Candidate Binary Systems Research Articles

Two dynamically discovered compact object candidate binary systems from LAMOST low-resolution survey

ABSTRACT We report two binary systems, LAMOST J035540 + 381550 (hereafter J035540) and LAMOST J035916 + 400732 (hereafter J035916), identified through the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) low-resolution survey (LRS). Each of these two systems contains an M-type star orbiting with a invisible compact object candidate. Follow-up spectroscopic observations of Palomar 200-in. telescope (P200) enhance radial velocity measurements. We use radial velocities from LAMOST and P200, as well as light curves from Zwicky Transient Facility (ZTF) to constrain orbital parameters. The masses of the visible M-type stars are estimated by fitting the MIST isochrones and spectral energy distributions. The mass functions for the unseen companions are: $0.22\pm 0.01\,{\rm M}_{\odot }$ for J035540 and $0.16\pm 0.01\, {\rm M}_{\odot }$ for J035916. With the orbital and stellar parameters derived above and assuming the orbital inclination is 90° (edge-on), we find that the minimum masses of the invisible companions exceeds that of the visible stars. The single-lined feature and the dynamical evidence suggest the presence of compact objects. J035540’s ZTF light curve, modelled with phoebe, yields a compact object mass of $0.70^{+0.12}_{-0.05}\, {\rm M}_{\odot }$. For J035916, ellipsoidal modulation analysis constrains the light-curve amplitude, yielding a compact object mass range of $0.57-0.90\, {\rm M}_{\odot }$. The mass estimates indicate that both are likely white dwarfs. These findings underscore the efficiency of optical time-domain surveys and dynamical methods in identifying faint, massive white dwarfs, along with other compact objects in binaries.

Evaluating Phase Relations in Molten Oxides for Electrochemical Operating Windows for Selective Metal Reduction

AbstractMolten oxide electrolysis is a promising pathway to decarbonize primary metal production. The oxide electrolyte is less hazardous and eco‐toxic than halides (molten salt electrolysis) and, with the use of renewably generated electricity and an inert anode, oxygen is produced as a by‐product instead of CO2. Building fundamental understanding of electrolytic operating windows requires starting with simple chemistries. Here we investigate a simplified binary oxide system as an electrolyte for titanium oxide reduction to metal. The TiO2−Na2O binary system forms a eutectic, reducing the liquidus temperature over a wide composition range. FactSage 8.1 predictions suggested Ti reduction would become favorable over Na reduction for compositions greater than 0.49 mole fraction TiO2. The prediction was validated by the detection of metallic Ti after electrolysis experiments. However, the reduction efficiency was too low (0.24±0.08 % at −0.1 V vs Ti reference electrode) for the TiO2−Na2O system to be a viable industrial electrolyte for Ti production. Scoping for other binary oxide systems was performed for electrolytic production of two critical metals, tantalum and neodymium. Based on TiO2−Na2O system's predicted behavior, candidate binary oxide systems were identified that contained congruently melting line compounds flanked by eutectic reactions from the ACerS‐NIST Phase Equilibria diagrams database.

15 000 ellipsoidal binary candidates in TESS: Orbital periods, binary fraction, and tertiary companions

