Periodic substorm activity in the geomagnetic tail

On 19 May 1978 an anusual series of events is observed with the Quadrispherical LEPEDEA on board the ISEE-1 satellite in the Earth's geomagnetic tail. For 13 hours periodic bursts of both ions and electrons are seen in all the particle detectors on the spacecraft. On this day periodic activity is also seen on the ground, where multiple intensifications of the electrojets are observed. At the same time the latitudinal component of the interplanetary magnetic field shows a number of strong southward deflections. It is concluded that an extended period of substorm activity is occurring, which causes repeated thinnings and recoveries of the plasma sheet. These are detected by ISEE, which is situated in the plasma sheet boundary layer, as periodic dropouts and reappearances of the plasma. Comparisons of the observations at ISEE with those at IMP-8, which for a time is engulfed by the plasma sheet, indicate that the activity is relatively localized in spatial extent. For this series of events it is clear that a global approach to magnetospheric dynamics, e.g., reconnection, is inappropriate

A review of technical factors to consider when designing neural networks for semantic segmentation of Earth Observation imagery

Semantic segmentation (classification) of Earth Observation imagery is a crucial task in remote sensing. This paper presents a comprehensive review of technical factors to consider when designing neural networks for this purpose. The review focuses on Convolutional Neural Networks (CNNs), Recurrent Neural Networks (RNNs), Generative Adversarial Networks (GANs), and transformer models, discussing prominent design patterns for these ANN families and their implications for semantic segmentation. Common pre-processing techniques for ensuring optimal data preparation are also covered. These include methods for image normalization and chipping, as well as strategies for addressing data imbalance in training samples, and techniques for overcoming limited data, including augmentation techniques, transfer learning, and domain adaptation. By encompassing both the technical aspects of neural network design and the data-related considerations, this review provides researchers and practitioners with a comprehensive and up-to-date understanding of the factors involved in designing effective neural networks for semantic segmentation of Earth Observation imagery.Comment: 145 pages with 32 figure

Pre-discovery and Follow-up Observations of the Nearby SN 2009nr: Implications for Prompt Type Ia SNe

We present photometric and spectroscopic observations of the Type Ia supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery announcement at what turned out to be ten days after peak, we detected it at V ~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North telescope 2 weeks prior to the peak, and then followed it up with telescopes ranging in aperture from 10-cm to 6.5-m. Using early photometric data available only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN 1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95 mag. The early post-maximum spectra closely resemble those of SN 1991T, while the late time spectra are more similar to those of normal Type Ia SNe. Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This indicates that the progenitor of SN 2009nr is not associated with a young stellar population, calling into question the conventional association of luminous SNe Ia with the "prompt" component directly correlated with current star formation. The pre-discovery observation of SN 2009nr using ASAS demonstrates the science utility of high cadence all sky surveys conducted using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.Comment: 11 pages, 11 figures, 4 tables. Accepted for publication in ApJ on 11/02/201

Quantitative spectroscopic analysis of and distance to SN1999em

This work presents a detailed quantitative spectroscopic analysis of, and the determination of the distance to, the type II supernovae (SN) SN1999em with CMFGEN (Dessart & Hillier 2005a), based on spectrophotometric observations at eight dates up to 40 days after discovery. We use the same iron-group metal content for the ejecta, the same power-law density distribution (with exponent n~10), and a Hubble-velocity law at all times. We adopt a H/He/C/N/O abundance pattern compatible with CNO-cycle equilibrium values for a RSG/BSG progenitor, with C/O enhanced and N depleted at later times. Based on our synthetic fits to spectrophotometric observations of SN1999em, we obtain a distance of 11.5Mpc, similar to that of Baron et al. (2004) and the Cepheid distance to the galaxy host of 11.7Mpc (Leonard et al. 2003). Similarly, based on such models, the Expanding Photosphere Method (EPM) delivers a distance of 11.6Mpc, with negligible scatter between photometric bandpass sets; there is thus nothing wrong with the EPM as such. Previous determinations using the tabulated correction factors of Eastman et al. (1996) all led to 30-50% underestimates: we find that this is caused by 1) an underestimate of the correction factors compared to the only other study of the kind by Dessart & Hillier (2005b), 2) a neglect of the intrinsic >20% scatter of correction factors, and 3) the use of the EPM at late times when severe line blanketing makes the method inaccurate. The need of detailed model computations for reliable EPM distance estimates thus defeats the appeal and simplicity of the method. However, detailed fits to SN optical spectra, based on tailored models for individual SN observations, offers a promising approach to obtaining distances with 10-20% accuracy, either through the EPM or a la Baron et al. (2004).Comment: 20 pages, 13 figures, accepted for publication in A&

KELT-4Ab: An inflated Hot Jupiter transiting the bright (V~10) component of a hierarchical triple

