Journal articles: 'Q-stars'

1

Lynn, Bryan W. "Q-stars." Nuclear Physics B 321, no. 2 (July 1989): 465–80. http://dx.doi.org/10.1016/0550-3213(89)90352-0.

Full text

APA, Harvard, Vancouver, ISO, and other styles

2

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.

Full text

APA, Harvard, Vancouver, ISO, and other styles

3

Bahcall, Safi, Bryan W. Lynn, and Stephen B. Selipsky. "Fermion Q-stars." Nuclear Physics B 325, no. 3 (October 1989): 606–18. http://dx.doi.org/10.1016/0550-3213(89)90498-7.

Full text

APA, Harvard, Vancouver, ISO, and other styles

4

Selipsky, Stephen B., Dallas C. Kennedy, and Bryan W. Lynn. "Non-abelian Q-stars." Nuclear Physics B 321, no. 2 (July 1989): 430–38. http://dx.doi.org/10.1016/0550-3213(89)90350-7.

Full text

APA, Harvard, Vancouver, ISO, and other styles

5

Becerril, R., A. Bernal, F. S. Guzmán, and U. Nucamendi. "Stability properties of Q-stars." Physics Letters B 657, no. 4-5 (December 2007): 263–68. http://dx.doi.org/10.1016/j.physletb.2007.07.077.

Full text

APA, Harvard, Vancouver, ISO, and other styles

6

Su, Ru-Keng, Cheng-Gang Su, and Rong-Shi Pan. "Q-stars at finite temperature." Physics Letters B 278, no. 3 (March 1992): 297–301. http://dx.doi.org/10.1016/0370-2693(92)90196-b.

Full text

APA, Harvard, Vancouver, ISO, and other styles

7

Prikas, Athanasios. "Q-stars in 2+1 dimensions." Nuclear Physics B 690, no. 3 (July 2004): 201–29. http://dx.doi.org/10.1016/j.nuclphysb.2004.05.005.

Full text

APA, Harvard, Vancouver, ISO, and other styles

8

Geng, Yuan-Yuan, Dong-Nuan Cui, Jiang Zhang, and Bo Zhang. "Exploring the nucleosynthesis region of metal-poor Stars." Proceedings of the International Astronomical Union 4, S252 (April 2008): 339–40. http://dx.doi.org/10.1017/s1743921308023144.

Full text

Abstract:

AbstractThe chemical abundances of the very metal poor double-enhanced stars are excellent information to set new constraints on models of neutron-capture processes at low metallicity. There have been many theoretical studies of s-process nucleosynthesis in low-mass AGB stars. Using the parametric approach based on the radiative s-process nucleosynthesis model, we calculate the following five parameters for a series of metal-poor stars. They are: the mass fraction of 13C pocket q, the overlap factor r, the neutron exposure per interpulse Δτ, and the component coefficients that correspond to relative contribution from the s-process and the r-process. We find that the mass fraction of 13C pocket q deduced for the Pb stars is comparable to the overlap factor r, which is about 10 times larger than normal AGB model; q ~ 0.05; and the neutron exposure per interpulse Δτ for all Pb stars are about 10 times smaller than the ST case (Δτ ~ 7.0mb−1). Although the two fundamental parameters Δτ and q obtained for the Pb stars are very different from the AGB stellar model, the results of the larger value of q and the smaller value of Δτ can also explain the abundance distribution of the Pb stars. This suggest that the q change to larger than that of normal AGB model. Then, this factor will result in the descent of the density of 13C in the nuclear synthesis region directly. So, the neutron exposure Δτ will also decrease to the same extent. Although the neutron number density in the larger initial mass AGB stars (m > 3M⊙) is high, the neutron irradiation time is shorter, obviously the neutron exposure per interpulse in the AGB stars should be smaller. It is noteworthy that the total amount of 13C in metal poor condition is close to the ST case, which is consistent with the primary nature of the neutron source.

APA, Harvard, Vancouver, ISO, and other styles

9

Prikas, Athanasios. "Q-Stars in Anti de Sitter Spacetime." General Relativity and Gravitation 36, no. 8 (August 2004): 1841–69. http://dx.doi.org/10.1023/b:gerg.0000035955.07614.0d.

Full text

APA, Harvard, Vancouver, ISO, and other styles

10

Madsen, Jes. "Detecting supersymmetric Q-balls with neutron stars." Physics Letters B 435, no. 1-2 (September 1998): 125–30. http://dx.doi.org/10.1016/s0370-2693(98)00789-8.

Full text

APA, Harvard, Vancouver, ISO, and other styles

11

Prikas, Athanasios. "Q-stars in scalar–tensor gravitational theories." Physics Letters B 620, no. 1-2 (July 2005): 88–96. http://dx.doi.org/10.1016/j.physletb.2005.06.022.

Full text

APA, Harvard, Vancouver, ISO, and other styles

12

Aidelman, Yael, and Lydia Sonia Cidale. "Reddening-Free Q Parameters to Classify B-Type Stars with Emission Lines." Galaxies 11, no. 1 (February 15, 2023): 31. http://dx.doi.org/10.3390/galaxies11010031.

Full text

Abstract:

The emission-line B-type stars constitute a heterogeneous group. Many of these stars show similar optical spectroscopic features and color indices, making it difficult to classify them adequately by means of photometric and spectroscopic techniques. Thus, it is relevant to deal with appropriate classification criteria to avoid as many selection effects as possible. For this purpose, we analyzed different reddening-free Q parameters, taking advantage of the Gaia and 2MASS photometric surveys, for both main sequence and emission-line B-type stars. Along with this work, we provided various criteria to search for normal and emission-line B-type stars, using different color–color, Q–color, and Q–Q diagrams. It was also possible to identify stars in different transition phases (i.e., (Rp−J) vs. (J−Ks) diagrams) and to classify them according to their NIR radiation excesses (i.e., the (Bp−Rp) vs. (H−Ks) diagram). Other diagrams, such as the QJKHK vs. (H−Ks) or QBpJHK vs. (Bp−Ks), were very useful to search for and classify different classes of B-type stars with emission lines. These diagrams highlighted the presence of several stars, classified as CBe, with large color excesses that seemed to be caused by the presence of dust in their envelopes. Therefore, these stars would be misclassified. Three groups of HAeBe stars with different intrinsic dust properties were also distinguished. The amount of intrinsic dust emission in the diverse groups of emission-line stars was well-recognized via the QJHK vs. QBpRpHK diagram. The different selection criteria are very important tools for automated designs of machine learning and optimal search algorithms.

