Variable Nebulae, 08 April 2008 -
06 June 2014
The images below illustrate the five variable nebulae visible from the northern hemisphere plus one (NGC6723) visible from the southern. I captured the images with the following telescopes:
- my 16 cm f2.5 Schmidt telescope and MX916 CCD,
- my 34 cm f4.0 Newtonian and MX916 CCD,
- my 30 cm f4.1 astrograph and MX916 or H16 CCD,
- the Sierra Stars Observatory Network (SSON, http://www.sierrastars.com/) Mount Lemmon 0.81 m Cassegrain telescope,
- three instruments in the iTelescope.net network:
- T11, a 0.5 m, f/4.5 reflector at New Mexico,
- T30, a 0.5 m, f/4.5 reflector at Siding Springs,
- T27, a 0.70 m, f/6.6 CDK astrograph also at Siding Springs.
North is up in all images below.
Gyulbudaghian's Nebula
Gyulbudaghian's Nebula is a little-observed and poorly understood variable nebula at the heart of which lies the recently-formed pre-main sequence star PV Cephei (typically magnitude 16-18). The nebula is usually small and faint.
My observations of the nebula coincided with an observational programme by the Deep Sky Section of the BAA, coordinated by Grant Privett, to monitor the object. Thanks to this programme, observations by BAA member David Boyd were made available for comparison purposes.
Figures 1-4 below show the appearance of the nebula over a period of 16 months, April 2008 - August 2009, and illustrate clearly changes in its appearance. Between April 2008 and October 2008, it appeared to become more extensive and the locus of its peak density moved further from PV Cep. Between October 2008 and August 2009, the nebulosity disappeared completely!
Figures 5-7 span a period of eight months from late March to early December 2012. David Boyd captured figure 5 on 28 March 2012; I took figure 6 using my Newtonian reflector on 16 October 2012; and David took figure 7 on 05 December 2012. (I am grateful to Stewart Moore for providing David's images.) The images show a significant patch of nebulosity becoming visible and brightening over a period of months.
Becoming increasingly frustrated with the weather in the UK shortly before Christmas 2012, I decided to try some remote observing. There are many telescopes available via the Internet and I chose to use one controlled by the SSON as I know people who have obtained good results with their equipment. SSON has three telescopes but, as Gyulbudaghian's Nebula is small and usually faint, I chose the largest, the Mount Lemmon 0.81 m Cassegrain reflector in Arizona. After some delays caused by a snow storm (36 cm of snow on the dome!), moonlight and Christmas I received my first images on 02 January 2013. I compiled figure 8 from the resulting stack of 5x2 minute exposures after some basic image processing. It is clearly superior to the earlier images with my 34 cm Newtonian!
Figure 9, again taken with the SSON 0.81 m Cassegrain reflector (using five 2 minute exposures), shows the nebula on 01 April 2013. Figure 10 compares side-by-side the images of the nebula on 02 January and 01 April 2013. Figure 11, taken with my 34 cm Newtonian (49x30 second exposures), shows the nebula on 07 May 2013. Clearly, there has been little change since the start of 2013.
Throughout summer 2013 I continued to monitor the nebula with the iTelescope.net T11 reflector in New Mexico. It appeared still bright with some very subtle changes from month to month. Maybe some structure was developing on the left hand edge? See figures 12 and 13.
In early September, for the first time since I started using remote telescopes, there were four consecutive days of bad weather in New Mexico and, as a result, I was unable to capture my monthly image of Gyulbudaghian’s nebula. However, I did have good conditions at home during this period and, on the evening of Saturday 07 September, managed to take probably the best image yet (figure 14) with my own equipment. Two factors contributed to the excellent quality of the image: I had the telescope mirror re-coated over the summer (a HiLux coating from Orion optics replacing the original aluminium coating applied 30 years ago!) and I spent an hour at the telescope taking very many images.
