We present new deep imaging of the central regions of the remote globular cluster NGC 2419, obtained with the F343N and F336W filters of HST/WFC3. The new data are combined with archival imaging to constrain nitrogen and helium abundance variations within the cluster. We find a clearly bimodal distribution of the nitrogen-sensitive F336W-F343N colours of red giants, from which we estimate that about 55% of the giants belong to a population with about normal (field-like) nitrogen abundances (P1), while the remaining 45% belong to a nitrogen-rich population (P2). On average, the P2 stars are more He-rich than the P1 stars, with an estimated mean difference of Delta Y = 0.05, but the P2 stars exhibit a significant spread in He content and some may reach Delta Y = 0.13. A smaller He spread may be present also for the P1 stars. Additionally, stars with spectroscopically determined low [Mg/Fe] ratios ([Mg/Fe]<0) are generally associated with P2. We find the P2 stars to be slightly more centrally concentrated in NGC 2419 with a projected half-number radius of about 10% less than for the P1 stars, but the difference is not highly significant (p=0.05). We find evidence of rotation for the P1 stars, whereas the results are inconclusive for the P2 stars, which are consistent with no rotation as well as the same average rotation found for the P1 stars. Because of the long relaxation time scale of NGC 2419, the radial trends and kinematic properties of the populations are expected to be relatively unaffected by dynamical evolution. Hence, they provide constraints on formation scenarios for multiple populations, which must account not only for the presence of He spreads within sub-populations identified via CNO variations, but also for the relatively modest differences in the spatial distributions and kinematics of the populations.
In this paper we present photometric CCD observations of the globular cluster NGC 6093 (M80) in filters B, V , R and I. We produce the colour-magnitude diagrams for this object and obtain values for its metallicity [Fe/H], reddening E(V-B), E(V-I) and distance modulus (m - M)_0.
We present BVRI photometry of supernova (SN) 2016coj in NGC 4125 from $9$ days before to $57$ days after its $B$-band maximum light. Our light curves and color curves suggest that this event belongs to the "normal" class of type Ia SNe, with a decline rate parameter $Δm_{15}(B) = 1.32 \pm 0.10$, and that it suffers little extinction. Adopting a distance modulus to its host galaxy of $(m - M) = 31.89$ mag, we compute extinction-corrected peak absolute magnitudes of $M_B = -19.01$, $M_V = -19.05$, $M_R = -19.03$, and $M_I = -18.79$. The explosion occurred close enough to the nucleus of NGC 4125 …
Following the earlier discovery of classical Cepheid variables in the Sculptor Group spiral galaxy NGC 7793 from an optical wide-field imaging survey, we have performed deep near-infrared $J$- and $K$-band follow-up photometry of a subsample of these Cepheids to derive the distance to this galaxy with a higher accuracy than what was possible from optical photometry alone, by minimizing the effects of reddening and metallicity on the distance result. Combining our new near-infrared period-luminosity relations with the previous optical photometry we obtain a true distance modulus to NGC 7793 of …
We present a photometric and spectroscopic study of multiple populations along the asymptotic-giant branch (AGB) of the intermediate-metallicity globular clusters (GCs) NGC2808 and NGC6121 (M4). Chemical abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Fe, Co, Ni, Zn, Y, and Ce in AGB stars from high-resolution FLAMES+UVES@VLT spectra are reported for both clusters. Our spectroscopic results have been combined with multi-wavelength photometry from the HST UV survey of Galactic GCs and ground-based photometry, plus proper motions derived by combining stellar positions from ground-based image…
As part of the Swift/UVOT Stars Survey, we present near-ultraviolet point-source photometry for 103 Galactic open clusters. These data, taken over the span of the mission, provide a unique and unprecedented set of near-ultraviolet point-source photometry on simple stellar populations. After applying membership analysis fueled mostly by GAIA DR2 proper motions, we find that 49 of these 103 have clear precise CMDs amenable to investigation. We compare the CMDs to theoretical isochrones and find good agreement between the theoretical isochrones and the CMDs. The exceptions are the fainter parts o…
