Sky Sketcher's Post Mortem 2

SKY SKETCHERS POST MORTEM

By: Scott Mellish

Messier objects.

Charles Messier (26 June 1730 – 12 April 1817) was a French astronomer most notable for publishing an astronomical catalogue consisting of deep sky objects such as nebulae and star clusters that came to be known as the 110 ‘Messier objects’. The purpose of the catalogue was to help astronomical observers, in particular comet hunters such as himself, distinguish between permanent and transient objects in the sky.

With this Post Mortem we will look at three Messier objects from the constellation of Virgo.

Messier 90

NGC 4569

Virgo

R.A 12 36 49.9 DEC +13 09 45

Discovered 1781 by Charles Messier. Messier 90 is one of the brighter spiral galaxies situated in the Virgo Cluster of Galaxies. Spiral galaxy M90 is one of the eight galaxies found and cataloged on March 18, 1781 by Charles Messier in the Coma-Virgo region, in addition to M92, the Hercules globular, to round up score to nine newly cataloged objects on that day.

M90 is one of the larger spirals in the Virgo Cluster of Galaxies. It has tightly wounded, smooth bright spiral arms, which appear to be completely "fossil", meaning that currently no star formation appears to take place, with the only exception of the inner disk region, near the darker dust lanes. J.D. Wray speculates that this galaxy may be on the way to evolve into a state similar to M64, and then into a lenticular (S0) system. Although M90 is conspicuous and big, Holmberg has derived quite a low value for its mass, which implies that this may be a very low density galaxy.

In my old 41 cm dob., this is a rather elegant galaxy at 210x magnification. A bright almost pinpoint core is punctuated by a faint central streak around 5’ in length. There is also a slight hint of some mottling present over the mostly smooth and soft halo.

Steve Gottlieb in the NGC/IC database describes NGC 4569 as follows:

“NGC 4569 = M90 = U07786 = MCG +02-32-155 = CGCG 070-192 = Arp 76 = PGC 42089

12 36 49.9 +13 09 44

V = 9.5; Size 9.5x4.4; SB = 13.4; PA = 23d

17.5": bright, large, very elongated 3:1 SSW-NNE, sharp concentration as suddenly increases to a bright stellar nucleus (possibly a superimposed star), fairly even surface brightness to halo. IC 3583 lies 6' NNW.”

M90 was included by Halton C. Arp in his Atlas of Peculiar Galaxies as No. 76 because it is a "Spiral with a High Surface Brightness Companion", 14-mag IC 3583, which is well visible in larger-field views of this galaxy such as the DSSM image of this galaxy, and appears somewhat distorted.

The spectrum of Messier 90 is blue shifted, which means that it is moving towards the Milky Way galaxy. This is not common as most of the more distant galaxies beyond the Local Group have spectra that are are redshifted. The blue shift was originally used to argue that Messier 90 was actually an object in the foreground of the Virgo Cluster.

However, since the phenomenon was limited mostly to galaxies in the same part of the sky as the Virgo Cluster, it occurred that this inference based on the blue shift was incorrect. Instead, the blue shift is thought to be evidence for the large range in velocities of objects within the Virgo Cluster itself. NGC 4569 is probably orbiting within the Virgo cluster at rate sufficient to overcome the Hubble velocity.

NGC 4569 is around mag 10.0 in brightness and some 10’ x 5’ in size.

Messier 89

NGC 4552

Virgo

R.A. 12 35 39.9 DEC +12 33 23

Messier 89 is another member of the Virgo Cluster of Galaxies. It is an exquisite example of a type E0 galaxy.

M89 is one of Charles Messier's own discoveries. He cataloged it on March 18, 1781, together with seven other newly discovered nebulae in the Coma-Virgo region, and globular cluster M92, to make this his most successful day of discoveries.

M89 is a large elliptical galaxy and almost exactly circular in shape. It appears to be smoothly textured. Whether or not it is actually of globular shape, or an oblate or prolate spheroid with the rotation axis directed to us, cannot currently be decided.

