Your search

Electron-multiplying CCD cameras are now being widely used in speckle imaging, and have been shown to deliver excellent photometric precision under good observing conditions. Successful image reconstructions have been made on binary stars fainter than 14th magnitude. However, improving the speckle signal-to-noise ratio and the fidelity of image reconstructions for faint sources would be extremely helpful in several areas of research where diffraction-limited images are required, including our own ongoing speckle observations of Kepler exoplanet candidate stars using the WIYN Telescope at Kitt Peak. In this paper, we investigate (1) robust cosmic ray rejection and (2) removal of low signal-to-noise frames as two ways to maximize data quality for faint source observations. Cosmic ray rejection is not normally a major concern in speckle imaging due to the brightness of the targets traditionally observed and the short frame times. Nonetheless, when imaging faint targets, more frames are needed to achieve a given signal-to-noise ratio, increasing the chance of cosmic ray events on the detector, and even a single cosmic ray hit in the frame sequence can significantly affect the source detection ability and photometry obtained in the observation. Similarly, faint sources often exhibit some frames with a well-defined image core while in other frames it is difficult to tell if the source is even present, primarily due to seeing variation during the observation. A new speckle reduction algorithm has been created that removes cosmic rays without throwing out frames and rejects frames with bad seeing, and its performance is investigated to determine to what extent this can improve source detection and photometric reliability in the final reconstructed image. Funding for this work was provided by the Kepler Science Center and by NSF Grant AST-0908125.

The Differential Speckle Survey Instrument (DSSI) is a dual-channel speckle imaging system that takes speckle patterns in two colors simultaneously using two electron-multiplying CCD cameras. The system has been shown to deliver excellent photometry of binary stars under good observing conditions, which raises the question of whether results of similar quality can be obtained on extended objects such as minor planets, and if so, to what limiting magnitude. In this study, we present speckle image reconstructions of images of 2 Pallas, 216 Kleopatra, and 283 Emma made from data taken at the WIYN 3.5-m Telescope at Kitt Peak. We compare two different phase reconstruction algorithms: (1) an iterative technique, and (2) a relaxation technique. Since Pallas is a flattened disk, Kleopatra has a dumbbell shape, and Emma is a binary asteroid with known orbital parameters, these three targets represent three distinct image morphologies that allow for a robust comparison of the two phase reconstruction programs. Prospects for future work in this area with DSSI are discussed. This work is funded by NSF grant AST-0908125.

Using our state-of-the-art 2-channel speckle imaging instrument, we have recently obtained diffraction-limited optical images at the 8-m Gemini-N telescope. The primary science goal was to search for faint (delta_mag = 4-6 mag) and nearby (<0.05") stellar companions around potential planet hosting stars as part of the small small exoplanet validation for the NASA Kepler and ESA CoRoT missions. As a demonstration of the instrument capabilities on Gemini, we achieved an angular resolution of ~20 mas which yielded the highest resolution ground-based optical image of the Pluto-Charon system ever obtained. Our instrument is likely to return to Gemini-N in mid-2013 for observations by general community programs

We measure the mass of a modestly irradiated giant or "warm Jupiter," KOI-94d, in order to calculate its density. We wish to determine whether this planet, which is in a 22 day orbit and receives 107 times as much incident flux as the Earth, is bloated like "hot Jupiters" or as dense as our own Jupiter. In addition to its warm Jupiter, KOI-94 hosts at least 3 smaller planets, all of which were detected through transits by the Kepler Mission. This presents the opportunity to characterize a multi-planet system and to test dynamic stability and formation theory through observations of the masses and orbital elements of these planets. With 26 radial velocity measurements of KOI-94 from the W. M. Keck Observatory/HIRES, we measure the mass of the giant planet and upper limits to the masses of the three smaller planets. Transit timing variations will allow us to hone the mass measurements of the three smaller planets. Using the KOI-94 system and all other planets with published values for both mass and radius, we establish two fundamental planes for exoplanets that relate their mass, incident flux, and radius from a few Earth masses up to ten Jupiter masses: log(Rp/RE) = 0.007 + 0.53 log(M/ME) - 0.001 log(F/[erg/s/cm^2]) for Mp < 150ME; log(Rp/RE) = 0.67 - 0.036 log(M/ME) + 0.06 log(F/[erg/s/cm^2]) for Mp > 150ME. We also solve these planes in density-mass-flux space: log(ρp/[g/cm^3]) = 0.69 - 0.57 log(M/ME) + 0.02 log(F/[erg/s/cm^2]) for Mp < 150ME; log(ρp/[g/cm^3]) = -1.23 + 1.10 log(M/ME) - 0.18 log(F/[erg/s/cm^2]) for Mp > 150ME.