APA, Harvard, Vancouver, ISO, and other styles

13

Yagi, K., and N. Yunes. "I-Love-Q: Unexpected Universal Relations for Neutron Stars and Quark Stars." Science 341, no. 6144 (July 25, 2013): 365–68. http://dx.doi.org/10.1126/science.1236462.

Full text

APA, Harvard, Vancouver, ISO, and other styles

14

Bonetti, Matteo, Alexander Rasskazov, Alberto Sesana, Massimo Dotti, Francesco Haardt, Nathan W. C. Leigh, Manuel Arca Sedda, Giacomo Fragione, and Elena Rossi. "On the eccentricity evolution of massive black hole binaries in stellar backgrounds." Monthly Notices of the Royal Astronomical Society: Letters 493, no. 1 (February 5, 2020): L114—L119. http://dx.doi.org/10.1093/mnrasl/slaa018.

Full text

Abstract:

ABSTRACT We study the dynamical evolution of eccentric massive black hole binaries (MBHBs) interacting with unbound stars by means of an extensive set of three-body scattering experiments. Compared to previous studies, we extend the investigation down to a MBHB mass ratio of q = m2/m1 = 10−4, where m1 and m2 are the masses of the primary and secondary hole, respectively. Contrary to a simple extrapolation from higher mass ratios, we find that for q ≲ 10−3 the eccentricity growth rate becomes negative, i.e. the binary circularizes as it shrinks. This behaviour is due to the subset of interacting stars captured in metastable counter-rotating orbits; those stars tend to extract angular momentum from the binary, promoting eccentricity growth for q > 10−3, but tend to inject angular momentum into the binary driving it towards circularization for q < 10−3. The physical origin of this behaviour requires a detailed study of the orbits of this subset of stars and is currently under investigation. Our findings might have important consequences for intermediate massive black holes (IMBHs) inspiralling on to MBHs (e.g. a putative $10^3\,\rm M_{\odot }$ black hole inspiralling on to Sgr A*).

APA, Harvard, Vancouver, ISO, and other styles

15

Yeung, Cheung-Hei, Lap-Ming Lin, Nils Andersson, and Greg Comer. "The I-Love-Q Relations for Superfluid Neutron Stars." Universe 7, no. 4 (April 20, 2021): 111. http://dx.doi.org/10.3390/universe7040111.

Full text

Abstract:

The I-Love-Q relations are approximate equation-of-state independent relations that connect the moment of inertia, the spin-induced quadrupole moment, and the tidal deformability of neutron stars. In this paper, we study the I-Love-Q relations for superfluid neutron stars for a general relativistic two-fluid model: one fluid being the neutron superfluid and the other a conglomerate of all charged components. We study to what extent the two-fluid dynamics might affect the robustness of the I-Love-Q relations by using a simple two-component polytropic model and a relativistic mean field model with entrainment for the equation-of-state. Our results depend crucially on the spin ratio Ωn/Ωp between the angular velocities of the neutron superfluid and the normal component. We find that the I-Love-Q relations can still be satisfied to high accuracy for superfluid neutron stars as long as the two fluids are nearly co-rotating Ωn/Ωp≈1. However, the deviations from the I-Love-Q relations increase as the spin ratio deviates from unity. In particular, the deviation of the Q-Love relation can be as large as O(10%) if Ωn/Ωp differ from unity by a few tens of percent. As Ωn/Ωp≈1 is expected for realistic neutron stars, our results suggest that the two-fluid dynamics should not affect the accuracy of any gravitational waveform models for neutron star binaries that employ the relation to connect the spin-induced quadrupole moment and the tidal deformability.

APA, Harvard, Vancouver, ISO, and other styles

16

Mustafa Alsulaimi, Nadeen. "Abraham Gazed upon the Stars and Said ‘innī saqīm’: The Influence of a ṣaḥīḥ ḥadīth on the Interpretation of Q. 37:88–89, and a Thematic and Structural Reading of Abraham's Story in the Qur'an." Journal of Qur'anic Studies 23, no. 2 (June 2021): 193–228. http://dx.doi.org/10.3366/jqs.2021.0472.

Full text

Abstract:

Historically mufassirs have disagreed on the meaning of the words innī saqīm spoken by Abraham as he gazed upon the stars in Q. 37:88–89. This lack of consensus can be traced back to the existence of a ṣaḥīḥ ḥadīth concerning the three lies that Abraham is said to have spoken in his lifetime. Some exegetes have attempted to reconcile the Qur'anic verses with this ḥadīth by emphasising Abraham's integrity and truthfulness and his use of white lies ( al-maʿārīḍ), while others have ignored the ḥadīth and instead rely on a contextual reading. This article analyses the meaning of Q. 37:88–89, and also explores the other suras that reference this narrative (Q. 6, Q. 21, and Q. 26). To do this it will utilise ring theory ( naẓariyyat al-tanāẓur) and exegesis of the Qur'an by the Qur'an ( tafsīr al-Qurʾān bi'l-Qurʾān), as well as the concept of the interconnectedness of Q. 37 and Q. 38 (inasmuch as these two consecutive suras both elaborate on the attributes of Abraham), so as to explore how this approach influences our understanding of this narrative. It will posit that the reference to ‘gazing upon the stars’ in Q. 37 is not synonymous with the reference to ‘looking at the planets’ in Q. 6, and that Abraham's people were well aware of his belief in God, and consequently did not correlate his gazing at the stars with belief in them. The study concludes that a contextual reading of the sura indicates that first, the phrase innī saqīm in Q. 37:88 connotes ‘contemplation’; second, the ‘sickness’ mentioned in Q. 37:89 denotes sickness of the body and mind, and that Q. 21 and Q. 26 affirm that Abraham's people understood it as such; and finally, that Q. 38 confirms the strength of Abraham's argument.

