A 21-cm Determination of the Principal Plane of the Galaxy (Paper II)

Interstellar extinction towards open clusters and Galactic structure

“…It is a well‐known fact that the formal Galactic plane does not coincide with the planes of symmetry defined by the different objects such as the neutral hydrogen layer (Gum, Kerr & Westerhout 1960), Cepheid variables (Fernie 1968), Wolf–Rayet stars (Stenholm 1975), H ii regions and supernova remnants (Lockman 1977), the molecular clouds (Cohen & Thaddeus 1977; Magnani, Blitz & Mundy 1985), open clusters (Lynga 1982; Pandey et al 1988), etc. To examine the relationship between the reddening plane and the formal Galactic plane, we also investigate the distribution of z in a 1‐kpc bin as a function of r following the approach given by Fernie (1968).…”

The solar acceleration obtained by VLBI observations

“…First, this plane defined by the H1 disk itself has a probable error of 0.12 o (Blaauw et al 1960) and this angular discrepancy corresponds to 17 pc distance at the place of R = 8.3 kpc. Secondly, the basic principle to define the Galactic plane according to H1 disk is that the Galactic neutral hydrogen is confined to a thin and flat layer in the inner regions of the Galaxy R < 7 kpc and is systematically distorted in the outer parts according to the studies of 21-cm radiation (Kerr et al 1957;Westerhout 1957;Gum et al 1960). On the contrary, this would imply that the present Galactic plane could not represent the dynamical plane near the Sun R > 7 kpc, where the neutral hydrogen has already been a distorted distribution.…”

Displacement of the Sun from the Galactic plane

“…In the past, several independent studies have been carried out to estimate z ⊙ using different types of astronomical object. For example, Gum, Kerr & Westerhout (1960) concluded that z ⊙ = 4 ± 12 pc from the neutral hydrogen layer, Kraft & Schmidt (1963) and Fernie (1968) used Cepheid variables to estimate z ⊙ ∼ 40 pc, while Stothers & Frogel (1974) determined z ⊙ = 24 ± 3 pc from B0–B5 stars within 200 pc from the Sun, all pointing to a broad range of z ⊙ . More recently, various different methods have been employed to estimate z ⊙ , for example, Cepheid variables (Caldwell & Coulson 1987), optical star count techniques (Yamagata & Yoshii 1992; Humphreys & Larsen 1995; Chen et al 2001), Wolf–Rayet stars (Conti & Vacca 1990), infrared surveys (Cohen 1995; Binney, Gerhard & Spergel 1997; Hammersley et al 1995) along with different simulations (Reed 1997; Méndez & van Altena 1998) and models (Chen et al 1999; Elias, Cabrera‐Caño & Alfaro 2006, hereafter ECA06).…”