Related papers: Keck constraints on a varying fine-structure const…
It was hypothesized in the literature that some physical parameters may be time-evolving and the astrophysical data can serve as a probe. Recently, James Webb Space Telescope (JWST) have released its early observations. In this work, we…
Astrophysical tests of the stability of fundamental couplings, such as the fine-structure constant $\alpha$, are becoming an increasingly powerful probe of new physics. Here we discuss how these measurements, combined with local atomic…
The constraints on the time variation of the fine structure constant at recombination epoch relative to its present value, $\Delta\alpha/\alpha \equiv (\alpha_{\mathrm{rec}} - \alpha_{\mathrm{now}})/\alpha_{\mathrm{now}}$, are obtained from…
We point out that the recent result of primordial helium-4 ($^4$He) abundance measurement by EMPRESS, which has reported a smaller $^4$He abundance than other measurements, can be well fitted by assuming a time-variation of the fine…
We present a series of systematic abundance measurements for 25 hot DA white dwarfs in the temperature range ~20000-110000K, based on far-UV spectroscopy with STIS/GHRS on HST, IUE and FUSE. Using our latest heavy element blanketed non-LTE…
We discuss how laboratory experiments can be used to place constraints on possible variations of the fine structure constant alpha in the observationally relevant redshift interval z ~= 0 - 5, within a rather general theoretical framework.…
From the Sloan Digital Sky Survey (SDSS) Data Release 12, which covers the full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate the possible variation of the fine-structure constant over cosmological time-scales.…
We present high resolution, high SNR spectra of the QSO Q2206-199 obtained with HIRES on the 10m W.M. Keck Telescope. Our analysis focuses on the two previously identified damped \lya systems found at $z=1.920$ and $z=2.076$. For each…
Dynamical models of dark energy can imply that the fine structure constant $\alpha$ varies over cosmological time scales. Data on shifts in resonance energies $E_r$ from the Oklo natural fission reactor have been used to place restrictive…
Weak lensing by large-scale structure provides a direct measurement of matter fluctuations in the universe. We report a measurement of this `cosmic shear' based on 271 WFPC2 archival images from the Hubble Space Telescope Medium Deep Survey…
We identify a systematic distortion of the gain-vs.-frequency function of radio telescopes caused by digital flattening ("whitening") of the signal's spectrum followed by re-quantization, a common pair of processes in the signal processing…
Quasar microlensing effects make it possible to measure the accretion disc sizes around distant supermassive black holes that are still well beyond the spatial resolution of contemporary instrumentation. The sizes measured with this…
Variability is a striking features of quasars, observed at all timescales wavelengths. Studying its properties and the correlations with the physical parameters (e.g. black hole mass and accretion rate) provides significant insights into…
This is the first paper of a series describing our measurement of weak lensing by large-scale structure using archival observations from the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST). In this work we…
A continuous set of echelle spectra of TW Hya, taken with the MIKE spectrograph on the Magellan2/Clay telescope at Las Campanas Observatory in April 2006 reveals systematic variations in the flux, velocity, and profile of the H-alpha…
We present an analysis of three years of precision radial velocity measurements of 160 metal-poor stars observed with HIRES on the Keck 1 telescope. We report on variability and long-term velocity trends for each star in our sample. We…
We study constraints on time variation of the fine structure constant alpha from cosmic microwave background (CMB) taking into account simultaneous change in alpha and the electron mass m_e which might be implied in unification theories. We…
We have compared the frequency of high-redshift Hydrogen HI 21 cm absorption with that of associated molecular absorption in two quasars to place new (1 sigma) upper limits on any variation in y = g_p.alpha^2 (where alpha is the fine…
One of the basic optoelectronic characteristics is the absorption of any optoelectronic device or material. We present the characteristics of pure GaAs and the deviation of ideal spectra. Due to crystal defects, vacancies, impurities, etc.,…
This paper describes a study of the Lyman-alpha forest absorption clouds along the quasar sightline Q0000-26 (zem=4.1). The spectrum was obtained with the High Resolution Spectrometer on the 10m Keck telescope. We derive accurate H I column…