The merger fraction of ultramassive white dwarfs Kilic, Mukremin; Moss, Adam G; Kosakowski, Alekzander ...
Monthly notices of the Royal Astronomical Society,
01/2023, Letnik:
518, Številka:
2
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ABSTRACT
We search for merger products among the 25 most massive white dwarfs in the Montreal White Dwarf Database 100 pc sample through follow-up spectroscopy and high-cadence photometry. We find an ...unusually high fraction, 40 per cent, of magnetic white dwarfs among this population. In addition, we identify four outliers in transverse velocity and detect rapid rotation in five objects. Our results show that $56^{+9}_{-10}$ per cent of the $M\approx 1.3\, {\rm M}_{\odot }$ ultramassive white dwarfs form through mergers. This fraction is significantly higher than expected from the default binary population synthesis calculations using the α prescription (with αλ = 2), and provides further support for efficient orbital shrinkage, such as with low values of the common-envelope efficiency.
A new gravitational wave verification source Kilic, Mukremin; Brown, Warren R; Gianninas, A ...
Monthly notices of the Royal Astronomical Society. Letters,
10/2014, Letnik:
444, Številka:
1
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We report the discovery of a detached 20-min orbital period binary white dwarf (WD). WD 0931+444 (SDSS J093506.93+441106.9) was previously classified as a WD + M dwarf system based on its optical ...spectrum. Our time-resolved optical spectroscopy observations obtained at the 8 m Gemini and 6.5 m MMT reveal peak-to-peak radial velocity variations of ≈400 km s−1 every 20 min for the WD, but no velocity variations for the M dwarf. In addition, high-speed photometry from the McDonald 2.1 m telescope shows no evidence of variability nor evidence of a reflection effect. An M dwarf companion is physically too large to fit into a 20 min orbit. Thus, the orbital motion of the WD is almost certainly due to an invisible WD companion. The M dwarf must be either an unrelated background object or the tertiary component of a hierarchical triple system. WD 0931+444 contains a pair of WDs, a 0.32 M⊙ primary and a ≥0.14 M⊙ secondary, at a separation of ≥0.19 R⊙. After J0651+2844, WD 0931+444 becomes the second shortest period detached binary WD currently known. The two WDs will lose angular momentum through gravitational wave radiation and merge in ≤9 Myr. The log h ≃ −22 gravitational wave strain from WD 0931+444 is strong enough to make it a verification source for gravitational wave missions in the milli-Hertz frequency range, e.g. the evolved Laser Interferometer Space Antenna (eLISA), bringing the total number of known eLISA verification sources to nine.
Abstract
We present minute cadence photometry of 31 732 point sources observed in one 3 $\rm deg^{2}$ DECam pointing centred at RA = 09:03:02 and Dec. = −04:35:00 over eight consecutive half-nights. ...We use these data to search for eclipse-like events consistent with a planetary transit of a white dwarf and other sources of stellar variability within the field. We do not find any significant evidence for minute-long transits around our targets, hence we rule out planetary transits around ∼370 white dwarfs that should be present in this field. Additionally, we identify 49 variables, including 40 new systems. These include 23 detached or contact stellar binaries, one eclipsing white dwarf + M dwarf binary, 16 δ Scuti, three RR Lyrae, and two ZZ Ceti pulsators. Results from the remaining two fields in our survey will allow us to place more stringent constraints on the frequency of planets orbiting white dwarfs in the habitable zone.
Kepler-16: A Transiting Circumbinary Planet Doyle, Laurance R.; Carter, Joshua A.; Fabrycky, Daniel C. ...
Science (American Association for the Advancement of Science),
09/2011, Letnik:
333, Številka:
6049
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We report the detection of a planet whose orbit surrounds a pair of low-mass stars. Data from the Kepler spacecraft reveal transits of the planet across both stars, in addition to the mutual eclipses ...of the stars, giving precise constraints on the absolute dimensions of all three bodies. The planet is comparable to Saturn in mass and size and is on a nearly circular 229-day orbit around its two parent stars. The eclipsing stars are 20 and 69% as massive as the Sun and have an eccentric 41-day orbit. The motions of all three bodies are confined to within 0.5° of a single plane, suggesting that the planet formed within a circumbinary disk.
We report the detection of orbital decay in the 12.75-minute, detached binary white dwarf (WD) SDSS J065133.338+284423.37 (hereafter J0651). Our photometric observations over a 13 month baseline ...constrain the orbital period to 765.206543(55) s and indicate that the orbit is decreasing at a rate of (-9.8 + or - 2.8) x 10 super(-12) s s super(-1) (or -0.31 + or - 0.09 ms yr super(-1)). We revise the system parameters based on our new photometric and spectroscopic observations: J0651 contains two WDs with M sub(1) = 0.26 + or - 0.04 M sub(middot in circle) and M sub(2) = 0.50 + or - 0.04 M sub(middot in circle). General relativity predicts orbital decay due to gravitational wave radiation of (-8.2 + or - 1.7) x 10 super(-12) s s super(-1) (or -0.26 + or - 0.05 ms yr super(-1)). Our observed rate of orbital decay is consistent with this expectation. J0651 is currently the second-loudest gravitational wave source known in the milli-Hertz range and the loudest non-interacting binary, which makes it an excellent verification source for future missions aimed at directly detecting gravitational waves. Our work establishes the feasibility of monitoring this system's orbital period decay at optical wavelengths.
