2019/04/05 by R. Liseau, Liseau, Rene'
Physics and Astronomy · #Astro and Planetary Science #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #Cosmology and Gravitation Theories #FOS: Physical sciences #Gamma-ray bursts and supernovae #Solar and Stellar Astrophysics (astro-ph.SR) #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.1904.03043
openalex publication_date 2019/04/05 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The observational study of stars in the sub-millimetre regime has only rather\nrecently begun and was made possible mainly by the Atacama Large\nMillimeter/submillimeter Array (ALMA). The emission mechanisms of this\nradiation from normal MS stars and its physical significance for the outer\natmospheric layers is the topic of intense contemporary study. Our previous\nALMA observations of the alpha Centauri binary system detected the submm\nemission originating in the chromospheres of these solar-type stars.\nObservations at another epoch are aiming at further characterising these\natmospheric layers and their behaviour with time. The comparison of data from\ntwo epochs should present the basis for more advanced theoretical modelling. In\nCycle 4, both stars were again detected in the same bands as in the earlier\nCycle 2. These early data suggested a flattening of the SED towards longer\nwavelengths. Now, the SEDs exhibit a single spectral slope over the entire\nfrequency range (90 to 675 GHz). The SEDs from Cycle 4 can be fit by power laws\nof the form S(f)~fa with a=1.76+/-0.01 for alpha Cen A and a=1.71+/-0.02 for\nalpha Cen B. In addition, we were aiming at clarifying the status of the\nrecently discovered U source and its relation to the alpha Cen system. Proper\nmotion data of the U source should establish its relation to the alpha Cen\nsystem, and the submm SED of U should provide information about its physical\nnature. For the U source, the upper limits on its proper motion are much\nsmaller than the pm of alpha Cen, which essentially excludes any physical\nrelationship with the binary. For the the ALMA-SED of U applies a=2.55+/-0.14.\nIf this emission from U is due to dust, its opacity exponent b=a-2 would be\nabout 0.5, indicative of particle sizes that are larger than those of the\ninterstellar medium, where b(ISM)~2), but comparable to those found in\ncircumstellar discs.\n