Siding Spring Research Articles

GRB 230911A: The First Discovery of a Fermi GRB Optical Counterpart with the Gravitational-wave Optical Transient Observer (GOTO)

We report on the detection of candidate optical counterpart GOTO23akf/AT2023shv to the GRB 230911A with the Gravitational-wave Optical Transient Observer (GOTO) instruments located at La Palma, Canary Islands, and Siding Spring Observatory, Australia. The Fermi Gamma-ray Burst Monitor, which finds gamma-ray bursts (GRBs) nearly every two days, detected GRB 230911A with a statistical uncertainty of 4.°1. However, the large (∼10–100 deg2) localization areas mostly impede the rapid identification of an optical counterpart. GOTO facilities fully covered 90% localization area of the GRB 230911A. We proposed GOTO23akf as the optical afterglow of GRB 230911A, subsequently confirmed through Swift-X-Ray Telescope observations in which an uncatalogued X-ray source spatially coincident with the GOTO candidate was detected. This is the first optical afterglow discovery for a Fermi GRB with the newly expanded GOTO network.

WiFeS observations of nearby southern Type Ia supernova host galaxies

Abstract We present high-resolution observations of nearby ( $z\lesssim0.1$ ) galaxies that have hosted Type Ia supernovae to measure systemic spectroscopic redshifts using the wide field spectrograph (WiFeS) instrument on the Australian National University 2.3 m telescope at Siding Spring Observatory. While most of the galaxies targeted have previous spectroscopic redshifts, we provide demonstrably more accurate and precise redshifts with competitive uncertainties, motivated by potential systematic errors that could bias estimates of the Hubble constant ( $H_0$ ). The WiFeS instrument is remarkably stable; after calibration, the wavelength solution varies by $\lesssim$ 0.5 Å in red and blue with no evidence of a trend over the course of several years. By virtue of the $25\times 38$ arcsec field of view, we are always able to measure the redshift of the galactic core, or the entire galaxy in the cases where its angular extent is smaller than the field of view, reducing any errors due to galaxy rotation. We observed 185 southern SN Ia host galaxies and measured the redshift of each via at least one spatial region of (a) the core and (b) the average over the full-field/entire galaxy. Overall, we find stochastic differences between historical redshifts and our measured redshifts on the order of $\lesssim10^{-3}$ with a mean offset of 4.3 ${\times 10^{-5}}$ and normalised median absolute deviation of 1.2 ${\times 10^{-4}}$ . We show that a systematic redshift offset at this level is not enough to bias cosmology, as $H_0$ shifts by $+0.1$ km s $^{-1}$ Mpc $^{-1}$ when we replace Pantheon+ redshifts with our own, but the occasional large differences are interesting to note.

The Peculiar Ejecta Rings in the O-Rich Supernova Remnant Puppis A: Evidence of a Binary Interaction?

Near the center of the Puppis A supernova remnant a series of nested, optically emitting rings of high-velocity ejecta (known as “the Swirl”) were identified several decades ago by Winkler et al. To date, no follow-up observations of these rings have been published, and their physical origin has remained a mystery. We present results of integral field spectroscopy of the Swirl using the Wide Field Integral Spectrograph on the 2.3 m telescope at Siding Spring Observatory in Australia. The outermost ring exhibits a nitrogen-rich spectrum blueshifted to 1350 km s−1, with smaller blueshifted rings within the first exhibiting mostly oxygen-rich spectra moving at 1000 and 750 km s−1. The structures are connected by material of intermediate velocity and variable composition, including sulfur-rich material. The Swirl is turbulent and shock-excited, and contains as much as 0.5 M ⊙ of metal-rich material. The chemical composition and exclusively blueshifted radial velocities of the Swirl are consistent with progressively deeper nucleosynthetic layers in a massive progenitor star. We suggest the possibility that the Swirl marks a “funnel” carved into the supernova ejecta by a close, massive binary companion at the moment of explosion.

