Observations from April New Moon (48")

[Steve Gottlieb]

In early April, Howard Banich and I observed 4 nights with Jimi's 48-inch f/4, along with Jim Chandler on the last night. In a series of posts, I'll highlight some of the showpiece galaxies we observed, along with some of the obscure, challenging stuff.

The first target is 10th-magnitude NGC 4559, which was discovered by William Herschel on 11 Apr 1785 and described as "vB vL, mE np sf, 10 or 12' long, four stars in it." John Herschel made three observations and logged "vL; gbM, but not to a nucleus; mE; has 3 stars south following. By a diagram, the southern end is broader than the norther, giving it a clubbed appeared."

Although NGC 4559 was observed twice at Birr Castle with the 72-inch, I'm surprised Bindon Stoney (observing assistant) didn't comment on any non-stellar knots. These were first catalogued by Max Wolf from a Heidelberg plate in 1903. IC 3550-52, IC 3555, and IC 3563-64 refer to HII regions and/or star clouds within the arms of NGC 4559 and IC 3554 is a star, which Wolf thought might be nebulous.

At 375x this showpiece galaxy extended 3:1 NW-SE, 9'x3' with a large bright core that gradually increased to the center. The core appeared irregular, mottled and dusty. The inner portion of the disc revealed weak spiral structure. At 488x, the outer halo was very patchy with several knots. Superimposed on the southeast side are three mag 12/12.5/13 stars between 1.5'-2' from center and the galaxy faded out rapidly beyond these stars to the southeast. Near the southeast end is IC 3563, a very compact HII region and IC 3564, a star association attached on the east side. Both objects were easily visible, but not resolved, as a fairly faint 20" patch, 3' SE of center.

The outer halo faded out gradually and extends much further on the northwest side, extending up to 5' NW of center. IC 3555 is faint, 20"x10" HII region, extended NW-SE, and situated 1.8' NNW of center in the halo. IC 3552, a smaller HII region close NW, was not seen. IC 3551 is faint, 10" HII knot on the west edge, 0.9' WNW of center. IC 3554 is a mag 15 star 2.1' SSW of center (at the edge of the visible disc) and IC 3550 = NGC 4559C was seen as a faint, 8" knot, that appears as a small, detached HII knot 0.8' WNW of the star.

I'm curious if others have looked for these HII regions and what have been the results?

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[Howard B]

Before getting to my observation of NGC 4559 made at the same time as Steve's on Jimi's 48 inch, I just have to comment that Steve is a master at taking high quality, detailed and accurate notes quickly. I'm impressed by how well prepared he was for each observation and his ability to maximize the relatively short amount of eyepiece time we each had, at least in contrast to when we have our own scopes to observe with. Group observing has a different pace, and when observing with Jimi and his fantastic scope it pays to be quick and accurate.

I was not as well prepared as Steve but made a quick sketch of most of the objects we observed from memory after coming down The Ladder. We generally got two or three turns per object but even so the pace was brisk and exciting. Sketching from memory is a new experience for me, and although the results turned out fairly well on most objects it does leave me itching for more. So my sketch of 4559 should be considered a quick impression rather than a rendering of all that was seen, as it obviously lacks the detail of Steve's terrific description.

It looks like I saw IC 3550 and 3551 and the 3563/3564 pair. The three stars arcing across the galaxy along with a fourth one near IC 3550 made the biggest visual impression with 3551 being the most prominent HII region in the galaxy - it caught my attention right away.

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My notes read:

"Disturbed shape with a broad tidal tail and two detached areas or companion galaxies (IC 3550 and 3563/3564). Several bright knots along with an elongated core give this galaxy a lumpy texture. 488x, 21.55 SQM"

By the way, I think Jimi's ladder should be referred to as The Ladder because it simply demands respect.

[Dragan]

Howard,

Its quite a feeling when Barbarella is pointing up anywhere near Dobs Hole. "The Ladder" is quite intimidating at that altitude. (And I mean altitude in the sense airplanes use altitudes, not declination of a telescope ;))

[Uwe Glahn]

Steve,

these HII knots really are obvious even with smaller aperture than 48". Thanks for posting that, NGC 4559 is a typically overlooked object because of its more famous neighborhood.

I could pick up some HII regions with my old 16". They were easy to detect and a remember the galaxy as a "fat pimply mite".

And yes, it is surprising, that Stoney did not mention the HII regions, especially because of the "red" regions and the relatively "red sensitive" mirror. I could only give account of it, that he saw these regions as stellar spots and described them also as "some stars involved", similar to for example the regions in M 51 or NGC 4485.

16", 257x, Seeing III, NELM 6m5+
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[Paul Alsing]

Its quite a feeling when Barbarella is pointing up anywhere near Dobs Hole. "The Ladder" is quite intimidating at that altitude. (And I mean altitude in the sense airplanes use altitudes, not declination of a telescope ;))

Watching Jimi scoot up and down that ladder is worth the price of admission, what a treat.

When Barbarella is pointing nearly straight up, the top of the ladder is hitting my upper thighs... not sure I could do it during the day, but I have the night-time mastered ;>) I calculate that my head is about 19 feet above the floor... looking forward to giving it another go...

[Steve Gottlieb]

Steve,

these HII knots really are obvious even with smaller aperture than 48". Thanks for posting that, NGC 4559 is a typically overlooked object because of its more famous neighborhood.

I could pick up some HII regions with my old 16". They were easy to detect and a remember the galaxy as a "fat pimply mite".

Excellent sketch, Uwe! I had made a single observation with my old 17.5" and only recorded "the overall surface brightness is noticeably irregular with hints of brighter and darker spots", but I didn't try to sketch or identify these "brighter" IC HII knots. I certainly plan to give it another try with my current 18" or 24".

[Ivan Maly]

Last night I observed NGC 4559 with my 16" under fine if unexceptional conditions at our remote dark site. The star IC 3554 was visible. The HII region IC 3550 was a very faint, amorphous glow with an indistinct outline and no concentration. The star association IC 3564, undoubtedly combined with the HII region IC 3563, was larger, but similarly amorphous and faint. Neither of these spots would be noticeable without knowing exactly where to look. The HII regions IC 3555 and 3551 flank a brighter anonymous star cloud on the NW edge of the galaxy's core. All three could be held at the same time, and the view reminded me of tightly packed nebulae and unresolved star clusters in the LMC as seen through a small scope. These three patches had definite outlines and exhibited concentration toward their centers, especially IC 3551. The small HII region IC 3552 NW of IC 3555 remained invisible. Much farther to the NW was a visually detached star cloud. Although comparatively faint, it was the only immediately noticeable feature in the galaxy after the inner core.

North up, west right. 16". 300x with ZAOII-6. SQM-L 21.89 at zenith, CBe near zenith. Object types according to NED. Observation time 1 h over 2 hrs.

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I thank the originator and participants of this thread for motivating me to undertake this observation.