APOD: NGC 2403 in Camelopardalis (2011 Jul 23)

[APOD Robot]

NGC 2403 in Camelopardalis

Explanation: Magnificent island universe NGC 2403 stands within the boundaries of the long-necked constellation Camelopardalis. Some 10 million light-years distant and about 50,000 light-years across, the spiral galaxy also seems to have more than its fair share of giant star forming HII regions, marked by the telltale reddish glow of atomic hydrogen gas. In fact, NGC 2403 closely resembles another galaxy with an abundance of star forming regions that lies within our own local galaxy group, M33 the Triangulum Galaxy. Of course, supernova explosions follow close on the heels of the formation of massive, short-lived stars and in 2004 one of the brightest supernovae discovered in recent times was found in NGC 2403. Easy to confuse with a foreground star in our own Milky Way Galaxy, the powerful supernova is seen here as the spiky, bright "star" at the left edge of the field. This stunning cosmic portrait is a composite of space and ground-based image data from the Hubble Legacy Archive and the 8.2 meter Subaru Telescope at the summit of Mauna Kea, Hawaii.

<< Previous APOD

Discuss Any APOD

Next APOD >>

[/b]

[neufer]

<<Allan Sandage detected Cepheid variables in NGC 2403 using the Hale telescope, making it the first galaxy beyond our local group to have Cepheids found in it. He derived a distance of a mere 8 kly. Today, it is thought to be a thousand times further away at about 8 Mly (3.6 Mpc).>>

[orin stepanek]

I must say when I first looked at today's APOD; I didn't recognise the picture as a galaxy until I saw the smaller view. The super nova at the left wasn't hard to find.

Click to view full size image

[ExplorerAtHeart]

Imagine all the planets in there.

[Ann]

This RGBHa image of a richly starforming galaxy represents the best image quality that modern astronomy can produce. The Hubble Space Telescope and the landbased 8.2 meter Subaru Telescope combined to gather the data for the image, and the masterful Robert Gendler processed the data. The fact that the image also shows a supernova in the galaxy in question is a fantastic added bonus.

Ann

[dlw]

This is one of the most interesting galaxies I've seen a picture of. There are so many interesting objects in it. I would think a further exploration/explanation of these objects would be quite instructive.

Besides lots of super nova remnant nebulae, here is a greenish nebula(?) near the upper right corner.

There are several nebulae with distinct, as opposed to fuzzy, boundaries. What does that imply?

There is an interesting bright blueish nebula on the lower right. I assume the stars are in the foreground. Is there anything unusual about that nebula?

Is there more that can be said about the bright super nova on the left ?

Near the upper left is an interesting "ring" with an object in the precise center; another remnant?

There is also a curious nebula in the upper left corner with a greenish center.

All in all a fascinating image.

[Ann]

dlw wrote:

Besides lots of super nova remnant nebulae, here is a greenish nebula(?) near the upper right corner.

Color is always a tricky business in pictures like this. A greenish nebula could be green because of OIII emission, which is caused by very hot stars. Carefully calibrated RGB images of the Orion Nebula will actually show the inner part of it to be yellowish or yellow-green. The yellow color is caused by a combination of blue-green OIII emission and red Ha emisson.

However, an interesting possibility is that the green color may actually be a signature of red giant stars. In a carefully calibrated RGB image, red giant stars should look yellow-orange. Since I couldn't see any obviously yellow-orange stars in NGC 2403, but I could see several yellow-green ones, I have to wonder if these greenish stars might possibly be red giants or supergiants. (interestingly, the yellow-green objects seem to be found only on the right side of the picture, which strengthens the probability that this is some kind of photographic effect.)

There are several nebulae with distinct, as opposed to fuzzy, boundaries. What does that imply?

Actually, the entire picture consists of parts that are sharp and extremely well-resolved and parts that are much fuzzier. The sharp parts were taken by the Hubble Telescope. The fuzzy parts were imaged by the Subaru Telescope only. The color data is probably mostly from the Subaru Telescope, although this is not absolutely certain.

There is an interesting bright blueish nebula on the lower right. I assume the stars are in the foreground. Is there anything unusual about that nebula?

