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The 22Ne(p,γ)23Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle is active in asymptotic giant branch stars as well as in novae and contributes to the nucleosythesis of neon and sodium isotopes. In order to reduce the uncertainties in the predicted nucleosynthesis yields, new experimental efforts to measure the 22Ne(p,γ)23Na cross section directly at the astrophysically relevant energies are needed. In the present work, a feasibility study for a 22Ne(p,γ)23Na experiment at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400\,kV accelerator deep underground in the Gran Sasso laboratory, Italy, is reported. The ion beam induced γ-ray background has been studied. The feasibility study led to the first observation of the Ep = 186\,keV resonance in a direct experiment. An experimental lower limit of 0.12\,×\,10−6\,eV has been obtained for the resonance strength. Informed by the feasibility study, a dedicated experimental setup for the 22Ne(p,γ)23Na experiment has been developed. The new setup has been characterized by a study of the temperature and pressure profiles. The beam heating effect that reduces the effective neon gas density due to the heating by the incident proton beam has been studied using the resonance scan technique, and the size of this effect has been determined for a neon gas target.

The strength of the Ep = 1.842 MeV resonance in the 40Ca(p,γ)41Sc reaction is determined with two different methods: First, by an absolute strength measurement using calcium hydroxide targets, and second, relative to the well-determined strength of the resonance triplet at Eα = 4.5 MeV in the 40Ca(α,γ)44Ti reaction. The present new value of ωγ = (0.192 ± 0.017) eV is 37% (equivalent to 3.5 σ) higher than the evaluated literature value. In addition, the ratio of the strengths of the 1.842 MeV 40Ca(p,γ)41Sc and 4.5 MeV 40Ca(α,γ)44Ti resonances has been determined to be 0.0229 ± 0.0018. The newly corrected strength of the 1.842-MeV resonance can be used in the future as a normalization point for experiments with calcium targets.

The radioactive nuclide 44Ti is believed to be produced in the α-rich freezeout preceding supernova explosions. The γ-rays from its decay have been observed in space-based γ-observatories for the Cassiopeia A and recently also SN 1987A supernova remnants. The rates of the nuclear reactions governing the production and destruction of 44Ti should therefore be known with high precision. Over the last years there have been various studies of the 40Ca(α,γ)44Ti reaction, which is dominating the 44Ti production in supernovae. Using the α-beam of the 3-MV Tandetron at Dresden, the strengths of 40Ca(α,γ)44Ti resonance triplet at 4.5 MeV laboratory α-energy has been studied by in-beam γ-spectroscopy and activation. In addition, preliminary results of resonance strengths between 3.5 and 3.8 MeV will be presented. The irradiated samples have been analyzed in the underground laboratory Dresden Felsenkeller. The target stoichiometry has been determined by nuclear reactions and by elastic recoil detection analysis (ERDA), whereby the strength of the Ep = 1.842 MeV resonance in the 40Ca(p,γ)41Sc reaction could be restudied.

The 40Ca(α,γ)44Ti reaction is believed to be the main production channel for the radioactive nuclide 44Ti in core-collapse supernovae. Radiation from decaying 44Ti has been observed so far for two supernova remnants, and a precise knowledge of the 44Ti production rate may help improve supernova models. The 40Ca(α,γ)44Ti astrophysical reaction rate is determined by a number of narrow resonances. Here, the resonance triplet at Eα = 4497, 4510, and 4523 keV is studied both by activation, using an underground laboratory for the counting, and by in-beam spectrometry. The target properties are determined by elastic recoil detection analysis and by nuclear reactions. The strengths of the three resonances are determined to ωγ = (0.92 ± 0.20), (6.2 ± 0.5), and (1.31 ± 0.24) eV, respectively, a factor of two more precise than before. The strengths of this resonance triplet may be used in future works as a point of reference. In addition, the present new data directly affect the astrophysical reaction rate at relatively high temperatures, above 3.5GK.

