ORCID Profile
0000-0001-9328-2905
Current Organisation
The University of Edinburgh
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: American Astronomical Society
Date: 23-05-2023
Abstract: The Vera C. Rubin Observatory is expected to start the Legacy Survey of Space and Time (LSST) in early to mid-2025. This multiband wide-field synoptic survey will transform our view of the solar system, with the discovery and monitoring of over five million small bodies. The final survey strategy chosen for LSST has direct implications on the discoverability and characterization of solar system minor planets and passing interstellar objects. Creating an inventory of the solar system is one of the four main LSST science drivers. The LSST observing cadence is a complex optimization problem that must balance the priorities and needs of all the key LSST science areas. To design the best LSST survey strategy, a series of operation simulations using the Rubin Observatory scheduler have been generated to explore the various options for tuning observing parameters and prioritizations. We explore the impact of the various simulated LSST observing strategies on studying the solar system’s small body reservoirs. We examine what are the best observing scenarios and review what are the important considerations for maximizing LSST solar system science. In general, most of the LSST cadence simulations produce ±5% or less variations in our chosen key metrics, but a subset of the simulations significantly hinder science returns with much larger losses in the discovery and light-curve metrics.
Publisher: EDP Sciences
Date: 05-2013
Publisher: American Astronomical Society
Date: 26-03-2010
Publisher: American Astronomical Society
Date: 16-08-2011
Publisher: American Astronomical Society
Date: 19-10-2009
Publisher: American Astronomical Society
Date: 02-02-2010
Publisher: American Astronomical Society
Date: 07-10-2010
Publisher: American Astronomical Society
Date: 11-2013
Publisher: American Astronomical Society
Date: 16-10-2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2014
Publisher: American Astronomical Society
Date: 09-06-2017
Publisher: IEEE
Date: 08-2011
Publisher: American Astronomical Society
Date: 27-06-2202
Publisher: Walter de Gruyter GmbH
Date: 23-10-2013
Abstract: In stressed power systems with large induction machine component, there exist und ed electromechanical modes and unstable monotonic voltage modes. This article proposes a sequential design of an excitation controller and a power system stabiliser (PSS) to stabilise the system. The operating region, with induction machines in stressed power systems, is often not captured using a linearisation around an operating point, and to alleviate this situation a robust controller is designed which guarantees stable operation in a large region of operation. A minimax linear quadratic Gaussian design is used for the design of the supplementary control to automatic voltage regulators, and a classical PSS structure is used to d electromechanical oscillations. The novelty of this work is in proposing a method to capture the unmodelled nonlinear dynamics as uncertainty in the design of the robust controller. Tight bounds on the uncertainty are obtained using this method which enables high-performance controllers. An IEEE benchmark test system has been used to demonstrate the performance of the designed controller.
Publisher: EDP Sciences
Date: 22-03-2016
Publisher: IEEE
Date: 06-2013
Publisher: Hindawi Limited
Date: 26-04-2014
DOI: 10.1002/ETEP.1739
Publisher: IEEE
Date: 06-2013
Publisher: American Astronomical Society
Date: 07-11-2016
Publisher: American Astronomical Society
Date: 06-07-2012
Publisher: EDP Sciences
Date: 07-2010
Publisher: EDP Sciences
Date: 12-04-2011
Publisher: American Astronomical Society
Date: 29-08-2016
Publisher: IEEE
Date: 07-2011
Publisher: Oxford University Press (OUP)
Date: 02-07-2012
Publisher: IEEE
Date: 2013
Publisher: EDP Sciences
Date: 25-06-2013
Publisher: American Astronomical Society
Date: 27-01-2014
Publisher: IEEE
Date: 06-2012
Publisher: EDP Sciences
Date: 08-10-2009
Publisher: American Astronomical Society
Date: 18-08-2023
Abstract: We present an analysis of microlensing event OGLE-2019-BLG-0825. This event was identified as a planetary candidate by preliminary modeling. We find that significant residuals from the best-fit static binary-lens model exist and a xallarap effect can fit the residuals very well and significantly improves χ 2 values. On the other hand, by including the xallarap effect in our models, we find that binary-lens parameters such as mass ratio, q , and separation, s , cannot be constrained well. However, we also find that the parameters for the source system such as the orbital period and semimajor axis are consistent between all the models we analyzed. We therefore constrain the properties of the source system better than the properties of the lens system. The source system comprises a G-type main-sequence star orbited by a brown dwarf with a period of P ∼ 5 days. This analysis is the first to demonstrate that the xallarap effect does affect binary-lens parameters in planetary events. It would not be common for the presence or absence of the xallarap effect to affect lens parameters in events with long orbital periods of the source system or events with transits to caustics, but in other cases, such as this event, the xallarap effect can affect binary-lens parameters.
