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Journal articles on the topic 'Low mass stars. Dwarf stars'

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Published: 4 June 2021

Last updated: 15 February 2022

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1

Kepler, S. O., Alejandra Daniela Romero, Ingrid Pelisoli, and Gustavo Ourique. "White Dwarf Stars." International Journal of Modern Physics: Conference Series 45 (January 2017): 1760023. http://dx.doi.org/10.1142/s2010194517600230.

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White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5[Formula: see text]000 to 39[Formula: see text]000. This number includes only white dwarf stars with [Formula: see text], i.e., excluding the Extremely Low Mass white dwarfs, which are necessarily the byproduct of stellar interaction

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2

France, Kevin, R. O. Parke Loyd, and Alex Brown. "Ultraviolet and X-ray irradiance and flares from low-mass exoplanet host stars." Proceedings of the International Astronomical Union 11, S320 (2015): 370–75. http://dx.doi.org/10.1017/s1743921315010765.

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AbstractThe spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. High-energy photons (X-ray to NUV) from these stars regulate the atmospheric temperature profiles and photochemistry on orbiting planets, influencing the production of potential “biomarker” gases. We report first results from the MUSCLES Treasury Survey, a study of time-resolved UV and X-ray spectroscopy of nearby M and K dwarf exoplanet host stars. This program uses contemporaneous Hubble Space Telescope and Chandra (or XMM) observations to

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3

Kepler, S. O., Ingrid Pelisoli, Detlev Koester, et al. "White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 14." Monthly Notices of the Royal Astronomical Society 486, no. 2 (2019): 2169–83. http://dx.doi.org/10.1093/mnras/stz960.

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ABSTRACT White dwarfs carry information on the structure and evolution of the Galaxy, especially through their luminosity function and initial-to-final mass relation. Very cool white dwarfs provide insight into the early ages of each population. Examining the spectra of all stars with 3σ proper motion in the Sloan Digital Sky Survey Data Release 14, we report the classification for 20 088 spectroscopically confirmed white dwarfs, plus 415 hot subdwarfs, and 311 cataclysmic variables. We obtain Teff, log g, and mass for hydrogen atmosphere white dwarf stars (DAs), warm helium atmosphere white d

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Jones, Hugh R. A., Yakiv Pavlenko, Serena Viti, et al. "Carbon monoxide in low-mass dwarf stars." Monthly Notices of the Royal Astronomical Society 358, no. 1 (2005): 105–12. http://dx.doi.org/10.1111/j.1365-2966.2005.08736.x.

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Giampapa, M. S., R. Rosner, V. Kashyap, T. A. Fleming, J. H. M. M. Schmitt, and J. A. Bookbinder. "The Coronae of Low-Mass Dwarf Stars." Astrophysical Journal 463 (June 1996): 707. http://dx.doi.org/10.1086/177284.

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6

Ruiz, María Teresa. "Do Low Luminosity Stars Matter?" Proceedings of the International Astronomical Union 5, H15 (2009): 47–60. http://dx.doi.org/10.1017/s1743921310008185.

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AbstractHistorically, low luminosity stars have attracted very little attention, in part because they are difficult to see except with large telescopes, however, by neglecting to study them we are leaving out the vast majority of stars in the Universe. Low mass stars evolve very slowly, it takes them trillions of years to burn their hydrogen, after which, they just turn into a He white dwarf, without ever going through the red giant phase. This lack of observable evolution partly explains the lack of interest in them. The search for the “missing mass” in the galactic plane turned things around

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Jones, Hugh R. A., John Barnes, Mikko Tuomi, James S. Jenkins, and Guillem Anglada-Escude. "Radial velocity studies of cool stars." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2014 (2014): 20130088. http://dx.doi.org/10.1098/rsta.2013.0088.

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Our current view of exoplanets is one derived primarily from solar-like stars with a strong focus on understanding our Solar System. Our knowledge about the properties of exoplanets around the dominant stellar population by number, the so-called low-mass stars or M dwarfs, is much more cursory. Based on radial velocity discoveries, we find that the semi-major axis distribution of M dwarf planets appears to be broadly similar to those around more massive stars and thus formation and migration processes might be similar to heavier stars. However, we find that the mass of M dwarf planets is relat

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Rana, N. C. "Scaleheights of Low Mass Stars from the Luminosity Function of the Local White Dwarfs." International Astronomical Union Colloquium 114 (1989): 152–55. http://dx.doi.org/10.1017/s0252921100099486.

