Journal articles: 'Stars'

1

Swann, Brian. "Stars Stars Stars." College English 57, no. 2 (February 1995): 196. http://dx.doi.org/10.2307/378810.

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Jacke, Christoph. "Stars, Anti-Stars, Anti-Star-Stars." Persona Studies 10, no. 1 (May 1, 2024): 56–73. http://dx.doi.org/10.21153/psj2024vol10no1art1872.

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The phenomenon of stars and celebrities in media cultures – and especially in popular music cultures – seems to be omnipresent. At the same time, there is an astounding lack of analysis and research on these media personalities and personas, and international celebrity studies only recently a developing new field. Similarly, these kinds of observations are still very rare especially in German sociology as well as communication, media, culture and popular music studies. In this article, I therefore want to concentrate on the foundations of studying stars and celebrities within the attention economies by undertaking a theoretical transmedia-cultural framing of media personas and suggesting a typology. This ensuing typology of stars, anti-stars, and anti-star stars – especially within popular music cultures – demonstrates how stars and celebrities and their quantities and qualities of success and peer-group specific values coming form programs of (media and music) culture can serve as persona-seismographs of socio-cultural change between tradition and innovation.

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3

Østgaard, Erlend. "Compact stars: Neutron stars or quark stars or hybrid stars?" Physics Reports 242, no. 4-6 (July 1994): 313–32. http://dx.doi.org/10.1016/0370-1573(94)90166-x.

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4

JAIKUMAR, P., C. GALE, D. PAGE, and M. PRAKASH. "DISTINGUISHING BARE QUARK STARS FROM NEUTRON STARS." International Journal of Modern Physics A 19, no. 31 (December 20, 2004): 5335–42. http://dx.doi.org/10.1142/s0217751x04022566.

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Observations to date cannot distinguish neutron stars from self-bound bare quark stars on the basis of their gross physical properties such as their masses and radii alone. However, their surface luminosity and spectral characteristics can be significantly different. Unlike a normal neutron star, a bare quark star can emit photons from its surface at super-Eddington luminosities for an extended period of time. We present a calculation of the photon bremsstrahlung rate from the bare quark star's surface, and indicate improvements that are required for a complete characterization of the spectrum. The observation of this distinctive photon spectrum would constitute an unmistakable signature of a strange quark star and shed light on color superconductivity at stellar densities.

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5

Dimitrijević, Milan S. "Stark broadening of stellar Pt II lines." Symposium - International Astronomical Union 162 (1994): 337–38. http://dx.doi.org/10.1017/s0074180900215258.

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Lines of Pt II have been discovered in Hg Mn stars by Dworetsky (1969). The analysis of a few strong Pt II transitions, which are also observed in IUE spectra of stars, has shown (Dworetsky et al., 1984) “that Pt is, like Hg, among the most overabundant elements in the atmospheres of Hg Mn stars, with enhancements of the order of 104 to 105 over the solar system abundances”. Dworetsky et al. (1984) selected also the four Pt II lines which might be used for astrophysical applications. Moreover, they determined the corresponding theoretical gf values. The aim of this contribution is to investigate the Stark broadening of these Pt II lines and to provide the corresponding Stark widths.

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6

Grassi, F. "Quark core stars, quark stars and strange stars." Zeitschrift f�r Physik C Particles and Fields 44, no. 1 (March 1989): 129–38. http://dx.doi.org/10.1007/bf01548591.

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7

Folsom, C. P., S. Bagnulo, G. A. Wade, J. D. Landstreet, and E. Alecian. "Chemical peculiarities in magnetic and non-magnetic pre-main sequence A and B stars." Proceedings of the International Astronomical Union 9, S302 (August 2013): 87–90. http://dx.doi.org/10.1017/s1743921314001781.

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AbstractIn A- and late B-type stars, strong magnetic fields are always associated with Ap and Bp chemical peculiarities. However, it is not clear at what point in a star's evolution those peculiarities develop. Strong magnetic fields have been observed in pre-main sequence A and B stars (Herbig Ae and Be stars), and these objects have been proposed to be the progenitors of Ap and Bp stars. However, the photospheric chemical abundances of these magnetic Herbig stars have not been studied carefully, and furthermore the chemical abundances of 'normal' non-magnetic Herbig stars remain poorly characterized. To investigate this issue, we have studied the photospheric compositions of 23 Herbig stars, four of which have confirmed magnetic fields. Surprisingly, we found that half the non-magnetic stars in our sample show λ Bootis chemical peculiarities to varying degrees. For the stars with detected magnetic fields, we find one chemically normal star, one star with λ Boo peculiarities, one star displaying weak Ap/Bp peculiarities, and one somewhat more evolved star with somewhat stronger Ap/Bp peculiarities. These results suggests that Ap/Bp peculiarities are preceded by magnetic fields, and that these peculiarities develop over the pre-main sequence lives of A and B stars. The incidence of λ Boo stars we find is much higher than that seen on the main sequence. We argue that a selective accretion model for the formation of λ Boo peculiarities is a natural explanation for this remarkably large incidence.