Structure design and dynamic analysis of a tensegrity-based carangiform robotic fish

<p indent="0mm">Bionic robots are widely used in various fields due to their high flexibility and mobility. When conducting complex underwater operations, it is expected to design a bionic robotic fish with good underwater navigation ability based on the excellent swimming performance of fish. At present, the tail swing mechanism of bionic robotic fish is mostly composed of serial rigid joints. Limited by their own materials and manufacturing process, the joints cannot undergo large elastic deformation, so the corresponding bionic robotic fish is far less flexible than fish in water. A flexible design is a natural choice to better mimic the movement of fish underwater. Tensegrity is a grid-like spatial structural system that consists of pre-tensioned strings and pre-compressed bars. Such structure has the advantages of light weight, flexible deformation, and impact resistance. Introducing tensegrity into the robot field has greater advantages than traditional rigid robots due to its flexibility and other characteristics. Based on a novel 2D tensegrity and the physiological characteristics of fish, this paper proposed a four-joint bionic robotic fish that imitates carangiform swimming motions. Referring to the shape characteristics of fish, the three-dimensional model of robotic fish is established using software. By simplifying several ropes as the external forces of the system, ignoring the parameters of gravity, buoyancy and mass of some parts, the dynamic equations of the two-joint model are established through the coordinate transformation matrix and further extended to the multi-joint system. Taking the single and four-joint systems as examples, the accuracy of the dynamic model is verified by Adams simulations, and the obtained results are consistent with the motion curve of fish during cruise. In order to improve the propulsion performance of robotic fish, some parameters of the system are analyzed. When the stiffness distribution between the joints is changed, the results show that reducing the spring stiffness of the tail fin joint can effectively reduce the influence on the front-end joint. Further analysis is carried out on reducing the stiffnesses of only side springs, or both side and center springs. It is found that reducing the stiffnesses of only side springs is more conducive to the improvement of the driving effect. The influence of the driving strategy on the dynamic performance of the system is discussed, and the application of step function and sinusoidal function to the robotic fish without/with damping is also analyzed. The results show that the fluctuation of the sinusoidal function driven system is larger under the condition of without damping, and the similar dynamic response can be obtained under the condition of damping. This work provides a theoretical basis and application reference for the design of flexible robotic fish. The proposed tensegrity-based carangiform robotic fish holds potential applications as exploration, search and rescue equipment in complex underwater environments.

LRO-LAMP Observations of the Preperihelion Coma of Comet C/2013 A1 (Siding Spring)

Abstract The Lyman-Alpha Mapping Project (LAMP) UV spectrograph on board the Lunar Reconnaissance Orbiter observed comet C/2013 A1 (Siding Spring) from lunar orbit at closest approach. On 2014 September 5, Siding Spring came within ∼0.89 au of the Earth–Moon system and provided an opportunity for LAMP to contribute to the broader campaign of observations. The comet coma was imaged during two consecutive orbits, approximately 2 hr apart. Coma emissions of atomic oxygen were resolved within LAMP observations at distances up to ∼1.4 × 106 km from the comet nucleus. We report an atomic production rate for the observed oxygen of 9.42 ± 0.22 × 1027 s−1. We additionally place upper limits on the column densities of candidate species including noble gases and primary transitions. Leveraging this, we place upper limits on the production of hydrogen and carbon of &lt;3.59 × 1026 s−1 and &lt;8.41 × 1025 s−1, respectively. Additionally, we derive OH and H2O production rates and estimate an upper limit on the production of CO. The H2O (8.17 ± 2.64 × 1027 s−1) and OH (7.53 ± 2.244 × 1027 s−1) production rates are found to be in general agreement with previous studies when production rates are derived utilizing oxygen observations, branching ratios, and empirical formulations. Similarly, the upper limit on the production of CO (&lt;1.33 × 1028 s−1) is found to be in good agreement with previous studies (within ∼10%) when we utilize the upper limit on CO Fourth Positive group emissions.