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It is shown that a combination of the observed luminosity function of the local white dwarfs and the theoretical cooling rates of a typical white dwarf suggests an approximately constant rate of formation of the white dwarfs. This rate is found to be about a factor of three lower than the observed birthrate of their immediate progenitors. This discrepancy is here interpreted as a three-fold increase in the scaleheight of the white dwarfs due to dynamical interaction with stars, molecular clouds; an average white dwarf being much more aged than an average progenitor. Since the low mass stars on

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Sánchez Arias, Julieta P., Alejandra D. Romero, Alejandro H. Córsico та ін. "Comparing the asteroseismic properties of pulsating pre-extremely low mass white dwarf and δ Scuti stars". Astronomy & Astrophysics 616 (серпень 2018): A80. http://dx.doi.org/10.1051/0004-6361/201731808.

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Context. Pulsating extremely low-mass pre-white dwarf stars (pre-ELMV), with masses between ~0.15 M⊙ and ~0.30 M⊙, constitute a new class of variable stars showing g- and possibly p-mode pulsations with periods between 320 and 6000 s (frequencies between 14.4 and 270 c/d), driven by the κ mechanism operating in the second He ionization zone. On the other hand, main sequence δ Scuti stars, with masses between 1.2 and 2.5 M⊙, pulsate in low-order g and p modes with periods in the range [700–28 800] s (frequencies in the range [3–123] c/d), driven by the κ mechanism operating in the He II ionizat

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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 (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

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Murdoch, Kaylene, and J. B. Hearnshaw. "High-Precision Radial Velocities of Southern Solar-Type Stars." International Astronomical Union Colloquium 135 (1992): 167–69. http://dx.doi.org/10.1017/s0252921100006321.

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AbstractWith a small telescope and conventional techniques we have achieved external radial-velocity errors for bright stars of only ±50 m/s by using an optical fibre feed between telescope and spectrograph. In a search for low-mass companions to solar-type dwarf stars, intrinsic radial-velocity variability was detected in some IAU radial-velocity standard stars but no convincing evidence was found of the presence of low-mass companions to the dwarfs.

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Mayor, M., A. Duquennoy, J. L. Halbwachs, and J. C. Mermilliod. "CORAVEL Surveys to Study Binaries of Different Masses and Ages." International Astronomical Union Colloquium 135 (1992): 73–81. http://dx.doi.org/10.1017/s0252921100006151.

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AbstractPreliminary results are given for a systematic survey of K-dwarf stars in the solar vicinity. Nine companions to the G and K dwarfs have very low M2 sin i, less than 0.08 M⊙. These detections from a sample of 540 G and K primary stars support the reality of the existence of companions with mass below 0.08 M⊙: brown dwarfs exist.A comparison of the relative mass function distribution f(m)/M1 between low-mass (M1 < 1.3 M⊙) and intermediate-mass (2 < M1 < 5 M⊙) binaries suggests a dependence of the mass-ratio distribution on the mass of the primary: f(q, M1).By combining the phot

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13

Liebert, James. "Molecular Opacities in Cool Dwarf Stars." International Astronomical Union Colloquium 146 (1994): 61–70. http://dx.doi.org/10.1017/s0252921100021242.

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The term dwarf stars identifies objects of small radius in the Hertzsprung-Russell (H-R) Diagram, but encompasses more than one phase of stellar evolution. The M dwarfs (type dM) populate the main sequence at the low mass end; these are the coolest core hydrogen-burning stars. They belong generally to the Galactic disk, or Population I, have relatively small space motions with respect to the Sun, and have similar metallicities to the Sun (although perhaps only within a factor of several). In particular, this means that the abundance of oxygen is always greater than that of carbon. The M subdwa

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14

Krzesinski, Jurek, and Adam Blokesz. "Searching for low-mass companions around white dwarfs and subdwarfs from Kepler field." Proceedings of the International Astronomical Union 15, S357 (2019): 41–44. http://dx.doi.org/10.1017/s174392132000023x.

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AbstractKnowing the late stages of the stellar evolution is crucial for understanding the fate of planets around subdwarfs and white dwarfs. Simulations by (Staff et al.2016) show, that exoplanets engulfed in the extending stellar envelope will quickly spiral down onto the parent star. Therefore, we do not expect to find planets on close by orbits to the subdwarfs (Blokesz et al.2019) or white dwarfs. However, the recent observation of planetary debris around WD 1145+017 white dwarf suggests, there might exists planets farther away from these stars. Using binarograms, O-C diagrams and Fourier

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15

Bate, Matthew R. "Stellar and brown dwarf properties from numerical simulations." Proceedings of the International Astronomical Union 5, H15 (2009): 769–70. http://dx.doi.org/10.1017/s174392131001152x.

