DSpace Angular :: Browsing by Author "Stetson, P. B."

Browsing by Author "Stetson, P. B."

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A Search for EHB Pulsators in the Globular Cluster NGC 6752
(2007) Catelan , Marcio; Prieto, G. E.; Zoccali, M.; Weidner, C.; Stetson, P. B.; Moni Bidin, C.; Altmann, M.; Smith, H. A.; Pritzl, B. J.; Borissova, J.; de Medeiros, J. R.
We describe the status of a project whose main goal is to detect variability along the extreme horizontal branch of the globular cluster NGC 6752. Based on Magellan 6.5-m data, preliminary light curves are presented for some candidate variables. By combining our time-series data, we also produce a deep CMD of unprecedented quality for the cluster which reveals a remarkable lack of main sequence binaries, possibly pointing to a low primordial binary fraction....
Constraints on the formation of the globular cluster IC 4499 from multiwavelength photometry
(2011) Walker, A. R.; Kunder, A. M.; Andreuzzi, G.; Di Cecco, A.; Stetson, P. B.; Monelli, M.; Cassisi, S.; Bono, G.; De Propris, R.; Dall'Ora, M.; Nemec, J. M.; Zoccali, M.
We present new multiband photometry for the Galactic globular cluster IC 4499 extending well past the main-sequence turn-off in the U, B, V, R, I and DDO51 bands. This photometry is used to determine that IC 4499 has an age of 12 +/- 1 Gyr and a cluster reddening of E(B - V) = 0.22 +/- 0.02. Hence, IC 4499 is coeval with the majority of Galactic globular clusters, in contrast to suggestions of a younger age. The density profile of the cluster is observed to not flatten out to at least r similar to 800 arcsec, implying that either the tidal radius of this cluster is larger than previously estimated, or that IC 4499 is surrounded by a halo. Unlike the situation in some other, more massive, globular clusters, no anomalous colour spreads in the ultraviolet are detected among the red giant branch stars. The small uncertainties in our photometry should allow the detection of such signatures apparently associated with variations of light elements within the cluster, suggesting that IC 4499 consists of a single stellar population.
Disentangling multiple stellar populations in globular clusters using the Strömgren system
(2015) Alonso-García, J.; Catelan, Márcio; Amigo, P.; Cortés, C.; Kuehn, C. A.; Grundahl, F.; López, G.; Salinas, R.; Smith, H. A.; Stetson, P. B.; Sweigart, Allen V.; Valcarce, Aldo A. R.; Zoccali, M.
An increasing amount of spectroscopic and photometric evidence is showing that the stellar populations of globular clusters are not as simple as they have been considered for many years. The presence of at least two different populations of stars is being discovered in a growing number of globular clusters, both in our Galaxy and in others. We have started a series of observations of Galactic globular clusters using the Strömgren photometric system in order to find the signatures of these multiple populations and establish their presence in a more complete sample of globular clusters in the Milky Way, and to study their radial distributions and extensions. We present here the first results of our survey....
Iron and s-elements abundance variations in NGC 5286: comparison with 'anomalous' globular clusters and Milky Way satellites
(2015) Marino, A. F.; Milone, A. P.; Karakas, A. I.; Casagrande, L.; Yong, D.; Shingles, L.; Da Costa, G.; Norris, J. E.; Stetson, P. B.; Lind, K.; Asplund, M.; Collet, R.; Jerjen, H.; Sbordone, L.; Aparicio, A.; Cassisi, S.
