Recent Evidence on the Rotation Curve of our Galaxy for R &gt; Ro

Jackson, P. D.; Fitz-Gerald, Max; Moffat, A. F. J.

doi:10.1007/978-94-009-9503-1_39

Cited by 7 publications

(3 citation statements)

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“…However, it is slightly higher than the value of 11.64 mag given by Joshi & Sagar (1977). The present determination of the distance modulus to the cluster Be 11 agrees very well with the value of 11.7 mag given by Jackson et al (1980).…”

Section: Discussionsupporting

confidence: 87%

“…For Tr 1, filled circles represent the CCD data of Phelps & Janes (1994) and triangles represent the photoelectric data of Joshi & Sagar (1977) . For Be 11 filled circles represent the photoelectric data of Jackson et al (1980) .…”

Section: Observational Datamentioning

confidence: 99%

“…It is a distant neglected compact young open cluster, apparently associated with the faint H ii region S 213. Only UBV photoelectric photometry of 24 bright stars has been carried out by Jackson, Fitzgerald & Moffat (1980). On the basis of this study, they found that this cluster has members of the earliest photometric type ∼b4 and is thus an extreme Population I object.…”

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confidence: 99%

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A deepUBVRICCD photometric study of the open clusters Tr 1 and Be 11

Yadav¹,

Sagar²

2002

Monthly Notices of the Royal Astronomical Society

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We present deep UBVRI charge-coupled device (CCD) photometry for the young open star clusters Tr 1 and Be 11. The CCD data for Be 11 are obtained for the first time. The sample consists of ∼1500 stars reaching down to V ∼ 21 mag. Analysis of the radial distribution of the stellar surface density indicates that radius values for Tr 1 and Be 11 are 2.3 and 1.5 pc, respectively. The interstellar extinction across the face of the imaged clusters region seems to be non-uniform with a mean value of E(B − V ) = 0.60 ± 0.05 and 0.95 ± 0.05 mag for Tr 1 and Be 11, respectively. A random positional variation of E(B − V ) is present in both the clusters. In the cluster Be 11, the reason for the random positional variation may be the apparent association of the H II region (S 213). The 2MASS JHK data in combination with the optical data in the cluster Be 11 yield E(J − K ) = 0.40 ± 0.20 mag and E(V − K ) = 2.20 ± 0.20 mag. Colour excess diagrams indicate a normal interstellar extinction law in the direction of the cluster Be 11.The distances to Tr 1 and Be 11 are estimated as 2.6 ± 0.10 and 2.2 ± 0.10 kpc, respectively, while the theoretical stellar evolutionary isochrones fitted to the bright cluster members indicate that the clusters Tr 1 and Be 11 are 40 ± 10 and 110 ± 10 Myr old, respectively. The mass functions corrected for both field star contamination and data incompleteness are derived for both clusters. The slopes 1.50 ± 0.40 and 1.22 ± 0.24 for Tr 1 and Be 11, respectively, are in agreement with the Salpeter value. Observed mass segregations in both clusters may be the result of dynamical evolutions or the imprint of star formation processes or both.

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Section: Discussionsupporting

confidence: 87%

Section: Observational Datamentioning

confidence: 99%

mentioning

confidence: 99%

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A deepUBVRICCD photometric study of the open clusters Tr 1 and Be 11

Yadav¹,

Sagar²

2002

Monthly Notices of the Royal Astronomical Society

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The importance of stellar distances in determining the rotation curve of the outer galaxy

Moffat

The Outer Galaxy

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The Structure of Our Galaxy Derived from Observations of Neutral Hydrogen

Burton¹

1988

Astronomy and Astrophysics Library

163

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Although insight into the structure of our Galaxy can be sought in various ways, study of the radio emission from the neutral hydrogen component is particularly suitable. Neutral atomic hydrogen, HI, is the main observed constituent of the interstellar medium; its physical properties are closely related to the properties of other Galactic constituents, both stellar and interstellar. The interstellar medium is transparent enough to hydrogen emission at the 21-cm radio wavelength that investigation of the entire Galaxy is possible, with the exception of a few directions along the Galactic equator. This transparency allows investigation of regions of the Galaxy which are too distant to be studied optically. HI is particularly important for the information it provides on the form and overall mass in the outer Galaxy, where it is the only directly observable constituent. Interstellar neutral hydrogen is so abundant and is distributed in such a general fashion throughout the Galaxy that the 21-cm hyperfine transition line has been detected in emission in every direction in the sky at which a suitably equipped radio telescope has been pointed. No time variation of a neutral hydrogen line has been found.The 21-cm line of atomic hydrogen results from a hyperfine transition in the ground state of the atom. This state is characterized by two possible relative orientations of the spins of the electron and proton; when the spins are parallel the energy of the system is slightly greater than when they are antiparallel. The energy separation between the two hyperfine sublevels corresponds to a quantum of radiation with a natural frequency of 1420.406 MHz. The probability that this spin-flip transition from the F = 1 to the F = 0 state will occur spontaneously is given by the Einstein emission coefficient, A 10 = 2.85 X to-15 S-1. Thus a spontaneous electron spin flip would occur after some eleven million years. In fact, atomic encounter collisions largely determine the relative populations of the two energy levels. At the typical HI densities of about 0.4 em -3 which characterize much of interstellar space, encounters result in reorientation of the spins of a hydrogen atom about once every three or four hundred years. Effects of ambient interstellar radiation field on the spin states are less important than those of encounters, except in certain unusual interstellar environments such as found near recent supernovae or near regions of intense star formation.

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Recent Evidence on the Rotation Curve of our Galaxy for R > Ro

Cited by 7 publications

References 0 publications

A deepUBVRICCD photometric study of the open clusters Tr 1 and Be 11

A deepUBVRICCD photometric study of the open clusters Tr 1 and Be 11

The importance of stellar distances in determining the rotation curve of the outer galaxy

The Structure of Our Galaxy Derived from Observations of Neutral Hydrogen

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