My “Non-Planetary Nebula” candidates

Pre Object 1 – Supernova Remnant?

I found this object using the Digitalized Sky Survey plates during a hunt for Deep Sky Objects in Cassiopeia. It’s a 4′ nebulosity with a green colour in SDSS. In DSS it appears best in the Red plates, but is also detectable in the Blue ones. The nebula is absent in the DSS IR plates.

Discovery Pre Object 1

Discovery images of Pre Object 1. The images have been slightly enhanced to better observe the filamentary structure of this object. Image credit: DSS2 and SDSS Aladin Lite.

In WISE it appears best in the W3 and W4 band, but also seems to be detectable in the W2 band. In IPHAS the nebula appears much brighter in the Halpha band than the r band. The nebula is undetectable in the IPHAS i filter. Despite having numerous characteristics of a Planetary Nebula, it displays a “chaotic” filamentary morphology, very much like one could expect from a Supernova Remnant (SNR).

Pre Object 1

Images of Pre Object 1 in the IPHAS r and Halpha band. Notice how mich brighter it appears in the latter images. Image credit: INT/IPHAS.

Wether this indeed is a true SNR, or not, is impossible to know with the currently available data. Spectroscopy or even narrow band observations (Halpha and SII, for example) will be needed to better classify this object.

Update: The object has been found to be an outlaying part of a larger and known SNR: CTB 160.

Pre Object 2, Pre Object 3 – Cometary Globules

I found these two nebulae when looking through SDSS images of the region surrounding planetary nebula candidate Pre 31. Pre Object 2 is an elliptically shaped nebula, with SDSS, Pan-STARRS1 colors of a cometary globule. The object is even well visible in DSS2-IR images, further supporting this classification. The nebula is weakly detectable in WISE, in the W3 and W4 filters. Pre Object 3 has all the same characteristics as Pre Object 2, but is fainter and lacks a WISE signal. This nebula I found in Pan-STARRS1 images while trying to find Pre Object 2.

Pre object 2 and 3

SDSS image extracts showing Pre Object 2 and Pre Object 3. Image credit: SDSS

Pre 24 – Active Galaxy (extract from blog post)

In August and September 2017, a team of French astronomers found that one previously classified Planetary Nebula candidate was in fact a Galaxy, most likely a Seyfert Galaxy! The object is named Pre 24, and was discovered by yours truly in August 2016 using the online Digitalized Sky Survey plates.

Pre 24 discovery imageEnhanced discovery image of Pre 24. Notice the arc-like morphology of the object, similar to many Planetary Nebulae. Image credit: Digitalized Sky Survey (DSS) Aladin Lite.

The team consisted of  Pierre Dubreuil ,Olivier Garde, Pascal Le Dû and Alain Lopez. Their mission was to confirm Planetary Nebula candidates via spectroscopy. Among eleven objects studied, seven were confirmed as true Planetary Nebulae, while the remaining four were found to be other objects. Among the latter were two galaxies.

Despite Pre 24 having been initially classified as a Planetary Nebula candidate, there were already hints of the object being a galaxy. This was especially supported by Pan-STARRS1 data when it was made publically available in late 2016. However, it was difficult to be sure, as the object had a morphology and an Infrared signal similar to many Planetary Nebulae. Only the the recently obtained spectra by the French team could confirm its galactic nature. Furthermore, their study revealed the galaxy to be about ~192 million Light years distant!

I’m greatful to Pierre Dubreuil ,Olivier Garde, Pascal Le Dû and Alain Lopez for choosing to study this object, and all the work they put in to confirming the nature of it. Further study of Pre 24 is expected to take place in the future.


Pre Object 4 – Cometary globule?

I found this faint nebula in the Cassiopeia constellation, when hunting around in DSS and SDSS plates. The nebula is fairly elongated, with aWISE signal rather typical of a Planetary nebula, but its colour and morphology in SDSS and Pan-STARRS1 was more like one of a cometary globule. In DSS2-IR the nature was a bit more circular.

pre object 4SDSS image extract of Pre Object 4. Notice its very elongated cometary morphology and its non-PN colour.  Image credit: SDSS-III

Pre Object 5 and Pre Object 6 – Cometary Globules?

I found these two nebulae when searching for Planetary Nebula candidates in Cassiopeia, in the region around Planetary Nebula candidate PN Mul 8. Mul 8 was discovered only a few years ago by Lionel Mulato (France) using WISE data, but appeared very well in optical images, especially  in SDSS. its colour in those images however are also in favour of a cometary globule (see image below).

PN Mul 8Planetary nebula candidate PN Mul 8 as seen in SDSS data. Despite being a good candidate, its colour and morphology in SDSS is that expected of a cometary globule. Image credit: SDSS Aladin Lite.

