Cluster Parallaxes Research Articles

Systematic effects in trigonometric parallaxes – III. Comparisons with spectroscopic and cluster parallaxes

Systematic effects in trigonometric parallaxes – III. Comparisons with spectroscopic and cluster parallaxes

Systematic effects in observed parallaxes

Several outstanding problems affecting the existing parallaxes should be resolved to form a coherent system for the new General Catalogue proposed by van Altena, as well as to improve luminosity calibrations and other parallax applications. Lutz has reviewed several of these problems, such as: (A) systematic differences between observatories, (B) external error estimates, (C) the absolute zero point, and (D) systematic observational effects (in right ascension, declination, apparent magnitude, etc.). Here we explore the use of cluster and spectroscopic parallaxes, and the distributions of observed parallaxes, to bring new evidence to bear on these classic problems. Several preliminary results have been obtained.

- and Broad-Band Photometry of Red Stars. II. Dwarfs

Broad-band (UBV) and narrow-band (RI) (102, 65, 62) photometry of 500 M dwarfs is discussed. The sample contains about 90 per cent of the stars brighter than visual magnitude 10 found in the McCormick (Vyssotsky) discovery lists, as well as 10 per cent of the fainter stars and an additional 100 stars not included in these lists but for which radial velocities and proper motions are known. The (Mv, R - I) and M(102), (102, 65) relations for all populations show little dispersion for the stars with color temperature greater than about 4000 K. These relations for the young disk population show little dispersion over the whole temperature range observed, but the meager data available for the halo population indicates that those cooler than about 4000 are displaced more than a magnitude below these relations. The majority of the old disk-population stars lie on the color-luminosity relations of the young disk population, but some representatives are displaced below these relations by amounts that range up to those found for the halo-population stars. An obvious expanation for these displacements is that they are caused by an effect of the chemical composition on the stellar opacities, and this effect is temperature-dependent. The agreement in the (Mv, R - I) relations for eight Hyades cluster dwarfs and for stars with parallaxes greater than 0'.'125 leaves little room for the speculation that the cluster parallax is seriously in error. The TiO bands in the dwarfs have similar strength to those in the giants to color temperatures near 3800 K, but for cooler stars they block approximately 20 per cent more radiation at a given temperature. A few stars, including members of the halo population, show large displacements below the normal (102, 65), (65, 62) relation, but the explanation may be other than the obvious one of larger than normal TiO absorption. Space motions of all 500 stars are discussed with reference to moving groups and to the presence of hydrogen emission. The stars are almost evenly divided between young and old disk populations and include, at most, a dozen members of the halo population.

A Comparison of Photometric Observations with Theoretical Predictions for Rotating Stellar Atmospheres.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Comparison of Photometric Observations with Theoretical Predictions for Rotating Stellar Atmospheres. Clapp, G. A. ; Neff, J. S. Abstract A preliminary comparison of photometric observations on the Chi system (Neff, J. S., and Travis, L. D., Astron. J. 72, 48,1967) and p observations with the rotating model atmospheres of Collins and Harrington (Collins, G. W., and Harrington, J. P., Astrophys. J. 146, 152, 1966) is described. A systematic correction of 0~.07 was applied to the theoretical flux ratios to bring them into agreement with observation. This is within the estimated uncertainty of the absolute calibration. The theoretical fl's were increased by 0w07 to bring them into agreement with observation. Theory and observation were compared on the A(0.33) log[F(0.33)/F 0.55)J relation, the P -A(0.33) relation, and the Mv~A(0.33) relation. The absolute magnitudes were calculated with trigonometric or cluster parallaxes. It was found that theory and observation were consistent. For six stars it was possible to estimate Ve and i with large estimatcd errors, M being the most uncertain quantity. The photometric value of V sin was calculated and compared with the spectroscopic value. The results were consistent within the estimated error although there was a tendency for the photometric values to be 20-50% larger than the observed values. A more accurate comparison between theory and observation can be made for stars with smaller masses than used above. This is because there are more nearby stars of this type and the photometric effects due to rotation appeared to be larger. Publication: The Astronomical Journal Pub Date: 1967 DOI: 10.1086/110428 Bibcode: 1967AJ.....72Q.789C full text sources ADS |

Cluster parallaxes : the nearest clusters.

Cluster parallaxes : the nearest clusters.

Photometric parallaxes of distant clusters.

Photometric parallaxes of distant clusters.

On the Relation Between Distance and Intensity For Interstellar Calcium and Sodium Lines

The results of spectrophotometric measurements of the intensities of the interstellar K and D lines carried out at the Dominion Astrophysical Observatory in the period 1928–1946 are presented in tabular form. The data relate to 1 055 medium-dispersion spectra of 182 stars, mostly of O and early B types, and include also measures of radial velocity for stellar and interstellar lines in most of the stars. The interstellar intensities are correlated with stellar distance, a variety of criteria being used for estimating the latter, including trigonometric parallaxes, parallactic motions, luminosities of eclipsing binaries, spectroscopic absolute magnitudes, cluster parallaxes and galactic rotation effects. The various criteria are weighted according to the intrinsic reliability of each method and to the number of stars concerned. The distance–intensity relations best satisfying the observations are : r =34·83 K =30·75 D , where r is the distance in parsecs, K the equivalent width of the calcium K line in km/sec and D the mean equivalent width of the sodium lines D1 and D2 in km/sec. Distances assigned to individual stars by using these relations should rarely be more than 25 per cent in error. The scatter is attributed to irregularity in distribution of the discrete clouds of interstellar gas and to uncertainties in the distance estimates. The distance–intensity relations found are compared with those of other observers.

The absolute magnitudes of the early A-type stars from hydrogen line absorption.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The absolute magnitudes of the early A-type stars from hydrogen line absorption. Petrie, R. M. ; Maunsell, C. D. Abstract The intensities of H~ have been determined, by spectrophotometric measures, in the spectra of 165 stars of spectral types B8 to A3. The measures have been calibrated against absolute magnitudes derived from trigonometric, spectroscopic, dynamical, and cluster parallaxes. The equivalent width of H~ is found to be capable of predicting the absolute magnitude of a normal star, white dwarfs being excepted. The mean residual from the trigonometric parallaxes is Q'.'00I ~ "001. Spectroscopic absolute magnitudes are given for 165 A stars. Dominion Astrophysical Observatory, Victoria, B. C., Canada. Publication: The Astronomical Journal Pub Date: September 1949 DOI: 10.1086/106259 Bibcode: 1949AJ.....54..193P full text sources ADS |

Note on the Parallaxes of Open and Moving Clusters

Note on the Parallaxes of Open and Moving Clusters

The Parallaxes of Globular Clusters and Spiral Nebulæ

The Parallaxes of Globular Clusters and Spiral Nebulæ