Astrophysics

We present new BVR band photometric light curves of BO Aries obtained in 2020 and combined them with the Transiting Exoplanet Survey Satellite (TESS) light curves. We obtained times of minima based on Gaussian and Cauchy distributions and then applied the Monte Carlo Markov Chain (MCMC) method to measure the amount of uncertainty from our CCD photometry and TESS data. A new ephemeris of the binary system was computed employing 204 times of minimum. The light curves were analyzed using the Wilson-Devinney binary code combined with the Monte Carlo (MC) simulation. For this light curve solution, we considered a dark spot on the primary component. We conclude that this binary is an A-type system with a mass ratio of q=0.2074+-0.0001, an orbital inclination of i=82.18+-0.02 deg, and a fillout factor of f=75.7+-0.8%. Our results for the a(Rsun) and q parameters are consistent with the results of the Xu-Dong Zhang and Sheng-Bang Qian (2020) model. The absolute parameters of the two components were calculated and the distance estimate of the binary system was found to be 142+-9 pc.

We present the discovery of CWISE J203546.35-493611.0, a peculiar M8 companion to the M4.5 star APMPM J2036-4936 discovered through the citizen science project Backyard Worlds: Planet 9. Given CWISE J203546.35-493611.0's proper motion ( μ α , μ δ ) = ( ??126 ± 22, ??478 ± 23) and angular separation of 34.2 ?��?from APMPM 2036-4936, we calculate a chance alignment probability of 1.15? 10 ?? . Both stars in this system appear to be underluminous, and the spectrum obtained for CWISE J203546.35-493611.0 shows a triangular H band. Further study of this system is warranted to understand these peculiarities.

We present a Bayesian method to cross-match 5,827,988 high proper motion Gaia sources ( μ>40 mas y r ?? ) to various photometric surveys: 2MASS, AllWISE, GALEX, RAVE, SDSS and Pan-STARRS. To efficiently associate these objects across catalogs, we develop a technique that compares the multidimensional distribution of all sources in the vicinity of each Gaia star to a reference distribution of random field stars obtained by extracting all sources in a region on the sky displaced 2 ??. This offset preserves the local field stellar density and magnitude distribution allowing us to characterize the frequency of chance alignments. The resulting catalog with Bayesian probabilities > 95% has a marginally higher match rate than current internal Gaia DR2 matches for most catalogs. However, a significant improvement is found with Pan-STARRS, where ??99.8% of the sample within the Pan-STARRS footprint is recovered, as compared to a low ??20.8% in Gaia DR2. Using these results, we train a Gaussian Process Regressor to calibrate two photometric metallicity relationships. For dwarfs of 3500< T eff <5280 K, we use metallicity values of 4,378 stars from APOGEE and Hejazi et al. (2020) to calibrate the relationship, producing results with a 1? precision of 0.12 dex and few systematic errors. We then indirectly infer the metallicity of 4,018 stars with 2850< T eff <3500 K, that are wide companions of primaries whose metallicities are estimated with our first regressor, to produce a relationship with a 1? precision of 0.21 dex and significant systematic errors. Additional work is needed to better remove unresolved binaries from this sample to reduce these systematic errors.

The impact of stellar rotation on the morphology of star cluster colour-magnitude diagrams is widely acknowledged. However, the physics driving the distribution of the equatorial rotation velocities of main-sequence turn-off (MSTO) stars is as yet poorly understood. Using Gaia Data Release 2 photometry and new Southern African Large Telescope medium-resolution spectroscopy, we analyse the intermediate-age ( ?? Gyr-old) Galactic open clusters NGC 3960, NGC 6134 and IC 4756 and develop a novel method to derive their stellar rotation distributions based on SYCLIST stellar rotation models. Combined with literature data for the open clusters NGC 5822 and NGC 2818, we find a tight correlation between the number ratio of slow rotators and the clusters' binary fractions. The blue-main-sequence stars in at least two of our clusters are more centrally concentrated than their red-main-sequence counterparts. The origin of the equatorial stellar rotation distribution and its evolution remains as yet unidentified. However, the observed correlation in our open cluster sample suggests a binary-driven formation mechanism.

The single degenerate (SD) model, one of the leading models for the progenitors of Type Ia supernovae (SNe Ia), predicts that there should be binary companions that survive the supernova explosion which, in principle, should be detectable in the Galaxy. The discovery of such surviving companions could therefore provide conclusive support for the SD model. Several years ago, a new type of mysterious variables was discovered, the so-called blue large-amplitude pulsators (BLAPs). Here we show that all the properties of BLAPs can be reasonably well reproduced if they are indeed such surviving companions, in contrast to other proposed channels. This suggests that BLAPs could potentially be the long-sought surviving companions of SNe Ia. Our model also predicts a new channel for forming single hot subdwarf stars, consistent with a small group in the present hot-subdwarf-star sample.

