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1

Statistical Indicators of Astrophysical Parameters

Wąż P., Bielińska-Wąż D., Strobel A., Pleskacz A.

Acta Astronomica

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2010

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Vol. 60, No. 3

283--293

EN

The aim of this paper is to introduce a new tool for a simple identification of spectral types. We use methods of statistical spectroscopy, in particular the method of intensity-distribution moments. The statistical approach revealed a characteristic behavior of moments of the stellar spectra for different spectral types. The transition from one spectral type to another may be expressed as a regular function of appropriate moments of the intensity distribution of the spectra. Moment-based diagrams localize particular spectral types in different areas of the plots. Since the intensity-distribution moments may be easily derived from the observed spectra, the presented method facilitates a simple auxiliary tool for the classification of stars to specific spectral types. It is also helpful in checking the correctness of the existing classifications. The intensity-distribution moments depend on all kinds of stellar characteristics, including the metallicity and the age. Therefore, using an inverse approach, from the knowledge of moments one may predict these properties.

2

Photometric Study of Kepler Asteroseismic Targets

Molenda-Żakowicz J., Jerzykiewicz M., Frasca A.

Acta Astronomica

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2009

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Vol. 59, No. 2

213--237

EN

Reported are UBV and uvbyβ observations of 15 candidates for Kepler primary asteroseismic targets and 14 other stars in the Kepler field, carried out at the M.G. Fracastoro station of the Catania Astrophysical Observatory. These data serve to plot the 29 stars in two-parameter diagrams with the photometric indices (such as B-V or δm1) and the atmospheric parameters (such as the MK type or [Fe/H]) as coordinates. The two-parameter diagrams show no evidence of interstellar reddening. The photometric indices B-V and β are then used to derive photometric effective temperatures, Teff(B-V) and Teff(β). For Teff(B-V)>6400 K, the photometric effective temperatures turn out to be systematically higher than spectroscopic effective temperatures by 311±34 K and 346±91 K for Teff(B-V) and Teff(β), respectively. For Teff(B-V)<6250 K, the agreement between Teff(B-V) and the spectroscopic effective temperatures is very good. The photometric surface gravities, derived from c1 and β, show a range of about a factor of two greater than their spectroscopic counterparts do.

3

Galactic Fundamental Mode RRLyrae Stars. Period-Amplitude Diagram, Metallicities and Distribution

Szczygieł D. M., Pojmański G., Pilecki B.

Acta Astronomica

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2009

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Vol. 59, No. 2

137--167

EN

We have analyzed 1455 fundamental mode RR Lyr stars of the Galactic field, using the All Sky Automated Survey (ASAS) data. The sample covers 75% of the sky and contains objects in the close neighborhood of the Sun, within 4 kpc distance. Unlike in the previous analysis of the close field RRab stars, we see a clear manifestation of the Oosterhoff groups on the period-amplitude diagram. The relation for Oosterhoff I type variables becomes strongly flattened at large V amplitudes, which was not observed for globular cluster RR Lyr. We calculate photometric metallicities using two available methods: one of Jurcsik and Kovács (1996) and the other of Sandage (2004). We find significant discrepancies between results from both methods. Comparison with spectroscopic metallicities undoubtedly favors the method of Jurcsik and Kovács (1996). In addition, we notice that RRab stars of Oosterhoff II type might follow a different metallicity-period-phase relation than Oosterhoff I type variables. The spatial distribution of Galactic field RRab stars does not show any metallicity gradients with distance from the Galactic center in either of the Oosterhoff groups. However, both the older, metal poor Oosterhoff II variables and the metal rich Oosterhoff I RRab stars become more concentrated to the Galactic plane with increasing metal content.

4

Spectroscopic Study of Candidates for Kepler Asteroseismic Targets - Solar-Like Stars

Molenda-Żakowicz J., Frasca A., Latham D. W.

Acta Astronomica

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2008

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Vol. 58, No. 4

419--431

EN

We report spectroscopic observations of 23 candidates for Kepler asteroseismic targets and 10 other stars in the Kepler field. For all these stars, we derive the radial velocities, effective temperature, surface gravity, metallicity, the projected rotational velocity, and estimate the MK type. HIP 97513 and HIP 92132 are classified as suspected new single-lined spectroscopic binaries. For 28 stars, the radial velocity is measured for the first time.

