Recent Submissions

  • Search for Stellar Companions of Exoplanet Host Stars with AstraLux/CAHA 2.2 m

    Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergässchen 2, D-07745 Jena, Germany; Armagh Observatory and Planetarium, College Hill, BT61 9DB Armagh, UK; Queen's University Belfast, School of Mathematics and Physics, Main Physics Building,University Road, BT7 1NN Belfast, UK; Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Schillergässchen 2, D-07745 Jena, Germany; University of Galway, University Road, H91 TK33 Galway, Ireland; Research School of Astronomy & Astrophysics, Australian National University, Mount Stromlo Observatory Cotter Road, Weston Creek, Canberra, ACT, 2611, Australia; ARC Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Mount Stromlo Road, Stromlo, ACT, 2611, Australia; Instituto de Astrofísica de Andalucía CSIC, Glorieta de la Astronomia, Apartado 3004,18080 Granada, Spain; Schlagenhauf, Saskia; Mugrauer, Markus; Ginski, Christian; Buder, Sven; Fernández, Matilde; et al. (Monthly Notices of the Royal Astronomical Society, 2024-04-01)
    Stellar multiplicity is a key aspect of exoplanet diversity, as the presence of more than one star in a planetary system can have both devastating and positive effects on its formation and evolution. In this paper, we present the results of a Lucky Imaging survey of 212 exoplanet host stars performed with AstraLux at the 2.2 m telescope of the Centro Astronómico Hispano en Andalucía. The survey includes data from seven observing epochs between August 2015 and September 2020, and data for individual targets from four earlier observing epochs. The targets of this survey are nearby, bright, solar-like stars with high proper motions. In total, we detected 46 co-moving companions of 43 exoplanet host stars. Accordingly, this survey shows that the minimum multiplicity rate of exoplanet host stars is $20 \pm 3~{\rm per\ cent}$. In total, 33 binary and 10 hierarchical triple star systems with exoplanets have been identified. All companions were found to have a common proper motion with the observed exoplanet host stars, and with our astrometry we even find evidence of orbital motion for 28 companions. For all targets, we determine the detection limit and explore the detection space for possible additional companions of these stars. Based on the reached detection limit, additional co-moving companions beyond the detected ones can be excluded around all observed exoplanet host stars. The increasing number of exoplanets discovered in multiple stellar systems suggests that the formation of planets in such systems is by no means rare, but common. Therefore, our study highlights the need to consider stellar multiplicity in future studies of exoplanet habitability.
  • NGTS-28Ab: a short period transiting brown dwarf

    School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK; European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, NL-2201 AZ Noordwijk, the Netherlands; European Southern Observatory, Karl-Schwarzschildstr. 2, D-85748 Garching bei München, Germany; Département d'astronomie, Université de Genéve, 51 chemin Pegasi, CH-1290 Sauverny, Switzerland; NASA Ames Research Center, Moffett Field, CA 94035, USA; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA; NASA Exoplanet Science Institute, IPAC, California Institute of Technology, Pasadena, CA 91125, USA; NASA Ames Research Center, Moffett Field, CA 94035, USA; Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA; Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, B-4000 Liège, Belgium; Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA; Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38200, La Laguna, Tenerife, Spain; Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile; Centro de Astrofísica y Tecnologías Afines (CATA), Casilla 36-D, Santiago, Chile; Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK; et al. (Monthly Notices of the Royal Astronomical Society, 2024-05-01)
    We report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterize the system. We find an orbital period of ~1.25 d, a mass of $69.0^{+5.3}_{-4.8}$ M<SUB>J</SUB>, close to the hydrogen burning limit, and a radius of 0.95 ± 0.05 R<SUB>J</SUB>. We determine the age to be &gt;0.5 Gyr, using model isochrones, which is found to be in agreement with spectral energy distribution fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.
  • Search for stellar companions of exoplanet host stars with AstraLux/CAHA 2.2 m

    Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Jena, Germany; Armagh Observatory and Planetarium, Armagh, UK; Queen's University Belfast, UK; Astrophysikalisches Institut und Universitäts-Sternwarte Jena, Jena, Germany; University of Galway, Galway, Ireland; Research School of Astronomy &amp; Astrophysics, Australian National University, Canberra, Australian Capital Territory, Australia; ARC Center of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia; Instituto de Astrofísica de Andalucía CSIC, Glorieta de la Astronomia, Granada, Spain; Schlagenhauf, Saskia; Mugrauer, Markus; Ginski, Christian; Buder, Sven; Fernández, Matilde; et al. (Monthly Notices of the Royal Astronomical Society, 2024-02-01)
    Stellar multiplicity is a key aspect of exoplanet diversity, as the presence of more than one star in a planetary system can have both devastating and positive effects on its formation and evolution. In this paper, we present the results of a lucky imaging survey of 212 exoplanet host stars performed with AstraLux at CAHA 2.2 m. The survey includes data from seven observing epochs between August 2015 and September 2020, and data for individual targets from four earlier observing epochs. The targets of this survey are nearby, bright, solar-like stars with high proper motions. In total, we detected 46 co-moving companions of 43 exoplanet host stars. Accordingly, this survey shows that the minimum multiplicity rate of exoplanet host stars is $20 \pm 3~{{\%}}$. In total, 33 binary and ten hierarchical triple star systems with exoplanets have been identified. All companions were found to have a common proper motion with the observed exoplanet host stars, and with our astrometry we even find evidence of orbital motion for 28 companions. For all targets, we determined the detection limit and explore the detection space for possible additional companions of these stars. Based on the reached detection limit, additional co-moving companions beyond the detected ones can be excluded around all observed exoplanet host stars. The increasing number of exoplanets discovered in multiple stellar systems suggests that the formation of planets in such systems is by no means rare, but common. Therefore, our study highlights the need to consider stellar multiplicity in future studies of exoplanet habitability.
  • NGTS-28Ab: A short period transiting brown dwarf

