Absolute Proper and Space Motion of the Globular Cluster M2

Geffert, M.; Forner, C.; Hiesgen, M.; Klemola, A. R.

doi:10.1007/978-94-011-1146-1_96

Cited by 2 publications

(1 citation statement)

References 3 publications

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“…The second method uses stars measured on plates of the Lick astrograph partly from the Lick Northern Proper Motion (NPM) program (Klemola et al 1987) as described in detail in Geffert et al (1997). 16 (NGC 4147) to 85 (NGC 7089) stars were used to calibrate our proper motions to an extragalactic reference frame by the determination of a constant offset of our proper motions with respect to the ones obtained from the Lick plates.…”

Section: Extragalactic Calibration Of the Proper Motionsmentioning

confidence: 99%

Absolute proper motions for the calibration of the Hipparcos proper motion system

Geffert

Klemola

Hiesgen

et al. 1997

Astron. Astrophys. Suppl. Ser.

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Abstract. Absolute proper motions of 48 Hipparcos stars in nine fields distributed over the northern hemisphere are presented. The proper motions have been recently used as part of the Bonn program for the extragalactic link of the Hipparcos proper motion system. We describe methods which have led to the absolute proper motions of the major part of the Bonn fields for the link. For six fields the extragalactic calibration was achieved using the bright quasar in the centre of the field. In addition, data of three fields of globular clusters were included. For these fields the link to an extragalactic reference system was performed by stars, whose absolute proper motions with respect to galaxies were determined on plates of the Lick astrograph. In addition, we used for the link in one field plates from the ESO Schmidt telescope in combination with measurements from glass copies of the Palomar Sky Survey. The accuracy of a single proper motion is of the order of 2 to 3 mas/a for each coordinate.

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Section: Extragalactic Calibration Of the Proper Motionsmentioning

confidence: 99%

Absolute proper motions for the calibration of the Hipparcos proper motion system

Geffert

Klemola

Hiesgen

et al. 1997

Astron. Astrophys. Suppl. Ser.

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Proper motions in the field of the globular cluster NGC 6934

Tucholke

1994

Astron Nachr

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We measured relative proper motions with a typical accuracy of 1.0 milliarcsec/year (mas/a) for 2000 stars in a 104 x 104 field around the low-latitude globular cluster NGC6934. Four plates taken with the Bonn double refractor, spanning an epoch difference of 62 years, were digitized completely. Within the tidal radius of the cluster, we find 106 stars with proper motion errors less than 5 mas/a. Membership probabilities are computed taking into account the individual proper motion errors and the radial distances to the cluster centre. We derive the mean relative proper motion of NGC 6934 using stars with high membership probabilities from radial velocities (Smith and Bell 1986) or from their location in the colour-magnitude diagram (Harris and Racine 1973). The relative proper motions of four Hipparcos stars in the field will be used to obtain the absolute proper motion of NGC 6934 once the extragalactically calibrated Hipparcos Output Catalogue is available. Rodgers and Paltoglou (1984) noted a group of globular clusters with similar metallicity and horizontal branch morphology, which show a mean retrograde rotation about the galactic center according to their positions and radial velocities. They speculated that this group of clusters might result from the accretion of a galactic satellite, supporting the Searle and Zinn (1978) proposal that the Galaxy continued to accrete protogalactic fragments after the formation of its central region had been completed. NGC6934 is the only cluster of the Bonn programme belonging to this group, making the determination of its absolute proper motion very desirable.NGC6934 is situated at a galactic latitude of -1809. Inspection of sky surveys shows that there is no sufficient number of suitable background objects for extragalactic calibration of the proper motions. In this paper we present relative proper motions for 2000 stars in the field of NGC6934, among them 106 stars within the tidal radius of the cluster. The relative proper motions are in the system of the PPM catalogue (Roser and Bastian 1991), which

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Absolute Proper and Space Motion of the Globular Cluster M2

Cited by 2 publications

References 3 publications

Absolute proper motions for the calibration of the Hipparcos proper motion system

Absolute proper motions for the calibration of the Hipparcos proper motion system

Proper motions in the field of the globular cluster NGC 6934

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