Physical and Chemical Properties of Wolf–Rayet Planetary Nebulae

Abstract Wolf–Rayet ([WR]) and weak-emission-line (wels) central stars of planetary nebulae (PNs) have hydrogen-deficient atmospheres, whose origins are not well understood. In the present study, we have conducted plasma diagnostics and abundance analyses of 18 Galactic PNs surrounding [WR] and wels nuclei, using collisionally excited lines (CELs) and optical recombination lines (ORLs) measured with the Wide Field Spectrograph on the Australian National University 2.3 m telescope at the Siding Spring Observatory complemented with optical archival data. Our plasma diagnostics imply that the electron densities and temperatures derived from CELs are correlated with the intrinsic nebular Hβ surface brightness and excitation class, respectively. Self-consistent plasma diagnostics of heavy-element ORLs of N2+ and O2+ suggest that a small fraction of cool (≲7000 K), dense (∼104–105 cm−3) materials may be present in some objects, though with large uncertainties. Our abundance analyses indicate that the abundance discrepancy factors (ADFs ≡ ORLs/CELs) of O2+ are correlated with the dichotomies between forbidden-line and He i temperatures. Our results likely point to the presence of a tiny fraction of cool, oxygen-rich dense clumps within diffuse warm ionized nebulae. Moreover, our elemental abundances derived from CELs are mostly consistent with asymptotic giant branch models in the range of initial masses from 1.5 to 5 M ⊙. Further studies are necessary to understand better the origins of abundance discrepancies in PNs around [WR] and wels stars.

Preview of Comet C/2021 A1 (Leonard) and Its Encounter with Venus

Abstract Long-period comet C/2021 A1 (Leonard) will approach Venus to within 0.029 au on 2021 December 18 and may subsequently graze the planet with its dust trail less than 2 days later. We observed C/2021 A1 with the Lowell Discovery Telescope on 2021 January 13 and March 3, as well as with the Palomar Hale Telescope on 2021 March 20, while the comet was inbound at heliocentric distances of r = 4.97, 4.46, and 4.28 au, respectively. Tail morphology suggests that the dust is optically dominated by ∼0.1–1 mm radius grains produced in the prior year. Neither narrowband imaging photometry nor spectrophotometry reveal any definitive gas emission, placing 3σ upper bounds on CN production of ≲1023 molec−1 at both of the latter two epochs. Trajectory analysis indicates that large (≳1 mm) grains ejected at extremely large heliocentric distances (r ≳ 30 au) are most strongly favored to reach Venus. The flux of such meteors on Venus, and thus their potential direct or indirect observability, is highly uncertain, as the comet’s dust production history is poorly constrained at these distances but will likely fall well below the meteor flux from comet C/2013 A1 (Siding Spring)'s closer encounter to Mars in 2014 and thus poses a negligible risk to any spacecraft in orbit around Venus. Dust produced in previous apparitions will not likely contribute substantially to the meteor flux, nor will dust from any future activity apart from an unlikely high-speed (≳0.5 km s−1) dust outburst prior to the comet reaching r ≈ 2 au in 2021 September.

The β Pictoris b Hill sphere transit campaign

Aims. Photometric monitoring of β Pic in 1981 showed anomalous fluctuations of up to 4% over several days, consistent with foreground material transiting the stellar disk. The subsequent discovery of the gas giant planet β Pic b and the predicted transit of its Hill sphere to within a 0.1 au projected separation of the planet provided an opportunity to search for the transit of a circumplanetary disk (CPD) in this 21 ± 4 Myr-old planetary system. We aim to detect, or put an upper limit on, the density and nature of the material in the circumplanetary environment of the planet via the continuous photometric monitoring of the Hill sphere transit that occurred in 2017 and 2018. Methods. Continuous broadband photometric monitoring of β Pic requires ground-based observatories at multiple longitudes to provide redundancy and to provide triggers for rapid spectroscopic follow-up. These include the dedicated β Pic monitoring bRing observatories in Sutherland and Siding Springs, the ASTEP400 telescope at Concordia, and the space observatories BRITE and the Hubble Space Telescope (HST). We search the combined light curves for evidence of short-period transient events caused by rings as well as for longer-term photometric variability due to diffuse circumplanetary material. Results. We find no photometric event that matches with the event seen in November 1981, and there is no systematic photometric dimming of the star as a function of the Hill sphere radius. Conclusions. We conclude that the 1981 event was not caused by the transit of a CPD around β Pic b. The upper limit on the long-term variability of β Pic places an upper limit of 1.8 × 1022 g of dust within the Hill sphere (comparable to the ~100 km radius asteroid 16 Psyche). Circumplanetary material is either condensed into a disk that does not transit β Pic, condensed into a disk with moons that has an obliquity that does not intersect with the path of β Pic behind the Hill sphere, or is below our detection threshold. This is the first time that a dedicated international campaign has mapped the Hill sphere transit of an extrasolar gas giant planet at 10 au.