Publisher: Oxford University Press (OUP)
Date: 10-07-2019
Abstract: We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing c aign. This is a remarkable microlensing event because its source is photometrically bright and variable, which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average time-scale of ∼9 d. The asteroseismic analysis also provides us source properties including the source angular size (∼27 $\\mu$as) and distance (∼11.5 kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional χ2 minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a ∼0.045 M⊙ brown dwarf at distance ∼9.0 kpc, or a ∼0.073 M⊙ ultracool dwarf at distance ∼9.8 kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a $\\sim 35{{\\ \\rm per\\ cent}}$ probability for the lens to be a bulge object and $\\sim 65{{\\ \\rm per\\ cent}}$ to be a background disc object.
Publisher: Elsevier BV
Date: 10-2013
Publisher: American Astronomical Society
Date: 11-2019
Publisher: IEEE
Date: 07-2012
Publisher: American Astronomical Society
Date: 12-10-2011
Publisher: American Astronomical Society
Date: 02-03-2016
Publisher: American Astronomical Society
Date: 23-04-2013
Publisher: American Astronomical Society
Date: 28-06-2016
Publisher: American Astronomical Society
Date: 04-06-2009
Publisher: IEEE
Date: 05-2012
Publisher: IEEE
Date: 06-2013
Publisher: American Astronomical Society
Date: 28-01-2011
Publisher: IEEE
Date: 05-2012
Publisher: IEEE
Date: 07-2014
Publisher: AIP Publishing
Date: 2019
DOI: 10.1063/1.5052492
Abstract: In this paper, a techno-economic optimum configuration process is assessed for hybrid power systems in terms of different generation capacities. It will provide a basis for the configuration of a practical microgrid. Initially, the actual power demand in a particular university area, namely, Khulna University of Engineering & Technology in Bangladesh, is measured, and then, the process of designing the optimized model is demonstrated with an initial choice of various parameters and constraints. Its inputs are climate data, electrical loads, technical and economic parameters of the equipment used for generation, sensitivity variables, grid parameters, and project economics and constraints. The best mix of solar photovoltaics (PV) and wind power is determined considering the most profitable size of the PV's inverter for different plants. The optimization results obtained through HOMER show that a specific PV panel does not need an inverter of the same capacity and a smaller one results in a lower investment. The analysis has been carried out by considering annual increase rates of both the load and the grid power price, which makes the result more realistic. The optimal size and control strategy are determined based on the net present cost, levelized cost of energy, increased rates of load and grid price, renewable fraction, and greenhouse gas emissions. A comparative analysis between the fixed and variable data for load and cost demonstrates that an optimal inverter-PV ratio, with the best mix of PV and wind energy, provides an optimum solution for all models. An economically viable plant size of 1.5 MW for the considered case is achieved.
Publisher: American Astronomical Society
Date: 26-10-2016
Publisher: American Astronomical Society
Date: 07-2022
DOI: 10.3847/PSJ/AC7A31
Abstract: The LCO Outbursting Objects Key (LOOK) Project uses the telescopes of the Las Cumbres Observatory (LCO) Network to (1) systematically monitor a s le of previously discovered over the whole sky, to assess the evolutionary state of these distant remnants from the early solar system, and (2) use alerts from existing sky surveys to rapidly respond to and characterize detected outburst activity in all small bodies. The data gathered on outbursts helps to characterize each outburst’s evolution with time, helps to assess the frequency and magnitude distribution of outbursts in general, and contributes to the understanding of outburst processes and volatile distribution in the solar system. The LOOK Project exploits the synergy between current and future wide-field surveys such as ZTF, Pan-STARRS, and LSST, as well as rapid-response telescope networks such as LCO, and serves as an excellent test bed for what will be needed for the much larger number of objects coming from Rubin Observatory. We will describe the LOOK Project goals, the planning and target selection (including the use of NEOexchange as a Target and Observation Manager or “TOM”), and results from the first phase of observations, including the detection of activity and outbursts on the giant comet C/2014 UN 271 (Bernardinelli–Bernstein) and the discovery and follow-up of 28 outbursts on 14 comets. Within these outburst discoveries, we present a high-cadence light curve of 7P/Pons–Winnecke with 10 outbursts observed over 90 days, a large outburst on 57P/duToit–Neujmin–Delporte, and evidence that comet P/2020 X1 (ATLAS) was in outburst when discovered.