APA, Harvard, Vancouver, ISO, and other styles

17

Straizys, V. "Photometric Classification of Carbon-Rich Stars." International Astronomical Union Colloquium 106 (1989): 62. http://dx.doi.org/10.1017/s0252921100062710.

Full text

Abstract:

The Vilnius seven-color photometric system with the mean wavelengths of bandpasses at 345, 374, 405, 466, 516, 544, and 656 nm is intended for photometric determination of spectral classes, absolute magnitudes, and metallicities of stars and the amount of interstellar reddening. At the same time, different reddening-free diagrams of the system make it possible to recognize stars with different peculiarities. Carbon-rich stars are among these types of objects. For separation of carbon, barium, and CH stars from normal stars, the diagram Q (345, 374, 466, 544), Q (405, 516, 656) is the best. Its merit is based on sensitivity of the 405 magnitude to the violet depression and of the 374 magnitude to the absorption of the C3, SiC, and CN bands, This diagram can be used to estimate the C/0 abundance ratio with corresponding calibration at hand.

APA, Harvard, Vancouver, ISO, and other styles

18

Zloshchastiev, Konstantin G. "Superfluid stars and Q-balls in curved spacetime." Low Temperature Physics 47, no. 2 (February 2021): 89–95. http://dx.doi.org/10.1063/10.0003166.

Full text

APA, Harvard, Vancouver, ISO, and other styles

19

Prikas, Athanasios. "Domain walls on the surface of q-stars." Journal of Mathematical Physics 47, no. 11 (November 2006): 112503. http://dx.doi.org/10.1063/1.2363254.

Full text

APA, Harvard, Vancouver, ISO, and other styles

20

Caimmi, R. "Fractional yields inferred from halo and thick disk stars." Serbian Astronomical Journal, no. 187 (2013): 19–41. http://dx.doi.org/10.2298/saj130924004c.

Full text

Abstract:

Linear [Q/H]-[O/H] relations, Q = Na, Mg, Si, Ca, Ti, Cr, Fe, Ni, are inferred from a sample (N = 67) of recently studied FGK-type dwarf stars in the solar neighbourhood including different populations (Nissen and Schuster 2010, Ramirez et al. 2012), namely LH (N = 24, low-? halo), HH (N = 25, high-? halo), KD (N = 16, thick disk), and OL (N = 2, globular cluster outliers). Regression line slope and intercept estimators and related variance estimators are determined. With regard to the straight line, [Q/H]=aQ[O/H]+bQ, sample stars are displayed along a "main sequence", [Q,O] = [aQ, bQ, ?bQ], leaving aside the two OL stars, which, in most cases (e.g. Na), lie outside. The unit slope, aQ = 1, implies Q is a primary element synthesised via SNII progenitors in the presence of a universal stellar initial mass function (defined as simple primary element). In this respect, Mg, Si, Ti, show ?Q = 1 within -+2^??Q; Cr, Fe, Ni, within -+3^??Q; Na, Ca, within -+r^??Q, r > 3. The empirical, differential element abundance distributions are inferred from LH, HH, KD, HA = HH + KD subsamples, where related regression lines represent their theoretical counterparts within the framework of simple MCBR (multistage closed box + reservoir) chemical evolution models. Hence, the fractional yields, ^pQ/^pO, are determined and (as an example) a comparison is shown with their theoretical counterparts inferred from SNII progenitor nucleosynthesis under the assumption of a power-law stellar initial mass function. The generalized fractional yields, CQ=ZQ/ZaQ O, are determined regardless of the chemical evolution model. The ratio of outflow to star formation rate is compared for different populations in the framework of simple MCBR models. The opposite situation of element abundance variation entirely due to cosmic scatter is also considered under reasonable assumptions. The related differential element abundance distribution fits to the data, as well as its counterpart inferred in the opposite limit of instantaneous mixing in the presence of chemical evolution, while the latter is preferred for HA subsample.

APA, Harvard, Vancouver, ISO, and other styles

21

Giovinazzi, Mark R., and Cullen H. Blake. "A Mass–Magnitude Relation for Low-mass Stars Based on Dynamical Measurements of Thousands of Binary Star Systems." Astronomical Journal 164, no. 4 (September 28, 2022): 164. http://dx.doi.org/10.3847/1538-3881/ac8cf7.

Full text

Abstract:

Abstract Stellar mass is a fundamental parameter that is key to our understanding of stellar formation and evolution, as well as the characterization of nearby exoplanet companions. Historically, stellar masses have been derived from long-term observations of visual or spectroscopic binary star systems. While advances in high-resolution imaging have enabled observations of systems with shorter orbital periods, measurements of stellar masses remain challenging, and relatively few have been precisely measured. We present a new statistical approach to measuring masses for populations of stars. Using Gaia astrometry, we analyze the relative orbital motion of >3800 wide binary systems comprising low-mass stars to establish a mass–magnitude relation in the Gaia G RP band spanning the absolute magnitude range 14.5 > M G RP > 4.0, corresponding to a mass range of 0.08 M ⊙ ≲ M ≲ 1.0 M ⊙. This relation is directly applicable to >30 million stars in the Gaia catalog. Based on comparison to existing mass–magnitude relations calibrated for K s magnitudes from the Two Micron All Sky Survey, we estimate that the internal precision of our mass estimates is ∼10%. We use this relation to estimate masses for a volume-limited sample of ∼18,200 stars within 50 pc of the Sun and the present-day field mass function for stars with M ≲ 1.0 M ⊙, which we find peaks at 0.16 M ⊙. We investigate a volume-limited sample of wide binary systems with early-K dwarf primaries, complete for binary mass ratios q > 0.2, and measure the distribution of q at separations >100 au. We find that our distribution of q is not uniform, rather decreasing toward q = 1.0.

