Near-Infrared Observations of RR Lyrae Variables in Galactic Globular Clusters. I. The Case of M92 (original) (raw)

The RR Lyrae period-K-luminosity relation for globular clusters: an observational approach

Monthly Notices of the Royal Astronomical Society, 2006

The period-metallicity-K-band luminosity (PL K) relation for RR Lyrae stars in 15 Galactic globular clusters and in the Large Magellanic Cloud (LMC) globular cluster Reticulum has been derived. It is based on accurate near-infrared (K) photometry combined with Two-Micron All-Sky Survey (2MASS) and other literature data. The PL K relation has been calibrated and compared with the previous empirical and theoretical determinations in literature. The zero point of the absolute calibration has been obtained from the K magnitude of RR Lyr whose distance modulus has been measured via trigonometric parallax with Hubble Space Telescope (HST). Using this relation, we obtain a distance modulus to the LMC of (m − M) 0 = 18.54 ± 0.15 mag, in good agreement with recent determinations based on the analysis of Cepheid variable stars.

Distance to Galactic globulars using the near-infrared magnitudes of RR Lyrae stars - IV. The case of M5 (NGC 5904)

Monthly Notices of the Royal Astronomical Society, 2011

We present new and accurate near-infrared (NIR) J, K-band time series data for the Galactic globular cluster (GC) M5 = NGC 5904. Data were collected with SOFI at the NTT (71 J + 120 K images) and with NICS at the TNG (25 J + 22 K images) and cover two orthogonal strips across the center of the cluster of ≈ 5 × 10 arcmin 2 each. These data allowed us to derive accurate mean K-band magnitudes for 52 fundamental (RR ab ) and 24 first overtone (RR c ) RR Lyrae stars. Using this sample of RR Lyrae stars, we find that the slope of the K-band Period Luminosity (PLK) relation (−2.33 ± 0.08) agrees quite well with similar estimates available in the literature. We also find, using both theoretical and empirical calibrations of the PLK relation, a true distance to M5 of 14.44 ± 0.02 mag. This distance modulus agrees very well (1σ) with distances based on main sequence fitting method and on kinematic method (14.44±0.41 mag, Rees 1996), while is systematically smaller than the distance based on the white dwarf cooling sequence (14. 67±0.18 mag, Layden et al. 2005), even if with a difference slightly larger than 1σ. The true distance modulus to M5 based on the PLJ relation (14.50 ± 0.08 mag) is in quite good agreement with the distance based on the PLK relation further supporting the use of NIR PL relations for RR Lyrae stars to improve the precision of the GC distance scale.

On the Distance of the Globular Cluster M4 (NGC 6121) Using RR Lyrae Stars. I. Optical and Near-Infrared Period-Luminosity and Period-Wesenheit Relations

The Astrophysical Journal, 2015

We present new distance determinations to the nearby globular M4 (NGC 6121) based on accurate optical and Near Infrared (NIR) mean magnitudes for fundamental (FU) and first overtone (FO) RR Lyrae variables (RRLs), and new empirical optical and NIR Period-Luminosity (PL) and Period-Wesenheit (PW) relations. We have found that optical-NIR and NIR PL and PW relations are affected by smaller standard deviations than optical relations. The difference is the consequence of a steady decrease in the intrinsic spread of cluster RRL apparent magnitudes at fixed period as longer wavelengths are considered. The weighted mean visual apparent magnitude of 44 cluster RRLs is V = 13.329 ± 0.001 (standard error of the mean) ±0.177 (weighted standard deviation) mag. Distances were estimated using RR Lyr itself to fix the zero-point of the empirical PL and PW relations. Using the entire sample (FU+FO) we found weighted mean true distance moduli of 11.35±0.03±0.05 mag and 11.32±0.02±0.07 mag. Distances were also evaluated using predicted metallicity dependent PLZ and PWZ relations. We found weighted mean true distance moduli of 11.283±0.010±0.018 mag (NIR PLZ) and 11.272±0.005±0.019 mag (optical-NIR and NIR PWZ). The above weighted mean true distance moduli agree within 1σ. The same result is found from distances based on PWZ relations in which the color index is independent of the adopted magnitude (11.272±0.004±0.013 mag). These distances agree quite well with the geometric distance provided by ) based on three eclipsing binaries. The available evidence indicates that this approach can provide distances to globulars hosting RRLs with a precision better than 2-3%.

The RR Lyrae distance scale from near-infrared photometry: current results

Arxiv preprint astro-ph/ …, 2006

We present new observational results on the RR Lyrae K-band Period-Luminosity relation (PLK). Data on the Galactic globular clusters NGC 3201 and NGC 4590 (M68), and on the Large Magellanic Cloud cluster Reticulum are shown. We compare the observed slopes of the PLK relations for these three clusters with those predicted by pulsational and evolutionary models, finding a fair agreement. Trusting on this finding we decided to adopt these theoretical calibrations to estimate the distance to the target clusters, finding a good agreement with optical-based RR Lyrae distances, but with a smaller formal scatter.

