Automated Planet Finder Telescope Research Articles

The TESS-Keck Survey. XXII. A Sub-Neptune Orbiting TOI-1437

Exoplanet discoveries have revealed a dramatic diversity of planet sizes across a vast array of orbital architectures. Sub-Neptunes are of particular interest; due to their absence in our own solar system, we rely on demographics of exoplanets to better understand their bulk composition and formation scenarios. Here, we present the discovery and characterization of TOI-1437 b, a sub-Neptune with a 18.84 day orbit around a near-solar analog (M ⋆ = 1.10 ± 0.10 M ☉, R ⋆=1.17 ± 0.12 R ☉). The planet was detected using photometric data from the Transiting Exoplanet Survey Satellite (TESS) mission and radial velocity (RV) follow-up observations were carried out as a part of the TESS-Keck Survey using both the HIRES instrument at Keck Observatory and the Levy Spectrograph on the Automated Planet Finder telescope. A combined analysis of these data reveal a planet radius of R p = 2.24 ± 0.23 R ⊕ and a mass measurement of M p = 9.6 ± 3.9 M ⊕). TOI-1437 b is one of few (∼50) known transiting sub-Neptunes orbiting a solar-mass star that has a RV mass measurement. As the formation pathway of these worlds remains an unanswered question, the precise mass characterization of TOI-1437 b may provide further insight into this class of planet.

The TESS-Keck Survey. VIII. Confirmation of a Transiting Giant Planet on an Eccentric 261 Day Orbit with the Automated Planet Finder Telescope*

Abstract We report the discovery of TOI-2180 b, a 2.8 M J giant planet orbiting a slightly evolved G5 host star. This planet transited only once in Cycle 2 of the primary Transiting Exoplanet Survey Satellite (TESS) mission. Citizen scientists identified the 24 hr single-transit event shortly after the data were released, allowing a Doppler monitoring campaign with the Automated Planet Finder telescope at Lick Observatory to begin promptly. The radial velocity observations refined the orbital period of TOI-2180 b to be 260.8 ± 0.6 days, revealed an orbital eccentricity of 0.368 ± 0.007, and discovered long-term acceleration from a more distant massive companion. We conducted ground-based photometry from 14 sites spread around the globe in an attempt to detect another transit. Although we did not make a clear transit detection, the nondetections improved the precision of the orbital period. We predict that TESS will likely detect another transit of TOI-2180 b in Sector 48 of its extended mission. We use giant planet structure models to retrieve the bulk heavy-element content of TOI-2180 b. When considered alongside other giant planets with orbital periods over 100 days, we find tentative evidence that the correlation between planet mass and metal enrichment relative to stellar is dependent on orbital properties. Single-transit discoveries like TOI-2180 b highlight the exciting potential of the TESS mission to find planets with long orbital periods and low irradiation fluxes despite the selection biases associated with the transit method.

Cosmological Insights into the Early Accretion of r-process-enhanced Stars. I. A Comprehensive Chemodynamical Analysis of LAMOST J1109+0754

Abstract This study presents a comprehensive chemodynamical analysis of LAMOST J1109+0754, a bright (V = 12.8), extremely metal-poor ([Fe/H] = −3.17) star, with a strong r-process enhancement ([Eu/Fe] = +0.94 ± 0.12). Our results are based on the 7D measurements supplied by Gaia and the chemical composition derived from a high-resolution (R ∼ 110,000), high signal-to-noise ratio ( optical spectrum obtained by the 2.4 m Automated Planet Finder Telescope at Lick Observatory. We obtain chemical abundances of 31 elements (from lithium to thorium). The abundance ratios ([X/Fe]) of the light elements (Z ≤ 30) suggest a massive Population III progenitor in the 13.4–29.5 M ⊙ mass range. The heavy-element (30 < Z ≤ 90) abundance pattern of J1109+075 agrees extremely well with the scaled-solar r-process signature. We have developed a novel approach to trace the kinematic history and orbital evolution of J1109+0754 with a cOsmologically deRIved timE-varyiNg Galactic poTential (the ORIENT) constructed from snapshots of a simulated Milky Way analog taken from the Illustris-TNG simulation. The orbital evolution within this Milky Way–like galaxy, along with the chemical abundance pattern, implies that J1109+0754 likely originated in a low-mass dwarf galaxy located ∼60 kpc from the center of the Galaxy, which was accreted ∼6–7 Gyr ago, and that the star now belongs to the outer-halo population.

