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1
Cederna, Camilla Maria. "Lost stars". Sigila N�41, n. 1 (2018): 96. http://dx.doi.org/10.3917/sigila.041.0096.
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Lappin, Louis, Maxwell Anderson e Kurt Weill. "Lost in the Stars". Theatre Journal 38, n. 4 (dicembre 1986): 479. http://dx.doi.org/10.2307/3208293.
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Vink, Jorick S. "Mass loss and stellar superwinds". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 375, n. 2105 (18 settembre 2017): 20160269. http://dx.doi.org/10.1098/rsta.2016.0269.
Testo completoAbstract (sommario):
Mass loss bridges the gap between massive stars and supernovae (SNe) in two major ways: (i) theoretically, it is the amount of mass lost that determines the mass of the star prior to explosion and (ii) observations of the circumstellar material around SNe may teach us the type of progenitor that made the SN. Here, I present the latest models and observations of mass loss from massive stars, both for canonical massive O stars, as well as very massive stars that show Wolf–Rayet type features. This article is part of the themed issue ‘Bridging the gap: from massive stars to supernovae’.
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Renzini, Alvio. "Hot Gas Flows in Elliptical Galaxies". Symposium - International Astronomical Union 171 (1996): 131–38. http://dx.doi.org/10.1017/s0074180900232257.
Testo completoAbstract (sommario):
Stars in elliptical galaxies lose mass at an overall present rate Ṁ∗ ≃ 1.5 × 10−11LBM⊙yr−1 (e.g., Faber & Gallagher 1976; Renzini & Buzzoni 1986). When allowing for the predicted increase back with cosmological time it turns out that over one Hubble time the stellar population of an elliptical galaxy has cumulatively lost 20-50% of its initial mass, the precise value depending on the IMF. This review focuses on two simple questions: what happens to the gas being lost by the stars? Where is it ultimately disposed?
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Gingerich, Owen. "Book Review: Troublesome Stars: Lost Stars: Lost, Missing, and Troublesome Stars from the Catalogues of Johannes Bayer, Nicholas-Louis de Lacaille, John Flamsteed, and Sundry others". Journal for the History of Astronomy 35, n. 2 (maggio 2004): 244–45. http://dx.doi.org/10.1177/002182860403500212.
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Liu, Cheng, Sofia Feltzing e Gregory Ruchti. "Finding the lost siblings of the Sun". Proceedings of the International Astronomical Union 9, S298 (maggio 2013): 426. http://dx.doi.org/10.1017/s1743921313006923.
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AbstractWe have performed a spectral analysis on 18 stars solar sibling candidate. We found that only one one of the candidateshas solar metallicity and at the same time might have an age comparable to that of the Sun.
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Taylor, Philip, Chiaki Kobayashi e Lisa J. Kewley. "Oxygen loss from simulated galaxies and the metal flow main sequence: predicting the dependence on mass and environment". Monthly Notices of the Royal Astronomical Society 496, n. 4 (7 luglio 2020): 4433–41. http://dx.doi.org/10.1093/mnras/staa1904.
Testo completoAbstract (sommario):
ABSTRACT We predict the mass fraction of oxygen lost from galaxies in a cosmological simulation as a function of stellar mass and environment at the present day. The distribution with stellar mass is bimodal, separating star-forming and quenched galaxies. The metallicity of gas and stars is self-consistently calculated using a chemical evolution model that includes Type II and Ia supernovae, hypernovae, and asymptotic giant branch stars. The mass of oxygen lost from each galaxy is calculated by comparing the existing oxygen in gas and stars in the galaxy to the oxygen that should have been produced by the present-day population of stars. More massive galaxies are able to retain a greater fraction of their metals (∼100 per cent) than low-mass galaxies (∼40–70 per cent). As in the star formation main sequence, star-forming galaxies follow a tight relationship also in terms of oxygen mass lost – a metal flow main sequence – whereas massive quenched galaxies tend to have lost a greater fraction of oxygen (up to 20 per cent), due to active galactic nucleus-driven winds. The amount of oxygen lost by satellite galaxies depends on the details of their interaction history, and those in richer groups tend to have lost a greater fraction of their oxygen. Observational estimates of metal retention in galaxies will provide a strong constraint on models of galaxy evolution.
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Marston, Anthony P. "Ring nebulae: what they tell us about Wolf-Rayet stars". Symposium - International Astronomical Union 193 (1999): 306–15. http://dx.doi.org/10.1017/s0074180900205573.
Testo completoAbstract (sommario):
The environments of evolved massive stars provide an opportunity of obtaining information on the past, as well as current, condition of the stars themselves. In this review we will look at the incidence of ring nebulae around Wolf-Rayet stars, their differing morphologies at various wavelengths and the existence of multiple, concentric shells. We use this information to show that WRs are indeed evolved stars and that the various phases of evolution for a WR star are evidenced in their environments. Abundance measurements and kinematics show that complex forms of mass ejection are likely to have occurred in the evolution of WR stars providing clumpy structures of dust, and both ionized and neutral gas. Gas kinematics also provide estimates to the time-scales of each of the evolutionary phases of WR stars, which can be combined with estimates of nebular masses to provide the approximate values for such crucial parameters as total mass-loss and historical mass-loss rates. Overall, it is illustrated that studies of the environments of WR stars have the potential to provide important information about the mass-loss history of very massive stars, including estimates of the time period of each mass-loss phase, typical mass loss rates, total mass lost and likely evolutionary path. Some of the remaining problems relating to the use of ring nebulae as probes to the evolutionary history of WR stars are also discussed.
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Koch, Andreas, Eva K. Grebel e Sarah L. Martell. "Purveyors of fine halos: Re-assessing globular cluster contributions to the Milky Way halo buildup with SDSS-IV". Astronomy & Astrophysics 625 (maggio 2019): A75. http://dx.doi.org/10.1051/0004-6361/201834825.
Testo completoAbstract (sommario):
There is ample evidence in the Milky Way for globular cluster (GC) disruption. It may therefore be expected that part of the Galactic halo field star population may also once have formed in GCs. We seek to quantify the fraction of halo stars donated by GCs by searching for stars that bear the unique chemical fingerprints typical for a subset of GC stars often dubbed “second-generation stars”. These are stars showing light-element abundance anomalies such as a pronounced CN-band strength accompanied by weak CH-bands. Based on this indicator, past studies have placed the fraction of halo stars with a GC origin between a few to up to 50%. Using low-resolution spectra from the most recent data release (DR14) of the latest extension of the Sloan Digital Sky Survey (SDSS-IV), we were able to identify 118 metal-poor (−1.8 ≤ [Fe/H] ≤ −1.3) CN-strong stars in a sample of 4470 halo giant stars out to ∼50 kpc. This increases the number of known halo stars with GC-like light-element abundances by a factor of two and results in an observed fraction of these stars of 2.6 ± 0.2%. Using an updated formalism to account for the fraction of stars lost early on in the GC evolution, we thus estimate the fraction of the Galactic halo that stems from disrupted clusters to be very low, at 11 ± 1%. This number would represent the case that stars lost from GCs were entirely from the first generation and is thus merely an upper limit. Our conclusions are sensitive to our assumptions of the mass lost early on from the first generation formed in the GCs, the ratio of first-to-second generation stars, and other GC parameters. We carefully tested the influence of varying these parameters on the final result and find that under realistic scenarios, this fraction depends on the main assumptions at less than 10 percentage points. We further recover a flat trend in this fraction with Galactocentric radius, with a marginal indication of a rise beyond 30 kpc that could reflect the ex situ origin of the outer halo as is also seen in other stellar tracers.
