APOD: Announcing Nova Carinae 2018 (2018 Mar 25)

[APOD Robot]

Announcing Nova Carinae 2018

Explanation: How bright will Nova Carinae 2018 become? The new nova was discovered only last week. Although novas occur frequently throughout the universe, this nova, cataloged as ASASSN-18fv, is so unusually bright in the skies of Earth that it is now easily visible through binoculars in the southern hemisphere. Identified by the arrow, the nova occurs near the direction of the picturesque Carina Nebula. A nova is typically caused by a thermonuclear explosion on the surface of a white dwarf star that is accreting matter from a binary companion, although details of this outburst are currently unknown. Both professional and amateur astronomers will be monitoring this unusual stellar outburst in the coming weeks, looking to see how Nova Carinae 2018 evolves, including whether it becomes bright enough to be visible to the unaided eye.

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[Ann]

Very, very interesting!

The nova is seemingly located right "below" a yellowish star. That star is HD 92063, a modest, boring star of spectral class K1III, some 260 light-years away from the solar system and about 50 times brighter than the Sun.

But right at the upper border of the picture, actually "cut in half" by the border, is another, more obviously yellow star. That is HD 92397, of spectral class K4/K5III. It is probably 2,000-2,500 light-years away and probably 5,000 times brighter than the Sun in visible light. That star is a whopper!

Below HD 92397 are two slightly bluish stars, HD 92399 and HD 92421. The latter has not been well measured, but HD 92399 has a larger (but very uncertain) parallax than HD 92397, but its proper motion is extremely similar to that of the bright orange star. Also, there are two small bluish stars at upper right, and at least one of them has the same proper motion as HD 92399 and HD 92397. And off the frame at upper right are two other blue B-type stars, whose parallaxes and proper motions are extremely similar to HD 92399 and HD 92397. In other words: There is an association of stars here, some 2,000-2,500 light-years away, with identical proper motions. HD 92399 is the most massive of these stars and the first to have evolved into a bright red giant.

What I'm wondering is if the star that went nova also belongs to this association of stars some 2,500 light-years away. But if it is, this star would have have been much fainter than very many of the other stars of this association. It may have been a faint white dwarf orbited by a small, faint and probably shrunken evolved star, similar to the yellow component of Algol. Or else, the star that went nova may have been a lot farther away than the association at some 2,500 light-years.

For now, I guess we have no information on the star that went nova. It is interesting to speculate, however!

Ann

[neufer]

The nova is seemingly located right "below" a yellowish star. That star is HD 92063, a modest, boring star of spectral class K1III,

Don't mind Ann, HD 92063.

I don't think you are boring or yellow.

[heehaw]

A star is born!

[neufer]

A star is born!

• One is temporarily reborn as another dies.

---

<<A Star Is Born is a 1937 romantic drama film starring Janet Gaynor (in her one and only Technicolor film) as aspiring Hollywood actress "Vicki Lester", and Fredric March (in his Technicolor debut) as a fading movie star Norman Maine who helps launch her career. [At the end] Vicki decides to give up her career in order to devote herself to Norman's rehabilitation. After Norman overhears her discussing her plan with Oliver Niles (Adolphe Menjou), he drowns himself in the Pacific Ocean.>>

<<Classical nova eruptions are when the orbital period falls in the range of several days to one day and the white dwarf is close enough to its companion star to start drawing accreted matter onto the surface of the white dwarf, which creates a dense but shallow atmosphere. This atmosphere is mostly hydrogen and is thermally heated by the hot white dwarf, which eventually reaches a critical temperature causing rapid runaway ignition by fusion. From the dramatic and sudden energies created, the now hydrogen-burnt atmosphere is then dramatically expelled into interstellar space, and its brightened envelope is seen as the visible light created from the nova event.>>

[MarkBour]

...
What I'm wondering is if the star that went nova also belongs to this association of stars some 2,500 light-years away. But if it is, this star would have have been much fainter than very many of the other stars of this association. It may have been a faint white dwarf orbited by a small, faint and probably shrunken evolved star, similar to the yellow component of Algol. Or else, the star that went nova may have been a lot farther away than the association at some 2,500 light-years.

For now, I guess we have no information on the star that went nova. It is interesting to speculate, however!

Ann

Thanks for the info, Ann. I love speculating too (it's probably a vice in my case).

When you refer to a stellar association, are you talking about a group of stars that were formed more or less together (e.g. from a common molecular cloud)? Do you imply anything about their age (e.g. they were born at about the same time)?

