NASA Logo

NTRS

NTRS - NASA Technical Reports Server

Back to Results
The Carnegie Chicago Hubble Program: The Mid-Infrared Colours of Cepheids and the Effect of Metallicity on the CO Band-Head at 4.6 MicronWe compare mid-infrared (IR) 3.6 and 4.5 micron Warm Spitzer observations for Cepheids in the Milky Way and the Large and Small Magellanic Clouds. Using models, we explore in detail the effect of the CO rotation-vibration band-head at 4.6 micron on the mid-IR photometry. We confirm the temperature sensitivity of the CO band-head at 4.6 micron and find no evidence for an effect at 3.6 micron. We compare the ([3.6]-[4.5]) period-colour relations in the MW, LMC and SMC. The slopes of the period-colour relations for the three galaxies are in good agreement, but there is a trend in zero-point with metallicity, with the lowest metallicity Cepheids having redder mid-IR colours. Finally, we present a colour-[Fe/H] relation based on published spectroscopic metallicities. This empirical relation, calibrated to the metallicity system of Genovali et al., demonstrates that the ([3.6]-[4.5]) colour provides a reliable metallicity indicator for Cepheids, with a precision comparable to current spectroscopic determinations.
Document ID
20170002501
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Scowcroft, Victoria (Carnegie Institution of Washington Pasadena, CA, United States)
Seibert, Mark (Carnegie Institution of Washington Pasadena, CA, United States)
Freedman, Wendy L. (Chicago Univ. Chicago, IL, United States)
Beaton, Rachael L. (Carnegie Institution of Washington Pasadena, CA, United States)
Madore, Barry F. (Carnegie Institution of Washington Pasadena, CA, United States)
Monson, Andrew J. (Pennsylvania State Univ. University Park, PA, United States)
Rich, Jeffery A. (Carnegie Institution of Washington Pasadena, CA, United States)
Rigby, Jane R. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
March 23, 2017
Publication Date
March 15, 2016
Publication Information
Publication: Monthly Notices of the Royal Astronomical Society
Volume: 459
Issue: 2
ISSN: 0035-8711
Subject Category
Astrophysics
Astronomy
Report/Patent Number
GSFC-E-DAA-TN40415
Distribution Limits
Public
Copyright
Other