Articles de revues : « Hertzsprung–Russell diagram »

1

Langer, N., et R. P. Kudritzki. « The spectroscopic Hertzsprung-Russell diagram ». Astronomy & ; Astrophysics 564 (avril 2014) : A52. http://dx.doi.org/10.1051/0004-6361/201423374.

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MacLeod, Morgan, Matteo Cantiello et Melinda Soares-Furtado. « Planetary Engulfment in the Hertzsprung–Russell Diagram ». Astrophysical Journal 853, n^o 1 (16 janvier 2018) : L1. http://dx.doi.org/10.3847/2041-8213/aaa5fa.

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van Loon, Jacco Th. « Cool Stars in the Hertzsprung–Russell Diagram ». Proceedings of the International Astronomical Union 11, A29B (août 2015) : 475–77. http://dx.doi.org/10.1017/s1743921316005925.

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AbstractAs the opening review to the focus meeting “Stellar Behemoths: Red Supergiants across the Local Universe”, I here provide a brief introduction to red supergiants, setting the stage for subsequent contributions. I highlight some recent activity in the field, and identify areas of progress, areas where progress is needed, and how such progress might be achieved.

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Christensen-Dalsgaard, Jørgen. « A Hertzsprung-Russell diagram for stellar oscillations ». Symposium - International Astronomical Union 123 (1988) : 295–98. http://dx.doi.org/10.1017/s0074180900158279.

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I present evolutionary tracks and curves of constant central hydrogen abundance in diagrams based on frequencies of high-order, low-degree p modes. For stars with masses between 0.7 and 1.5 M⊙, a clean separation is obtained between the effects of varying mass and varying evolutionary state.

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Zaninetti, L. « Semi-analytical formulas for the Hertzsprung-Russell diagram ». Serbian Astronomical Journal, n^o 177 (2008) : 73–85. http://dx.doi.org/10.2298/saj0877073z.

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The absolute visual magnitude as function of the observed color (B-V), also named Hertzsprung-Russell diagram, can be described through five equations; that when calibrated stars are available means eight constants. The developed framework allows to deduce the remaining physical parameters, mass, radius and luminosity. This new technique is applied to the first 10 pc, the first 50 pc, the Hyades and to the determination of the distance of a cluster. The case of the white dwarfs is analyzed assuming the absence of calibrated data: our equation produces a smaller ?2 with respect to the standard color-magnitude calibration when applied to the Villanova Catalog of Spectroscopically Identified White Dwarfs. The theoretical basis of the formulas for the colors and the bolometric correction of the stars is clarified by a Taylor expansion in the temperature of the Planck distribution.

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Doom, C., J. P. de Greve et C. de Loore. « Stellar evolution in the upper Hertzsprung-Russell diagram ». Astrophysical Journal 303 (avril 1986) : 136. http://dx.doi.org/10.1086/164060.

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Hubrig, S., P. North et G. Mathys. « Magnetic Ap Stars in the Hertzsprung‐Russell Diagram ». Astrophysical Journal 539, n^o 1 (10 août 2000) : 352–63. http://dx.doi.org/10.1086/309189.

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Jao, Wei-Chun, et Gregory A. Feiden. « An Enhanced Hertzsprung–Russell Diagram Using Gaia EDR3 Data ». Research Notes of the AAS 5, n^o 5 (1 mai 2021) : 124. http://dx.doi.org/10.3847/2515-5172/ac053a.

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Farag, Ebraheem, F. X. Timmes, Morgan Taylor, Kelly M. Patton et R. Farmer. « On Stellar Evolution in a Neutrino Hertzsprung–Russell Diagram ». Astrophysical Journal 893, n^o 2 (23 avril 2020) : 133. http://dx.doi.org/10.3847/1538-4357/ab7f2c.

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Arsentieva, A. A., et I. I. Shevchenko. « Host Stars of Planets on the Hertzsprung–Russell Diagram ». Astronomy Letters 47, n^o 9 (septembre 2021) : 651–60. http://dx.doi.org/10.1134/s1063773721080016.

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Reed, B. Cameron. « Vela OB1 : Probable New Members and Hertzsprung-Russell Diagram ». Astronomical Journal 119, n^o 4 (avril 2000) : 1855–59. http://dx.doi.org/10.1086/301313.

