scholarly journals Star counts, local density and KZ force

1985 ◽  
Vol 106 ◽  
pp. 153-160
Author(s):  
Bengt Strömgren
Keyword(s):  
Galactic Plane ◽  
Local Density ◽  
Mass Density ◽  
Homogeneous Groups ◽  
Local Mass ◽  
The North ◽  
Galaxy Model ◽  
F Stars ◽  
North Galactic

The approach by Bahcall and Soneira to the determination of galactic parameters through the use of star counts is referred to, and tests of the Bahcall-Soneira Galaxy model based on additional observational data are discussed.The determination of the local mass density by Hill, Hilditch and Barnes through studies of A and F stars in the region of the North Galactic Pole is briefly discussed, as is a recent investigation of the problem by Bahcall.In the determination of the galactic force Kz and the local mass density from the density distribution ν(z) and the distribution f(W) of velocities at right angles to the galactic plane for a group of tracer stars, it is important to secure homogeneity of the tracer group. This has led Hill, Hilditch and Barnes in a continuation of their investigation to use photoelectric uvby photometry to segregate homogeneous groups of F stars. A similar approach is followed by Danish astronomers, whose work is briefly described.

scholarly journals Studies of a and F Stars in the Region of the North Galactic Pole

1977 ◽  
Vol 4 (2) ◽  
pp. 71-71
Author(s):  
R. W. Hilditch ◽  
Graham Hill
Keyword(s):  
Total Mass ◽  
Mass Density ◽  
Coma Cluster ◽  
Broad Distribution ◽  
Short Account ◽  
Component Distribution ◽  
Narrow Component ◽  
The North ◽  
F Stars ◽  
North Galactic

A short account was given of results recently published (Hill et al. 1976; Hilditch et al. 1976a, b) of a spectroscopic and photometric study of 310 A0-F8 stars within 15° of the north galactic pole. Using these data, it has been found that δmo for the programme stars is constant out to 250 pc and corresponds, via Crawford’s (1975) calibration, to the solar value of [Fe/H]. The distribution of radial velocities of A0-F8 stars is asymmetric and may be interpreted as showing a broad distribution of mean −7 kms−1 and dispersion σ ~ 11 kms−1 together with a superposed narrow distribution of mean 0 kms-1 and dispersion σ ~ 3 kms-1. The narrow component originates from a group of 37 stars which appear to be kinematically and spatially associated with the Coma cluster. Only 14 of these 37 stars are recognised members of the Coma cluster. Removal of these 37 stars from the sample results in a distribution which matches closely the W component distribution of A0-F8 stars in Gliese’s (1969) catalogue. Thus Oort’s “well-mixed” hypothesis seems to be confirmed out to 250 pc. Much additional work on the space motions is required before the hypothesis of the ‘Coma group’ can be thoroughly tested. Results of this analysis and a preliminary value for the total mass density in the solar neighbourhood is expected to be completed during the next few months.

On the determination of the North galactic Pole from Cepheid variables.

1952 ◽  
Vol 56 ◽  
pp. 204 ◽  
Author(s):  
J. Ashbrook ◽  
R. L. Duncombe
Keyword(s):  
The North ◽  
Cepheid Variables ◽  
North Galactic

scholarly journals The Frequency of Faint M Giant Stars at High Galactic Latitudes

1977 ◽  
Vol 4 (2) ◽  
pp. 35-36 ◽  
Author(s):  
N. Sanduleak
Keyword(s):  
Main Sequence ◽  
Galactic Plane ◽  
Absolute Magnitude ◽  
Main Sequence Stars ◽  
Giant Stars ◽  
The North ◽  
Objective Prism ◽  
M Stars ◽  
Low Dispersion ◽  
North Galactic

