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 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.

scholarly journals A New Program to Determine K(z) from Main Sequence Stars

1977 ◽  
Vol 4 (2) ◽  
pp. 75-76
Author(s):  
A. R. Upgren
Keyword(s):  
Velocity Distribution ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Gaussian Distributions ◽  
Giant Stars ◽  
The North ◽  
The Stability ◽  
North Galactic ◽  
Stability Of The Solution

Recently Dessureau and Upgren (1975) redetermined the velocity distribution of giant stars in the north galactic pole direction using Upgren’s (1962) catalogue and Oort’s (1960) determination of K(z). The velocities were assumed to be represented by n Gaussian distributions with no further constraints imposed. The velocities are well represented by three such distributions whose properties disagree with those found by Oort. A larger number did not improve the stability of the solution. Without radial velocities, however, they could not redetermine the K(z) force itself.

Photoelectric spectrophotometry of G-type main-sequence stars

1966 ◽  
Vol 24 ◽  
pp. 132-140
Author(s):  
S. van den Bergh
Keyword(s):  
Main Sequence ◽  
Wavelength Dependence ◽  
High Resolution Spectroscopy ◽  
Main Sequence Stars ◽  
Stellar Radiation ◽  
Stellar Energy ◽  
Objective Prism ◽  
Almost All ◽  
Low Dispersion ◽  
Very High

Almost all our information about stars is ultimately derived from analysis of the wavelength dependence of stellar radiation. Traditionally the stellar energy distribution has been studied at very high resolution (spectroscopy) and very low resolution (photometry). Until quite recently the intermediate resolution range, involving investigations with a resolution (spectral purity) of between 10Å and 100Å, has been rather neglected. The intermediate resolution range may be studied using low dispersion objective-prism spectra, narrow-band filters or photo-electric spectrophotometers.

scholarly journals Fast-rotating giant stars behind the Coma Berenices star cluster

2020 ◽  
Vol 497 (3) ◽  
pp. 2562-2568
Author(s):  
Estefanía Casal ◽  
Matilde Fernández ◽  
Emilio J Alfaro ◽  
Víctor Casanova ◽  
Ángel Tobaruela
Keyword(s):  
Main Sequence ◽  
Star Cluster ◽  
Stellar Clusters ◽  
Main Sequence Stars ◽  
Cluster Membership ◽  
Giant Stars ◽  
Data Release ◽  
Magnitude Diagram ◽  
M Stars ◽  
Fast Rotating

ABSTRACT In the frame of a study of the empirical isochrones of young stellar clusters, we have carried out BVIc Johnson–Cousins photometry of a sample of K and M stars of the Coma Berenices star cluster. All these stars have known rotational periods. Our main goal is to get a valuable reference on the colour–magnitude diagram, Mv versus B − V, for stars with ages within 400–800 Myr. For this purpose, we obtained BVIc photometry with an average upper limit for the precision of about 0.025 mag and used parallaxes from the Gaia Data Release 2. We found that one-third of our sample is located well above the cluster main sequence and these stars are confirmed as background giants by their radial velocities in the Gaia Data Release 2. This misclassification shows that giants with short-surface rotational periods can mimic main-sequence stars if they are located at the appropriate distance. We recommend caution when using rotational periods in order to determine cluster membership. Besides, the gyrochronology technique should be used only when the luminosity class of the stars is well known. Finally, our cleared sample supports an age of ∼600 Myr for Coma Berenices, rather than an age of ∼800 Myr.

scholarly journals The Gravitational Field of the Galaxy in the Z Direction

1977 ◽  
Vol 4 (2) ◽  
pp. 65-66
Author(s):  
R. F. Griffin
Keyword(s):  
Galactic Plane ◽  
Narrow Band ◽  
Radial Velocities ◽  
Photoelectric Photometry ◽  
Giant Stars ◽  
The North ◽  
The Galaxy ◽  
Absolute Magnitudes ◽  
North Galactic ◽  
K Giants

