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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Identification of more than 40 gravitationally magnified stars in a galaxy at redshift 0.725

Strong gravitational magnification enables the detection of faint background sources and allows researchers to resolve their internal structures and even identify individual stars in distant galaxies. Highly magnified individual stars are useful in various applications, including studies of stellar populations in distant galaxies and constraining dark matter structures in the lensing plane. However, these applications have been hampered by the small number of individual stars observed, as typically one or a few stars are identified from each distant galaxy. Here, we report the discovery of more than 40 microlensed stars in a single galaxy behind Abell 370 at redshift of 0.725 (dubbed ‘the Dragon arc’) when the Universe was half of its current age, using James Webb Space Telescope observations with the time-domain technique. These events were found near the expected lensing critical curves, suggesting that these are magnified stars that appear as transients from intracluster stellar microlenses. Through multi-wavelength photometry, we constrained their stellar types and found that many of them are consistent with red giants or supergiants magnified by factors of hundreds. Furthermore, this finding reveals a high occurrence of microlensing events in the Dragon arc and demonstrates that time-domain observations by the James Webb Space Telescope could lead to the possibility of conducting statistical studies of high-redshift stars.

Early universe↗
DOE OSTI2013

MOA-2010-BLG-073L: AN M-DWARF WITH A SUBSTELLAR COMPANION AT THE PLANET/BROWN DWARF BOUNDARY

We present an analysis of the anomalous microlensing event, MOA-2010-BLG-073, announced by the Microlensing Observations in Astrophysics survey on 2010 March 18. This event was remarkable because the source was previously known to be photometrically variable. Analyzing the pre-event source light curve, we demonstrate that it is an irregular variable over timescales >200 days. Its dereddened color, (V - I) {sub S,0}, is 1.221 {+-} 0.051 mag, and from our lens model we derive a source radius of 14.7 {+-} 1.3 R {sub Sun }, suggesting that it is a red giant star. We initially explored a number of purely microlensing models for the event but found a residual gradient in the data taken prior to and after the event. This is likely to be due to the variability of the source rather than part of the lensing event, so we incorporated a slope parameter in our model in order to derive the true parameters of the lensing system. We find that the lensing system has a mass ratio of q = 0.0654 {+-} 0.0006. The Einstein crossing time of the event, t {sub E} = 44.3 {+-} 0.1 days, was sufficiently long that the light curve exhibited parallax effects. In addition, the source trajectory relative to the large caustic structure allowed the orbital motion of the lens system to be detected. Combining the parallax with the Einstein radius, we were able to derive the distance to the lens, D{sub L} = 2.8 {+-} 0.4 kpc, and the masses of the lensing objects. The primary of the lens is an M-dwarf with M {sub L,1} = 0.16 {+-} 0.03 M {sub Sun }, while the companion has M {sub L,2} = 11.0 {+-} 2.0 M {sub J}, putting it in the boundary zone between planets and brown dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

MOA-2010-BLG-523: 'FAILED PLANET' = RS CVn STAR

The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing light curve near the peak of an A {sub max} {approx} 265 high-magnification microlensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken near peak to demonstrate that this is an RS CVn variable, so that planetary microlensing is not required to explain the light-curve deviations. This is the first spectroscopically confirmed RS CVn star discovered in the Galactic bulge.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

The average size and temperature profile of quasar accretion disks

We use multi-wavelength microlensing measurements of a sample of 10 image pairs from 8 lensed quasars to study the structure of their accretion disks. By using spectroscopy or narrowband photometry, we have been able to remove contamination from the weakly microlensed broad emission lines, extinction, and any uncertainties in the large-scale macro magnification of the lens model. We determine a maximum likelihood estimate for the exponent of the size versus wavelength scaling (r{sub s} ∝λ {sup p}, corresponding to a disk temperature profile of T∝r {sup –1/p}) of p=0.75{sub −0.2}{sup +0.2} and a Bayesian estimate of p = 0.8 ± 0.2, which are significantly smaller than the prediction of the thin disk theory (p = 4/3). We have also obtained a maximum likelihood estimate for the average quasar accretion disk size of r{sub s}=4.5{sub −1.2}{sup +1.5} lt-day at a rest frame wavelength of λ = 1026 Å for microlenses with a mean mass of M = 1 M {sub ☉}, in agreement with previous results, and larger than expected from thin disk theory.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

MOA-2011-BLG-262Lb: A sub-Earth-mass moon orbiting a gas giant primary or a high velocity planetary system in the galactic Bulge

