Precision Millimeter Astrometry of the α Centauri AB System

Akeson, Rachel; Beichman, Charles; Kervella, P.; Fomalont, Edward B.; Benedict, G. F.

doi:10.3847/1538-3881/abfaff

Cited by 16 publications

(21 citation statements)

References 58 publications

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“…Proxima Centauri yielded a precise value (Table 1), but the other components of the α Cen system were too bright to be included in Gaia EDR3 and they may have to be tied to the Gaia reference frame by means of other instruments (e.g. Akeson et al 2021) or await future exploration of space observations. Already now, the method permits one to estimate gravitational redshifts of white dwarfs and to set limits on convective shifts in other stars.…”

Section: Discussionmentioning

confidence: 99%

Astrometric radial velocities for nearby stars

Lindegren

Dravins

2021

A&A

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Context. Under certain conditions, stellar radial velocities can be determined from astrometry, without any use of spectroscopy. This enables us to identify phenomena, other than the Doppler effect, that are displacing spectral lines. Aims. The change of stellar proper motions over time (perspective acceleration) is used to determine radial velocities from accurate astrometric data, which are now available from the Gaia and HIPPARCOS missions. Methods. Positions and proper motions at the epoch of HIPPARCOS are compared with values propagated back from the epoch of the Gaia Early Data Release 3. This propagation depends on the radial velocity, which obtains its value from an optimal fit assuming uniform space motion relative to the solar system barycentre. Results. For 930 nearby stars we obtain astrometric radial velocities with formal uncertainties better than 100 km s−1; for 55 stars the uncertainty is below 10 km s−1, and for seven it is below 1 km s−1. Most stars that are not components of double or multiple systems show good agreement with available spectroscopic radial velocities. Conclusions. Astrometry offers geometric methods to determine stellar radial velocity, irrespective of complexities in stellar spectra. This enables us to segregate wavelength displacements caused by the radial motion of the stellar centre-of-mass from those induced by other effects, such as gravitational redshifts in white dwarfs.

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Section: Discussionmentioning

confidence: 99%

Astrometric radial velocities for nearby stars

Lindegren

Dravins

2021

A&A

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“…Further atmospheric characterization with JWST (Gardner et al 2006) would likely be necessary in trying to distinguish between the reflectivity of ice or clouds. For 𝛼 Centauri AB the initial step of planet detection has been elusive, but Beichman et al (2020) proposed a path forward using JWST and others in recent years are attempting to detect planets orbiting either star using data taken from ground-based facilities (Trigilio et al 2018;Zhao et al 2018;Kasper et al 2019;Wagner et al 2021;Akeson et al 2021).…”

Section: Discussionmentioning

confidence: 99%

Milankovitch Cycles for a Circumstellar Earth-analog within $α$ Centauri-like Binaries

Quarles,

Li,

Lissauer

2021

Preprint

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An Earth-analog orbiting within the habitable zone of 𝛼 Centauri B was shown to undergo large variations in its obliquity, or axial tilt, which affects the planetary climate by altering the radiative flux for a given latitude (Quarles et al. 2019). We examine the potential implications of these obliquity variations for climate through Milankovitch cycles using an energy balance model with ice sheets. Similar to previous studies, the largest amplitude obliquity variations from spin-orbit resonances induce snowball states within the habitable zone, while moderate variations can allow for persistent ice caps or an ice belt. Particular outcomes for the global ice distribution can depend on the planetary orbit, obliquity, spin precession, binary orbit, and which star the Earth-analog orbits. An Earth-analog with an inclined orbits relative to the binary orbit can periodically transition through several global ice distribution states and risk runaway glaciation when periods of ice caps and an ice belt overlap. When determining the potential habitability for planets in stellar binaries, more care must be taken due to the orbital and spin dynamics.

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“…Naturally, systems where stellar components might be in jeopardy of not being fully gravitationally bound to the system are those with the largest values for a bin 2 ( ) , the larger of the two separation distances (semimajor axes); see Table 6 , which are HD 126614, HD 40979, HD 196050, and the Alpha and Proxima Centauri system. For the latter, a bin 2 ( ) is identified as approximately 8200 au based on recent ALMA data (Akeson et al 2021).…”

Section: Validation Of the Stellar Componentsmentioning

confidence: 99%

“…In 2017 radial velocity measurements have been precise enough to demonstrate that Proxima Centauri is gravitationally bound to Cen AB. Proxima Cen is currently about 13,000 au away from the Cen AB owing to the relatively high orbital eccentricity given as 0.497 0.060 0.057 -+ (Akeson et al 2021). Due to their closeness to Earth and the orbital eccentricities of Cen AB and Cen C, the position angles continuously change throughout their projected orbits, whereas the orbital parameters remain largely unaltered.…”

Section: Validation Of the Stellar Componentsmentioning

confidence: 99%

An Early Catalog of Planet-hosting Multiple-star Systems of Order Three and Higher

Cuntz

Luke

Millard

et al. 2022

ApJS

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We present a catalog (status 2022 July 1) of triple and higher-order systems identified containing exoplanets based on data from the literature, including various analyses. We explore statistical properties of the systems with a focus on both the stars and the planets. So far, about 30 triple systems and one to three quadruple systems, including (mildly) controversial cases, have been found. The total number of planets is close to 40. All planet-hosting triple-star systems are highly hierarchic, consisting of a quasi-binary complemented by a distant stellar component, which is in orbit about the common center of mass. Furthermore, the quadruple systems are in fact pairs of close binaries (“double–doubles”), with one binary harboring a planet. For the different types of star–planet systems, we introduce a template for the classifications of planetary orbital configurations in correspondence to the hierarchy of the system and the planetary host. The data show that almost all stars are main-sequence stars, as expected. However, the stellar primaries tend to be more massive (i.e., corresponding to spectral types A, F, and G) than expected from single-star statistics, a finding also valid for stellar secondaries but less pronounced. Tertiary stellar components are almost exclusively low-mass stars of spectral type M. Almost all planets have been discovered based on either the Radial Velocity method or the Transit method. Both gas giants (the dominant type) and terrestrial planets (including super-Earths) have been identified. We anticipate the expansion of this database in the light of future planetary search missions.

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Precision Millimeter Astrometry of the α Centauri AB System

Cited by 16 publications

References 58 publications

Astrometric radial velocities for nearby stars

Astrometric radial velocities for nearby stars

Milankovitch Cycles for a Circumstellar Earth-analog within $α$ Centauri-like Binaries

An Early Catalog of Planet-hosting Multiple-star Systems of Order Three and Higher

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