Engineering topics

Diddams, Scott A.

Publications and source records attributed to Diddams, Scott A..

6 records

DOE OSTI2021

TOI-532b: The Habitable-zone Planet Finder confirms a Large Super Neptune in the Neptune Desert orbiting a metal-rich M-dwarf host

We confirm the planetary nature of TOI-532b, using a combination of precise near-infrared radial velocities with the Habitable-zone Planet Finder, Transiting Exoplanet Survey Satellite (TESS) light curves, ground-based photometric follow up, and high-contrast imaging. TOI-532 is a faint (J ~ 11.5) metal-rich M dwarf with T{sub eff} = 3957 ± 69 K and [Fe/H] = 0.38 ± 0.04; it hosts a transiting gaseous planet with a period of ~2.3 days. Joint fitting of the radial velocities with the TESS and ground-based transits reveal a planet with radius of 5.82 ± 0.19 R {sub ⊕}, and a mass of 61.5{sub -9.3}{sup +9.7} M {sub ⊕}. TOI-532b is the largest and most massive super Neptune detected around an M dwarf with both mass and radius measurements, and it bridges the gap between the Neptune-sized planets and the heavier Jovian planets known to orbit M dwarfs. It also follows the previously noted trend between gas giants and host-star metallicity for M-dwarf planets. In addition, it is situated at the edge of the Neptune desert in the Radius–Insolation plane, helping place constraints on the mechanisms responsible for sculpting this region of planetary parameter space.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Nondetection of Helium in the Upper Atmospheres of TRAPPIST-1b, e, and f

We obtained high-resolution spectra of the ultracool M-dwarf TRAPPIST-1 during the transit of its planet “b” using two high-dispersion near-infrared spectrographs, the Infrared Doppler (IRD) instrument on the Subaru 8.2m telescope, and the Habitable Zone Planet Finder (HPF) instrument on the 10 m Hobby–Eberly Telescope. These spectroscopic observations are complemented by a photometric transit observation for planet “b” using the APO/ARCTIC, which assisted us in capturing the correct transit times for our transit spectroscopy. Using the data obtained by the new IRD and HPF observations, as well as the prior transit observations of planets “b,” “e” and “f” from IRD, we attempt to constrain the atmospheric escape of the planet using the He i triplet 10830 Å absorption line. We do not detect evidence for any primordial extended H-He atmospheres in all three planets. To limit any planet-related absorption, we place an upper limit on the equivalent widths of <7.754 mÅ for planet “b,” <10.458 mÅ for planet “e,” <4.143 mÅ for planet “f” at 95% confidence from the IRD data, and <3.467 mÅ for planet “b” at 95% confidence from HPF data. Using these limits along with a solar-like composition isothermal Parker wind model, we attempt to constrain the mass-loss rates for the three planets. For TRAPPIST-1b, our models exclude the highest possible energy-limited rate for a wind temperature <5000 K. This nondetection of extended atmospheres with low mean-molecular weights in all three planets aids in further constraining their atmospheric composition by steering the focus toward the search of high-molecular-weight species in their atmospheres.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2021

Stellar Activity Manifesting at a One-year Alias Explains Barnard b as a False Positive

Barnard’s star is among the most studied stars given its proximity to the Sun. It is often considered the radial velocity (RV) standard for fully convective stars due to its RV stability and equatorial decl. Recently, an Msin i=3.3M{sub ⊕} super-Earth planet candidate with a 233 day orbital period was announced by Ribas et al. New observations from the near-infrared Habitable-zone Planet Finder (HPF) Doppler spectrometer do not show this planetary signal. We ran a suite of experiments on both the original data and a combined original + HPF data set. These experiments include model comparisons, periodogram analyses, and sampling sensitivity, all of which show the signal at the proposed period of 233 days is transitory in nature. The power in the signal is largely contained within 211 RVs that were taken within a 1000 day span of observing. Our preferred model of the system is one that features stellar activity without a planet. We propose that the candidate planetary signal is an alias of the 145 day rotation period. This result highlights the challenge of analyzing long-term, quasi-periodic activity signals over multiyear and multi-instrument observing campaigns.