We present the first microlensing candidate for a free-floating exoplanet-exomoon system, MOA-2011-BLG-262, with a primary lens mass of M {sub host} ∼ 4 Jupiter masses hosting a sub-Earth mass moon. The argument for an exomoon hinges on the system being relatively close to the Sun. The data constrain the product M{sub L} π{sub rel} where M{sub L} is the lens system mass and π{sub rel} is the lens-source relative parallax. If the lens system is nearby (large π{sub rel}), then M{sub L} is small (a few Jupiter masses) and the companion is a sub-Earth-mass exomoon. The best-fit solution has a large lens-source relative proper motion, μ{sub rel} = 19.6 ± 1.6 mas yr{sup –1}, which would rule out a distant lens system unless the source star has an unusually high proper motion. However, data from the OGLE collaboration nearly rule out a high source proper motion, so the exoplanet+exomoon model is the favored interpretation for the best fit model. However, there is an alternate solution that has a lower proper motion and fits the data almost as well. This solution is compatible with a distant (so stellar) host. A Bayesian analysis does not favor the exoplanet+exomoon interpretation, so Occam's razor favors a lens system in the bulge with host and companion masses of M{sub host}=0.12{sub −0.06}{sup +0.19} M{sub ⊙} and m{sub comp}=18{sub −10}{sup +28} M{sub ⊕}, at a projected separation of a{sub ⊥}=0.84{sub −0.14}{sup +0.25} AU. The existence of this degeneracy is an unlucky accident, so current microlensing experiments are in principle sensitive to exomoons. In some circumstances, it will be possible to definitively establish the mass of such lens systems through the microlensing parallax effect. Future experiments will be sensitive to less extreme exomoons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

CAN THE MASSES OF ISOLATED PLANETARY-MASS GRAVITATIONAL LENSES BE MEASURED BY TERRESTRIAL PARALLAX?

Recently Sumi et al. reported evidence for a large population of planetary-mass objects (PMOs) that are either unbound or orbit host stars in orbits ≥10 AU. Their result was deduced from the statistical distribution of durations of gravitational microlensing events observed by the MOA collaboration during 2006 and 2007. Here we study the feasibility of measuring the mass of an individual PMO through microlensing by examining a particular event, MOA-2011-BLG-274. This event was unusual as the duration was short, the magnification high, the source-size effect large, and the angular Einstein radius small. Also, it was intensively monitored from widely separated locations under clear skies at low air masses. Choi et al. concluded that the lens of the event may have been a PMO but they did not attempt a measurement of its mass. We report here a re-analysis of the event using re-reduced data. We confirm the results of Choi et al. and attempt a measurement of the mass and distance of the lens using the terrestrial parallax effect. Evidence for terrestrial parallax is found at a 3σ level of confidence. The best fit to the data yields the mass and distance of the lens as 0.80 ± 0.30 M {sub J} and 0.80 ± 0.25 kpc respectively. We exclude a host star to the lens out to a separation ∼40 AU. Drawing on our analysis of MOA-2011-BLG-274 we propose observational strategies for future microlensing surveys to yield sharper results on PMOs including those down to super-Earth mass.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

OGLE-2012-BLG-0563Lb: A saturn-mass planet around an M dwarf with the mass constrained by Subaru AO imaging

We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet–star mass ratio of ∼1×10{sup −3}. Intensive photometric observations of a high-magnification microlensing event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK′-band images obtained by the Subaru/AO188 and Infrared Camera and Spectrograph instruments, allowing us to constrain the absolute physical parameters of the planetary system. With the help of spectroscopic information about the source star obtained during the high-magnification state by Bensby et al., we find that the lens system is located at 1.3{sub −0.8}{sup +0.6} kpc from us, and consists of an M dwarf (0.34 {sub −0.20}{sup +0.12}M{sub ⊙}) orbited by a Saturn-mass planet (0.39 {sub −0.23}{sup +0.14}M{sub Jup}) at the projected separation of 0.74{sub −0.42}{sup +0.26} AU (close model) or 4.3{sub −2.5}{sup +1.5} AU (wide model). The probability of contamination in the host star’s flux, which would reduce the masses by a factor of up to three, is estimated to be 17%. This possibility can be tested by future high-resolution imaging. We also estimate the (J−K{sub s}) and (H−K{sub s}) colors of the host star, which are marginally consistent with a low metallicity mid-to-early M dwarf, although further observations are required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2<m{sub p}/M{sub Jup}<1) microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest of sub-Jupiters around M dwarfs is contrasted with a possible paucity of ∼1–2 Jupiter-mass planets around the same type of star, which can be explained by the planetary formation process in the core-accretion scheme.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Simulations of axion minihalos