RR Lyrae-based calibration of the Globular Cluster Luminosity Function

Monthly Notices of the Royal Astronomical Society, 2005

We test whether the peak absolute magnitude M V (TO) of the Globular Cluster Luminosity Function (GCLF) can be used for reliable extragalactic distance determination. Starting with the luminosity function of the Galactic Globular Clusters listed in Harris catalogue, we determine M V (TO) either using current calibrations of the absolute magnitude M V (RR) of RR Lyrae stars as a function of the cluster metal content [Fe/H] and adopting selected cluster samples. We show that the peak magnitude is slightly affected by the adopted M V (RR)-[Fe/H] relation, with the exception of that based on the revised Baade-Wesselink method, while it depends on the criteria to select the cluster sample. Moreover, grouping the Galactic Globular Clusters by metallicity, we find that the metal-poor (MP) ([Fe/H]< −1.0, [Fe/H] ∼ −1.6) sample shows peak magnitudes systematically brighter by about 0.36 mag than those of the metal-rich (MR) ([Fe/H]> −1.0, ([Fe/H] ∼ −0.6) one, in substantial agreement with the theoretical metallicity effect suggested by synthetic Globular Cluster populations with constant age and mass function. Moving outside the Milky Way, we show that the peak magnitude of the MP clusters in M31 appears to be consistent with that of Galactic clusters with similar metallicity, once the same M V (RR)-[Fe/H] relation is used for distance determination. As for the GCLFs in other external galaxies, using Surface Brightness Fluctuations (SBF) measurements we give evidence that the luminosity functions of the blue (MP) Globular Clusters peak at the same luminosity within ∼0.2 mag, whereas for the red (MR) samples the agreement is within ∼0.5 mag even accounting for the theoretical metallicity correction expected for clusters with similar ages and mass distributions. Then, using the SBF absolute magnitudes provided by a Cepheid distance scale calibrated on a fiducial distance to Large Magellanic Cloud (LMC), we show that the M V (TO) value of the MP clusters in external galaxies is in excellent agreement with the value of both Galactic and M31 ones, as inferred by an RR Lyrae distance scale referenced to the same LMC fiducial distance. Eventually, adopting µ 0 (LMC) = 18.50 mag, we derive that the luminosity function of MP clusters in the Milky Way, M31, and external galaxies peak at M V (TO) = −7.66 ± 0.11, − 7.65 ± 0.19 and −7.67 ± 0.23 mag, respectively. This would suggest a value of −7.66 ± 0.09 mag (weighted mean), with any modification of the LMC distance modulus producing a similar variation of the GCLF peak luminosity.

Near-infrared integrated spectra of Galactic globular clusters: testing simple stellar population models

Monthly Notices of the Royal Astronomical Society, 2011

We present SOAR/OSIRIS cross-dispersed near-infrared (NIR) integrated spectra of 12 Galactic globular clusters that are employed to test Maraston (2005, hereafter M05) NIR Evolutionary Population Synthesis (EPS) models, and to provide spectral observational constraints to calibrate future models. We measured Equivalent Widths (W λ ) of the most prominent NIR absorption features: λ 1.49µm, Mg I λ 1.58µm, Fe I/Mg I, λ 1.59µm, Si I, λ 1.71µm, Mg I, λ 2.21µm, Na I and λ 2.26µm, Ca I as well as the λ 1.62µm, λ 2.29µm, CO and λ 2.05µm, CN molecular bands. Optical W λ of G-band (4300Å), Hβ, Mg 2 , Fe I (4531Å, 527Å and 5335Å), and Na I (5897Å) were also measured. The globular clusters W λ were compared with model predictions with ages within 4 -15 Gyr, and metallicities between 1 200 Z⊙ and 2 Z⊙. Observed integrated colours (B − V , V − I and V − K s ) were also compared with models. The NIR integrated spectra among our sample appear qualitatively similar in most the absorption features. The M05 models can properly predict the optical W λ observed in globular clusters. Regarding the NIR, they do underestimate the strength of Mg I 1.49µm, but they can reproduce the observed W λ of Fe I 1.58µm, Si I 1.59µm, and CO 2.29µm, in about half of our sample. The remaining objects require the inclusion of intermediate-age populations. Thus, we suggest that the presence of C-and O-rich stars in models is important to reproduce the observed strengths of metallic lines. Another possibility is the lack of α-enhancement in the models. In the case of the optical and NIR Fe I lines, standard models and those that include blue horizontal branch stars, produce similar results. A similar trend is observed for Na I 5895Å, while in the case of the G-band, the models with blue horizontal branch do describe better the observations. For most of the sample the optical to NIR colours are well described by the M05 models.In general, M05 models can provide reliable information on the NIR stellar population of galaxies, but only when W λ and colours are taken together, in other words, W λ and continuum fluxes should be simultaneously fitted. However, the results should be taken with caution, since the models tend to predict results biased towards young ages.