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AbstractWe review the statistical properties of stars and brown dwarfs obtained from the first hydrodynamical simulation of star cluster formation to produce more than a thousand stars and brown dwarfs while simultaneously resolving the lowest mass brown dwarfs (those with masses set by the opacity limit for fragmentation), binaries with separations down to ~ 1 AU, and discs with radii greater than ~ 10 AU. In particular, we present the eccentricity distribution of the calculation's very-low-mass and brown dwarf binaries which has not been previously published.

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Bharat Kumar, Y., X.-M. Kong, G. Zhao, and J.-K. Zhao. "s-process abundances of Primary stars in the Sirius-like Systems: Constraints on pollution from AGB stars." Proceedings of the International Astronomical Union 14, S343 (2018): 351–52. http://dx.doi.org/10.1017/s1743921318006580.

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AbstractWe present the results from the abundance analysis of 21 primary stars in Sirius-like systems with various masses of white dwarf companions and orbital separation to understand the origin and nature of Ba stars. Three new Ba dwarfs are found for which masses are relatively low compared to Ba giants. Large fraction of the sample are found to be non-Ba stars, however, some of them have required WD mass and/or close orbital separation. Observed s-process abundances in Ba dwarfs are in good agreement with AGB models of respective WD companion mass, however, it required different pollution

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17

Lada, Charles J. "On the origin of dwarf stars." Symposium - International Astronomical Union 137 (1990): 347–61. http://dx.doi.org/10.1017/s0074180900187996.

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The origin of dwarf or low mass stars is one of the most interesting and challenging problems of modern astrophysics. In recent years advances in observational technology particularly at infrared and millimeter wavelengths, have produced an avalanche of revealing new data, unexpected discoveries and new mysteries about the process of star formation. From this new knowledge a complete empirical picture of stellar origins is being synthesized and a more profound and penetrating understanding of the physical process of star formation in our galaxy is beginning to emerge. It is now apparent, for e

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Andersen, Jan Marie, and Heidi Korhonen. "Activity-Induced Radial Velocity Variation of M Dwarf Stars." Proceedings of the International Astronomical Union 8, S293 (2012): 197–200. http://dx.doi.org/10.1017/s1743921313012829.

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AbstractStellar magnetic activity manifests itself in a variety of ways including starspots–cool, dark regions on the stellar surface. Starspots can cause variations (‘jitter’) in spectral line-profiles which can mimic the radial velocity (RV) variations caused by an orbiting planet, or create RV noise that can drown out a planetary signature. Cool, low-mass M dwarf stars can be highly active, which can make detection of potentially habitable planets around these stars difficult. We investigate radial velocity variations caused by different activity (spot) patterns on M dwarf stars in order to

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Larsen, Søren S. "Massive Star Clusters in Dwarf Galaxies." Proceedings of the International Astronomical Union 12, S316 (2015): 91–98. http://dx.doi.org/10.1017/s1743921315010509.

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AbstractDwarf galaxies can have very high globular cluster specific frequencies, and the GCs are in general significantly more metal-poor than the bulk of the field stars. In some dwarfs, such as Fornax, WLM, and IKN, the fraction of metal-poor stars that belong to GCs can be as high as 20%–25%, an order of magnitude higher than the 1%–2% typical of GCs in halos of larger galaxies. Given that chemical abundance anomalies appear to be present also in GCs in dwarf galaxies, this implies severe difficulties for self-enrichment scenarios that require GCs to have lost a large fraction of their init

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Caplan, M. E. "Black dwarf supernova in the far future." Monthly Notices of the Royal Astronomical Society 497, no. 4 (2020): 4357–62. http://dx.doi.org/10.1093/mnras/staa2262.

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ABSTRACT In the far future, long after star formation has ceased, the universe will be populated by sparse degenerate remnants, mostly white dwarfs, though their ultimate fate is an open question. These white dwarfs will cool and freeze solid into black dwarfs while pycnonuclear fusion will slowly process their composition to iron-56. However, due to the declining electron fraction, the Chandrasekhar limit of these stars will be decreasing and will eventually be below that of the most massive black dwarfs. As such, isolated dwarf stars with masses greater than ∼1.2 M⊙ will collapse in the far

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Whitehouse, L. J., J. Farihi, I. D. Howarth, et al. "Carbon-enhanced stars with short orbital and spin periods." Monthly Notices of the Royal Astronomical Society 506, no. 4 (2021): 4877–92. http://dx.doi.org/10.1093/mnras/stab1913.