The axion, motivated as a solution to the strong CP problem, is also a viable dark matter candidate. The axion field takes random values in causally disconnected regions if the symmetry breaking that establishes the particle occurs after inflation, leading to white-noise density fluctuations at low wave numbers and forming dense minihalos with sub-planetary masses subsequently. There have been two recent proposals that appear capable of testing this scenario, namely using pulsar timing arrays and studying cosmological microlensing caustics. Motivated by these proposals, we use N-body simulations to study the formation of substructures from white-noise density fluctuations. The density profiles of our relaxed axion minihalos can be described by the Navarro–Frenk–White profile, and the minihalos’ concentration number agrees well with a simple, physically-motivated model. We develop a semi-analytic formula to fit the mass function from our simulation, which agrees broadly at different redshifts and only differs at factor of two level from classic halo mass functions. This analytic mass function allows us to consider uncertainties in the post-inflation axion scenario, as well as extrapolate our high-redshift simulations results to the present. Our work estimates the present-day abundance of axion substructures, as is necessary for predicting their effect on cosmological microlensing caustics and pulsar timing. Our calculations suggest that if pulsar timing and microlensing probes can reach recent sensitivity forecasts, they may be sensitive to the post-inflation axion dark matter scenario, even when accounting for uncertainties pertaining to axion strings. For pulsar timing, the most significant caveat is whether axion minihalos are disrupted by stars, which our estimates show is mildly important at the most relevant masses. In conclusion, as our gravitational simulations are scale invariant, the results can be extended to models where the dark matter is comprised of other axion-like particles and even clusters of primordial black holes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Phenomenology of bubble size distributions in a first-order phase transition

In a cosmological first-order phase transition (FOPT), the true and false vacuum bubble radius distributions are not expected to be monochromatic, as is usually assumed. Consequently, Fermi balls (FBs) and primordial black holes (PBHs) produced in a dark FOPT will have extended mass distributions. We show how gravitational wave (GW), microlensing and Hawking evaporation signals for extended bubble radius/mass distributions deviate from the case of monochromatic distributions. The peak of the GW spectrum is shifted to lower frequencies, and the spectrum is broadened at frequencies below the peak frequency. Thus, the radius distribution of true vacuum bubbles introduces another uncertainty in the evaluation of the GW spectrum from a FOPT. The extragalactic gamma-ray signal at AMEGO-X/e-ASTROGAM from PBH evaporation may evince a break in the power-law spectrum between 5 MeV and 10 MeV for an extended PBH mass distribution. Optical microlensing surveys may observe PBH mass distributions with average masses below 10 -10 M ⊙ , which is not possible for monochromatic mass distributions. This expands the FOPT parameter space that can be explored with microlensing.

Marfatia, Danny [Univ. of Hawaii at Manoa, Honolul↗
DOE OSTI2017

Direct Writing of X-ray Gratings Using Zone-Plate-Array Lithography (ZPAL)

With the objective of providing the synchrotron and free-electron-laser communities with rapid turnaround and low prices for the highest quality and most advanced gratings and diffractive-focusing optics, LumArray has made specific improvements to its ZP-150 maskless photolithography system, which is based on Zone-Plate-Array Lithography (ZPAL), a technology unique to Lumarray. ZPAL’s advantages include an ability to correct in software for systematic patterning errors. Emphasis was placed on interferometric measurements of various contributors to patterning errors using Fizeau interferometry and a Mireau technique that was developed specifically for measuring errors within a micron-scale area. Average line-placement error was reduced below 20 nm using both pattern-file distortion and address-grid modification. The preferred implementation, address-grid modification, is hardware-based and requires no user intervention while also correcting more types of error. With continued iteration and refinement of the error measurements, we anticipate achieving global line-placement error below10nm. In order to investigate line-edge smoothness and high-frequency line-placement errors, a scheme for inspecting micron-sized areas was invented and implemented based on Mireau interferometry. This enabled the various contributions to be separately evaluated and measured. These included: exposure-dose variation, pattern-writing strategy and errors in the positioning of the microlenses. Deleterious crosstalk between microlenses was minimized via a pattern-dependent software modification. The impact of exposure threshold was revealed and adjustment made. The impact of address-grid fineness on line-edge roughness was likewise shown. Lastly, techniques were developed to measure and correct errors in the positioning of microlenses within the array. We expect final calibration of microlens positions to within 5nm.

