HD 101584 seen by ALMA. The blue component moves towards the observer and the red component moves away from the observer. The green component has the same speed as the binary system, seen as a green point source in the middle. Credit: ALMA (ESO/NAOJ/NRAO), Olofsson et al. Acknowledgement: Robert Cumming
HD 101584 has been given the variable star designation V885 Centauri. The International Variable Star Index states that the star varies between visual magnitude 6.90 and 7.02, over a period of 87.9 days.[7] However Koen and Eyer detected, in the star's Hipparcos data, an oscillation of the star's brightness with a period of 6.744 days and an amplitude of only 0.02 magnitudes.[8]
Nebula
The Hubble Space Telescope image shows a diffuse circumstellar environment with a circular ring around HD 101584. ALMA mapped the nebula around HD 101584 and was able to map the region close to the central binary. The nebula consists of a central compact source, an equatorial density enhancement (disk), a high-velocity bipolar outflow and an hourglass structure surrounding the outflow. The outflow reaches a maximum velocity of about 150 km/s and is inclined to the line of sight by 10+10 −5°. There is evidence for a second bipolar outflow with a different orientation from the major outflow.[3] The inner disk, heated to 1540 K, currently has been sublimated by the increasing luminosity of the star.[9]
Evolution
The companion of this system was captured a few hundred years ago, for example when the red giant reached its critical size. It spiralled towards the red giant but stopped before it merged with the core of the primary. During this stage the outer layers of the red giant were ejected. During the common envelope phase the red giant phase of the primary was terminated and the core was revealed.[3] Later, the bipolar jets formed and met the ejected material, forming the hourglass-shaped structure.[5] Ejected material shows prominent spectral features of magnesium,[10] while outer ejected structures contain methanol and formaldehyde.[11]
^Olofsson, H.; Black, J. H.; Khouri, T.; Vlemmings, W. H. T.; Humphreys, E. M. L.; Lindqvist, M.; Maercker, M.; Nyman, L.; Ramstedt, S.; Tafoya, D. (2021). "Heavy-element Rydberg transition line emission from the post-giant-evolution star HD 101584". Astronomy and Astrophysics. 651: A35. arXiv:2105.00699. Bibcode:2021A&A...651A..35O. doi:10.1051/0004-6361/202140537. S2CID233481052.
^Kluska, J.; Olofsson, H.; Van Winckel, H.; Khouri, T.; Wittkowski, M.; De Wit, W. J.; Humphreys, E. M. L.; Lindqvist, M.; Maercker, M.; Ramstedt, S.; Tafoya, D.; Vlemmings, W. H. T. (2020), "VLTI/PIONIER reveals the close environment of the evolved system HD 101584", Astronomy & Astrophysics, 642: A152, arXiv:2008.11555, Bibcode:2020A&A...642A.152K, doi:10.1051/0004-6361/202037946, S2CID221319788