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The search for roAp stars: null results and new candidates from Strmgren-Crawford photometry

Research in Astronomy and Astrophysics 2018年第11期18卷 43-54页

作者： Ernst Paunzen Gerald Handler Katerina Honkova Jakub Jurysek Martin Masek Marek Drozdz Jan Janik Waldemar Ogtoza Lars Hermansson Mats Johansson Martin Jelinek Marek Skarka Miloslav Zejda Department of Theoretical Physics and Astrophysics Masaryk UniversityKotlarska 2CZ-61137Czech Republic Nicolaus Copernicus astronomical Center Bartycka 1800-716WarsawPoland variable star and exoplanet section of czech astronomical society Vsetinska 941/78CZ-75701Valasske MeziriciCzech Republic Institute of Physics The Czech Academy of SciencesNa Slovance 1999/2CZ-18221PrahaCzech Republic Mt.Suhora Observatory Pedagogical UniversityPodchorazych 230-084KrakowPoland Sandvretens Observatory Linnegatan 5A75332UppsalaSweden astronomical Institute Czech Academy of Sciences(ASU CAS)OndrejovCzech Republic

The rapidly oscillating Ap(roAp) stars exhibit pulsational photometric and/or radial velocity variations on time scales of several minutes, which are essential to test current pulsation models as well as our assumptions of atmospheric structure characteristics. In addition, their chemical peculiarity makes them very interesting for probing stellar formation and evolution in the presence of a global magnetic field. To date, a limited number of only 61 roAp stars is known to show photometric variability. On the other hand, a literature survey yields 619 unique stars that have unsuccessfully been searched for variability of this kind. Str o¨mgren-Crawford uvbyβ photometry of stars from both subgroups was used to investigate whether there is a selection bias for the investigated stars. We also present new photometric measurements(202 hours on 59 different nights) of 55 roAp candidates. We did not detect any new roAp star. Although our detection limits are comparable to other surveys, we also did not find pulsations in the known roAp star HD 12098, which may be a consequence of temporal amplitude changes. On the other hand, we do find some evidence for photometric variability of beta CrB at its spectroscopically derived pulsation period. From the uvbyβ photometry we conclude that the blue border of the roAp instability strip appears observationally well defined, whereas the red border is rather poorly known and *** these boundaries, a total of 4646 candidates were identified which appear worth investigating for short-term pulsational variability.

关键词： stars: chemically peculiar stars: early-type stars: variables: general techniques: photometric

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Thermonuclear ^19F(p,α0)^16O reaction rate

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Chinese Physics C 2018年第1期42卷 135-144页

作者：何建军 Ivano Lombardo Daniele Dell’Aquila 徐毅张立勇柳卫平 Key Laboratory of Optical Astronomy National Astronomical Observatories Chinese Academy of Sciences Beijing 100012 China INFN - Sezione di Catania via S. Sofia 1-95123 Catania Italy Dip. di Fisica Univ. di Napoli Federico II via Cintia 1-80126 Napoli Italy INFN - Sezione di Napoli via Cintia 1-80126 Napoli Italy Extreme Light Infrastructure - Nuclear Physics 30 Reactorului Street P.O. Box MG-6 077125 Magurele jud. Ilfov Romania Nuclear Physics Institute Czech Academy of Sciences Rez. 25068 Czech Republic China Institute of Atomic Energy P. O. Box 275(10) Beijing 102413 China

The thermonuclear^19F（p,α0）16O reaction rate in the temperature region 0.007–10 GK has been derived by re-evaluating the available experimental data, together with the low-energy theoretical R-matrix *** new rate deviates by up to about 30% compared to the previous results, although all rates are consistent within the uncertainties. At very low temperature（e.g. 0.01 GK） our reaction rate is about 20% lower than the most recently published rate, because of a difference in the low energy extrapolated S-factor and a more accurate estimate of the reduced mass used in the calculation of the reaction rate. At temperatures above ^1 GK, our rate is lower, for instance, by about 20% around 1.75 GK, because we have re-evaluated the previous data（Isoya et al., Nucl. Phys.7, 116（1958）） in a meticulous way. The present interpretation is supported by the direct experimental data. The uncertainties of the present evaluated rate are estimated to be about 20% in the temperature region below 0.2 GK,and are mainly caused by the lack of low-energy experimental data and the large uncertainties in the existing *** giant branch（AGB） stars evolve at temperatures below 0.2 GK, where the^19F（p,α）16O reaction may play a very important role. However, the current accuracy of the reaction rate is insufficient to help to describe, in a careful way, the fluorine over-abundances observed in AGB stars. Precise cross section（or S factor） data in the low energy region are therefore needed for astrophysical nucleosynthesis studies.

关键词： asymptotic giant branch(AGB) star nucleosynthesis astrophysical S factor cross section reaction rate

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