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ABSTRACT Many characteristics of dwarf carbon stars are broadly consistent with a binary origin, including mass transfer from an evolved companion. While the population overall appears to have old-disc or halo kinematics, roughly 2 per cent of these stars exhibit Hα emission, which in low-mass main-sequence stars is generally associated with rotation and relative youth. Its presence in an older population therefore suggests either irradiation or spin-up. This study presents time-series analyses of photometric and radial-velocity data for seven dwarf carbon stars with Hα emission. All are shown

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Baraffe, I., and F. Allard. "Atmosphere models for very low mass stars, brown dwarfs and exoplanets." Symposium - International Astronomical Union 189 (1997): 227–33. http://dx.doi.org/10.1017/s0074180900116729.

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Over the past decade considerable effort, both observational and theoretical, has been directed towards a more accurate determination of the stellar lower main sequence and of the sub-stellar domain covered by Brown Dwarfs and Planets. Astronomers have been looking for brown dwarfs for more than a decade, either with standard astronomical technics or with microlensing experiments. A breakthrough in the search for brown dwarfs was very recently achieved with the discovery of the first cool brown dwarf GL 229B (Nakajima et al. 1995). At the same epoch, the search for planets blossomed with the d

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Webbink, R. F. "The Formation and Evolution of Symbiotic Stars." International Astronomical Union Colloquium 103 (1988): 311–21. http://dx.doi.org/10.1017/s025292110010377x.

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AbstractThe evolutionary origins of symbiotic stars containing (i) disk-accreting main sequence stars, (ii) wind-fed, shell-burning white dwarfs, and (iii) disk-accreting neutron stars are described. Of particular interest are those white dwarf systems which have orbital periods too short to have escaped tidal mass transfer prior to becoming symbiotics. We show here that, under suitable circumstances, low-mass, long period binaries may undergo quasi-conservative mass transfer, rather than evolving through common envelope evolution to the cataclysmic variable state, thus accounting for the exis

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Lodders, Katharina. "Titanium and Vanadium Chemistry in Low‐Mass Dwarf Stars." Astrophysical Journal 577, no. 2 (2002): 974–85. http://dx.doi.org/10.1086/342241.

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Maldonado, J., G. Micela, M. Baratella, et al. "HADES RV programme with HARPS-N at TNG." Astronomy & Astrophysics 644 (December 2020): A68. http://dx.doi.org/10.1051/0004-6361/202039478.

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Context. Most of our current knowledge on planet formation is still based on the analysis of main sequence, solar-type stars. Conversely, detailed chemical studies of large samples of M dwarfs hosting planets are still missing. Aims. Correlations exist between the presence of different types of planets around FGK stars and metallicity, individual chemical abundance, and stellar mass. We aim to test whether or not these correlations still hold for the less-massive M dwarf stars. Methods to determine stellar abundances of M dwarfs from high-resolution optical spectra in a consistent way are stil

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Calcaferro, Leila M., Alejandro H. Córsico, Leandro G. Althaus, and Keaton J. Bell. "A new instability domain of CNO-flashing low-mass He-core stars on their early white-dwarf cooling branches." Astronomy & Astrophysics 647 (March 2021): A140. http://dx.doi.org/10.1051/0004-6361/202039831.

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Context. Before reaching their quiescent terminal white-dwarf cooling branch, some low-mass helium-core white dwarf stellar models experience a number of nuclear flashes which greatly reduce their hydrogen envelopes. Just before the occurrence of each flash, stable hydrogen burning may be able to drive global pulsations that could be relevant in shedding some light on the internal structure of these stars through asteroseismology, similarly to what occurs with other classes of pulsating white dwarfs. Aims. We present a pulsational stability analysis applied to low-mass helium-core stars on the

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Manjavacas, E., N. Lodieu, V. J. S. Béjar, M. R. Zapatero-Osorio, S. Boudreault, and M. Bonnefoy. "Spectral library of age-benchmark low-mass stars and brown dwarfs." Monthly Notices of the Royal Astronomical Society 491, no. 4 (2019): 5925–50. http://dx.doi.org/10.1093/mnras/stz3441.

