Draco II. Dwarf galaxy or star cluster?

[symmetal]

I haven't found any images of Draco II and just two published papers.

2016  Is Draco II one of the faintest dwarf galaxies?

2018  Pristine dwarf galaxy survey...of the very metal-poor Draco II satellite

Draco II is likely among the faintest, most compact, and closest satellite dwarf galaxies. Visually it certainly doesn't stand out, and its individual stars are indistinguishable from the Milky Way stars in the foreground.

The first paper lists 9 observed stars while the second paper lists 14 stars as belonging to Draco II in the appendix at the end. I made a custom catalogue to load into PI's annotation script, but there's a discrepancy as two of the observed stars don't seem to be in the 14 star list so I have 16 stars plotted with the 9 observed stars given the numbers assigned. The latter list includes numerous Milky Way stars as well as the 14 Draco II members so maybe two of the first list have been demoted to Milky Way stars.

The table columns g0 and i0 have values one of which could be apparent magnitudes.

The image is comprised of 3 hours of 2 min subs using a RASA 11 and ASI2600MC. Stacked in APP and processed in PI and PS, and no star removal processing was performed. I've included a crop of Draco II at the end.

Area containing Draco II.  But... I can't see it😟

 Here it is... 😁 Note all the stars seem to have the same colour.

Crop

I wonder if the authors of the reports would be interested in the image? Or perhaps send it in to the most underwhelming picture competition. 😊

Alan

 

[symmetal]

The first paper stated that the Sloan Digital Sky Survey (SDSS), Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1), and the Dark Energy Survey (DES) allowed for the discovery of faint Milky Way satellites. I thought I'd see what was available to download from these surveys and got these:

It was just outside the SDSS coverage area so no data.

Dark Energy Survey

The bright stars easily line up with those seen in the marked area in my image. 🙂

Alan

[wimvb]

Great!

It's nice to see a fellow astrophotographer also go for the fainter than faint. It seems you've accepted the challenge. 😄

The first reference that I've found on your target is from 2015

https://iopscience.iop.org/article/10.1088/0004-637X/813/1/44

This is truly an intriguing deep sky object, and at first I thought that 3 hours of imaging time wouldn't be nearly enough. But you are using a photon hoover (aka RASA).

Well done.

[wimvb]

On 10/06/2023 at 03:25, symmetal said:

I wonder if the authors of the reports would be interested in the image? Or perhaps send it in to the most underwhelming picture competition. 😊

 

In all fairness, I'm not so sure that the authors of those papers can get more information out of your data than what they already have collected. As you haven't used photometric filters, it will be difficult to extract data for a calibrated colour magnitude diagram from your masters.

What you could do, is try to extract a C-M diagram from your image with a wider field than what was included in the 2018 article you refered to in your original post. That would be a challenge, and you'd learn a lot about what professional astronomers do.

I found this book a great help (the one or so time I've tried it on my own data, and never on such faint signal)

https://link.springer.com/book/10.1007/978-3-319-23377-2

Chapter 10 is about creating C-M diagrams

[symmetal]

Thanks @wimvb for your comments and for the link to the earlier article. I could try adding more data and see if it shows signs of an overdensity which appears to be the first indication for study. Compared to the other dwarfs studied I wonder what first drew them to Draco II as it doesn't indicate an overdensity. It's very similar to Ursa Major I in that respect.

The stars plotted are in the magnitude 18 to 21 range with star 25 (just visible on the image) being given mag 21.58

I forgot to say that Draco II distance is given as 70,124 light years, so it's just outside the Milky Way. I assume distances given are corrected as being from the Milky Way centre rather than from the observer.

I just thought the authors might like an picture for their wall really, rather than for further study, but the book you linked to looks interesting. 🙂

Alan

[wimvb]

37 minutes ago, symmetal said:

Compared to the other dwarfs studied I wonder what first drew them to Draco II as it doesn't indicate an overdensity. It's very similar to Ursa Major I in that respect.

I think that sky survey data is systematically scanned for "abnormal" stars. First by citizen scientists, and students, but now also by AI. Any interesting areas are then studied further and findings published. Before deep sky surveys were common, such investigations were impossible, because no one knew where to start looking. It's not just finding the needle in the hay stack, but rather finding the wooden splinter in the hay stack.

42 minutes ago, symmetal said:

just thought the authors might like an picture for their wall

You can always contact one of them. The first author of scientific publications is usually the young one on the team, who has to gain academic recognition. Most likely this author has earned his degree by now, and may have moved on, either as a post doc or as a senior researcher/assistant professor. One of the last names on the author list, and recurring on many publications in the field, is usually the established professor who supervises the team of researchers.

52 minutes ago, symmetal said:

the book you linked to looks interesting

Two pieces of software are used in the book, both freeware

APT - aperture photometry tool

TOPCAT - data management and diagramming software