Analysis of the Gravity Mode of a Pulsating Doradus-type Star

International audienceIn recent decades, asteroseismology has become a powerful tool in checking models for the structure and evolution of stars. From the perspective of asteroseismology, pulsating stars are invaluable. For this type of star, Doradus-type stars have a special feature. Since the atmosphere of such stars is in the transition phase from radiant state to convection state, gravity mode oscillations are visible in these stars. Since gravity modes are originated from central stellar regions, detecting them provides valuable information about these regions. In this study, photometric data of KIC11826272 provided by the Kepler satellite has been analyzed. The gravity mode's pattern and the average period have been determined. Deviation from the uniform ∆ in the form of a pattern is due to the mean rotation of the star. The rotational frequency splitting effect has increased the gravity mode's frequency. A decaying deviation found in the pattern represents prograde modes that are moving in the direction of rotation of the star. Finally, the degree of gravity mode has been determined

Evolution of the galaxy luminosity function in progenitors of fossil groups

Using the semi-analytic models based on the Millennium simulation, we trace back the evolution of the luminosity function of galaxies residing in progenitors of groups classified by the magnitude gap at redshift zero. We determine the luminosity function of galaxies within $0.25R_{200}, 0.5R_{200}$, and $R_{200}$ for galaxy groups/clusters. The bright end of the galaxy luminosity function of fossil groups shows a significant evolution with redshift, with changes in $M^*$ by $\sim$ 1-2 mag between $z\sim0.5$ and $z=0$ (for the central $0.5R_{200}$), suggesting that the formation of the most luminous galaxy in a fossil group has had a significant impact on the $M^{*}$ galaxies e.g. it is formed as a result of multiple mergers of the $M^{*}$ galaxies within the last $\sim5$ Gyr. In contrast, the slope of the faint end, $\alpha$, of the luminosity function shows no considerable redshift evolution and the number of dwarf galaxies in the fossil groups exhibits no evolution, unlike in non-fossil groups where it grows by $\sim25-42\%$ towards low redshifts. In agreement with previous studies, we also show that fossil groups accumulate most of their halo mass earlier than non-fossil groups. Selecting the fossils at a redshift of 1 and tracing them to a redshift 0, we show that $80\%$ of the fossil groups ($10^{13} M_{\odot} h^{-1}<M_{200}<10^{14} M_{\odot} h^{-1}$) will lose their large magnitude gaps. However, about $40\%$ of fossil clusters ($M_{200}>10^{14} M_{\odot} h^{-1}$) will retain their large gaps.Comment: Accepted for publication in A&A. 13 pages, 15 figure

Exoplanets prediction in multiplanetary systems

We present the results of a search for additional exoplanets in allmultiplanetary systems discovered to date, employing a logarithmic spacing between planets in our Solar System known as the Titius-Bode (TB) relation. We use theMarkov Chain Monte Carlo method and separately analyse 229 multiplanetary systems that house at least three or more confirmed planets. We find that the planets in similar to 53% of these systems adhere to a logarithmic spacing relation remarkably better than the Solar System planets. Using the TB relation, we predict the presence of 426 additional exoplanets in 229 multiplanetary systems, of which 197 candidates are discovered by interpolation and 229 by extrapolation. Altogether, 47 predicted planets are located within the habitable zone of their host stars, and 5 of the 47 planets have a maximum mass limit of 0.1-2 M-circle plus and a maximum radius lower than 1.25 R-circle plus. Our results and prediction of additional planets agree with previous studies' predictions; however, we improve the uncertainties in the orbital period measurement for the predicted planets significantly.Peer reviewe

f(T) cosmology against the cosmographic method: A new study using mock and observational data

In this paper, we study the power-law $f(T)$ model using Hubble diagrams of type Ia supernovae (SNIa), quasars (QSOs), Gamma Ray Bursts (GRBs) and the measurements from baryonic acoustic oscillations (BAO) in the framework of the cosmographic method. Using mock data for SNIa, QSOs and GRBs generated based on the power-law $f(T)$ model, we show whether different cosmographic methods are suitable to reconstruct the distance modulus or not. In particular, we investigate the rational PADE polynomials $(3,2)$ and $(2,2)$ in addition to the fourth- and fifth- order Taylor series. We show that PADE $(3,2)$ is the best approximation that can be used in the cosmographic method to reconstruct the distance modulus at both low and high redshifts. In the context of PADE $(3,2)$ cosmographic method, we show that the power-law $f(T)$ model is well consistent with the real observational data from the Hubble diagrams of SNIa, QSOs and GRBs. Moreover, we find that the combination of the Hubble diagram of SNIa and the BAO observation leads to better consistency between the model-independent cosmographic method and the power-law $f(T)$ model. Finally, our observational constraints on the parameter of the effective equation of state of DE, described by the power-law $f(T)$ model, show the phantom-like behavior, especially when the BAO observations are included in our analysis.Comment: 19 pages, 10 figures, 6 table

