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RR Lyrae stars both in the field and in clusters can be used to derive the metal abundance of the regions and systems where they are found.
(1) New data have been collected on a sample of field ab-type RR Lyraes with the aim of studying the composition of the halo and the disk of the galaxy, (Clementini et al. 1992a, in preparation), using the relation found by Clementini et al. (1991), (hereafter CTM91), between [Fe/H] and the equivalent width of the Ca II K-line W‘(K). (2) A quantitative chemical abundance analysis of the ab type RR Lyrae (V29) in the globular cluster M4 has been performed using high resolution, high S/N spectroscopy. We obtain [Fe/H]=–1.3 ± 0.2 and the α– elements (Mg and Ti) are overabundant by 0.6 dex. These results are in good agreement with determinations from high resolution spectra of giants and blue horizontal branch stars (Clementini et al. 1992b, in preparation).
The discrepancy between the long distance scale as derived, e.g., from Hipparcos-based distances to globular clusters via main sequence fitting to local subdwarfs, and the short distance scale as derived, e.g., from the absolute magnitude of field RR Lyrae stars via statistical parallaxes and the Baade–Wesselink method, could be accounted for if an intrinsic difference in luminosity of about 0.1−0.2 mag were found to exist between horizontal branch (HB) stars populating the sparse general field and the dense globular clusters.
The Large Magellanic Cloud (LMC) is widely considered a corner-stone of the astronomical distance scale. However, a difference of 0.2−0.3 mag exists in its distance as predicted by the short and long distance scales. Distances to the LMC from Population II objects are founded on the RR Lyrae variables. We have undertaken an observational campaign devoted to the definition of the average apparent luminosity, and to the study of the mass–metallicity relation for RR Lyrae stars in the bar of the LMC. These are compared with analogous quantities for cluster RR Lyrae stars. The purpose is to see whether an intrinsic difference in luminosity, possibly due to a difference in mass, might exist between field and cluster RR Lyrae stars, which could be responsible for the well-known dichotomy between short and long distance scales. Preliminary results are presented on the V and B − V light curves, the average apparent visual magnitude, and the pulsational properties of 102 RR Lyrae stars in the bar of the LMC, observed at ESO in January 1999. The photometric data are accurately tied to the Johnson photometric system. Comparison is presented with the photometry of RR Lyrae stars in the bar of the LMC obtained by the MACHO collaboration (Alcock et al. 1996). Our sample includes 9 double-mode RR Lyrae stars selected from Alcock et al. (1997) for which an estimate of the metal abundance from the ΔS method is presented.
Despite the great progress which is being continuously made towards direct photoelectric recording, it is almost certain that for many years to come photographic plates will remain the most common means for detecting images of stars and stellar spectra, whether directly or through the intermediary of an image intensifier.
The photographic image of the spectrum of a star contains an enormous wealth of information whose utilization is one of the most important tasks of observational astrophysics. To achieve this task many difficult problems must be solved, the first being to express the information in a form which lends itself to further processing.
This is usually done by means of two different kinds of instruments.
In this contribution we give summaries of the oral and poster papers presented in Joint Discussion Session 4, Astrophysical Impact of Abundances in Globular Cluster Stars, at the XXVth IAU General Assembly. The full text of the papers can be found in Volume 75, issue 2, of the MEMORIE della Società Astronomica Italiana (Journal of the Italian Astronomical Society; see the web address: <sait.oat.ts.astro.it>).
The power of micro-arcsecond (μas) astrometry is about to be unleashed. ESA's Gaia mission, now headed towards the end of the first year of routine science operations, will soon fulfil its promise for revolutionary science in countless aspects of Galactic astronomy and astrophysics. The potential of Gaia position measurements for important contributions to the astrophysics of planetary systems is huge. We focus here on the expectations for detection and improved characterization of ‘young’ planetary systems in the neighborhood of the Sun using a combination of Gaia μas astrometry and direct imaging techniques.
This paper considers four alternative sets of actions that a pilot may use to recover an aeroplane from the stall. These actions: those published by the UK CAA and the US FAA, as well as a power delayed sequence and a pitch delayed sequence, were evaluated on 14 single engine piston aeroplane types. In a limited number of types (five in cruise configuration, two in landing configuration) the pitch delayed recovery gave a safe response and least height loss, but in a greater number of types (six and eight in cruise and landing configurations respectively) it resulted in further post-stall uncommanded motion. The other sets of actions all gave a consistent recovery from the stall, but the least height loss in recovery was also consistently the CAA sequence of simultaneous full power and nose-down pitching input, which normally resulted in approximately two thirds the height loss of the FAA’s pitch first then power method, which in turn resulted in about 90% of the height loss of the trialled power delayed recovery. Additionally the CAA recovery gave the least variation in height loss during stall recovery. It was also found that all of the aeroplane types evaluated except for one microlight aeroplane of unusual design, displayed a pitch-up with increased power in the normal (pre-stall) flight regime. Reducing this to separate components it was therefore shown that pitch control is of primary importance and should be used to provide immediate stall recovery. The thrust control can additionally be used as early as possible to minimise height loss, but if the thrust control is used before the pitch control in the stall or post-stall flight regime, there is some risk of subsequent loss of control. Finally, from the discussion on stall recovery methods, questions for Regulatory Authorities are put forward that should address the current practices.
