arXiv subjects

Emily Lubar

Publications and source records attributed to Emily Lubar.

14 recordsLinked to original sources

arXiv2024

Jitter Across 15 Years: Leveraging Precise Photometry from Kepler and TESS to Extract Exoplanets from Radial Velocity Time Series

Stellar activity contamination of radial velocity (RV) data is one of the top challenges plaguing the field of extreme precision RV (EPRV) science. Previous work has shown that photometry can be very effective at removing such signals from RV data, especially stellar activity caused by rotating star spots and plage.The exact utility of photometry for removing RV activity contamination, and the best way to apply it, is not well known. We present a combination photometric and RV study of eight Kepler/K2 FGK stars with known stellar variability. We use NEID RVs acquired simultaneously with TESS photometry, and we perform injection recovery tests to quantify the efficacy of recent TESS photometry versus archival Kepler/K2 photometry for removing stellar variability from RVs. We additionally experiment with different TESS sectors when training our models in order to quantify the real benefit of simultaneously acquired RVs and photometry. We conclude that Kepler photometry typically performs better than TESS at removing noise from RV data when it is available, likely due to longer baseline and precision. In contrast, for targets with available K2 photometry, especially those most active, and with high precision ($\sigma_{NEID}$ $<$ 1 m s$^{-1}$) NEID RVs, TESS may be the more informative dataset. However, contrary to expectations, we have found that training on simultaneous photometry does not always achieve the best results.

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arXiv2024

Utilizing Photometry from Multiple Sources to Mitigate Stellar Variability in Precise Radial Velocities: A Case Study of Kepler-21

We present a new analysis of Kepler-21, the brightest (V = 8.5) Kepler system with a known transiting exoplanet, Kepler-21 b. Kepler-21 b is a radius valley planet ($R = 1.6\pm 0.2 R_{\oplus}$) with an Earth-like composition (8.38$\pm$1.62 g/cc), though its mass and radius fall in the regime of possible "water worlds." We utilize new Keck/HIRES and WIYN/NEID radial velocity (RV) data in conjunction with Kepler and TESS photometry to perform a detailed study of activity mitigation between photometry and RVs. We additionally refine the system parameters, and we utilize Gaia astrometry to place constraints on a long-term RV trend. Our activity analysis affirms the quality of Kepler photometry for removing correlated noise from RVs, despite its temporal distance, though we reveal some cases where TESS may be superior. Using refined orbital parameters and updated composition curves, we rule out a ``water world" scenario for Kepler-21 b, and we identify a long period super-Jupiter planetary candidate, Kepler-21 (c).

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arXiv2023

TOI-1670 c, a 40-day Orbital Period Warm Jupiter in a Compact System, is Well-aligned

We report the measurement of the sky-projected obliquity angle $\lambda$ of the Warm Jovian exoplanet TOI-1670 c via the Rossiter-McLaughlin effect as part of the Stellar Obliquities in Long-period Exoplanet Systems (SOLES) project. We observed the transit window during UT 20 April 2023 for 7 continuous hours with NEID on the 3.5 m WIYN Telescope at Kitt Peak National Observatory. TOI-1670 hosts a sub-Neptune (P ~11 days; planet b) interior to the Warm Jovian (P ~40 days; planet c), which presents an opportunity to investigate the dynamics of a Warm Jupiter with an inner companion. Additionally, TOI-1670 c is now among the longest-period planets to date to have its sky-projected obliquity angle measured. We find planet c is well-aligned to the host star, with $\lambda$ = -0.3 +/- 2.2 degrees. TOI-1670 c joins a growing census of aligned Warm Jupiters around single stars and aligned planets in multi-planet systems.

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arXiv2023

Stable fiber-illumination for extremely precise radial velocities with NEID

NEID is a high-resolution red-optical precision radial velocity (RV) spectrograph recently commissioned at the WIYN 3.5 m telescope at Kitt Peak National Observatory, Arizona, USA. NEID has an extremely stable environmental control system, and spans a wavelength range of 380 to 930 nm with two observing modes: a High Resolution (HR) mode at R $\sim$ 112,000 for maximum RV precision, and a High Efficiency (HE) mode at R $\sim$ 72,000 for faint targets. In this manuscript we present a detailed description of the components of NEID's optical fiber feed, which include the instrument, exposure meter, calibration system, and telescope fibers. Many parts of the optical fiber feed can lead to uncalibratable RV errors, which cannot be corrected for using a stable wavelength reference source. We show how these errors directly cascade down to performance requirements on the fiber feed and the scrambling system. We detail the design, assembly, and testing of each component. Designed and built from the bottom-up with a single-visit instrument precision requirement of 27 $\textrm{cm~s}^{-1}$, close attention was paid to the error contribution from each NEID subsystem. Finally, we include the lab and on-sky tests performed during instrument commissioning to test the illumination stability, and discuss the path to achieving the instrumental stability required to search for a true Earth twin around a Solar-type star.

