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DOE OSTI2020

Exoplanet Sciences with Nulling Interferometers and a Single-mode Fiber-fed Spectrograph

Understanding the atmospheres of exoplanets is a milestone to decipher their formation history and potential habitability. High-contrast imaging and spectroscopy of exoplanets is the major pathway toward the goal. Direct imaging of an exoplanet requires high spatial resolution. Interferometry has proven to be an effective way of improving spatial resolution. However, means of combining interferometry, high-contrast imaging, and high-resolution spectroscopy have been rarely explored. To fill in the gap, we present the dual-aperture fiber nuller (FN) for current-generation 8–10 m telescopes, which provides the necessary spatial and spectral resolution to (1) conduct follow-up spectroscopy of known exoplanets and (2) detect planets in debris-disk systems. The concept of feeding an FN to a high-resolution spectrograph can also be used for future space and ground-based missions. We present a case study of using the dual-aperture FN to search for biosignatures in rocky planets around M stars for a future space interferometry mission. Moreover, we discuss how an FN can be equipped on future extremely large telescopes by using the Giant Magellan Telescope as an example.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2020

KELT-11 b: Abundances of Water and Constraints on Carbon-bearing Molecules from the Hubble Transmission Spectrum

In the past decade, the analysis of exoplanet atmospheric spectra has revealed the presence of water vapor in almost all the planets observed, with the exception of a fraction of overcast planets. Indeed, water vapor presents a large absorption signature in the wavelength coverage of the Hubble Space Telescope’s (HST) Wide Field Camera 3 (WFC3), which is the main space-based observatory for atmospheric studies of exoplanets, making its detection very robust. However, while carbon-bearing species such as methane, carbon monoxide, and carbon dioxide are also predicted from current chemical models, their direct detection and abundance characterization has remained a challenge. Here we analyze the transmission spectrum of the puffy, clear hot-Jupiter KELT-11 b from the HST WFC3 camera. We find that the spectrum is consistent with the presence of water vapor and an additional absorption at longer wavelengths than 1.5 μm, which could well be explained by a mix of carbon bearing molecules. CO{sub 2}, when included is systematically detected. One of the main difficulties to constrain the abundance of those molecules is their weak signatures across the HST WFC3 wavelength coverage, particularly when compared to those of water. Through a comprehensive retrieval analysis, we attempt to explain the main degeneracies present in this data set and explore some of the recurrent challenges that are occurring in retrieval studies (e.g., the impact of model selection, the use of free versus self-consistent chemistry, and the combination of instrument observations). Our results make this planet an exceptional example of a chemical laboratory to test current physical and chemical models of the atmospheres of hot Jupiters.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2011

Vacuum Nuller Testbed Performance, Characterization and Null Control

The Visible Nulling Coronagraph (VNC) can detect and characterize exoplanets with filled, segmented and sparse aperture telescopes, thereby spanning the choice of future internal coronagraph exoplanet missions. NASA/Goddard Space Flight Center (GSFC) has developed a Vacuum Nuller Testbed (VNT) to advance this approach, and assess and advance technologies needed to realize a VNC as a flight instrument. The VNT is an ultra-stable testbed operating at 15 Hz in vacuum. It consists of a MachZehnder nulling interferometer; modified with a "W" configuration to accommodate a hexpacked MEMS based deformable mirror (DM), coherent fiber bundle and achromatic phase shifters. The 2-output channels are imaged with a vacuum photon counting camera and conventional camera. Error-sensing and feedback to DM and delay line with control algorithms are implemented in a real-time architecture. The inherent advantage of the VNC is that it is its own interferometer and directly controls its errors by exploiting images from bright and dark channels simultaneously. Conservation of energy requires the sum total of the photon counts be conserved independent of the VNC state. Thus sensing and control bandwidth is limited by the target stars throughput, with the net effect that the higher bandwidth offloads stressing stability tolerances within the telescope. We report our recent progress with the VNT towards achieving an incremental sequence of contrast milestones of 10(exp 8) , 10(exp 9) and 10(exp 10) respectively at inner working angles approaching 2A/D. Discussed will be the optics, lab results, technologies, and null control. Shown will be evidence that the milestones have been achieved.

