Near-Infrared Photometry of the Globular Cluster Palomar 6 (original) (raw)
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Unveiling palomar 2: The most obscure globular cluster in the outer halo
The Astronomical Journal, 1997
We present the first color-magnitude study for Palomar 2, a distant and heavily obscured globular cluster near the Galactic anticenter. Our (V, V − I) color-magnitude diagram (CMD), obtained with the UH8K camera at the CFHT, reaches V (lim) ≃ 24 and clearly shows the principal sequences of the cluster, though with substantial overall foreground absorption and differential reddening. The CMD morphology shows a well populated red horizontal branch with a sparser extension to the blue, similar to clusters such as NGC 1261, 1851, or 6229 with metallicities near [Fe/H] ≃ −1.3. From an average of several indicators, we estimate the foreground reddening at E(B − V ) = 1.24 ± 0.07 and obtain a true distance modulus (m − M) 0 = 17.1 ± 0.3, placing it ≃ 34 kpc from the Galactic center. We use starcounts of the bright stars to measure the core radius, half-mass radius, and central concentration of the cluster. Its integrated luminosity is M t V ≃ −7.9, making it clearly brighter and more massive than most other clusters in the outer halo. Very rough arguments based on its half-mass radius and radial velocity suggest that Palomar 2 is now moving in toward perigalacticon on a highly elliptical orbit (e ∼ > 0.7).
CCD photometry of the globular cluster Palomar�13
Astronomy and Astrophysics Supplement Series, 1997
A new CCD photometry of the halo cluster Palomar 13 is used to construct a color − magnitude diagram in the Thuan−Gunn and the B, V photometric systems 1. The color−magnitude diagram of the cluster shows as already noted by Ortolani et al. (1985) an extremely poor red horizontal branch and a very sparsely populated giant branch. Seven BSS candidates are identified in the field of Palomar 13. The age of the cluster determined by fitting with the isochrones of Proffitt & Vanden Berg (1991) and Bergbusch & Vanden Berg (1992) and by a differential comparison of the color−magnitude diagram with that of Pal 5 is 12 ± 2 Gyr.
Colour Magnitude Diagrams of the moderately metal-rich globular clusters NGC 6569 and Palomar 11
Astronomy & Astrophysics, 2001
For the first time Colour-Magnitude Diagrams are presented for NGC 6569 and Palomar 11. NGC 6569 is a rather concentrated cluster whereas Palomar 11 is loose and sparsely populated. Cluster parameters are derived from V and I photometry. These are red Horizontal Branch globular clusters, with metallicities comparable to that of 47 Tucanae. We derive a reddening E(B − V) ≈ 0.53 and a distance from the Sun d ≈ 9.8 kpc for NGC 6569, and E(B − V) ≈ 0.35 and d ≈ 13.2 kpc for Palomar 11. NGC 6569 is located in the bulge, while Palomar 11, despite its rather high metallicity, is in the inner halo, a rare case similar to that of 47 Tucanae.
Palomar 13: An Unusual Stellar System in the Galactic Halo
The Astrophysical Journal, 2002
We report the first results of a program to study the internal kinematics of globular clusters in the outer halo of the Milky Way. Using the Keck telescope and High Resolution Echelle Spectrometer, we have measured precise radial velocities for 30 candidate red giants in the direction of Palomar 13, an object traditionally cataloged as a compact, low-luminosity globular cluster. We have combined these radial velocities with published proper motion membership probabilities and new CCD photometry from the Keck and Canada-France-Hawaii telescopes, to isolate a sample of 21 probable members. We find a systemic velocity of v r s = 24.1±0.5 km s −1 and a projected, intrinsic velocity dispersion of σ p = 2.2±0.4 km s −1 . Although small, this dispersion is nevertheless several times larger than that expected for a globular cluster of this luminosity and central concentration. Taken at face value, this dispersion implies a mass-to-light ratio of Υ V = 40 +24 −17 based on the best-fit King-Michie model. The surface density profile of Palomar 13 also appears to be anomalous among Galactic globular clusters -depending upon the details of background subtraction and model-fitting, Palomar 13 either contains a substantial population of "extra-tidal" stars, or it is far more spatially extended than previously suspected. The full surface density profile is equally well-fit by a King-Michie model having a high concentration and large tidal radius, or by a NFW model. We examine -and tentatively reject -a number of possible explanations for the observed characteristics of Palomar 13 (e.g., velocity "jitter" among the red giants, spectroscopic binary stars, non-standard mass functions, modified Newtonian dynamics), and conclude that the two most plausible scenarios are either catastrophic heating during a recent perigalacticon passage, or the presence of a massive dark halo. Thus, the available evidence suggests that Palomar 13 is either a globular cluster which is now in the process of dissolving into the Galactic halo, or a faint, dark-matter-dominated stellar system.