We present the discovery of five new unbound hypervelocity stars (HVSs) in the outer Milky Way halo. Using a conservative estimate of Galactic escape velocity, our targeted spectroscopic survey has ...now identified 16 unbound HVSs as well as a comparable number of HVSs ejected on bound trajectories. A Galactic center origin for the HVSs is supported by their unbound velocities, the observed number of unbound stars, their stellar nature, their ejection time distribution, and their Galactic latitude and longitude distribution. Other proposed origins for the unbound HVSs, such as runaway ejections from the disk or dwarf galaxy tidal debris, cannot be reconciled with the observations. An intriguing result is the spatial anisotropy of HVSs on the sky, which possibly reflects an anisotropic potential in the central 10-100 pc region of the Galaxy. Further progress requires measurement of the spatial distribution of HVSs over the southern sky. Our survey also identifies seven B supergiants associated with known star-forming galaxies; the absence of B supergiants elsewhere in the survey implies there are no new star-forming galaxies in our survey footprint to a depth of 1-2 Mpc.
Given the social nature of participation in sport, we hypothesized that club sports participants would have greater well-being and quality of life than participants in other forms of physical ...activity (PA).
The purpose of this study was to examine health-related quality of life and life satisfaction in women who participate in three contrasting forms of PA: club sport, gym activities, and walking.
This was a cross-sectional study of the relationship between type of PA setting and measures of health-related quality of life (Short-Form Health Survey SF-36) and life satisfaction in 818 women living in rural Victoria, Australia, in 2007. Data were also compared with those from a normative sample of 2345 women.
After adjustment for potential confounders (age, education, marital status, children aged <16 yr, perceived financial stress, and level of recreational PA), four of the eight SF-36 subscales, the SF-36 mental health component summary score, and life satisfaction were significantly higher in the club sport group than that in the other groups.
Although cross-sectional research cannot establish causal links, the results suggest that participation in club sport may enhance the health benefits of PA.
We consider how the gravity of the Galactic disk and the Large Magellanic Cloud (LMC) modifies the radial motions of hypervelocity stars (HVSs) ejected from the Galactic center (GC). For typical HVSs ...ejected toward low (high) Galactic latitudes, the disk bends trajectories by up to 30° (3°-10°). For many lines of sight through the Galaxy, the LMC produces similar and sometimes larger deflections. Bound HVSs suffer larger deflections than unbound HVSs. Gravitational focusing by the LMC also generates an overdensity of a factor of two along the line of sight toward the LMC. With large enough samples, observations can detect the non-radial orbits and the overdensity of HVSs toward the LMC. For any Galactic potential model, the tangential velocity in the Galactic rest frame provides an excellent way to detect unbound and nearly bound HVSs within 10 kpc of the Sun. Similarly, the radial velocity in the rest frame isolates unbound HVSs beyond 10-15 kpc from the Sun. Among samples of unbound HVSs, measurements of the radial and tangential velocities serve to distinguish GC ejections from other types of high-velocity stars.
Abstract
We report the discovery of the first millisecond pulsar with a pulsating white dwarf (WD) companion. Following the recent discoveries of pulsations in extremely low-mass (ELM, ≤0.3 M⊙) WDs, ...we targeted ELM WD companions to two millisecond pulsars with high-speed Gemini photometry. We find significant optical variability in PSR J1738+0333 with periods between roughly 1790–3060 s, consistent in time-scale with theoretical and empirical observations of pulsations in ≈0.17 M⊙ He-core ELM WDs. We additionally put stringent limits on a lack of variability in PSR J1909−3744, showing this ELM WD is not variable to <0.1 per cent amplitude. Thanks to the accurate distance and radius estimates from radio timing measurements, PSR J1738+0333 becomes a benchmark for low-mass, pulsating WDs. Future, more extensive time series photometry of this system offers an unprecedented opportunity to constrain the physical parameters (including the cooling age) and interior structure of this ELM WD, and in turn, the mass and spin-down age of its pulsar companion.
We report the discovery of pulsations in three mixed-atmosphere, extremely low-mass white dwarf (ELM WD, M< or =, slant 0.3 M sub(middot in circle)) precursors. Following the recent discoveries of ...pulsations in both ELM and pre-ELM WDs, we targeted pre-ELM WDs with mixed H/He atmospheres with high-speed photometry. We find significant optical variability in all three observed targets with periods in the range 320-590 s, consistent in timescale with theoretical predictions of p-mode pulsations in mixed-atmosphere approximate0.18 M sub(middot in circle) He-core pre-ELM WDs. This represents the first empirical evidence that pulsations in pre-ELM WDs can only occur if a significant amount of He is present in the atmosphere. Future, more extensive, timeseries photometry of the brightest of the three new pulsators offers an excellent opportunity to constrain the thickness of the surface H layer, which regulates the cooling timescales for ELM WDs.
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