[Paper Review] Theta Hya: Spectroscopic identification of a second B star + white dwarf binary

M. R. Burleigh, M. A. Barstow|arXiv (Cornell University)|Oct 7, 1998

Stellar, planetary, and galactic studies1 references3 citations

TL;DR

This paper presents the spectroscopic identification of a hot white dwarf companion to the B-type star Theta Hya using Extreme Ultraviolet Explorer (EUVE) data, marking the second confirmed B star + white dwarf binary system. The authors constrain the white dwarf's temperature to 25,000–31,000 K, enabling observational limits on the initial-final mass relation and the maximum progenitor mass for white dwarfs.

ABSTRACT

We report the identification, in an Extreme Ultraviolet Explorer (EUVE) spectrum, of a hot white dwarf companion to the 3rd magnitude late-B star Theta Hya (HR3665, HD79469). This is the second B star + white dwarf binary to be conclusively identified; Vennes, Berghofer and Christian (1997), and Burleigh and Barstow (1998) had previously reported the spectroscopic discovery of a hot white dwarf companion to the B5V star y Pup (HR2875). Since these two degenerate stars must have evolved from main sequence progenitors more massive than their B star companions, they can be used to place observational lower limits on the maximum mass for white dwarf progenitors, and to investigate the upper end of the initial-final mass relation. Assuming a pure hydrogen composition, we constrain the temperature of the white dwarf companion to Theta Hya to lie between 25,000K and 31,000K. We also predict that a third bright B star, 16 Dra (B9.5V), might also be hiding an unresolved hot white dwarf companion.

Motivation & Objective

• To identify and characterize a white dwarf companion to the B-type star Theta Hya using extreme ultraviolet observations.
• To establish a second confirmed B star + white dwarf binary system, enhancing statistical constraints on white dwarf formation.
• To use the system to derive observational lower limits on the maximum mass of white dwarf progenitors.
• To investigate the upper end of the initial-final mass relation through observed white dwarf temperatures and masses.

Proposed method

• Analysis of Extreme Ultraviolet Explorer (EUVE) spectra to detect emission from a hot white dwarf companion to Theta Hya.
• Spectral fitting assuming a pure hydrogen composition to constrain the white dwarf's effective temperature.
• Comparison with previous detections, such as the y Pup system, to validate the identification method.
• Use of atmospheric modeling to interpret the observed EUV flux and derive temperature bounds.
• Application of evolutionary models to infer progenitor mass limits based on the derived white dwarf temperature.

Experimental results

Research questions

• RQ1 Can a hot white dwarf companion to the B-type star Theta Hya be spectroscopically identified in EUVE data?
• RQ2 What is the effective temperature range of the white dwarf companion to Theta Hya, assuming a pure hydrogen composition?
• RQ3 How does the discovery of this system contribute to constraints on the initial-final mass relation for white dwarfs?
• RQ4 What is the inferred maximum progenitor mass for white dwarfs based on the observed properties of this system?
• RQ5 Could other bright B stars, such as 16 Dra, also host unresolved hot white dwarf companions?

Key findings

• A hot white dwarf companion to Theta Hya was spectroscopically identified in Extreme Ultraviolet Explorer (EUVE) data.
• The white dwarf's effective temperature is constrained to lie between 25,000 K and 31,000 K, assuming a pure hydrogen composition.
• This system represents the second confirmed B star + white dwarf binary, following the earlier detection around y Pup.
• The discovery provides observational lower limits on the maximum mass of white dwarf progenitors.
• The authors predict that 16 Dra (B9.5V) may also host an unresolved hot white dwarf companion.
• The system supports constraints on the upper end of the initial-final mass relation through observed white dwarf temperatures.