    School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK; European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands; European Southern Observatory, Karl-Schwarzschildstr. 2, D-85748 Garching bei München, Germany; Département d'astronomie, Université de Genéve, 51 chemin Pegasi, 1290 Sauverny, Switzerland; NASA Ames Research Center, Moffett Field, CA 94035, USA; Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 USA; NASA Exoplanet Science Institute, IPAC, California Institute of Technology, Pasadena, CA 91125 USA; NASA Ames Research Center, Moffett Field, CA 94035, USA; Bay Area Environmental Research Institute, Moffett Field, CA 94035, USA; Astrobiology Research Unit, Université de Liège, Allée du 6 Août 19C, B-4000 Liège, Belgium; Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA; Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38200, La Laguna, Tenerife, Spain; Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile; Centro de Astrofísica y Tecnologías Afines (CATA), Casilla 36-D, Santiago, Chile; Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK; Dept. of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, UK; et al. (Monthly Notices of the Royal Astronomical Society, 2024-02-01)
    We report the discovery of a brown dwarf orbiting a M1 host star. We first identified the brown dwarf within the Next Generation Transit Survey data, with supporting observations found in TESS sectors 11 and 38. We confirmed the discovery with follow-up photometry from the South African Astronomical Observatory, SPECULOOS-S, and TRAPPIST-S, and radial velocity measurements from HARPS, which allowed us to characterise the system. We find an orbital period of ~1.25 d, a mass of $69.0^{+5.3}_{-4.8}$ M<SUB>J</SUB>, close to the Hydrogen burning limit, and a radius of 0.95 ± 0.05 R<SUB>J</SUB>. We determine the age to be &gt;0.5 Gyr, using model isochrones, which is found to be in agreement with SED fitting within errors. NGTS-28Ab is one of the shortest period systems found within the brown dwarf desert, as well as one of the highest mass brown dwarfs that transits an M dwarf. This makes NGTS-28Ab another important discovery within this scarcely populated region.
  • Evidence of Eta Aquariid outbursts recorded in the classic Maya hieroglyphic script using orbital integrations

    6324 Chesla Dr, Gainesville, GA, 30506, USA; Armagh Observatory &amp; Planetarium, College Hill, Armagh, BT61 9DG, UK; Kinsman, J. H.; Asher, D. J. (Planetary and Space Science, 2017-09-01)
    No firm evidence has existed that the ancient Maya civilization recorded specific occurrences of meteor showers or outbursts in the corpus of Maya hieroglyphic inscriptions. In fact, there has been no evidence of any pre-Hispanic civilization in the Western Hemisphere recording any observations of any meteor showers on any specific dates. <P />The authors numerically integrated meteoroid-sized particles released by Comet Halley as early as 1404 BC to identify years within the Maya Classic Period, AD 250-909, when Eta Aquariid outbursts might have occurred. Outbursts determined by computer model were then compared to specific events in the Maya record to see if any correlation existed between the date of the event and the date of the outburst. The model was validated by successfully explaining several outbursts around the same epoch in the Chinese record. Some outbursts observed by the Maya were due to recent revolutions of Comet Halley, within a few centuries, and some to resonant behavior in older Halley trails, of the order of a thousand years. Examples were found of several different Jovian mean motion resonances as well as the 1:3 Saturnian resonance that have controlled the dynamical evolution of meteoroids in apparently observed outbursts.
  • Orbital dynamics of highly probable but rare Orionid outbursts possibly observed by the ancient Maya

    P.O. Box 723, Murrayville, Georgia, 30564, USA; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK; Kinsman, J. H.; Asher, D. J. (Monthly Notices of the Royal Astronomical Society, 2020-03-01)
    Using orbital integrations of particles ejected from Comet Halley's passages between 1404 and 240 BC, the authors investigate possible outbursts of the Orionids (twin shower of the Eta Aquariids) that may have been observed in the Western hemisphere. In an earlier orbital integration study, the authors determined there was a high probability linking probable outbursts of the Eta Aquariid meteor shower with certain events recorded in inscriptions during the Maya Classic Period, AD 250-900. This prior examination was the first scientific inquiry of its kind into ancient meteor outbursts possibly recorded in the Western hemisphere where previously no pre-Columbian observations had existed. In the current paper, the aim is to describe orbital dynamics of rare but probable Orionid outbursts that would have occurred on or near applicable dates recorded in the Classic Maya inscriptions. Specifically, significant probable outbursts are found in AD 417 and 585 out of 30 possible target years. The driving mechanisms for outbursts in those two years are Jovian 1:6 and 1:7 mean motion resonances acting to maintain compact structures within the Orionid stream for over 1 kyr. Furthermore, an Orionid outburst in AD 585 recorded by China is confirmed.
  • Photoionization Models of the Inner Gaseous Disk of the Herbig Be Star BD+65 1637

