Historical Light Curve Research Articles

Long-term Optical Polarization Variability and Multiwavelength Analysis of Blazar Mrk 421

Abstract The results of 8 yr R-band photopolarimetric data of blazar Mrk 421 collected from 2008 February to 2016 May are presented, along with extensive multiwavelength observations covering radio to TeV γ-rays around the flares observed in 2008 May, 2010 March, and 2013 April. The most important results are found in 2013, when the source displayed in the R band a very high brightness state of 11.29 ± 0.03 mag (93.60 ± 1.53 mJy) on April 10 and a polarization degree of 11.00% ± 0.44% on May 13. The analysis of the optical data shows that the polarization variability is due to the superposition of two polarized components that might be produced in two distinct emitting regions. An intranight photopolarimetric variability study carried out over seven nights after the 2013 April maximum found flux and polarization variations on the nights of April 14, 15, 16, and 19. In addition, the flux shows a minimum variability timescale of Δt = 2.34 ± 0.12 hr, and the polarization degree presents variations of ∼1%–2% on a timescale of Δ t ∼ minutes. Also, a detailed analysis of the intranight data shows a coherence length of the large-scale magnetic field of pc, which is the same order of magnitude as the distance traveled by the relativistic shocks. This result suggests that there is a connection between the intranight polarimetric variations and spatial changes of the magnetic field. Analysis of the complete R-band data along with the historical optical light curve found for this object shows that Mrk 421 varies with a period of 16.26 ± 1.78 yr.

On the jet of a young star RWAurA and related problems

Comparing the images of the jet of the young star RW Aur A, separated by a period of 21.3 years, we found that the outermost jet's knots have emerged $\approx 350$ yr ago. We argue that at that moment the jet itself has appeared and intensive accretion onto the star has began due to the rearrangement of its protoplanetary disk structure caused by the tidal effect of the companion RW Aur B. More precisely, we assume that the increase of accretion is a response to changing conditions in the outer disk regions, which followed after the sound wave, generated by these changes, crossed the disk in a radial direction. The difference in the parameters of the blue and red lobes of the RW Aur A jet, according to our opinion, is a result of the asymmetric distribution of the circumstellar matter above and below the disk, due to a fly-by of the companion. It was found from the analysis of RW Aur historical light curve that deep and long $(\Delta t>150$ days) dimmings of RW Aur A observed after 2010 yr, had no analogues in the previous 110 years. We also associate the change in the character of the photometric variability of the star with the rearrangement of the structure of inner $(r<1$ a.u.) regions of its protoplanetary disk and discuss why these changes began only 350 years after the beginning of the active accretion phase.

Multiwavelength variability study and search for periodicity of PKS 1510–089

Blazars are the most luminous and variable AGNs, and thus excellent probes of accretion and emission processes close to the central engine. We focus on PKS 1510-089 ($z=0.36$), one of the brightest gamma-ray sources in the Fermi LAT catalog, to study its complex multi-wavelength variability. PKS 1510-089 was observed twice in hard X-rays with the IBIS instrument onboard INTEGRAL during the flares of Jan 2009 and Jan 2010, and simultaneously with Swift and NOT, in addition to the constant Fermi monitoring. The optical polarization was measured in several bands on 18 Jan 2010 at the NOT. Using our and archival data we constructed historical light curves at gamma-to-radio wavelengths covering nearly 20 years and applied variability tests. We assembled SEDs in 2009 and 2010 and compared them with those at two previous epochs and with a model based on synchrotron and inverse Compton (IC) radiation. The SED modeling suggests that the physical quantities that undergo the largest variations are the total power injected into the emitting region and the random Lorentz factor of the electron distribution cooling break, that are higher in the higher gamma-ray states. This suggests a correlation of the injected power with enhanced activity of the acceleration mechanism. The cooling likely takes place at a much smaller distance ($\sim$0.03 pc) than the BLR radius. The emission at a few hundred GeV can be reproduced with IC scattering of highly relativistic electrons off FIR photons at $\sim$0.2 pc, presumably in a dusty torus. DCF analysis between the long-term optical and gamma-ray light curves yields a good correlation with no measurable delay. Our time analysis of the RXTE PCA and Fermi LAT light curves reveals no obvious (quasi-)periodicities, up to the maximum time scale (a few years) probed by the light curves, which are severely affected by red noise.

