arXiv subjects

B. Scott Gaudi

Publications and source records attributed to B. Scott Gaudi.

At least 73 records · Page 4Linked to original sources

arXiv2021

Classifying High-cadence Microlensing Light Curves I; Defining Features

Microlensing is a powerful tool for discovering cold exoplanets, and the The Roman Space Telescope microlensing survey will discover over 1000 such planets. Rapid, automated classification of Roman's microlensing events can be used to prioritize follow-up observations of the most interesting events. Machine learning is now often used for classification problems in astronomy, but the success of such algorithms can rely on the definition of appropriate features that capture essential elements of the observations that can map to parameters of interest. In this paper, we introduce tools that we have developed to capture features in simulated Roman light curves of different types of microlensing events, and evaluate their effectiveness in classifying microlensing light curves. These features are quantified as parameters that can be used to decide the likelihood that a given light curve is due to a specific type of microlensing event. This method leaves us with a list of parameters that describe features like the smoothness of the peak, symmetry, the number of peaks, and width and height of small deviations from the main peak. This will allow us to quickly analyze a set of microlensing light curves and later use the resulting parameters as input to machine learning algorithms to classify the events.

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arXiv2020

The Demographics of Exoplanets

In the broadest sense, the primary goal of exoplanet demographic surveys is to determine the frequency and distribution of planets as a function of as many of the physical parameters that may influence planet formation and evolution as possible, over as broad of a range of these parameters as possible. Empirically-determined exoplanet demographics provide the ground truth that all planet formation and evolution theories must reproduce. By comparing these planet distributions to the predictions of planet formation theories, we can begin to both test and refine these theories. In this chapter, we review the major results on exoplanet demographics to date. In this context, we identify a set of important open questions that remain to be answered. We outline the challenges of measuring the demographics of exoplanets using the variety of detection methods at our disposal. Finally, we summarize some of the future opportunities for refining and expanding our understanding of exoplanet demographics.

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arXiv2020

An Extreme-mass Ratio, Short-period Eclipsing Binary Consisting of a B Dwarf Primary and a Pre-main Sequence M Star Companion Discovered by KELT

We present the discovery of \thisstar\ (HD 58730), a very low mass ratio ($q \equiv M_2/M_1 \approx 0.07$) eclipsing binary (EB) identified by the Kilodegree Extremely Little Telescope (KELT) survey. We present the discovery light curve and perform a global analysis of four high-precision ground-based light curves, the Transiting Exoplanets Survey Satellite (TESS) light curve, radial velocity (RV) measurements, Doppler Tomography (DT) measurements, and the broad-band spectral energy distribution (SED). Results from the global analysis are consistent with a fully convective ($M_2 = 0.22 \pm 0.02\ M_{\odot})$ M star transiting a late-B primary ($M_1 = 3.34^{+0.07}_{-0.09}\ M_{\odot};\ T_{\rm eff,1} = 11960^{+430}_{-520}\ {\rm K}$). We infer that the primary star is $183_{-30}^{+33}$ Myr old and that the companion star's radius is inflated by $26 \pm 8\%$ relative to the predicted value from a low-mass isochrone of similar age. We separately and analytically fit for the variability in the out-of-eclipse TESS phase curve, finding good agreement between the resulting stellar parameters and those from the global fit. Such systems are valuable for testing theories of binary star formation and understanding how the environment of a star in a close-but-detached binary affects its physical properties. In particular, we examine how a star's properties in such a binary might differ from the properties it would have in isolation.

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arXiv2020

Two Planets Straddling the Habitable Zone of The Nearby K Dwarf Gl 414A

We present the discovery of two planets orbiting the nearby (D=11.9 pc) K7 dwarf Gl 414A. Gl 414A b is a sub-Neptune mass planet with M$_b \sin{i_b} = 9.28^{+3.19}_{-2.54}$ M$_\oplus$ and a semi-major axis of 0.24 $\pm$ 0.01 au. Gl 414A c is a sub-Saturn mass planet with $M_c \sin{i_c} = 59.48^{+9.98}_{-9.69}$ M$_\oplus$ and a semi-major axis of 1.43 $\pm$ 0.06 au. We jointly analyzed radial velocity data from Keck/HIRES and the Automated Planet Finder at Lick Observatory, as well as photometric data from KELT, to detect the two planets as well as two additional signals related to the rotationally-modulated activity and the long term magnetic activity cycle of the star. The outer planet in this system may be a potential candidate for future direct imaging missions.

