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Register a new userAn 8.8 minute orbital period eclipsing detached double white dwarf binary
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We report the discovery of ZTF J2243+5242, an eclipsing double white dwarf binary with an orbital period of just $8.8$ minutes, the second known eclipsing binary with an orbital period less than ten minutes. The system likely consists of two low-mass white dwarfs, and will merge in approximately 400,000 years to form either an isolated hot subdwarf or an R Coronae Borealis star. Like its $6.91, rm min$ counterpart, ZTF J1539+5027, ZTF J2243+5242 will be among the strongest gravitational wave sources detectable by the space-based gravitational-wave detector The Laser Space Interferometer Antenna (LISA) because its gravitational-wave frequency falls near the peak of LISAs sensitivity. Based on its estimated distance of $d=2120^{+131}_{-115},rm pc$, LISA should detect the source within its first few months of operation, and should achieve a signal-to-noise ratio of $87pm5$ after four years. We find component masses of $M_A= 0.349^{+0.093}_{-0.074},M_odot$ and $M_B=0.384^{+0.114}_{-0.074},M_odot$, radii of $R_A=0.0308^{+0.0026}_{-0.0025},R_odot$ and $R_B = 0.0291^{+0.0032}_{-0.0024},R_odot$, and effective temperatures of $T_A=22200^{+1800}_{-1600},rm K$ and $T_B=16200^{+1200}_{-1000},rm K$. We determined all of these properties, and the distance to this system, using only photometric measurements, demonstrating a feasible way to estimate parameters for the large population of optically faint ($r>21 , m_{rm AB}$) gravitational-wave sources which the Vera Rubin Observatory (VRO) and LISA should identify.
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The Zwicky Transient Facility has begun to discover binary systems with orbital periods that are less than 1,hr. Combined with dedicated follow-up systems, which allow for high-cadence photometry of these sources, systematic confirmation and characterization of these sources are now possible. Here, we report the discovery of ZTF J190125.42+530929.5, a 40.6,min orbital period, eclipsing double white-dwarf binary. Both photometric and spectroscopic modeling confirm its nature, yielding an estimated inclination of $i = 86.2^{+0.6}_{-0.2},rm degrees$ and primary and secondary effective temperatures of $textrm{T}_textrm{eff} = 28,000^{+500}_{-500},K$ and $textrm{T}_textrm{eff} = 17,600^{+400}_{-400},K$ respectively. This system adds to a growing list of sources for future gravitational-wave detectors and contributes to the demographic analysis of double degenerates.
General relativity predicts that short orbital period binaries emit significant gravitational radiation, and the upcoming Laser Interferometer Space Antenna (LISA) is expected to detect tens of thousands of such systems; however, few have been identified, and only one is eclipsing--the double white dwarf binary SDSS J065133.338+284423.37, which has an orbital period of 12.75 minutes. Here, we report the discovery of an eclipsing double white dwarf binary system with an orbital period of only 6.91 minutes, ZTF J153932.16+502738.8. This system has an orbital period close to half that of SDSS J065133.338+284423.37 and an orbit so compact that the entire binary could fit within the diameter of the planet Saturn. The system exhibits a deep eclipse, and a double-lined spectroscopic nature. We observe rapid orbital decay, consistent with that expected from general relativity. ZTF J153932.16+502738.8 is a significant source of gravitational radiation close to the peak of LISAs sensitivity, and should be detected within the first week of LISA observations.
We report the discovery of a 1201 s orbital period binary, the third shortest-period detached binary known. SDSS J232230.20+050942.06 contains two He-core white dwarfs orbiting with a 27 deg inclination. Located 0.76 kpc from the Sun, the binary has an estimated LISA 4-yr signal-to-noise ratio of 40. J2322+0509 is the first He+He white dwarf LISA verification binary, a source class that is predicted to account for one-third of resolved LISA ultra-compact binary detections.
We report the discovery of two detached double white dwarf (WD) binaries, SDSS J082239.546+304857.19 and SDSS J104336.275+055149.90, with orbital periods of 40 and 46 min, respectively. The 40 min system is eclipsing; it is composed of a 0.30 Msun and a 0.52 Msun WD. The 46 min system is a likely LISA verification binary. The short 20 Myr and ~34 Myr gravitational wave merger times of the two binaries imply that many more such systems have formed and merged over the age of the Milky Way. We update the estimated Milky Way He+CO WD binary merger rate and affirm our previously published result: He+CO WD binaries merge at a rate at least 40 times greater than the formation rate of stable mass-transfer AM~CVn binaries, and so the majority must have unstable mass-transfer. The implication is that spin-orbit coupling in He+CO WD mergers is weak, or perhaps nova-like outbursts drive He+CO WDs into merger as proposed by Shen.
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 Msun) helium-core white dwarf in a 5.6 hr orbit. To date such extremely-low mass WDs, 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) multi-color 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 WDs mass. Over the full range of possible envelope thicknesses we find that our primary mass (0.136-0.162 Msun) and surface gravity (log(g)=6.32-6.38; radii are 0.0423-0.0433 Rsun) constraints do not agree with previous spectroscopic determinations. We use precise eclipse timing to detect the Romer delay at 7 sigma significance, providing an additional weak constraint on the masses and limiting the eccentricity to e*cos(omega)= -4e-5 +/- 5e-5. Finally, we use multi-color data to constrain the secondarys effective temperature (7600+/-120 K) and cooling age (1.6-1.7 Gyr).
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