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Time-variable absorption by water vapor in Earth’s atmosphere presents an important source of systematic error for a wide range of ground-based astronomical measurements, particularly at near-infrared wavelengths. We present results from the first study on the temporal and spatial variability of water vapor absorption at Apache Point Observatory (APO). We analyze ∼400,000 high-resolution, near-infrared (H-band) spectra of hot stars collected as calibration data for the APO Galactic Evolution Experiment (APOGEE) survey. We fit for the optical depths of telluric water vapor absorption features in APOGEE spectra and convert these optical depths to Precipitable Water Vapor (PWV) using contemporaneous data from a GPS-based PWV monitoring station at APO. Based on simultaneous measurements obtained over a 3° field of view, we estimate that our PWV measurement precision is ±0.11 mm. We explore the statistics of PWV variations over a range of timescales from less than an hour to days. We find that the amplitude of PWV variations within an hour is less than 1 mm for most (96.5%) APOGEE field visits. By considering APOGEE observations that are close in time but separated by large distances on the sky, we find that PWV is homogeneous across the sky at a given epoch, with 90% of measurements taken up to 70° apart within 1.5 hr having ΔPWV < 1.0 mm. Our results can be used to help simulate the impact of water vapor absorption on upcoming surveys at continental observing sites like APO, and also to help plan for simultaneous water vapor metrology that may be carried out in support of upcoming photometric and spectroscopic surveys.

Precise near-infrared radial velocimetry enables efficient detection and transit verification of low-mass extrasolar planets orbiting M-dwarf hosts, which are faint for visible-wavelength radial velocity surveys. The TripleSpec Exoplanet Discovery Instrument (TEDI) is the combination of a variable-delay Michelson interferometer and a medium-resolution ( R = 2700 R = 2700 ) near-infrared spectrograph on the Palomar 200 inch (5 m) Hale Telescope. We used TEDI to monitor GJ 699, a nearby mid-M dwarf, over 11 nights spread across 3 months. Analysis of 106 independent observations reveals a root-mean-squared precision of less than37 m s-1 37     m   s - 1 for 5 minutes of integration time. This performance is within a factor of 2 of our expected photon-limited precision. We further decompose the residuals into a33 m s-1 33     m   s - 1 white noise component and a15 m s-1 15     m   s - 1 systematic noise component, which we identify as being likely due to contamination by telluric absorption lines. With further development this technique holds promise for broad implementation on medium-resolution near-infrared spectrographs to search for low-mass exoplanets orbiting M dwarfs and to verify low-mass transit candidates.

Time-variable absorption by water vapor in Earth's atmosphere presents an important source of systematic error for a wide range of ground-based astronomical measurements, particularly at near-infrared wavelengths. We present results from the first study on the temporal and spatial variability of water vapor absorption at Apache Point Observatory (APO). We analyze ∼400,000 high-resolution, near-infrared (H-band) spectra of hot stars collected as calibration data for the APO Galactic Evolution Experiment (APOGEE) survey. We fit for the optical depths of telluric water vapor absorption features in APOGEE spectra and convert these optical depths to Precipitable Water Vapor (PWV) using contemporaneous data from a GPS-based PWV monitoring station at APO. Based on simultaneous measurements obtained over a 3° field of view, we estimate that our PWV measurement precision is 0.11 mm. We explore the statistics of PWV variations over a range of timescales from less than an hour to days. We find that the amplitude of PWV variations within an hour is less than 1 mm for most (96.5%) APOGEE field visits. By considering APOGEE observations that are close in time but separated by large distances on the sky, we find that PWV is homogeneous across the sky at a given epoch, with 90% of measurements taken up to 70° apart within 1.5 hr having ΔPWV < 1.0 mm. Our results can be used to help simulate the impact of water vapor absorption on upcoming surveys at continental observing sites like APO, and also to help plan for simultaneous water vapor metrology that may be carried out in support of upcoming photometric and spectroscopic surveys.

