June 2, 2020

Astro-Event of the Week-Redder than Red: V Hydrae.

This week, we here at Astroguyz are going to introduce you to a star that isn’t on the top 10 star party faves, but perhaps should be; V Hydrae. A carbon star, V Hya also makes our list of the 10 reddest stars in the sky. In fact, I would say that only Hind’s Crimson Star may be the only carbon star that beats this one out in the redness category. Many people are surprised by the sight of this cherry red ember in the eyepiece, including some seasoned amateurs. Lying on the Hydra/Crater border, this star rides high in the evenings for northern hemisphere viewers in late spring and early summer evenings. To find it, draw a line about five degrees south of Nu Hydrae and about 1 degree to the east. V Hya is also known as HIP53085 in the Hipparcos catalog, or Burnham 1428, and for those with setting circles, the 2000 coordinates are:

R.A. 10h 51m 37s

Dec: -21° 14.9’

V Hya is also a variable star, oscillating between magnitudes 7.2 and 9.5 over a period of about 530 days. This cycle is also superimposed over a longer period of about 18 years that can plunge the star to magnitude +12. Currently, V Hya is toward the low end of the brightness scale, so this one would be worth monitoring over the next year as it begins to brighten again. V Hya is estimated to be about 1300 light years distant. A companion star +11.5 magnitude lies about 47” distant.  It’s also interesting to note how the color and intensity change as the brightness varies on this long period variable. At a B-V value of +5.5, V Hya is one of the most colorful stars out there. Let us know what you see; we’ll be checking in on this interesting star as it reaches maximum brightness next summer!

This week’s astro-term of the week is: Helium Flash. No, this isn’t a classic DC superhero… stars such as our Sun undergo an expansion into a red giant stage towards the end of their life. Once a majority of their hydrogen fuel is exhausted, they begin fusing heavier helium into carbon in what is known as the triple-alpha process. This causes a violet expansion and cooling, and occurs over a relatively short period of a life of a star, only several 100 million years. Stars of an order of more than 2.25 solar masses begin helium fusion much earlier, and do not experience a core helium flash. White dwarfs accreting material also undergo a similar event but of the shell helium flash variety, where fusion re-ignites briefly against the pressure of built up material versus electron degeneracy. It should be noted that the core flash itself is not observable, as it happens deep within the star. Stars such as V Hydrae have a dense carbon atmosphere, and it is through this “soot” that we see light filtered through.  As it nears the end of its life, V Hya also gives astrophysicists the rare opportunity to study the final stages of a star’s life as it produces a large jet outflow and enters it planetary nebula phase. And its sobering to think that this entire process contributes to the seeding of carbon in the cosmos, carbon that makes trees, cheeseburgers, and even sentient blogging life forms possible!


  1. [...] are some of our “surprise faves” to show off to folks when it comes to variable stars. Objects like V Hydrae and R Leporis, otherwise known as Hind’s Crimson Star exhibit a cherry red hue as they fatten up on [...]

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