We present the most extensive and detailed reddening maps of the Magellanic Clouds (MCs) derived from the color properties of Red Clump (RC) stars. The analysis is based on the deep photometric maps ...from the fourth phase of the Optical Gravitational Lensing Experiment (OGLE-IV), covering approximately 670 deg2 of the sky in the Magellanic System region. The resulting maps provide reddening information for 180 deg2 in the Large Magellanic Cloud (LMC) and 75 deg2 in the Small Magellanic Cloud (SMC), with a resolution of 1 7 × 1 7 in the central parts of the MCs, decreasing to approximately 27′ × 27′ in the outskirts. The mean reddening is E(V − I) = 0.100 0.043 mag in the LMC and E(V − I) = 0.047 0.025 mag in the SMC. We refine methods of calculating the RC color to obtain the highest possible accuracy of reddening maps based on RC stars. Using spectroscopy of red giants, we find the metallicity gradient in both MCs, which causes a slight decrease of the intrinsic RC color with distance from the galaxy center of ∼0.002 mag/deg in the LMC and between 0.003 and 0.009 mag/deg in the SMC. The central values of the intrinsic RC color are 0.886 and 0.877 mag in the LMC and SMC, respectively. The reddening map of the MCs is available both in downloadable form and as an interactive interface.
We use gravitational microlensing of the four images of the z = 0.658 quasar RXJ 1131-1231 to measure the sizes of the optical and X-ray emission regions of the quasar. The (face-on) scale length of ...the optical disk at rest frame 400 nm is R{sub l}ambda{sub ,O} = 1.3 x 10{sup 15} cm, while the half-light radius of the rest frame 0.3-17 keV X-ray emission is R{sub 1/2,X} = 2.3 x 10{sup 14} cm. The formal uncertainties are factors of 1.6 and 2.0, respectively. With the exception of the lower limit on the X-ray size, the results are very stable against any changes in the priors used in the analysis. Based on the Hbeta line width, we estimate that the black hole mass is M{sub 1131} approx = 10{sup 8} M{sub sun}, which corresponds to a gravitational radius of r{sub g} approx = 2 x 10{sup 13} cm. Thus, the X-ray emission is emerging on scales of approx10r{sub g} and the 400 nm emission on scales of approx70r{sub g} . A standard thin disk of this size should be significantly brighter than observed. Possible solutions are to have a flatter temperature profile or to scatter a large fraction of the optical flux on larger scales after it is emitted. While our calculations were not optimized to constrain the dark matter fraction in the lens galaxy, dark matter-dominated models are favored. With well-sampled optical and X-ray light curves over a broad range of frequencies, there will be no difficulty in extending our analysis to completely map the structure of the accretion disk as a function of wavelength.
We model the time variability of {approx}9000 spectroscopically confirmed quasars in SDSS Stripe 82 as a damped random walk (DRW). Using 2.7 million photometric measurements collected over 10 yr, we ...confirm the results of Kelly et al. and Kozlowski et al. that this model can explain quasar light curves at an impressive fidelity level (0.01-0.02 mag). The DRW model provides a simple, fast (O(N) for N data points), and powerful statistical description of quasar light curves by a characteristic timescale ({tau}) and an asymptotic rms variability on long timescales (SF{sub {infinity}}). We searched for correlations between these two variability parameters and physical parameters such as luminosity and black hole mass, and rest-frame wavelength. Our analysis shows SF{sub {infinity}} to increase with decreasing luminosity and rest-frame wavelength as observed previously, and without a correlation with redshift. We find a correlation between SF{sub {infinity}} and black hole mass with a power-law index of 0.18 {+-} 0.03, independent of the anti-correlation with luminosity. We find that {tau} increases with increasing wavelength with a power-law index of 0.17, remains nearly constant with redshift and luminosity, and increases with increasing black hole mass with a power-law index of 0.21 {+-} 0.07. The amplitude of variability is anti-correlated with the Eddington ratio, which suggests a scenario where optical fluctuations are tied to variations in the accretion rate. However, we find an additional dependence on luminosity and/or black hole mass that cannot be explained by the trend with Eddington ratio. The radio-loudest quasars have systematically larger variability amplitudes by about 30%, when corrected for the other observed trends, while the distribution of their characteristic timescale is indistinguishable from that of the full sample. We do not detect any statistically robust differences in the characteristic timescale and variability amplitude between the full sample and the small subsample of quasars detected by ROSAT. Our results provide a simple quantitative framework for generating mock quasar light curves, such as currently used in LSST image simulations.
Abstract
Long secondary periods (LSPs), observed in a third of pulsating red giant stars, are the only unexplained type of large-amplitude stellar variability known at this time. Here we show that ...this phenomenon is a manifestation of a substellar or stellar companion orbiting the red giant star. Our investigation is based on a sample of about 16,000 well-defined LSP variables detected in the long-term OGLE photometric database of the Milky Way and Magellanic Clouds, combined with the mid-infrared data extracted from the NEOWISE-R archive. From this collection, we selected about 700 objects with stable, large-amplitude, well-sampled infrared light curves and found that about half of them exhibit secondary eclipses, thus presenting an important piece of evidence that the physical mechanism responsible for LSPs is binarity. Namely, the LSP light changes are due to the presence of a dusty cloud orbiting the red giant together with the companion and obscuring the star once per orbit. The secondary eclipses, visible only in the infrared wavelength, occur when the cloud is hidden behind the giant. In this scenario, the low-mass companion is a former planet that has accreted a significant amount of mass from the envelope of its host star and grown into a brown dwarf.
