Lowell Observatory Research Articles

Modelling the seasonal cycle of Uranus’s colour and magnitude, and comparison with Neptune

ABSTRACT We present a quantitative analysis of the seasonal record of Uranus’s disc-averaged colour and photometric magnitude in Strömgren b and y filters (centred at 467 and 551 nm, respectively), recorded at the Lowell Observatory from 1950 to 2016, and supplemented with HST/WFC3 observations from 2016 to 2022. We find that the seasonal variations of magnitude can be explained by the lower abundance of methane at polar latitudes combined with a time-dependent increase of the reflectivity of the aerosol particles in layer near the methane condensation level at 1 – 2 bar. This increase in reflectivity is consistent with the addition of conservatively scattering particles to this layer, for which the modelled background haze particles are strongly absorbing at both blue and red wavelengths. We suggest that this additional component may come from a higher proportion of methane ice particles. We suggest that the increase in reflectivity of Uranus in both filters between the equinoxes in 1966 and 2007, noted by previous authors, might be related to Uranus’s distance from the Sun and the production rate of dark photochemical haze products. Finally, we find that although the visible colour of Uranus is less blue than Neptune, due to the increased aerosol thickness on Uranus, and this difference is greatest at Uranus’s solstices, it is much less significant than is commonly believed due to a long-standing misperception of Neptune’s ‘true’ colour. We describe how filter-imaging observations, such as those from Voyager-2/ISS and HST/WFC3, should be processed to yield accurate true colour representations.

Developing STEM Curriculum Units to Engage 4th-8th Grade Navajo Students as Part of In-Class Outreach

The Native American Astronomy Outreach Program (NAAOP) at Lowell Observatory is an in-class STEM enrichment program that pairs astronomers with 4th-8th grade teachers at Native-serving schools in northern Arizona. The astronomer works with the teacher to present hands-on astronomy activities to their class with the goal of getting students excited about STEM and STEM careers. Over three school years (2018-2021), a special collaboration with teachers at the Navajo Nation’s Kayenta Unified School District was used to develop and implement curriculum units for each grade level with potential for a high impact on students. The curriculum used Project Based Learning to better enable students to see themselves as scientists, and it included cultural and local connections related to the science content to encourage students to see science as relevant to themselves. Although impacted by the COVID19 pandemic, student surveys suggest that these curriculum units along with other aspects of the program had a positive impact on students’ interest in STEM.

The astorb database at Lowell Observatory

The astorb database at Lowell Observatory is an actively curated catalog of all known asteroids in the Solar System. astorb has heritage dating back to the 1970s and has been publicly accessible since the 1990s. Work began in 2015 to modernize the underlying database infrastructure, operational software, and associated web applications. That effort involved the expansion of astorb to incorporate new data such as physical properties (e.g. albedo, colors, spectral types) from a variety of sources. The data in astorb are used to support a number of research tools hosted at https://asteroid.lowell.edu. Here we present a full description of the software tools, computational foundation, and data products upon which the astorb ecosystem has been built.

Observations with the Southern Connecticut Stellar Interferometer. I. Instrument Description and First Results

Abstract We discuss the design, construction, and operation of a new intensity interferometer, based on the campus of Southern Connecticut State University in New Haven, Connecticut. While this paper will focus on observations taken with an original two-telescope configuration, the current instrumentation consists of three portable 0.6 m Dobsonian telescopes with single-photon avalanche diode detectors located at the Newtonian focus of each telescope. Photons detected at each station are time stamped and read out with timing correlators that can give cross-correlations in timing to a precision of 48 ps. We detail our observations to date with the system, which has now been successfully used at our university in 16 nights of observing. Components of the instrument were also deployed on one occasion at Lowell Observatory, where the Perkins and Hall telescopes were made to function as an intensity interferometer. We characterize the performance of the instrument in detail. In total, the observations indicate the detection of a correlation peak at the level of 6.76σ when observing unresolved stars, and consistency with partial or no detection when observing at a baseline sufficient to resolve the star. Using these measurements, we conclude that the angular diameter of Arcturus is larger than 15 mas and that of Vega is between 0.8 and 17 mas. While the uncertainties are large at this point, both results are consistent with measures from amplitude-based long baseline optical interferometers.

