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Andrzej Udalski

Publications and source records attributed to Andrzej Udalski.

At least 163 records · Page 9Linked to original sources
arXiv2019

Masses and Distances of Planetary Microlens Systems with High Angular Resolution Imaging

Microlensing is the only method that can detect and measure mass of wide orbit, low mass, solar system analog exoplanets. Mass measurements of such planets would yield massive science on planet formation, exoplanet demographics, free floating planets, planet frequencies towards the galaxy. High res follow-up observations of past microlens targets provide a mass measurement of microlens planets and hosts at an uncertainty of <20%. This will be primary method for mass measurement with WFIRST. We advocate for the fact that high resolution observations with AO, HST and JWST(in future) remain necessary in coming decade to develop the methods, to determine the field and filter selection, understand the systematics and to develop a robust pipeline to release high quality data products from WFIRST microlensing survey such that the astronomy community can promptly engage in the science. We also support future high res obs with US ELTs with advanced Laser AO systems in context of enhancing the science return of WFIRST microlensing survey. We endorse the 2018 Exoplanet Science Strategy report published by the National Academy. This white paper extends and complements the material presented therein. In particular, this white paper supports the recommendation of the National Academy Exoplanet Science Strategy report that: NASA should launch WFIRST to conduct its microlensing survey of distant planets and to demonstrate the technique of coronagraphic spectroscopy on exoplanet targets. This white paper also supports to the finding from that report which states "A number of activities, including precursor and concurrent observations using ground- and space-based facilities, would optimize the scientific yield of the WFIRST microlensing survey."

astro-ph.EP↗
arXiv2019

The SMC X-ray binary SXP4.78 : a new Type II outburst and the identification and study of the optical counterpart

SXP4.78 was originally discovered in 2000 as a pulsar in the Small Magellanic Cloud (SMC) by the Rossi X-ray Timing Explorer (RXTE) but it was not spatially located at that time. A new detection in 2018 with the Neil Gehrels Swift Observatory during a Type II outburst permitted its position to be accurately located and its optical counterpart identified. We report X-ray and optical monitoring covering epochs before and during the outburst. Using photometric data we show the long-term variability of the Be disc where we present flux and colour changes associated with the disc growth and decay over a period of ~6000 days. We show evidence of disc growth during the recent outburst through an increase in the H-alpha equivalent width and photometric flux. Period analysis was performed using both optical photometric and spectroscopic data, but with no significant detection of an orbital period. A modest periodic signature of 2.65 days was detected from the OGLE I band data, however, but we attribute that to the non-radial pulsations (NRPs) of the Be star. We also obtained a blue spectrum from the Southern African Large Telescope (SALT) which permits us to classify the spectral type as B0.5 IV-V.

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arXiv2019

Spitzer Microlensing of MOA-2016-BLG-231L : A Counter-Rotating Brown Dwarf Binary in the Galactic Disk

We analyze the binary microlensing event MOA-2016-BLG-231, which was observed from the ground and from Spitzer. The lens is composed of very low-mass brown dwarfs (BDs) with $M_1 = 21^{+12}_{-5} \ M_J$ and $M_2 = 9^{+5}_{-2}\ M_J$, and it is located in the Galactic disk $D_{\rm L} = 2.85^{+0.88}_{-0.50}\ {\rm kpc}$. This is the fifth binary brown dwarf discovered by microlensing, and the BD binary is moving counter to the orbital motion of disk stars. Constraints on the lens physical properties come from late time, non-caustic-crossing features of the Spitzer light curve. Thus, MOA-2016-BLG-231 shows how Spitzer plays a crucial role in resolving the nature of BDs in binary BD events with short timescale ($\lesssim 10$ days).

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arXiv2019

Time delay measurement of Mg II line in CTS C30.10 with SALT

We report 6 yr monitoring of a distant bright quasar CTS C30.10 (z = 0.90052) with the Southern African Large Telescope (SALT). We measured the rest-frame time-lag of $562\pm 2$ days between the continuum variations and the response of the Mg II emission line, using the Javelin approach. More conservative approach, based on five different methods, imply the time delay of $564^{+109}_{-71}$ days. This time delay, combined with other available measurements of Mg II line delay, mostly for lower redshift sources, shows that the Mg II line reverberation implies a radius-luminosity relation very similar to the one based on a more frequently studied H$β$ line.

