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We present a study of spectral line width measurements from the Extreme Ultraviolet Imaging Spectrometer (EIS) on {\it Hinode}. We used spectral line profiles of Fe {\sc xvi} 262.984 {\AA}, Fe {\sc xiv} 264.787 {\AA}, Fe {\sc xiv} 270.519 {\AA}, Fe {\sc xiv} 274.203 {\AA}, and Fe {\sc xv} 284.160 {\AA}, and studied 11 active regions. Previous studies of spectral line widths have shown that in hot loops in the cores of active regions, the observed non-thermal velocities are smaller than predicted from models of reconnection jets in the corona or shock heating associated with Alfv\'{e}n waves. The observed line widths are also inconsistent with models of chromospheric evaporation due to coronal nanoflares. We show that recent advances in higher resolution Alfv\'{e}n wave turbulence modeling enables us to obtain non-thermal velocities similar to those measured in active regions. The observed non-thermal velocities for the 11 active regions in our study are in the range of 17$-$30 $\rm km ~ s^{-1}$, consistent with the spectral line non-thermal widths predicted from our model of 16 interacting flux tubes, which are in the range of ~15$-$37 $\rm km ~ s^{-1}$.

We have incorporated our experimentally derived thermal rate coefficients for C + H$_3^+$ forming CH$^+$ and CH$_2^+$ into a commonly used astrochemical model. We find that the Arrhenius-Kooij equation typically used in chemical models does not accurately fit our data and use instead a more versatile fitting formula. At a temperature of 10 K and a density of 10$^4$ cm$^{-3}$, we find no significant differences in the predicted chemical abundances, but at higher temperatures of 50, 100, and 300 K we find up to factor of 2 changes. Additionally, we find that the relatively small error on our thermal rate coefficients, $\sim15\%$, significantly reduces the uncertainties on the predicted abundances compared to those obtained using the currently implemented Langevin rate coefficient with its estimated factor of 2 uncertainty., Comment: 19 pages, 5 figures. Accepted for publication in ApJ

We report measured rate coefficients for electron-ion recombination for Si10+ forming Si9+ and for Si9+ forming Si8+, respectively. The measurements were performed using the electron-ion merged-beams technique at a heavy-ion storage ring. Electron-ion collision energies ranged from 0 to 50 eV for Si9+ and from 0 to 2000 eV for Si10+, thus, extending previous measurements for Si10+ [Orban et al. 2010, Astrophys. J. 721, 1603] to much higher energies. Experimentally derived rate coefficients for the recombination of Si9+ and Si10+ ions in a plasma are presented along with simple parameterizations. These rate coefficients are useful for the modeling of the charge balance of silicon in photoionized plasmas (Si9+ and Si10+) and in collisionally ionized plasmas (Si10+ only). In the corresponding temperature ranges, the experimentally derived rate coefficients agree with the latest corresponding theoretical results within the experimental uncertainties., Comment: 17 pages, 7 figures, 3 tables, 66 references, submitted to the J. Phys. B special issue on atomic and molecular data for astrophysicists

We demonstrate the use of high power diode laser stacks to photodetach fast hydrogen and carbon anions and produce ground term neutral atomic beams. We achieve photodetachment efficiencies of $\sim$7.4\% for H$^-$ at a beam energy of 10\,keV and $\sim$3.7\% for C$^-$ at 28\,keV. The diode laser systems used here operate at 975\,nm and 808\,nm, respectively, and provide high continuous power levels of up to 2\,kW, without the need of additional enhancements like optical cavities. The alignment of the beams is straightforward and operation at constant power levels is very stable, while maintenance is minimal. We present a dedicated photodetachment setup that is suitable to efficiently neutralize the majority of stable negative ions in the periodic table.

We have measured the reaction of O + H3+ forming OH+ and H2O+. This is one of the key gas-phase astrochemical processes initiating the formation of water molecules in dense molecular clouds. For this work, we have used a novel merged fast-beams apparatus which overlaps a beam of H3+ onto a beam of ground-term neutral O. Here, we present cross section data for forming OH+ and H2O+ at relative energies from \approx 3.5 meV to \approx 15.5 and 0.13 eV, respectively. Measurements were performed for statistically populated O(3PJ) in the ground term reacting with hot H3+ (with an internal temperature of \approx 2500-3000 K). From these data, we have derived rate coefficients for translational temperatures from \approx 25 K to \approx 10^5 and 10^3 K, respectively. Using state-of-the-art theoretical methods as a guide, we have converted these results to a thermal rate coefficient for forming either OH+ or H2O+, thereby accounting for the temperature dependence of the O fine-structure levels. Our results are in good agreement with two independent flowing afterglow measurements at a temperature of \approx 300 K, and with a corresponding level of H3+ internal excitation. This good agreement strongly suggests that the internal excitation of the H3+ does not play a significant role in this reaction. The Langevin rate coefficient is in reasonable agreement with the experimental results at 10 K but a factor of \approx 2 larger at 300 K. The two published classical trajectory studies using quantum mechanical potential energy surfaces lie a factor of \approx 1.5 above our experimental results over this 10-300 K range., Comment: 43 pages, 11 figures. Submitted to the Astrophysical Journal

We have measured electron impact ionization (EII) for Fe 7+ from the ionization threshold up to 1200 eV. The measurements were performed using the TSR heavy ion storage ring. The ions were stored long enough prior to measurement to remove most metastables, resulting in a beam of 94% ground state ions. Comparing with the previously recommended atomic data, we find that the Arnaud & Raymond (1992) cross section is up to about 40\% larger than our measurement, with the largest discrepancies below about 400~eV. The cross section of Dere (2007) agrees to within 10%, which is about the magnitude of the experimental uncertainties. The remaining discrepancies between measurement and the most recent theory are likely due to shortcomings in the theoretical treatment of the excitation-autoionization contribution., Comment: Submitted to the Astrophysical Journal

