Earth and Planetary Astrophysics (astro-ph.EP)

Stellar X-Ray Variability and Planetary Evolution in the DS Tucanae System

Sat, 01 Feb 2025 00:00:00 GMT

Stellar X-Ray Variability and Planetary Evolution in the DS Tucanae System King, George W.; Corrales, Lía R.; Bourrier, Vincent; Dos Santos, Leonardo A.; Doyle, Lauren; Lavie, Baptiste; Ramsay, Gavin; Wheatley, Peter J. We present an analysis of four Chandra observations of the 45 Myr old DS Tuc binary system. We observed X-ray variability of both stars on timescales from hours to months, including two strong X-ray flares from star A. The implied flaring rates are in agreement with past observations made with XMM-Newton, though these rates remain imprecise due to the relatively short total observation time. We find a clear, monotonic decline in the quiescent level of the star by a factor of 1.8 across 8 months, suggesting stellar variability that might be due to an activity cycle. If proven through future observations, DS Tuc A would be the youngest star for which a coronal activity cycle has been confirmed. The variation in our flux measurements across the four visits is also consistent with the scatter in empirical stellar X-ray relationships with Rossby number. In simulations of the possible evolution of the currently super-Neptune-sized planet DS Tuc A b, we find a range of scenarios for the planet once it reaches a typical field age of 5 Gyr, from Neptune size down to a completely stripped super-Earth. Improved constraints on the planet's mass in the future would significantly narrow these possibilities. We advocate for further Chandra observations to better constrain the variability of this important system.

The PLATO field selection process: II. Characterization of LOPS2, the first long-pointing field

Sat, 01 Feb 2025 00:00:00 GMT

The PLATO field selection process: II. Characterization of LOPS2, the first long-pointing field Nascimbeni, V.; Piotto, G.; Cabrera, J.; Montalto, M.; Marinoni, S.; Marrese, P. M.; Aerts, C.; Altavilla, G.; Benatti, S.; Börner, A.; Deleuil, M.; Desidera, S.; Gizon, L.; Goupil, M. J.; Granata, V.; Heras, A. M.; Magrin, D.; Malavolta, L.; Mas-Hesse, J. M.; Osborn, H. P.; Pagano, I.; Paproth, C.; Pollacco, D.; Prisinzano, L.; Ragazzoni, R.; Ramsay, G.; Rauer, H.; Tkachenko, A.; Udry, S. PLAnetary Transits and Oscillations of stars (PLATO) is an ESA M-class mission to be launched by the end of 2026 to discover and characterize transiting planets around bright and nearby stars, and in particular habitable rocky planets hosted by solar-like stars. Over the mission lifetime, an average of 8% of the science data rate will be allocated to Guest Observer programs selected by ESA through public calls. Hence, it is essential for the community to know in advance where the observing fields will be located. In a previous paper, we identified two preliminary long-pointing fields (LOPN1 and LOPS1) for PLATO, respectively in the northern and southern hemispheres. Here we present LOPS2, a slightly adjusted version of the southern field that has recently been selected by the PLATO Science Working Team as the first field to be observed by PLATO for at least two continuous years, following the scientific requirements. In this paper, we describe the astrophysical content of LOPS2 in detail, including known planetary systems, bright stars, variables, binary stars, star clusters, and synergies with other current and future facilities.

Cross Validation of Albedo Determination for 1627 Ivar from Three Different Techniques

Sat, 01 Feb 2025 00:00:00 GMT

Cross Validation of Albedo Determination for 1627 Ivar from Three Different Techniques Selmi, Elena; Devogèle, M.; Masiero, J. R.; Santiago, N. Vega; Wright, E. L.; Ferrais, M.; Fernández-Valenzuela, E.; Borisov, G.; Bendjoya, Ph.; Rivet, J. -P.; Abe, L.; Vernet, D.; Cellino, A. Near-Earth asteroids are of great interest to the scientific community due to their proximity to Earth, making them both potential hazards and possible targets for future missions, as they are relatively easy to reach by spacecraft. A number of techniques and models can be used to constrain their physical parameters and build a comprehensive assessment of these objects. In this work, we compare physical property results obtained from improved H_V absolute magnitude values, thermophysical modeling, and polarimetry data for the well-known Amor-class NEO 1627 Ivar. We show that our fits for albedo are consistent with each other, thus demonstrating the validity of this cross-referencing approach, and propose a value for Ivar's albedo of . Future observations will extend this work to a larger sample size, increasing the reliability of polarimetry for rapid asteroid property characterization as a technique independent of previously established methods and requiring significantly fewer observations.

NGTS-33b: a young super-Jupiter hosted by a fast-rotating massive hot star

Wed, 01 Jan 2025 00:00:00 GMT

NGTS-33b: a young super-Jupiter hosted by a fast-rotating massive hot star Alves, Douglas R.; Jenkins, James S.; Vines, Jose I.; Battley, Matthew P.; Lendl, Monika; Bouchy, François; Nielsen, Louise D.; Gill, Samuel; Moyano, Maximiliano; Anderson, D. R.; Burleigh, Matthew R.; Casewell, Sarah L.; Goad, Michael R.; Hawthorn, Faith; Kendall, Alicia; McCormac, James; Osborn, Ares; Smith, Alexis M. S.; Udry, Stéphane; Wheatley, Peter J.; Saha, Suman; Parc, Léna; Nigioni, Arianna; Apergis, Ioannis; Ramsay, Gavin In the last few decades, planet search surveys have been focusing on solar-type stars, and only recently the high-mass regimes. This is mostly due to challenges arising from the lack of instrumental precision, and more importantly, the inherent active nature of fast-rotating massive stars. Here, we report NGTS-33b (TOI-6442b), a super-Jupiter planet with mass, radius, and orbital period of 3.6

$\pm$

0.3 M

$_{\rm J}$

, 1.64

$\pm$

0.07 R

$_{\rm J}$

, and

$2.827\,972 \pm 0.000\,001$

d, respectively. The host is a fast-rotating (

$0.6654 \pm 0.0006$

d) and hot (T

$_{\rm eff}$

= 7437

$\pm$

72 K) A9V type star, with a mass and radius of 1.60

$\pm$

0.11 M

$_{\odot }$

and 1.47

$\pm$

0.06 R

$_{\odot }$

, respectively. Planet structure and gyrochronology models show that NGTS-33 is also very young with age limits of 10-50 Myr. In addition, membership analysis points towards the star being part of the Vela OB2 association, which has an age of

$\sim$

20-35 Myr, thus providing further evidence about the young nature of NGTS-33. Its low bulk density of 0.19

$\pm$

0.03 g cm

$^{-3}$

is 13 per cent smaller than expected when compared to transiting hot Jupiters (HJs) with similar masses. Such cannot be solely explained by its age, where an up to 15 per cent inflated atmosphere is expected from planet structure models. Finally, we found that its emission spectroscopy metric is similar to JWST community targets, making the planet an interesting target for atmospheric follow-up. Therefore, NGTS-33b's discovery will not only add to the scarce population of young, massive and HJs, but will also help place further strong constraints on current formation and evolution models for such planetary systems.