Seeing-limited Coupling of Starlight into Single-mode Fiber with a Small Telescope

An optical fiber link to a telescope provides many advantages for spectrometers designed to detect and characterize extrasolar planets through precise radial velocity (PRV) measurements. In the seeing-limited regime, a multi-mode fiber is typically used so that a significant amount of starlight may be captured. In the near-diffraction-limited case, either with an adaptive optics system or with a small telescope at an excellent site, efficiently coupling starlight into a much smaller, single-mode fiber may be possible. In general, a spectrometer designed for single-mode fiber input will be substantially less costly than one designed for multi-mode fiber input. We describe the results of tests coupling starlight from a 70 cm telescope at Mt. Hopkins, Arizona into the single-mode fiber of the MINERVA-Red spectrometer at a wavelength of ~850 nm using a low-speed tip/tilt image stabilization system comprising all commercial, off-the-shelf components. We find that approximately 0.5% of the available starlight is coupled into the single-mode fiber under seeing conditions typical for observatories hosting small telescopes, which is close to the theoretical expectation. We discuss scientific opportunities for small telescopes paired with inexpensive, high-resolution spectrometers, as well as upgrade paths that should significantly increase the coupling efficiency for the MINERVA-Red system.Comment: 8 pages, 4 figures. Accepted for publication in Astronomische Nachrichte

A novel method for identifying exoplanetary rings

ABSTRACT: The discovery of rings around extrasolar planets (“exorings”) is one of the next breakthroughs in exoplanetary research. Previous studies have explored the feasibility of detecting exorings with present and futuren photometric sensitivities by seeking anomalous deviations in the residuals of a standard transit light curve fit, at the level of ~-100 ppm for Kronian rings. In this work, we explore two much larger observational consequences of exorings: (1) the significant increase in transit depth that may lead to the misclassification of ringed planetary candidates as false-positives and/or the underestimation of planetary density; and (2) the so-called “photo-ring” effect, a new asterodensity profiling effect, revealed by a comparison of the light curve derived stellar density to that measured with independent methods (e.g., asteroseismology). While these methods do not provide an unambiguous detection of exorings, we show that the large amplitude of these effects, combined with their relatively simple analytic description, makes them highly suited to large-scale surveys to identify candidate ringed planets worthy of more detailed investigation. Moreover, these methods lend themselves to ensemble analyses seeking to uncover evidence of a population of ringed planets. We describe the method in detail, develop the basic underlying formalism, and test it in the parameter space of rings and transit configuration. We discuss the prospects of using this method for the first systematic search of exoplanetary rings in the Kepler database and provide a basic computational code for implementing it

KELT-20b: A Giant Planet With A Period Of P ~ 3.5 Days Transiting The V ~ 7.6 Early A Star HD 185603

We report the discovery of KELT-20b, a hot Jupiter transiting a early A star, HD 185603, with an orbital period of days. Archival and follow-up photometry, Gaia parallax, radial velocities, Doppler tomography, and AO imaging were used to confirm the planetary nature of KELT-20b and characterize the system. From global modeling we infer that KELT-20 is a rapidly rotating ( ) A2V star with an effective temperature of K, mass of , radius of , surface gravity of , and age of . The planetary companion has a radius of , a semimajor axis of au, and a linear ephemeris of . We place a upper limit of on the mass of the planet. Doppler tomographic measurements indicate that the planetary orbit normal is well aligned with the projected spin axis of the star ( ). The inclination of the star is constrained to , implying a three-dimensional spin–orbit alignment of . KELT-20b receives an insolation flux of , implying an equilibrium temperature of of ∼2250 K, assuming zero albedo and complete heat redistribution. Due to the high stellar , KELT-20b also receives an ultraviolet (wavelength nm) insolation flux of , possibly indicating significant atmospheric ablation. Together with WASP-33, Kepler-13 A, HAT-P-57, KELT-17, and KELT-9, KELT-20 is the sixth A star host of a transiting giant planet, and the third-brightest host (in V ) of a transiting planet

KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V=8 Subgiant HD 93396

We report the discovery of a transiting exoplanet, KELT-11b, orbiting the bright ($V=8.0$) subgiant HD 93396. A global analysis of the system shows that the host star is an evolved subgiant star with $T_{\rm eff} = 5370\pm51$ K, $M_{*} = 1.438_{-0.052}^{+0.061} M_{\odot}$, $R_{*} = 2.72_{-0.17}^{+0.21} R_{\odot}$, log $g_*= 3.727_{-0.046}^{+0.040}$, and [Fe/H]$= 0.180\pm0.075$. The planet is a low-mass gas giant in a $P = 4.736529\pm0.00006$ day orbit, with $M_{P} = 0.195\pm0.018 M_J$, $R_{P}= 1.37_{-0.12}^{+0.15} R_J$, $\rho_{P} = 0.093_{-0.024}^{+0.028}$ g cm$^{-3}$, surface gravity log ${g_{P}} = 2.407_{-0.086}^{+0.080}$, and equilibrium temperature $T_{eq} = 1712_{-46}^{+51}$ K. KELT-11 is the brightest known transiting exoplanet host in the southern hemisphere by more than a magnitude, and is the 6th brightest transit host to date. The planet is one of the most inflated planets known, with an exceptionally large atmospheric scale height (2763 km), and an associated size of the expected atmospheric transmission signal of 5.6%. These attributes make the KELT-11 system a valuable target for follow-up and atmospheric characterization, and it promises to become one of the benchmark systems for the study of inflated exoplanets.Comment: 15 pages, Submitted to AAS Journal

