Journal articles: 'M-DWARF BINARY'

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Hogg, M. A., S. L. Casewell, G. A. Wynn, E. S. Longstaff, I. P. Braker, M. R. Burleigh, R. H. Tilbrook, et al. "Confirming new white dwarf-ultracool dwarf binary candidates." Monthly Notices of the Royal Astronomical Society 498, no. 1 (August 10, 2020): 12–24. http://dx.doi.org/10.1093/mnras/staa2233.

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ABSTRACT We present the results of a study to discover prospective new white dwarf-L dwarf binaries as identified by their near-infrared excesses in the UKIDSS catalogue. We obtained optical spectra to validate the white dwarf nature for 22 of the candidate primary stars, confirming ten as white dwarfs and determining their effective temperatures and gravities. For all 10 white dwarfs, we determined that the near-infrared excess was indeed indicative of a cool companion. Six of these are suggestive of late M dwarf companions, and three are candidate L dwarf companions, with one straddling the M−L boundary. We also present near-infrared spectra of eight additional candidate white dwarf-ultracool dwarf binaries, where the white dwarf primary had been previously confirmed. These spectra indicate one candidate at the M−L boundary, three potential L dwarf companions, and one suspected M dwarf, which showed photometric variability on a ∼6 h period, suggesting the system may be close. Radial velocity follow-up is required to confirm whether these systems are close, or widely separated.

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Han, Cheongho, Chung-Uk Lee, Yoon-Hyun Ryu, Doeon Kim, Michael D. Albrow, Sun-Ju Chung, Andrew Gould, et al. "KMT-2019-BLG-0797: Binary-lensing event occurring on a binary stellar system." Astronomy & Astrophysics 649 (May 2021): A91. http://dx.doi.org/10.1051/0004-6361/202040149.

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Aims. We analyze the microlensing event KMT-2019-BLG-0797. The light curve of the event exhibits two anomalous features from a single-lens single-source model, and we aim to reveal the nature of the anomaly. Methods. It is found that a model with two lenses plus a single source (2L1S model) can explain one feature of the anomaly, but the other feature cannot be explained. We test various models and find that both anomalous features can be explained by introducing an extra source to a 2L1S model (2L2S model), making the event the third confirmed case of a 2L2S event, following MOA-2010-BLG-117 and OGLE-2016-BLG-1003. It is estimated that the extra source comprises ∼4% of the I-band flux from the primary source. Results. Interpreting the event is subject to a close–wide degeneracy. According to the close solution, the lens is a binary consisting of two brown dwarfs with masses (M1, M2) ∼ (0.034, 0.021) M⊙, and it is located at a distance of DL ∼ 8.2 kpc. According to the wide solution, on the other hand, the lens is composed of an object at the star–brown dwarf boundary and an M dwarf with masses (M1, M2) ∼ (0.06, 0.33) M⊙ located at DL ∼ 7.7 kpc. The source is composed of a late G dwarf to early K dwarf primary and an early-to-mid M dwarf companion.

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Landstreet, John D., and Stefano Bagnulo. "Discovery of a Sirius-like binary system with a very strongly magnetic white dwarf." Astronomy & Astrophysics 634 (February 2020): L10. http://dx.doi.org/10.1051/0004-6361/201937301.

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Non-interacting binary systems containing a magnetic white dwarf and a main-sequence star are considered extremely rare, perhaps non-existent. In the course of a search of magnetic fields in high-mass white dwarfs we have discovered a Sirius-like wide binary system composed of a main-sequence G0 star and an M ∼ 1.1 M⊙ white dwarf with a huge (hundreds of MG) magnetic field. This star, WDS J03038+0608B, shows a circular polarisation amplitude of 5% in the continuum, with no evidence of variability on a 1 d timescale, little or no linear polarisation in the blue part of the spectrum, and about 2% linear polarisation in the red part of the optical spectrum. A search in the literature reveals the existence of four more binary systems that include a magnetic white dwarf and a non-degenerate companion; three such systems passed unremarked in previous studies. We estimate that up to a few percent of magnetic white dwarfs may be found to occur in wide binary pairs. However, at least four of the five known binary systems with a magnetic white dwarf are too widely separated to be expected to evolve into systems experiencing Roche-lobe overflow, and cannot be considered as progenitors of magnetic cataclysmic variable (AM Her and DQ Her) systems.

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Wolz, Anna, Kent Yagi, Nick Anderson, and Andrew J. Taylor. "Measuring individual masses of binary white dwarfs with space-based gravitational-wave interferometers." Monthly Notices of the Royal Astronomical Society: Letters 500, no. 1 (November 15, 2020): L52—L56. http://dx.doi.org/10.1093/mnrasl/slaa183.

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ABSTRACT Unlike gravitational waves from merging black holes and neutron stars that chirp significantly over the observational period of ground-based detectors, gravitational waves from binary white dwarfs are almost monochromatic. This makes it extremely challenging to measure their individual masses. Here, we take a novel approach of using finite-size effects and applying certain universal relations to measure individual masses of binary white dwarfs using Laser Interferometer Space Antenna. We found quasi-universal relations among the mass, moment of inertia, and tidal deformability of a white dwarf that do not depend sensitively on the white dwarf composition. These relations allow us to rewrite the moments of inertia and tidal deformabilities in the waveform in terms of the masses. We then carried out a Fisher analysis to estimate how accurately one can measure the individual masses from the chirp mass and finite-size measurements. We found that the individual white dwarf masses can be measured with LISA for a 4-yr observation if the initial frequency is high enough (∼0.02 Hz) and either the binary separation is small (∼1 kpc) or the masses are relatively large (m ≳ 0.8 M⊙). This opens a new possibility of measuring individual masses of binary white dwarfs with space-based interferometers.

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Zheng, Ling-Lin, Wei-Min Gu, Mouyuan Sun, Zhi-Xiang Zhang, Tuan Yi, Jianfeng Wu, Junfeng Wang, et al. "A White Dwarf–Main-sequence Binary Unveiled by Time-domain Observations from LAMOST and TESS." Astrophysical Journal 936, no. 1 (August 29, 2022): 33. http://dx.doi.org/10.3847/1538-4357/ac853f.