The blue color suggests a star cluster or an association with a high density of A- and B-type stars, but a lack of O-type stars. Alternatively, there may simply be a lack of gas in here, so that the O-type stars have nothing to ionize. My guess, however, is that we are seeing a large rich association of mostly A- and B-type stars. You may compare this region with NGC 206 in the Andromeda Nebula, which contains many A-and B-type stars but little gas:

Click to view full size image

NGC 206 in the Andromeda Galaxy. Photo: Carsten A. Arnholm.

Also look at this image of the Eta Carina region on the right and the rich star cluster NGC 3532 on the left:

Click to view full size image

NGC 3532 consists mostly of A-type stars. The cluster has no gas and is therefore not linked to any nebulosity. Photo: Bill Christie.

Is there more that can be said about the bright super nova on the left ?

There is some more information about the supernova (SN 2004dj) here: http://www.supernovae.net/sn2004/sn2004dj.html

A few things are immediately obvious. The supernova is not exceedingly bright. The galaxy, NGC 2403, is about half as bright as the Milky Way, and the supernova is nowhere near as bright as the galaxy.

The supernova is apparently of Type IIP. "Type II" generally means that there is hydrogen in the spectrum of the supernova, and it also usually means that this is an explosion of a massive star undergoing core collapse because it has built up a dead iron core. The "P" probably means that the supernova is somewhat peculiar. (EDIT: I take back the "peculiar" bit. See neufer's post.)

Near the upper left is an interesting "ring" with an object in the precise center; another remnant?

I'm not quite sure which object you mean. In any case, we seem to have "moved out of Hubble territory" and "into Subaru only territory", so the resolution isn't great, making it harder to judge what we are seeing. Personally, I think that the pink semicircle with a small isolated object inside it looks like a likely supernova remnant. The pink "halo object" which appears to be filled with something grayish looks mostly strange to me, and I can't guess what it is. Possibly a photographic artifact.

There is also a curious nebula in the upper left corner with a greenish center.

Okay, that appears to be what I called a pink halo object with a grayish interior. I think it looks strange, and I would guess that it might be a photographic artifact.

Ann

[neufer]

This is one of the most interesting galaxies I've seen a picture of. There are so many interesting objects in it.
I would think a further exploration/explanation of these objects would be quite instructive.

Let's send a manned mission there!

Besides lots of super nova remnant nebulae,
here is a greenish nebula(?) near the upper right corner.

. .

There are several nebulae with distinct, as opposed to fuzzy, boundaries. What does that imply?

Alien mathematicians are trying to catch a lion

How to catch a lion in the Sahara desert: 5) The Kalra method:
Make a list of the lion's whereabouts. Classify them into different fuzzy sets.
The lion will get confused and fall into your trap.

There is an interesting bright blueish nebula on the lower right. I assume the stars are in the foreground. Is there anything unusual about that nebula?

Nah! .

Is there more that can be said about the bright super nova on the left ?

<<SN 2004dj was the brightest supernova since SN 1987A at the time of its discovery.

This Type II-P supernova was discovered by Koichi Itagaki, a Japanese astronomer on July 31, 2004. At the time of its discovery, its apparent brightness was 11.2 visual magnitude; the discovery occurred after the supernova had reached its peak magnitude. The supernova's progenitor is a star in a young, compact star cluster in the galaxy NGC 2403, in Camelopardalis. The cluster had been cataloged as the 96th object in a list of luminous stars and clusters by Allan Sandage in 1984; the progenitor is therefore commonly referred to as Sandage 96. This cluster is easily visible in a Kitt Peak National Observatory image and appears starlike.

When the spectrum of a Type II supernovae is examined, it normally displays Balmer absorption lines—the characteristic frequencies where hydrogen atoms absorbs energy. The presence of these lines are used to distinguish this category of supernova from a Type Ia supernova.

This graph of the luminosity as a function of time shows
the characteristic shapes of the light curves for
a Type II-L and II-P supernova.

