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A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. VIII. NGC 6834

Jerzykiewicz M., Kopacki G., Pigulski A., Kołaczkowski Z., Kim S.-L.

Acta Astronomica

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2011

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Vol. 61, No. 3

247--273

EN

We present results of a CCD variability search in the field of the young open cluster NGC 6834. We discover 15 stars to be variable in light. The brightest, a multiperiodic γ Doradus-type variable is a foreground star. The eight fainter ones, including a γ Cassiopeiae-type variable, two λ Eridani-type variables, an ellipsoidal variable, an EB-type eclipsing binary, and three variable stars we could not classify, all have E(B-V) within proper range, thus fulfilling the necessary condition to be members. One of the three unclassified variables may be a non-member on account of its large angular distance from the center of the cluster. Four of the six faintest variable stars, which include two eclipsing binaries and two very red stars showing year-to-year variations, are certain non-members. One of the remaining two faintest variable stars, an EA-type eclipsing binary may be a member, while the faintest one, a W Ursae Majoris-type variable, is probably a non-member. For 6937 stars we provide the V magnitudes and V-IC color indices on the standard system. Because of nonuniform reddening over the cluster's face, a direct comparison of these data with theoretical isochrones is not possible. We therefore obtain E(B-V) from available UBV photometry, determine the lower and upper bound of E(B-V) for NGC 6834, and then fit properly reddened Padova isochrones to the data. Assuming HDE 332843, an early-F supergiant, to be a member we obtain log(age/yr)=7.70, V0-MV=12.10 mag. For 103 brightest stars in our field we obtained the α index, a measure of the equivalent widths of the Hα line. We find Hα emission in five stars, including the γ Cas-type variable and the two λ Eri-type variables.

2

The Period and the Cause of Variability of the Magnetic Ap Star V473 Tauri

Jerzykiewicz M.

Acta Astronomica

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2009

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Vol. 59, No. 3

307--323

EN

The ground based UBV observations and Hipparcos Hp magnitudes of this well known magnetic variable are analyzed. The period of the star's light variation is improved. The improved value, accounting for the available photometric data from the 1963-1964 Lowell observations of Rakosch to the 1990-1993 Hp magnitudes, is equal to 1.4068541±0.0000029 d. The effective temperature and bolometric correction are then derived from the de-reddened B-V color index and the star is plotted in the theoretical H-R diagram using the luminosity obtained from the Hipparcos parallax. Finally, the cause of variability of V473 Tau is discussed in terms of two propositions: (1) the oblique rotator model, and (2) pulsation in a high radial-order g-mode. Hitherto unpublished UBV photometry of V473 Tau is presented in the Appendix.

3

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.

4

δ Ceti from the Ground and from MOST

Jerzykiewicz M.

Acta Astronomica

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2007

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Vol. 57, No. 1

33--47

EN

Strömgren b-light curves of δ Cet, well known β Cep type star, obtained in 1990 December and 1991 January at SAAO and in 2003 October at Lowell are presented. The two epochs of maximum light, derived from these data, cannot be reconciled with the constant rate of secular period change found earlier. By a stroke of luck, the Lowell data were taken at the time when δ Cet was observed by MOST. A comparison of these two sets of data reveals discrepancies between the Lowell and MOST light curves, and between the MOST fluxes available on the net and the MOST magnitudes reported by Aerts et al. (2006). This had motivated us to reanalyze the MOST data. We find that the second strongest periodic signal in the MOST photometry of the star has frequency equal to the reciprocal of synodic month. We show further that the three lowest amplitude periodic terms derived by the above-mentioned authors and taken as a proof of multiperiodicity are significant only if one ignores the increase of the noise level toward lower frequencies, seen in the amplitude spectra of the MOST magnitudes. We conclude that the issue of multiperiodicity of δ Cet is debatable. We warn, therefore, that results of seismic modeling based on frequencies of these low amplitude terms, such as the core overshooting parameter or the inclination of the star's axis of rotation, should be treated with caution.

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

A CCD Search for Variable Stars of Spectral Type B in the Northern Hemisphere Open Clusters. V. NGC 2169

Jerzykiewicz M., Kopacki G., Molenda-Żakowicz J., Kołaczkowski Z.

