Espectroscopia das estrelas jovens HD 141569, HD 144432, HD 163296 e o aglomerado aberto NGC 1981

Abstract

Stars are born within molecular clouds which, from their fragmentation and gravitational collapse, can form isolated stars, associations or stellar clusters. To understand in detail the star formation a study of the mechanisms of accretion and mass ejection is necessary. Like as the characterization of a sample of young open cluster provides information about the stellar evolution and formation. In this work the Herbig Ae/Be stars HD 141569, HD 144432 and HD 163296 and the open cluster NGC1981 were investigated. With high resolution spectroscopic data collected at ESO, synthetic photospheric spectra were constructed to determine the parameters of Herbig stars and subtract from the observed ones to get the circumstellar spectrum. Data from DR2 and EDR3 of the GAIA mission and medium resolution spectra obtained from CASLEO and OPD were used to characterize NGC 1981 with the astrometric decontamination method and analyse the radial velocity of member stars. With the circumstellar spectra and the correlation matrix technique, the spectroscopic variability of Herbig Ae/Be stars was studied. Were determined Teff, [Fe/H], vsini, logg and Vrad for HD 141569(10000 ± 200 K, −0.5 ± 0.1 dex, 231 ± 15 km/s, 4.3 ± 0.2 dex, −13 ± 2 km/s) that shows no spectroscopic variability, while HD 144432 (7250 ± 150 K, 0.3 ± 0.1 dex, 73 ± 6 km/s, 3.8 ± 0.2 dex, −5.8 ± 2 km/s) and HD 163296 (9250 ± 200 K, 0.2 ± 0.1 dex, 123 ± 9 km/s, 4.0 ± 0.2 dex, −4.5 ± 2 km/s) show indicators of magnetospheric accretion and presence of a wind zone with spacial inhomogeneities, besides correlation between these mechanisms in different regions in the stars. Through the astrometric decontamination method were characterize NGC 1981 and neighbor cluster that was contaminating the region, NGC1977, where were determined, respectively, the central coordinates ((RA,DEC) = 83.83◦, -4.35◦ & 83.85◦, -4.81◦), proper motions ((μα,μδ) = 1.2, 0.6 & 1.4, -0.75 mas/yr), parallax (ϖ = 2.53 & 2.56mas), limit radius (Rlim = 1062 ± 57 ” & 1000 ± 57 ”). With the membership list and an isochrone fitting were determinated the reddening (E(B-V) = 0.05 +0.03 -0.05 & 0.07 +0.03 -0.04), distance modulus ((m - M) = 7.95 +0.25 -0.30 & 8.1 ± 0.3), age (log t = 6.90 ± 0.05 & 6.60 ± 0.10) and metallicity ([M/H] = 0.0152 ± 0.01 & 0.0152 +0.02 -0.01). The average radial velocity calculated for NGC 1981 was 41.6 ± 8.3 km/s. The dispersion in astrometry of member stars suggest that NGC 1981 is undergoing through the infant mortality process.