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arXiv2020

Predictions of the Nancy Grace Roman Space Telescope Galactic Exoplanet Survey II: Free-Floating Planet Detection Rates

The Nancy Grace Roman Space Telescope (Roman) will perform a Galactic Exoplanet Survey (RGES) to discover bound exoplanets with semi-major axes greater than 1 au using gravitational microlensing. Roman will even be sensitive to planetary mass objects that are not gravitationally bound to any host star. Such free-floating planetary mass objects (FFPs) will be detected as isolated microlensing events with timescales shorter than a few days. A measurement of the abundance and mass function of FFPs is a powerful diagnostic of the formation and evolution of planetary systems, as well as the physics of the formation of isolated objects via direct collapse. We show that Roman will be sensitive to FFP lenses that have masses from that of Mars ($0.1 M_\oplus$) to gas giants ($M\gtrsim100M_\oplus$) as isolated lensing events with timescales from a few hours to several tens of days, respectively. We investigate the impact of the detection criteria on the survey, especially in the presence of finite-source effects for low-mass lenses. The number of detections will depend on the abundance of such FFPs as a function of mass, which is at present poorly constrained. Assuming that FFPs follow the fiducial mass function of cold, bound planets adapted from Cassan et al. (2012), we estimate that Roman will detect $\sim250$ FFPs with masses down to that of Mars (including $\sim 60$ with masses $\le M_\oplus$). We also predict that Roman will improve the upper limits on FFP populations by at least an order of magnitude compared to currently-existing constraints.

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arXiv2020

OGLE-2017-BLG-0406: ${\it Spitzer}$ Microlens Parallax Reveals Saturn-mass Planet orbiting M-dwarf Host in the Inner Galactic Disk

We report the discovery and analysis of the planetary microlensing event OGLE-2017-BLG-0406, which was observed both from the ground and by the ${\it Spitzer}$ satellite in a solar orbit. At high magnification, the anomaly in the light curve was densely observed by ground-based-survey and follow-up groups, and it was found to be explained by a planetary lens with a planet/host mass ratio of $q=7.0 \times 10^{-4}$ from the light-curve modeling. The ground-only and ${\it Spitzer}$-"only" data each provide very strong one-dimensional (1-D) constraints on the 2-D microlens parallax vector $\bf{π_{\rm E}}$. When combined, these yield a precise measurement of $\bf{π_{\rm E}}$, and so of the masses of the host $M_{\rm host}=0.56\pm0.07\,M_\odot$ and planet $M_{\rm planet} = 0.41 \pm 0.05\,M_{\rm Jup}$. The system lies at a distance $D_{\rm L}=5.2 \pm 0.5 \ {\rm kpc}$ from the Sun toward the Galactic bulge, and the host is more likely to be a disk population star according to the kinematics of the lens. The projected separation of the planet from the host is $a_{\perp} = 3.5 \pm 0.3 \ {\rm au}$, i.e., just over twice the snow line. The Galactic-disk kinematics are established in part from a precise measurement of the source proper motion based on OGLE-IV data. By contrast, the ${\it Gaia}$ proper-motion measurement of the source suffers from a catastrophic $10\,σ$ error.