Kepler-432: a red giant interacting with one of its two long period giant planets

We report the discovery of Kepler-432b, a giant planet ($M_b = 5.41^{+0.32}_{-0.18} M_{\rm Jup}, R_b = 1.145^{+0.036}_{-0.039} R_{\rm Jup}$) transiting an evolved star $(M_\star = 1.32^{+0.10}_{-0.07} M_\odot, R_\star = 4.06^{+0.12}_{-0.08} R_\odot)$ with an orbital period of $P_b = 52.501129^{+0.000067}_{-0.000053}$ days. Radial velocities (RVs) reveal that Kepler-432b orbits its parent star with an eccentricity of $e = 0.5134^{+0.0098}_{-0.0089}$, which we also measure independently with asterodensity profiling (AP; $e=0.507^{+0.039}_{-0.114}$), thereby confirming the validity of AP on this particular evolved star. The well-determined planetary properties and unusually large mass also make this planet an important benchmark for theoretical models of super-Jupiter formation. Long-term RV monitoring detected the presence of a non-transiting outer planet (Kepler-432c; $M_c \sin{i_c} = 2.43^{+0.22}_{-0.24} M_{\rm Jup}, P_c = 406.2^{+3.9}_{-2.5}$ days), and adaptive optics imaging revealed a nearby (0\farcs87), faint companion (Kepler-432B) that is a physically bound M dwarf. The host star exhibits high signal-to-noise asteroseismic oscillations, which enable precise measurements of the stellar mass, radius and age. Analysis of the rotational splitting of the oscillation modes additionally reveals the stellar spin axis to be nearly edge-on, which suggests that the stellar spin is likely well-aligned with the orbit of the transiting planet. Despite its long period, the obliquity of the 52.5-day orbit may have been shaped by star-planet interaction in a manner similar to hot Jupiter systems, and we present observational and theoretical evidence to support this scenario. Finally, as a short-period outlier among giant planets orbiting giant stars, study of Kepler-432b may help explain the distribution of massive planets orbiting giant stars interior to 1 AU.Comment: 22 pages, 19 figures, 5 tables. Accepted to ApJ on Jan 24, 2015 (submitted Nov 11, 2014). Updated with minor changes to match published versio

First radial velocity results from the MINiature Exoplanet Radial Velocity Array (MINERVA)

The MINiature Exoplanet Radial Velocity Array (MINERVA) is a dedicated observatory of four 0.7m robotic telescopes fiber-fed to a KiwiSpec spectrograph. The MINERVA mission is to discover super-Earths in the habitable zones of nearby stars. This can be accomplished with MINERVA's unique combination of high precision and high cadence over long time periods. In this work, we detail changes to the MINERVA facility that have occurred since our previous paper. We then describe MINERVA's robotic control software, the process by which we perform 1D spectral extraction, and our forward modeling Doppler pipeline. In the process of improving our forward modeling procedure, we found that our spectrograph's intrinsic instrumental profile is stable for at least nine months. Because of that, we characterized our instrumental profile with a time-independent, cubic spline function based on the profile in the cross dispersion direction, with which we achieved a radial velocity precision similar to using a conventional "sum-of-Gaussians" instrumental profile: 1.8 m s$^{-1}$ over 1.5 months on the RV standard star HD 122064. Therefore, we conclude that the instrumental profile need not be perfectly accurate as long as it is stable. In addition, we observed 51 Peg and our results are consistent with the literature, confirming our spectrograph and Doppler pipeline are producing accurate and precise radial velocities.Comment: 22 pages, 9 figures, submitted to PASP, Peer-Reviewed and Accepte

KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting The \u3cem\u3eV\u3c/em\u3e = 8 Subgiant HD 93396

We report the discovery of a transiting exoplanet, KELT-11b, orbiting the bright (V = 8.0) subgiant HD 93396. A global analysis of the system shows that the host star is an evolved subgiant star with Teff = 5370 ± 51 K, M* = 1.438 (+0.061)/(-0.052) M⊙, R* = 2.72 (+0.21)/(-0.17) R⊙, logg* = 3.727 (+0.040)/(-0.046), and [Fe/H] = 0.180 ± 0.075. The planet is a low-mass gas giant in a P = 4.736529 ± 0.00006 day orbit, with MP = 0.195 ± 0.018 MJ, RP = 1.37 (+0.15)/(-0.12) RJ, ρP = 0.093 (+0.028)/(-0.024) g cm⁻³, surface gravity loggP = 2.407 (+0.080)/(-0.086), and equilibrium temperature Teq = 1712 (+51)/(-46) K. KELT-11 is the brightest known transiting exoplanet host in the southern hemisphere by more than a magnitude and is the sixth brightest transit host to date. The planet is one of the most inflated planets known, with an exceptionally large atmospheric scale height (2763 km), and an associated size of the expected atmospheric transmission signal of 5.6%. These attributes make the KELT-11 system a valuable target for follow-up and atmospheric characterization, and it promises to become one of the benchmark systems for the study of inflated exoplanets