We present the validation and characterization of Kepler-61b: a 2.5 R_Earth planet orbiting near the inner edge of the habitable zone of a low-mass star. Our characterization of the host star Kepler-61 is based upon our identification of a spectroscopically similar star located 4.9 pc from Earth. This proxy star to Kepler-61 has a published direct interferometric radius and effective temperature measurement, which we apply in tandem with the Kepler photometry to characterize the planet Kepler-61b. The technique of identifying a nearby proxy star with directly measured properties allows for an independent check on stellar characterization via the traditional measurements with stellar spectra and evolutionary models. In this case, such a check had profound implications for the putative habitability of Kepler-61b. This work was performed in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program

We report on the work to validate twelve candidate-transiting planets from Kepler with orbital periods ranging from 34 to 207 days initially identified in the pipeline search of three years of Kepler data from quarters 1 to 12. The candidates were selected based on pipeline Data Validation models indicating that they are small and potentially in the habitable zone (HZ) of their parent stars. As their expected Doppler signals are too small for a direct measure of their masses, we verify their planetary nature by validating them statistically using the BLENDER technique. BLENDER simulates large numbers of false-positive scenarios and compares the resulting light curves with the Kepler photometry, taking into account additional information from the analysis of Kepler flux centroids and new follow-up observations, including high-resolution optical and NIR spectroscopy, adaptive optics imaging, and speckle imaging. For eleven of the candidates we show that the likelihood they are true planets is far greater than that of a false positive, to a 99.73% confidence level. For the twelfth candidate, the planet confidence level is about 99.2%. Using improved stellar parameters for the host stars, we derive planetary radii ranging from 1.12 to 2.73 R⊕. All twelve objects are confirmed to be in the HZ, and nine are small enough to be rocky. Excluding three of the candidates that have been previously validated by others, our study doubles the number of known potentially rocky planets in the HZ.

The NASA K2 mission is finding many high-value exoplanets and world-wide follow-up is ensuing. The NASA TESS mission will soon be launched, requiring additional ground-based observations as well. As a part of the NASA-NSFNN-EXPLORE program to enable exoplanet research, our group is building two new speckle interferometry cameras for the Kitt Peak WIYN 3.5-m telescope and the Gemini-N 8-m telescope. Modeled after the successful DSSI visitor instrument that has been used at these telescopes for many years, speckle observations provide the highest resolution images available today from any ground- or space-based single telescope. They are the premier method through which small, rocky exoplanets can be validated. Available for public use in early 2017, WIYNSPKL and GEMSPKL will obtain simultaneous images in two filters with fast EMCCD readout, "speckle" and “wide-field” imaging modes, and user support for proposal writing, observing, and data reduction. We describe the new cameras, their design, and their benefits for exoplanet follow-up, characterization, and validation. Funding for this project comes from the NASA Exoplanet Exploration Program and NASA HQ.

The high-spatial-resolution technique of speckle interferometry has been in use at Lowell Observatory's Discovery Channel Telescope since 2014 with the Dual-channel Stellar Speckle Imager (DSSI; Horch et al. 2009) as a visiting instrument. Using its standard bandpasses of 692 and 880nm, we have used highly efficient DSSI instrument to inspect over a thousand stellar systems over the course of 2014 (Horch et al. 2015). We have also demonstrated the usefulness of the DSSI@DCT system for resolved observations of high-altitude (>1,000 miles) man-made satellites in highly non-sidereal rate orbits.

The Lowell Observatory Discovery Channel Telescope (DCT) has been in full science operation for 2 years (2015 and 2016). Five instruments have been commissioned during that period, and two additional instruments are planned for 2017. These include:+ Large Monolithic Imager (LMI) - a CCD imager (12.6 arcmin FoV)+ DeVeny - a general purpose optical spectrograph (2 arcmin slit length, 10 grating choices)+ NIHTS - a low resolution (R=160) YJHK spectrograph (1.3 arcmin slit)+ DSSI - a two-channel optical speckle imager (5 arcsec FoV)+ IGRINS - a high resolution (45,000) HK spectrograph, on loan from the University of Texas.In the upcoming year, instruments will be delivered from the University of Maryland (RIMAS - a YJHK imager/spectrograph) and from Yale University (EXPRES - a very high resolution stabilized optical echelle for PRV).Each of these instruments will be described, along with their primary science goals.