Metal-poor Stars Observed with the Automated Planet Finder Telescope. II. Chemodynamical Analysis of Six Low-metallicity Stars in the Halo System of the Milky Way

In this work, we study the chemical compositions and kinematic properties of six metal-poor stars with [Fe/H] $< -2.5$ in the Galactic halo. From high-resolution (R $\sim$~110,000) spectroscopic observations obtained with the Lick/APF, we determined individual abundances for up to 23 elements, to quantitatively evaluate our sample. We identify two carbon-enhanced metal-poor stars (J1630+0953 and J2216+0246) without enhancement in neutron-capture elements (CEMP-no stars), while the rest of our sample stars are carbon-intermediate. By comparing the light-element abundances of the CEMP stars with predicted yields from non-rotating zero-metallicity massive-star models, we find that possible the progenitors of J1630+0953 and J2216+0246 could be in the 13-25 M$_{\odot}$ mass range, with explosion energies 0.3-1.8$ \times 10^{51}$ erg. In addition, the detectable abundance ratios of light and heavy elements suggest that our sample stars are likely formed from a well-mixed gas cloud, which is consistent with previous studies. We also present a kinematic analysis, which suggests that most of our program stars likely belong to the inner-halo population, with orbits passing as close as $\sim$ 2.9 kpc from the Galactic center. We discuss the implications of these results on the critical constraints on the origin and evolution of CEMP stars, as well as the nature of the Population III progenitors of the lowest metallicity stars in our Galaxy.

Metal-poor Stars Observed with the Automated Planet Finder Telescope. I. Discovery of Five Carbon-enhanced Metal-poor Stars from LAMOST

Abstract We report on the discovery of five carbon-enhanced metal-poor (CEMP) stars in the metallicity range of −3.3 &lt; [Fe/H] &lt; −2.4. These stars were selected from the LAMOST DR3 low-resolution (R ∼ 2000) spectroscopic database as metal-poor candidates and followed up with high-resolution spectroscopy (R ∼ 110,000) with the Lick/APF. Stellar parameters and individual abundances for 25 chemical elements (from Li to Eu) are presented for the first time. These stars exhibit chemical abundance patterns that are similar to those reported in other literature studies of very and extremely metal-poor stars. One of our targets, J2114−0616, shows high enhancement in carbon ([C/Fe] = 1.37), nitrogen ([N/Fe] = 1.88), barium ([Ba/Fe] = 1.00), and europium ([Eu/Fe] = 0.84). Such chemical abundance pattern suggests that J2114−0616 can be classified as CEMP-r/s star. In addition, the star J1054+0528 can be classified as a CEMP-rI star, with [Eu/Fe] = 0.44 and [Ba/Fe] = −0.52. The other stars in our sample show no enhancements in neutron-capture elements and can be classified as CEMP-no stars. We also performed a kinematic and dynamical analysis of the sample stars based on Gaia DR2 data. The kinematic parameters, orbits, and binding energy of these stars show that J2114−0616 is member of the outer-halo population, while the remaining stars belong to the inner-halo population but with an accreted origin. Collectively, these results add important constraints on the origin and evolution of CEMP stars as well as on their possible formation scenarios.

The Breakthrough Listen Search for Intelligent Life: No Evidence of Claimed Periodic Spectral Modulations in High-resolution Optical Spectra of Nearby Stars

We report on high-resolution spectra obtained by the Automated Planet Finder and high-resolution optical Levy Spectrometer to search for periodic spectral modulations, such as those reported in Borra & Trottier. In their analysis of 2.5 million spectra from the Sloan Digital Sky Survey, Borra & Trottier report periodic spectral modulations in 234 stars, and suggest that these signals may be evidence of extraterrestrial civilizations. To evaluate this claim, we observed three of the 234 stars with the Automated Planet Finder Telescope and Levy Spectrometer including all stars brighter than a visual magnitude of 14. Fourier analysis of the resultant spectra of these three sources does not reveal any periodic spectral modulations at the reported period, nor at any other period.

Simulating the M–R Relation from APF Follow-up of TESS Targets: Survey Design and Strategies for Overcoming Mass Biases

Abstract We present simulations of multi-year radial velocity (RV) follow-up campaigns of the TESS exoplanet yield on the Automated Planet Finder telescope, using four different schemes to sample the transiting planets’ RV phase curves. For planets below roughly 10 M ⊕, we see a systematic bias of measured masses that are higher than the true planet mass, regardless of the observing scheme used. This produces a statistically significant difference in the mass–radius relation we recover, where planet masses are predicted to be too high and too similar across the entire super-Earth to Neptune radius range. This bias is due in part to only reporting masses that are measured with high statistical significance. Incorporating all mass measurements, even those that are essentially only upper limits, significantly mitigates this bias. We also find statistically significant differences between the mean number of planets measured at the 1-, 3-, and 5σ K level by the different prioritization schemes. Our results show that prioritization schemes which more evenly sample the RV phase curves produce a larger number of significant mass detections. The scheme that aims to most uniformly sample the phase curve performs best, followed closely by the scheme that randomly samples, and then an in-quadrature sampling approach. The fourth scheme, out of quadrature, performs noticeably worse. These results have important implications for determining accurate planet compositions and for designing effective RV follow-up campaigns in the era of large planet detection surveys such as K2, TESS, and PLATO.