The light curve of KIC 8462852, a.k.a Boyajian's Star, undergoes deep dips the origin of which remains unclear. A faint star ??2\arcsec to the east was discovered in Keck/NIRC2 imaging in Boyajian et al. (2016), but its status as a binary, and possible contribution to the observed variability, was unclear. Here, we use three epochs of Keck/NIRC2 imaging, spanning five years, in JHK near-infrared bands to obtain 1-mas precision astrometry. We show that the two objects exhibit common proper motion, measure a relative velocity of μ=0.14±0.44 mas yr ?? ( μ=0.30±0.93 km s ?? ) and conclude that they are a binary pair at 880±10 AU projected separation. There is marginal detection of possible orbital motion, but our astrometry is insufficient to characterize the orbit. We show that two other point sources are not associated with KIC 8462852. We recommend that attempts to model KIC 8462852 A's light curve should revisit the possibility that the bound stellar companion may play a role in causing the irregular brightness variations, for example through disruption of the orbits of bodies around the primary due to long-term orbital evolution of the binary orbit.

We construct C2 representations of the background quantities that characterize the interior of the Sun and its atmosphere starting from the data-points of the standard solar model S. This model is further extended considering an isothermal atmosphere, that we refer to as model AtmoI. It is not trivial to build the C2 representations of the parameters from a discrete set of values, in particular in the transition region between the end of model S and the atmosphere. This technical work is needed as a crucial building block to study theoretically and numerically the propagation of waves in the Sun, using the equations of solar oscillations (also referred to as Galbrun's equation in aeroacoustics). The constructed models are available at this http URL.

Coronal mass ejections (CMEs) and solar energetic particles (SEPs) are two phenomena that can cause severe space weather effects throughout the heliosphere. The evolution of CMEs, especially in terms of their magnetic structure, and the configuration of the interplanetary magnetic field (IMF) that influences the transport of SEPs are currently areas of active research. These two aspects are not necessarily independent of each other, especially during solar maximum when multiple eruptive events can occur close in time. Accordingly, we present the analysis of a CME that erupted on 2012 May 11 (SOL2012-05-11) and an SEP event following an eruption that took place on 2012 May 17 (SOL2012-05-17). After observing the May 11 CME using remote-sensing data from three viewpoints, we evaluate its propagation through interplanetary space using several models. Then, we analyse in-situ measurements from five predicted impact locations (Venus, Earth, the Spitzer Space Telescope, the Mars Science Laboratory en route to Mars, and Mars) in order to search for CME signatures. We find that all in-situ locations detect signatures of an SEP event, which we trace back to the May 17 eruption. These findings suggest that the May 11 CME provided a direct magnetic connectivity for the efficient transport of SEPs. We discuss the space weather implications of CME evolution, regarding in particular its magnetic structure, and CME-driven IMF preconditioning that facilitates SEP transport. Finally, this work remarks the importance of using data from multiple spacecraft, even those that do not include space weather research as their primary objective.

Masses of classical Cepheids of 3 to 11 M ??are predicted by theory but those measured, clump between 3.6 and 5 M ??. As a result, their mass-luminosity relation is poorly constrained, impeding our understanding of basic stellar physics and the Leavitt Law. All Cepheid masses come from the analysis of 11 binary systems, including only 5 double-lined and well-suited for accurate dynamical mass determination. We present a project to analyze a new, numerous group of Cepheids in double-lined binary (SB2) systems to provide mass determinations in a wide mass interval and study their evolution. We analyze a sample of 41 candidate binary LMC Cepheids spread along the P-L relation, that are likely accompanied by luminous red giants, and present indirect and direct indicators of their binarity. In a spectroscopic study of a subsample of 18 brightest candidates, for 16 we detected lines of two components in the spectra, already quadrupling the number of Cepheids in SB2 systems. Observations of the whole sample may thus lead to quadrupling all the Cepheid mass estimates available now. For the majority of our candidates, erratic intrinsic period changes dominate over the light travel-time effect due to binarity. However, the latter may explain the periodic phase modulation for 4 Cepheids. Our project paves the way for future accurate dynamical mass determinations of Cepheids in the LMC, Milky Way, and other galaxies, which will potentially increase the number of known Cepheid masses even 10-fold, hugely improving our knowledge about these important stars.

O-stars are known to experience a wide range of variability mechanisms originating at both their surface and their near-core regions. Characterization and understanding of this variability and its potential causes are integral for evolutionary calculations. We use a new extensive high-resolution spectroscopic data set to characterize the variability observed in both the spectroscopic and space-based photometric observations of the O+B eclipsing binary HD~165246. We present an updated atmospheric and binary solution for the primary component, involving a high level of microturbulence ( 13 +1.0 ??.3 km\,s ?? ) and a mass of M 1 = 23.7 +1.1 ??.4 ~M ??, placing it in a sparsely explored region of the Hertzsprung-Russell diagram. Furthermore, we deduce a rotational frequency of 0.690±0.003 d ?? from the combined photometric and line-profile variability, implying that the primary rotates at 40\% of its critical Keplerian rotation rate. We discuss the potential explanations for the overall variability observed in this massive binary, and discuss its evolutionary context.