Progress of light curve inversion technology for resident space object characteristics

The characteristics of space objects such as shape, size, attitude, angular velocity, reflectivity and material play a significant role in certain application fields like space object identification, track prediction and collision avoidance. The ground space optical observation system as one of the main measurement methods to observe space objects is difficult to form high-solution images for small objects or objects located in LEO and MEO, which can only appear several light spots with limited pixels due to the impacts of atmospheric conditions, observing distance and resolution ratio. Through the light curves of space objects obtained from the ground-based optical observation system, the characteristics of objects can be inversed as it is closely related to the brightness of these objects. The technology based on the characteristics of ground-based light curves and objective modeling are two main ways of light curve inversion, through the analysis of inversion technology in recent 10 years. Overall, the principle of the inversion technology based on light curve features is ordinary with easy and fast calculations. Firstly, based on the periodic features of the light curves, the rotation period of a spinning space object can be accurately identified, so this method is widely used in the inversion of the characteristics of spinning space objects. Secondly, based on the general features of light curves, the operating state of a three axis stabilized space object can be identified visually. When the three axis stabilized space object was failure, the light curve often presents a periodic trend. Otherwise the light curve often has obvious periodic variation when the space object was in a normal operation state. In addition, the bus type of space object can be inversed because of the general features of light curve, thus we can immediately classified the space object. The upper and lower bounds of the angular velocity of the three axis stabilized space object can be estimated roughly according to the extremum features of light curves, in this way the attitude change of object can also be analyzed. The technology based on objective modeling improved the accuracy of inversion to a certain extent by establishing complex models. The principle of the light curve inversion methods for space objects relied on modeling the objects as a closed set of facets which is relatively simple. This method can determine characteristics like shapes and orientation of satellites, rocket bodies, and space debris as well, however, it is more suitable for convex objects’ characteristics inversion. The two-facet model simplified the space objects as the combination of two facets, one facet represents the solar panel and the other represents the body, but this simplification process reduced the inversion accuracy. The machine learning inversion method will obtain more accurate results, but it require enough historical light curves for modeling objects. If there have inadequate priori datas of a space object, this method often performs large error compared with the true value. The nonlinear filtering method can be used to accurately determine the size, shape, position, velocity, attitude, angular rates, surface parameter and other characteristics of the space object from sparse light curve data, and it can also detect the change of these characteristics. Therefore, this method has more superiority than other inversion techniques. This paper has summarized researching development of the inversion technology in recent 10 years. The purpose, advantages and disadvantages of each technology are analyzed in detail and the future research direction in this field is also proposed.

Hamburger Sternwarte plate archives: Historic long‐term variability study of active galaxies based on digitized photographic plates

BackgroundAt the Hamburger Sternwarte, an effort was started in 2010 with the aim of digitizing its more than 45,000 photographic plates and films stored in its plate archives. At the time of writing, more than 31,000 plates have already been made available on the Internet for researchers, historians, and the interested public.Materials and MethodsThe digitization process and the Internet presentation of the plates and accompanying handwritten material (plate envelopes, logbooks, observer notes) are presented here. To fully exploit the unique photometric and astrometric data, stored on the plates, further processing steps are required including registering the plate to celestial coordinates, masking of the plates, and a calibration of the photoemulsion darkening curve. To demonstrate the correct functioning of these procedures, historical light curves of two bright BL Lac‐type active galactic nuclei are extracted.ResultsThe resulting light curve of the blazar 1ES 1215+303 exhibits a large decrease in the magnitude from to in about 300 days, which proves the variability in the optical region. Furthermore, we compare the measured magnitudes for the quasar 3C 273 with contemporaneous measurements and find good agreement.