47 OTHER INSTRUMENTATION↗

DOE OSTI2021

Broadband Stability of the Habitable Zone Planet Finder Fabry–Pérot Etalon Calibration System: Evidence for Chromatic Variation

The comblike spectrum of a white light–illuminated Fabry–Pérot etalon can serve as a cost-effective and stable reference for precise Doppler measurements. Understanding the stability of these devices across their broad (hundreds of nanometers) spectral bandwidths is essential to realizing their full potential as Doppler calibrators. However, published descriptions remain limited to small bandwidths or short time spans. We present an ∼6 month broadband stability monitoring campaign of the Fabry–Pérot etalon system deployed with the near-infrared Habitable Zone Planet Finder (HPF) spectrograph. We monitor the wavelengths of each of ∼3500 resonant modes measured in HPF spectra of this Fabry–Pérot etalon (free spectral range = 30 GHz, bandwidth = 820–1280 nm), leveraging the accuracy and precision of an electro-optic frequency comb reference. These results reveal chromatic structure in the Fabry–Pérot mode locations and their evolution with time. We measure an average drift on the order of 2 cm s{sup –1} day{sup −1}, with local departures up to ±5 cm s{sup –1} day{sup −1}. We discuss these behaviors in the context of the Fabry–Pérot etalon mirror dispersion and other optical properties of the system and the implications for the use of similar systems for precise Doppler measurements. Our results show that this system supports the wavelength calibration of HPF at the ≲10 cm s{sup −1} level over a night and the ≲30 cm s{sup −1} level over ∼10 days. Our results also highlight the need for long-term and spectrally resolved study of similar systems that will be deployed to support Doppler measurement precision approaching ∼10 cm s{sup −1}.

42 ENGINEERING↗

DOE OSTI2020

A Mini-Neptune and a Radius Valley Planet Orbiting the Nearby M2 Dwarf TOI-1266 in Its Venus Zone: Validation with the Habitable-zone Planet Finder

We report on the validation of two planets orbiting the nearby (36 pc) M2 dwarf TOI-1266 observed by the TESS mission. This system is one of a few M dwarf multiplanet systems with close-in planets where the inner planet is substantially larger than the outer planet. The inner planet is sub-Neptune-sized (R = 2.46 ± 0.08 R ⊕ ) with an orbital period of 10.9 days, while the outer planet has a radius of 1.67 -0.11 +0.09 R ⊕ and resides in the exoplanet radius valley—the transition region between rocky and gaseous planets. With an orbital period of 18.8 days, the outer planet receives an insolation flux of 2.4 times that of Earth, similar to the insolation of Venus. Using precision near-infrared radial velocities with the Habitable-zone Planet Finder Spectrograph, we place upper mass limits of 15.9 and 6.4 M ⊕ at 95% confidence for the inner and outer planet, respectively. A more precise mass constraint of both planets, achievable with current radial velocity instruments given the host star brightness (V = 12.9, J = 9.7), will yield further insights into the dominant processes sculpting the exoplanet radius valley.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

The Habitable Zone Planet Finder Reveals a High Mass and Low Obliquity for the Young Neptune K2-25b

Using radial velocity data from the Habitable Zone Planet Finder, we have measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity of its M4.5 dwarf host star in the 600–800 Myr Hyades cluster. This is one of the youngest planetary systems for which both of these quantities have been measured and one of the very few M dwarfs with a measured obliquity. Based on a joint analysis of the radial velocity data, time-series photometry from the K2 mission, and new transit light curves obtained with diffuser-assisted photometry, the planet’s radius and mass are 3.44 ± 0.12 R {sub ⊕} and 24.5{sub −5.2}{sup +5.7}M{sub ⊕}. These properties are compatible with a rocky core enshrouded by a thin hydrogen–helium atmosphere (5% by mass). We measure an orbital eccentricity of e = 0.43 ± 0.05. The sky-projected stellar obliquity is λ = 3° ± 16°, compatible with spin–orbit alignment, in contrast to other “hot Neptunes” that have been studied around older stars.

79 ASTRONOMY AND ASTROPHYSICS↗