Abstract
We obtain new and precise information on the double white dwarf (DWD) population and on its gravitational-wave-driven merger rate by combining the constraints on the DWD population from two ...previous studies on radial velocity variation. One of the studies is based on a sample of white dwarfs (WDs) from the Sloan Digital Sky Survey (SDSS, which with its low spectral resolution probes systems at separations a < 0.05 au) and the other is based on the ESO-VLT Supernova-Ia Progenitor surveY (SPY, which with its high spectral resolution is sensitive to a < 4 au). From a joint likelihood analysis, the DWD fraction among WDs is fbin = 0.095 ± 0.020 (1σ, random) +0.010 (systematic) in the separation range ≲4 au. The index of a power-law distribution of initial WD separations (at the start of solely gravitational-wave-driven binary evolution), N(a)da ∝ aαda, is α = −1.30 ± 0.15 (1σ) +0.05 (systematic). The Galactic WD merger rate per WD is Rmerge = (9.7 ± 1.1) × 10−12 yr−1. Integrated over the Galaxy lifetime, this implies that 8.5–11 per cent of all WDs ever formed have merged with another WD. If most DWD mergers end as more-massive WDs, then some 10 per cent of WDs are DWD-merger products, consistent with the observed fraction of WDs in a ‘high-mass bump’ in the WD mass function. The DWD merger rate is 4.5–7 times the Milky Way's specific Type Ia supernova (SN Ia) rate. If most SN Ia explosions stem from the mergers of some DWDs (say, those with massive-enough binary components) then ∼15 per cent of all WD mergers must lead to a SN Ia.
(ProQuest: ... denotes formulae and/or non-USASCII text omitted) We use multi-epoch spectroscopy of ~4000 white dwarfs in the Sloan Digital Sky Survey to constrain the properties of the Galactic ...population of binary white dwarf systems and calculate their merger rate. With a Monte Carlo code, we model the distribution of Delta RV sub(max), the maximum radial velocity shift between exposures of the same star, as a function of the binary fraction within 0.05 AU, f sub(bin), and the power-law index in the separation distribution at the end of the common-envelope phase, alpha . Although there is some degeneracy between f sub(bin) and alpha , the 15 high- Delta RV sub(max) systems that we find constrain the combination of these parameters, which determines a white dwarf merger rate per unit stellar mass of ... x 10 super(-13) yr super(?1) ... (1sigma limits). This is remarkably similar to the measured rate of Type Ia supernovae (SNe Ia) per unit stellar mass in Milky-Way-like Sbc galaxies. The rate of super-Chandrasekhar mergers is only ... x 10 super(-14) yr super(?1) ... We conclude that there are not enough close binary white dwarf systems to reproduce the observed SN Ia rate in the "classic" double degenerate super-Chandrasekhar scenario. On the other hand, if sub-Chandrasekhar mergers can lead to SNe Ia, as has been recently suggested by some studies, they could make a major contribution to the overall SN Ia rate. Although unlikely, we cannot rule out contamination of our sample by M-dwarf binaries or non-Gaussian errors. These issues will be clarified in the near future by completing the follow-up of all 15 high- Delta RV sub(max) systems.
We use the supernova remnants (SNRs) in the two Magellanic Clouds (MCs) as a supernova (SN) survey, ‘conducted’ over tens of kyr, from which we derive the current SN rate, and the SN delay time ...distribution (DTD), i.e. the SN rate versus time that would follow a hypothetical brief burst of a star formation. In a companion paper we have compiled a list of 77 SNRs in the MCs, and argued that it is a fairly complete record of the SNRs that are now in the Sedov phase of their expansions. We recover the SN DTD by comparing the numbers of SNRs observed in small individual ‘cells’ in these galaxies to the star formation histories of each cell, as calculated from resolved stellar populations by Harris & Zaritsky. We identify the visibility times of SNRs in each cell with the Sedov-phase lifetimes, which depend on the local ambient densities. The local densities are estimated from 21-cm emission, from an inverse Schmidt–Kennicutt law based on either Hα emission or the star formation rate from the resolved stellar populations, and from combinations of these tracers. This is the first SN DTD that is based on resolved stellar populations. We detect a population of ‘prompt’ Type Ia SNe (that explode within 330 Myr of star formation) at >99 per cent confidence level (CL). The best fit for the number of prompt Type Ia SNe per stellar mass formed is 2.7 –11.0 × 10−3 M−1⊙, depending on the density tracer used. The 95 per cent CL range for a ‘delayed’ (from 330 Myr to a Hubble time) Type Ia component is <1.6 × 10−13 SN yr−1 M−1⊙, consistent with rate measurements in old populations. The current total (core-collapse+Ia) SN rate in the MCs is 2.5–4.6 SNe per millennium (68 per cent CL+systematics), or 1.7–3.1 SNuM SNe (100 yr 1010 M⊙) −1, in agreement with the historical record and with rates measured in other dwarf irregulars. Conversely, assuming the SNRs are in free expansion, rather than in their Sedov phase, would impose on the SNRs a maximum age of 6 kyr, and would imply an MC SN rate per unit mass that is five times higher than in any type of galaxy, and a low-mass limit for core-collapse progenitors in conflict with stellar evolution theory.