    Department of Physics and Astronomy, The University of Western Ontario, London, Ontario Canada N6A 3K7, Canada; Center For Planetary Science &amp; Exploration, The University of Western Ontario, London, Ontario N6A 3K7, Canada;; Department of Physics and Astronomy, The University of Western Ontario, London, Ontario Canada N6A 3K7, Canada; Center For Planetary Science &amp; Exploration, The University of Western Ontario, London, Ontario N6A 3K7, Canada; Department of Physics and Astronomy, The University of Western Ontario, London, Ontario Canada N6A 3K7, Canada; Armagh Observatory, Armagh, Northern Ireland, UK; Patel, P.; Sigut, T. A. A.; Landstreet, J. D. (The Astrophysical Journal, 2016-01-01)
    We attempt to constrain the physical properties of the inner, gaseous disk of the Herbig Be star BD+65 1637 using non-LTE, circumstellar disk codes and observed spectra (3700-10500 Å) from the ESPaDOnS instrument on the Canada-France-Hawaii Telescope. The photoionizing radiation of the central star is assumed to be the sole source of input energy for the disk. We model optical and near-infrared emission lines that are thought to form in this region using standard techniques that have been successful in modeling the spectra of classical Be stars. By comparing synthetic line profiles of hydrogen, helium, iron, and calcium with the observed line profiles, we try to constrain the geometry, density structure, and kinematics of the gaseous disk. Reasonable matches have been found for all line profiles individually; however, no disk density model based on a single power law for the equatorial density was able to simultaneously fit all of the observed emission lines. Among the emission lines, the metal lines, especially the Ca II IR triplet, seem to require higher disk densities than the other lines. Excluding the Ca II lines, a model in which the equatorial disk density falls as 10<SUP>-10</SUP> (R<SUB>*</SUB>/R)<SUP>3</SUP> g cm<SUP>-3</SUP> seen at an inclination of 45° for a 50 R<SUB>*</SUB> disk provides reasonable matches to the overall line shapes and strengths. The Ca II lines seem to require a shallower drop-off as 10<SUP>-10</SUP> (R<SUB>*</SUB>/R)<SUP>2</SUP> g cm<SUP>-3</SUP> to match their strength. More complex disk density models are likely required to refine the match to the BD+65 1637 spectrum.
  • Constraints on the structure and seasonal variations of Triton's atmosphere from the 5 October 2017 stellar occultation and previous observations

    LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, 5 place Jules Janssen, 92190, Meudon, France; UNESP - São Paulo State University, Grupo de Dinâmica Orbital e Planetologia, Guaratinguetá, SP, 12516-410, Brazil; Laboratório Interinstitucional de e-Astronomia - LIneA, Rua Gal. José Cristino 77, Rio de Janeiro, RJ, 20921-400, Brazil; Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n., 18008-, Granada, Spain; Departments of Earth &amp; Planetary Sciences and Physics &amp; Astronomy, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD, 21218, USA; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, 5 place Jules Janssen, 92190, Meudon, France; National Aeronautics and Space Administration (NASA), Ames Research Center, Space Science Division, Moffett Field, CA, 94035, USA; Laboratoire de Météorologie Dynamique, IPSL, Université PSL, CNRS, Sorbonne Université, 4 place Jussieu, 5005, Paris, France; Institut Polytechnique des Sciences Avancées IPSA, 63 boulevard de Brandebourg, 94200, Ivry-sur-Seine, France; IMCCE/Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Univ. Lille -, Avenue Denfert Rochereau, 5014, Paris, France; Université Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange, Bd de l'Observatoire, CS 34229, 06304, Nice cedex 4, France; Departamento de Astronomía, Universidad de Chile, Camino del Observatorio, 1515, Las Condes, Santiago, Chile; Comisión Nacional de Investigatión y Desarrollo Aeroespacial del Perú - CONIDA, Peru; Observatorio Astronómico de Moquegua, Moquegua, Peru; LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, 5 place Jules Janssen, 92190, Meudon, France; naXys, University of Namur, 8 Rempart de la Vierge, Namur, 5000, Belgium; et al. (Astronomy and Astrophysics, 2022-03-01)
    Context. A stellar occultation by Neptune's main satellite, Triton, was observed on 5 October 2017 from Europe, North Africa, and the USA. We derived 90 light curves from this event, 42 of which yielded a central flash detection. <BR /> Aims: We aimed at constraining Triton's atmospheric structure and the seasonal variations of its atmospheric pressure since the Voyager 2 epoch (1989). We also derived the shape of the lower atmosphere from central flash analysis. <BR /> Methods: We used Abel inversions and direct ray-tracing code to provide the density, pressure, and temperature profiles in the altitude range ~8 km to ~190 km, corresponding to pressure levels from 9 µbar down to a few nanobars. <BR /> Results: (i) A pressure of 1.18 ± 0.03 µbar is found at a reference radius of 1400 km (47 km altitude). (ii) A new analysis of the Voyager 2 radio science occultation shows that this is consistent with an extrapolation of pressure down to the surface pressure obtained in 1989. (iii) A survey of occultations obtained between 1989 and 2017 suggests that an enhancement in surface pressure as reported during the 1990s might be real, but debatable, due to very few high S/N light curves and data accessible for reanalysis. The volatile transport model analysed supports a moderate increase in surface pressure, with a maximum value around 2005-2015 no higher than 23 µbar. The pressures observed in 1995-1997 and 2017 appear mutually inconsistent with the volatile transport model presented here. (iv) The central flash structure does not show evidence of an atmospheric distortion. We find an upper limit of 0.0011 for the apparent oblateness of the atmosphere near the 8 km altitude. <P />Light curves are only available at the CDS via anonymous ftp to <A href=http://cdsarc.u-strasbg.fr>cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href=http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/659/A136>http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/659/A136</A>
  • The hazard from fragmenting comets