Astrophysical Applications of Aluminum, Strontium Lanthanate Phosphors Doped with Terbium and Europium

Al2Sr2La2O8 doped (ASL) with terbium and europium ion was synthesized by solid state reaction under air atmosphere. Its characterization was systematically analyzed by SEM, X-ray diffraction (XRD) and photoluminescence spectra (PL). Photoluminescence emission spectra having excitations at around 254, 268, 278nm revealed that Eu ions were present in trivalent oxidation states. The emission peaks are found at 540(green), 588,(Yellow) and 626nm(red) are observed. Scanning Electron Microscopy (SEM) was implemented to investigate the surface morphology of present phosphor. The obtained results on Al2Sr2La2O8: Tb, Eu is suitable for green-red light source using UV light as the primary excitation. In addition with Aluminum, Strontium Lanthanate phosphors are used for lighting can work to minimize electricity usage, and decreases the excess light pollution, minimizing light pollution has benefits for people and for the surrounding ecosystems. The best example of ASL is lighting use is around Peurto Mosquito, a bioluminescent bay on vieques, peurto rico ,the bioluminescence is more visible and healthier, and people's eyes get a few more minutes to adjust to the dark. Another use of the ASL is lighting is around the lowell astrophysical observatory. Astrophysical observatories require low lighting to properly see stars and often use best practices in light-pollution safe lighting. Now the observatory is lined with paths that glow at night. Researchers and visitors to safely find their way in the dark, without the use of bright electric lights.

Occultation of a Large Star by the Large Plutino (28978) Ixion on 2020 October 13 UTC

Abstract We observed the occultation of the star Gaia DR2 4056440205544338944 by (28978) Ixion. The event was observed from two Lowell Observatory sites, using the 4.3 m Lowell Discovery Telescope (LDT), near Happy Jack, AZ, USA, and a 0.32 m telescope co-mounted with the Titan Monitoring telescope on Lowell’s Mars Hill campus in Flagstaff, AZ. The LDT chord, at 44.86 s, was roughly 30% longer than the longest predicted possible chord. Under the assumption of a spherical body, Ixion’s fitted diameter D = 709.6 ± 0.2 km. The LDT light-curve profile was used to place an upper limit on the surface pressure P < 2 μbar on any possible atmosphere of Ixion. At the distance of Ixion, the occulted star had a fitted projected diameter of 19.25 ± 0.3 km assuming uniform disk illumination, giving a stellar angular diameter of 0.675 ± 0.010 mas. Using the Gaia EDR3 parallax of 0.565 mas, the stellar radius is . The measured size is consistent with prior spectral classification of this star as a reddened mid-M giant. This is one of only a modest number of M5 III stars to have a directly measured diameter, and is more distant than most.

Science Commissioning of NIHTS: The Near-infrared High Throughput Spectrograph on the Lowell Discovery Telescope

The Near-Infrared High Throughput Spectrograph (NIHTS) is in operation on the 4.3 m Lowell Discovery Telescope (LDT) in Happy Jack, AZ. NIHTS is a low-resolution spectrograph (R ∼ 200) that operates from 0.86 to 2.45 microns. NIHTS is fed by a custom dichroic mirror which reflects near-infrared wavelengths to the spectrograph and transmits the visible to enable simultaneous imaging with the Large Monolithic Imager (LMI), an independent visible wavelength camera. The combination of premier tracking and acquisition capabilities of the LDT, a several arcminutes field of view on LMI, and high spectral throughput on NIHTS enables novel studies of a number of astrophysical and planetary objects including Kuiper Belt Objects, asteroids, comets, low mass stars, and exoplanet hosts stars. We present a summary of NIHTS operations, commissioning, data reduction procedures with two approaches for the correction of telluric absorption features, and an overview of select science cases that will be pursued by Lowell Observatory, Northern Arizona University, and LDT partners.