Lyon, R. G.↗

NASA NTRS2011

Advancing Technology for Starlight Suppression via an External Occulter

External occulters provide the starlight suppression needed for detecting and characterizing exoplanets with a much simpler telescope and instrument than is required for the equivalent performing coronagraph. In this paper we describe progress on our Technology Development for Exoplanet Missions project to design, manufacture, and measure a prototype occulter petal. We focus on the key requirement of manufacturing a precision petal while controlling its shape within precise tolerances. The required tolerances are established by modeling the effect that various mechanical and thermal errors have on scatter in the telescope image plane and by suballocating the allowable contrast degradation between these error sources. We discuss the deployable starshade design, representative error budget, thermal analysis, and prototype manufacturing. We also present our meteorology system and methodology for verifying that the petal shape meets the contrast requirement. Finally, we summarize the progress to date building the prototype petal.

high-contrast imaging↗

NASA NTRS2019

Rethinking CO Antibiosignatures in the Search for Life Beyond the Solar System

Some atmospheric gases have been proposed as counter indicators to the presence of life on an exoplanet if remotely detectable at sufficient abundance (i.e., antibiosignatures), informing the search for biosignatures and potentially fingerprinting uninhabited habitats. However, the quantitative extent to which putative antibiosignatures could exist in the atmospheres of inhabited planets is not well understood. The most commonly referenced potential antibiosignature is CO, because it represents a source of free energy and reduced carbon that is readily exploited by life on Earth and is thus often assumed to accumulate only in the absence of life. Yet, biospheres actively produce CO through biomass burning, photooxidation processes, and release of gases that are photochemically converted into CO in the atmosphere. We demonstrate with a 1D ecosphere-atmosphere model that reducing biospheres can maintain CO levels of approximately 100 ppmv (parts per million by volume) even at low H2 fluxes due to the impact of hybrid photosynthetic ecosystems. Additionally, we show that photochemistry around M dwarf stars is particularly favorable for the buildup of CO, with plausible concentrations for inhabited, oxygen-rich planets extending from hundreds of ppm to several percent. Since CH4 buildup is also favored on these worlds, and because O2 and O3 are likely not detectable with the James Webb Space Telescope, the presence of high CO (greater than 100 ppmv) may discriminate between oxygen-rich and reducing biospheres with near-future transmission observations. These results suggest that spectroscopic detection of CO can be compatible with the presence of life and that a comprehensive contextual assessment is required to validate the significance of potential antibiosignatures.

Earth↗

NASA NTRSDate not supplied

Habitability of Cloudy Worlds: Intersecting Constraints and Unknowns

"Follow the water" has long been a theme of astrobiology. Where there are terrestrial worlds with water, there are likely to be clouds. Earth's clouds carry active microbes, in addition to inactive life that comprises a significant minority of dry dust. Both Venus and Mars are believed to have had significant early water; on Venus, the limited water retained in the clouds has been suggested as a potential refuge for life, a parallel to Mars's subsurface water. Conversely, as microbes on Earth do not stay airborne for very long, a hypothetical exoplanet with more persistent cloud cover could be even more favorable to an airborne biosphere than Earth. Airborne microbiology is significant at a planetary scale for Earth. Effects include weather (microbes as condensation and ice nuclei), climate (alteration of cloud and surface albedo), and water and air chemistry (through metabolic processing). Some of these effects, if present on exoplanets, could be detectable through remote observation. Understanding the parameters that constrain the habitability of clouds is therefore necessary to help guide the search for life. Paper includes the extended abstract.

Habitability↗

NASA NTRSDate not supplied

Leveraging the Roman Coronagraph Approach for the HWO Error Budget

The Habitable Worlds Observatory (HWO) is currently being considered as a future, coronagraph-equipped space telescope that would fulfill the top priority of Astro-2020. The top priority stated is the building of a telescope capable of detecting and characterizing exoplanets with sensitivity down to Earth-like planets. In a coronagraph approach, the methodology for setting up the error budget and performance model can benefit directly from the Nancy Grace Roman Space Telescope (RST) experience. RST’s Coronagraph Instrument (CGI) is a direct precursor to the HWO coronagraph, with performance reaching below 10 −7 in contrast demonstrated in very recent thermal-vac testing, and the possibility that it will perform better with more time on orbit. The RST CGI development benefited significantly from an error budget approach and analytical model focused on the noise incurred in measuring a planet’s flux ratio. In this brief paper we outline the current state of the application of the Roman approach to an HWO flux ratio noise error budget, including reasonable allocations informed by the Roman experience, and recent studies of narrow angle scatter done independently.