Publisher: American Astronomical Society
Date: 07-09-2030
Publisher: American Astronomical Society
Date: 07-04-2009
Publisher: IEEE
Date: 09-2016
Publisher: EDP Sciences
Date: 2018
Publisher: American Astronomical Society
Date: 14-10-2010
Publisher: Informa UK Limited
Date: 27-02-2014
Publisher: Oxford University Press (OUP)
Date: 09-12-2016
Publisher: American Astronomical Society
Date: 23-11-2015
Publisher: IEEE
Date: 08-2013
Publisher: Oxford University Press (OUP)
Date: 10-2013
Publisher: American Astronomical Society
Date: 17-08-2010
Publisher: Institution of Engineering and Technology (IET)
Date: 08-10-2019
Publisher: American Astronomical Society
Date: 07-04-2014
Publisher: American Astronomical Society
Date: 13-08-2012
Publisher: Institution of Engineering and Technology (IET)
Date: 02-05-2019
Publisher: American Astronomical Society
Date: 02-2012
Publisher: IEEE
Date: 06-2013
Publisher: Elsevier BV
Date: 2015
Publisher: IEEE
Date: 07-2014
Publisher: Oxford University Press (OUP)
Date: 29-01-2019
DOI: 10.1093/MNRAS/STZ306
Publisher: Springer Science and Business Media LLC
Date: 08-02-2023
Publisher: American Astronomical Society
Date: 30-05-2012
Publisher: Copernicus GmbH
Date: 23-09-2022
DOI: 10.5194/EPSC2022-989
Abstract: & & The discovery of long period comet C/2014 UN271 (Bernardinelli-Bernstein) announced in June 2021 quickly suggested an inactive nucleus with an absolute magnitude of H& sub& V& /sub& = 7.8 mag [1], which implied a diameter between 130 and 260 km assuming geometric albedos between 2% and 8%. Immediate follow-up observations with our Las Cumbres Observatory (LCO) Outbursting Objects Key project (LOOK) [2] as well as with SkyGems Namibia [3] revealed that the comet was active at 20.18 au. Evidence was quickly found that C/2014 UN271 had been active since 2018 and possibly even active at the time it was first observed in 2014 (at 29 au) [4,5]. After the discovery announcement, follow-up observations with ALMA and HST determined that Bernardinelli-Bernstein has a cometary albedo (0.033 & #177 0.009) and an effective diameter of 137 & #177 17 km, distinguishing it as the largest observed Oort-cloud comet [6,7].& & & & Prior to the observations of C/2014 UN271, the most distant comet discoveries were C/2010 U3 and C/2017 K2, which were made between 15 and 20 au, but for which pre-discovery images indicate activity beyond 20 au [8,9]. C/2014 UN271 was significantly brighter than those comets at the same distance, which provided an exceptional opportunity to characterize its very distant comet activity close to 20 au. In this presentation we will report the results of our observing program with FORS2 on ESO& #8217 s 8-meter VLT in July and August 2021. The VLT/FORS data are interpreted in combination with targeted observations with the 4.1-m SOAR and the long-term monitoring c aign with 1-m facilities within the LOOK Project [10,11].& & & & & The multi-facility long-term photometric monitoring of C/2014 UN271 enabled our team to identify three outbursts between June and September 2021, indicating that the comet's optical brightness was dominated by cometary outbursts during the VLT observing run. Our VLT/FORS2 multi-band imaging and spectroscopic observations allowed us therefore to characterize the comet& #8217 s outburst in terms of spectral slope and coma morphology, including arc-like features. We will also present our efforts to characterize the comet& #8217 s short-term variability and rotation period.& & & & & & & & & & & & em& References: [1] & /em& & em& ec/K21/K21M53.html& /em& & em& [2] Kokotanekova, R., et al. (2021), ATel, 14733 [3] & /em& & em& ec/K21/K21M83.html& /em& & em& [4] & /em& & em& ec/K21/K21M83.html& /em& & em& [5] Farnham, T. (2021), ATel, 14759& & /em& [6] Lellouch, E. et al. (2022) A& ,659, L1, 8 [7] & em& Hui, M.-T., et al. (2022) ApJL, 929, 1, L12, 7& & /em& & em& [8] Hui, M.-T., et al. (2019) AJ 157 [9] Jewitt, D. et al. (2021) AJ 161, 188 [10] Lister et al., submitted [11] Kelley et al., submitted.& /em& & & & & & br /& & br /& & &
Publisher: American Astronomical Society
Date: 11-02-2019
Publisher: American Astronomical Society
Date: 23-05-2016
Publisher: American Astronomical Society
Date: 12-11-2013
Publisher: Elsevier BV
Date: 12-2013
Publisher: EDP Sciences
Date: 04-03-2008
Publisher: American Astronomical Society