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8

Vickers, J. J., A. P. Huxor, and E. K. Grebel. "Blue Horizontal Branch Stars in Pan-STARRS." EAS Publications Series 67-68 (2014): 183–86. http://dx.doi.org/10.1051/eas/1567032.

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9

Bagnulo, S. "Statistical Properties of Magnetic CP Stars." Symposium - International Astronomical Union 210 (2003): 209–20. http://dx.doi.org/10.1017/s0074180900133376.

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Magnetic fields of chemically peculiar (CP) stars of the upper main sequence are characterised by a geometry organised at a large scale, permeating the entire photosphere, and with a typical strength of the order of 0.1–30 kG. Here I review the results obtained from statistical studies of the structures of the magnetic fields of CP stars, which are aimed at finding how magnetic strength and morphology are correlated with other stellar characteristics and with the star's evolutionary state.

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10

Gondek, Dorota. "Neutron stars and strange stars." International Astronomical Union Colloquium 160 (1996): 133–34. http://dx.doi.org/10.1017/s0252921100041282.

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If strange quark plasma is the real ground state of baryonic matter (Witten 1984), then some of neutron stars (NS) could actually be strange stars (SS). It is difficult to distinguish SS from NS observationally. They have similar radii and masses and their crusts are built of the same matter. It seems that a good method for testing the existence of SS would be the studies of phenomena related to the stellar pulsations. In 1976 Boriakoff proposed that radial oscillations of NS could be observed within radio subpulses of pulsars. While various modes of pulsations of NS were studied by a number of authors, little attention was paid to seismological signatures of SS. The radial oscilations of bare SS were studied by Väth & Chanmugam (1992). Recently Weber (this volume) studied properties of stars made of matter described by BPS equation of state (EOS) (Baym et al. 1971) with a ball of strange matter inside, but they mainly concentrated on stability of white-dwarf-like SS. In this work I present fully relativistic calculations of the radial oscillation frequencies of SS. I determined the fundamental frequency for bare SS and SS with two different types of crusts depending on origin (Alcock et al. 1986) of SS and showed differences between them.

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11

Gondek-Rosińska, D., P. Haensel, and J. L. Zdunik. "Protoneutron stars and neutron stars." International Astronomical Union Colloquium 177 (2000): 663–64. http://dx.doi.org/10.1017/s0252921100060942.

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AbstractWe find constraints on minimum and maximum mass of ordinary neutron stars imposed by their early evolution (protoneutron star stage). We calculate models of protoneutron stars using a realistic standard equation of state of hot, dense matter valid for both supranuclear and subnuclear densities. Results for different values of the nuclear incompressibility are presented.

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12

Dumitrescu, Adrian, Csaba D. Tóth, and Guangwu Xu. "On stars and Steiner stars." Discrete Optimization 6, no. 3 (August 2009): 324–32. http://dx.doi.org/10.1016/j.disopt.2009.04.003.

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13

Bahcall, Safi, Bryan W. Lynn, and Stephen B. Selipsky. "Are neutron stars Q-stars?" Nuclear Physics B 331, no. 1 (February 1990): 67–79. http://dx.doi.org/10.1016/0550-3213(90)90018-9.

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14

Smith, Robert Connon. "The Evolution of Rapidly Rotating B Stars (Review Paper)." International Astronomical Union Colloquium 92 (August 1987): 486–99. http://dx.doi.org/10.1017/s0252921100116665.

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AbstractBe stars are located in or near the main-sequence band for non-rotating stars. Although this stage of evolution is relatively well understood, there are two main effects that make it impossible to say whether all Be stars are in the same stage of evolution and, if so, what that stage is. One effect is the spread in observed magnitude and colour as a result of rotation. Correction for rotation is not possible because of the unknown inclination of any particular star's rotation axis to the line of sight and because it is not clear what the internal angular momentum distribution is or how it changes as a result of evolution. The other effect is that there are uncertainties in the theoretical evolutionary tracks because the amount of convective overshooting is unclear. Other mixing mechanisms that might in principle also confuse the tracks seem to be small near the main sequence. If Be stars are related to the β Cephei and 53 Persei stars in the same part of the HR diagram, then the non-radial pulsation properties of Be stars may give a clue to their evolutionary state. The existence of a circumstellar disc or ring, however, tells us very little about the evolutionary stage of the underlying star. A useful way forward may be to try to understand individual stars in as much detail as possible.