OPTICAL MONITORING OF NGC4151 DURING 110 YEARS

We present the historical light curve of NGC 4151 for 1906–2016. The light curve (Oknyanskij and Lyuty, 2007) is primarily based on our published photoelectric data (1968–2007, about 1040 nightly mean measurements (Oknyanskij and Lyuty, 2007)) and photographic estimates (mostlyOdessaandMoscowplates taken in 1906 – 1982 (Oknyanskij, 1978, 1983), about 350 measurements). Additionally, we include all data obtained prior to 1968 (de Vaucouleurs and de Vaucouleurs, 1968; Barnes 1968; Sandage, 1967; Wisniewski and Kleinmann, 1968; Fitch et al., 1967) in total, 19 photoelectric observations from 1958–1967, were reduced by us to the same diaphragm aperture as that used in our measurements) as well as photographic data (Pacholczyk et al., 1983) (Harvard and Steward observatories' patrol plates taken in 1910–1968, about 210 measurements). The light curve includes our old and new photometrical data obtained during last years at SAI, ShAO and Weihai Observatory as well as other published data (Roberts and Rumstey, 2012; Schnulle et al., 2015). All these data were reduced to an uniform photometric system.Applying Fourier (CLEAN algorithm) we have found periodic component ~16 years in the 110 years light curve. 40 years ago about the same period was firstly reviled fromOdessa's photometrical data (Oknyanskij, 1977; 1978). This “period” seen in the light curve was then found independently in the spectral variability and interpreted as a case of the supermassive binary black hole (Bon et al., 2012). We interpret these circles as some accretion dynamic time.

THE CHANGING LOOK AGNS MONITORING PROJECT

The Changing Look AGNs (CL AGNs) are objects which undergo dramatic variability of the emission line profiles and classification type of which can move from one spectral class to another within very short time interval (from days to years). We start the project of spectral and photometric multiwavelength (from IR to X-ray) monitoring which include the selected set of AGNs also known as the CL AGNs. We are going to use 2-m Zeiss telescope (ShAO) for optical spectral observations, 2.5-m telescope of SAI for IR JHK photometry and spectrophotometery, small telescopes Zeiss-600, AZT-5 for BVRI photometry. We are also going to search for the new CL AGNs using the MASTER data. Furthermore, we can get historical light curves for the known and the new discovered objects using the MASTER opportunities. We are planning to apply for X-ray and UV observations of some CL AGNs with the SWIFT . We present some results of such monitoring of the transient object NGC2617. The main goal of the project is to investigate the possibilities for the repeating cases of the strong changes of spectral type at the CL AGNs. Investigation of such type of objects can be very informative for understanding the nature of these fast variations as well as physics of the AGNs.

Optical light curves of FUor and FUor-like objects

AbstractUsing recent data from photometric monitoring and data from the photographic plate archives we aim to study, the long-term photometric behavior of FUors. The construction of the historical light curves of FUors could be very important for determining the beginning of the outburst, the time to reach the maximum light, the rate of increase and decrease in brightness, the pre-outburst variability of the star. Our CCD photometric observations were performed with the telescopes of the Rozhen (Bulgaria) and Skinakas (Crete, Greece) observatories. Most suitable for long-term photometric study are the plate archives of the big Schmidt telescopes, as the telescopes at Kiso Observatory, Asiago Observatory, Palomar Observatory and others. In comparing our results with light curves of the well-studied FUors, we conclude that every new FUor object shows different photometric behavior. Each known FUor has a different rate of increase and decrease in brightness and a different light curve shape.