APA, Harvard, Vancouver, ISO, and other styles

22

Hamdy, M. A., M. S. Abo Elazm, and S. M. Saad. "Spectral reclassification of some Be stars using ?Q method." Astrophysics and Space Science 186, no. 1 (1991): 161–64. http://dx.doi.org/10.1007/bf00644632.

Full text

APA, Harvard, Vancouver, ISO, and other styles

23

Dornan, V., and C. C. Lovekin. "The Effects of Metallicity on Convective Overshoot Behavior in Models of δ Scuti Variable Stars." Astrophysical Journal 924, no. 2 (January 1, 2022): 130. http://dx.doi.org/10.3847/1538-4357/ac3980.

Full text

Abstract:

Abstract δ Scuti variables are stars which exhibit periodic changes in their luminosity through radial and nonradial pulsations. Internally, these stars have relatively small convective cores, and convective overshoot can significantly affect the size. Recently, models of radial pulsation in δ Scuti stars found a strong correlation between the pulsation constant (Q) as a function of effective temperature and the amount of convective overshoot within the star. However, only models with metallicities of Z = 0.02 were examined, leaving the dependence of` this relationship on chemical composition unknown. In this work, we have extended the model grid to cover a range of metallicities using Modules for Experiments in Stellar Astrophysics (), and analyzed the models’ pulsation properties using GYRE. By varying the models’ mass, rotation speed, convective overshoot, and metallicity, we studied the behavior of Q at low temperature. We found that the updated convective boundary treatment in MESA changes the overshoot dependence found previously, and the value of the slope depends on both rotation and overshoot. We also found that there is a metallicity dependence in the Q values. The lowest metallicity models in our grid reached higher temperatures than previously studied, revealing a parabolic relation between log Q and log T eff .

APA, Harvard, Vancouver, ISO, and other styles

24

Pedron, Isabel Tamara, and Carlos H. Coimbra-Araújo. "Brownian motion of black holes in stellar systems with non-Maxwellian distribution of the field stars." Proceedings of the International Astronomical Union 2, S238 (August 2006): 427–28. http://dx.doi.org/10.1017/s1743921307005789.

Full text

Abstract:

AbstractA massive black hole at the center of a dense stellar system, such as a globular cluster or a galactic nucleus, is subject to a random walk due gravitational encounters with nearby stars. It behaves as a Brownian particle, since it is much more massive than the surrounding stars and moves much more slowly than they do. If the distribution function for the stellar velocities is Maxwellian, there is a exact equipartition of kinetic energy between the black hole and the stars in the stationary state. However, if the distribution function deviates from a Maxwellian form, the strict equipartition cannot be achieved.The deviation from equipartition is quantified in this work by applying the Tsallis q-distribution for the stellar velocities in a q-isothermal stellar system and in a generalized King model.

APA, Harvard, Vancouver, ISO, and other styles

25

Pinçon, C., M. J. Goupil, and K. Belkacem. "Probing the mid-layer structure of red giants." Astronomy & Astrophysics 634 (February 2020): A68. http://dx.doi.org/10.1051/0004-6361/201936864.

Full text

Abstract:

Context. The space-borne missions CoRoT and Kepler have already brought stringent constraints on the internal structure of low-mass evolved stars, a large part of which results from the detection of mixed modes. However, all the potential of these oscillation modes as a diagnosis of the stellar interior has not been fully exploited yet. In particular, the coupling factor or the gravity-offset of mixed modes, q and εg, are expected to provide additional constraints on the mid-layers of red giants, which are located between the hydrogen-burning shell and the neighborhood of the base of the convective zone. The link between these parameters and the properties of this region, nevertheless, still remains to be precisely established. Aims. In the present paper, we investigate the potential of the coupling factor in probing the mid-layer structure of evolved stars. Methods. Guided by typical stellar models and general physical considerations, we modeled the coupling region along with evolution. We subsequently obtained an analytical expression of q based on the asymptotic theory of mixed modes and compared it to observations. Results. We show that the value of q is degenerate with respect to the thickness of the coupling evanescent region and the local density scale height. On the subgiant branch and the beginning of the red giant branch (RGB), the model predicts that the peak in the observed value of q is necessarily associated with the important shrinking and the subsequent thickening of the coupling region, which is located in the radiative zone at these stages. The large spread in the measurement is interpreted as the result of the high sensitivity of q to the structure properties when the coupling region becomes very thin. Nevertheless, the important degeneracy of q in this regime prevents us from unambiguously concluding on the precise structural origin of the observed values. In later stages, the progressive migration of the coupling region toward the convective zone is expected to result in a slight and smooth decrease in q, which is in agreement with observations. At one point just before the end of the first-dredge up and the luminosity bump, the coupling region becomes entirely located in the convective region and its continuous thickening is shown to be responsible for the observed decrease in q. We demonstrate that q has the promising potential to probe the migration of the base of the convective region as well as convective extra-mixing during this stage. We also show that the frequency-dependence of q cannot be neglected in the oscillation spectra of such evolved RGB stars, which is in contrast with what is assumed in the current measurement methods. This fact can have an influence on the physical interpretation of the observed values. In red clump stars, in which the coupling regions are very thin and located in the radiative zone, the small variations and spread observed in q suggest that their mid-layer structure is very stable. Conclusions. A structural interpretation of the global observed variations in q was obtained and the potential of this parameter in probing the dynamics of the mid-layer properties of red giants is highlighted. This analytical study paves the way for a more quantitative exploration of the link of q with the internal properties of evolved stars using stellar models for a proper interpretation of the observations. This will be undertaken in the following papers of this series.

