Nova-induced mass transfer variations

We investigate variations of the mass transfer rate in cataclysmic variables (CVs) that are induced by nova outbursts. The ejection of nova shells leads to a spread of transfer rates in systems with similar orbital period. The effect is maximal if the specific angular momentum in the shell is the same as the specific orbital angular momentum of the white dwarf. We show analytically that in this case the nova-induced widening of the mass transfer rate distribution can be significant if the system, in the absence of nova outbursts, is close to mass transfer instability (i.e., within a factor of ~1.5 of the critical mass ratio). Hence the effect is negligible below the period gap and for systems with high-mass white dwarfs. At orbital periods between about 3 and 6 hrs the width of the mass transfer rate distribution exceeds an order of magnitude if the mass accreted on the white dwarf prior to the runaway is larger than a few 10^{-4} M_sun. At a given orbital period in this range, systems with the highest transfer rate should on average have the largest ratio of donor to white dwarf mass. We show results of population synthesis models which confirm and augment the analytic results.Comment: ApJ, in press; 14 pages (incl. 7 figures), emulateapj styl

A New Evolutionary Picture for CVs and LMXBs

We consider an alternative to the standard picture of CV and LMXB evolution, namely the idea that most CVs (and by extension LMXBs) may not yet have had time to evolve to their theoretical minimum orbital periods. We call this the Binary Age Postulate (BAP). The observed short-period cutoff in the CV histogram emerges naturally as the shortest period yet reached in the age of the Galaxy, while the post-minimum-period space density problem is removed. The idea has similar desirable consequences for LMXBs. In both cases systems with nuclear-evolved secondary stars form a prominent part of the short-period distributions. Properties such as the existence and nature of ultrashort-period systems, and the spread in mass transfer rates at a given orbital period, are naturally reproduced.Comment: 10 pages, 6 figures; to appear in 'The Physics of Cataclysmic Variables and Related Objects', Goettingen, August 5-10, 200

A New Evolutionary Picture for CVs and LMXBs II. The Impact of Thermal-Timescale Mass Transfer

Depending on the outcome of pre-CV formation, mass transfer may set in under thermally unstable conditions in a significant number of systems. Full computations have shown that such an early phase of thermal-timescale mass transfer usually leads to ordinary looking CVs, but these do also show some unusual properties (e.g. chemical anomalies in later stages). Rather than investigating the common envelope evolution leading to pre-CVs, we study the properties of multiple evolutionary tracks starting with a phase of thermal-timescale mass transfer. Apart from fitting unusual CVs (like AE Aqr), global properties of the CV population as a whole give indications that this is indeed the channel where many CVs come from.Comment: 10 pages, 4 figures; to appear in 'The Physics of Cataclysmic Variables and Related Objects', Goettingen, August 5-10, 200

Properties of discontinuous and nova-amplified mass transfer in CVs

We investigate the effects of discontinuous mass loss in recurrent outburst events on the long-term evolution of cataclysmic variables (CVs). Similarly we consider the effects of frictional angular momentum loss (FAML), i.e. interaction of the expanding nova envelope with the secondary. Numerical calculations of CV evolution over a wide range of parameters demon- strate the equivalence of a discontinuous sequence of nova cycles and the corresponding mean evolution (replacing envelope ejection by a continuous wind), even close to mass transfer instability. A formal stability analysis of discontinuous mass transfer confirms this, independent of details of the FAML model. FAML is a consequential angular momentum loss which amplifies the mass transfer rate driven by systemic angular momentum losses such as magnetic braking. We show that for a given v_exp and white dwarf mass the amplification increases with secondary mass and is significant only close to the largest secondary mass consistent with mass transfer stability. The amplification factor is independent of the envelope mass ejected during the outburst, whereas the mass transfer amplitude induced by individual nova outbursts is proportional to it.Comment: 16 pages, 19 figures; to appear in MNRA

The Swiss Mass Immigration Initiative: The Impact of Increased Policy Uncertainty on Expected Firm Behaviour