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15

Georgy, Cyril, Georges Meynet, and André Maeder. "Wind anisotropy and stellar evolution." Proceedings of the International Astronomical Union 4, S255 (June 2008): 199–203. http://dx.doi.org/10.1017/s1743921308024824.

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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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16

Barnes, Sydney A. "A nonlinear model for rotating cool stars." Proceedings of the International Astronomical Union 6, S273 (August 2010): 465–68. http://dx.doi.org/10.1017/s174392131101578x.

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AbstractA simple nonlinear model is introduced here to describe the rotational evolution of main sequence cool (FGKM) stars. It is formulated only in terms of the ratio of a star's rotation period, P, to its convective turnover timescale, τ, and two dimensionless constants which are specified using solar- and open cluster data. The model explains the origin of the two sequences, C/fast and I/slow, of rotating stars observed in open cluster color-period diagrams, and describes their evolution from C-type to I-type through the rotational gap, g, separating them. It explains why intermediate-mass open cluster stars have the longest periods, while higher- and lower-mass cool stars have shorter periods. It provides an exact expression for the age of a rotating cool star in terms of P and τ, thereby generalizing gyrochronology. The possible range of initial periods is shown to contribute upto 128 Myr to the gyro age errors of solar mass field stars. A transformation to color-period space shows how this model explains some detailed features in the color-period diagrams of open clusters, including the shapes and widths of the sequences, and the observed number density of stars across these diagrams.

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17

Beall, Abigail. "STARS." New Scientist 255, no. 3397 (July 2022): 39–41. http://dx.doi.org/10.1016/s0262-4079(22)01356-2.

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18

Janeczko, Paul B. "Stars." English Journal 81, no. 3 (March 1992): 93. http://dx.doi.org/10.2307/820214.

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19

Liu, Rui, Runze Liu, Andrea Pugliese, and V. S. Subrahmanian. "STARS." ACM Transactions on Intelligent Systems and Technology 11, no. 5 (September 5, 2020): 1–25. http://dx.doi.org/10.1145/3397463.

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20

Seubert, Christoph N. "Stars." Anesthesiology 133, no. 5 (September 8, 2020): 1152–53. http://dx.doi.org/10.1097/aln.0000000000003533.

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21

Adebayo, Mojisola. "STARS." Wasafiri 34, no. 2 (April 3, 2019): 35–37. http://dx.doi.org/10.1080/02690055.2019.1576969.

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22

Hallworth, Mike. "STARS." Clinical Chemistry 59, no. 2 (February 1, 2013): 449–50. http://dx.doi.org/10.1373/clinchem.2012.197814.

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23

Stoddart, Greta. "Stars." Ploughshares 41, no. 1 (2015): 200. http://dx.doi.org/10.1353/plo.2015.0032.

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24

Rodrigues, Hilário, Sérgio Barbosa Duarte, and José Carlos T. de Oliveira. "MASSIVE COMPACT STARS AS QUARK STARS." Astrophysical Journal 730, no. 1 (March 1, 2011): 31. http://dx.doi.org/10.1088/0004-637x/730/1/31.

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25

Ananthaswamy, Anil. "Quark stars: when neutron stars melt." New Scientist 220, no. 2946 (December 2013): 42–45. http://dx.doi.org/10.1016/s0262-4079(13)62856-0.

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26

Olinto, Angela. "Converting neutron stars into strange stars." Nuclear Physics B - Proceedings Supplements 24, no. 2 (December 1991): 103–9. http://dx.doi.org/10.1016/0920-5632(91)90306-y.

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27

Drago, Alessandro, and Andrea Lavagno. "From quark stars to hybrid stars." Physics Letters B 511, no. 2-4 (July 2001): 229–34. http://dx.doi.org/10.1016/s0370-2693(01)00579-2.

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28

Dworetsky, M. M. "Hg-Mn Stars Versus Normal Stars." International Astronomical Union Colloquium 138 (1993): 1–17. http://dx.doi.org/10.1017/s0252921100020248.

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AbstractThe literature concerning spectroscopic studies, abundances, photometry and systematics of Hg-Mn stars is reviewed since the last international meeting on chemically peculiar stars in the Crimea in 1985, and is intended to be complete to the end of 1991.

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29

Jones, Samuel, Raphael Hirschi, Falk Herwig, Bill Paxton, Francis X. Timmes, and Ken'ichi Nomoto. "Progenitors of electron-capture supernovae." Proceedings of the International Astronomical Union 7, S279 (April 2011): 341–42. http://dx.doi.org/10.1017/s1743921312013257.

