Star of the Month
V Hydrae
Position: 10 hrs 51.6 min -21 deg 15 min.
Due south at 22:15 (BST) on 15 April 2020
V Hydrae with an 11th magnitude star underneath it
Image: Simbad (http://simbad.u-strasbg.fr/simbad/)
V Hydrae is a carbon star like R Leporis (Star of the Month for January 2020) and like R Leporis it is a red giant near the end of its life. It is phenomenally red; with a B-V value of 5.4 it is one of the reddest stars in the sky. However it has its own particular claim to fame: every 8.5 years it fires off great balls of fire (apologies to Jerry Lee Lewis). Thanks to the Hubble telescope, we now have an explanation for this strange behaviour. It has a small unseen companion which every 8.5 years enters the bloated atmosphere of V Hydrae and gathers material from it. Instead of becoming a nova or supernova, it spits out balls of superhot plasma into space. In due course, and perhaps before very long (in astronomical terms), this companion will help to transform V Hydrae into a spectacular planetary nebula. In the meantime, we observe V Hydrae in all its redness and imagine the balls of fire hurling away from it. As it is only magnitude 7, you are probably best advised to use go-to, but it lies under the middle of the base of the cup shape formed by neighbouring constellation Crater and beneath the relatively bright third magnitude star Nu Hydrae. With a declination of -21 it hugs the horizon even in April, but it has a decent height of 17 degrees when due south.
This four-panel graphic illustrates how the binary-star system V Hydrae is launching balls of plasma into space. Credit: NASA, ESA, and A. Feild (STScI)