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Title: Properties of an eclipsing double white dwarf binary NLTT 11748

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 {sub ☉}) 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 {sub ☉}) and surface gravity (log (g) = 6.32-6.38; radii are 0.0423-0.0433 R {sub ☉}) constraints do not agree with previous spectroscopic determinations. We use precise eclipse timingmore » 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{sup –5}. Finally, we use multicolor data to constrain the secondary's effective temperature (7600 ± 120 K) and cooling age (1.6-1.7 Gyr).« less
Authors:
;  [1] ; ; ;  [2] ;  [3] ;  [4] ; ;  [5] ;  [6] ;  [7] ;  [8]
  1. Physics Department, University of Wisconsin-Milwaukee, Milwaukee, WI 53211 (United States)
  2. Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)
  3. Kavli Institute for Theoretical Physics and Department of Physics, Kohn Hall, University of California, Santa Barbara, CA 93106 (United States)
  4. Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom)
  5. Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH (United Kingdom)
  6. NASA Ames Research Center, Moffett Field, CA 94035 (United States)
  7. California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States)
  8. Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106 (United States)
Publication Date:
OSTI Identifier:
22348233
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCURACY; ATMOSPHERES; BINARY STARS; CARBON; ECLIPSE; GRAVITATION; HELIUM; LAYERS; LIMITING VALUES; MASS TRANSFER; ORBITS; OXYGEN; PHOTOMETRY; SURFACES; THICKNESS; WHITE DWARF STARS