Jacob Lyle Bean

HUBBLE SPACE TELESCOPE FINE GUIDANCE SENSOR PARALLAXES OF GALACTIC CEPHEID VARIABLE STARS: PERIOD-LUMINOSITY RELATIONS ∗

We present new absolute trigonometric parallaxes and relative proper motions for nine Galactic Cepheid variable stars: l Car, ζ Gem, β Dor, W Sgr, X Sgr, Y Sgr, FF Aql, T Vul, and RT Aur. We obtain these results with astrometric data from Fine Guidance Sensor 1r, a white-light interferometer on the Hubble Space Telescope. We find absolute parallaxes in milliarcseconds: l Car, 2.01 ± 0.20 mas; ζ Gem, 2.78 ± 0.18 mas; β Dor, 3.14 ± 0.16 mas; W Sgr, 2.28 ± 0.20 mas; X Sgr, 3.00 ± 0.18 mas; Y Sgr, 2.13 ± 0.29 mas; FF Aql, 2.81 ± 0.18 mas; T Vul, 1.90 ± 0.23 mas; and RT Aur, 2.40 ± 0.19 mas; average σπ/π = 8%. Two stars (FF Aql and W Sgr) required the inclusion of binary astrometric perturbations, providing Cepheid mass estimates. With these parallaxes we compute absolute magnitudes in V, I, K, and Wesenheit WVI bandpasses, corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Adding our previous absolute magnitude determination for δ Cep, we construct period-luminosity relations (PLRs) for 10 Galactic Cepheids. We compare our new PLRs with those adopted by several recent investigations, including the Freedman and Sandage H0 projects. Adopting our PLR would tend to increase the Sandage H0 value, but leave the Freedman H0 unchanged. Comparing our Galactic Cepheid PLR with those derived from LMC Cepheids, we find the slopes for K and WVI to be identical in the two galaxies within their respective errors. Our data lead to a WVI distance modulus for the LMC m - M = 18.50 ± 0.03, uncorrected for any metallicity effects. Applying recently derived metallicity corrections yields a corrected LMC distance modulus of (m - M)0 = 18.40 ± 0.05. Comparing our PLR to solar-metallicity Cepheids in NGC 4258 results in a distance modulus 29.28 ± 0.08 that agrees with one derived from maser studies.

Accurate M DWARF metallicities from spectral synthesis : A critical test of model atmospheres

We describe a method for accurately determining M dwarf metallicities with spectral synthesis based on abundance analyses of visual binary stars. We obtained high-resolution, high-signal-to-noise ratio spectra of each component of five visual binary pairs at McDonald Observatory. The spectral types of the components range from F7 to K3 V for the primaries and from M0.5 to M3.5 V for the secondaries. We have determined the metallicities of the primaries differentially with respect to the Sun by fitting synthetic spectra to Fe I line profiles in the observed spectra. In the course of our analysis of the M dwarf secondaries, we have made significant improvements to the PHOENIX cool-star model atmospheres and the spectrum analysis code MOOG. Our analysis yields an rms deviation of 0.11 dex in metallicity values between the binary pairs. We estimate the uncertainties in the derived stellar parameters for the M dwarfs to be 48 K, 0.10 dex, 0.12 dex, 0.15 km s-1, and 0.20 km s-1 for Teff, log g, [M/H], ξ, and η, respectively. Accurate stellar evolutionary models are needed to progress further in the analysis of cool-star spectra; the new model atmospheres warrant recalculation of the evolutionary models.

A Planetary System around HD 155358: The Lowest Metallicity Planet Host Star*

We report the detection of two planetary mass companions to the solar-type star HD 155358. The two planets have orbital periods of 195.0 and 530.3 days, with eccentricities of 0.11 and 0.18. The minimum masses for these planets are 0.89 and 0.50 MJ, respectively. The orbits are close enough to each other, and the planets are sufficiently massive, that the planets are gravitationally interacting with each other, with their eccentricities and arguments of periastron varying with periods of 2300-2700 yr. While large uncertainties remain in the orbital eccentricities, our orbital integration calculations indicate that our derived orbits would be dynamically stable for at least 108 yr. With a metallicity [Fe/H] of -0.68, HD 155358 is tied with the K1 III giant planet host star HD 47536 for the lowest metallicity of any planet host star yet found. Thus, a star with only 21% of the heavy-element content of our Sun was still able to form a system of at least two Jovian-mass planets and have their orbits evolve to semimajor axes of 0.6-1.2 AU.

Metallicities of M Dwarf Planet Hosts from Spectral Synthesis

We present the first spectroscopic metallicities of three M dwarfs with known or candidate planetary mass companions. We have analyzed high-resolution, high signal-to-noise ratio spectra of these stars, which we obtained at McDonald Observatory. Our analysis technique is based on spectral synthesis of atomic and molecular features using recently revised cool-star model atmospheres and spectrum synthesis code. The technique has been shown to yield results consistent with the analyses of solar-type stars and allows measurements of M dwarf [M/H] values to 0.12 dex precision. From our analysis, we find [M/H] = -0.12, -0.32, and -0.33 for GJ 876, GJ 436, and GJ 581, respectively. These three M dwarf planet hosts have subsolar metallicities, a surprising departure from the trend observed in FGK-type stars. This study is the first part of our ongoing work to determine the metallicities of the M dwarfs included in the McDonald Observatory planet search program.