GR 290 (ROMANO’S STAR). II. LIGHT HISTORY AND EVOLUTIONARY STATE

ABSTRACT We have investigated the past light history of the luminous variable star GR 290 (M33/V532, Romano’s Star) in the M33 galaxy, and collected new spectrophotometric observations in order to analyze links between this object, the LBV category, and the Wolf–Rayet stars of the nitrogen sequence. We have built the historical light curve of GR 290 back to 1901, from old observations of the star found in several archival plates of M33. These old recordings together with published and new data on the star allowed us to infer that for at least half a century the star was in a low luminosity state, with B ≃ 18–19, most likely without brighter luminosity phases. After 1960, five large variability cycles of visual luminosity were recorded. The amplitude of the oscillations was seen increasing toward the 1992–1994 maximum, then decreasing during the last maxima. The recent light curve indicates that the photometric variations have been quite similar in all the bands and that the B – V color index has been constant within ±0.1 m despite the 1.5 m change of the visual luminosity. The spectrum of GR 290 at the large maximum of 1992–94 was equivalent to late-B-type, while, during 2002–2014, it varied between WN10h-11h near the visual maxima to WN8h-9h at the luminosity minima. We have detected, during this same period, a clear anti-correlation between the visual luminosity, the strength of the He ii 4686 Å emission line, the strength of the 4600–4700 Å lines’ blend, and the spectral type. From a model analysis of the spectra collected during the whole 2002–2014 period, we find that the Rosseland radius R 2/3, changed between the minimum and maximum luminosity phases by a factor of three while T eff varied between about 33,000 and 23,000 K. We confirm that the bolometric luminosity of the star has not been constant, but has increased by a factor of ∼1.5 between minimum and maximum luminosity, in phase with the apparent luminosity variations. Presently, GR 290 falls in the H–R diagram close to WN8h stars and is probably younger than them. In the light of current evolutionary models of very massive stars, we find that GR 290 has evolved from an ∼60 M ☉ progenitor star and should have an age of about four million years. From its physical charcteristics, we argue that GR 290 has left the LBV stage and is presently moving from the LBV stage to a Wolf–Rayet stage of a late nitrogen spectral type.

Outburst evolution, historic light curve and a flash-ionized nebula around the WZ Sge-type object PNV J03093063+2638031

We have monitored the 2014 superoutburst of the WZ Sge-type transient PNV J03093063+2638031 for more than four months, from V=11.0 maximum brightness down to V=18.4 mag, close to quiescence value, by obtaining BVRI photometry and low resolution fluxed spectroscopy. The evolution was normal and no late-time `echo' outbursts were observed. The absolute integrated flux of emission lines kept declining along the superoutburst, and their increasing contrast with the underlying continuum was simply the result of the faster decline of the continuum compared to the emission lines. Inspection of historical Harvard plates covering the 1899-1981 period did not reveal previous outbursts, neither `normal' nor 'super'. We discovered an extended emission nebula (radius ~1 arcmin) around PNV J03093063+2638031, that became visible for a few months as the result of photo-ionization from the superoutburst of the central star. It is not present on Palomar I and II sky survey images and it quickly disappeared when the outburst was over. From the rate at wich the inization front swept through the nebula, we derive a distance of ~120 pc to the system. The nebula is density bounded with an outer radius of 0.03 pc, and the absolute magnitude of the central star in quiescence is M(V)~14.2 mag. The electron density in the nebula is estimated to be 10(+5) cm(-3) from the observed recombination time scale. Given the considerable substructures seen across the nebula, a low filling factor is inferred. Similar nebulae have not been reported for other WZ Sge objects and the challenges posed to models are considered.

On the triple peaks of SNHunt248 in NGC 5806

We present our findings on a supernova (SN) impostor, SNHunt248, based on optical and near-IR data spanning $\sim$15 yrs before discovery, to $\sim$1 yr post-discovery. The light curve displays three distinct peaks, the brightest of which is at $M_{R} \sim -15.0$ mag. The post-discovery evolution is consistent with the ejecta from the outburst interacting with two distinct regions of circumstellar material. The 0.5 - 2.2 $\mu$m spectral energy distribution at -740 d is well-matched by a single 6700 K blackbody with $\log(L/L_\odot) \sim 6.1$. This temperature and luminosity support previous suggestions of a yellow hypergiant progenitor; however, we find it to be brighter than the brightest and most massive Galactic late-F to early-G spectral type hypergiants. Overall the historical light curve displays variability of up to $\sim \pm1$ mag. At current epochs ($\sim$1 yr post-outburst), the absolute magnitude ($M_{R} \sim -9$ mag) is just below the faintest observed historical absolute magnitude $\sim$10 yrs before discovery.

