Estimation of the Radial Scale Length and Vertical Scale Height of the Galactic Thin Disk from Cepheids

Abstract

Up-to-date data on 2214 classical Cepheids have been used. The model of an exponential matter density distribution in the Galactic thin disk has been applied. New estimates of the radial disk scale length $h_R,$ the distance of the Sun from the symmetry plane $z_{\odot }$, and the vertical disk scale height $h_z$ have been obtained. Based on samples of 1087 Cepheids younger than 120 Myr and 1127 Cepheids older than 120 Myr, we have found $h_R=2.30\pm 0.09$ kpc and $h_R=1.96\pm 0.12$ kpc, respectively. It has turned out that an unambiguous estimate of $h_R$ cannot be obtained from their overall radial distribution. However, we have constructed the radial distribution of 806 Cepheids of different ages at the time of their birth from which we have found $h_R=2.36\pm 0.24$ kpc. We show that $h_z$ depends strongly on the age of stars. For example, from 705 Cepheids younger than 120 Myr with heliocentric distances $r<6$ kpc we have found $z_{\odot }=-17\pm 4$ pc and $h_z=75\pm 5$ pc. From 393 Cepheids older than 120 Myr at $r<6$ kpc, we have found $z_{\odot }=-39\pm 11$ pc and $h_z=131\pm 10$ pc.

13 pages, 8 figures, 2 tables

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