WIYN Open Cluster Study. XXXVIII. Stellar Radial Velocities in the Young Open Cluster M35 (NGC 2168)

We present 5201 radial-velocity measurements of 1144 stars, as part of an ongoing study of the young (150 Myr) open cluster M35 (NGC 2168). We have observed M35 since 1997, using the Hydra Multi-Object Spectrograph on the WIYN 3.5m telescope. Our stellar sample covers main-sequence stars over a magnitude range of 13.0<V<16.5 (1.6 - 0.8 Msun) and extends spatially to a radius of 30 arcminutes (7 pc in projection at a distance of 805 pc or 4 core radii). Due to its youth, M35 provides a sample of late-type stars with a range of rotation periods. Therefore, we analyze the radial-velocity measurement precision as a function of the projected rotational velocity. For narrow-lined stars (v sin i < 10 km/s), the radial velocities have a precision of 0.5 km/s, which degrades to 1.0 km/s for stars with v sin i = 50 km/s. The radial-velocity distribution shows a well-defined cluster peak with a central velocity of -8.16 +/- 0.05 km/s, permitting a clean separation of the cluster and field stars. For stars with >=3 measurements, we derive radial-velocity membership probabilities and identify radial-velocity variables, finding 360 cluster members, 55 of which show significant radial- velocity variability. Using these cluster members, we construct a color-magnitude diagram for our stellar sample cleaned of field star contamination. We also compare the spatial distribution of the single and binary cluster members, finding no evidence for mass segregation in our stellar sample. Accounting for measurement precision, we place an upper limit on the radial-velocity dispersion of the cluster of 0.81 +/- 0.08 km/s. After correcting for undetected binaries, we derive a true radial-velocity dispersion of 0.65 +/- 0.10 km/s.Comment: accepted for publication in A

Drivers of Change of Thwaites Glacier, West Antarctica, Between 1995 and 2015

We run several transient numerical simulations applying these three perturbations individually. Our results show that ocean-induced ice-shelf thinning generates most of the observed grounding line retreat, inland speed-up, and mass loss, in agreement with previous work. We improve the agreement with observed inland speed-up and thinning by prescribing changes in ice-shelf geometry and a reduction in basal traction over areas that became ungrounded since 1995, suggesting that shelf breakups and thinning-induced reduction in basal traction play a critical role on Thwaites's dynamics, as pointed out by previous studies. These findings suggest that modeling Thwaites's future requires reliable ocean-induced melt estimates in models that respond accurately to downstream perturbations

The transferability of adjoint inversion products between different ice flow models

Among the most important challenges faced by ice flow models is how to represent basal and rheological conditions, which are challenging to obtain from direct observations. A common practice is to use numerical inversions to calculate estimates for the unknown properties, but there are many possible methods and not one standardised approach. As such, every ice flow model has a unique initialisation procedure. Here we compare the outputs of inversions from three different ice flow models, each employing a variant of adjoint-based optimisation to calculate basal sliding coefficients and flow rate factors using the same observed surface velocities and ice thickness distribution. The region we focus on is the Amundsen Sea Embayment in West Antarctica, the subject of much investigation due to rapid changes in the area over recent decades. We find that our inversions produce similar distributions of basal sliding across all models, despite using different techniques, implying that the methods used are highly robust and represent the physical equations without much influence by individual model behaviours. Transferring the products of inversions between models results in time-dependent simulations displaying variability on the order of or lower than existing model intercomparisons. Focusing on contributions to sea level, the highest variability we find in simulations run in the same model with different inversion products is 32 , over a 40-year period, a difference of 3.67 mm. There is potential for this to be improved with further standardisation of modelling processes, and the lowest variability within a single model is 13 , or 1.82 mm over 40 years. While the successful transfer of inversion outputs from one model to another requires some extra effort and technical knowledge of the particular models involved, it is certainly possible and could indeed be useful for future intercomparison projects

Variability in automated responses of commercial buildings and industrial facilities to dynamic electricity prices

Changes in the electricity consumption of commercial buildings and industrial facilities (C&I facilities) during Demand Response (DR) events are usually estimated using counterfactual baseline models. Model error makes it difficult to precisely quantify these changes in consumption and understand if C&I facilities exhibit event-to-event variability in their response to DR signals. This paper seeks to understand baseline model error and DR variability in C&I facilities facing dynamic electricity prices. Using a regression-based baseline model, we present a method to compute the error associated with estimates of several DR parameters. We also develop a metric to determine how much observed DR variability results from baseline model error rather than real variability in response. We analyze 38 C&I facilities participating in an automated DR program and find that DR parameter errors are large. Though some facilities exhibit real DR variability, most observed variability results from baseline model error. Therefore, facilities with variable DR parameters may actually respond consistently from event to event. Consequently, in DR programs in which repeatability is valued, individual buildings may be performing better than previously thought. In some cases, however, aggregations of C&I facilities exhibit real DR variability, which could create challenges for power system operation

