A Cepheid is No More: Hubble's Variable 19 in M33

Abstract

We report on the remarkable evolution in the light curve of a variable star discovered by Hubble (1926) in M33 and classified by him as a Cepheid. Early in the 20th century, the variable, designated as V19, exhibited a 54.7 day period, an intensity-weighted mean B magnitude of 19.59+/-0.23 mag, and a B amplitude of 1.1 mag. Its position in the P-L plane was consistent with the relation derived by Hubble from a total of 35 variables. Modern observations by the DIRECT project show a dramatic change in the properties of V19: its mean B magnitude has risen to 19.08 +/- 0.05 mag and its B amplitude has decreased to less than 0.1 mag. V19 does not appear to be a classical (Population I) Cepheid variable at present, and its nature remains a mystery. It is not clear how frequent such objects are nor how often they could be mistaken for classical Cepheids.

Accepted for publication in the Astrophysical Journal Letters. Finding charts and photometry data can be downloaded from http://cfa-www.harvard.edu/~kstanek/DIRECT/

References in corpus (3)

• NICMOS Observations of Extragalactic Cepheids. I. Photometry Database and a Test of the Standard Extinction Law
• DIRECT Distances to Nearby Galaxies Using Detached Eclipsing Binaries and Cepheids. VI. Variables in the Central Part of M33
• The DIRECT Project: Catalogs of Stellar Objects in Nearby Galaxies. I. The Central Part of M33

Cited by in corpus (4)

• System description and first light-curves of HAT, an autonomous observatory for variability search
• Long-Term V-Band Monitoring of the Bright Stars of M33 at the Wise Observatory
• GALEX Catalog of UV Point Sources in M33
• Discovery of a peculiar Cepheid-like star towards the northern edge of the Small Magellanic Cloud