May be planets in the orbits of cruel dead stars, and now we know how to find them

(ORDO NEWS) — Have you heard of LU Camelopardalis, QZ Serpentis, V1007 Herculis and BK Lyncis? No, these are not members of a boy band from Ancient Rome. These are Cataclysmic variables, binary stars that are so close to each other that one star takes material from its sister. This causes the brightness of the pair to fluctuate wildly.

Can planets exist in this chaotic environment? Can we detect them? The new study gives a positive answer to both questions.

Cataclysmic variables (CVs) undergo a significant increase in brightness. All stars change their brightness to some extent, even our Sun. But in HF, the increase in brightness is much more pronounced than in stars like our Sun, and occurs 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 move in a close orbit, and one of the stars is more massive than the other.

The more massive star is called the primary, and it consumes gas from a smaller mass star, which astronomers call a donor star.

The primary star in CV is a white dwarf and the donor star is usually a red dwarf. Red dwarf stars are colder and less massive than white dwarfs.

They have a mass between 0.07 and 0.30 solar masses and a radius of about 20 percent of that of the Sun. Primary white dwarf stars have a typical mass of about 0.75 solar masses, but a much smaller radius, about the same as that of the Earth.

As the primary takes material from the donor star, the material forms an accretion disk around the primary. The material in the accretion disk heats up, which leads to an increase in luminosity. This increase can overpower the light from a couple of stars.

If the system has a dim third body – a planet, then its gravity can affect the transfer of material from the donor star to the primary star. These perturbations affect the brightness of the system, and this is what lies at the heart of the new study.

The authors of the study show how the chaotic environment around CV can host planets and explain how astronomers can detect them. The study is called “Testing the Third Body Hypothesis in Cataclysmic Variables LU Camelopardalis, QZ Serpentis, V1007 Herculis and BK Lyncis”.

Article published in Monthly Notices of the Royal Astronomical Society (MNRAS). The lead author is Dr. Carlos Chavez of the Autonomous University of Nuevo Leon in Mexico.

Material attracted to the primary star collects in an accretion ring and heats up, creating increased luminosity. But the transfer of material to disk is not permanent; it rises and falls as the stars in CV revolve around each other. In their study, Chavez and colleagues looked at four cataclysmic variables: LU Camelopardalis, QZ Serpentis, V1007 Herculis, and BK Lyncis.

These four CVs exhibit very long photometric periods (VLPPs), periods of increased luminosity that do not match the orbital periods of the binars.

Between both stars and the third body there is a point called the L1 point, or Lagrange point. This is the point of gravitational equilibrium between stars. Point L1 is dynamic, and its position changes as the stars move. Lead author Chavez has shown in previous work that a third body, a planet, can oscillate at L1.

When the position of the point L1 changes, the amount of material drawn into the main star changes – the mass transfer rate. A change in the mass transfer rate leads to a change in the luminosity of the entire three-body system.

By measuring changes in the brightness of four CVs, the researchers calculated the distances and masses of potential third bodies in the systems based on the changes in brightness in each system.

Their calculations showed that the oscillations have much longer periods than the orbital periods of the stars. According to the team, two of the four CVs studied have “planet-like bodies” in orbit.

“Our work has proven that a third body can perturb the cataclysmic variable in such a way that it can cause brightness changes in the system,” Chavez said in a press release.

“These perturbations can explain both the very long periods that have been observed – from 42 to 265 days – and the amplitude of these brightness changes. Of the four systems we studied, our observations suggest that two out of four have planetary-mass objects in orbit around them.” .

This is not the first time that scientists have been looking at CVs and trying to find an explanation for fluctuations in luminosity.

In 2017, a separate group of researchers published a paper presenting four CVs and their VLPPs. They suggested that the cause is the planets. But they said that “… the orbital plane of the third body must be greater than 39.2 degrees for this mechanism to effectively perturb the inner binary.”

“Here we explore a new possibility, namely that a secular perturbation from a third object with low eccentricity and low inclination explains the VLPP, as well as the change in magnitude observed in these four CVs,” write Chavez and his co-authors in their paper.

They state that “… a third body in a close almost circular flat orbit can create disturbances in the eccentricity of the central binar.”

According to Chavez, their work represents a new way to detect exoplanets. Planet hunters find most exoplanets using the transit system. When an exoplanet passes in front of its star, there is a noticeable dip in the star’s light.

While effective – we’ve found thousands of planets this way – the transit method has its limitations. It only works when everything is lined up correctly. We must look at it as if from the side, otherwise the planet will not pass the star from our point of view, and then there will be no gap in the light of the star.

But the method developed by Chavez and his colleagues does not depend on planetary transits. It relies on an internal change in luminosity that can be observed from different angles.

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