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Glanz, J. "Astronomy: Dust Grains Bring Long-Lost Stars Into the Laboratory". Science 274, n. 5290 (15 novembre 1996): 1078a—1079. http://dx.doi.org/10.1126/science.274.5290.1078a.
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Ramstedt, Sofia. "The mass-loss characteristics of AGB stars An observational view". Proceedings of the International Astronomical Union 14, S343 (agosto 2018): 150–58. http://dx.doi.org/10.1017/s174392131800724x.
Testo completoAbstract (sommario):
AbstractThe massive outflows of gas and dust which characterize giant stars on the Asymptotic Giant Branch (AGB), build cool circumstellar envelopes readily observed at infrared (IR) and sub-millimeter wavelengths. The observations will give the amount of matter lost by the star, the wind velocity (in the case of spectral line observations), and, when the spatial resolution is sufficient, the wind evolution over time. To gain detailed insight into the mass-loss process, we study the nearby (closer than 1 kpc) stars. Through these investigations we aim to determine the best constrained wind properties available. By combining this with theoretical results, mass-loss estimates for more distant sources can also be significantly improved. ALMA has opened up new opportunities to study the winds of AGB stars. The DEATHSTAR project (www.astro.uu.se/deathstar) has mapped the circumstellar CO emission from so far ∼50 nearby M- and C-type AGB stars. The data will initially be used to give a definitive mass-loss prescription for the sample sources, but the large-bandwidth observations opens for many different legacy projects. The current status and results are presented.
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Doom, C. "Atmospheric Diagnostics of Wolf-Rayet Stars". International Astronomical Union Colloquium 108 (1988): 148–49. http://dx.doi.org/10.1017/s0252921100093659.
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Wolf-Rayet (WR) stars are the descendants of massive stars that have lost their hydrogen rich envelope. Recently more accurate data on WR stars have become available: mass-loss rates (van der Hucht et al. 1986), radii and luminosities (Underhill 1983, Nussbaumer et al. 1982).It may therefore be worthwhile to investigate if combinations of observed parameters shed some light on the structure of the extended stellar wind of WR stars.In many WR stars the photosphere is situated in the stellar wind. We assume that the wind is stationary and isotropic. Further we assume a velocity law v(r)=v∞(1−Rs/r)β where v∞ is the terminal velocity of the wind in km/s, Rs is the radius where the wind acceleration starts and β > 0 is a free parameter. We can then easily compute the level R in the wind where the photosphere is located (de Loore et al. 1982): R is the solution of the equation 6.27 10−9 τat R v∞/ = fβ(Rs/R) where τat is the optical depth at the photosphere (2/3 or 1), (>0) is the mass loss rate in M⊙/yr and fβ > 1 is a slowly varying function (Doom 1987).
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Groenewegen, Martin, e Teije De Jong. "Synthetic AGB Evolution in the LMC: The Abundances of PN". Symposium - International Astronomical Union 155 (1993): 585. http://dx.doi.org/10.1017/s0074180900172596.
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We have developed a model to calculate the evolution of AGB stars in a synthetic way. The evolution is started at the first thermal pulse (TP) and ends when the envelope mass has been lost due to mass loss or when the core mass reaches the Chandrasekhar mass.
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Abbott, David C. "3. Wolf-Rayet star atmospheres". Transactions of the International Astronomical Union 19, n. 1 (1985): 510–13. http://dx.doi.org/10.1017/s0251107x0000657x.
Testo completoAbstract (sommario):
Wolf-Rayet (WR) stars are the helium-burning remnants of massive stars (initial mass ≲30 M©), which have lost their outer hydrogen-rich layers through the processes of Roche lobe overflow to a companion or mass loss by a strong stellar wind. The characteristic emission-line spectrum which defines the WR spectral type is produced by a stellar wind that is so dense and opaque, that the radiation of all lines and continua arise from material in the wind. Because the wind completely screens any radiation emitted by the hydrostatic core of the star, the spectra of WR stars are nearly impossible to interpret quantitatively, and the basic parameters — such as mass, luminosity, temperature, and chemical composition — are poorly determined.
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Morford, Jack, Raman Prinja e Danielle Fenech. "e-MERLIN Radio Continuum Measurements of OB Star Winds in CYG OB2". Proceedings of the International Astronomical Union 12, S316 (agosto 2015): 169–70. http://dx.doi.org/10.1017/s1743921315006882.
Testo completoAbstract (sommario):
AbstractHere, we report on the first results from the e-MERLIN Cyg OB2 Radio Survey (COBRaS), which is designed to exploit e-MERLIN’s enhanced capabilities to conduct deep-field mapping of the tremendously rich Cyg OB2 association. The project aims to deliver the most detailed radio census of the most massive OB association in the northern hemisphere. There exists considerable evidence for clumping in the winds of hot stars, which has hugely important consequences for mass-loss determinations. The amount of mass lost from a massive star is a crucial parameter required for stellar and cluster evolution models that are paramount to our understanding of the formation and evolution of massive star clusters. Presenting some of the first 20cm (L band) detections of massive stars in Cyg OB2, both accurate mass-loss determinations and constraints upon clumping within their winds are made. These data substantially increase the observational detections of the outer wind of massive stars and in combination with other observations at different wavelengths, COBRaS will greatly advance our knowledge of clumping as a function of radial distance around massive stars.
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Mirzoyan, L. V. "The Red Dwarf Star Population in the Galaxy". International Astronomical Union Colloquium 151 (1995): 55–56. http://dx.doi.org/10.1017/s0252921100034564.
Testo completoAbstract (sommario):
Red dwarf stars in the Galaxy occur in three forms: as flare stars, T Tau stars and red dwarf stars of constant brightness. Haro (1957) suggested that all these stars present regular evolutionary stages of red dwarf stars.The space distribution of UV Cet flare stars in the solar vicinity indicates that these low luminosity stars belong to the disk population of the Galaxy. Therefore one can suppose that all red dwarf stars have a space distribution which is similar to that of the flare stars (Mirzoyan et al. 1988a). Only a small part of them is found in star clusters and associations. The T Tau stars are an exception: because of their very short lifetime, all of them are found in stellar associations.The space distribution of red dwarf stars is determined by the fact that all of them are formed in star clusters and associations and are finally lost from their stellar systems and merge into the general galactic field (Mirzoyan 1995).
