An alleged exoplanet orbiting a star in the associated constellation Eridanus Star TrekPerhaps Vulcan’s fictional homeworld was just a figment of the star’s spectrum – a spectral ghost.
Analysis of detection data on several exoplanets across the galaxy revealed that many of the detections were in fact false positives: fluctuations in light emitted by the star alone, rather than interacting with an exoplanet orbiting the solar system.
So hopes for a Vulcan planet have been dashed – at least for the time being – but it’s a result that should produce more powerful exoplanets in the future.
Results accepted The Astronomical Journal It is available on a prepress server arXiv.
The discovery of an exoplanet was announced in 2018: a world named 40 Eridani b, orbiting the star 40 Eridani A, a giant rocky Earth that orbits the star once every 42 Earth days or so.
It was discovered based on a property known as radial velocity, a faint momentum that manifests itself in wavelength fluctuations of light coming from a star.
A star surrounded by planets is not affected by the gravitational effects of the planets’ orbits. Bodies rotate, not one around the other, but both around a common center of gravity.
This means that the star wobbles slightly instantaneously as the exoplanet moves around it; This can be detected in their light.
Any light emitted by a star or part of a star that is moving toward us is compressed slightly, moving toward the blue end of the spectrum. The light from something moving away from us gets elongated slightly, and turns red.
When it is caused by an exoplanet, it can be detected because the entire stellar spectrum moves slightly back and forth on regular time scales.
But it’s not always easy to tease an exoplanet out of this apparent oscillation. If there is any activity on the star’s surface—bright spots, or interstellar spots—it will produce a oscillation in the spectrum as well, with a frequency consistent with the star’s rotation, as it rotates in and out of view.
And this is where we run into problems with 40 Eridani b.
The orbital period of the putative exoplanet was very close to that of the star’s rotation, somewhere between 37 and 43 days.
At the time, the researchers said it was possible that what they interpreted as an exoplanet signal could be a rotation signal but an exact rotation period for the star could not be obtained.
Since then, other astronomers have taken a closer look. a 2021 sheets which used a newly developed pipeline to identify radial velocity signals found that the detection of 40 Eridani b was a false positive. a 2022 sheets He was unable to draw a conclusion.
Now, a team led by physicist Kathryn Laliotis of Ohio State University has taken a closer look at 40 Eridani b, and identified other stars based on radial velocity, and discovered the possibility of a false signal.
They said that many of the periodic signals they found in the star are entirely consistent with stellar activity, such as magnetic cycles and stellar rotation, while others could not be validated because the star’s region of space is unobservable for much of an Earth year.
“Therefore we,” They write in their papersClassify this as a false positive signal.
They also found several other potentially ghost exoplanets in the data, too. Radial velocity data are interpreted to derive the super-Earth exoplanets HD 20794 c And HD 85512 b They were also false positives caused by stellar activity, the team reports, and the gas giant HD 114613 b It also seems questionable.
On the other hand, the researchers were able to identify two new exoplanet candidates to be followed up with further observation and analysis to determine their nature.
So, swings and carousels. Farewell Vulcan, hello HD 192310 RV Signal IV and HD 146233 RV Signal III (they’ll probably come up with more catchy names later if the exoplanets are confirmed).
These findings suggest that as we obtain more and more detailed data, it is useful to revisit older, potentially obscure detections, to clarify observed signals and ensure that our exoplanet detections are as clear as possible. In the process, we can also learn a lot about stellar activity.
“We expect that the discovery and characterization of Earth’s analog planets will be a very challenging task due to challenges posed by observational limitations, instrumentation systematics and, most importantly, the diversity of the stars themselves,” write the researchers.
“The observation of customized radial velocity, high cadence, and high resolution will enable the characterization and potential mitigation of signals of stellar variability on time scales of hours to years along with the discovery of additional currently unknown planetary companions.
“Knowing how to properly model and demote the signals of both layers will be critical to any future efforts to measure the exact masses of Earth analog planets.”
The team’s research was accepted at The Astronomical Journal and available at arXiv.
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