WIYN Open Cluster Study. II. [ITAL]UBVRI[/ITAL] CCD Photometry of the Open Cluster NGC 188

Sarajedini, Ata; Hippel, Ted von; Kozhurina-Platais, V.; Demarque, P.

doi:10.1086/301149

Cited by 126 publications

(170 citation statements)

References 30 publications

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“…This E(BϪV) reddening was taken from the dust maps by Schlegel, Finkbeiner, & Davis (1998). The low value agrees with that from Strömgren intermediateband photometry of individual M67 member stars by Nissen, Twarog, & Crawford (1987) and from the latest analysis of the two-color diagram by Sarajedini et al (1999) Table 3. differences with the Hyades. The many divergent determinations of reddening and distance moduli in the literature were also discussed in these papers, including the earliest V, BϪV data measured by Johnson & Sandage (1955) for their initial diagram.…”

Section: M67supporting

confidence: 74%

The Age of the Oldest Stars in the Local Galactic Disk fromHipparcosParallaxes of G and K Subgiants

Sandage

Lubin

VandenBerg

2003

PUBL ASTRON SOC PAC

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ABSTRACT. We review the history of the discovery of field subgiant stars, the role that they played in the development of the early understanding of stellar evolution, and their importance in the age dating of the Galactic disk. We use the cataloged data from the Hipparcos satellite in this latter capacity.Based on Hipparcos parallaxes with relative accuracies of , the absolute magnitude of the lower , as well as to the envelope of the reddest main-sequence stars at . The rededge of the densest part of the distribution of field giants is, however, most readily matched by isochrones having [Fe/H . Such high metal abundances are evidently confirmed by the spectroscopically observed high ] ≈ ϩ0.23 metallicity (between [Fe/H and ϩ0.4) of the old thick-disk Galactic cluster NGC 6791, whose color-] p ϩ0.2 magnitude diagram can be made to fit either of these red boundaries by adopting suitable values for the reddening and distance modulus (from within the observed ranges of uncertainties of these quantities).The age of the field stars in the solar neighborhood is found to be Gyr (or Gyr if the stellar 7.9 ‫ע‬ 0.7 7.4 ‫ע‬ 0.7 models allow for the effects of diffusive processes) by fitting the theoretical isochrones for [Fe/H to the ] p ϩ0.37 lower envelope of the Hipparcos subgiants. However, this age is a function of metallicity. The models show a dependence of at for metallicities between 0.00 and ϩ0.37. The same grid dt p Ϫ3.99([Fe/H] Ϫ 0.37) M ∼ ϩ4 V of isochrones yields ages, in turn, of , , and 7.5 to 10 Gyr (depending on the assumed reddening) 4.0 ‫ע‬ 0.2 6.2 ‫ע‬ 0.5 for the old Galactic clusters M67, NGC 188, and NGC 6791 using metal abundances, distance moduli, and reddenings adopted in the text. Although the distance (and hence age) of NGC 6791 is somewhat uncertain, the ages of both the Galactic disk in the solar neighborhood and of NGC 6791 are, nevertheless, likely between 3 and 5 Gyr younger than the oldest halo globular clusters, which have ages of ∼13.5 Gyr. The conclusion is the same as that reached earlier by Liu & Chaboyer, who used Hipparcos parallax stars that were mainly near the main-sequence turnoff rather than at the lower bound of the subgiant luminosity that we determine here. The most significant results are (1) the supermetallicity of the oldest local disk stars and (2) the large age difference between the most metal poor component of the halo and the thick and thin disk in the solar neighborhood, confirming Liu & Chaboyer. These facts are undoubtedly related and pose again the problem of the proper scenario for the timing of events in the formation of the halo and the Galactic disk in the solar neighborhood.1 Part review of the history of the discovery of subgiants and part new results from Hipparcos.