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AbstractWe investigate the lowest mass stars that produce Type-II supernovae, motivated by recent results showing that a large fraction of type-II supernova progenitors for which there are direct detections display unexpectedly low luminosity (for a review see e.g. Smartt 2009). There are three potential evolutionary channels leading to this fate. Alongside the standard ‘massive star’ Fe-core collapse scenario we investigate the likelihood of electron capture supernovae (EC-SNe) from super-AGB (S-AGB) stars in their thermal pulse phase, from failed massive stars for which neon burning and other advanced burning stages fail to prevent the star from contracting to the critical densities required to initiate rapid electron-capture reactions and thus the star's collapse. We find it indeed possible that both of these relatively exotic evolutionary channels may be realised but it is currently unclear for what proportion of stars. Ultimately, the supernova light curves, explosion energies, remnant properties (see e.g. Knigge et al. 2011) and ejecta composition are the quantities desired to establish the role that these stars at the lower edge of the massive star mass range play.

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30

Farrell, Delaney, Pierre Baldi, Jordan Ott, Aishik Ghosh, Andrew W. Steiner, Atharva Kavitkar, Lee Lindblom, Daniel Whiteson, and Fridolin Weber. "Deducing neutron star equation of state parameters directly from telescope spectra with uncertainty-aware machine learning." Journal of Cosmology and Astroparticle Physics 2023, no. 02 (February 1, 2023): 016. http://dx.doi.org/10.1088/1475-7516/2023/02/016.

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Abstract Neutron stars provide a unique laboratory for studying matter at extreme pressures and densities. While there is no direct way to explore their interior structure, X-rays emitted from these stars can indirectly provide clues to the equation of state (EOS) of the superdense nuclear matter through the inference of the star's mass and radius. However, inference of EOS directly from a star's X-ray spectra is extremely challenging and is complicated by systematic uncertainties. The current state of the art is to use simulation-based likelihoods in a piece-wise method which relies on certain theoretical assumptions and simplifications about the uncertainties. It first infers the star's mass and radius to reduce the dimensionality of the problem, and from those quantities infer the EOS. We demonstrate a series of enhancements to the state of the art, in terms of realistic uncertainty quantification and a path towards circumventing the need for theoretical assumptions to infer physical properties with machine learning. We also demonstrate novel inference of the EOS directly from the high-dimensional spectra of observed stars, avoiding the intermediate mass-radius step. Our network is conditioned on the sources of uncertainty of each star, allowing for natural and complete propagation of uncertainties to the EOS.

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31

Chehlaeh, Nareemas, Tatphicha Promfu, and Nusreen Masae. "Frequency Analysis of High Amplitude δ Scuti Star V593 Lyr by American Association of Variable Stars Observers International Database." ASEAN Journal of Scientific and Technological Reports 26, no. 1 (March 21, 2023): 32–39. http://dx.doi.org/10.55164/ajstr.v26i1.247847.

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The new results of light variability and frequency analysis of a high amplitude δ Scuti star (HADS) V593 Lyr were reported. δ Scuti-type variable stars are fascinating short-period stars with luminosity classes from III to V and spectral types from A0 to F6. Their location on the Hertzsprung-Russell (H-R) diagram is in the classical cepheid instability strip. The photometric data in the V filter and clear filter of V593 Lyr were collected from the American Association of Variable Stars Observers (AAVSO) international database. Discrete Fourier transformation and pre-whitening methods were used in the Period04 package to examine time-series light curve data. During 15 observational nights, we obtained 28 times of new light maxima magnitude variability and significant pulsation frequencies for the star. The study found that the fundamental frequency of V593 Lyr is 9.7894180 ± 0.0000002 d−1, corresponding to the main pulsation period of about 0.1021511 d and detected its second to fifth harmonics with a signal-to-noise ratio (S/N) of more than four. A study of the pulsation frequencies and period change of HADS stars can estimate their pulsation modes and evolution. Moreover, HADS stars are suitable targets for understanding asteroseismology, which is the subject that applies a star's pulsations to investigate its internal structure, and the high amplitude stars provide reference points for calculating cosmic distances in the Universe.

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Werber, Zach, Kevin Wagner, and Dániel Apai. "The Direct Mid-infrared Detectability of Habitable-zone Exoplanets around Nearby Stars." Astronomical Journal 165, no. 3 (February 27, 2023): 133. http://dx.doi.org/10.3847/1538-3881/acaf5d.