The 22Ne(p,γ)23Na reaction belongs to the catalytic neon-sodium cycle and has an important role in the explosive hydrogen burning. The neon-sodium cycle takes place at temperatures of T = 0:1 - 0:5GK and is assumed to occur in different astrophysical systems: e.g. in novae, in super novae of type Ia and during the shell-burning of red giant branch stars. The implications of 22Ne(p,γ)23Na and the neon-sodium cycle in a nova scenario have been studied by using the nuclear network code libnucnet at GSI in Darmstadt. A nova is an outburst of matter in a binary system consisting of a white dwarf and a red giant star. It is therefore a representative phenomenon for explosive hydrogen burning. For the calculation of the nucleosynthesis during the nova outburst, the code libnucnet requires the initial mass composition of the novae partners, the temperature and density proles of the nova explosion and the thermonuclear reaction rates of the participating reactions. In the following, the code determined the ow and the nal atomic abundance in the neon-sodium cycle during the entire nova process. Additionally, the in uence of the temperature prole of the novae outburst as well as the thermonuclear reaction rate of the 22Ne(p,γ)23Na reaction on the nal atomic abundance in the outburst has been studied. A characteristic measure for the reactions in astrophysical environments is the thermonuclear reaction rate. The reaction rate of 22Ne(p,γ)23Na has still strong uncertainties in the temperature range of T = 0:03-0:3 GK. These uncertainties are based on insucient upper limits of the resonance strengths as well as the possible existence of tentative states that are populated in the energy range of Elabp = 30 - 300 keV. The research presented in this thesis is dedicated to the experimental study of the 22Ne(p,γ)23Na reaction for an improved determination of the thermonuclear reaction rate. Furthermore, the implications of 22Ne(p,γ)23Na and the neon-sodium-cycle in novae scenarios are discussed. The data taking has been performed at the Laboratori Nazionali del Gran Sasso, Italy. This laboratory provides the LUNA facility (Laboratory for Underground Nuclear Astrophysics) for the measurement of small reaction cross sections. The LUNA facility includes a 400 kV ion accelerator, a windowless gas target system and a HPGe-detector. Based on the measurements of the 22Ne(p,γ)23Na reaction at LUNA, upper limits for the strengths of ve isolated resonances in the energy range of Elabp = 150 - 340 keV have been determined. For the nuclear resonance at Elabres = 186 keV, a positive resonance strength has been measured for the rst time in literature.

Nuclear resonance fluorescence experiments have been performed at the bremsstrahlung facility of the ELBE accelerator in Dresden-Rossendorf. The electromagnetic dipole strength below the neutron separation energy of several nuclei in the chain of Xenon isotopes has been investigated. The measurements in chain of gaseous isotopes allowed a comparison of the summed strength not only as a function of the neutron-to-proton ratio but also of the nuclear quadrupole deformation. Experiments and calculations using a quasiparticle random-phase approximation have been used in the chain of Xenon isotopes to estimate the importance nuclear deformation in the energy region on the pygmy strength.

Modelle einer Kernkollaps-Supernova sagen vorher, dass Titan-44 (Halbwertszeit = 58,9 a) produziert wird. Dementsprechend werden mehrere Titan-44-Gammastrahlungsquellen in unserer Galaxie erwartet. Jedoch konnte Titan-44 bisher nur in den Supernovaüberresten Cassiopeia A und SN 1987A nachgewiesen werden. 40Ca(𝛼,𝛾)44Ti ist die wichtigste Reaktion, die Titan-44 erzeugt. Ihre Reaktionsrate wird durch mehrere Resonanzen dominiert. Am 3.3 MV Tandetron des Helmholtz-Zentrums Dresden-Rossendorf werden die Verzweigungsverhältnisse mittels in-beam 𝛾-Spektrometrie untersucht und anschließend die Resonanzstärken durch eine Aktivierungsmessung im Niederniveaumesslabor Felsenkeller bestimmt.

