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Ultralong-period Cepheids: a possible primary distance indicator?

Published online by Cambridge University Press:  26 February 2013

G. Fiorentino ,
F. Annibali ,
G. Clementini ,
R. Contreras Ramos ,
M. Marconi ,
I. Musella ,
A. Saha ,
M. Tosi ,
A. Aloisi  and
R. van der Marel
G. Fiorentino
Affiliation:
INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna email: [email protected]
F. Annibali
Affiliation:
INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna email: [email protected]
G. Clementini
Affiliation:
INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna email: [email protected]
R. Contreras Ramos
Affiliation:
INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna email: [email protected]
M. Marconi
Affiliation:
INAF–Osservatorio Astronomico di Capodimonte, vicolo Moiariello 16, 40127, Napoli, Italy
I. Musella
Affiliation:
INAF–Osservatorio Astronomico di Capodimonte, vicolo Moiariello 16, 40127, Napoli, Italy
A. Saha
Affiliation:
National Optical Astronomy Observatory, P. O. Box 26732, Tucson, AZ 85726, USA
M. Tosi
Affiliation:
INAF–Osservatorio Astronomico di Bologna, via Ranzani 1, 40127, Bologna email: [email protected]
A. Aloisi
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
R. van der Marel
Affiliation:
Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
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Abstract

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We present a project that aims to provide a complete theoretical and observational framework for an as yet unexplored class of variable stars, the ultralong-period Cepheids (P longer than 80–100 days). Given their very high luminosities (MV up to −7 mag), with the Hubble Space Telescope we will be able to observe them easily in stellar systems located at large distances (~ 100 Mpc). This limit will be further increased, out to the Hubble flow (~ 350 Mpc), using future ground-based facilities such as the European Extremely Large Telescope. The nature of their pulsation is as yet unclear, as is their evolutionary status, which seems different from the central helium-burning phase generally associated with classical Cepheids. These objects have been found to cover a very large metallicity range, from [Fe/H] ~ −2 dex to solar values, and they are located in heterogeneous stellar systems, from dwarf to spiral galaxies. Once completely characterized, they could provide a crucial test, since they have been found in all Type Ia supernova host spiral galaxies that have been monitored for variability over long periods and that currently offer sound constraints on the estimated value of the Hubble constant.

Keywords

stars: distancesstars: variables: other
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 8 , Symposium S289: Advancing the Physics of Cosmic Distances , August 2012 , pp. 282 - 286
Copyright
Copyright © International Astronomical Union 2013

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