The aerodynamic flow conditions on wings and tail surfaces due to the rotational motion of a spinning aeroplane have been investigated in a full-scale spin flight research programme at the Brunel Flight Safety Laboratory. The wing upper surface vortex has been visualised using smoke and tufts on the wing of a Slingsby Firefly. The flow structures on top of both wings, and on top of the horizontal tail surfaces, have also been studied on a Saab Safir. The development of these rotational flow effects has been related to the spin motion and the effect on the spin dynamics has been studied and discussed. Evidence suggests that the turbulent wake from the wing upper surface vortex impinges the tail of the aircraft during the spin entry. It is hypothesised that the turbulent flow structure on the outside upper wing surface is due to additional accelerations induced by the rotational motion of the aeroplane. Furthermore, the lightening in stick force during spin entry and the apparent increase in push force required for spin recovery corresponds to the observed change in flow condition on the horizontal tail. The difference in pressure on the upper and lower horizontal tail surfaces have been measured using differential pressure sensors, and the result corresponds both with the observed flow conditions and earlier research results from NASA.
Next year the second generation instrument SPHERE will begin science operations at the Very Large Telecope (ESO). This instrument will be dedicated to the search for exoplanets through the direct imaging techniques, with the new generation extreme adaptive optics. In this poster, we present the performances of one of the focal instruments, the Infra-Red Dual-beam Imaging and Spectroscopy (IRDIS). All the results have been obtained with tests in laboratory, simulating the observing conditions in Paranal. We tested several configurations using the sub-system Integral Field Spectrograph (IFS) in parallel and simulating long coronographic exposures on a star, calibrating instrumental ghosts, checking the performance of the adaptive optics system and reducing data with the consortium pipeline. The contrast one can reach with IRDIS is of the order of 10−6 at 0.5 arcsec separation from the central star.
We review spectroscopic evidence of multiple stellar populations in globular clusters. First, we lay down the basic data: the C-N, Na-O, Mg-Al anti-correlations among red giants and main sequence stars, and discuss how they appear to be general properties of globular clusters, in spite of cluster-to-cluster differences. We will then describe what is currently known about He from spectroscopy. We will then present the implications and current observations for the interpretation of the horizontal branches, showing that the multiple population phenomenon is strongly related to the distribution of stars along them. We will briefly mention the spectroscopic evidence related to some less understood cases, like the clusters with multiple subgiant branches. Finally, we summarize the relation between multiple populations and general properties for globular clusters, and their implications for the formation scenario.
Motion and airflow during a two-turn erect spin of an aerobatic light aeroplane have been analysed. An alternative method, based upon camera tracking, has been used to capture the spin motion. A CAD model of the Slingsby Firefly was created using laser scanning. Formation flights with a helicopter have been flown and high-quality video and still imagery obtained. Camera tracking has produced data and unique illustrations of the spinning Slingsby. To further investigate the aerodynamic flow of a spinning aeroplane, full-scale, flow visualisation flights have been flown using wool tufts on wing, fuselage and empennage. Tufts indicate that a large vortex forms on the outside wing. The spanwise motion of this vortex has been studied and related to the spin motion. Furthermore, tufts on the horizontal tail indicate the presence of a leading edge vortex with the flow mainly in a spanwise outwards direction. The effects observed are clearly three dimensional and time dependent. Finally, it is discussed how this new knowledge does not correspond with the spin theories of the past.
We present the radial velocity planet search in moderately wide binaries
with similar components (twins) ongoing at Telescopio Nazionale Galileo (TNG) using the
Galileo High Resolution
Spectrograph (Spettrografo Alta Risoluzione Galileo, SARG).
We discuss the sample selection, the observing and
procedures, the main results of the radial velocity monitoring and the
implications in terms of planet frequency in binary systems. We also briefly
discuss the second major science goal of the SARG survey, the search for
abundance anomalies caused by the ingestion of planetary material by the
central star. Finally, we present some preliminary conclusions regarding the
frequency of planets in binary systems.
