J/A+A/693/L11 SDSS J125733.63+542850.5 spectrum (Aros-Bunster+, 2025)
The third known triple white dwarf: the close double white dwarf
SDSS J125733.63+542850.5 hosts a white dwarf tertiary.
Aros-Bunster C., Schreiber M.R., Toloza O., Hernandez M.S., Belloni D.,
El-Badry K., Vanderbosch Z., Lagos-Vilches F., Gansicke T.B., Koester D.
<Astron. Astrophys. 693, L11 (2025)>
=2025A&A...693L..11A 2025A&A...693L..11A (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Stars, white dwarf ; Spectroscopy ;
Optical
Keywords: binaries: close - stars: evolution - white dwarfs
Abstract:
The white dwarf (WD) binary SDSS J1257+5428 comprises an extremely
low-mass WD with a mass of 0.1-0.24M☉ and a more massive
companion of ∼1M☉ that is more than 0.6Gyr younger. The origin
of this system has been termed paradoxical because current theories
for the formation of WD binaries are unable to explain its existence.
Any additional observational constraint on the formation of SDSS
J1257+5428 might provide important insights into double WD formation
in general. We present the discovery of a tertiary WD, which makes
SDSS J1257+5428 the third known triple WD. We used KECK/LRIS
spectroscopy, Gaia and SDSS photometry, and WD atmosphere models to
characterize the distant tertiary (projected separation ∼8000au). We
find the tertiary WD to be cool (6200-6400K) and massive
(log(g)=8.88-8.97), which translates to a cooling age of ≳4Gyr. This
cooling age represents a lower limit on the total age of the triple
system. While at first glance it seems likely that the inner binary
formed through a stable mass transfer phase followed by common
envelope evolution, reproducing the stellar mass and period required
for the progenitor of the ∼1M☉WD in the inner binary through
stable mass transfer seems impossible. We therefore speculate that the
system might be the descendant of a cataclysmic variable with an
evolved donor.
Description:
Spectrum of the tertiary WD in the hierarchical triple system
SDSS J125733.63+542850.5.
Data obtained using the Keck Observatory LRIS instrument.
1. The spectrum has been flux-calibrated using standard star
observations and matched to Gaia and SDSS photometry
(in Fig. one of the paper).
2. Galactic extinction has been corrected assuming E(B-V)=0.02.
3. The spectral resolution is 0.1nm.
4. The wavelength coverage spans from approximately
3062Å to 7829Å.
5. The spectrum reveals no Balmer lines, consistent with either a
helium-dominated atmosphere or a strongly magnetic
hydrogen-dominated atmosphere.
Objects:
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RA (2000) DE Designation(s)
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12 57 33.65 +54 28 50.4 SDSS J125733.63+542850.5 = WD 1255+547
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
spectrum.dat 88 5125 Calibrated spectrum of the tertiary WD
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Byte-by-byte Description of file: spectrum.dat
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Bytes Format Units Label Explanations
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1- 10 F10.4 0.1nm lambda Wavelength in Angstroems
13- 24 E12.6 10mW/m2/nm Flux ?=- Calibrated flux density
27- 37 E11.6 10mW/m2/nm SkyFlux Sky flux density
40- 50 E11.6 10mW/m2/nm e_Flux Uncertainty in the flux density
55- 58 I4 pix Xpos X position on the CCD
62- 68 F7.3 pix Ypos Y position on the CCD
71- 81 E11.5 --- Response Response function
84- 88 F5.3 --- Flag Data flag
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Acknowledgements:
Matthias Schreiber, matthias.schreiber(at)usm.cl
(End) M. Schreiber [Univ. Federico Santa Maria], P. Vannier [CDS] 20-Dec-2024