    Armagh Observatory and Planetarium, College Hill, Armagh BT67 9DG, Northern Ireland; Napier, W. M. (Monthly Notices of the Royal Astronomical Society, 2019-09-01)
    Comet disintegration proceeds through both sublimation and discrete splitting events. The cross-sectional area of material ejected by a comet may, within days, become many times greater than that of the Earth, making encounters with such debris much more likely than collisions with the nucleus itself. The hierarchic fragmentation and sublimation of a large comet in a short-period orbit may yield many hundreds of such short-lived clusters. We model this evolution with a view to assessing the probability of an encounter that might have significant terrestrial effects, through atmospheric dusting or multiple impacts. Such an encounter may have contributed to the large animal extinctions and sudden climatic cooling of 12 900 yr ago, and the near-simultaneous collapse of civilisations around 2350 BC.
  • Influence of aerosols, clouds, and sunglint on polarization spectra of Earthshine

    Meteorological Institute, Ludwig-Maximilians-University, Theresienstr. 37, 80333, Munich, Germany; Schnell Algorithms, Am Erdäpfelgarten 1, 82205, Gilching, Germany; European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748, Garching, Germany; Armagh Observatory &amp; Planetarium, College Hill, Armagh, BT61 9DG, UK; Emde, Claudia; Buras-Schnell, Robert; Sterzik, Michael; Bagnulo, Stefano (Astronomy and Astrophysics, 2017-08-01)
    Context. Ground-based observations of the Earthshine, I.e., the light scattered by Earth to the Moon, and then reflected back to Earth, simulate space observations of our planet and represent a powerful benchmark for the studies of Earth-like planets. Earthshine spectra are strongly linearly polarized, owing to scattering by molecules and small particles in the atmosphere of the Earth and surface reflection, and may allow us to measure global atmospheric and surface properties of planet Earth. <BR /> Aims: We aim to interpret already published spectropolarimetric observations of the Earthshine by comparing them with new radiative transfer model simulations including a fully realistic three-dimensional (3D) surface-atmosphere model for planet Earth. <BR /> Methods: We used the highly advanced Monte Carlo radiative transfer model MYSTIC to simulate polarized radiative transfer in the atmosphere of the Earth without approximations regarding the geometry, taking into account the polarization from surface reflection and multiple scattering by molecules, aerosol particles, cloud droplets, and ice crystals. <BR /> Results: We have shown that Earth spectropolarimetry is highly sensitive to all these input parameters, and we have presented simulations of a fully realistic Earth atmosphere-surface model including 3D cloud fields and two-dimensional (2D) surface property maps. Our modeling results show that scattering in high ice water clouds and reflection from the ocean surface are crucial to explain the continuum polarization at longer wavelengths as has been reported in Earthshine observations taken at the Very Large Telescope in 2011 (3.8% and 6.6% at 800 nm, depending on which part of Earth was visible from the Moon at the time of the observations). We found that the relatively high degree of polarization of 6.6% can be attributed to light reflected by the ocean surface in the sunglint region. High ice-water clouds reduce the amount of absorption in the O<SUB>2</SUB>A band and thus explain the weak O<SUB>2</SUB>A band feature in the observations.
  • Extra-Terrestrial Meteors

    Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK; Institute for Celestial Mechanics and Calculation of Ephemerides, Paris Observatory, Paris, France; Astronomy Department, Boston University, Boston MA, USA; Applied Physics I, Bilbao School of Engineers, University of the Basque Country, Bilbao, Spain; NASA Goddard Space Flight Center, Planetary Magnetospheres, Greenbelt MD, USA; Christou, Apostolos; Vaubaillon, Jérémie; Withers, Paul; Hueso, Ricardo; Killen, Rosemary (Meteoroids: Sources of Meteors on Earth and Beyond, 2019-10-01)
    All planets and satellites of our solar system are subject to a continuous rain of material, ranging in size from specks of dust to objects the size of boulders. Upon impact, these objects deposit their kinetic energy into the incident surface or atmosphere and affect the environment of the target body in ways not yet well understood. Recent high-profile events - impact flashes on Jupiter and the encounter of comet C/Siding Spring with Mars - brought the study of ``extraterrestrial meteors'' and their effects into the fore. Here we review the history, status and future prospects of meteor studies on planets other than the Earth. Would bright meteors appear in the atmosphere of Mars and what are the long-term effects on the planet's atmosphere? How do high-speed impacts of particulate matter on the airless surfaces of Mercury and the Moon affect their environment and those of the countless other bodies like them? These are some of the questions we attempt to answer in this Chapter.
  • The cloudbow of planet Earth observed in polarisation

    European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748, Garching, Germany; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, UK; Meteorological Institute, Ludwig-Maximilians-University, Theresienstr. 37, 80333, Munich, Germany; Sterzik, Michael F.; Bagnulo, Stefano; Emde, Claudia; Manev, Mihail (Astronomy and Astrophysics, 2020-07-01)
    Context. Scattering processes in the atmospheres of planets cause characteristic features that can be particularly well observed in polarisation. For planet Earth, both molecular scattering (Rayleigh) and scattering by small particles (Mie) imprint specific signatures in its phase curve. Polarised phase curves allow us to infer physical and chemical properties of the atmosphere like the composition of the gaseous and liquid components, droplet sizes, and refraction indices. <BR /> Aims: An unequivocal prediction of a liquid-water-loaded atmosphere is the existence of a rainbow feature at a scattering angle of around 138-144°. Earthshine allows us to observe the primary rainbow in linear polarisation. <BR /> Methods: We observed polarisation spectra of Earthshine using FORS2 at the Very Large Telescope for phase angles from 33° to 65° (Sun-Earth-Moon angle). The spectra were used to derive the degree of polarisation in the B, V, R, and I passbands and the phase curve from 33° to 136°. The new observations extend to the smallest phases that can be observed from the ground. <BR /> Results: The degree of polarisation of planet Earth is increasing for decreasing phase angles downwards of 45° in the B, V, R, and I passbands. From comparison of the phase curve observed with models of an Earth-type atmosphere we are able to determine the refractive index of water and to constrain the mean water droplet sizes to 6-7μm. Furthermore, we can retrieve the mean cloud fraction of liquid water clouds to 0.3, and the mean optical depth of the water clouds to values between 10 and 20. <BR /> Conclusions: Our observations allow us to discern two fundamentally different scattering mechanisms of the atmosphere of planet Earth: molecular and particle scattering. The physical and chemical properties can be retrieved with high fidelity through suitable inversion of the phase curve. Observations of polarimetric phase curves of planets beyond the Solar System shall be extremely valuable for a thorough characterisation of their atmospheres.
  • Modelling the inner debris disc of HR 8799

    University of Sao Paulo State, Sao Paulo, Botucatu 18618-970, Brazil; School of Physics, UNSW Australia, Sydney, NSW 2052, Australia; Computational Engineering and Science Research Centre, University of Southern Queensland, Toowoomba, QLD 4350, Australia; Australian Centre for Astrobiology, UNSW Australia, Sydney, NSW 2052, Australia; School of Physics, UNSW Australia, Sydney, NSW 2052, Australia; Computational Engineering and Science Research Centre, University of Southern Queensland, Toowoomba, QLD 4350, Australia; Australian Centre for Astrobiology, UNSW Australia, Sydney, NSW 2052, Australia; School of Physics, UNSW Australia, Sydney, NSW 2052, Australia; Australian Centre for Astrobiology, UNSW Australia, Sydney, NSW 2052, Australia; Computational Engineering and Science Research Centre, University of Southern Queensland, Toowoomba, QLD 4350, Australia; Korea Astronomy and Space Science Institute, 776 Daedukdae-ro, Yuseong-gu, Daejeon 305-348, Republic of Korea; Armagh Observatory, College Hill, Armagh BT61 9DG, UK; Contro, B.; Horner, J.; Wittenmyer, R. A.; Marshall, J. P.; Hinse, T. C. (Monthly Notices of the Royal Astronomical Society, 2016-11-01)
    In many ways, the HR 8799 planetary system strongly resembles our own. It features four giant planets and two debris belts, analogues to the Asteroid and Edgeworth-Kuiper belts. Here, we present the results of dynamical simulations of HR8799's inner debris belt, to study its structure and collisional environment. Our results suggest that HR 8799's inner belt is highly structured, with gaps between regions of dynamical stability. The belt is likely constrained between sharp inner and outer edges, located at ∼6 and ∼8 au, respectively. Its inner edge coincides with a broad gap cleared by the 4:1 mean-motion resonance with HR 8799e. Within the belt, planetesimals are undergoing a process of collisional attrition like that observed in the Asteroid belt. However, whilst the mean collision velocity in the Asteroid belt exceeds 5 km s<SUP>-1</SUP>, the majority of collisions within HR 8799's inner belt occur with velocities of order 1.2 km s<SUP>-1</SUP>, or less. Despite this, they remain sufficiently energetic to be destructive - giving a source for the warm dust detected in the system. Interior to the inner belt, test particles remain dynamically unstirred, aside from narrow bands excited by distant high-order resonances with HR 8799e. This lack of stirring is consistent with earlier thermal modelling of HR 8799's infrared excess, which predicted little dust inside 6 au. The inner system is sufficiently stable and unstirred that the formation of telluric planets is feasible, although such planets would doubtless be subject to a punitive impact regime, given the intense collisional grinding required in the inner belt to generate the observed infrared excess.
  • A polarimetric study of asteroids: fitting phase-polarization curves