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Abstract We report a single-lined white dwarf–main-sequence binary system, LAMOST J172900.17+652952.8, which is discovered by the Large Sky Area Multi-Object Fibre Spectroscopic Telescope (LAMOST)’s medium-resolution time-domain surveys. The radial-velocity semi-amplitude and orbital period of the optical visible star are measured by using follow-up observations with the Palomar 200 inch telescope and light curves from the Transiting Exoplanet Survey Satellite (TESS). Thus the mass function of the invisible candidate white dwarf is derived, f(M 2) = 0.120 ± 0.003 M ⊙. The mass of the visible star is measured based on a spectral energy distribution fitting, M 1 = 0.81 − 0.06 + 0.07 M ⊙ . Hence, the mass of its invisible companion is M 2 ≳ 0.63 M ⊙. The companion ought to be a compact object rather than a main-sequence star owing to the mass ratio q = M 2/M 1 ≳ 0.78 and the single-lined spectra. The compact object is likely to be a white dwarf if the inclination angle is not small, i ≳ 40°. By using the Galaxy Evolution Explorer (GALEX) near-UV flux, the effective temperature of the white dwarf candidate is constrained as T eff WD ≲ 12,000–13,500 K. It is difficult to detect white dwarfs which are outshone by their bright companions via single-epoch optical spectroscopic surveys. Therefore, optical time-domain surveys can play an important role in unveiling invisible white dwarfs and other compact objects in binaries.

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Creevey, O. L., G. F. Benedict, T. M. Brown, R. Alonso, P. Cargile, G. Mandushev, D. Charbonneau, et al. "A New Detached M Dwarf Eclipsing Binary." Astrophysical Journal 625, no. 2 (May 11, 2005): L127—L130. http://dx.doi.org/10.1086/431278.

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Wilson, R. E., C. A. Pilachowski, and Dirk Terrell. "THE M DWARF ECLIPSING BINARY CU CANCRI." Astrophysical Journal 835, no. 2 (February 1, 2017): 251. http://dx.doi.org/10.3847/1538-4357/835/2/251.

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Maxted, P. F. L., T. R. Marsh, L. Morales-Rueda, M. A. Barstow, P. D. Dobbie, M. R. Schreiber, V. S. Dhillon, and C. S. Brinkworth. "RX J2130.6+4710 - an eclipsing white dwarf-M-dwarf binary star." Monthly Notices of the Royal Astronomical Society 355, no. 4 (December 2004): 1143–54. http://dx.doi.org/10.1111/j.1365-2966.2004.08393.x.

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Rebassa-Mansergas, Alberto, Siyi Xu, Roberto Raddi, Anna F. Pala, Enrique Solano, Santiago Torres, Francisco Jiménez-Esteban, and Patricia Cruz. "Gaia 0007–1605: An Old Triple System with an Inner Brown Dwarf–White Dwarf Binary and an Outer White Dwarf Companion." Astrophysical Journal Letters 927, no. 2 (March 1, 2022): L31. http://dx.doi.org/10.3847/2041-8213/ac5a55.

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Abstract We identify Gaia 0007–1605 A,C as the first inner brown dwarf–white dwarf binary of a hierarchical triple system in which the outer component is another white dwarf (Gaia 0007–1605 B). From optical/near-infrared spectroscopy obtained at the Very Large Telescope with the X-Shooter instrument and/or from Gaia photometry plus spectral energy distribution fitting, we determine the effective temperatures and masses of the two white dwarfs (12,018 ± 68 K and 0.54 ± 0.01 M ⊙ for Gaia 0007–1605 A and 4445 ± 116 K and 0.56 ± 0.05 M ⊙ for Gaia 0007–1605 B) and the effective temperature of the brown dwarf (1850 ± 50 K; corresponding to spectral type L3 ± 1). By analyzing the available TESS light curves of Gaia 0007–1605 A,C we detect a signal at 1.0446 ± 0.0015 days with an amplitude of 6.25 ppt, which we interpret as the orbital period modulated from irradiation effects of the white dwarf on the brown dwarf’s surface. This drives us to speculate that the inner binary evolved through a common-envelope phase in the past. Using the outer white dwarf as a cosmochronometer and analyzing the kinematic properties of the system, we conclude that the triple system is about 10 Gyr old.

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Clark, Catherine A., Gerard T. van Belle, Elliott P. Horch, Kaspar von Braun, David R. Ciardi, Jennifer G. Winters, and Rocio Kiman. "The POKEMON Speckle Survey of Nearby M Dwarfs. I. New Discoveries." Astronomical Journal 164, no. 2 (July 4, 2022): 33. http://dx.doi.org/10.3847/1538-3881/ac739c.

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Abstract M dwarfs are favorable targets for exoplanet detection with current instrumentation, but stellar companions can induce false positives and inhibit planet characterization. Knowledge of stellar companions is also critical to our understanding of how binary stars form and evolve. We have therefore conducted a survey of stellar companions around nearby M dwarfs, and here we present our new discoveries. Using the Differential Speckle Survey Instrument at the 4.3 m Lowell Discovery Telescope, and the similar NN-EXPLORE Exoplanet Stellar Speckle Imager at the 3.5 m WIYN telescope, we carried out a volume-limited survey of M-dwarf multiplicity to 15 parsecs, with a special emphasis on including the later M dwarfs that were overlooked in previous surveys. Additional brighter targets at larger distances were included for a total sample size of 1070 M dwarfs. Observations of these 1070 targets revealed 26 new companions; 22 of these systems were previously thought to be single. If all new discoveries are confirmed, then the number of known multiples in the sample will increase by 7.6%. Using our observed properties, as well as the parallaxes and 2MASS K magnitudes for these objects, we calculate the projected separation, and estimate the mass ratio and component spectral types, for these systems. We report the discovery of a new M-dwarf companion to the white dwarf Wolf 672 A, which hosts a known M-dwarf companion as well, making the system trinary. We also examine the possibility that the new companion to 2MASS J13092185-2330350 is a brown dwarf. Finally, we discuss initial insights from the POKEMON survey.

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Casewell, S. L., C. Belardi, S. G. Parsons, S. P. Littlefair, I. P. Braker, J. J. Hermes, J. Debes, et al. "WD1032 + 011, an inflated brown dwarf in an old eclipsing binary with a white dwarf." Monthly Notices of the Royal Astronomical Society 497, no. 3 (August 14, 2020): 3571–80. http://dx.doi.org/10.1093/mnras/staa1608.

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ABSTRACT We present the discovery of only the third brown dwarf known to eclipse a non-accreting white dwarf. Gaia parallax information and multicolour photometry confirm that the white dwarf is cool (9950 ± 150 K) and has a low mass (0.45 ± 0.05 M⊙), and spectra and light curves suggest the brown dwarf has a mass of 0.067 ± 0.006 M⊙ (70MJup) and a spectral type of L5 ± 1. The kinematics of the system show that the binary is likely to be a member of the thick disc and therefore at least 5-Gyr old. The high-cadence light curves show that the brown dwarf is inflated, making it the first brown dwarf in an eclipsing white dwarf-brown dwarf binary to be so.

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Malpas, Amber, Michael D. Albrow, Jennifer C. Yee, Andrew Gould, Andrzej Udalski, Antonio Herrera Martin, Charles A. Beichman, et al. "OGLE-2017-BLG-1038: A Possible Brown-dwarf Binary Revealed by Spitzer Microlensing Parallax." Astronomical Journal 164, no. 3 (August 18, 2022): 102. http://dx.doi.org/10.3847/1538-3881/ac7d4c.

