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1

Does the A-type Metallic-Line Star IW Persei Have Non-Uniform Chemical Anomaly on the Surface?

Takeda Y.

Acta Astronomica

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2023

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Vol. 73, No. 1

35--55

EN

IW Per, a single-lined spectroscopic binary with a short period of 0.92 d, is known to be a A-type metallic-line (Am) star showing anomalous line strengths of specific elements. It was previously reported that its equivalent widths of CaII 3934, SrII 4215, and ScII 4320 lines (important key lines characterizing the Am anomaly) show cyclic variations in accordance with the rotation phase, implying that the chemical peculiarities on the surface are not uniform but of rather patchy distribution. However, no attempts of reconfirmation have been done so far. In order to check the validity of this finding, ten high-dispersion spectra of IW Per covering different phases were analyzed for these lines by using the spectrum-fitting technique to determine the abundances of Ca, Sr, and Sc and the corresponding equivalent widths. It turned out, however, that no firm evidence of such phase-dependent line-strength variations could be found, suggesting that significant chemical inhomogeneity on the surface of IW Per is unlikely to exist, at least during the period of our observations (2010 December). Meanwhile, the abundances of O, Si, Ca, Ba, and Fe resulting from the 6130-6180 Å region corroborate that IW Per is a distinct Am star (though the degree of peculiarity differs from element to element) despite that its rotational velocity (≈100 km/s) is near to the limit of Am phenomenon.

2

Hen 3-160 - the First Symbiotic Binary with Mira Variable S Star

Gałan C., Mikołajewska J., Monard B., Iłkiewicz K., Pieńkowski D., Gromadzki M.

Acta Astronomica

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2019

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Vol. 69, No. 1

25--44

EN

Hen 3-160 is reported in Belczyński et al. catalog as a symbiotic binary system with M7 giant donor. Using V- and I-band photometry collected over 20 years we have found that the giant is a Mira variable pulsating with 242.5-day period. The period-luminosity relation locates Hen 3-160 at the distance of about 9.4 kpc, and its Galactic coordinates (l=267.°7, b=-7.°9) place it ≈1.3 kpc above the disk. This position combined with relatively high proper motions (μαcosδ=-1.5 mas/yr, μ_δ=+2.9 mas/yr, Gaia DR2) indicates that Hen 3-160 has to be a Galactic extended thick-disk object. Our red optical and infrared spectra show the presence of ZrO and YO molecular bands that appear relatively strong compared to the TiO bands. Here we propose that the giant in this system is intrinsic S star, enriched in products of slow neutron capture processes occurring in its interior during an AGB phase which would make Hen 3-160 the first symbiotic system with Mira variable S star.

3

Metallicity Estimates for Double-Mode Cepheids from Photometry

Szilàdi K., Vinkò J., Szabados L.

Acta Astronomica

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2018

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Vol. 68, No. 2

111--123

EN

We investigate the effect of different metallicities on the light curve shape of classical double-mode (beat) Cepheids pulsating in the fundamental and first overtone modes by correlating the light curve Fourier parameters with [Fe/H] ratios. We combine data of known Galactic beat Cepheids with those from both Magellanic Clouds assembled by the OGLE-III and OGLE-IV surveys. The [Fe/H] values for the Galactic sample are based on recent high-resolution spectroscopy. For the Magellanic sample we apply the metallicity-period-period ratio relationship to estimate individual [Fe/H] values. We confirm that the metallicity is most strongly correlated with the amplitude of the light curve and the amplitude ratio of the first and second harmonics (R21), similar to single-mode classical Cepheids found by Klagyivik. We also show that the metallicity is less correlated with φ31 parameter in our sample, as compared with the case of the RR Lyr type variables. We derive empirical formulae that can be used to estimate the [Fe/H] of classical Cepheids that extends well below the metallicity of the Milky Way disk, down to the lower metallicities of the Magellanic Clouds.

4

OGLE-ing the Magellanic System: Photometric Metallicity from Fundamental Mode RR Lyrae Stars

Skowron D. M., Soszyński I., Udalski A., Szymański M. K., Pietrukowicz P., Skowron J., Poleski J., Wyrzykowski Ł., Ulaczyk K., Kozłowski S., Mróz P., Pawlak M.