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Escorza, A., H. M. J. Boffin, A. Jorissen, S. Van Eck, L. Siess, H. Van Winckel, D. Karinkuzhi, S. Shetye et D. Pourbaix. « Hertzsprung-Russell diagram and mass distribution of barium stars ». Astronomy & ; Astrophysics 608 (décembre 2017) : A100. http://dx.doi.org/10.1051/0004-6361/201731832.

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Castro, N., L. Fossati, N. Langer, S. Simón-Díaz, F. R. N. Schneider et R. G. Izzard. « The spectroscopic Hertzsprung-Russell diagram of Galactic massive stars ». Astronomy & ; Astrophysics 570 (octobre 2014) : L13. http://dx.doi.org/10.1051/0004-6361/201425028.

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Feoli, A., et L. Mancini. « A HERTZSPRUNG-RUSSELL-LIKE DIAGRAM FOR GALAXIES : THEM•VERSUSMGσ2RELATION ». Astrophysical Journal 703, n^o 2 (10 septembre 2009) : 1502–10. http://dx.doi.org/10.1088/0004-637x/703/2/1502.

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de Jager, C., et H. Nieuwenhuijzen. « Stellar atmospheric instability in the upper part of the Hertzsprung-Russell diagram ». Symposium - International Astronomical Union 116 (1986) : 255–56. http://dx.doi.org/10.1017/s0074180900149046.

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The upper limt of stellar luminosity in the Hertzsprung-Russell diagram is a line running approximately from (log Teff; log (L/L⊙) = (4.5; 6.3) via (4.0; 5.74) to (3.5; 5.7) (Humphreys and Davidson, 1979; Humpreys, 1983).

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Jeffries, R. D. « Age spreads in star forming regions ? » Proceedings of the International Astronomical Union 4, S258 (octobre 2008) : 95–102. http://dx.doi.org/10.1017/s1743921309031743.

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AbstractRotation periods and projected equatorial velocities of pre-main-sequence (PMS) stars in star forming regions can be combined to give projected stellar radii. Assuming random axial orientation, a Monte-Carlo model is used to illustrate that distributions of projected stellar radii are very sensitive to ages and age dispersions between 1 and 10Myr which, unlike age estimates from conventional Hertzsprung-Russell diagrams, are relatively immune to uncertainties due to extinction, variability, distance etc. Application of the technique to the Orion Nebula cluster reveals radius spreads of a factor of 2–3 (FWHM) at a given effective temperature. Modelling this dispersion as an age spread suggests that PMS stars in the ONC have an age range larger than the mean cluster age, that could be reasonably described by the age distribution deduced from the Hertzsprung-Russell diagram. These radius/age spreads are certainly large enough to invalidate the assumption of coevality when considering the evolution of PMS properties (rotation, disks etc.) from one young cluster to another.

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Fang, Min, Jinyoung Serena Kim, Ilaria Pascucci et Dániel Apai. « An Improved Hertzsprung–Russell Diagram for the Orion Trapezium Cluster ». Astrophysical Journal 908, n^o 1 (1 février 2021) : 49. http://dx.doi.org/10.3847/1538-4357/abcec8.

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Daszyńska-Daszkiewicz, Jadwiga. « Energetic properties of stellar pulsations across the Hertzsprung-Russell diagram ». EPJ Web of Conferences 101 (2015) : 01002. http://dx.doi.org/10.1051/epjconf/201510101002.

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Escorza, A., H. M. J. Boffin, A. Jorissen, S. Van Eck, L. Siess, H. Van Winckel, D. Karinkuzhi, S. Shetye et D. Pourbaix. « Hertzsprung-Russell diagram and mass distribution of barium stars (Corrigendum) ». Astronomy & ; Astrophysics 625 (mai 2019) : C3. http://dx.doi.org/10.1051/0004-6361/201731832e.

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Handler, G. « The domain of Doradus variables in the Hertzsprung-Russell diagram ». Monthly Notices of the Royal Astronomical Society 309, n^o 2 (21 octobre 1999) : L19—L23. http://dx.doi.org/10.1046/j.1365-8711.1999.03005.x.