The radioactive nuclide 44Ti is believed to be produced in the α-rich freezeout preceding supernova explosions. The γ-rays from its decay have been observed in space-based γ-observatories for the Cassiopeia A and very recently also SN 1987A supernova remnants. The rates of the nuclear reactions governing the production and destruction of 44Ti should therefore be known with high precision. Over the last years there have been various studies of the 40Ca(α,γ)44Ti reaction, which is dominating the 44Ti production in supernovae. Those studies have been performed using in-beam γ-spectroscopy, activation, accelerator mass spectrometry (AMS), and recoil mass spectrometry via inverse kinematics. However, there are still discrepancies in the resulting reaction rates. Using an α-beam of 1-2 A intensity the strengths of the strongest 40Ca(α,γ)44Ti resonances from 3.5 to 4.5 MeV laboratory α-energy have been studied by in-beam γ-counting and activation. The samples have been analyzed in the ultra-low-background underground γ-counting facility "Felsenkeller Dresden". The target stoichiometry has been determined by nuclear reactions and by elastic recoil detection analysis (ERDA). An AMS measurement of the activated samples is in preparation.

Das radioaktive Nuklid Titan-44 wird Modellrechnungen zufolge in Kernkollaps-Supernovae erzeugt. Die Gammastrahlung aus seinem Zerfall kann als Werkzeug zum Test von Supernova-Modellen genutzt werden, weil sie zumindest für einen Supernova-Überrest durch satellitengestützte Gamma-Teleskope nachweisbar ist. Zur Interpretation dieser Messungen ist eine genaue Kenntnis der Kernreaktionsraten für die Erzeugung und Zerstörung von Titan-44 erforderlich. Die 40Ca(alpha,gamma)44Ti-Reaktion dominiert die Erzeugung von Titan-44. Ihre Rate wird je nach Temperatur von mehreren Resonanzen dominiert. Die Stärken der Resonanzen bei 3.5 - 3.7 MeV alpha-Energie werden am Dresdner 3MV Tandetron sowohl mittels in-beam Gamma-Spektrometrie als auch durch eine Aktivierungsmessung im Felsenkeller-Niederniveaumesslabor bestimmt. Gefördert von der EU (FP7-SPIRIT 227012) und der DFG (BE 4100/2-1).

The 22Ne(p,g)23Na reaction takes part in the so called neon-sodium-cycle of hydrogen burning. This cycle is important at higher temperature than those experienced in the sun and plays a role in explosive hydrogen burning in an astrophysical nova. In addition, this reaction possibly depletes the supply of 22Ne in the accreting white dwarf preceeding a supernova of type Ia. The rate of this reaction depends on the strengths of several resonances in the energy range of the LUNA 0.4 MV accelerator which have never been observed in direct experiments. A related study is under preparation at LUNA. The poster will show the experimental set-up and planned measurement strategy.

The radioactive nuclide 44Ti is believed to be produced in the alpha-rich freezeout preceding supernova explosions. The γ-lines from its decay have been observed in space-based gamma-observatories for the Cassiopeia A supernova remnant. The rates of the nuclear reactions governing the production and destruction of 44Ti should therefore be known with precision. Using the α-beam of the 3.3 MV Tandetron of Helmholtz-Zentrum Dresden-Rossendorf, the strengths of the 40Ca(α,γ)44Ti resonance triplet at 4.5 MeV α-energy have been restudied by activation. The samples have been analyzed in the Felsenkeller underground γ-counting facility. Preliminary data on lower-lying resonances will be presented, as well.

SPIDERS (SPectroscopic IDentification of eROSITA Sources) is an SDSS-IV survey running in parallel to the eBOSS cosmology project. SPIDERS will obtain optical spectroscopy for large numbers of X-ray-selected AGN and galaxy cluster members detected in wide area eROSITA, XMM-Newton and ROSAT surveys. We describe the methods used to choose spectroscopic targets for two sub-programmes of SPIDERS: X-ray selected AGN candidates detected in the ROSAT All Sky and the XMM-Newton Slew surveys. We have exploited a Bayesian cross-matching algorithm, guided by priors based on mid-IR colour-magnitude information from the WISE survey, to select the most probable optical counterpart to each X-ray detection. We empirically demonstrate the high fidelity of our counterpart selection method using a reference sample of bright well-localised X-ray sources collated from XMM-Newton, Chandra and Swift-XRT serendipitous catalogues, and also by examining blank-sky locations. We describe the down-selection steps which resulted in the final set of SPIDERS-AGN targets put forward for spectroscopy within the eBOSS/TDSS/SPIDERS survey, and present catalogues of these targets. We also present catalogues of ~12000 ROSAT and ~1500 XMM-Newton Slew survey sources which have existing optical spectroscopy from SDSS-DR12, including the results of our visual inspections. On completion of the SPIDERS program, we expect to have collected homogeneous spectroscopic redshift information over a footprint of ~7500 deg$^2$ for >85 percent of the ROSAT and XMM-Newton Slew survey sources having optical counterparts in the magnitude range 17, Comment: MNRAS, accepted

