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We combined the ( K, J− K) data in Laney et al. (Mon. Not. R. Astron. Soc. 419:1637, ) with the V apparent magnitudes and trigonometric parallaxes taken from the Hipparcos catalogue and used them to fit the $M_{K_{s}}$ absolute magnitude to a linear polynomial in terms of V− K colour. The mean and standard deviation of the absolute magnitude residuals, −0.001 and 0.195 mag, respectively, estimated for 224 red clump stars in Laney et al. () are (absolutely) smaller than the corresponding ones estimated by the procedure which adopts a mean $M_{K_{s}}=-1.613~\mbox{mag}$ absolute magnitude for all red clump stars, −0.053 and 0.218 mag, respectively. The statistics estimated by applying the linear equation to the data of 282 red clump stars in Alves (Astrophys. J. 539:732, ) are larger, $\Delta M_{K_{s}}=0.209$ and σ=0.524 mag, which can be explained by a different absolute magnitude trend, i.e. condensation along a horizontal distribution. [ABSTRACT FROM AUTHOR]

The Ultraviolet Imaging Telescope (UVIT) is scheduled to be launched as a part of the ASTROSAT satellite. As part of the mission planning for the instrument we have studied the efficacy of UVIT observations for interstellar extinction measurements. We find that in the best case scenario, the UVIT can measure the reddening to an accuracy of about 0.02 magnitudes, which combined with the derived distances to the stars, will enable us to model the three-dimensional distribution of extinction in our Galaxy. The knowledge of the distribution of the ISM will then be used to study distant objects, affected by it. This work points the way to further refining the UVIT mission plan to best satisfy different science studies. [ABSTRACT FROM AUTHOR]

The analysis of deep imaging data of bright elliptical galaxies is capable of providing fundamental information on the stellar content and the distance of the target, via the Surface Brightness Fluctuation method (SBF hereafter). Here, I present the study of the properties of two ellipticals in the Virgo cluster, NGC 4621 and NGC 4374, based on deep BVR imaging data obtained with the FORS2 camera at the VLT. The V and R SBF measures are used to get accurate distances of the targets. In addition, since both galaxies hosted type Ia Supernova events, I also compare the new SBF distances with the ones based on SNe Ia lightcurve analysis. In all cases SBF distances agree well with distances obtained by other distance indicators. For what concerns stellar population analysis, I present a detailed comparison between SBF data and models to constrain the properties of the dominant stellar components. Among the other results, the measures presented here seem to suggest that the B-band SBF can be reconciled to model predictions only through the presence of a percentage of hot-HB stars 'polluting' the old and metal rich dominant stellar population. [ABSTRACT FROM AUTHOR]

RR Lyrae variables play an important role in several fields of stellar evolution and cosmology, moreover, they are the most popular primary standard candles for Population II stellar systems. In this paper, their properties are examined within the framework of modern computations of stellar evolution and pulsation models in order to discuss their use as distance indicators. The comparison between selected observed data and predicted relations, for the determination of both apparent and intrinsic distance moduli, is also presented. [ABSTRACT FROM AUTHOR]

AGB variables, particularly the large amplitude Mira type, are a vital step on the distance scale ladder. They will prove particularly important in the era of space telescopes and extremely large ground-based telescopes with adaptive optics, which will be optimized for infrared observing. Our current understanding of the distances to these stars is reviewed with particular emphasis on improvements that came from Hipparcos as well as on recent work on Local Group galaxies. In addition to providing the essential calibration for extragalactic distances Gaia may also provide unprecedented insight into the poorly understood mass-loss process itself. [ABSTRACT FROM AUTHOR]

Factors contributing to the scatter around the ridge-line period-luminosity relationship are listed, followed by a discussion how to eliminate the adverse effects of these factors (mode of pulsation, crossing number, temperature range, reddening, binarity, metallicity, non-linearity of the relationship, blending), in order to reduce the dispersion of the P- L relationship. [ABSTRACT FROM AUTHOR]

