We present a new complete near-infrared (NIR, JHK(s)) census of RR Lyrae stars (RRLs) in the globular omega Cen (NGC 5139). We collected 15,472 JHKs images with 4-8 m class telescopes over 15 years (2000-2015) covering a sky area around the cluster center of 60 x 34 arcmin(2). These images provided calibrated photometry for 182 out of the 198 cluster RRL candidates with 10 to 60 measurements per band. We also provide new homogeneous estimates of the photometric amplitude for 180 (J), 176 (H) and 174 (K-s) RRLs. These data were supplemented with single-epoch JK(s) magnitudes from VHS and with single-epoch H magnitudes from 2MASS. Using proprietary optical and NIR data together with new optical light curves (ASAS-SN) we also updated pulsation periods for 59 candidate RRLs. As a whole, we provide JHKs magnitudes for 90 RRab (fundamentals), 103 RRc (first overtones) and one RRd (mixed-mode pulsator). We found that NIR/optical photometric amplitude ratios increase when moving from first overtone to fundamental and to long-period (P > 0.7 days) fundamental RRLs. Using predicted period-luminosity-metallicity relations, we derive a true distance modulus of 13.674 +/- 0.008 +/- 0.038 mag (statistical error and standard deviation of the median) based on spectroscopic iron abundances, and of 13.698 +/- 0.004 +/- 0.048 mag based on photometric iron abundances. We also found evidence of possible systematics at the 5%-10% level in the zero-point of the period-luminosity relations based on the five calibrating RRLs whose parallaxes had been determined with the HST.

The formal division of the distance indicators into primary and secondary leads to difficulties in description of methods which can actually be used in two ways: with, and without the support of the other methods for scaling. Thus instead of concentrating on the scaling requirement we concentrate on all methods of distance determination to extragalactic sources which are designated, at least formally, to use for individual sources. Among those, the Supernovae Ia is clearly the leader due to its enormous success in determination of the expansion rate of the Universe. However, new methods are rapidly developing, and there is also a progress in more traditional methods. We give a general overview of the methods but we mostly concentrate on the most recent developments in each field, and future expectations.

The nature of the Triangulum-Andromeda (TriAnd) system has been debated since the discovery of this distant, low-latitude Milky Way (MW) overdensity more than a decade ago. Explanations for its origin are either as a halo substructure from the disruption of a dwarf galaxy, or a distant extension of the Galactic disk. We test these hypotheses using the chemical abundances of a dozen TriAnd members from the Sloan Digital Sky Survey-IV's (SDSS-IV's) 14th Data Release (DR14) of Apache Point Observatory Galactic Evolution Experiment (APOGEE) data to compare to APOGEE abundances of stars with similar metallicity from both the Sagittarius (Sgr) dSph and the outer MW disk. We find that TriAnd stars are chemically distinct from Sgr across a variety of elements, (C+N), Mg, K, Ca, Mn, and Ni, with a separation in [X/Fe] of about 0.1 to 0.4 dex depending on the element. Instead, the TriAnd stars, with a median metallicity of about -0.8, exhibit chemical abundance ratios similar to those of the lowest metallicity ([Fe/H] similar to-0.7)stars in the outer Galactic disk, and are consistent with expectations of extrapolated chemical gradients in the outer disk of the MW. These results suggest that TriAnd is associated with the MW disk, and, therefore, that the disk extends to this overdensity-i.e., past a Galactocentric radius of 24 kpc -albeit vertically perturbed about 7 kpc below the nominal disk midplane in this region of the Galaxy.

We developed a new approach to provide accurate estimates of the metal content, reddening, and true distance modulus of RR Lyrae stars (RRLs). The method is based on homogeneous optical (BVI) and near-infrared (JHK) mean magnitudes and on predicted period-luminosity-metallicity relations (IJHK) and absolute mean magnitude-metallicity relations (BV). We obtained solutions for three different RRL samples in omega Cen: first overtone (RRc, 90), fundamental (RRab, 80), and global (RRc+RRab) in which the period of first overtones were fundamentalized. The metallicity distribution shows a well defined peak at [Fe/H]similar to-1.98 and a standard deviation of sigma = 0.54 dex. The spread is, as expected, metal-poor ([Fe/H] <= -2.3) objects. The current metallicity distribution is similar to 0.3 dex more metal-poor than similar estimates for RRLs available in the literature. The difference vanishes if the true distance modulus we estimated is offset by -0.06/-0.07. mag in true distance modulus. We also found a cluster true distance modulus of mu = 13.720 +/- 0.002 +/- 0.030 mag, where the former error is the error on the mean and the latter is the standard deviation. Moreover, we found a cluster reddening of E(B-V) = 0.132 +/- 0.002 +/- 0.028 mag and spatial variations of the order of a few arcmin across the body of the cluster. Both the true distance modulus and the reddening are slightly larger than similar estimates available in the literature, but the difference is within 1 sigma. The metallicity dependence of distance diagnostics agrees with theory and observations, but firm constraints require accurate and homogeneous spectroscopic measurements.