We have systematically investigated the energy resolution of a magnetic micro-calorimeter (MMC) for atomic and molecular projectiles at impact energies ranging from $E\approx13$ to 150 keV. For atoms we obtained absolute energy resolutions down to $\Delta E \approx 120$ eV and relative energy resolutions down to $\Delta E/E\approx10^{-3}$. We also studied in detail the MMC energy-response function to molecular projectiles of up to mass 56 u. We have demonstrated the capability of identifying neutral fragmentation products of these molecules by calorimetric mass spectrometry. We have modeled the MMC energy-response function for molecular projectiles and conclude that backscattering is the dominant source of the energy spread at the impact energies investigated. We have successfully demonstrated the use of a detector absorber coating to suppress such spreads. We briefly outline the use of MMC detectors in experiments on gas-phase collision reactions with neutral products. Our findings are of general interest for mass spectrometric techniques, particularly for those desiring to make neutral-particle mass measurements.

Innershell ionization of a $1s$ electron by either photons or electrons is important for X-ray photoionized objects such as active galactic nuclei and electron-ionized sources such as supernova remnants. Modeling and interpreting observations of such objects requires accurate predictions for the charge state distribution (CSD) which results as the $1s$-hole system stabilizes. Due to the complexity of the complete stabilization process, few modern calculations exist and the community currently relies on 40-year-old atomic data. Here, we present a combined experimental and theoretical study for innershell photoionization of neutral atomic nitrogen for photon energies of $403-475$~eV. Results are reported for the total ion yield cross section, for the branching ratios for formation of N$^+$, N$^{2+}$, and N$^{3+}$, and for the average charge state. We find significant differences when comparing to the data currently available to the astrophysics community. For example, while the branching ratio to N$^{2+}$ is somewhat reduced, that for N$^+$ is greatly increased, and that to N$^{3+}$, which was predicted not to be zero, grows to $\approx 10\%$ at the higher photon energies studied. This work demonstrates some of the shortcomings in the theoretical CSD data base for innershell ionization and points the way for the improvements needed to more reliably model the role of innershell ionization of cosmic plasmas., Comment: Submitted to The Astrophysical Journal, 19 pages, 2 tables, and 3 figures

We present new experimentally measured and theoretically calculated rate coefficients for the electron-ion recombination of W$^{18+}$([Kr] $4d^{10}$ $4f^{10}$) forming W$^{17+}$. At low electron-ion collision energies, the merged-beam rate coefficient is dominated by strong, mutually overlapping, recombination resonances. In the temperature range where the fractional abundance of W$^{18+}$ is expected to peak in a fusion plasma, the experimentally derived Maxwellian recombination rate coefficient is 5 to 10 times larger than that which is currently recommended for plasma modeling. The complexity of the atomic structure of the open-$4f$-system under study makes the theoretical calculations extremely demanding. Nevertheless, the results of new Breit-Wigner partitioned dielectronic recombination calculations agree reasonably well with the experimental findings. This also gives confidence in the ability of the theory to generate sufficiently accurate atomic data for the plasma modeling of other complex ions., Comment: 11 pages, 4 figures, 2 tables, 40 references, accepted for publication in Physical Review A

We have investigated the chemistry of ${\rm C + H_3^+}$ forming CH$^+$, CH$_2^+$, and CH$_3^+$. These reactions are believed to be some of the key gas-phase astrochemical processes initiating the formation of organic molecules in molecular clouds. For this work we have constructed a novel merged fast-beams apparatus which overlaps a beam of molecular ions onto a beam of ground-term neutral atoms. Here we present cross section data for forming CH$^+$ and CH$_2^+$ at collision energies from $\approx 9$ meV to $\approx20$ and 3 eV, respectively. Using these data we have derived thermal rate coefficients for reaction temperatures from $\approx72$ K to $\approx2.3 \times 10^5$ and $3.4 \times 10^4$ K, respectively. For the formation of CH$_3^+$ we are able only to put an upper limit on the rate coefficient. Our results for CH$^+$ and CH$_2^+$ are in good agreement with the mass-scaled results from a previous ion trap study of ${\rm C + D_3^+}$ at a reaction temperature of $\sim 1000$ K. At molecular cloud temperatures our thermal rate coefficient for forming CH$^+$ lies a factor of $\sim 2-4$ below the Langevin rate coefficient currently given in astrochemical databases and below the published semi-classical calculations. Our results for CH$_2^+$ formation are a factor of $\sim 26$ above the semi-classical results. Astrochemical databases do not currently include this channel., Comment: Accepted for publication in the Astrophysical Journal Supplement

We have investigated dissociative recombination (DR) of NH$^+$ with electrons using a merged beams configuration at the TSR heavy-ion storage ring located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We present our measured absolute merged beams recombination rate coefficient for collision energies from 0 to 12 eV. From these data we have extracted a cross section which we have transformed to a plasma rate coefficient for the collisional plasma temperature range from $T_{\rm pl} = 10$ to $18000$ K. We show that the NH$^+$ DR rate coefficient data in current astrochemical models are underestimated by up to a factor of $\sim 9$. Our new data will result in predicted NH$^+$ abundances lower than calculated by present models. This is in agreement with the sensitivity limits of all observations attempting to detect NH$^+$ in interstellar clouds., Comment: July 1st 2014: Accepted for publication in ApJ

