Preliminary orbital elements of six visual binary stars

Preliminary new orbital elements were computed for the visual binary stars A 1 ‐ ADS 1345, A 2629 ‐ ADS 3610, BU 560 ‐ ADS 4371, STF 3115 ‐ ADS 4376, STF 1426 AB ‐ ADS 7730 and STF 2437 ‐ ADS 11956. Using Straizys and Kuriliene's data, we derived new formulae for computing dynamical parallaxes for luminosity classes IV and V. The values found for those systems are in agreement with the Hipparcos parallaxes and the corresponding systemic masses are consistent with the spectral types. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Observations of double stars at Pulkovo with 65 cm Zeiss refractor

Some results of the photographic observations of double stars with 65 cm refractor of Pulkovo observatory are presented. We use the apparent motion parameters (AMP) method which allows to determine the orbits and to carry out the dynamical investigation of wide binaries on the basis of a short arc of their orbital motion. We have determined more than 40 orbits for wide pairs and also the sum of masses and in some cases—the mass-ratio of components. The references to our works and the basic results of observations are contained in Kisselev et al. [2004. Catalogue of relative positions of visual double stars made on the observations with 26^″ refractor of Pulkovo observatory. Strassbourg, I/297]. We apply two ways of revealing the hidden mass of our stars, namely: revealing of possible perturbations from comparison of observational and calculated positions using differences O-C (for instance, perturbations in the orbital motion of ADS 15571) and also by means of comparison of the sum of the masses obtained by us and the sum of the masses obtained by means of the mass-luminosity relation. An excess of masses of about 1-3 solar masses is detected for binaries: ADS 497, ADS 8450 and ADS 10329 by means of last method.The estimations of the masses for some binaries are discussed. Also we justify the necessity of precise parallaxes and relative radial velocities of stars, which could be measured by space telescopes such as the GAIA as the additional parameters for determination of orbits of binaries.     

Close binaries in multiple-star systems. I. Eclipsing variables in Orbital Visual Binaries

We made up a list of eclipsing variables from The Sixth Catalog of Orbits of Visual Binary Stars and supplemented it with physical parameters and some orbital elements of triple stars. A histogram of the angles between the orbital planes of close and wide pairs was built. These angles were shown to be no greater than 20° in two-thirds of cases, and the difference between the angles was shown to increase with semimajor axis of visual orbit. The distribution of the ratios between long and short periods has local maxima in certain intervals. The dynamical sum of the masses of triple-system components turned out to be in good agreement with the sum of the masses of close binary components estimated by precise methods and the mass of the tertiary component determined from the mass-luminosity relation. Most of tertiary components were found to have masses half as large as the sums of the masses of close pair components. Our estimates suggest that the precession periods of the orbits of close binary systems range from several thousand to several tens of million years.     

Dynamical states and dynamical evolution of the selected triple star systems

The general problem of investigating multiple stellar systems is formulated. It is shown that the complete solution of this problem requires 1) a complex of astrometric and astrophysical observations of multiple stars, and the 2) maximum attainable precision of such observations. The conditions under which this precision can be achieved are discussed.The most important characteristics of the dynamical states of multiple systems are the total energy E and the relative energies E_ij of the bodies in these systems. For eight triple systems (ADS 1630, 2926, 6175, 6650, 6811, 7114, 9626, 9909), statistical tests — a method of calculating the uncertainties _E and _Eij from the errors of the observational data — are used to find the probabilities for dynamical states and the values E_tr±E_tr and E_bin±E_bin.Only three triple stars appear certain to be physical systems with a dynamical connection between the components — ADS 6175 and 9909 with the probabilities P>0.80 are dynamical non-hierarchical unstable triple systems with a complicated motions of the components; the final state of these systems is an escape. In the triple system ADS 1630 a qualitative course of the component motions has not been determined because of the larger errors in the observed data. The dynamical evolution of the triple system ADS 9909 is under study.     