The discovery of Earth-like exoplanets has profound implications for our understanding of the origins and diversity of life in our universe. As such, developing new and improved Doppler radial velocity (RV) spectrometers capable of discovering and characterizing these planets is a high priority in the astronomical community. However, detection of true Earth-analogs remains beyond the technical reach of current Doppler RV instruments. This thesis discusses a number of technological developments designed specifically to overcome classical instrumental limitations of high precision Doppler RV measurements. These technologies are essential components of next generation instruments that aim to achieve the RV precision necessary to detect low-mass planets. This instrumentation research is driven by the development of the Habitable-zone Planet Finder (HPF), a near-infrared (NIR) Doppler spectrograph currently under development at Penn State that will detect terrestrial-mass planets orbiting nearby M-dwarfs. Furthermore, many technologies discussed will also be applied to the NASA-NSF Extreme Precision Doppler Spectrometer concept NEID, a Doppler RV instrument for the 3.5 meter WIYN telescope, slated for delivery in 2019. NEID is an ultra-stable, high resolution optical spectrometer also under development at Penn State. This thesis describes new specialized optical fiber delivery systems, designed to significantly improve instrument illumination stability, modal noise suppression systems, which suppress mode interference in optical fibers and allow spectrometers to fully realize the exquisite precision of modern wavelength calibration sources, and new photonic calibration sources, which show significant promise as potential Doppler wavelength references. These technologies represent important steps in enabling next generation instruments to reach precisions sufficient to detect terrestrial-mass planets orbiting in the Habitable-zones of nearby stars. Improving measurement capabilities in both the optical and NIR is not only essential for enabling precision RV studies on a wide variety of stars, but can also aid in disentangling stellar activity signals from true reflex motion. Beyond independent planet discoveries, these instruments will be indispensable tools for measuring masses and densities of planets identified by future space observatories, and play key roles in directing future atmospheric characterization studies with the James Webb Space Telescope.

Transmission spectroscopy allows us to detect molecules in planetary atmospheres, but is subject to contamination from inhomogeneities on the stellar surface. Quantifying the extent of this contamination is essential for accurate measurements of atmospheric composition, as stellar activity can manifest as false atmospheric signals in planetary transmission spectra. We present a study of hot Jupiter HD 189733b, which has over 50 hours of JWST observations scheduled or taken, to measure the activity level of the host star at the current epoch. We utilize high-resolution spectra of the H\\(\\) line from the MEGARA spectrograph on the 10-m GTC to examine the activity level of HD 189733 during a transit. We measure H\\(\\) becoming shallower mid-transit by an H\\(\\) index of \\(\\) = 0.00156 \\(\\) 0.00026, which suggests that HD 189733b crosses an active region as it transits. We posit this deviation is likely caused by a spot along the transit chord with an approximate radius of \\(R_spot\\) = 3.47 \\(\\) 0.30R\\(\\) becoming occulted during transit. Including an approximation for unocculted spots, we estimate that this spot could result in transit depth variations of \\(\\)17 ppm at the 4.3 micron CO2 feature. Since this is comparable to JWST NIRCam Grism mode's noise floor of \\(\\)20 ppm, it could bias atmospheric studies by altering the inferred depths of the planet's features. Thus, we suggest ground-based high-resolution monitoring of activity indicator species concurrently taken with JWST data when feasible to disentangle stellar activity signals from planetary atmospheric signals during transit.

Although many cases of stellar spin-orbit misalignment are known, it is usually unclear whether a single planet's orbit was tilted or if the entire protoplanetary disk was misaligned. Measuring stellar obliquities in multi-transiting planetary systems helps to distinguish these possibilities. Here, we present a measurement of the sky-projected spin-orbit angle for TOI-880 c (TOI-880.01), a member of a system of three transiting planets, using the Keck Planet Finder (KPF). We found that the host star is a K-type star (\\(T_ eff=5050 100\\) K). Planet b (TOI-880.02) has a radius of \\(2.190.11R_\\) and an orbital period of \\(2.6\\) days; planet c (TOI-880.01) is a Neptune-sized planet with \\(4.950.20R_\\) on a \\(6.4\\)-day orbit; and planet d (TOI-880.03) has a radius of \\(3.40_-0.21^+0.22R_\\) and a period of \\(14.3\\) days. By modeling the Rossiter-McLaughlin (RM) effect, we found the sky-projected obliquity to be$|\\lambda_c| = 7.4_{-7.2}^{+6.8}$ $^{\\circ}\\(, consistent with a prograde, well-aligned orbit. The lack of detectable rotational modulation of the flux of the host star and a low \\)\\rm v\\sin{i_\\star}\\( (1.6~km/s) imply slow rotation and correspondingly slow nodal precession of the planetary orbits and the expectation that the system will remain in this coplanar configuration. TOI-880 joins a growing sample of well-aligned, coplanar, multi-transiting systems. Additionally, TOI-880 c is a promising target for JWST follow-up, with a transmission spectroscopy metric (TSM) of \\)\\sim 170\\(. We could not detect clear signs of atmospheric erosion in the H\\)\\alpha$line from TOI-880 c, as photoevaporation might have diminished for this mature planet.

