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

Journal Article · Thu Aug 01 04:00:00 EDT 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/772/2/130· OSTI ID:22121782

Majaess, D.; Turner, D. G. ^[1]

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1. Department of Astronomy and Physics, Saint Mary's University, Halifax, NS B3H 3C3 (Canada)

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 corrected 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.

• OSTI ID: 22121782
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 772; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CEPHEIDS
COLOR
COSMIC DUST
DIAGRAMS
DISTANCE
GALAXIES
METALS
NONLINEAR PROBLEMS
POLYNOMIALS
SPITZER THEORY