Formation of galactic subsystems in light of the magnesium abundance in field stars: The halo

Data from our compiled catalog of spectroscopically determined magnesium abundances in dwarfs and subgiants with accurate parallaxes are used to select Galactic halo stars according to kinematic criteria and to identify presumably accreted stars among them. Accreted stars are shown to constitute the majority in the Galactic halo. They came into the Galaxy from disrupted dwarf satellite galaxies. We analyze the relations between the relative magnesium abundances, metallicities, and Galactic orbital elements for protodisk and accreted halo stars. We show that the relative magnesium abundances in protodisk halo stars are virtually independent of metallicity and lie within a fairly narrow range, while presumably accreted stars demonstrate a large spread in relative magnesium abundances up to negative [Mg/Fe]. This behavior of protodisk halo stars suggests that the interstellar matter in the early Galaxy mixed well at the halo formation phase. The mean metallicity of magnesium-poor ([Mg/Fe] < 0.2 dex) accreted stars has been found to be displaced toward the negative values when passing from stars with low azimuthal velocities (|Θ| < 50 km s^?1) to those with high ones at Δ[Fe/H] ≈ ?0.5 dex. The mean apogalactic radii and inclinations of the orbits also increase with increasing absolute value of |Θ|, while their eccentricities decrease. As a result, negative radial and vertical gradients in relative magnesium abundances are observed in the accreted halo in the absence of correlations between the [Mg/Fe] ratios and other orbital elements, while these correlations are found at a high significance level for genetically related Galactic stars. Based on the above properties of accreted stars and our additional arguments, we surmise that as the masses of dwarf galaxies decrease, the maximum SN II masses and, hence, the yield of α-elements in them also decrease. In this case, the relation between the [Mg/Fe] ratios and the inclinations and sizes of the orbits of accreted stars is in complete agreement with numerical simulations of dynamical processes during the interaction of galaxies. Thus, the behavior of the magnesium abundance in accreted stars suggests that the satellite galaxies are disrupted and lose their stars en masse only after dynamical friction reduces significantly the sizes of their orbits and drags them into the Galactic plane. Less massive satellite galaxies are disrupted even before their orbits change appreciably under tidal forces.     

Estimating masses of selected stars in the Pulkovo program by means of astrometry methods

Stars in the Pulkovo Observatory program are observed with a 65-cm refractor during many years to study their positions and movements. We present examples of two visual binary stars, for which orbits and masses of components were determined, and two astrometric stars, for which masses of their unseen companions were estimated. The first two stars are ADS 14636(61 Cygni) and ADS 7251,and the others are Gliese 623 and ADS 8035(Alpha UMa). Direct astrometric methods are used for estimation of mass-ratio and masses.     

The triple system HR 7272

A combined spectroscopic-interferometric orbit is computed for the primary component of the visual binary star HR 7272=ADS 12101. The orbital period is 3.55 years; semimajor axis 0.″074. Radial velocities of both components were determined by correlation techniques; their semi-amplitudes are 6.6 and 8.4 km s^?1. Because those amplitudes are so modest, the correlation dips are never well resolved, and the mass ratio and orbital parallax remain poorly determined. Adopting normal masses for the components, we obtain the dynamical parallax; the Hipparcos parallax for this star seems to have a large error, probably because the orbital motion was not taken into account. The visual component B belongs to this system and has a constant radial velocity.     

Determining the minimum sum of the component masses for a binary with a known parallax from observations of a short arc of its apparent motion

An inequality that allows the minimum sum of the component masses for a binary, M₀, to be determined was derived from simple geometric considerations. This quantity satisfies the observed orbital motion according to Newton's law with a known parallax. The M₀ value can be calculated if the apparent-motion parameters for the components, including the curvature of the observed short orbital arc, were determined from observations. We estimated M₀ for 14 Pulkovo program stars for which the apparent orbital arc covered with observations was no less than 10°. We compare M₀ with the masses estimated from the mass-luminosity relation. A significant mass excess was found for the star ADS 10329.     

Stellar adiabatic mass loss model and applications

Roche-lobe overflow and common envelope evolution are very important in binary evolution, which is believed to be the main evolutionary channel to hot subdwarf stars. The details of these processes are difficult to model, but adiabatic expansion provides an excellent approximation to the structure of a donor star undergoing dynamical time scale mass transfer. We can use this model to study the responses of stars of various masses and evolutionary stages as potential donor stars, with the urgent goal of obtaining more accurate stability criteria for dynamical mass transfer in binary population synthesis studies. As examples, we describe here several models with the initial masses equal to 1 M _⊙ and 10 M _⊙, and identify potential limitations to the use of our results for giant-branch stars.     