WIYN Open Cluster Study. XLVIII. The Hard-Binary Population of NGC 188

(abridged) We present an in-depth study of the hard-binary population of the old (7 Gyr) open cluster NGC 188. The main-sequence solar-type hard binaries in NGC 188 are nearly indistinguishable from similar binaries in the Galactic field. We find a global solar-type main-sequence hard-binary frequency in NGC 188 of 29 +/- 3 % for binaries with periods less than 10^4 days. For main-sequence hard binaries in the cluster we observe a log-period distribution that rises towards our detection limit, a roughly Gaussian eccentricity distribution centered on e = 0.35 (for binaries with periods longer than the circularization period), and a secondary-mass distribution that rises towards lower-mass companions. Importantly, the NGC 188 blue straggler binaries show significantly different characteristics than the solar-type main sequence binaries in NGC 188. We observe a blue straggler hard-binary frequency of 76 +/- 19 %, three times that of the main sequence. The blue straggler binary eccentricity - log period distribution is distinct from that of the main sequence at the 99% confidence level, with the majority of the blue straggler binaries having periods of order 1000 days and lower eccentricities. The secondary-mass distribution for these long-period blue straggler binaries is narrow and peaked with a mean value of about 0.5 Msun. Predictions for mass-transfer products are most closely consistent with the binary properties of these NGC 188 blue stragglers, which comprise two-thirds of the blue straggler population. Additionally we compare the NGC 188 binaries to those evolved within the sophisticated Hurley et al. (2005) N-body open cluster simulation. We find that additional simulations with initial conditions that are better motivated by observations are necessary to properly investigate the dynamical evolution of a rich binary population in open clusters like NGC 188.Comment: 23 pages, 22 figures, accepted for publication in A

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions - notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods - taking a secondary role. © 2020 Wolters Kluwer Medknow Publications. All rights reserved

Results of the third Marine Ice Sheet Model Intercomparison Project (MISMIP+)

We present the result of the third Marine Ice Sheet Model Intercomparison Project, MISMIP+. MISMIP+ is intended to be a benchmark for ice-flow models which include fast sliding marine ice streams and floating ice shelves and in particular a treatment of viscous stress that is sufficient to model buttressing, where upstream ice flow is restrained by a downstream ice shelf. A set of idealized experiments first tests that models are able to maintain a steady state with the grounding line located on a retrograde slope due to buttressing and then explore scenarios where a reduction in that buttressing causes ice stream acceleration, thinning, and grounding line retreat. The majority of participating models passed the first test and then produced similar responses to the loss of buttressing. We find that the most important distinction between models in this particular type of simulation is in the treatment of sliding at the bed, with other distinctions – notably the difference between the simpler and more complete treatments of englacial stress but also the differences between numerical methods – taking a secondary role

It's getting hot in here – Microcontextual study of a potential pit hearth at the Middle Paleolithic site of El Salt, Spain

By studying combustion structures, which conceal information about anthropogenic activity, we might learn about their makers. This is especially important for remote time periods like the Middle Paleolithic, whose archaeological record comprises numerous combustion structures. The majority of these are simple, flat, open hearths, although a small number of features situated in pit-like depressions have been recorded. Given that hearths built on a flat surface can result in pit-like color alteration of the underlying sediment, accurate identification of pit hearths is a crucial step prior to behavioral interpretation. Here we present a comprehensive study of a possible pit hearth from the Middle Paleolithic site of El Salt, Spain, using a microcontextual approach combining micromorphology, lipid biomarker analysis, archaeomagnetism and zooarchaeology. This pit hearth involves a true depression containing a thick plant ash deposit. It reached very high temperatures, possibly multiple burning events and long combustion times. Morphologically distinct combustion structures in a single archaeological context may indicate different functions and thus a diverse fire technology, pointing to Neanderthal behavioral variability.ERC Consolidator Grant project PALEOCHAR – 648871 https://erc.europa.eu/funding/consolidator-grants, I + D Project HAR2008-06117/HIST, HAR2015-68321-P (MINECO-FEDER/UE), and the Cultural Heritage Department of the Valencia Government and the Archaeological Museum Camil Visedo of Alcoy, under the direction of Professor Bertila Galván of Universidad de La Laguna, Junta de Castilla y León (project BU235P18), the European Fund for Economic and Regional Development (EFRD) and the project PID2019-105796 GB-I00 of the Agencia Estatal de Investigación (AEI/10.13039/501100011033