How many K dwarfs have “kids?” Stellar multiplicity fractions have been obtained for most spectral types, most recently by Raghavan et al. (2010) and Winters et al. (2015), finding rates of 50% for solar-type stars and 27% for M dwarfs, respectively. These findings will be crucial to improving our understanding of solar-system formation, but there has not yet been a statistically significant survey for K dwarfs to bridge the gap between G and M stars. To create a sample for a robust multiplicity survey, an initial set of 1048 K dwarfs was built using the Hipparcos and 2MASS catalogs, the companions of which are called “K-KIDS.” Future releases from Gaia will help us to expand K-KIDS into a volume-complete sample out to 50-pc, and we project that the final sample will contain over 3000 stars, making this the largest volume-complete multiplicity survey ever undertaken. For observational purposes, the targeted K dwarfs are confined equatorially to -30 < DEC < +30 to ensure all stars are observable from either hemisphere. The survey for K-KIDS is split into three companion-separation regimes: small (0.02 - 2.00 arcseconds), medium (2.00 - 10.00 arcseconds), and distant (10.00+ arcseconds). Small separation companions are resolved using the Differential Speckle Survey Instrument, with which we have observed 964 out of 1048 systems to date, already finding 135 new K-KIDS. Medium separation companions are observed via a series of three observations per star at the CTIO 0.9-m telescope, integrating for 3, 30, and 300 seconds to reveal companions of various brightnesses. Finally, a common proper-motion search is used to find companions at distant separations via blinking of digitialized images in the SuperCOSMOS archive, in addition to a large-scale literature survey for previously-discovered multiples. The small and distant surveys are nearing completion, and continued progress on the medium survey ensures that a statistically significant multiplicity rate for K dwarfs will soon be in achieved. Furthermore, a new RV survey is planned using the CHIRON high-resolution spectrograph to find companions that cannot be directly imaged. This effort has been supported by the NSF through grants AST-1412026 and AST-1517413.

Speckle interferometry at Yale started in 1994 with a three-year program of observations at the Yale Southern Observatory at El Leoncito, Argentina. After this experience, we began a long-term program of speckle observations at the WIYN 3.5-m telescope at Kitt Peak National Observatory, first using a MAMA detector, then CCD and finally EMCCD technology. We describe the evolution of the program, its main results in terms of discovered components, orbital parameters and masses. While the Yale program ended in 2013, it provided the springboard for continued speckle efforts at WIYN, the Discovery Channel 4.3-m Telescope, and the Gemini 8.1-m Telescopes for binary star research, exoplanet science, and other projects. An important outcome of this research will be the incorporation of the soon to be released high-precision Gaia parallaxes into our observations.

Theoretical models show the main sequence gap is a result of the mixing of 3He during the merger of envelope and core convection zones. Unlike stars the either side of the gap, stars in a narrow mass range will go through instability phases, where their dynamos could switch between the αΩ dynamo like the Sun and Ω2 dynamo like late M dwarfs. At the same time, they show radial pulsation and their fluxes fluctuate, which resemble the pulsations observed in evolved stars like red giants and asymptotic giant branch stars. Consequently, they are a unique type of dwarf like no other on the main sequence. In this work, we would like to know 1) will the unstable interior structures result in observable characteristics such as flaring and spots, and 2) what is the mass range for these stars observationally? Here we present our preliminary results: 1) stars in the gap have higher percentage rate of activities than their adjacent regions, and 2) high resolution speckle results yield promising close binaries to yield dynamical masses in the future.

