I present V-band CCD photometry for a sample of 103 RR Lyrae variables selected from the General Catalogue of Variable Stars to lie in the inner halo of the Galaxy. I also describe a method for obtaining the mean apparent magnitude and the epoch at maximum light of an RR Lyrae star. The method requires as few as five photometric observations, and simulations demonstrate that the associated errors are relatively small. I employ this method to derive the mean magnitudes and maximum light epochs of the 103 RR Lyrae stars observed. These stars were selected, based on their Galactic coordinates and original photographic photometry, to lie near their orbital tangent points, thus providing a sample well suited for measuring the rotational kinematics of the inner halo. Using interstellar reddenings from the literature and the observed mean V magnitudes, I derive distances for these stars and show that their actual locations in the Galaxy are indeed suitable for use in a kinematic study, despite the large zero-point errors in the survey photographic photometry.
RR Lyrae stars in the Milky Way are good tracers to study the kinematic behaviour and spatial distribution of older stellar populations. A recently established well documented sample of 217 RR Lyr stars with V<12.5mag, for which accurate distances and radial velocities as well as proper motions from the Hipparcos and Tycho-2 catalogues are available, has been used to reinvestigate these structural parameters. The kinematic parameters allowed to calculate the orbits of the stars. Nearly 1/3 of the stars of our sample have orbits staying near the Milky Way plane.
CCD time-series observations of the central region of the globular cluster NGC 3201 were obtained with the aim of performing the Fourier decomposition of the light curves of the RR Lyrae stars present in that field. This procedure gave the mean values, for the metallicity, of [Fe/H]_ZW_=-1.483+/-0.006 (statistical) +/-0.090 (systematical), and for the distance, 5.000+/-0.001kpc (statistical) +/-0.220 (systematical). The values found from two RRc stars are consistent with those derived previously. The differential reddening of the cluster was investigated and individual reddenings for the RR Lyrae stars were estimated from their V-I curves. We found an average value of E(B-V)=0.23+/-0.02. An investigation of the light curves of stars in the blue stragglers region led to the discovery of three new SX Phe stars. The period-luminosity relation of the SX Phe stars was used for an independent determination of the distance to the cluster and of the individual reddenings. We found a distance of 5.0kpc
We present a theoretical investigation on periods and amplitudes of RR Lyrae pulsators by adopting stellar parameters which cover the range of theoretical evolutionary expectations. Extensive grids of nonlinear, nonlocal and time-dependent convective RR Lyrae envelope models have been computed to investigate the pulsational behavior in both fundamental and first overtone modes at selected luminosity levels and over an effective temperature range which covers the whole instability region. In order to avoid spurious evaluations of modal stability and pulsation amplitudes, the coupling between pulsation and convection was followed through a direct time integration of the leading equations until radial motions approached their limiting amplitude. Blue and red boundaries for pulsational instability into the HR diagram are presented for three different mass values M=0.75, 0.65 and 0.58M_{sun}_, together with an atlas of full amplitude theoretical light curves for both fundamental and first overtone pulsators and for two different assumptions of stellar masses: M=0.75 and 0.65M_{sun}_.
We present a catalog of RR Lyrae stars distributed across ~14000deg^2^ of the sky from the combined data of the Sloan Digital Sky Survey (SDSS, http://www.sdss.org), the Panoramic Survey Telescope and Rapid Response System 1 (PS1, Kaiser et al., 2002, SPIE, 4836, 154), and the second photometric catalogue from the Catalina Survey (CS2, http://nesssi.cacr.caltech.edu/DataRelease), out of these, ~2021 RRL stars (~572 RRab and 1449 RRc) are new discoveries. The RRL stars have heliocentric distances in the 4-28kpc distance range. Our catalog has a completeness level of ~50 per cent for both RRab and RRc stars, and an efficiency of ~99 and ~87 per cent for RRab and RRc stars, respectively. We provide the positions, CSDR2 mean magnitudes, CSDR2 amplitudes, subtypes, periods, ephemeris, and the heliocentric distances of our RRab and RRc stars.
