Technetium and the third dredge up in AGB stars. I. Field stars

We searched for Tc in a sample of long period variables selected by stellar luminosity derived from Hipparcos parallaxes. Tc, as an unstable s-process element, is a good indicator for the evolutionary status of stars on the asymptotic giant branch (AGB). In this paper we study the occurrence of Tc as a function of luminosity to provide constraints on the minimum luminosity for the third dredge up as estimated from recent stellar evolution models. A large number of AGB stars above the estimated theoretical limit for the third dredge up are found not to show Tc. We confirm previous findings that only a small fraction of the semiregular variables show Tc lines in their spectra. Contrary to earlier results by Little et al. (1987) we find also a significant number of Miras without Tc. The presence and absence of Tc is discussed in relation to the mass distribution of AGB stars. We find that a large fraction of the stars of our sample must have current masses of less than 1.5 M_{\sun}. Combining our findings with stellar evolution scenarios we conclude that the fraction of time a star is observed as a SRV or a Mira is dependent on its mass.Comment: 10 pages, 4 figures, accepted for publication in A&

Working Fluid Quantity Effect on Magnetic Field Control of Heat Pipes

This paper deals with heat pipes controlled by a static magnetic field and with an important side effect – the quantity of working fluid. Heat pipes are able to provide very effective heat transport. Several standard regulation methods are commonly used for this purpose. In previous experiments implemented in our laboratory, we have observed the significant influence of a magnetic field on the heat conductance of the selected heat pipe. A special heat pipe was manufactured for this purpose and pure oxygen was chosen as a working fluid, due to its suitable magnetic properties. The heat pipe operation and the magnetic field control depend on various parameters. This paper is focused on the influence of the quantity of working fluid. Some important results of our experiments are presented and discussed.

The PTI Carbon Star Angular Size Survey: Effective Temperatures and Non-Sphericity

We report new interferometric angular diameter observations of 41 carbon stars observed with the Palomar Testbed Interferometer (PTI). Two of these stars are CH carbon stars and represent the first such measurements for this subtype. Of these, 39 have Yamashita (1972,1975) spectral classes and are of sufficiently high quality that we may determine the dependence of effective temperature on spectral type. We find that there is a tendency for the effective temperature to increase with increasing temperature index by ~120K per step, starting at T_EFF ~= 2500K for C3,y, although there is a large amount of scatter about this relationship. Overall, the median effective temperature for the carbon star sample is found to be 2800 +- 270K, and the median linear radius is 360 +- 100 R_SUN. We also find agreement on average within 15K with the T_EFF determinations of Bergeat (2001,2002a,b), and a refinement of carbon star angular size prediction based on V & K magnitudes is presented that is good to an rms of 12%. A subsample of our stars have sufficient {u,v} coverage to permit non-spherical modeling of their photospheres, and a general tendency for detection of statistically significant departures from sphericity with increasing signal-to-noise of the interferometric data is seen. The implications of most - and potentially all - carbon stars being non-spherical is considered in the context of surface inhomogeneities and a rotation-mass loss connection.Comment: 59 pages, 15 figures, 6 tables; accepted for publication in Ap

The complex environment of the bright carbon star TX Psc as probed by spectro-astrometry

Context: Stars on the asymptotic giant branch (AGB) show broad evidence of inhomogeneous atmospheres and circumstellar envelopes. These have been studied by a variety of methods on various angular scales. In this paper we explore the envelope of the well-studied carbon star TX Psc by the technique of spectro-astrometry. Aims: We explore the potential of this method for detecting asymmetries around AGB stars. Methods:We obtained CRIRES observations of several CO $\Delta$v=1 lines near 4.6 $\mu$m and HCN lines near 3 $\mu$m in 2010 and 2013. These were then searched for spectro-astrometric signatures. For the interpretation of the results, we used simple simulated observations. Results: Several lines show significant photocentre shifts with a clear dependence on position angle. In all cases, tilde-shaped signatures are found where the positive and negative shifts (at PA 0deg) are associated with blue and weaker red components of the lines. The shifts can be modelled with a bright blob 70 mas to 210 mas south of the star with a flux of several percent of the photospheric flux. We estimate a lower limit of the blob temperature of 1000 K. The blob may be related to a mass ejection as found for AGB stars or red supergiants. We also consider the scenario of a companion object. Conclusions: Although there is clear spectro-astrometric evidence of a rather prominent structure near TX Psc, it does not seem to relate to the other evidence of asymmetries, so no definite explanation can be given. Our data thus underline the very complex structure of the environment of this star, but further observations that sample the angular scales out to a few hundred milli-arcseconds are needed to get a clearer picture

