Day 1752

Tuesday.

2008.12799

DebrisWatch I: a survey of faint geosynchronous debris

Blake, et al

Recent anomalies exhibited by satellites and rocket bodies have highlighted that a population of faint debris exists at geosynchronous (GEO) altitudes, where there are no natural removal mechanisms. Despite previous optical surveys probing to around 10-20 cm in size, regular monitoring of faint sources at GEO is challenging, thus our knowledge remains sparse. It is essential that we continue to explore the faint debris population using large telescopes to better understand the risk posed to active GEO satellites. To this end, we present photometric results from a survey of the GEO region carried out with the 2.54 m Isaac Newton Telescope in La Palma, Canary Islands. We probe to 21st visual magnitude (around 10 cm, assuming Lambertian spheres with an albedo of 0.1), uncovering 129 orbital tracks with GEO-like motion across the eight nights of dark-grey time comprising the survey. The faint end of our brightness distribution continues to rise until the sensitivity limit of the sensor is reached, suggesting that the modal brightness could be even fainter. We uncover a number of faint, uncatalogued objects that show photometric signatures of rapid tumbling, many of which straddle the limiting magnitude of our survey over the course of a single exposure, posing a complex issue when estimating object size. This work presents the first instalment of DebrisWatch, an ongoing collaboration between the University of Warwick and the Defence Science and Technology Laboratory (UK) investigating the faint population of GEO debris.

2008.13154

Clustering of red-sequence galaxies in the fourth data release of the Kilo-Degree Survey

Vakili, Hoekstra, et al

We present a sample of luminous red-sequence galaxies to study the large-scale structure in the fourth data release of the Kilo-Degree Survey. The selected galaxies are defined by a red-sequence template, in the form of a data-driven model of the colour-magnitude relation conditioned on redshift. In this work, the red-sequence template is built using the broad-band optical+near infrared photometry of KiDS-VIKING and the overlapping spectroscopic data sets. The selection process involves estimating the red-sequence redshifts, assessing the purity of the sample, and estimating the underlying redshift distributions of redshift bins. After performing the selection, we mitigate the impact of survey properties on the observed number density of galaxies by assigning photometric weights to the galaxies. We measure the angular two-point correlation function of the red galaxies in four redshift bins, and constrain the large scale bias of our red-sequence sample assuming a fixed $\Lambda$CDM cosmology. We find consistent linear biases for two luminosity-threshold samples (dense and luminous). We find that our constraints are well characterized by the passive evolution model.

2008.13180

South American auroral reports during the Carrington storm

Hayakawa, et al

The importance of the investigation of magnetic superstorms is not limited to academic interest, because these superstorms can cause catastrophic impact on the modern civilisation due to our increasing dependency on technological infrastructure. In this context, the Carrington storm in September 1859 is considered as a benchmark of observational history owing to its magnetic disturbance and equatorial extent of the auroral oval. So far, several recent auroral reports at that time have been published but those reports are mainly derived from the Northern Hemisphere. In this study, we analyse datable auroral reports from South America and its vicinity, assess the auroral extent using philological and astrometric approaches, identify the auroral visibility at - 17.3{\deg} magnetic latitude and further poleward and reconstruct the equatorial boundary of the auroral oval to be 25.1{\deg} +/- 0.5{\deg} in invariant latitude. Interestingly, brighter and more colourful auroral displays were reported in the South American sector than in the Northern Hemisphere. This north-south asymmetry is presumably associated with variations of their magnetic longitude and the weaker magnetic field over South America compared to the magnetic conjugate point and the increased amount of magnetospheric electron precipitation into the upper atmosphere. These results attest that the magnitude of the Carrington storm indicates that its extent falls within the range of other superstorms, such as those that occurred in May 1921 and February 1872, in terms of the equatorial boundary of the auroral oval.