42 ENGINEERING↗
DOE OSTI2019

From Stars to Compact Objects: The Initial-Final Mass Relation

One of the key phases of stellar evolution that remains poorly understood is stellar death. We lack a predictive model for how a star of a given mass explodes and what kind of remnant it leaves behind (i.e. the initial-final mass relation, IFMR). Progress has been limited due to the difficulty in finding and weighing black holes and neutron stars in large numbers. Technological advances that allow for sub-milliarcsecond astrometry in crowded fields have opened a new window for finding black holes and neutron stars: astrometric gravitational lensing. Finding and weighing a sample of compact objects with astrometric microlensing will allow us to place some of the first constraints on the present-day mass function of isolated black holes and neutron stars, their multiplicity, and their kick velocities. All of these are fundamental inputs into understanding the death phase of stellar evolution, improving supernovae models, and interpreting LIGO detections in an astrophysical context. To achieve these goals, we require large area surveys, such as the WFIRST exoplanet microlensing survey, to photometrically identify long-duration (>120 day), un-blended microlensing events as candidate compact objects. We also require high-precision astrometric follow-up monitoring using extremely large telescopes, equipped with adaptive optics, such as TMT and GMT.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Observations of the lensed quasar Q2237+0305 with Canaricam at GTC

We present new mid-IR observations of the quadruply lensed quasar Q2237+0305 taken with CanariCam on the Gran Telescopio Canarias. Mid-IR emission by hot dust, unlike the optical and near-IR emission from the accretion disk, is unaffected by the interstellar medium (extinction/scattering) or stellar microlensing. We compare these “true” ratios to the (stellar) microlensed flux ratios observed in the optical/near-IR to constrain the structure of the quasar accretion disk. We find a half-light radius of R{sub 1/2}=3.4{sub −2.1}{sup +5.3}√(〈M〉/0.3M{sub ⊙}) lt-day at λ{sub rest}=1736 A-ring and an exponent for the temperature profile R∝λ{sup p} of p=0.79±0.55, where p=4/3 for a standard thin-disk model. If we assume that the differences in the mid-IR flux ratios measured over the years are due to microlensing variability, we find a lower limit for the size of the mid-IR-emitting region of R{sub 1/2}≳200 √(〈M〉/0.3M{sub ⊙}) lt-day. We also test for the presence of substructure/satellites by comparing the observed mid-IR flux ratios with those predicted from smooth lens models. We can explain the differences if the surface density fraction in satellites near the lensed images is α=0.033{sub −0.019}{sup +0.046} for a singular isothermal ellipsoid plus external shear mass model or α=0.013{sub −0.008}{sup +0.019} for a mass model combining ellipsoidal NFW and de Vaucouleurs profiles in an external shear.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

OGLE-2018-BLG-0022: A Nearby M-dwarf Binary

We report observations of the binary microlensing event OGLE-2018-BLG-0022, provided by the Robotic Observations of Microlensing Events (ROME)/Reactive Event Assessment (REA) Survey, which indicate that the lens is a low-mass binary star consisting of M3 (0.375 ± 0.020 M {sub ⊙}) and M7 (0.098 ± 0.005 M {sub ⊙}) components. The lens is unusually close, at 0.998 ± 0.047 kpc, compared with the majority of microlensing events, and despite its intrinsically low luminosity, it is likely that adaptive optics observations in the near future will be able to provide an independent confirmation of the lens masses.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Systematic KMTNet Planetary Anomaly Search. I. OGLE-2019-BLG-1053Lb, a Buried Terrestrial Planet

In order to exhume the buried signatures of “missing planetary caustics” in Korea Microlensing Telescope Network (KMTNet) data, we conducted a systematic anomaly search of the residuals from point-source point-lens fits, based on a modified version of the KMTNet EventFinder algorithm. This search revealed the lowest-mass-ratio planetary caustic to date in the microlensing event OGLE-2019-BLG-1053, for which the planetary signal had not been noticed before. The planetary system has a planet–host mass ratio of q = (1.25 ± 0.13) × 10{sup -5}. A Bayesian analysis yielded estimates of the mass of the host star, M{sub host}=0.61{sub -0.24}{sup +0.29} M{sub ⊙}, the mass of its planet, M{sub planet}=2.48{sub -0.98}{sup +1.19} M{sub ⊕}, the projected planet–host separation, a{sub ⊥}=3.4{sub -0.5}{sup +0.5} au, and the lens distance, D{sub L}=6.8{sub -0.9}{sup +0.6} kpc. The discovery of this very-low-mass-ratio planet illustrates the utility of our method and opens a new window for a large and homogeneous sample to study the microlensing planet–host mass ratio function down to q ~ 10{sup -5}.