The image from 07 September appears to show the brightening on the left hand side of the nebula has increased in extent over the preceding month. Clearly better conditions and more signal might reveal more structure, but I think the change is real given that the brightening wasn’t visible previously in images with bigger telescopes from better sites. Figure 15 is a greatly stretched negative image to highlight the "new" appendage. It’s nice to see some change at last!
Figure 16, taken on 04 October 2013 using the iTelescope.net T11 reflector, appears to show some further change. The eastern extension of the nebula looks narrower and fainter than in the image taken at the beginning of September (figure 14). Perhaps this section of nebulosity is fading? Figure 17 provides a negative view of the same field.
Figure 18, taken on 01 November 2013, provides the obligatory monthly watch for changes. The image is similar to that of the previous month, although the long eastern extension may now be thinner.
Bad weather in New Mexico in early December meant that I had to do my own imaging (!) using my 30 cm F4.1 astrograph. The images aren't up to the standard of those taken with the much larger instrument in New Mexico, but do maintain monthly monitoring of the nebula. Figure 19 was taken on 04 December 2013. Figure 20 is a rather over-stretched full field view which starts to show the large dust cloud within which the the nebula is embedded. This is a typical environment for all the variable nebulae as they are associated with newly formed stars.
Figure 21, taken on 01 January 2014 with the iTelescope.net T11 reflector, shows that the nebula has changed little in the previous month.
Figure 22, taken on 28 February 2014, shows that remote telescopes don't always deliver excellent results! It was taken with the iTelescope.net T11 telescope and, unfortunately, is degraded by slight trailing and poor focus. This may be a result of the relatively low altitude of the target. Despite the degradation, the image shows that the nebula remains relatively "bright" with a shape that has changed little in the last year.
Figure 23, taken 04 March 2014 with the iTelescope.net T11 instrument, still shows some image degradation. The image is based on ten 2 minute exposures stacked to give increased depth and reveal some of the background interstellar cloud.
Taken one month after the previous image, figure 24, taken with the iTelescope.net T11 instrument, shows no significant change in the nebula. At least the image isn't trailed.
Figure 25: another month, another image! The figure was captured on 03-04 May 2014 with the iTelescope.net T11 instrument. It comprises a stack of ten 2 minute exposures, which reduces the noise.
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Hind’s Varable Nebula (NGC1554)
Hind’s Varable Nebula (NGC1554) lies close to the Hyades star cluster in Taurus. The object next to it in the images below is the very young variable star T Tauri.
I captured figure 1 below from my home in October 2008. Over four years later, in January 2013, I used the SSON 0.81 m reflector to capture figure 2. The nebula doesn’t appear to have changed significantly during the intervening period. (Note that, after I submitted the imaging request to the SSON, I realised that Jupiter was in the Hyades, close to the nebula. However the quality of the telescope and sky conditions on Mount Lemmon are such that the planet caused no serious glare in the image.)
I captured figure 3 with my 30 cm F4.1 astrograph on 04 December 2013. Figure 4 is a highly-stretched image taken on the same date which shows the dust cloud enveloping the nebula.
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McNeil’s Nebula
McNeil’s Nebula lies just south of M78 in Orion. It was discovered on 23 January 2004 by US amateur astronomer Jay McNeil. It is variable and brightened in late 2008.
I captured figure 1 below from my home in January 2009. (In the full image [not the thumbnail], M78 is overexposed to bring out faint detail in the nebula.) Four years later, I used the SSON 0.81 mm reflector to capture figure 2. The nebula doesn’t appear to have changed significantly during the intervening period.
One year later still, on 28 December 2013, I decided to check again for change, using the SSON 0.81 m reflector. Figure 3 compares the appearance of the nebula on 04 January and 28 December 2013. The nebula appears to have changed little in the intervening period, but I guess that in itself is useful information.
