Search

In addition to the complete set of fundamental parameters of its individual components, we present the solution for the discrepancy between the two main astrometric space telescopes Gaia and Hipparcos, in their measurements of the trigonometric parallax for the stellar binary system Hip 84976. In our analysis of the system, we followed Al-Wardat's method for analyzing binary and multiple stellar systems along with Tokovinin's dynamical method. Using these two methods, we estimated the system's atmospheric, dynamical, and geometrical parameters including the individual masses. The estimated masses and the modified orbital elements were used to give a new dynamical parallax for the system as ( π Dyn = 11.48 ± 0.45 mas), which lies between the measurements given by the old (9.01 ± 1.22 mas) and the new (11.80 ± 1.23 mas) Hipparcos catalogs. It also shows that Hipparcos 2's (2007) parallax measurement is more accurate than that given by Gaia DR3 (12.5899 ± 0.3496 mas) for this system, while that given by Gaia DR2 (24.1841 ± 1.8560 mas) is far from accurate. The results were used to put the two components of the system on the right positions on the H-R diagram, evolutionary tracks, and isochrones, and proposed that the system was formed by fragmentation 1.99 Gyr ago. [ABSTRACT FROM AUTHOR]

Let T be a tree with vertex set V (T) = { 1 , 2 , ... , n }. The Steiner distance of a subset S ⊆ V (T) of vertices of T is defined to be the number of edges in a smallest connected subtree of T that contains all the vertices of S. The k -Steiner distance matrix D k (T) of T is the ( n k ) × ( n k ) matrix whose rows and columns are indexed by subsets of vertices of size k. The entry in the row indexed by P and column indexed by Q is equal to Steiner distance of P ∪ Q. We consider the case when k = 2 and show that rank (D 2 (T)) = 2 n − p − 1 where p is the number of pendant vertices (or leaves) in T. We construct a basis B for the row space of D 2 (T) and obtain a formula for the inverse of the nonsingular square submatrix D = D 2 (T) [ B , B ]. We also compute the determinant of D and show that its absolute value is independent of the structure of T and apply it to obtain the inertia of D 2 (T). Lastly, we determine the spectrum of 2-Steiner distance matrix of the star tree. [ABSTRACT FROM AUTHOR]

The relative proper motions of eight A–F type runaway candidate stars, from the eleven cataloged stars by Platais et al. (2018) in the 30 Doradus (30 Dor) region of the Large Magellanic Cloud (LMC), are investigated using Gaia DR3 data. We cross-matched the coordinates presented by the authors with Gaia DR3 coordinates, and we took only eight stars that match Gaia DR3 coordinates within a 0.01 arcsec radius. From the relative proper motions of the target stars with respect to the field stars and the distance to 30 Dor, we estimated the relative tangential velocities of our target stars. We use the astrometric excess noise information to filter the field stars from star like objects, such as unresolved binaries. To eliminate foreground contamination of the field stars used to figure out the relative proper motions of the target stars, we made a parallax cut and a Color Magnitude Diagram (CMD) cut. Three stars, ID 204988, ID 271782, and ID 358858, are fast runaways, and two stars, ID 325244 and ID 373715, are slow runaways in the tangential plane of the 30 Dor region with relative proper motions of μ ≤ 3. 92 m a s y r − 1 with respect to their neighbors and μ ≤ 4. 05 m a s y r − 1 with respect to the central cluster R136, which correspond to a tangential velocity of 920.58 km s − 1 , and 951.30 km s − 1 , respectively. The remaining three sources ID 223800, ID 346142, and ID 371614, could be unresolved binaries because their astrometric excess noise values are different from zero and need further study to decide. The flight times of the target stars to the young, massive cluster R136 (kinematic ages) are calculated using angular separations from the cluster and their relative proper motions with respect to the cluster. Based on the calculated values of the flight time and relative proper motions, the stars ID 204988, ID 325244, ID 358858, and ID 373715 have proper motions and positions consistent with the runaway scenario from R136. The stars ID 204988, ID 325244, and ID 373715 have flight times from R136 agreed with ejection from the cluster more or less during the last half of the age of the cluster, whereas the star ID 358858 has flight times from R136 agree with ejection from the cluster during or shortly after the cluster is formed. The origin of the remaining one star, ID 271782, could not be R136 as it has a direction of motion different from the runaway scenario from R136, although its flight time to R136 agreed with ejection from the cluster. • We revisit the runaway status of A-F runaway candidates in 30 Doradus region, presented by Platais et al. (2018), using Gaia DR3 proper motions. • The high quality of GAIA DR3 proper motions merits us to study the status of the candidates and we exclude three of the previously presented candidates from analysis, because the coordinates do not match Gaia DR3 coordinates within a 0.01 arcsec radius. • We used Gaia DR3 data to calculate relative proper motion of A-F type runaway candidate stars and only five of the candidates are confirmed as runaway in this study. [ABSTRACT FROM AUTHOR]