Rate coefficients for photorecombination (PR) and cross sections for electron-impact ionization (EII) of Fe$^{14+}$ forming Fe$^{13+}$ and Fe$^{15+}$, respectively, have been measured by employing the electron-ion merged-beams technique at a heavy-ion storage ring. Rate coefficients for PR and EII of Fe$^{14+}$ ions in a plasma are derived from the experimental measurements. Simple parametrizations of the experimentally derived plasma rate coefficients are provided for use in the modeling of photoionized and collisionally ionized plasmas. In the temperature ranges where Fe$^{14+}$ is expected to form in such plasmas the latest theoretical rate coefficients of Altun et al. [Astron. Astrophys. 474, 1051 (2007)] for PR and of Dere [Astron. Astrophys. 466, 771 (2007)] for EII agree with the experimental results to within the experimental uncertainties. Common features in the PR and EII resonance structures are identified and discussed., Comment: 12 pages, 6 figures, 3 tables, submitted for publication to Physical Review A

We have measured dissociative recombination of HCl+ with electrons using a merged beams configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We present the measured absolute merged beams recombination rate coefficient for collision energies from 0 to 4.5 eV. We have also developed a new method for deriving the cross section from the measurements. Our approach does not suffer from approximations made by previously used methods. The cross section was transformed to a plasma rate coefficient for the electron temperature range from T=10 to 5000 K. We show that the previously used HCl+ DR data underestimate the plasma rate coefficient by a factor of 1.5 at T=10 K and overestimate it by a factor of 3.0 at T=300 K. We also find that the new data may partly explain existing discrepancies between observed abundances of chlorine-bearing molecules and their astrochemical models., Comment: Accepted for publication in ApJ (July 7, 2013)

We report measurements of electron impact ionization (EII) for Fe^13+, Fe^16+, and Fe^17+ over collision energies from below threshold to above 3000 eV. The ions were recirculated using an ion storage ring. Data were collected after a sufficiently long time that essentially all the ions had relaxed radiatively to their ground state before data were collected. For single ionization of $\fethirteen$ we find that previous single pass experiments are more than 40% larger than our results. Compared to our work, the theoretical cross section recommended by Arnaud & Raymond (1992) is more than 30% larger, while that of Dere (2007) is about 20% greater. Much of the discrepancy with Dere (2007) is due to the theory overestimating the contribution of excitation-autoionization via n=2 excitations. Double ionization of Fe^13+ is dominated by direct ionization of an inner shell electron accompanied by autoionization of a second electron. Our results for single ionization of Fe^16+ and Fe^17+ agree with theoretical calculations to within the experimental uncertainties., Comment: Accepted for the Astrophysical Journal

We present a new diagnostic allowing one to measure the anisotropy of ion temperatures and non-thermal velocities as well as Doppler shifts with respect to the ambient magnetic field. This method provides new results, as well as independent test for previous measurements obtained with other techniques. Our spectral data come from observations of a low latitude, on-disk coronal hole. A potential field source surface model was used to calculate the angle between the magnetic field lines and the line of sight for each spatial bin of the observation. A fit was performed to determine the line widths and Doppler shifts parallel and perpendicular to the magnetic field. For each line width component we derived parallel and perpendicular ion temperatures and non-thermal velocities. The perpendicular ion temperature was cooler than off-limb polar coronal hole measurements. The parallel ion temperature was consistent with a uniform temperature of 1.8 +/- 0.2 x 10^{6} K for each ion. Since parallel ion heating is expected to be weak, this ion temperature should reflect the proton temperature. A comparison between our results and others implies a large proton temperature gradient around 1.02 R_sun. The non-thermal velocities are thought to be proportional to the amplitudes of various waves. Our results for the perpendicular non-thermal velocity agree with Alfv\'en wave amplitudes inferred from off-limb polar coronal hole line width measurements. Our parallel non-thermal velocity results are consistent with slow magnetosonic wave amplitudes inferred from Fourier analysis of time varying intensity fluctuations. Doppler shift measurements yield outflows of ~5 km s^-1 for ions formed over a broad temperature range. This differs from other studies which found a strong Doppler shift dependence on formation temperature., Comment: Accepted for The Astrophysical Journal

We have measured electron-ion recombination for Fe XII forming Fe XI using a merged beams configuration at the heavy-ion storage ring TSR located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The measured merged beams recombination rate coefficient (MBRRC) for collision energies from 0 to 1500 eV is presented. This work uses a new method for determining the absolute MBRRC based on a comparison of the ion beam decay rate with and without the electron beam on. For energies below 75 eV, the spectrum is dominated by dielectronic recombination (DR) resonances associated with 3s-3p and 3p-3d core excitations. At higher energies we observe contributions from 3-N' and 2-N' core excitations DR. We compare our experimental results to state-of-the-art multi-configuration Breit-Pauli (MCBP) calculations and find significant differences, both in resonance energies and strengths. We have extracted the DR contributions from the measured MBRRC data and transformed them into a plasma recombination rate coefficient (PRRC) for temperatures in the range of 10^3 to 10^7 K. We show that the previously recommended DR data for Fe XII significantly underestimate the PRRC at temperatures relevant for both photoionized plasmas (PPs) and collisionaly ionized plasmas (CPs). This is to be contrasted with our MCBP PRRC results which agree with the experiment to within 30% at PP temperatures and even better at CP temperatures. We find this agreement despite the disagreement shown by the detailed comparison between our MCBP and experimental MBRRC results. Lastly, we present a simple parameterized form of the experimentally derived PRRC for easy use in astrophysical modelling codes., Comment: April 24, 2012: accepted for publication in The Astrophysical Journal