We present a high-resolution spectroscopic analysis of 62 red giants in the Milky Way globular cluster (GC) NGC 5286. We have determined abundances of representative light proton-capture, a, Fe-peak and neutron-capture element groups, and combined them with photometry of multiple sequences observed along the colour-magnitude diagram. Our principal results are: (i) a broad, bimodal distribution in s-process element abundance ratios, with two main groups, the s-poor and s-rich groups; (ii) substantial star-to-star Fe variations, with the s-rich stars having higher Fe, e.g. <[Fe/H]>(s-rich) - <[Fe/H]>(s-poor) similar to 0.2 dex; and (iii) the presence of O-Na-Al (anti) correlations in both stellar groups. We have defined a new photometric index, c(BVI) = (B - V) -(V - I), to maximize the separation in the colour-magnitude diagram between the two stellar groups with different Fe and s-element content, and this index is not significantly affected by variations in light elements (such as the O-Na anticorrelation). The variations in the overall metallicity present in NGC 5286 add this object to the class of anomalous GCs. Furthermore, the chemical abundance pattern of NGC 5286 resembles that observed in some of the anomalous GCs, e.g. M 22, NGC 1851, M 2, and the more extreme omega Centauri, that also show internal variations in s-elements, and in light elements within stars with different Fe and s-elements content. In view of the common variations in s-elements, we propose the term s-Fe-anomalous GCs to describe this sub-class of objects. The similarities in chemical abundance ratios between these objects strongly suggest similar formation and evolution histories, possibly associated with an origin in tidally disrupted dwarf satellites.
Multiple populations in Galactic globular clusters from a Strömgren perspective
(2014) Alonso-García, J.; Catelan, Márcio; Amigo, P.; Cortés, C.; Kuehn, C. A.; Grundahl, F.; López, G.; Salinas, R.; Smith, H. A.; Stetson, P. B.; Sweigart, Allen V.; Valcarce, Aldo A. R.; Zoccali, M.
Our view of the stellar populations in globular clusters has radically changed in the last years. Now we are coming to believe that all globular clusters host at least two distinct stellar populations. We present in this contribution preliminary results of a photometric survey we are currently conducting to disentangle photometrically the several populations in a significant number of Galactic globular clusters, using the Strömgren system, aiming to characterize their relative ratios and their radial distributions....
Multiple populations in Galactic globular clusters: a survey in the Strömgren system
(2013) Alonso-García, J.; Catelan, Márcio; Amigo, P.; Cortés, C.; Kuehn, C. A.; Grundahl, F.; López, G.; Salinas, R.; Smith, H. A.; Stetson, P. B.; Sweigart, Allen V.; Valcarce, Aldo A. R.; Zoccali, M.
We are coming to believe that stellar populations in globular clusters are not as simple as they were once thought to be. A growing amount of photometric and spectroscopic evidence shows that globular clusters host at least two different stellar populations. In our contribution to these proceedings we present the first results of a survey we are conducting to look for the presence of multiple populations in a significant number of Galactic globular clusters, using the Strömgren system. We intend to photometrically separate these populations and characterize their radial distributions and extensions....
New near-infrared JHK_s light-curve templates for RR Lyrae variables
(2019) Braga, V. F.; Stetson, P. B.; Bono, G.; Dall'Ora, M.; Ferraro, I; Fiorentino, G.; Iannicola, G.; Inno, L.; Marengo, M.; Neeley, J.; Beaton, R. L.; Buonanno, R.; Calamida, A.; Ramos, R. Contreras; Chaboyer, B.; Fabrizio, M.; Freedman, W. L.; Gilligan, C. K.; Johnston, K., V; Lub, J.; Madore, B. F.; Magurno, D.; Marconi, M.; Marinoni, S.; Marrese, P. M.; Mateo, M.; Matsunaga, N.; Minniti, D.; Monson, A. J.; Monelli, M.; Nonino, M.; Persson, S. E.; Pietrinferni, A.; Sneden, C.; Storm, J.; Walker, A. R.; Valenti, E.; Zoccali, M.
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.
ON THE RADIAL DISTRIBUTION OF HORIZONTAL BRANCH STARS IN NGC 2808
(2009) Iannicola, G.; Monelli, M.; Bono, G.; Stetson, P. B.; Buonanno, R.; Calamida, A.; Zoccali, M.; Caputo, F.; Castellani, M.; Corsi, C. E.; Dall'Ora, M.; Di Cecco, A.; Degl'Innocenti, S.; Ferraro, I.; Nonino, M.; Pietrinferni, A.; Pulone, L.; Moroni, P. G. Prada; Romaniello, M.; Sanna, N.; Walker, A. R.
