Browsing by Author "Prudil, Z."

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    Humps and bumps: the effects of shocks on the optical light curves of fundamental-mode RR Lyrae stars
    (EDP SCIENCES S A, 2020) Prudil, Z.; Dekany, I.; Smolec, R.; Catelan, M.; Grebel, E. K.; Kunder, A.
    We present the most extended and homogeneous study carried out so far of the main and early shocks in 1485 RR Lyrae stars in the Galactic bulge observed by the Optical Gravitational Lensing Experiment. We selected nonmodulated fundamental-mode RR Lyrae stars with good-quality photometry. Using a self-developed method, we determined the centers and strengths of main and early shock features in the phased light curves. We found that the positions of both humps and bumps are highly correlated with the pulsation properties of the studied variables. Pulsators with a pronounced main shock are concentrated in the low-amplitude regime of the period-amplitude diagram, while stars with a strong early shock have average and above-average pulsation amplitudes. A connection between the main and early shocks and the Fourier coefficients is also observed. In the color-magnitude diagram, we see a separation between stars with strong and weak shocks. Variables with a pronounced main shock cluster close to the fundamental red edge of the instability strip (IS), while stars with a strong early shock tend to clump in the center and near the fundamental blue edge of the IS. The appearance of shocks and their properties appear to be independent of the direction of evolution estimated from the period change rate of the studied stars. In addition, the differences in the period change rate between the two main Oosterhoff groups found in the Galactic bulge suggest that stars of Oosterhoff type I are located close to the zero-age horizontal branch while Oosterhoff type II variables are on their way toward the fundamental red edge of the instability strip, and have therefore already left the zero-age horizontal branch.
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    Main and Early Shocks in RR Lyrae Photometric Light Curves
    (2021) Prudil, Z.; Smolec, R.; Catelan, Márcio; Dékány, I.; Grebel, E. K.; Kunder, A.
    We explore the effect of the main and early shocks (giving rise to the so-called hump and bump features in the light curves, respectively) on the pulsation properties of non-modulated fundamental mode RR Lyrae stars. We utilized I-band photometry from the fourth release of the Optical Gravitational Lensing Experiment (OGLE). We determined the centers and strengths of humps and bumps in the phased light curves of the studied stars. The positions of both shock events in the phased light curves are highly correlated with the amplitudes, pulsation periods, and Fourier coefficients. RR Lyrae stars with prominent humps are located at the low-amplitude regime of the Bailey diagram, while variables with pronounced bumps have average and above average amplitudes. RR Lyrae stars close to the red edge of the instability strip have pronounced humps, while variables with a strong bump are located at the center and close to the blue edge of the instability strip. In general, the effect of the main and early shocks provides a new view on the period-amplitude distribution of fundamental mode RR Lyrae stars....
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    On the Oosterhoff dichotomy in the Galactic bulge - II. Kinematical distribution
    (2019) Prudil, Z.; Dekany, Istvan; Grebel, E.K.; Catelan, Márcio; Skarka, M.; Smolec, R.
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    On the Oosterhoff dichotomy in the Galactic bulge : I. Spatial distribution
    (2019) Prudil, Z.; Dekany, Istvan; Catelan, Márcio; Smolec, R.; Grebel, E.K.; Skarka, M.
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    On the Use of Field RR Lyrae as Galactic Probes. II. A New ΔS Calibration to Estimate Their Metallicity*
    (2021) Crestani, J.; Fabrizio, M.; Braga, V. F.; Sneden, C.; Preston, G.; Ferraro, I.; Iannicola, G.; Bono, G.; Alves-Brito, A.; Nonino, M.; D'Orazi, V.; Inno, L.; Monelli, M.; Storm, J.; Altavilla, G.; Chaboyer, B.; Dall'Ora, M.; Fiorentino, G.; Gilligan, C.; Grebel, E. K.; Lala, H.; Lemasle, B.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C. E.; Matsunaga, N.; Mullen, J. P.; Neeley, J.; Prudil, Z.; da Silva, R.; Stetson, P. B.; Thevenin, F.; Valenti, E.; Walker, A.; Zoccali, M.
    We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured 6300 high-resolution (HR, R similar to 35,000) spectra for 143 RRLs (111 fundamental, RRab; 32 first-overtone, RRc). The atmospheric parameters were estimated by using the traditional approach and the iron abundances were measured by using an LTE line analysis. The resulting iron distribution shows a well-defined metal-rich tail approaching solar iron abundance. This suggests that field RRLs experienced a complex chemical enrichment in the early halo formation. We used these data to develop a new calibration of the Delta S method. This diagnostic, based on the equivalent widths of Ca ii K and three Balmer (H-delta,H-gamma,H-beta) lines, traces the metallicity of RRLs. For the first time, the new empirical calibration: (i) includes spectra collected over the entire pulsation cycle; (ii) includes RRc variables; (iii) relies on spectroscopic calibrators covering more than three dex in iron abundance; and (iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to a data set of both SEGUE-SDSS and degraded HR spectra totalling 6451 low-resolution (R similar to 2000) spectra for 5001 RRLs (3439 RRab, 1562 RRc). This resulted in an iron distribution with a median eta = -1.55 0.01 and sigma = 0.51 dex, in good agreement with literature values. We also found that RRc are 0.10 dex more metal-poor than RRab variables, and have a distribution with a smoother metal-poor tail. This finding supports theoretical prescriptions suggesting a steady decrease in the RRc number when moving from metal-poor to metal-rich stellar environments.
