Have you heard of LU Camelopardalis, QZ Serpentis, V1007 Herculis and BK Lyncis? No, they are not members of a boy band in ancient Rome. They are cataclysmic variables, binary stars that are so close together that one star pulls material from its sister. This causes the pair to vary greatly in brightness.
Can planets exist in this chaotic environment? Can we detect them? A new study answers both in the affirmative.
cataclysmic variables (CV) experience large increases in brightness. All stars vary in brightness to some degree, including our own sun. But CV’s brightening is much more pronounced than that of stars like our Sun, and they occur irregularly.
There are different types of cataclysmic variables: classical novae, dwarf novae, some supernovae, and others. All types share the same basic mechanics. A pair of stars orbit each other very closely, and one of the stars is more massive than the other. The most massive is called the parent star, and it draws gas from the lower-mass star, which astronomers call the donor star.
The main star in a CV is a white dwarf and the donor star is usually a red dwarf. Red dwarf stars are cooler and less massive than white dwarfs. They have masses between 0.07 and 0.30 solar masses and a radius of about 20 percent that of the Sun. Primary white dwarf stars have a typical mass of about 0.75 solar masses but much smaller radii, about the same than those on Earth.
When the primary star extracts material from the donor star, the material forms an accretion disk around the primary star. The material in the accretion disk heats up and that causes a higher luminosity. The increase can overpower the light from the star pair.
If there is a third faint body, a planet, in the system, then its gravity can affect the transfer of material from the donor to the parent star. These perturbations affect the brightness of the system, and that’s the core of the new study.
The study authors show how the chaotic environments around CVs can host planets and explain how astronomers can detect them. The study is “Test of the third body hypothesis in the cataclysmic variables LU Camelopardalis, QZ Serpentis, V1007 Herculis and BK Lyncis.” It is published in the Royal Astronomical Society Monthly Notices (MNRAS). The lead author is Dr. Carlos Chavez, from the Autonomous University of Nuevo León in Mexico.
Material attracted by the primary star gathers in an accretion ring and heats up, creating a higher luminosity. But the transfer of material to the disk is not constant; it rises and falls as the stars in the CV orbit each other. Chávez and his colleagues examined four cataclysmic variables in their study: LU Camelopardalis, Serpentis QZV1007 Hercules, and lyncis.
All four CVs exhibit very long photometric periods (VLPPs), which are periods of enhanced luminosity that do not fit binary orbital periods.
There is a point between both stars and the third body called the L1 point, or Lagrangian One point. It is a point of gravitational equilibrium between the stars. The L1 point is dynamic and its position changes as the stars move. Lead author Chavez showed in a previous article that a third body, a planet, can cause oscillations at the L1 point.
As the L1 point changes, the amount of material attracted to the primary star, the rate of mass transfer, changes. A change in the rate of mass transfer creates a change in the luminosity of the entire three-body system.
By measuring the changes in brightness of the four CVs, the researchers calculated the distances and masses of possible third bodies in the systems based on the changes in brightness in each system.
His calculations show that the variations have periods much longer than the orbital periods of the stars. depending on the teamtwo of the four CVs they studied have “planet-like bodies” orbiting them.
“Our work has shown that a third body can disturb a cataclysmic variable in such a way that it can induce brightness changes in the system”, Chávez said in a press release. “These perturbations can explain both the very long periods that have been observed, between 42 and 265 days, and the amplitude of those changes in brightness. Of the four systems we studied, our observations suggest that two of the four have objects of mass planetary orbit around them”.
This is not the first time that scientists have tackled CVs and tried to find an explanation for variations in luminosity.
In 2017, a separate team of researchers published an article presenting all four CVs and their VLPPs. They suggested that the planets were the cause. But they said that “…the orbital plane of the third body must be greater than 39.2 degrees for this mechanism to be effective in perturbing the inner binary effectively.”
“Here we explore a new possibility, namely, that secular perturbation by a third low-eccentricity, low-inclination object explains the VLPP and also the magnitude change observed in these four CVs,” Chavez and coauthors. write on your paper. They say that “…a third body in a near circular planar orbit could produce perturbations in the central binary eccentricity”.
According to Chavez, his work amounts to a new way of detecting exoplanets. Planet hunters find most exoplanets using the transit system. When an exoplanet transits in front of its star, there is a detectable dip in the star’s light.
While effective – we’ve found thousands of planets this way – the transit method has limitations. It only works when things are lined up right. We have to look at it from the side, so to speak, or else the planet doesn’t transit the star from our point of view, and there’s no dip in starlight.
But the method that Chavez and his colleagues developed does not depend on planetary transits. It is based on the intrinsic change in luminosity that is observable from different angles.
This article was originally published by universe today. Read the Original article.