Forecasting ozone concentrations in the east of Croatia using nonparametric Neural Network Models

Ozone is one of the most significant secondary pollutants with numerous negative effects on human health and environment including plants and vegetation. Therefore, more effort is made recently by governments and associations to predict ozone concentrations which could help in establishing better plans and regulation for environment protection. In this study, we use two Artificial Neural Network based approaches (MPL and RBF) to develop, for the first time, accurate ozone prediction models, one for urban and another one for rural area in the eastern part of Croatia. The evaluation of actual against the predicted ozone concentrations revealed that MLP and RBF models are very competitive for the training and testing data in the case of Kopa?ki Rit area whereas in the case of Osijek city, MLP shows better evaluation results with 9% improvement in the correlation coefficient. Furthermore, subsequent feature selection process has improved the prediction power of RBF network.     

Stars with Discrepant <Emphasis Type="Italic">v</Emphasis> sin <Emphasis Type="Italic">i</Emphasis> as Derived from the Ca II 3933 and Mg II 4481 Å Lines. VII. HD9531 (SB), HD31592 (SB2), HD129174 (SB?)

In this paper of the series we analyze three stars listed among stars with discrepant v sin i: HD9531 and HD31592, which also show radial velocity variations inherent to spectroscopic binaries, and HD129174 which is an Mn-type star with a possible magnetic field. In HD9531 we confirm the radial velocity derived fromthe hydrogen lines as well as fromthe Ca II line at 3933 Å as variable. The profile of the calcium line also appears variable, and with the estimated magnetic induction B_e = ?630 ± 1340 G, this suggests that the abundance of calcium possibly varies over the surface of the star. We identified the lines of the secondary component in the spectrum of HD31592 revealing thus it is an SB2 binary with B9.5V and A0V components. While the primary star rotates with v sin i = 50 km s^?1, the secondary star is faster with v sin i = 170 km s^?1. We find that only 60% of the Mn lines identified in the spectrum of HD129174 can be fitted with a unique abundance value, whereas the remaining lines are stronger or fainter. We also identified two Xe II lines at 5339.33 Å and 5419.15 Å and estimated their log g f.     

Stars with discrepant <Emphasis Type="Italic">v</Emphasis> sin <Emphasis Type="Italic">i</Emphasis> as derived from the Ca II 3933 and Mg II 4481 Å lines. VI. HD 199892 — an SB2 spectroscopic binary

We analyzed the spectra of a well known SB1 binary HD199892 for which the projected rotational velocity v sin i, introduced in the literature, significantly differs when determined from the lines of Ca II at 3933 Å and ofMg II at 4481 Å. Contrary to the former findings, we discovered the signs of spectral lines of a companion star in the profile of Hβ as well as weak metallic lines in the high resolution high S/N spectra covering the most of the visual region. We estimated the secondary star to be a main sequence A4V star with a mass of 2.2M _⊙ and derived its radial velocity which resulted in the mass of the primary M = 4.6M _⊙. Short sections of the spectra in the Mg II 4481 Å and Ca II 3933 Å regions are analyzed as well.     

Study of the Element Distribution on the Surface of the He-weak star 36 lyn

Photographic spectra obtained with the Coudé-spectrograph of the 2-m telescope of BNAO – Rozhen have been used for mapping the elements surface distribution of 36 Lyn. The maps of the distribution of helium, silicon, chromium and magnesium are presented. The results show that helium, silicon and chromium are concentrated mainly in the magnetic equator region. Magnesium is distributed more or less uniformly on the stellar surface.     

Stars with discrepant <Emphasis Type="Italic">υ</Emphasis> sin <Emphasis Type="Italic">i</Emphasis> as derived from Ca II 3933 and Mg II 4481 Å lines. II. Multiple star HD 90569

Axial rotation of a star plays an important role in its evolution, physical condition in its atmosphere and appearance of its spectrum. Methods of determinations of υ sin i are based on comparison of the observed profiles of spectral lines with theoretical ones. Their accuracy depends on the kind and quality of spectrograms as well as on the algorithms used. A frequently used method is the simple comparing of one line, e.g. the Ca II at 3933 Å or Mg ii at 4481 Å. This however, may result in a false value of υ sin i if low dispersion spectra are used. In this work we studied contemporary CCD as well as older photographic spectra of the multiple star HD90569. We determined the projected rotational velocity value to be υ sin i = 11 km/s. Besides formerly reported enhancing of lines of Cr, Fe, Mn and Sr, we found also large overabundances of rare earths, gallium and platinum. Helium, carbon, nitrogen, oxygen, aluminium, calcium, scandium and nickel are in deficit. The spectrum of the occultation double was not identified to be of the SB2-type, however, there are some observable evidences that the pair creates a binary with a long orbital period. Despite this there are also observations that leave such interpretation uncertain.     