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Abstract We report the analysis of microlensing event OGLE-2017-BLG-1038, observed by the Optical Gravitational Lensing Experiment, Korean Microlensing Telescope Network, and Spitzer telescopes. The event is caused by a giant source star in the Galactic Bulge passing over a large resonant binary-lens caustic. The availability of space-based data allows the full set of physical parameters to be calculated. However, there exists an eightfold degeneracy in the parallax measurement. The four best solutions correspond to very-low-mass binaries near ( M 1 = 170 − 50 + 40 M J and M 2 = 110 − 30 + 20 M J ), or well below ( M 1 = 22.5 − 0.4 + 0.7 M J and M 2 = 13.3 − 0.3 + 0.4 M J ) the boundary between stars and brown dwarfs. A conventional analysis, with scaled uncertainties for Spitzer data, implies a very-low-mass brown-dwarf binary lens at a distance of 2 kpc. Compensating for systematic Spitzer errors using a Gaussian process model suggests that a higher mass M-dwarf binary at 6 kpc is equally likely. A Bayesian comparison based on a galactic model favors the larger-mass solutions. We demonstrate how this degeneracy can be resolved within the next 10 years through infrared adaptive-optics imaging with a 40 m class telescope.

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Clark, Benjamin M., Cullen H. Blake, and Gillian R. Knapp. "THE CLOSE BINARY FRACTION OF DWARF M STARS." Astrophysical Journal 744, no. 2 (December 20, 2011): 119. http://dx.doi.org/10.1088/0004-637x/744/2/119.

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Acton, Jack S., Michael R. Goad, Sarah L. Casewell, Jose I. Vines, Matthew R. Burleigh, Philipp Eigmüller, Louise D. Nielsen, et al. "An eclipsing M-dwarf close to the hydrogen burning limit from NGTS." Monthly Notices of the Royal Astronomical Society 498, no. 3 (August 20, 2020): 3115–24. http://dx.doi.org/10.1093/mnras/staa2513.

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ABSTRACT We present the discovery of NGTS J0930−18, an extreme mass ratio eclipsing M-dwarf binary system with an early M-dwarf primary and a late M-dwarf secondary close to the hydrogen burning limit. Global modelling of photometry and radial velocities reveals that the secondary component (NGTS J0930−18 B) has a mass of M* = $0.0818 ^{+0.0040}_{-0.0015}$ M⊙ and radius of R* = $0.1059 ^{+0.0023}_{-0.0021}$ R⊙, making it one of the lowest mass stars with direct mass and radius measurements. With a mass ratio of q = $0.1407 ^{+0.0065}_{-0.017}$, NGTS J0930−18 has the lowest mass ratio of any known eclipsing M-dwarf binary system, posing interesting questions for binary star formation and evolution models. The mass and radius of NGTS J0930−18 B is broadly consistent with stellar evolutionary models. NGTS J0930−18 B lies in the sparsely populated mass radius parameter space close to the substellar boundary. Precise measurements of masses and radii from single lined eclipsing binary systems of this type are vital for constraining the uncertainty in the mass–radius relationship – of importance due to the growing number of terrestrial planets being discovered around low-mass stars.

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Hutchings, J. B., D. Crampton, A. P. Cowley, P. C. Schmidtke, T. K. McGrath, and Y. H. Chu. "An X-Ray Selected White Dwarf + M Dwarf Binary: RX J0458.9-6628." Publications of the Astronomical Society of the Pacific 107 (October 1995): 931. http://dx.doi.org/10.1086/133641.

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McCleery, Jack, Pier-Emmanuel Tremblay, Nicola Pietro Gentile Fusillo, Mark A. Hollands, Boris T. Gänsicke, Paula Izquierdo, Silvia Toonen, Tim Cunningham, and Alberto Rebassa-Mansergas. "Gaia white dwarfs within 40 pc II: the volume-limited Northern hemisphere sample." Monthly Notices of the Royal Astronomical Society 499, no. 2 (July 13, 2020): 1890–908. http://dx.doi.org/10.1093/mnras/staa2030.

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ABSTRACT We present an overview of the sample of Northern hemisphere white dwarfs within 40 pc of the Sun detected from Gaia Data Release 2 (DR2). We find that 521 sources are spectroscopically confirmed degenerate stars, 111 of which were first identified as white dwarf candidates from Gaia DR2 and followed up recently with the William Herschel Telescope and Gran Telescopio Canarias. Three additional white dwarf candidates remain spectroscopically unobserved and six unresolved binaries are known to include a white dwarf but were not in our initial selection in the Gaia DR2 Hertzsprung–Russell diagram. Atmospheric parameters are calculated from Gaia and Pan-STARRS photometry for all objects in the sample, confirming most of the trends previously observed in the much smaller 20 pc sample. Local white dwarfs are overwhelmingly consistent with Galactic disc kinematics, with only four halo candidates. We find that DAZ white dwarfs are significantly less massive than the overall DA population ($\overline{M}_\mathrm{DAZ}$ = 0.59 M⊙, $\overline{M}_\mathrm{DA}$ = 0.66 M⊙). It may suggest that planet formation is less efficient at higher mass stars, producing more massive white dwarfs. We detect a sequence of crystallized white dwarfs in the mass range from 0.6 $\lesssim M/\mbox{$\mathrm{M}_\odot $}\ \lesssim$ 1.0 and find that the vast majority of objects on the sequence have standard kinematic properties that correspond to the average of the sample, suggesting that their nature can be explained by crystallization alone. We also detect 26 double degenerates and white dwarf components in 56 wide binary systems.

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Shipman, Harry L., and Jeanne Geczi. "An Unsuccessful Search for White Dwarf Companions to Nearby Main Sequence Stars." International Astronomical Union Colloquium 114 (1989): 134–37. http://dx.doi.org/10.1017/s0252921100099437.

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AbstractMany of the nearest white dwarf stars (e.g., Sirius B and Procyon B) are in such binaries and would have remained undiscovered if they were even a little bit further away. White dwarfs which are sufficiently hot (T(eff) > 10,000 K) would, if present in binary systems with a relatively cool (F, G, K, or M) main–sequence secondary, be visible in IUE images as a hot companion to the main sequence star. We systematically examined 318 IUE images of 280 different G, K, and M stars which had been observed for other purposes. No previously undiscovered white dwarf stars were found.

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Shaw, A. W., C. O. Heinke, K. Mukai, J. A. Tomsick, V. Doroshenko, V. F. Suleimanov, D. J. K. Buisson, et al. "Measuring the masses of magnetic white dwarfs: a NuSTAR legacy survey." Monthly Notices of the Royal Astronomical Society 498, no. 3 (August 26, 2020): 3457–69. http://dx.doi.org/10.1093/mnras/staa2592.