Near-IR photometry of five Galactic Globular Clusters

Astronomy & Astrophysics, 2004

We present near--infrared J and K observations of giant stars in five metal-poor Galactic Globular Clusters (namely M3, M5, M10, M13 and M92) obtained at the Telescopio Nazionale Galileo (TNG). This database has been used to determine the main photometric properties of the red giant branch (RGB) from the (K,J-K) and, once combined with the optical data, in the (K,V-K) Color Magnitude Diagrams. A set of photometric indices (the RGB colors at fixed magnitudes) and the major RGB evolutionary features (slope, bump, tip) have been measured. The results have been compared with the relations obtained by Ferraro et al. 2000 and with the theoretical expectations, showing a very good agreement.

A deep near-infrared view of the Galactic globular cluster 2 MASS GC 02

Astronomy and Astrophysics, 2007

Context. We have obtained deep infrared images and K-band spectra of the Galactic globular cluster 2 MASS GC 02. A variable star search has also been carried out. Aims. Some basic physical properties of the cluster, such as metallicity, reddening, distance modulus and radial velocity, are derived. Methods. These measurements are based on an analysis of the J − K s versus K s color-magnitude diagram of the cluster. Spectroscopically derived metallicities and radial velocities of 15 stars are presented. In addition, periods and amplitudes are provided for five RR Lyrae stars discovered in the field. Results. The cluster is moderately metal-rich and has a relatively high radial velocity. Its horizontal branch appears to be predominantly red, though our photometry cannot rule out the presence of a blue component as seen in NGC 6388 and NGC 6441. Similar to these two clusters, the detected RR Lyrae stars in GC 02 have anomalously long periods for the cluster's moderately high metallicity, which suggests that it too is an Oosterhoff type III cluster. Conclusions. Comparison with the existing kinematic and abundance information for the Galactic globular clusters shows that GC 02 most probably belongs to the bulge sub population, although an inner halo association cannot be ruled out.

Extragalactic globular clusters in the near-infrared

Astronomy and Astrophysics, 2002

In this third paper of our series on near-IR and optical photometry of globular cluster systems in early-type galaxies we concentrate on the photometric results for NGC 5846 and NGC 7192, two group ellipticals, and on a first comparison between the globular cluster systems investigated so far. In NGC 5846 the colour-colour diagram shows clear bi-modality in (V − K), which is confirmed by a KMM test. The mean colour of both peaks were estimated to be (V − K) blue =2.57±0.06 and (V − K) red =3.18±0.06. The situation in NGC 7192 is different, in that the colour-colour diagram gives no evidence for a distinct second population of globular clusters. Using simulated colour distributions of globular cluster systems, we make a first step in quantifying the cumulative age distribution in globular cluster systems. Also here the result for NGC 5846 leads us to the conclusion that its metal-rich globular cluster population contains two globular cluster populations which differ in age by several Gyr. The age structure for NGC 7192 shows instead strong similarity with a single-age population.

The Clusters AgeS Experiment (CASE): RR Lyrae variables in the globular cluster NGC 6362

Monthly Notices of The Royal Astronomical Society, 2001

We present V- and B-band charge-coupled device (CCD) photometry of 35 RR Lyr stars in the Southern hemisphere globular cluster NGC 6362. Fourier decomposition of the light curves was used to estimate the basic properties of these variables. From the analysis of the RRc stars we obtain a mean mass M=0.531±0.014 M⊙, luminosity log L/L⊙=1.656±0.006, effective temperature Teff=7429±20 and helium abundance Y=0.292±0.002. The mean values of the absolute magnitude, metallicity (on Jurcsik's scale) and effective temperature for 14 RRab stars with ‘regular’ light curves are: MV=0.86±0.01,[Fe/H]=−0.93±0.04 and Teff=6555±25, respectively. From the B−V colours, periods and metallicities of the RRab stars we estimate the colour excess for NGC 6362 to be equal to E(B−V)=0.08±0.01. Using this value we derive the colours of the blue and red edges of the instability strip in NGC 6362 to be (B−V)BE0=0.17 and (B−V)RE0=0.43. From the relations between the Fourier coefficients of RRab and RRc stars and their absolute magnitudes we estimate the apparent distance modulus to NGC 6362 to be (m−M)V=14.46±0.10. From the mean value of log L/L⊙ of the RRc stars we obtain 14.59±0.03.The V-band light curves of three of the RRc stars exhibit changes in amplitude of over 0.1 mag on the time-scale of around one week. Near the radial first overtone frequency we find one or two peaks, which strongly suggests that these variables belong to the newly identified group of non-radial pulsating RR Lyr stars.