APOD: The Dark River to Antares (2015 Feb 22)

[APOD Robot]

The Dark River to Antares

Explanation: Connecting the Pipe Nebula to the colorful region near bright star Antares is a dark cloud dubbed the Dark River, flowing from the picture's left edge. Murky looking, the Dark River's appearance is caused by dust obscuring background starlight, although the dark nebula contains mostly hydrogen and molecular gas. Surrounded by dust, Antares, a red supergiant star, creates an unusual bright yellowish reflection nebula. Above it, bright blue double star Rho Ophiuchi is embedded in one of the more typical bluish reflection nebulae, while red emission nebulae are also scattered around the region. Globular star cluster M4 is just seen above and right of Antares, though it lies far behind the colorful clouds, at a distance of some 7,000 light-years. The Dark River itself is about 500 light years away. The colorful skyscape is a mosaic of telescopic images spanning nearly 10 degrees (20 Full Moons) across the sky in the constellation of the Scorpion (Scorpius).

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[Boomer12k]

Beautiful.... To me it looks like an Iris... Or Foxglove....

:---[===] *

[Ann]

And the small sort of bisected bluish nebula at 2 o'clock, IC 4603, is where a lot of the star forming action of this region is taking place.

Nice image! I'm particularly glad that today's APOD shows us Tau Scorpii, which can be seen at bottom left of center. Tau Scorpii is a relatively impressive blue star surrounded by a large but faint pink emission nebula. It seems fairly obvious that this emission nebula influences the color of parts of the yellow-orange reflection nebula that surrounds Antares.

Ann

[Peter Smith]

I like the near perfect pentagon of bright stars.

[BDanielMayfield]

I like the near perfect pentagon of bright stars.

Yes, that's a very attractive grouping Peter. One of the "bright stars" is actually M4, a globular cluster containing, what, more than a hundred thousand stars or so? I couldn't find an estimate for M4's total population. Does anyone know?

Bruce

[jimbo48]

With close examination of the full size image I see two other globular clusters besides M4. One just to the left of M4 (above and to the right of Antares). The other is near the top of the image directly above M4.
Can anyone else confirm that these are globulars as well?

[Chris Peterson]

With close examination of the full size image I see two other globular clusters besides M4. One just to the left of M4 (above and to the right of Antares). The other is near the top of the image directly above M4.
Can anyone else confirm that these are globulars as well?

The globular at the top is M80. The one next to M4 is NGC 6144.

[dlw]

There's an interesting red straight bar shaped blob above a star above M44 M4 in the image. Might it be an artifact or something seen edge-on?
It's curious that it appears to be long and straight.

What is this red thing?

[geckzilla]

There's an interesting red straight bar shaped blob above a star above M44 in the image. Might it be an artifact or something seen edge-on?
It's curious that it appears to be long and straight.

Looks like a glowing cloud of hydrogen to me. One way to rule out artifacts is to simply look at another image of the same region. If it's present in both, it is more likely to be a real thing. Check out this previous APOD to compare. It's even easier to see in Rogelio's.

[LocalColor]

Beautiful.... To me it looks like an Iris... Or Foxglove....

:---[===] *

A dancing fairy or pixie.

[Ann]

There's an interesting red straight bar shaped blob above a star above M44 in the image. Might it be an artifact or something seen edge-on?
It's curious that it appears to be long and straight.

Red Blob.jpg

M44 is an open cluster in Cancer, so it can't be seen in this picture. But the red "bar" is indeed glowing hydrogen. The star responsible for ionizing it is Sigma Scorpii, a multiple star which according to Jim Kaler consists of no fewer than five components:

Jim Kaler wrote:
The system is dominated by a brilliant double star (seen as one with eye) that is too close to separate in any way other than with the spectrograph. The two hot components, one a class O (O9) hydrogen- fusing dwarf, the other a class B (B2) giant, go around each other in a mere 33 days, and are separated by only about the distance of Venus from the Sun. Still close, but still resolvable (only 0.4 seconds of arc away) lies another, what is probably a mid-class B star two magnitudes fainter, and farther out yet is a telescopic (ninth magnitude) companion of cooler class B (B9 or so).

It is perhaps possible that the interaction between these four star creates a particularly strong flow of ultraviolet photons preferentially in one direction. Another possibility is that there might be more gas and dust in one direction than in the others, and that the gas and dust gets "piled up" there.

This picture shows that the red emission nebula surrounds Sigma Scorpii, but it is particularly strong in one direction.

Ann

[Nitpicker]

The Rho Oph star system looks like three stars in the APOD, but is probably five. The brightest one we can see in the APOD is the "bright blue double star" mentioned in the description, denoted by Rho Oph AB, with A and B separated by only 3.1 arcsec (according to Wikipedia). Does anyone know of an image resolving stars A and B?

[geckzilla]

The Rho Oph star system looks like three stars in the APOD, but is probably five. The brightest one we can see in the APOD is the "bright blue double star" mentioned in the description, denoted by Rho Oph AB, with A and B separated by only 3.1 arcsec (according to Wikipedia). Does anyone know of an image resolving stars A and B?

Someone was doing spectroscopy on this system last September with Hubble. If you ask him nicely maybe he's got a picture. (Just kidding. Don't do it. I think they hate that.)
You'll have to wait until the year is up to see unless someone else finds another capable telescope has looked at it.
http://archive.stsci.edu/proposal_searc ... t&id=13365

[Nitpicker]

The Rho Oph star system looks like three stars in the APOD, but is probably five. The brightest one we can see in the APOD is the "bright blue double star" mentioned in the description, denoted by Rho Oph AB, with A and B separated by only 3.1 arcsec (according to Wikipedia). Does anyone know of an image resolving stars A and B?