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Ekström, Sylvia, Georges Meynet, Raphael Hirschi e André Maeder. "Powerful explosions atZ= 0?" Proceedings of the International Astronomical Union 4, S255 (giugno 2008): 194–98. http://dx.doi.org/10.1017/s1743921308024812.
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AbstractMetal-free stars are assumed to evolve at constant mass because of the very low stellar winds. This leads to large CO-core mass at the end of the evolution, so primordial stars with an initial mass between 25 and 85M⊙are expected to end as direct black holes, the explosion energy being too weak to remove the full envelope.We show that when rotation enters into play, some mass is lost because the stars are prone to reach the critical velocity during the main sequence evolution. Contrary to what happens in the case of very low- but non zero-metallicity stars, the enrichment of the envelope by rotational mixing is very small and the total mass lost remains modest. The compactness of the primordial stars lead to a very inefficient transport of the angular momentum inside the star, so the profile of Ω(r) is close to Ωr2= const. As the core contracts, the rotation rate increases, and the star ends its life with a fast spinning core. Such a configuration has been shown to modify substantially the dynamics of the explosion. Where one expected a weak explosion or none at all, rotation might boost the explosion energy and drive a robust supernova. This will have important consequences in the way primordial stars enriched the early Universe.
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Andrews, H., D. Fenech, R. K. Prinja, J. S. Clark e L. Hindson. "A radio census of the massive stellar cluster Westerlund 1". Astronomy & Astrophysics 632 (25 novembre 2019): A38. http://dx.doi.org/10.1051/0004-6361/201936256.
Testo completoAbstract (sommario):
Context. Massive stars and their stellar winds are important for a number of feedback processes. The mass lost in the stellar wind can help determine the end-point of the star as a neutron star (NS) or a black hole (BH). However, the impact of mass loss on the post-main sequence evolutionary stage of massive stars is not well understood. Westerlund 1 is an ideal astrophysical laboratory in which to study massive stars and their winds in great detail over a large range of different evolutionary phases. Aims. We aim to study the radio emission from Westerlund 1, in order to measure radio fluxes from the population of massive stars, and determine mass-loss rates and spectral indices where possible. Methods. Observations were carried out in 2015 and 2016 with the Australia Telescope Compact Array (ATCA) at 5.5 and 9 GHz using multiple configurations, with maximum baselines ranging from 750 m to 6 km. Results. Thirty stars are detected in the radio from the fully concatenated dataset, ten of which are Wolf-Rayet stars (WRs) (predominantly late type WN stars), five yellow hypergiants (YHGs), four red supergiants (RSGs), one luminous blue variable (LBV), the sgB[e] star W9, and several OB supergiants. New source detections in the radio are found for five WR stars, and five OB supergiants. These detections lead to evidence for three new OB supergiant binary candidates, which is inferred from derived spectral index limits. Conclusions. Spectral indices and index limits were determined for massive stars in Westerlund 1. For cluster members found to have partially optically thick emission, mass-loss rates were calculated. Under the approximation of a thermally emitting stellar wind and a steady mass-loss rate, clumping ratios were then estimated for eight WRs. Diffuse radio emission was detected throughout the cluster. Detections of knots of radio emission with no known stellar counterparts indicate the highly clumped structure of this intra-cluster medium, likely shaped by a dense cluster wind.
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Georgy, Cyril, Georges Meynet e André Maeder. "Wind anisotropy and stellar evolution". Proceedings of the International Astronomical Union 4, S255 (giugno 2008): 199–203. http://dx.doi.org/10.1017/s1743921308024824.
Testo completoAbstract (sommario):
AbstractMass loss is a determinant factor which strongly affects the evolution and the fate of massive stars. At low metallicity, stars are supposed to rotate faster than at the solar one. This favors the existence of stars near the critical velocity. In this rotation regime, the deformation of the stellar surface becomes important, and wind anisotropy develops. Polar winds are expected to be dominant for fast rotating hot stars.These polar winds allow the star to lose large quantities of mass and still retain a high angular momentum, and they modify the evolution of the surface velocity and the final angular momentum retained in the star's core. We show here how these winds affect the final stages of massive stars, according to our knowledge about Gamma Ray Bursts. Computation of theoretical Gamma Ray Bursts rate indicates that our models have too fast rotating cores, and that we need to include an additional effect to spin them down. Magnetic fields in stars act in this direction, and we show how they modify the evolution of massive star up to the final stages.
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Woolf, Peter Grahame. "Review: Lost in the Stars: The Forgotten Musical Life of Alexander Siloti". Music and Letters 85, n. 3 (1 agosto 2004): 480–83. http://dx.doi.org/10.1093/ml/85.3.480-a.
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Thompson, Brian C. "Lost in the Stars: The Forgotten Musical Life of Alexander Siloti (review)". Notes 60, n. 3 (2004): 692–94. http://dx.doi.org/10.1353/not.2004.0042.
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Tailo, M., A. P. Milone, E. P. Lagioia, F. D’Antona, S. Jang, E. Vesperini, A. F. Marino et al. "Mass-loss law for red giant stars in simple population globular clusters". Monthly Notices of the Royal Astronomical Society 503, n. 1 (1 marzo 2021): 694–703. http://dx.doi.org/10.1093/mnras/stab568.
Testo completoAbstract (sommario):
ABSTRACT The amount of mass lost by stars during the red-giant branch (RGB) phase is one of the main parameters to understand and correctly model the late stages of stellar evolution. Nevertheless, a fully comprehensive knowledge of the RGB mass-loss is still missing. Galactic Globular Clusters (GCs) are ideal targets to derive empirical formulations of mass-loss, but the presence of multiple populations with different chemical compositions has been a major challenge to constrain stellar masses and RGB mass-losses. Recent work has disentangled the distinct stellar populations along the RGB and the horizontal branch (HB) of 46 GCs, thus providing the possibility to estimate the RGB mass-loss of each stellar population. The mass-losses inferred for the stellar populations with pristine chemical composition (called first-generation or 1G stars) tightly correlate with cluster metallicity. This finding allows us to derive an empirical RGB mass-loss law for 1G stars. In this paper, we investigate seven GCs with no evidence of multiple populations and derive the RGB mass-loss by means of high-precision Hubble-Space Telescope photometry and accurate synthetic photometry. We find a cluster-to-cluster variation in the mass-loss ranging from ∼0.1 to ∼0.3 M⊙. The RGB mass-loss of simple-population GCs correlates with the metallicity of the host cluster. The discovery that simple-population GCs and 1G stars of multiple population GCs follow similar mass-loss versus metallicity relations suggests that the resulting mass-loss law is a standard outcome of stellar evolution.
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Liebert, James. "White Dwarfs and Planetary Central Stars". Symposium - International Astronomical Union 131 (1989): 545–54. http://dx.doi.org/10.1017/s0074180900139166.