Revisiting mass-radius relationships for exoplanet populations: a machine learning insight

The growing number of exoplanet discoveries and advances in machine learning techniques have opened new avenues for exploring and understanding the characteristics of worlds beyond our Solar System. In this study, we employ efficient machine learning approaches to analyze a dataset comprising 762 confirmed exoplanets and eight Solar System planets, aiming to characterize their fundamental quantities. By applying different unsupervised clustering algorithms, we classify the data into two main classes: 'small' and 'giant' planets, with cut-off values at $R_{p}=8.13R_{\oplus}$ and $M_{p}=52.48M_{\oplus}$. This classification reveals an intriguing distinction: giant planets have lower densities, suggesting higher H-He mass fractions, while small planets are denser, composed mainly of heavier elements. We apply various regression models to uncover correlations between physical parameters and their predictive power for exoplanet radius. Our analysis highlights that planetary mass, orbital period, and stellar mass play crucial roles in predicting exoplanet radius. Among the models evaluated, the Support Vector Regression consistently outperforms others, demonstrating its promise for obtaining accurate planetary radius estimates. Furthermore, we derive parametric equations using the M5P and Markov Chain Monte Carlo methods. Notably, our study reveals a noteworthy result: small planets exhibit a positive linear mass-radius relation, aligning with previous findings. Conversely, for giant planets, we observe a strong correlation between planetary radius and the mass of their host stars, which might provide intriguing insights into the relationship between giant planet formation and stellar characteristics.Comment: Accepted for publication in MNRAS. 17 pages, 18 figure

KIC~8975515: a fast-rotating (γ\gamma Dor - δ\delta Sct) hybrid star with Rossby modes and a slower δ\delta Sct companion in a long-period orbit

{KIC~8975515 is a \emph{Kepler} double-lined spectroscopic binary system with hybrid pulsations. Two components have similar atmospheric properties (T$_{\rm eff}$ $\sim$ 7400~K), and one of them is a fast rotator ($v\sin i = 162$ versus 32 km/s). Our aim is to study the \emph {Kepler} light curve in great detail in order to determine the frequencies of the pulsations, to search for regular spacing patterns in the Fourier spectrum, if any, and to discuss their origin in the context of binarity and fast rotation. In this paper, we study the properties of the stellar pulsations based on a careful analysis in the low-, intermediate- and high-frequency regions of the Fourier spectrum. This is done by performing repeated frequency-search analyses with successive prewhitenings of all the significant frequencies detected in the spectrum. Moreover, we searched for regular period spacings among the $g$ modes, as well as frequency splitting among the $g$ and $p$ modes. In the low-frequency regime, five regular period spacing patterns including one series of prograde $g$ modes and four series of retrograde $r$ modes were detected. The $r$ modes are well-distributed with respect to the harmonics of the rotational frequency of the fast-rotating star $f_{\rm rot}$ = 1.647 d$^{-1}$. The dominant $g$ mode is $f_{2}$ = 2.37 d$^{-1}$. The strongest p mode, at $f_{1}$ = 13.97 d$^{-1}$, forms a singlet. In the high-frequency region, we identified two multiplets of regularly split $p$ modes with mean frequency spacings of 0.42 d$^{-1}$ and 1.65 d$^{-1}$. We detected some series of retrograde $r$ and prograde $g$ modes as well as two multiplets of $p$ modes with frequency spacings related to the stellar rotation of both components of the twin system KIC~8975515. We identified the fast-rotating component as a hybrid pulsator with $r$ modes and the slowly-rotating component as a $\delta$ Sct pulsator.Comment: Accepted to publish on A \&

The Effect of Cosmological Background Dynamics on the Spherical Collapse in MOND

The effect of background dynamics of the universe on formation of large scale structures in the framework of Modified Newtonian Dynamics (MOND) is investigated. A spherical collapse model is used for modeling the formation of the structures. This study is done in two extreme cases: ({\it i}) assuming a universe with a low-density baryonic matter without any cold dark matter and dark energy; ({\it ii}) a dark energy dominated universe with baryonic matter, without cold dark matter. We show that for the case ({\it ii}) the structures virialize at lower redshifts with larger radii compared to the low-density background universe. The dark energy slow downs the collapse of the structures. We show that our results are compatible with recent simulations of the structure formation in MOND.Comment: 16 pages, 4 Figures, accepted by New Astronom