When the luminosity of a Type II supernova is plotted over a period of time, it shows a characteristic rise to a peak brightness followed by a decline. These light curves have an average decay rate of 0.008 magnitudes per day; much lower than the decay rate for Type Ia supernovae. Type II are sub-divided into two classes, depending on the shape of the light curve. The light curve for a Type II-L supernova shows a steady (linear) decline following the peak brightness. By contrast, the light curve of a Type II-P supernova has a distinctive flat stretch (called a plateau) during the decline; representing a period where the luminosity decays at a slower rate. The net luminosity decay rate is lower, at 0.0075 magnitudes per day for Type II-P, compared to 0.012 magnitudes per day for Type II-L.

The difference in the shape of the light curves is believed to be caused, in the case of Type II-L supernovae, by the expulsion of most of the hydrogen envelope of the progenitor star. The plateau phase in Type II-P supernovae is due to a change in the opacity of the exterior layer. The shock wave ionizes the hydrogen in the outer envelope—stripping the electron from the hydrogen atom—resulting in a significant increase in the opacity. This prevents photons from the inner parts of the explosion from escaping. Once the hydrogen cools sufficiently to recombine, the outer layer becomes transparent.>>

[dlw]

Very interestng! Thanks to both of you for elaborating so well on this image.

FWIW, here are the 2 objects tht caught my attention in the upper left corner.upper left corner. The semi-circle might be the outer shell of an old supernova that has been disrupted by particle streams. It is interesting that it is brightest at opposite sides (upper right & lower left).

Thanks again for satisfying my curiosity.

[Case]

This stunning cosmic portrait is a composite of space and ground-based image data from the Hubble Legacy Archive and the 8.2 meter Subaru Telescope at the summit of Mauna Kea, Hawaii.

Status of the Subaru Telescope
An incident occurred at the Subaru Telescope during the early morning of Saturday, July 2nd, toward the end of the nighttime observations. Coolant leaked from the top of the telescope. The coolant’s mixture of water and ethylene glycol reached the Subaru Prime Focus Camera (Suprime-Cam), the primary mirror, and the Faint Object Camera and Spectrometer (FOCAS, a Cassegrain instrument), but it was contained within the building which houses the telescope. Nighttime observations and daytime summit tour programs are suspended until further notice.
Crews at the Subaru Telescope continue to perform inspections and restoration work.

[dp]

Just below the nova is an inverted 'V' string of stars. All over this galaxy can be seen similar strings of 'pearls' like this. In fact such strings show up in very many of the APOD images. Is there something about the formation of stars that causes such strings or is it a trick of the mind and chance colocation of stars that forms these patterns?

[Star*Hopper]

Imagine all the planets in there.

Yeah --- places to go-o-oo, people to se-e-ee.......

[Star*Hopper]

Just below the nova is an inverted 'V' string of stars. All over this galaxy can be seen similar strings of 'pearls' like this. In fact such strings show up in very many of the APOD images. Is there something about the formation of stars that causes such strings or is it a trick of the mind and chance colocation of stars that forms these patterns?

But of course!
http://www.youtube.com/watch?v=UYxzPdv67yA



\Godroll
\\Neuf made me do it

[Ann]

Just below the nova is an inverted 'V' string of stars. All over this galaxy can be seen similar strings of 'pearls' like this. In fact such strings show up in very many of the APOD images. Is there something about the formation of stars that causes such strings or is it a trick of the mind and chance colocation of stars that forms these patterns?

It is probably a trick of the mind, and it can also be a random effect of seeing stars at slightly different distances from us along the line of sight.

But personally I believe that stars and star clusters can indeed form along "strings" of dust. Stars are born out of thick pockets of dust, but these pockets often line up along elongated dust lanes.

Click to view full size image

The Cocoon Nebula is located at one end of a long "string" of dust. For now there is no sign of star formation anywhere else along this string of dust (as far as I know), but star formation somewhere else along this dust feature might conceivably happen later. (More information about the picture can be found here: http://www.cloudynights.com/ubbthreads/ ... er=2632683)

Here is a link to a somewhat similar starforming region of the sky: http://nightskypictures.com/iris.htm

NGC 7023, the Iris Nebula, is located in a dusty part of the sky. The dust extends more to one side of the Iris Nebula than to the other.

Ann