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arXiv2019

OGLE-2016-BLG-0156: Microlensing Event With Pronounced Microlens-Parallax Effects Yielding Precise Lens Mass Measurement

We analyze the gravitational binary-lensing event OGLE-2016-BLG-0156, for which the lensing light curve displays pronounced deviations induced by microlens-parallax effects. The light curve exhibits 3 distinctive widely-separated peaks and we find that the multiple-peak feature provides a very tight constraint on the microlens-parallax effect, enabling us to precisely measure the microlens parallax $π_{\rm E}$. All the peaks are densely and continuously covered from high-cadence survey observations using globally located telescopes and the analysis of the peaks leads to the precise measurement of the angular Einstein radius $θ_{\rm E}$. From the combination of the measured $π_{\rm E}$ and $θ_{\rm E}$, we determine the physical parameters of the lens. It is found that the lens is a binary composed of two M dwarfs with masses $M_1=0.18\pm 0.01\ M_\odot$ and $M_2=0.16\pm 0.01\ M_\odot$ located at a distance $D_{\rm L}= 1.35\pm 0.09\ {\rm kpc}$. According to the estimated lens mass and distance, the flux from the lens comprises an important fraction, $\sim 25\%$, of the blended flux. The bright nature of the lens combined with the high relative lens-source motion, $μ=6.94\pm 0.50\ {\rm mas}\ {\rm yr}^{-1}$, suggests that the lens can be directly observed from future high-resolution follow-up observations.

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arXiv2019

$Spitzer$ Microlensing Parallax for OGLE-2017-BLG-0896 Reveals a Counter-Rotating Low-Mass Brown Dwarf

The kinematics of isolated brown dwarfs in the Galaxy, beyond the solar neighborhood, is virtually unknown. Microlensing has the potential to probe this hidden population, as it can measure both the mass and five of the six phase-space coordinates (all except the radial velocity) even of a dark isolated lens. However, the measurements of both the microlens parallax and finite-source effects are needed in order to recover the full information. Here, we combine $Spitzer$ satellite parallax measurement with the ground-based light curve, which exhibits strong finite-source effects, of event OGLE-2017-BLG-0896. We find two degenerate solutions for the lens (due to the known satellite-parallax degeneracy), which are consistent with each other except for their proper motion. The lens is an isolated brown dwarf with a mass of either $18\pm1M_J$ or $20\pm1M_J$. This is the lowest isolated-object mass measurement to date, only $\sim$45\% more massive than the theoretical deuterium-fusion boundary at solar metallicity, which is the common definition of a free-floating planet. The brown dwarf is located at either $3.9\pm0.1$ kpc or $4.1\pm0.1$ kpc toward the Galactic bulge, but with proper motion in the opposite direction of disk stars, with one solution suggesting it is moving within the Galactic plane. While it is possibly a halo brown dwarf, it might also represent a different, unknown population.

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arXiv2018

Blazhko Effect in the first overtone RR Lyrae stars of the OGLE Galactic bulge collection

We present the analysis of the Blazhko effect - quasi-periodic modulation of pulsation amplitude and/or phase - in the Galactic bulge first overtone RR Lyrae stars (RRc). We used the data gathered during the fourth phase of the Optical Gravitational Lensing Experiment (OGLE). Out of 10 826 analyzed RRc stars, Blazhko effect was detected in 607 stars which constitute 5.6 percent of the sample. It is the largest and most homogeneous sample of modulated RRc stars analyzed so far. Modulation periods cover a wide range, from slightly above 2 d to nearly 3000 d. Multiperiodic modulation was detected in 47 stars. The appearance of modulation in the frequency domain was studied in detail. Modulation manifests either as close doublets or as equidistant triplets and multiplets centered on radial mode frequency and its harmonics. In a significant fraction (29 percent) of stars, we have detected the modulation frequency itself, which corresponds to the modulation of the mean stellar brightness. Our search for period doubling effect, that was discovered recently in modulated fundamental mode RR Lyrae stars, and triggered development of new model behind the Blazhko modulation, yielded negative result. In 104 stars we detected additional signals that could correspond to both radial and non-radial modes. Statistical properties of modulated stars were analyzed in detail and confronted with properties of non-modulated stars and of modulated fundamental mode RR Lyrae stars. Our analysis provides constraints for the models to explain the Blazhko phenomenon, which still remains a puzzle more than hundred years after its discovery.

