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IC 2448 (5,911 of 18,816)

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IC 2448

IC 2448, ESO 61-1, HD 78991, Hen 2-19, PK 285-14 1, PN Sa 2-34, PN VV' 84, PN VV 49, PN StWr 3-8, PN G285.7-14.9, Wray 16-34

RA: 09h 07m 6.26s
Dec: −69° 56′ 30.7″

Con: Carina
Ch: MSA:1017, U2:448, SA:25

Ref: SIMBAD

(reference key)

Type: planetary nebula

Mag: B=11.1, V=?

Size: ?
PA: ?

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Sketches  (1)

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Photos  (1)

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Published comments

Burnham's Celestial Handbook

Burnham calls this 12th magnitude, very small and round, appearing nearly stellar.

Evans & Thackeray (1950)

A photographic survey of bright southern planetary nebulae. M.N.R.A.S., 110(5), 429-439.

"This planetary was found on the basis of its spectrum by MRs Fleming, who designated it as 'planetary, stellar'. Campbell and Moore give a diameter of 8'', mag 9, ... VV gives diamter 8'', integrated mag 11.5. Our plates, Fig.2, show a bright central star, with a small oval patch of luminosity placed slightly eccentrically; dimensions 9''x7''.

Photo index

Photo Index by Jim Lucyk: Cat.of South.Peculiar Gal.and Ass. Vol 2 (Arp&Madore, 1987) p25.1.

Modern observations

Hartung, E.J. (1968) Astron.Obj.South.Tel

Hartung writes: "This conspicuous planetary nebula was missed by John Herschel and discovered by Fleming spectroscopically; it is 8 arcsec across and the brightest object in a field of scattered stars."

ASV Journal (1971)

ASV Journal Vol 24 No 3 June 1971: "at limit in 4-inch 200x."

James, Andrew (1998+)

From: "Neat Southern Planetaries - IIX."

This area of southern Carina and into eastern Volans is a wonderful place to explore during the autumn months. The selected planetary this month is IC 2448 - certainly one of the southern gems for the smaller telescopes. I also include a globular star cluster, galaxies, two asterisms, a variables and number of pairs - all within a 7O field of view. We conclude with number of challenging planetaries are also included for those who like to search for difficult objects.

IC 2448/ He 2-19/ SA2-34/WRAY 16-34/ PK 285.7-14.1 (09072-6957) (Carina) lies close to the border of Volans, near the bright star Beta Carinae (Miaplacidus), first discovered by Fleming in 1898. In my mind, it is one of the easiest planetaries to find. In the C8 using a 26mm. Plossel, both Miaplacidus and IC 2448 are seen at the edges of the same field, respectfully NE and SW. [My observing logbook of 1982, however, has an unforgiving 'curse' about this object, as my body was contorted to braking point attempting to use the direct finder close to the fork of the ye' old C-8!] For specific directions it is 34.7'min.arc. S.E.E, but it is best to centre the telescope on Miaplacidus, and move in an easterly direction by about 32'min.arc., then south by 13'min.arc. The field view of IC 2448 can be seen in Figure 1. Visually the observed field contains a number of 12th and 13th magnitude stars, with the 10.2 magnitude (Mph=11.5) planetary being the brightest 'stellar' object in the field. (Burnham's 'Celestial Handbook' and NGC 2000.0 incorrectly says the magnitude is 12th, and similarly, the photographic magnitudes are also underestimated by these same sources as 11.5.)

Medium magnification reveals a tiny featureless greyish disk. My eyes suggested a hint of blue colouration, but this is by no means prominent. The planetary is classified as Type 2b - smooth disk with uniform brightness. Using a 20cm., I could not distinguish any internal structure, and I assume even large apertures will do no better. A description by Burnham's gives a better extension than Fleming's original NGC one - 'vS (very small), R (Round), appearance nearly stellar.' An O-III filter produced a prominent jump in brightness, yet no visible structure. Some debate exists about the actual diameter, with most saying the visual disk is between 8.0" and 10.0"sec.arc. For example, AOST1, Sky Catalogue 2000.0 and Burnham's state 8"sec.arc. Megastar states the diameter is 9"sec.arc., while AOST2 is 10"sec.arc. and Perek/ Kohoutek in 1967 states that the optical diameter is greater than 10"sec.arc. For my eyes, the 10"sec.arc. seems closer to the truth. Photographic images display a slightly larger 12.0"sec.arc. IRAS (1982) shows an infrared diameter of 33"sec.arc., whose emissions are strong at 100Ám. This for all planetaries is typical as the circumstellar envelope from the AGB phase discards most of the stellar atmosphere in the surrounding space. For IC 2488 this corresponds to a distance more than one light year from the PNN.