The spatially resolved gas and dust connection in neutral inflows and outflows in nearby AGN

ABSTRACT Dusty, neutral outflows and inflows are a common feature of nearby star-forming galaxies. We characterize these flows in eight galaxies – mostly active galactic nuclei (AGN) – selected for their widespread Na i D signatures from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). This survey employs deep, wide field-of-view (FOV) integral field spectroscopy at moderate spectral resolution (R = 7000 at Na i D). We significantly expand the sample of sightlines in external galaxies in which the spatially resolved relationship has been studied between cool, neutral gas properties – N(Na i), Weq(Na i D) – and dust – E(B − V) from both stars and gas. Our sample shows strong, significant correlations of total Weq with E(B − V)⋆ and g − i colour within individual galaxies; correlations with E(B − V)gas are present but weaker. Regressions yield slope variations from galaxy to galaxy and intrinsic scatter ∼1 Å. The sample occupies regions in the space of N(Na i) and $W_\mathrm{eq}^\mathrm{abs}$ versus E(B − V)gas that are consistent with extrapolations from other studies to higher colour excess [E(B − V)gas ∼ 1]. For perhaps the first time in external galaxies, we detect inverse P Cygni profiles in the Na i D line, presumably due to inflowing gas. Via Doppler-shifted Na i D absorption and emission lines, we find ubiquitous flows that differ from stellar rotation by $\gtrsim$100 km s−1 or have $|v_{\mathrm{ abs}} - v_{\mathrm{ em}}|\gtrsim 100$ km s−1. Inflows and outflows extend towards the edge of the detected stellar disc/FOV, together subtend 10–40 per cent of the projected disc, and have similar mean N(Na i) and Weq(Na i D). Outflows are consistent with minor axis or jet-driven flows, while inflows tend towards the projected major axis. The inflows may result from non-axisymmetric potentials, tidal motions, or halo infall.

A spectroscopically confirmed Gaia-selected sample of 318 new young stars within ∼200 pc

ABSTRACT In the Gaia era, the majority of stars in the Solar neighbourhood have parallaxes and proper motions precisely determined while spectroscopic age indicators are still missing for a large fraction of low-mass young stars. In this work, we select 756 overluminous late K and early M young star candidates in the southern sky and observe them over 64 nights with the ANU 2.3-m Telescope at Siding Spring Observatory using the Echelle (R = 24 000) and Wide Field spectrographs (WiFeS, R = 3000–7000). Our selection is kinematically unbiased to minimize the preference against low-mass members of stellar associations that dissipate first and to include potential members of diffuse components. We provide measurements of Hα and calcium H&amp;K emission, as well as of Li i 6708 Å in absorption. This enables identification of stars as young as 10–30 Myr – a typical age range for stellar associations. We report on 346 stars showing detectable lithium absorption, 318 of which are not included in existing catalogues of young stars. We also report 125 additional stars in our sample presenting signs of stellar activity indicating youth but with no detectable lithium. Radial velocities are determined for WiFeS spectra with a precision of 3.2 km s−1 and 1.5 km s−1 for the Echelle sample.