Binary stars are as common as single stars. Binary stars are of immense importance to astrophysicists because that they allow us to determine the masses of the stars independent of their distances. They are the cornerstone of the understanding of stellar evolutionary theory and play an essential role in cosmic distance measurement, galactic evolution, nucleosynthesis and the formation of important objects such as cataclysmic variable stars, X-ray binaries, Type Ia supernovae, and gravitational wave-producing double compact objects. In this article, we review the significant theoretical and observational progresses in addressing binary stars in the new millennium. Increasing large survey projects have led to the discovery of enormous numbers of binary stars, which enables us to conduct statistical studies of binary populations, and therefore provide unprecedented insight into the stellar and binary evolution physics. Meanwhile, the rapid development of theoretical concepts and numerical approaches for binary evolution have made a substantial progress on the alleviation of some long-standing binary-related problems such as the stability of mass transfer and common envelope evolution. Nevertheless, it remains a challenge to have a full understanding of fundamental problems of stellar and binary astrophysics. The upcoming massive survey projects and increasingly sophisticated computational methods will lead to future progress. [ABSTRACT FROM AUTHOR]

Abstract We introduce MulensModel, a software package for gravitational microlensing modeling. The package provides a framework for calculating microlensing model magnification curves and goodness-of-fit statistics for microlensing events with single and binary lenses as well as a variety of higher-order effects: extended sources with limb-darkening, annual microlensing parallax, satellite microlensing parallax, and binary lens orbital motion. The software could also be used for analysis of the planned microlensing survey by the NASA flag-ship WFIRST satellite. MulensModel is available at https://github.com/rpoleski/MulensModel/. [ABSTRACT FROM AUTHOR]

A novel, robust, and fast star identification algorithm based on an OSP ∗ pattern is presented in this paper. This new algorithm is appropriate for star sensors in the initial acquisition mode, in which no priori attitude information is available. The OSP pattern is constrained with the k -Nearest Neighbor algorithm with a specified order; hence, this pattern is very robust for star identification. In addition, a new hash search approach for accessing the star pattern database is proposed to improve identification speed. The proposed hash search approach is built on the identification error limit and quantified star angular distance. Analysis of numerical results shows that, with increases in the star centroid error, the ISR † of the proposed algorithm is high and stable, while the ISR values of the triangle algorithm, grid algorithm, and pyramid algorithm decrease rapidly. When the star centroid error is three pixels, the ISR of the proposed algorithm is 99.8%, which is 16% higher than the ISR values of the triangle algorithm and grid algorithm, and nearly 10% higher than that of the pyramid algorithm. Similarly, when the number of false stars is increased, the ISR of the proposed algorithm is high and stable, whereas the ISR values of the triangle algorithm, grid algorithm, and pyramid algorithm decrease rapidly. When there are three false stars in an image, the ISR of the proposed algorithm is 98.4%, which is 13% higher than the ISR values of the triangle algorithm and grid algorithm, and 3% higher than that of the pyramid algorithm. Furthermore, the time complexity of the proposed hash search approach is O ( 1 ) , which is significantly faster than the time complexities of the linear search and k -vector search, which are O ( n ) and O ( k ) , respectively. Compared with the traditional hash search approach, the proposed approach is much faster when using a compatible database. [ABSTRACT FROM AUTHOR]

The recent fast growth of a population of millisecond pulsars with precisely measured mass provides an excellent opportunity to characterize these compact stars at an unprecedented level. This is because the stellar parameter values can be accurately computed for known mass and spin rate and an assumed equation of state (EoS) model. For each of the 16 such pulsars and for a set of EoS models from nucleonic, hyperonic, strange quark matter and hybrid classes, we numerically compute fast spinning stable stellar parameter values considering the full effect of general relativity. This first detailed catalogue of the computed parameter values of observed millisecond pulsars provides a testbed to probe the physics of compact stars, including their formation, evolution and EoS. We estimate uncertainties on these computed values from the uncertainty of the measured mass, which could be useful to quantitatively constrain EoS models. We note that the largest value of the central density ρ c in our catalogue is ∼5.8 times the nuclear saturation density ρ sat , which is much less than the expected maximum value 13 ρ sat . We argue that the ρ c -values of at most a small fraction of compact stars could be much larger than 5.8 ρ sat . Besides, we find that the constraints on EoS models from accurate radius measurements could be significantly biased for some of our pulsars, if stellar spinning configurations are not used to compute the theoretical radius values. [ABSTRACT FROM AUTHOR]

