Spectroscopic Detection of the Pre-White Dwarf Companion of Regulus

Abstract

Mass transfer in an interacting binary will often strip the mass donor of its entire envelope and spin up the mass gainer to near critical rotation. The nearby B-type star Regulus represents a binary in the post-mass transfer stage: it is a rapid rotator with a very faint companion in a 40 d orbit. Here we present the results of a search for the spectral features of the stripped-down star in an extensive set of high S/N and high resolution spectra obtained with the CFHT/ESPaDOnS and TBL/NARVAL spectrographs. We first determine revised orbital elements in order to set accurate estimates of the orbital Doppler shifts at the times of observation. We then calculate cross-correlation functions of the observed and model spectra, and we search for evidence of the companion signal in the residuals after removal of the strong primary component. We detect a weak peak in the co-added residuals that has the properties expected for a faint pre-white dwarf. We use the dependence of the peak height and width on assumed secondary velocity semiamplitude to derive the semiamplitude, which yields masses of $M_1/M_{\odot }=3.7\pm 1.4$ and $M_2/M_{\odot }=0.31\pm 0.10$ (assuming orbital inclination equals the spin inclination of Regulus). We estimate the pre-white dwarf temperature $T_{\mathrm{eff}}=(20\pm 4)$~kK through tests with differing temperature model spectra, and we find the radius $R_2/R_{\odot }=0.061\pm 0.011$ from the component temperatures and the flux ratio associated with the amplitude of the signal in the cross-correlation residuals.

arXiv commentAccepted for publication in ApJ

References in corpus (30)

• Validation of the new Hipparcos reduction
• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 parsecs: The Northern Sample I
• The incidence of stellar mergers and mass gainers among massive stars
• A spectroscopic survey on the multiplicity of high-mass stars
• The MiMeS Survey of Magnetism in Massive Stars: Introduction and overview
• Extracting Radial Velocities of A- and B-type Stars from Echelle Spectrograph Calibration Spectra
• Spectral models for binary products: Unifying Subdwarfs and Wolf-Rayet stars as a sequence of stripped-envelope stars
• Models of low-mass helium white dwarfs including gravitational settling, thermal and chemical diffusion, and rotational mixing
• First Results from the CHARA Array. I. An Interferometric and Spectroscopic Study of the Fast Rotator alpha Leonis (Regulus)
• Detached white dwarf main-sequence star binaries
• PolarBase: a data base of high resolution spectropolarimetric stellar observations
• The impact of companions on stellar evolution
• Cross-Correlation and Maximum Likelihood Analysis: A New Approach to Combine Cross-Correlation Functions
• UVBLUE: a new high-resolution theoretical library of ultraviolet stellar spectra
• Colder and Hotter: Interferometric imaging of β Cassiopeiae and α Leonis
• Testing the white dwarf mass-radius relationship with eclipsing binaries
• Detection of additional Be+sdO systems from IUE spectroscopy
• EL CVn-type binaries - Discovery of 17 helium white dwarf precursors in bright eclipsing binary star systems
• The mass of the white dwarf in the old nova BT Mon
• Near-Infrared Photometry of Globular Clusters Towards the Galactic Bulge: Observations and Photometric Metallicity Indicators
• A Spectroscopic Orbit for Regulus
• The Past and Future History of Regulus
• Discovery of Two New Thermally Bloated Low-Mass White Dwarfs Among the Kepler Binaries
• Discovery of 36 eclipsing EL CVn binaries found by the Palomar Transient Factory
• A spectroscopic search for faint secondaries in cataclysmic variables
• Constraining Mass Transfer Histories of Blue Straggler Stars with COS Spectroscopy of White Dwarf Companions
• Stellar parameters for the central star of the planetary nebula PRTM 1 using the German Astrophysical Virtual Observatory service TheoSSA
• Lunar occultations of 184 stellar sources in two crowded regions towards the galactic bulge
• A quick guide to FXCOR

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