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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Effect of Mg doping on carrier recombination in GaN

Time-resolved photoluminescence measurements have been performed on Mg-doped GaN for Mg concentrations in the low- to mid-10 19 cm -3 . As-grown and annealed (600–675 °C) samples were studied. In the as-grown samples, the nonradiative carrier lifetime was found to be about 200 ps and nearly independent of the Mg concentration. Upon annealing, the carrier lifetimes shorten to ~150 ps but, again, show little dependence on the annealing temperature. The analysis of possible Shockley–Read–Hall recombination centers and their behavior during doping and annealing suggests that the main nonradiative recombination center is the Mg–nitrogen vacancy complex. The weak dependence of the PL decay times on temperature indicates that carrier capture into this center has a very low potential barrier, and the nonradiative recombination dominates even at low temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Comparison of Mg-based liquid metal ion sources for scalable focused-ion-implantation doping of GaN

We compare the suitability of various magnesium-based liquid metal alloy ion sources (LMAISs) for scalable focused-ion-beam (FIB) implantation doping of GaN. We consider GaMg, MgSO 4 $\bullet$7H 2 O, MgZn, AlMg, and AuMgSi alloys. Although issues of oxidation (GaMg), decomposition (MgSO 4 $\bullet$7H 2 O), and excessive vapor pressure (MgZn and AlMg) were encountered, the AuMgSi alloy LMAIS operating in a Wien-filtered FIB column emits all Mg isotopes in singly and doubly charged ionization states. We discuss the operating conditions to achieve <20 nm spot size Mg FIB implantation and present Mg depth profile data from time-of-flight secondary ion mass spectrometry. We also provide insight into implantation damage and recovery based on cathodoluminescence spectroscopy before and after rapid thermal processing. Prospects for incorporating the Mg LMAIS into high-power electronic device fabrication are also discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ultrahigh-pressure disordered eight-coordinated phase of Mg 2 GeO 4 : Analogue for super-Earth mantles

Mg 2 GeO 4 is important as an analog for the ultrahigh-pressure behavior of Mg 2 SiO 4 , a major component of planetary interiors. In this study, we have investigated magnesium germanate to 275 GPa and over 2,000 K using a laser-heated diamond anvil cell combined with in situ synchrotron X-ray diffraction and density functional theory (DFT) computations. The experimental results are consistent with the formation of a phase with disordered Mg and Ge, in which germanium adopts eightfold coordination with oxygen: the cubic, Th 3 P 4 -type structure. DFT computations suggest partial Mg-Ge order, resulting in a tetragonal $I\bar{4}2d$ structure indistinguishable from $I\bar{4}3d$ Th 3 P 4 in our experiments. If applicable to silicates, the formation of this highly coordinated and intrinsically disordered phase may have important implications for the interior mineralogy of large, rocky extrasolar planets.

58 GEOSCIENCES↗
DOE OSTI2022

Nature of the galaxies on top of quasars producing Mg ii absorption

ABSTRACT Quasar–galaxy pairs at small separations are important probes of gas flows in the disc–halo interface in galaxies. We study host galaxies of 198 Mg ii absorbers at 0.39 ≤ zabs ≤ 1.05 that show detectable nebular emission lines in the Sloan Digital Sky Survey (SDSS) spectra. We report measurements of impact parameter (5.9 ≤ D [kpc] ≤ 16.9) and absolute B-band magnitude (−18.7 ≤ MB ≤ −22.3 mag) of host galaxies of 74 of these absorbers using multiband images from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Survey, more than doubling the number of known host galaxies with D ≤ 17 kpc. This has allowed us to quantify the relationship between Mg ii rest equivalent width (W2796) and D, with best-fitting parameters of W2796 (D = 0) = 3.44 ± 0.20 Å and an exponential scale length of 21.6$^{+2.41}_{-1.97}\, \mathrm{ kpc}$. We find a significant anticorrelation between MB and D, and MB and W2796, consistent with the brighter galaxies producing stronger Mg ii absorption. We use stacked images to detect average emissions from galaxies in the full sample. Using these images and stacked spectra, we derive the mean stellar mass (9.4 ≤ log(M*/M⊙) ≤ 9.8), star formation rate (2.3 ≤ SFR [M⊙ yr−1] ≤ 4.5), age (2.5–4 Gyr), metallicity (12 + log(O/H) ∼ 8.3), and ionization parameter (log q [cm s−1] ∼ 7.7) for these galaxies. The average M* found is less than that of Mg ii absorbers studied in the literature. The average SFR and metallicity inferred are consistent with that expected in the main sequence and the known stellar mass–metallicity relation, respectively. High spatial resolution follow-up spectroscopic and imaging observations of this sample are imperative for probing gas flows close to the star-forming regions of high-z galaxies.

Astronomy & Astrophysics↗
DOE OSTI2023

OzDES Reverberation Mapping Programme: Mg ii lags and R − L relation

ABSTRACT The correlation between the broad line region radius and continuum luminosity (R–L relation) of active galactic nuclei (AGNs) is critical for single-epoch mass estimates of supermassive black holes (SMBHs). At z ∼ 1–2, where AGN activity peaks, the R–L relation is constrained by the reverberation mapping (RM) lags of the Mg ii line. We present 25 Mg ii lags from the Australian Dark Energy Survey RM project based on 6 yr of monitoring. We define quantitative criteria to select good lag measurements and verify their reliability with simulations based on both the damped random walk stochastic model and the rescaled, resampled versions of the observed light curves of local, well-measured AGN. Our sample significantly increases the number of Mg ii lags and extends the R–L relation to higher redshifts and luminosities. The relative iron line strength $\mathcal {R}_{\rm Fe}$ has little impact on the R–L relation. The best-fitting Mg iiR–L relation has a slope α = 0.39 ± 0.08 with an intrinsic scatter $\sigma _{\rm rl} = 0.15^{+0.03}_{-0.02}$ . The slope is consistent with previous measurements and shallower than the H β R–L relation. The intrinsic scatter of the new R–L relation is substantially smaller than previous studies and comparable to the intrinsic scatter of the H β R–L relation. Our new R–L relation will enable more precise single-epoch mass estimates and SMBH demographic studies at cosmic noon.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Host galaxies of ultra-strong Mg ii absorbers at z ∼ 0.7

ABSTRACT We report spectroscopic identification of the host galaxies of 18 ultra-strong Mg ii systems (USMg ii) at 0.6 ≤ z ≤ 0.8. We created the largest sample by merging these with 20 host galaxies from our previous survey within 0.4 ≤ z ≤ 0.6. Using this sample, we confirm that the measured impact parameters ($\rm 6.3\leqslant D[kpc] \leqslant 120$ with a median of 19 kpc) are much larger than expected, and the USMg ii host galaxies do not follow the canonical $\rm {\it W}_{2796}-{\it D}$ anticorrelation. We show that the presence and significance of this anticorrelation may depend on the sample selection. The $\rm {\it W}_{2796}-{\it D}$ anticorrelation seen for the general Mg ii absorbers show a mild evolution at low $\rm W_{2796}$ end over the redshift range 0.4 ≤ z ≤ 1.5 with an increase of the impact parameters. Compared to the host galaxies of normal Mg ii absorbers, USMg ii host galaxies are brighter and more massive for a given impact parameter. While the USMg ii systems preferentially pick star-forming galaxies, they exhibit slightly lower ongoing star-forming rates compared to main sequence galaxies with the same stellar mass, suggesting a transition from star-forming to quiescent states. For a limiting magnitude of mr < 23.6, at least 29 per cent of the USMg ii host galaxies are isolated, and the width of the Mg ii absorption in these cases may originate from gas flows (infall/outflow) in isolated haloes of massive star forming but not starbursting galaxies. We associate more than one galaxy with the absorber in $\ge 21~{{\ \rm per\ cent}}$ cases, where interactions may cause wide velocity spread.

Astronomy & Astrophysics↗
DOE OSTI2021

Spectroscopy of 33 Mg with knockout reactions

In this work, the structure of 33 Mg was investigated by means of two knockout reactions, one-neutron removal from 34 Mg and one-proton removal from 34 Al. Using comparative analysis of the population of observed excited states in the residual 33 Mg, the nature of these states can be deciphered. In addition, the long-standing controversy about the parity of the 33 Mg ground state is resolved using momentum distribution analysis, showing a clear signature for negative parity. Partial cross section measurements are compared with the results of eikonal reaction theory combined with large-scale shell model calculations of this complex nucleus located in the island of inversion, where configuration mixing plays a major role.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

New energy for the 133-keV resonance in the 23 Na(p,γ) 24 Mg reaction and its impact on nucleosynthesis in globular clusters

Globular cluster stars exhibit star-to-star anticorrelations between oxygen and sodium in their atmospheres. An improved description of the sodium-destroying 23 Na +p reaction rates is essential to understanding these observations. We present an energy analysis of 24 Mg states based on a new measurement of the 23 Na( 3 He, d) 24 Mg reaction. A key resonance in 23 Na(p, γ) 24 Mg is found to be at $E$ $^{c.m.}_{r}$ = 133(3) keV, 5 keV lower than previously adopted. This finding has a dramatic effect on the 23 Na(p, γ) 24 Mg reaction rate, increasing it by a factor of 2 for the recommended rate. Furthermore, the nucleosynthesis impact of this change is investigated.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

𝐵⁡(𝐸⁢2) measurements in the yrast band of 28 Mg: Implications for the 𝑁 = 20 island of inversion

High-precision lifetime measurements in 28 Mg were performed to study neutron shell evolution in Mg isotopes and the onset of the N = 20 island of inversion. Here, using both the recoil distance and Doppler shift attenuation methods, five lifetimes were measured in addition to six upper limits. The observation of two long-lived, negative-parity states demonstrate the importance of studying Mg isotopes for the contribution of intruder configurations to sd-shell nuclei. Lifetimes of the $2^+_1$ and $4^+_1$ states of 1.81(5) ps and 172⁢($^{+11}_{–10}$) stat.⁢ (4) stop. ⁢(8) feed.⁢ (4) targ. fs, respectively, demonstrate a loss of collectivity with increasing spin in the yrast band, permitting for distinguishing between current theoretical models. These measurements also highlight the progression of yrast structure across the Mg isotopic chain from rotational at N = 12 to large shape mixing at N = 16 and back to collective behavior at N = 20 but with dominating intruder configurations.

20 ≤ A ≤ 38↗
DOE OSTI2020

Intermediate Yb valence in the Zintl phases Yb 14 MSb 11 (M=Zn,Mn,Mg): XANES, magnetism, and heat capacity

Yb 14 Mn Sb 11 is a magnetic Zintl compound as well as being one of the best high temperature p -type thermoelectric materials. According to the Zintl formalism, which defines intermetallic phases where cations and anions are valence satisfied, this structure type is nominally made up of 14 Yb 2 + , 1 MnSb 4 9 - , 1 Sb 3 7 - , and 4 Sb 3 - atoms. When Mn is replaced by Mg or Zn, the Zintl defined motifs become 13 Yb 2 + , 1 Yb 3 + , 1 (Mg, Zn) Sb 4 10 - , 1 Sb 3 7 - , and 4 Sb 3 - . The predicted existence of Yb 3 + based on simple electron counting rules of the Zintl formalism calls the Yb valence of these compounds into question. X-ray absorption near-edge structure, magnetic susceptibility, and specific heat measurements on single crystals of the three analogs show signatures of intermediate valence Yb behavior and in particular, reveal the heavy fermion nature of Yb 14 MgSb 11 . In these isostructural compounds, Yb can exhibit a variety of electronic configurations from intermediate ( M = Zn ), mostly 2+ ( M = Mn ), to 3+ ( M = Mg ). In all cases, there is a small amount of intermediate valency at the lowest temperatures. The amount of intermediate valency is constant for M = Mn , Mg and temperature dependent for M = Zn . The evolution of the Yb valence correlated to the transport properties of these phases is highlighted. The presence of Yb in this structure type allows for fine tuning of the carrier concentration and thereby the possibility of optimized thermoelectric properties along with unique magnetic phenomena.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Photo-response of the $N=Z$ nucleus $^{24}$Mg

The electric E1 and magnetic M1 dipole responses of the N = Z nucleus 24 Mg were investigated in an inelastic photon scattering experiment. The 13.0 MeV electrons, which were used to produce the unpolarised bremsstrahlung in the entrance channel of the 24 Mg(γ,γ') reaction, were delivered by the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. The collimated bremsstrahlung photons excited one J π = 1 – , four J π = 1 + , and six J π = 2 + states in 24 Mg. De-excitation γ rays were detected using the four high-purity germanium detectors of the γELBE setup, which is dedicated to nuclear resonance fluorescence experiments. In the energy region up to 13.0 MeV a total B(M1)↑ = 2.7(3) $μ$$^{2}_{N}$ is observed, but this N = Z nucleus exhibits only marginal E1 strength of less than ΣB(E1)↑≤ 0.61 × 10 –3 e 2 fm 2 . The B(Π1, $1$$^{π}_{i}$ → $2$$^{+}_{1}$)/B(Π1,$1$$^{π}_{i}$ → $0$$^{+}_{gs}$) branching ratios in combination with the expected results from the Alaga rules demonstrate that K is a good approximative quantum number for 24 Mg. The use of the known ρ 2 (E0, $0$$^{+}_{2}$ → $0$$^{+}_{gs}$) strength and the measured B(M1,1 + → $0$$^{+}_{2}$)/B(M1,1 + → $0$$^{+}_{gs}$) branching ratio of the 10.712 MeV 1 + level allows, in a two-state mixing model, an extraction of the difference Δ$β$$^{2}_{2}$ between the prolate ground-state structure and shape-coexisting superdeformed structure built upon the 6432-keV $0$$^{+}_{2}$ level.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Nano Scale Poly(vinylidene chloride-co-acrylonitrile) Protection for Reversible and Stable Mg Anode Interface

This study investigates the efficacy of a polymer coating, PVdC-co-AN, in enhancing the stability and reversibility of the electrochemical Mg anode interface. Coated electrodes, immersed in a 0.25 M Mg(TFSI) 2 −0.50 M MgCl 2 /dimethoxyethane (DME) electrolyte, exhibit notable improvements. Cyclic voltammetry demonstrates consistent behavior with the coated electrode, while the uncoated electrode changes dramatically. During extended open circuit potential conditions, the coated electrode maintains much higher coulombic efficiency (93%) compared to the uncoated electrode (62%). Galvanostatic cycling test over 200 cycles further show the benefits of the PVdC-co-AN coating, decreasing the overpotential of Mg plating and improving long-term stability. The coated electrodes also demonstrate improved rate capability at higher current densities. Surface analysis reveals differences in the formation of byproducts between the coated and uncoated electrodes, indicating a more stable and uniform interface in the former. Nuclear magnetic resonance (NMR) spectroscopy suggests that the polymer influences ion mobility through tuning the solvation environments which results in better kinetics and fewer byproducts. In summary, the study affirms that the PVdC-co-AN coating significantly improves the stability and performance of Mg electrochemistry, offering a promising advancement for practical battery applications.

25 ENERGY STORAGE↗
DOE OSTI2020

Phase Transitions in (Mg,Fe) 2 SiO 4 Olivine under Shock Compression

The response of forsterite, Mg 2 SiO 4 , under dynamic compression is of fundamental importance for understanding its phase transformations and high-pressure behavior. Here, we have carried out an in situ X-ray diffraction study of laser-shocked polycrystalline and single-crystal forsterite from 19 to 122 GPa using the Matter in Extreme Conditions end-station of the Linac Coherent Light Source. Under laser-based shock loading, forsterite does not transform to the high-pressure equilibrium assemblage of MgSiO 3 bridgmanite and MgO periclase, as has been suggested previously. Instead, we observe forsterite and forsterite III, a metastable polymorph of Mg 2 SiO 4 , coexisting in a mixed-phase region from 33 to 75 GPa for both polycrystalline and single-crystal samples. Densities inferred from X-ray diffraction are consistent with earlier gas-gun shock data. At higher stress, the response is sample-dependent. Polycrystalline samples undergo amorphization above 79 GPa. For [010]- and [001]-oriented crystals, a mixture of crystalline and amorphous material is observed to 108 GPa, whereas the [100]-oriented forsterite adopts an unknown phase at 122 GPa. The first two sharp diffraction peaks of amorphous Mg 2 SiO 4 show a similar trend with compression as those observed for MgSiO 3 in both recent static- and laser-driven shock experiments. This study provides new insight into the transformation of forsterite under nanosecond-duration shock loading. This work emphasizes the importance of formation of metastable phases along the Hugoniot and adds to evidence that the 300-K single-crystal diamond anvil cell experiments have relevance for understanding structures formed under shock compression. In particular, the metastable phase forsterite III has now been shown to form under dynamic compression from 10s to 100s of nanoseconds as well as under 300-K static compression. Upon compression to higher pressures, Mg 2 SiO 4 transforms to an amorphous phase. These results have broad relevance for understanding the behavior of silicates under dynamic compression.

36 MATERIALS SCIENCE↗
DOE OSTI2021

USAMP Low-Cost Mg Sheet Component Development and Demonstration Project

The overarching objective of this USAMP project was to develop and demonstrate door panels made from magnesium (Mg) sheet with a cost penalty over conventional steel stampings of no more than $\$5.50$/kg saved. The technical approach integrated experiments with advanced computational tools based on Integrated Computational Materials Engineering (ICME) methods to develop new alloy chemistries and their thermomechanical processing that promise improved formability and lower forming temperatures. A penultimate task before finally forming the stampings was to incorporate actual microstructure into models that would enable formability simulations. This approach would, for the first time, account for individual magnesium grains moving in an anisotropic fashion unlike that for aluminum or steel that have isotropic properties upon which the current simulation tools are based. In separate activities, new coatings and lubricants to facilitate forming and improved corrosion protection and joining strategies, were developed to ensure that the door could be produced with stated product requirements. A technical cost model, which included parts production, assembly, and paint for a door specifically designed for Mg sheet, showed the cost penalty to be between $\$4.26$ to $\$6.60$/kg saved, which enveloped the project’s cost targets. The cost of the coated Mg sheet was identified as the key driver for the cost penalty. The mass of the Mg-intensive door was 7.9 kg, which was 54% less than the baseline steel door.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Verification Testing of OLI Systems Mixed Solvent Electrolyte Model for the Na-K-Mg-Ca-H-Cl-SO 4 -OH-HCO 3 -CO 3 -CO 2 -H 2 ) System to High Ionic Strength at 25°C

This technical report summarizes model verification results and summary statistics for 41 evaporite mineral solubility cases evaluated by Savannah River National Laboratory using OLI Systems’ aqueous electrolyte thermodynamic modeling software. The 41 verification cases containing a total of 60 solubility curves comprise mineral solubility data from low to high ionic strength at 25°C for the eight-component system Na-K-Mg-Ca-H-Cl-SO 4 -OH-HCO 3 -CO 3 -CO 2 -H 2 O as reported by Harvie et al. (1984). Thermodynamic calculations were executed using OLI Systems’ Stream Analyzer computation module within the OLI Studio software platform (Ver. 11.0, Rev. 11.0.1.9). The Mixed Solvent Electrolyte (MSE) thermodynamic framework was chosen for this investigation because of its superiority in modeling high ionic-strength inorganic salt solutions and actinide redox chemistry and solubility, both of which are relevant to the geological repository conditions at the Waste Isolation Pilot Plant in Carlsbad, New Mexico. Mineral solubility data in various inorganic salt solutions were digitized and extracted from figures generated by Harvie et al. (1984). For each of the 60 solubility curves, a case-specific chemistry model and input file were generated in OLI Studio using OLI Stream Analyzer and the MSE (H 3 O + ion) public databank provided by OLI Systems. Model simulation results were exported to Microsoft Excel to calculate summary statistics and to generate graphs comparing the OLI model predictions to the solubility data. Summary statistics include residuals (model – data) and concordance (accuracy × precision, where precision is indicated by the Pearson correlation coefficient and accuracy accounts for bias and scale differential). Private databanks were not developed, and activity coefficient model regressions were not performed to improve OLI model fits to the data. Of the 41 model verification plots, 83% have a mean of the percent residuals less than or equal to 25%. Similarly, 75% display a concordance greater than or equal to 0.75. Only seven of the 41 verification plots fail to show good agreement between the model and data. Of these seven, three are relevant to the WIPP repository because they involve the Mg-OH-Cl-SO 4 -CO 3 aqueous system. The remaining four address salt solubilities at the pH extremes (strong acid and strong base). It should be noted that in two of the three Mg-OH-Cl-SO 4 -CO 3 system cases, the regressed Harvie et al. (1984) solubility curve also deviated from the data. Lack of agreement between the OLI model-predicted solubility curves and the data is attributable to one or more of the following: specific solid species are not included in the OLI MSE databank; there is significant variation among the different solubility datasets chosen by Harvie et al. (1984); the OLI MSE model’s thermodynamic parameters were determined using different solubility datasets; and the activity coefficient parameters for certain relevant ion-ion and ion-molecule pairs have not been optimized via data regression. Two recommendations for future work are to (1) evaluate solubility data for the Mg-OH-Cl-SO 4 -CO 3 system at high ionic strength and, if necessary, develop a private OLI MSE database that includes missing species and, where necessary, regressed standard state properties and interaction parameters; (2) perform similar verification testing of the OLI model for actinide solubility data.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Violation of the T –1 Relationship in the Lattice Thermal Conductivity of Mg 3 Sb 2 with Locally Asymmetric Vibrations

Most crystalline materials follow the guidelines of T –1 temperature-dependent lattice thermal conductivity (κ L ) at elevated temperatures. Here, we observe a weak temperature dependence of κ L in Mg 3 Sb 2 , T –0.48 from theory and T –0.57 from measurements, based on a comprehensive study combining ab initio molecular dynamics calculations and experimental measurements on single crystal Mg 3 Sb 2 . These results can be understood in terms of the so-called “phonon renormalization” effects due to the strong temperature dependence of the interatomic force constants (IFCs). The increasing temperature leads to the frequency upshifting for those low-frequency phonons dominating heat transport, and more importantly, the phonon-phonon interactions are weakened. In-depth analysis reveals that the phenomenon is closely related to the temperature-induced asymmetric movements of Mg atoms within MgSb 4 tetrahedron. With increasing temperature, these Mg atoms tend to locate at the areas with relatively low force in the force profile, leading to reduced effective 3 rd -order IFCs. The locally asymmetrical atomic movements at elevated temperatures can be further treated as an indicator of temperature-induced variations of IFCs and thus relatively strong phonon renormalization. The present work sheds light on the fundamental origins of anomalous temperature dependence of κ L in thermoelectrics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Detecting and Characterizing Mg ii Absorption in DESI Survey Validation Quasar Spectra

Abstract We present findings of the detection of Magnesium II (Mg ii , λ = 2796, 2803 Å) absorbers from the early data release of the Dark Energy Spectroscopic Instrument (DESI). DESI is projected to obtain spectroscopy of approximately 3 million quasars (QSOs), of which over 99% are anticipated to be at redshifts greater than z > 0.3, such that DESI would be able to observe an associated or intervening Mg ii absorber illuminated by the background QSO. We have developed an autonomous supplementary spectral pipeline that detects these systems through an initial line-fitting process and then confirms the line properties using a Markov Chain Monte Carlo sampler. Based upon a visual inspection of the resulting systems, we estimate that this sample has a purity greater than 99%. We have also investigated the completeness of our sample in regard to both the signal-to-noise properties of the input spectra and the rest-frame equivalent width ( W 0 ) of the absorber systems. From a parent catalog containing 83,207 quasars, we detect a total of 23,921 Mg ii absorption systems following a series of quality cuts. Extrapolating from this occurrence rate of 28.8% implies a catalog at the completion of the five-year DESI survey that will contain over eight hundred thousand Mg ii absorbers. The cataloging of these systems will enable significant further research because they carry information regarding circumgalactic medium environments, the distribution of intervening galaxies, and the growth of metallicity across the redshift range 0.3 ≤ z < 2.5.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

Observations of the stellar Mg II resonance doublet at 2795 and 2802 A.

Spectrophotometry of the Mg II resonance doublet at 2795.5 and 2802.7 A has been performed for five stars with a balloon-borne telescope and spectrometer. Spectral resolution attained was between 0.25 and 0.5 A. A description of the payload and flight operations is given. In beta Lyr the Mg II doublet displayed P Cygni characteristics, while in gamma Lyr the doublet was observed only in absorption. The star beta Cas shows broad overlapping Mg II absorption lines with possible weak emission at the line bottom. In alpha CMi, both components of the doublet are seen in emission at the bottom of the broad absorption feature. The Mg II doublet in alpha Ori is entirely in emission, with each component showing distinct self-reversal.

Kondo, Y.↗