Local effects in astrometric binary orbits: perspective transformation and light-travel time

The next generation of astrometric instruments will reach accuracies deserving new treatments. In order to get astrometric parameters achieving the precision permitted by the measurements, it will be necessary to take into account effects that were neglected until the present time. Two effects concerning the orbital elements of binary stars are considered hereafter: the former is the local perspective (LP) effect, which is due to the variation of the distance and of the orientation of the orbital plane during the observation time-span; the equations describing this effect are derived for the first time. The latter effect is the light-travel time (LTT), which is also related to the orientation of the orbital plane, and which is as efficient as the preceding one. Taking these effects into account would allow to find the ascending nodes of the orbits, and lead to orbital elements more accurate than when they are ignored.
It is derived from simulations that, at a distance of 5 pc, and assuming velocities typical of Population I stars, the position of the right ascending node could be derived for a few simulated unresolved binaries when the astrometric measurements have errors around 1 μas. For the resolved brown dwarf binary 2MASS J07464256+2000321, it appears that ignoring the LP effect would result in underestimating the masses of the components by 14 per cent of the errors as soon as the astrometric errors are around 20 μas for each measurement. However, a 'degenerate LP solution', taking into account the variation of the semimajor axis when the distance is varying, should provide reliable masses when the measurement errors are larger than 1 or 2 μas. A few binaries in the Gaia program could deserve a degenerate LP solution, whereas a complete LP+LTT solution could be justified for resolved binaries observed with Space Interferometry Mission ( SIM ).     

X-ray Emission from the Pre-Main Sequence Systems FU Orionis and T Tauri

We present new results from recent X-ray observations of the accreting pre-main sequence stars FU Orionis and T Tauri. XMM-Newton observations of the close binary system FU Ori reveal an unusual X-ray spectrum consisting of a cool moderately-absorbed component and a hot component viewed through much higher absorption. The two components thus originate in physically distinct regions. The double absorption spectrum is qualitatively different than observed in typical coronal sources and may signal either non-coronal emission or separate unresolved X-ray contributions from more than one star in the system. High-resolution Chandra imaging of the T Tau triple system shows that its X-ray emission is dominated by the optically-revealed northern component T Tau N. X-ray spectra of T Tau obtained with XMM can be acceptably fitted with a moderately absorbed two-temperature thermal plasma model. Its spectral properties are similar to those seen in coronal X-ray sources.     

Orbits of new Hipparcos binaries: III

We present apparent orbits and fundamental parameters of three pairs of early M-type dwarfs. The orbital elements are determined from speckle interferometric observations at the 6-m BTA telescope of the Special Astrophysical Observatory. The orbits of two pairs, HIP39402 and HIP 104565 are built for the first time. The orbit of HIP106972 is revised using new observational data obtained in 2007–2008. The periods of motion and semimajor axes of all the three binaries have very similar values, namely 13 years and 5.5–6 AU, respectively. The dynamical total masses of the systems, obtained from the orbital elements are determined with quite large errors of 25–40%, which is due to the parallax errors.     

Linear radial perturbations of supermassive stars

Numerical integration of the linear non-adiabatic equations for radial perturbations of physical models of supermassive stars confirm the existence of both dynamical and secular instabilities above a critical mass. The value of the latter agrees very well with that deduced from approximate stability criteria. The present analysis brings out for the first time the existence of a continuous transition between dynamical and secular modes in a sequence of models of different masses.     

Fast and accurate computational tools for gravitational waveforms from binary stars with any orbital eccentricity

The relevance of orbital eccentricity in the detection of gravitational radiation from (steady state) binary stars is emphasized. Computationally effective (fast and accurate) tools for constructing gravitational wave templates from binary stars with any orbital eccentricity are introduced including tight estimation criteria of the pertinent truncation and approximation errors.     

Velocity curve analysis of the spectroscopic binary stars by the non-linear least squares

We introduce a new method to derive the orbital parameters of spectroscopic binary stars by a non-linear least squares analysis of residuals. Using measured radial velocity data of four double lined spectroscopic binary systems RZ Cas, CC Cas, V1130 Tau and Y Cygni, we find corresponding orbital and spectroscopic elements. Our numerical results are in good agreement with those obtained by others using more traditional methods.     