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Section: M67supporting

confidence: 74%

The Age of the Oldest Stars in the Local Galactic Disk fromHipparcosParallaxes of G and K Subgiants

Sandage

Lubin

VandenBerg

2003

PUBL ASTRON SOC PAC

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“…We have chosen such a high-Z cluster to avoid strong gradient at the beginning of the simulation. Old "survivors" like M 67 (Fan et al 1996) or NGC 188 (Sarajedini et al 1999) have total masses of this order, and follow such high-Z orbits (see Carraro & Chiosi 1994). Figure 9 shows that the OC mass loss by the disk-shocking is about 1.5% of its total mass in one Z-oscillation.…”

Section: Discussionmentioning

confidence: 99%

Gravitational tidal effects on galactic open clusters

Bergond

Léon

Guibert

2001

A&A

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Abstract.We have investigated the 2-D stellar distribution in the outer parts of three nearby open clusters: NGC 2287 (≡M 41), NGC 2516, and NGC 2548 (≡M 48). Wide-field star counts have been performed in two colours on pairs of digitized ESO and SRC Schmidt plates, allowing us to select likely cluster members in the colour-magnitude diagrams. Cluster tidal extensions were emphasized using a wavelet transform. Taking into account observational biases, namely the galaxy clustering and differential extinction in the Galaxy, we have associated these stellar overdensities with real open cluster structures stretched by the galactic gravitational field. As predicted by theory and simulations, and despite observational limitations, we detected a general elongated (prolate) shape in a direction parallel to the galactic Plane, combined with tidal tails extended perpendicularly to it. This geometry is due both to the static galactic tidal field and the heating up of the stellar system when crossing the Disk. The time varying tidal field will deeply affect the cluster dynamical evolution, and we emphasize the importance of adiabatic heating during the Disk-shocking. In the case of NGC 2548, our dating of the last shocking with the Plane (based on a tidal clump) is consistent with its velocity. During the 10-20 Z-oscillations experienced by a cluster before its dissolution in the Galaxy, crossings through the galactic Disk contribute to at least 15% of the total mass loss. Using recent age estimations published for open clusters, we find a destruction time-scale of about 600 Myr for clusters in the solar neighbourhood.

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“…A number of excellent studies have previously been performed for NGC 188 that have accurately determined its physical parameters (von Hippel & Sarajedini 1998;Sarajedini et al 1999;Platais et al 2003;Michaud et al 2004;Stetson et al 2004;. NGC 188 is used as a fiducial cluster, and a precise age is obtained for Berkeley 17 relative to NGC 188.…”

Section: Introductionmentioning

confidence: 99%

UBVICCD Photometry of the Old Open Cluster Berkeley 17

Krusberg¹,

Chaboyer²

2006

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Photometric UBVI CCD photometry is presented for NGC 188 and Berkeley 17. Color-magnitude diagrams (CMDs) are constructed and reach well past the main-sequence turnoff for both clusters. Cluster ages are determined by means of isochrone fitting to the cluster CMDs. These fits are constrained to agree with spectroscopic metallicity and reddening estimates. Cluster ages are determined to be 7:0 AE 0:5 Gyr for NGC 188 and 10:0 AE 1:0 Gyr for Berkeley 17, where the errors refer to uncertainties in the relative age determinations. These ages are compared to the ages of relatively metal-rich inner halo/thick-disk globular clusters and other old open clusters. Berkeley 17 and NGC 6791 are the oldest open clusters, with ages of 10 Gyr. They are 2 Gyr younger than the thick-disk globular clusters. These results confirm the status of Berkeley 17 as one of the oldest known open clusters in the Milky Way, and its age provides a lower limit to the age of the Galactic disk.

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WIYN Open Cluster Study. II. [ITAL]UBVRI[/ITAL] CCD Photometry of the Open Cluster NGC 188

Cited by 126 publications

References 30 publications

The Age of the Oldest Stars in the Local Galactic Disk fromHipparcosParallaxes of G and K Subgiants

The Age of the Oldest Stars in the Local Galactic Disk fromHipparcosParallaxes of G and K Subgiants

Gravitational tidal effects on galactic open clusters

UBVICCD Photometry of the Old Open Cluster Berkeley 17

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