We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively ...short event timescale of tE ∼ 7.5 days. The Einstein radius is unusually small, θE = 0.065 mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses and source-lens distance , implying that this is a brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location that is also consistent with the relatively low lens-source relative proper motion = 3.2 0.5 mas yr−1. The projected companion-host separation is , indicating that the planet is placed beyond the snow line of the host, i.e., asl ∼ 0.12 au. Planet formation scenarios combined with the small companion-host mass ratio q ∼ 0.016 and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown-dwarf host.
Current microlensing surveys are sensitive to free-floating planets down to Earth-mass objects. All published microlensing events attributed to unbound planets were identified based on their short ...timescale (below two days), but lacked an angular Einstein radius measurement (and hence lacked a significant constraint on the lens mass). Here, we present the discovery of a Neptune-mass free-floating planet candidate in the ultrashort (tE = 0.320 0.003 days) microlensing event OGLE-2016-BLG-1540. The event exhibited strong finite-source effects, which allowed us to measure its angular Einstein radius of θE = 9.2 0.5 as. There remains, however, a degeneracy between the lens mass and distance. The combination of the source proper motion and source-lens relative proper motion measurements favors a Neptune-mass lens located in the Galactic disk. However, we cannot rule out that the lens is a Saturn-mass object belonging to the bulge population. We exclude stellar companions up to ∼15 au.
We present the discovery and statistical analysis of 12,660 spotted variable stars toward and inside the Galactic bulge from the Optical Gravitational Lensing Experiment (OGLE) data that are over two ...decades long. We devise a new method of dereddening of individual stars toward the Galactic bulge where strong and highly nonuniform extinction is present. In effect, 11,812 stars were classified as giants and 848 as dwarfs. Well-defined correlations among the luminosity, variability amplitude, and rotation period were found for the giants. Rapidly rotating dwarfs with periods P ≤ 2 days show I-band amplitudes <0.2 mag, which is substantially less than the amplitudes of up to 0.8 mag observed in giants and slowly rotating dwarfs. We also notice that amplitudes of stars brighter than I0 16 mag do not exceed 0.3-0.4 mag. We divide the stars into three groups characterized by correlation between light and color variations. The positive correlation is characteristic for stars that are cooler when fainter, which results from the variable coverage of the stellar surface with spots similar to the sunspots. The variability of stars that are cooler when brighter (negative correlation) can be characterized by chemical spots with an overabundance of heavy elements inside and a variable line-blanketing effect, which is observed in chemically peculiar stars. The null correlation may result from a very high level of the magnetic activity with rapidly variable magnetic fields. This division is readily visible on the color-magnitude diagram (CMD), which suggests that it may depend on the radius of the stars. We detect 79 flaring objects and discuss briefly their properties. Among others, we find that relative brightening during flares is correlated with brightness amplitude.
This paper presents the results of research conducted with the use of water physical model of refining ladle for production of high-carbon FeSi alloys. The purpose of the research was to determine ...the possibilities to enhance the efficiency of the production process by using combined gas injection into the bath. The research involved analysis of four variants of the experiment. Those variants varied in terms of the location of a purging plug fitted in the model bottom and the application of immersion lance to support the process. The research involved the analysis of changes in the hydrodynamic effects in the ladle model occurring as a result of the gas injection. The tests consisted in a qualitative analysis (process visualisation) in order to identify the movement of the modelling liquid and the mechanism of gas bubbles behaviour in the liquid.
Abstract We report the discovery of the classical Cepheid OGLE-GD-CEP-1884 (= GDS_J1535467-555656) with the longest pulsation period known in our Galaxy. The period of 78.14 days is nearly 10 days ...longer than that of the previous record-holding Cepheid, S Vulpeculae, and thus, OGLE-GD-CEP-1884 can be categorized as the first ultra-long-period Cepheid in the Milky Way. This star is present in the ASAS-SN and Gaia DR3 catalogs of variable stars, but it has been classified as a long-period variable in those catalogs. Based on more than 10 yr of the photometric monitoring of this star carried out by the OGLE project in the I and V bands and a radial velocity curve from the Gaia Focused Product Release, we unequivocally demonstrate that this object is a fundamental-mode classical Cepheid. By employing the mid-infrared period–luminosity relation, we determine the distance to OGLE-GD-CEP-1884 (4.47 ± 0.34 kpc) and place it on the Milky Way map, along with about 2400 other classical Cepheids. We also discuss the potential of finding additional ultra-long-period Cepheids in our Galaxy.
The design, manufacturing and field tests of a new astronomical telescope mount are the main topics of this paper. The new robotic mount dedicated for 0.5 m class telescopes is the first mount ...developed, developed and produced as fully Polish concept by engineers and researchers representing the automation and robotics discipline (Pozna University of Technology) and astronomy (Nicolaus Copernicus Astronomical Centre of the Polish Academy of Sciences). The mount is an alt-azimuth fork-type design which allows tracking of typical astronomical targets (sidereal tracking) but also man made objects (satellite tracking). Thanks to a unique mechanical design based on direct drive motors and high precision encoders coupled with custom electronics and on-board software implementing modern control theory achievements it was possible to obtain very good trajectory tracking precision throughout the entire dynamic range defined by the user scenarios. Additionally, the used control algorithms are robust to some class of disturbances such as friction which in turn allows for very high precision tracking in a wide range of angular velocities-from quasi-static movements to high-velocity satellite tracking. The test-bed infrastructure of the system is located in a dedicated astronomical research laboratory at the Pozna University of Technology campus. Local, remote as well as automatic observations can be carried out in the facility.
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