| Website | https://avapolzin.github.io |
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It's becoming increasingly clear to me that Reflect Orbital's fucking stupid giant mirror satellite, with absolutely NOTHING useful to offer, which will cause countless safety issues, ecological disasters, and destroy the night sky, is going to launch.
A bunch of astronomers and I have sent out a fact sheet about them to a bunch of journalists, but very few are going to write about this. So, let me try posting it all here.
Here's what I know about Reflect Orbital and all the downsides:
In the same vein as the below, and for talks/papers/posters or even March Madness, here’s a little package with >80 university-inspired matplotlib color palettes and colormaps :)
https://github.com/avapolzin/rahrah
#science #visualization #software
From: @avapolzin
https://mastodon.social/@avapolzin/110992373748257160
Paper day! I introduce a new all-in-one tool to generate and drizzle/resample space-based point spread functions for more accurate photometry ✨
https://arxiv.org/abs/2503.02288
Code here: https://github.com/avapolzin/spike
#Astrodon #astrophysics #astronomy #space #paper #science #physics
A point spread function (PSF) describes the distribution of light for a pure point source in an astronomical image due to the optics of the instrument. An accurate PSF is key for deconvolution, point source photometry and source removal. Space-based telescopes can then pose a challenge because their PSFs are influenced by their complex construction, and the myriad of pointings and rotations used to capture deep images. These telescopes also capture the highest resolution images of astronomical sources, resolving stars in even relatively distant galaxies. Proper co-addition of PSFs at a specific source position for space-based imaging is then both critical and challenging. The library described in this work, spike, generates model PSFs and runs them through the same processing pipeline used to derive deep, co-added images, providing correctly co-added and resampled PSFs for images from the Hubble Space Telescope, the James Webb Space Telescope, and the Nancy Grace Roman Space Telescope.
Our Picture an Astronomer series starts in just over a week! Free to attend (in person in Chicago and online) and an incredible opportunity to engage directly with the scientists behind cutting edge astrophysics research.
More info (including registration) at https://pictureanastronomer.github.io
#chicago #science #lecture #event #astronomy #space #physics #astrophysics #Astrodon
It got a bit lost with everything else going on this week, but my (high school!) research student, Jack, has been working with me on building a low-cost home radio telescope to map Galactic 21 cm features, and his tutorial for others to do the same is now up on arXiv:
https://arxiv.org/abs/2411.00057
This study presents the methodology for creating a cost-efficient radio astronomy telescope that can be used to detect 21 cm emissions (1420.405 MHz) and determine the distribution and kinematics of neutral hydrogen specifically in the Milky Way. By measuring the Doppler shifts of the 21 cm emission, the velocities of hydrogen clouds relative to Earth can be determined. This enables the identification of these clouds' movements, their positions within the galaxy's spiral arms, and their roles in the overall rotational dynamics of the Milky Way. The setup is designed to be accessible to amateurs, enabling others to conduct similar projects. The measurement apparatus consists of a 1-meter parabolic dish, a H1-LNA for 21 cm emissions, an SDR, and a Raspberry Pi. This paper also provides an overview of the data processing required to detect the hydrogen line and generate velocity profiles. Additionally, it examines RFI mitigation techniques, such as spectral filtering and instrument shielding, which enhance observational clarity even in urban environments like Los Angeles. This study also analyzes the observed velocities of different galactic arms, as well as measurements across the sky.
Happy Women in #Physics Day! Perhaps more timely now than ever:
We are hosting a scientific symposium (among other events -- see pic) at UChicago, focused on promoting and retaining women in #astrophysics Symposium registration is open through Jan. 30 and we offer hybrid attendance.
More details and registration information at https://pictureanastronomer.github.io
Though all of the speakers are women, we encourage attendance from everyone!
Paper day! With Andrey Kravtsov, Vadim Semenov, and Nick Gnedin:
https://arxiv.org/abs/2407.11125
We find that the star formation efficiency per free-fall time has a characteristic value of ~0.01 in star-forming gas, regardless of local galaxy properties like metallicity, ionizing radiation field strength, or density of gas and stars.
We analyze high-resolution hydrodynamics simulations of an isolated disk dwarf galaxy with an explicit model for unresolved turbulence and turbulence-based star formation prescription. We examine the characteristic values of the star formation efficiency per free-fall time, $ε_\mathrm{ff}$, and its variations with local environment properties, such as metallicity, UV flux, and surface density. We show that the star formation efficiency per free-fall time in $\approx 10$ pc star-forming regions of the simulated disks has values in the range $ε_\mathrm{ff}\approx 0.01-0.1$, similar to observational estimates, with no trend with metallicity and only a weak trend with the UV flux. Likewise, $ε_{\rm ff}$ estimated using projected patches of 500 pc size does not vary with metallicity and shows only a weak trend with average UV flux and gas surface density. The characteristic values of $ε_\mathrm{ff}\approx 0.01-0.1$ arise naturally in the simulations via the combined effect of dynamical gas compression and ensuing stellar feedback that injects thermal and turbulent energy. The compression and feedback regulate the virial parameter, $α_\mathrm{vir}$, in star-forming regions, limiting it to $α_\mathrm{vir}\approx 3-10$. Turbulence plays an important role in the universality of $ε_\mathrm{ff}$ because turbulent energy and its dissipation are not sensitive to metallicity and UV flux that affect thermal energy. Our results indicate that the universality of observational estimates of $ε_\mathrm{ff}$ can be plausibly explained by the turbulence-driven and feedback-regulated properties of star-forming regions.
Paper day! Led by Tim Miller, we present a new method for directly recovering galaxy distances from just broadband survey image cutouts.
With upcoming wide field surveys from the ground and space the number of known dwarf galaxies at $\lesssim 25$ Mpc is expected to dramatically increase. Insight into their nature and analyses of these systems' intrinsic properties will rely on reliable distance estimates. Traditional techniques such as tip of the red giant branch (TRGB) or surface brightness fluctuations (SBF) are limited in their widespread applicability, especially in the semi-resolved regime. In this work we turn to the rapidly growing field of simulation based inference to infer distances, and other physical properties, of dwarf galaxies directly from multi-band images. We introduce Silkscreen: a code leveraging neural posterior estimation to infer the posterior distribution of parameters while simultaneously training a convolutional neural network to extract summary statistics from the images. Utilizing this combination of machine learning and Bayesian inference, we demonstrate the method's ability to recover accurate distances from ground-based survey images for a set of nearby galaxies ($2 < D ({\rm Mpc)} < 12$) with measured SBF or TRGB distances. We discuss caveats of the current implementation along with future prospects, focusing on the goal of amortized inference. For surveys like LSST, Silkscreen, once amortized, will facilitate inference for new dwarf galaxies in a matter of seconds using only broadband cutouts. While we focus here on dwarf galaxies, we note that this method can be generalized to more luminous systems as well.
The Space Weather Prediction Center (link) has recently noted strong solar activity as part of the ongoing solar maximum (see the images below from 10 May and 11 May). The result on 11 May was an aurora borealis observed south into the United States. The Day Night Band image above, from Suomi-NPP, shows the light […]
Prof. Sam Lawler
Kelsey Jordahl