Abell 41, He 2-236, PK 009+10.1

Planetary Nebula

Serpens

RA: 17 29 02.0
DEC: -15 13 04.5

Mag: 15.6

Diam: 0.3' x 0.1'


This week's OOTW is about the relation ship between the shape of planetary nebulae and their central stars. As most of us probably know, planetary nebulae not always are nice, round, spherically symmetrical bubbles of gas. Instead up to 80% of them (!) show complex structures. As a matter of fact:

"Planetary nebulae are classified by different authors into: stellar, disk, ring, irregular, helical, bipolar, quadrupolar, and other types, although the majority of them belong to just three types: spherical, elliptical and bipolar. [cut]

The huge variety of the shapes is partially the projection effect - the same nebula when viewed under different angles will appear different. Nevertheless, the reason for the huge variety of physical shapes is not fully understood. Gravitational interactions with companion stars if the central stars are binary stars may be one cause. Another possibility is that planets disrupt the flow of material away from the star as the nebula forms. It has been determined that the more massive stars produce more irregularly shaped nebulae. In January 2005, astronomers announced the first detection of magnetic fields around the central stars of two planetary nebulae, and hypothesized that the fields might be partly or wholly responsible for their remarkable shapes."

(The above two paragraphs almost literally were copied and pasted from Wikipedia.)

Back to our OOTW. About 2º west of Xi Serpentis lies the planetary nebula Abell 41. It's central star is a short period variable known as MT Serpentis. MT Ser has a very short period of 0.11322653 days or about 2.7 hours. At first it was thought that MT Ser is a cataclysmic variable. This means a white dwarf and a "normal" star orbiting each other. It was long thought that MT Ser was the shortest period cataclysmic variable known. However, more recent research seems to indicate that this in fact is a system of two white dwarfs orbiting each other in 0.22645306 days or about 5.4 hours.

(Source https://www.aanda.org/articles/aa/pd...39/aah2736.pdf)

In 2010 a observations were published showing evidence that the "symmetry axis of the model nebula is within 5º of perpendicular to the orbital plane of the central binary system. This provides strong evidence that the close-binary system, MT Ser, has directly affected the shaping of its nebula, Abell 41."

(Source https://arxiv.org/abs/1006.5873)

Here are images from respectively SDSS, ESO and POSS for Abell 41. I have not been able to find higher resolution images (not sure if the one on Flickr actually is of this nebula!).

Screenshot 2022-07-04 at 14.12.14.jpg Screenshot 2022-07-04 at 14.13.41.png Screenshot 2022-07-04 at 14.14.55.png

I observed this nebula in August 2016 using my 20" dob. My notes read

"At 256x visible without a filter as a tiny disk. UHC gives a beautiful view of a disk in a rich star field. It forms a triangle with a faint double star and a single star of about m=12. OIII dims the stars too much. H-Beta makes the disk disappear."


As always,

"Give it a go and let us know!
Good luck and great viewing!"