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arXiv2022

A Green Bank Telescope search for narrowband technosignatures between 1.1-1.9 GHz during 12 Kepler planetary transits

A growing avenue for determining the prevalence of life beyond Earth is to search for "technosignatures" from extraterrestrial intelligences/agents. Technosignatures require significant energy to be visible across interstellar space and thus intentional signals might be concentrated in frequency, in time, or in space, to be found in mutually obvious places. Therefore, it could be advantageous to search for technosignatures in parts of parameter space that are mutually-derivable to an observer on Earth and a distant transmitter. In this work, we used the L-band (1.1-1.9 GHz) receiver on the Robert C. Byrd Green Bank Telescope (GBT) to perform the first technosignature search pre-synchronized with exoplanet transits, covering 12 Kepler systems. We used the Breakthrough Listen turboSETI pipeline to flag narrowband hits ($\sim$3 Hz) using a maximum drift rate of $\pm$614.4 Hz/s and a signal-to-noise threshold of 5 - the pipeline returned $\sim 3.4 \times 10^5$ apparently-localized features. Visual inspection by a team of citizen scientists ruled out 99.6% of them. Further analysis found 2 signals-of-interest that warrant follow-up, but no technosignatures. If the signals-of-interest are not re-detected in future work, it will imply that the 12 targets in the search are not producing transit-aligned signals from 1.1-1.9 GHz with transmitter powers $>$60 times that of the former Arecibo radar. This search debuts a range of innovative technosignature techniques: citizen science vetting of potential signals-of-interest, a sensitivity-aware search out to extremely high drift rates, a more flexible method of analyzing on-off cadences, and an extremely low signal-to-noise threshold.

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arXiv2021

Observing the Sun as a star: Design and early results from the NEID solar feed

Efforts with extreme-precision radial velocity (EPRV) instruments to detect small-amplitude planets are largely limited, on many timescales, by the effects of stellar variability and instrumental systematics. One avenue for investigating these effects is the use of small solar telescopes which direct disk-integrated sunlight to these EPRV instruments, observing the Sun at high cadence over months or years. We have designed and built a solar feed system to carry out "Sun-as-a-star" observations with NEID, a very high precision Doppler spectrometer recently commissioned at the WIYN 3.5m Telescope at Kitt Peak National Observatory. The NEID solar feed has been taking observations nearly every day since December 2020; data is publicly available at the NASA Exoplanet Science Institute (NExScI) NEID Solar Archive: \url{https://neid.ipac.caltech.edu/search_solar.php}. In this paper, we present the design of the NEID solar feed and explanations behind our design intent. We also present early radial velocity (RV) results which demonstrate NEID's RV stability on the Sun over 4 months of commissioning: 0.66~m/s RMS under good sky conditions and improving to 0.41~m/s RMS under best conditions.

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arXiv2021

The Warm Neptune GJ 3470b has a Polar Orbit

The warm Neptune GJ 3470b transits a nearby ($d=29$pc) bright slowly rotating M1.5-dwarf star. Using spectroscopic observations during two transits with the newly commissioned NEID spectrometer on the WIYN 3.5m Telescope at Kitt Peak Observatory, we model the classical Rossiter-Mclaughlin effect yielding a sky-projected obliquity of $\lambda=98_{-12}^{+15\:\circ}$ and a $v \sin i = 0.85_{-0.33}^{+0.27}$km/s. Leveraging information about the rotation period and size of the host star, our analysis yields a true obliquity of $\psi=95_{-8}^{+9\:\circ}$, revealing that GJ 3470b is on a polar orbit. Using radial velocities from HIRES, HARPS and the Habitable-zone Planet Finder, we show that the data are compatible with a long-term RV slope of $\dot{\gamma} = -0.0022 \pm 0.0011$m/s/day over a baseline of 12.9 years. If the RV slope is due to acceleration from another companion in the system, we show that such a companion is capable of explaining the polar and mildly eccentric orbit of GJ 3470b using two different secular excitation models. The existence of an outer companion can be further constrained with additional RV observations, Gaia astrometry, and future high-contrast imaging observations. Lastly, we show that tidal heating from GJ 3470b's mild eccentricity has most likely inflated the radius of GJ 3470b by a factor of $\sim$1.5-1.7, which could help account for its evaporating atmosphere.