Bijan Nemati↗

NASA NTRS2018

HOMES: Holographic Method for Exoplanet Spectroscopy

The search for habitable exoplanets in the "neighborhood," that is within 10 parsecs (pc),invites new observational techniques, because telescopes available today have significant limitations. For example, gravitational micro-lensing is a deep field method that has little or no utility within 10 pc. Photometry of transits reduces the availability of exoplanets to a probability of approximately a 1%, and fewer than 1 out of 100 earth twins would ever be seen. For the 1% of exoplanets seen in transit, spectra of albedos cannot be taken.Even more limiting, Doppler shift studies are indirect and cannot characterize exoplanets other than by their orbits and masses through stellar radial velocity (RV). Moreover, RV by Doppler shift cannot detect planets in orbits on a plane perpendicular to our line of sight. Astrometry can be used to measure stellar orbital wobble for those exoplanetary systems in the plane perpendicular to our line of sight, as was contemplated for the cancelled NASA SIM mission 1 and rests now with ESA's GAIA2. In either case, the exoplanets detected by stellar RV or astrometry would not be directly observed, so the assumption that the three phases of water could exist does not answer a key question of habitability. Is there water on the exoplanet? Moreover, the discovery of water on an exoplanet in the habitable zone, exciting though it would be, is insufficient to determine just how habitable the exoplanet might possibly be. Like Goldilocks' porridge - there are many other ingredients beyond water alone in a life-sustaining soup.We propose a new species of optical telescope that has as one of its capabilities the high resolution spectrographic characterization of exoplanets on stars within 10 pc of the observatory. To achieve this performance specification, we propose to break with convention by taking advantage of an optical technology unknown until relatively recent times: the hologram. In this Report we show how holograms used in primary and secondary can extract spectrograms from exoplanets at distances reaching 33 light years from our solar system. We describe a notional space telescope using these novel optics that could make its observations in a space deployment scenario.

Ditto, Thomas↗

NASA NTRS2022

Three New Brown Dwarfs and A Massive Hot Jupiter Revealed By TESS Around Early-Type Stars

Context. The detection and characterization of exoplanets and brown dwarfs around massive AF-type stars is essential to investigate and constrain the impact of stellar mass on planet properties. However, such targets are still poorly explored in radial velocity (RV) surveys because they only feature a small number of stellar lines and those are usually broadened and blended by stellar rotation as well as stellar jitter. As a result, the available information about the formation and evolution of planets and brown dwarfs around hot stars is limited. Aims. We aim to increase the sample and precisely measure the masses and eccentricities of giant planets and brown dwarfs transiting early-type stars detected by the Transiting Exoplanet Survey Satellite (TESS). Methods. We followed bright (V < 12 mag) stars with T eff > 6200 K that host giant companions (R > 7 R ⊕ ) using ground-based photometric observations as well as high precision radial velocity measurements from the CORALIE, CHIRON, TRES, FEROS, and MINERVA-Australis spectrographs. Results. In the context of the search for exoplanets and brown dwarfs around early-type stars, we present the discovery of three brown dwarf companions, TOI-629b, TOI-1982b, and TOI-2543b, and one massive planet, TOI-1107b. From the joint analysis of TESS and ground-based photometry in combination with high precision radial velocity measurements, we find the brown dwarfs have masses between 66 and 68 M Jup , periods between 7.54 and 17.17 days, and radii between 0.95 and 1.11 R Jup . The hot Jupiter TOI-1107b has an orbital period of 4.08 days, a radius of 1.30 R Jup , and a mass of 3.35 M Jup . As a by-product of this program, we identified four low-mass eclipsing components (TOI-288b, TOI-446b, TOI-478b, and TOI-764b). Conclusions. Both TOI-1107b and TOI-1982b present an anomalously inflated radius with respect to the age of these systems. TOI-629 is among the hottest stars with a known transiting brown dwarf. TOI-629b and TOI-1982b are among the most eccentric brown dwarfs. The massive planet and the three brown dwarfs add to the growing population of well-characterized giant planets and brown dwarfs transiting AF-type stars and they reduce the apparent paucity.