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ABSTRACT The hard X-ray spectrum of magnetic cataclysmic variables can be modelled to provide a measurement of white dwarf mass. This method is complementary to radial velocity measurements, which depend on the (typically rather uncertain) binary inclination. Here, we present results from a Legacy Survey of 19 magnetic cataclysmic variables with NuSTAR. We fit accretion column models to their 20–78 keV spectra and derive the white dwarf masses, finding a weighted average $\bar{M}_{\rm WD}=0.77\pm 0.02$ M⊙, with a standard deviation σ = 0.10 M⊙, when we include the masses derived from previous NuSTAR observations of seven additional magnetic cataclysmic variables. We find that the mass distribution of accreting magnetic white dwarfs is consistent with that of white dwarfs in non-magnetic cataclysmic variables. Both peak at a higher mass than the distributions of isolated white dwarfs and post-common-envelope binaries. We speculate as to why this might be the case, proposing that consequential angular momentum losses may play a role in accreting magnetic white dwarfs and/or that our knowledge of how the white dwarf mass changes over accretion–nova cycles may also be incomplete.

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van den Besselaar, E. J. M., R. Greimel, L. Morales-Rueda, G. Nelemans, J. R. Thorstensen, T. R. Marsh, V. S. Dhillon, et al. "DE CVn: A Bright, Eclipsing Red Dwarf – White Dwarf Binary." Proceedings of the International Astronomical Union 2, S240 (August 2006): 105–8. http://dx.doi.org/10.1017/s1743921307003882.

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AbstractDE CVn is a relatively unstudied eclipsing binary where one of the components is an M dwarf and the other is a white dwarf. Its brightness makes it an ideal system for a detailed study in the context of common-envelope evolution of a detached white dwarf – red dwarf binary with a relatively short orbital period (∼8.7 hours). We present a detailed study of the basic parameters (e.g. orbital period, components' masses and spectral types) for this system from photometric and spectroscopic studies. The eclipses observed during several photometric observing runs were used to derive the ephemeris. We have used spectroscopic data to derive the radial velocity variations of the emission lines and these are used to determine the components' masses and the orbital separation. The secondary component in DE CVn is an M3 main-sequence star and the primary star, which only contributes to the blue continuum, is a cool white dwarf with a temperature of ∼8000 K. From the photometry and spectroscopy together, we have set a limit on the binary inclination. This system is a post-common-envelope system where the progenitor of the present day white dwarf was a low-mass star (M≤2M⊙). The time before DE CVn becomes a semi-detached system is longer than the Hubble time.

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Acton, Jack S., Michael R. Goad, Liam Raynard, Sarah L. Casewell, James A. G. Jackman, Richard D. Alexander, David R. Anderson, et al. "NGTS J214358.5−380102 – NGTS discovery of the most eccentric known eclipsing M-dwarf binary system." Monthly Notices of the Royal Astronomical Society 494, no. 3 (April 8, 2020): 3950–61. http://dx.doi.org/10.1093/mnras/staa928.

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ABSTRACT We present the discovery of NGTS J214358.5–380102, an eccentric M-dwarf binary discovered by the Next-Generation Transit Survey (NGTS). The system period of 7.618 d is greater than many known eclipsing M-dwarf binary systems. Its orbital eccentricity of $0.323^{+0.0014}_{-0.0037}$ is large relative to the period and semimajor axis of the binary. Global modelling of photometry and radial velocities indicates stellar masses of MA = $0.426 ^{+0.0056}_{-0.0049}$ M⊙, MB = $0.455 ^{+0.0058}_{-0.0052}$ M⊙ and stellar radii RA = $0.461 ^{+0.038}_{-0.025}$ R⊙, RB = $0.411 ^{+0.027}_{-0.039}$ R⊙, respectively. Comparisons with stellar models for low-mass stars show that one star is consistent with model predictions whereas the other is substantially oversized. Spectral analysis of the system suggests a primary of spectral type M3V, consistent with both modelled masses and radii, and with spectral energy distribution fitting of NGTS photometry. As the most eccentric eclipsing M-dwarf binary known, NGTS J214358.5–380102 provides an interesting insight into the strength of tidal effects in the circularization of stellar orbits.

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Mayor, M., S. Udry, J. L. Halbwachs, and F. Arenou. "Binaries at the Bottom of the Main Sequence and below." Symposium - International Astronomical Union 200 (2001): 45–54. http://dx.doi.org/10.1017/s0074180900225047.

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Long-term radial-velocity surveys of G, K and M dwarfs of the solar neighbourhood are presented. The inferred orbital elements are discussed, focusing on the (e, log P) diagram, the mass-ratio and secondary mass distributions, and on the binary frequency of the studied samples. The proportion of companions to M dwarfs is found to be not significantly different from the binary frequency among G- and K-dwarf primaries. The mass function of stellar and planetary companions to solar-type stars strongly suggests different formation and evolution mechanisms for the two populations. Finally, beautiful mass-luminosity relations are obtained from low-mass binaries with high-precision radial-velocity measurements and adaptive optics visual data.

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Harlow, Jason J. B. "The M Dwarf Double-Lined Spectrscopic Binary Gliese 372." Astronomical Journal 112 (November 1996): 2222. http://dx.doi.org/10.1086/118174.

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Tomkin, Jocelyn, and Bjorn R. Pettersen. "The M dwarf double-lined spectroscopic binary Gliese 268." Astronomical Journal 92 (December 1986): 1424. http://dx.doi.org/10.1086/114278.

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Street, R. A., E. Bachelet, Y. Tsapras, M. P. G. Hundertmark, V. Bozza, M. Dominik, D. M. Bramich, et al. "OGLE-2018-BLG-0022: A Nearby M-dwarf Binary." Astronomical Journal 157, no. 6 (May 7, 2019): 215. http://dx.doi.org/10.3847/1538-3881/ab1538.

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Hsu, Chih-Chun, Adam J. Burgasser, Christopher A. Theissen, Christopher R. Gelino, Jessica L. Birky, Sharon J. M. Diamant, Daniella C. Bardalez Gagliuffi, Christian Aganze, Cullen H. Blake, and Jacqueline K. Faherty. "The Brown Dwarf Kinematics Project (BDKP). V. Radial and Rotational Velocities of T Dwarfs from Keck/NIRSPEC High-resolution Spectroscopy." Astrophysical Journal Supplement Series 257, no. 2 (November 29, 2021): 45. http://dx.doi.org/10.3847/1538-4365/ac1c7d.