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arXiv2020

KELT-9 b's Asymmetric TESS Transit Caused by Rapid Stellar Rotation and Spin-Orbit Misalignment

KELT-9 b is an ultra hot Jupiter transiting a rapidly rotating, oblate early-A-type star in a polar orbit. We model the effect of rapid stellar rotation on KELT-9 b's transit light curve using photometry from the Transiting Exoplanet Survey Satellite (\tess) to constrain the planet's true spin-orbit angle and to explore how KELT-9 b may be influenced by stellar gravity darkening. We constrain the host star's equatorial radius to be $1.089\pm0.017$ times as large as its polar radius and its local surface brightness to vary by $\sim38$\% between its hot poles and cooler equator. We model the stellar oblateness and surface brightness gradient and find that it causes the transit light curve to lack the usual symmetry around the time of minimum light. We take advantage of the light curve asymmetry to constrain KELT-9 b's true spin orbit angle (${87^\circ}^{+10^\circ}_{-11^\circ}$), agreeing with \citet{gaudi2017giant} that KELT-9 b is in a nearly polar orbit. We also apply a gravity darkening correction to the spectral energy distribution model from \citet{gaudi2017giant} and find that accounting for rapid rotation gives a better fit to available spectroscopy and yields a more reliable estimate for the star's polar effective temperature.

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arXiv2020

The Habitable Exoplanet Observatory (HabEx) Mission Concept Study Final Report

The Habitable Exoplanet Observatory, or HabEx, has been designed to be the Great Observatory of the 2030s. For the first time in human history, technologies have matured sufficiently to enable an affordable space-based telescope mission capable of discovering and characterizing Earthlike planets orbiting nearby bright sunlike stars in order to search for signs of habitability and biosignatures. Such a mission can also be equipped with instrumentation that will enable broad and exciting general astrophysics and planetary science not possible from current or planned facilities. HabEx is a space telescope with unique imaging and multi-object spectroscopic capabilities at wavelengths ranging from ultraviolet (UV) to near-IR. These capabilities allow for a broad suite of compelling science that cuts across the entire NASA astrophysics portfolio. HabEx has three primary science goals: (1) Seek out nearby worlds and explore their habitability; (2) Map out nearby planetary systems and understand the diversity of the worlds they contain; (3) Enable new explorations of astrophysical systems from our own solar system to external galaxies by extending our reach in the UV through near-IR. This Great Observatory science will be selected through a competed GO program, and will account for about 50% of the HabEx primary mission. The preferred HabEx architecture is a 4m, monolithic, off-axis telescope that is diffraction-limited at 0.4 microns and is in an L2 orbit. HabEx employs two starlight suppression systems: a coronagraph and a starshade, each with their own dedicated instrument.

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arXiv2020

Evidence for H$_{2}$ Dissociation and Recombination Heat Transport in the Atmosphere of KELT-9b

Phase curve observations provide an opportunity to study the full energy budgets of exoplanets by quantifying the amount of heat redistributed from their daysides to their nightsides. Theories explaining the properties of phase curves for hot Jupiters have focused on the balance between radiation and dynamics as the primary parameter controlling heat redistribution. However, recent phase curves have shown deviations from the trends that emerge from this theory, which has led to work on additional processes that may affect hot Jupiter energy budgets. One such process, molecular hydrogen dissociation and recombination, can enhance energy redistribution on ultra-hot Jupiters with temperatures above $\sim2000$ K. In order to study the impact of H$_{2}$ dissociation on ultra-hot Jupiters, we present a phase curve of KELT-9b observed with the Spitzer Space Telescope at 4.5 $μ$m. KELT-9b is the hottest known transiting planet, with a 4.5-$μ$m dayside brightness temperature of $4566^{+140}_{-136}$ K and a nightside temperature of $2556^{+101}_{-97}$ K. We observe a phase curve amplitude of $0.609 \pm 0.020$ and a hot spot offset of $18.7^{+2.1}_{-2.3}$ degrees. The observed amplitude is too small to be explained by a simple balance between radiation and advection. General circulation models (GCMs) and an energy balance model that include the effects of H$_{2}$ dissociation and recombination provide a better match to the data. The GCMs, however, predict a maximum hot spot offset of $5$ degrees, which disagrees with our observations at $>5σ$ confidence. This discrepancy may be due to magnetic effects in the planet's highly ionized atmosphere.