A systematic survey for z&amp;lt; 0.04 CLAGNs

ABSTRACT We have conducted a systematic survey for z &amp;lt; 0.04 active Galactic nuclei (AGNs) that may have changed spectral class over the past decade. We use SkyMapper, Pan-STARRS and the Véron-Cetty &amp; Véron catalogue to search the entire sky for these ‘changing-look’ AGNs (CLAGNs) using a variety of selection methods, where Pan-STARRS has a coverage of 3$\pi$ steradians (sky north of Declination −30○) and SkyMapper has coverage of ∼21000 $~\rm {deg^2}$ (sky south of Declination 0○). We use small aperture photometry to measure how colour and flux have changed over time, where a change may indicate a change in spectral type. Optical colour and flux are used as a proxy for changing Hα equivalent width, while WISE 3.4 μm flux is used to look for changes in the hot dust component. We have identified four AGNs with varying spectra selected using our optical colour selection method. Three AGNs were confirmed from recent observations with WiFeS on the 2.3 m telescope at Siding Spring and the other was identified from archival spectra alone. From this, we identify two new CLAGNs; NGC 1346 and 2MASX J20075129–1108346. We also recover Mrk 915 and Mrk 609, which are known to have varying spectra in the literature, but they do not meet our specific criteria for CLAGNs.

Surfaces of (Nearly) Dormant Comets and the Recent History of the Quadrantid Meteor Shower

Abstract The parent of the Quadrantid meteor shower is the inactive solar system small body (196256) 2003 EH1. EH1 has likely only gone dormant in the past few hundred years, and may be related to the bright comet C/1490 Y1. Compared with the other best-studied inactive meteor shower parent (3200) Phaethon, EH1 has received comparatively minimal characterization of its surface properties. We present the first reflectance spectrum and additional photometry of EH1, as well as new spectra of the nuclei of three nearly dormant comets P/2006 HR30 (Siding Spring), 364P/Pan-STARRS, and 249P/LINEAR for comparison. We also present new short-term high-resolution orbital integrations of these bodies for context. EH1s spectrum is red in color below 0.8 μm in between C and D types, consistent with previous photometric measurements, but is blue beyond 0.8 μm until at least 1.02 μm. 249P and 364P have both red slopes consistent with C taxonomic types and HR30 has a classic comet nucleus D-type slope. If the downturn in EH1’s spectrum is due to an absorption feature, magnetite and olivine are plausible candidates, but more data are needed. 249P and 364P have similar recent and historical dynamical evolutions in addition to their similar surface properties. We discuss the interrelation between the dynamical histories and modern surfaces of these four objects and suggest avenues for further study to better constrain how the Quadrantids and Geminids were created.

Orbital analysis of small bodies in co-orbital motion with Jupiter through the torus structure

ABSTRACT In this paper, based on the torus structure, we investigate the orbital characteristics of Jupiter Trojans and Jupiter-family comets (JFCs) in co-orbital motion with Jupiter. The motivation of this paper is to test whether the semi-analytical approach and conclusions of the torus structure proposed in the circular restricted three-body problem are still valid for real small bodies in the ephemeris model, and how long they follow the prediction of the semi-analytical approach. Based on the topological structure of the co-orbital motion in the torus space, we propose a method for estimating the libration amplitude for Trojans. 873 Jupiter Trojans with well-determined orbits are picked as examples to demonstrate the validity of our estimation method. Numerical analysis reveals that the difference between the osculating semimajor axes of the Trojan and Jupiter can influence the accuracy of our estimation method significantly. Based on the semi-analytical approach, we predict orbital behaviours of three JFCs, 85P/Boethin, P/2012 US27 (Siding Spring), and P/2019 A1 (PANSTARRS). Numerical integration in the ephemeris model indicates that their real orbital behaviours are consistent with our predictions. In particular, we find that the current quasi-satellite state of P/2012 US27 (Siding Spring) can remain for about 1.5 × 105 yr, much longer than those that correspond to other previously reported QS companions of Jupiter.