THREE FUNDAMENTAL PERIODS IN AN 87 YEAR LIGHT CURVE OF THE SYMBIOTIC STAR MWC 560

We have constructed a visual light curve of the symbiotic star MWC covering the last 87 years of its history. The data were assembled from the literature and from the AAVSO data bank. Most of the periodic components of the system brightness variation can be accounted for by the operation of 3 basic clocks of the periods P1=19000 d, P2=1943 d and P3=722 d. These periods can plausibly, and consistently with the observations, be attributed to 3 physical mechanisms in the system. They are, respectively, the working of a solar-like magnetic dynamo cycle in the outer layers of the giant star of the system, the binary orbit cycle and the sidereal rotation cycle of the giant star. MWC 560 is the 7th symbiotic star with historical light curves that reveal similar basic characteristics of the systems. The light curves of all these stars are well interpreted on the basis of current understanding of the physical processes that are the major sources of the optical luminosity of these symbiotic systems.

THE PHYSICAL NATURE AND ORBITAL BEHAVIOR OF THE ECLIPSING SYSTEM DK CYGNI

New CCD photometry is presented for the hot overcontact binary DK Cyg, together with reasonable explanations for the light and period variations. Historical light and velocity curves from 1962 to 2012 were simultaneously analyzed with the Wilson-Devinney (W-D) synthesis code. The brightness disturbances were satisfactorily modeled by applying a magnetic cool spot on the primary star. Based on 261 times of minimum light including 116 new timings and spanning more than 87 yrs, a period study reveals that the orbital period has varied due to a periodic oscillation superposed on an upward parabola. The period and semi-amplitude of the modulation are about 78.1 yrs and 0.0037 d, respectively. This detail is interpreted as a light-travel-time effect due to a circumbinary companion with a minimum mass of $M_3$=0.065 $M_\odot$, within the theoretical limit of $\sim$0.07 M$_\odot$ for a brown dwarf star. The observed period increase at a fractional rate of $+$2.74 $\times $10$^{-10}$ is in excellent agreement with that calculated from our W-D synthesis. Mass transfer from the secondary to the primary component is mainly responsible for the secular period change. We examined the evolutionary status of the DK Cyg system from the absolute dimensions.

Electron-capture supernovae exploding within their progenitor wind

The most massive stars on the asymptotic giant branch (AGB), or the so-called super-AGB stars, are thought to produce supernovae triggered by electron captures in their degenerate O+Ne+Mg cores. Super-AGB stars are expected to have slow winds with high mass-loss rates, so their circumstellar density is high. The explosions of super-AGB stars are therefore presumed to occur in this dense circumstellar environment. We provide the first synthetic light curves for such events by exploding realistic electron-capture supernova progenitors within their super-AGB winds. We find that the early light curve – that is, before the recombination wave reaches the bottom of the hydrogen-rich envelope of supernova ejecta (the plateau phase) – is not affected by the dense wind. However, after the luminosity drop following the plateau phase, the luminosity remains much higher when the super-AGB wind is taken into account. We compare our results to the historical light curve of SN 1054, the progenitor of the Crab Nebula, and show that the explosion of an electron-capture supernova within an ordinary super-AGB wind can explain the observed light curve features. We conclude that SN 1054 could have been a Type IIn supernova without any extra extreme mass loss, which was previously suggested to be necessary to account for its early high luminosity. We also show that our light curves match Type IIn supernovae with an early plateau phase or the so-called Type IIn-P supernovae, and suggest that they are electron-capture supernovae within super-AGB winds. Although some electron-capture supernovae can be bright in the optical spectral range due to the large progenitor radius, their X-ray luminosity from the interaction does not necessarily get as bright as other Type IIn supernovae whose optical luminosities are also powered by the interaction. Thus, we suggest that optically bright X-ray-faint Type IIn supernovae can emerge from electron-capture supernovae. Optically faint Type IIn supernovae, such as SN 2008S, can also originate from electron-capture supernovae if their hydrogen-rich envelope masses are small. We argue that some of them can be observed as Type IIn-b supernovae due to the small hydrogen-rich envelope mass.