We present accurate new ultraviolet and optical BVI photometry for the Galactic globular cluster NGC 2808 based on both ground-based and archival Hubble Space telescope imagery. From this we have selected a sample of similar to 2000 Horizontal Branch (HB) stars; given the extensive wavelength range considered and the combination of both high angular resolution and wide-field photometric coverage, our sample should be minimally biased. We divide the HB stars into three radial bins and find that the relative fractions of cool, hot, and extreme HB stars do not change radically when moving from the center to the outskirts of the cluster: the difference is typically smaller than similar to 2 sigma. These results argue against the presence of strong radial differentiation among any stellar subpopulations having distinctly different helium abundances. The ratio between HB and red giant (RG) stars brighter than the ZAHB steadily increases when moving from the innermost to the outermost cluster regions. The difference is larger than similar to 4 sigma and indicates a deficiency of bright RGs in the outskirts of the cluster.
On the Use of Field RR Lyrae as Galactic Probes. II. A New ΔS Calibration to Estimate Their Metallicity*
(2021) Crestani, J.; Fabrizio, M.; Braga, V. F.; Sneden, C.; Preston, G.; Ferraro, I.; Iannicola, G.; Bono, G.; Alves-Brito, A.; Nonino, M.; D'Orazi, V.; Inno, L.; Monelli, M.; Storm, J.; Altavilla, G.; Chaboyer, B.; Dall'Ora, M.; Fiorentino, G.; Gilligan, C.; Grebel, E. K.; Lala, H.; Lemasle, B.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C. E.; Matsunaga, N.; Mullen, J. P.; Neeley, J.; Prudil, Z.; da Silva, R.; Stetson, P. B.; Thevenin, F.; Valenti, E.; Walker, A.; Zoccali, M.
We performed the largest and most homogeneous spectroscopic survey of field RR Lyraes (RRLs). We secured 6300 high-resolution (HR, R similar to 35,000) spectra for 143 RRLs (111 fundamental, RRab; 32 first-overtone, RRc). The atmospheric parameters were estimated by using the traditional approach and the iron abundances were measured by using an LTE line analysis. The resulting iron distribution shows a well-defined metal-rich tail approaching solar iron abundance. This suggests that field RRLs experienced a complex chemical enrichment in the early halo formation. We used these data to develop a new calibration of the Delta S method. This diagnostic, based on the equivalent widths of Ca ii K and three Balmer (H-delta,H-gamma,H-beta) lines, traces the metallicity of RRLs. For the first time, the new empirical calibration: (i) includes spectra collected over the entire pulsation cycle; (ii) includes RRc variables; (iii) relies on spectroscopic calibrators covering more than three dex in iron abundance; and (iv) provides independent calibrations based on one/two/three Balmer lines. The new calibrations were applied to a data set of both SEGUE-SDSS and degraded HR spectra totalling 6451 low-resolution (R similar to 2000) spectra for 5001 RRLs (3439 RRab, 1562 RRc). This resulted in an iron distribution with a median eta = -1.55 0.01 and sigma = 0.51 dex, in good agreement with literature values. We also found that RRc are 0.10 dex more metal-poor than RRab variables, and have a distribution with a smoother metal-poor tail. This finding supports theoretical prescriptions suggesting a steady decrease in the RRc number when moving from metal-poor to metal-rich stellar environments.
On the Use of Field RR Lyrae as Galactic Probes. III. The α-element Abundances*
(2021) Crestani, J.; Braga, V. F.; Fabrizio, M.; Bono, G.; Sneden, C.; Preston, G.; Ferraro, I.; Iannicola, G.; Nonino, M.; Fiorentino, G.; Thevenin, F.; Lemasle, B.; Prudil, Z.; Alves-Brito, A.; Altavilla, G.; Chaboyer, B.; Dall'Ora, M.; D'Orazi, V.; Gilligan, C.; Grebel, E. K.; Koch-Hansen, A. J.; Lala, H.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C.; Matsunaga, N.; Monelli, M.; Mullen, J. P.; Neeley, J.; da Silva, R.; Stetson, P. B.; Salaris, M.; Storm, J.; Valenti, E.; Zoccali, M.