Someone was doing spectroscopy on this system last September with Hubble. If you ask him nicely maybe he's got a picture. (Just kidding. Don't do it. I think they hate that.)
You'll have to wait until the year is up to see unless someone else finds another capable telescope has looked at it.
http://archive.stsci.edu/proposal_searc ... t&id=13365

I'm surprised, given Damian Peach managed a clear resolution on a seemingly comparable system, Rho Herculis, with only an 8 inch telescope operating at f/34:

Click to view full size image

http://www.damianpeach.com/images/astro ... o_herc.jpg

[geckzilla]

I don't really know which telescopes are capable. I just looked for it in Hubble's archive since it's so easily searchable. Someone out there probably imaged it.

[Nitpicker]

Someone out there probably imaged it.

Yeah, probably, but Google couldn't find it for me. Maybe the wider area is far too pretty, so only a few narrow images are attempted around the Rho Oph star system.

Does the wider area, with all the colours and different nebulae have a name? I assume the Rho Ophiuchi Cloud Complex is just the blue cloud at the top.

[geckzilla]

Someone out there probably imaged it.

Yeah, probably, but Google couldn't find it for me. Maybe the wider area is far too pretty, so only a few narrow images are attempted around the Rho Oph star system.

Does the wider area, with all the colours and different nebulae have a name? I assume the Rho Ophiuchi Cloud Complex is just the blue cloud at the top.

In my searches for nebula names they usually don't give them to vast complexes like this. Planetaries and SN remnants get a lot of names because they are distinct and associated with a particular point source. If there's no point source clearly associated with some cloud then it's hard to define exactly what you're naming. I've seen plenty of "part of cloud" designations for when astronomers need to reference a particular thing or another in a paper. Herbig-Haro objects also all get cataloged as they are found.

[Ann]

Nitpicker wrote:
Does the wider area, with all the colours and different nebulae have a name? I assume the Rho Ophiuchi Cloud Complex is just the blue cloud at the top.

The blue cloud at the top surrounds the star(s) called Rho Ohpiuchi, so that is definitely the Rho Ophiuchi reflection nebula. But I think that the designation "The Rho Ophiuchi Cloud Complex" is often used to refer to the entire colorful complex of blue, red and yellow nebulosity.

Ann

[Nitpicker]

Nitpicker wrote:
Does the wider area, with all the colours and different nebulae have a name? I assume the Rho Ophiuchi Cloud Complex is just the blue cloud at the top.

The blue cloud at the top surrounds the star(s) called Rho Ohpiuchi, so that is definitely the Rho Ophiuchi reflection nebula. But I think that the designation "The Rho Ophiuchi Cloud Complex" is often used to refer to the entire colorful complex of blue, red and yellow nebulosity.

Ann

Thanks Ann. You could well be right. The whole area is certainly beautiful enough and prominent enough to deserve a name.

[Visual_Astronomer]

Nitpicker wrote:
Does the wider area, with all the colours and different nebulae have a name? I assume the Rho Ophiuchi Cloud Complex is just the blue cloud at the top.

The blue cloud at the top surrounds the star(s) called Rho Ohpiuchi, so that is definitely the Rho Ophiuchi reflection nebula. But I think that the designation "The Rho Ophiuchi Cloud Complex" is often used to refer to the entire colorful complex of blue, red and yellow nebulosity.

Ann

Thanks Ann. You could well be right. The whole area is certainly beautiful enough and prominent enough to deserve a name.

I've tried several times to see this, but have had no success. It is exceedingly faint.
Most of the named features in the sky are so called becuase of their visual appearance, not their photographic image.

[starsurfer]

Nitpicker wrote:
Does the wider area, with all the colours and different nebulae have a name? I assume the Rho Ophiuchi Cloud Complex is just the blue cloud at the top.

The blue cloud at the top surrounds the star(s) called Rho Ohpiuchi, so that is definitely the Rho Ophiuchi reflection nebula. But I think that the designation "The Rho Ophiuchi Cloud Complex" is often used to refer to the entire colorful complex of blue, red and yellow nebulosity.

Ann

The Rho Ophiuchi Nebula refers only to the large blue reflection nebula near the top that also coincidentally has Rho Ophiuchi near its centre. This nebula is also catalogued as IC 4604 and I think it might have been discovered in a photographic plate taken by the astronomer Edward Emerson Barnard.

The smaller blue nebula below it is IC 4603 with the even smaller blue nebula to the north of Antares being catalogued as IC 4605.

The nebula around Antares is known as the Antares Nebula and is also catalogued as IC 4606.

The pink nebula is catalogued as Sh2-9.

Interestingly all bright patches have their own separate designations in the vdB catalogue of reflection nebulae.

The various dark nebulae have their own entries in the Barnard and LDN catalogues but there are too many that I'm not going to bother mentioning them.

[starsurfer]

There's an interesting red straight bar shaped blob above a star above M44 M4 in the image. Might it be an artifact or something seen edge-on?
It's curious that it appears to be long and straight.

Red Blob.jpg

This is the emission nebula Sh2-9, which was catalogued by the astronomer Stewart Sharpless in the 1950's. Interestingly the Sharpless catalogue of HII regions also includes planetary nebulae, supernova remnants, Wolf Rayet nebulae, dust clouds and even some galaxies!

[starsurfer]

Something that makes this area even more colourful and unusual is the presence of a rare yellow reflection nebula. I feel compelled to share a few other yellow reflection nebulae:

IC 2220 by Rob Gendler
vdB135 by Bernhard Hubl
vdB136 by Tom Davis

There are a few other yellow nebulae known but they are generally very small such as the ones associated with V1331 Cygni and V1515 Cygni.

[starsurfer]

Not only is this area so pretty in optical, it also appears beautiful in infrared images! There is actually a lot of star formation taking place in this region that also includes an embedded cluster!