APA, Harvard, Vancouver, ISO, and other styles

26

Guo, Yanjun, Jiao Li, Jianping Xiong, Jiangdan Li, Luqian Wang, Heran Xiong, Feng Luo, et al. "The Binarity of Early-type Stars from LAMOST medium-resolution Spectroscopic Survey." Research in Astronomy and Astrophysics 22, no. 2 (February 1, 2022): 025009. http://dx.doi.org/10.1088/1674-4527/ac3e5a.

Full text

Abstract:

Abstract Massive binaries play significant roles in many fields. Identifying massive stars, particularly massive binaries, is of great importance. In this paper, by adopting the technique of measuring the equivalent widths of several spectral lines, we identified 9382 early-type stars from the LAMOST medium-resolution survey and divided the sample into four groups, T1 (∼O-B4), T2 (∼B5), T3 (∼B7) and T4 (∼B8-A). The relative radial velocities RVrel were calculated using Maximum Likelihood Estimation. The stars with significant changes of RVrel and at least larger than 15.57 km s−1 were identified as spectroscopic binaries. We found that the observed spectroscopic binary fractions for the four groups are 24.6% ± 0.5%, 20.8% ± 0.6%, 13.7% ± 0.3% and 7.4% ± 0.3%, respectively. Assuming that orbital period (P) and mass ratio (q) have intrinsic distributions as f(P) ∝ P π (1 < P < 1000 days) and f(q) ∝ q κ (0.1 < q < 1), respectively, we conducted a series of Monte-Carlo simulations to correct observational biases for estimating the intrinsic multiplicity properties. The results show that the intrinsic binary fractions for the four groups are 68% ± 8%, 52% ± 3%, 44% ± 6% and 44% ± 6%, respectively. The best estimated values for π are −1 ± 0.1, −1.1 ± 0.05, −1.1 ± 0.1 and −0.6 ± 0.05, respectively. The κ cannot be constrained for groups T1 and T2 and is −2.4 ± 0.3 for group T3 and −1.6 ± 0.3 for group T4. We confirmed the relationship of a decreasing trend in binary fractions toward late-type stars. No correlation between the spectral type and orbital period distribution has been found yet, possibly due to the limitation of observational cadence.

APA, Harvard, Vancouver, ISO, and other styles

27

Chulkov, Dmitry. "Pairing function of visual binary stars." Monthly Notices of the Royal Astronomical Society 501, no. 1 (November 20, 2020): 769–83. http://dx.doi.org/10.1093/mnras/staa3601.

Full text

Abstract:

ABSTRACT An all-sky sample of 1227 visual binaries based on Washington Double Star catalogue is constructed to infer the initial mass function (IMF), mass ratio, and projected distance distribution with a dedicated population synthesis model. Parallaxes from Gaia DR2 and Hipparcos are used to verify the distance distribution. The model is validated on the single-star Tycho-2 sample and successfully reproduces the observed magnitudes and angular separations. The projected separation distribution follows f(s) ∼ s−1.2 in 102–2 × 103 au range for 1–4.5 m⊙ primary stars. Several algorithms are explored as pairing functions. Random pairing is confidently rejected. Primary-constrained pairing (PCP) and split-core pairing (SCP), the scenarios adopting primary component’s or total system’s mass as fundamental, are considered. The preferred IMF slope is α ∼ 2.8 either way. A simple power-law mass ratio distribution is unlikely, but the introduction of a twin excess provides a favourable result. PCP with f(q) ∼ q−1 is preferred with a tiny twin fraction, models with f(q) ∼ q−1.5 are acceptable when a larger twin excess is allowed. SCP is similar to PCP when a larger slope of the power law is adopted: f(q) ∼ qβ + 0.7.

APA, Harvard, Vancouver, ISO, and other styles

28

Watson, R. D. "Colour changes in mid-B star variables." Publications of the Astronomical Society of Australia 7, no. 1 (1987): 38–41. http://dx.doi.org/10.1017/s1323358000021809.

Full text

Abstract:

AbstractModel predictions of light changes due to non-radial stellar pulsation have been compared with the observations of light and colour changes in mid-B star variables made by Waelkens and Rufener (1985). It is concluded that these observations are consistent with the presence of low l (dipole and quadrupole) non-radial pulsations in the stars. This strengthens Waelkens and Rufener’s hypothesis that these variables may be identified with the 53 Persei stars. The differences between the model predictions for these large Q variables, which have periods in the 1 to 3 day range, and the predictions of small Q models, which apply to β Cephei variables, are explained.

APA, Harvard, Vancouver, ISO, and other styles

29

Bošković, Mateja, and Enrico Barausse. "Soliton boson stars, Q-balls and the causal Buchdahl bound." Journal of Cosmology and Astroparticle Physics 2022, no. 02 (February 1, 2022): 032. http://dx.doi.org/10.1088/1475-7516/2022/02/032.

Full text

Abstract:

Abstract Self-gravitating non-topological solitons whose potential admits multiple vacua are promising candidates for exotic compact objects. Such objects can arise in several extensions of the Standard Model and could be produced in the early Universe. In this work, we focus on objects made from complex scalars (gravitating Q-balls/soliton boson stars), deriving analytic solutions in spherical symmetry and comparing them with fully numerical ones. In the high-compactness limit we find that these objects present an effectively linear equation of state, thus saturating the Buchdahl limit with the causality constraint. Far from that limit, these objects behave either as flat space-time Q-balls or (in the low-compactness limit) as mini boson stars stabilized by quantum pressure. We establish the robustness of this picture by analyzing a variety of potentials (including cosine, quartic and sextic ones).

APA, Harvard, Vancouver, ISO, and other styles

30

Prikas, Athanasios. "q stars in scalar-tensor gravitational theories in extra dimensions." Journal of Mathematical Physics 47, no. 8 (August 2006): 082501. http://dx.doi.org/10.1063/1.2245208.