Listed as object #274 in AOST2, the planetary is quoted as; "...about 10" across, slightly oval and the brightest object in a field of scattered stars. Even a 7.5cm. shows the single prism image plainly; it is bright through an O-III filter."

Steve Crouch (Southern Sky 1,4 pg.55) also states;" ...,IC 2448, about one low-power field away to the south west. This is a very prominent object in a 28cm., but a fair amount of magnification is needed for its circular, basically colourless, 8" disk to stand out clearly."

Explanation of the cause of the O-III brightness can be seen in Figure 2. Line intensities are based on the Hydrogen Beta wavelength, measured in milliwatts per square metre (mW.m-2), being set at an arbitrary value of 100. All other wavelengths are then based on this value. The individual line intensities for IC 2448 used in the profile are; H / 100, HeII/ 46, OIII/ 16, OIII/ 1253, He I/ 8, H / 348, NII/ 2.5, SII/ 1 and SII/ 1. Technically, magnitudes of planetaries are set by measuring the major contributors of energy output - Hydrogen-Beta and Oxygen III. In all it these two wavelengths that reflect the integrated magnitude calculated on the cumulative strengths of the all other wavelengths. As O-III (and H ) outputs are close to the visual acuity of the eye, other wavelength play little role in the final magnitude, and are therefore can be ignored. Thus, these two wavelengths are mainly used in the calculation of a visual magnitude.Much professional work has been done on this 'elliptical' nebula since the early 1980's. The PNN (HD 78991) of spectral type 'O' is invisible to most amateur telescopes. It has a visual magnitude of 14.32 ('B' mag. 13.97) - one magnitude less than stated in Sky Cat. 2000.0. Detail on the central star's temperature in the literature (1982-1989) varies considerably. A mean value is c.76 500OK▒ 17 000O and the Zanstra temperature is set at 83 000OK. Later observations according to the more accurate 'PN Morphologies Central Star Mass and Nebular Properties.' by Gorney et.al. A&A 318,256 (1997) show a lower Zanstra Temperature of 45 700OK▒ 800O (Stated 3.5%). Absolute magnitude of the PNN is 0.48, and is said to be 1 800 times more luminous than the Sun. The central mass (1997) is calculated at 0.579 solar masses. For the nebulosity the mass totals some 0.019 (1.9x10-2) solar masses, with an electron density of 40 000 electrons per cubic centimetre. (4x104 cm-3) Electron density tells the observer of the amount of energy available to enable ionisation of the surrounding gas. (However, this parameter is difficult to determine, and is only stated for the brightest of planetaries.) The large this value - the brighter the visual appearance of the nebula. Electron density is studied because it happens to be closely related to both temperature and the mass of the PNN. Morphologies of visible structures for the early stages of PN formation are also likely linked to this parameter. One or two papers on this particular issue has appeared in the professional literature as recently as late 1997.

According to M.Perinotto, IC 2448's PNN has shown some aspects of the P Cygni phenomenon - characteristic of an expanding envelope. The phenomenon observes particular emission lines with a brighter absorption line next to, but always towards the bluer part of the spectrum. This assumption is based on the narrow spectral profiles of the lines of H (656.3nm.) and HeII (468.6nm), which are used to determine the radial velocity -24.0kms-1▒4.0 (1983) that indicates it is travelling towards us. From the broadening of the spectral lines the expansion velocity of the inner nebulae is found to be between 11.5 and 13.5km.sec-1 depending on the spectral line in question, though the outer portions of the nebula are travelling at a slower 7kms-1. In size, the true diameter is calculated to be some 0.34 light years or 32 billion kilometres! The evolutionary age of the bright nebulosity is predicted to be a mere 5 500 years.

For distance, the values quoted in the literature vary widely. AOST1 quotes a distance of 1.8 kpc. and this is about half the present estimates. 'Strasbourg-ESO Catalogue of Galactic Planetary Nebulae' by Acker et.al. (1984 &1992); and Cahn and Kaler; (AJ. Sup. Series 22, 319-368 (1987)) both state 3.5kpc. Gorky et.al. (1997) quotes 3.6kpc. This slightly larger value is based on both the diameter and luminosity calculations given above.

Some sources use calculations based on so-called statistical distances, which is an overall average from all 'reputable' sources. Earlier observations are notorious for being underestimates of true distances. In most planetaries, and this tends to make such values lower than the latter day values. For IC 2448, a number of statistical distances quoted in the Strasbourg-ESO Catalogue are; 2.81 (1978) (Source in Sky Cat. 2000.0), 2.54 (1982) and 1.90 (1984).

Since Fleming's discovery 100 years ago, this planetary has become a classical example for the amateurs' eye.

Surrounding Field of IC 2448.