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arXiv2018

A deep survey for symbiotic stars in the Magellanic Clouds - 1. Methodology and first discoveries in the SMC

We have initiated a survey aimed at locating a nearly complete sample of classical symbiotic stars (SySt) in the Magellanic Clouds. Such a sample is nearly impossible to obtain in the Milky Way, and is essential to constrain the formation, evolution and demise of these strongly interacting, evolved binary stars. We have imaged both Clouds in Halpha and He II 4686 narrow-band filters deeply enough to detect all known symbiotic stars. While He II 4686 is not present in all SySt, our method should yield a high success rate because the mimics of SySt are not as likely as true symbiotics to show this emission line. We demonstrate the viability of our method through the discovery and characterization of three new SySt in the Small Magellanic Cloud: 2MASS J00411657-7233253, 2MASS J01104404-7208464 and 2MASS J01113745-7159023. Enigmatic variability was observed in 2MASS J01113745-7159023, where changes in the amplitude of its quasi-periodic variability may suggest an enhanced mass transfer rate during a periastron passage on an elliptical orbit. 2MASS J01104404-7208464 is an ellipsoidal variable with an orbital period of 403d.

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arXiv2018

Identification of blazar candidates behind Small and Large Magellanic Clouds

We report the identification of blazar candidates behind the Magellanic Clouds. The objects were selected from the Magellanic Quasars Survey (MQS), which targeted the entire Large Magellanic Cloud (LMC) and 70\% of the Small Magellanic Cloud (SMC). Among the 758 MQS quasars and 898 of unidentified (featureless spectra) objects, we identified a sample of 44 blazar candidates, including 27 flat spectrum radio quasars and 17 BL Lacertae objects, respectively. All the blazar candidates from our sample were identified with respect to their radio, optical, and mid-infrared properties. The newly selected blazar candidates possess the long-term, multi-colour photometric data from the Optical Gravitational Lensing Experiment, multi-colour mid-infrared observations, and archival radio data for one frequency at least. In addition, for nine of them the radio polarization data are available. With such data, these objects can be used to study the physics behind the blazar variability detected in the optical and mid-infrared bands, as a tool to investigate magnetic field geometry of the LMC and SMC, and as an exemplary sample of point like sources most likely detectable in $γ$-ray range with the newly emerging Cherenkov Telescope Array.

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arXiv2018

The Araucaria Project: High-precision Cepheid astrophysics from the analysis of variables in double-lined eclipsing binaries

Based on new observations and improved modeling techniques, we have reanalyzed seven Cepheids in the Large Magellanic Cloud. Improved physical parameters have been determined for the exotic system OGLE LMC-CEP-1718 composed of two first-overtone Cepheids and a completely new model was obtained for the OGLE LMC-CEP-1812 classical Cepheid. This is now the shortest period Cepheid for which the projection factor is measured. The typical accuracy of our dynamical masses and radii determinations is 1%. The radii of the six classical Cepheids follow period--radius relations in the literature. Our very accurate physical parameter measurements allow us to calculate a purely empirical, tight period--mass--radius relation that agrees well with theoretical relations derived from non-canonical models. This empirical relation is a powerful tool to calculate accurate masses for single Cepheids for which precise radii can be obtained from Baade--Wesselink-type analyses. The mass of the type-II Cepheid $κ$ Pav, $0.56 \pm 0.08 M_\odot$, determined using this relation is in a very good agreement with theoretical predictions. We find large differences between the p-factor values derived for the Cepheids in our sample. Evidence is presented that a simple period--p-factor relation shows an intrinsic dispersion, hinting at the relevance of other parameters, such as the masses, radii, and radial velocity variation amplitudes. We also find evidence that the systematic blueshift exhibited by Cepheids, is primarily correlated with their gravity. The companion star of the Cepheid in the OGLE LMC-CEP-4506 system has a very similar temperature and luminosity, and is clearly located inside the Cepheid instability strip, yet it is not pulsating.