Speckle observations with PISCO in Merate: IV. Astrometric measurements of visual binaries in 2005

We present relative astrometric measurements of visual binaries made during the second semester of 2005, with the speckle camera PISCO at the 102 cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our sample contains orbital couples as well as binaries whose motion is still uncertain. The purpose of this long term program is to improve the accuracy of the orbits and determine the masses of the components. We performed 130 new observations of 120 objects, with most of the angular separations in the range 0″.1–4″, and with an average accuracy of 0″.01. Most of the position angles could be determined without the usual 180. ambiguity with the application of triple‐correlation techniques, and their mean error is 0°8. We have found a possible new triple system: ADS 11077. The measurements of the closest binaries were made with a new data reduction procedure, based on model fitting of the background of the auto‐correlations. As this procedure proved to be very efficient, we have re‐processed the old observations of close binaries made with PISCO in Merate since 2004. We thus improved 20 measurements already published and obtained 7 new measurements for observations that were previously reported as “unresolved”. We finally present revised orbits for ADS 684, MCA 55Aac (in the Beta 1 Cyg–Albireo multiple system) and ADS 14783 for which the previously published orbits led to large residuals with our measurements and for which the new observations made since their computation allowed a significant improvement of those old orbits. The sum of the masses that we derived for those systems are consistent with the spectral type of the stars and the dynamic parallaxes are in good agreement with the parallaxes measured by Hipparcos. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The orbit of the visual binary ADS 8630 (γ Vir)

We present a new orbit for the visual binary ADS 8630 = γ Vir. Although it is one of the first visual double stars discovered, its orbital elements were still poorly known. Indeed the very high eccentricity of the orbit and the difficulty of observing the pair at periastron passage in 1836 has meant that it is only now that sufficient measures of the recent close approach in 2005 have allowed an orbital analysis which predicts the angular motion to an acceptable degree of accuracy. We present a series of 35 speckle measurements of ADS 8630 obtained with PISCO in Merate between 2004 and 2006. Those measures have been crucial for determining the new orbital elements since they cover an arc of 130 degrees in the apparent orbit and include the periastron passage of 2005. The masses of the individual F0V components of the binary are found to be 1.40 M_⊙ with an accuracy of about 3%. We also investigate in detail the possibility of the presence of a third body in the system, that was proposed by other authors. The high‐angular resolution infra‐red image of γ Vir that we obtained in June 2006 with the LuckyCam instrument on the ESO NTT shows the absence of any companion as faint as a M0V star at a distance larger than 0.4″. Combined with the analysis of the residuals of our orbit, the values found for the masses of the individual components and the radial velocity measurements, this observation rules out the presence in the system of a third companion with a mass larger than 0.3 M_⊙. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Speckle observations with PISCO in Merate: XIII. Astrometric measurements of visual binaries in 2012, and new orbits for ADS 10786 BC, 12144, 12515, 16314 and 16539

We present relative astrometric measurements of visual binaries, made in 2012 with the speckle camera PISCO at the 102‐cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained 355 new measurements of 344 visual binary stars, with angular separations in the range 0′.14–6′.9, and an average accuracy of 0.′02. The mean error on the position angles is 0°.5. Most of the position angles were determined without the usual 180° ambiguity with the application of triple‐correlation techniques and/or by inspection of the long integration files. We also present new revised orbits for ADS 10786 BC, 12144, 12515, 16314, and 16539, partly derived from PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Estimates of dynamic parameters and boundaries of habitable zones of selected stars of the Pulkovo program

A list of selected binary stars is presented that have been observed for several decades using a 26-inch refractor at the Pulkovo Observatory. These stars are at a distance from 3.5 to 25 pc from the Sun. They belong to spectral classes F, G, K, and M. Their masses range from 0.3 to 1.5 solar masses. We have analyzed them as possible parent stars for exoplanets taking into account the physical characteristics of these stars. In view of dynamic parameters and orbital elements that we have obtained by Pulkovo observations, ephemerides of positions for the coming years are calculated. The boundaries of the habitable zones around these stars are calculated. The astrometric signal that depends on the gravitational influence of hypothetical planets is estimated. Space telescopes for astrometric observations with microsecond accuracy can be used to detect Earth-like planets near the closest stars of this program. This paper presents an overview of astrometric programs of searches for exoplanets.     

Speckle observations with PISCO in Merate (Italy): XIV. Astrometric measurements of visual binaries in 2013 and new orbits for ADS 1097, 5871, 7203, 7775, 9378, 9578, and 11186

We present relative astrometric measurements of visual binaries made in 2013 with the speckle camera PISCO at the 102‐cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained 134 new measurements of 129 visual binary stars, with angular separations in the range 0.≈23–5 and an average accuracy of 0.≈01. The mean error on the position angles is 0.°5. Most of the position angles were determined without the usual 180° ambiguity with the application of triple‐correlation techniques and/or by inspection of the long integration files. We also present new revised orbits for ADS 1097, 5871, 7203, 7775, 9378, 9578, and 11186, partly derived from PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)