The Mass of the Candidate Exoplanet Companion to HD 33636 from Hubble Space Telescope Astrometry and High-Precision Radial Velocities

We have determined a dynamical mass for the companion to HD 33636 which indicates it is a low-mass star instead of an exoplanet. Our result is based on an analysis of Hubble Space Telescope (HST) astrometry and ground-based radial velocity data. We have obtained high-cadence radial velocity measurements spanning 1.3 years of HD 33636 with the Hobby-Eberly Telescope at McDonald Observatory. We combined these data with previously published velocities to create a data set that spans nine years. We used this data set to search for, and place mass limits on, the existence of additional companions in the HD 33636 system. Our high-precision astrometric observations of the system with the HST Fine Guidance Sensor 1r span 1.2 years. We simultaneously modeled the radial velocity and astrometry data to determine the parallax, proper motion, and perturbation orbit parameters of HD 33636. Our derived parallax, pi = 35.6 +/- 0.2 mas, agrees within the uncertainties with the Hipparcos value. We find a perturbation period P = 2117.3 +/- 0.8 days, semimajor axis a_A = 14.2 +/- 0.2 mas, and system inclination i = 4.1 +/- 0.1 deg. Assuming the mass of the primary star M_A = 1.02 +/- 0.03 M_sun, we obtain a companion mass M_B = 142 +/- 11 M_jup = 0.14 +/- 0.01 M_sun. The much larger true mass of the companion relative to its minimum mass estimated from the spectroscopic orbit parameters (M sin i = 9.3 M_jup) is due to the near face-on orbit orientation. This result demonstrates the value of follow-up astrometric observations to determine the true masses of exoplanet candidates detected with the radial velocity method.

Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope

We report the discovery of a third planetary-mass companion to the G0 star HD 74156. High-precision radial velocity measurements made with the Hobby-Eberly Telescope aided the detection of this object. The best-fit triple-Keplerian model to all the available velocity data yields an orbital period of 347 days and a minimum mass of 0.4 MJup for the new planet. We determine revised orbital periods of 51.7 and 2477 days and minimum masses of 1.9 and 8.0 MJup, respectively, for the previously known planets. Preliminary calculations indicate that the derived orbits are stable, although all three planets have significant orbital eccentricities (e = 0.64, 0.43, and 0.25). With our detection, HD 74156 becomes the eighth normal star known to host three or more planets. Further study of this systems dynamical characteristics will likely give important insight into planet formation and evolutionary processes.

The Solar Neighborhood. VII. Discovery and Characterization of Nearby Multiples in the CTIO Parallax Investigation

We report the discovery of eight new multiple star systems among 191 stellar systems targeted for parallax determinations in the RECONS (Research Consortium on Nearby Stars) southern parallax program, CTIOPI (Cerro Tololo Inter-American Observatory Parallax Investigation). The eight new companions have separations of 1>42 to 14>90 and instrumental magnitude differences at VRI of 0.06–6.07 mag. Orbital motion has not been detected in any of these systems. These new companions increase the multiplicity fraction of this sample, made up primarily of nearby (less than 25 pc) M dwarfs, to 15%. Comparison with samples that have been more completely scrutinized for companions indicates that probably only half of all multiples have so far been discovered. Given the large number of frames acquired for the astrometric series, the eight new systems and 16 known multiples have been searched for variability at VRI during the 3 year duration of CTIOPI. A flare has been detected in the secondary of the RX J1132� 264 system, while at least one component in the GJ 2006 system is a probable long-term variable. Variables were detected in only 9% of the systems searched, primarily as a result of the restrictive 0.05 mag threshold required for variability confirmation.

Detection of Stellar Pulsations in the Planet Host Star γ Cephei A by High Precision Radial Velocity Measurements

We present a first analysis of our asteroseismology campaign on the planet host star γ Cep A. We used seven consecutive nights at the Harlan J. Smith 2.7 m telescope at McDonald Observatory to obtain 1200 highly precise radial velocity measurements. We find the star to be a multi‐periodic pulsator with a frequency spacing of 15 μHz.

Time series observations with the mid-infrared instrument (MIRI) on JWST

Time-variable phenomena such as transiting exoplanets will be a major science theme for the James Webb Space Telescope (JWST). For Guaranteed Time and Early Release Science Observations, over 500 hours of JWST time have been allocated to time series observations (TSOs) of transiting exoplanets. Several dedicated observing modes are available in the instrument suite, whose operations are specifically tailored to these challenging ob- servations. MIRI, the only JWST instrument covering the wavelength range longwards of 5 µm on JWST, will offer TSOs in two of its modes: the low resolution spectrometer, and the imager. In this paper we will describe these modes for MIRI, and discuss how they differ operationally from regular (non-TSO) observations. We will show performance estimates based on ground testing and modeling, discuss the most relevant detector effects for high precision (spectro-)photometry, and provide some guidelines for planning MIRI TSOs.

The GMT-consortium large earth finder (G-CLEF): an optical echelle spectrograph for the Giant Magellan Telescope (GMT)

The GMT-Consortium Large Earth Finder (G-CLEF) is an instrument that is being designed to exceed the state-of-the-art radial velocity (RV) precision achievable with the current generation of stellar velocimeters. It is simultaneously being designed to enable a wide range of scientific programs, prominently by operating to blue wavelengths (< 3500Å). G-CLEF will be the first light facility instrument on the Giant Magellan Telescope (GMT) when the GMT is commissioned in 2023. G-CLEF is a fiber-fed, vacuum-enclosed spectrograph with an asymmetric white pupil echelle design. We discuss several innovative structural, optical and control system features that differentiate G-CLEF from previous precision RV instruments.