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Universe ◽  
2022 ◽  
Vol 8 (1) ◽  
pp. 45
Author(s):  
Paolo Ventura ◽  
Flavia Dell’Agli ◽  
Marco Tailo ◽  
Marco Castellani ◽  
Ester Marini ◽  
...  

We discuss the evolution of stars through the asymptotic giant branch, focusing on the physical mechanisms potentially able to alter the surface chemical composition and on how changes in the chemistry of the external regions affect the physical properties of the star and the duration of this evolutionary phase. We focus on the differences between the evolution of low-mass stars, driven by the growth of the core mass and by the surface carbon enrichment, and that of their higher mass counterparts, which experience hot bottom burning. In the latter sources, the variation of the surface chemical composition reflects the equilibria of the proton capture nucleosynthesis experienced at the base of the convective envelope. The pollution expected from this class of stars is discussed, outlining the role of mass and metallicity on the chemical composition of the ejecta. To this aim, we considered evolutionary models of 0.7–8 M⊙ stars in a wide range of metallicities, extending from the ultra-metal-poor domain to super-solar chemistries.


2022 ◽  
Vol 924 (1) ◽  
pp. 9
Author(s):  
Tim Hallatt ◽  
Eve J. Lee

Abstract The sub-Saturn (∼4–8 R ⊕) occurrence rate rises with orbital period out to at least ∼300 days. In this work we adopt and test the hypothesis that the decrease in their occurrence toward the star is a result of atmospheric mass loss, which can transform sub-Saturns into sub-Neptunes (≲4 R ⊕) more efficiently at shorter periods. We show that under the mass-loss hypothesis, the sub-Saturn occurrence rate can be leveraged to infer their underlying core mass function, and, by extension, that of gas giants. We determine that lognormal core mass functions peaked near ∼10–20 M ⊕ are compatible with the sub-Saturn period distribution, the distribution of observationally inferred sub-Saturn cores, and gas-accretion theories. Our theory predicts that close-in sub-Saturns should be ∼50% less common and ∼30% more massive around rapidly rotating stars; this should be directly testable for stars younger than ≲500 Myr. We also predict that the sub-Jovian desert becomes less pronounced and opens up at smaller orbital periods around M stars compared to solar-type stars (∼0.7 days versus ∼3 days). We demonstrate that exceptionally low-density sub-Saturns, “super-puffs,” can survive intense hydrodynamic escape to the present day if they are born with even larger atmospheres than they currently harbor; in this picture, Kepler 223 d began with an envelope ∼1.5× the mass of its core and is currently losing its envelope at a rate of ∼2 × 10−3 M ⊕ Myr−1. If the predictions from our theory are confirmed by observations, the core mass function we predict can also serve to constrain core formation theories of gas-rich planets.


2022 ◽  
Vol 924 (2) ◽  
pp. 66
Author(s):  
Mitchell E. Yenawine ◽  
William F. Welsh ◽  
Jerome A. Orosz ◽  
Allyson Bieryla ◽  
William D. Cochran ◽  
...  

Abstract We explore the fascinating eclipses and dynamics of the compact hierarchical triple-star system KOI-126 (KIC 5897826). This system is composed of a pair of M-dwarf stars (KOI-126 B and C) in a 1.74 day orbit that revolve around an F star (KOI-126 A) every 34 days. Complex eclipse shapes are created as the M stars transit the F star, due to two effects: (1) the duration of the eclipse is a significant fraction of the M-star orbital period, so the prograde or retrograde motion of the M stars in their orbit lead to unusually short or long duration eclipses; (2) due to 3-body dynamics, the M-star orbit precesses with an astonishingly quick timescale of 1.74 yr for the periastron (apsidal) precession, and 2.73 yr for the inclination and nodal angle precession. Using the full Kepler data set, supplemented with ground-based photometry, plus 29 radial velocity measurements that span 6 yr, our photodynamical modeling yields masses of M A = 1.2713 ± 0.0047 M ⊙ (0.37%), M B = 0.23529 ± 0.00062 M ⊙ (0.26%), and M C = 0.20739 ± 0.00055 M ⊙ (0.27%) and radii of R A = 1.9984 ± 0.0027 R ⊙ (0.14%), R B = 0.25504 ± 0.00076 R ⊙ (0.3%), and R C = 0.23196 ± 0.00069 R ⊙ (0.3%). We also estimate the apsidal motion constant of the M dwarfs, a parameter that characterizes the internal mass distribution. Although it is not particularly precise, we measure a mean apsidal motion constant, k 2 ¯ , of 0.046 − 0.028 + 0.046 , which is approximately 2σ lower than the theoretical model prediction of 0.150. We explore possible causes for this discrepancy.


2021 ◽  
pp. 122-130
Author(s):  
Raymond T. Pierrehumbert
Keyword(s):  
The Sun ◽  
Low Mass ◽  
Break Up ◽  

‘How it all ends’ reflects on the different ways that the Solar System can end. Some six billion years from now, if anybody is left standing on Earth to witness it, they will see the Sun begin to go through some alarming transformations. Earth will cross the runaway greenhouse threshold in about a half billion years, whereafter the oceans will evaporate away, the surface will be heated to sterilizing temperatures, and water will break up and be irretrievably lost to space. Meanwhile, planets around low mass M stars will not suffer a crisis by fire because such stars evolve very slowly. Such planets end their lives in ice instead.


