A method for measuring the difference between centroids of polarized flux and total flux of an astronomical object – polaroastrometry – is proposed. The deviation of the centroid of flux ...corresponding to Stokes parameter Q or U from the centroid of total flux multiplied by dimensionless Stokes parameter q or u, respectively, was used as a signal. The efficiency of the method is demonstrated on the basis of observations made in the V band by using an instrument combining features of a two-beam polarimeter with a rotating half-wave plate and a speckle interferometer. The polaroastrometric signal noise is 60–70 μas rms for a total number of accumulated photoelectrons N
e of 109 from a 70-cm telescope; this corresponds to a total integration time of 500 s and an object magnitude V = 6 mag. At smaller N
e, the noise increases as
${\approx} 1.7\,{\rm arcsec}/\sqrt{N_{\rm e}}$
, while at larger N
e, it remains the same owing to imperfection of the half-wave plate. For main-sequence stars that are unpolarized and polarized by interstellar dust and the Mira-type variable R Tri the signal was undetectable. For the Mira-type variable χ Cyg the polaroastrometric signal is found to be 310 ± 70 and 300 ± 70 μas for Stokes Q and U, respectively; for o Cet these values are 490 ± 100 and 1160 ± 100 μas. The significant value of the polaroastrometric signal provides evidence of the asymmetry of the polarized flux distribution.
ABSTRACT
The secondary of the famous young binary RW Aur is much less studied than the primary. To rectify this shortcoming, we present here the results of UBVRIJHK photometric, VRI polarimetric and ...optical spectral observations of RW Aur B. The star demonstrates chaotic brightness variations in the optical band, with irregular, short (∼1-d) dimmings with an amplitude ΔV up to 1.3 mag. The dimmings are accompanied by an increase in the linear polarization (up to 3 per cent in the I band), presumably as a result of the scattering of stellar radiation by dust in the circumstellar disc, which means that RW Aur B can be classified as a UX Ori-type star. We conclude that the observed excess emission at λ ≲ 0.45 μm and longwards of ~2 μm as well as the variability of fluxes and profiles of the H i, He i and Na i D emission lines are due to the accretion process. At the same time, emission components of Ca ii lines indicate that RW Aur B has a powerful chromosphere. Assuming solar elemental abundances, we find the following parameters for the star: Teff = 4100–4200 K, AV = 0.6 ± 0.1 (out of the dimming events), L* ≈ 0.6 ${\rm L}_\odot ,\, R_* \approx 1.5$ ${\rm R}_\odot ,\, M\approx 0.85$ M$_\odot ,\, \dot{M}_{\rm acc}\lt 5\times 10^{-9}$ M⊙ yr−1. Finally, we discuss possible reasons for the different levels of accretion activity of the RW Aur binary components and present arguments in favour of the fact that the components are gravitationally bound.
The speckle polarimeter is a facility instrument of the 2.5-mSAIMSU telescope that combines the features of a speckle interferometer and a polarimeter. The speckle polarimeter is designed for ...observations in several visible bands in the following modes: speckle interferometry, polarimetry, speckle polarimetry, and polaroastrometry. In this paper we describe the instrument design and the procedures for determining the angular scale of the camera and the position angle of the camera and the polarimeter. Our measurements of the parameters for the binary star HD 9165 are used as an example to demonstrate the technique of speckle interferometry. For bright objects the accuracy of astrometry is limited by the error of the correction for the distortion caused by the atmospheric dispersion compensator. At zenith distances less than 45◦ the additional relative measurement error of the separation is 0.7%, while the additional error of the position angle is 0.3°. In the absence of a dispersion compensator the accuracy of astrometry is limited by the uncertainty in the scale and position angle of the camera, which are 0.15% and 0.06°, respectively. We have performed polarimetric measurements of unpolarized stars and polarization standards. The instrumental polarization at the Cassegrain focus in the
V
band does not exceed 0.01%. The instrumental polarization for the Nasmyth focus varies between 2 and 4% within the visible range; we have constructed its model and give a method for its elimination from the measurements. For stars with an intrinsic polarization of less than 0.2% during observations at the Cassegrain focus the error is determined mainly by the photon and readout noises and can reach 5 × 10
−5
.
ABSTRACT
We present the results of our new observations of the young binary ZZ Tau with a circumbinary disc. The system was found to consist of two coeval (age < 2 Myr) classical T Tauri stars with ...the total mass 0.86 ± 0.09 M⊙, orbital period 46.8 ± 0.8 yr, semimajor axis 88.2 ± 2.1 mas, eccentricity 0.58 ± 0.02, and the orbital inclination 123${_{.}^{\circ}}$8 ± 1${_{.}^{\circ}}$0. The accretion rate of ZZ Tau A and ZZ Tau B is approximately 7 × 10−10 and 2 × 10−10 M⊙ yr−1, respectively. No correlation was found between the long-term photometric variability of ZZ Tau and orbital position of its components. The periodic light variations with P = 4.171 ± 0.002 d were observed in the BVRI bands presumably connected with an accretion (hot) spot on the surface of the primary (ZZ Tau A). At the same time, no periodicity was observed in the U band nor in the emission line profile variations probably, due to the significant contribution of ZZ Tau B’s emission, which dominates shortward of λ ≈ 0.4 $\mu$m. We argue that the extinction in the direction to the primary is noticeably larger than that to the secondary. It appeared that the rotation axis of the primary is inclined to the line of sight by ≈31° ± 4°. We also concluded that ZZ Tau is the source of a CO molecular outflow; however, ZZ Tau IRS rather than ZZ Tau is the source of the Herbig–Haro object HH393.