Testo completoAbstract (sommario):
Studies of hot white dwarf samples constrain the properties and evolution of planetary nuclei and the nebulae. In particular, the white dwarf and planetary nebulae formation rates are compared. I discuss the overlap of the sequences of white dwarfs having hydrogen (DA) and helium-rich (DO) atmospheres with known central stars of high surface gravity. There is evidence that the hydrogen atmosphere nuclei have “thick” outer hydrogen layers (≳ 10−4 M⊙), but that DA white dwarfs may have surface hydrogen layers orders of magnitude thinner. Finally, a DA planetary nucleus is discussed (0950+139) which has undergone a late nebular ejection; this object may be demonstrating that a hydrogen layer can be lost even after the star has entered the white dwarf cooling sequence.
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Marino, S., M. Flock, Th Henning, Q. Kral, L. Matrà e M. C. Wyatt. "Population synthesis of exocometary gas around A stars". Monthly Notices of the Royal Astronomical Society 492, n. 3 (29 gennaio 2020): 4409–29. http://dx.doi.org/10.1093/mnras/stz3487.
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ABSTRACT The presence of CO gas around 10–50 Myr old A stars with debris discs has sparked debate on whether the gas is primordial or secondary. Since secondary gas released from planetesimals is poor in H2, it was thought that CO would quickly photodissociate never reaching the high levels observed around the majority of A stars with bright debris discs. Kral et al. showed that neutral carbon produced by CO photodissociation can effectively shield CO and potentially explain the high CO masses around 9 A stars with bright debris discs. Here, we present a new model that simulates the gas viscous evolution, accounting for carbon shielding and how the gas release rate decreases with time as the planetesimal disc loses mass. We find that the present gas mass in a system is highly dependant on its evolutionary path. Since gas is lost on long time-scales, it can retain a memory of the initial disc mass. Moreover, we find that gas levels can be out of equilibrium and quickly evolving from a shielded on to an unshielded state. With this model, we build the first population synthesis of gas around A stars, which we use to constrain the disc viscosity. We find a good match with a high viscosity (α ∼ 0.1), indicating that gas is lost on time-scales ∼1–10 Myr. Moreover, our model also shows that high CO masses are not expected around FGK stars since their planetesimal discs are born with lower masses, explaining why shielded discs are only found around A stars. Finally, we hypothesize that the observed carbon cavities could be due to radiation pressure or accreting planets.
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Schootemeijer, A., e N. Langer. "Wolf–Rayet stars in the Small Magellanic Cloud as testbed for massive star evolution". Astronomy & Astrophysics 611 (marzo 2018): A75. http://dx.doi.org/10.1051/0004-6361/201731895.
Testo completoAbstract (sommario):
Context. The majority of the Wolf–Rayet (WR) stars represent the stripped cores of evolved massive stars who lost most of their hydrogen envelope. Wind stripping in single stars is expected to be inefficient in producing WR stars in metal-poor environments such as the Small Magellanic Cloud (SMC). While binary interaction can also produce WR stars at low metallicity, it is puzzling that the fraction of WR binaries appears to be about 40%, independent of the metallicity.Aim. We aim to use the recently determined physical properties of the twelve known SMC WR stars to explore their possible formation channels through comparisons with stellar models.Methods. We used the MESA stellar evolution code to construct two grids of stellar models with SMC metallicity. One of these consists of models of rapidly rotating single stars, which evolve in part or completely chemically homogeneously. In a second grid, we analyzed core helium burning stellar models assuming constant hydrogen and helium gradients in their envelopes.Results. We find that chemically homogeneous evolution is not able to account for the majority of the WR stars in the SMC. However, in particular the apparently single WR star SMC AB12, and the double WR system SMC AB5 (HD 5980) appear consistent with this channel. We further find a dichotomy in the envelope hydrogen gradients required to explain the observed temperatures of the SMC WR stars. Shallow gradients are found for the WR stars with O star companions, while much steeper hydrogen gradients are required to understand the group of hot apparently single WR stars.Conclusions. The derived shallow hydrogen gradients in the WR component of the WR+O star binaries are consistent with predictions from binary models where mass transfer occurs early, in agreement with their binary properties. Since the hydrogen profiles in evolutionary models of massive stars become steeper with time after the main sequence, we conclude that most of the hot (Teff > 60 kK ) apparently single WR stars lost their envelope after a phase of strong expansion, e.g., as the result of common envelope evolution with a lower mass companion. The so far undetected companions, either main sequence stars or compact objects, are then expected to still be present. A corresponding search might identify the first immediate double black hole binary progenitor with masses as high as those detected in GW150914.
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Johnston, Kathryn V., Stein Sigurdsson e Lars Hernquist. "Measuring Mass Loss Rates from Galactic Satellites". International Astronomical Union Colloquium 172 (1999): 397–98. http://dx.doi.org/10.1017/s0252921100072882.
Testo completoAbstract (sommario):
Number count profiles of many Galactic and some extra-galactic satellite systems show evidence for associated stars beyond the cut-off in density that is identified as the point of tidal limitation (e.g. Irwin & Hatzidimitriou 1995, Grillmair et al. 1995). These “extra-tidal” stars are assumed to be debris lost from the satellite due to heating or stripping by the Galactic tidal field or (in the case of globular clusters) evaporation of stars over the tidal boundary. In this contribution we present a method for using these features to measure the mass loss rate from the satellite, and test it on the results of numerical simulations of satellite disruption. A more detailed discussion of all aspects of this work can be found in Johnston, Sigurdsson & Hemquist (1998).In the numerical simulations, the satellite’s evolution along an orbit in a three component rigid model of the Galaxy is followed using a self-consistent field (SCF) code (developed by Hernquist & Ostriker 1992) to calculate the mutual interactions of stars in the satellite. Figure 1 shows the annularly averaged number surface density from one example simulation “observed” from the viewpoint of the center of the Galaxy after several Gigayears. The closed (open) symbols show the profile recovered if only bound (all) stars are considered. Clearly there is a break in the open symbols at the radius rbreak where the analysis becomes dominated by unbound stars.
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Sharina, M. E., L. N. Makarova e D. I. Makarov. "Population gradients in dwarf spheroidal galaxies KKs 3 and ESO 269-66". Proceedings of the International Astronomical Union 14, S344 (agosto 2018): 420–21. http://dx.doi.org/10.1017/s1743921318005550.
Testo completoAbstract (sommario):
AbstractWe compare the properties of stellar populations for globular clusters (GCs) and field stars in two dwarf spheroidal galaxies (dSphs): ESO269-66, a close neighbour of NGC5128, and KKs3, one of the few isolated dSphs within 10 Mpc. We analyse the surface density profiles of low and high metallicity (blue and red) stars in two galaxies using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favour of the metallicity and age gradients in dSphs; 2) globular clusters in KKs3 and ESO 269-66 contain 4 and 40 percent of all stars with [Fe / H] ~ 1.6 dex and the age of 12 Gyr, correspondingly. Therefore, GCs are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO269-66, probably, thanks to its isolation.