An emerging theme in modern astrophysics is the connection between astronomical observations and the underlying physical phenomena that drive our cosmos. Both the mechanisms responsible for the observed astrophysical phenomena and the tools used to probe such phenomena - the radiation and particle spectra we observe - have their roots in atomic, molecular, condensed matter, plasma, nuclear and particle physics. Chemistry is implicitly included in both molecular and condensed matter physics. This connection is the theme of the present report, which provides a broad, though non-exhaustive, overview of progress in our understanding of the cosmos resulting from recent theoretical and experimental advances in what is commonly called laboratory astrophysics. This work, carried out by a diverse community of laboratory astrophysicists, is increasingly important as astrophysics transitions into an era of precise measurement and high fidelity modeling., Comment: 61 pages. 11 figures; to appear in Reports on Progress in Physics

The hyperfine induced 2s 2p 3P0 -> 2s2 1S0 transition rate in Be-like sulfur was measured by monitoring the decay of isotopically pure beams of 32-S12+ and 33-S12+ ions in a heavy-ion storage ring. Within the 4% experimental uncertainty the experimental value of 0.096(4)/s agrees with the most recent theoretical results of Cheng et al. [Phys. Rev. A 77, 052504 (2008)] and Andersson et al. [Phys. Rev. A 79, 032501 (2009)]. Repeated experiments with different magnetic fields in the storage-ring bending magnets demonstrate that artificial quenching of the 2s 2p 3P0 state by these magnetic fields is negligible., Comment: 11 pages, 7 figures, 5 tables

Using a merged beams apparatus we have measured the associative detachment (AD) reaction of ${\rm H}^- + {\rm H} \to {\rm H}_2 + e^-$ for relative collision energies up to \textit{E}$_{\rm{r}} \leq 4.83$ eV. These data extend above the 1 eV limit of our earlier results. We have also updated our previous theoretical work to account for AD via the repulsive $^2\Sigma^+_{\rm g}$ H$_2^-$ potential energy surface and for the effects at $E_{\rm r} \ge 0.76$ eV on the experimental results due to the formation of H$_2$ resonances lying above the ${\rm H} + {\rm H}$ separated atoms limit. Merging both experimental data sets, our results are in good agreement with our new theoretical calculations and confirm the prediction that this reaction essentially turns off for $E_{\rm r} \gtrsim 2$ eV. Similar behavior has been predicted for the formation of protonium from collisions of antiprotons and hydrogen atoms., Comment: Accepted for publication Phys. Rev. A

We report ionization cross section measurements for electron impact single ionization (EISI) of Fe^11+$ forming Fe^12+ and electron impact double ionization (EIDI) of Fe^11+ forming Fe^13+. The measurements cover the center-of-mass energy range from approximately 230 eV to 2300 eV. The experiment was performed using the heavy ion storage ring TSR located at the Max-Planck-Institut fur Kernphysik in Heidelberg, Germany. The storage ring approach allows nearly all metastable levels to relax to the ground state before data collection begins. We find that the cross section for single ionization is 30% smaller than was previously measured in a single pass experiment using an ion beam with an unknown metastable fraction. We also find some significant differences between our experimental cross section for single ionization and recent distorted wave (DW) calculations. The DW Maxwellian EISI rate coefficient for Fe^11+ forming Fe^12+ may be underestimated by as much as 25% at temperatures for which Fe^11+ is abundant in collisional ionization equilibrium. This is likely due to the absence of 3s excitation-autoionization (EA) in the calculations. However, a precise measurement of the cross section due to this EA channel was not possible because this process is not distinguishable experimentally from electron impact excitation of an n=3 electron to levels of n > 44 followed by field ionization in the charge state analyzer after the interaction region. Our experimental results also indicate that the double ionization cross section is dominated by the indirect process in which direct single ionization of an inner shell 2l electron is followed by autoionization resulting in a net double ionization., Comment: Accepted for publication in Astrophysical Journal

Dielectronic recombination (DR) of xenonlike W20+ forming W19+ has been studied experimentally at a heavy-ion storage-ring. A merged-beams method has been employed for obtaining absolute rate coefficients for electron-ion recombination in the collision energy range 0-140 eV. The measured rate coefficient is dominated by strong DR resonances even at the lowest experimental energies. At plasma temperatures where the fractional abundance of W20+ is expected to peak in a fusion plasma, the experimentally derived plasma recombination rate coefficient is over a factor of 4 larger than the theoretically-calculated rate coefficient which is currently used in fusion plasma modeling. The largest part of this discrepancy stems most probably from the neglect in the theoretical calculations of DR associated with fine-structure excitations of the W20+([Kr] 4d10 4f8) ion core., Comment: 7 pagers, 4 figures, accepted for publication in Physical Review A

We report measurements of a polar coronal hole during the recent solar minimum using the Extreme Ultraviolet Imaging Spectrometer on Hinode. Five observations are analyzed that span the polar coronal hole from the central meridian to the boundary with the quiet Sun corona. We study the observations above the solar limb in the height range of 1.03 - 1.20 solar radii. The electron temperature Te and emission measure EM are found using the Geometric mean Emission Measure (GEM) method. The EM derived from the elements Fe, Si, S, and Al are compared in order to measure relative coronal-to-photospheric abundance enhancement factors. We also studied the ion temperature Ti and the non-thermal velocity Vnt using the line profiles. All these measurements are compared to polar coronal hole observations from the previous (1996-1997) solar minimum and to model predictions for relative abundances. There are many similarities in the physical properties of the polar coronal holes between the two minima at these low heights. We find that Te, electron density Ne, and Ti are comparable in both minima. Te shows a comparable gradient with height. Both minima show a decreasing Ti with increasing charge-to-mass ratio q/M. A previously observed upturn of Ti for ions above q/M > 0.25 was not found here. We also compared relative coronal-to-photospheric elemental abundance enhancement factors for a number of elements. These ratios were about 1 for both the low first ionization potential (FIP) elements Si and Al and the marginally high FIP element S relative to the low FIP element Fe, as is expected based on earlier observations and models for a polar coronal hole. These results are consistent with no FIP effect in a polar coronal hole., Comment: Accepted for publication in the Astrophysical Journal