We provide homogeneous optical (UBVRI) and near-infrared (NIR, JHK) time series photometry for 254 cluster (omega Cen, M 4) and field RR Lyrae (RRL) variables. We ended up with more than 551 000 measurements, of which only 9% are literature data. For 94 fundamental (RRab) and 51 first overtones (RRc) we provide a complete optical/NIR characterization (mean magnitudes, luminosity amplitudes, epoch of the anchor point). The NIR light curves of these variables were adopted to provide new light-curve templates for both RRc and RRab variables. The templates for the J and the H bands are newly introduced, together with the use of the pulsation period to discriminate among the different RRab templates. To overcome subtle uncertainties in the fit of secondary features of the light curves we provide two independent sets of analytical functions (Fourier and periodic Gaussian series). The new templates were validated by using 26 omega Cen and Bulge RRLs. We find that the difference between the measured mean magnitude along the light curve and the mean magnitude estimated by using the template on a single randomly extracted phase point is better than 0.01 mag (sigma = 0.04 mag). We also validated the template on variables for which at least three phase points were available, but without information on the phase of the anchor point. We find that the accuracy of the mean magnitudes is also similar to 0.01 mag (sigma = 0.04 mag). The new templates were applied to the Large Magellanic Cloud (LMC) globular cluster Reticulum and by using literature data and predicted PLZ relations we find true distance moduli mu = 18.47 +/- 0.10 (rand.) +/- 0.03 (syst.) mag (J) and 18.49 +/- 0.09 +/- 0.05 mag (K). We also used literature optical and mid-infrared data and we found a mean mu of 18.47 +/- 0.02 +/- 0.06 mag, suggesting that Reticulum is similar to 1 kpc closer than the LMC.

Old-aged stellar distance indicators are present in all Galactic structures (halo, bulge, disk) and in galaxies of all Hubble types and, thus, are immensely powerful tools for understanding our Universe. Here we present a comprehensive review for three primary standard candles from Population II: (i)RR Lyrae type variables (RRL), (ii)type II Cepheid variables (T2C), and (iii)the tip of the red giant branch (TRGB). The discovery and use of these distance indicators is placed in historical context before describing their theoretical foundations and demonstrating their observational applications across multiple wavelengths. The methods used to establish the absolute scale for each standard candle is described with a discussion of the observational systematics. We conclude by looking forward to the suite of new observational facilities anticipated over the next decade; these have both a broader wavelength coverage and larger apertures than current facilities. We anticipate future advancements in our theoretical understanding and observational application of these stellar populations as they apply to the Galactic and extragalactic distance scale.

We use surface brightness fluctuation (SBF) measurements to constrain the distance to low surface brightness (LSB) dwarfs in the vicinity of M101. Recent work has discovered many LSB candidate satellite companions of M101. However, without accurate distances, it is problematic to identify these dwarfs as physical satellites of M101. We use CFHT Legacy Survey data to measure the SBF signal for 43 candidate dwarfs. The data are deep enough that we constrain 33 of these to be unassociated background galaxies by their lack of SBF. We measure high S/N SBF signals for two of the candidate dwarfs, which are consistent with being at the distance of M101. The remaining candidates are too LSB and/or small for their distances to be constrained. Still, by comparison with Local Group dwarfs, we argue that the M101 satellite system is likely now complete down to stellar masses of similar to 5 x 10(5) M-circle dot. We also provide a new SBF distance for the nearby dwarf UGC 8882, which suggests that it might be a physical satellite of M101; however, further study is merited. By constraining the distances to a majority of the candidates using only archival data, our work demonstrates the usefulness of SBF for nearby LSB galaxies and for studying the satellite systems of nearby massive galaxies.

We explore the use of ground-based surface brightness fluctuation (SBF) measurements to constrain distances to nearby dwarf galaxies. Using archival CFHT Megacam imaging data for a sample of 28 nearby dwarfs, we demonstrate that reliable SBF measurements and distances accurate to 15% are possible even for very low surface brightness (mu(0i) > 24 mag arcsec(-2)) galaxies with modest, similar to hour-long exposures with CFHT. Combining our sample with a recent sample of six dwarfs with SBF measured with Hubble Space Telescope (HST) from the literature, we provide the most robust empirical SBF calibration to date for the blue colors expected for these low-mass systems. Our calibration is credible over the color range 0.3 less than or similar to g - i less than or similar to 0.8 mag. It is also the first SBF calibration tied completely to tip of the red giant branch (TRGB) distances as each galaxy in the sample has a literature TRGB distance. We find that even though the intrinsic scatter in SBF increases for blue galaxies, the rms scatter in the calibration is still less than or similar to 0.3 mag. We verify our measurements by comparing with HST SBF measurements and detailed image simulations. We argue that ground-based SBF is a very useful tool for characterizing dwarf satellite systems and field dwarfs in the nearby, D less than or similar to 20 Mpc universe.

Context. In the era of massive spectroscopy surveys, automated stellar parameter pipelines and their validation are extremely important for an efficient scientific exploitation of the spectra.

We present the first release of the MaNGA Stellar Library (MaStar), which is a large, well-calibrated, high-quality empirical library covering the wavelength range 3622-10354 angstrom at a resolving power of R similar to 1800. The spectra were obtained using the same instrument as used by the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) project, by piggybacking on the Sloan Digital Sky Survey (SDSS-IV)/Apache Point Observatory Galaxy Evolution Experiment 2-N ( APOGEE-2N) observations. Compared to previous empirical libraries, the MaStar library will have a higher number of stars and a more comprehensive stellar-parameter coverage, especially of cool dwarfs, low-metallicity stars, and stars with different [alpha/Fe], achieved by a sophisticated target-selection strategy that takes advantage of stellar-parameter catalogs from the literature. This empirical library will provide a new basis for stellar-population synthesis and is particularly well suited for stellar-population analysis of MaNGA galaxies. The first version of the library contains 8646 high-quality per-visit spectra for 3321 unique stars. Compared to photometry, the relative flux calibration of the library is accurate to 3.9% in g - r, 2.7% in r - i, and 2.2% in i - z. The data are released as part of SDSS Data Release 15. We expect the final release of the library to contain more than 10,000 stars.