Full text

APA, Harvard, Vancouver, ISO, and other styles

31

Johnson, J. H. "Stars, maximal rectangles, lattices: a new perspective on Q-analysis." International Journal of Man-Machine Studies 24, no. 3 (March 1986): 293–99. http://dx.doi.org/10.1016/s0020-7373(86)80027-x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

32

Yagi, Kent, and Nicolás Yunes. "I -Love- Q relations: from compact stars to black holes." Classical and Quantum Gravity 33, no. 9 (April 12, 2016): 095005. http://dx.doi.org/10.1088/0264-9381/33/9/095005.

Full text

APA, Harvard, Vancouver, ISO, and other styles

33

Raduta, Adriana R., Micaela Oertel, and Armen Sedrakian. "Proto-neutron stars with heavy baryons and universal relations." Monthly Notices of the Royal Astronomical Society 499, no. 1 (August 19, 2020): 914–31. http://dx.doi.org/10.1093/mnras/staa2491.

Full text

Abstract:

ABSTRACT We use covariant density functional theory to obtain the equation of state (EoS) of matter in compact stars at non-zero temperature, including the full baryon octet as well as the Δ(1232) resonance states. Global properties of hot Δ-admixed hypernuclear stars are computed for fixed values of entropy per baryon (S/A) and lepton fraction (YL). Universal relations between the moment of inertia, quadrupole moment, tidal deformability, and compactness of compact stars are established for fixed values of S/A and YL that are analogous to those known for cold catalyzed compact stars. We also verify that the I–Love–Q relations hold at finite temperature for constant values of S/A and YL.

APA, Harvard, Vancouver, ISO, and other styles

34

Jorissen, A., H. M. J. Boffin, D. Karinkuzhi, S. Van Eck, A. Escorza, S. Shetye, and H. Van Winckel. "Barium and related stars, and their white-dwarf companions." Astronomy & Astrophysics 626 (June 2019): A127. http://dx.doi.org/10.1051/0004-6361/201834630.

Full text

Abstract:

Context. Barium and S stars without technetium are red giants and are suspected of being members of binary systems due to their overabundances in heavy elements. These elements are produced by the s-process of nucleosynthesis, despite the stars not being evolved enough to be able to activate the s-process in their interiors. A companion formerly on the asymptotic giant branch (now a white dwarf) is supposed to be responsible for the barium- and S-star enrichment in s-process elements through mass transfer. Aims. This paper provides both long-period and revised orbits for barium and S stars, adding to previously published orbits. The sample of barium stars with strong anomalies (i.e., those classified as Ba3, Ba4, or Ba5 in the Warner scale) comprises all known stars of that kind, and in that sense forms a complete sample that allows us to investigate several orbital properties of these post-mass-transfer binaries in an unbiased way. Methods. Orbital elements are derived from radial velocities collected from a long-term radial-velocity monitoring campaign performed with the HERMES spectrograph mounted on the Mercator 1.2 m telescope. These new measurements were combined with older, CORAVEL measurements. With the aim of investigating possible correlations between orbital properties and abundances, we also collected a set of abundances for barium stars with orbital elements that is as homogeneous as possible. When unavailable in the literature, abundances were derived from high-resolution HERMES spectra. Results. We find orbital motion for all barium and extrinsic S stars monitored (except for the mild barium star HD 95345). We obtain the longest period known so far for a spectroscopic binary involving an S star, namely 57 Peg with a period of the order of 100−500 yr. We present the mass distribution for the barium stars, which ranges from 1 to 3 M⊙, with a tail extending up to 5 M⊙ in the case of mild barium stars. This high-mass tail is mostly comprised of high-metallicity objects ([Fe/H] ≥ −0.1). The distribution of the companion masses was extracted from the barium-star mass distribution combined with the finding that Q ≡ f(MBa,MWD)/sin3 i = MWD3/(MBa + MWD)2 is peaked at 0.057 ± 0.009 and 0.036 ± 0.027 M⊙ for strong and mild barium stars, respectively (f(MBa, MWD) is the mass function obtained from the orbital elements of spectroscopic binaries with one observable spectrum). Mass functions are compatible with WD companions whose masses range from 0.5 to 1 M⊙. Strong barium stars have a tendency to be found in systems with shorter periods than mild barium stars, although this correlation is rather lose, with metallicity and WD mass also playing a role. Using the initial–final mass relationship established for field WDs, we derived the distribution of the mass ratio q′=MAGB, ini/MBa (where MAGB, ini is the WD progenitor initial mass, i.e., the mass of the former primary component of the system) which is a proxy for the initial mass ratio (the less mass the barium star has accreted, the better the proxy). It appears that the distribution of q′ is highly nonuniform, and significantly different for mild and strong barium stars, the latter being characterized by values mostly in excess of 1.4, whereas mild barium stars occupy the range 1−1.4. Conclusions. The orbital properties presented in this paper pave the way for a comparison with binary-evolution and nucleosynthesis models, which should account for the various significant correlations found between abundances and dynamical parameters (e.g. between MBa on one hand and MWD, [Fe/H], and [s/Fe] on the other hand, between q′ and [s/Fe], between P and e, and between P and [s/Fe] altogether).

APA, Harvard, Vancouver, ISO, and other styles

35

Townsend, R. H. D. "Improved asymptotic expressions for the eigenvalues of Laplace’s tidal equations." Monthly Notices of the Royal Astronomical Society 497, no. 3 (July 25, 2020): 2670–79. http://dx.doi.org/10.1093/mnras/staa2159.