This review summarizes the present status of an ongoing experimental effort to provide reliable rate coefficients for dielectronic recombination of highly charged iron ions for the modeling of astrophysical and other plasmas. The experimental work has been carried out over more than a decade at the heavy-ion storage-ring TSR of the Max-Planck-Institute for Nuclear Physics in Heidelberg, Germany. The experimental and data reduction procedures are outlined. The role of previously disregarded processes such as fine-structure core excitations and trielectronic recombination is highlighted. Plasma rate coefficients for dielectronic recombination of Fe$^{q+}$ ions (q=7-10, 13-22) and Ni$^{25+}$ are presented graphically and in a simple parameterized form allowing for easy use in plasma modeling codes. It is concluded that storage-ring experiments are presently the only source for reliable low-temperature dielectronic recombination rate-coefficients of complex ions., Comment: This replacement corrects the coefficients for q=15 in the last column of Table II and Figure 7 accordingly. The previous coefficients were other than stated for 3->3 DR only. The present coefficients comprise 3->3 and 3->4 DR as stated and reproduce the Fe15+ DR plasma rate coefficient from Figure 7 of Ref. 5. We thank Houke Huang (IMP, Lanzhou, China) for pointing out the error

Comparison of appropriate theoretical derived line ratios with observational data can yield estimates of a plasma's physical parameters, such as electron density or temperature. The usual practice in the calculation of the line ratio is the assumption of excitation by electrons/protons followed by radiative decay. Furthermore, it is normal to use the so-called coronal approximation, i.e. one only considers ionization and recombination to and from the ground state. A more accurate treatment is to include the ionization/recombination to and from meta-stable levels. Here, we apply this to two lines from adjacent ionization stages; Mg IX 368A and Mg X 625A, which has been shown to be a very useful temperature diagnostic. At densities typical of coronal hole conditions, the difference between the electron temperature derived assuming the zero density limit compared with the electron density dependent ionization/recombination is small. This however is not the case for flares where the electron density is orders of magnitude larger. The derived temperature for the coronal hole at solar maximum is around 1.04 MK compared to just below 0.82 MK at solar minimum., Comment: 5 pages

We have measured electron-ion recombination for Fe$^{9+}$ forming Fe$^{8+}$ and for Fe$^{10+}$ forming Fe$^{9+}$ using merged beams at the TSR heavy-ion storage-ring in Heidelberg. The measured merged beams recombination rate coefficients (MBRRC) for relative energies from 0 to 75 eV are presented, covering all dielectronic recombination (DR) resonances associated with 3s->3p and 3p->3d core transitions in the spectroscopic species Fe X and Fe XI, respectively. We compare our experimental results to multi-configuration Breit-Pauli (MCBP) calculations and find significant differences. From the measured MBRRC we have extracted the DR contributions and transform them into plasma recombination rate coefficients (PRRC) for astrophysical plasmas with temperatures from 10^2 to 10^7 K. This spans across the regimes where each ion forms in photoionized or in collisionally ionized plasmas. For both temperature regimes the experimental uncertainties are 25% at a 90% confidence level. The formerly recommended DR data severely underestimated the rate coefficient at temperatures relevant for photoionized gas. At the temperatures relevant for photoionized gas, we find agreement between our experimental results and MCBP theory. At the higher temperatures relevant for collisionally ionized gas, the MCBP calculations yield a Fe XI DR rate coefficent which is significantly larger than the experimentally derived one. We present parameterized fits to our experimentally derived DR PRRC., Comment: 44 Pages, 5 Figures. Accepted for publication in Astrophys. J

Dielectronic recombination (DR) of singly charged ions is a reaction pathway that is commonly neglected in chemical models of molecular clouds. In this study we include state-of-the-art DR data for He$^+$, C$^+$, N$^+$, O$^+$, Na$^+$, and Mg$^+$ in chemical models used to simulate dense molecular clouds, protostars, and diffuse molecular clouds. We also update the radiative recombination (RR) rate coefficients for H$^+$, He$^+$, C$^+$, N$^+$, O$^+$, Na$^+$, and Mg$^+$ to the current state-of-the-art values. The new RR data has little effect on the models. However, the inclusion of DR results in significant differences in gas-grain models of dense, cold molecular clouds for the evolution of a number of surface and gas-phase species. We find differences of a factor of 2 in the abundance for 74 of the 655 species at times of $10^4$--$10^6$ years in this model when we include DR. Of these 74 species, 16 have at least a factor of 10 difference in abundance. We find the largest differences for species formed on the surface of dust grains. These differences are due primarily to the addition of C$^+$ DR, which increases the neutral C abundance, thereby enhancing the accretion of C onto dust. These results may be important for the warm-up phase of molecular clouds when surface species are desorbed into the gas phase. We also note that no reliable state-of-the-art RR or DR data exist for Si$^+$, P$^+$, S$^+$, Cl$^+$, and Fe$^+$. Modern calculations for these ions are needed to better constrain molecular cloud models., Comment: 24 pages, 2 tables, 9 figures. Submitted to ApJ

