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DOE OSTI2022

The EBLM project – IX. Five fully convective M-dwarfs, precisely measured with CHEOPS and TESS light curves

ABSTRACT Eclipsing binaries are important benchmark objects to test and calibrate stellar structure and evolution models. This is especially true for binaries with a fully convective M-dwarf component for which direct measurements of these stars’ masses and radii are difficult using other techniques. Within the potential of M-dwarfs to be exoplanet host stars, the accuracy of theoretical predictions of their radius and effective temperature as a function of their mass is an active topic of discussion. Not only the parameters of transiting exoplanets but also the success of future atmospheric characterization relies on accurate theoretical predictions. We present the analysis of five eclipsing binaries with low-mass stellar companions out of a subsample of 23, for which we obtained ultra-high-precision light curves using the CHEOPS satellite. The observation of their primary and secondary eclipses are combined with spectroscopic measurements to precisely model the primary parameters and derive the M-dwarfs mass, radius, surface gravity, and effective temperature estimates using the PYCHEOPS data analysis software. Combining these results to the same set of parameters derived from TESS light curves, we find very good agreement (better than 1 per cent for radius and better than 0.2 per cent for surface gravity). We also analyse the importance of precise orbits from radial velocity measurements and find them to be crucial to derive M-dwarf radii in a regime below 5 per cent accuracy. These results add five valuable data points to the mass–radius diagram of fully convective M-dwarfs.

Sebastian, D. (ORCID:0000000222149258)↗

DOE OSTI2023

Abundances and Transients from Neutron Star–White Dwarf Mergers

Abstract We systematically investigate the mergers of neutron star–white dwarf binaries from beginning to end, with a focus on the properties of the inflows and outflows in accretion disks and their electromagnetic emissions. Using population synthesis models, we determine a subset of these binaries in which the white dwarf companion undergoes unstable mass transfer and complete tidal disruption, forming a large accretion disk around the neutron star. The material evolves according to a one-dimensional advection-dominated accretion-disk model with nuclear burning, neutrino emissions, and disk-surface wind ejection. The extreme dynamics of the entire process have proven difficult to analyze, and thus currently, the properties are poorly understood. The outflows from the mergers are iron- and nickel-rich, giving rise to optical and infrared emissions powered by the decay of the radioactive iron-type isotopes, calculated via the SuperNu light-curve code. We find these systems capable of powering bright, yet short-lived, optical transients with the potential to power gamma-ray bursts.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1976

A model for the X-ray nova A0620-00

The model involves a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay timescale of the optical counterpart are explained in terms of re-emission of X-radiation intercepted by the subgiant. It was concluded that A0620-00 can provide an excellent test case for numerical models of stellar atmospheres irradiated by an external X-ray flux.

Endal, A. S.↗

NASA NTRS1976

A model for the X-ray nova A0620-00

A model is proposed for the transient X-ray source A0620-00 involving a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay timescale of the optical counterpart are explained in terms of re-emission of X-radiation intercepted by the subgiant. A0620-00 should provide an excellent test case for numerical models of stellar atmospheres irradiated by an external X-ray flux.

Endal, A. S.↗

NASA NTRS1987

On the Holmberg asymmetry of the satellites of disk galaxies

A tidal explanation for the observation by Holmberg that the satellites of edge-on disk galaxies tend to avoid the sector within + or - 30 deg of the major axes of the disk galaxies is considered. It is shown that satellites with small orbit-to-disk inclinations are likely to become compact and consequently be left out in Holmberg's survey due to the resemblance to stars. The explanation is supported by the observation of an excess of compact galaxies near the major-axis direction of edge-on disk galaxies. The disk tidal explanation also predicts that the asymmetry should be weaker with larger satellites. It is found that the Karachentsev (1972, 1980) binary galaxy sample, where the typical companion is comparable to the primary galaxy, shows no Holmberg effect. The case of M32 as a compact satellite of the Andromeda galaxy is discussed as a nearby observationally supported example of the above processes.