Acta Astronomica

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2016

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Vol. 66, No. 3

269--292

EN

In an era of extensive photometric observations, the catalogs of RR Lyr type variable stars number tens of thousands of objects. The relation between the iron abundance [Fe/H] and the Fourier parameters of the stars light curve allows us to investigate mean metallicities and metallicity gradients in various stellar environments, independently of time-consuming spectroscopic observations. In this paper we use almost 6500 V- and I-band light curves of fundamental mode RR Lyr stars from the OGLE-IV survey to provide a relation between the V- and I-band phase parameter ϕ31 used to estimate [Fe/H]. The relation depends on metallicity, which limits its applicability. We apply this relation to metallicity formulae developed for the Johnson V- and the Kepler Kp-band to obtain the relation between [Fe/H] and ϕ31 for the I-band photometry. Last, we apply the new relation of Nemec to the OGLE-IV fundamental mode RR Lyr stars data and construct a metallicity map of the Magellanic Clouds. Median [Fe/H] is -1.39±0.44 dex for the LMC and -1.77±0.48 dex for the SMC, on the Jurcsik metallicity scale. We also find a metallicity gradient within the LMC with a slope of -0.029±0.002 dex/kpc in the inner 5 kpc and -0.030±0.003 dex/kpc beyond 8 kpc, and no gradient in-between (-0.019±0.002 dex/kpc integrally). We do not observe a metallicity gradient in the SMC, although we show that the metal-rich RRab stars are more concentrated toward the SMC center than the metal-poor.

5

Principal Component Abundance Analysis of Microlensed Bulge Dwarf and Subgiant Stars

Andrews B. H., Weinberg D. H., Johnson J. A., Bensby T., Feltzing S.

Acta Astronomica

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2012

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Vol. 62, No. 3

269--279

EN

Elemental abundance patterns can provide vital clues to the formation and enrichment history of a stellar population. Here we present an investigation of the Galactic bulge, where we apply principal component abundance analysis (PCAA) - a principal component decomposition of relative abundances [X/Fe] - to a sample of 35 microlensed bulge dwarf and subgiant stars, characterizing their distribution in the 12-dimensional space defined by their measured elemental abundances. The first principal component PC1, which suffices to describe the abundance patterns of most stars in the sample, shows a strong contribution from α-elements, reflecting the relative contributions of Type II and Type Ia supernovae. The second principal component PC2 is characterized by a Na-Ni correlation, the likely product of metallicity-dependent Type II supernova yields. The distribution in PC1 is bimodal, showing that the bimodality previously found in the [Fe/H] values of these stars is robustly and independently recovered by looking at only their relative abundance patterns. The two metal-rich stars that are α-enhanced have outlier values of PC2 and PC3, respectively, further evidence that they have distinctive enrichment histories. Applying PCAA to a sample of local thin and thick disk dwarfs yields a nearly identical PC1. In PC1, the metal-rich and metal-poor bulge dwarfs track kinematically selected thin and thick disk dwarfs, respectively, suggesting broadly similar α-enrichment histories. However, the disk PC2 is dominated by a Y-Ba correlation, likely indicating a contribution of s-process enrichment from long-lived asymptotic giant branch stars that is absent from the bulge PC2 because of its rapid formation.

6

Oxygen Issue in Core Collapse Supernovae

Elmhamdi A.

Acta Astronomica

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2011

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Vol. 61, No. 2

179--198

EN

We study the spectroscopic properties of a selected sample of 26 events within Core Collapse Supernovae (CCSNe) family. Special attention is paid to the nebular oxygen forbidden line [OI] 6300, 6364 Å doublet. We analyze the line flux ratio F6300/F6364 and infer information about the optical depth evolution, densities, volume-filling factors in the oxygen emitting zones. The line luminosity is measured for the sample events and its evolution is discussed on the basis of the bolometric light curve properties in type II and in type Ib-c SNe. The luminosities are then translated into oxygen abundances using two different methods. The results are combined with the determined 56Ni masses and compared with theoretical models by means of the [O/Fe] vs. Mms diagram. Two distinguishable and continuous populations, corresponding to Ib-c and type II SNe, are found. The higher mass nature of the ejecta in type II objects is also imprinted in the [CaII] 7291, 7324Å to [OI] 6300, 6364Å luminosity ratios. Our results may be used as input parameters for theoretical models studying the chemical enrichment of galaxies.

7

Metallicity Dependence of the Blazhko Effect

Smolec R.

