Little Gem (NGC 6445) + Globular Cluster NGC 6440

History

On 28 May 1786, William Herschel discovered two nebulae, which he catalogued as I 150 and II 586. Class I stood for bright nebulae and II for faint nebulae. For I 150 (NGC 6440) he noted: «Considerably bright, round, very gradually much brighter in the middle, about 1.5' diameter.» For II 586 (NGC 6445) he noted: «pretty bright, small, irregular faint.» [464]

Planetary Nebula NGC 6445

NGC 6445
NGC 6445: Section of PanSTARRS1 DR1 color [147]

NGC 6445 is a bipolar planetary nebula. Distances range from 1.38 kpc [153] to 2.5 kpc [141]. Surrounding the nebula is a fine halo, whose filaments are visible far out on H-II images. [152]

NGC 6445 is sometimes called the «Little Gem Nebula», a name also used for the planetary nebula NGC 6818. The name «Crescent Nebula» is also sometimes encountered, but this name is more common for the galactic nebulaNGC 6888. One can also find «Box Nebula» for this, but NGC 6309 is more commonly known by this name.

«Strasbourg-ESO Catalogue of Galactic Planetary Nebulae» Acker et al., 1992 [141]
DesignationsPN G008.0+03.9: NGC 6445, PK 8+03.1, ARO 67, He 2- 290, Sa 2-248, ESO 589-09, VV 118, VV' 260
Right Ascension (J2000.0)17h 49m 16s
Declination (J2000.0)-20° 00' 35"
Dimensions 33." (optical), > 34." (radio)
Distance 2.5 kpc
Radial Velocity+16.2 km/s ± 0.5 km/s
Expansion Velocity 38.0 km/s (O-III)
C-Star DesignationsAG82 266, CSI -20 -17462, HD 161944
C-Star Magnitude19.04 mag (B filter), 19.00 mag (V filter)
C-Star Spectral TypeContin.
DiscovererPICKERING 1882

Globular Cluster NGC 6440

NGC 6440
NGC 6440: Section of PanSTARRS1 DR1 color [147]

According to Simbad, NGC 6440 is moving towards us at 69 km/s. A distance measurement is not given. [145]

«Revised NGC/IC», «Historic NGC/IC», Version 2022-09-01, © Dr. Wolfgang Steinicke [277]
DesignationNGC 6440
TypeGCL (V)
Right Ascension17h 48m 52.6s
Declination-20° 21' 32"
Diameter4.4 arcmin
Visual magnitude9.3 mag
Metric Distance8.500 Mpc
Dreyer DescriptionpB, pL, R, bM
Identification, RemarksGCL 77, ESO 589-SC8

Finder Chart

The open star cluster M 23 in the Sagittarius constellation leads directly to the planetary nebula NGC 6445. The southern globular star cluster NGC 6440 also serves as a further search aid. The sought-after planetary nebula is located directly west of a mag 7.5 star.

Sagittarius: NGC 6440, NGC 6445
Chart NGC 6440, NGC 6445
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

Visual Observation

NGC 6445
NGC 6445: Pencil drawing; 14" PWO-Dobson f/4.6, TV-Nagler-Zoom 6 mm, 267x, 0.19°; Honegg 1460 m; © 30. 7. 2003, 00:15 Eduard von Bergen

350 mm aperture: A fine circle surrounds the planetary nebula NGC 6445. The cap-shaped bright spots in the north and south of the nebula are striking. The nebula smolders delicately in its inner region. It is advantageous to use a relatively high magnification, greater than 200x, so that the shape of the planetary nebula is also fully revealed. [192]

14" PWO-Dobson, F:4.6 / TV-Nagler-Zoom 6mm, 266x, 0.19°,
Eduard von Bergen

References

141Strasbourg-ESO Catalogue of Galactic Planetary Nebulae; A. Acker, F. Ochsenbein, B. Stenholm, R. Tylenda, J. Marcout, C. Schohn; European Southern Observatory; ISBN 3-923524-41-2 (1992); cdsarc.unistra.fr/viz-bin/cat/V/84 (2021-02-18)
145SIMBAD astronomical database; simbad.u-strasbg.fr/simbad
147Aladin Lite; aladin.u-strasbg.fr/AladinLite (2020-12-23)
149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
152«Extended Structures of Planetary Nebulae Detected in H2 Emission»; Xuan Fang, Yong Zhang, Sun Kwok, Chih-Hao Hsia, Wayne Chau, Gerardo Ramos-Larios, Martin A. Guerrero; arXiv:1804.08840; DOI:10.3847/1538-4357/aac01e
153«The Magellanic Cloud Calibration of the Galactic Planetary Nebula Distance Scale» Letizia Stanghellini, Richard A. Shaw, and Eva Villaver; The Astrophysical Journal, Volume 689, Number 1, 2008; DOI:10.1086/592395
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form
192Deep-Sky Guide; fernrohr.ch/1d_deep-sky-guide.html (2020-12-25)
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; klima-luft.de/steinicke (2021-02-17)
464«Catalogue of a second thousand of new nebulae and clusters of stars; with a few introductory remarks on the construction of the heavens» William Herschel, Philosophical Transactions of the Royal Society of London, 1 January 1789; DOI:10.1098/rstl.1789.0021