brown dwarfs↗

NASA NTRS2017

Atmospheric Beacons of Life from Exoplanets Around G and K Stars

The current explosion in detection and characterization of thousands of extrasolar planets from the Kepler mission, the Hubble Space Telescope, and large ground-based telescopes opens a new era in searches for Earth-analog exoplanets with conditions suitable for sustaining life. As more Earth-sized exoplanets are detected in the near future, we will soon have an opportunity to identify habitale worlds. Which atmospheric biosignature gases from habitable planets can be detected with our current capabilities? The detection of the common biosignatures from nitrogen-oxygen rich terrestrial-type exoplanets including molecular oxygen (O2), ozone (O3), water vapor (H2O), carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) requires days of integration time with largest space telescopes, and thus are very challenging for current instruments. In this paper we propose to use the powerful emission from rotational-vibrational bands of nitric oxide, hydroxyl and molecular oxygen as signatures of nitrogen, oxygen, and water rich atmospheres of terrestrial type exoplanets "highlighted" by the magnetic activity from young G and K main-sequence stars. The signals from these fundamental chemical prerequisites of life we call atmospheric "beacons of life" create a unique opportunity to perform direct imaging observations of Earth-sized exoplanets with high signal-to-noise and low spectral resolution with the upcoming NASA missions.

exoplanets↗

NASA NTRS2008

The Mid-infrared Spectrum of the Transiting Exoplanet HD 209458b

We report the spectroscopic detection of mid-infrared emission from the transiting exoplanet HD 209458b. Using archive data taken with the Spitzer IRS instrument, we have determined the spectrum of HD 209458b between 7.46 and 15.25 micrometers. We have used two independent methods to determine the planet spectrum, one differential in wavelength and one absolute, and find the results are in good agreement. Over much of this spectral range, the planet spectrum is consistent with featureless thermal emission. Between 7.5 and 8.5 m, we find evidence for an unidentified spectral feature. If this spectral modulation is due to absorption, it implies that the dayside vertical temperature profile of the planetary atmosphere is not entirely isothermal. Using the IRS data, we have determined the broadband eclipse depth to be 0:00315 +/- 0:000315, implying significant redistribution of heat from the dayside to the nightside. This work required the development of improved methods for Spitzer IRS data calibration that increase the achievable absolute calibration precision and dynamic range for observations of bright point sources.

data analysis↗

NASA NTRS2019

Prospects for TTV Detection and Dynamical Constraints with TESS

We consider the potential for the Transiting Exoplanet Survey Satellite (TESS) to detect transit timing variations (TTVs) during both its nominal and extended mission phases. Building on previous estimates of the overall yield of planetary systems from the TESS mission, we predict that during its nominal two-year mission, TESS will observe measurable TTVs in ~30 systems, from which planet will get precise mass measurements from TTVs alone, ~5 planets will have significant constraints placed on their masses from TTVs, and over a dozen systems will be singly transiting TTV systems. We consider a number of different extended mission scenarios, and predict that in a typical scenario, an extended mission will allow TESS to increase the number of systems with measurable TTVs to a total of ~90, from which ~15 planets will have precise mass measurements, another ~15 will have significant constraints placed on their masses, and ~60 will be singly transiting TTV systems. We also describe how follow-up transit observations of multiplanet systems discovered by the TESS mission can be optimally planned to maximize TTV mass and eccentricity constraints.

planets↗

NASA NTRS2008

The James Webb Space Telescope and its Potential for Exoplanet Science

The James Webb Space Telescope (JWST) is a large aperture (6.5 meter), cryogenic space telescope with a suite of near and mid-infrared instruments covering the wavelength range of 0.6 microns to 28 microns. JWST s primary science goal is to detect and characterize the first galaxies. It will also study the assembly of galaxies, star formation, and the formation of evolution of planetary systems. Recent progress in hardware development for the observatory will be presented, including a discussion of the status of JWST s optical system and Beryllium mirror fabrication, progress with sunshield prototypes, and recent changes in the integration and test configuration. We also review the expected scientific performance of the observatory for observations of exosolar planets by means of transit imaging and spectroscopy and direct imaging. We also review the recent discovery of Fomalhaut B and implications for debris disk imaging nd exoplanet detection with JWST.

Clampin, Mark↗

NASA NTRS2019

Challenges and Opportunities for Ensuring Entry System Technology Readiness for Ice Giants Probe Missions

