The Strange Case of Hubble's V19 in M33: Monitoring the Remarkable Changes and Possible Real-Time Evolution of a Classical Cepheid

Details The Strange Case of Hubble's V19 in M33: Monitoring the Remarkable Changes and Possible Real-Time Evolution of a Classical Cepheid The Strange Case of Hubble's V19 in M33: Monitoring the Remarkable Changes and Possible Real-Time Evolution of a Classical Cepheid

Jan 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21734206e&link_type=abstract

American Astronomical Society, AAS Meeting #217, #342.06; Bulletin of the American Astronomical Society, Vol. 43, 2011

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In the influential work "A Spiral Nebula as a Stellar System: Messier 33” (Hubble 1926) Edwin Hubble determined the distance to M33 by using 35 Cepheids he discovered. One of those Cepheids was designated V19. Observations revealed V19 to have a 54.7-day period and B-band (converted from photographic magnitudes) light amplitude of 1.1-mag. Its mean B-magnitude was 19.59+/-0.23. Its properties were consistent with the Period-Luminosity Law for M33 derived by Hubble at that time. Follow up observations in 1996-1997 as part of the DIRECT Program (Macri et al. 2001), however, revealed large and surprising changes in the properties of V19. Its mean B-magnitude had risen to 19.05+/-0.05 and its amplitude had fallen to < 0.1-mag. The DIRECT study thoroughly checked for possible misclassifications of the variable or contamination by nearby objects, and found none. For all intents and purposes, V19 was no longer a Classical Cepheid, or at least varying below the detectable levels of the photometry. The only other well-documented instance of Cepheid pulsations declining over time is in the case of Polaris - whose V-band amplitude fell from just over 0.1-mag to below 0.03-mag over the course of a century (Engle et al 2004). Also, a study of Polaris’ visual magnitudes over the past two millennia has shown a possible increase in brightness of 1-mag over the past 1000 years. The changes present in V19 are obviously on a much more dramatic scale.
We report on our continuing efforts to monitor the behavior and properties of Hubble's V19 in M33. Photometry has been carried out with the WIYN 3.5-m telescope and the 1.3-m RCT (Robotically Controlled Telescope) at KPNO. It is our hope that these observations will help solve the mystery of V19 and its unprecedented evolutionary behavior.
We gratefully acknowledge NASA/HST grant and NSF/RUI grant AST1009903.

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