Astronomers used the James Webb Space Telescope to analyze HAT-P-18 b, revealing water vapor and CO2 in its atmosphere. They highlight the challenge of distinguishing between atmospheric and stellar signals and suggest that star speckles have a significant impact on data interpretation. (Artist’s concept) Credit: SciTechDaily.com
Astronomers used JWST to study the atmosphere. exoplanet HAT-P-18 b, discovers water vapor and CO2, emphasizing the influence of host star properties on data analysis.
A team of astronomers led by researchers at the Trottier Institute for Exoplanet Research (iREx) at the University of Montreal is harnessing the power of the revolutionary James Webb Space Webb Telescope (JWST) to study “hot planets.” did. SaturnExoplanet HAT-P-18 b.
Their findings were published in the journal last month Royal Astronomical Society Monthly Noticespaints a complete picture of HAT-P-18 b’s atmosphere, exploring the major challenge of distinguishing HAT-P-18 b’s atmospheric signal from stellar activity.
HAT-P-18 b is more than 500 light-years away and has a mass similar to Saturn, but its size is closer to it than Saturn. Jupiter. As a result, exoplanets have “inflated” atmospheres that are particularly ideal for analysis.
![Exoplanet HAT-P-18 b](https://scitechdaily.com/images/Exoplanet-HAT-P-18-b-777x437.jpg)
Artistic representation of the “hot Saturn” exoplanet, HAT-P-18 b.Credit: NASA/Eye of the Exoplanet
pass over a spotted star
The observations from JWST were made while HAT-P-18 b was passing in front of a Sun-like star. This moment, called a transit, is crucial for detecting and further characterizing exoplanets with amazing precision from hundreds of light-years away.
Astronomers do not observe light emitted directly from distant planets. Rather, they study how the light of a central star is blocked and influenced by planets orbiting around it, so that some signals are caused by the presence of a planet and others caused by the properties of the star itself. An attempt is needed to unravel this.
A light curve shows the brightness or brightness of a star over time. When an exoplanet passes over a star (known as a transit), some of the star’s light is blocked by the exoplanet. As a result, the brightness of the star decreases. When a star spot is obscured by a star’s surface, or when an exoplanet passes over a dark spot, astronomers can see the signal in the light curve in the form of a small bump at the bottom of the passing light curve. Masu. Watch the entire animation of this infographic below.Credit: B. Gougeon/University of Montreal
Like our Sun, stars do not have uniform surfaces. They have dark star spots and bright regions that could produce a signal that mimics the planet’s atmospheric attributes. A recent study of the exoplanet TRAPPIST-1 b and its star TRAPPIST-1, led by UdeM PhD student Olivia Lim, witnessed an eruption or flare on the star’s surface that affected observations. it was done.
In the case of planet HAT-P-18 b, Webb precisely captured the exoplanet passing over the dark spot of star HAT-P-18. This is called a spot crossing event, and its effects were evident in data collected for the new study. The iREx team also reported the presence of numerous other star spots on HAT-P-18’s surface that were not obscured by the exoplanet.
To accurately determine the composition of an exoplanet’s atmosphere, researchers needed to simultaneously model the planet’s atmosphere and star characteristics. In their study, they point out that such considerations are critical to dealing with and maximizing the potential of future exoplanet observations by Webb.
“We found that accounting for stellar contamination implies the presence of spots and clouds rather than haze, resulting in almost an order of magnitude lower water vapor recovery,” said lead author Marie-Lou Fournier Tondreau. .
“Thus, considering the host star of the system makes a big difference,” added Fournier Tondreau, who worked on the research as a master’s student at iREx and is currently pursuing a PhD.in oxford university.
“In fact, for the first time we have been able to clearly disentangle the characteristics of haze and star spots thanks to Canada’s NIRISS (Near Infrared Imager and Slitless Spectrometer) instrument, which extends into the visible light range. It provides a wider wavelength range.”
H2O, CO2 and clouds in the scorching atmosphere
After modeling exoplanets and stars in the HAT-P-18 system, iREx astronomers performed a thorough analysis of HAT-P-18 b’s atmospheric composition. By examining the light passing through the exoplanet’s atmosphere as it passes by its host star, researchers identified the presence of water vapor (H2O) and carbon dioxide (CO2).
Researchers also detected the possible presence of sodium and observed strong signs of a cloud layer in HAT-P-18 b’s atmosphere. Cloud layers appear to weaken the signals of many molecules found within them. They also concluded that the star’s surface is covered with many dark spots that can significantly affect the interpretation of the data.
An earlier analysis of the same JWST data led by a team at Johns Hopkins University also revealed that water and CO2 were clearly detected, but at higher altitudes small particles called haze were detected and methane (CH4 ) has also been reported to have been found. iREx astronomers paint a different picture.
No CH4 detection was confirmed, and the water abundance they measured was 10 times lower than previously found. They also found that the haze detected in previous studies could be caused by stellar spots on the star’s surface, underscoring the importance of considering stars in the analysis.
Could life exist on exoplanets? Unlikely. Molecules such as water, carbon dioxide, and methane, in specific ratios or in combination with other molecules, can be interpreted as biosignatures, or signs of life, but HAT-P-18 b’s scorching temperatures of nearly 600 degrees teeth, Celsius It doesn’t bode well for Earth’s habitability.
Future observations with another JWST instrument, the Near Infrared Spectrometer (NIRSpec), will help refine the team’s results, including CO2 detection, and further unravel the complexity of this hot Saturnian exoplanet. Hope it helps.
Reference: “Near-infrared transmission spectroscopy of HAT-P-18 b with NIRISS: Unraveling planetary and stellar features during the JWST era” Marylou Fournier-Tondreau, Ryan J MacDonald, Michael Radica, David Lafrenière, Luis Welbanks, Caroline Written by Piaulet, Louis-Philippe Coulon, Romain Arard, Kim Morel, Etienne Artigau, Loic Albert, Olivia Lim, René Doyon, Bjorn Beneke, Jason F. Lowe, Antoine Darvaux-Bernier, Nicolas B. Cowan, Nicole K. Lewis, Neil James Cook, Laura Flagg, Frederick Genest, Stephen Pelletier, Doug Johnston, Lisa Dunn, Lisa Kaltenegger, Jake Taylor, Jake D. Turner , December 9, 2023 Royal Astronomical Society Monthly Notices.
DOI: 10.1093/mnras/stad3813