We extend results first announced by Franz et al. (1998), that identified vA351 = H346 in the Hyades as a multiple star system containing a white dwarf. With Hubble Space Telescope Fine Guidance Sensor fringe tracking and scanning, and more recent speckle observations, all spanning 20.7 years, we establish a parallax, relative orbit, and mass fraction for two components, with a period, P = 2.70y and total mass 2.1M⊙. With ground-based radial velocities, we find that component B consists of BC, two M dwarf stars orbiting with a very short period (PBC = 0.749 days), having a mass ratio MC/MB=0.95. We confirm that the total mass of the system can only be reconciled with the distance and component photometry by including a fainter, higher mass component. The quadruple system consists of three M dwarfs (A,B,C) and one white dwarf (D); MA=0.57M⊙, MB=0.48M⊙, and MC=0.45M⊙. The WD mass, 0.53M⊙, comes from cooling models, an assumed Hyades age of 670My, and consistency with all previous and derived astrometric, photometric, and RV results. Velocities from Hα and He I emission lines confirm the BC period derived from absorption lines, with similar (HeI) and higher (Hα) velocity amplitudes. We ascribe the larger Hα amplitude to emission from a region each component shadows from the other, depending on the line of sight.

The RECONS (REsearch Consortium On Nearby Stars, www.recons.org) team continues to explore the solar neighborhood by evaluating the nearest stars, both individually and as a population. Key points are becoming clear: we now know that 86% of all stars are K and M dwarfs, and we need to reach to 50 pc and 25 pc, respectively, to create samples of 5000 and 3000 primaries each. These two sizable samples allow us to understand the outcome of the star formation process across a factor of ten in mass as never before. Here we focus on one crucial area of research --- stellar companions --- with results of our surveys combining radial velocities, astrometry, high-resolution imaging, and trawls of catalogs and the literature. The surveys are carried out primarily at the CTIO/SMARTS 0.9m and 1.5m, the SOAR 4.1m, and both Gemini 8.1m telescopes. We reveal companions at separations from less than 1 AU to more than 1000 AU from the K and M dwarfs, with the key result that these stellar partners are found most often at separations similar to our Solar System. Thus, the star and planet formation processes work on the same spatial scales ... a fact that we must keep in mind as our solar neighborhood becomes enriched with planetary discoveries at distances comparable to where stellar companions are found. This work has been supported by NSF grants AST-0507711, AST-0908402, AST-1109445, AST-1411206, and AST-1715551, AST-1910130, and the SMARTS Consortium.

We present the first results from the POKEMON (Pervasive Overview of Kompanions of Every M-dwarf in Our Neighborhood) survey, the largest speckle survey of stellar multiplicity ever produced for the objects that comprise over 70% of the stars in our galaxy: the M-dwarfs. We have conducted a volume-limited survey through M9 that inspected, at diffraction-limited resolution, every M-dwarf out to 15pc, with additional brighter targets to 25pc. POKEMON utilized the Differential Speckle Survey Instrument (DSSI) at the 4.3m Lowell Discovery Telescope, along with the NN-Explore Exoplanet Stellar Speckle Imager (NESSI) on the 3.5-m WIYN telescope. We report the discovery of 30+ new companions to these nearby M-dwarfs. Given the priority these targets have for exoplanet studies with TESS, and in the future JWST - and the degree to which initially undetected multiplicity has skewed Kepler results - a comprehensive survey of our nearby low-mass neighbors provides a homogeneous, complete catalog of fundamental utility. Prior knowledge of secondary objects - or robust non-detections, as captured by this survey - immediately clarify the nature of exoplanet transit detections from these current and upcoming missions.

Comprising three out of every four stars, the M dwarfs form a unique sample that can host companions orbiting at Solar System scales and spanning a factor of 100,000 in mass. Targeting 120 M dwarf binaries within 25 parsecs, we are determining the period vs. eccentricity distribution for M dwarf stellar companions with orbital periods up to 6 years and semimajor axes up to 5 AU. This range is enabled by our combination of multiple observational methods: long-term astrometry from our RECONS program at the CTIO/SMARTS 0.9m is characterizing orbits on decades-long timescales, while our speckle interferometry survey at SOAR with HRCAM+SAM maps shorter orbits of systems identified from Gaia DR2, while also providing resolutions and masses for our long-period astrometric binaries. We will supplement these results with orbits from the literature, from both radial velocity and high-resolution imaging surveys, to ensure that our sample is rich with companions of all types orbiting within 5 AU. Initial results of this work so far suggest a notable paucity of M dwarf stellar companions with circular orbits greater than 5 years in period, showcasing the additional leverage provided by this combination of long-term astrometry and high-resolution imaging. Ultimately, when compared to the orbits of brown dwarf and planetary companions, such structures will be critical to understanding the formation mechanisms of these systems.