Optical monitoring of the Seyfert galaxy NGC 4151 and possible periodicities in its historical light curve

We report B, V and R band CCD photometry of the Seyfert galaxy NGC 4151 obtained with the 1.0 m telescope at Weihai Observatory of Shandong University and the 1.56 m telescope at Shanghai Astronomical Observatory from 2005 December to 2013 February. Combining all available data from literature, we have constructed a historical light curve from 1910 to 2013 to study the periodicity of the source using three different methods (the Jurkevich method, the Lomb-Scargle periodogram method and the Discrete Correlation Function method). We find possible periods of P1 = 4 ± 0.1, P2 = 7.5 ± 0.3 and P3 = 15.9 ± 0.3 yr.

Kinematic study of the parsec-scale jet of the quasar PKS 1741–03

We present 23 interferometric images of parsec-scale jet of the quasar PKS 1741--03 at 15, 24 and 43 GHz spanning about 13 yr. We model the images as a superposition of discrete two--dimensional elliptical Gaussian components, with parameters determined by the cross--entropy technique. All the images present a spatially unresolved component (core) and usually two or three components receding from it. The same components were found in simultaneous 24 and 43 GHz maps, showing the robustness of our model-fitting. The core-shift opacity effect between these frequencies is weak. We have identified seven components moving along straight lines at constant apparent superluminal speeds ($3.5\le\beta_\mathrm{obs}\le 6.1$), with different sky position angles ($-186\deg\le \eta\le -125\deg$). The core flux density tracks quite well the fluctuations seen in the historical single-dish light curve at 14.5 GHz, with no measurable delay. The total flux density from the moving jet components is delayed $\sim$2 yr in relation to the core light curve, roughly the same as the lag between the ejection epoch and the maximum flux density in the light curves of the jet components. We propose that there are three non-exclusive mechanisms for producing these delays. From the kinematics of the most robust jet components and the core brightness temperature, we determined the bulk Lorentz factor ($4.8\le\gamma\le 24.5$) and the jet viewing angle ($0.\deg 35 \le \theta \le 4.\deg 2$); these values agree with previous estimates from the spectral energy distribution of PKS 1741--03 and its radio variability.

PHYSICAL NATURE AND TIMING VARIATIONS OF THE ECLIPSING SYSTEM V407 PEGASI

New multiband CCD photometry is presented for V407 Peg; the $R_{\rm C}$ light curves are the first ever compiled. Our light curves, displaying a flat bottom at secondary minimum and an O'Connell effect, were simultaneously analyzed with the radial-velocity (RV) curves given by Rucinski et al. (2008). The light changes of the system are best modeled by using both a hot spot on the secondary star and a third light. The model represents historical light curves also. All available minimum epochs, including our six timing measurements, have been examined and indicate that the eclipse timing variation is mainly caused by light asymmetries due to the spot activity detected in the light-curve synthesis. The hot spot may be produced as a result of the impact of the gas stream from the primary star. Our light and velocity solutions indicate that V407 Peg is a totally-eclipsing A-type overcontact binary with values of $q$=0.251, $i$=87$^\circ.6$, $\Delta T$=496 K, $f$=61 $\%$, and $l_3$=11$\sim$16 $\%$. Individual masses and radii of both components are determined to be $M_1$=1.72 M$_\odot$, $M_2$=0.43 M$_\odot$, $R_1$=2.15 R$_\odot$, and $R_2$=1.21 R$_\odot$. These results are very different from previous ones, which is probably caused by the light curves with distorted and inclined eclipses used in those other analyses. The facts that there are no objects optically related with the system and that the seasonal RVs show a large discrepancy in systemic velocity indicate that the third light source most likely arises from a tertiary component orbiting the eclipsing pair.

