The density profile of 47 tucanae

Guido De Marchi; Francesco Paresce; Maria Giuliana Stratta; Ronald L. Gilliland; Ralph C. Bohlin

doi:10.1086/310230

The density profile of 47 tucanae

Guido De Marchi, Francesco Paresce, Maria Giuliana Stratta, Ronald L. Gilliland, Ralph C. Bohlin

Astronomy & Astrophysics

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Abstract

We have used high-resolution HST-WF/PC images of the core of the globular cluster 47 Tucanae in the U-band to determine its radial density profile. The exceptional photometric quality of the data set ensures highly reliable measurements since no photometric completeness correction is required for stars at and above the turn-off luminosity over the whole field. The position of the center of gravity of the cluster is found to agree very well with that provided by previous FOC observations but differs by ∼6″ from the position of the luminosity center as measured from the ground. Within the ∼40″ radius of the cluster center sampled by this data set, the density distribution of stars with masses ≳0.85 M_⊙ is well fitted by a King-type profile with r_c ≃ 12.″2 ± 2.″1. Values of r_c larger than ∼15″ are not compatible with the data and therefore are at variance with those obtained by both ground-based (r_c ≃ 23″) or previous WF/PC studies (r_c ≃ 23″). We show that the discrepancy with earlier results can be ascribed entirely to the effects of photometric incompleteness.

Original language	English (US)
Pages (from-to)	L51-L54
Journal	Astrophysical Journal
Volume	468
Issue number	1 PART II
DOIs	https://doi.org/10.1086/310230
State	Published - 1996

All Science Journal Classification (ASJC) codes

Astronomy and Astrophysics
Space and Planetary Science

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10.1086/310230

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@article{f4487b445c5e479db4e0898c21e9719b,

title = "The density profile of 47 tucanae",

abstract = "We have used high-resolution HST-WF/PC images of the core of the globular cluster 47 Tucanae in the U-band to determine its radial density profile. The exceptional photometric quality of the data set ensures highly reliable measurements since no photometric completeness correction is required for stars at and above the turn-off luminosity over the whole field. The position of the center of gravity of the cluster is found to agree very well with that provided by previous FOC observations but differs by ∼6″ from the position of the luminosity center as measured from the ground. Within the ∼40″ radius of the cluster center sampled by this data set, the density distribution of stars with masses ≳0.85 M⊙ is well fitted by a King-type profile with rc ≃ 12.″2 ± 2.″1. Values of rc larger than ∼15″ are not compatible with the data and therefore are at variance with those obtained by both ground-based (rc ≃ 23″) or previous WF/PC studies (rc ≃ 23″). We show that the discrepancy with earlier results can be ascribed entirely to the effects of photometric incompleteness.",

author = "{De Marchi}, Guido and Francesco Paresce and Stratta, {Maria Giuliana} and Gilliland, {Ronald L.} and Bohlin, {Ralph C.}",

note = "Funding Information: This work was supported by NASA through grants number AR4913 and GO-4664.01-92A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. M. G. S. is grateful to the ST ScI and ESO for their support as a summer student.",

year = "1996",

doi = "10.1086/310230",

language = "English (US)",

volume = "468",

pages = "L51--L54",

journal = "Astrophysical Journal",

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TY - JOUR

T1 - The density profile of 47 tucanae

AU - De Marchi, Guido

AU - Paresce, Francesco

AU - Stratta, Maria Giuliana

AU - Gilliland, Ronald L.

AU - Bohlin, Ralph C.

N1 - Funding Information: This work was supported by NASA through grants number AR4913 and GO-4664.01-92A from the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS5-26555. M. G. S. is grateful to the ST ScI and ESO for their support as a summer student.

PY - 1996

Y1 - 1996

N2 - We have used high-resolution HST-WF/PC images of the core of the globular cluster 47 Tucanae in the U-band to determine its radial density profile. The exceptional photometric quality of the data set ensures highly reliable measurements since no photometric completeness correction is required for stars at and above the turn-off luminosity over the whole field. The position of the center of gravity of the cluster is found to agree very well with that provided by previous FOC observations but differs by ∼6″ from the position of the luminosity center as measured from the ground. Within the ∼40″ radius of the cluster center sampled by this data set, the density distribution of stars with masses ≳0.85 M⊙ is well fitted by a King-type profile with rc ≃ 12.″2 ± 2.″1. Values of rc larger than ∼15″ are not compatible with the data and therefore are at variance with those obtained by both ground-based (rc ≃ 23″) or previous WF/PC studies (rc ≃ 23″). We show that the discrepancy with earlier results can be ascribed entirely to the effects of photometric incompleteness.

AB - We have used high-resolution HST-WF/PC images of the core of the globular cluster 47 Tucanae in the U-band to determine its radial density profile. The exceptional photometric quality of the data set ensures highly reliable measurements since no photometric completeness correction is required for stars at and above the turn-off luminosity over the whole field. The position of the center of gravity of the cluster is found to agree very well with that provided by previous FOC observations but differs by ∼6″ from the position of the luminosity center as measured from the ground. Within the ∼40″ radius of the cluster center sampled by this data set, the density distribution of stars with masses ≳0.85 M⊙ is well fitted by a King-type profile with rc ≃ 12.″2 ± 2.″1. Values of rc larger than ∼15″ are not compatible with the data and therefore are at variance with those obtained by both ground-based (rc ≃ 23″) or previous WF/PC studies (rc ≃ 23″). We show that the discrepancy with earlier results can be ascribed entirely to the effects of photometric incompleteness.

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IS - 1 PART II

ER -

The density profile of 47 tucanae

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