Geothermal Resources Database in Saudi Arabia (GRDiSA): GIS model and geothermal favorability map

The Kingdom of Saudi Arabia has many geothermal resources along the Red Sea coast, volcanoes, and hot springs. Geoscience researchers within Saudi Arabia were looking for this type of energy five decades ago or even more, but studies are still in academic shelves and no economic geothermal project. The economic vision of Saudi Arabia attempts to use this type of energy for new projects. In the current research, we are trying to collect the previous studies and literatures in geothermal energy to be in a database format. This database will assist decision-makers in drawing up a road map to explore, evaluate, and assess geothermal energy exploration in the Kingdom of Saudi Arabia. Accordingly, geological, geophysical, and related studies are collected in a digital form to build the first Geothermal Resources Database in Saudi Arabia (GRDiSA) using the power full of the GIS environment. Additionally, built-in GIS extension is used as a modeler tool to target the potentiality of geothermal resources in Saudi Arabia. As a result, the first geothermal favorability map is generated based on the GIS model, indicating that the western side, where volcanoes and hot springs are located, is favorable for further geothermal exploration development.

Martian Oxygen and Hydrogen Upper Atmospheres Responding to Solar and Dust Storm Drivers: Hisaki Space Telescope Observations

AbstractWe present variations of oxygen 130.4 nm and hydrogen Ly‐β airglow of the Martian upper atmosphere observed by the Hisaki spacecraft in the Earth orbit. In 5‐year intermittent observations covering various Mars seasons, the 130.4 nm brightness varied from ∼700 to ∼1,200 Rayleigh, correlated with the solar 130.4 nm flux. The Ly‐β brightness, on the other hand, varied from ∼50 to ∼260 Rayleigh, correlated with the column dust optical depth rather than the solar Ly‐β flux. This suggests that the global oxygen column density in the upper atmosphere was relatively stable over the observations while the hydrogen column density was highly variable, controlled by dust storms. Although the observations were made in different Mars Years, we suggest that the hydrogen column density increased by at least 2–5 times from non‐dusty to dusty seasons. The source of the hydrogen atoms is likely water vapor transported from the lower atmosphere which subsequently photodissociate into hydrogen atoms. The amount of oxygen atoms dissociated from water vapor is small compared with those dissociated from the main CO2 atmosphere. Large brightness of both emissions was detected during the comet siding spring (CSS) approach. We suggest that a large solar 130.4 nm flux caused the large 130.4 nm brightness and an effect of the CSS approach was small. For Ly‐β, a regional dust storm during the CSS approach likely caused the large brightness. Although it is possible that the hydrogen atoms are transported from the comet, we leave the effect of CSS on the Ly‐β brightness uncertain.

Prolonged Lifetime of the Transient Ionized Layer in the Martian Atmosphere Caused by Comet Siding Spring

AbstractIn October 2014, the close encounter between Mars and comet Siding Spring produced a transient ionized layer in the upper atmosphere composed primarily of Mg+ and Fe+ ions. The layer was detected by instruments on three spacecraft, including the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on Mars Express. Analyses of the MARSIS data indicated the transient layer persisted up to 19 h after the comet's closest approach. We report MARSIS observations that suggest the transient layer lasted at least 7 days—and potentially as long as 32 days—after closest approach. During this period, the transient layer was mostly confined to a narrow latitude range between 20°N and 60°N and a longitude range spanning 275°E to 95°E. Since this period coincided with a highly active Sun, we discuss how solar flares may have contributed to the layer's prolonged lifetime.

Lyα Observations of Comet C/2013 A1 (Siding Spring) Using MAVEN IUVS Echelle

Abstract The close approach of comet C/2013 A1 (Siding Spring) to Mars in 2014 October provided a unique opportunity to observe a dynamically new Oort cloud comet with potential for interaction with a planet’s atmosphere. The water-originating hydrogen coma of the comet extended to over 20 million km from the nucleus. Determining the properties of this coma contributes to characterizing the comet’s water content and production rate. The present study analyzes a unique data set of high spectral resolution UV observations of comet C/2013 A1 Siding Spring measured by the Mars Atmosphere and Volatile Evolution spacecraft. The Siding Spring observations capture Lyα emissions from the Martian corona, the interplanetary medium, as well as the cometary H and D reservoirs. The isolated cometary spectra are analyzed to reveal a velocity distribution of H atoms that are consistent with model estimates of H2O photodissociated H emissions and of OH photodissociated H emissions, Doppler shifted from the main comet H emission line center by 18 km s−1 and 8 km s−1, respectively. The variations in comet H brightness with distance from the nucleus are used to constrain cometary water production to a rate of 0.5 × 1028 molecules s−1 at a time when Siding Spring was at 1.5 au, pre-perihelion.