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Charbonnel, Corinne. "Globular cluster abundances: the imprint of first-generation massive stars". Proceedings of the International Astronomical Union 5, S266 (agosto 2009): 131–42. http://dx.doi.org/10.1017/s1743921309990974.
Testo completoAbstract (sommario):
AbstractGalactic globular cluster (GC) stars exhibit abundance patterns that are not shared by their field counterparts, namely the well-documented O–Na, C–N and Mg–Al anticorrelations. Recent observations provide compelling evidence that these abundance anomalies were already present in the intracluster gas from which the presently observed stars formed. The current explanation is that the gas was polluted very early in the history of the GC by material processed through H burning at high temperatures and then lost by stars more massive than the long-lived stars we still observe today. However the ‘polluters’ have not yet been unambiguously identified. Most studies have focused on asymptotic giant brach stars, but rotating massive stars present an interesting alternative. Here, we critically analyse the pros and cons of both potential stellar polluters. We discuss the constraints that the observational data provide on stellar nucleosynthesis and hydrodynamics, as well as on the formation and early evolution of very massive star clusters.
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Vlemmings, W. H. T. "Magnetic fields around AGB stars and Planetary Nebulae". Proceedings of the International Astronomical Union 9, S302 (agosto 2013): 389–97. http://dx.doi.org/10.1017/s1743921314002580.
Testo completoAbstract (sommario):
AbstractStars with a mass up to a few solar masses are one of the main contributors to the enrichment of the interstellar medium in dust and heavy elements. However, while significant progress has been made, the process of the mass-loss responsible for this enrichment is still not exactly known and forces beyond radiation pressure might be required. Often, the mass lost in the last phases of the stars life will become a spectacular planetary nebula. The shaping process of often strongly a-spherical PNe is equally elusive. Both binaries and magnetic fields have been suggested to be possible agents although a combination of both might also be a natural explanation.Here I review the current evidence for magnetic fields around AGB and post-AGB stars pre-Planetary Nebulae and PNe themselves. Magnetic fields appear to be ubiquitous in the envelopes of apparently single stars, challenging current ideas on its origin, although we have found that binary companions could easily be hidden from view. There are also strong indications of magnetically collimated outflows from post-AGB/pre-PNe objects supporting a significant role in shaping the circumstellar envelope.
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Verbeke, Robbert, Bert Vandenbroucke e Sven De Rijcke. "How the first stars shaped the faintest gas-dominated dwarf galaxies". Proceedings of the International Astronomical Union 11, S317 (agosto 2015): 360–61. http://dx.doi.org/10.1017/s174392131500856x.
Testo completoAbstract (sommario):
AbstractCosmological simulations predict that dark matter halos with circular velocities lower than 30 km/s should have lost most of their neutral gas by heating of the ultra-violet background. This is in stark contrast with gas-rich galaxies such as e.g. Leo T, Leo P and Pisces A, which all have circular velocities of ~15 km/s (Ryan-Weber et al. 2008, Bernstein-Cooper et al. 2014, Tollerud et al. 2015). We show that when we include feedback from the first stars into our models, simulated dwarfs have very different properties at redshift 0 than when this form of feedback is not included. Including this Population-III feedback leads to galaxies that lie on the baryonic Tully-Fisher relation over the entire mass range of star forming dwarf galaxies, as well as reproducing a broad range of other observational properties.
31
Boulangier, J., D. Gobrecht e L. Decin. "Dynamics, temperature, chemistry, and dust: Ingredients for a self-consistent AGB wind". Proceedings of the International Astronomical Union 14, S343 (agosto 2018): 129–33. http://dx.doi.org/10.1017/s1743921318005094.
Testo completoAbstract (sommario):
AbstractUnderstanding Asymptotic Giant Branch (AGB) stars is important as they play a vital role in the chemical life cycle of galaxies. AGB stars are in a phase of their life time where they have almost ran out of fuel and are losing vast amounts of material to their surroundings, via stellar winds. As this is an evolutionary phase of low mass stars, almost all stars go through this phase making them one of the main contributors to the chemical enrichment of galaxies. It is therefore important to understand what kind of material is being lost by these stars, and how much and how fast. This work summarises the steps we have taken towards developing a self-consistent AGB wind model. We improve on current models by firstly coupling chemical and hydrodynamical evolution, and secondly by upgrading the nucleation theory framework to investigate the creation of TiO2, SiO, MgO, and Al2O3 clusters.
32
Bowen, George H. "Pulsation and Mass Loss in LPVs". International Astronomical Union Colloquium 139 (1993): 191. http://dx.doi.org/10.1017/s0252921100117300.
Testo completoAbstract (sommario):
AbstractThe large-amplitude pulsation of long-period variables, together with a number of other interacting processes and phenomena, causes a rich variety of effects on the structure and behavior of the stars. Outflowing winds result, causing extensive mass loss, with profound consequences for stellar evolution. The present status of modeling calculations for LPVs will be discussed first, with various examples. Emphasis will be given to the great importance of complex, nonlinear, time-dependent interactions between things such as the waves and atmospheric shocks that result from pulsation; non-LTE radiative transfer; non-equilibrium chemistry; the growth, changing optical properties, and dynamics of grains; and radiation pressure on both grains and molecules. I will then survey the developing implications and insights from new results and from work now in progress. Some of these concern the structure and the behavior of individual stars (e.g. determination of the pulsation mode and limiting amplitude; properties of more massive stars); some relate to the evolution of individual stars (e.g. evolution of the wind and the mass loss rate; the wind and circumstellar region during helium shell flashes; effects of the star's metallicity); and some relate to the evolution of populations of stars (e.g. the white dwarf mass distribution). All of these, and many more, offer new perspectives and new understanding concerning the character of LPVs and their role in stellar evolution.
33
Li, Bao Hua, Jing Li e Xi Jun Chen. "An Autonomous Predictive Centroiding Algorithm for Star Sensor". Applied Mechanics and Materials 128-129 (ottobre 2011): 510–15. http://dx.doi.org/10.4028/www.scientific.net/amm.128-129.510.
Testo completoAbstract (sommario):
Of all current methods for measuring spacecraft attitude, the use of star sensors produces the most accurate measurements. Conventional star sensors repeat these processes with Lost-In-Space case. To advance the methods available to solve these problems, this paper presents an autonomous predictive centroiding algorithm for the star sensor. The star sensor works in the star predictive centroiding case while few recognized stars within the FOV (Field of View). The ideal locations of unrecognized stars and recognized stars in star image are predicted at first. Then the corresponding real locations of recognized stars and unrecognized stars are obtained in the threshold scan window of predictive centroiding. It enables only several hundred pixels to be scanned. The speed and the accuracy of this algorithm are successfully demonstrated in comparison with the ordinary centroiding algorithms which don't use the previous image data. Finally the autonomous predictive centroiding algorithm was successfully demonstrated with real sky experiment in 2008 and on-orbit in 2010.
