Last year I wrote a blog post on the numerous Planetary Nebula (PN) candidates discovered by the Atacama Photographic Observatory (APO), a French trio of amateur astronomers/astrophotographers (Thierry Demange, Richard Galli and Thomas Petit). The article can be found here. Since the time that post was published (February 2018), the team has added an extra 18 candidates to their catalogue, with a current total of 71 PN candidates! In this article I describe several of these new finds in detail. The work includes my personal analysis of the objects according to public survey imagery. Hope you enjoy! 🙂
Figure 1: Image extract of [SII] +Halpha +[OIII] (SHO) image of the RCW 19 and RCW 20 star forming regions. This is also the disocvery image of several Planetary Nebula candidates, including DeGaPe 52, DeGaPe 54, DeGaPe 58 and DeGaPe 59. Planetary Nebulae can easily be spotted in SHO images due to their strong emission in [OIII] and Halpha, making them appear fluorescent in such imagery! (c) APO Team.
The Atacama Photographic Observatory (APO) is a remotely controlled observory in the Atacama desert run by French amateur astronomers Thierry Demange, Richard Galli and Thomas Petit (the APO team). Its chosen location makes it ideal to observe the wonders of the Southern Sky, with stunning images having been taken of the Carina and Prawn Nebula, among many others (see gallery)! Their results are regularly featured in French popular astronomy magazines, such as Astrosurf and Ciel & Espace. Many of their images, (e.g. figure 1) are a combination of individual [SII], Halpha and [OIII] exposures. Such combinations are referred to as SHO images. Planetary Nebula (PNe) are often easy to spot in such images do to their generally strong emissions in [OIII] and Halpha. Consequently, in SHO imagery, their emissions causes them to appear unusually green, turqouise or blue in comparison to the surrounding star field. Figure 2 shows some examples of known PNe as seen in the APO Team’s SHO images.
Figure 2: Known Planetary Nebulae as seen in SHO imagery from the APO team. Notice their unusually blue or green colours in comparison to the background star field. This is due to their significant [OIII] and Halpha emissions. (c) APO team.
However, in addition to the known PNe, the APO team detects a large number of uncatalogued objects displaying PN-like colours in their SHO images. These are regularly reported to the French PN database and are given the designation “DeGaPe” (Demange – Galli – Petit). Their latest find (as of currently) is DeGaPe 69, the team’s 69th PN candidate (not including KnDeGaPe 1 and KnDeGaPe 2). This makes them one of the leading discoverers of PN candidates in France! Their discoveries can be found on their website and on the PlanetaryNebulae.net website. Figure 3 displays some of their recent candidates that display hints of nebulosity.
Figure 3: Nebulous APO Planetary Nebula candidates as seen their [discovery] images. Notice that DeGaPe 53 and DeGaPe 63 are apparently large (>50.’) and very diffuse, while DeGaPe 55 and DeGaPe 64 appear to be much more compact in comparison (~10″). (c) APO team.
Perhaps one of the more remarkable objects recently discovered by the APO team is DeGaPe 64. Indeed, this small compact nebula (~10″ in diameter) displays all the characteristics expected of a PN, both in survey imagery and in narrow-band images (likely dominated by [OIII] emissions, see figure 3). Firstly, the Mid-IR signal matches that typically displayed by many compact PNe, both in WISE (Acker et al., 2016) and Spitzer (see here) . Secondly, DECaPS imagery confirms the object’s nebulous nature (see figure 4), and the SHS Halpha plates also show the nebula to significantly emit in Halpha.
Figure 4: DECaPS image extract showing DeGaPe 64 (center). The object appears to be a compact elliptical nebula, well within a dense star field. Image credit: Aladin Lite.
DeGaPe 55 is also quite interesting. It shares some characteristics with DeGaPe 64, including its size and morphology according to the APO images. Unlike DeGaPe 64 however, this object appears to be dominated by Halpha emissions rather than [OIII]. This is the case of many PNe (e.g. EM* VRMF 90 [figure 2]). Strangely, DeGaPe 55 appears to be stellar in survey imagery, including in the Halpha SHS survey plates (see figure 5)! Moreover, the object’s photometric properties are typical of a red giant star (see figure 5). The latter is confirmed by its variable nature, and has already been officially classified as a Mira star by Jayasinghe et al. (2018). Perhaps the nebulous appearance in the APO team’s SHO image is an artefact?
Figure 5: DECaPS image extract showing DeGaPe 55. The object is stellar with colours typical of a red giant star. The star is recognized by the Variable Star Index (VSX) under the designation ASASSN-V J081826.63-344332.1. Image credit: Aladin Lite.