Modelling the atmosphere of the carbon-rich Mira RU Vir

Context. We study the atmosphere of the carbon-rich Mira RU Vir using the mid-infrared high spatial resolution interferometric observations from VLTI/MIDI. Aims. The aim of this work is to analyse the atmosphere of the carbon-rich Mira RU Vir, with state of the art models, in this way deepening the knowledge of the dynamic processes at work in carbon-rich Miras. Methods. We compare spectro-photometric and interferometric measurements of this carbon-rich Mira AGB star, with the predictions of different kinds of modelling approaches (hydrostatic model atmospheres plus MOD-More Of Dusty, self-consistent dynamic model atmospheres). A geometric model fitting tool is used for a first interpretation of the interferometric data. Results. The results show that a joint use of different kind of observations (photometry, spectroscopy, interferometry) is essential to shed light on the structure of the atmosphere of a carbon-rich Mira. The dynamic model atmospheres fit well the ISO spectrum in the wavelength range {\lambda} = [2.9, 25.0] {\mu}m. Nevertheless, a discrepancy is noticeable both in the SED (visible), and in the visibilities (shape and level). A possible explanation are intra-/inter-cycle variations in the dynamic model atmospheres as well as in the observations. The presence of a companion star and/or a disk or a decrease of mass loss within the last few hundred years cannot be excluded but are considered unlikely.Comment: 15 pages. Accepted in A&

Catching the fish - Constraining stellar parameters for TX Psc using spectro-interferometric observations

Stellar parameter determination is a challenging task when dealing with galactic giant stars. The combination of different investigation techniques has proven to be a promising approach. We analyse archive spectra obtained with the Short-Wavelength-Spectrometer (SWS) onboard of ISO, and new interferometric observations from the Very Large Telescope MID-infrared Interferometric instrument (VLTI/MIDI) of a very well studied carbon-rich giant: TX Psc. The aim of this work is to determine stellar parameters using spectroscopy and interferometry. The observations are used to constrain the model atmosphere, and eventually the stellar evolutionary model in the region where the tracks map the beginning of the carbon star sequence. Two different approaches are used to determine stellar parameters: (i) the 'classic' interferometric approach where the effective temperature is fixed by using the angular diameter in the N-band (from interferometry) and the apparent bolometric magnitude; (ii) parameters are obtained by fitting a grid of state-of-the-art hydrostatic models to spectroscopic and interferometric observations. We find a good agreement between the parameters of the two methods. The effective temperature and luminosity clearly place TX Psc in the carbon-rich AGB star domain in the H-R-diagram. Current evolutionary tracks suggest that TX Psc became a C-star just recently, which means that the star is still in a 'quiet' phase compared to the subsequent strong-wind regime. This is in agreement with the C/O ratio being only slightly larger than 1.Comment: 11 pages, 9 figures, 5 table