Observations of Binary Stars with the Differential Speckle Survey Instrument. IX. Observations of Known and Suspected Binaries, and a Partial Survey of Be Stars

Abstract We report 370 measures of 170 components of binary and multiple-star systems, obtained from speckle imaging observations made with the Differential Speckle Survey Instrument at Lowell Observatory’s Discovery Channel Telescope in 2015 through 2017. Of the systems studied, 147 are binary stars, 10 are seen as triple systems, and 1 quadruple system is measured. Seventy-six high-quality nondetections and 15 newly resolved components are presented in our observations. The uncertainty in relative astrometry appears to be similar to our previous work at Lowell, namely, linear measurement uncertainties of approximately 2 mas, and the relative photometry appears to be uncertain at the 0.1–0.15 mag level. Using these measures and those in the literature, we calculate six new visual orbits, including one for the Be star 66 Oph and two combined spectroscopic–visual orbits. The latter two orbits, which are for HD 22451 (YSC 127) and HD 185501 (YSC 135), yield individual masses of the components at the level of 2% or better, and independent distance measures that in one case agrees with the value found in the Gaia DR2 and in the other disagrees at the 2σ level. We find that HD 22451 consists of an F6V+F7V pair with orbital period of 2401.1 ± 3.2 days and masses of 1.342 ± 0.029 and . For HD 185501, both stars are G5 dwarfs that orbit one another with a period of 433.94 ± 0.15 days, and the masses are 0.898 ± 0.012 and . We discuss the details of both the new discoveries and the orbit objects.

Cometary Activity Discovered on a Distant Centaur: A Nonaqueous Sublimation Mechanism

Abstract Centaurs are minor planets thought to have originated in the outer solar system region known as the Kuiper Belt. Active Centaurs enigmatically display comet-like features (e.g., tails, comae) even though they orbit in the gas giant region where it is too cold for water to readily sublimate. Only 18 active Centaurs have been identified since 1927 and, consequently, the underlying activity mechanism(s) have remained largely unknown up to this point. Here we report the discovery of activity emanating from Centaur 2014 OG392, based on archival images we uncovered plus our own new observational evidence acquired with the Dark Energy Camera (Cerro Tololo Inter-American Observatory Blanco 4 m telescope), the Inamori-Magellan Areal Camera & Spectrograph (Las Campanas Observatory 6.5 m Walter Baade Telescope), and the Large Monolithic Imager (Lowell Observatory 4.3 m Discovery Channel Telescope). We detect a coma as far as 400,000 km from 2014 OG392, and our novel analysis of sublimation processes and dynamical lifetime suggest carbon dioxide and/or ammonia are the most likely candidates for causing activity on this and other active Centaurs. We find 2014 OG392 is optically red, but CO2 and NH3 are spectrally neutral in this wavelength regime so the reddening agent is as yet unidentified.

Cloud Identification from All-sky Camera Data with Machine Learning

Abstract Most ground-based observatories are equipped with wide-angle all-sky cameras to monitor the night sky conditions. Such camera systems can be used to provide an early warning of incoming clouds that can pose a danger to the telescope equipment through precipitation, as well as for sky quality monitoring. We investigate the use of different machine-learning approaches for automating the identification of mostly opaque clouds in all-sky camera data as a cloud warning system. In a deep-learning approach, we train a residual neural network (ResNet) on pre-labeled camera images. Our second approach extracts relevant and localized image features from camera images and uses these data to train a gradient-boosted tree-based model (lightGBM). We train both model approaches on a set of roughly 2000 images taken by the all-sky camera located at Lowell Observatory’s Discovery Channel Telescope, in which the presence of clouds has been labeled manually. The ResNet approach reaches an accuracy of 85% in detecting clouds in a given region of an image, but requires a significant amount of computing resources. Our lightGBM approach achieves an accuracy of 95% with a training sample of ∼1000 images and rather modest computing resources. Based on different performance metrics, we recommend the latter feature-based approach for automated cloud detection. Code that was built for this work is available online.