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Schmitt, J. H. M. M. « Magnetic activity of cool stars in the Hertzsprung-Russell diagram ». Proceedings of the International Astronomical Union 7, S286 (octobre 2011) : 296–306. http://dx.doi.org/10.1017/s1743921312005005.

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AbstractI review the X-ray emission from cool stars with outer convection zones in comparison to the Sun with a focus on the properties of low-activity stars. I present the recent results of long-term X-ray monitoring which demonstrate the existence of X-ray cycles on stars with known calcium cycles. The evidence of a minimum stellar X-ray flux is presented and arguments are put forward for the view that the Sun in its extended minimum between 2008 - 2009 behaved very much like a Maunder-minimum Sun.

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Chu, You-Hua. « Ring nebulae around massive stars throughout the Hertzsprung-Russell diagram ». Symposium - International Astronomical Union 212 (2003) : 585–95. http://dx.doi.org/10.1017/s0074180900212965.

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Massive stars evolve across the H-R diagram, losing mass along the way and forming a variety of ring nebulae. During the main sequence stage, the fast stellar wind sweeps up the ambient interstellar medium to form an interstellar bubble. After a massive star evolves into a red giant or a luminous blue variable, it loses mass copiously to form a circumstellar nebula. As it evolves further into a WR star, the fast WR wind sweeps up the previous mass loss and forms a circumstellar bubble. Observations of ring nebulae around massive stars not only are fascinating, but also are useful in providing templates to diagnose the progenitors of supernovae from their circumstellar nebulae. In this review, I will summarize the characteristics of ring nebulae around massive stars throughout the H-R diagram, show recent advances in X-ray observations of bubble interiors, and compare supernovae's circumstellar nebulae with known types of ring nebulae around massive stars.

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Malyuto, V., S. Zubarev et T. Shvelidze. « Homogenized Hertzsprung-Russell diagram for the open cluster NGC 188 ». Astronomische Nachrichten 335, n^o 8 (octobre 2014) : 850–64. http://dx.doi.org/10.1002/asna.201312112.

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Scholz, G. « The position of ET And in the Hertzsprung-Russell diagram ». Astronomische Nachrichten : A Journal on all Fields of Astronomy 307, n^o 1 (1986) : 21–25. http://dx.doi.org/10.1002/asna.2113070109.

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de Jager, Cornells, et Arnout M. van Genderen. « Luminous Blue Variables need not be blue ». International Astronomical Union Colloquium 113 (1989) : 127–30. http://dx.doi.org/10.1017/s0252921100004371.

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AbstractA number of yellow and red super- and hypergiants show phenomena that are similar to those shown by Luminous Blue Variables. The LBV phenomenon may not be restricted to the blue part of the Hertzsprung-Russell diagram and the conventional name ‘S Dor variables’ seems more appropriate.

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Overduin, James, Jacob Buchman, Jonathan Perry et Thomas Krause. « The Scourge of Online Solutions and an Academic Hertzsprung–Russell Diagram ». Physics Educator 03, n^o 02 (juin 2021) : 2150007. http://dx.doi.org/10.1142/s2661339521500074.

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We report on preliminary results of a statistical study of student performance in more than a decade of calculus-based introductory physics courses. Treating average homework and test grades as proxies for student effort and comprehension, respectively, we plot comprehension versus effort in an academic version of the astronomical Hertzsprung–Russell diagram (which plots stellar luminosity versus temperature). We study the evolution of this diagram with time, finding that the “academic main sequence” has begun to break down in recent years as student achievement on tests has become decoupled from homework grades. We present evidence that this breakdown is likely related to the emergence of easily accessible online solutions to most textbook problems, and discuss possible responses and strategies for maintaining and enhancing student learning in the online era.

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Wang, Song, Yu Bai, Lin He et Jifeng Liu. « Stellar X-Ray Activity Across the Hertzsprung–Russell Diagram. I. Catalogs ». Astrophysical Journal 902, n^o 2 (19 octobre 2020) : 114. http://dx.doi.org/10.3847/1538-4357/abb66d.

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Elbakyan, Vardan G., Eduard I. Vorobyov, Christian Rab, Dominique M.-A. Meyer, Manuel Güdel, Takashi Hosokawa et Harold Yorke. « Episodic excursions of low-mass protostars on the Hertzsprung–Russell diagram ». Monthly Notices of the Royal Astronomical Society 484, n^o 1 (31 décembre 2018) : 146–60. http://dx.doi.org/10.1093/mnras/sty3517.

