Blazhko type fundamental-mode RR Lyrae stars in the globular cluster, M3

Blazhko stars from the extended $BVI_{\mathrm C}$ time series of RRab stars in the globular cluster, M3, are analysed. This is the largest sample of Blazhko stars with full details of their Blazhko properties in a homogeneous stellar system. Blazhko periods and light-curve solutions are determined/estimated for 83 fundamental-mode variables. The lack of phase modulation in Oosterhoff-type~II stars and the diminishing relative strength of the modulation in long-period Oosterhoff-type~I stars are the regular tendencies found between the pulsation and modulation properties of Blazko stars. Similarly to previous results, no modulation of the longest-period stars is detected. The onset of the modulation in a previously regular RRab star, and the similar distribution of modulated and non-modulated stars imply that the modulation is a temporal property of RRL stars, which may occur at any time in any RRab star except the coolest ones. Comparing the modulation periods in M3 and in other samples of Blazhko stars, the mean log$(P_{\mathrm {mod}})$ value is found to depend on the metallicity of the system. The separation of the temperature- and radius-change induced variations supports our previous finding that the photometric radius variation does not show any modulation. The pulsation-averaged mean brightness and temperature of Blazhko stars are found to be larger in the large-amplitude phase of the modulation than in the small-amplitude phase. The larger the amplitude of the modulation, the larger changes of the mean parameters are detected.Comment: 18 pages, 12 figures Accepted for publication in MNRA

Spatial metallicity asymmetry in ω\omega Centauri

The compilation of the metallicity values of $\omega$~Centauri stars led to detection of spatial asymmetry in the metallicity distribution of the bright giants. It was found that the most and least metal-poor objects are separated along galactic latitude. Statistical tests show that the chance occurrence of the phenomenon is very low. The subgiant and the RR~Lyrae samples do not show, however, similar segregation of the different metallicity objects. The physical parameters of the variables calculated by using empirical formulae indicate that the bulk of the RRab stars comprises a very homogeneous group regarding both their metallicity and mass values. These stars are most probably already in the evolved stage of their horizontal branch evolution.Comment: 9 pages, 4 Postscript figures, accepted for publication in ApJ Letter

RRab variables with identical light-curve shapes at different pulsation periods

In this paper, we report on the detection of RRab stars with quasi-identical-shape light curves but period differences as large as $0.05-0.21$ d using the Galactic bulge data of the OGLE-IV survey. We have examined stars with shorter periods than the Oosterhoff~I ridge of the bulge. These stars generally have smaller amplitudes and larger Fourier phase-differences than the typical bulge RRab stars have at the same period. Many of these "anomalous" stars have good-quality light curves without any sign of the Blazhko modulation. Examining their Fourier parameters revealed that several of these stars show very similar light-curve to the typical bulge RR Lyrae. We found hundreds of quasi-identical-shape light-curve pairs with different periods between the "anomalous"- and the "normal"-position RRab stars based on the OGLE $I$-band data. The OGLE $V$-band, and the archive VVV and MACHO surveys $K_s$-, $b$- and $r$-band data of these stars were also checked for light-curve-shape similarity. Finally, 149 pairs with identical-shape light curves in each available photometric band were identified. Calculating the physical properties of the variables using empirical formulae, on average, $-0.5$~dex, $-0.13$~mag, 0.67, and 165~K differences between the [Fe/H], $M_V$, $R/R_\odot$, and $T_{\mathrm{eff}}$ values of the members of the pairs are derived, being the short-period stars less metal-poor, fainter, smaller and hotter than the long-period variables. To explain the existence of variables with different physical properties and pulsation periods but with identical-shape light curves is a challenging task for modelling.Comment: 11 pages, 8 figures, accepted for publication in MNRA

Photometric metallicities of fundamental-mode RR Lyr stars from Gaia GG-band photometry of globular-cluster variables

Photometric metallicity formulae of fundamental-mode RR Lyr (RRab) stars are presented using globular-cluster data exclusively. The aim is to check whether this selection may help increasing the overall accuracy of the fits and eliminating the systematic bias of the photometric results, namely that they tend to overestimate [Fe/H] of the most metal-poor variables. The $G$-band time-series data available in the Gaia DR3 archive and a new compilation of the published spectroscopic globular cluster [Fe/H] values on a uniform solar reference metallicity scale are utilized. We have derived a new ${\mathrm{[Fe/H]}}_{\mathrm{phot}}- P,\varphi_{31}$ formula, and have diagnosed that no significant increase in the accuracy of the fit can be achieved using non-linear or multi-parameter formulae. The best result is obtained when different formulae are applied for variables with Oosterhoff-type I and II properties. However, even this solution cannot eliminate the systematic bias of the results completely. This separation of the variables has also led to the conclusion that the photometric estimates of the [Fe/H] are less reliable for the Oo-type II variables than for the Oo-type I sample. Published ${\mathrm{[Fe/H]}}_{\mathrm{phot}}$ values and the results of the available photometric formulae in the Gaia $G$-band are compared with the present results. It is found that each of the solutions yields very similar results, with similar accuracy and systematic biases. Major differences are detected only in the zero-points of the [Fe/H] scales, and these offsets are larger than differences in the accepted solar reference values would explain.Comment: MNRAS, accepte