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Abstract Giant planets within the habitable zones of the closest several stars can currently be imaged with ground-based telescopes. Within the next decade, the Extremely Large Telescopes (ELTs) will begin to image the habitable zones of a greater number of nearby stars with much higher sensitivity, potentially imaging exo-Earths around the closest stars. To determine the most promising candidates for observations over the next decade, we establish a theoretical framework for the direct detectability of Earth- to super-Jovian-mass exoplanets in the mid-infrared based on available atmospheric and evolutionary models. Of the 83 closest BAFGK-type stars, we select 37 FGK-type stars within 10 pc and 34 BA-type stars within 30 pc with reliable age constraints. We prioritize targets based on a parametric model of a planet’s effective temperature based on a star's luminosity, distance, and age, and on the planet’s orbital semimajor axis, radius, and albedo. We then predict the most likely planets to be detectable with current 8 m telescopes and with a 39 m ELT with up to 100 hr of observation per star. Putting this together, we recommend observation times needed for the detection of habitable-zone exoplanets spanning the range from very nearby temperate Earth-sized planets to more distant young giant planets. We then recommend ideal initial targets for current telescopes and the upcoming ELTs.

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33

Pretel, Juan M. Z., and Chen Zhang. "Universal relations for anisotropic interacting quark stars." Journal of Cosmology and Astroparticle Physics 2024, no. 10 (October 1, 2024): 032. http://dx.doi.org/10.1088/1475-7516/2024/10/032.

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Abstract Interacting quark stars, which are entirely composed of interacting quark matter including perturbative QCD corrections and color superconductivity, can meet constraints from various pulsar observations. In realistic scenarios, pressure anisotropies are expected in the star's interior. Recently, the stellar structural properties of anisotropic interacting quark stars have been investigated. In this study, we further explore the universal relations (URs) related to the moment of inertia I, tidal deformability Λ, compactness C, and the f-mode nonradial pulsation frequency for such stars. Our results reveal that these approximate URs generally hold, being insensitive to both the EOS variations as well as to the presence of anisotropy. In contrast to previous studies on anisotropic neutron stars, we find that more positive anisotropy tends to enhance the I-Λ and I-C URs, but weakens the C-Λ UR. For all the URs involving f-mode frequency, we find that they are enhanced by the inclusion of anisotropy (whether positive or negative). Utilizing these URs and the tidal deformability constraint from the GW170817 event, we put limits on the structural properties of isotropic and anisotropic quark stars, such as the moment of inertia I 1.4, the canonical radius R 1.4 and the canonical f-mode frequency f f,1.4, all of which are very different compared to those of neutron stars.

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Underwood, D. R., B. W. Jones, and P. N. Sleep. "The evolution of habitable zones during stellar lifetimes and its implications on the search for extraterrestrial life." International Journal of Astrobiology 2, no. 4 (October 2003): 289–99. http://dx.doi.org/10.1017/s1473550404001715.

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A stellar evolution computer model has been used to determine changes in the luminosity L and effective temperature Te of single stars during their time on the main sequence. The range of stellar masses investigated was from 0.5 to 1.5 times that of the Sun, each with a mass fraction of metals (metallicity, Z) from 0.008 to 0.05. The extent of each star's habitable zone (HZ) has been determined from its values of L and Te. These stars form a reference framework for other main sequence stars. All of the 104 main sequence stars known to have one or more giant planets have been matched to their nearest stellar counterpart in the framework, in terms of mass and metallicity, hence closely approximating their HZ limits. The limits of HZ, for each of these stars, have been compared to their giant planet(s)'s range of strong gravitational influence. This allows a quick assessment as to whether Earth-mass planets could exist in stable orbits within the HZ of such systems, both presently and at any time during the star's main sequence lifetime. A determination can also be made as to the possible existence of life-bearing satellites of giant planets, which orbit within HZs. Results show that about half of the 104 known extrasolar planetary systems could possibly have been housing an Earth-mass planet in HZs during at least the past billion years, and about three-quarters of the 104 could do so for at least a billion years at some time during their main sequence lives. Whether such Earth-mass planets could have formed is an urgent question now being investigated by others, with encouraging results.

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Speck, Angela, Mike Barlow, Roger Wesson, Geoff Clayton, and Kevin Volk. "Unidentified infrared bands and the formation of PAHs around carbon stars." Proceedings of the International Astronomical Union 4, S251 (February 2008): 195–96. http://dx.doi.org/10.1017/s1743921308021546.