47 OTHER INSTRUMENTATION↗
NASA NTRS1993

The velocity dispersion of the caustic network due to random motion of individual stars in the lensing galaxy

We present a method of computing the velocity distribution of the caustic network due to the random motion of stars in the lensing galaxy. This method is illustrated on the example of the two-point mass lens and then applied to a large sample of stars. We conclude that the proper motion of the stars increases significantly the frequency of the high magnification events in comparison with a static lens configuration with constant stream or constant bulk velocity. The stream velocity is the velocity of the star field relative to the global bulk velocity of the galaxy. We show that the global bulk and the stream velocity of the star field have to be considered separately for any microlensing situation. The higher the surface mass density of the stars in the lensing galaxy, the higher the influence of proper motion of stars on the statistics of high magnification events. The influence of a Gaussian velocity distribution of the stars in the lensing galaxy compared with a constant stream velocity of the stars increases the number of high magnification events by a factor 1.30 +/- 0.06 for a normalized surface density of the stars cr = 0.1 and by a factor 1.7 +/- 0.1 for sigma = 0.5. This means that for some microlensing situations the proper motion of the stars in a lensing galaxy has to be considered for exact microlensing predictions.

Kundik, Tomislav↗
NASA NTRS2011

Discovery and Mass Measurements of a Cold, 10-Earth Mass Planet and Its Host Star

We present the discovery and mass measurement of the cold, low-mass planet MOA-2009-BLG-266Lb, made with the gravitational microlensing method. This planet has a mass of mp = 10.4 +/- M(Earth) and orbits a star of Mstar = 0.56 +/- 0.09 M(Sun) at a semi-major axis of a = 3.2 + 1.9/-0.5 AU, and an orbital period of 7.6 +7.7/-1.5 yrs. The planet and host star mass measurements are due to the measurement of the microlensing parallax effect. This measurement was primarily due to the orbital motion of the Earth, but the analysis also demonstrates the capability measure micro lensing parallax with the Deep Impact (or EPOXI) spacecraft in a Heliocentric orbit. The planet mass and orbital distance are similar to predictions for the critical core mass needed to accrete a substantial gaseous envelope, and thus may indicate that this planet is a failed gas giant. This and future microlensing detections will test planet formation theory predictions regarding the prevalence and masses of such planets

Barry, Richard K.↗
NASA NTRS2020

A Wide-orbit Exoplanet OGLE-2012-BLG-0838Lb

We present the discovery of a planet on a very wide orbit in the microlensing event OGLE-2012-BLG-0838. The signal of the planet is well separated from the main peak of the event and the planet–star projected separation is found to be twice the Einstein ring radius, which corresponds to a projected separation of ≈4au. Similar planets around low-mass stars are very hard to find using any technique other than microlensing. We discuss microlensing model fitting in detail and discuss the prospects for measuring the mass and distance of the lens system directly.

R. Poleski↗
NASA NTRS2020

Keck Observations Confirm a Super-Jupiter Planet Orbiting M Dwarf OGLE-2005 BLG-071L

We present adaptive optics imaging from the NIRC2 instrument on the Keck II telescope that resolves the exoplanet host (and lens) star as it separates from the brighter source star. These observations yield the K-band brightness of the lens and planetary host star, as well as the lens-source relative proper motion, μ(rel,H), in the heliocentric reference frame. The μ(rel,H) measurement allows for the determination of the microlensing parallax vector, π(E), which had only a single component determined by the microlensing light curve. The combined measurements of μ(rel,H) and K(L) provide the masses of the host star, M(host) = 0.426 ± 0.037M(ʘ), and planet, m(p)=3.27±0.32M(Jupiter) with a projected separation of 3.4±0.5 au. This confirms the tentative conclusion of a previous paper that this super-Jupiter mass planet, OGLE-2005-BLG-071Lb, orbits an M dwarf. Such planets are predicted to be rare by the core accretion theory and have been difficult to find with other methods, but there are two such planets with firm mass measurements from microlensing, and an additional 11 planetary microlens events with host mass estimates <0.5M(ʘ) and planet mass estimates >2 Jupiter masses that could be confirmed by high angular follow-up observations. We also point out that OGLE-2005-BLG-071L has separated far enough from its host star that it should be possible to measure the host-star metallicity with spectra from a high angular resolution telescope such as Keck, the Very Large Telescope, the Hubble Space Telescope, or the James Webb Space Telescope.

David P Bennett↗