David Malin has investigated M89 by using deep photography back in the late 70’s with the UK Schmidt telescope. While this galaxy looks like the prototype of a normal E0 galaxy, and was merely known as only weak radio source, Malin's high sensitivity photographs revealed a faint enveloping structure, which is best visible to the northwestern and southern direction of the galaxy. Therefore, M89 was the first enveloped galaxy discovered, the envelope being extended to more than 150,000 light years from the galaxy. Moreover, a jetlike structure seems to extend to over 100,000 light years distance; this may be a smaller galaxy which is in process of being disrupted by the tidal gravitational force of M89 during an encounter.

Like most of the big elliptical galaxies it contains a vast number of globular clusters, current estimates put the tally at over 2000.

In the 41cm dob at 382x, the galaxy views as a bright compact core around 1.0’ x 1.0’ in size with a soft diffuse outer halo extending out to about 7.0’ x 7.0’ in size. It is not a particularly impressive object as it looks rather bland, but it is bright and would make a good backyard scope target from suburbia.

Another observing report appears below:

“NGC 4552 = M89 = U07760 = MCG +02-32-149 = CGCG 070-184 = PGC 41968

12 35 39.9 +12 33 20

V = 9.8; Size 5.1x4.7; SB = 13.2

17.5": very bright, irregularly round, fairly small but high surface brightness with an intense, very small bright core and substellar nucleus. Forms a pair with N4550/N4551 pair 20' S.”

by Steve Gottlieb

Messier 89 is at close to mag 10.0 in brightness making an object suitable for almost any sized telescope.

Messier 58

NGC 4579

Virgo

R.A.12 37 43.5 DEC+11 49 05

NGC 4579 is one of the four barred spiral galaxies in Messier's catalog although it is sometimes classified as intermediate between normal and barred spirals. It is one of the brightest galaxies in the Virgo cluster. Charles Messier discovered M58, together with the apparently nearby elliptical galaxies M59 and M60, on the occasion of following the comet of 1779, and cataloged it on April 15, 1779. M58 is one of the earliest recognized spiral galaxies, and listed by Lord Rosse as one of 14 "spiral nebulae" discovered to 1850.

Smaller telescopes show it to look very similar to an elliptical galaxy, and in the 41cm this is quite apparent showing mostly its bright nucleus with only a faint elongated outer halo giving its disguise away. Under good sky conditions, 4-inch or larger scope can show a halo of uneven brightness with condensations that seem to coincide with brighter areas of the spiral arms.

There have been two supernovae observed in M58 over the years, the first was a type II supernova designated 1988A, found by Ikeya on the 18th January 1988 some 40" south of the nucleus at mag 13.5. The other was a type I supernova designated 1989M, discovered by Kimeridze on the 28th June 28, 1989 and it reached mag 12.2 33"N, 44"W of M58's center.

In the 41cm dob at 382x, NGC 4579 views as rather bland in appearance with a soft oval core some surrounded by a faint slightly elongated outer halo extending out to about 6’ x 5’ in size. I was not all that enamored by the visual appearance of Messier 58, but as it is one of the brighter Virgo cluster members it is certainly worth a visit.

The galaxy has a visual mag of 10.0 with a surface brightness around 13.4. Lew Gramer on SEDS observed Messier 58 in a 20 inch at 70x from Deerfield Township, OH, USA, his report is as follows:

“The first glimmerings of dawn began to wash out detail in "faint fuzzies", leaving me just time for a cursory glance at lovely M58. At 70x, it appeared as a broad disc of faint light, only slightly elongated E-W. At the center was a condensed brightening set amid an inner halo, lying inside the fainter disc of the outer halo. Though rapidly washed out, a hint of darker mottling could definitely be seen near the SE "boundary" between these inner and outer halos. No spiral arms were in evidence tonight - again, merely an effect of twilight.”

Clear Skies.

References: Wikipedia, NGC/IC Database, SEDS.