The Astronomical Journal, 1999
We have used the WFPC2 camera on the Hubble Space Telescope to obtain photometry of the outer-halo globular clusters Palomar 3, Palomar 4, and Eridanus. These three are classic examples of the \second parameter" anomaly because of their red horizontal-branch morphologies in combination with their low-to-intermediate metallicities. Our color-magnitude diagrams in (V;V{I) reach V lim ' 27:0, clearly delineating the subgiant and turno regions and about three magnitudes of the unevolved main sequences. The slopes and dereddened colors of the giant branches are consistent with published [Fe/H] estimates that rank the clusters (Pal 3, Eridanus, Pal 4) in order of increasing metallicity, with all three falling near or between the abundance values of the classic nearby halo clusters M 3 and M 5. Dierential ts of their color-magnitude diagrams are made to each other and to M 3 and M 5 for relative age determinations. We nd that the three outer-halo cluster CMDs dier from the nearby clusters in a way that is consistent with their being younger by 1:5 2 Gyr, if we h a v e correctly estimated the clusters' chemical-abundance ratios. Conversely, the inferred age dierence could be smaller (< 1 Gyr) if either [Fe/H] or [/Fe] for the outer-halo clusters is signicantly lower than we have assumed. Possible age spreads of order 1 Gyr among both the nearby and outer-halo clusters may also be present.
Near-infrared photometry of four metal-rich bulge globular clusters: NGC 6304, 6569, 6637 and 6638
Monthly Notices of The Royal Astronomical Society, 2005
We present high-quality near-infrared (near-IR) photometry of four bulge metal-rich globular clusters, namely NGC 6304, 6569, 6637 and 6638. By using the observed colour-magnitude diagrams we derived photometric estimates of the cluster reddening and distance. We performed a detailed analysis of the red giant branch (RGB), presenting a complete description of its morphologic parameters and evolutionary features (bump and tip). Photometric estimates of the cluster metallicity were obtained using the updated data set (published by our group) linking metal abundance to a variety of near-IR indices measured along the RGB. The detection of the RGB bump and tip is also presented and briefly discussed.
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.
The Main-Sequence Luminosity Function of Palomar 5 from THE [ITAL]HUBBLE SPACE TELESCOPE[/ITAL]
The Astronomical Journal, 2001
A low mass, large core radius, low central concentration, and strong tidal tails suggest that the globular cluster Palomar 5 has lost a large fraction of its initial mass over time. If the dynamical evolution of Palomar 5 has been dominated by the effects of mass loss, then theoretical arguments suggest that the luminosity function should be deficient in low-mass stars. Using deep WFPC2 F555W and F814W photometry, we determine the main sequence luminosity functions both near the cluster center and in a field near the half-light radius. A comparison of these luminosity functions yields no compelling evidence of mass segregation within the cluster, in accord with expectations for low-concentration clusters. On the other hand, a comparison of the global mass function of Palomar 5 with that of ω Cen and M55 indicates an increasing deficiency of stars with progressively lower masses. A fit of the observed luminosity function to theoretical models indicates a mass function for Palomar 5 of dN/dm ∝ m −0.5 , which is notably more deficient in low-mass stars than other globular clusters that have been studied with HST. The flatness of the mass function is consistent with models of the dynamical evolution of globular clusters that have lost ∼ 90% of their original stellar mass. We suggest that, like NGC 6712, Pal 5 has lost a large percentage of its original stellar content as a result of tidal shocking.
The Astronomical Journal, 1999
A catalog including a set of the most recent Color Magnitude Diagrams (CMDs) is presented for a sample of 61 Galactic Globular Clusters (GGCs). We used this data-base to perform an homogeneous systematic analysis of the evolved sequences (namely, Red Giant Branch (RGB), Horizontal Branch (HB) and Asymptotic Giant Branch (AGB)). Based on this analysis, we present: (1) a new procedure to measure the level of the ZAHB (V ZAHB ) and an homogeneous set of distance moduli obtained adopting the HB as standard candle; (2) an independent estimate for RGB metallicity indicators and new calibrations of these parameters in terms of both spectroscopic ([Fe/H] CG97 ) and global metallicity ([M/H], including also the α−elements enhancement). The set of equations presented can be used to simultaneously derive a photometric estimate of the metal abundance and the reddening from the morphology and the location of the RGB in the (V, B − V )-CMD. (3) the location of the RGB-Bump (in 47 GGCs) and the AGB-Bump (in 9 GGCs). The dependence of these features on the metallicity is discussed. We find that by using the latest theoretical models and the new metallicity scales the earlier discrepancy between theory and observations (∼ 0.4 mag) completely disappears.
Photometric membership and metallicities of red giant candidates in selected open clusters
Astronomische Nachrichten, 2008
Lodén 807)-stars: abundances-techniques: photometry-techniques: radial velocities As part of a long-term project to determine abundances and astrophysical properties of evolved red stars in open clusters, we present high-precision DDO photoelectric observations for a sample of 33 red giant candidates projected in the fields of nine Galactic open clusters. These data are supplemented with UBV photoelectric photometry of 24 of these stars as well as with CORAVEL radial-velocity observations for 13 red giant candidates in four of the clusters. We also present Washington photoelectric photometry of a small sample of red giant candidates of the open cluster Ruprecht 97. The likelihood of cluster membership for each star photometrically observed and for 23 additional red giant candidates with UBV and DDO data available in the literature, is evaluated by using two independent photometric criteria. Nearly 82% of the analysed stars are found to have a high probability of being cluster giants. Photometric membership probabilities show very good agreement with those obtained from CORAVEL radial velocities. While E(B − V) colour excesses were determined from combined B − V and DDO colours, calibrations of the DDO system were used to derive MK spectral types, effective temperatures and metallicities.The derived DDO metallicities range between values typical of moderately metal-poor clusters ([Fe/H] =-0.19) to moderately metal-rich ([Fe/H] = 0.25) ones.