Shannon Brown

Max Planck Institute for Astronomy

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S. J. Bolton

Southwest Research Institute

A. G. A. Brown

Leiden University

J. Torra

Universitat Politècnica de Catalunya

P. Ortiz

University of Leicester

C. Fabricius

Universitat de Barcelona

S. Galleti

Osservatorio di Astrofisica e Scienza dello Spazio

M. Weiler

Goethe University Frankfurt

F. De Luise

Collurania Teramo Observatory

A. Bragaglia

National Institute for Astrophysics

ŁW

Ł. Wyrzykowski

University of Warsaw

Cooperative Institutions

Max Planck Society

415

Centre National de la Recherche Scientifique

252

Université Paris Cité

106

Université Paris Sciences et Lettres

100

European Space Astronomy Centre

Observatoire de Paris

National Institute for Astrophysics

Max Planck Institute for Astronomy

University of Cambridge

Sorbonne Université

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Recent results from the imagery of Juno’s Stellar Reference Unit

Heidi N. Becker James Alexander S. K. Atreya S. J. Bolton Martin Brennan

<p>The Juno Mission has recast its spacecraft engineering star camera as a visible wavelength science imager. Developed and primarily used to support onboard attitude determination, Juno&#8217;s Stellar Reference Unit (SRU) has been put to use as an in situ high energy particle detector for profiling Jupiter&#8217;s radiation belts and as a low light sensitive camera for exploring multiple phenomena and features of the Jovian system. Juno&#8217;s unprecedented polar orbit and closest approach of ~4000 km have yielded high resolution SRU imagery of Jupiter&#8217;s lightning and aurorae from as little as 50,000 km from the 1 bar level and unique Jovian dust ring and satellite images. We will present recent SRU results and discuss the implications for Jupiter&#8217;s atmosphere that stem from the SRU lightning observations.</p>

Panchromatic film

10.5194/egusphere-egu2020-9585

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Quantifying coastal evolution and project performance at beaches by using satellite imagery

Ian Conery Nicholas R. Olsen Shannon Brown Katherine Brodie

Accurately delineating the shoreline is crucial for tracking coastal evolution, community vulnerability, storm impacts, and for coastal management decision-making. However, existing shoreline measurement methods are often time-consuming and expensive and therefore, USACE Districts are often forced to narrow areas of interest or monitoring frequency, decreasing the likelihood of making data-driven management decisions, especially over regional scales. In the last decade, space-borne earth observations have captured images subweekly, and can potentially be used for shoreline monitoring. This work investigated the Python-based CoastSat toolkit and compared the shorelines derived from publicly available satellite imagery to ground truth surveys at 37 sites across the nation chosen in coordination with Districts. Mean horizontal errors ranged from 4.21 to 20.58 m with an overall mean of 11.32 m. Tidal corrections improved accuracies at 82% of sites. The CoastSat slope function was tested and there were negligible differences in shoreline accuracy when compared with user-defined slopes. Twenty-year satellite-derived trends generally align well with ground truth trends. The satellite approach identified quantifying storm impacts and recovery, beach nourishment equilibration, diffusion and decay, shoreline response to nearshore berm placements and decadal shoreline evolution at the evaluated district sites. Work is ongoing to transition to a user-friendly software tool.

Ground truth

Coastal Management

Berm

10.21079/11681/48671

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Citations (2)

HD 117214 debris disk: scattered-light images and constraints on the presence of planets

Astronomy and Astrophysics (2020)