A noninteracting low-mass black hole-giant star binary system Thompson, Todd A; Kochanek, Christopher S; Stanek, Krzysztof Z ...
Science (American Association for the Advancement of Science),
11/2019, Letnik:
366, Številka:
6465
Journal Article
Recenzirano
Odprti dostop
Black hole binary systems with companion stars are typically found via their x-ray emission, generated by interaction and accretion. Noninteracting binaries are expected to be plentiful in the Galaxy ...but must be observed using other methods. We combine radial velocity and photometric variability data to show that the bright, rapidly rotating giant star 2MASS J05215658+4359220 is in a binary system with a massive unseen companion. The system has an orbital period of ~83 days and near-zero eccentricity. The photometric variability period of the giant is consistent with the orbital period, indicating star spots and tidal synchronization. Constraints on the giant's mass and radius imply that the unseen companion is Formula: see text solar masses, indicating that it is a noninteracting low-mass black hole or an unexpectedly massive neutron star.
Supernova remnants (SNRs) in Local Group galaxies offer unique insights into the origin of different types of supernovae (SNe). In order to take full advantage of these insights, one must understand ...the intrinsic and environmental diversity of SNRs in the context of their host galaxies. We introduce a semi-analytic model that reproduces the statistical properties of a radio continuum-selected SNR population, taking into account the detection limits of radio surveys, the range of SN kinetic energies, the measured interstellar medium (ISM) and stellar mass distribution in the host galaxy from multi-wavelength images and the current understanding of electron acceleration and magnetic field amplification in SNR shocks from first-principle kinetic simulations. Applying our model to the SNR population in M33, we reproduce the SNR radio luminosity function with a median SN rate of ~3.1 x 10 super( -3) per year and an electron acceleration efficiency, ... ~ 4.2 x 10 super( -3). We predict that the radio visibility times of ~70 per cent of M33 SNRs will be determined by their Sedov-Taylor lifetimes, and correlated with the measured ISM column density, NH (t ...N..., with a ~ 0.33) while the remaining will have visibility times determined by the detection limit of the radio survey. These observational constraints on the visibility time of SNRs will allow us to use SNR catalogues as 'SN surveys' to calculate SN rates and delay-time distributions in the Local Group. (ProQuest: ... denotes formulae/symbols omitted.)
A long-standing problem is identifying the elusive progenitors of Type Ia supernovae (SNe Ia), which can roughly be split into Chandraksekhar and sub-Chandrasekhar-mass events. An important ...difference between these two cases is the nucleosynthetic yield, which is altered by the increased neutron excess in Chandrasekhar progenitors due to their pre-explosion simmering and high central density. Based on these arguments, we show that the chemical composition of the most metal-rich star in the Ursa Minor dwarf galaxy, COS 171, is dominated by nucleosynthesis from a low-metallicity, low-mass, sub-Chandrasekhar-mass SN Ia. Key diagnostic abundance ratios include Mn/Fe and Ni/Fe, which could not have been produced by a Chandrasekhar-mass SN Ia. Large deficiencies of Ni/Fe, Cu/Fe and Zn/Fe also suggest the absence of alpha-rich freeze-out nucleosynthesis, favoring low-mass white dwarf progenitors of SNe Ia, near 0.95 M , from comparisons to numerical detonation models. We also compare Mn/Fe and Ni/Fe ratios to the recent yields predicted by Shen et al., finding consistent results. To explain the Fe/H at −1.35 dex for COS 171 would require dilution of the SN Ia ejecta with ∼104 M of material, which is expected for an SN remnant expanding into a warm interstellar medium with n ∼ 1 cm−3. In the future, finding more stars with the unique chemical signatures we highlight here will be important for constraining the rate and environments of sub-Chandrasekhar SNe Ia.