Studies of the formation of metal-free Population III stars usually focus primarily on the role played by H2 cooling, on account of its large chemical abundance relative to other possible molecular or ionic coolants. However, while H2 is generally the most important coolant at low gas densities, it is not an effective coolant at high gas densities, owing to the low critical density at which it reaches local thermodynamic equilibrium (LTE) and to the large opacities that develop in its emission lines. It is therefore possible that emission from other chemical species may play an important role in cooling high density primordial gas. A particularly interesting candidate is the H3+ molecular ion. This ion has an LTE cooling rate that is roughly a billion times larger than that of H2, and unlike other primordial molecular ions such as H2+ or HeH+, it is not easily removed from the gas by collisions with H or H2. It is already known to be an important coolant in at least one astrophysical context -- the upper atmospheres of gas giants -- but its role in the cooling of primordial gas has received little previous study. In this paper, we investigate the potential importance of H3+ cooling in primordial gas using a newly-developed H3+ cooling function and the most detailed model of primordial chemistry published to date. We show that although H3+ is, in most circumstances, the third most important coolant in dense primordial gas (after H2 and HD), it is nevertheless unimportant, as it contributes no more than a few percent of the total cooling. We also show that in gas irradiated by a sufficiently strong flux of cosmic rays or X-rays, H3+ can become the dominant coolant in the gas, although the size of the flux required renders this scenario unlikely to occur., Comment: 60 pages, 22 figures. Submitted to MNRAS

We have reanalyzed SUMER observations of a parcel of coronal gas using new collisional ionization equilibrium (CIE) calculations. These improved CIE fractional abundances were calculated using state-of-the-art electron-ion recombination data for K-shell, L-shell, Na-like, and Mg-like ions of all elements from H through Zn and, additionally, Al- through Ar-like ions of Fe. They also incorporate the latest recommended electron impact ionization data for all ions of H through Zn. Improved CIE calculations based on these recombination and ionization data are presented here. We have also developed a new systematic method for determining the average emission measure ($EM$) and electron temperature ($T_e$) of an isothermal plasma. With our new CIE data and our new approach for determining average $EM$ and $T_e$, we have reanalyzed SUMER observations of the solar corona. We have compared our results with those of previous studies and found some significant differences for the derived $EM$ and $T_e$. We have also calculated the enhancement of coronal elemental abundances compared to their photospheric abundances, using the SUMER observations themselves to determine the abundance enhancement factor for each of the emitting elements. Our observationally derived first ionization potential (FIP) factors are in reasonable agreement with the theoretical model of Laming (2008)., Comment: 147 pages (102 of which are online only tables and figures). Submitted to ApJ. Version 2 is updated addressing the referee's report

The electron-ion recombination rate coefficient for Si IV forming Si III was measured at the heavy-ion storage-ring TSR. The experimental electron-ion collision energy range of 0-186 eV encompassed the 2p(6) nl n'l' dielectronic recombination (DR) resonances associated with 3s to nl core excitations, 2s 2p(6) 3s nl n'l' resonances associated with 2s to nl (n=3,4) core excitations, and 2p(5) 3s nl n'l' resonances associated with 2p to nl (n=3,...,infinity) core excitations. The experimental DR results are compared with theoretical calculations using the multiconfiguration Dirac-Fock (MCDF) method for DR via the 3s to 3p n'l' and 3s to 3d n'l' (both n'=3,...,6) and 2p(5) 3s 3l n'l' (n'=3,4) capture channels. Finally, the experimental and theoretical plasma DR rate coefficients for Si IV forming Si III are derived and compared with previously available results., Comment: 13 pages, 9 figures, 3 tables. Accepted for publication in Physical Review A

We have measured resonance strengths and energies for dielectronic recombination (DR) of Mg-like Fe XV forming Al-like Fe XIV via N=3 -> N' = 3 core excitations in the electron-ion collision energy range 0-45 eV. All measurements were carried out using the heavy-ion Test Storage Ring at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. We have also carried out new multiconfiguration Breit-Pauli (MCBP) calculations using the AUTOSTRUCTURE code. For electron-ion collision energies < 25 eV we find poor agreement between our experimental and theoretical resonance energies and strengths. From 25 to 42 eV we find good agreement between the two for resonance energies. But in this energy range the theoretical resonance strengths are ~ 31% larger than the experimental results. This is larger than our estimated total experimental uncertainty in this energy range of +/- 26% (at a 90% confidence level). Above 42 eV the difference in the shape between the calculated and measured 3s3p(^1P_1)nl DR series limit we attribute partly to the nl dependence of the detection probabilities of high Rydberg states in the experiment. We have used our measurements, supplemented by our AUTOSTRUCTURE calculations, to produce a Maxwellian-averaged 3 -> 3 DR rate coefficient for Fe XV forming Fe XIV. The resulting rate coefficient is estimated to be accurate to better than +/- 29% (at a 90% confidence level) for k_BT_e > 1 eV. At temperatures of k_BT_e ~ 2.5-15 eV, where Fe XV is predicted to form in photoionized plasmas, significant discrepancies are found between our experimentally-derived rate coefficient and previously published theoretical results. Our new MCBP plasma rate coefficient is 19-28% smaller than our experimental results over this temperature range.