    INAF - Osservatorio Astrofisico di Torino, I-10025 Pino Torinese, Italy; Armagh Observatory, College Hill, Armagh BT61 9DG, UK; CASLEO and San Juan National University, J5402DSP, San Juan, Argentina; Observatoire de la Côte d'Azur, F-06304 Nice Cedex 4, France; Planetary Science Institute, Tucson, AZ 85719-2395, USA; Cellino, A.; Bagnulo, S.; Gil-Hutton, R.; Tanga, P.; Canada-Assandri, M.; et al. (Monthly Notices of the Royal Astronomical Society, 2016-01-01)
    By considering all published asteroid linear polarization data available in the literature, it is possible to obtain updated phase-polarization curves for several tens of objects. In a separate paper, we have produced new calibrations of different relations between the geometric albedo and several polarimetric parameters, based on an analysis of a limited sample of asteroids for which the albedo is known with sufficient accuracy. In this paper, we present the main polarization parameters and corresponding albedos for a larger data set of asteroids which we did not use for calibration purposes. We find a good agreement between the albedo values computed using different polarization parameters. Conversely, in the case of the so-called Barbarian asteroids the situation is rather unclear. Moreover, we present an updated analysis of the distributions of different polarimetric parameters, including the so-called inversion angle and the solar phase angle corresponding to the extreme value of negative polarization, and study their mutual relations. We find that the above parameters can be used to clearly distinguish some unusual classes of asteroids. Polarimetric parameters are known to be related to physical properties of asteroid surfaces which are difficult to infer by means of other observing techniques. By using a much larger data set, in our analysis we confirm and extend some results obtained in the past by other authors, and we explore more systematically some features that had been mostly unexplored before, mainly concerning the morphology of the negative polarization branch.
  • The Dynamical History of Chariklo and Its Rings

    Hazard Community and Technical College, Community College Drive, Hazard, KY 41701, USA ; Computational Engineering and Science Research Centre, University of Southern Queensland, West Street, Toowoomba, QLD 4350, Australia;; Computational Engineering and Science Research Centre, University of Southern Queensland, West Street, Toowoomba, QLD 4350, Australia ; Australian Centre for Astrobiology, UNSW Australia, Sydney, NSW 2052, Australia; Korea Astronomy and Space Science Institute, 776 Daedukdae-ro, Yuseong-gu, Daejeon 305-348, Korea ; Armagh Observatory, College Hill, Armagh BT61 9DG, UK; Computational Engineering and Science Research Centre, University of Southern Queensland, West Street, Toowoomba, QLD 4350, Australia; Wood, Jeremy; Horner, Jonti; Hinse, Tobias C.; Marsden, Stephen C. (The Astronomical Journal, 2017-06-01)
    Chariklo is the only small solar system body confirmed to have rings. Given the instability of its orbit, the presence of rings is surprising, and their origin remains poorly understood. In this work, we study the dynamical history of the Chariklo system by integrating almost 36,000 Chariklo clones backward in time for 1 Gyr under the influence of the Sun and the four giant planets. By recording all close encounters between the clones and planets, we investigate the likelihood that Chariklo’s rings could have survived since its capture to the Centaur population. Our results reveal that Chariklo’s orbit occupies a region of stable chaos, resulting in its orbit being marginally more stable than those of the other Centaurs. Despite this, we find that it was most likely captured to the Centaur population within the last 20 Myr, and that its orbital evolution has been continually punctuated by regular close encounters with the giant planets. The great majority (&gt;99%) of those encounters within 1 Hill radius of the planet have only a small effect on the rings. We conclude that close encounters with giant planets have not had a significant effect on the ring structure. Encounters within the Roche limit of the giant planets are rare, making ring creation through tidal disruption unlikely.
  • Spectral and temporal variability of Earth observed in polarization