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arXiv2019

KMT-2018-BLG-0029Lb: A Very Low Mass-Ratio Spitzer Microlens Planet

At $q=1.81\pm 0.20 \times 10^{-5}$, KMT-2018-BLG-0029Lb has the lowest planet-host mass ratio $q$ of any microlensing planet to date by more than a factor of two. Hence, it is the first planet that probes below the apparent "pile-up" at $q=5$--10 $\times 10^{-5}$. The event was observed by {\it Spitzer}, yielding a microlens-parallax $π_{\rm E}$ measurement. Combined with a measurement of the Einstein radius $θ_{\rm E}$ from finite-source effects during the caustic crossings, these measurements imply masses of the host $M_{\rm host}=1.14^{+0.10}_{-0.12}\, M_\odot$ and planet $M_{\rm planet} = 7.59^{+0.75}_{-0.69}\,M_\oplus$, system distance $D_L = 3.38^{+0.22}_{-0.26}\,\,{\rm kpc}$ and projected separation $a_\perp = 4.27^{+0.21}_{-0.23}\,{\rm au}$. The blended light, which is substantially brighter than the microlensed source, is plausibly due to the lens and could be observed at high resolution immediately.

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arXiv2019

KELT-25b and KELT-26b: A Hot Jupiter and a Substellar Companion Transiting Young A-stars Observed by TESS

We present the discoveries of KELT-25b (TIC 65412605, TOI-626.01) and KELT-26b (TIC 160708862, TOI-1337.01), two transiting companions orbiting relatively bright, early A-stars. The transit signals were initially detected by the KELT survey, and subsequently confirmed by \textit{TESS} photometry. KELT-25b is on a 4.40-day orbit around the V = 9.66 star CD-24 5016 ($T_{\rm eff} = 8280^{+440}_{-180}$ K, $M_{\star}$ = $2.18^{+0.12}_{-0.11}$ $M_{\odot}$), while KELT-26b is on a 3.34-day orbit around the V = 9.95 star HD 134004 ($T_{\rm eff}$ =$8640^{+500}_{-240}$ K, $M_{\star}$ = $1.93^{+0.14}_{-0.16}$ $M_{\odot}$), which is likely an Am star. We have confirmed the sub-stellar nature of both companions through detailed characterization of each system using ground-based and \textit{TESS} photometry, radial velocity measurements, Doppler Tomography, and high-resolution imaging. For KELT-25, we determine a companion radius of $R_{\rm P}$ = $1.64^{+0.039}_{-0.043}$ $R_{\rm J}$, and a 3-sigma upper limit on the companion's mass of $\sim64~M_{\rm J}$. For KELT-26b, we infer a planetary mass and radius of $M_{\rm P}$ = $1.41^{+0.43}_{-0.51}$ $M_{\rm J}$ and $R_{\rm P}$ = $1.940^{+0.060}_{-0.058}$ $R_{\rm J}$. From Doppler Tomographic observations, we find KELT-26b to reside in a highly misaligned orbit. This conclusion is weakly corroborated by a subtle asymmetry in the transit light curve from the \textit{TESS} data. KELT-25b appears to be in a well-aligned, prograde orbit, and the system is likely a member of a cluster or moving group.

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arXiv2019

TESS Reveals HD 118203 b to be a Transiting Planet

The exoplanet HD 118203 b, orbiting a bright (V = 8.05) host star, was discovered using the radial velocity method by da Silva et al. (2006), but was not previously known to transit. TESS photometry has revealed that this planet transits its host star. Five planetary transits were observed by TESS, allowing us to measure the radius of the planet to be $1.133 \pm 0.031 R_J$, and to calculate the planet mass to be $2.173 \pm 0.078 M_J$. The host star is slightly evolved with an effective temperature of $T_{\rm eff} = 5692 \pm 83$ K and a surface gravity of ${\rm log}(g) = 3.891 \pm 0.019$. With an orbital period of $6.134980 \pm 0.000038$ days and an eccentricity of $0.316 \pm 0.021$, the planet occupies a transitional regime between circularized hot Jupiters and more dynamically active planets at longer orbital periods. The host star is among the ten brightest known to have transiting giant planets, providing opportunities for both planetary atmospheric and asteroseismic studies.