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    On the Use of Field RR Lyrae as Galactic Probes. III. The α-element Abundances*
    (2021) Crestani, J.; Braga, V. F.; Fabrizio, M.; Bono, G.; Sneden, C.; Preston, G.; Ferraro, I.; Iannicola, G.; Nonino, M.; Fiorentino, G.; Thevenin, F.; Lemasle, B.; Prudil, Z.; Alves-Brito, A.; Altavilla, G.; Chaboyer, B.; Dall'Ora, M.; D'Orazi, V.; Gilligan, C.; Grebel, E. K.; Koch-Hansen, A. J.; Lala, H.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C.; Matsunaga, N.; Monelli, M.; Mullen, J. P.; Neeley, J.; da Silva, R.; Stetson, P. B.; Salaris, M.; Storm, J.; Valenti, E.; Zoccali, M.
    We provide the largest and most homogeneous sample of alpha-element (Mg, Ca, Ti) and iron abundances for field RR Lyrae (RRLs; 162 variables) by using high-resolution spectra. The current measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample of old (t >= 10 Gyr), low-mass stellar tracers (208 RRLs: 169 fundamental, 38 first overtone, and 1 mixed mode) covering 3 dex in iron abundance (-3.00 <= [Fe/H] <= 0.24). We found that field RRLs are similar to 0.3 dex more alpha poor than typical halo tracers in the metal-rich regime ([Fe/H] >= -1.2), while in the metal-poor regime ([Fe/H] <= -2.2) they seem to be on average similar to 0.1 dex more alpha enhanced. This is the first time that the depletion in alpha elements for solar iron abundances is detected on the basis of a large, homogeneous, and coeval sample of old stellar tracers. Interestingly, we also detected a close similarity in the [alpha/Fe] trend between alpha-poor, metal-rich RRLs and red giants (RGs) in the Sagittarius dwarf galaxy as well as between alpha-enhanced, metal-poor RRLs and RGs in ultrafaint dwarf galaxies. These results are supported by similar elemental abundances for 46 field horizontal branch stars. These stars share with RRLs the same evolutionary phase and the same progenitors. This evidence further supports the key role that old stellar tracers play in constraining the early chemical enrichment of the halo and, in particular, in investigating the impact that dwarf galaxies have had in the mass assembly of the Galaxy.
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    On the Use of Field RR Lyrae as Galactic Probes. V. Optical and Radial Velocity Curve Templates
    (2021) Braga, V. F.; Crestani, J.; Fabrizio, M.; Bono, G.; Sneden, C.; Preston, G. W.; Storm, J.; Kamann, S.; Latour, M.; Lala, H.; Lemasle, B.; Prudil, Z.; Altavilla, G.; Chaboyer, B.; Dall'Ora, M.; Ferraro, I; Gilligan, C. K.; Fiorentino, G.; Iannicola, G.; Inno, L.; Kwak, S.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C. E.; Monelli, M.; Mullen, J. P.; Matsunaga, N.; Neeley, J.; Stetson, P. B.; Valenti, E.; Zoccali, M.
    We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including approximate to 20,000 high-, medium-, and low-resolution spectra for approximate to 10,000 RRLs. We provide the analytical forms of radial velocity curve (RVC) templates. These were built using 36 RRLs (31 fundamental-split into three period bins-and five first-overtone pulsators) with well-sampled RVCs based on three groups of metallic lines (Fe, Mg, Na) and four Balmer lines (H- alpha , H- beta , H- gamma , H- delta ). We tackled the long-standing problem of the reference epoch to anchor light-curve and RVC templates. For the V-band, we found that the residuals of the templates anchored to the phase of the mean magnitude along the rising branch are similar to 35% to similar to 45% smaller than those anchored to the phase of maximum light. For the RVC, we used two independent reference epochs for metallic and Balmer lines and we verified that the residuals of the RVC templates anchored to the phase of mean RV are from 30% (metallic lines) up to 45% (Balmer lines) smaller than those anchored to the phase of minimum RV. We validated our RVC templates by using both the single-point and the three phase point approaches. We found that barycentric velocities based on our RVC templates are two to three times more accurate than those available in the literature. We applied the current RVC templates to Balmer lines RVs of RRLs in the globular NGC 3201 collected with MUSE at VLT. We found the cluster barycentric RV of V ( gamma ) = 496.89 +/- 8.37(error) +/- 3.43 (standard deviation) km s(-1), which agrees well with literature estimates.
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    Spatial and Kinematical Study of the Oosterhoff Dichotomy in the Galactic Bulge
    (2020) Prudil, Z.; Dékány, I.; Catelan, Marcio; Grebel, E. K.; Smolec, R.; Skarka, M.
    We present results of spatial and kinematical studies on the Oosterhoff dichotomy in the Galactic bulge based on data from the fourth data release of the Optical Gravitational Lensing Experiment (OGLE). The Oosterhoff groups I and II were separated by conventional augmenting techniques as well as by using a dimensionality reduction machine learning algorithm accompanied by a clustering algorithm. We find, as also seen in globular clusters, that the Oosterhoff II RR Lyrae stars are on the average cooler, more metal-poor, and more massive than RR Lyrae variables associated with the Oosterhoff I group. In addition, neither group seems to be spatially associated with the Galactic bar. For a fraction of our sample, we were able to obtain a 6D kinematical solution, and for these stars, the two Oosterhoff groups do not show a systematic difference in their space velocity distribution. Based on their orbits we estimate that 8 % of the bulge RR Lyrae stars are halo interlopers, and the majority of the studied stars are well confined within the Galactic bulge....