Reliably interpreting spectra from electron-ionized cosmic plasmas requires accurate ionization balance calculations for the plasma in question. However, much of the atomic data needed for these calculations have not been generated using modern theoretical methods and are often highly suspect. This translates directly into the reliability of the collisional ionization equilibrium (CIE) calculations. We make use of state-of-the-art calculations of dielectronic recombination (DR) rate coefficients for the hydrogenic through Na-like ions of all elements from He up to and including Zn. We also make use of state-of-the-art radiative recombination (RR) rate coefficient calculations for the bare through Na-like ions of all elements from H through to Zn. Here we present improved CIE calculations for temperatures from $10^4$ to $10^9$ K using our data and the recommended electron impact ionization data of \citet{Mazz98a} for elements up to and including Ni and Mazzotta (private communication) for Cu and Zn. DR and RR data for ionization stages that have not been updated are also taken from these two additional sources. We compare our calculated fractional ionic abundances using these data with those presented by Mazzotta et al. for all elements from H to Ni. The differences in peak fractional abundance are up to 60%. We also compare with the fractional ionic abundances for Mg, Si, S, Ar, Ca, Fe, and Ni derived from the modern DR calculations of \citet{Gu03a,Gu04a} for the H-like through Na-like ions, and the RR calculations of \citet{Gu03b} for the bare through F-like ions. These results are in better agreement with our work, with differences in peak fractional abundance of less than 10%., Comment: 83 pages, 38 figures, 41 tables Accepted to ApJS

Recent spectroscopic models of active galactic nuclei (AGN) have indicated that the recommended electron-ion recombination rate coefficients for iron ions with partially filled M-shells are incorrect in the temperature range where these ions form in photoionized plasmas. We have investigated this experimentally for Fe XIV forming Fe XIII. The recombination rate coefficient was measured employing the electron-ion merged beams method at the Heidelberg heavy-ion storage-ring TSR. The measured energy range of 0-260 eV encompassed all dielectronic recombination (DR) 1s2 2s2 2p6 3l 3l' 3l'' nl''' resonances associated with the 3p1/2 -> 3p3/2, 3s -> 3p, 3p -> 3d and 3s -> 3d core excitations within the M-shell of the Fe XIV 1s2 2s2 2p6 3s2 3p parent ion. This range also includes the 1s2 2s2 2p6 3l 3l' 4l'' nl''' resonances associated with 3s -> 4l'' and 3p -> 4l'' core excitations. We find that in the temperature range 2--14 eV, where Fe XIV is expected to form in a photoionized plasma, the Fe XIV recombination rate coefficient is orders of magnitude larger than previously calculated values., Comment: 4 pages, 4 figures, 1 table submitted to ApJ

We have investigated the accuracy of the 1s-vacancy fluorescence data base of Kaastra & Mewe (1993, A&AS, 97, 443) resulting from the initial atomic physics calculations and the subsequent scaling along isoelectronic sequences. In particular, we have focused on the relatively simple Be-like and F-like 1s-vacancy sequences. We find that the earlier atomic physics calculations for the oscillator strengths and autoionization rates of singly-charged B II and Ne II are in sufficient agreement with our present calculations. However, the substantial charge dependence of these quantities along each isoelectronic sequence, the incorrect configuration averaging used for B II, and the neglect of spin-orbit effects (which become important at high-Z) all cast doubt on the reliability of the Kaastra & Mewe data for application to plasma modeling., Comment: 19 pages with 6 figures, AAS TeX, accepted for publication in ApJ

The basic approach for measuring electron-ion recombination rate coefficients in merged-beams electron-ion collision experiments at heavy-ion storage rings is outlined. As an example experimental results for the low temperature recombination of C IV ions are compared with the recommended theoretical rate coefficient by Mazzotta et al. The latter deviates by factors of up to 5 from the experimental one., Comment: 5 pages, 3 figures, Workshop on Stellar Coronae in the Chandra and XMM-Newton era, June 2001, Noordwijk, The Netherlands, for a recent theoretical treatment of C IV DR see Pradhan and al., Phys. Rev. Lett. 87, 183201 (2001)

We have measured the resonance strengths and energies for dielectronic recombination (DR) of Fe XX forming Fe XIX via N=2 --> N'=2 (Delta_N=0) core excitations. We have also calculated the DR resonance strengths and energies using AUTOSTRUCTURE, HULLAC, MCDF, and R-matrix methods, four different state-of-the-art theoretical techniques. On average the theoretical resonance strengths agree to within <~10% with experiment. However, the 1 sigma standard deviation for the ratios of the theoretical-to-experimental resonance strengths is >~30% which is significantly larger than the estimated relative experimental uncertainty of <~10%. This suggests that similar errors exist in the calculated level populations and line emission spectrum of the recombined ion. We confirm that theoretical methods based on inverse-photoionization calculations (e.g., undamped R-matrix methods) will severely overestimate the strength of the DR process unless they include the effects of radiation damping. We also find that the coupling between the DR and radiative recombination (RR) channels is small. We have used our experimental and theoretical results to produce Maxwellian-averaged rate coefficients for Delta_N=0 DR of Fe XX. For kT>~1 eV, which includes the predicted formation temperatures for Fe XX in an optically thin, low-density photoionized plasma with cosmic abundances, our experimental and theoretical results are in good agreement. We have also used our R-matrix results, topped off using AUTOSTRUCTURE for RR into J>=25 levels, to calculate the rate coefficient for RR of Fe XX. Our RR results are in good agreement with previously published calculations., Comment: To be published in ApJS. 65 pages with 4 tables and lots of figures