34
Arun, Kenath. "Some Aspects of Binary Compact Astrophysical Objects". Mapana - Journal of Sciences 7, n. 1 (31 maggio 2008): 64–70. http://dx.doi.org/10.12723/mjs.12.6.
Testo completoAbstract (sommario):
This paper shall look into the systems of compact astrophysical objects (black holes, neutron stars and white dwarfs) concerning mainly with binary systems. Determination of the orbital periods, velocities, etc, for such systems and also, the energy lost from the system through gravitational waves has been made, From the concept of energy loss, the merger of the two black holes in the system has been considered and the typical time required for the merger is calculated.
35
Lev, Assaf, e Shlomo Weinish. "Lost in transition: analyzing the lifecycle of Israeli football stars in becoming coaches". Israel Affairs 26, n. 4 (4 giugno 2020): 555–72. http://dx.doi.org/10.1080/13537121.2020.1775940.
Testo completo
36
Wannier, P. G., R. Sahai, B. G. Andersson e H. R. Johnson. "Mass loss from red giant stars. II - Carbon stars". Astrophysical Journal 358 (luglio 1990): 251. http://dx.doi.org/10.1086/168980.
Testo completo
37
Engels, Dieter. "Masers: Probing the mass loss process in PPN". Symposium - International Astronomical Union 180 (1997): 348–49. http://dx.doi.org/10.1017/s0074180900131249.
Testo completoAbstract (sommario):
With the advent of the IRAS All-Sky Survey a sizeable number of transition objects between the AGB and the PN-phase were found - the Proto Planetary Nebulae (PPN). Oxygen-rich AGB stars often show prominent masers of SiO, H2O, and OH, which are lost during the transition process. The heavy mass loss on the AGB however does not stop abruptly and a new axisymmetric wind develops during the PPN phase. These winds both may host new masers and they can be used to study the changes of the mass loss process after that the stars have stopped their large-amplitude variations on the AGB. Several PPN are known to have OH masers, and at least in one case, HD 101584, the presence of a bipolar outflow could be proven (te Lintel Hekkert et al. 1992). Lewis (1989) found that main-line OH masers become prominent again. I will discuss here conclusions, which can be drawn from observations of H2O masers in PPN.
38
Wong, Michael. "Astrocyte Networks and Epilepsy: When Stars Collide". Epilepsy Currents 9, n. 4 (luglio 2009): 113–15. http://dx.doi.org/10.1111/j.1535-7511.2009.01310.x.
Testo completoAbstract (sommario):
Loss of Astrocytic Domain Organization in the Epileptic Brain. Oberheim NA, Tian GF, Han X, Peng W, Takano T, Ransom B, Nedergaard M. J Neurosci 2008;28(13):3264–3276. Gliosis is a pathological hallmark of posttraumatic epileptic foci, but little is known about these reactive astrocytes beyond their high glial fibrillary acidic protein (GFAP) expression. Using diolistic labeling, we show that cortical astrocytes lost their nonoverlapping domain organization in three mouse models of epilepsy: posttraumatic injury, genetic susceptibility, and systemic kainate exposure. Neighboring astrocytes in epileptic mice showed a 10-fold increase in overlap of processes. Concurrently, spine density was increased on dendrites of excitatory neurons. Suppression of seizures by the common antiepileptic, valproate, reduced the overlap of astrocytic processes. Astrocytic domain organization was also preserved in APP transgenic mice expressing a mutant variant of human amyloid precursor protein despite a marked upregulation of GFAP. Our data suggest that loss of astrocytic domains was not universally associated with gliosis, but restricted to seizure pathologies. Reorganization of astrocytes may, in concert with dendritic sprouting and new synapse formation, form the structural basis for recurrent excitation in the epileptic brain. Astroglial Metabolic Networks Sustain Hippocampal Synaptic Transmission. Rouach N, Koulakoff A, Abudara V, Willecke K, Giaume C. Science 2008;322(5907):1551–1555. Astrocytes provide metabolic substrates to neurons in an activity-dependent manner. However, the molecular mechanisms involved in this function, as well as its role in synaptic transmission, remain unclear. Here, we show that the gap-junction subunit proteins connexin 43 and 30 allow intercellular trafficking of glucose and its metabolites through astroglial networks. This trafficking is regulated by glutamatergic synaptic activity mediated by AMPA receptors. In the absence of extracellular glucose, the delivery of glucose or lactate to astrocytes sustains glutamatergic synaptic transmission and epileptiform activity only when they are connected by gap junctions. These results indicate that astroglial gap junctions provide an activity-dependent intercellular pathway for the delivery of energetic metabolites from blood vessels to distal neurons.
39
Charpinet, Stephane, Noemi Giammichele, Weikai Zong, Valérie Van Grootel, Pierre Brassard e Gilles Fontaine. "Rotation in sdB stars as revealed by stellar oscillations". Open Astronomy 27, n. 1 (1 luglio 2018): 112–19. http://dx.doi.org/10.1515/astro-2018-0012.
Testo completoAbstract (sommario):
Abstract An interesting opportunity offered by the detection of stellar oscillations is the possibility to infer the internal rotation rate of a star through the so-called rotational splittings. Such seismic measurements remained rather scarce for hot B subdwarf (sdB) stars until the advent of space observations with the Kepler spacecraft. Nowadays, however, a number of rotation measurements have become available, offering a glimpse on the global rotational properties of sdB stars. Here, we briefly discuss what asteroseismology starts to reveal on the rotation rate of these stars. We also make connections with the internal rotation of red-giant and white-dwarf stars. In particular, we show that the very slow rotation rates derived for single sdB stars, and their similarities with the dynamical properties of the cores of red-clump stars, strongly suggest that they evolved from red-giants rather than merger events.We also point out that no more angular momentum seems to be lost by stellar cores throughout the helium burning phase until the cooling white-dwarf stage, indicating that all the braking occurs before, most likely during red-giant branch evolution.
40
Koopmans, L. V. E. "Strong Gravitational Lensing: Bright Galaxies & Lost Dark-Matter". Proceedings of the International Astronomical Union 3, S244 (giugno 2007): 196–205. http://dx.doi.org/10.1017/s1743921307013993.
Testo completoAbstract (sommario):
AbstractGravitational lensing and stellar dynamics provide two complementary methods to probe the smooth and clumpy stellar and dark-matter mass distribution in early-type galaxies, currently already over a range of two orders of magnitude in virial mass, more than ten orders of magnidude in dynamic mass range in each galaxy (i.e. from stars, CDM substructure to massive dark-matter halos), over 0–1 in redshift, and a range of 0–100 effective radii. This makes their unification a powerful new tool in the study of the formation, structure and evolution of these massive systems. I review recent results that we obtained, based on gravitational lens systems from the Sloan Lens ACS Survey (SLACS), and outline some ongoing and future work.
