Proplyds and proplyd-like objects

In a previous post I did mention proplyds we found in the Milky Way Project. Here I want to tell the story about the discovery of proplyds and proplyd-like objects in the MWP phase 3, called phoenix.

Everything began with the Subject 2871496 and the discussion I started:

b6db20eb-0221-4bda-83e0-60600aa60deb

@Melina_t: I don’t know what these two tadpole-like green-yellow objects are. Does anyone know more about this or has seen similar objects?

@jules: There’s a similar green one here. Not quite yellowballs and not quite pillars. Are these interesting by any chance @povich?

@povich: Neat! Thanks for pointing these out!

As we often find in astronomy, the universe doesn’t like to be sorted into our tidy classification boxes. I agree that these are something in between #yellowball and #pillar— I’d wager they are massive analogs to the famous Orion proplyds. I personally would lean toward a #pillar classification for these, but let’s just call them #tadpoles for now! The upper #tadpole contains one tiny star, just emerging from its dust cocoon, while lower one doesn’t reveal any stars, but probably contains at least one. Unlike #yellowballs (but like #pillars) these “proplyds” are being irradiated like crazy from the outside by hot, massive stars to the left, out of the frame of this image. If they formed in isolation, they would likely be yellowballs that would turn into bubbles, but the external irradiation is blowing away the dust too quickly for this to happen, so they’ll probably never become bubbles.

So I started collecting every “tadpole” over months. After Jules did create “The #Hashtag Glossary” and added the #tadpole hashtag, I could collect a lot more tadpoles (more than 400 subjects).
But if you know how the Milky Way Project works, you realize that every tadpole appears in multiple subjects. How can you find proplyds and proplyd-like objects in this large set of data?

First I have to know how proplyds and proplyd-like objects look like. I had to define the colors and shape of these objects. I did first look for proplyd-like objects in Cygnus X data. I did pick out the sources with Wright et al. 2012:

As you can see they are yellow-green, dense and have a smooth texture. As I looked at other objects like pillars or EGGs, those other objects were less dense, had less smooth texture and were sometimes yellow-red.

I did need some time to realize that the first “tadpoles” were actually proplyd-like objects! I even said they are green-yellow months ago. I was really happy!

Now I had to look into the environment of those objects. It was important to find more objects, the resposible cluster or star association, etc. etc.
I was surprised as I found 10 candidates, nine of them pointing into the direction of the Cluster Havlen&Moffat No.1. Because we know only a handful of those objects (near Cygnus OB2 and NGC3603), this was a jackpot.

Number 10 was found later in Herschel data. Now I was able to analyse them a bit. At first I found a relationship between size and distance to Cl HM1 in two groups. And the smaller group was located around two smaller clusters. I think this is a sign for the FUV/EUV influence of the smaller clusters and also a sign for the proplyd-nature of proplyd-like object, which was mistrusted in the past.
Later I did discover the strong relationship between a the WR-shell of the Wolf-Rayet star WR87 and the proplyd-like objects. To summarize the finding: The WR-nebula formed many new young stellar objects as it hit the clouds of the molecular cloud RCW122 and RCW122C (cloud-cloud collision). You can also see this in APEX data.


Next I wanted to look for proplyds. This is a lot more difficult than looking for proplyd-like objects. Only if the proplyds have a dusty tail at 24 µm (red in the MWP), then they are easy to locate. It did take a while to find three proplyds, pointing into the direction of one star:

fig-11a

This source star has to be at least a B1-Type star, but SIMBAD does not show anything, not even a star-cluster in this region.


Is this enough? Sure it is enough for a paper, but I want more. The question was: How can I improve the search for proplyds and proplyd-like objects?

The answer lies in basic parameters of the clusters that host proplyds and proplyd-like objects:

I used a catalog of visible clusters from the ESO: Dias et al. 2002-2015. At first I did create two lists: Younger than 6 Million years for proplyd-like objects and younger than 11 Million years for proplyds.
I did try a lot and found something good:

fig-1a

Extinction vs. Diameter was what I was searching for. Now the search did improve from a “all Spitzer search” to a “systematical search”. The filled rectangles are the new findings:

The cluster Collinder 69 had a dusty-tail proplyd close to Lambda Orionis in WISE data:

fig-2

The cluster NGC 3324 had a small proplyd pointing into the direction of CD-57 3378 in Hubble data:

fig-4

But this was topped with the discovery of a 70,000 AU large proplyd-like object pointing into the direction of O-Type stars in the Omega Nebula!
It is clearly visible in an ESO press release image, taken with the WFI of the MPG/ESO 2.2-metre telescope. Multiple features are visible: Two ~10,000 AU large disks with NIR-sources (UKIRT). One of the disk is edge-on and has two massive jets, the other is face-on. I found unexpected outflows that can also be found in one other proplyd-like object near Cl HM1. These outflows, called “fins”, are connected to missing areas in the proplyd-like objects.

fig-3a

Now we can say that proplyd-like objects are indeed the result of photoevaporation of massive (protoplanetary-)disks.

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