Ultra Long Period Cepheid

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Ultra Long Period Cepheids , or ULPC for short , are a class of pulsation-variable stars with periods between 80 and 150 days. The yellow giants are an important intermediate step in the cosmic ladder of distance through their period-luminosity relationship .

Cepheids are pulsation-variable stars with periods of a few days up to 80 days. The upper limit results from a gradual transition to the semi-regular stars , since the light curves no longer repeat themselves regularly. Period doubling and other non-linear processes occur in the transition area .

A small part of the pulsation-variable yellow giants with periods between 80 and 150 days show a relatively regular Cepheid-like light change. These stars are known as Ultra Long Period Cepheids, where the light curves can show differences between cycles of up to 0.15 mag . Their period-luminosity relationship is a continuation of the classic type I Cepheids, although the ULPC have a lower slope. If the pulsation period is lengthened, the mean brightness no longer increases as quickly as in normal Cepheids. A decomposition of the light curves of ultra-long-period Cepheids by means of a Fourier analysis leads to results that are more typical for Mira stars than for Cepheids. The ULPCs with periods of more than 120 days cannot recreate current star models as post-main sequence stars like the Cepheids that burn helium in their core . So far, no Ultra Long Period Cepheids have been found in the Milky Way and they mainly occur in galaxies with a low level of metallicity such as in the Magellanic Clouds .

Cepheids are important standard candles for measuring distances in the cosmos. However, with current technology, their range is limited to distances of up to 20 mega parsec . ULPCs can be observed up to a distance of 120 megaparsecs due to their greater absolute brightness of approximately M V = −7 or M I = −7.9. This enables a better calibration of the absolute brightness of supernovae by means of the Phillips relation and the expanding photosphere method , since considerably more supernovae were observed in this area of ​​space.

Examples

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  • Chien-Hsiu Lee, Chow-Choong Ngeow, Michael Ting-Chang Yang, Wing-Huen Ip, Albert Kwok-Hing Kong, Russ R. Laher, Jason Surace: Using the Palomar Transient Factory to Search for Ultra-Long-Period Cepheid Candidates in M31 . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1309.5127v1 .
  • Chow-Choong Ngeow, Scott Lucchini, Shashi Kanbur, Brittany Barrett, Bin Lin: Preliminary Analysis of ULPC Light Curves Using Fourier Decomposition Technique . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1309.4297v1 .
  • Fiorentino, G., Clementini, G., Marconi, M., Musella, I., Saha, A., Tosi, M., Contreras Ramos, R., Annibali, F., Aloisi, A., van der Marel, R: Ultra Long Period Cepheids: a primary standard candle out to the Hubble flow . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1203.0026v1 .
  • Jonathan C. Bird, KZ Stanek, Jose L. Prieto: Using Ultra Long Period Cepheids to Extend the Cosmic Distance Ladder to 100 Mpc and Beyond . In: Astrophysics. Solar and Stellar Astrophysics . 2008, arxiv : 0807.4933v2 .