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Abstract We report multiepoch radial velocities, rotational velocities, and atmospheric parameters for 37 T-type brown dwarfs observed with Keck/NIRSPEC. Using a Markov Chain Monte Carlo forward-modeling method, we achieve median precisions of 0.5 and 0.9 km s−1 for radial and rotational velocities, respectively. All of the T dwarfs in our sample are thin-disk brown dwarfs. We confirm previously reported moving group associations for four T dwarfs. However, the lack of spectral indicators of youth in two of these sources suggests that these are chance alignments. We confirm two previously unresolved binary candidates, the T0+T4.5 2MASS J11061197+2754225 and the L7+T3.5 2MASS J21265916+7617440, with orbital periods of 4 and 12 yr, respectively. We find a kinematic age of 3.5 ± 0.3 Gyr for local T dwarfs, consistent with nearby late M dwarfs (4.1 ± 0.3 Gyr). Removal of thick-disk L dwarfs in the local ultracool dwarf sample gives a similar age for L dwarfs (4.2 ± 0.3 Gyr), largely resolving the local L dwarf age anomaly. The kinematic ages of local late M, L, and T dwarfs can be accurately reproduced with population simulations incorporating standard assumptions of the mass function, star formation rate, and brown dwarf evolutionary models. A kinematic dispersion break is found at the L4–L6 subtypes, likely reflecting the terminus of the stellar main sequence. We provide a compilation of precise radial velocities for 172 late M, L, and T dwarfs within ∼20 pc of the Sun.

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Bonavita, M., V. D’Orazi, D. Mesa, C. Fontanive, S. Desidera, S. Messina, S. Daemgen, et al. "Orbiting a binary." Astronomy & Astrophysics 608 (December 2017): A106. http://dx.doi.org/10.1051/0004-6361/201731003.

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Aims. In this paper we present the results of the SPHERE observation of the HD 284149 system, aimed at a more detailed characterisation of both the primary and its brown dwarf companion. Methods. We observed HD 284149 in the near-infrared with SPHERE, using the imaging mode (IRDIS+IFS) and the long-slit spectroscopy mode (IRDIS-LSS). The data were reduced using the dedicated SPHERE pipeline, and algorithms such as PCA and TLOCI were applied to reduce the speckle pattern. Results. The IFS images revealed a previously unknown low-mass (~0.16 M⊙) stellar companion (HD 294149 B) at ~0.1′′, compatible with previously observed radial velocity differences, as well as proper motion differences between Gaia and Tycho-2 measurements. The known brown dwarf companion (HD 284149 b) is clearly visible in the IRDIS images. This allowed us to refine both its photometry and astrometry. The analysis of the medium resolution IRDIS long slit spectra also allowed a refinement of temperature and spectral type estimates. A full reassessment of the age and distance of the system was also performed, leading to more precise values of both mass and semi-major axis. Conclusions. As a result of this study, HD 284149 ABb therefore becomes the latest addition to the (short) list of brown dwarfs on wide circumbinary orbits, providing new evidence to support recent claims that object in such configuration occur with a similar frequency to wide companions to single stars.

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Kilic, Mukremin, P. Bergeron, Simon Blouin, and A. Bédard. "The most massive white dwarfs in the solar neighbourhood." Monthly Notices of the Royal Astronomical Society 503, no. 4 (March 16, 2021): 5397–408. http://dx.doi.org/10.1093/mnras/stab767.

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ABSTRACT We present an analysis of the most massive white dwarf candidates in the Montreal White Dwarf Database 100 pc sample. We identify 25 objects that would be more massive than $1.3\, {\rm M}_{\odot }$ if they had pure H atmospheres and CO cores, including two outliers with unusually high photometric mass estimates near the Chandrasekhar limit. We provide follow-up spectroscopy of these two white dwarfs and show that they are indeed significantly below this limit. We expand our model calculations for CO core white dwarfs up to M = 1.334 M⊙, which corresponds to the high-density limit of our equation-of-state tables, ρ = 109 g cm−3. We find many objects close to this maximum mass of our CO core models. A significant fraction of ultramassive white dwarfs are predicted to form through binary mergers. Merger populations can reveal themselves through their kinematics, magnetism, or rapid rotation rates. We identify four outliers in transverse velocity, four likely magnetic white dwarfs (one of which is also an outlier in transverse velocity), and one with rapid rotation, indicating that at least 8 of the 25 ultramassive white dwarfs in our sample are likely merger products.

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Lang, Kenneth R. "Radio Evidence for Nonthermal Particle Acceleration on Stars of Late Spectral Type." International Astronomical Union Colloquium 142 (1994): 753–64. http://dx.doi.org/10.1017/s0252921100078064.

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AbstractRadio evidence for nonthermal particle acceleration on stars of late spectral type (G, K, and M) is reviewed, including the pre-main-sequence T Tauri stars, the dwarf M flare stars, and the RS CVn binary stars. Both the long-lasting radio emission and the transient radio flares can be attributed to nonthermal electrons accelerated in magnetically confined coronae, radiating by either incoherent gyrosynchrotron radiation or by coherent processes. Related observations of the Sun provide the framework for interpreting the radio emission of late-type stars. We review recent VLBI observations of single and binary stars, observations of rapid acceleration and dynamic spectra of dwarf M flare stars, and models for long-lasting radio emission from dwarf M flare stars and RS CVn stars. The VLBI data provide evidence for nonthermal particle acceleration in large-scale magneto-spheres several times larger than the stellar radius for T Tauri and RS CVn stars. In contrast, rapid radio flares on dwarf M stars require sources much smaller than the visible star in size, and this is consistent with the VLBI data.Dynamic spectra suggest particle acceleration by relativistic electron beams on dwarf M stars. The long-lived radio radiation of dwarf M stars and RS CVn stars requires more-or-less continuous particle acceleration over periods of hours, perhaps by persistent low-amplitude flaring.Subject headings: acceleration of particles — binaries: close — radio continuum: stars — stars: flare — stars: late-type — stars: pre-main-sequence

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Marsh, T. R., and S. R. Duck. "A detached white dwarf/M dwarf binary with an orbital period of 2.47 h." Monthly Notices of the Royal Astronomical Society 278, no. 2 (January 11, 1996): 565–76. http://dx.doi.org/10.1093/mnras/278.2.565.

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Pass, Emily K., David Charbonneau, Jonathan M. Irwin, and Jennifer G. Winters. "Constraints on the Spindown of Fully Convective M Dwarfs Using Wide Field Binaries." Astrophysical Journal 936, no. 2 (September 1, 2022): 109. http://dx.doi.org/10.3847/1538-4357/ac7da8.