Tracing the development of dust around evolved stars: The case of 47 Tuc

We observed mid-infrared (7.5-22 mum) spectra of AGB stars in the globular cluster 47 Tuc with the Spitzer telescope and find significant dust features of various types. Comparison of the characteristics of the dust spectra with the location of the stars in a logP-K-diagram shows that dust mineralogy and position on the AGB are related. A 13 mum feature is seen in spectra of low luminosity AGB stars. More luminous AGB stars show a broad feature at 11.5 mum. The spectra of the most luminous stars are dominated by the amorphous silicate bending vibration centered at 9.7 mum. For 47 Tuc AGB stars, we conclude that early on the AGB dust consisting primarily of Mg-, Al- and Fe oxides is formed. With further AGB evolution amorphous silicates become the dominant species.Comment: 2 figures, accepted for publication in ApJ Letter

Technetium and the third dredge up in AGB stars II. Bulge stars

We searched for Technetium (Tc) in a sample of bright oxygen-rich asymptotic giant branch (AGB) stars located in the outer galactic bulge. Tc is an unstable element synthesised via the s-process in deep layers of AGB stars, thus it is a reliable indicator of both recent s-process activity and third dredge-up. We aim to test theoretical predictions on the luminosity limit for the onset of third dredge-up. Using high resolution optical spectra obtained with the UVES spectrograph at ESO's VLT we search for resonance lines of neutral Tc in the blue spectral region of our sample stars. These measurements allow us to improve the procedure of classification of stars with respect to their Tc content by using flux ratios. Synthetic spectra based on MARCS atmospheric models are presented and compared to the observed spectra around three lines of Tc. Bolometric magnitudes are calculated based on near infrared photometry of the objects. Among the sample of 27 long period bulge variables four were found to definitely contain Tc in their atmospheres. The luminosity of the Tc rich stars is in agreement with predictions from AGB evolutionary models on the minimum luminosity at the time when third dredge-up sets in. However, AGB evolutionary models and a bulge consisting of a single old population cannot be brought into agreement. This probably means that a younger population is present in the bulge, as suggested by various authors, which contains the Tc-rich stars here identified

EVALUATION OF ECONOMIC EFFICIENCY OF PROCESS IMPROVEMENT IN FOOD PACKAGING

Abstract HRON, J., MACÁK, T., JINDROVÁ, A.: Evaluation of economic effi ciency of process improvement in food packaging. Acta univ. agric. et silvic. Mendel. Brun., 2012, LX, No. 4, pp. 115-120 In general, we make gains in process by the three fundamental ways. First, we defi ne or redefi ne our process in a strategic sense. Second, once defi ned or redefi ned, we commence process operations and use process control methods to target and stabilize our process. Third, we use process improvement methods, as described in this paper, along with process control to fully exploit our process management and/or technology. Process improvement is focused primarily in our subprocesses and sub-subprocesses. Process leverage is the key to process improvement initiatives. This means that small improvements of the basic manufacturing operations can have (with the assumption of mass repetition of the operation) a big impact on the functioning of the whole production unit. The complexity within even small organizations, in people, products, and processes, creates signifi cant challenges in eff ectively and effi ciently using these initiatives tools. In this paper we are going to place process purposes in the foreground and initiatives and tools in the background as facilitator to help accomplish process purpose. Initiatives and tools are not the ends we are seeking; result/ outcomes in physical, economics, timeliness, and customer service performance matter. In the paper process boundaries (in a generic sense) are set by our process purpose and our process defi nition. Process improvement is initiated within our existing process boundaries. For example, in a fast-food restaurant, if we defi ne our cooking process around a frying technology, then we provide process improvements within our frying technology. On the other hand, if we are considering changing to a broiling technology, then we are likely faced with extensive change, impacting our external customers, and a process redefi nition may be required. The result / aim of the paper are based on the example of the process improving of a food packaging quality. Specifi cally, the integration of two approaches: statistical process control (SPC) and quality control based on stochastic principle. Both approaches are represented in the quality control of food packaging. Based on the obtained data set of weld strength packaging fi lms (in units of MPa) was tested by the statistical hypothesis that innovation in the implementation of the weld has a positive impact on the quality of the fi nished weld. From basic data analysis, which focused on the assessment of normality in the distribution of values of the parameter using the Shapiro-Wilkes test it can be seen (o