Geochronologic evidence for Early Cretaceous volcanic activity on Barton Peninsula, King George Island, Antarctica

Ages of six volcanic and plutonic rocks on Barton Peninsula, King George Island, were determined using ⁴⁰Ar/³⁹Ar and K-Ar isotopic systems. The ⁴⁰Ar/³⁹Ar and K-Ar ages of basaltic andesite and diorite range from 48 My to 74 My and systematically decrease toward the upper stratigraphic section. Two specimens of basaltic andesite which occur in the lowermost sequence of the peninsula, however, apparently define two distinct plateau ages of 52-53 My and 119-120 My. The latter is interpreted to represent the primary cooling age of basaltic andesite, whereas the former is interpreted as the thermally-reset age caused by the intrusion of Tertiary granitic pluton. The isochron ages calculated from the isotope correlation diagram corroborate our interpretation based on the apparent plateau ages. It is therefore likely that volcanism was active during the Early Cretaceous on Barton Peninsula. When the K-Ar ages of previous studies are taken into account with our result, the ages of basaltic andesite in the northern part of the Barton Peninsula are significantly older than those in the southern part. Across the north-west-south-east trending Barton fault bounding the two parts, there are significant differences in geochronologic and geologic aspects.     

Spectroscopic study of the weak magnetic star HD220825-κPsc

The star HD220825 is studied as part of a program to investigate the chemical abundance of CP stars with weak magnetic fields. Its magnetic field is found to be Be < 100 G. The chemical abundance appears to correspond to that of CP stars with high magnetic fields. The present results and other data imply that the magnetic field has little effect on the degree of anomaly in the chemical abundance, although it undoubtedly has an effect. The rotation speed of the star is 37.5 km/s, substantially lower than for normal stars with the same temperature. The weak magnetic field raises difficulties for the hypothesis that the loss of angular momentum involves the magnetic field. __________ Translated from Astrofizika, Vol. 49, No. 4, pp. 585–594 (November 2006).     

Stars with discrepant v sin i as derived from Ca II 3933 and Mg II 4481 Å lines. I. Composite-spectrum star HD 2913

Axial rotation of a star plays an important role in its evolution, physical conditions in its atmosphere and the shape of its spectrum. Methods of determining of v sin i are based on comparison of the observed profiles of spectral lines with the theoretical ones. Their accuracy depends on the type and quality of spectrograms, as well as on the algorithms used. A frequently used method is a simple comparison of one line, e.g. the Ca ii at 3933 Å or Mg ii at 4481 Å. This, however, may result in a false value of v sin i in case when low-dispersion spectra are used. We investigate the spectra of stars with a significant discrepancy of their rotational velocities introduced in various sources, and analyze the corresponding spectral region from the point of view of possible admixed features, which may mask the true line profiles. We use CCD spectra of the stars having this discrepancy, to compare with theoretical spectra. We also studied photographic spectra, obtained during the 1970s and 1980s. In this work we studied the spectra of the binary HD 2913A, and identified the spectrum of its weaker component designated as “Ab”. We estimated the effective temperature, surface gravity and projected rotational velocity of the weaker component that classify it as an early F-type Main Sequence star. The discrepancy between the values of v sin i derived from the two lines of calcium and magnesium is explained as a consequence of superposition of the pair’s spectra. The cooler component contributes by a strong Ca ii-K line, and thus significantly broadens the observed line profile.     

Exoplanet status report: Observation, characterization and evolution of exoplanets and their host stars

After the discovery of more than 400 planets beyond our Solar System, the characterization of exoplanets as well as their host stars can be considered as one of the fastest growing fields in space science during the past decade. The characterization of exoplanets can only be carried out in a well coordinated interdisciplinary way which connects planetary science, solar/stellar physics and astrophysics. We present a status report on the characterization of exoplanets and their host stars by reviewing the relevant space- and ground-based projects. One finds that the previous strategy changed from space mission concepts which were designed to search, find and characterize Earth-like rocky exoplanets to: A statistical study of planetary objects in order to get information about their abundance, an identification of potential target and finally its analysis. Spectral analysis of exoplanets is mandatory, particularly to identify bio-signatures on Earth-like planets. Direct characterization of exoplanets should be done by spectroscopy, both in the visible and in the infrared spectral range. The way leading to the direct detection and characterization of exoplanets is then paved by several questions, either concerning the pre-required science or the associated observational strategy.