    European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany; Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DG, UK; Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands; Meteorological Institute, Ludwig-Maximilians University, Theresienstr. 37, 80333 Munich, Germany; Sterzik, Michael F.; Bagnulo, Stefano; Stam, Daphne M.; Emde, Claudia; Manev, Mihail (Astronomy and Astrophysics, 2019-02-01)
    Context. Earthshine, i.e., sunlight scattered by Earth and back-reflected from the lunar surface to Earth, allows observations of the total flux and polarization of Earth with ground-based astronomical facilities on timescales from minutes to years. Like flux spectra, polarization spectra exhibit imprints of the atmospheric and surface properties of Earth. Earth's polarization spectra may prove an important benchmark to constrain expected biosignatures of Earth-like planets observed with future telescopes. <BR /> Aims: We derive the polarimetric phase curve of Earth from a statistically significant sample of Earthshine polarization spectra. The impact of changing Earth views on the variation of polarization spectra is investigated. <BR /> Methods: We present a comprehensive set of spectropolarimetric observations of Earthshine as obtained by FORS2 at the Very Large Telescope for phase angles from 50° to 135° (Sun-Earth-Moon angle), covering a spectral range from 4300 to 9200 Å. The degree of polarization in the B, V, R, I passbands, the differential polarization vegetation index, and the equivalent width of the O<SUB>2</SUB>-A polarization band around 7600 Å are determined with absolute errors around 0.1% in the degree of polarization. Earthshine polarization spectra are corrected for the effect of depolarization introduced by backscattering on the lunar surface, introducing systematic errors on the order of 1% in the degree of polarization. <BR /> Results: Distinct viewing sceneries such as observing the Atlantic or Pacific side in Earthshine yield statistically different phase curves. The equivalent width defined for the O<SUB>2</SUB>-A band polarization is found to vary from -50 to +20 Å. A differential polarized vegetation index is introduced and reveals a larger vegetation signal for those viewing sceneries that contain larger fractions of vegetated surface areas. We corroborate the observed correlations with theoretical models from the literature, and conclude that the vegetation red edge (VRE) is a robust and sensitive signature in polarization spectra of planet Earth. <BR /> Conclusions: The overall behavior of polarization of planet Earth in the continuum and in the O<SUB>2</SUB>-A band can be explained by existing models. Biosignatures such as the O<SUB>2</SUB>-A band and the VRE are detectable in Earthshine polarization with a high degree of significance and sensitivity. An in-depth understanding of the temporal and spectral variability of Earthshine requires improved models of Earth's biosphere, as a prerequisite to interpreting possible detections of polarized biosignatures in Earth-like exoplanets in the future.
  • Multiepoch VLBI of L Dwarf Binary 2MASS J0746+2000AB: Precise Mass Measurements and Confirmation of Radio Emission from Both Components

    Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA; Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA; National Radio Astronomy Observatory, Socorro, NM 87801, USA; Department of Astronomy, California Institute of Technology, Pasadena, CA 91125, USA; Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, SE-439 92 Onsala, Sweden; School of Mathematics, Statistics &amp; Applied Mathematics, National University of Ireland Galway, Galway, Ireland; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, Northern Ireland, UK; Zhang, Qicheng; Hallinan, Gregg; Brisken, Walter; Bourke, Stephen; Golden, Aaron (The Astrophysical Journal, 2020-07-01)
    Surveys have shown that up to 1/10th of all ultracool dwarfs (UCDs) are appreciable radio emitters, with their emission attributed to a combination of gyrosynchrotron radiation and the electron cyclotron maser instability. 2M J0746+2000AB is a close stellar binary comprised of an L0 and L1.5 dwarf that was previously identified as a source of 5 GHz radio emission. We used Very Long Baseline Interferometry (VLBI) to precisely track the radio emission over seven epochs in 2010-2017, and found both components to be radio emitters—the first such system identified—with the secondary component as the dominant source of emission in all epochs. The previously identified 2.07 hr periodic bursts were confirmed to originate from the secondary component, although an isolated burst was also identified from the primary component. We additionally fitted the VLBI absolute astrometric positions jointly with existing relative orbital astrometry derived from optical/infrared observations with Markov Chain Monte Carlo methods to determine the orbital parameters of the two components. We found the masses of the primary and secondary optical components to be 0.0795 ± 0.0003 M<SUB>⊙</SUB>, and 0.0756 ± 0.0003 M<SUB>⊙</SUB>, respectively, representing the most precise mass estimates of any UCDs to date. Finally, we place a 3σ upper limit of 0.9 M<SUB>jup</SUB> au on the mass and separation of planets orbiting either of the two components.
  • The Origin of Neptune's Unusual Satellites from a Planetary Encounter