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Scholz, R. D., S. Drew Chojnowski et S. Hubrig. « Strongly magnetic Ap stars in the Gaia DR2 Hertzsprung-Russell diagram ». Astronomy & ; Astrophysics 628 (août 2019) : A81. http://dx.doi.org/10.1051/0004-6361/201935752.

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Context. Knowing the distribution of strongly magnetic Ap stars in the Hertzsprung-Russell diagram (HRD) allows us to study the evolution of their magnetic fields across the main sequence (MS). With a newly extended Ap star sample from APOGEE and available Gaia DR2 data, we can now critically review the results of previous studies based on HIPPARCOS data. Aims. To investigate our targets in the Gaia DR2 HRD, we need to define astrometric and photometric quality criteria to remove unreliable data from the HRD. Methods. We used the Gaia DR2 renormalised unit weight error RUWE as our main quality criterion. We considered known (close) binaries in our sample compared to their (partly affected) astrometry and used the Gaia DR2 data to find common parallax and proper motion (CPPM) wide companions and open cluster members. We studied G, BP, and RP variability amplitudes and their significance as a function of magnitude. In colour-magnitude diagrams (CMDs) with absolute G magnitude (determined from inverted parallax) versus BP − RP colour and HRDs, where BP − RP is replaced by effective temperature, we studied the appearance of outliers with respect to their astrometric quality, binarity, and variability. Results. We present a catalogue of 83 previously known and 154 new strongly magnetic Ap stars with Gaia DR2 data, including astrometric quality parameters, binary flags, information on cluster membership, variability amplitudes, and data from HIPPARCOS. Our astrometrically cleaned subsamples include 47 and 46 old and new Ap stars with parallaxes > 2 mas. Most of the known 26 binaries among all 237 stars and 14 out of 15 CMD/HRD outliers were excluded by astrometric criteria. The remaining 11 known binaries and a few highly variable objects mainly appear in the bright and red CMD/HRD parts. A CMD based on HIPPARCOS photometry and Gaia DR2 parallaxes shows a much more narrow distribution in the absolute V magnitudes of 75 common Ap stars over the full B − V colour range than the corresponding CMD based on HIPPARCOS parallaxes.

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Bohannan, Bruce. « The distribution of types of Luminous Blue Variables ». International Astronomical Union Colloquium 113 (1989) : 35–44. http://dx.doi.org/10.1017/s0252921100004267.

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AbstractIf Luminous Blue Variables (LBVs) are not each unique types, three broad groups can be characterized depending on the luminosity and location ofLBVsin the Hertzsprung-Russell diagram. To assist in defining the evolutionary nature ofLBVs, connections are made to stars that have similar spectral character with the suggestion that some of these objects that may someday becomeLBVs.

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Cox, Arthur N., Joyce A. Guzik, Michael S. Soukup et Siobahn M. Morgan. « Theoretical Pulsations of Luminous Blue Variables ». International Astronomical Union Colloquium 155 (1995) : 192–93. http://dx.doi.org/10.1017/s0252921100036952.

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AbstractBoth radial and low degree and order g-mode nonradial pulsations are predicted for luminous blue variables that occur in the blue supergiant region of the Hertzsprung-Russell diagram. It is found that the radial strange modes have very large growth rates due to helium ionization in models at surface effective temperatures between 10,000 and 20,000 K.

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ZHANG, CHENGMIN, YUANYUE PAN et ALI TAANI. « PULSAR DISTRIBUTIONS IN THE MAGNETIC AND SPIN PERIOD DIAGRAM ». International Journal of Modern Physics : Conference Series 23 (janvier 2013) : 165–69. http://dx.doi.org/10.1142/s2010194513011240.

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The various types of pulsars are classified in the magnetic and spin period (B-P) diagram, by which one can recognize their properties there. We also investigate the relation of radio pulsars and X-ray neutron stars, and their distribution characteristics, implying their evolution links. B-P diagram is divided by the special lines, e.g. spin-up line and "death line", which indicate the evolution information of pulsars. Like Hertzsprung-Russell (H-R) diagram of showing the stellar evolution or "lives of stars", we try to develop B-P diagram as a function of representing the evolution track of neutron star.