We provide the largest and most homogeneous sample of alpha-element (Mg, Ca, Ti) and iron abundances for field RR Lyrae (RRLs; 162 variables) by using high-resolution spectra. The current measurements were complemented with similar abundances available in the literature for 46 field RRLs brought to our metallicity scale. We ended up with a sample of old (t >= 10 Gyr), low-mass stellar tracers (208 RRLs: 169 fundamental, 38 first overtone, and 1 mixed mode) covering 3 dex in iron abundance (-3.00 <= [Fe/H] <= 0.24). We found that field RRLs are similar to 0.3 dex more alpha poor than typical halo tracers in the metal-rich regime ([Fe/H] >= -1.2), while in the metal-poor regime ([Fe/H] <= -2.2) they seem to be on average similar to 0.1 dex more alpha enhanced. This is the first time that the depletion in alpha elements for solar iron abundances is detected on the basis of a large, homogeneous, and coeval sample of old stellar tracers. Interestingly, we also detected a close similarity in the [alpha/Fe] trend between alpha-poor, metal-rich RRLs and red giants (RGs) in the Sagittarius dwarf galaxy as well as between alpha-enhanced, metal-poor RRLs and RGs in ultrafaint dwarf galaxies. These results are supported by similar elemental abundances for 46 field horizontal branch stars. These stars share with RRLs the same evolutionary phase and the same progenitors. This evidence further supports the key role that old stellar tracers play in constraining the early chemical enrichment of the halo and, in particular, in investigating the impact that dwarf galaxies have had in the mass assembly of the Galaxy.
On the Use of Field RR Lyrae as Galactic Probes. V. Optical and Radial Velocity Curve Templates
(2021) Braga, V. F.; Crestani, J.; Fabrizio, M.; Bono, G.; Sneden, C.; Preston, G. W.; Storm, J.; Kamann, S.; Latour, M.; Lala, H.; Lemasle, B.; Prudil, Z.; Altavilla, G.; Chaboyer, B.; Dall'Ora, M.; Ferraro, I; Gilligan, C. K.; Fiorentino, G.; Iannicola, G.; Inno, L.; Kwak, S.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C. E.; Monelli, M.; Mullen, J. P.; Matsunaga, N.; Neeley, J.; Stetson, P. B.; Valenti, E.; Zoccali, M.
We collected the largest spectroscopic catalog of RR Lyrae (RRLs) including approximate to 20,000 high-, medium-, and low-resolution spectra for approximate to 10,000 RRLs. We provide the analytical forms of radial velocity curve (RVC) templates. These were built using 36 RRLs (31 fundamental-split into three period bins-and five first-overtone pulsators) with well-sampled RVCs based on three groups of metallic lines (Fe, Mg, Na) and four Balmer lines (H- alpha , H- beta , H- gamma , H- delta ). We tackled the long-standing problem of the reference epoch to anchor light-curve and RVC templates. For the V-band, we found that the residuals of the templates anchored to the phase of the mean magnitude along the rising branch are similar to 35% to similar to 45% smaller than those anchored to the phase of maximum light. For the RVC, we used two independent reference epochs for metallic and Balmer lines and we verified that the residuals of the RVC templates anchored to the phase of mean RV are from 30% (metallic lines) up to 45% (Balmer lines) smaller than those anchored to the phase of minimum RV. We validated our RVC templates by using both the single-point and the three phase point approaches. We found that barycentric velocities based on our RVC templates are two to three times more accurate than those available in the literature. We applied the current RVC templates to Balmer lines RVs of RRLs in the globular NGC 3201 collected with MUSE at VLT. We found the cluster barycentric RV of V ( gamma ) = 496.89 +/- 8.37(error) +/- 3.43 (standard deviation) km s(-1), which agrees well with literature estimates.
ON THE ΔV_HB^bump PARAMETER IN GLOBULAR CLUSTERS
(2010) Di Cecco, A.; Bono, G.; Stetson, P. B.; Pietrinferni, A.; Becucci, R.; Cassisi, S.; Degl'Innocenti, S.; Iannicola, G.; Moroni, P. G. Prada; Buonanno, R.; Calamida, A.; Caputo, F.; Castellani, M.; Corsi, C. E.; Ferraro, I.; Dall'Ora, M.; Monelli, M.; Nonino, M.; Piersimoni, A. M.; Pulone, L.; Romaniello, M.; Salaris, M.; Walker, A. R.; Zoccali, M.
