Have you heard of LU Camelopardalis, QZ Serpentis, V1007 Herculis, and BK Lyncis? No, they are not members of the boy bands in ancient Rome. They are cataclysmic variables, binary stars that are so close together that a star draws material from its sibling. This causes the pair to vary wildly in brightness.
Could planets exist in this chaotic environment? Can we find them? A new study answers yes to both.
Catastrophic variables (CVs) undergo a large increase in brightness. All stars vary in brightness to some degree, even our own Sun. But the increased brightness in CVs is much more pronounced than in stars like our Sun, and they occur randomly.
There are different types of cataclysmic novae: classical nova, dwarf nova, some supernova, and others. All variants share the same basic mechanics. A pair of stars orbit each other, and one of those stars is more massive than the other. The more massive one is called the primary star, and it draws gas from the lower-mass star, which astronomers call the donor star.
The primary star in 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 a mass between 0.07 and 0.30 solar masses and their radius is about 20 percent that of the Sun. White dwarf primary stars have a typical mass of about 0.75 solar masses, but a much smaller radius, similar to that of Earth.
When the primary star draws material from the donor star, the material forms an accretion disk around the primary star. The material in the accretion disk heats up, and this increases the brightness. The growth may be dominated by light from the pair of stars.
If there is a dim third object in the system – a planet – then its gravity can affect the transfer of material from the donor to the primary star. These disturbances affect the brightness of the system, and this is at the heart of the new study.
The study’s authors describe how the chaotic environment around CVs can host planets and explain how astronomers can spot them. The study is a test of the third-body hypothesis in “catastrophic variables LU Camelopardalis, QZ Serpentis, V1007 Herculis, and BK Lyncis.” it is published in Monthly Notice of the Royal Astronomical Society ,Manarsa) The lead author is Dr. Carlos Chavez from the Universidad Autónoma de Nuevo León in Mexico.
Material drawn toward the primary star collects in the accretion ring and heats up, increasing the brightness. But the transfer of content to disk is not stable; It rises and falls in CV orbit as stars orbit each other. Chavez and colleagues examined four cataclysmic variables in their study: Alu camelopardalis, QZ serpentis, V1007 hercules, and BK linsis.
The four CVs exhibit a very long photometric period (VLPP), a period of increased brightness that does not correspond to the binary’s orbital period.
Between both stars and the third body there is a point called the L1 point or Lagrangian one point. This is the gravitational equilibrium point between the stars. The L1 point is dynamic, and its position changes as the stars move. Lead author Chavez showed in a previous paper that a third body, a planet, could produce excitation in the L1 point.
As the L1 point changes, the amount of material pulled into the primary star – the mass transfer rate – changes. A change in the mass transfer rate causes a change in the brightness of the entire three-body system.
By measuring the change in brightness of the four CVs, the researchers calculated the distance and mass of a possible third of the bodies in the system based on the brightness changes in each system.
Their calculations show that the variations have periods much longer than the stars’ orbital periods. According to the team, two of the four CVs they studied have “planetary-like bodies” orbiting them.
“Our work has proven that a third body can perturb a cataclysmic variable in a way that can cause changes in brightness in the system,” Chavez said in a press release. “These disturbances could explain both the very long periods observed—between 42 and 265 days—and the amplitude of those changes in brightness. Our observations of the four systems we studied suggest that two out of four have planetary mass objects in orbit around them.”
This isn’t the first time scientists have encountered CV and tried to find an explanation for the variation in brightness.
In 2017 a different team of researchers published a paper presenting four CVs and their VLPPs. He suggested that the planets were the cause. But he added that “…for this mechanism to be effective in effectively perturbing the inner binary the third-body orbital plane must be greater than 39.2 degrees.”
Chávez and his co-authors write in their paper, “Here we explore a new possibility, namely that secular perturbations by a low eccentricity and low inclination third object explain the VLPP and the magnitude change observed in these four CVs. ” They state that “… a third object in a near-circular planar orbit may cause disturbances at the central binary singularity.”
According to Chavez, their work equates to a new way of detecting exoplanets. Planet-hunters find most exoplanets using transit systems. As an exoplanet passes in front of its star, there is a detectable dip in starlight.
While effective – we have discovered thousands of planets this way – there are limitations to the transit method. It only works if things are lined up correctly. We have to look at it from that side, as it were, otherwise the planet doesn’t cross the star from our point of view, and there’s no drop in starlight.
But the method Chavez and his colleagues developed does not depend on planetary transits. It depends on the internal change in brightness that can be seen from different angles.
This article was originally published by Universe Today. Read the original article.