Using published measurements of dielectronic recombination (DR) resonance strengths and energies for C V to C IV and O VIII to O VII, we have calculated the DR rate coefficient for these ions. Our derived rates are in good agreement with multiconfiguration, intermediate-coupling and multiconfiguration, fully-relativistic calculations as well as with most LS coupling calculations. Our results are not in agreement with the recommended DR rates commonly used for modeling cosmic plasmas. We have used theoretical radiative recombination (RR) rates in conjunction with our derived DR rates to produce a total recombination rate for comparison with unified RR+DR calculations in LS coupling. Our results are not in agreement with undamped, unified calculations for C V but are in reasonable agreement with damped, unified calculations for O VIII. For C V, the Burgess general formula (GF) yields a rate which is in very poor agreement with our derived rate. The Burgess & Tworkowski modification of the GF yields a rate which is also in poor agreement. The Merts et al. modification of the GF yields a rate which is in fair agreement. For O VIII the GF yields a rate which is in fair agreement with our derived rate. The Burgess & Tworkowski modification of the GF yields a rate which is in good agreement. And the Merts et al. modification yields a rate which is in very poor agreement. These results suggest that for DN=1 DR it is not possible to know a priori which formula will yield a rate closer to the true DR rate. We describe the technique used to obtain DR rate coefficients from laboratory measurements of DR resonance strengths and energies. For use in plasma modeling, we also present easy-to-use fitting formulae for the experimentally derived DR rates., Comment: 16 pages including 6 figures, AASTeX, to appear in ApJ

In photoionized gases with cosmic abundances, dielectronic recombination (DR) proceeds primarily via nlj --> nl'j' core excitations (Dn=0 DR). We have measured the resonance strengths and energies for Fe XVIII to Fe XVII and Fe XIX to Fe XVIII Dn=0 DR. Using our measurements, we have calculated the Fe XVIII and Fe XIX Dn=0 DR DR rate coefficients. Significant discrepancies exist between our inferred rates and those of published calculations. These calculations overestimate the DR rates by factors of ~2 or underestimate it by factors of ~2 to orders of magnitude, but none are in good agreement with our results. Almost all published DR rates for modeling cosmic plasmas are computed using the same theoretical techniques as the above-mentioned calculations. Hence, our measurements call into question all theoretical Dn=0 DR rates used for ionization balance calculations of cosmic plasmas. At temperatures where the Fe XVIII and Fe XIX fractional abundances are predicted to peak in photoionized gases of cosmic abundances, the theoretical rates underestimate the Fe XVIII DR rate by a factor of ~2 and overestimate the Fe XIX DR rate by a factor of ~1.6. We have carried out new multiconfiguration Dirac-Fock and multiconfiguration Breit-Pauli calculations which agree with our measured resonance strengths and rate coefficients to within typically better than <~30%. We provide a fit to our inferred rate coefficients for use in plasma modeling. Using our DR measurements, we infer a factor of ~2 error in the Fe XX through Fe XXIV Dn=0 DR rates. We investigate the effects of this estimated error for the well-known thermal instability of photoionized gas. We find that errors in these rates cannot remove the instability, but they do dramatically affect the range in parameter space over which it forms., Comment: To appear in ApJS, 44 pages with 13 figures, AASTeX with postsript figures

The Toolbox for Research and Exploration (TREX) is a NASA SSERVI (Solar System Exploration Research Virtual Institute) node. TREX (trex.psi.edu) aims to decrease risk to future missions, specifically to the Moon, the Martian moons, and near- Earth asteroids, by improving mission success and assuring the safety of astronauts, their instruments, and spacecraft. TREX studies will focus on characteristics of the fine grains that cover the surfaces of these target bodies - their spectral characteristics and the potential resources (such as H2O) they may harbor. TREX studies are organized into four Themes (Laboratory- Studies, Moon-Studies, Small-Bodies Studies, and Field-Work). In this presentation, we focus on the work targeted by the Small-Bodies Theme. The Small-Bodies' Theme delves into several topics, many which overlap or are synergistic with the other TREX Themes. The main topics include photometry, spectral modeling, laboratory simulations of space weathering processes relevant to asteroids, the assembly of an asteroid regolith database, the dichotomy between nuclear and reflectance spectroscopy, and the dynamical evolution of asteroids and the implications for the retention of volatiles.

The purpose of the Laboratory Astrophysics Division (LAD) is to advance our understanding of the Universe through the promotion of fundamental theoretical and experimental research into the underlying processes that drive the Cosmos. LAD represents all areas of astrophysics and planetary sciences. The first new AAS Division in more than 30 years, the LAD traces its history back to the recommendation from the scientific community via the White Paper from the 2006 NASA-sponsored Laboratory Astrophysics Workshop. This recommendation was endorsed by the Astronomy and Astrophysics Advisory Committee (AAAC), which advises the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and the U.S. Department of Energy (DOE) on selected issues within the fields of astronomy and astrophysics that are of mutual interest and concern to the agencies. In January 2007, at the 209th AAS meeting, the AAS Council set up a Steering Committee to formulate Bylaws for a Working Group on Laboratory Astrophysics (WGLA). The AAS Council formally established the WGLA with a five-year mandate in May 2007, at the 210th AAS meeting. From 2008 through 2012, the WGLA annually sponsored Meetings in-a-Meeting at the AAS Summer Meetings. In May 2011, at the 218th AAS meeting, the AAS Council voted to convert the WGLA, at the end of its mandate, into a Division of the AAS and requested draft Bylaws from the Steering Committee. In January 2012, at the 219th AAS Meeting, the AAS Council formally approved the Bylaws and the creation of the LAD. The inaugural gathering and the first business meeting of the LAD were held at the 220th AAS meeting in Anchorage in June 2012. You can learn more about LAD by visiting its website at http://lad.aas.org/ and by subscribing to its mailing list.