We present new empirical estimates of the del V-HB(bump) parameter for 15 Galactic globular clusters (GGCs) using accurate and homogeneous ground-based optical data. Together with similar evaluations available in the literature, we ended up with a sample of 62 GGCs covering a very broad range in metal content (-2.16 dex <= [M/H] <= -0.58 dex). Adopting the homogeneous metallicity scale provided either by Kraft & Ivans or by Carretta et al., we found that the observed del V-HB(bump) parameters are larger than predicted. In the metal-poor regime ([M/H] less than or similar to -1.7, -1.6 dex) 40% of GCs show discrepancies of 2s (approximate to 0.40 mag) or more. Evolutionary models that account either for alpha- and CNO-enhancement or for helium enhancement do not alleviate the discrepancy between theory and observations. The outcome is the same if we use the new solar heavy-element mixture. The comparison between alpha- and CNO-enhanced evolutionary models and observations in the Carretta et al. metallicity scale also indicates that observed del V-HB(bump) parameters, in themetal- rich regime ([M/H] >= 0), might be systematically smaller than predicted.
The RR Lyrae Instability Strip in the Split Horizontal Branch Globular Cluster NGC 6569
(2015) Kunder, A.; Stetson, P. B.; Catelan, Marcio; Walker, A.; Cassisi, S.; Johnson, C.; Soto, M.
The first calibrated broadband BVI time-series photometry is obtained for the RR Lyrae variable stars in the split horizontal branch (HB) cluster NGC 6569. As a result, a sizeable population of 27 RR Lyrae variables has been identified. An eclipsing binary in the RR Lyrae instability strip was also found, which is most likely a field star. The 12 fundamental-mode RR Lyrae variables (RR0) have an average period of [P]RR0= 0.57±0.02 d and the 15 first-overtone variables (RR1) have an average period of [P]RR1=0.30±0.01 d. The mean periods of the RR Lyrae stars are consistent with an Oosterhoff I designation, and the number ratio of RR1- to RR0-type variables, N1/NRR=0.56, is more consistent with an Oosterhoff II designation. Compared to the M3 variables, the NGC 6569 RR Lyrae variables are not shifted to a longer periods at a given amplitude, making it unlikely that these stars are He-enhanced. The similarity in the periods and amplitudes between the RR Lyrae stars in NGC 6569 and the bulge field RR Lyrae population may indicate similar formation conditions.
The soundtrack of RR Lyrae in omega Cen at high-frequency.
(2015) Calamida, A.; Randall, S. K.; Monelli, M.; Bono, G.; Buonanno, R.; Strampelli, G.; Catelan, Marcio; Van Grootel, V.; Alonso, M. L.; Stetson, P. B.; Stellingwerf, R. F.
We present preliminary Sloan u',g'-band light curves for a sample of known RR Lyrae variables in the Galactic globular cluster omega Cen. Results are based on the partial reduction of multi-band time series photometric data collected during six consecutive nights with the visitor instrument ULTRACAM mounted on the New Technology Telescope (La Silla, ESO). This facility allowed us to simultaneously observe in three different bands (Sloan u',g',r') a field of view of ∼ 6×6 arcminutes. The telescope and the good seeing conditions allowed us to sample the light curves every 15 seconds. We ended up with a data set of ∼ 6,000 images per night per filter, for a total of more than 200,000 images of the selected field. This data set allowed us to detect different kind of variables, such as RR-Lyraes, SX Phoenicis, eclipsing binaries, semi-regulars. More importantly, we were able for the first time to sample at high-frequency cluster RR Lyraes in the u',g'-band and to show in detail the pulsation phases across the dip located along the rising branch of RR-Lyraes. Based on data collected with ULTRACAM@NTT (La Silla, ESO, PID: 087.D-0216)...
Theoretical modeling of the RR Lyrae variables in NGC 1851
(2015) Kunder, A.; Salaris, M.; Cassisi, S.; de Propris, R.; Walker, A.; Stetson, P. B.; Catelan, Marcio; Amigo, P.