N. Engler C. Lazzoni R. Gratton J. Milli H. M. Schmid

We performed observations of the Sco-Cen F star HD 117214 aiming at a search for planetary companions and the characterization of the debris disk structure. HD 117214 was observed with the SPHERE subsystems IRDIS, IFS and ZIMPOL at optical and near-IR wavelengths using angular and polarimetric differential imaging techniques. This provided the first images of scattered light from the debris disk with a spatial resolution reaching 25 mas and an inner working angle $< 0.1''$. With the observations with IRDIS and IFS we derive detection limits for substellar companions. The geometrical parameters of the detected disk are constrained by fitting 3D models for the scattering of an optically thin dust disk. Investigating the possible origin of the disk gap, we introduced putative planets therein and modeled the planet-disk and planet-planet dynamical interactions. The obtained planetary architectures are compared with the detection limit curves. The debris disk has an axisymmetric ring structure with a radius of $0.42(\pm 0.01)''$ or $\sim45$ au and an inclination of $71(\pm 2.5)^\circ$ and exhibits a $0.4''$ ($\sim40$ au) wide inner cavity. From the polarimetric data, we derive a polarized flux contrast for the disk of $(F_{\rm pol})_{\rm disk}/F_{\rm \ast}> (3.1 \pm 1.2)\cdot 10^{-4}$ in the RI band. The fractional scattered polarized flux of the disk is eight times smaller than the fractional infrared flux excess. This ratio is similar to the one obtained for the debris disk HIP 79977 indicating that dust radiation properties are not very different between these two disks. Inside the disk cavity we achieve the high sensitivity limits on planetary companions with a mass down to $\sim 4 M_{\rm J}$ at projected radial separations between $0.2''$ and $0.4''$. We can exclude the stellar companions at a radial separation larger than 75 mas from the star.

Debris disk

Position angle

10.1051/0004-6361/201936828

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Citations (14)

Molly Wood’s Bush: Settler Colonialism, Queer Activism, and Commemoration in Toronto

Journal of Canadian Studies (2020)

Shannon Brown

This article explores the relationship between queer activism and settler colonialism in Toronto from the 1970s to the 2000s through the commemoration of Alexander Wood, a nineteenth-century magistrate. Over the course of these three decades, Wood was reclaimed as a historical gay man by a variety of queer activists who sought to incorporate lessons from the past into their work. After briefly introducing the early liberationist interpretations of Wood, this article investigates the process through which Toronto’s gay village, Church-Wellesley Village, became legible as “Molly Wood’s Bush,” a piece of land Wood purchased in the 1820s with roughly the same geographic boundaries. Emerging homonationalist forms of queer activism that placed queer life within the bounds of national belonging provoked a reinterpretation of Wood, making him into a gay pioneer and culminating in the creation of a statue to mark the Village as queer territory. By examining a series of rewritings of Wood’s history as well as their reception in Toronto, this article argues that the role of commemoration in creating maps of belonging that facilitate integration into the settler colonial order must be included in understandings of queer activism in Canada.

Reinterpretation

Magistrate

10.3138/jcs-2020-0016

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Citations (2)

Supplementary material to "Retrieval of Atmospheric Water Vapor and Temperature Profiles over Antarctica through Iterative Approach"

Zhimeng Zhang Shannon Brown Andreas Colliander

10.5194/egusphere-2024-2578-supplement

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Electrode level Monte Carlo model of radiation damage effects on astronomical CCDs

Monthly Notices of the Royal Astronomical Society (2011)

T. Prod’homme A. G. A. Brown L. Lindegren A. Short Shannon Brown

Current optical space telescopes rely upon silicon charge-coupled devices (CCDs) to detect and image the incoming photons. The performance of a CCD detector depends on its ability to transfer electrons through the silicon efficiently, so that the signal from every pixel may be read out through a single amplifier. This process of electron transfer is highly susceptible to the effects of solar proton damage (or non-ionizing radiation damage). This is because charged particles passing through the CCD displace silicon atoms, introducing energy levels into the semiconductor band gap which act as localized electron traps. The reduction in charge transfer efficiency (CTE) leads to signal loss and image smearing. The European Space Agency’s astrometric Gaia mission will make extensive use of CCDs to create the most complete and accurate stereoscopic map to date of the Milky Way. In the context of the Gaia mission CTE is referred to with the complementary quantity charge transfer inefficiency (CTI = 1-CTE). CTI is an extremely important issue that threatens Gaia’s performances: the CCDs are very large so that the electrons need to be transferred a long way; the focal plane is also very large and difficult to shield; the mission will operate at second Lagrange point where the direct solar protons are highly energetic (penetrating) and the science requirements on image quality are very stringent. In order to tackle this issue, in depth experimental studies and modelling efforts are being conducted to explore the possible consequences and to mitigate the anticipated effects of radiation damage. We present here a detailed Monte Carlo model that has been developed to simulate the operation of a damaged CCD at the pixel electrode level. This model implements a new approach to both the charge density distribution within a pixel and the charge capture and release probabilities, which allows the reproduction of CTI effects on a variety of measurements for a large signal level range in particular for signals of the order of a few electrons.