Recent work has revealed two classes of Globular Clusters (GCs), dubbed Type-I and Type-II. Type-II GCs are characterized by a blue- and a red- red giant branch composed of stars with different metallicities, often coupled with distinct abundances in the slow-neutron capture elements (s-elements). Here we continue the chemical tagging of Type-II GCs by adding the two least-massive clusters of this class, NGC1261 and NGC6934. Based on both spectroscopy and photometry, we find that red stars in NGC1261 are slightly enhanced in [Fe/H] by ~0.1 dex and confirm that red stars of NGC 6934 are enhance…
Aims. We present a new technique to estimate the relative ages of multiple stellar populations hosted by five globular clusters: NGC 104 (47 Tuc), NGC 6121 (M4), NGC 6352, NGC 6362 and NGC 6723. Methods. We used the catalogs of the database "HST UV Globular cluster Survey (HUGS)" to create color-magnitude and two-color diagrams of the Globular Clusters. We identified the multiple populations within each globular cluster, and we divided them into two main stellar populations: POPa or first generation (1G) and POPb, composed of all the successive generations of stars. The new technique allows us…
In this paper, we present our results for the photometric and kinematical studies of old open cluster NGC 188. We determined various astrophysical parameters like limited radius, core and tidal radii, distance, luminosity and mass functions, total mass, relaxation time etc. for the cluster using 2MASS catalog. We obtained the cluster's distance from the Sun as 1721+/-41 pc and log (age)= 9.85+/-0.05 at Solar metallicity. The relaxation time of the cluster is smaller than the estimated cluster age which suggests that the cluster is dynamically relaxed. Our results agree with the values mentione…
We present the photometric analysis of the external regions of three Galactic Globular Clusters: NGC 6121, NGC 6397 and NGC 6752. The main goal is the characterization of the multiple stellar populations along the main sequence (MS) and the study of the radial trend of the different populations hosted by the target clusters. The data have been collected using FORS2 mounted at the ESO/VLT@UT1 telescope in UBVI filters. From these data sets we extracted high-accuracy photometry and constructed color-magnitude diagrams. We exploit appropriate combination of colors and magnitudes which are powerfu…
We present the results of CCD UBV observations of the open cluster NGC 6819. We calculated the stellar density profile in the cluster's field to determine the structural parameters of NGC 6819. Using the existing astrometric data, we calculated the probabilities of the stars being physical members of the cluster, and used these objects in the determination of the astrophysical parameters of NGC 6819. We inferred the reddening and metallicity of the cluster as $E(B-V)=0.130\pm0.035$ mag and $[Fe/H]=+0.051\pm 0.020$ dex, respectively, using the U-B vs B-V two-colour diagram and UV excesses of th…
Spectroscopic studies have demonstrated that nearly all Galactic globular clusters (GCs) harbour multiple stellar populations with different chemical compositions. Moreover, colour-magnitude diagrams based exclusively on Strömgrem photometry have allowed us to identify and characterise multiple populations along the RGB of a large number of clusters. In this paper we show for the first time that Strömgren photometry is also very effcient at identifying multiple populations along the AGB, and demonstrate that the AGB of M3, M92, NGC362, NGC1851, and NGC6752 are not consistent with a single stel…
We present an improved data-reduction technique to obtain high-precision proper motions (PMs) of globular clusters using Hubble Space Telescope data. The new reduction is superior to the one presented in the first paper of this series for the faintest sources in very crowded fields. We choose the globular cluster NGC 362 as a benchmark to test our new procedures. We measure PMs of 117 450 sources in the field, showing that we are able to obtain a PM precision better than 10 $μ$as yr$^{-1}$ for bright stars. We make use of this new PM catalog of NGC 362 to study the cluster's internal kinematic…
A recent study of hot (20,000 to 30,000 K) extreme horizontal branch (EHB) stars in globular clusters (GCs) has led to the discovery of their variability. It is suggested that this variability is driven by the projected rotation of magnetic spots on the stellar surfaces and is expected to have higher amplitudes at shorter wavelengths. Here, we present the analysis of such hot stars in the massive GC NGC 2808 using the Ultraviolet Imaging Telescope (UVIT), aboard AstroSat. We use the UVIT data in combination with the Hubble Space Telescope UV Globular Cluster Survey (HUGS) data for the central …
