M 38, NGC 1907 and Abell 9

Messier 38, NGC 1907
Messier 38, NGC 1907: Open clusters. Section of the STScI Digitized Sky Survey [147]

Open Cluster M 38

The open star cluster Messier 38 was discovered by Le Gentil in 1749. It is a loose and irregular cluster with a relatively empty center. The brightest stars form the shape of a crooked cross or the somewhat clumsily written Greek letter π. The diameter is about 21 minutes of arc and the cluster contains well over 100 stars. The distance to M 38 is about 4200 light years, which results in a true diameter of the cluster of around 25 light years. A value that is comparable to that of M 37.

The earliest member stars are giants of the spectral class B5 with an absolute magnitude of around -1.5 mag. The cluster also contains a number of A-type main sequence stars and some G-type giants. The brightest star in the cluster is a yellow G0 giant with a visual magnitude of 7.9 mag, which is about 900 times the luminosity of the sun. The sun at the same distance would appear to us to be about 15.3 magnitudes bright. [4]

«Revised New General Catalogue and Index Catalogue» Dr. Wolfgang Steinicke, 2021 [277]
DesignationNGC 1912
TypeOCL (II2r)
Right Ascension05h 28m 43.0s
Declination+35° 51' 18"
Diameter15.00 arcmin
Visual magnitude6.4 mag
Dreyer DescriptionCl, B, vL, vRi, iF, st L & S
IdentificationM 38, OCL 433

Open Cluster NGC 1907

NGC 1907 is a small open star cluster about 35 arc minutes southwest of M 38. John L. E. Dreyer described it as a round, crowded cluster, fairly rich in stars from 9 to 12 magnitudes. [142]

«Revised New General Catalogue and Index Catalogue» Dr. Wolfgang Steinicke, 2021 [277]
DesignationNGC 1907
TypeOCL (II1m)
Right Ascension05h 28m 04.5s
Declination+35° 19' 32"
Diameter5.00 arcmin
Visual magnitude8.2 mag
Dreyer DescriptionCl, pRi, pC, R, st 9…12
IdentificationOCL 434

Planetary Nebula Abell 9

Abell 9
Abell 9: Section of the STScI DSS, 2nd Generation Survey [147]

Abell 9 is an often overlooked planetary nebula, although it is only about 12 arc minutes north of M 38. At 37 arc seconds, the angular diameter is smaller than that of Jupiter. The photographic brightness is given as 18.9 magnitudes. The central star is 23.5 magnitudes weak. Distances vary from 37'000 to 51'000 light years.

Some are not yet sure whether Abell 9 is really a planetary nebula, because it is listed as a possible PN in the 1992 edition of the Strasbourg-ESO Catalog of Galactic Planetary Nebulae [141]. The post-processed section from the STScI Digitized Sky Survey (Fig. 3) shows a PN-typical appearance. The object is also known under the names VV 31 (Vorontsov-Velyaminov) and ARO 122 (Algonquin Radio Observatory).

The planetary nebula Abell 9 represents a difficult object and lies beyond the range that can be visually recognized by amateur astronomers, but it should represent an interesting test object for CCD images. It can hardly be seen on the DSS section.

Further infos at CDS: PN A66 9

Typ   : Planetary Nebula:
Name  : Abell 9, PK 172+0.1, VV 31, ARO 122
R.A.  : 05h 29m 00s
Dec.  : +36° 02' 00"
Diam. : 37"
p Mag.: > 18.9m
v Mag.: .
* Mag.: 23.5m

Finder Chart

The open star cluster Messier 38 is located in the constellation Auriga (Charioteer) and is best visible in the winter months. Connect the two stars θ Aurigae (2.62 mag) and ι Aurigae (2.69 mag). Messier 38 is about halfway between the two stars, slightly inward, so that the smallest Telrad circle comes to lie on the connecting line.

Chart Messier 38
Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

References

4«Burnham's Celestial Handbook: An Observer's Guide to the Universe Beyond the Solar System» by Robert Burnham; Dover Publications, Inc.; Voume I: ISBN 0-486-23567-X; Volume II: ISBN 0-486-23568-8; Volume III: ISBN 0-486-23673-0
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)
142NGC 2000.0, The Complete New General Catalogue and Index Catalogue of Nebulae and Star Clusters by J.L.E. Dreyer; edited by Roger W. Sinnott; Sky Publishing Corporation and Cambridge University Press (1988); cdsarc.unistra.fr/viz-bin/cat/VII/118 (2021-02-18)
147Aladin Lite; aladin.u-strasbg.fr/AladinLite (2020-12-23)
149SkySafari 6 Pro, Simulation Curriculum; skysafariastronomy.com
160The STScI Digitized Sky Survey; archive.stsci.edu/cgi-bin/dss_form
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; klima-luft.de/steinicke (2021-02-17)