Capabilities and performance of the Automated Planet Finder telescope with the implementation of a dynamic scheduler

We report initial performance results emerging from 600 h of observations with the Automated Planet Finder (APF) telescope and Levy spectrometer located at UCO/Lick Observatory. We have obtained multiple spectra of 80 G, K, and M-type stars, which comprise 4954 individual Doppler radial velocity (RV) measurements with a median internal uncertainty of 1.35 ms−1. We find a strong, expected correlation between the number of photons accumulated in the 5000 to 6200 Å iodine region of the spectrum and the resulting internal uncertainty estimates. Additionally, we find an offset between the population of G and K stars and the M stars within the dataset when comparing these parameters. As a consequence of their increased spectral line densities, M-type stars permit the same level of internal uncertainty with 2× fewer photons than G-type and K-type stars. When observing M stars, we show that the APF/Levy has essentially the same speed-on-sky as Keck/high resolution echelle spectrometer (HIRES) for precision RVs. In the interest of using the APF for long-duration RV surveys, we have designed and implemented a dynamic scheduling algorithm. We discuss the operation of the scheduler, which monitors ambient conditions and combines on-sky information with a database of survey targets to make intelligent, real-time targeting decisions.

SIX PLANETS ORBITING HD 219134

We present new, high-precision Doppler radial velocity (RV) data sets for the nearby K3V star HD 219134. The data include 175 velocities obtained with the HIRES Spectrograph at the Keck I Telescope, and 101 velocities obtained with the Levy Spectrograph at the Automated Planet Finder Telescope (APF) at Lick Observatory. Our observations reveal six new planetary candidates, with orbital periods of P=3.1, 6.8, 22.8, 46.7, 94.2 and 2247 days, spanning masses of msini=3.8, 3.5, 8.9, 21.3, 10.8 and 108 M_earth respectively. Our analysis indicates that the outermost signal is unlikely to be an artifact induced by stellar activity. In addition, several years of precision photometry with the T10 0.8~m automatic photometric telescope (APT) at Fairborn Observatory demonstrated a lack of brightness variability to a limit of ~0.0002 mag, providing strong support for planetary-reflex motion as the source of the radial velocity variations. The HD 219134 system, with its bright (V=5.6) primary provides an excellent opportunity to obtain detailed orbital characterization (and potentially follow-up observations) of a planetary system that resembles many of the multiple-planet systems detected by Kepler, and which are expected to be detected by NASA's forthcoming TESS Mission and by ESA's forthcoming PLATO Mission.

THREE SUPER-EARTHS ORBITING HD 7924

We report the discovery of two super-Earth mass planets orbiting the nearby K0.5 dwarf HD 7924 which was previously known to host one small planet. The new companions have masses of 7.9 and 6.4 M$_\oplus$, and orbital periods of 15.3 and 24.5 days. We perform a joint analysis of high-precision radial velocity data from Keck/HIRES and the new Automated Planet Finder Telescope (APF) to robustly detect three total planets in the system. We refine the ephemeris of the previously known planet using five years of new Keck data and high-cadence observations over the last 1.3 years with the APF. With this new ephemeris, we show that a previous transit search for the inner-most planet would have covered 70% of the predicted ingress or egress times. Photometric data collected over the last eight years using the Automated Photometric Telescope shows no evidence for transits of any of the planets, which would be detectable if the planets transit and their compositions are hydrogen-dominated. We detect a long-period signal that we interpret as the stellar magnetic activity cycle since it is strongly correlated with the Ca II H and K activity index. We also detect two additional short-period signals that we attribute to rotationally-modulated starspots and a one month alias. The high-cadence APF data help to distinguish between the true orbital periods and aliases caused by the window function of the Keck data. The planets orbiting HD 7924 are a local example of the compact, multi-planet systems that the Kepler Mission found in great abundance.

TIME-VARYING POTASSIUM IN HIGH-RESOLUTION SPECTRA OF THE TYPE IA SUPERNOVA 2014J

We present a time series of the highest resolution spectra yet published for the nearby Type Ia supernova (SN) 2014J in M82. They were obtained at 11 epochs over 33 days around peak brightness with the Levy Spectrograph (resolution R~110,000) on the 2.4m Automated Planet Finder telescope at Lick Observatory. We identify multiple Na I D and K I absorption features, as well as absorption by Ca I H & K and several of the more common diffuse interstellar bands (DIBs). We see no evolution in any component of Na I D, Ca I, or in the DIBs, but do establish the dissipation/weakening of the two most blueshifted components of K I. We present several potential physical explanations, finding the most plausible to be photoionization of circumstellar material, and discuss the implications of our results with respect to the progenitor scenario of SN 2014J.

A FOUR-PLANET SYSTEM ORBITING THE K0V STAR HD 141399

We present precision radial velocity (RV) data sets from Keck-HIRES and from Lick Observatory's new Automated Planet Finder Telescope and Levy Spectrometer on Mt. Hamilton that reveal a multiple-planet system orbiting the nearby, slightly evolved, K-type star HD 141399. Our 91 observations over 10.5 years suggest the presence of four planets with orbital periods of 94.35, 202.08, 1070.35, and 3717.35 days and minimum masses of 0.46, 1.36, 1.22, and 0.69 Jupiter masses respectively. The orbital eccentricities of the three inner planets are small, and the phase curves are well sampled. The inner two planets lie just outside the 2:1 resonance, suggesting that the system may have experienced dissipative evolution during the protoplanetary disk phase. The fourth companion is a Jupiter-like planet with a Jupiter-like orbital period. Its orbital eccentricity is consistent with zero, but more data will be required for an accurate eccentricity determination.