The Complex Rotational Light Curve of (385446) Manwë–Thorondor, a Multicomponent Eclipsing System in the Kuiper Belt

Abstract Kuiper Belt Object (385446) Manwë–Thorondor is a multiobject system with mutual events predicted to occur from 2014 to 2019. To detect the events, we observed the system at 4 epochs (UT 2016 August 25 and 26, 2017 July 22 and 25, 2017 November 9, and 2018 October 6) in g, r, and VR bands using the 4 m SOAR and the 8.1 m Gemini South telescopes at Cerro Pachón, Chile, and Lowell Observatory’s 4.3 m Discovery Channel Telescope at Happy Jack, Arizona. These dates overlap the uncertainty range (±0.5 day) for four inferior events (Thorondor eclipsing Manwë). We clearly observe variability for the unresolved system with a double-peaked period 11.88190 ± 0.00005 hr and ∼0.5 mag amplitude together with much longer-term variability. Using a multicomponent model, we simultaneously fit our observations and earlier photometry measured separately for Manwë and Thorondor with the Hubble Space Telescope. Our fit suggests Manwë is bilobed, close to the “barbell” shape expected for a strengthless body with density ∼0.8 g cm−3 in hydrostatic equilibrium. For Manwë, we thereby derive maximum width to length ratio ∼0.30, surface area equivalent to a sphere of diameter 190 km, geometric albedo 0.06, mass 1.4 × 1018 kg, and spin axis oriented ∼75° from Earth’s line of sight. Changes in Thorondor’s brightness by ∼0.6 mag with a ∼300 day period may account for the system’s long-term variability. Mutual events with unexpectedly shallow depth and short duration may account for residuals to the fit. The system is complex, providing a challenging puzzle for future modeling efforts.

The High-redshift Clusters Occupied by Bent Radio AGN (COBRA) Survey: Follow-up Optical Imaging

Abstract Here we present new red sequence overdensity measurements for 77 fields in the high-z Clusters Occupied by Bent Radio AGN (COBRA) survey, based on r- and i-band imaging taken with the Lowell Observatory’s Discovery Channel Telescope. We observe 38 COBRA fields in the r-band and 90 COBRA fields in the i-band. By combining the r- and i-band photometry with our 3.6 and 4.5 μm Spitzer IRAC observations, we identify 39 red sequence cluster candidates that host a strong overdensity of galaxies when measuring the excess of red sequence galaxies relative to a background field. We initially treat the radio host as the cluster center and then determine a new cluster center based on the surface density of red sequence sources. Using our color selection, we identify which COBRA cluster candidates have strong red sequence populations. By removing foreground and background contaminants, we more securely determine which fields include cluster candidates with a higher significance than our single-band observations. Additionally, of the 77 fields we analyze with a redshift estimate, 26 include newly estimated photometric redshifts.

TREADING CAREFULLY: V.M. SLIPHER, C.O. LAMPLAND, E.C. SLIPHER AND THEIR AMBIVALENT RELATIONSHIP WITH PERCIVAL LOWELL'S MARS

V.M. Slipher joined Lowell Observatory as an assistant in 1901, C.O. Lampland the following year, and E.C. Slipher, V.M.'s younger brother, in 1907. All three were to remain loyal to the observatory's founder Percival Lowell, and thus avoided the fate of Andrew Ellicott Douglass, who was dismissed in 1901 for having developed independent views (guestioning the reality of the markings Lowell had seen on Mars and especially Venus). Because of Lowell's tendency to generate controversy, the observatory was largely ostracized by professional astronomers during Lowell's lifetime, though his assistants—especially V.M.—managed, by eschewing controversial views and publishing rather sparsely—to gradually build up respect for the observatory in the years after Lowell's death in 1916. After a draining legal battle with Lowell's widow, the observatory's finances were stabilized and in 1927 Roger Lowell Putnam took over as Sole Trustee, marking a new era of relative prosperity for the observatory. Putnam's priorities were to revive the founder's unfinished legacies: to update Lowell's Mars theories, and to search for Planet X. The first priority called on the three senior staff members to write what I have called the "Great Lowell Observatory Mars Book," and considerable effort was expended. For reasons explained here, it was never completed, though rather belatedly, E.C. Slipher did produce a book on Mars in 1962 that comes as close as anything to its fulfillment.

