Isotope shift and search for metastable superheavy elements in astrophysical data [CL]

Spectral lines belonging to the short-lifetime heavy radioactive elements up to Es ($Z$=99) have been found in the spectra of the Przybylski’s star. We suggest that these unstable elements may be decay products of a “magic” metastable nucleus belonging to the the island of stability where the nuclei have a magic number of neutrons $N=184$. The laboratory-produced nuclei have a significantly smaller number of neutrons. To identify spectra of the $N=184$ isotopes of these nuclei and their neutron-reach superheavy decay products in astrophysical data we calculate the isotope shift which should be added to the laboratory – measured wavelenghs. The results for the isotopic shifts in the strongest optical electromagnetic transitions in No, Lr, Nh, Fl,and $Z$=120 elements are presented.

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V. Dzuba, V. Flambaum and J. Webb
Tue, 14 Mar 17

Comments: 4 pages, no figures

Charge exchange in the ultraviolet: implication for interacting clouds in the core of NGC 1275 [GA]

Charge exchange emission is known to provide a key diagnostic to the interface between hot and cold matter in many astrophysical environments. Most of the recent charge exchange studies focus on its emission in the X-ray band, but few on the UV part, although the latter can also provide a powerful probe of the charge exchange process. An atomic calculation, as well as an application to observed data, are presented to explore and describe the potential use of the UV data for the study of cosmic charge exchange. Using the newest charge exchange model in the SPEX code v3.03, we re-analyze an archival Hubble STIS data of the central region of NGC 1275. The NGC 1275 spectrum shows hints for three possible weak lines at about 1223.6~{\AA}, 1242.4~{\AA}, and 1244.0~{\AA}, each with a significance of about $2-3\sigma$. The putative features are best explained by charge exchange between highly ionized hydrogen, neon, and sulfur with neutral matter. The wavelengths of the charge exchange lines are found robustly with uncertainties $\leq 0.3$~{\AA}. The possible charge exchange emission shows a line-of-sight velocity offset of about $-3400$ km s$^{-1}$ with respect to the NGC 1275 nucleus, which resembles one of the Ly$\alpha$ absorbers reported in Baum et al. (2005). This indicates that the charge exchange lines might be emitted as the same position of the absorber, which could be ascribed to outflowing gas from the nucleus.

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L. Gu, J. Mao, C. ODea, et. al.
Mon, 6 Mar 17

Comments: accepted for publication in A&A

Radiative association of C(${}^3P$) and H${}^+$: Triplet states [CL]

The radiative association of C(${}^3P$) and H${}^+$ is investigated by calculating cross sections for photon emission into bound ro-vibrational states of CH${}^+$ from the vibrational continua of initial triplet d$\,{}^3\Pi$ or b$\,{}^3\Sigma^-$ states. Potential energy curves and transition dipole moments are calculated using multi-reference configuration interaction (MRCI) methods with AV6Z basis sets. The cross sections are evaluated using quantum-mechanical methods and rate coefficients are calculated. The rate coefficients are about 100 times larger than those for radiative association of C${}^+({}^2{P^o})$ and H from the A$\,{}^1\Pi$ state. We also confirm that the formation of CH${}^+$ by radiative association of C${}^+({}^2{P^o})$ and H via the triplet c$\,{}^3\Sigma^+$ state is a minor process.

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J. Babb and B. McLaughlin
Tue, 28 Feb 17

Comments: 7 pages

Experimental demonstration of a fifth force due to chameleon field via cold atoms [CEA]

We tested a fifth force using cold atom experiments. The accelerated expansion of the universe implies the possibility of the presence of a scalar field throughout the universe driving the acceleration. This field would result in a detectable force between normal-matter objects. Theory of the chameleon field states that the force should be strong in a thin shell near the surface of a source object but greatly suppressed inside and outside of the source object. We used two atom clouds: one as the source and the other as the test mass; so the test mass can pass through the thin-shell region of the source mass. We detected the chameleon force and obtained the couple constant of about 4.5E11 between matter and the field. The chameleon force is considerably larger than Newtonian gravity at short distance; the interaction range is short enough to satisfy all experimental bounds on deviations from general relativity.

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H. Zhang
Mon, 13 Feb 17

Comments: 18 pages, 5 figures

Testing atomic collision theory with the two-photon continuum of astrophysical nebulae [CEA]

Accurate rates for energy-degenerate l-changing collisions are needed to determine cosmological abundances and recombination. There are now several competing theories for the treatment of this process, and it is not possible to test these experimentally. We show that the H I two-photon continuum produced by astrophysical nebulae is strongly affected by l-changing collisions. We perform an analysis of the different underlying atomic processes and simulate the recombination and two-photon spectrum of a nebula containing H and He. We provide an extended set of effective recombination coefficients and updated l-changing 2s-2p transition rates using several competing theories. In principle, accurate astronomical observations could determine which theory is correct.

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F. Guzman, N. Badnell, M. Chatzikos, et. al.
Mon, 30 Jan 17

Comments: 7 pages, 6 fig, 2 tables, accepted in MNRAS

PAMOP project: computations in support of experiments and astrophysical applications [CL]

Our computation effort is primarily concentrated on support of current and future measurements being carried out at various synchrotron radiation facilities around the globe, and photodissociation computations for astrophysical applications. In our work we solve the Schr\”odinger or Dirac equation for the appropriate collision problem using the R-matrix or R-matrix with pseudo-states approach from first principles. The time dependent close-coupling (TDCC) method is also used in our work. A brief summary of the methodology and ongoing developments implemented in the R-matrix suite of Breit-Pauli and Dirac-Atomic R-matrix codes (DARC) is presented.

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B. McLaughlin, C. Ballance, M. Pindzola, et. al.
Tue, 17 Jan 17

Comments: 17 pages, 10 figures: chapter in the book, High Performance Computing in Science and Engineering’16, edited by W. E. Nagel, D. B. Kr\”oner, and M. Reich (Springer, New York and Berlin, 2017)

Radiative data for highly excited 3d8 4d levels in Ni II from laboratory measurements and atomic calculations [SSA]

This work reports new experimental radiative lifetimes and calculated oscillator strengths for transitions from 3d8 4d levels of astrophysical interest in singly ionized nickel. Radiative lifetimes of seven high-lying levels of even parity in Ni II (98400 -100600 cm-1) have been measured using the time-resolved laser-induced fluorescence method. Two-step photon excitation of ions produced by laser ablation has been utilized to populate the levels. Theoretical calculations of the radiative lifetimes of the measured levels and transition probabilities from these levels are reported. The calculations have been performed using a pseudo-relativistic Hartree-Fock method, taking into account core polarization effects. A new set of transition probabilities and oscillator strengths has been deduced for 477 Ni II transitions of astrophysical interest in the spectral range 194 – 520 nm depopulating even parity 3d8 4d levels. The new calculated gf-values are, on the average, about 20 % higher than a previous calculation by Kurucz (this http URL) and yield lifetimes within 5 % of the experimental values.

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H. Hartman, L. Engstrom, H. Lundberg, et. al.
Wed, 11 Jan 17

Comments: 17 pages