Abstract
The aim of this article is to determine the dynamical parameters of the asteroid (22) Kalliope with its satellite Linus, based on astrometric observations of this system. We use a model of ...the motion taking into account the gravitational influence of the primary’s axisymmetric non-sphericity. This factor leads to precession of the line of apsides of the satellite, as well as precession of its orbit around the primary’s axis of symmetry. The axisymmetric gravitational field of the primary is formed by the time-averaged field of the fast-rotating body of Kalliope. All available observations of the Kalliope–Linus system were divided into groups, each containing observations close in time. For each group, parameters of the fixed Keplerian orbit were determined. Thus, the behaviour of the satellite’s orbit axis over about 16-yr time intervals was studied. Contrary to the expected uniform precession of the orbital plane, we discovered abnormal prograde motion of the ascending node in the first seven years, which became retrograde in the next nine years. The amplitude of the change is about 120°. We make an attempt to explain such motion by effects not taken into account in the adopted dynamical model. It is shown that effects not taken into account cannot explain the oscillatory motion of the orbital node found. Using 121 available observations, two formal solutions for all fitted parameters were determined.
Several site-testing programmes and observatories currently use combined Multi-Aperture Scintillation Sensor (MASS)–Differential Image Motion Monitor (DIMM) instruments for monitoring parameters of ...optical turbulence. The instrument is described here. After a short recall of the measured quantities and operational principles, the optics and electronics of MASS–DIMM, interfacing to telescopes and detectors, and operation are covered in some detail. Particular attention is given to the correct measurement and control of instrumental parameters to ensure valid and well-calibrated data, to the data quality and filtering. Examples of MASS–DIMM data are given, followed by the list of present and future applications.
In 2011 and 2015–2018 the classical T Tauri star RW Aur A dimmed by 2–
. Previously, no such dimmings had been observed in historical observations since 1895: the variability amplitude did not exceed
.... During these eclipses the star showed evidence of UX Ori variability: a decrease in color index and an increase in polarization. To clarify the nature of the eclipses and the high polarization associated with them, we observed the object in the visible
bands by the method of differential speckle polarimetry with the 2.5-m telescope at the Caucasus Mountain Observatory of the Sternberg Astronomical Institute of the Moscow State University. The observations were carried out on October 23, 2016, at the end of a long and deep eclipse. As a simple geometric model shows, the polarized flux was reliably resolved. Using the MC3D radiative transfer simulation code, we have considered several three-dimensional dust envelope models. The two-component model that consists of a protoplanetary disk and a cone explains quantitatively the dimming and the shape of the resolved envelope. The typical size of the dust cone is 5–10 AU; this cone may be a dusty disk wind. However, our model does not reproduce the source of polarized radiation that coincides with the star and gives the bulk of the polarized flux from the object. The scattering envelope near the star unresolvable in our observations or the star itself, if its direct radiation is absorbed by aligned dust grains, can be this source.
In 2022 we carried out an upgrade of the speckle polarimeter (SPP)—the facility instrument of the 2.5-m telescope of the Caucasian Observatory of the SAI MSU. During the overhaul, CMOS Hamamatsu ...ORCA-Quest qCMOS C15550-20UP was installed as the main detector, some drawbacks of the previous version of the instrument were eliminated. In this paper, we present a description of the instrument, as well as study some features of the CMOS detector and ways to take them into account in speckle interferometric processing. Quantitative comparison of CMOS and EMCCD in the context of speckle interferometry is performed using numerical simulation of the detection process. Speckle interferometric observations of 25 young variable stars are given as an example of astronomical result. It was found that BM And is a binary system with a separation of 273 mas. The variability of the system is dominated by the brightness variations of the main component. A binary system was also found in NSV 16694 (TYC 120-876-1). The separation of this system is 202 mas.
The metal content of tube bundles of rigid-type shell-and-tube heat exchangers is analyzed in terms of their design options and used materials. Outer tube diameters, tube material, wall thickness, ...pressure in the tubes, and inner diameter of the exchanger are considered as the influencing factors. Use of tube bundles consisting of strong tubes is proposed for reducing metal content of tube bundles. High-strength low-alloy steel tubes are recommended for medium and high pressures in the tubes. In the case of low pressure in the tubes, the difference in metal content of carbon steel and high-strength low-alloy steel tube bundles is negligible.
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