We report the discovery of KELT-4Ab, an inflated, transiting Hot Jupiter orbiting the brightest component of a hierarchical triple stellar system. The host star is an F star with T_(eff) = 6206 ± 75 K, log g = 4.108 ± 0.014, [Fe/H] = -0.116_(-0.069)^(+0.065, M_* = 1.201_(-0.061)^(+0.067) M_☉, and R_* = 1.603_(-0.038)^(+0.039) R_☉. The best-fit linear ephemeris is BJD_(TDB); = 2456193.29157 ± 0.00021 + E(2.9895936 ± 0.0000048). With a magnitude of V ~ 10, a planetary radius of 1.699_(-0.045)^(+0.046); R_J, and a mass of 0.902_(-0.059)^(+0.060) M_J, it is the brightest host among the population of inflated Hot Jupiters (R_P > 1.5 R_J), making it a valuable discovery for probing the nature of inflated planets. In addition, its existence within a hierarchical triple and its proximity to Earth (210 pc) provide a unique opportunity for dynamical studies with continued monitoring with high resolution imaging and precision radial velocities. The projected separation between KELT-4A and KELT-4BC is 328 ± 16 AU and the projected separation between KELT-4B and KELT-4C is 10.30 ± 0.74 AU. Assuming face-on, circular orbits, their respective periods would be 3780 ± 290 and 29.4 ± 3.6 years and the astrometric motions relative to the epoch in this work of both the binary stars around each other and of the binary around the primary star would be detectable now and may provide meaningful constraints on the dynamics of the system

Distance determinations using type II supernovae and the expanding photosphere method

Due to their high intrinsic brightness, type II supernovae (SN) can be used as lighthouses to constrain distances in the Universe using variants of the Baade-Wesselink method. Based on a large set of CMFGEN models (Hillier & Miller 1998) covering the photospheric phase of type II SN, we study the various concepts entering one such technique, the Expanding Photosphere Method (EPM). We compute correction factors $\xi$ needed to approximate the synthetic Spectral Energy Distribution (SED) with that of a blackbody at temperature $T$. Our $\xi$, although similar, are systematically greater, by $\sim 0.1$, than the values obtained by Eastman et al. (1996). This translate into a systematic enhancement of 10-20% in EPM-distances. We find that line emission and absorption, not directly linked to color temperature variations, can considerably alter the synthetic magnitude, and cause above-unity $\xi$-values. Optically-thick lines, present in the optical at late-times, can also introduce a strong wavelength-dependence of the photospheric radius, invalidating the use of the Baade method. Both the impact of line-blanketing on the SED and the photospheric radius at low $T$ suggest that the EPM is best used at early times, when the outflow is fully ionized and line-opacity mostly confined to the UV range. We also investigate how reliably one can measure the photospheric velocity from P-Cygni line profiles. Contrary to the usually held belief, the velocity at maximum absorption in the P-Cygni trough of optically-thick lines can both {\it overestimate or underestimate} the photospheric velocity, with a magnitude that depends on the SN outflow density gradient and the optical thickness of the line.Comment: 16 pages, 19 figures, accepted for publication in A&

Managing digital coordination of design: emerging hybrid practices in an institutionalized project setting

What happens when digital coordination practices are introduced into the institutionalized setting of an engineering project? This question is addressed through an interpretive study that examines how a shared digital model becomes used in the late design stages of a major station refurbishment project. The paper contributes by mobilizing the idea of ‘hybrid practices’ to understand the diverse patterns of activity that emerge to manage digital coordination of design. It articulates how engineering and architecture professions develop different relationships with the shared model; the design team negotiates paper-based practices across organizational boundaries; and diverse practitioners probe the potential and limitations of the digital infrastructure. While different software packages and tools have become linked together into an integrated digital infrastructure, these emerging hybrid practices contrast with the interactions anticipated in practice and policy guidance and presenting new opportunities and challenges for managing project delivery. The study has implications for researchers working in the growing field of empirical work on engineering project organizations as it shows the importance of considering, and suggests new ways to theorise, the introduction of digital coordination practices into these institutionalized settings

The Mass of the Black Hole in the Quasar PG 2130+099

We present the results of a recent reverberation-mapping campaign undertaken to improve measurements of the radius of the broad line region and the central black hole mass of the quasar PG 2130+099. Cross correlation of the 5100 angstrom continuum and H-beta emission-line light curves yields a time lag of 22.9 (+4.4 - 4.3) days, corresponding to a central black hole mass MBH= 3.8 (+/- 1.5) x 10^7 Msun. This value supports the notion that previous measurements yielded an incorrect lag. We re-analyzed previous datasets to investigate the possible sources of the discrepancy and conclude that previous measurement errors were apparently caused by a combination of undersampling of the light curves and long-term secular changes in the H-beta emission-line equivalent width. With our new measurements, PG 2130+099 is no longer an outlier in either the R-L or the MBH-Sigma relationships.Comment: 21 pages, 7 figures; Accepted for publication in Ap