ABSTRACT We present a homogeneously selected sample of 15 779 candidate binary systems with main sequence primary stars and orbital periods shorter than 5 d. The targets were selected from TESS full-frame image light curves on the basis of their tidally induced ellipsoidal modulation. Spectroscopic follow-up suggests a sample purity of 83 ± 13 per cent. Injection-recovery tests allow us to estimate our overall completeness as 28 ± 3 per cent with Porb < 3 d and to quantify our selection effects. 39 ± 4 per cent of our sample are contact binary systems, and we disentangle the period distributions of the contact and detached binaries. We derive the orbital period distribution of the main-sequence binary population at short orbital periods, finding a distribution continuous with the lognormal distribution previously found for solar-type stars at longer periods, but with a significant steepening at Porb ≲ 3 d, and a pile-up of contact binaries at Porb ≈ 0.4 d. Companions in the period range of 1–5 d are an order of magnitude more frequent around stars hotter than $\approx 6250\, \rm K$ (the Kraft break) when compared to cooler stars, suggesting that magnetic braking shortens the lifetime of cooler binary systems. However, the period distribution in the range 1–10 d is independent of temperature. We detect resolved tertiary companions to 9.0 ± 0.2 per cent of our binaries with a median separation of 3200 au. The frequency of tertiary companions rises to 29 ± 5 per cent among the systems with the shortest ellipsoidal periods. This large binary sample with quantified selection effects will be a powerful resource for future studies of detached and contact binary systems with Porb<5 d.

Spectral characterization of newly detected young substellar binaries with SINFONI

We observe 14 young low-mass substellar objects using the VLT/SINFONI integral field spectrograph with laser guide star adaptive optics to detect and characterize three candidate binary systems. All three binary candidates show strong signs of youth, with two of them likely belonging to young moving groups. Together with the adopted young-moving-group ages we employ isochrones from the BT-Settle CIFIST substellar evolutionary models to estimate individual masses for the binary components. We find 2MASS J15104786–2818174 to be part of the ≈30−50 Myr Argus moving group and to be composed of a 34−48 MJup primary brown dwarf with spectral type M9γ and a fainter 15−22 MJup companion, separated by ≈100 mas. 2MASS J22025794–5605087 is identified as an almost equal-mass binary in the AB Dor moving group, with a projected separation of ≈60 mas. Both components share spectral type M9γ/β, which with the adopted age of 120−200 Myr yields masses in the range of 50−68 MJup for each component individually. The observations of 2MASS J15474719–2423493 are of lower quality and we obtain no spectral characterization for the target, but resolve two components separated by ≈170 mas which with the predicted young field age of 30−50 Myr yields individual masses below 20 MJup. Out of the three candidate binary systems, 2MASS J22025794–5605087 has unambiguous spectroscopic signs of being a bona-fide binary, while the other two will require second-epoch confirmation. The small projected separations between the binary components correspond to physical separations of ≈4−7 AU, meaning that astrometric monitoring of just a few years would be adequate to generate constrained orbital fits and dynamical masses for the systems. In combination with their young ages, these binaries will prove to be excellent benchmarks for calibrating substellar evolutionary models down to a very low-mass regime.

Robo-AO Discovery and Basic Characterization of Wide Multiple Star Systems in the Pleiades, Praesepe, and NGC 2264 Clusters

Abstract We identify and roughly characterize 66 candidate binary star systems in the Pleiades, Praesepe, and NGC 2264 star clusters, based on robotic adaptive optics imaging data obtained using Robo-AO at the Palomar 60″ telescope. Only ∼10% of our imaged pairs were previously known. We detect companions at red optical wavelengths, with physical separations ranging from a few tens to a few thousands of au. A three-sigma contrast curve generated for each final image provides upper limits to the brightness ratios for any undetected putative companions. The observations are sensitive to companions with a maximum contrast of ∼6m at larger separations. At smaller separations, the mean (best) raw contrast at 2″ is 3.ͫ8 (6m), at 1″ is 3.ͫ0 (4.ͫ5), and at 0.″5 is 1.ͫ9 (3m). Point-spread function subtraction can recover nearly the full contrast in the closer separations. For detected candidate binary pairs, we report separations, position angles, and relative magnitudes. Theoretical isochrones appropriate to the Pleiades and Praesepe clusters are then used to determine the corresponding binary mass ratios, which range from 0.2 to 0.9 in . For our sample of roughly solar-mass (FGK type) stars in NGC 2264 and sub-solar-mass (K and early M-type) primaries in the Pleiades and Praesepe, the overall binary frequency is measured at ∼15.5% ± 2%. However, this value should be considered a lower limit to the true binary fraction within the specified separation and mass ratio ranges in these clusters, given that complex and uncertain corrections for sensitivity and completeness have not been applied.