DeGaPe 53 and DeGaPe 63 show hints of being highly evolved PNe. Firstly, these nebulae appear better in [OIII] images than in optical survey images (e.g. DECaPS and DSS). Furthermore, DeGaPe 53 displays a PN-like Mid-IR excess according to WISE, while DeGaPe 63 appears as an arc in DECaPS (see figure 7), which is a morphology commonly observed in many PNe DeGaPe 53 also appears circular in DECaPS (see figure 6). However, it is also possible that these objects may be reflection nebulosity associated with nearby star forming regions, rather than true PNe. Only spectra can confirm the true nature of these objects!
Figure 6: Enhanced DECaPS image extract showing DeGaPe 53. Notice the relatively circular nature of the nebula. Note also that it surrounds several bright white stars (possibly young OB stars), suggesting that it may be a reflection nebula rather than a true PN. Image credit: Aladin Lite.
Figure 7: DECaPS image extract showing DeGaPe 63. Notice the nebulous arc positioned southward that appears to be associated with the nebula. While this might be a sign of a highly evolved PN, the nebulosity may be linked to surrounding star forming regions. Image credit: Aladin Lite.
However, only a minority of the APO team’s finds are actually nebulous. In fact, most of their candidates are actually stellar in appearance, even in high resolution survey imagery! Figure 1and Figure 8 show many such objects.
Figure 8: Stellar APO Planetary Nebula candidates as seen their [discovery] images. DeGaPe 54 and DeGaPe 68 are located in the field of dark nebulae (c) APO team.
Similarly to DeGaPe 64, DeGaPe 61 also show several signs in favour of a true PN. Firstly, the object displays a WISE signal similar to many PNe (see figure 9). Secondly, no evident variability was detected in ASAS-SN data and in the DSS plates. The object’s Halpha emissions are clearly visible in the APO team’s SHO image (see figure 8) and in SHS Halpha plates. Coincidentally, the objects is only ~30′ of another known PN candidate, PaMo 1 (see figure 9), a probable PN that was only discovered in 2018.
Figure 9: AllWISE (W1 + W2 +W4 filters) image extract showing Planetary Nebula candidates PaMo 1 and DeGaPe 61. Their colours in this image are typical of PNe, being much brighter in the W4, in comparison to W1 and W2 (indicating Mid-IR excess). Image credit: Aladin Lite.
Similarly to DeGaPe 55, DeGaPe 57 also appears to be a possible Mira star. Indeed, the object’s photometric properties ressemble those of red giant stars, and the DSS plates show the object to significant fluctuate in brightness (see figure 10). Unlike DeGaPe 55, this star has not yet been recognized as a variable star. A report was just recently been submitted to the Variable Star Index (VSX) by myself.
Figure 10: DSS image plate comparison (Red filter) used to discover the variability of DeGaPe 57. Image credit: SuperCosmos Sky Survey.
Figure 11: DECaPS image extract showing DeGaPe 57. The object is stellar with colours typical of a red giant star. Image credit: Aladin Lite.
DeGaPe 54 and DeGaPe 68 appear to be located infront (or within) dark nebulae, deep within the active star forming region RCW 19. This suggests that these two objects may be Young Stellar Objects (YSOs) rather than true PNe. Indeed, as visible in the SHO images and the SHS Halpha plates, the objects appear to display strong Halpha emissions, typical of young YSOs (e.g. Classic TT Tauri stars). The Mid-IR signals also appear to be quite similar to many known YSOs (see figure 12). Furthermore, DeGaPe 68 appears to be associated with a faint nebula (likely reflection nebulosity, see figure 13) similar to that surrounding the YSO IRAS 17079-4032 (see figure 13) However, unlike many YSOs, I was unable to find traces of variability in ASAS-SN and in the DSS plates. Perhaps this is an indication that DeGaPe 68 may be a highly reddened PN?
Figure 12: AllWISE image extracts showing DeGaPe 54, DeGaPe 68 and two confirmed YSOs. Notice their similar colours, suggesting that the two DeGaPe finds may also be YSOs rather than true PNe. Image credit: Aladin Lite.
Figure 13: Comparison between DeGaPe 68 and IRAS 17079-4032 as seen in DECaPS. IRAS 17079-4032 is a known YSO with a reflection nebula, located within the Barnard 58 dark nebula. DeGaPe 68 is also located within a dark nebula, and shows a small tail-like object similar in colour to IRAS 17079-4032. This suggesting that DeGaPe 68 may also be a YSO, rather than a true PN.
Since February 2018, the APO team has discovered many new awesome objects! While it is evident that DeGaPe 64 is likely a true PN, many other of their finds appear to be more difficult to classify, despite their PN-like colours in SHO images. Indeed, some objects (e.g. DeGaPe 54 and DeGaPe 68) show strong evidence in favour of YSOs, while others appear to likely be Red giant stars (e.g. DeGaPe 55 and DeGaPe 57) based on public survey imagery. Spectra are required to formally confirm the nature of these objects! 🙂