Visible Spectroscopy from the Mission Accessible Near-Earth Object Survey (MANOS): Taxonomic Dependence on Asteroid Size

Abstract The Mission Accessible Near-Earth Object Survey (MANOS) aims to observe and characterize small (mean absolute magnitude H ∼ 25 mag) Near-Earth Objects (NEOs) that are accessible by spacecraft (mean Δv ∼ 5.7 km s−1) and that make close approaches with the Earth (mean Minimum Orbital Intersection Distance MOID ∼ 0.03 au). We present here the first results of the MANOS visible spectroscopic survey. The spectra were obtained from August 2013 to March 2018 at Lowell Observatory’s Discovery Channel 4.3 m telescope, and both Gemini North and South facilities. In total, 210 NEOs have been observed and taxonomically classified. Our taxonomic distribution shows significant variations with respect to surveys of larger objects. We suspect these to be due to a dependence of Main Belt source regions on object size. Compared to previous surveys of larger objects, we report a lower fraction of S+Q-complex asteroids of 43.8 ± 4.6%. We associate this decrease with a lack of Phocaea family members at very small size. We also report higher fractions of X-complex and A-type asteroids of 23.8 ± 3.3% and 3.8 ± 1.3% respectively due to an increase of Hungaria family objects at small size. We find a strong correlation between the Q/S ratio and perihelion distance. We suggest this correlation is due to planetary close encounters with Venus playing a major role in turning asteroids from S to Q-type. This hypothesis is supported by a similar correlation between the Q/S ratio and Venus MOID.

Inversion of asteroid photometry from Gaia DR2 and the Lowell Observatory photometric database

Context. Rotation properties (spin-axis direction and rotation period) and coarse shape models of asteroids can be reconstructed from their disk-integrated brightness when measured from various viewing geometries. These physical properties are essential for creating a global picture of structure and dynamical evolution of the main belt. Aims. The number of shape and spin models can be increased not only when new data are available, but also by combining independent data sets and inverting them together. Our aim was to derive new asteroid models by processing readily available photometry. Methods. We used asteroid photometry compiled in the Lowell Observatory photometry database with photometry from the Gaia Data Release 2. Both data sources are available for about 5400 asteroids. In the framework of the Asteroids@home distributed computing project, we applied the light curve inversion method to each asteroid to find its convex shape model and spin state that fits the observed photometry. Results. Due to the limited number of Gaia DR2 data points and poor photometric accuracy of Lowell data, we were able to derive unique models for only ∼1100 asteroids. Nevertheless, 762 of these are new models that significantly enlarge the current database of about 1600 asteroid models. Conclusions. Our results demonstrate the importance of a combined approach to inversion of asteroid photometry. While our models in general agree with those obtained by separate inversion of Lowell and Gaia data, the combined inversion is more robust, model parameters are more constrained, and unique models can be reconstructed in many cases when individual data sets alone are not sufficient.

Outdoor Areas Lighting with LEDs – the Competition Between Scotopic Efficacy and Light Pollution