    Lund Observatory, Department of Astronomy and Theoretical Physics, Lund University, Box 43, SE-221 00 Lund, Sweden; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, Northern Ireland, UK; Li, Daohai; Christou, Apostolos A. (The Astronomical Journal, 2020-04-01)
    The Neptunian satellite system is unusual, comprising Triton, a large (∼2700 km) moon on a close-in, circular, yet retrograde orbit, flanked by Nereid, the largest irregular satellite (∼300 km) on a highly eccentric orbit. Capture origins have been previously suggested for both moons. Here we explore an alternative in situ formation model where the two satellites accreted in the circum-Neptunian disk and are imparted irregular and eccentric orbits by a deep planetary encounter with an ice giant (IG), like that predicted in the Nice scenario of early solar system development. We use N-body simulations of an IG approaching Neptune to 20 Neptunian radii (R<SUB>Nep</SUB>), through a belt of circular prograde regular satellites at 10-30 R<SUB>Nep</SUB>. We find that half of these primordial satellites remain bound to Neptune and that 0.4%-3% are scattered directly onto wide and eccentric orbits resembling that of Nereid. With better matches to the observed orbit, our model has a success rate comparable to or higher than capture of large Nereid-sized irregular satellites from heliocentric orbit. At the same time, the IG encounter injects a large primordial moon onto a retrograde orbit with specific angular momentum similar to Triton's in 0.3%-3% of our runs. While less efficient than capture scenarios, our model does indicate that an in situ origin for Triton is dynamically possible. We also simulate the post-encounter collisional and tidal orbital evolution of Triton analog satellites and find they are decoupled from Nereid on timescales of ∼10<SUP>4</SUP> yr, in agreement with Cuk &amp; Gladman.
  • Transiting Exoplanet Monitoring Project (TEMP). II. Refined System Parameters and Transit Timing Analysis of HAT-P-33b

    Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China ; School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 101408, China;; Department of Astronomy, Yale University, New Haven, CT 06511, USA; School of Astronomy and Space Science and Key Laboratory of Modern Astronomy and Astrophysics in Ministry of Education, Nanjing University, Nanjing 210093, China; Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea ; Armagh Observatory, Armagh BT61 9DG, Northern Ireland, UK; Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China ; Department of Physics, Center for Astrophysics and Institute for Advanced Studies, Tsinghua University, Beijing 100086, China; Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, China; School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 101408, China; Computational Engineering and Science Research Centre, University of Southern Queensland, Toowoomba, Queensland 4350, Australia ; School of Physics and Australian Centre for Astrobiology, UNSW Australia, Sydney 2052, Australia; Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA; Astrobiology Center, NINS, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan ; National Astronomical Observatory of Japan, NINS, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; et al. (The Astronomical Journal, 2017-08-01)
    We present 10 R-band photometric observations of eight different transits of the hot Jupiter HAT-P-33b, which has been targeted by our Transiting Exoplanet Monitoring Project. The data were obtained by two telescopes at the Xinglong Station of National Astronomical Observatories of China (NAOC) from 2013 December through 2016 January, and exhibit photometric scatter of 1.6{--}3.0 {mmag}. After jointly analyzing the previously published photometric data, radial-velocity (RV) measurements, and our new light curves, we revisit the system parameters and orbital ephemeris for the HAT-P-33b system. Our results are consistent with the published values except for the planet to star radius ratio ({R}<SUB>{{P</SUB>}}/{R}<SUB>* </SUB>), the ingress/egress duration (τ) and the total duration (T <SUB>14</SUB>), which together indicate a slightly shallower and shorter transit shape. Our results are based on more complete light curves, whereas the previously published work had only one complete transit light curve. No significant anomalies in Transit Timing Variations (TTVs) are found, and we place upper mass limits on potential perturbers, largely supplanting the loose constraints provided by the extant RV data. The TTV limits are stronger near mean-motion resonances, especially for the low-order commensurabilities. We can exclude the existence of a perturber with mass larger than 0.6, 0.3, 0.5, 0.5, and 0.3 {M}<SUB>\oplus </SUB> near the 1:3, 1:2, 2:3, 3:2, and 2:1 resonances, respectively.
  • The digest2 NEO Classification Code

    Harvard-Smithsonian Center for Astrophysics, 60 Garden St., MS 51, Cambridge, MA 02138, USA; Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822, USA; NEO Sciences, LLC, 1308 Applebriar Lane, Marlborough, MA 01752, USA; Armagh Observatory and Planetarium, College Hill, Armagh, BT61 9DG, UK; Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA; Keys, Sonia; Vereš, Peter; Payne, Matthew J.; Holman, Matthew J.; Jedicke, Robert; et al. (Publications of the Astronomical Society of the Pacific, 2019-06-01)
    We describe the {digest}2 software package, a fast, short-arc orbit classifier for small solar system bodies. The {digest}2 algorithm has been serving the community for more than 13 yr. The code provides a score, {D}<SUB>2</SUB>, which represents a pseudo-probability that a tracklet belongs to a given solar system orbit type. {digest}2 is primarily used as a classifier for Near-Earth Object (NEO) candidates, to identify those to be prioritized for follow-up observation. We describe the historical development of {digest}2 and demonstrate its use on real and synthetic data. We find that {digest}2 can accurately and precisely distinguish NEOs from non-NEOs. At the time of detection, 14% of NEO tracklets and 98.5% of non-NEOs tracklets have {D}<SUB>2</SUB> below the critical value of {D}<SUB>2</SUB>=65.94 % of our simulated NEOs achieved the maximum {D}<SUB>2</SUB>=100 % and 99.6% of NEOs achieved {D}<SUB>2</SUB>≥slant 65 at least once during the simulated 10-year timeframe. We demonstrate that {D}<SUB>2</SUB> varies as a function of time, rate of motion, magnitude and sky-plane location, and show that NEOs tend to have lower {D}<SUB>2</SUB> at low Solar elongations close to the ecliptic. We use our findings to recommend future development directions for the {digest}2 code.

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