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The conditional mean spectra by disaggregating the eta spectral shape indicator
摘要： Conditional spectra are a recent development in this field, which utilizes the advantages of spectral shape indicators, for example, epsilon and eta. The application of an eta indicator in conditional spectra calculations depends mainly on calculating the peak ground velocity epsilon, data about which are not readily available in the current literature. This issue has been solved by linear regression between the conventional epsilon and the peak ground velocity epsilon. However, not enough attention has been paid in the literature to the disaggregation of the eta indicator. For this reason, the disaggregation of seismic hazard based on the use of an eta indicator has been investigated in this paper, based on a simplified linear seismic source. The obtained results were compared with the available approach in the literature, which shows that this refinement has a meaningful effect on the conditional spectra specifically in the short period range. Furthermore, eta‐based conditional spectra are used at different hazard levels to select ground‐motion records. A three‐storeyed building is then analysed, and the corresponding annual probability of failure is calculated based on the full dataset as well as on the records, which were selected based on conditional spectra.
关键词： genetic algorithm,eta,seismic hazard analysis,ground‐motion prediction equation (GMPE),epsilon
更新于2025-09-23 15:23:52
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Eta Carinae’s 2014.6 spectroscopic event: Clues to the long-term recovery from its Great Eruption
摘要： Aims. Every 5.5 years, η Car’s light curve and spectrum change remarkably across all observed wavelength bands. These so-called spectroscopic events are most likely caused by the close approach of a companion. We compare the recent spectroscopic event in mid-2014 to the events in 2003 and 2009 and investigate long-term trends. Methods. Eta Car was observed with HST STIS, VLT UVES, and CTIO 1.5 m CHIRON for a period of more than two years in 2012?2015. Archival observations with these instruments cover three orbital cycles and the events of 2003.5, 2009.1, and 2014.6. The STIS spectra provide high spatial resolution and include epochs during the 2014 event when observations from most ground-based observatories were not feasible. The strategy for UVES observations allows for a multidimensional analysis, because each location in the re?ection nebula is correlated with a di?erent stellar latitude. Results. Important spectroscopic diagnostics during η Car’s events show signi?cant changes in 2014 compared to previous events. While the timing of the ?rst He ii λ4686 ?ash was remarkably similar to previous events, the He ii equivalent widths were slightly larger, and the line ?ux increased by a factor of ～7 compared to 2003. The second He ii peak occurred at about the same phase as in 2009, but was stronger. The He i line ?ux grew by a factor of ～8 in 2009?2014 compared to 1998?2003. The N ii emission lines also increased in strength. On the other hand, Hα and Fe ii lines show the smallest emission strengths ever observed in η Car. The optical continuum brightened by a factor of ～4 in the past 10?15 years. The polar spectrum shows fewer changes in the broad wind emission lines: the Fe ii emission strength decreased by a factor of ～2 (compared to a factor of ～4 in our direct line of sight). The He ii equivalent widths at FOS4 were larger in 2009 and 2014 than during the 2003 event. Conclusions. The basic character of η Car’s spectroscopic events has changed in the past two to three cycles. The ionizing UV radiation dramatically weakened during each pre-2014 event but not in 2014. The strengthening of He i and N ii emission and the weakening of the lower-excitation Hα and Fe ii wind features in our direct line of sight implies a substantial change in the physical parameters of the emitting regions. The polar spectrum at FOS4 shows fewer changes in the broad wind emission lines, which may be explained by the latitude-dependent wind structure of η Car. The quick and strong recovery of the He ii emission in 2014 supports a scenario, in which the wind-wind shock may not have completely collapsed as was proposed for previous events. As a result, the companion did not accrete as much material as in previous events. All this may be the consequence of just one elementary change, namely a strong decrease in the primary’s mass-loss rate. This would mark the beginning of a new phase, in which the spectroscopic events can be described as an occultation by the primary’s wind.
关键词： stars: mass-loss,stars: massive,stars: winds, out?ows,stars: individual: eta Carinae,stars: variables: S Doradus
更新于2025-09-04 15:30:14