[orin stepanek]

When I first saw today's Announcement; I thought old Eta might have finally blown her self up! Imagine the disappointment!

[BillT]

When I first saw today's Announcement; I thought old Eta might have finally blown her self up! Imagine the disappointment!

I guess not as much disappointment as when a certain Professor recently announced the discovery of a > 1st magnitude transient in Sagittarius which turned out to be Mars

[Ann]

...
What I'm wondering is if the star that went nova also belongs to this association of stars some 2,500 light-years away. But if it is, this star would have have been much fainter than very many of the other stars of this association. It may have been a faint white dwarf orbited by a small, faint and probably shrunken evolved star, similar to the yellow component of Algol. Or else, the star that went nova may have been a lot farther away than the association at some 2,500 light-years.

For now, I guess we have no information on the star that went nova. It is interesting to speculate, however!

Ann

Thanks for the info, Ann. I love speculating too (it's probably a vice in my case).

When you refer to a stellar association, are you talking about a group of stars that were formed more or less together (e.g. from a common molecular cloud)? Do you imply anything about their age (e.g. they were born at about the same time)?

Click to view full size image

Scorpius and the Sco-Cen association.
Source: http://www.abc.net.au/science/starhunt/ ... /scorpius/

Well, I call them an association, because they are too far away from one another to be called a cluster.

Look at the picture at left of Scorpius and the Sco-Cen association. Most of the bright stars of Scorpius, particularly in the upper part of Scorpius, are of a similar age and were born at more or less the same time, but they are too far away from one another to be called a cluster.

The Sco-Cen association continues "to the lower right" of Scorpius in the picture at left.

I was thinking that the stars near Nova Carina might also belong to an association, and if so, they may be, perhaps, 10-15 million years old. But I'm only guessing.

Were they born from "one and the same" molecular cloud? Well, that depends on how big that cloud was. The stars of the Sco-Cen association were probably not all born from the same molecular cloud, but maybe from big "neighboring" clouds?

Ann

[MarkBour]

I was thinking that the stars near Nova Carina might also belong to an association, and if so, they may be, perhaps, 10-15 million years old. But I'm only guessing.

Ann

Ah. And a white dwarf could very well be about the same age as some red giants.

Is this also true of blue giants? I actually thought that blue giants were massive, short-lived stars. But looking a bit further in an article, it seems they can also be a late phase of evolved main-sequence stars, so maybe they can be both a short-lived phase, and yet also actually born a long time ago (?)

[Ann]

I was thinking that the stars near Nova Carina might also belong to an association, and if so, they may be, perhaps, 10-15 million years old. But I'm only guessing.

Ann

Ah. And a white dwarf could very well be about the same age as some red giants.

Is this also true of blue giants? I actually thought that blue giants were massive, short-lived stars. But looking a bit further in an article, it seems they can also be a late phase of evolved main-sequence stars, so maybe they can be both a short-lived phase, and yet also actually born a long time ago (?)

Click to view full size image

Metal-poor globular cluster M55 color-magnitude diagram.
Note the blue horizontal branch stars.
B.J. Mochejska, J. Kaluzny (CAMK), 1m Swope Telescope

Usually, blue giants are young, some 10 million years old or so. But there is a special case of age-old blue giants, the blue horizontal branch stars. These blue giants are not particularly massive, and they may, in fact, be less massive than the Sun. They are typically some 12 billion years old, and they are extremely metal-poor. If they were not extremely metal-poor, they would not evolve into blue giants.

Click to view full size image

Not so metal-poor globular cluster 47 Tuc color-magnitude diagram.
Note the very short and non-blue horizontal branch.
Source: http://spiff.rit.edu/classes/phys301/le ... _size.html

Click to view full size image

Color-magnittude diagram of a metal-poor globular cluster.
Note the arrows indicating the stellar evolution:
First the (moderately massive) stars turn into red giants,
then into blue horizontal branch stars.

As you can see from the diagrams, metal-poor globular cluster contain blue giant stars belonging to the blue horizontal branch. The blue horizontal stars first evolved off the main sequence and turned into red giants, and thereafter they turned on their helium fusion in their cores and turned into blue giants. The blue giants are very much smaller than the red giants, and they are fainter than the red giants, too. But they are considerably brighter than the Sun. How much brighter? I don't know... 30-40 times brighter, perhaps?

Less metal-poor globular clusters, like 47 Tuc (also known as NGC 104), contain few or no blue horizontal branch stars. These globular do contain a horizontal branch, but the stars on the horizontal branch in these globulars are not blue, but just a bit less red than the red giants. Let's call them yellow.

Ann