The ESA Gaia mission will bring a new era to the domain of standard candles. Progresses in this domain will be achieved thanks to unprecedented astrometric precision, whole-sky coverage and the combination of photometric, spectrophotometric and spectroscopic measurements. The fundamental outcome of the mission will be the Gaia catalogue produced by the Gaia Data Analysis and Processing Consortium (DPAC), which will contain a variable source classification and specific properties for stars of specific variability types. We review what will be produced for Cepheids, RR Lyrae, Long Period Variable stars and eclipsing binaries. [ABSTRACT FROM AUTHOR]

In the last decade or so, there have been numerous searches for hot subdwarfs in close binaries. There has been little to no attention paid to wide binaries, however. The advantages of understanding these systems can be many. The stars can be assumed to be coeval, which means they have common properties. The distance and metallicity, for example, are both unknown for the subdwarf component, but may be determinable for the secondary, allowing other properties of the subdwarf to be estimated. With this in mind, we have started a search for common proper motion pairs containing a hot subdwarf component. We have uncovered several promising candidate systems, which are presented here. [ABSTRACT FROM AUTHOR]

We present timing measurements, astrometry, and high-resolution spectra of a number of nearby, thermally emitting, isolated neutron stars. We use these to infer magnetic field strengths and distances, but also encounter a number of puzzles. We discuss three specific ones in detail: (i) For RX J0720.4-3125 and RX J1308.6+2127, the characteristic ages are in excess of 1 Myr, while their temperatures and kinematic ages indicate that they are much younger; (ii) For RX J1856.5-3754, the brightness temperature for the optical emission is in excess of that measured at X-ray wavelengths for reasonable neutron-star radii; (iii) For RX J0720.4-3125, the spectrum changed from an initially featureless state to one with an absorption feature, yet there was only a relatively small change in T eff. Furthermore, we attempt to see whether the spectra of all seven sources, in six of which absorption features have now been found, can be understood in the context of strongly magnetised hydrogen atmospheres. We find that the energies of the absorption features can be reproduced, but that it remains puzzling that, for J0720.4-3125 specifically, the spectrum was featureless in one state, and that, generally, the spectra do not have high-energy tails that are harder than the Wien-like ones obseved. [ABSTRACT FROM AUTHOR]

In this study, we carried out CCD UBV photometry of eight open clusters, ASCC 115, Collinder 421, NGC 6793, NGC 7031, NGC 7039, NGC 7086, Roslund 1, Stock 21, and determined their reddening, metallicity, distance, age, and mass functions. We used new Gaia Data Release 2 (DR2) astrometric data to separate cluster member stars from the field stars and obtain precise structural and astrophysical parameters. To identify cluster member stars we utilized an unsupervised membership assignment code (UPMASK), which is based on the photometric and astrometric data. The density distributions for the open clusters show good fits with the empirical King model except for Roslund 1 and Stock 21 not having central concentration. The colour excesses and metallicities were derived separately using U − B × B − V two-colour diagrams. Keeping these parameters as constants, we simultaneously calculated distance moduli and ages of the clusters from V × B − V and V × U − B colour-magnitude diagrams using PARSEC theoretical isochrones. Taking into account Gaia DR2 proper motion components and parallaxes of the member stars, we also calculated mean proper motions and distances for the clusters. Distances derived both from isochrone fitting to colour-magnitude diagrams of the clusters and Gaia DR2 trigonometric parallaxes are compatible with each other. Slopes of the mass functions of the eight open clusters are in good agreement with Salpeter (Astrophys. J. 121:161, 1955) value of 1.35. [ABSTRACT FROM AUTHOR]

HD 179821 is classified as G5 Ia star. From the IRAS colors and spectral energy distributions it was classified as a post-AGB star. But some studies classify it as a massive (30 to 19M⊙) post-red supergiant evolving to become a Type II supernova. Its mass and evolutionary status remained a hotly debated question even after several detailed spectroscopic studies as the distance was not known. We use the parallax of HD 179821 from the second Gaia data release, and deduce its distance 2959±409pc and its absolute magnitude MV=−5.7±0.3. Using the absolute magnitude determined in this paper, we show that HD 179821 fits very well with post-AGB tracks in the H−R diagram. Our results clearly confirm that HD 179821 is a post-AGB star of mass in the range of 0.70 to 0.75 solar mass. It is not a 30M⊙ red supergiant. The progenitor mass of this post-AGB star may be in the range of 4M⊙ but may be a bit more. [ABSTRACT FROM AUTHOR]