This is a progress report of a project designed to find the component, perpendicular to the Galactic plane, of the gravitational potential of the Galaxy. The principle is to measure the radial velocities and distances of a large number of K-giant stars near the North Galactic Pole. My student G. A. Radford is masterminding the project; collaborating with us are Drs. J. E. Gunn of the Hale Observatories and L. Hansen and K. Gyldenkerne of Copenhagen.We have measured the radial velocities of all the HD stars of type KO and later, and many of the G5 stars, within 15°of the Galactic Pole, using the Cambridge photoelectric spectrometer. In addition, we have observed all the stars classified as K giants by Upgren in his declination zones 25° to 31°, using the spectrometer on the Hale telescope. There are about 900 stars observed altogether, including about 200 Upgren stars, running down to twelfth magnitude or so, which are not in the Henry Draper Catalogue. To determine the distances of all these stars we are now trying to determine the absolute magnitudes by narrow-band photoelectric photometry in the Copenhagen system. Most of the observations have been made, thanks largely to the very generous grants of observing time given by the Hale Observatories earlier this year; but the reductions have only been completed for about 300 stars (including 244 K giants) which were observed last year at Kitt Peak, and the present, very preliminary, discussion is based on those stars alone.

scholarly journals RGU Three-Colour-Photometry Towards the North Galactic Pole: Halo-To-Disk Mass Ratio

1977 ◽  
Vol 4 (2) ◽  
pp. 53-54
Author(s):  
R. P. Fenkart ◽  
U. W. Steinlin
Keyword(s):  
Main Sequence ◽  
Rotational Symmetry ◽  
Absolute Magnitude ◽  
Galactic Centre ◽  
Density Functions ◽  
Mass Ratio ◽  
The North ◽  
Disk Mass ◽  
Absolute Magnitudes ◽  
North Galactic

The halo program of the Basel observatory, initiated by Becker in 1965, is based on a three colour photometry in test fields along the circle through the galactic centre and the galactic poles. The more favourable direction of the blanketing vector relative to the main sequence in the two colour diagram for RGU makes it possible to separate at least statistically the disk population and the halo populatior within the interval of absolute magnitudes + 3 ≦ MG ≦ + 8. It is therefore possible to derive density functions for both populations and for different intervals in absolute magnitude for each test direction within the test plane defined above. This allows one to draw isodensity curves in the test plane and, assuming rotational symmetry of the halo, also isodensity surfaces. The last assumption is tested at least locally by test fields with different inclinations towards the test plane (Fenkart, R.P. and Wagner, R., 1975).

Luminosity and Intrinsic Color Calibration of Main-Sequence Stars With 2Mass Photometry: All Sky Local Extinction

2003 ◽  
Vol 12 (4) ◽  
Author(s):  
Jens Knude ◽  
Claus Fabricius
Keyword(s):  
Color Index ◽  
Main Sequence ◽  
Absolute Magnitude ◽  
Interstellar Extinction ◽  
Local Extinction ◽  
Sequence Information ◽  
Main Sequence Stars ◽  
Color Calibration

AbstractWe present a new color index vs. absolute magnitude calibration of 2MASS JHK photometry. For the A0 to ~G5 and M segments of the main sequence information on the amount of interstellar extinction and its location in space may be obtained.

scholarly journals Medium Resolution Spectroscopy at 1-2 Microns

1979 ◽  
Vol 47 ◽  
pp. 239-246
Author(s):  
J. R. Mould
Keyword(s):  
Fourier Transform ◽  
Main Sequence ◽  
Classification Criteria ◽  
Fourier Transform Spectrometer ◽  
Main Sequence Stars ◽  
Composite Spectra ◽  
Medium Resolution ◽  
M Stars

AbstractThe need for establishing classification criteria at long wavelengths is stressed. The usefulness of doing this is illustrated with a discussion of the composite spectra of FU Orionis stars. Spectra of these pre-main-sequence stars from 1.5-2.5μ were obtained with a Fourier Transform Spectrometer. Luminosity criteria in the l-2μ range are also discussed with application to M stars.

scholarly journals A comparison of the density gradients of main sequence stars obtained by two different methods in different galactic latitudes

1970 ◽  
Vol 38 ◽  
pp. 232-235
Author(s):  
W. Becker ◽  
R. Fenkart
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Absolute Magnitude ◽  
Galactic Centre ◽  
Density Gradients ◽  
The Sun ◽  
Main Sequence Stars

The Basel Observatory program of the determination of disc- and halo-density gradients for different intervals of absolute magnitude comprises in addition to Milky Way fields several directions, all pointing to Selected Areas near a plane perpendicular to the galactic equator and passing through the sun and the galactic centre. It was started with SA 51 (Becker, 1965) and continued with Sa 57, 54 and 141 (Fenkart, 1967, 1968, 1969).

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