The white dwarf companion of the B a 2 star zeta Cap

The Ba II star zeta Cap has a white dwarf companion. Its T (sub eff) is determined to be 22000 K, its mass is approximately one solar mass. The importance of this finding for the explanation of abundance peculiarities is discussed

Outlook for ultraviolet astronomy

A brief overview of galactic and extragalactic research is given with emphasis on the problems of temperature determination, chemical abundance determination, and the question about the energy sources for the high temperature regions. Stellar astronomy, stellar winds, and the interstellar medium are among the topics covered

Search for white dwarf companions of cool stars with peculiar element abundances

A search for a white dwarf companions of cool stars with peculiar element abundances was undertaken. One additional star the xi Cet, was found with a white dwarf companion. It was found that HR 1016, 56Uma, 16 Ser, have high excitation emission lines which indicate a high temperature object in the system. It is suggested that since these indications for high temperature companions were seen for all nearby Ba stars, it is highly probable that all Ba stars have white dwarf companions, and that the peculiar element abundances seen in the Ba stars are due to mass transfer. Observations, arguments and conclusions are presented. White dwarf companions were not found. Together with the Li and Be abundances and the chromospheric emission line spectra in these stars were studied. No white dwarf companions were seen for subgiant CH stars

Internal kinematics of modelled interacting disc galaxies

We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys disturb the velocity fields significantly and hence the RCs of the interacting galaxies, leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are significantly rising or falling profiles in the direction of the companion galaxy and pronounced bumps in the RCs. In addition, tidal tails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshift galaxies, on which we focus our investigations. We use a quantitative measure for the asymmetry of rotation curves to show that the appearance of these distortions strongly depends on the viewing angle. We also find in this way that the velocity fields settle back into relatively undisturbed equilibrium states after unequal mass mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no severe distortions anymore. These results are consistent with previous theoretical and observational studies. As an illustration of our results, we compare our simulated velocity fields and direct images with rotation curves from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find remarkable similarities.Comment: 13 pages, 14 figures, accepted for publication in A&A, some improvements and changes, main conclusions are unaffecte

Human Factors of Flight-deck Automation: NASA/Industry Workshop

The scope of automation, the benefits of automation, and automation-induced problems were discussed at a workshop held to determine whether those functions previously performed manually on the flight deck of commercial aircraft should always be automated in view of various human factors. Issues which require research for resolution were identified. The research questions developed are presented

Essays on Business Cycles and Stabilization Policy.

This dissertation is a collection of essays on fiscal policy, monetary policy and the international transmission of business cycle shocks. Chapter 1 highlights the importance of distinguishing durable and nondurable goods when conducting countercyclical fiscal policy. It shows that the fiscal multiplier for purchases of durable goods is much smaller than the multiplier for nondurable goods. Standard models predict small durables multipliers because private sector purchases of durable goods are highly intertemporally substitutable and therefore easily crowded out. Empirical estimates based on U.S. data confirm this result. In aggregate time series data output rises by about 50 cents less if the government purchases 1$ of durable rather than nondurable goods. Industry-level estimates also point to smaller durable goods multipliers. The findings of this chapter suggest that infrastructure spending which is frequently part of fiscal stimulus packages is relatively ineffective at raising aggregate demand. Chapter 2, joint with Christopher L. House, shifts focus to monetary policy and analyzes the optimal Taylor rule in a standard New Keynesian model. If the central bank can observe the output gap and inflation without error, then it is typically optimal to respond infinitely strongly to observed deviations from the central bank’s targets. If it observes inflation and the output gap with error, the central bank will temper its responses so as not to impart unnecessary volatility to the economy. If the Taylor rule is expressed in terms of estimated output and inflation then it is optimal to respond infinitely strongly to estimated deviations from the targets. Under such a Taylor rule the estimates of inflation and the output gap should be perfectly negatively correlated. In the data, inflation and the output gap are weakly correlated, suggesting that the central bank is systematically underreacting. Chapter 3, joint with Aaron Flaaen and Nitya Pandalai-Nayar, studies the cross-country transmission of shocks. Using the 2011 Tohoku earthquake as a natural experiment, the study shows that firms reliant on Japanese intermediates experienced significant drops in production after the disruption. These findings imply that supply chains are sufficiently inflexible to play an important role in the international transmission of shocks.PhDEconomicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/120791/1/chrisboe_1.pd

The ultraviolet spectrum of HH 24A and its relation to optical spectra

The spectrum of the brightest part (HH 24A) of the complex Herbig-Haro object HH 24 in the short wavelength UV range was studied. The object is of special interest since it is known that in the optical range the continuum is due to dust scattered light originating in a young stellar object while the shock excited emission lines are formed in HH 24A itself. The spectrum shows only a continuum or a quasi-continuum and is not comparable to that of the typical high excitation object like HH1 or HH2 nor to that of a low excitation object like HH3 or HH47