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ABSTRACT In recent years, some extremely red brown dwarfs have been discovered. They were believed to have a low surface gravity, but many of their spectral characteristics are similar to those of high-surface-gravity brown dwarfs, showing that the spectral characteristics of young brown dwarfs are poorly understood. We aim to test surface-gravity indicators in late-M and early-L brown dwarf spectra using data obtained with the X-shooter spectrograph at the Very Large Telescope. We select a benchmark sample of brown dwarf members of Chamaeleon I (∼2 Myr), Upper Scorpius (5−10 Myr), the Pleiade

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Jeffery, C. S., and H. Saio. "Pulsation in extremely low-mass helium stars." Proceedings of the International Astronomical Union 9, S301 (2013): 425–26. http://dx.doi.org/10.1017/s1743921313014877.

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AbstractWe explore the stability of extremely low-mass stars (M < 0.25 M⊙) across a wide range of composition, effective temperature, and luminosity. We identify the instability boundaries associated with radial oscillations. These are a strong function of both composition and radial order (0 ≤ n ≤ 13). The classical blue edge shifts to higher effective temperature and luminosity with decreasing hydrogen abundance. Higher-order modes are more easily excited, and small islands of instability develop. Short-period oscillations have been discovered in the low-mass pre-white dwarf component of

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Gill, S., P. F. L. Maxted, J. A. Evans, et al. "The EBLM project." Astronomy & Astrophysics 626 (June 2019): A119. http://dx.doi.org/10.1051/0004-6361/201833054.

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Some M-dwarfs around F-/G-type stars have been measured to be hotter and larger than predicted by stellar evolution models. Inconsistencies between observations and models need to be addressed with more mass, radius, and luminosity measurements of low-mass stars to test and refine evolutionary models. Our aim is to measure the masses, radii and ages of the stars in five low-mass eclipsing binary systems discovered by the WASP survey. We used WASP photometry to establish eclipse-time ephemerides and to obtain initial estimates for the transit depth and width. Radial velocity measurements were s

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Venn, Kim A., Pascale Jablonka, Vanessa Hill, et al. "Chemical Abundances of Metal-poor stars in Dwarf Galaxies." Proceedings of the International Astronomical Union 11, S317 (2015): 159–63. http://dx.doi.org/10.1017/s1743921316000107.

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AbstractStars in low-mass dwarf galaxies show a larger range in their chemical properties than those in the Milky Way halo. The slower star formation efficiency make dwarf galaxies ideal systems for testing nucleosynthetic yields. Not only are alpha-poor stars found at lower metallicities, and a higher fraction of carbon-enhanced stars, but we are also finding stars in dwarf galaxies that appear to be iron-rich. These are compared with yields from a variety of supernova predictions.

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Monty, Stephanie, Kim A. Venn, James M. M. Lane, Deborah Lokhorst, and David Yong. "Chemo-dynamics of outer halo dwarf stars, including Gaia-Sausage and Gaia-Sequoia candidates." Monthly Notices of the Royal Astronomical Society 497, no. 1 (2020): 1236–55. http://dx.doi.org/10.1093/mnras/staa1995.

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ABSTRACT The low-metallicity, kinematically interesting dwarf stars studied by Stephens & Boesgaard (2002, SB02) are re-examined using Gaia DR2 astrometry, and updated model atmospheres and atomic line data. New stellar parameters are determined based on the Gaia DR2 parallactic distances and Dartmouth Stellar Evolution Database isochrones. These are in excellent agreement with spectroscopically determined stellar parameters for stars with [Fe/H] &gt; −2; however, large disagreements are found for stars with [Fe/H] ≤ −2, with offsets as large as ΔTeff ∼ +500 K and Δlog g ∼ +1.0. A subs

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Grieves, Nolan, François Bouchy, Monika Lendl, et al. "Populating the brown dwarf and stellar boundary: Five stars with transiting companions near the hydrogen-burning mass limit." Astronomy & Astrophysics 652 (August 2021): A127. http://dx.doi.org/10.1051/0004-6361/202141145.

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We report the discovery of five transiting companions near the hydrogen-burning mass limit in close orbits around main sequence stars originally identified by the Transiting Exoplanet Survey Satellite (TESS) as TESS objects of interest (TOIs): TOI-148, TOI-587, TOI-681, TOI-746, and TOI-1213. Using TESS and ground-based photometry as well as radial velocities from the CORALIE, CHIRON, TRES, and FEROS spectrographs, we found the companions have orbital periods between 4.8 and 27.2 days, masses between 77 and 98 MJup , and radii between 0.81 and 1.66 RJup . These targets have masses near the unc

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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 abs

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Fontaine, G., and F. Wesemael. "Asteroseismological Probing of the Thermal Evolution of White Dwarf Stars." Highlights of Astronomy 9 (1992): 643–45. http://dx.doi.org/10.1017/s1539299600009916.

