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Title: ON THE FORM OF THE SPITZER LEAVITT LAW AND ITS DEPENDENCE ON METALLICITY

The form and metallicity dependence of Spitzer mid-infrared Cepheid relations are a source of debate. Consequently, Spitzer 3.6 and 4.5 {mu}m period-magnitude and period-color diagrams were re-examined via robust routines, thus providing an alternative interpretation to consider. The relations (nearly mean-magnitude) appear non-linear over an extensive baseline (0.45 < log P{sub 0} < 2.0), particularly the period-color trend, which to first order follows constant (3.6-4.5) color for shorter-period Cepheids and may transition into a bluer convex trough at longer periods. The period-magnitude functions can be described by polynomials (e.g., [3.6 {mu}m] = K{sub 0} - (3.071 {+-} 0.059)log P{sub 0} - (0.120 {+-} 0.032)log P{sub 0} {sup 2}), and Cepheid distances computed using 3.6 and 4.5 {mu}m relations agree with each other and the latter provides a first-order consistency check (CO sampled at 4.5 {mu}m does not seriously compromise those distances). The period-magnitude relations appear relatively insensitive to metallicity variations ([Fe/H] {approx} 0 to -0.75 |{gamma}| < 0.1 mag dex{sup -1}), a conclusion inferred partly from comparing galaxy distances established from those relations and NED-D (n > 700), yet a solid conclusion awaits comprehensive mid-infrared observations for metal-poor Cepheids in IC 1613 ([Fe/H] {approx} -1). The Cepheid-based distances were correctedmore » for dust obscuration using a new ratio (i.e., A{sub 3.6}/E{sub B-V} = 0.18 {+-} 0.06) deduced from GLIMPSE (Spitzer) data.« less
Authors:
;  [1] ;  [2]
  1. Department of Astronomy and Physics, Saint Mary's University, Halifax, NS B3H 3C3 (Canada)
  2. Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion (Chile)
Publication Date:
OSTI Identifier:
22121782
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 772; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CEPHEIDS; COLOR; COSMIC DUST; DIAGRAMS; DISTANCE; GALAXIES; METALS; NONLINEAR PROBLEMS; POLYNOMIALS; SPITZER THEORY