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Bi, S. L., et N. Gai. « Solar-like oscillations in red giant ϵ Ophiuchi ». Proceedings of the International Astronomical Union 4, S252 (avril 2008) : 243–44. http://dx.doi.org/10.1017/s1743921308022874.

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AbstractAsteroseismology is a powerful tool to help determining the internal structure of the stars. Solar-like oscillations have been discovered in the G9.5 red giant ϵ Ophiuchi, and it opened up a new part of the Hertzsprung-Russell diagram to be explored with asteroseismic techniques. We present the detailed study of the properties of ϵ Oph including convective overshooting and extra-mixing.

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Mirzoyan, L. V., V. V. Hambarian et A. T. Garibjanian. « Spectral observations of flare stars ». Symposium - International Astronomical Union 137 (1990) : 95–98. http://dx.doi.org/10.1017/s0074180900187510.

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Spectral observations of 6 flare stars in the Pleiades cluster are carried out which occupy different positions on the Hertzsprung-Russell diagram relative to the main sequence: above and below it. The spectral indices which are sensible to luminosity or temperature of the star photosphere are determined. Significant differences between indices of the stars belongings to these two groups are not detected.

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Nardetto, Nicolas, Jesper Storm, Wolfgang Gieren, Grzegorz Pietrzyński et Ennio Poretti. « The Araucaria Project : the Baade-Wesselink projection factor of pulsating stars ». Proceedings of the International Astronomical Union 9, S301 (août 2013) : 145–48. http://dx.doi.org/10.1017/s1743921313014233.

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AbstractThe projection factor used in the Baade-Wesselink method of determining the distance of Cepheids makes the link between stellar physics and the cosmological distance scale. A coherent picture of this physical quantity is now provided based on several approaches. We present the latest news on the expected projection factor for different kinds of pulsating stars in the Hertzsprung-Russell diagram.

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Meyer, D. M.-A., L. Haemmerlé et E. I. Vorobyov. « On the episodic excursions of massive protostars in the Hertzsprung–Russell diagram ». Monthly Notices of the Royal Astronomical Society 484, n^o 2 (10 janvier 2019) : 2482–98. http://dx.doi.org/10.1093/mnras/sty3527.

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Couteau, P. « Un Diagramme Fondamental Luminosite-Type Spectral Pour Les Etoiles Doubles ». Symposium - International Astronomical Union 111 (1985) : 391–96. http://dx.doi.org/10.1017/s0074180900079043.

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In the Hertzsprung-Russell diagram, which is not well known for the binary stars, we can use the unit-mass brightness instead of the brightness itself. For each component this parameter can be obtained using the photometry and the orbital elements of the system. It is only through the orbital constant that the parallax comes in the calculation. This new diagram can be applied to any component of binary stars which orbit and class are known. By using a mass luminosity relationship one can define the zero-age main sequence on the diagram. The evolved stars can thus easily be noticed on the diagram; the mean age of the solar vicinity binary systems should be about 1010 years.

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Abril, Javier, Linda Schmidtobreick, Alessandro Ederoclite et Carlos López-Sanjuan. « Disentangling cataclysmic variables in Gaia’s HR diagram ». Monthly Notices of the Royal Astronomical Society : Letters 492, n^o 1 (16 décembre 2019) : L40—L44. http://dx.doi.org/10.1093/mnrasl/slz181.

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ABSTRACT Cataclysmic variables (CVs) are interacting binaries consisting of at least three components that control their colour and magnitude. Using Gaia, we here investigate the influence of the physical properties of these binaries on their position in the Hertzsprung–Russell (HR) diagram. The CVs are on average located between the main sequence and the white dwarf regime, the maximum density being at GBP − GRP ∼ 0.56 and Gabs ∼ 10.15. We find a trend of the orbital period with colour and absolute brightness: with decreasing period, the CVs become bluer and fainter. We also identify the location of the various CV subtypes in the HR diagram and discuss the possible location of detached CVs, going through the orbital period gap.

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Shibata, Kazunari, et Takaaki Yokoyama. « A Hertzsprung‐Russell–like Diagram for Solar/Stellar Flares and Corona : Emission Measure versus Temperature Diagram ». Astrophysical Journal 577, n^o 1 (20 septembre 2002) : 422–32. http://dx.doi.org/10.1086/342141.

