University of Geneva | Via PhysOrg | 2015 May 12
[img3="Bow Shock around Star Delta CepheiTo measure distances in the universe, astronomers use cepheids, a family of variable stars whose luminosity varies with time. Their role as distance calibrators has brought them attention from researchers for more than a century. While it was thought that nearly everything was known about the prototype of cepheids, named Delta Cephei, a team of researchers at the University of Geneva (UNIGE), the Johns Hopkins University, and the European Space Agency (ESA), have now discovered that this star has a hidden companion. They have published an article about the discovery in The Astrophysical Journal.
Credit: NASA/JPL-Caltech/M. Marengo (Iowa State)"]http://photojournal.jpl.nasa.gov/jpeg/PIA13781.jpg[/img3][hr][/hr]
Delta Cephei, prototype of the cepheids, which has given its name to all similar variable stars, was discovered 230 years ago by the English astronomer John Goodricke. Since the early 20th century, scientists have been interested in measuring cosmic distances using a relationship between these stars' periods of pulsation and their luminosities (intrinsic brightness), discovered by the American Henrietta Leavitt. Today, researchers from the Astronomical Observatory of UNIGE, Johns Hopkins University and the ESA show that Delta Cephei is, in fact, a double star, made up of a cepheid-type variable star and a companion that had thus far escaped detection, probably because of its low luminosity. Yet, pairs of stars, called binaries, complicate the calibration of the period-luminosity relationship, and can bias the measurement of distances. This is a surprising discovery, since Delta Cephei is one of the most studied stars, of which scientists thought they knew almost everything.
A secret companion
As the scientists from Geneva and Baltimore measured Delta Cephei's pulsations with the Hermes spectrograph, installed at the Mercator telescope based on La Palma, one of the Canary Islands, an unexpected signal was detected. Using high-precision Doppler spectroscopy (developed and used for researching exoplanets), the researchers discovered that the speed with which Delta Cephei approaches the sun is not constant, but changes with time in a characteristic fashion. This change of speed can only be explained by the presence of another star orbiting around Delta Cephei. In other words, there is a secret companion, whose existence we did not suspect. By combining their own observations with data from the scientific literature, the researchers determined the orbit of the two stars and observed that the mass of the companion is low, around 10 times lower than the mass of Delta Cephei. ...
Revealing δ Cephei's Secret Companion and Intriguing Past - Richard I. Anderson et al
- Astrophysical Journal 804(2) 144 (2015 May 10) DOI: 10.1088/0004-637X/804/2/144
arXiv.org > astro-ph > arXiv:1503.04116 > 13 Mar 2015