The RR Lyrae instability strip (IS) in NGC 1851 is investigated, and a model is presented which reproduces the pulsational properties of the RR Lyrae population. In our model, a stellar component within the IS that displays minor helium variations (Y∼0.248-0.270) is able to reproduce the observed periods and amplitudes of the RR Lyrae variables, as well as the frequency of fundamental and first-overtone RR Lyrae variables. The RR Lyrae variables therefore may belong to an He-enriched second generation of stars. The RR Lyrae variables with a slightly enhanced helium (Y∼0.270-0.280) have longer periods at a given amplitude, as is seen with Oosterhoff II (OoII) RR Lyrae variables, whereas the RR Lyrae variables with Y∼0.248-0.270 have shorter periods, exhibiting properties of Oosterhoff I (OoI) variables. %.
unVEil the darknesS of The gAlactic buLgE (VESTALE)
(2018) Bono, G.; Dall'Ora, M.; Fabrizio, M.; Crestani, J.; Braga, V. F.; Fiorentino, G.; Altavilla, G.; Botticella, M. T.; Calamida, A.; Castellani, M.; Catelan, Marcio; Chaboyer, B.; Chiappini, C.; Clarkson, W.; Contreras Ramos, R.; Creevey, O.; da Silva, R.; Debattista, V.; Degl'Innocenti, S.; Ferraro, I.; Gilligan, C. K.; Gonzalez, O.; Hambleton, K.; Iannicola, G.; Inno, L.; Kunder, A.; Lemasle, B.; Magrini, L.; Magurno, D.; Marconi, M.; Marengo, M.; Marinoni, S.; Marrese, P. M.; Martinez-Vazquez, C. E.; Matsunaga, N.; Monelli, M.; Prada Moroni, P. G.; Musella, I.; Navarro, M. G.; Neeley, J.; Nonino, M.; Pietrinferni, A.; Pulone, L.; Rich, M. R.; Ripepi, V.; Sacco, G.; Saha, A.; Salaris, M.; Sneden, C.; Stetson, P. B.; Street, R. A; Szabo, R.; Tantalo, M.; Tognelli, E.; Torelli, M.; Valenti, E.; Walker, A. R.; Zoccali, M.
The main aim of this experiment is to provide a complete census of old (t > 10 Gyr, RR Lyrae, type II Cepheids, red horizontal branch), intermediate age (red clump, Miras) and young (classical Cepheids) stellar tracers across the Galactic Bulge. To fully exploit the unique photometric quality of LSST images, we plan to perform a Shallow minisurvey (ugrizy, -20 < l < 20 deg, -15 < b < 10 deg) and a Deep minisurvey (izy, -20 < l < 20 deg, -3 < b < 3 deg). The former one is aimed at constraining the 3D structure of the galactic Bulge across the four quadrants, and in particular, the transition between inner and outer Bulge. The u,g,r,i,z,y LSST bands provide fundamental diagnostics to constrain the evolutionary properties of low and intermediate-mass stars when moving from a metal-poor to a metal-rich regime. The deep minisurvey is aimed at tracing RR Lyrae, Red Clump stars, Miras and classical Cepheids in highly reddened regions of the Galactic center. These images will allow us to investigate the role that baryonic mass and dark matter played in the early formation and evolution of the MW....
Variable Stars in the Inner Region of NGC 6388
(2005) Pritzl, B. J.; Stetson, P. B.; Smith, H. A.; Catelan, Marcio; Layden, A. C.; Kinemuchi, K.; Rich, R. M.; Sweigart, A. V.
The metal-rich globular clusters NGC 6388 and NGC 6441 ([Fe/H] ∼-0.6) have unusual sloping blue horizontal branches that extend from a prominent red clump through the RR Lyrae instability strip to a well-populated blue tail. The RR Lyrae variables found from ground-based studies in these clusters have unusually long periods for their metallicities and may represent a new Oosterhoff group. As part of a Hubble Space Telescope Snapshot program we have obtained ACS images of the inner, compact region of NGC 6388 and use archival WFPC2 images to search for additional variable stars. Here we present the results of this variable star search. The properties of the newly discovered RR Lyrae variables will be used to further define the nature of these unusual globular clusters. We gratefully acknowledge financial support through the HST grant GO-09821.09-A.

Browsing by Author "Stetson, P. B."

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