The Ice Giants represent a distinct class of planets within our solar system, and appear to be similar to most exoplanets that have been detected thus far. Exploring Ice Giants in our Solar System would allow us to better understand their formation and evolution processes, and thus help establish scientific links to exoplanets. In situ exploration using probes similar to Galileo, along with an orbiter or a relay spacecraft, will require entry followed by deployment of the descent probe containing science instruments into Uranus or Neptune atmosphere. The challenge is not in the deployment of the probe, but in the atmospheric entry prior to deployment. The entry system has to have a capable, robust and efficient ablative thermal protection system (TPS) designed to protect the descent probe from the thermal and mechanical entry loads. Although entries into Ice Giants may not be as demanding as the Galileo entry at Jupiter, the entry environments will be more severe than environments for Mars, Sample Return missions, and Venus, and will therefore require robust TPS. While Galileo Probe’s success, nearly 25 years ago, should give us confidence, the recession data from the Galileo entry informs us that the entry environment was under-predicted and the design thickness was barely adequate. The lesson learned from the Galileo probe for future Ice Giant missions will require us to be cautious and demand a more robust design. The TPS technology used on the Galileo entry system no longer exists due to atrophy of manufacturing processes. Instead of attempting to revive Galileo-legacy TPS technology, NASA invested in a new and innovative TPS called HEEET (Heat-shield for Extreme Entry Environment Technology). HEEET has been matured, and is now ready to support future missions not only to the Ice Giants but also for Venus, high-speed sample return, and Saturn probe missions. This lead talk, intended for the technology section of the workshop, will cover entry, descent, and deployment (EDD), with an emphasis on entry. A brief history of the TPS challenges for extreme entry missions will be given, along with a quick overview of the concept of operations for EDD. The development and maturation of HEEET system capability will be described. Data gathered in ground-test facilities in the US will be highlighted to show that the technology is mature and ready for Ice Giant missions. All thermal protection systems carry some risk as a result of ground test limitations and Ice Giant missions present some unique challenges. These challenges are not only technical, but also due to limitations in the currently established manufacturing and integration. In addition, the concerns that arise due to the potential for atrophy for future Ice Giant missions a decade or more from now will be analyzed. Plausible avenues for mitigation will be presented. There are two planned companion presentations by Dr. Prabhu and Dr. Hwang that will dive deeper into the challenges and opportunities. This intended talk will set the stage for their presentations.

Venkatapathy, Ethiraj↗

NASA NTRS2019

Challenges and Opportunities For Ensuring Entry System Technology Readiness For Ice Giants Probe Missions

The Ice Giants represent a distinct class of planets within our solar system, and appear to be similar to most exoplanets that have been detected thus far. Exploring Ice Giants in our Solar System would allow us to better understand their formation and evolution processes, and thus help establish scientific links to exoplanets. In situ exploration using probes similar to Galileo, along with an orbiter or a relay spacecraft, will require entry followed by deployment of the descent probe containing science instruments into Uranus or Neptune atmosphere. The challenge is not in the deployment of the probe, but in the atmospheric entry prior to deployment. The entry system has to have a capable, robust and efficient ablative thermal protection system (TPS) designed to protect the descent probe from the thermal and mechanical entry loads. Although entries into Ice Giants may not be as demanding as the Galileo entry at Jupiter, the entry environments will be more severe than environments for Mars, Sample Return missions, and Venus, and will therefore require robust TPS. While Galileo Probe’s success, nearly 25 years ago, should give us confidence, the recession data from the Galileo entry informs us that the entry environment was under predicted and the design thickness was barely adequate. The lesson learned from Galileo probe for future Ice Giant missions will require us to be cautious and demand a more robust design. The TPS technology used on Galileo entry system no longer exists due to atrophy of manufacturing processes. Instead of attempting to revive Galileo-legacy TPS technology, NASA invested in a new and innovative TPS called HEEET (Heat-shield for Extreme Entry Environment Technology). HEEET has been matured, and is now ready to support future missions not only to the Ice Giants but also for Venus, high-speed sample return, and Saturn probe missions. This lead talk, intended for the technology section of the workshop, will cover entry, descent, and deployment (EDD), with an emphasis on entry. A brief history of the TPS challenges for extreme entry missions will be given along with a quick overview of the concept of operations for EDD. The development and maturation of HEEET system capability will be described. Data gathered in ground-test facilities in the US will be highlighted to show that the technology is mature and ready for Ice Giant missions. All thermal protection systems carry some risk as a result of ground test limitations and Ice Giant missions present some unique challenges. These challenges are not only technical, but also due to limitations in the currently established manufacturing and integration. In addition, the concerns that arise due to potential for atrophy for future Ice Giant mission a decade or more from now will be analyzed. Plausible avenues for mitigation will be presented. There are two companion planned presentations by Dr. Prabhu and Dr. Hwang will dive deeper in the challenges and opportunities. This intended talk will set the stage for their presentations.