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arXiv2019

Eating Planets for Lunch and Dinner: Signatures of Planet Consumption by Evolving Stars

Exoplanets have been observed around stars at all stages of stellar evolution, in many cases orbiting in configurations that will eventually lead to the planets being engulfed or consumed by their host stars, such as Hot Jupiters or ultra-short period planets. Furthermore, objects such as polluted white dwarfs provide strong evidence that the consumption of planets by stars is a common phenomenon. This consumption causes several significant changes in the stellar properties, such as changes to the stellar spin, luminosity, chemical composition, or mass loss processes. Here, we explore this wide variety of effects for a comprehensive range of stellar and planetary masses and stages of stellar evolution, from the main sequence over red giants to the white dwarfs. We determine that planet consumption can cause transient luminosity features that last on the order of centuries to millennia, and that the post-consumption stellar spins can often reach break-up speeds. Furthermore, stellar moss loss can be caused by this spin-up, as well as through surface grazing interactions, leading to to the formation of unusual planetary nebula shapes or collimated stellar gas ejections. Our results highlight several observable stellar features by which the presence or previous existence of a planet around a given star can be deduced. This will provide future observational campaigns with the tools to better constrain exoplanet demographics, as well as planetary formation and evolution histories.

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arXiv2019

KELT-24b: A 5M$_{\rm J}$ Planet on a 5.6 day Well-Aligned Orbit around the Young V=8.3 F-star HD 93148

We present the discovery of KELT-24 b, a massive hot Jupiter orbiting a bright (V=8.3 mag, K=7.2 mag) young F-star with a period of 5.6 days. The host star, KELT-24 (HD 93148), has a $T_{\rm eff}$ =$6509^{+50}_{-49}$ K, a mass of $M_{*}$ = $1.460^{+0.055}_{-0.059}$ $M_{\odot}$, radius of $R_{*}$ = $1.506\pm0.022$ $R_{\odot}$, and an age of $0.78^{+0.61}_{-0.42}$ Gyr. Its planetary companion (KELT-24 b) has a radius of $R_{\rm P}$ = $1.272\pm0.021$ $R_{\rm J}$, a mass of $M_{\rm P}$ = $5.18^{+0.21}_{-0.22}$ $M_{\rm J}$, and from Doppler tomographic observations, we find that the planet's orbit is well-aligned to its host star's projected spin axis ($λ$ = $2.6^{+5.1}_{-3.6}$). The young age estimated for KELT-24 suggests that it only recently started to evolve from the zero-age main sequence. KELT-24 is the brightest star known to host a transiting giant planet with a period between 5 and 10 days. Although the circularization timescale is much longer than the age of the system, we do not detect a large eccentricity or significant misalignment that is expected from dynamical migration. The brightness of its host star and its moderate surface gravity make KELT-24b an intriguing target for detailed atmospheric characterization through spectroscopic emission measurements since it would bridge the current literature results that have primarily focused on lower mass hot Jupiters and a few brown dwarfs.

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arXiv2019

A Great Successor to the Hubble Space Telescope

The Hubble Space Telescope (HST) has been the most impactful science-driven mission ever flown by NASA. However, when HST reaches the end of its life, there will be a void due to the loss of some of the science capabilities afforded by HST to astronomers world-wide. The previous 2010 Decadal Survey (DS) noted this void, arguing for the need for a successor to HST with UV capabilities in three separate places in the main report (pp. 190, 203, and 220). The large strategic missions that will follow HST, namely JWST and WFIRST, will continue to spark the interest of the public in space-based astronomy. In order to ensure continued US preeminence in the arena of large space-based astrophysics missions, and a seamless transition after WFIRST, a future flagship mission must be waiting in the wings. Anticipating this need, NASA initiated four large strategic mission concept studies (HabEx, LUVOIR, Lynx, and Origins), which have mature designs, including detailed technology assessments and development plans. Two of these concepts, HabEx and LUVOIR, are responsive to the recommendations of the previous DS regarding a UV-capable mission. Both are more powerful successors to HST, with UV-to-optical capabilities that range from significant enhancements to orders-of-magnitude improvement. At the same time, technological and scientific advances over the past decade only now make it feasible to marry such a mission with one that can search for life outside the solar system. Acknowledging that the constraints that the Astro2020 DS must consider may be difficult to anticipate, the HabEx and LUVOIR studies present eleven different variants, each of which enable groundbreaking science, including the direct imaging and characterization of exoplanets. The HabEx and LUVOIR mission studies offer a full suite of options to the Astro2020 DS, with corresponding flexibility in budgeting and phasing.