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Hubble’s Variable Nebula (NGC 2261)
Hubble’s Variable Nebula is the most famous of the five variable nebulae visible in the northern hemisphere. It is located north of the Rosette Nebula in Monoceros and has a striking comet-like shape. I captured figure 1 from my home on 03 January 2009. Four years later, on 07 January 2013, I used the SSON 0.81 m reflector to capture figure 2. The shape of the nebula appears to have changed slightly during the intervening period.
One year later still, on 28 December 2013, I decided to check again for change, using the SSON 0.81 m reflector. Figure 3 compares the appearance of the nebula on 07 January and 28 December 2013. Change is apparent in structure close to the star at the base of the nebula but structure further out appears relatively unchanged.
On 21 February 2014, with the Moon not rising until after midnight, it was a good time to take another look at the nebula. I used the iTelescope.net T11 instrument to capture figure 4, based on five 3 minute exposures through a luminance filter. There are subtle changes in structure since my last image on 28 December 2013, showing that the nebula is well worth monitoring on a regular basis.
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Thommes' Nebula
Thommes' Nebula is relatively recent addition to the group. It was discovered by a Californian amateur astronomer in November 2009 - see http://www.ifa.hawaii.edu/users/reipurth/PREPRINTS/ms_V900Mon.pdf for details. Although the nebula is not visually impressive, it does illustrate the fact that there are still things out there waiting to be discovered! The star V900 Mon and its associated nebula are in the centre of fig 32 below.
Figure 1 was captured on 11 January 2013 with the SSON 0.81 m telescope. Five 120 second exposures. FoV is 11x11 arcmin.
Fig. 1. 11 January 2013. SSON 0.81 m reflector. 5x120s exposures. FoV 11x11 arcmin.
NGC6729
Variable nebulae NGC6729, lying in the constellation Corona Australis at declination -37°, cannot be observed from the UK, so I used telescopes T27 and T30 from iTelescope.net at Siding Springs, Australia. Note that the variable nebula lies close to the irregular nebulae NGC6726 and NGC6727 and the globular cluster NGC6729, which appear in several of the images below.
Figure 1 is an all-sky image taken on 20 March 2013, one day before my first image of NGC6729. The position of the nebula is marked with a red arrow. Note the unexpected light pollution from the zodiacal light at top left!
Figure 2, taken on 21 March 2013, is the full field view from T30, showing NGC6729 at bottom left together with irregular nebulae NGC6726-7 and globular cluster NGC6723 at top right. (I deliberately offset the field to capture the latter.)
Figure 3, also taken on 21 March 2013, is an enlarged view showing detail in the variable nebula.
Figure 4, taken on 04 October 2013, was inspired by a presentation by Jeremy Shears, at the "The Astronomer" 2013 AGM, on Harold Knox-Shaw and the Helwan Observatory (see www.theastronomer.org/). In the presentation, Jeremy showed an image of NGC6729 taken by Knox-Shaw in Egypt early in the 20th Century. The image prompted me to make another observation of the object with T30 (figure 4,) and to compare it with the earlier image in figure 3. There appear to be some subtle changes between the two figures; however, note that figure 4 represents a first pass at a new image and I need to do further careful processing to confirm that the apparent changes are real. Unfortunately there are confounding factors: exposure times of the two images are slightly different (I didn’t book enough time to take all five exposures first time round!) and the orientation of the CCD on the telescope has been rotated through 90°.
Figure 5 was taken on 06 May 2014 with T30. Figure 6 is a composite image, comparing the nebula on three dates from early 2013 to early 2014 (specifically 21 March 2013, 04 October 2013 and 06 May 2014). There are some clear changes going on in the nebula, or at least in its illumination, so I intend to take images monthly from now on to monitor it more closely.
Figure 7, taken on 02 June 2014, is my first image with T27 (a 0.7 m astrograph). The telescope has a 3056 x 3056 pixel CCD which gives superb resolution throughout a 27x27 arcminute FoV. The image below is at half the original size. Figure 8 is a full resolution 5x5 arcminute view of the variable nebula itself.
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Mike Harlow