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Cheng, Sihao. « Two delays in white dwarf evolution revealed by Gaia ». Proceedings of the International Astronomical Union 15, S357 (octobre 2019) : 175–78. http://dx.doi.org/10.1017/s1743921320000460.

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AbstractBy comparing two age indicators of high-mass white dwarfs (WDs) derived from Gaia data, two discoveries have been made recently: one is the existence of a cooling anomaly that produces the Q branch structure on the Hertzsprung–Russell diagram, and the other is the existence of high-mass WDs as double-WD merger products. The former poses a challenge for WD cooling models, and the latter has implications on binary evolution and type-Ia supernovae.

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Shetye, Shreeya, Sophie Van Eck, Alain Jorissen, Hans Van Winckel et Lionel Siess. « The TGAS HR diagram of S-type stars ». Proceedings of the International Astronomical Union 12, S330 (avril 2017) : 345–47. http://dx.doi.org/10.1017/s1743921317005610.

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AbstractS-type stars are late-type giants enhanced with s-process elements originating either from nucleosynthesis during the Asymptotic Giant Branch (AGB) or from a pollution by a binary companion. The former are called intrinsic S stars, and the latter extrinsic S stars. The atmospheric parameters of S stars are more numerous than those of M-type giants (C/O ratio and s-process abundances affect the thermal structure and spectral synthesis), and hence they are more difficult to derive. Nevertheless, high-resolution spectroscopic data of S stars combined with the TGAS (Tycho-Gaia Astrometric solution) parallaxes were used to derive effective temperatures, surface gravities, and luminosities. These parameters allow to locate the intrinsic and extrinsic S stars in the Hertzsprung-Russell diagram.

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Evans, Christopher J. « The properties of early-type stars in the Magellanic Clouds ». Proceedings of the International Astronomical Union 4, S256 (juillet 2008) : 325–36. http://dx.doi.org/10.1017/s1743921308028664.

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AbstractThe past decade has witnessed impressive progress in our understanding of the physical properties of massive stars in the Magellanic Clouds, and how they compare to their cousins in the Galaxy. I summarise new results in this field, including evidence for reduced mass-loss rates and faster stellar rotational velocities in the Clouds, and their present-day compositions. I also discuss the stellar temperature scale, emphasizing its dependence on metallicity across the entire upper-part of the Hertzsprung-Russell diagram.

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Mowlavi, Nami, Sophie Saesen, Fabio Barblan et Laurent Eyer. « On the new late B- and early A-type periodic variable stars ». Proceedings of the International Astronomical Union 9, S301 (août 2013) : 43–46. http://dx.doi.org/10.1017/s1743921313014051.

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AbstractWe summarize the properties of the new periodic, small-amplitude, variable stars recently discovered in the open cluster NGC 3766. They are located in the region of the Hertzsprung-Russell diagram between δ Sct and slowly pulsating B stars, a region where no sustained pulsation is predicted by standard models. The origin of their periodic variability is currently unknown. We also discuss how the Gaia mission, launched at the end of 2013, can contribute to our knowledge of those stars.

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Werner, Klaus, Stefan Dreizler, Ulrich Heber et Thomas Rauch. « Confining the Edges of the GW Vir Instability Strip ». International Astronomical Union Colloquium 152 (1996) : 229–34. http://dx.doi.org/10.1017/s0252921100036022.

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We report on our NLTE model atmosphere analyses of PG 1159 stars. The results enable us to confine the location of the GWVir instability region in the Hertzsprung-Russell diagram. The analysis of a spectrum of the non-pulsator PG 1520+525 taken with the EUVE satellite in comparison with HST data of the pulsating protoype PG 1159-035 (=GW Vir) locates the blue edge of the instability strip near Teff=140 000 K for stars in the respective luminosity range.

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Gregory, S. G., J. F. Donati, J. Morin, G. A. J. Hussain, N. J. Mayne, L. A. Hillenbrand et M. Jardine. « Can we predict the magnetic properties of PMS stars from their H-R diagram location ? » Proceedings of the International Astronomical Union 9, S302 (août 2013) : 40–43. http://dx.doi.org/10.1017/s1743921314001677.