Byrd, Gene G.↗

NASA NTRS1993

The orbit and companion of the Cepheid S Sge - A probable triple system

New radial velocities for the classical Cepheid S Sge have been obtained and combined with previous observations to derive a new orbit. The revised orbital elements are: gamma, -10.3 +/- 0.4 km/s; K, 15.5 +/- 0.2 km/s; e, 0.23 +/- 0.02; omega, 203.1 +/- 4.2 deg; T0, 39902.3 +/- 6.6 JD; P, 675.79 +/- 0.18 days; f(m), 0.239 +/- 0.010 solar masses; a sin i, 0.935 AU = 139.9 +/- 2.0 x 10 exp 6 km; s.e., 1.2 km/s. The revised elements differ very little from the orbit determined by Herbig and Moore (1952). We have also obtained low resolution IUE spectra to search for the companion. The IUE spectra show excess flux at 1800 A when compared with spectra of the single Cepheid Delta Cep at the same (B-V)0. The spectral type of the companion determined from this flux excess is A7 V to F0 V. However, the mass of such a companion (1.7 to 1.5 solar masses) is smaller than the minimum mass (2.8 solar masses) required by the mass function and an evolutionary mass of the Cepheid. We infer that the companion is itself a short period binary.

Evans, Nancy R.↗

NASA NTRS1994

A near infrared speckle imaging study of T Tauri stars

The results of a speckle imaging survey of T Tauri stars suggest that most, if not all, young low mass stars have companions. Repeated observations of these young binary stars have revealed orbital motion in the closest pairs (less than or = 0.3 sec), providing that these systems are indeed gravitationally bound and providing the basis for mass estimates in the upcoming years. These mass estimates are necessary to distinguish between the various binary star formation mechanisms that have been proposed to date.

Ghez, A. M.↗

NASA NTRS1995

X-ray emission from the PSR B1259-63 system near apastron

The PSR B1259-63 system contains a 47 ms radio pulsar in a highly eccentric binary with a Be-star companion. Strongly time-variable X-ray emission was reported from this system as the pulsar was near apastron in 1992- early 1993. The variability was primarily deduced from an apparent nondetection of the PSR B1259-63 system during a first preapastron ROSAT observation in 1992 February. We have reanalyzed the ROSAT observations of the PSR B1259-63 system. Contrary to the results of a previous analysis, we find that the PSR B1259-63 system was detected by ROSAT during the first off-axis 1992 February observation. The intensity of the soft X-ray emission of the PSR B1259-63 system before and after the 1992 apastron appears to vary at most by a factor of approx. 2. Our results sensibly constrain theoretical models of X-ray emission from the PSR B1259-63 system.

Greiner, J.↗

NASA NTRS1997

The bursting pulsar GRO J1744-28

The source GRO J1744-28 was discovered on 2 December 1995 with the burst and transient source experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO) when a series of 80 untriggered, hard X-ray bursts were recorded. The direction of the observed bursts was consistant with the Galactic center. The source was observed to emit at a constant rate of between 20 and 30 bursts per day for a five month period finishing the 2 May 1996. In mid-December 1996, a persistent source appeared from the same general direction which was identified as a binary pulsar orbiting a low mass companion. Pulsations were discovered in the bursts, thus establishing a common identity for the source of the bursts and the pulsar. The BATSE observations in the temporal and spectral domains are reviewed. Results of the subsequent multiwavelength observations are described.

Kouveliotou, C.↗

NASA NTRS2003

Ring Around the Black Hole

Regardless of size, black holes easily acquire accretion disks. Supermassive black holes can feast on the bountiful interstellar gas in galactic nuclei. Small black holes formed from collapsing stars often belong to binary systems in which a bulging companion star can spill some of its gas into the black hole s reach. In the chaotic mess of the accretion disk, atoms collide with one another. Swirling plasma reaches speeds upward of 10% that of light and glows brightly in many wavebands, particularly in X-rays. Gas gets blown back by a wind of radiation from the inner disk. New material enters the disks from different directions.

