Spectroscopic Orbital Elements for the Helium-Rich Subdwarf Binary PG1544+488

Abstract

PG1544+488 is an exceptional short-period spectroscopic binary containing two subdwarf B stars. It is also exceptional because the surfaces of both components are extremely helium-rich. We present a new analysis of spectroscopy of PG1544+488 obtained with the William Herschel Telescope. We obtain improved orbital parameters and atmospheric parameters for each component. The orbital period $P=0.496\pm 0.002$\,d, dynamical mass ratio $M_{\mathrm{B}}/M_{\mathrm{A}}=0.911\pm 0.015$, and spectroscopic radius ratio $R_{\mathrm{B}}/R_{\mathrm{A}}=0.939\pm 0.004$ indicate a binary consisting of nearly identical twins. The data are insufficient to distinguish any difference in surface composition between the components, which are slightly metal-poor (1/3 solar) and carbon-rich (0.3% by number). The latter indicates that the hotter component, at least, has ignited helium. The best theoretical model for the origin of PG1544+488 is by the ejection of a common envelope from a binary system in which both components are giants with helium cores of nearly equal mass. Since precise tuning is necessary to yield two helium cores of similar masses at the same epoch, the mass ratio places very tight constraints on the dimensions of the progenitor system and on the physics of the common-envelope ejection mechanism.

References in corpus (12)

• The Origin of Subdwarf B Star (I): the Formation Channels
• Non-linear Least Squares Fitting in IDL with MPFIT
• The binary fraction of extreme horizontal branch stars
• Flash Mixing on the White Dwarf Cooling Curve: Understanding Hot Horizontal Branch Anomalies in NGC 2808
• Hot subdwarfs from the ESO Supernova Ia Progenitor Survey: II. Atmospheric parameters of subdwarf O stars
• Modeling He-rich subdwarfs through the hot-flasher Scenario
• Flash Mixing on the White Dwarf Cooling Curve: FUSE Observations of three He-rich sdB Stars
• Hot subdwarf stars in close-up view I. Rotational properties of subdwarf B stars in close binary systems and nature of their unseen companions
• On the formation of single and binary helium-rich sdO stars
• Abundance analyses of helium-rich subluminous B stars
• Spectroscopic analysis of sdB stars from the ESO Supernova Ia Progenitor Survey
• Evidence for Flash Mixing in He-rich sdB Stars

Cited by in corpus (10)

• Hot subluminous stars
• New binaries among UV-selected, hot subdwarf stars and population properties
• The catalogue of radial velocity variable hot subluminous stars from the MUCHFUSS project
• A Catalogue of Potential Post Common Envelope Binaries
• The SALT survey of helium-rich hot subdwarfs: methods, classification, and coarse analysis
• Radial velocity variability and evolution of hot subdwarf stars
• GALEX J184559.8-413827: a new extreme helium star identified using SALT
• A 500 pc volume-limited sample of hot subluminous stars II. Atmospheric parameters, mass distribution, and kinematics
• One of Everything: The Breakthrough Listen Exotica Catalog
• Challenges in Forming Millisecond Pulsar-Black Holes from Isolated Binaries