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AbstractAlthough unidentified infrared bands (UIBs) have been observed in many astrophysical environments, there is one notable exception: carbon (C) stars. Only a handful of C stars have been shown to emit UIBs and most have hot companions. This makes C stars with hot companions an ideal location to investigate the emitters of the UIBs. PAHs are excited by absorption of single photons whose energy is then distributed over the whole molecule. These molecules then emit the energy at the characteristic wavelengths, but the precise wavelengths and strength ratios depend on the size, composition and charge state of the individual PAHs. Furthermore, the wavelength of photons needed to excite PAHs depends on their size and charge state. While small PAHs undoubtedly need higher energy (UV) photons, it has been suggested that large or ionized PAHS (>100 C atoms) can be excited by visible or even near-IR photons. The lack of PAH emission from single carbon stars suggests that either PAHs do not form around C stars or that only small neutral grains form, which cannot be excited by a C star's radiation field.There are two competing formation mechanisms for PAHs around C stars: (1) “bottom-up” where acetylene molecules react to form aromatic rings, building up to PAHs; or (2) “top-down”, where small carbon grains react with H atoms and desorb PAHsUsing spatially resolved spectroscopic observations from Gemini/Michelle, of five carbon stars with hot companions, we investigate the circumstance under which PAH emission occurs and try to discriminate between formation mechanisms.

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Lu 卢, Xu 旭., and Yi 懿. Xie 谢. "Prediction of Astrometric and Timing Microlensing Events with Pulsars by ATNF Catalog and Gaia DR3." Astrophysical Journal 962, no. 1 (February 1, 2024): 56. http://dx.doi.org/10.3847/1538-4357/ad1929.

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Abstract Determining the mass of neutron stars is crucial for understanding their formation, evolution, and interior structure. Currently, only a few dozen neutron stars have had their masses measured, and most of them belong to binary systems. However, there are a huge number of isolated neutron stars with unknown masses. Microlensing events with neutron stars provide unique opportunities for knowing these compact objects. Astrometric microlensing with a background source lensed by a neutron star might be used to determine the neutron star's mass by measuring the deviation of the motion of the centroid of the images from its unlensed one. We search and predict these recent and future events based on the Australia Telescope National Facility Pulsar Catalog and Gaia DR3. We find 60 candidate astrometric microlensing events caused by neutron stars and the probability distributions of their observables by the Monte Carlo sampling. We also find four candidate “timing microlensing” events with a pulsar lensed by a foreground object that might be detected by timing measurements. While some of these events may be verified by future astrometric missions or pulsar-timing observations, we note that our prediction of these events is significantly restricted by the uncertainties of the available astrometric and timing measurements after assessing and comparing our results with previous works.

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DAI, SHI, and RENXIN XU. "QUARK-CLUSTER STARS: HINTS FROM THE SURFACE." International Journal of Modern Physics: Conference Series 10 (January 2012): 137–46. http://dx.doi.org/10.1142/s2010194512005855.

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The matter inside pulsar-like compact stars could be in a quark-cluster phase since in cold dense matter at a few nuclear densities (ρ ~ 2 - 10ρ0), quarks could be coupled still very strongly and condensate in position space to form quark clusters. Quark-cluster stars are chromatically confined and could initially be bare, therefore the surface properties of quark-cluster stars would be quite different from that of conventional neutron stars. Some facts indicate that a bare and self-confined surface of pulsar-like compact stars might be necessary in order to naturally understand different observational manifestations. On one hand, as for explaining the drifting sub-pulse phenomena, the binding energy of particles on pulsar surface should be high enough to produce vacuum gaps, which indicates that pulsar's surface might be strongly self-confined. On the other hand, a bare surface of quark-cluster star can overcome the baryon contamination problem of γ-ray burst as well as promote a successful core-collapse supernova. What is more, the non-atomic thermal spectra of dead pulsars may indicate also a bare surface without atmosphere, and the hydro-cyclotron oscillation of the electron sea above the quark-cluster star surface could be responsible for those absorption features detected. These hints could reflect the property of compact star's surface and possibly the state of condensed matter inside, and then might finally result in identifying quark-cluster stars.

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Meurs, E. J. A., and E. P. J. van den Heuvel. "The galactic number of Wolf-Rayet stars produced via close binary evolution." Symposium - International Astronomical Union 163 (1995): 329–30. http://dx.doi.org/10.1017/s0074180900202246.