Venkatapathy, Ethiraj↗

NASA NTRS2011

Non-Detection of L-Band Line Emission from the Exoplanet HD 189733b

We attempt to confirm bright non-local thermodynamic equilibrium (non-LTE) emission from the exoplanet HD 189733b at 3.25 microns, as recently reported by Swain et al. based on observations at low spectral resolving power (lambda/delta lambda approximately equals 30). Non-LTE emission lines from gas in an exoplanet atmosphere will not be significantly broadened by collisions, so the measured emission intensity per resolution element must be substantially brighter when observed at high spectral resolving power. We observed the planet before, during, and after a secondary eclipse event at a resolving power lambda/delta lambda equals 27,000 using the NIRSPEC spectrometer on the Keck II telescope. Our spectra cover a spectral window near the peak found by Swain et al., and we compare emission cases that could account for the magnitude and wavelength dependence of the Swain et al. result with our final spectral residuals. To model the expected line emission, we use a general non-equilibrium formulation to synthesize emission features from all plausible molecules that emit in this spectral region. In every case, we detect no line emission to a high degree of confidence. After considering possible explanations for the Swain et at., results and the disparity with our own data, we conclude that an astrophysical source for the putative non-LTE emission is unlikely. We note that the wavelength dependence of the signal seen by Swain et al. closely matches the 2(sub 1/2) band of water vapor at 300 K, and we suggest that an imperfect correction for telluric water is the source of the feature claimed by Swain et al.

Mandell, Avi M.↗

DOE OSTI2021

Detection Limits of Low-mass, Long-period Exoplanets Using Gaussian Processes Applied to HARPS-N Solar Radial Velocities

Radial velocity (RV) searches for Earth-mass exoplanets in the habitable zone around Sun-like stars are limited by the effects of stellar variability on the host star. In particular, suppression of convective blueshift and brightness inhomogeneities due to photospheric faculae/plage and starspots are the dominant contribution to the variability of such stellar RVs. Gaussian process (GP) regression is a powerful tool for statistically modeling these quasi-periodic variations. We investigate the limits of this technique using 800 days of RVs from the solar telescope on the High Accuracy Radial velocity Planet Searcher for the Northern hemisphere (HARPS-N) spectrograph. These data provide a well-sampled time series of stellar RV variations. Into this data set, we inject Keplerian signals with periods between 100 and 500 days and amplitudes between 0.6 and 2.4 m s{sup −1}. We use GP regression to fit the resulting RVs and determine the statistical significance of recovered periods and amplitudes. We then generate synthetic RVs with the same covariance properties as the solar data to determine a lower bound on the observational baseline necessary to detect low-mass planets in Venus-like orbits around a Sun-like star. Our simulations show that discovering planets with a larger mass (∼0.5 m s{sup −1}) using current-generation spectrographs and GP regression will require more than 12 yr of densely sampled RV observations. Furthermore, even with a perfect model of stellar variability, discovering a true exo-Venus (∼0.1 m s{sup −1}) with current instruments would take over 15 yr. Therefore, next-generation spectrographs and better models of stellar variability are required for detection of such planets.

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

Dynamical Packing in the Habitable Zone: The Case of Beta CVn

Uncovering the occurrence rate of terrestrial planets within the habitable zone (HZ) of their host stars has been a particular focus of exoplanetary science in recent years. The statistics of these occurrence rates have largely been derived from transiting planet discoveries, and have uncovered numerous HZ planets in compact systems around M-dwarf host stars. Here we explore the width of the HZ as a function of spectral type, and the dynamical constraints on the number of stable orbits within the HZ for a given star. We show that, although the Hill radius for a given planetary mass increases with larger semimajor axis, the width of the HZ for earlier-type stars allows for more terrestrial planets in the HZ than late-type stars. In general, dynamical constraints allow ∼6 HZ Earth-mass planets for stellar masses ≳0.7M {sub ⊙}, depending on the presence of farther out giant planets. As an example, we consider the case of Beta CVn, a nearby bright solar-type star. We present 20 yr of radial velocities (RV) from the Keck/High Resolution Echelle Spectrometer (HIRES) and Automated Planet Finder (APF) instruments and conduct an injection-recovery analysis of planetary signatures in the data. Our analysis of these RV data rule out planets more massive than Saturn within 10 au of the star. These system properties are used to calculate the potential dynamical packing of terrestrial planets in the HZ and show that such nearby stellar targets could be particularly lucrative for HZ planet detection by direct imaging exoplanet missions.

79 ASTRONOMY AND ASTROPHYSICS↗