5

Spectroscopic Study of Kepler Asteroseismic Targets

Molenda-Żakowicz J., Frasca A., Latham D. W., Jerzykiewicz M.

Acta Astronomica

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2007

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Vol. 57, No. 4

301--321

EN

Reported are spectroscopic observations of 15 candidates for Kepler primary asteroseismic targets and 14 other stars in the Kepler field, carried out at three observatories. For all these stars, the radial velocities, effective temperature, surface gravity, metallicity, and the projected rotational velocity are derived from two separate sets of data by means of two independent methods. In addition, MK type is estimated from one of these sets of data. Three stars, HIP 94335, HIP 94734, and HIP 94743, are found to have variable radial-velocity. For HIP 94335=FL Lyr, a well-known Algol-type eclipsing variable and a double-lined spectroscopic binary, the orbital elements computed from our data agree closely with those of Popper et al. For HIP 94734 and HIP 94743=V2077 Cyg, which we discover to be single-lined systems, orbital elements are derived. In addition, from our value of the orbital period and the Hipparcos epoch photometry, HIP 94743 is demonstrated to be a detached eclipsing binary.

6

Physical Parameters of Components in Close Binary Systems: VI

Gazeas K. D., Niarchos P. G., Zola S., Kreiner J. M., Rucinski S. M.

Acta Astronomica

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2006

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Vol. 56, No. 1

127--143

EN

New high-quality CCD photometric light curves for the W UMa-type systems V410 Aur, CK Boo, FP Boo, V921 Her, ET Leo, XZ Leo, V839 Oph, V2357 Oph, AQ Psc and VY Sex are presented. The new multicolor light curves, combined with the spectroscopic data recently obtained at David Dunlap Observatory, are analyzed with the Wilson-Devinney code to yield the physical parameters (masses, radii and luminosities) of the components. Our models for all ten systems resulted in a contact configuration. Four binaries (V921 Her, XZ Leo, V2357 Oph and VY Sex) have low, while two (V410 Aur and CK Boo) have high fill-out factors. FP Boo, ET Leo, V839 Oph and AQ Psc have medium values of the fill-out factor. Three of the systems (FP Boo, V921 Her and XZ Leo) have very bright primaries as a result of their high temperatures and large radii.

7

Frequency of Hot Jupiters and Very Hot Jupiters from the OGLE-III Transit Surveys toward the Galactic Bulge and Carina

Gould A., Dorscher S., Gaudi B. S., Udalski A.

Acta Astronomica

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2006

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Vol. 56, No. 1

1--50

EN

We derive the frequencies of hot Jupiters (HJs) with 3-5 day periods and very hot Jupiters (VHJs) with 1-3 day periods by comparing the planets actually detected in the OGLE-III survey with those predicted by our models. The models are constructed following Gould and Morgan (2003) by populating the line of sight with stars drawn from the Hipparcos Catalogue. Using these, we demonstrate that the number of stars with sensitivity to HJs and VHJs is only 5-16% of those in the OGLE-III fields satisfying the spectroscopic-follow-up limit of Vmax17.5 mag. Hence, the frequencies we derive are much higher than a naive estimate would indicate. We find that at 90% confidence the fraction of stars with planets in the two period ranges is (1/320)(1±[+1.37][-0.59]) for HJs and (1/710)(1±[+1.10][-0.54]) for VHJs. The HJ rate is statistically indistinguishable from that found in radial velocity (RV) studies. However, we note that magnitude-limited RV samples are heavily biased toward metal-rich (hence, planet-bearing) stars, while transit surveys are not, and therefore we expect that more sensitive transit surveys should find a deficit of HJs as compared to RV surveys. The detection of three transiting VHJs, all with periods less than 2 days, is marginally consistent with the complete absence of such detections in RV surveys. The planets detected are consistent with being uniformly distributed between 1.00 and 1.25 Jovian radii, but there are too few in the sample to map this distribution in detail.