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Wolf-Rayet stars may have evolved from massive close binary systems, as a result of the mass transfer processes in such systems. A substantial fraction of all WR stars known is, indeed, found in close binaries, with massive early-type companions. After the outer layers of the initial primary have been removed during Roche Lobe Over-Flow, the remaining stellar core may be a helium-burning helium star, classified observation ally as a WR star. The fraction of such evolved binaries among main-sequence stars can be computed, following recipes from stellar- and galactic evolution and assuming steady, standard-IMF star formation over the last ∼ 109 yr in our Galaxy. Combining these results with the stellar PMF yields the total galactic number of such objects, or alternatively the number expected within, e.g., 3 kpc from the Sun. Comparison with observed numbers shows that the close binary produced WR stars should constitute a significant fraction of all WR stars, the exact fraction being dependent on the lower mass limit for WR star production (and also the duration of WR characteristics in the helium star's lifetime). The mass transfer processes in close binary systems probably allow this limit to be lower than in the case of a single WR star. Another favourable comparison regards the computed and observed numbers of persistent strong, massive X-ray binaries. Finally, second-phase WR stars are likely to comprise 5 — 10 % of the number of normal, first-stage WR binaries.

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39

Alford, Mark, Matt Braby, Mark Paris, and Sanjay Reddy. "Hybrid Stars that Masquerade as Neutron Stars." Astrophysical Journal 629, no. 2 (August 20, 2005): 969–78. http://dx.doi.org/10.1086/430902.

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HAFIZI, M. "PRECARIOUS STARS — A VARIETY OF BOSON STARS." International Journal of Modern Physics D 07, no. 06 (December 1998): 975–87. http://dx.doi.org/10.1142/s0218271898000656.

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In this paper we study boson stars made up of real scalar λϕ4 self-interacting fields at finite temperature. For the reason of their equation of state, we call these configurations "precarious stars." The equation of state for these stars follows from the Gaussian approximation applied to real scalar λϕ4 self-interacting fields. We numerically calculate these configurations in the frame of general relativity. We obtain masses, radii, surface temperatures and other characteristics. After a numerical analysis of the thermal radiation emitted from their surface, we conclude that these stars radiate rapidly all their energy and mass. Nevertheless, we raise the question of the role these configurations may have played in formation of the large scale structures of the Universe.

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Yusof, Norhasliza. "Wolf-Rayet stars from Very Massive Stars." Proceedings of the International Astronomical Union 9, S307 (June 2014): 152–53. http://dx.doi.org/10.1017/s1743921314006632.

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AbstractMany studies focused on very massive stars (VMS) within the framework of Pop. III stars, because this is where they were thought to be abundant. In this work, we focus on the evolution of VMS in the local universe following the discovery of VMS in the R136 cluster in the Large Magellanic Cloud (LMC). We computed grids of VMS evolutionary tracks in the range 120–500 M⊙ with solar, LMC and Small Magellanic Cloud metallicities. All models end their lives as Wolf-Rayet (WR) stars of the WC (or WO) type. We discuss the evolution and fate of VMS around solar metallicity with particular focus on the WR phase. For example, we show that a distinctive feature that may be used to disentangle Wolf-Rayet stars originating from VMS from those originating from lower initial masses is the enhanced abundances of Ne and Mg at the surface of WC stars.

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42

Hillier, D. J. "WC stars - Hot stars with cold winds." Astrophysical Journal 347 (December 1989): 392. http://dx.doi.org/10.1086/168127.

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Neves, Juliano C. S., and Fernando G. Gardim. "Stars and quark stars in bumblebee gravity." Annals of Physics 475 (April 2025): 169950. https://doi.org/10.1016/j.aop.2025.169950.

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Wing, Robert F., and Pedro Saizar. "Hydrogen Deficiency in Peculiar Red Giants." International Astronomical Union Colloquium 106 (1989): 151. http://dx.doi.org/10.1017/s0252921100062813.

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Hydrogen abundances (or H/He ratios) are hard to determine in stars cooler than the Sun because the Balmer lines, when visible at all, are formed largely in the chromosphere, while the bands of CH and NH are often strongly saturated and badly blended with atomic lines. A few stars (the hydrogen-deficient carbon or HdC stars) are known to be extremely hydrogen-deficient, as their G bands of CH are absent despite an overabundance of carbon. A means of detecting less extreme cases of hydrogen deficiency would improve our understanding of red giant evolution. Minor variations in hydrogen content may be expected as the result of the mixing of processed material to the surface, and more radical changes might result from a star's shedding its entire hydrogen-rich envelope, say in the course of binary-star evolution.

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Ryabchikova, T., G. A. Wade, and F. Leblanc. "Observational Evidence for the Stratification of Chemical Abundances in Stellar Atmospheres." Symposium - International Astronomical Union 210 (2003): 301–12. http://dx.doi.org/10.1017/s0074180900133443.