In this paper the effect of typical outdoor LED lamps on star visibility index SVI was analyzed. For those lamps the spectral power distribution SPD, the nearest color temperature CCT [K] and efficacy n [lm/W] are provided. For given lamp, the SVI has been defined as ratio of its scotopic flux to scotopic flux created by full moon. The calculations shows that, the use of lamps with low CCT does not significantly affect the of the value SVI. Unfortunately from an economic point of view, those kind of lamps are less attractive in applications because of their low n. Full Text: PDF ReferencesC. Rich, T. Longcore, eds., Ecological Consequences of Artificial Night Lighting, Island Press, Washington, DC (2006) DirectLink T. Longcore, C. Rich, Ecological light pollution. Front Ecol Environ 2(4), (2004). CrossRef K. J. Navara, R. J. Nelson, The dark side of light at night: physiological, epidemiological, and ecological consequences. J Pineal Res 43, (2007) CrossRef A. Bierman, Will switching to LED outdoor lighting increase sky glow, Lighting Res. Technol., Vol. 44, (2012). CrossRef Ch. B. Luginbuhl, P. A. Boley, D. R. Davis, The impact of light source spectral power distributionon sky glow, Journal of Quantitative Spectroscopy and Radiative Transfer, (2014). CrossRef M. Aube, J. Roby J, M. Kocifaj, Evaluating Potential Spectral Impacts of Various Artificial Lights on Melatonin Suppression, Photosynthesis, and Star Visibility. PLOS ONE, Vol. 8, (2013). CrossRef J. A. Brons, J. D. Bullough, M. S. Rea, Outdoor site-lighting performance: A comprehensive and quantitative framework for assessing light pollution, Lighting Res. Technol., Vol. 40, (2008). CrossRef I. Fryc, P. Tabaka, The night sky light pollution created by outdoor luminaires, Przeglad Elektrotechniczny, R. 93, No. 6, (2017). CrossRef I. Fryc, F. Bisegna, P. Tabaka, Lighting of recreation grounds as a source of sky glow - the influence of luminaire type on this phenomenon, 1st IEEE International Conference On Environment And Electrical Engineering and 17th IEEE Industrial And Commercial Power Systems Europe (2017). CrossRef Chr. B. Luginbuhl, C. E. Walker, R. J. Wainscoat, Lighting and astronomy, Physics Today 62, 12, 32 (2009). CrossRef G. W. Lockwood, D. T. Thompson, and R. D. Floyd, Sky glow and outdoor lighting trends since 1976 at The Lowell Observatory, Publications of the Astronomical Society of the Pacific, Volume 102, Number 650, (1990). CrossRef Ch. B. Luginbuhl, P. A. Boley, D. R. Davis, D. M. Duriscoe, The effects of lamp spectral distribution on sky glow over observatories. Highlights ofastronomy Vol. 16, 2014, as presented at the XXVIIIth generalassembly of the international Astronomical Union, Beijing, China,August 20-31, (2012). CrossRef

The Peculiar Volatile Composition of CO-dominated Comet C/2016 R2 (PanSTARRS)

Abstract Comet C/2016 R2 (PanSTARRS) has a peculiar volatile composition, with CO being the dominant volatile, as opposed to H2O, and one of the largest N2/CO ratios ever observed in a comet. Using observations obtained with the Spitzer Space Telescope, NASA’s Infrared Telescope Facility, the 3.5 m Astrophysical Research Consortium telescope at Apache Point Observatory, the Discovery Channel Telescope at Lowell Observatory, and the Arizona Radio Observatory 10 m Submillimeter Telescope, we quantified the abundances of 12 different species in the coma of R2 PanSTARRS: CO, CO2, H2O, CH4, C2H6, HCN, CH3OH, H2CO, OCS, C2H2, NH3, and N2. We confirm the high abundances of CO and N2 and heavy depletions of H2O, HCN, CH3OH, and H2CO compared to CO reported by previous studies. We provide the first measurements (or most sensitive measurements/constraints) on H2O, CO2, CH4, C2H6, OCS, C2H2, and NH3, all of which are depleted relative to CO by at least 1–2 orders of magnitude compared to values commonly observed in comets. The observed species also show strong enhancements relative to H2O, and, even when compared to other species like CH4 or CH3OH, most species show deviations from typical comets by at least a factor of 2–3. The only mixing ratios found to be close to typical are CH3OH/CO2 and CH3OH/CH4. The CO2/CO ratio is within a factor of 2 of those observed for C/1995 O1 (Hale-Bopp) and C/2006 W3 (Christensen) at a similar heliocentric distance, though it is at least an order of magnitude lower than many other comets observed with AKARI. While R2 PanSTARRS was located at a heliocentric distance of 2.8 au at the time of our observations in 2018 January/February, we argue, using sublimation models and comparison to other comets observed at similar heliocentric distance, that this alone cannot account for the peculiar observed composition of this comet and therefore must reflect its intrinsic composition. We discuss possible implications for this clear outlier in compositional studies of comets obtained to date and encourage future dynamical and chemical modeling in order to better understand what the composition of R2 PanSTARRS tells us about the early solar system.

