He2-97 in Musca

One final planetary nebulae in Musca completes those featured here in the Neat Southern Planetary series. This is Henize PNe, He2-97 that is placed in the southwestern Musca, and merely 22′ west of the shared Musca-Apus border. While it is reasonably bright and easy to find, He2-97 is a fairly small 5 arcsec.

He2-97 / Sa2-98 / Wray 16-135 / PK 307-9.1 / PN G307.2-9.0 (13454-7129) lies 3.4°E (PA 94°) of pale orange 3.6 magnitude star, δ Mus / Delta Muscae / HIP 63613 / SB 746 / Delmus” (13023-7133). The immediate field appears as brightish pale orange star some 3.3′NNE (PA 21°), being 7.2v magnitude, HIP 67098 / HD 119286 (13451-7132). Alongside it is a unrelated fainter field star of about 13th magnitude just 11.6 arcsec away (PA 76°) that is readily seen in 15cm in dark skies.

He2-97 Small

Figures 1 & 2. He2-97 in Musca

Fig.1 (left) Wide field image. Size: 12.5′×12.5′ taken from the CDS ALADIN previewer. Image composite is Red: AAO/R/DSS2; Blue: SER/I/ DSS2; Green: average. Red/blue image modified by Silvering”, and slightly reducing saturation.
Fig.2 (right) Image size: c.30×30 arcsec, being obtained from the wider image and blurred sightly to eliminate some of the pixelation. He2-97 is the lower orange-yellow object, with the higher white star being about 13th magnitude, some 12 arcsec away in PA 76°

He2-97 was discovered by K.G. Henize in 1964 from Mt. Stromlo near Canberra in his dedicated photographic Hα survey in search of new southern PNe. He2-97 shines at 12.6B magnitude, with this tiny 5.0 arcsec plain disk appears like a tiny spherical planetary smudge without mottling nor any features. It is easily spotted using 10.5cm., although the disk appears far more obvious in 20cm. or larger. The nebulosity responds well with the [O-III] filter.

The white dwarf central star is listed as 15.35V, 15.3p, but remains invisible to the visual telescopist. According to Phillips (2005), the PNN Zanstra temperature from the HeII emissions is 57,000K, with an absolute magnitude of 9.15 — or about one-hundredth the solar brightness.

Phillips (2005) finds an enormous distance of 5.53kpc., which exceeds the usual more distant Henize PNe discussed in this series by a factor of two! This quoted distance is seemingly the only one I have found in the current literature.


  1. Phillips, J.P., The distances of less-evolved planetary nebulae: a further test of statistical distance scales.”, MNRAS., 293, 847 (2005)

Surrounding Fields : Visual Double Stars

Δ140 (13458-7159) is a Musca pair near the border with Apus, being located 30′S (PA 176°) from PN, He2-97. Its field contains several faintish stars, but locating Δ140 is a difficult to find pair for the lack of bright reference stars. I found it best to use δ Mus, and move the telescope 3.4°E and 0.2Z°S. Once found it cannot be mistaken for any other system. This happens to be one of the fainter and closer Dunlop pairs, being currently listed as magnitudes 8.7v and 9.7v (8.74V & 9.70V). Separation is presently about 9.8 arcsec along PA 75°, which has widened by about 1 arcsec while the PA has decreased by about 6°.

WDS02 actually states the PA is 0°, but this is only because it was not initially measured by Dunlop. Later versions of the WDS, I.e. WDS11, state Dunlop̵s PA is now 90°. I visually saw the colours of both being white in 7.5cm., 10.5cm. and 20cm.

Oddly this pair does not feature in Innes (1899) Southern Double Star Catalogue, even though it is easily within his self-imposed separation limit of twenty arcsec and roughly 10th brightness.

It is likely that these two stars are attached, as the proper motions are similar, but from the lack of any HIP parallax, we can say little of the connectivity of the system. Δ140 will be an interesting pair to observe in the future for any change in relative motions

HJ 4586 (13284-6752) is a bright white pair that has been known as an attractive system for small telescopes. It can be found 1.2°ESE (PA 244°) from Sa2-96. Discovered by John Herschel in 1837, the 7.3v and 9.1v (7.33V & 9.09V) magnitude pair has slowly been decreasing. In 1837 the separation was 3.7 arcsec, while the latest position in 1991 WDS11 was 2.9 arcsec. I looked at this pair in 1994, and the separation did seem slightly smaller than this. Position angle has also reduced by about 9° (PA 150° to 141°).

This duo will be interesting to watch, as the narrowing separation will make it difficult to separate in modest apertures. If the separation continues to decrease at this rate, it will become an impossible target for apertures less than 30cm in about 2090AD. Looking at the shared individual proper motions of -51.60±0.67 mas.yr-1 and -12.19±0.49 mas.yr-1, HJ 4586 is likely a true binary system, though it will take many centuries to tie down the orbital parameters adequately for predicting its future positions. Combined spectral class is A5III/IV.

Hipparcos (HIP2) measures that HIP 65719 (HJ 4568AB) parallax as 7.04±0.67 mas., making distance as 142±14 parsecs or 463±44 ly. The maximum projected true separation, at least when John Herschel measured 3.67 arcsec is 521 AU, making the minimum period at this distance as 5900 years or so. (This is not incongruous with the observed motion, though the change of 0.7 arcsec in about 150 years seems a bit larger than would be expected.) Absolute magnitudes are 1.3 and 2.7, respectively, whose estimated masses are 2.4 and 1.9 suns. Combined spectral class is A5III/IV.

A worthy southern pair to look out for.

Table 1: Selected Measures for HJ 4486

PA     Sep. Year      Source      
149.4  3.67 1837.4    J.Herschel  
148.9  3.87 1872.93   H.C. Russell
142.9  3.76 1879.4    CGA         
144    3.1  1929      IDS76       
142    2.8  1986      WDS96       
141    2.9  1991      HIP n=16    

I 923 (13216-6630) this near equal magnitude yellow pair was discovered by Innes in 1911. The WDS96 gives 9.4v and 9.9v. Its PA of 133° has changed little since this time, though the separation has slowly increased from 1.3 to 2.1 arcsec. Looking at the poorly known proper motions, it is likely this pair is an optical one and that the angle will continue to widen. Seen with care in 7.5cm, it should be easily visible in apertures above 10.5cm.

Table 2: Selected Measures for I 923

PA   Sep  Year  Source 
130  1.2  1910  Innes  
132  1.3  1911  Innes  
132  1.7  1942  IDS    
132  2.1  1989  WDS96  
133  2.1  1991  HIP n=6

The rest of the new NSP series will continue in Universe in December / January 2012 issue — and into the future — at least fitted in by the necessary whims of the Editors availability of space against other submitted material by other authors!


I have been working on the older NSP Series and bring all of it up to date on this very website.


NSPs 14, 15, 18, 19, 20, 22, 22a, 23, and this page, NSP 24.

The BACK and NEXT buttons below will cycle through these 9 Pages made so far.

I will add the remainder in coming weeks as time permits.



Last Update : 24th October 2011

Southern Astronomical Delights © (2011)

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