Beehive Cluster. Credit: Sven Kohle and Till Credner
Astronomers have detected a new low-mass eclipsing binary star in an open cluster named NGC 2632, better known as the Beehive Cluster (or Praesepe). The newly identified binary, designated PTFEB132.707+19.810, contains two late-type stars much smaller and less massive than the sun.
NGC 2632 is an open star cluster that looks like a hive of bees in the constellation Cancer. Located some 577 light years away, it is one of the nearest open clusters to the solar system. Due to its proximity, this cluster is the target of numerous observations conducted by astronomers searching for new objects, including eclipsing binaries. Such binaries could be very helpful in improving our known theoretical stellar evolution models.
Although PTFEB132.707+19.810 was identified in 2002, its true nature remained unclear until the research conducted by Kraus’ team. The new study confirms that this star is a low-mass eclipsing binary. PTFEB132.707+19.810 has an orbital period of 6 days and comprises 2 late-type M stars. The primary star has a radius of about 0.36 solar radii and a mass of nearly 0.4 solar masses. The secondary star is much smaller, as its radius equals ~0.27 solar radii. It is also much less massive—with a mass of 0.21 solar masses. These parameters indicate that PTFEB132.707+19.810 is one of the few low-mass eclipsing binaries to be found in an open cluster.
Given the masses of the components of PTFEB132.707+19.810, neither star of the system meets the predictions of stellar evolutionary models. “The primary star has the expected radius, but it is cooler and less luminous than models would predict, while the secondary star has the expected luminosity, but it is cooler and substantially larger (by 20 percent) than models would predict,” the paper reads.
Moreover, the scientists found that at least the primary star is not tidally locked to the orbital period. To obtain the parameters of the system, the researchers analyzed the light curve provided by Samuel Oschin telescope at the Palomar Observatory in California as part of the Palomar Transient Factory (PTF) survey. They have also analyzed follow-up spectroscopic data obtained by the High Resolution Echelle Spectrometer (HIRES) at the Keck Observatory, located near the summit of Mauna Kea, Hawaii, as well as the newly released light curve of PTFEB132.707+19.810 by NASA’s prolonged Kepler mission known as K2.
https://phys.org/news/2017-07-bee-beehive-astronomers-binary-star.html
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