N VEL (N Velorum). Bayer could not see most of the stars of Argo. The Greek letters were assigned in the
1700s by that intrepid explorer of the southern skies, Nicolas de
Lacaille. Breaking giant Argo into three parts, he distributed Greek letters among them, but then assigned
Roman letters, first lower case and then upper case, within each of
them. It's a testimony to the plethora of bright stars in Vela (the Sails: the other parts Carina, the Keel, and Puppis, the Stern) that third magnitude
(3.13) N Velorum was placed so far down on the list. Anywhere else
it would probably be a notable part of the constellation outline. Of course it could
always be added in as the outlines are hardly official. Just past
the eastern edge of the "False Cross" (made of Delta and Kappa
Vel and Iota and Epsilon Carinae), which might fool the unwary
into thinking it is the Southern Cross,
N Vel is just barely north of the border with Carina. It is thus
the southernmost lettered star in Vela. (There are no Flamsteed numbers in the deep
southern hemisphere, and of such numbers assigned by others only 30
Doradus, a massive diffuse nebula in the Large Magellanic Cloud,
and the globular cluster 47 Tucanae survive.) Aside from standing out as a
rather bright star, N Vel is a more or less ordinary orange class
K giant 239 light years away
(give or take 2), albeit at subclass K5 a bit cooler (4045 Kelvin)
than most of them. Commonality, however, hardly takes away from
significance. That there appear to be so many class K giants is an
example of observational selection.
Compared to the general stellar population there are not that many,
but they stand out because of their brightness. None of the most
common kind of stars, the red class M dwarfs (like Proxima Centauri), is bright enough to
be seen with the naked eye. But back to our orange giant. After
correction for a fair bit of infrared radiation, we see that
N Vel shines brightly, with the luminosity of 642 Suns, not bad for any star, which leads to a
radius of 52 times that of the Sun, nearly a quarter of an Astronomical
Unit, 62 percent the size of Mercury's orbit. Theory then spots the
mass at around 3.5 times solar and the age at maybe 200-plus million
years. Correction for an uncertain amount of dimming by interstellar dust increases the
luminosity by 16 percent and the radius by 8 percent, but makes little
difference in the mass. Possibly an irregular variable (magnitudes
3.10 to 3.16), N Vel is most likely brightening and preparing to fire
its helium core or brightening for the second time with a dead carbon
core. Only time will tell. However, nobody nearby will witness it,
as the star seems decidedly single. N Vel will eventually slough off
its outer layers and turn into a white dwarf with a mass of
about 55 percent that of the Sun.
Written byJim Kaler 5/09/14. Return to STARS.