BVRI photometric calibration of the Nedeljkovic telescope

We have done photometric calibration of the 60 cm Nedeljkovic telescope equipped with the FLI PL 230 CCD camera, mounted at the Astronomical Station Vidojevica (Serbia), using standard stars from the Landolt catalog. We have imaged 31 fields of standard stars using Johnson's BVRI filters during three nights in August 2019. We have measured both extinction and color correction. Relating our calibrated magnitudes to the magnitudes of standard stars from the Landolt catalog, we have achieved accuracy of 2%-5% for the BVRI magnitudes.

Investigating close binary supermassive black holes at high angular resolution

Gravitational waves (GW) in the nano-Hz domain are expected to be radiated by close-binaries of supermassive black holes (CB-SMBHs; components bound in a Keplerian binary at mutual distance less than ~ 0.1 pc), which are relicts of galaxy mergers and anticipated to be measured via the Pulsar Timing Array (PTA) technique. The challenge of present CB-SMBH investigations is that their signatures are elusive and not easily disentangled from a single SMBH. PTAs will typically have a glimpse of an early portion of the binary inspiral to catch the frequency evolution of the binary only with sufficiently high mass and initially high eccentricity. Thus, we have to make use of electromagnetic observations to determine orbital parameters of CB-SMBHs and test nano-Hz GW properties. The 2D reverberation mapping (RM) is a powerful tool for probing kinematics and geometry of ionized gas in the SMBHs (single or binary) vicinity, yet it can lose information due to projection on the line of sight of the observer. Nevertheless, spectroastrometry with AMBER, GRAVITY, and successors can provide an independent measurement of the emitting region's size, geometry, and kinematics. These two techniques combined can resolve CB-SMBHs. In this review, we focus on RM and spectroastrometry observational signatures of CB-SMBHs with non-zero eccentricity from recent simulations with particular attention to recent developments and open issues.

Influence of the initial orbital period and accretion efficiency on the low-mass binary evolution

This paper presents detailed evolutionary models of low-mass binary systems (1.25 + 1 M?) with initial orbital periods of 10, 50 and 100 days and accretion efficiency of 10%, 20%, 50%, and a conservative assumption. All models are calculated with the MESA (Modules for Experiments in Stellar Astrophysics) evolutionary code. We show that such binary systems can evolve via a stable Case B mass transfer into long period helium white dwarf systems.

Independent analysis of γδ data of ILS and INDLS catalogs to obtain the spin of the bright Gaia DR2 reference frame

The Gaia DR2 reference frame should be without relative rotation to the quasars (QSOs) and consistent with the International Celestial Reference System (ICRS). For the faint part of DR2 (stars with Gaia magnitude G ? 16) that task was done via Gaia's observations of QSOs (G ? 17 mag), but the bright DR2 (G ? 13 mag) is difficult to validate and it rotates relative to the faint DR2 at rate of the order of 0.1 mas/yr. Very bright DR2 stars (G ? 6 mag) mostly have inferior astrometry. Here, the aim is to determine two spin components (?X and ?Y) of the bright DR2 using International Latitude Service (ILS, for 387 stars) and independent latitude stations (INDLS, for 682 stars) catalogs of proper motion in declination ??; both are referred to the Hipparcos reference frame and their stars are mostly from 4 to 8 mag in the V-band (critical part of DR2). Also, using the new Hipparcos (NHIP) values ?? for ILS and INDLS stars, we can see that the merit of the ILS and INDLS is the long time baseline (?t ? 90 years) important for ?? because the standard deviation of ?? is opposite to ?t. Applying the least squares method (LSM) to the differences of ?? between two catalogs (ILS-DR2, INDLS-DR2, etc.), our results support the mentioned spin. The 3? criterion and Tukey's fences method were used to reject some stars, the Abbe criterion to explain the variability in ILS-DR2 and other ?? differences, and the Shapiro-Wilk test to check the standard distribution of differences. The obtained ?Y is significant at the 2 ? level, and the ILS and INDLS catalogs could be useful for validation of the bright reference frame of Gaia DR2.

The physical and dynamical characteristics of the asteroid 4940 Polenov

The asteroid (1986 QY4) 4940 Polenov is the first Solar system object whose 3D shape is determined using the observations from the newly built Astronomical Station Vidojevica (ASV). Here we present the results of photometric observations for Polenov, gathered from the ASV, and from the Bulgarian National Astronomical Observatory (BNAO) Rozhen, during 2014, 2019 and 2020 apparitions. Polenov is a 17.8km object located in the outer part of the main belt and belongs to the asteroid family Themis. We have determined the lightcurves, the synodic period of 4.161?0.001 h, as well as the solution for the shape and spin axis. Using the lightcurve inversion method, the combination of our lightcurves and the sparse data from ATLAS{HKO and ATLAS-MLO, we also found the sidereal period, indicating a retrograde rotation of the asteroid, with two possible mirrored pole solutions. The ratio of the largest to smallest reecting surface is about 1.4. In addition, we studied the dynamical properties of the asteroid and obtained a long stability time that exceeds 0.4 Gyrs.