2021 ◽  
Vol 913 (1) ◽  
pp. 22
Author(s):  
Takashi Kojima ◽  
Masami Ouchi ◽  
Michael Rauch ◽  
Yoshiaki Ono ◽  
Kimihiko Nakajima ◽  
...  
Keyword(s):  
M Stars ◽  

Author(s):  
Sam Walker ◽  
Maxwell Andrew Millar-Blanchaer ◽  
Bin Ren ◽  
Paul Kalas ◽  
John Carpenter

Abstract We present observations of three protoplanetary disks in visible scattered light around M-type stars in the Upper Scorpius OB association using the STIS instrument on the Hubble Space Telescope. The disks around stars 2MASS J16090075–1908526, 2MASS J16142029–1906481 and 2MASS J16123916–1859284 have all been previously detected with ALMA, and 2MASS J16123916–1859284 has never previously been imaged at scattered light wavelengths. We process our images using Reference Differential Imaging, comparing and contrasting three reduction techniques – classical subtraction, Karhunen-Loéve Image Projection and Non-Negative Matrix Factorisation, selecting the classical method as the most reliable of the three for our observations. Of the three disks, two are tentatively detected (2MASS J16142029–1906481 and 2MASS J16123916–1859284), with the third going undetected. Our two detections are shown to be consistent when varying the reference star or reduction method used, and both detections exhibit structure out to projected distances of ≳ 200 au. Structures at these distances from the host star have never been previously detected at any wavelength for either disk, illustrating the utility of visible-wavelength observations in probing the distribution of small dust grains at large angular separations.


Universe ◽  
2021 ◽  
Vol 7 (4) ◽  
pp. 88
Author(s):  
Jonathan H. Jiang ◽  
Daniel Zhao ◽  
Xuan Ji ◽  
Bohan Xie ◽  
Kristen A. Fahy

The growing database of exoplanets has shown us the statistical characteristics of various exoplanet populations, providing insight towards their origins. Observational evidence suggests that the process by which gas giants are conceived in the stellar disk may be disparate from that of smaller planets. Using NASA’s Exoplanet Archive, we analyzed the relationships between planet mass and stellar metallicity, as well as planet mass and stellar mass for low-mass exoplanets (MP < 0.13 MJ) orbiting spectral class G, K, and M stars. We performed further uncertainty analysis to confirm that the exponential law relationships found between the planet mass, stellar mass, and the stellar metallicity cannot be fully explained by observation biases alone.


2021 ◽  
Vol 504 (1) ◽  
pp. 146-154
Author(s):  
Jorick S Vink ◽  
Erin R Higgins ◽  
Andreas A C Sander ◽  
Gautham N Sabhahit

ABSTRACT At the end of its life, a very massive star is expected to collapse into a black hole (BH). The recent detection of an 85  M⊙ BH from the gravitational wave event GW 190521 appears to present a fundamental problem as to how such heavy BHs exist above the approximately 50  M⊙ pair-instability (PI) limit where stars are expected to be blown to pieces with no remnant left. Using mesa, we show that for stellar models with non-extreme assumptions, 90–100  M⊙ stars at reduced metallicity ($Z/\mbox{ $\mathrm{Z}_{\odot }$}\le 0.1$) can produce blue supergiant progenitors with core masses sufficiently small to remain below the fundamental PI limit, yet at the same time lose an amount of mass via stellar winds that is small enough to end up in the range of an ‘impossible’ 85  M⊙ BH. The two key points are the proper consideration of core overshooting and stellar wind physics with an improved scaling of mass-loss with iron (Fe) contents characteristic for the host galaxy metallicity. Our modelling provides a robust scenario that not only doubles the maximum BH mass set by PI, but also allows us to probe the maximum stellar BH mass as a function of metallicity and cosmic time in a physically sound framework.


2021 ◽  
Vol 503 (3) ◽  
pp. 3660-3676
Author(s):  
E Pancino ◽  
N Sanna ◽  
G Altavilla ◽  
S Marinoni ◽  
M Rainer ◽  
...  

ABSTRACT We present the flux tables of the spectrophotometric standard stars (SPSS) used to calibrate in flux the Gaia DR2 and (E)DR3 data releases. The latest SPSS grid version contains 112 stars, whose flux tables agree to better than 1 per cent with the CALSPEC spectra of 11 flux standards for the calibration of the Hubble Space Telescope. The synthetic magnitudes computed on the SPSS spectra also agree to better than 1 per cent with the Landolt magnitudes of 37 stars in common. The typical spreads in both comparisons are of the order of 1 per cent. These uncertainties already meet the initial requirements for the Gaia SPSS project, but further improvements are expected in the next SPSS versions, that will be used to calibrate future Gaia releases. We complement the SPSS flux tables with literature spectra of 60 additional stars that did not pass all the criteria to be SPSS, the Passband Validation Library (PVL). The PVL contains stars of extreme spectral types, such as bright O and B stars and late M stars and brown dwarfs, and was useful to investigate systematic effects in the previous Gaia DR2 release and to minimize them in the EDR3 one. The PVL literature spectra are recalibrated as accurately as possible on to the SPSS reference scale, so that the two sets together can be used in a variety of validation and comparison studies.


2021 ◽  
Vol 253 (1) ◽  
pp. 19
Author(s):  
Li-yun Zhang ◽  
Gang Meng ◽  
Liu Long ◽  
Jianrong Shi ◽  
Ming Zhong ◽  
...  

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