Wanjek, Christopher↗

NASA NTRS2005

Observations with NASA's Rossi X-ray Timing Explorer (RXTE)

Over the past decade our understanding of accreting neutron stars has been revolutionized. Observations with NASA's Rossi X-ray Timing Explorer (RXTE) have resulted in the discovery of fast, coherent X-ray intensity oscillations (hereafter, "burst oscillations") during thermonuclear X-ray bursts from 13 low mass X-ray binaries (LMXBs). Although many of their detailed properties remain to be fully understood, it is now beyond doubt that these oscillations result from spin modulation of the thermonuclear burst flux from the neutron star surface. In addition, RXTE observations led to the discovery of the first accreting millisecond pulsars, the sample of which now includes six systems, several of which are in extremely compact binary systems with essentially massive planet companions. These millisecond timing phenomena are providing powerful new probes of the formation, evolution and structure of neutron stars. I will describe recent efforts to constrain neutron star structure using detailed modelling of their properties. I will also discuss what the observed distribution of neutron star spin frequencies is telling us about the torques which may act to limit the ultimate spin up of accreting neutron stars.

Source record↗

DOE OSTI2024

Using the COSMIC Population Synthesis Code to Investigate How Metallicity Affects the Rates of Interacting Binaries

We use COSMIC, a galaxy population synthesis code, to investigate how metallicity affects the rate of formation of massive stars with a closely orbiting compact object companion. Metallicity—a crucial component to stellar evolution and binary system formation—can affect how and when these systems form. We present the formation time of these systems at different metallicities, and the anti-correlation the rates have with metallicity. In particular, these systems occur about 10 times more frequently at metallicities between Z = 2 × 10 −4 and 2 × 10 −3 , compared to those between Z = 2 × 10 −3 and 2 × 10 −2 . This work serves as a prerequisite to predicting global rates of these systems as a function of redshift, ultimately giving crucial insight into our understanding of the progenitors of long gamma-ray bursts and their evolution over cosmic time.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Different to the core: The pre-supernova structures of massive single and binary-stripped stars

The majority of massive stars live in binary or multiple systems and will interact with a companion during their lifetimes, which helps to explain the observed diversity of core-collapse supernovae. Donor stars in binary systems can lose most of their hydrogen-rich envelopes through mass transfer. As a result, not only are the surface properties affected, but so is the core structure. However, most calculations of the core-collapse properties of massive stars rely on single-star models. We present a systematic study of the difference between the pre-supernova structures of single stars and stars of the same initial mass (11–21 M ⊙ ) that have been stripped due to stable post-main-sequence mass transfer at solar metallicity. We present the pre-supernova core composition with novel diagrams that give an intuitive representation of the isotope distribution. As shown in previous studies, at the edge of the carbon-oxygen core, the binary-stripped star models contain an extended gradient of carbon, oxygen, and neon. This layer remains until core collapse and is more extended in mass for higher initial stellar masses. It originates from the receding of the convective helium core during core helium burning in binary-stripped stars, which does not occur in single-star models. We find that this same evolutionary phase leads to systematic differences in the final density and nuclear energy generation profiles. Binary-stripped star models have systematically higher total masses of carbon at the moment of core collapse compared to single-star models, which likely results in systematically different supernova yields. In about half of our models, the silicon-burning and oxygen-rich layers merge after core silicon burning. We discuss the implications of our findings for the “explodability”, supernova observations, and nucleosynthesis of these stars. Our models are publicly available and can be readily used as input for detailed supernova simulations.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1994

The binary system containing the classical Cepheid T Mon

Several new results are presented for the binary system containing the 27(sup d) classical Cepheid T Mon. New radial velocities for the Cepheid have been obtained, which confirm the decreasing orbital motion at the current epoch. The spectral type of the companion (B9.8 V) has been determined from an International Ultraviolet Explorer (IUE) low resolution spectrum. An IUE high resolution spectrum has been measured to search for the velocity of the companion. A velocity signal at +36 km/s on JD 2,446,105.21 has been tentatively identified as the velocity of the companion, but confirmation of this velocity would be very valuable. Results based on this tentative identification of the velocity are that the companion does not have a high projected rotation velocity, that the companion is unlikely to be a short period binary, and that the gamma velocity of the system is between 20 and 36 km/s. The luminosity and temperature of both the Cepheid and the companion are well determined from the satellite and ground-based observations and the Cepheid PLC relation. However, the companion is above the ZAMS in the H-R diagram, which is inconsistent with the large luminosity difference between the two stars. High rotation for the companion (viewed pole-on) is a possible explanation. The lower limit to the mass function (from the lower limits to the orbital period and amplitude) requires a very high eccentricity for the system for reasonable estimates for the masses of the two stars.