Double detonations in double white dwarf (WD) binaries undergoing unstable mass transfer have emerged in recent years as one of the most promising Type Ia supernova (SN Ia) progenitor scenarios. One ...potential outcome of this "dynamically driven double-degenerate double-detonation" (D6) scenario is that the companion WD survives the explosion and is flung away with a velocity equal to its >1000 km s−1 pre-SN orbital velocity. We perform a search for these hypervelocity runaway WDs using Gaia's second data release. In this paper, we discuss seven candidates followed up with ground-based instruments. Three sources are likely to be some of the fastest known stars in the Milky Way, with total Galactocentric velocities between 1000 and 3000 km s−1, and are consistent with having previously been companion WDs in pre-SN Ia systems. However, although the radial velocity of one of the stars is >1000 km s−1, the radial velocities of the other two stars are puzzlingly consistent with 0. The combined five-parameter astrometric solutions from Gaia and radial velocities from follow-up spectra yield tentative 6D confirmation of the D6 scenario. The past position of one of these stars places it within a faint, old SN remnant, further strengthening the interpretation of these candidates as hypervelocity runaways from binary systems that underwent SNe Ia.
Close Companions around Young Stars Kounkel, Marina; Covey, Kevin; Moe, Maxwell ...
The Astronomical journal,
05/2019, Letnik:
157, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Multiplicity is a fundamental property that is set early during stellar lifetimes, and it is a stringent probe of the physics of star formation. The distribution of close companions around young ...stars is still poorly constrained by observations. We present an analysis of stellar multiplicity derived from Apache Point Observatory Galactic Evolution Experiment-2 spectra obtained in targeted observations of nearby star-forming regions. This is the largest homogeneously observed sample of high-resolution spectra of young stars. We developed an autonomous method to identify double-lined spectroscopic binaries (SB2s). Out of 5007 sources spanning the mass range of ∼0.05-1.5 M , we find 399 binaries, including both radial velocity (RV) variables and SB2s. The mass ratio distribution of SB2s is consistent with being uniform for q < 0.95 with an excess of twins for q > 0.95. The period distribution is consistent with what has been observed in close binaries (<10 au) in the evolved populations. Three systems are found to have q ∼ 0.1, with a companion located within the brown dwarf desert. There are no strong trends in the multiplicity fraction as a function of cluster age from 1 to 100 Myr. There is a weak dependence on stellar density, with companions being most numerous at * ∼ 30 stars/pc−2 and decreasing in more diffuse regions. Finally, disk-bearing sources are deficient in SB2s (but not RV variables) by a factor of ∼2; this deficit is recovered by the systems without disks. This may indicate a quick dispersal of disk material in short-period equal-mass systems that is less effective in binaries with lower q.
We use the multi-epoch radial velocities acquired by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey to perform a large-scale statistical study of stellar multiplicity for ...field stars in the Milky Way, spanning the evolutionary phases between the main sequence (MS) and the red clump. We show that the distribution of maximum radial velocity shifts (ΔRVmax) for APOGEE targets is a strong function of log g, with MS stars showing ΔRVmax as high as ∼300 , and steadily dropping down to ∼30 for log g ∼ 0, as stars climb up the red giant branch (RGB). Red clump stars show a distribution of ΔRVmax values comparable to that of stars at the tip of the RGB, implying they have similar multiplicity characteristics. The observed attrition of high ΔRVmax systems in the RGB is consistent with a lognormal period distribution in the MS and a multiplicity fraction of 0.35, which is truncated at an increasing period as stars become physically larger and undergo mass transfer after Roche Lobe overflow during H-shell burning. The ΔRVmax distributions also show that the multiplicity characteristics of field stars are metallicity-dependent, with metal-poor (Fe/H −0.5) stars having a multiplicity fraction a factor of 2-3 higher than metal-rich (Fe/H 0.0) stars. This has profound implications for the formation rates of interacting binaries observed by astronomical transient surveys and gravitational wave detectors, as well as the habitability of circumbinary planets.
ABSTRACT Despite decades of intense efforts, many fundamental aspects of Type Ia supernovae (SNe Ia) remain elusive. One of the major open questions is whether the mass of an exploding white dwarf ...(WD) is close to the Chandrasekhar limit. Here, we report the detection of strong K-shell emission from stable Fe-peak elements in the Suzaku X-ray spectrum of the Type Ia supernova remnant (SNR) 3C 397. The high Ni/Fe and Mn/Fe mass ratios (0.11-0.24 and 0.018-0.033, respectively) in the hot plasma component that dominates the K-shell emission lines indicate a degree of neutronization in the supernova ejecta that can only be achieved by electron capture in the dense cores of exploding WDs with a near-Chandrasekhar mass. This suggests a single-degenerate origin for 3C 397, since Chandrasekhar mass progenitors are expected naturally if the WD accretes mass slowly from a companion. Together with other results supporting the double-degenerate scenario, our work adds to the mounting evidence that both progenitor channels make a significant contribution to the SN Ia rate in star-forming galaxies.
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