This paper presents a survey of X-ray selected active galactic nuclei (AGN) with optical spectroscopic follow-up in a $\sim 18\, \rm{deg^2}$ area of the equatorial XMM-XXL north field. A sample of 8445 point-like X-ray sources detected by XMM-Newton above a limiting flux of $F_{\rm 0.5-10\, keV} > 10^{-15} \rm\,erg\, cm^{-2}\, s^{-1}$ was matched to optical (SDSS) and infrared (WISE) counterparts. We followed up 3042 sources brighter than $r=22.5$ mag with the SDSS BOSS spectrograph. The spectra yielded a reliable redshift measurement for 2578 AGN in the redshift range $z=0.02-5.0$, with $0.5-2\rm\, keV$ luminosities ranging from $10^{39}-10^{46}\rm\,erg\,s^{-1}$. This is currently the largest published spectroscopic sample of X-ray selected AGN in a contiguous area. The BOSS spectra of AGN candidates show a bimodal distribution of optical line widths allowing a separation between broad- and narrow-emission line AGN. The former dominate our sample (70 per cent) due to the relatively bright X-ray flux limit and the optical BOSS magnitude limit. We classify the narrow emission line objects (22 per cent of full sample) using standard BPT diagnostics: the majority have line ratios indicating the dominant source of ionization is the AGN. A small number (8 per cent of full sample) exhibit the typical narrow line ratios of star-forming galaxies, or only have absorption lines in their spectra. We term the latter two classes "elusive'' AGN. We also compare X-ray, optical and infrared color AGN selections in this field. X-ray observations reveal, the largest number of AGN. The overlap between the selections, which is a strong function of the imaging depth in a given band, is also remarkably small. We show using spectral stacking that a large fraction of the X-ray AGN would not be selectable via optical or IR colours due to host galaxy contamination., 26 pages, 21 figures. Accepted for publication in MNRAS. We publicly release the catalogue of X-ray selected AGN on the following webpage: http://www.mpe.mpg.de/XraySurveys/XMM-XXL/

The $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction takes part in the neon-sodium cycle of hydrogen burning. This cycle is active in asymptotic giant branch stars as well as in novae and contributes to the nucleosythesis of neon and sodium isotopes. In order to reduce the uncertainties in the predicted nucleosynthesis yields, new experimental efforts to measure the $^{22}$Ne(p,$\gamma$)$^{23}$Na cross section directly at the astrophysically relevant energies are needed. In the present work, a feasibility study for a $^{22}$Ne(p,$\gamma$)$^{23}$Na experiment at the Laboratory for Underground Nuclear Astrophysics (LUNA) 400\,kV accelerator deep underground in the Gran Sasso laboratory, Italy, is reported. The ion beam induced $\gamma$-ray background has been studied. The feasibility study led to the first observation of the $E_{\rm p}$ = 186\,keV resonance in a direct experiment. An experimental lower limit of 0.12\,$\times$\,10$^{-6}$\,eV has been obtained for the resonance strength. Informed by the feasibility study, a dedicated experimental setup for the $^{22}$Ne(p,$\gamma$)$^{23}$Na experiment has been developed. The new setup has been characterized by a study of the temperature and pressure profiles. The beam heating effect that reduces the effective neon gas density due to the heating by the incident proton beam has been studied using the resonance scan technique, and the size of this effect has been determined for a neon gas target., Comment: Minor errors corrected; final version