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arXiv2019

Spitzer Phase Curves of KELT-1b and the Signatures of Nightside Clouds in Thermal Phase Observations

We observed two full orbital phase curves of the transiting brown dwarf KELT-1b, at 3.6um and 4.5um, using the Spitzer Space Telescope. Combined with previous eclipse data from Beatty et al. (2014), we strongly detect KELT-1b's phase variation as a single sinusoid in both bands, with amplitudes of $964\pm36$ ppm at 3.6um and $979\pm54$ ppm at 4.5um, and confirm the secondary eclipse depths measured by Beatty et al. (2014). We also measure noticeable Eastward hotspot offsets of $28.4\pm3.5$ degrees at 3.6um and $18.6\pm5.2$ degrees at 4.5um. Both the day-night temperature contrasts and the hotspot offsets we measure are in line with the trends seen in hot Jupiters (e.g., Crossfield 2015), though we disagree with the recent suggestion of an offset trend by Zhang et al. (2018). Using an ensemble analysis of Spitzer phase curves, we argue that nightside clouds are playing a noticeable role in modulating the thermal emission from these objects, based on: 1) the lack of a clear trend in phase offsets with equilibrium temperature, 2) the sharp day-night transitions required to have non-negative intensity maps, which also resolves the inversion issues raised by Keating & Cowan (2017), 3) the fact that all the nightsides of these objects appear to be at roughly the same temperature of 1000K, while the dayside temperatures increase linearly with equilibrium temperature, and 4) the trajectories of these objects on a Spitzer color-magnitude diagram, which suggest colors only explainable via nightside clouds.

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arXiv2019

Community Involvement in the WFIRST Exoplanet Microlensing Survey

WFIRST is NASA's first flagship mission with pre-defined core science programs to study dark energy and perform a statistical census of wide orbit exoplanets with a gravitational microlensing survey. Together, these programs are expected to use more than half of the prime mission observing time. Previously, only smaller, PI-led missions have had core programs that used such a large fraction of the observing time, and in many cases, the data from these PI-led missions was reserved for the PI's science team for a proprietary period that allowed the PI's team to make most of the major discoveries from the data. Such a procedure is not appropriate for a flagship mission, which should provide science opportunities to the entire astronomy community. For this reason, there will be no proprietary period for WFIRST data, but we argue that a larger effort to make WFIRST science accessible to the astronomy community is needed. We propose a plan to enhance community involvement in the WFIRST exoplanet microlensing survey in two different ways. First, we propose a set of high level data products that will enable astronomers without detailed microlensing expertise access to the statistical implications of the WFIRST exoplanet microlensing survey data. And second, we propose the formation of a WFIRST Exoplanet Microlensing Community Science Team that will open up participation in the development of the WFIRST exoplanet microlensing survey to the general astronomy community in collaboration for the NASA selected science team, which will have the responsibility to provide most of the high level data products. This community science team will be open to volunteers, but members should also have the opportunity to apply for funding.

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arXiv2019

OGLE-2017-BLG-1186: first application of asteroseismology and Gaussian processes to microlensing

We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing campaign. This is a remarkable microlensing event because its source is photometrically bright and variable, which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average timescale of $\sim 9$ d. The asteroseismic analysis also provides us source properties including the source angular size ($\sim 27~μ{\rm as}$) and distance ($\sim 11.5$ kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian Processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional $χ^2$ minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a $\sim 0.045~M_{\odot}$ brown dwarf at distance $\sim 9.0$ kpc, or a $\sim 0.073~M_{\odot}$ ultracool dwarf at distance $\sim 9.8$ kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a $\sim 35$ per cent probability for the lens to be a bulge object and $\sim 65$ per cent to be a background disc object.

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