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AbstractIt is generally believed that the immediate progenitors of most white dwarfs are nuclei of planetary nebulae, themselves the products of intermediate- and low-mass main sequence evolution. Stars that begin their lifes with masses less than about 7-8 M⊙ (i.e., the vast majority of them) are expected to become white dwarfs. Among those which have already had the time to become white dwarfs since the formation of the Galaxy, a majority have burnt hydrogen and helium in their interiors. Consequently, most of the mass of a typical white dwarf is contained in a core made of the products of h

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Tutukov, A. V., and L. R. Yungelson. "The Formation and Evolution of Low-Mass Close Binaries with Compact Components." International Astronomical Union Colloquium 93 (1987): 15–33. http://dx.doi.org/10.1017/s0252921100104592.

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AbstractWe discuss the formation and evolution of interacting low-mass close binaries with a He-ICO- or ONe-dwarf neutron star or a black hole as a compact component. Mass exchange leads to cataclysmic events in such systems. The rate of semidetached low-mass close binary formation is 5×10−3 yr−1 if the accreting component is a He degenerate dwarf, 5×10−3 yr−1 if it is a CO-dwarf and 3×10−8 yr−1 if it is a neutron star. Systems with compact accretors arise as the result of the common envelope phase of close binary evolution or due to collisions of single neutron stars or dwarfs with low-mass s

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Calcaferro, Leila M., Leandro G. Althaus, and Alejandro H. Córsico. "The coolest extremely low-mass white dwarfs." Astronomy & Astrophysics 614 (June 2018): A49. http://dx.doi.org/10.1051/0004-6361/201732551.

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Context. Extremely low-mass white dwarf (ELM WD; M⋆ ≲ 0.18–0.20 M⊙) stars are thought to be formed in binary systems via stable or unstable mass transfer. Although stable mass transfer predicts the formation of ELM WDs with thick hydrogen (H) envelopes that are characterized by dominant residual nuclear burning along the cooling branch, the formation of ELM WDs with thinner H envelopes from unstable mass loss cannot be discarded. Aims. We compute new evolutionary sequences for helium (He) core WD stars with thin H envelopes with the main aim of assessing the lowest Teff that could be reached b

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Kouwenhoven, M. B. N., Yun Li, D. Stamatellos, and S. P. Goodwin. "Circumstellar disk fragmentation and the origin of massive planetary companions, brown dwarfs, and very low-mass stars." Proceedings of the International Astronomical Union 14, S345 (2018): 239–40. http://dx.doi.org/10.1017/s174392131800827x.

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AbstractThe low-mass end of the initial mass function remains poorly understood. In this mass range, very low-mass stars, brown dwarfs, and massive planets are able to form through a variety of physical processes. Here, we study the long-term evolution of disk-fragmented systems around low-mass stars, for the epoch up to 10 Myr (the typical lifetime of an embedded cluster) and up to 10 Gyr (the age of the Milky Way). We carry out N-body simulations to study the decay of disk-fragmented systems and the resulting end products. Our simulations indicate rapid decay and frequent physical collisions

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Hernandez, M. S., M. R. Schreiber, S. G. Parsons, et al. "The White Dwarf Binary Pathways Survey – IV. Three close white dwarf binaries with G-type secondary stars." Monthly Notices of the Royal Astronomical Society 501, no. 2 (2020): 1677–89. http://dx.doi.org/10.1093/mnras/staa3815.

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ABSTRACT Constraints from surveys of post-common envelope binaries (PCEBs) consisting of a white dwarf plus an M-dwarf companion have led to significant progress in our understanding of the formation of close white dwarf binary stars with low-mass companions. The white dwarf binary pathways project aims at extending these previous surveys to larger secondary masses, i.e. secondary stars of spectral-type AFGK. Here, we present the discovery and observational characterization of three PCEBs with G-type secondary stars and orbital periods between 1.2 and 2.5 d. Using our own tools as well as MESA

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Rebolo, Rafael, Eduardo L. Martin, and Antonio Magazzu. "A Search for Lithium in Brown Dwarf Candidates." International Astronomical Union Colloquium 137 (1993): 171–73. http://dx.doi.org/10.1017/s0252921100017693.

