分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Gravitational microlensing has the potential to provide direct gravitational masses of single, free-floating brown dwarfs, independent of evolutionary and atmospheric models. The proper motions and parallaxes of nearby brown dwarfs can be used to predict close future alignments with distant background stars that cause a microlensing event. Targeted astrometric follow up of the predicted microlensing events permits the brown dwarf's mass to be measured. Predicted microlensing events are typically found via searching for a peak threshold signal using an estimate of the lens mass. We develop a novel method that finds predicted events that instead will lead to a target lens mass precision. The main advantage of our method is that it does not require a lens mass estimate. We use this method to search for predicted astrometric microlensing events occurring between 2014 - 2032 using a catalog of 1225 low mass star and brown dwarf lenses in the Solar Neighborhood of spectral type M6 or later and a background source catalog from DECaLS Data Release 9. The background source catalog extends to $g = $ 23.95, providing a more dense catalog compared to Gaia. Our search did not reveal any upcoming microlensing events. We estimate the rate of astrometric microlensing event for brown dwarfs in the Legacy Survey and find it to be low $\sim10^{-5}$yr$^{-1}$. We recommend carrying out targeted searches for brown dwarfs in front of the Galactic Bulge and Plane to find astrometric microlensing events that will allow the masses of single, free-floating brown dwarfs to be measured.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Sam M. Ward
Stephen Thorp
Kaisey S. Mandel
Suhail Dhawan
David O. Jones
Kirsty Taggart
Ryan J. Foley
Gautham Narayan
Kenneth C. Chambers
David A. Coulter
Kyle W. Davis
Thomas de Boer
Kaylee de Soto
Nicholas Earl
Alex Gagliano
Hua Gao
Jens Hjorth
Mark E. Huber
Luca Izzo
Danial Langeroodi
摘要： To improve Type Ia supernova (SN Ia) standardisability, the consistency of distance estimates to siblings -- SNe in the same host galaxy -- should be investigated. We present Young Supernova Experiment Pan-STARRS-1 $grizy$ photometry of SN 2021hpr, the third spectroscopically confirmed SN Ia in the high-stellar-mass Cepheid-calibrator galaxy NGC 3147. We analyse NGC 3147's trio of SN Ia siblings: SNe 1997bq, 2008fv and 2021hpr, using a new version of the BayeSN model of SN Ia spectral-energy distributions, retrained simultaneously using optical-NIR $BgVrizYJH$ (0.35--1.8 $\mu$m) data. The distance estimates to each sibling are consistent, with a sample standard deviation $\lesssim$0.01 mag, much smaller than the total intrinsic scatter in the training sample: $\sigma_0\approx0.09$ mag. Fitting normal SN Ia siblings in three additional galaxies, we estimate a $\approx$90% probability that the siblings' intrinsic scatter is smaller than $\sigma_0$. We build a new hierarchical model that fits light curves of siblings in a single galaxy simultaneously; this yields more precise estimates of the common distance and the dust parameters. Fitting the trio for a common dust law shape yields $R_V=2.69\pm0.52$. Our work motivates future hierarchical modelling of more siblings, to tightly constrain their intrinsic scatter, and better understand SN-host correlations. Finally, we estimate the Hubble constant, using a Cepheid distance to NGC 3147, the siblings trio, and 109 Hubble flow ($0.01 < z_{\rm{CMB}} < 0.08$) SNe Ia; marginalising over the siblings' and population's intrinsic scatters, and the peculiar velocity dispersion, yields $H_0=77.9\pm6.5 \text{ km s}^{-1}\text{Mpc}^{-1}$.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Peter McGill
Jay Anderson
Stefano Casertano
Kailash C. Sahu
Pierre Bergeron
Simon Blouin
Patrick Dufour
Leigh C. Smith
N. Wyn Evans
Vasily Belokurov
Richard L. Smart
Andrea Bellini
Annalisa Calamida
Martin Dominik
Noé Kains
Jonas Klüter
Martin Bo Nielsen
Joachim Wambsganss
摘要： In November 2019, the nearby single, isolated DQ-type white dwarf LAWD 37 (WD 1142-645) aligned closely with a distant background source and caused an astrometric microlensing event. Leveraging astrometry from \Gaia{} and followup data from the \textit{Hubble Space Telescope} we measure the astrometric deflection of the background source and obtain a gravitational mass for LAWD~37. The main challenge of this analysis is in extracting the lensing signal of the faint background source whilst it is buried in the wings of LAWD~37's point spread function. Removal of LAWD 37's point spread function induces a significant amount of correlated noise which we find can mimic the astrometric lensing signal. We find a deflection model including correlated noise caused by the removal of LAWD~37's point spread function best explains the data and yields a mass for LAWD 37 of $0.56\pm0.08 M_{\odot}$. This mass is in agreement with the theoretical mass-radius relationship and cooling tracks expected for CO core white dwarfs. Furthermore, the mass is consistent with no or trace amounts of hydrogen that is expected for objects with helium-rich atmospheres like LAWD 37. We conclude that further astrometric followup data on the source is likely to improve the inference on LAWD 37's mass at the $\approx3$ percent level and definitively rule out purely correlated noise explanations of the data. This work provides the first semi-empirical test of the white dwarf mass-radius relationship using a single, isolated white dwarf and supports current model atmospheres of DQ white dwarfs and white dwarf evolutionary theory.
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