The resolved structure of the extragalactic supernova remnant SNR 4449−1

We present very long baseline interferometry (VLBI) observations of the milliarcsecond-scale radio structure of the supernova remnant SNR 4449$-$1 in the galaxy NGC 4449. This young and superluminous remnant was observed at 1.6 GHz ($\lambda = 18$\,cm) with the European VLBI Network. The observations confirm earlier identifications of this object with a supernova remnant (SNR) while revealing a somewhat different morphology compared with the structure reported by Bietenholz et al. from VLBI observations at 1.4 GHz. This difference is discussed here in the context of structural sensitivity of both observations. The 1.6 GHz image yields accurate estimates of the size (0.0422 arcsec $\times$ 0.0285 arcsec and 0.8 $\times$ 0.5 pc) and age ($\sim$55 yr) of SNR 4449$-$1. With a total flux of 6.1 $\pm$ 0.6 mJy measured in the VLBI image, the historical lightcurve of the source can be well represented by a power-law decay with a power index of $-$1.19 $\pm$ 0.07. The SNR exhibits a decline rate of the radio emission of 2.2$%$ $\pm$ 0.1$%$ yr$^{-1}$ and a radio luminosity of 1.74 $\times$ 10$^{35}$ erg s$^{-1}$.

Photometric and spectroscopic variability of the FUor star V582 Aurigae

We carried out BVRI CCD photometric observations in the field of V582 Aur from 2009 August to 2013 February. We acquired high-, medium-, and low-resolution spectroscopy of V582 Aur during this period. To study the pre-outburst variability of the target and construct its historical light curve, we searched for archival observations in photographic plate collections. Both CCD and photographic observations were analyzed using a sequence of 14 stars in the field of V582 Aur calibrated in BVRI. The pre-outburst photographic observations of V582 Aur show low-amplitude light variations typical of T Tauri stars. Archival photographic observations indicate that the increase in brightness began in late 1984 or early 1985 and the star reached the maximum level of brightness at 1986 January. The spectral type of V582 Aur can be defined as G0I with strong P Cyg profiles of H alpha and Na I D lines, which are typical of FU Orionis objects. Our BVRI photometric observations show large amplitude variations V~2.8 mag. during the 3.5 year period of observations. Most of the time, however, the star remains in a state close to the maximum brightness. The deepest drop in brightness was observed in the spring of 2012, when the brightness of the star fell to a level close to the pre-outburst. The multicolor photometric data show a color reversal during the minimum in brightness, which is typical of UX Ori variables. The corresponding spectral observations show strong variability in the profiles and intensities of the spectral lines (especially H alpha), which indicate significant changes in the accretion rate. On the basis of photometric monitoring performed over the past three years, the spectral properties of the maximal light, and the shape of the long-term light curve, we confirm the affiliation of V582 Aur to the group of FU Orionis objects.

PRECURSOR FLARES IN OJ 287

We have studied three most recent precursor flares in the light curve of the blazar OJ 287 while invoking the presence of a precessing binary black hole in the system to explain the nature of these flares. Precursor flare timings from the historical light curves are compared with theoretical predictions from our model that incorporate effects of an accretion disk and post-Newtonian description for the binary black hole orbit. We find that the precursor flares coincide with the secondary black hole descending towards the accretion disk of the primary black hole from the observed side, with a mean z-component of approximately z_c = 4000 AU. We use this model of precursor flares to predict that precursor flare of similar nature should happen around 2020.96 before the next major outburst in 2022.