properties.

The binary companion is a low-mass main sequence star with an orbital period of 8.25 hours.

Abstract

As part of a concentrated effort to understand and exploit better the seismic properties of Feige 48, we reestimated its atmospheric parameters using, for the first time, a self-consistent approach based on the detailed metal abundances that have been determined in previous studies of both its UV and optical spectrum. We computed a small 3D grid of 150 fully line-blanketed, NLTE model atmospheres incorporating the 8 most abundant metals found in the atmosphere of that star. We next compared quantitatively the synthetic spectra that we calculated from these models with three observed spectra having different resolutions (1 A, 6 A, and 8.7 A) and wavelength ranges. Our findings are Teff = 29,890 K, log g = 5.46, and log N(He)/N(H) = -2.88, with very small formal fitting errors. These estimates are in good agreement with those of previous studies, thus showing that the presence of metals do not affect significantly the bulk atmospheric properties of Feige 48. We also modeled the He II line at 1640 A from the STIS spectrum of the star and we found with this line an effective temperature and a surface gravity that match well the values obtained with the optical data. We also present a radial velocity curve based on several years of observing Feige 48 at the MMT. This curve indicates a precise orbital period of 8.25 h. Coupled to our discovery of a weak but very real periodicity of 8.25 h in the light curve of Feige 48, that was gathered during a recent extensive photometric campaign at the Mount Bigelow 1.55 m Kuiper Telescope, we conclude that there is a reflection effect in the system, and that the unseen companion is a low mass MS star and not a white dwarf as has been previously suggested.