Gas Jet Morphology and the Very Rapidly Increasing Rotation Period of Comet 41P/Tuttle–Giacobini–Kresák

Abstract We present results from our 47 night imaging campaign of Comet 41P/Tuttle–Giacobini–Kresák conducted from Lowell Observatory between 2017 February 16 and July 2. Coma morphology revealed gas jets, whose appearance and motion as a function of time yielded the rotation period and other properties. All narrowband CN images exhibited either one or two jets; one jet appeared as a partial face-on spiral with clockwise rotation, while the second jet evolved from a side-on corkscrew, through face-on, to corkscrew again, with only a slow evolution throughout the apparition due to progressive viewing geometry changes. A total of 78 period determinations were made over a 7 week interval, yielding a smooth and accelerating rotation period starting at 24 hr (March 21 and 22) and passing 48 hr on April 28. While this is by far the fastest rate of change ever measured for a comet nucleus, the torque required is readily within what can exist given likely properties of the nucleus. If the torque remained constant, we estimate that the nucleus could have stopped rotating and/or begun to tumble as soon as only 2 months following perihelion and will certainly reach this stage by early in the next apparition. Working backward in time, Tuttle–Giacobini–Kresák would have been rotating near its rotational breakup velocity three to four orbits earlier, suggesting that its extreme 7 mag outburst observed in 2001 might have been caused by a partial fragmentation at that time, as might the pair of 1973 8 mag outbursts if there had been an earlier spin-down and spin-up cycle.

Final compilation of photometry of Uranus and Neptune, 1972–2016.

Photometric observations of Uranus and Neptune made each year since 1972 at Lowell Observatory in the b (472 nm) and y (551 nm) filters of the Strömgren photometric system recorded the mainly seasonal variations of disk-integrated albedos of these objects. The measurements predate Voyager and Hubble Telescope multi-wavelength imaging and overlap more than a decade of ground-based adaptive optics near-IR imaging. This paper is a final archive and brief summarizing discussion of observations through 2016 and includes electronic tables of 360 observations of Uranus and 433 observations of Neptune.

Coma Morphology, Numerical Modeling, and Production Rates for Comet C/Lulin (2007 N3)

Abstract We report on narrowband photometry and extensive imaging observations of comet C/Lulin (2007 N3) obtained at Lowell Observatory during 2008 and 2009. Enhanced CN images revealed a double-corkscrew morphology with two near-polar jets oriented approximately east–west, and both CN and dust images showed nightly rotational variability and seasonal changes in bulk morphology. We determined a rotational pole direction of R.A./decl. = 81°/+29° with an obliquity of 97° and a sidereal rotation period of 41.45 ± 0.05 hr. Monte Carlo numerical modeling best replicated the observed CN features with an eastern source area at lat/long −80°/125° and an ∼10° radius and a western source area at lat/long +77°/245° and an ∼20° radius, ∼4× larger than the eastern source. An additional small, near-equatorial source was necessary to reproduce some dust features. Water morphology based on OH was quite different from that of the carbon-bearing species, implying a different driver for the polar jets such as CO or CO2. Ion tails were detected in decontaminated images from both the dust and NH filters, likely being H2O+ and OH+, respectively. We measured water production both before and after perihelion and extrapolated peak water production at perihelion to be about 1.0 × 1029 molecules s−1. We estimated an active fraction of only 4%–5% and a nucleus radius of up to ∼8 km. Our data suggest that Lulin, defined as dynamically new in a statistical sense, behaves more like a long-period comet due to its nearly asteroidal early appearance, isolated source regions, and dust properties.