Using archival multi-epoch ACS/WFC images in the F606W and F814W filters of a resolved stellar field in Local Group dwarf elliptical galaxy M 32 we have made an accurate Colour-Magnitude Diagram and a careful search for RR Lyr variable stars. We identified 416 bona fide RR Lyr stars over our field of view, and their spatial distribution shows a rising number density towards the centre of M 32. These new observations clearly confirm the tentative result of Fiorentino et al. (2010ApJ...708..817F), on a much smaller field of view, associating an ancient population of RR Lyr variables to M 32. We associate at least 83 RR Lyr stars in our field to M 32.
A set of photometric observations of the symbiotic nova RR Tel in different wavelength bands - visual from 1949 to 2002 and near-infrared (JHKL) from 1975 to 2002 - are presented. Near-infrared photometry is used to identify and study three periods during which the Mira component was heavily obscured by dust. The variability due to the normal Mira pulsation was removed from the JHKL data, which were then compared with the AAVSO visual light curve. We discuss these obscuration events as observed in the different wavelength bands. A change in the colour trend was observed with the colour becoming redder after JD2446000. Generally J-K was comparable while K-L was larger than typical values for solitary Miras. A distance estimate of 2.5kpc, based on the IR data, is given. A study of the behaviour of the permitted Fe II and forbidden [FeII] emission lines during the 1996-2000 obscuration episode suggests a larger flux decrease for the permitted than for the forbidden lines. No other correlation with line properties have been found. The most attractive model involves obscuration by optically thick clouds in the outer layers.
We present the most comprehensive red supergiant (RSG) sample for the Small Magellanic Cloud (SMC) to date, including 1239 RSG candidates. The initial sample was derived based on a source catalog for the SMC with conservative ranking. Additional spectroscopic RSGs were retrieved from the literature, and RSG candidates were selected based on the inspection of Gaia and 2MASS color-magnitude diagrams (CMDs). We estimate that there are in total ~1800 or more RSGs in the SMC. We purify the sample by studying the infrared CMDs and the variability of the objects, though there is still an ambiguity between asymptotic giant branch stars (AGBs) and RSGs at the red end of our sample. One heavily obscured target was identified based on multiple near-IR (NIR) and mid-IR (MIR) CMDs. The investigation of color-color diagrams (CCDs) shows that there are fewer RSGs candidates (~4%) showing PAH emission features compared to the Milky Way and LMC (~15%). The MIR variability of RSG sample increases with luminosity. We separate the RSG sample into two subsamples (risky and safe), and identify one M5e AGB star in the risky subsample based on simultaneous inspection of variabilities, luminosities, and colors. The degeneracy of mass loss rate (MLR), variability, and luminosity of the RSG sample is discussed, indicating that most of the targets with high variability are also the bright ones with high MLR. Some targets show excessive dust emission, which may be related to previous episodic mass loss events. We also roughly estimate the total gas and dust budget produced by entire RSG population as ~1.9^+2.4^_-1.1_x10^-6^M_{sun}_/yr in the most conservative case, according to the derived MLR from IRAC1-IRAC4 color. Based on the MIST models, we derive a linear relation between T_eff_ and observed J-Ks color with reddening correction for the RSG sample. By using a constant bolometric correction and this relation, the Geneva evolutionary model is compared with our RSG sample, showing a good agreement and a lower initial mass limit of ~7M_{sun}_ for the RSG population. Finally, we compare the RSG sample in the SMC and the LMC. Despite the incompleteness of LMC sample in the faint end, the result indicates that the LMC sample always shows redder color (except for the IRAC1-IRAC2 and WISE1-WISE2 colors due to CO absorption) and higher variability than the SMC sample, which is likely due to a positive relation between MLR, variability and the metallicity.