Beta Carinae/ SAO 250495/ Miaplacidus (09132-6943) is one of the brighter stars of the southern skies, and can be found about halfway between the Southern Cross and Canopus. From Sydney it is a circumpolar star. Although today it is in the modern day constellation of Carina, it was once, prior to the mid-17th Century, to lie within the super-constellation of Argo Navis. Later, Argo gained a new sub-constellation called Robur Carolinum. Created by Edmond Halley and officially published in 1679, Robur was made to commemorate the place known as the Royal Oak. This location protected the defeated Charles II, after his army was routed by Oliver Cromwell at the Battle of Worcester in September 1651. La Caille complained bitterly about Halley's addition because it destroyed most of the prominent stars in the Ship. (Halley, however, didn't complain. It ensured that he received his Masters Degrees by royal proclamation!) From about 1720, popularity for the constellation of 'The Oak' was slowly reclaimed back into Argo Navis. Its common usage probably ended in 1800 with Johann Elert Bode's star atlas 'Uranographica'. From then, like many others, Robur simply fell into antiquity as an obscure constellation. American astronomer Benjamin Apthorp Gould in 1879 subdivided this part of Argo Navis into smaller constellations, and Miaplacidus became part of Carina. This change was permanently adopted by the IAU in 1930.

Once known as Alpha Roburis, Miaplacidus was supposed to have been derived from the Arabic Mi'ak or 'waters', while the Latin 'placidus' was added much later. I assume that from Arabia, the Chaldeans would have seen this bright star in Summer glimmering close to the southern horizon of the Indian Ocean. Today, however, Miaplacidus is fully translated to mean 'placid waters' - appropriate because the star lies in the bilge of the ship!

This white star culminates annually at 9 pm. on the 26th March. In order of brightness, the visual magnitude is 1.674, making it 28th among the naked-eye stars. Distance is given as 26.1 parsecs (85 light-years), though the latest information of the Hipparcos astrometric satellite gives a much further distance of 34.09 parsecs (111.2 light-years). The spectrum of this giant star was for many years given as A0 III, though it has recently been downgraded to an A2 IV, indicating a surface temperature of 8 700OK. Measurements suggest an absolute magnitude of -0.4, so the true luminosity is about sixty times brighter than the Sun. Miaplacidus has been shown from the radial velocity that it is approaching us at a pedestrian 5km.sec-1. This is similar to the first measure in 1927, from the famous southern station of Harvard University in Chile. By 1970, careful inspection of the broadening of the spectral lines showed that the rotational (V.sin i.) velocity is c.145km.sec-1. Using general stellar evolution theory, the rotation of the star would have a 'stellar day' possibly as long as c.60 hours (or 2.5 days) for its nine million kilometre girth. Proper motion measures is 36.7"sec.arc. per century towards the constellation of Volans, which it will crawl into about the year 9 800 AD. Also in the future it will become the southern pole star in 6 200 AD, approaching by some 5O 42'. It is interesting to note that about the same time, Alpha and Beta Centauri will also be making their closest approach, at a mere 23'min.arc. Today, it stands as a lonely sentinel on the edges of the magnificent southern Milky Way.

Asterism - 'Southern Ursa Major.' or 'Delphinus Australis.' (09079-6442) is a pretty little asterism of nine stars between the magnitudes 8.4 and 11.4, and orientated in an east-west direction. Finding is easy as it lies some 20'min.arc. north of planetary IC 2448. I found it during a broad sweep of the area while moving the telescope towards the charming globular star cluster NGC 2808 - some 2.3O directly north of Miaplacidus. In size, it is about 35'min.arc. in length, with the trapezium shaped 'head' to the west. It is easily visible in a 7.5cm., and using a wide-field with a low magnification is best.

Brian Skiff

QBS: OX, no details.

15cm - distinctly non*ar @ 80x, mod br, m10.0. 295x: circ, 10" diam, wkly

annular w/cen * and/or *ing on NW side of ring: both come & go. BS,

16Feb1990, LCO.

Contemporary observations

Auke Slotegraaf

1998 February 23

1998-02-23/24, 6-inch f/8.6 Newtonian, Stellenbosch Rifle Range site. 6.0 (naked eye), seeing very good. West-southwest of Beta Carinae. The sweeper shows a small star. 144x (K9) shows the round, even fuzzy non-stellar disk easily; double-checked with other stars, just in case.

Richard Ford

2009 March 21

Perdeberg

12-inch Dobsonian f5 (EP: 20mm UW, 7mm UW)

Conditions: The fainter parts of the Milky Way are barely visible. Haziness only visible on the horizon. Atmosphere stable with little interference. Limiting Magnitude: 4.9.

IC 2448 is a very faint, well-defined oval nebula. It is difficult to observe. A 7-mm eyepiece (214x) shows it as a round extremely faint smudge of light, white in colour, with no central star.

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