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arXiv2020

Precise Blaze Angle Measurements of Lithographically Fabricated Silicon Immersion Gratings

Silicon immersion gratings and grisms enable compact, near-infrared spectrographs with high throughput. These instruments find use in ground-based efforts to characterize stellar and exoplanet atmospheres, and in space-based observatories. Our grating fabrication technique uses x-ray crystallography to orient silicon parts prior to cutting, followed by lithography and wet chemical etching to produce the blaze. This process takes advantage of the crystal structure and relative difference in etching rates between the (100) and (111) planes such that we can produce parts that have surface errors < λ/4. Previous measurements indicate that chemical etching can yield a final etched blaze that slightly differs from the orientation of the (111) plane. This difference can be corrected by the mechanical mount in the case of the immersion gratings, but doing so may compromise grating throughput due to shadowing. In the case of the grisms, failure to take the actual blaze into account will reduce the brightness of the undeviated ray. We report on multiple techniques to precisely measure the blaze of our in-house fabricated immersion gratings. The first method uses a scanning electron microscope to image the blaze profile, which yields a measurement precision of 0.5 degrees. The second method is an optical method of measuring the angle between blaze faces using a rotation stage, which yields a measurement precision of 0.2 degrees. Finally, we describe a theoretical blaze function modeling method, which we expect to yield a measurement precision of 0.1 degrees. With these methods, we can quantify the accuracy with which the wet etching produces the required blaze and further optimize grating and grism efficiencies.

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arXiv2020

Ghosts of NEID's Past

The NEID spectrograph is a R $\sim$ 120,000 resolution fiber-fed and highly stabilized spectrograph for extreme radial velocity (RV) precision. It is being commissioned at the 3.5 m WIYN telescope in Kitt Peak National Observatory with a desired instrumental precision of better than 30 \cms{}. NEID's bandpass of 380 -- 930 nm enables the simultaneous wavelength coverage of activity indicators from the Ca HK lines in the blue to the Ca IR triplet in the IR. In this paper we will present our efforts to characterize and mitigate optical ghosts in the NEID spectrograph during assembly, integration and testing, and highlight several of the dominant optical element contributors such as the cross dispersion prism and input optics. We shall present simulations of the 2-D spectrum and discuss the predicted ghost features on the focal plane, and how they may impact the RV performance for NEID. We also present the mitigation strategy adopted for each ghost which may be applied to future instrument designs. This work will enable other instrument builders to potentially avoid some of these issues, as well as outline mitigation strategies.

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arXiv2020

Evidence for He I 10830 Å~ absorption during the transit of a warm Neptune around the M-dwarf GJ 3470 with the Habitable-zone Planet Finder

Understanding the dynamics and kinematics of out-flowing atmospheres of hot and warm exoplanets is crucial to understanding the origins and evolutionary history of the exoplanets near the evaporation desert. Recently, ground based measurements of the meta-stable Helium atom's resonant absorption at 10830 Å~has become a powerful probe of the base environment which is driving the outflow of exoplanet atmospheres. We report evidence for the He I 10830 Å~in absorption (equivalent width $\sim$ $0.012 \pm 0.002$ Å) in the exosphere of a warm Neptune orbiting the M-dwarf GJ 3470, during three transits using the Habitable Zone Planet Finder (HPF) near infrared spectrograph. This marks the first reported evidence for He I 10830 Å\, atmospheric absorption for a planet orbiting an M-dwarf. Our detected absorption is broad and its blueshifted wing extends to -36 km/sec, the largest reported in the literature to date. We modelled the state of Helium atoms in the exosphere of GJ3470b based on assumptions on the UV and X-ray flux of GJ 3470, and found our measurement of flux-weighted column density of meta-stable state Helium $(N_{He^2_3S} = 2.4 \times 10^{10} \mathrm{cm^{-2}})$, derived from our transit observations, to be consistent with model, within its uncertainties. The methodology developed here will be useful to study and constrain the atmospheric outflow models of other exoplanets like GJ 3470b which are near the edge of the evaporation desert.

