A Versatile Technique to Enable Sub-Milli-Kelvin Instrument Stability for Precise Radial Velocity Measurements: Tests With the Habitable-Zone Planet Finder*

Cañas

Wisniewski

et al. 2020

Self Cite

109

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 pc, G 9-40b is the second closest transiting planet discovered by K2 to date. The planet's large transit depth (∼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 ∼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 eff = 3404 ± 73K, and metallicity of [Fe/H] = −0.08 ± 0.13. Our RVs, when coupled with the orbital parameters derived from the transit photometry, exclude planet masses above 11.7M ⊕ with 99.7% confidence assuming a circular orbit. From its radius, we predict a mass of M = 5.0 +3.8 −1.9 M ⊕ and an RV semi-amplitude of K = 4.1 +3.1 −1.6 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.

Section: High-resolution Doppler Spectroscopymentioning

confidence: 99%

A Sub-Neptune-sized Planet Transiting the M2.5 Dwarf G 9-40: Validation with the Habitable-zone Planet Finder

Cañas

Wisniewski

et al. 2020

Self Cite

109

“…The upper and lower lids of the vacuum chamber are sealed with Viton O-rings, resulting in a total O-ring length of 20 m. This corresponds to a total gas load of 2 × 10 −5 Torr∕L∕s due to O-ring permeation, 18 assuming a standard Viton permeation rate of 2.5 × 10 −8 Torr∕L∕s∕in. 20 Based on this leak rate, as well as experience from similar vacuum chambers used by APOGEE 21 and HPF, 18 our charcoal getters are sized to maintain the vacuum pressures nominally at P < 10 −6 Torr for 3 years without saturating, so internal instrument maintenance requirements should be minimal.…”

Section: Ecs Design Conceptmentioning

confidence: 99%

“…The NEID ECS is conceptually similar to that of HPF, which has already demonstrated sub-milliKelvin temperature stability in both warm (T ∼ 300 K) and cold (T ∼ 180 K) operation (see Ref. 18, hereafter S16). The NEID design includes a number of improvements and optimizations from the HPF baseline, some of which were propagated to the final HPF ECS installation as well.…”

Section: Introductionmentioning

confidence: 99%

Ultrastable environment control for the NEID spectrometer: design and performance demonstration

Robertson

Anderson

J. Astron. Telesc. Instrum. Syst.

et al. 2019

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 thermomechanically stabilizing the instrument to unprecedented levels. 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 a root mean square (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 system.

“…From Equation 5, we estimate RV semi-amplitudes of 12.03 +9.92 −5.16 m/s and 5.29 +4.17 −2.39 m/s for K2-28b, and K2-100b, respectively. Being an M-dwarf, K2-28 will be most efficiently observed with precise ultra-stabilized near-infrared radial velocity spectrographs, including e.g., CARMENES (Quirrenbach et al 2012), the stabilized Habitable-zone Planet Finder (HPF; Mahadevan et al (2012); Stefansson et al (2016)), the Infrared Doppler Instrument (IRD) for Subaru (Kotani et al 2014), or Spirou (Artigau et al 2014. Meanwhile K2-100b would be most efficiently be observed in the optical by e.g., CARMENES (Quirrenbach et al 2012), ESPRESSO (Pepe et al 2014), EXPRES (Jurgenson et al 2016), G-CLEF (Szentgyorgyi et al 2012), HARPS (Mayor et al 2003), or NEID (Schwab et al 2016), and/or other instruments in the growing worldwide network of precision radial velocity spectrographs (Wright & Robertson 2017).…”

Section: Possibility For Future Rv Observationsmentioning

confidence: 99%

Diffuser-assisted Photometric Follow-up Observations of the Neptune-sized Planets K2-28b and K2-100b

Mahadevan

et al. 2018

Self Cite

We present precision transit observations of the Neptune-sized planets K2-28b and K2-100b, using the Engineered Diffuser on the ARCTIC imager on the ARC 3.5m Telescope at Apache Point Observatory. K2-28b is a R p = 2.56R ⊕ mini-Neptune transiting a bright (J=11.7) metal-rich M4 dwarf, offering compelling prospects for future atmospheric characterization. K2-100b is a R p = 3.45R ⊕ Neptune in the Praesepe Cluster and is one of few planets known in a cluster transiting a host star bright enough (V = 10.5) for precision radial velocity observations. Using the precision photometric capabilities of the diffuser/ARCTIC system, allows us to achieve a precision of 105 +87 −37 ppm, and 38 +21 −11 ppm in 30 minute bins for K2-28b, and K2-100b, respectively. Our jointfits to the K2 and ground-based light-curves give an order of magnitude improvement in the orbital ephemeris for both planets, yielding a timing precision of 2 min in the JWST era. Although we show that the currently available broad-band measurements of K2-28b's radius are currently too imprecise to place useful constraints on K2-28b's atmosphere, we demonstrate that JWST/NIRISS will be able to discern between a cloudy/clear atmosphere in a modest number of transit observations. Our light-curve of K2-100b marks the first transit follow-up observation of this challenging-to-observe transit, where we obtain a transit depth of 819 ± 50 ppm in the SDSS i band. We conclude that diffuser-assisted photometry can play an important role in the TESS era to perform timely and precise follow-up of the expected bounty of TESS planet candidates.