Date: 20-10-2016
Publisher: American Astronomical Society
Date: 20-06-2011
Publisher: American Astronomical Society
Date: 28-04-2015
Publisher: American Astronomical Society
Date: 31-07-2012
Publisher: American Astronomical Society
Date: 27-04-2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2014
Publisher: IEEE
Date: 08-2013
Publisher: IOP Publishing
Date: 25-10-2016
Publisher: IEEE
Date: 08-2013
Publisher: The Royal Society
Date: 29-05-2017
Publisher: American Astronomical Society
Date: 28-12-2017
Publisher: Springer Science and Business Media LLC
Date: 18-12-2017
Publisher: Springer Science and Business Media LLC
Date: 2006
DOI: 10.1038/NATURE04441
Abstract: In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. Around M-dwarf stars (the most common stars in our Galaxy), this model favours the formation of Earth-mass (M(o)) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (au), which is consistent with the small number of gas giant planets known to orbit M-dwarf host stars. More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune's mass or less have not hitherto been detected at separations of more than 0.15 au from normal stars. Here we report the discovery of a 5.5(+5.5)(-2.7) M(o) planetary companion at a separation of 2.6+1.5-0.6 au from a 0.22+0.21-0.11 M(o) M-dwarf star, where M(o) refers to a solar mass. (We propose to name it OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.) The mass is lower than that of GJ876d (ref. 5), although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2015
Publisher: Wiley
Date: 2009
Publisher: American Astronomical Society
Date: 11-08-2015
Publisher: Springer Science and Business Media LLC
Date: 09-02-2018
Publisher: EDP Sciences
Date: 25-10-2012
Publisher: American Astronomical Society
Date: 27-12-2020
Publisher: American Astronomical Society
Date: 22-03-2016
Publisher: Oxford University Press (OUP)
Date: 07-2017
Publisher: American Astronomical Society
Date: 14-11-2012
Publisher: EDP Sciences
Date: 27-03-2013
Publisher: American Astronomical Society
Date: 27-11-2013
Publisher: American Astronomical Society
Date: 24-09-2014
Publisher: IEEE
Date: 11-2011
Publisher: American Astronomical Society
Date: 17-01-2013
Publisher: American Astronomical Society
Date: 06-05-2013
Publisher: Oxford University Press (OUP)
Date: 11-05-2009
Publisher: American Astronomical Society
Date: 18-08-2017
Publisher: American Astronomical Society
Date: 07-2022
Abstract: We report the first unambiguous detection and mass measurement of an isolated stellar-mass black hole (BH). We used the Hubble Space Telescope (HST) to carry out precise astrometry of the source star of the long-duration ( t E ≃ 270 days), high-magnification microlensing event MOA-2011-BLG-191/OGLE-2011-BLG-0462 (hereafter designated as MOA-11-191/OGLE-11-462), in the direction of the Galactic bulge. HST imaging, conducted at eight epochs over an interval of 6 yr, reveals a clear relativistic astrometric deflection of the background star’s apparent position. Ground-based photometry of MOA-11-191/OGLE-11-462 shows a parallactic signature of the effect of Earth’s motion on the microlensing light curve. Combining the HST astrometry with the ground-based light curve and the derived parallax, we obtain a lens mass of 7.1 ± 1.3 M ⊙ and a distance of 1.58 ± 0.18 kpc. We show that the lens emits no detectable light, which, along with having a mass higher than is possible for a white dwarf or neutron star, confirms its BH nature. Our analysis also provides an absolute proper motion for the BH. The proper motion is offset from the mean motion of Galactic disk stars at similar distances by an amount corresponding to a transverse space velocity of ∼45 km s −1 , suggesting that the BH received a “natal kick” from its supernova explosion. Previous mass determinations for stellar-mass BHs have come from radial velocity measurements of Galactic X-ray binaries and from gravitational radiation emitted by merging BHs in binary systems in external galaxies. Our mass measurement is the first for an isolated stellar-mass BH using any technique.
Publisher: American Astronomical Society
Date: 02-05-2012
Publisher: IEEE
Date: 07-2014
Publisher: American Astronomical Society
Date: 08-01-2013
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Colin Snodgrass.