Toward more accurate RR Lyrae metallicities

By using a large sample of published spectroscopic iron abundances, we point out the importance of gravity correction in deriving more accurate metal abundances for RR Lyrae stars. For the 197 stars with multiple spectra we find overall [Fe/H] standard deviations of 0.167 (as published), 0.145 (shifted by data source zero points) and 0.121 (both zero point-shifted and gravity-corrected). These improvements are significant at the ~2 sigma level at each correction step, leading to a clearly significant improvement after both corrections applied. The higher quality of the gravity-corrected metallicities is strongly supported also by the tighter correlation with the metallicities predicted from the period and Fourier phase phi_31. This work underlines the need for using some external estimates of the temporal gravity in the chemical abundance analysis rather than relying on a full-fetched spectrum fit that leads to large correlated errors in the estimated parameters.Comment: Submitted to A&A. After the 2nd (less negative/almost positive) referee report. 1.2Mb, 10 pages (7+3 with appendices). Aesthetic old-fashioned references with clickable ADS link

The Remarkable Evolution of the Post-AGB Star FG Sge

FG Sagittae is one of the most important key objects for post-AGB stellar evolut ionary studies. As a consequence of a final helium shell flash, this unique vari able has shown real evolutionary changes on human timescales during this century . The recently observed variations in the emission lines of the surrounding old planetary nebula prove that there is no hot exciting object hidden inside the ne bula, thus there is only one central star, namely FG Sge itself. Consequently, w e are witnessing the rapid evolution of a single star. Turning to an R CrB type variable in the early 90s, FG Sge also solved the question of the evolutionary s tate of this type of stars. Some aspects of the observational history of FG Sge are reviewed in this paper a nd compared with predictions from model calculation results

New Galactic multi-mode Cepheids from the ASAS-SN Survey

A systematic search for multi-mode Cepheids using the database of the ASAS-SN survey has led to the detection of thirteen new double-mode and two triple-mode Cepheids in the Galactic disk. These discoveries have increased the number of Galactic disk multi-mode Cepheids by 33%. One of the new triple-mode variables pulsates simultaneously in the fundamental and in the first and the second radial overtone modes and the other in the first three radial overtone modes. Overtone triple-mode Cepheids were identified only in the Galactic bulge and in the Large and Small Magellanic Clouds previously.Comment: Accepted for publication in Acta Astronomica; 10 pages, 2 figures, 3 tables; v2: corrected minor typos and added clarification about the ASAS-SN classification probability parameter

Blazhko-type fundamental-mode RR Lyrae stars in the globular cluster M3

Blazhko stars from the extended BVIC time series of RRab stars in the globular cluster M3 are analysed. This is the larges sample of Blazhko stars with full details of their Blazhko properties i a homogeneous stellar system. Blazhko periods and light-curve solution are determined/estimated for 83 fundamental-mode variables. The lack o phase modulation in Oosterhoff type II stars and the diminishin relative strength of the modulation in long-period Oosterhoff type stars are regular tendencies found between the pulsation and modulatio properties of Blazko stars. Similarly to previous results, no modulatio of the longest-period stars is detected. The onset of modulation in previously regular RRab star and the similar distribution of modulate and non-modulated stars imply that the modulation is a temporal propert of RR Lyrae (RRL) stars, which may occur at any time in any RRab sta except the coolest ones. Comparing the modulation periods in M3 and i other samples of Blazhko stars, the mean log(Pmod) value i found to depend on the metallicity of the system. The separation o temperature- and radius-change induced variations supports our previou finding that the photometric radius variation does not show an modulation. The pulsation-averaged mean brightness and temperature o Blazhko stars are found to be larger in the large-amplitude phase of th modulation than in the small-amplitude phase. The larger the amplitud of the modulation, the larger the changes of the mean parameter detected

RRab variables with identical light-curve shapes at different pulsation periods

In this paper, we report on the detection of RRab stars with quasi-identical-shape light curves but period differences as large as 0.05–0.21 d using the Galactic bulge data of the OGLE-IV survey. We have examined stars with shorter periods than the Oosterhoff I ridge of the bulge. These stars generally have smaller amplitudes and larger Fourier phase-differences than the typical bulge RRab stars have at the same period. Many of these ‘anomalous’ stars have good-quality light curves without any sign of the Blazhko modulation. Examining their Fourier parameters revealed that several of these stars show very similar light curve to the typical bulge RR Lyrae. We found hundreds of quasi-identical-shape light-curve pairs with different periods between the ‘anomalous’- and the ‘normal’-position RRab stars based on the OGLE I-band data. The OGLE V-band, and the archive VVV and MACHO surveys Ks-, b- and r-band data of these stars were also checked for light-curve-shape similarity. Finally, 149 pairs with identical-shape light curves in each available photometric band were identified. Calculating the physical properties of the variables using empirical formulae, on average, −0.5 dex, −0.13 mag, 0.67, and 165 K differences between the [Fe/H], MV, R/R⊙, and Teff values of the members of the pairs are derived, being the short-period stars less metal-poor, fainter, smaller, and hotter than the long-period variables. To explain the existence of variables with different physical properties and pulsation periods but with identical-shape light curves is a challenging task for modelling