Survey of secular resonances in the asteroid belt

Using a recently introduced synthetic method to compute the asteroid secular frequencies (Knezevic and Milani 2019), in this paper we survey the locations of secular resonances in the 9 dynamically distinct zones of the asteroid belt. Positions of all resonances up to order four, of a significant fraction of the order six resonances, and of a several order eight ones were determined, plotted in the space of proper elements, and discussed in relation to the local dynamics and to the structure and shape of the nearby asteroid collisional families. Only the resonant combinations with fundamental frequencies of Jupiter and Saturn were considered, with a few special cases involving other planets and largest asteroids. Accuracy of the polynomial fit to determine the frequencies was found to be satisfactory for the purpose of determination of secular resonance positions. This enabled a precise identification of dynamical mechanisms affecting the computation of frequencies (close vicinity of the mean motion resonances and libration in secular resonances), and of the \cycle slips" as a primary technical drawback causing deterioration of the results. For each zone we also presented and discussed a fairly complete sample of recent works dealing with interaction of the secular resonances with asteroid families present in that zone. Finally, a few words were devoted to possibilities for future work.

Photometry, light curve solution and period study of contact binary BX And

The photometry of the binary star BX And (HIP 10027) is performed during several nights in October and November 2019, and October 2020 using B, V, and R Johnson-Cousins filters in Dr. Mojtahedi Observatory of the University of Birjand. Astronomical image processing and data reduction are performed by the IRIS software and light curves are obtained. These curves, along with the radial velocity data of the binary star, are analyzed by the Phoebe program to determine the physical and geometric parameters of the system. The evolutionary state of this system is investigated using the Hertzsprung-Russell (H-R) and density vs color index diagrams. The O-C curve is plotted using the eclipse times obtained in this study and those reported in the literature. By fitting a quadratic function to this curve, a new linear ephemeris is obtained for the system, and the mass transfer rate between the components of the system is determined. A periodic behavior is observed in the residuals, after subtracting the quadratic function from the O-C curve. These periodic changes are attributed to the presence of a third component in the system. The parameters of the third component are determined by fitting the light-time function to the residuals curve.

The past, present and future of gravitational wave astronomy

Gravitational Waves (GWs) have become a major source of insight in Multi Messenger Astronomy since their first direct detection in 2015 (Abbott et al. 2016) where the Nobel prize in Physics was awarded in 2017 to LIGO founders Barry C. Barish, Kip S. Thorne, and Rainer Weiss. They complement electromagnetic and particle measurements by providing cosmic scale evidence which cannot be detected in any other way. Their rise to prominence has not been straightforward since the founder of general relativity, Albert Einstein, who predicted GWs, was nevertheless skeptical of their existence and detectability. This skepticism put a damper on Gravitational Wave (GW) research that was not overcome until the 1950's, the decade of Einstein's death. Since then, ever more sensitive GW detectors have been designed for construction on earth and in space. Each of these detector approaches was designed to expand the types of cosmic events that could be detected.

X-ray cavities in the G50 bright group-centered galaxy NGC 5846

We present results based on analysis of the currently available 29.86 ks Chandra data on the Bright Group-Centered Galaxy (BGG) NGC 5846 of G50 group. A pair of X-ray cavities have been detected within a radius ? 1 kpc along the North-East and South-West directions. The analysis yielded the average cavity energy, ages and mechanical power equal to ~ 3:1 x 1048 erg, 0:61 x 107 yr and, 3:78 x 1041 erg s-1, respectively. The luminosity of X-ray emitting gas within the cooling radius (20 kpc) was found to be 2.4 x 1041 erg s??1, in agreement with the mechanical cavity power. The ratio of radio luminosity to mechanical cavity power is found to be 10??4. The Bondi accretion rate of the central supermassive black hole (SMBH) is ~ 5:95 x 10-5 M? yr-1 and the black-hole mass derived using the Bondi-accretion rate was found to be ~ 3:74 x 108 M?.

Long-term optical photometric monitoring of the FUor star V900 Mon

We present results from photometric monitoring of V900 Mon, one of the newly discovered and still under-studied object from the FU Orionis type. The FUor phenomenon is very rarely observed, but it is essential for stellar evolution. Since we only know about twenty stars of this type, the study of each new object is very important for our knowledge. Our data were obtained in optical spectral region with the BVRI Johnson-Cousins set of filters during the period from September 2011 to April 2021. In order to follow the photometric history of the object, we measured its stellar magnitudes on available plates from the Mikulski Archive for Space Telescopes. The collected archival data suggest that the rise in brightness of V900 Mon began after January 1989 and the outburst goes on so far. In November 2009, when the outburst was registered, the star had already reached the level of brightness close to the current one. Our observations indicate that during the period 2011-2017 the stellar magnitude increased gradually in each pass band. The observed amplitude of the outburst is about 4 magnitudes (R). During the last three years, the increase in brightness has stopped and there has even been a slight decline. The comparison of light curves of the known FUor objects shows that they are very diverse and are rarely repeated. However, the photometric data we have so far show that V900 Mon's light curve is somewhat similar to those of V1515 Cyg and V733 Cep.