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Variable Stars in M13. II. The Red Variables and the Globular Cluster Period-Luminosity Relation

Osborn W., Layden A., Kopacki G., Smith H., Anderson M., Kelly A., McBride K., Pritzl B.

Acta Astronomica

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2017

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Vol. 67, No. 2

131--158

EN

New CCD observations have been combined with archival data to investigate the nature of the red variables in the globular cluster M13. Mean magnitudes, colors and variation ranges on the UBVIC system have been determined for the 17 cataloged red variables. 15 of the stars are irregular or semi-regular variables that lie at the top of the red giant branch in the color-magnitude diagram. Two stars are not, including one with a well-defined period and a light curve shape indicating it is an ellipsoidal or eclipsing variable. All stars redder than (V-IC)0=1.38 mag vary, with the amplitudes being larger with increased stellar luminosity and with bluer filter passband. Searches of the data for periodicities yielded typical variability cycle times ranging from 30 d up to 92 d for the most luminous star. Several stars have evidence of multiple periods. The stars' period-luminosity diagram compared to those from microlensing survey data shows that most M13 red variables are overtone pulsators. Comparison with the diagrams for other globular clusters shows a correlation between red variable luminosity and cluster metallicity.

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The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. XV. Long-Period Variables in the Galactic Bulge

Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Poleski R., Kozłowski S., Pietrukowicz P., Skowron J.

Acta Astronomica

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2013

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Vol. 63, No. 1

21--36

EN

The fifteenth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains 232406 long-period variables (LPVs) detected in the OGLE-II and OGLE-III fields toward the Galactic bulge. The sample consists of 6528 Mira stars, 33235 semiregular variables and 192643 OGLE small amplitude red giants. The catalog data and data resources that are being published include observational parameters of stars, finding charts, and time-series I- and V-band photometry obtained between 1997 and 2009. We discuss statistical features of the sample and compare it with collections of LPVs in the Magellanic Clouds. The vast majority of red giant stars in the Galactic bulge have an oxygen-rich chemistry. Mira variables form a separate group in the period-amplitude diagram, which was not noticed for oxygen-rich Miras in the Magellanic Clouds. We find a clear deficit of long-secondary period stars toward the Galactic center compared to the sample of Magellanic Clouds' LPVs.

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The Optical Gravitational Lensing Experiment. The OGLE-III Catalog of Variable Stars. XIII. Long-Period Variables in the Small Magellanic Cloud

Soszyński I., Udalski A., Szymański M. K., Kubiak M., Pietrzyński G., Wyrzykowski Ł., Ulaczyk K., Poleski R., Kozłowski S., Pietrukowicz P.

Acta Astronomica

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2011

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Vol. 61, No. 3

217--230

EN

The thirteenth part of the OGLE-III Catalog of Variable Stars (OIII-CVS) contains 19 384 long-period variables (LPVs) detected in the Small Magellanic Cloud. The sample is composed of 352 Mira stars, 2222 semiregular variables (SRVs) and 16 810 OGLE Small Amplitude Red Giants (OSARGs). Sources are divided into oxygen-rich and carbon-rich stars. The catalog includes time-series VI photometry obtained between 1997 and 2009. Methods used to select and classify variable stars are described. We show some statistical properties of the sample, and compare it with LPVs in the Large Magellanic Cloud. Additionally, we present objects of particular interest, e.g., a SRV with outbursts, and a Mira star with the longest known pulsation period P=1860 days.

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The Optical Gravitational Lensing Experiment. Miras and Semiregular Variables in the Large Magellanic Cloud

Soszyński I., Udalski A., Kubiak M., Szymański M. K., Pietrzyński G., Żebruń K., Szewczyk O., Wyrzykowski Ł., Ulaczyk K.

Acta Astronomica

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2005

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Vol. 55, No. 4

331--348

EN

We use the OGLE-II and OGLE-III data in conjunction with the 2MASS near-infrared (NIR) photometry to identify and study Miras and Semiregular Variables (SRVs) in the Large Magellanic Cloud. We found in total 3221 variables of both types, populating two of the series of NIR period-luminosity (PL) sequences. The majority of these objects are double periodic pulsators, with periods belonging to both PL ridges. We indicate that in the period - Wesenheit index plane the oxygen-rich and carbon-rich AGB stars from the NIR PL sequences C, C' and D split into well separated ridges. Thus, we discover an effective method of distinguishing between O-rich and C-rich Miras, SRVs and stars with Long Secondary Periods using their V and I-band photometry. We present an empirical method of estimating the mean Ks magnitudes of the Long Period Variables using single-epoch Ks measurements and complete light curves in the I-band. We utilize these corrected magnitudes to show that the O-rich and C-rich Miras and SRVs follow somewhat different Ks-band PL relations.

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The Optical Gravitational Lensing Experiment. Small Amplitude Variable Red Giants in the Magellanic Clouds

Soszyński I., Udalski A., Kubiak M., Szymański M., Pietrzyński G., Żebruń K., Szewczyk O., Wyrzykowski Ł.

Acta Astronomica

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2004

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Vol. 54, No. 2

129--152

EN

We present analysis of the large sample of variable red giants from the Large and Small Magellanic Clouds detected during the second phase of the Optical Gravitational Lensing Experiment (OGLE-II) and supplemented with OGLE-III photometry. Comparing pulsation properties of detected objects we find that they constitute two groups with clearly distinct features. In this paper we analyze in detail small amplitude variable red giants (about 15400 and 3000 objects in the LMC and SMC, respectively). The vast majority of these objects are multi-periodic. At least 30% of them exhibit two modes closely spaced in the power spectrum, what likely indicates non-radial oscillations. About 50% exhibit additional so called Long Secondary Period. To distinguish between AGB and RGB red giants we compare PL diagrams of multi-periodic red giants located above and below the tip of the Red Giant Branch (TRGB). The giants above the TRGB form four parallel ridges in the PL diagram. Among much more numerous sample of giants below the TRGB we find objects located on the low luminosity extensions of these ridges, but most of the stars are located on the ridges slightly shifted in log P. We interpret the former as the second ascent AGB red giants and the latter as the first ascent RGB objects. Thus, we empirically show that the pulsating red giants fainter than the TRGB are a mixture of RGB and AGB giants. Finally, we compare the Petersen diagrams of the LMC, SMC and Galactic bulge variable red giants and find that they are basically identical indicating that the variable red giants in all these different stellar environments share similar pulsation properties.