An article published in “The Astrophysical Journal” reports the results of observations of the star R Leporis conducted using the ALMA radio telescope with its receivers at their highest frequencies and an antenna array configuration spread over an area with a diameter of 16 kilometers. R Leporis, or simply R Lep, is a so-called carbon star, a red giant whose atmosphere is particularly rich in carbon in a phase in which oxygen is normally in greater quantities. Unprecedented observations made it possible to detect details of a natural maser around a star that is reaching the end of its life.
The image (Y. Asaki – ALMA (ESO/NAOJ/NRAO)) shows the star R Leporis as seen by the ALMA radio telescope. Submillimeter-wave emissions from the stellar surface are shown in orange. Hydrogen cyanide maser emissions at 891 GHz are shown in blue.
Just over 1,500 light-years away from Earth, R Leporis is nicknamed the Hind’s Crimson Star after astronomer John Russell Hind, who discovered it and described it as a crimson star in 1845. It’s a variable star that has a pulsation period of 427 days. In its state, it’s ejecting its outer layers with very strong stellar winds.
The ALMA radio telescope is often used to observe protostars and newborn stars with protoplanetary disks but it can also be very useful for studying stars close to their death. R Leporis has been the subject of this type of observation with unprecedented resolution making the most of ALMA’s power. Its array’s 66 antennas can be used in different configurations by moving them to different positions. In this case, they were used at their most extended configuration, with a maximum distance of 16 kilometers. The receivers were used at the highest frequencies possible for ALMA, up to 950 GHz.
Essentially, the ALMA radio telescope was pushed to its limits to capture unprecedented details of the star R Leporis, particularly the natural maser around it. These are the most detailed detections of a maser around an evolved star in the Milky Way. Such a phenomenon occurs around dying stars when certain conditions lead molecules such as hydrogen cyanide to release energy in a coordinated way, creating a powerful microwave signal.
The resolution of these observations by R Leporis is such that it was compared to the possibility of observing a 10-meter-long bus on the Moon. This also allowed to observe a ring of materials being emitted from the star into interstellar space. This is a step forward for radio astronomy that improves the study of cosmic objects and phenomena. The next-generation SKA radio telescope is under construction but ALMA continues more than ever to be a point of reference for many astronomy and astrophysics studies.