Noticing that there might be similar nebulosity to Mul 8 in the vicinity, I decided to hunt for such objects. The first one I found was Pre Object 5, which layed just South of Mul 8. This object was very obvious in optical data, and has the WISE signal typical of a Planetary Nebyla. Unfortunatey though, its morphology, SDSS and DSS colours are more in favor of a Cometary Globule, hence its name.

Pre Object 5SDSS image extract of Pre Object 5. Notice its very obvious cometary morphology. Image credit: SDSS Aladin Lite.

As I continued searching the area, scrolling south through the SDSS plates, I stumbled upon a second nebula with similar characteristics to Mul 8. This one was fainter than Pre Object 5, and had a more elliptical morphology. Its SDSS and DSS colours however are those of a cometary globule, hence its designation being Pre Object 6.

Pre Object 6SDSS image extract of Pre Object 6. Notice its elongated nature, which might possibly be hints of cometary morphology. Image credit: SDSS Aladin Lite.

After another while when scrolling southward through SDSS, I noticed a much larger, circular object with similar characteristics. This one however showed more characteristics of a Planetary Nebula than the previous two objects above, hence was designated Pre 36 (see My Planetary Nebula candidates rubric).


Pre Object 7 – Possible Proto-Planetary Nebula

On August 13th, 2018, I noticed this bright bipolar nebula while hunting for Planetary Nebulae and Proto-Planetary Nebula in WISE and DECaPS imagery. In WISE  first spotted the object as it appeared similar to a well evolved red giant star (as do many PPNe), however DECaPS clearly confirmed the star to no longer be a pulsating red giant, but a likely post-AGB object due to its non-red colours and bipolar nebulosity. The core appears to emit in Halpha, according to the SHS Halpha plates, similarly to quite a few PPN cores (even Pre 30). ASAS-SN indicated no obvious PPN like variations in luminosity (perhaps too weak amplitude). Follow-up using higher resolution magnitude data could maybe confirm the LPV variations.

Pre_Object_7DECaPS image extract showing the bright bipolar nature of Pre Object 7. Image credit: DECaPS Aladin Lite.

Perhaps the relatively significant Halpha emissions and lack of obvious varitions are indicative of more evolved nature than Pre 30 and Pre 33? This is nothing but a guess on my end. However the WISE signal of Pre Object 7 is much more like a red giant than Pre 30 and Pre 33, but I have stumbled upon known PNe with clear optical colours of a PN, but with a WISE signal similar to Pre Object 7 (but very rarely though). At first glance, this could even be an indication that Pre Object 7 is actually a PN, however, it doesn’t seem likely that OIII emissions are present, as this object has already been catalogued an emission-line star based on its Halpha signal (and apparently nothing else). Otherwise it would likely have been classified as a PN long ago. Furthermore, like Pre 30 and Pre 33, the nebulosity does not seem to emit in Halpha, as one would expect from a PN.

Pre Object 7 WISEDiscovery AllWISE image of Pre Object 7. Notice its “green-yellow” tint, similar to evolved AGB stars, rather atypical of PNe. Image credit: AllWISE Aladin Lite.

The previous paragraph is just a complilation of thoughts on my end, hence they are to be taken with a “grain of salt”. I need to look further into the subject… 🙂


PreMo Object 1 – Reflection nebula associated with an HII region

This nebula I first noticed when hunting for previously unknown Open Clusters in WISE and DECaPS imagery. In DECaPS, PreMo Object 1 appears to be a blue nebulosity, obviously due to light reflected off the molecular cloud surrounding the young O and B-type stars making up this young cluster. PreMo Object 1 is clearly a confirmation of these stars being located within the molecular cloud. The molecular cloud emits in the Mid-IR, with a signal similar to many PNe. While I reported this object (mainly the cluster) to the DSH as part of a open cluster, Sankalp Mohan (India) independenlty reported the nebulosity directly to Pascal Le Dû. Consequently, it was given dual-credit designation and an entry in the List II of non-PN object in the french PN database.

PreMo Object 1PreMo Object 1 as seen in DECaPS. Notice how it surrounds at least three O and/or B-type stars, associated with a highly obscured open cluster mostly hidden behind the thick molecular cloud in which gave birth to the open cluster. Image credit: DECaPS Aladin Lite.

Prestgard_115 2MASSThe Open Cluster as seen in 2MASS, where close to individual stars can be seen! One can some slight effects of reddening in these images too, indicating that the stars are suffering a visual magnitude extinction more than 20 mag! PreMo object 1 is absent in this image, as it does not emit in the near-IR.