Spectra of molecular hydrogen (H\(_2\)) are employed to search for a possible proton-to-electron mass ratio (\(\mu\)) dependence on gravity. The Lyman transitions of H\(_2\), observed with the Hubble ...Space Telescope towards white dwarf stars that underwent a gravitational collapse, are compared to accurate laboratory spectra taking into account the high temperature conditions (\(T \sim 13\,000\) K) of their photospheres. We derive sensitivity coefficients \(K_i\) which define how the individual H\(_2\) transitions shift due to \(\mu\)-dependence. The spectrum of white dwarf star GD133 yields a \(\Delta\mu/\mu\) constraint of \((-2.7\pm4.7_{\rm stat}\pm 0.2_{\rm sys})\times10^{-5}\) for a local environment of a gravitational potential \(\phi\sim10^4\ \phi_\textrm{Earth}\), while that of G29\(-\)38 yields \(\Delta\mu/\mu=(-5.8\pm3.8_{\rm stat}\pm 0.3_{\rm sys})\times10^{-5}\) for a potential of \(2 \times 10^4\) \(\phi_\textrm{Earth}\).
Torsion-rotation transitions in molecules exhibiting hindered internal rotation possess enhanced sensitivities to a variation of the proton-to-electron mass ratio. This enhancement occurs due to a ...cancellation of energies associated with the torsional and rotational degrees of freedom of the molecule. This effect occurs generally in every internal rotor molecule, but is exceptionally large in methanol. In this paper we calculate the sensitivity coefficients of methyl mercaptan, the thiol analogue of methanol. The obtained sensitivity coefficients in this molecule range from \(K_\mu=-14.8\) to \(+12.2\) for transitions with a lower-level excitation energy below 10\,cm\(^{-1}\).
The remarkable precision of frequency comb (FC) lasers is transferred to the extreme ultraviolet (XUV, wavelengths shorter than 100 nm), a frequency region previously not accessable to these devices. ...A frequency comb at XUV wavelengths near 51 nm is generated by amplification and coherent upconversion of a pair of pulses originating from a near-infrared femtosecond FC laser. The phase coherence of the source in the XUV is demonstrated using Helium atoms as a ruler and phase detector. Signals in the form of stable Ramsey-like fringes with high contrast are observed when the FC laser is scanned over P states of Helium, from which the absolute transition frequency in the XUV can be extracted. This procedure yields a 4He ionization energy at h 5945204212(6) MHz, improved by nearly an order of magnitude in accuracy, thus challenging QED calculations of this two-electron system.
Molecular transitions recently discovered at redshift z_abs=2.059 toward the bright background quasar J2123-0050 are analysed to limit cosmological variation in the proton-to-electron mass ratio, ...mu=m_p/m_e. Observed with the Keck telescope, the optical spectrum has the highest resolving power and largest number (86) of H_2 transitions in such analyses so far. Also, (7) HD transitions are used for the first time to constrain mu-variation. These factors, and an analysis employing the fewest possible free parameters, strongly constrain mu's relative deviation from the current laboratory value: dmu/mu =(+5.6+/-5.5_stat+/-2.7_sys)x10^{-6}. This is the first Keck result to complement recent constraints from three systems at z_abs>2.5 observed with the Very Large Telescope.
Molecular transitions recently discovered at redshift z_abs=2.059 toward the bright background quasar J2123-0050 are analysed to limit cosmological variation in the proton-to-electron mass ratio, ...mu=m_p/m_e. Observed with the Keck telescope, the optical echelle spectrum has the highest resolving power and largest number (86) of H_2 transitions in such analyses so far. Also, (seven) HD transitions are used for the first time to constrain mu-variation. These factors, and an analysis employing the fewest possible free parameters, strongly constrain mu's relative deviation from the current laboratory value: dmu/mu =(+5.6+/-5.5_stat+/-2.9_sys)x10^{-6}, indicating an insignificantly larger mu in the absorber. This is the first Keck result to complement recent null constraints from three systems at z_abs>2.5 observed with the Very Large Telescope. The main possible systematic errors stem from wavelength calibration uncertainties. In particular, distortions in the wavelength solution on echelle order scales are estimated to contribute approximately half the total systematic error component, but our estimate is model dependent and may therefore under or overestimate the real effect, if present. To assist future mu-variation analyses of this kind, and other astrophysical studies of H_2 in general, we provide a compilation of the most precise laboratory wavelengths and calculated parameters important for absorption-line work with H_2 transitions redwards of the hydrogen Lyman limit.
Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We ...study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling, and fundamental physics in the search for variation in the fine structure constant. This variation manifests as shifts in the observed wavelengths of absorption lines, such as quadruply ionized iron (FeV) and quadruply ionized nickel (NiV), when compared to laboratory wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801) demonstrated the validity of such an analysis using high-resolution Space Telescope Imaging Spectrograph (STIS) spectra of G191-B2B. We have made three important improvements by: (a) using three new independent sets of laboratory wavelengths; (b) analysing a sample of objects; and (c) improving the methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method). A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. Here we describe our approach and present preliminary results from nine objects using both FeV and NiV.
PDF