Due to their extreme helium abundance, the multiple stellar populations of the globular cluster NGC 2808 have been widely investigated from a photometric, spectroscopic, and kinematic perspective. The most striking feature of the color-magnitude diagram of NGC 2808 is the triple main sequence (MS), with the red MS corresponding to a stellar population with primordial helium, and the middle and the blue MS being enhanced in helium up to Y$\sim$0.32 and $\sim$0.38, respectively. A recent study has revealed that this massive cluster hosts at least five distinct stellar populations (A, B, C, D, an…
We present BV and u'g'r'i' CCD photometry of the central region of NGC 2482. We also present BVu'g' CCD photometry of five clusters that have been poorly studied in the past: Ruprecht 42, Ruprecht 51, Ruprecht 153, Ruprecht 154; and AH03 J0748-26.9, which to our knowledge has not been studied before. Using a global optimization technique that eliminates much of the subjectivity previously inherent in main sequence fitting studies, we obtain values of the distances, ages, and metallicities of the clusters, with robust estimates of the uncertainties of these fundamental parameters. Four of our c…
Determination of the physical characteristics of the variable stars in the direction of the open cluster NGC 6811 through $uvbyβ$ photoelectric photometry
We present results of an optical search for Cepheid variable stars using the Hubble Space Telescope (HST) in 19 hosts of Type Ia supernovae (SNe Ia) and the maser-host galaxy NGC 4258, conducted as part of the SH0ES project (Supernovae and H0 for the Equation of State of dark energy). The targets include 9 newly imaged SN Ia hosts using a novel strategy based on a long-pass filter that minimizes the number of HST orbits required to detect and accurately determine Cepheid properties. We carried out a homogeneous reduction and analysis of all observations, including new universal variability sea…
The Hubble Space Telescope UV Legacy survey of Galactic Globular Clusters (GC) is characterising many different aspects of their multiple stellar populations. The "Grundahl-jump" (G-jump) is a discontinuity in ultraviolet brightness of blue horizontal branch (HB) stars, signalling the onset of radiative metal levitation. The HB Legacy data confirmed that the G-jump is located at the same T$_{eff}$ ($\simeq$11,500 K) in nearly all clusters. The only exceptions are the metal-rich clusters NGC 6388 and NGC 6441, where the G-jump occurs at T$_{eff}\simeq$13-14,000K. We compute synthetic HB models …
We present year-long, near-infrared Hubble Space Telescope WFC3 observations used to search for Mira variables in NGC 1559, the host galaxy of the Type Ia supernova (SN Ia) 2005df. This is the first dedicated search for Miras, highly-evolved low-mass stars, in a SN Ia host and subsequently the first calibration of the SN Ia luminosity using Miras in a role historically played by Cepheids. We identify a sample of 115 O-rich Miras with P < 400 days based on their light curve properties. We find that the scatter in the Mira Period-Luminosity Relation (PLR) is comparable to Cepheid PLRs seen in SN…
We present results of a search for variable stars in a region of the globular cluster NGC 4147 based on photometric observations with 4k x 4k CCD imager mounted at the axial port of the recently installed 3.6 m Devasthal optical telescope at Aryabhatta Research Institute of Observational Sciences, Nainital, India. We performed time series photometry of NGC 4147 in V and R bands, and identified 42 periodic variables in the region of NGC 4147, 28 of which have been detected for the first time. Seventeen variable stars are located within the half light radius $\lesssim$ 0.48 arcmin, of which 10 s…
Broadband $BVRI$ light curves of SN 2017eaw in NGC 6946 reveal the classic elements of a Type II-P supernova. The observations were begun on 16 May 2017 (UT), approximately 1 day after the discovery was announced, and the photometric monitoring was carried out over a period of nearly 600 days. The light curves show a well-defined plateau and an exponential tail which curves slightly at later times. An approximation to the bolometric light curve is derived and used to estimate the amount of $^{56}$Ni created in the explosion; from various approaches described in the literature, we obtain $M$($^…
The four-year Kepler mission collected long cadence images of the open clusters NGC 6791 and NGC 6819, known as "superstamps." Each superstamp region is a 200-pixel square that captures thousands of cluster members, plus foreground and background stars, of which only the brightest were targeted for long or short cadence photometry during the Kepler mission. Using image subtraction photometry, we have produced light curves for every object in the Kepler Input Catalog that falls on the superstamps. The IRIS catalog includes light curves for 9,150 stars, and contains a wealth of new data: 8,427 o…