Acta Astronomica

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2003

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Vol. 56, No. 2

151--165

EN

We present results of a search for variable stars in the field of the young open cluster NGC 2169. The General Catalogue of Variable Stars (GCVS, http://www.sai.msu.su/groups/cluster/gcvs/) lists four variable stars in the field we observed, viz., two β Cep stars, V 916 and V 917 Ori, an α2 CVn variable, V 1356 Ori, and an RRc variable, V 1154 Ori. We find V 916 and V 1154 Ori to be constant in light. We confirm the variability of V 917 Ori, but not the period given in GCVS. For the chemically peculiar A0 V Si star V 1356 Ori we definitely establish the period of 1.565 d, thus settling the uncertainty persisting in the literature since the star was discovered to be variable. In addition, we find two other stars to be variable in light. Both show irregular variations. For V 917 Ori, one of the two GCVS &beta Cep variables, we determine a period of 0.267 d (frequency 3.7477 d-1). However, prewhitening with this period leaves a significant amount of the star's light-variation unaccounted for. Since the star shows emission at Hα, we hypothesize that the unaccounted for variation is caused by an erratic, Be-type activity. As to the periodic term, we consider three hypotheses: (1) β Cep-type pulsation, (2) rotational modulation of the λ Eri type, and (3) ellipsoidal variation due to distorted primary component in a close binary system. After deriving the star's effective temperature from Strömgren indices and the luminosity from the distance modulus of the cluster, we show that while the third hypothesis is untenable, the first two should be retained. However, neither is entirely satisfactory. For a number of stars we provide the V magnitudes. For 14 brightest stars in our field we also obtain the photometric α-index, a measure of the Hα equivalent width. From the α index, we detect mild emission at Hα in two stars, V 917 Ori and NGC 2169-8.

7

Eclipsing Binaries and the Lutz-Kelker Bias

Jerzykiewicz M.

Acta Astronomica

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2001

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Vol. 51, No. 2

151--158

EN

Using examples from the literature, we demonstrate that ignoring the Lutz-Kelker bias may degrade agreement between results derived from eclipsing binaries and those based on trigonometric parallaxes. In addition, we show that eclipsing binaries are excellent standard candles.

8

Empirical Luminosities and Radii of Early-Type Stars after Hipparcos

Jerzykiewicz M., Molenda-Żakowicz J.

Acta Astronomica

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2000

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Vol. 50, No. 3

369--380

EN

Using Hipparcos parallaxes we derive empirical luminosities and radii of the early-type stars for which the effective temperatures are known from directly measured angular diameters and total absolute fluxes. The empirical luminosities allow a direct comparison of the position of these stars in the fundamental HR diagram with evolutionary tracks. The comparison shows an overall agreement with the Y=0.30 and Z=0.02 tracks computed with OPAL opacities and moderate amount of overshooting from the convective core. In addition, we present evidence that systematic errors of the masses read off the evolutionary tracks are below 10%. Consequently, the surface gravities obtained from these "evolutionary" masses and the empirical radii are very nearly model-independent. Spectrographic and photometric observations of these stars can therefore be used for verifying model atmospheres and calibrating photometric log g indices.

9

Kompleksy beta-diketonianowe metali w porostach i ich reakcja z ditlenkiem azotu. Badania powstających rodników iminoksylowych metodą EPR.

Jezierski A., Bylińska E., Czechowski F., Jerzykiewicz M.

Chemia i Inżynieria Ekologiczna

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1999

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Vol. 6, nr 5-6

445-452

PL

Badano oddziaływanie [wzór] z plechami porostów. Metodą elektronowego rezonansu paramagnetycznego (EPR) stwierdzono powstanie rodników iminoksylowych o wzorze [wzór]; warunkiem powstania rodników tego typu jest obecność beta-diketonów lub innych związków z aktywną grupą metylenową, i/albo beta-diketonianowych kompleksów metali d-elektronowych. Reakcji tej sprzyjają ogólne zniszczenia wolnorodnikowe materiału. Jeśli wyrazem owych zniszczeń w plechach porostów jest, jak udowodniono uprzednio, istnienie dużych stężeń rodników typu semichinonowego, to również wydajność tworzenia się rodników iminoksylowych może być miarą ogólnego stanu środowiska, stwierdza się bowiem liniową korelację między stężeniem rodników semichininowych a wydajnością tworzenia rodników iminoksylowych pod wpływem reakcji z [wzór]. Stężenia rodników iminoksylowych generowanych w materiale pochodzenia roślinnego nie przekraczają milionowych części mola; spektroskopia EPR okazuje sie zatem bardzo czułą , aczkolwiek pośrednią metodą wykrywania związków beta-diketonowych w materiałach naturalnych.

EN

Interaction of [formula] with lichen thalli was investigated. On the basis of electron paramagnetic resonance spectroscopy (EPR) the formed iminoxy radicals of formula [formula] were detected and characterised. These radicals are synthetised when beta-diketones (or similar compounds with active methylene group) and/or metal diketonate complexes are present in the investigated materials. The reaction seems to be effective in the case of the high radical destruction of the material. On the basis of previous investigations the concentration of the semiquinone radicals in lichen thalli may be used as a measure of the environmental damage factors. The linear dependance between the concentration of the semiquinone radicals and concentrations of formed iminoxyls is observed; thus, the concentration of the iminoxyls may be used as a measure of the destructive processes in the environment. Concentrations of the iminoxyls in the lichen thalli not exceed several ppm; EPR method detecting the iminoxyls formed during reaction of beta-diketone compounds with [formula] is a sensitive analytical tool for assessment of the beta-diketones present in the lichen thalli and other natural materials.