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arXiv2018

A Planetary Microlensing Event with an Unusually Red Source Star: MOA-2011-BLG-291

We present the analysis of planetary microlensing event MOA-2011-BLG-291, which has a mass ratio of $q=(3.8\pm0.7)\times10^{-4}$ and a source star that is redder (or brighter) than the bulge main sequence. This event is located at a low Galactic latitude in the survey area that is currently planned for NASA's WFIRST exoplanet microlensing survey. This unusual color for a microlensed source star implies that we cannot assume that the source star is in the Galactic bulge. The favored interpretation is that the source star is a lower main sequence star at a distance of $D_S=4.9\pm1.3\,$kpc in the Galactic disk. However, the source could also be a turn-off star on the far side of the bulge or a sub-giant in the far side of the Galactic disk if it experiences significantly more reddening than the bulge red clump stars. However, these possibilities have only a small effect on our mass estimates for the host star and planet. We find host star and planet masses of $M_{\rm host} =0.15^{+0.27}_{-0.10}M_\odot$ and $m_p=18^{+34}_{-12}M_\oplus$ from a Bayesian analysis with a standard Galactic model under the assumption that the planet hosting probability does not depend on the host mass or distance. However, if we attempt to measure the host and planet masses with host star brightness measurements from high angular resolution follow-up imaging, the implied masses will be sensitive to the host star distance. The WFIRST exoplanet microlensing survey is expected to use this method to determine the masses for many of the planetary systems that it discovers, so this issue has important design implications for the WFIRST exoplanet microlensing survey.

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arXiv2018

OGLE-2014-BLG-0962 and the First Statistical Validation of Bayesian Priors for Galactic Microlensing

OGLE-2014-BLG-0962 (OB140962) is a stellar binary microlensing event that was well-covered by observations from the Spitzer satellite as well as ground-based surveys. Modelling yields a unique physical solution: a mid-M+M-dwarf binary with $M_{\rm prim} = 0.20 \pm 0.01 M_\odot$ and $M_{\rm sec} = 0.16 \pm 0.01 M_\odot$, with projected separation of $2.0 \pm 0.3$ AU. The lens is only $D_{\rm LS} = 0.41 \pm 0.06$ kpc in front of the source, making OB140962 a bulge lens and the most distant Spitzer binary lens to date. In contrast, because the Einstein radius ($θ_{\rm E} = 0.143 \pm 0.007$ mas) is unusually small, a standard Bayesian analysis, conducted in the absence of parallax information, would predict a brown dwarf binary. We test the accuracy of Bayesian analysis over a set of Spitzer lenses, finding overall good agreement throughout the sample. We also illustrate the methodology for probing the Galactic distribution of planets by comparing the cumulative distance distribution of the Spitzer 2-body lenses to that of the Spitzer single lenses.

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arXiv2018

The late type eclipsing binaries in the Large Magellanic Cloud: catalogue of fundamental physical parameters

We present a determination of precise fundamental physical parameters of twenty detached, double- lined, eclipsing binary stars in the Large Magellanic Cloud (LMC) containing G- or early K-type giant stars. Eleven are new systems, the remaining nine are systems already analyzed by our team for which we present updated parameters. The catalogue results from our long-term survey of eclipsing binaries in the Magellanic Clouds suitable for high-precision determination of distances (the Araucaria project). The V-band brightnesses of the systems range from 15.4 mag to 17.7 mag and their orbital periods range from 49 days to 773 days. Six systems have favorable geometry showing total eclipses. The absolute dimensions of all eclipsing binary components are calculated with a precision of better than 3% and all systems are suitable for a precise distance determination. The measured stellar masses are in the range 1.4 to 4.6 M_sun and comparison with the MESA isochrones gives ages between 0.1 and 2.1 Gyr. The systems show some weak age-metallicity relation. Two systems have components with very different masses: OGLE LMC-ECL-05430 and OGLE LMC-ECL-18365. Neither system can be fitted by single stellar evolution isochrone, explained by a past mass transfer scenario in the case of ECL-18365 and a gravitational capture or a hierarchical binary merger scenario in the case of ECL-05430. The longest period system OGLE LMC SC9 230659 shows a surprising apsidal motion which shifts the apparent position of the eclipses. In one spectrum of OGLE LMC-ECL-12669 we noted a peculiar dimming of one of the components by 65% well outside of the eclipses. We interpret this observation as arising from an extremely rare occultation event as a foreground Galactic object covers only one component of an extragalactic eclipsing binary.

