NEAT SOUTHERN PLANETARIES : 14
NGC 5315 in Circinus

NGC 5315 / He2-100 / Sa2-100 / Wray 16-140 / PK 309-4.2 / PN G309.1-04.3 (13540-6631) [U452] lies in the southern constellation of Circinus. It planetary nebula nature was discovered in 1883 spectroscopically by Scottish born Ralph Copeland (1837-1905), but was oddly not noticed in the early sweeps between 1834 and 1838 by the usually highly meticulous observer, John Herschel. It was J.L.E. Dreyer who recorded in the NGC as “…;stellar=10.5 mag.”, giving the catalogued number NGC 5315. This PNe is bright 9.6v / 9.8p magnitude of high surface brightness, and to me appears like a very pretty small nebulous smudge. Visually, I thought the planetary was slightly elongated at about PA 50°, whose observed diameter is between 3 and 5 arcsec. Photographically it is claimed as about 6.1 arcsec. Sky Catalogue 2000.0 (1986) lists the diameter as 5.0 arcsec. Using the Vorontsov-Velyaminov Classification is given as Class II — 2. Its central PNN star is 11.3v and 13.4p magnitude.

NGC 5315 is placed 29′E of the shared Circinus/ Musca border, and can be readily found some 5.2°WSW (PA 248°;) from α Cir / Alpha Circini / Δ166 (14425-6458). Alternatively, use β Mus / Beta Muscae / R207 (12463-6806), lying 6.7°E (PA 84°) away, with NGC 5315 found conveniently about halfway between α Cir and β Mus.

Observations of NGC 5315

E.J. Hartung writes in AOST1 and AOST2:

“In a beautiful field with a bright pale yellow star [SAO 252498] 4′ preceding is this bright small nebula showing a strong elliptical prism image with a smaller fainter one on the violet side, from oxygen and hydrogen respectively. The nebulae is fairly well defined, about 5 arcsec across and 10.5cm (not 3 arcsec as quoted in the Companion to the Uranometria shows it clearly as a bluish star while the prism image is easy in a 7.5cm (AOST1 continues) R is estimated as about 3,500 pc.”

Kent Wallace using a 8-inch SCT.from Western Australia on 2nd August 1999 describes;

“At 62.5× can see directly as a relatively bright star with an even brighter one nearby. Through the O-III filter the PN becomes brighter than its mate. Good response to the O-III & UHC filters. No response to the Hβ filter. At 100× the PN still appears stellar. At 200× the PN looks slightly non-stellar.”

Sanford says;

“…appears as a small, disk-shaped object, differing from a star only because of its bluish-green colour in low-power eyepieces. A high-power eyepiece will show a fairly bright, featureless disk about 5 arcseconds in diameter. The central [PNN] star is listed at mag 11.4.”

Franschoek using 15cm f/8.6 Newtonian and observed this planetary from a mountain pass summit, haze, thin clouds. Here he quotes;

“Easy as a star of 10th magnitude, perhaps with an envelope. Up to 186× shows no obvious disc. A moderately bright field star conveniently nearby allows precise focussing to be checked.”

Technical Data on MGC 5315

The expansion velocity of the nebula is 37.5 km.s^-1. Total mass of the nebulosity is 0.01, ionised by a moderately strong electron density of 2×10⁴. In 1981, infrared observations indicates that the nebulosity contains significant numbers of Silicon Carbide (SiC) particles, with an average particle size about 11.3μm. Ratio of Carbon to Oxygen, [C/O] is 2.5 — moderately high in abundance compared to most PNe. NGC 5315 is relatively strong radio source when compared to most planetaries. The envelope is expanding at the relatively pedestrian rate of >4km.s^-1.

First determined by the International Ultra-Violet Explorer (IUE), the central star is spectral class WC6 with an effective surface temperature of 70,000K. This satellite observatory also confirmed its rare PN Type I — a unique evolution classes first defined by Peimbert in 1978. NGC 5315 PNN has the luminosity estimated to be a thousand times that of the Sun.

The spectral signature implies that the radial velocity is -32km.s^-1 away from us. Distance is presently estimated between 1.3kpc and 4.2kpc. (4,150 to 13,600ly.) Sky Catalogue 2000.0 quotes the value as the mean of the two, 2.8kpc. It seems that the problem of interstellar absorption is particularly uncertain towards this region of the sky. I.e. E(B-V)=0.41. Lower values of 1.3kpc assumes no absorption and is based on the extinction distance. It is likely that the distance of the planetary is likely about 3.0kpc., though Gathier, Pottasch & Pel (1986) finds an error prone 2620±1030pc.

Surrounding Fields of NGC 5315

Sa3-23 (13525-6623) is another PNe in the same field as NGC 5315. I did not see this in 20cm even when using the O-III filter. Lying merely 11′NW (PA 311°), its distinctive location is easily identified between the midway point between two stars at 9.5 and 8.8, respectively. The latter being 1.6′ENE at PA 60°. Using the ESO-Strasbourg Catalogue of Planetary Nebula shows no listing of magnitude, though the size is given as 17 arcsec. Looking at the STScI image, it is unlikely that apertures below 40cm would see it. Those with large apertures when checking out NGC 5315, may like to report any visual sightings.

Δ145 (13546-6654) was found by Dunlop in 1837 and is located 23′S of NGC 5315. The current separation is 24.1 arcsec along PA 48°. Since discovery, little has changed, except for the small 2° decrease in PA. Magnitudes are stated as 8.2v and 9.2v, though I thought the difference in Δm was more like 0.7. According to my observing log, and using the 32mm Erfle, I could fit both objects within “…the very starry field.” Finding this bluish-white/ white pair (B9/A0) alone is more than worthwhile!

Last Update : 04th November 2011

Southern Astronomical Delights © (2011)

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