We report the discovery of TOI-4127 b, a transiting, Jupiter-sized exoplanet on a long-period (\\(P = 56.39879^+0.00010_-0.00010\\) d), high-eccentricity orbit around a late F-type dwarf star. This warm Jupiter was first detected and identified as a promising candidate from a search for single-transit signals in TESS Sector 20 data, and later characterized as a planet following two subsequent transits (TESS Sectors 26 and 53) and follow-up ground-based RV observations with the NEID and SOPHIE spectrographs. We jointly fit the transit and RV data to constrain the physical (\\(R_p = 1.096^+0.039_-0.032 R_J\\), \\(M_p = 2.30^+0.11_-0.11 M_J\\)) and orbital parameters of the exoplanet. Given its high orbital eccentricity (\\(e=0.7471^+0.0078_-0.0086\\)), TOI-4127 b is a compelling candidate for studies of warm Jupiter populations and of hot Jupiter formation pathways. We show that the present periastron separation of TOI-4127 b is too large for high-eccentricity tidal migration to circularize its orbit, and that TOI-4127 b is unlikely to be a hot Jupiter progenitor unless it is undergoing angular momentum exchange with an undetected outer companion. Although we find no evidence for an external companion, the available observational data are insufficient to rule out the presence of a perturber that can excite eccentricity oscillations and facilitate tidal migration.

We present high-resolution observations of a flaring event in the M8 dwarf vB 10 using the near-infrared Habitable zone Planet Finder (HPF) spectrograph on the Hobby Eberly Telescope (HET). The high stability of HPF enables us to accurately subtract a VB 10 quiescent spectrum from the flare spectrum to isolate the flare contributions, and study the changes in the relative energy of the Ca II infrared triplet (IRT), several Paschen lines, the He 10830 \\AA~ triplet lines, and select iron and magnesium lines in HPF`s bandpass. Our analysis reveals the presence of a red asymmetry in the He 10830 \\AA~ triplet; which is similar to signatures of coronal rain in the Sun. Photometry of the flare derived from an acquisition camera before spectroscopic observations, and the ability to extract spectra from up-the-ramp observations with the HPF infrared detector, enables us to perform time-series analysis of part of the flare, and provide coarse constraints on the energy and frequency of such flares. We compare this flare with historical observations of flares around vB 10 and other ultracool M dwarfs, and attempt to place limits on flare-induced atmospheric mass loss for hypothetical planets around vB 10.

The NEID Earth Twin Survey (NETS) has been delivering a rich set of precise radial velocity (RV) measurements for 41 bright, nearby main sequence stars. Here, we describe the status of the survey after three years on sky and we present the full set of RV measurements and accompanying stellar activity indicators. We discuss intermediate survey diagnostics, including calibration of the known RV zero point offset introduced following the Contreras fire in 2022 and the identification of an undiagnosed and previously unknown zero point offset in 2021. An analysis of our data set using RVSearch demonstrates that for these target stars, NEID is independently sensitive to nearly all known planets with periods shorter than the NETS observing baseline. We also highlight a number of newly detected RV signals, which present exciting opportunities for future investigations.

We confirm the planetary nature of TOI-532b, using a combination of precise near-infrared radial velocities with the Habitable-zone Planet Finder, TESS light curves, ground based photometric follow-up, and high-contrast imaging. TOI-532 is a faint (J\\(\\sim 11.5\\)) metal-rich M dwarf with Teff = \\(3957\\pm69\\) K and [Fe/H] = \\(0.38\\pm0.04\\); it hosts a transiting gaseous planet with a period of \\(\\sim 2.3\\) days. Joint fitting of the radial velocities with the TESS and ground-based transits reveal a planet with radius of \\(5.82\\pm0.19\\) R\\(_{\\oplus}\\), and a mass of \\(61.5_{-9.3}^{+9.7}\\) M\\(_{\\oplus}\\). 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.