Highlights: [•] We obtained BVgri photometry of 100,000 stars over the Aquarius stream sky area. [•] 15 separate observing epochs were used in looking for RR Lyr variables. [•] 71 RR Lyr variables were discovered providing a census complete to V=15.2 or 8kpc. [•] Pulsation periods, temperatures, lightcurves, magnitudes and distances are given. [ABSTRACT FROM AUTHOR]

Highlights: [•] Accurate and extensive BVRI photometry during post-outburst quiescence. [•] Revision to the use of B-band magnitudes to calibrate old plates. [•] Quiescence brightness and variability similar across 2009 outburst. [•] Too bright in quiescence for the distance estimated via MMRD relations. [•] Confirmation and revised ephemeris for the 752day period. [ABSTRACT FROM AUTHOR]

Abstract: Astrometry using H2O maser sources in star forming regions is expected to be a powerful tool to study the structures and dynamics of our Galaxy. (hereafter H2007) claimed that the annual parallax of Sharpless 269 is determined within an error of 0.008marcs (mas), concluding that S269 is located at 5.3kpc ±0.2kpc from the sun, and its galactrocetnric distance is R =13.1kpc. From the proper motion, they claimed that the galacto-centric rotational velocity of S269 is equal to that of the sun within a 3% error. This small error, however, is hardly understood when taking into account the results of other observations and theoretical studies of galactic dynamics. We here reanalyzed the VERA archival data using the self calibration method (hybrid mapping), and found that clusters of maser features of S269 are distributed in much wider area than that investigated in H2007. We confirmed that, if we make a narrow region image without considering the presence of multiple maser spots, and only the phase calibration is applied, we can reproduce the same maser structures in a maser feature investigated in H2007. The distribution extent of maser spots in the feature differs 0.2mas from east to west between our results and H2007. Moreover, we found that change of relative positions of maser spots in the cluster reaches 0.1mas or larger between observational epochs. This suggests that if one simply assumes the time-dependent, widely distributed maser sources as a stable single point source, it could cause errors of up to 0.1 mas in the annual parallax of S269. Taking into account the internal motions of maser spot clusters, the proper motion of S269 cannot be determined precisely. We estimated that the peculiar motion of S269 with respect to a Galactic circular rotation is ∼20kms−1. These results imply that the observed kinematics of maser emissions in S269 cannot give a strong constraint on dynamics of the outer part of the Galaxy, in contrast to the claim by H2007. [Copyright &y& Elsevier]

Abstract: While modern SETI experiments are often highly sensitive, reaching detection limits of 10−25 W/m2 Hz in the radio, interstellar distances imply that if extraterrestrial societies are using isotropic or broad-beamed transmitters, the power requirements for their emissions are enormous. Indeed, isotropic transmissions to the entire Galaxy, sufficiently intense to be detectable by our current searches, would consume power comparable to the stellar insolation of an Earth-size planet. In this paper we consider how knowledge can be traded for power, and how, and to what degree, astronomical accuracy can reduce the energy costs of a comprehensive transmission program by putative extraterrestrials. Indeed, an exploration of how far this trade-off might be taken suggests that extraterrestrial transmitting strategies of civilizations only modestly more advanced than our own would be, as are our SETI receiving experiments, inexpensive enough to allow multiple efforts. We explore the consequences this supposition has for our SETI listening experiments. [Copyright &y& Elsevier]

Abstract: Currently we are aware of only one biosphere in the entire Universe, our own. Various ongoing observational programmes are, however, attempting to locate more. These searches for extraterrestrial life are among the most challenging and interesting tasks of modern science. The Universe is immense, and even the distances to the nearest stars are beyond our present capabilities to traverse, so that search strategies must be thought through carefully in terms of how, where and what to search for. Life is undoubtedly more likely in some environments than others, and environmental criteria must be fulfilled for life to arise, survive, evolve and thrive. As search resources are limited we should concentrate our search on habitable zones that are suitable for the kind of life we can most easily recognise, in other words, searches should be guided by our own biosphere. [Copyright &y& Elsevier]

Contact binaries can be used for distance determinations of stellar systems. They are easy to discover and identify and are very abundant among solar-type stars, particularly for MV>+3. The period–luminosity–colour (PLC) relations have similar properties to those for pulsating stars and can currently predict individual values of MV to about ±0.25 mag. [Copyright &y& Elsevier]