Stellar Metallicities from SkyMapper Photometry I: A Study of the Tucana II Ultra-faint Dwarf Galaxy

Abstract We present a study of the ultra-faint Milky Way dwarf satellite galaxy Tucana II using deep photometry from the 1.3 m SkyMapper telescope at Siding Spring Observatory, Australia. The SkyMapper filter set contains a metallicity-sensitive intermediate-band v filter covering the prominent Ca ii K feature at 3933.7 Å. When combined with photometry from the SkyMapper u, g, and i filters, we demonstrate that v-band photometry can be used to obtain stellar metallicities with a precision of ∼0.20 dex when [Fe/H] &gt; −2.5, and ∼0.34 dex when [Fe/H] &lt; −2.5. Since the u and v filters bracket the Balmer Jump at 3646 Å, we also find that the filter set can be used to derive surface gravities. We thus derive photometric metallicities and surface gravities for all stars down to a magnitude of g ∼ 20 within ∼75′ of Tucana II. Photometric metallicity and surface gravity cuts remove nearly all foreground contamination. By incorporating Gaia proper motions, we derive quantitative membership probabilities that recover all known members of the red giant branch of Tucana II. Additionally, we identify multiple likely new members in the center of the system, as well as candidate members several half-light radii from the center of the system. Finally, we present a metallicity distribution function derived from the photometric metallicities of likely Tucana II members. This result demonstrates the utility of wide-field imaging with the SkyMapper filter set in studying ultra-faint dwarf galaxies, and in general, low surface brightness populations of metal-poor stars. Upcoming work will clarify the membership status of several distant stars identified as candidate members of Tucana II.

Mars' Ionospheric Interaction With Comet C/2013 A1 Siding Spring's Coma at Their Closest Approach as Seen by Mars Express

AbstractOn 19 October 2014, Mars experienced a close encounter with Comet C/2013 A1 Siding Spring. Using data from the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board Mars Express (MEX), we assess the interaction of the Martian ionosphere with the comet's coma and possibly magnetic tail during the orbit of their closest approach. The topside ionospheric electron density profile is evaluated from the altitude of the peak density of the ionosphere up to the MEX altitude. We find complex and rapid variability in the ionospheric profile along the MEX orbit, not seen even after the impact of a large coronal mass ejection. Before closest approach, large electron density reductions predominate, which could be caused either by comet water damping or comet magnetic field interactions. After closest approach, a substantial electron density rise predominates. Moreover, several extra topside layers are visible along the whole orbit at different altitudes, which could be related to different processes as we discuss.

Bright Southern Variable Stars in the bRing Survey

Abstract In addition to monitoring the bright star β Pic during the near-transit event for its giant exoplanet, the β Pictoris b Ring (bRing) observatories at Siding Springs Observatory, Australia and Sutherland, South Africa have monitored the brightnesses of bright stars (V ≃ 4–8 mag) centered on the south celestial pole (δ ≤ −30°) for approximately two years. Here we present a comprehensive study of the bRing time-series photometry for bright southern stars monitored between 2017 June and 2019 January. Of the 16,762 stars monitored by bRing, 353 were found to be variable. Of the variable stars, 80% had previously known variability and 20% were new variables. Each of the new variables was classified, including three new eclipsing binaries (HD 77669, HD 142049, HD 155781), 26 δ Scutis, 4 slowly pulsating B stars, and others. This survey also reclassified four stars based on their period of pulsation, light curve, spectral classification, and color–magnitude information. The survey data were searched for new examples of transiting circumsecondary disk systems, but no candidates were found.