An ultra-short period exoplanet discovered with TESS

TESS target pixel file image of HD 20329 observed in sector 42. Credit: Murgas et al, 2022

Using NASA’s Transiting Exoplanet Survey Satellite (TESS), an international team of astronomers has detected a new ultra-short-period exoplanet. The alien new world, designated HD 20329 b, orbits its host star in just under a day. The discovery was presented Nov. 4 on

TESS is conducting a survey of around 200,000 of the brightest stars near the sun with the aim of looking for transiting exoplanets. So far, it has identified nearly 6,000 exoplanet candidates (TESS Objects of Interest, or TOI), of which 268 have been confirmed so far.

Now, a group of astronomers led by Felipe Murgas of the University of La Laguna in Spain recently confirmed another TOI monitored by TESS. In a recently published research paper, they report that a transit signal has been identified in the light curve of the solar-type star HD 20329 (or TOI-4524). The planetary nature of this signal was confirmed by subsequent radial velocity measurements made with the HARPS-N spectrograph.

“Here we report the discovery of HD 20329 b, a USP [ultra-short-period] planet around a bright G-type star (V = 8.74 magnitude, J = 7.5 magnitude), which was discovered using the TESS data,” the researchers wrote in the study.

HD 20329 b has a radius of 1.72 Earth radii and is about 7.42 times as massive as our planet, which gives an average bulk density of about 8.06 g/cm3. This exoplanet takes about 22.2 hours to completely orbit its host. The results show that HD 20329 b is only 0.018 AU from the star and its equilibrium temperature is estimated at a level of 2,000 K.

Thus, HD 20329 b is the latest addition to the list of about 120 known ultra-short-period exoplanets, joining about 30 USPs with Doppler beam and mass measurements. The authors of the article do not rule out the possibility that there are multiple objects in the HD 20329 system, but further observations are needed to confirm this.

“We note that after subtracting the USP planetary signal from the RV [radial velocity] measurements, the RV remnants exhibit a slope that could indicate the presence of another low-mass object orbiting HD 20329,” the researchers wrote.

They added that the emission spectroscopy metric for HD 20329 b indicates that this planet has favorable conditions for secondary transit follow-up with NASA’s James Webb Space Telescope (JWST).

Regarding the parameters of the host star HD 20329, the study revealed that it has a radius of about 1.13 solar radii and is about 10% less massive than the sun. The star is 11 billion years old, has a metallicity at a level of -0.07, and its measured effective temperature is 5,596 K. The distance from the system is estimated to be about 207.6 light-years.

More information:
F. Murgas et al, HD 20329b: An ultra-short period planet around a solar-type star found by TESS, arXiv (2022). DOI: 10.48550/arxiv.2211.02547

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