41
Savino, A., e L. Posti. "Gaia DR2 orbital properties for field stars with globular cluster-like CN band strengths". Astronomy & Astrophysics 624 (aprile 2019): L9. http://dx.doi.org/10.1051/0004-6361/201935417.
Testo completoAbstract (sommario):
Context. Large spectroscopic surveys of the Milky Way have revealed that a small population of stars in the halo have light element abundances comparable to those found in globular clusters. The favoured explanation for the peculiar abundances of these stars is that they originated inside a globular cluster and were subsequently lost. Aims. Using orbit calculations we assess the likelihood that an existing sample of 57 field stars with globular cluster-like CN band strength originated in any of the currently known Milky Way globular clusters. Methods. Using Sloan Digital Sky Survey and Gaia data, we determine orbits and integrals of motion of our sample of field stars, and use these values and metallicity to identify likely matches to globular clusters. The pivot hypothesis is that had these stars been stripped from such objects, they would have remained on very similar orbits. Results. We find that ∼70% of the sample of field stars have orbital properties consistent with the halo of the Milky Way; however, only 20 stars have likely orbital associations with an existing globular cluster. The remaining ∼30% of the sample have orbits that place them in the outer Galactic disc. No cluster of similar metallicity is known on analogous disc orbits. Conclusions. The orbital properties of the halo stars seem to be compatible with the globular cluster escapee scenario. The stars in the outer disc are particularly surprising and deserve further investigation to establish their nature.
42
Rubin, Douglas, e Abraham Loeb. "Constraining the Stellar Mass Function in the Galactic Center via Mass Loss from Stellar Collisions". Advances in Astronomy 2011 (2011): 1–19. http://dx.doi.org/10.1155/2011/174105.
Testo completoAbstract (sommario):
The dense concentration of stars and high-velocity dispersions in the Galactic center imply that stellar collisions frequently occur. Stellar collisions could therefore result in significant mass loss rates. We calculate the amount of stellar mass lost due to indirect and direct stellar collisions and find its dependence on the present-day mass function of stars. We find that the total mass loss rate in the Galactic center due to stellar collisions is sensitive to the present-day mass function adopted. We use the observed diffuse X-ray luminosity in the Galactic center to preclude any present-day mass functions that result in mass loss rates>10-5M⨀yr−1in the vicinity of~1″. For present-day mass functions of the form,dN/dM∝M-α, we constrain the present-day mass function to have a minimum stellar mass≲7M⨀and a power-law slope≳1.25. We also use this result to constrain the initial mass function in the Galactic center by considering different star formation scenarios.
43
Ebisuzaki, Toshikazu. "X-ray Spectra and Atmospheric Structures of Bursting Neutron Stars". Symposium - International Astronomical Union 125 (1987): 250. http://dx.doi.org/10.1017/s0074180900160863.
Testo completoAbstract (sommario):
High quality spectra of Japanese X-ray satellite TENMA permit us detailed studies of X-ray burst on color temperature vs. luminosity diagram. Using this diagram, Sugimoto Ebisuzaki and Hanawa (1984) divided bursts from MXB1636-536 into two classes: bright class and faint class. In the decay phase of bright class bursts, surface of neutron star should be covered with pure helium matter processed on the surface of neutron star because hydrogen-rich matter is completely lost due to mass loss. On the other hand, surface of neutron star should be covered by hydrogen-rich matter in the case of faint class bursts because any mass loss is not driven in the faint class bursts. I constructed color temperature vs. luminosity diagrams of X-ray burst sources MXB1636-536 and MXB1608-522 using data of Japanese X-ray satellite TENMA and found systematic deviations between evolutional paths of the bright class and faint class bursts on these diagrams. The deviations are successfully accounted for by the difference in chemical composition between bright class and faint class bursts: evolutional paths of bright class and faint class are respectively in good agreement with theoretical curves for pure helium and hydrogen-rich matter. This is a direct evidence of ejection of hydrogen-rich envelope in the bright class bursts.
44
Mallik, D. C. V. "Initial Masses". Symposium - International Astronomical Union 131 (1989): 493–504. http://dx.doi.org/10.1017/s0074180900139063.
Testo completoAbstract (sommario):
Planetary nebulae represent a transitory stage in the life of the majority of stars as they proceed towards the end of their nuclear evolution and descend to the domain of white dwarfs. The immediate precursors of the central stars are probably red giants which populate a part of the HR diagram far removed from the region inhabited by the central stars of well recognised nebulae. The problem of determining the initial masses is complicated by the widespread occurrence of massloss on the red giant branch. The total amount of mass lost by a star must depend upon a number of stellar parameters including the initial mass, but the exact nature of this dependence remains to be discovered and a unique relation between the final masses and initial main sequence masses is not yet available. Thus even though the mass distribution of the nuclei of planetary nebulae (NPN) has been derived in the last few years, it has not been possible to deduce from this an unambiguous initial mass distribution of the progenitors. Further, an observed sample always suffers from selection effects and, in the particular case of NPN mass distribution, this has led to irretrievable loss of information.
45
MacLennan, Toby. "Presentation of Playing the Stars". Culture and Cosmos 16, n. 1 and 2 (ottobre 2012): 443–50. http://dx.doi.org/10.46472/cc.01216.0275.
Testo completoAbstract (sommario):
This talk reports on a performance of the planetarium event Singing the stars with sculptures, which was performed at the H.R. Macmillan Planetarium in Vancouver and the Seneca College Planetarium in Ontario. Subsequent performances were done at the Art Gallery of Ontario, P.S.1, New York City, the 10th International Sculpture Conference, Toronto, and The National Gallery of Canada. It was reviewed in the Village Voice, Arts Canada, The New Art Examiner, Vanguard Magazine, and CBC Radio: Out of the belly of Vancouver’s H.R. Macmillan Planetarium, the star-making machine rises to the star chamber, carrying three musicians with their instruments, and three sculptures. Atop each sculpture is an overhanging frame of five wooden bars, which acts as a musical score. Lights go down over the planetarium audience. Stars move across the sky. Only the constellations and the luminous bars atop the sculptures are visible. Swept up by the grandeur of the constellations, the musicians look up through the bars atop their sculptures and give a concert playing the stars. The concert is inspired by a story from my book, Singing the Stars. A village of people has lost the power of night, which once resided within them. The people attempt to lure the night back with the help of sculptures, which will enable them to play and sing the stars. They hope that, lured by the music, the night will come close to their faces, and bits of darkness will fall into their ears, eyes and mouths and gradually fill up their bodies with the night sky.
46
Spada, F., e A. C. Lanzafame. "Competing effect of wind braking and interior coupling in the rotational evolution of solar-like stars". Astronomy & Astrophysics 636 (aprile 2020): A76. http://dx.doi.org/10.1051/0004-6361/201936384.