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AbstractWe are conducting a search for lithium in very low mass objects with the aim of discriminating between stellar and substellar objects. Lithium is expected to be preserved in brown dwarfs with M/M⊙ ≤0.06, while it is known to be efficiently destroyed in low mass stars. In this paper we present high resolution observations in the region of the λ 6708 Li I resonance line of 5 very low mass dwarfs. In none of them lithium is detected, implying a Li destruction in their atmospheres of about four orders of magnitude. Our results suggest that these objects are probably very low mass stars rat

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De Gerónimo, F. C., L. G. Althaus, A. H. Córsico, A. D. Romero, and S. O. Kepler. "Asteroseismology of ZZ Ceti stars with full evolutionary white dwarf models." Astronomy & Astrophysics 613 (May 2018): A46. http://dx.doi.org/10.1051/0004-6361/201731982.

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Context. The thermally pulsing phase on the asymptotic giant branch (TP-AGB) is the last nuclear burning phase experienced by most low- and intermediate-mass stars. During this phase, the outer chemical stratification above the C/O core of the emerging white dwarf (WD) is built up. The chemical structure resulting from progenitor evolution strongly impacts the whole pulsation spectrum exhibited by ZZ Ceti stars, which are pulsating C/O core white dwarfs located on a narrow instability strip at Teff ~ 12 000 K. Several physical processes occurring during progenitor evolution strongly affect the

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Zawadzki, Brianna, Daniel Carrera, and Eric B. Ford. "Rapid formation of super-Earths around low-mass stars." Monthly Notices of the Royal Astronomical Society 503, no. 1 (2021): 1390–406. http://dx.doi.org/10.1093/mnras/stab603.

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ABSTRACT NASA’s TESS mission is expected to discover hundreds of M dwarf planets. However, few studies focus on how planets form around low-mass stars. We aim to better characterize the formation process of M dwarf planets to fill this gap and aid in the interpretation of TESS results. We use ten sets of N-body planet formation simulations that vary in whether a gas disc is present, initial range of embryo semimajor axes, and initial solid surface density profile. Each simulation begins with 147 equal-mass embryos around a 0.2 solar mass star and runs for 100 Myr. We find that planets form rap

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Bischoff-Kim, Agnès. "Constraints on stellar evolution from white dwarf asteroseismology." Proceedings of the International Astronomical Union 9, S307 (2014): 211–12. http://dx.doi.org/10.1017/s1743921314006747.

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AbstractHigh mass and low mass stars follow a similar evolution until the inert core phase that follows the end of the core helium burning stage. In particular, one common phase of stellar evolution is the alpha capture reaction that turns carbon into oxygen in the core. We can obtain constraints on this reaction rate by studying the remnants of low mass stars, as this is the ultimate reaction that occurs in their core. We also present results that allow us to test the time dependent calculations of diffusion in dense interiors.

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Reid, I. N. "Low-Luminosity Stars: Past and Future." Highlights of Astronomy 11, no. 1 (1998): 433–34. http://dx.doi.org/10.1017/s1539299600021663.

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The expression “low luminosity stars” is a descriptive category which spans a wide range of objects, from the oldest stellar remnants in the Galaxy (Wood) through failed stars (Jones, Gould) to the enigmatic MACHOs, discernible not in themselves but only through their effects on others (Bennet). All of these have attracted considerable attention in recent years, and significant progress has been achieved in each case, even if our understanding has failed to keep up with observations. However, it is in the area of brown dwarfs where the most dramatic results have been obtained. The existence of

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Bell, K. J., I. Pelisoli, S. O. Kepler, et al. "The McDonald Observatory search for pulsating sdA stars." Astronomy & Astrophysics 617 (September 2018): A6. http://dx.doi.org/10.1051/0004-6361/201833279.

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Context. The nature of the recently identified “sdA” spectroscopic class of stars is not well understood. The thousands of known sdAs have H-dominated spectra, spectroscopic surface gravity values between main sequence stars and isolated white dwarfs, and effective temperatures below the lower limit for He-burning subdwarfs. Most are likely products of binary stellar evolution, whether extremely low-mass white dwarfs and their precursors or blue stragglers in the halo. Aims. Stellar eigenfrequencies revealed through time series photometry of pulsating stars sensitively probe stellar structural

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Boss, Alan P., Alycia J. Weinberger, Guillem Anglada-Escudé, Ian B. Thompson, and Rafael Brahm. "Habitable Worlds Around M Dwarf Stars: The CAPSCam Astrometric Planet Search." Proceedings of the International Astronomical Union 8, S293 (2012): 183–88. http://dx.doi.org/10.1017/s1743921313012799.