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We present spectroscopic and photometric observational evidence for abundance stratification in stellar atmospheres. Attention is given to chemically peculiar (Ap) stars in which magnetic fields stabilize the atmosphere, allowing diffusion processes to establish abundance stratification during the early stages of star's life. The results of recent empirical modelling of chemically stratified atmospheres are briefly discussed, and a comparison is given with the predictions of self-consistent atmospheric models which include radiative diffusion.The importance of abundance stratification analysis is demonstrated for rapidly oscillating (roAp) stars in which the amplitudes of the radial velocity pulsations are different for the lines of different elements in different ionization stages. We also demonstrate that chemical stratification has important effects on the Zeeman Stokes IQUV profiles of Ap stars, indicating that stratification must be taken into account in detailed modelling of their magnetic fields.

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Bowen, George H. "Pulsation and Mass Loss in LPVs." International Astronomical Union Colloquium 139 (1993): 191. http://dx.doi.org/10.1017/s0252921100117300.

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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.

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Woltjer, L. "Where Neutron Stars Come From, How Neutron Stars Evolve, and Neutron Stars Go." Symposium - International Astronomical Union 125 (1987): 559–62. http://dx.doi.org/10.1017/s007418090016142x.

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Vidotto, A. A. "The effects of stellar winds and magnetic fields on exoplanets." Proceedings of the International Astronomical Union 9, S302 (August 2013): 228–36. http://dx.doi.org/10.1017/s1743921314002154.

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AbstractThe great majority of exoplanets discovered so far are orbiting cool, low-mass stars whose properties are relatively similar to the Sun. However, the stellar magnetism of these stars can be significantly different from the solar one, both in topology and intensity. In addition, due to the present-day technology used in exoplanetary searches, most of the currently known exoplanets are found orbiting at extremely close distances to their host stars (< 0.1 au). The dramatic differences in stellar magnetism and orbital radius can make the interplanetary medium of exoplanetary systems remarkably distinct from that of the Solar System. To constrain interactions between exoplanets and their host-star's magnetised winds and to characterise the interplanetary medium that surrounds exoplanets, more realistic stellar wind models, which account for factors such as stellar rotation and the complex stellar magnetic field configurations of cool stars, must be employed. Here, I briefly review the latest progress made in data-driven modelling of magnetised stellar winds. I also show that the interaction of the stellar winds with exoplanets can lead to several observable signatures, some of which that are absent in our own Solar System.

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Dixon, William V. "Observations of the Ultraviolet-bright Star III-60 in the Globular Cluster NGC 6723." Astrophysical Journal 980, no. 1 (January 30, 2025): 5. https://doi.org/10.3847/1538-4357/ada604.

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Abstract We have analyzed archival far-ultraviolet spectra of the UV-bright star III-60 in the globular cluster NGC 6723 obtained with the Far Ultraviolet Spectroscopic Explorer and the Cosmic Origins Spectrograph. We find that the star's photospheric parameters (effective temperature T eff = 44,800 ± 1200 K, surface gravity log g = 4.89 ± 0.18 , and helium abundance log N ( He ) / N ( H ) = − 0.84 ± 0.29 ) are consistent with the values derived from its optical spectrum, suggesting that optically derived values are generally accurate for evolved stars with T eff ≲ 50,000 K. Relative to the cluster's red giant branch stars, III-60 is enhanced in nitrogen and depleted in carbon and oxygen. The star exhibits strong P Cygni profiles in both components of the N v λ1240 doublet, but the resonance lines of other species show no evidence of a stellar wind. The star's effective temperature and luminosity place it on the evolutionary tracks of stars evolving from the blue horizontal branch, but its high mass (∼1.2 M ⊙) indicates that it is the product of a stellar merger. Its helium, carbon, and nitrogen abundances suggest that it is following an evolutionary path similar to that of the low-carbon, intermediate helium-rich hot subdwarfs.

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Baines, Ellyn K., Jeremy Jones, James H. Clark, Henrique R. Schmitt, and Jordan M. Stone. "Eighteen Exoplanet Host Stars from the NPOI Data Archive." Astronomical Journal 169, no. 2 (January 20, 2025): 83. https://doi.org/10.3847/1538-3881/ad9bb1.

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Abstract During the course of publishing angular diameters from the Navy Precision Optical Interferometer data archive, we found we had data on 17 confirmed exoplanet host stars and 1 exoplanet candidate (HD 20902/α Per). Here, we update our previously published stellar radii with more precise Gaia parallaxes when available, and use our radius and effective temperature measurements to fit each star's mass and age using MIST models. The mass changed by more than 10% for 9 of the 18 stars. Combining our updated masses, radii, and temperatures, we present refined planetary masses as well as habitable zone calculations.

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Journal articles on the topic 'Stars'

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