Testo completoAbstract (sommario):
Solar-like stars (M ≲ 1.3 M⊙) lose angular momentum through their magnetized winds. The resulting evolution of the surface rotation period, which can be directly measured photometrically, has the potential to be an accurate indicator of stellar age, and is constrained by observations of rotation periods of coeval stars, such as members of Galactic open clusters. A prominent observational feature of the mass–rotation period diagrams of open clusters is a sequence of relatively slower rotators. The formation and persistence of this slow-rotator sequence across several billion years imply an approximately coherent spin-down of the stars that belong to it. In particular, the sequence is observed to evolve coherently toward longer periods in progressively older clusters. Recent observations of the ≈700 Myr Praesepe and the 1 Gyr NGC 6811 clusters, however, are not fully consistent with this general pattern. While the stars of 1 M⊙ on the slow-rotator sequence of the older NGC 6811 have longer periods than their counterparts in the younger Praesepe, as expected, the two sequences essentially merge at lower masses (≲0.8 M⊙). In other words, it seems that low-mass stars have not been spinning down in the intervening 300 Myr. Here we show that this behavior is a manifestation of the variable rotational coupling in solar-like stars. The resurfacing of angular momentum from the interior can temporarily compensate for that lost at the surface due to wind braking. In our model the internal redistribution of angular momentum has a steep mass dependence; as a result, the re-coupling occurs at different ages for stars of different masses. The semi-empirical mass dependence of the rotational coupling timescale included in our model produces an evolution of the slow-rotator sequence in very good agreement with the observations. Our model, in particular, explains the stalled surface spin-down of low-mass stars between Praesepe and NGC 6811, and predicts that the same behavior should be observable at other ages in other mass ranges.
47
Tanabé, T., S. Nishida, Y. Nakada, T. Onaka, I. S. Glass e M. Sauvage. "Systematic study of AGB stars in the intermediate-age globular clusters in the Magellanic Clouds". Symposium - International Astronomical Union 191 (1999): 573–78. http://dx.doi.org/10.1017/s0074180900203574.
Testo completoAbstract (sommario):
We performed systematic infrared observations of the intermediate-age Magellanic Clouds clusters NGC 419, NGC 1783 and NGC 1978. Mid-infrared stars discovered in NGC 419 and NGC 1978 are very red and must be undergoing intense mass loss (comparable to superwinds). They are probably carbon stars but do not seem to show any FIR excesses. Three optically visible carbon stars as well as (at least) 2 near-infrared carbon stars observed with ISOPHOT show 60 μm excesses which may indicate mass loss in the past. It seems that the MIR stars are fainter than the AGB tip luminosity and that their Mbols are close to those of the transition luminosity from M type to C stars. Therefore, these MIR stars may not be in the final stage of the AGB phase. This may suggest that AGB stars lose mass heavily at some other time, possibly during the transition from M type to C stars.
48
Flor-Torres, L. M., R. Coziol, K. P. Schröder, D. Jack e J. H. M. M. Schmitt. "CONNECTING THE FORMATION OF STARS AND PLANETS. II: COUPLING THE ANGULAR MOMENTUM OF STARS WITH THE ANGULAR MOMENTUM OF PLANETS". Revista Mexicana de Astronomía y Astrofísica 57, n. 1 (1 aprile 2021): 217–31. http://dx.doi.org/10.22201/ia.01851101p.2021.57.01.16.
Testo completoAbstract (sommario):
A sample of 46 stars, host of exoplanets, is used to search for a connection between their formation process and the formation of the planets rotating around them. Separating our sample into two, stars hosting high-mass exoplanets (HMEs) and low-mass exoplanets (LMEs), we found the former to be more massive and to rotate faster than the latter. We also found the HMEs to have higher orbital angular momentum than the LMEs and to have lost more angular momentum through migration. These results are consistent with the view that the more massive the star and the higher its rotation, the more massive was its protoplanetarys disk and rotation, and the more efficient was the extraction of angular momentum from the planets.
49
Kite, Edwin S., e Megan N. Barnett. "Exoplanet secondary atmosphere loss and revival". Proceedings of the National Academy of Sciences 117, n. 31 (21 luglio 2020): 18264–71. http://dx.doi.org/10.1073/pnas.2006177117.
Testo completoAbstract (sommario):
The next step on the path toward another Earth is to find atmospheres similar to those of Earth and Venus—high–molecular-weight (secondary) atmospheres—on rocky exoplanets. Many rocky exoplanets are born with thick (>10 kbar) H2-dominated atmospheres but subsequently lose their H2; this process has no known Solar System analog. We study the consequences of early loss of a thick H2atmosphere for subsequent occurrence of a high–molecular-weight atmosphere using a simple model of atmosphere evolution (including atmosphere loss to space, magma ocean crystallization, and volcanic outgassing). We also calculate atmosphere survival for rocky worlds that start with no H2. Our results imply that most rocky exoplanets orbiting closer to their star than the habitable zone that were formed with thick H2-dominated atmospheres lack high–molecular-weight atmospheres today. During early magma ocean crystallization, high–molecular-weight species usually do not form long-lived high–molecular-weight atmospheres; instead, they are lost to space alongside H2. This early volatile depletion also makes it more difficult for later volcanic outgassing to revive the atmosphere. However, atmospheres should persist on worlds that start with abundant volatiles (for example, water worlds). Our results imply that in order to find high–molecular-weight atmospheres on warm exoplanets orbiting M-stars, we should target worlds that formed H2-poor, that have anomalously large radii, or that orbit less active stars.
50
Bastian, Nate, Sebastian Kamann, Louis Amard, Corinne Charbonnel, Lionel Haemmerlé e Sean P. Matt. "On the origin of the bimodal rotational velocity distribution in stellar clusters: rotation on the pre-main sequence". Monthly Notices of the Royal Astronomical Society 495, n. 2 (16 maggio 2020): 1978–83. http://dx.doi.org/10.1093/mnras/staa1332.
Testo completoAbstract (sommario):
ABSTRACT We address the origin of the observed bimodal rotational distribution of stars in massive young and intermediate age stellar clusters. This bimodality is seen as split main sequences at young ages and also has been recently directly observed in the Vsini distribution of stars within massive young and intermediate age clusters. Previous models have invoked binary interactions as the origin of this bimodality, although these models are unable to reproduce all of the observational constraints on the problem. Here, we suggest that such a bimodal rotational distribution is set-up early within a cluster’s life, i.e. within the first few Myr. Observations show that the period distribution of low-mass ($\lesssim\! 2 \, \mathrm{M}_\odot$) pre-main-sequence (PMS) stars is bimodal in many young open clusters, and we present a series of models to show that if such a bimodality exists for stars on the PMS that it is expected to manifest as a bimodal rotational velocity (at fixed mass/luminosity) on the main sequence for stars with masses in excess of ∼1.5 M⊙. Such a bimodal period distribution of PMS stars may be caused by whether stars have lost (rapid rotators) or been able to retain (slow rotators) their circumstellar discs throughout their PMS lifetimes. We conclude with a series of predictions for observables based on our model.