Acta Astronomica

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2005

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Vol. 55, No. 1

59--84

EN

The microlensing surveys, such as OGLE or MACHO, have led to the discovery of thousands of RR Lyr stars in the Galactic bulge and in the Magellanic Clouds, allowing for detailed investigation of these stars, especially the still mysterious Blazhko phenomenon. Higher incidence rate of Blazhko (BL) variables in the more metal-rich Galactic bulge than in the LMC, suggests that occurrence of Blazhko effect correlates with metallicity. To investigate this problem, we calibrate the photometric method of determining the metallicity of RRab stars in the I-band and apply it to the OGLE Galactic bulge and LMC data. In both systems, metallicities of non Blazhko and Blazhko variables are close to each other. The LMC Blazhko pulsators prefer slightly lower metallicities. The different metallicities of the Galactic bulge and the LMC, cannot explain the observed incidence rates. As a by-product of our metallicity estimates, we investigate the luminosity--metallicity relation, finding a steep dependence of the luminosity on [Fe/H].

8

Metal Abundance of Red Clump Stars in Baade's Window

Kubiak M., McWilliam A., Udalski A., Górski K.

Acta Astronomica

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2002

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Vol. 52, No. 2

159--175

EN

Thirteen red clump stars from Baade's window were observed with high resolution in the red part of the optical spectrum with the UVES echelle spectrograph at the Mount Paranal ESO Observatory. The model atmosphere abundance analysis placed their [Fe/H] values in a range from 0.0 to -1.52 dex. Present results, based on direct measurements of iron abundance, confirm former suggestions that the I-band brightness of the red clump giants only weakly depends on [Fe/H]. The determined values of [Fe/H] may contain a slight systematic error connected with still now unexplained difference in colors between stars in the Galactic bulge and in the solar vicinity.

9

Petersen Diagram for RRd Stars in the Magellanic Clouds

Popielski B. L., Dziembowski W. A., Cassisi S.

Acta Astronomica

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2000

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Vol. 50, No. 4

491--507

EN

RRd stars from the Magellanic Clouds form a well-defined band in the Petersen diagram. We explain this observed band with our evolutionary and pulsation calculations with assumed metallicity [Fe/H]=(-2,-1.3). Vast majority of RRd stars from LMC is confined to a narrower range of (-1.7,-1.3). The width of the band, at specified fundamental mode period, may be explained by mass spread at given metallicity. The shape of the band reflects the path of RRd stars within the RR Lyr instability strip. We regard the success in explaining the Petersen diagram as a support for our evolutionary models, which yield mean absolute magnitude in the mid of the instability strip, ⟨MV⟩, in the range 0.4 to 0.65 mag implying distance modulus to the LMC of 18.4 mag.

10

The Optical Gravitational Lensing Experiment. UBVI Photometry of Stars in Baade's Window

Paczyński B., Udalski A., Szymański M., Kubiak M., Pietrzyński G., Soszyński I., Woźniak P., Żebruń K.

Acta Astronomica

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1999

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Vol. 49, No. 3

319--339

EN

We present UBVI photometry for 8530 stars in Baade's Window obtained during the OGLE-II microlensing survey. Among these are over one thousand red clump giants. 1391 of them have photometry with errors smaller than 0.04, 0.06, 0.12, and 0.20 mag in the I, V, B, and U-band, respectively. We constructed a map of interstellar reddening. The corrected colors of the red clump giants: (U-B)0, (B-V)0, and (V-I)0 are very well correlated, indicating that a single parameter determines the observed spread of their values, reaching almost 2 mag in the (U-B)0. It seems most likely that heavy element content is the dominant parameter, but it is possible that another parameter: the age (or mass) of a star moves it along the same trajectory in the color-color diagram as the metallicity. The current ambiguity can be resolved with spectral analysis, and our catalog may be useful as a finding list of red clump giants. We point out that these K giants are more suitable for a fair determination of the distribution of metallicity than brighter M giants. We also present a compilation of UBVI data for 308 red clump giants near the Sun, for which Hipparcos parallaxes are more accurate than 10%. Spectral analysis of their metallicity may provide information about the local metallicity distribution as well as the extent to which mass (age) of these stars affects their colors. It is remarkable that in spite of a number of problems, stellar models agree with observations at the 0.1-0.2 mag level, making red clump giants not only the best calibrated but also the best understood standard candle.

11

Metallicity of Red Clump Giants in Baade's Window

Paczyński B.

Acta Astronomica

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1998

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Vol. 48, No. 3

405--412

EN

The red clump giants are potentially very useful as standard candles. There is some controversy about the stability of their I-band absolute magnitude, but it does not seem to be serious. No controversy was anticipated about their colors, with metal rich giants expected to be redder and cooler than the metal poor giants. The purpose of this paper is to point out that no such correlation is apparent between [Fe/H] and Teff as determined with Washington CCD photometry for the giants in Baade's Window. No explanation is offered for this surprising result. It is also unknown why the Galactic bulge red clump giants are redder than the clump giants near the Sun by 0.2 mag in the (V-I)0 color.