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arXiv2018

Measurement of Source Star Colors with the K2C9-CFHT Multi-color Microlensing Survey

K2 Campaign 9 (K2C9) was the first space-based microlensing parallax survey capable of measuring microlensing parallaxes of free-floating planet candidate microlensing events. Simultaneous to K2C9 observations we conducted the K2C9 Canada-France-Hawaii Telescope Multi-Color Microlensing Survey (K2C9-CFHT MCMS) in order to measure the colors of microlensing source stars to improve the accuracy of K2C9's parallax measurements. We describe the difference imaging photometry analysis of the K2C9-CFHT MCMS observations, and present the project's first data release. This includes instrumental difference flux lightcurves of 217 microlensing events identified by other microlensing surveys, reference image photometry calibrated to PanSTARRS data release 1 photometry, and tools to convert between instrumental and calibrated flux scales. We derive accurate analytic transformations between the PanSTARRS bandpasses and the Kepler bandpass, as well as angular diameter-color relations in the PanSTARRS bandpasses. To demonstrate the use of our data set, we analyze ground-based and K2 data of a short timescale microlensing event, OGLE-2016-BLG-0795. We find the event has a timescale $t_{\rm E}=4.5 \pm 0.1$~days and microlens parallax $π_{\rm E}=0.12 \pm 0.03$ or $0.97 \pm 0.04$, subject to the standard satellite parallax degeneracy. We argue that the smaller value of the parallax is more likely, which implies that the lens is likely a stellar-mass object in the Galactic bulge as opposed to a super-Jupiter mass object in the Galactic disk.

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arXiv2018

A D'-type symbiotic binary in the planetary nebula SMP LMC 88

SMP LMC 88 is one of the planetary nebulae (PN) in the Large Magellanic Cloud. We identify in its spectrum Raman scattered O VI lines at 6825 and 7083A. This unambiguously classifies the central object of the nebula as a symbiotic star (SySt). We identified the cold component to be a K-type giant, making this the first D'-type (yellow) SySt discovered outside the Galaxy. The photometric variability in SMP LMC 88 resembles the the orbital variability of Galactic D'-type SySt with its low amplitude and sinusoidal lightcurve shape. The SySt classification is also supported by the He I diagnostic diagram.

astro-ph.SR↗
arXiv2017

No large population of unbound or wide-orbit Jupiter-mass planets

Gravitational microlensing is the only method capable of exploring the entire population of free-floating planets down to Mars-mass objects, because the microlensing signal does not depend on the brightness of the lensing object. A characteristic timescale of microlensing events depends on the mass of the lens: the less massive the lens, the shorter the microlensing event. A previous analysis of 474 microlensing events found an excess of very short events (1-2 days) - more than known stellar populations would suggest - indicating the existence of a large population of unbound or wide-orbit Jupiter-mass planets (reported to be almost twice as common as main-sequence stars). These results, however, do not match predictions of planet formation theories and are in conflict with surveys of young clusters. Here we report the analysis of a six times larger sample of microlensing events discovered during the years 2010-2015. Although our survey has very high sensitivity (detection efficiency) to short-timescale (1--2 days) microlensing events, we found no excess of events with timescales in this range, with a 95% upper limit on the frequency of Jupiter-mass free-floating or wide-orbit planets of 0.25 planet per main-sequence star. We detected a few possible ultrashort-timescale events (with timescales of less than 0.5 day), which may indicate the existence of Earth- and super-Earth-mass free-floating planets, as predicted by planet-formation theories. [abridged]

astro-ph.EP↗
arXiv2016

A new gamma-ray loud, eclipsing low-mass X-ray binary

We report the discovery of an eclipsing low-mass X-ray binary at the center of the 3FGL error ellipse of the unassociated Fermi/Large Area Telescope gamma-ray source 3FGL J0427.9-6704. Photometry from OGLE and the SMARTS 1.3-m telescope and spectroscopy from the SOAR telescope have allowed us to classify the system as an eclipsing low-mass X-ray binary (P = 8.8 hr) with a main sequence donor and a neutron star accretor. Broad double-peaked H and He emission lines suggest the ongoing presence of an accretion disk. Remarkably, the system shows shows separate sets of absorption lines associated with the accretion disk and the secondary, and we use their radial velocities to find evidence for a massive (~ 1.8-1.9 M_sun) neutron star primary. In addition to a total X-ray eclipse of duration ~ 2200 s observed with NuSTAR, the X-ray light curve also shows properties similar to those observed among known transitional millisecond pulsars: short-term variability, a hard power-law spectrum (photon index ~ 1.7), and a comparable 0.5-10 keV luminosity (~ 2.4 x 10^33 erg/s). We find tentative evidence for a partial (~ 60%) gamma-ray eclipse at the same phase as the X-ray eclipse, suggesting the gamma-ray emission may not be confined to the immediate region of the compact object. The favorable inclination of this binary is promising for future efforts to determine the origin of gamma-rays among accreting neutron stars.

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