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arXiv2019

A sub-Neptune sized planet transiting the M2.5-dwarf G 9-40: Validation with the Habitable-zone Planet Finder

We validate the discovery of a 2 Earth radii sub-Neptune-size planet around the nearby high proper motion M2.5-dwarf G 9-40 (EPIC 212048748), using high-precision near-infrared (NIR) radial velocity (RV) observations with the Habitable-zone Planet Finder (HPF), precision diffuser-assisted ground-based photometry with a custom narrow-band photometric filter, and adaptive optics imaging. At a distance of $d=27.9\mathrm{pc}$, G 9-40b is the second closest transiting planet discovered by K2 to date. The planet's large transit depth ($\sim$3500ppm), combined with the proximity and brightness of the host star at NIR wavelengths (J=10, K=9.2) makes G 9-40b one of the most favorable sub-Neptune-sized planet orbiting an M-dwarf for transmission spectroscopy with JWST, ARIEL, and the upcoming Extremely Large Telescopes. The star is relatively inactive with a rotation period of $\sim$29 days determined from the K2 photometry. To estimate spectroscopic stellar parameters, we describe our implementation of an empirical spectral matching algorithm using the high-resolution NIR HPF spectra. Using this algorithm, we obtain an effective temperature of $T_{\mathrm{eff}}=3404\pm73$K, and metallicity of $\mathrm{[Fe/H]}=-0.08\pm0.13$. Our RVs, when coupled with the orbital parameters derived from the transit photometry, exclude planet masses above $11.7 M_\oplus$ with 99.7% confidence assuming a circular orbit. From its radius, we predict a mass of $M=5.0^{+3.8}_{-1.9} M_\oplus$ and an RV semi-amplitude of $K=4.1^{+3.1}_{-1.6}\mathrm{m\:s^{-1}}$, making its mass measurable with current RV facilities. We urge further RV follow-up observations to precisely measure its mass, to enable precise transmission spectroscopic measurements in the future.

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arXiv2019

Ultra-Stable Environment Control for the NEID Spectrometer: Design and Performance Demonstration

Two key areas of emphasis in contemporary experimental exoplanet science are the detailed characterization of transiting terrestrial planets, and the search for Earth analog planets to be targeted by future imaging missions. Both of these pursuits are dependent on an order-of-magnitude improvement in the measurement of stellar radial velocities (RV), setting a requirement on single-measurement instrumental uncertainty of order 10 cm/s. Achieving such extraordinary precision on a high-resolution spectrometer requires thermo-mechanically stabilizing the instrument to unprecedented levels. Here, we describe the Environment Control System (ECS) of the NEID Spectrometer, which will be commissioned on the 3.5 m WIYN Telescope at Kitt Peak National Observatory in 2019, and has a performance specification of on-sky RV precision < 50 cm/s. Because NEID's optical table and mounts are made from aluminum, which has a high coefficient of thermal expansion, sub-milliKelvin temperature control is especially critical. NEID inherits its ECS from that of the Habitable-zone Planet Finder (HPF), but with modifications for improved performance and operation near room temperature. Our full-system stability test shows the NEID system exceeds the already impressive performance of HPF, maintaining vacuum pressures below $10^{-6}$ Torr and an RMS temperature stability better than 0.4 mK over 30 days. Our ECS design is fully open-source; the design of our temperature-controlled vacuum chamber has already been made public, and here we release the electrical schematics for our custom Temperature Monitoring and Control (TMC) system.

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arXiv2019

Stellar Spectroscopy in the Near-infrared with a Laser Frequency Comb

The discovery and characterization of exoplanets around nearby stars is driven by profound scientific questions about the uniqueness of Earth and our Solar System, and the conditions under which life could exist elsewhere in our Galaxy. Doppler spectroscopy, or the radial velocity (RV) technique, has been used extensively to identify hundreds of exoplanets, but with notable challenges in detecting terrestrial mass planets orbiting within habitable zones. We describe infrared RV spectroscopy at the 10 m Hobby-Eberly telescope that leverages a 30 GHz electro-optic laser frequency comb with nanophotonic supercontinuum to calibrate the Habitable Zone Planet Finder spectrograph. Demonstrated instrument precision <10 cm/s and stellar RVs approaching 1 m/s open the path to discovery and confirmation of habitable zone planets around M-dwarfs, the most ubiquitous type of stars in our Galaxy.

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arXiv2018

Overview of the spectrometer optical fiber feed for the Habitable-zone Planet Finder

The Habitable-zone Planet Finder (HPF) is a highly stabilized fiber fed precision radial velocity (RV) spectrograph working in the Near Infrared (NIR): 810 - 1280 nm . In this paper we present an overview of the preparation of the optical fibers for HPF. The entire fiber train from the telescope focus down to the cryostat is detailed. We also discuss the fiber polishing, splicing and its integration into the instrument using a fused silica puck. HPF was designed to be able to operate in two modes, High Resolution (HR- the only mode mode currently commissioned) and High Efficiency (HE). We discuss these fiber heads and the procedure we adopted to attach the slit on to the HR fibers.

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