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Published January 10, 2014 | Published + Submitted
Journal Article Open

Properties of an Eclipsing Double White Dwarf Binary NLTT 11748

Abstract

We present high-quality ULTRACAM photometry of the eclipsing detached double white dwarf binary NLTT 11748. This system consists of a carbon/oxygen white dwarf and an extremely low mass (<0.2 M_☉) helium-core white dwarf in a 5.6 hr orbit. To date, such extremely low-mass white dwarfs, which can have thin, stably burning outer layers, have been modeled via poorly constrained atmosphere and cooling calculations where uncertainties in the detailed structure can strongly influence the eventual fates of these systems when mass transfer begins. With precise (individual precision ≈1%), high-cadence (≈2 s), multicolor photometry of multiple primary and secondary eclipses spanning >1.5 yr, we constrain the masses and radii of both objects in the NLTT 11748 system to a statistical uncertainty of a few percent. However, we find that overall uncertainty in the thickness of the envelope of the secondary carbon/oxygen white dwarf leads to a larger (≈13%) systematic uncertainty in the primary He WD's mass. Over the full range of possible envelope thicknesses, we find that our primary mass (0.136-0.162 M_☉) and surface gravity (log (g) = 6.32-6.38; radii are 0.0423-0.0433 R_☉) constraints do not agree with previous spectroscopic determinations. We use precise eclipse timing to detect the Rømer delay at 7σ significance, providing an additional weak constraint on the masses and limiting the eccentricity to ecos ω = (– 4 ± 5) × 10^(–5). Finally, we use multicolor data to constrain the secondary's effective temperature (7600 ± 120 K) and cooling age (1.6-1.7 Gyr).

Additional Information

© 2014 American Astronomical Society. Received 2013 July 19; accepted 2013 November 21; published 2013 December 20. We thank the anonymous referee for helpful comments. This work was supported by the National Science Foundation under grants PHY 11-25915 and AST 11-09174. T.R.M. was supported under a grant from the UK's Science and Technology Facilities Council (STFC), ST/F002599/1. V.S.D., S.P.L., and ULTRACAM were supported by the STFC. A.N.W. was supported by the University of Wisconsin, Milwaukee Office of Undergraduate Research. We thank the staff of Gemini for assisting in planning and executing these demanding observations. We thank D. Foreman-Mackey for help using emcee and L. Althaus for supplying evolutionary models. Based on observations obtained at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States); the National Research Council (Canada); CONICYT (Chile); the Australian Research Council (Australia); Ministério da Ciência, Tecnologia, e Inovação (Brazil); and Ministerio de Ciencia, Tecnología, e Innovaciόn Productiva (Argentina). Facilities: Gemini:Gillett (NIRI), NTT (ULTRACAM), ING:Herschel (ULTRACAM)

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Published - 0004-637X_780_2_167.pdf

Submitted - 1311.6831v2.pdf

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Additional details

Created:
August 22, 2023
Modified:
October 26, 2023