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Abstract M dwarfs remain active over longer timescales than their Sunlike counterparts, with potentially devastating implications for the atmospheres of their planets. However, the age at which fully convective M dwarfs transition from active and rapidly rotating to quiescent and slowly rotating is poorly understood, as these stars remain rapidly rotating in the oldest clusters that are near enough for a large sample of low-mass M dwarfs to be studied. To constrain the spindown of these low-mass stars, we measure photometric rotation periods for field M dwarfs in wide binary systems, primarily using the Transiting Exoplanet Survey Satellite and MEarth. Our analysis includes M–M pairs, which are coeval but of unknown age, as well as M dwarfs with white dwarf or Sunlike primaries, for which we can estimate ages using techniques like white-dwarf cooling curves, gyrochronology, and lithium abundance. We find that the epoch of spindown is strongly dependent on mass. Fully convective M dwarfs initially spin down slowly, with the population of 0.2–0.3 M ⊙ rapid rotators evolving from P rot < 2 days at 600 Myr to 2 < P rot < 10 days at 1–3 Gyr before rapidly spinning down to long rotation periods at older ages. However, we also identify some variability in the spindown of fully convective M dwarfs, with a small number of stars having substantially spun down by 600 Myr. These observations are consistent with models of magnetic morphology-driven spindown, where angular momentum loss is initially inefficient until changes in the magnetic field allow spindown to progress rapidly.

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Lee (李見修), Chien-Hsiu. "A Double-line M-dwarf Eclipsing Binary from CSS × SDSS." Astronomical Journal 153, no. 3 (February 21, 2017): 118. http://dx.doi.org/10.3847/1538-3881/153/3/118.

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Kochukhov, Oleg, and Denis Shulyak. "Magnetic Field of the Eclipsing M-dwarf Binary YY Gem." Astrophysical Journal 873, no. 1 (March 6, 2019): 69. http://dx.doi.org/10.3847/1538-4357/ab06c5.

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Davenport, James R. A., Andrew C. Becker, Andrew A. West, John J. Bochanski, Suzanne L. Hawley, Jon Holtzman, Heather C. Gunning, Eric J. Hilton, Ferah A. Munshi, and Meagan Albright. "THE VERY SHORT PERIOD M DWARF BINARY SDSS J001641–000925." Astrophysical Journal 764, no. 1 (January 28, 2013): 62. http://dx.doi.org/10.1088/0004-637x/764/1/62.

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Hussain, G. A. J., N. S. Brickhouse, A. K. Dupree, F. Reale, F. Favata, and M. M. Jardine. "Chandra study of the eclipsing M dwarf binary, YY Gem." Monthly Notices of the Royal Astronomical Society 423, no. 1 (May 1, 2012): 493–504. http://dx.doi.org/10.1111/j.1365-2966.2012.20894.x.

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Kasper, M., B. A. Biller, A. Burrows, W. Brandner, J. Budaj, and L. M. Close. "The very nearby M/T dwarf binary SCR 1845-6357." Astronomy & Astrophysics 471, no. 2 (June 26, 2007): 655–59. http://dx.doi.org/10.1051/0004-6361:20077881.

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Butler, C. J., N. Erkan, E. Budding, J. G. Doyle, B. Foing, G. E. Bromage, B. J. Kellett, et al. "A multiwavelength study of the M dwarf binary YY Geminorum." Monthly Notices of the Royal Astronomical Society 446, no. 4 (December 11, 2014): 4205–19. http://dx.doi.org/10.1093/mnras/stu2398.

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Dame, Kyra, Claudia Belardi, Mukremin Kilic, Armin Rest, A. Gianninas, Sara Barber, and Warren R. Brown. "The DECam minute cadence survey – II. 49 variables but no planetary transits of a white dwarf." Monthly Notices of the Royal Astronomical Society 490, no. 1 (February 13, 2019): 1066–75. http://dx.doi.org/10.1093/mnras/stz398.

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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.

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Burgasser, Adam J., Saurav Dhital, and Andrew A. West. "RESOLVED SPECTROSCOPY OF M DWARF/L DWARF BINARIES. III. THE “WIDE” L3.5/L4 DWARF BINARY 2MASS J15500845+1455180AB." Astronomical Journal 138, no. 6 (October 23, 2009): 1563–69. http://dx.doi.org/10.1088/0004-6256/138/6/1563.

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Singh, K. K., P. J. Meintjes, and K. K. Yadav. "Properties of white dwarf in the binary system AR Scorpii and its observed features." Modern Physics Letters A 36, no. 13 (April 26, 2021): 2150096. http://dx.doi.org/10.1142/s0217732321500966.

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The binary system AR Scorpii hosts an M-type main sequence cool star orbiting around a magnetic white dwarf in the Milky Way Galaxy. The broadband non-thermal emission over radio, optical and X-ray wavebands observed from AR Scorpii indicates strong modulations on the spin frequency of the white dwarf as well as the spin-orbit beat frequency of the system. Therefore, AR Scorpii is also referred to as a white dwarf pulsar wherein a fast spinning white dwarf star plays very crucial role in the broadband non-thermal emission. Several interpretations for the observed features of AR Scorpii appear in the literature without firm conclusions. In this paper, we investigate connection between some of the important physical properties like spin-down power, surface magnetic field, equation of state, temperature and gravity associated with the white dwarf in the binary system AR Scorpii and its observational characteristics. We explore the plausible effects of white dwarf surface magnetic field on the absence of substantial accretion in this binary system and also discuss the gravitational wave emission due to magnetic deformation mechanism.

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E. Potter, Daniel, Eduardo L. Martín, and Michael C. Cushing. "A Search for Brown Dwarfs around Young Solar-Analog Stars Using the Hōkūpa'a/Gemini Adaptive Optics System." Symposium - International Astronomical Union 211 (2003): 265–68. http://dx.doi.org/10.1017/s007418090021070x.

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We present the results of a search for low-mass companions around a sample of young, solar-analog stars using the Hōkūpa'a adaptive optics instrument mounted on the Gemini North 8 m telescope. Out of 31 stars observed, one binary brown dwarf system was found as a companion to the star HD 130948 (HIP 72567), as confirmed by proper motion and near-IR spectra. Orbital motion between the two brown dwarfs was measured, but our 14 month time baseline is inadequate to accurately measure the system's dynamical mass. Upcoming spectroscopic observations of the brown dwarfs will measure their lithium absorption lines to provide a more accurate age estimate of the system. The eventual dynamical mass determination coupled with the age determination will provide a valuable check of brown dwarf evolutionary models.

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Souto, Diogo, Katia Cunha, Verne V. Smith, C. Allende Prieto, Kevin Covey, D. A. García-Hernández, Jon A. Holtzman, et al. "Detailed Chemical Abundances for a Benchmark Sample of M Dwarfs from the APOGEE Survey." Astrophysical Journal 927, no. 1 (March 1, 2022): 123. http://dx.doi.org/10.3847/1538-4357/ac4891.