Evans, Nancy Remage↗

DOE OSTI2022

Measuring the mass of the black widow PSR J1555-2908

ABSTRACT Accurate measurements of the masses of neutron stars are necessary to test binary evolution models, and to constrain the neutron star equation of state. In pulsar binaries with no measurable post-Keplerian parameters, this requires an accurate estimate of the binary system’s inclination and the radial velocity of the companion star by other means than pulsar timing. In this paper, we present the results of a new method for measuring this radial velocity using the binary synthesis code Icarus. This method relies on constructing a model spectrum of a tidally distorted, irradiated star as viewed for a given binary configuration. This method is applied to optical spectra of the newly discovered black widow PSR J1555–2908. By modeling the optical spectroscopy alongside optical photometry, we find that the radial velocity of the companion star is 397 ± 4 km s−1 (errors quoted at 95 per cent confidence interval), as well as a binary inclination of >75°. Combined with γ-ray pulsation timing information, this gives a neutron star mass of 1.67$^{+0.15}_{-0.09}$ M⊙ and a companion mass of 0.060$^{+0.005}_{-0.003}$ M⊙, placing PSR J1555–2908 at the observed upper limit of what is considered a black widow system.

Kennedy, M. R.↗

NASA NTRS2012

Multi-Wavelength Implications of the Companion Star in eta Carinae

Eta-Carinae is considered to be a massive colliding wind binary system with a highly eccentric (e approximately 0.9), 5.54-yr orbit. However, the companion star continues to evade direct detection as the primary dwarfs its emission at most wavelengths. Using three-dimensional (3-D) SPH simulations of eta-Car's colliding winds and radiative transfer codes, we are able to compute synthetic observables across multiple wavebands for comparison to the observations. The models show that the presence of a companion star has a profound influence on the observed HST/STIS UV spectrum and H-alpha line profiles, as well as the ground-based photometric monitoring. Here, we focus on the Bore Hole effect, wherein the fast wind from the hot secondary star carves a cavity in the dense primary wind, allowing increased escape of radiation from the hotter/deeper layers of the primary's extended wind photosphere. The results have important implications for interpretations of eta-Car's observables at multiple wavelengths.

Madura, Thomas I.↗

NASA NTRS1976

Skylab ultraviolet stellar spectra - Cool stars with hot secondaries

A hot companion to the G5 III star HR 3080, a single-line spectroscopic binary, has been discovered from spectra in the vacuum-ultraviolet. The companion must be a subdwarf or pre-white dwarf. A list of previously known systems of the zeta Aur and VV Cep type observed with the ultraviolet spectrograph on Skylab is also given.

Parsons, S. B.↗

DOE OSTI2022

Search for High-energy Neutrino Emission from Galactic X-Ray Binaries with IceCube

We present the first comprehensive search for high-energy neutrino emission from high- and low-mass X-ray binaries conducted by IceCube. Galactic X-ray binaries are long-standing candidates for the source of Galactic hadronic cosmic rays and neutrinos. The compact object in these systems can be the site of cosmic-ray acceleration, and neutrinos can be produced by interactions of cosmic rays with radiation or gas, in the jet of a microquasar, in the stellar wind, or in the atmosphere of the companion star. We study X-ray binaries using 7.5 yr of IceCube data with three separate analyses. In the first, we search for periodic neutrino emission from 55 binaries in the Northern Sky with known orbital periods. In the second, the X-ray light curves of 102 binaries across the entire sky are used as templates to search for time-dependent neutrino emission. Finally, we search for time-integrated emission of neutrinos for a list of 4 notable binaries identified as microquasars. In the absence of a significant excess, we place upper limits on the neutrino flux for each hypothesis and compare our results with theoretical predictions for several binaries. In addition, we evaluate the sensitivity of the next generation neutrino telescope at the South Pole, IceCube-Gen2, and demonstrate its power to identify potential neutrino emission from these binary sources in the Galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