10.1111/j.1365-2966.2011.18537.x

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Citations (19)

Gaia Data Release 1. Open cluster astrometry: performance, limitations, and future prospects

Astronomy and Astrophysics (2017)

F. van Leeuwen A. Vallenari C. Jordi L. Lindegren U. Bastian

Context. The first Gaia Data Release contains the Tycho-Gaia Astrometric Solution (TGAS). This is a subset of about 2 million stars for which, besides the position and photometry, the proper motion and parallax are calculated using Hipparcos and Tycho-2 positions in 1991.25 as prior information. Aims. We investigate the scientific potential and limitations of the TGAS component by means of the astrometric data for open clusters. Methods. Mean cluster parallax and proper motion values are derived taking into account the error correlations within the astrometric solutions for individual stars, an estimate of the internal velocity dispersion in the cluster, and, where relevant, the effects of the depth of the cluster along the line of sight. Internal consistency of the TGAS data is assessed. Results. Values given for standard uncertainties are still inaccurate and may lead to unrealistic unit-weight standard deviations of least squares solutions for cluster parameters. Reconstructed mean cluster parallax and proper motion values are generally in very good agreement with earlier Hipparcos-based determination, although the Gaia mean parallax for the Pleiades is a significant exception. We have no current explanation for that discrepancy. Most clusters are observed to extend to nearly 15 pc from the cluster centre, and it will be up to future Gaia releases to establish whether those potential cluster-member stars are still dynamically bound to the clusters. Conclusions. The Gaia DR1 provides the means to examine open clusters far beyond their more easily visible cores, and can provide membership assessments based on proper motions and parallaxes. A combined HR diagram shows the same features as observed before using the Hipparcos data, with clearly increased luminosities for older A and F dwarfs.

Astrometry

Parallax

Proper motion

Pleiades

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Citations (108)

Searching for the near-infrared counterpart of Proxima c using multi-epoch high-contrast SPHERE data at VLT

Astronomy and Astrophysics (2020)

R. Gratton A. Zurlo H. Le Coroller M. Damasso Fabio Del Sordo

Proxima Centauri is known to host an earth-like planet in its habitable zone; very recently a second candidate planet was proposed based on radial velocities. At quadrature, the expected projected separation of this new candidate is larger than 1 arcsec, making it a potentially interesting target for direct imaging. While difficult, identification of the optical counterpart of this planet would allow detailed characterization of the closest planetary system. We searched for a counterpart in SPHERE images acquired during four years through the SHINE survey. In order to account for the large orbital motion of the planet, we used a method that assumes the circular orbit obtained from radial velocities and exploits the sequence of observations acquired close to quadrature in the orbit. We checked this with a more general approach that considers keplerian motion, K-stacker. We did not obtain a clear detection. The best candidate has S/N=6.1 in the combined image. A statistical test suggests that the probability that this detection is due to random fluctuation of noise is < 1% but this result depends on the assumption that distribution of noise is uniform over the image. The position of this candidate and the orientation of its orbital plane fit well with observations in the ALMA 12m array image. However, the astrometric signal expected from the orbit of the candidate we detected is 3-sigma away from the astrometric motion of Proxima as measured from early Gaia data. This, together with the unexpectedly high flux associated with our direct imaging detection, means we cannot confirm that our candidate is indeed Proxima c. On the other hand, if confirmed, this would be the first observation in imaging of a planet discovered from radial velocities and the second one (after Fomalhaut b) of reflecting circumplanetary material. Further confirmation observations should be done as soon as possible.

Proper motion

Orbit (dynamics)

Orbital motion

Position angle

Circular orbit

10.1051/0004-6361/202037594

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Citations (13)

A multi-instrument analysis of Juno data to investigate the sources of non-thermal radiation at Jupiter

Japan Geoscience Union (2018)

Daniel Santos‐Costa S. J. Bolton S. Levin Fabiano Oyafuso Shannon Brown

Jupiter (rocket family)