In Switzerland a sudden policy uncertainty shock happened in February 2014 with the close and largely unexpected acceptance of a referendum aiming at limiting free movement of persons. The referendum requires Switzerland to reintroduce annual quotas for immigrants within three years. The referendum is vaguely formulated and its actual consequences are largely unknown. Yet, the vote reduced the expected future availability of qualified labour, put at stake several economically important agreements between Switzerland and the European Union, and reduced expected future domestic demand for firms. This paper uses a special survey conducted by the KOF Swiss Economic Institute to analyse the short- to medium-run expected consequences of this substantial policy uncertainty shock on firms' private fixed investment and employment plans. We find that those firms that believe that potential growth in Switzerland will deteriorate and those that report that investment uncertainty has increased are also the ones that see a significant reduction in their future investment activities and their expected employment due to the vote, so that an uncertainty effect is present. We also provide evidence that the short-term effect of policy uncertainty on investment is economically significant.Die knappe Annahme der Initiative gegen Masseneinwanderung im Februar 2014 führte zu einem unerwarteten Anstieg der Unsicherheit über die zukünftigen politischen Rahmenbedingen in der Schweiz. Die Initiative verpflichtet den Bundesrat zur gesetzlichen Einführung fixer Kontingente innerhalb der nächsten drei Jahre. Die weit gefasste Formulierung des Initiativtextes verhindert jedoch das Vorhersehen der genauen Umsetzung und erhöht damit den Spielraum möglicher Auswirkungen, was letztlich in einem Anstieg der Unsicherheit resultiert. Die geforderten Kontingente beschränken den Zugang Schweizer Firmen zu ausländischen Arbeitskräften und erhöhen die Gefahr eines zukünftigen Mangels an Fachkräften. Zudem sind Kontingente mit dem bestehenden Vertrag der Personenfreizügigkeit unvereinbar, bei dessen Auflösung käme es zur Kündigung aller mit der Personenfreizügigkeit verbunden bilateralen Abkommen. Die Aussicht auf die Kündigung der bilateralen Verträge erhöht die Unsicherheit über den Zugang Schweizer Unternehmen zum Binnenmarkt der Europäischen Union und senkt letztlich die Erwartungen der zukünftigen Gesamtnachfrage. In diesem Artikel untersuchen wir die kurz- bis mittelfristigen Auswirkungen der Annahme der Initiative auf Beschäftigung und Investitionen. Unsere Analysen basieren auf einer Sonderumfrage der KOF Konjunkturforschungsstelle und zeigen, dass die gestiegene Unsicherheit bereits jetzt zu einer Reduktion der Investitionspläne und zukünftigen Beschäftigung führt

Multi-scale thermal pattern monitoring of a large lake (Lake Geneva) using a multi-sensor approach

The applicability of satellite imagery products from different sensors (AVHRRderived multi-channel sea surface temperature (MCSST), MODIS sea surface temperature (SST) products 5-Min L2 Swath 1 km and Landsat TM band 6 thermal signature) for the comprehensive monitoring of temperature and its temporal patterns over a large lake is tested in this study. The coverage of cloudfree satellite data for Lake Geneva is reported throughout a year and, more specifically, during a 13 day period in summer 2003. In a second step, we demonstrate the feasibility of the AVHRR/MODIS imagery to discern day and night temperature patterns, by generating day and night climatologies and various spatial statistics over the 13 day period. The different day and night surface thermal patterns observed by satellite imagery could be linked to the thermal structure existing in deeper water using the concept of the diurnal decoupled layer. The forcing of the persistent patterns, two warm cores divided by a saddle-shaped cold anomaly, is explained by wind periodicity and insolation conditions. The patterns can be matched to features postulated by findings of different limnologists in the past. Other surface temperature related phenomena such as water upwelling and downwelling and the occurrence of plumes are related to meteorological and hydrological events. The lakewide average lake surface water temperature (LSWT) trends for day and night during the study period are roughly parallel. A sudden loss of stored heat can be explained by episodes of long fetch, synoptic wind (bise) that interrupted the predominant breeze regime