Poking the Beehive from Space: K2 Rotation Periods for Praesepe

We analyze {\it K2} light curves for 794 low-mass ($1 > M_* > 0.1$ $M_{\odot}$) members of the $\approx$650-Myr-old open cluster Praesepe, and measure rotation periods ($P_{rot}$) for 677 of these stars. We find that half of the rapidly rotating $>$0.3 $M_{\odot}$ stars are confirmed or candidate binary systems. The remaining $>0.3$ $M_{\odot}$ fast rotators have not been searched for companions, and are therefore not confirmed single stars. We found previously that nearly all rapidly rotating $>$0.3 $M_{\odot}$ stars in the Hyades are binaries, but we require deeper binary searches in Praesepe to confirm whether binaries in these two co-eval clusters have different $P_{rot}$ distributions. We also compare the observed $P_{rot}$ distribution in Praesepe to that predicted by models of angular-momentum evolution. We do not observe the clear bimodal $P_{rot}$ distribution predicted by Brown (2014) for $>$0.5 $M_{\odot}$ stars at the age of Praesepe, but 0.25$-$0.5 $M_{\odot}$ stars do show stronger bimodality. In addition, we find that $>$60\% of early M dwarfs in Praesepe rotate more slowly than predicted at 650 Myr by Matt et al. (2015), which suggests an increase in braking efficiency for these stars relative to solar-type stars and fully convective stars. The incompleteness of surveys for binaries in open clusters likely impacts our comparison with these models, since the models only attempt to describe the evolution of isolated single stars.

A SEARCH FOR PHOTOMETRIC VARIABILITY IN L- AND T-TYPE BROWN DWARF ATMOSPHERES

Using the Gemini infrared camera on the 3-meter Shane telescope at Lick Observatory, we have searched for broad-band J and K' photometric variability for a sample of 15 L and T-type brown dwarfs, including 7 suspected spectral binaries. Four of the dwarfs - 2MASS J0939-2448, 2MASS J1416+1348A, 2MASS J1711+2232, and 2MASS J2139+0220 - exhibit statistically significant variations over timescales ranging from ~0.5 hr to 6 days. Our detection of variability in 2MASS J2139+0220 confirms that reported by Radigan et al., and periodogram and phase dispersion minimization analysis also confirms a variability period of approximately 7.6 +/- 0.2 hours. Remarkably, two of the four variables are known or candidate binary systems, including 2MASS J2139+0220, for which we find only marginal evidence of radial velocity variation over the course of a year. This result suggests that some spectral binary candidates may appear as such due to the blending of cloudy and non-cloudy regions in a single "patchy" atmosphere. Our results are consistent with an overall variability fraction of 35 +/- 5 %, with no clear evidence of greater variability among brown dwarfs at the L dwarf/T dwarf transition.

THE EVOLUTION OF PRIMORDIAL BINARY OPEN STAR CLUSTERS: MERGERS, SHREDDED SECONDARIES, AND SEPARATED TWINS

The basic properties of the candidate binary cluster population in the Magellanic Clouds and Galaxy are similar. The fraction of candidate binary systems is $\sim$10% and the pair separation histogram exhibits a bimodal distribution commonly attributed to their transient nature. However, if primordial pairs cannot survive for long as recognizable bound systems, how are they ending up? Here, we use simulations to confirm that merging, extreme tidal distortion and ionization are possible depending on the initial orbital elements and mass ratio of the pair. The nature of the dominant evolutionary path largely depends on the strength of the local tidal field. Merging is observed for initially close primordial binary clusters but also for wider pairs in nearly parabolic orbits. Its characteristic timescale depends on the initial orbital semi-major axis, eccentricity, and cluster pair mass ratio, becoming shorter for closer, more eccentric equal mass pairs. Shredding or extreme tidal distortion of the less massive cluster and subsequent separation is observed in all pairs with appreciably different masses. Wide pairs steadily evolve into the separated twins state characterized by the presence of tidal bridges and separations of 200-500 pc after one Galactic orbit. In the Galaxy, the vast majority of observed binary candidates appear to be following this evolutionary path which translates into the dominant peak (25-30 pc) in the pair separation distribution. The secondary peak at smaller separations (10-15 pc) can be explained as due to close pairs in almost circular orbits and/or undergoing merging. Merged clusters exhibit both peculiar radial density and velocity dispersion profiles shaped by synchronization and gravogyro instabilities. Both simulations and observations show that, for the range of parameters studied here, long term binary cluster stability in the Galactic disk is unlikely.

