Day 1578

Friday.


1905.12682
Dark Energy Survey Year 1 Results: wide field mass maps via forward fitting in harmonic space
Mawdsley, et al

We present new wide-field weak lensing mass maps for the Year 1 Dark Energy Survey data, generated via a forward fitting approach. This method of producing maps does not impose any prior constraints on the mass distribution to be reconstructed. The technique is found to improve the map reconstruction on the edges of the field compared to the conventional Kaiser-Squires method, which applies a direct inversion on the data; our approach is in good agreement with the previous direct approach in the central regions of the footprint. The mapping technique is assessed and verified with tests on simulations; together with the Kaiser-Squires method, the technique is then applied to data from the Dark Energy Survey Year 1 data and the differences between the two methods are compared. We also produce the first DES measurements of the convergence Minkowski functionals and compare them to those measured in simulations.

1905.12710

The delayed evolution of high-mass white dwarfs: the Q branch and double-white-dwarf mergers

Cheng, Cummings, Ménard

Studying high-mass white dwarfs (WDs) can shed light on the progenitors of Type Ia supernovae. Recently, the unprecedented power of Gaia Data Release 2 (DR2) has revealed an enhancement of high-mass WDs on the H-R diagram, called the Q branch. This branch is located at the high-mass end of the crystallisation branch identified by Tremblay et al. (2019). However, investigating its properties, we find that the number density and the fraction of fast-moving WDs on the Q branch cannot be explained by crystallisation alone, suggesting the existence of an extra cooling delay. To explore the properties of this delay, we compare two WD age indicators -- the dynamical age reflected by transverse velocity and the photometric age -- for more than one thousand high-mass WDs (1.08-1.23 $M_\odot$). We show that, in addition to crystallisation and merger delays, an 8-Gyr cooling delay is required on the Q branch, which affects about $7\%$ of high-mass WDs. $^{22}$Ne settling in some WDs may account for this extra delay. We also show that $20\pm6\%$ of high-mass WDs originate from double-WD mergers, corresponding to a merger rate of $(2.1\pm0.6)\times10^{-14}M_\odot^{-1}yr^{-1}$ in this mass range. This is a direct observational constraint on the rate of double-WD mergers, which is a promising channel of Type Ia supernova explosion.

1905.13036

An observer's view on the future of astroseismology

Paparó

Scientific research is a continuous process, and the speed of future progress can be estimated by the pace of finding explanations for previous research questions. In this observers based view of stellar pulsation and asteroseismology, we start with the earliest observations of variable stars and the techniques used to observe them. The earliest variable stars were large amplitude, radial pulsators but were followed by other classes of pulsating stars. As the field matured, we outline some cornerstones of research into pulsating star research with an emphasis on changes in observational techniques. Improvements from photographs, to photometry, CCDs, and space telescopes allowed researchers to separate out pulsating stars from other stars with light variations, recognize radial and nonradial pulsation courtesy of increased measurement precision, and then use nonradial pulsations to look inside the stars, which cannot be done any other way. We follow several highlighted problems to show that even with excellent space data, there still may not be quick theoretical explanations. As the result of technical changes, the structure of international organizations devoted to pulsating stars has changed, and an increasing number of conferences specialized to space missions or themes are held. Although there are still many unsolved problems, such as mode identification in non-asymptotic pulsating stars, the large amount of data with unprecedented precision provided by space missions (MOST, CoRoT, Kepler) and upcoming missions allow us to use asteroseismology to its full potential. However, the enormous flow of data will require new techniques to extract the science before the next missions. The future of asteroseismology will be successful if we learn from the past and improve with improved techniques, space missions, and a properly educated new generation.

1905.13189

A beginner's guide to working with astronomical data

Póssel

This elementary review covers the basics of working with astronomical data, notably with images, spectra and higher-level (catalog) data. The basic concepts and tools are presented using both application software (DS9 and TOPCAT) and Python. The level of presentation is suitable for undergraduate students, but should also be accessible to advanced high school students.