Full text

Abstract:

ABSTRACT Laplace’s tidal equations govern the angular dependence of oscillations in stars when uniform rotation is treated within the so-called traditional approximation. Using a perturbation expansion approach, I derive improved expressions for the eigenvalue associated with these equations, valid in the asymptotic limit of large spin parameter q. These expressions have a relative accuracy of order q−3 for gravito-inertial modes, and q−1 for Rossby and Kelvin modes; the corresponding absolute accuracy is of order q−1 for all three mode types. I validate my analysis against numerical calculations, and demonstrate how it can be applied to derive formulae for the periods and eigenfunctions of Rossby modes.

APA, Harvard, Vancouver, ISO, and other styles

36

Halbedel, Elaine M. "Photometric determination of spectral types for Be stars - The Q method." Publications of the Astronomical Society of the Pacific 105 (May 1993): 465. http://dx.doi.org/10.1086/133179.

Full text

APA, Harvard, Vancouver, ISO, and other styles

37

Hovhannessian, R. Kh. "Classification of Stars by the Reddening-Free Paraneters Q and D." Astrophysics 47, no. 4 (October 2004): 499–504. http://dx.doi.org/10.1023/b:asys.0000049788.48071.55.

Full text

APA, Harvard, Vancouver, ISO, and other styles

38

Doneva, Daniela D., Stoytcho S. Yazadjiev, Nikolaos Stergioulas, and Kostas D. Kokkotas. "BREAKDOWN OF I -LOVE- Q UNIVERSALITY IN RAPIDLY ROTATING RELATIVISTIC STARS." Astrophysical Journal 781, no. 1 (December 23, 2013): L6. http://dx.doi.org/10.1088/2041-8205/781/1/l6.

Full text

APA, Harvard, Vancouver, ISO, and other styles

39

McNamara, D. H., and John M. Powell. "A Theoretical Period-Luminosity Relation of Dwarf Cepheids." International Astronomical Union Colloquium 138 (1993): 437–38. http://dx.doi.org/10.1017/s025292110002087x.

Full text

Abstract:

Dwarf Cepheids (large-amplitude δ Sct variables and SXPhe variables in the GCVS) are late A-type stars near light maximum and early-F stars near light minimum. In the lower part of the instability strip where these stars are found the pulsation constant Q varies only slightly. As pointed out by Andreasen, Hejlesen, and Petersen (1983) this makes it easy to transform a theoretical HR or alternatively a (logTe, logg) diagram to a theoretical logTe, logP0) diagram by the use of the relation. This follows from the equations:where P0 is the fundamental period of pulsation. The periods, of course, can be determined with very high accuracy.

APA, Harvard, Vancouver, ISO, and other styles

40

Hattori, Kohei, Monica Valluri, and Eugene Vasiliev. "Action-based distribution function modelling for constraining the shape of the Galactic dark matter halo." Monthly Notices of the Royal Astronomical Society 508, no. 4 (October 8, 2021): 5468–92. http://dx.doi.org/10.1093/mnras/stab2898.

Full text

Abstract:

ABSTRACT We estimate the 3D density profile of the Galactic dark matter (DM) halo within r ≲ 30 kpc from the Galactic centre by using the astrometric data for halo RR Lyrae stars from Gaia DR2. We model both the stellar halo distribution function and the Galactic potential, fully taking into account the survey selection function, the observational errors, and the missing line-of-sight velocity data for RR Lyrae stars. With a Bayesian method, we infer the model parameters, including the density flattening of the DM halo q, which is assumed to be constant as a function of radius. We find that 99 per cent of the posterior distribution of q is located at q > 0.963, which strongly disfavours a flattened DM halo. We cannot draw any conclusions as to whether the Galactic DM halo at $r \lesssim 30 \, \mathrm{kpc}$ is prolate, because we restrict ourselves to axisymmetric oblate halo models with q ≤ 1. Our DM density profile might be biased especially in the inner few kpc, due to the uncertainty in the baryonic distribution. Our result is in tension with predictions from cosmological hydrodynamical simulations that advocate more oblate (〈q〉 ∼ 0.8 ± 0.15) DM haloes within ${\sim}15{{\ \rm per\ cent}}$ of the virial radius for Milky-Way-sized galaxies. An alternative possibility, based on our validation tests with a cosmological simulation, is that the true value q of the Galactic halo could be consistent with cosmological simulations but that disequilibrium in the Milky Way potential is inflating our measurement of q by 0.1–0.2. As a by-product, our model constrains the DM density in the Solar neighbourhood to be $\rho _{\mathrm{DM},\odot } = (9.01^{+0.18}_{-0.20})\times 10^{-3}{\,\rm M_\odot} \mathrm{pc}^{-3} = 0.342^{+0.007}_{-0.007}$ GeVcm−3, consistent with other recent measurements.

APA, Harvard, Vancouver, ISO, and other styles

41

Tang, Yan-Ke, Ya-Ni Guo, Kai Li, Ning Gai, and Zhi-Kai Li. "The First Photometric Analysis of Two Low Mass Ratio Totally Eclipsing Contact Binaries: TIC 393943031 and TIC 89428764." Research in Astronomy and Astrophysics 22, no. 3 (February 11, 2022): 035009. http://dx.doi.org/10.1088/1674-4527/ac4705.

Full text

Abstract:

Abstract Photometric analysis of the contact binaries TIC 393943031 and TIC 89428764 was carried out using Transiting Exoplanet Survey Satellite and SuperWASP data for the first time. Using the Wilson–Devinney code, we have found that TIC 393943031 is a low-mass-ratio deep contact binary with a fillout factor of 50.9(±1)% and a mass ratio of q = 0.163 ± 0.001. TIC 89428764 is a medium and low-mass-ratio contact binary with a fillout factor of 34.5(±1)% and a mass ratio of q = 0.147 ± 0.001. Furthermore, the period study reveals both the stars exhibit continuously increasing periods, the increasing rate is 4.21 × 10−7 day yr−1 for TIC 393943031 while 6.36 × 10−7 day yr−1 for TIC 89428764. The possible reason is mass transfer from the secondary component to the primary component for both stars. Meanwhile, we discussed their evolutionary phases and orbital angular momenta.