We present an analysis of how bisectors of spectral lines
for a few stars
observed during the high-accuracy radial-velocity planet survey ongoing
at the Telescopio Nazionale Galileo (TNG) using the
Galileo High Resolution
Spectrograph (Spettrografo Alta Risoluzione Galileo, SARG),
and discuss their relation with differential radial velocities. The iodine cell
lines employed in the radial velocity measurements were used to improve the wavelength
calibration and then removed before bisector analysis. The line bisectors were then
computed from average absorption profiles obtained by cross-correlation of the stellar
spectra with a mask made from suitable lines of a solar catalog. Bisector velocity
spans were determined and the run of bisector velocity span against radial velocity
was studied to search for correlations between line asymmetries and radial velocity
variations. We present an analysis of spectra of HD 216122B that show a slight contamination
likely to be due to a stellar companion, and an analysis of spectra of HD 76036A, a case where the
line bisectors are useful for improving the RV measurements. These systems are part of
a survey sample being observed with adaptive optics (AdOpt at the TNG since 2006) in an
attempt to visually resolve stellar companions.
The frequency of planets in binaries is an important issue in the field of extrasolar planet studies, because of its relevance in the estimate of the global planet population of our Galaxy and the clues it can give to our understanding of planet formation and evolution.
Here we present an update of the results discussed in Bonavita & Desidera (2007) (hereafter BD07), where we reported the outcomes of our literature search for binaries and multiple systems among the sample with uniform detectability (UD) defined by Fischer & Valenti (2005) (hereafter FV05).
The available results of deep imaging searches for planetary companions around nearby stars provide us useful constraints on the frequencies of giant planets in very wide orbits.
Here we present some preliminary results of the Monte Carlo simulation which compare the published detection limits with the generated planetary masses and orbital parameters.
This allow us to consider the impications of the null detection, which comes from the direct imaging techniques, on the distributions of mass and semimajor axis derived from the results of the other search techniques and also to check the agreement of the observations with the available planetary formation models.
We derive abundances of Fe, Na, O, α and s-elements from GIRAFFE@VLT spectra for more than 200 red giant stars in the Milky Way satellite ω Centauri. Our preliminary results are that: (i) we confirm that ω Centauri exhibits large star-to-star metallicity variation (~1.4 dex); (ii) the metallicity distribution reveals the presence of at least five stellar populations with different [Fe/H]; (iii) a distinct Na-O anticorrelation is clearly observed for the metal-poor and metal-intermediate stellar populations while apparently the anticorrelation disappears for the most metal rich populations. Interestingly the Na level grows with iron.
The single stable isotope of beryllium is a pure product of cosmic-ray spallation in the ISM. Assuming that the cosmic-rays are globally transported across the Galaxy, the beryllium production should be a widespread process and its abundance should be roughly homogeneous in the early-Galaxy at a given time. Thus, it could be useful as a tracer of time. In an investigation of the use of Be as a cosmochronometer and of its evolution in the Galaxy, we found evidence that in a log(Be/H) vs. [α/Fe] diagram the halo stars separate into two components. One is consistent with predictions of evolutionary models while the other is chemically indistinguishable from the thick-disk stars. This is interpreted as a difference in the star formation history of the two components and suggests that the local halo is not a single uniform population where a clear age-metallicity relation can be defined. We also found evidence that the star formation rate was lower in the outer regions of the thick disk, pointing towards an inside-out formation.
Beryllium stellar abundances were suggested to be a good tracer of time in the early Galaxy. In an investigation of its use as a cosmochronometer, using a large sample of local halo and thick-disk dwarfs, evidence was found that in a log(Be/H) vs. [α/Fe] diagram the halo stars separate into two components. One is consistent with predictions of evolutionary models while the other is chemically indistinguishable from the thick-disk stars. This is interpreted as a difference in the star formation history of the two components and suggests that the local halo is not a single uniform population where a clear age-metallicity relation can be defined.
We study the stability of the cold-plasma dispersion relation for circularly polarized waves in a plasma composed of an ion background and an ion beam. The presence of the beam introduces a resonant branch into the dispersion relation for right-hand-polarized waves propagating in the direction of the external magnetic field, which, for V>Vφ, has negative energy (here V is the beam velocityVφ is the wave phase velocity). Therefore this branch may give rise to explosive instabilities when the waves experience parametric decays. It is shown graphically that resonant right-hand-polarized and non-resonant left-hand-polarized waves, propagating parallel to the external magnetic field, can be unstable. It is also shown that the instability region can extend to large frequencies and wavenumnbers, and that the instability regions have a band structure. The parametric dependence of instability thresholds and marginal modes is also studied.