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Abstract Individual chemical abundances for 14 elements (C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni) are derived for a sample of M dwarfs using high-resolution, near-infrared H-band spectra from the Sloan Digital Sky Survey-IV/Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The quantitative analysis included synthetic spectra computed with 1D LTE plane-parallel MARCS models using the APOGEE Data Release 17 line list to determine chemical abundances. The sample consists of 11 M dwarfs in binary systems with warmer FGK dwarf primaries and 10 measured interferometric angular diameters. To minimize atomic diffusion effects, [X/Fe] ratios are used to compare M dwarfs in binary systems and literature results for their warmer primary stars, indicating good agreement (<0.08 dex) for all studied elements. The mean abundance difference in primaries minus this work’s M dwarfs is −0.05 ± 0.03 dex. It indicates that M dwarfs in binary systems are a reliable way to calibrate empirical relationships. A comparison with abundance, effective temperature, and surface gravity results from the APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) Data Release 16 finds a systematic offset of [M/H], T eff, log g = +0.21 dex, −50 K, and 0.30 dex, respectively, although ASPCAP [X/Fe] ratios are generally consistent with this study. The metallicities of the M dwarfs cover the range of [Fe/H] = −0.9 to +0.4 and are used to investigate Galactic chemical evolution via trends of [X/Fe] as a function of [Fe/H]. The behavior of the various elemental abundances [X/Fe] versus [Fe/H] agrees well with the corresponding trends derived from warmer FGK dwarfs, demonstrating that the APOGEE spectra can be used to examine Galactic chemical evolution using large samples of selected M dwarfs.

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Xu, Hu-Shan, Li-Ying Zhu, Sarotsakulchai Thawicharat, Soonthornthum Boonrucksar, and Liang Liu. "Red dwarf contact binary V0627 Hydrae." Publications of the Astronomical Society of Japan 74, no. 2 (February 17, 2022): 326–33. http://dx.doi.org/10.1093/pasj/psab128.

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Abstract New complete light curves in B, V, RC, and IC bands for the short-period eclipsing binary V0627 Hya (period shorter than 0.22 d) are presented. From the longer wavelength to the shorter one, the amplitudes of the light variation become larger. The different height of the successive maxima in each band’s light curve could be seen clearly. We analyzed those multi-wavelength light curves using the Wilson–Devinney code and derived the photometric solutions of V0627 Hya for the first time. It is found that V0627 Hya is a W-type shallow-contact binary. Combined with the GAIA parallax, the absolute parameters of this system are obtained: M1 = 0.31 M⊙, M2 = 0.64 M⊙, R1 = 0.50 R⊙, R2 = 0.69 R⊙, L1 = 0.06 L⊙, L2 = 0.08 L⊙. Thus, V0627 Hya is a new member of the red dwarf contact binary class. The asymmetry in the light curves could be explained by the spot model due to the magnetic activity of its late-type component. The amplitude differences in the different bands’ light curves imply the existence of a cool third body, which is supported by the third light contribution in the photometric solutions. The third body in this system may play an important role in its formation and evolution by removing the angular momentum. More red dwarf contact binaries need to be found and studied, since they are rare and not enough is known to reveal their mysteries at present.

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Baroch, D., J. C. Morales, I. Ribas, L. Tal-Or, M. Zechmeister, A. Reiners, J. A. Caballero, et al. "The CARMENES search for exoplanets around M dwarfs." Astronomy & Astrophysics 619 (November 2018): A32. http://dx.doi.org/10.1051/0004-6361/201833440.

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Context. The CARMENES spectrograph is surveying ∼300 M dwarf stars in search for exoplanets. Among the target stars, spectroscopic binary systems have been discovered, which can be used to measure fundamental properties of stars. Aims. Using spectroscopic observations, we determine the orbital and physical properties of nine new double-line spectroscopic binary systems by analysing their radial velocity curves. Methods. We use two-dimensional cross-correlation techniques to derive the radial velocities of the targets, which are then employed to determine the orbital properties. Photometric data from the literature are also analysed to search for possible eclipses and to measure stellar variability, which can yield rotation periods. Results. Out of the 342 stars selected for the CARMENES survey, 9 have been found to be double-line spectroscopic binaries, with periods ranging from 1.13 to ∼8000 days and orbits with eccentricities up to 0.54. We provide empirical orbital properties and minimum masses for the sample of spectroscopic binaries. Absolute masses are also estimated from mass-luminosity calibrations, ranging between ∼0.1 and ∼0.6 M⊙. Conclusions. These new binary systems increase the number of double-line M dwarf binary systems with known orbital parameters by 15%, and they have lower mass ratios on average.

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Kuszlewicz, James S., Thomas S. H. North, William J. Chaplin, Allyson Bieryla, David W. Latham, Andrea Miglio, Keaton J. Bell, et al. "KOI-3890: a high-mass-ratio asteroseismic red giant+M-dwarf eclipsing binary undergoing heartbeat tidal interactions." Monthly Notices of the Royal Astronomical Society 487, no. 1 (May 2, 2019): 14–23. http://dx.doi.org/10.1093/mnras/stz1185.

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Abstract KOI-3890 is a highly eccentric, 153-d period eclipsing, single-lined spectroscopic binary system containing a red giant star showing solar-like oscillations alongside tidal interactions. The combination of transit photometry, radial velocity observations, and asteroseismology has enabled the detailed characterization of both the red giant primary and the M-dwarf companion, along with the tidal interaction and the geometry of the system. The stellar parameters of the red giant primary are determined through the use of asteroseismology and grid-based modelling to give a mass and radius of $M_{\star }=1.04\pm 0.06 \, \textrm{M}_{\odot }$ and $R_{\star }=5.8\pm 0.2 \, \textrm{R}_{\odot }$, respectively. When combined with transit photometry, the M-dwarf companion is found to have a mass and radius of $M_{\mathrm{c}}=0.23\pm 0.01 \, \textrm{M}_{\odot }$ and $R_{\mathrm{c}}=0.256\pm 0.007 \, \textrm{R}_{\odot }$. Moreover, through asteroseismology we constrain the age of the system through the red giant primary to be $9.1^{+2.4}_{-1.7}\,\mathrm{Gyr}$. This provides a constraint on the age of the M-dwarf secondary, which is difficult to do for other M-dwarf binary systems. In addition, the asteroseismic analysis yields an estimate of the inclination angle of the rotation axis of the red giant star of $i=87.6^{+2.4}_{-1.2}$ degrees. The obliquity of the system – the angle between the stellar rotation axis and the angle normal to the orbital plane – is also derived to give $\psi =4.2^{+2.1}_{-4.2}$ degrees, showing that the system is consistent with alignment. We observe no radius inflation in the M-dwarf companion when compared to current low-mass stellar models.

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Quiroga-Nuñez, L. H., H. T. Intema, J. R. Callingham, J. Villadsen, H. J. van Langevelde, P. Jagannathan, T. W. Shimwell, and E. P. Boven. "Differences in radio emission from similar M dwarfs in the binary system Ross 867-8." Astronomy & Astrophysics 633 (January 2020): A130. http://dx.doi.org/10.1051/0004-6361/201936491.