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AbstractM dwarf stars are attractive targets in the search for habitable worlds as a result of their relative abundance and proximity, making them likely targets for future direct detection efforts. Hot super-Earths as well as gas giants have already been detected around a number of early M dwarfs, and the former appear to be the high-mass end of the population of rocky, terrestrial exoplanets. The Carnegie Astrometric Planet Search (CAPS) program has been underway since March 2007, searching ~ 100 nearby late M, L, and T dwarfs for gas giant planets on orbits wide enough for habitable worlds

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Marchi, Guido De, Francesco Paresce, and Martino Romaniello. "Low Mass Stars and White Dwarfs in NGC 6397." Symposium - International Astronomical Union 164 (1995): 408. http://dx.doi.org/10.1017/s0074180900109258.

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Deep WFPC2 images in wide bands centered at 606 and 802 nm were taken with the HST 5.6 arcminutes from the center of the galactic globular cluster NGC 6397. The images were used to accurately position ~ 2120 stars detected in the field on a color magnitude diagram down to a limiting magnitude m814 ≃ mI ≃ 26 determined reliably and solely by counting statistics. A white dwarf sequence and a rich, narrow cluster main sequence are detected for the first time, the latter stretching from m814 = 18.5 to m814 = 24.0 where it becomes indistinguishable from the field population. Two changes of slope of

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Guenther, Eike, and Guenther Wuchterl. "Searching for Planets of Brown Dwarfs." Symposium - International Astronomical Union 211 (2003): 225–32. http://dx.doi.org/10.1017/s0074180900210632.

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Up to now, most planet search projects have concentrated on G and K stars. In order to considerably widen the view, we have stated a survey for planets of old, nearby brown dwarfs and very low-mass stars. Using UVES, we have observed 26 brown dwarfs and very low-mass stars. As it turned out these objects are very inactive and thus highly suitable for such a project. For 19 objects, we can exclude a planet with the mass of 3 MJ, and a period of 100 days or less with a probability of more than 60%. For these objects, we can also exclude Pegasi-planets with a high probability. For another 4 objec

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Skillman, Evan D. "Dwarf Galaxies as Low Surface Brightness Galaxies." International Astronomical Union Colloquium 171 (1999): 169–76. http://dx.doi.org/10.1017/s0252921100054270.

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AbstractBecause of the weak correlation between surface brightness and luminosity, as galaxy surveys reach to lower surface brightnesses, increasing numbers of dwarf galaxies are found. Thus, studies of dwarf galaxies are relevant to our understanding of the low surface brightness universe. In particular, studies of nearby LSB dwarfs may help to answer questions concerning: (1) star formation in low abundance and low mass surface density envrionments, (2) star formation histories of galaxies and the relative youth of LSB galaxies, and (3) the chemical evolution of LSB galaxies. HST WFPC2 photo

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Liebert, J., and C. C. Dahn. "Peculiar Stars of Low Luminosity." Symposium - International Astronomical Union 166 (1995): 157–62. http://dx.doi.org/10.1017/s0074180900228015.

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Precise trigonometric parallax measurements orders of magnitude more accurate than a milliarcsecond will contribute greatly to our understanding of peculiar, low luminosity stellar objects of several types. First, the volume of space out to which luminosities may be determined to the accuracy of the best, very-nearby stars will be increased greatly. For the relatively rare field Population II stars, this will lead to the first accurate empirical calibrations of the main sequence at the low mass end, for comparison with globular clusters of various metallicities. Parallaxes at 1 kpc or farther

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Heap, Sara. "Role of massive stars in the evolution of primitive galaxies." Proceedings of the International Astronomical Union 10, H16 (2012): 370. http://dx.doi.org/10.1017/s1743921314011429.

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AbstractAn important factor controlling galaxy evolution is feedback from massive stars. It is believed that the nature and intensity of stellar feedback changes as a function of galaxy mass and metallicity. At low mass and metallicity, feedback from massive stars is mainly in the form of photoionizing radiation. At higher mass and metallicity, it is in stellar winds. I Zw 18 is a local blue, compact dwarf galaxy that meets the requirements for a primitive galaxy: low halo mass <109M⊙, strong photoionizing radiation, no galactic outflow, and very low metallicity, log(O/H)+12=7.2. We will de

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