Based on the observations of M giant stars in the north galactic polar objective-prism survey of Upgren (1960) and the data summarized by Blanco (1965) the overall space density of all M-type giants as a function of distance from the galactic plane at the position of the sun can be approximated by,where z is in kpc and ρ(z) is the number of stars per 106 pc3. This relationship is derived from the observed fall-off in space densities up to a distance of about 2 kpc.The question arises as to the validity of extrapolation equation (1) to larger z distances so as to predict the number of faint M giants expected per unit area near the galactic poles. Adopting for the M giants a mean visual absolute magnitude of −1.0 (Blanco 1965), one finds that equation (1) predicts that less than one giant fainter than V~12 should be expected in a region of 200 square degrees. This expectation formed the hypothesis of a thesis study (Sanduleak 1965) in which it was assumed that the very faint M stars detected in a deep, infrared objective-prism survey at the NGP were main-sequence stars, since this could not be ascertained spectroscopically on the very low-dispersion plates used.

scholarly journals Age dependence of the vertical distribution of Cepheids

2004 ◽  
Vol 193 ◽  
pp. 158-161
Author(s):  
A.K. Dambis
Keyword(s):  
Galactic Plane ◽  
Local Density ◽  
Mass Density ◽  
Local Population ◽  
Vertical Scale ◽  
Visible Matter ◽  
Classical Cepheids ◽  
Density Values ◽  
Standard Models ◽  
The Vertical Distribution

AbstractThe wavelike oscillations of the vertical scale height of the local population of classical Cepheids located at Galactocentric distances R0 – 1 kpc < Rg < R0 + 1 kpc is analyzed using Cepheid ages computed in terms of evolutionary models of Pols et al. (1998) with and without the allowance for convective overshooting. The resulting periods of vertical oscillations of stars about the galactic plane are found to be PZ = 74 ± 2 Myr and PZ = 104 ± 2 Myr for standard models and models with overshooting, respectively. If interpreted as a manifestation of vertical virial oscillations, the pattern found implies local mass density values of ρstd = 0.118 ± 0.007 M⊙ pc−3 and ρovs = 0.060 ± 0.004 M⊙ pc−3, respectively. The latter value is totally incompatible with recent estimates based on Hipparcos data and the former value, combined with recent estimates of the local density of visible matter, sets an upper limit of 0.023 M⊙ pc−3 for the local density of dark matter.

scholarly journals The Luminosity Function of Late-Type Main-Sequence Stars in the Direction of the North Galactic Cap

1977 ◽  
Vol 4 (2) ◽  
pp. 31-31 ◽  
Author(s):  
Donna Weistrop
Keyword(s):  
Luminosity Function ◽  
Main Sequence ◽  
Galactic Plane ◽  
Absolute Magnitude ◽  
Apparent Magnitude ◽  
Late Type ◽  
Main Sequence Stars ◽  
Photoelectric Photometry ◽  
The North ◽  
North Galactic

As a result of the recent discussion concerning the luminosity function of late-type main-sequence stars (Weistrop 1976 and references therein), a program of photoelectric photometry of all red stars in a field near the North Galactic Pole was undertaken. The sample is complete for stars redder than (B - V) = 1.40 magnitude for the following apparent magnitude and area limits: V = 12.0-14.0 magnitudes, 13.5 square degrees; V = 14.0-15.0 magnitudes, 3.0 square degrees; V = 15.0-17.5 magnitudes, 1.0 square degree. Observations in BVRI have been obtained for the 44 stars in the sample. Giants and dwarfs are distinguished by their location in the (B - V)-(V - I) diagram or from published proper motion data, where available. The absolute magnitudes of the dwarfs are determined from the MR - (R - I) relation.The density distribution perpendicular to the galactic plane of the dwarfs is consistent with the distribution for K giants found by Oort (1960). The derived luminosity function does not differ significantly from that determined by Wielen (1974) for stars close to the Sun. The local space density for stars in the interval MV = 8.5-14.0 magnitudes is 0.099 stars pc−3. The corresponding stellar density derived from Wielen’s luminosity function is >0.066 stars pc−3. Sixty-six percent of the density derived here is contributed by two stars with absolute magnitude in the range MV = 13.0−14.0 magnitudes.

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