The luminosity index as a distance indicator and the structure of the Virgo cluster.
Abstract
In a recent paper, Sandage, Binggeli, and Tammann (SBT) contend to have shown that the luminosity index Λ is an unreliable distance indicator, because of the large dispersion (σ ≈ 1.0 mag, at Λ = const.) of apparent magnitudes in a sample of galaxies which they claim to be in - or at the same distance as - the Virgo cluster. A critical examination of their data shows that this large dispersion is the result of (1) the inclusion of many galaxies outside the Virgo cluster proper (the S cloud), including the background Sarcmin, X, M, and W clouds, (2) the presence of large systematic and accidental errors in their type classifications T (and to a lesser extent in their L classifications), (3) their use of low-precision eye estimates for some of the apparent magnitudes, particularly at BT > 14, and (4) their neglet of the important inclination corrections to magnitudes BT and luminosity classifications L. When the necessary corrections and rejections are made, and the comparison restricted to the Virgo S cloud (whose members are all at the same distance to within ±10%), there is no serious disagreement between the slopes and zero points of the magnitude-luminosity index relations defined by the SBT data and the RC2 data.
- Publication:
-
The Astronomical Journal
- Pub Date:
- October 1986
- DOI:
- 10.1086/114208
- Bibcode:
- 1986AJ.....92..722D
- Keywords:
-
- Astrometry;
- Distance;
- Luminosity;
- Virgo Galactic Cluster;
- Classifications;
- Color;
- Correlation;
- Error Analysis;
- Magnitude;
- Astrophysics