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AbstractSpectropolarimetric observations combined with tomographic imaging techniques have revealed that all pre-main sequence (PMS) stars host multipolar magnetic fields, ranging from strong and globally axisymmetric with ≳kilo-Gauss dipole components, to complex and non-axisymmetric with weak dipole components (≲0.1 kG). Many host dominantly octupolar large-scale fields. We argue that the large-scale magnetic properties of a PMS star are related to its location in the Hertzsprung-Russell diagram. This conference paper is a synopsis of Gregory et al. (2012), updated to include the latest results from magnetic mapping studies of PMS stars.

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Bowman, D. M., S. Burssens, S. Simón-Díaz, P. V. F. Edelmann, T. M. Rogers, L. Horst, F. K. Röpke et C. Aerts. « Photometric detection of internal gravity waves in upper main-sequence stars ». Astronomy & ; Astrophysics 640 (août 2020) : A36. http://dx.doi.org/10.1051/0004-6361/202038224.

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Context. Massive stars are predicted to excite internal gravity waves (IGWs) by turbulent core convection and from turbulent pressure fluctuations in their near-surface layers. These IGWs are extremely efficient at transporting angular momentum and chemical species within stellar interiors, but they remain largely unconstrained observationally. Aims. We aim to characterise the photometric detection of IGWs across a large number of O and early-B stars in the Hertzsprung–Russell diagram, and explain the ubiquitous detection of stochastic variability in the photospheres of massive stars. Methods. We combined high-precision time-series photometry from the NASA Transiting Exoplanet Survey Satellite with high-resolution ground-based spectroscopy of 70 stars with spectral types O and B to probe the relationship between the photometric signatures of IGWs and parameters such as spectroscopic mass, luminosity, and macroturbulence. Results. A relationship is found between the location of a star in the spectroscopic Hertzsprung–Russell diagram and the amplitudes and frequencies of stochastic photometric variability in the light curves of massive stars. Furthermore, the properties of the stochastic variability are statistically correlated with macroturbulent velocity broadening in the spectral lines of massive stars. Conclusions. The common ensemble morphology for the stochastic low-frequency variability detected in space photometry and its relationship to macroturbulence is strong evidence for IGWs in massive stars, since these types of waves are unique in providing the dominant tangential velocity field required to explain the observed spectroscopy.

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Szczerba, R. « A New Method for Observational Testing of the Planetary Nebulae Nuclei Evolution ». Symposium - International Astronomical Union 131 (1989) : 539. http://dx.doi.org/10.1017/s0074180900139105.

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Planetary nebulae (PNe) are very useful as a tool for testing the theory of stellar evolution. The most widely applied method in this respect is the Hertzsprung-Russell (H-R) diagram. However, the observed positions of planetary nebulae nuclei (PNNi) on the H-R diagram are subject to large uncertainties, mostly due to inaccurate distances to them. On the other hand, the (absolute visual magnitude, age)-diagram also is not free of this problem. Therefore, an attempt has been done to develop a new method which is distance-independent. For comparison between theory and observations we propose the I (Hell λ 4686) /I(H β) versus log [I(H β, PN)/IC (H β, PNN)] diagram. Both ratios reflect the evolutionary status of the central star and the surrounding nebula. Consequently, such diagram is a valuable tool for studying common evolution of the PNN-PN system.

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El Eid, M. F. « Effect of convective mixing on the red-blue loops in the Hertzsprung-Russell diagram ». Monthly Notices of the Royal Astronomical Society 275, n^o 4 (15 août 1995) : 983–1002. http://dx.doi.org/10.1093/mnras/275.4.983.

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Castro, N., M. S. Oey, L. Fossati et N. Langer. « The Spectroscopic Hertzsprung–Russell Diagram of Hot Massive Stars in the Small Magellanic Cloud ». Astrophysical Journal 868, n^o 1 (20 novembre 2018) : 57. http://dx.doi.org/10.3847/1538-4357/aae6d0.

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Stothers, Richard B., et Chao-Wen Chin. « Luminous blue variables at quiescence : The zone of avoidance in the Hertzsprung-Russell diagram ». Astrophysical Journal 426 (mai 1994) : L43. http://dx.doi.org/10.1086/187335.

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