FLAMES spectroscopy of low-mass stars in the young clusters σ Ori and λ Ori

Aims. We performed a detailed membership selection and studied the accretion properties of low-mass stars in the two apparently very similar young (1–10 Myr) clusters σ Ori and λ Ori. Methods. We observed 98 and 49 low-mass (0.2–1.0 M� ) stars in σ Ori and λ Ori respectively, using the multi-object optical spectrograph FLAMES at the VLT, with the high-resolution (R ∼ 17 000) HR15N grating (6470–6790 A). We used radial velocities, Li and Hα to establish cluster membership and Hα and other optical emission lines to analyze the accretion properties of members. Results. We identified 65 and 45 members of the σ Ori and λ Ori clusters, respectively, and discovered 16 new candidate binary systems. We also measured rotational broadening for 20 stars and estimated the mass accretion rates in 25 stars of the σ Ori cluster, f

Magnetic White Dwarfs in the Two Micron All Sky Survey: A Search for Candidate Binary Systems

ABSTRACTOur understanding of the formation and evolution of magnetic cataclysmic variables from initially detached, post–common‐envelope binary stars containing a magnetic white dwarf and a main‐sequence star is currently poorly constrained, due to the lack of observational identification of the progenitor systems. Very few potential pre–cataclysmic variables containing a magnetic white dwarf are known, compared with ≈25% of the cataclysmic variable population that contain magnetic white dwarfs. We present the results of a search for candidate binary systems containing a magnetic white dwarf, which utilized photometric data from the Two Micron All Sky Survey (2MASS; as well as Hubble Space Telescope and WIYN Observatory follow‐up data for several objects). Our target sample was drawn primarily from the comprehensive list of magnetic white dwarfs by Wickramasinghe & Ferrario, plus several recently identified objects selected from the literature. Out of 51 2MASS detections, no convincing binary candidates were found. However, six objects merit additional observation to determine the origin of a small near‐infrared excess that could be attributed to a very low mass stellar or substellar companion. An additional four white dwarfs are possibly at the centers of previously unknown, and likely unresolved, planetary nebulae.

Eclipse monitoring of eccentric binary systems

The observation of apsidal motions in eclipsing binaries is a very rewarding area of research which requires only moderate or small telescopes equipped with a photoelectric photometer. Important contributions can be made to the study of stellar internal structure through these observations, as well as the verification of the theory of general relativity using the equations of orbital motion. The main objectives of such an observational effort are described, together with a list of candidate binary systems. An appeal to photometrists with small telescopes around the world is made to observe these eccentric and well-detached eclipsing binaries.

X-ray observations of possible binary clusters of galaxies

Many studies of superclusters of galaxies have been conducted, taking into account also superclusters representing candidate binary cluster systems. The present investigation is concerned with further studies of potential binary cluster systems, giving attention to a sample of six cluster pairs, in which the redshifts and X-ray luminosities of each member of a pair have been measured. One of the objectives of the investigation was related to a search for X-ray evidence that the clusters interact in these potentially binary systems. A second objective was to provide a measure of the mass of hot gas in the clusters. Two new systems in which the two clusters may have a physical association were found.