APA, Harvard, Vancouver, ISO, and other styles

42

WORMAN, CHRIS, and J. MARK KEIL. "POLYGON DECOMPOSITION AND THE ORTHOGONAL ART GALLERY PROBLEM." International Journal of Computational Geometry & Applications 17, no. 02 (April 2007): 105–38. http://dx.doi.org/10.1142/s0218195907002264.

Full text

Abstract:

A decomposition of a polygon P is a set of polygons whose geometric union is exactly P. We study a polygon decomposition problem that is equivalent to the Orthogonal Art Gallery problem. Two points are r-visible if the orthogonal bounding rectangle for p and q lies within P. A polygon P is an r-star if there exists a point k ∈ P such that for each point q ∈ P, q is r-visible from k. In this problem we seek a minimum cardinality decomposition of a polygon into r-stars. We show how to compute the minimum r-star cover of an orthogonal polygon in polynomial time.

APA, Harvard, Vancouver, ISO, and other styles

43

Schmeja, S., M. S. N. Kumar, D. Froebrich, and R. S. Klessen. "Changing Structures in Galactic Star Clusters." Proceedings of the International Astronomical Union 3, S246 (September 2007): 50–54. http://dx.doi.org/10.1017/s1743921308015263.

Full text

Abstract:

AbstractWe investigate the structures of embedded and open clusters using statistical methods, in particular the combined parameter $\Q$, which permits to quantify the cluster structure. Star clusters build up from several subclusters evolving from a structured to a more centrally concentrated stage. The evolution is not only a function of time, but also of the mass of the objects. Massive stars are usually centrally concentrated, while lower-mass stars are more widespread, reflecting the effect of mass segregation. Using this method we find that in IC 348 and the Orion Nebula Cluster the spatial distribution of brown dwarfs does not follow the central clustering of stars, giving important clues to their formation mechanism by supporting the ejected embryo scenario.

APA, Harvard, Vancouver, ISO, and other styles

44

Jiang, Dengkai, Jiangcheng Wang, Zhanwen Han, Tianyu Jiang, and Lifang Li. "The energy transfer in W UMa binary stars." Proceedings of the International Astronomical Union 4, S252 (April 2008): 433–34. http://dx.doi.org/10.1017/s1743921308023430.

Full text

Abstract:

AbstractThe properties of W UMa binary stars are studied based on the well-determined physical parameters of 132 W UMa systems. It is found that the energy transfer rate has a maximum value at q ~ 0.58. The relation between the energy transfer rate and the temperature deviation is also investigated, and the temperature of the secondary component is related to the energy transfer rate.

APA, Harvard, Vancouver, ISO, and other styles

45

Lèbre, Agnès, Michel Aurière, Nicolas Fabas, Denis Gillet, Eric Josselin, Philippe Mathias, and Pascal Petit. "Full Stokes IQUV spectropolarimetry of AGB and post-AGB stars: probing surface magnetism and atmospheric dynamics." Proceedings of the International Astronomical Union 10, S305 (December 2014): 47–52. http://dx.doi.org/10.1017/s1743921315004500.

Full text

Abstract:

AbstractFull Stokes spectropolarimetric observations of a Mira star (χ Cyg) and a RV Tauri star (R Sct) are presented and analyzed comparatively. From their Stokes V data (circular polarization), we report the detection of a weak magnetic field at the surface of these cool and evolved radially pulsating stars. For both stars, we analyse this detection in the framework of their complex atmospheric dynamics, with the possibility that shock waves may imprint an efficient compressive effect on the surface magnetic field. We also report strong Stokes U and Stokes Q signatures associated to metallic lines (as a global trend), those linear polarimetric features appear to be time variable along the pulsating phase. More surprising, in the Stokes U and Stokes Q data, we also detect signatures associated to individual metallic lines (such as Sr i 460.7 nm, Na D2588.9 nm), that are known (from the solar case) to be easily polarizable in case of a global asymmetry at the photospheric level.

APA, Harvard, Vancouver, ISO, and other styles

46

Miller, J. C., T. Shahbaz, and L. A. Nolan. "Are Q-stars a serious threat for stellar-mass black hole candidates?" Monthly Notices of the Royal Astronomical Society 294, no. 2 (February 21, 1998): L25—L29. http://dx.doi.org/10.1111/j.1365-8711.1998.01384.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

47

Gupta, Toral, Barun Majumder, Kent Yagi, and Nicolás Yunes. "I-Love-Q relations for neutron stars in dynamical Chern Simons gravity." Classical and Quantum Gravity 35, no. 2 (December 19, 2017): 025009. http://dx.doi.org/10.1088/1361-6382/aa9c68.

Full text

APA, Harvard, Vancouver, ISO, and other styles

48

Miller, Shahbaz, and Nolan. "Are Q-stars a serious threat for stellar-mass black hole candidates?" Monthly Notices of the Royal Astronomical Society 294, no. 2 (February 1998): L25—L29. http://dx.doi.org/10.1046/j.1365-8711.1998.01384.x.

Full text

APA, Harvard, Vancouver, ISO, and other styles

49

Boshkayev, K., and H. Quevedo. "Non-validity of I–Love–Q Relations for Hot White Dwarf Stars." Monthly Notices of the Royal Astronomical Society 478, no. 2 (May 11, 2018): 1893–99. http://dx.doi.org/10.1093/mnras/sty1227.

Full text

APA, Harvard, Vancouver, ISO, and other styles

50

Haskell, B., R. Ciolfi, F. Pannarale, and L. Rezzolla. "On the universality of I-Love-Q relations in magnetized neutron stars." Monthly Notices of the Royal Astronomical Society: Letters 438, no. 1 (December 13, 2013): L71—L75. http://dx.doi.org/10.1093/mnrasl/slt161.

Full text

APA, Harvard, Vancouver, ISO, and other styles

Journal articles on the topic 'Q-stars'

Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles