VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'The R-Process Alliance: fourth data release from the search for r-process-enhanced stars in the Galactic halo.' (bibcode: 2020ApJS..249...30H) Copyright: Refer to CDS usage

VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'The R-Process Alliance: spectroscopic follow-up of low-metallicity star candidates from the Best & Brightest Survey.' (bibcode: 2019ApJ...870..122P) Copyright: Refer to CDS usage

VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'The R-process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5-455510' (bibcode: 2020ApJ...897...78P) Copyright: Refer to CDS usage

We present new observational benchmarks of rapid neutron-capture process (r-process) nucleosynthesis for elements at and between the first (A similar to 80) and second (A similar to 130) peaks. Our analysis is based on archival ultraviolet and optical spectroscopy of eight metal-poor stars with Se (Z = 34) or Te (Z = 52) detections, whose r-process enhancement varies by more than a factor of 30 (-0.22 <= [Eu/Fe] <= +1.32). We calculate ratios among the abundances of Se, Sr through Mo (38 <= Z <= 42), and Te. These benchmarks may offer a new empirical alternative to the predicted solar system r-process residual pattern. The Te abundances in these stars correlate more closely with the lighter r-process elements than the heavier ones, contradicting and superseding previous findings. The small star-to-star dispersion among the abundances of Se, Sr, Y, Zr, Nb, Mo, and Te (<= 0.13 dex, or 26%) matches that observed among the abundances of the lanthanides and third r-process-peak elements. The concept of r-process universality that is recognized among the lanthanide and third-peak elements in r-process-enhanced stars may also apply to Se, Sr, Y, Zr, Nb, Mo, and Te, provided the overall abundances of the lighter r-process elements are scaled independently of the heavier ones. The abundance behavior of the elements Ru through Sn (44 <= Z <= 50) requires further study. Our results suggest that at least one relatively common source in the early Universe produced a consistent abundance pattern among some elements spanning the first and second r-process peaks.

We present a nearly complete rapid neutron-capture process (r-process) chemical inventory of the metal-poor ([Fe/H] = -1.46 +/- 0.10) r-process-enhanced ([Eu/Fe] = +1.32 +/- 0.08) halo star HD 222925. This abundance set is the most complete for any object beyond the solar system, with a total of 63 metals detected and seven with upper limits. It comprises 42 elements from 31 <= Z <= 90, including elements rarely detected in r-process-enhanced stars, such as Ga, Ge, As, Se, Cd, In, Sn, Sb, Te, W, Re, Os, Ir, Pt, and Au. We derive these abundances from an analysis of 404 absorption lines in ultraviolet spectra collected using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope and previously analyzed optical spectra. A series of appendices discusses the atomic data and quality of fits for these lines. The r-process elements from Ba to Pb, including all elements at the third r-process peak, exhibit remarkable agreement with the solar r-process residuals, with a standard deviation of the differences of only 0.08 dex (17%). In contrast, deviations among the lighter elements from Ga to Te span nearly 1.4 dex, and they show distinct trends from Ga to Se, Nb through Cd, and In through Te. The r-process contribution to Ga, Ge, and As is small, and Se is the lightest element whose production is dominated by the r-process. The lanthanide fraction, log X (La) = -1.39 +/- 0.09, is typical for r-process-enhanced stars and higher than that of the kilonova from the GW170817 neutron-star merger event. We advocate adopting this pattern as an alternative to the solar r-process-element residuals when confronting future theoretical models of heavy-element nucleosynthesis with observations.

VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'The r-process Alliance: chemodynamically tagged groups of halo r-process-enhanced stars reveal a shared chemical-evolution history.' (bibcode: 2021ApJ...908...79G) Copyright: Refer to CDS usage

VizieR online Data Catalogue associated with article published in journal Astronomical Journal (AAS) with title 'The R-Process Alliance: a nearly complete r-process abundance template derived from ultraviolet spectroscopy of the r-process-enhanced metal-poor star HD222925.' (bibcode: 2022ApJS..260...27R) Copyright: Refer to CDS usage

In situ angle-dispersive x-ray diffraction (ADXD) measurement by synchrotron beam under high pressure was performed and pressure-induced amorphization (PIA) and YO6 octahedral changes were investigated for both Y2O3/Eu3+ nanotubes and the bulk sample. The cubic structure of Y2O3/Eu3+ nanotubes transforms into an amorphous phase at a pressure of 21.9 GPa. Differential nano-effects in the radial and axial directions of nanotubes causes distinct compression behaviors for Y-O bonds. The variation in Y-O bonds of nanotubes exhibits disorder with pressure unlike that of bulk sample, which instead exhibits linear decreases. The YO6 octahedra of Y2O3/Eu3+ nanotubes are deformed in disorder under high pressure which abrogates the ordered long-distance octahedral arrangement, thus resulting in the amorphous transition.

We present the discovery of nine quasars at z similar to 6 identified in the Sloan Digital Sky Survey (SDSS) imaging data. This completes our survey of z similar to 6 quasars in the SDSS footprint. Our final sample consists of 52 quasars at 5.7 < z << 6.4, including 29 quasars with z(AB) <= 20 mag selected from 11,240 deg(2) of the SDSS single-epoch imaging survey (the main survey), 10 quasars with 20 <= z(AB) <= 20.5 selected from 4223 deg2 of the SDSS overlap regions (regions with two or more imaging scans), and 13 quasars down to z(AB) approximate to 22 mag from the 277 deg2 in Stripe 82. They span a wide luminosity range of -29.0 <= M-1450 <= -24.5. This well-defined sample is used to derive the quasar luminosity function (QLF) at z similar to 6. After combining our SDSS sample with two faint (M-1450 >= -23 mag) quasars from the literature, we obtain the parameters for a double power-law fit to the QLF. The bright-end slope beta of the QLF is well constrained to be beta = -2.8 +/- 0.2. Due to the small number of low-luminosity quasars, the faint-end slope a and the characteristic magnitude M*(1450) are less well constrained, with alpha = -1.90(-0.44)(+0.58) and M* = -25.2(-3.8)(+1.2) mag. The spatial density of luminous quasars, parametrized as rho(M-1450 < -26, z) = rho(z = 6)10(k(z-6)), drops rapidly from z similar to 5 to 6, with k = -0.72 +/- 0.11. Based on our fitted QLF and assuming an intergalactic medium (IGM) clumping factor of C = 3, we find that the observed quasar population cannot provide enough photons to ionize the z similar to 6 IGM at similar to 90% confidence. Quasars may still provide a significant fraction of the required photons, although much larger samples of faint quasars are needed for more stringent constraints on the quasar contribution to reionization.