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Serendipitously, we rediscovered radio emission from the binary system Ross 867 (M4.5V) and Ross 868 (M3.5V) while inspecting archival Giant Metrewave Radio Telescope (GMRT) observations. The binary system consists of two M-dwarf stars that share common characteristics such as spectral type, astrometric parameters, age, and emission at infrared, optical, and X-ray frequencies. The GMRT data at 610 MHz taken on July 2011 shows that the radio emission from Ross 867 is polarized and highly variable on hour timescales with a peak flux of 10.4 ± 0.7 mJy beam−1. Additionally, after reviewing archival data from several observatories (VLA, GMRT, JVLA, and LOFAR), we confirm that although the two stars are likely coeval, only Ross 867 was detected, while Ross 868 remains undetected at radio wavelengths. As the stars have a large orbital separation, this binary stellar system provides a coeval laboratory to examine and constrain the stellar properties linked to radio activity in M dwarfs. We speculate that the observed difference in radio activity between the dwarfs could be due to vastly different magnetic field topologies or that Ross 867 has an intrinsically different dynamo.

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Tout, Christopher A. "White Dwarf Remnants of Binary Star Evolution." Proceedings of the International Astronomical Union 7, S281 (July 2011): 44–51. http://dx.doi.org/10.1017/s1743921312014676.

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AbstractWhite dwarfs grow as the cores of red giants and, in particular, carbon-oxygen white dwarfs grow in asymptotic giant branch (AGB) stars. The evolution of an AGB star is a competition between growth of the core and loss of the stellar envelope, typically in a wind. It is complicated by thermal pulses driven periodically by unstable helium shell burning. Dredge up following such pulses delays core growth. The compression at the center of a cold carbon-oxygen core means that carbon ignites when it reaches a mass of 1.38 M⊙. This begins the familiar thermonuclear runaway of the Type Ia supernova (SN Ia). At higher temperatures carbon can ignite more gently and burn mostly to neon to leave a core rich in oxygen, neon and magnesium. Such cores can go on to collapse to neutron stars with a release of only neutrinos. Accepted mass-loss prescriptions for giants mean that the range of masses of single stars that leave carbon-oxygen white dwarfs is somewhere from around 1 to 8 M⊙. We investigate how unusual mass loss, perhaps brought about by interaction with a binary companion, can radically alter the single star picture. Though population syntheses treat some possibilities with various prescriptions, there is sufficient doubt over the physics, the observations, and the implementation of mass loss and binary interaction that there is scope for several more unusual progenitors of carbon-oxygen white dwarfs and hence SNe Ia.

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Laithwaite, R. C., and S. J. Warren. "The absolute magnitudes MJ, the binary fraction, and the binary mass ratios of M7–M9.5 dwarfs." Monthly Notices of the Royal Astronomical Society 499, no. 2 (October 6, 2020): 2587–97. http://dx.doi.org/10.1093/mnras/staa2979.

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ABSTRACT We use the large homogeneous sample of late M dwarfs, M7–M9.5, of Ahmed & Warren (2019) matched to Gaia DR2, to measure the relation between absolute magnitude and spectral type, and to infer the multiplicity fraction of the population, and the distribution of mass ratios in the binary systems. Binaries are identified photometrically as overluminous sources. In order to define a sample that is unbiased with respect to multiplicity we use distance limits that are a function of G − J colour to define a volume-complete sample of 2706 systems. The G − J colours are very precise, with random errors all less than 0.02. We measure absolute magnitudes MJ that are on average 0.5 mag brighter than previous determinations. We find evidence that the discrepancies arise from differences in spectral types in different samples. The measured binary fraction is $16.5\pm 0.8{{\ \rm per\ cent}}$, of which $98{{\ \rm per\ cent}}$ are unresolved: both values are consistent with results of previous studies. The distribution of excess flux in the binaries, compared to the singles, is used to infer the mass ratio distribution f(q)∝qγ, where q = Ms/Mp. We infer a very steep distribution over this spectral range, with γ > 10 ($99{{\ \rm per\ cent}}$ probability). This says that unresolved ultracool M dwarf binaries reside almost exclusively in equal mass systems, and implies that the spectral types of the unresolved binaries match to with 0.5 spectral subtypes. The intrinsic scatter in absolute magnitude MJ for ultracool M dwarfs at fixed G − J colour is measured to be 0.21 mag.

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Soethe, L. T. T., and S. O. Kepler. "Convection and rotation boosted prescription of magnetic braking: application to the formation of extremely low-mass white dwarfs." Monthly Notices of the Royal Astronomical Society 506, no. 3 (July 9, 2021): 3266–81. http://dx.doi.org/10.1093/mnras/stab1916.

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ABSTRACT Extremely low-mass white dwarfs (ELM WDs) are the result of binary evolution in which a low-mass donor star is stripped by its companion leaving behind a helium-core white dwarf (WD). We explore the formation of ELM WDs in binary systems considering the Convection And Rotation Boosted magnetic braking treatment. Our evolutionary sequences were calculated using the Modules for Experiments in Stellar Astrophysics code, with initial masses of 1.0 and 1.2 M⊙ (donor), and 1.4 (accretor), compatible with low-mass X-ray binary (LMXB) systems. We obtain ELM models in the range 0.15–0.27 M⊙ from a broad range of initial orbital periods, 1–25 d. The bifurcation period, where the initial period is equal to the final period, ranges from 20 to 25 d. In addition to LMXBs, we show that ultracompact X-ray binaries (UCXBs) and wide-orbit binary millisecond pulsars can also be formed. The relation between mass and orbital period obtained is compatible with the observational data from He WD companions to pulsars.

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Stamatellos, Dimitris, and Anthony Whitworth. "The formation of brown dwarfs in discs: Physics, numerics, and observations." Proceedings of the International Astronomical Union 6, S270 (May 2010): 223–26. http://dx.doi.org/10.1017/s174392131100041x.

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AbstractA large fraction of brown dwarfs and low-mass stars may form by gravitational fragmentation of relatively massive (a few 0.1 M⊙) and extended (a few hundred AU) discs around Sun-like stars. We present an ensemble of radiative hydrodynamic simulations that examine the conditions for disc fragmentation. We demonstrate that this model can explain the low-mass IMF, the brown dwarf desert, and the binary properties of low-mass stars and brown dwarfs. Observing discs that are undergoing fragmentation is possible but very improbable, as the process of disc fragmentation is short lived (discs fragment within a few thousand years).

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Barry, R. K., B. O. Demory, D. Ségransan, T. Forveille, W. C. Danchi, E. Di Folco, D. Queloz, et al. "A PRECISE PHYSICAL ORBIT FOR THE M-DWARF BINARY GLIESE 268." Astrophysical Journal 760, no. 1 (November 2, 2012): 55. http://dx.doi.org/10.1088/0004-637x/760/1/55.

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Journal articles on the topic 'M-DWARF BINARY'

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