#1  
Old 22-11-2011, 05:49 PM
SteveG (Steve)
Registered User

SteveG is offline
 
Join Date: Jan 2010
Location: Berkeley, CA, USA
Posts: 39
Observations with a 48-inch dob (part 1)

During the October new moon window, I had the opportunity to observe for 5 nights with Jimi Lowrey and Jim Chandler at Fort Davis, Texas using Jimi's 48-inch f/4.0 dobsonian, certainly one of the largest amateur telescopes in the world. For those interested in the construction, see this article). Needless to say, a tremendous amount of structure in galaxies is visible in a scope this size.

Although we spent most of the time hunting down more obscure objects, it's always fun to check out big, bright stuff with such a large aperture. I took notes on 200 objects but here are many of the brighter objects we observed. (I'll post the more exotic objects later).

NGC 520
01 24 34.4 +03 47 42
V = 11.4; Size 4.5'x1.8'; Surf Br = 13.6; PA = 130d

The view of this very bright, highly irregular, disrupted galaxy was fascinating at 488x. The most prominent feature is a very high surface brightness curving "bar" oriented NW-SE, bending out in the middle towards the southwest, and fading out on the SE end with a faint extension. The total length of the banana-shaped bar is close to 2.5'. The brightest part is at the NW end, where there is a large, bright knot, 24" diameter that increases to the center. This knot is referred to as the northern nucleus in a 2007 paper (AJ, 134, 212) by Rossa et al. The edge of the bar is very well defined along the north side.At the SE end of the main bar, the brightness dims sharply but a much fainter hazy glow continues further SE and spreads out.

On the south side is a fairly bright, elongated section oriented WNW-ESE, that is separated from the northern "bar" by a prominent, irregular dark lane running NW to SE, paralleling the bar in the central region. A slightly brighter "knot" is located is the middle of the southern section. According to the Rossa paper, the dust lane just north of this knot optically obscures the southern nucleus. At the southeast end, the glow dims rapidly and fans out further southeast.
------------

M74
01 36 41.6 +15 47 03
V = 9.4; Size 10.5'x9.5'; Surf Br = 14.2

Beautiful face-on spiral with long, graceful arms wrapping around an intense 1' core that increases towards the center, but there is no sharp nucleus. At first glance at 375x there appeared to be four arms, but with a more careful look there are two main arms that each wrap more than 360 around the core as well as a couple of side branches. Each arm is studded with a number of non-stellar HII regions that highlight the arms. In addition, a number of stars are superimposed, both in the inner region (two faint stars are within 25" of the center) and around the edge of the halo, which extends to 7'-8' diameter.

The more prominent arm "southern" arm is very regular - emerging from the core on the south side and wrapping counterclockwise around the core to the north, unwinding gradually as it curves to the east and then pulls away from the central region more suddenly on the south side. This arm is very patchy and delineated by a large number of HII knots with the two most prominent ones near the outer southern end. The "northern" arm begins to emerge from north of the core, tightly wraps counterclockwise around the core, passing near or through a few superimposed stars on the south side of the core, unwinding more as it stretches again to the north. The arm structure is a bit more complex on the north side due to side branches and the embedded HII knots are more scattered.

The HII regions were viewed more carefully at 610x. The following identifications are from Paul Hodge's 1976 "HII regions in NGC 628" (ApJ, 205, 728), which lists over 700 HII knots. The brightest is #627, near the end of the outer southern arm 2.7' SSW of center. It appeared fairly bright, fairly small, round, ~20" diameter. Moving clockwise along this arm towards the core, the next prominent knot is #598 situated 2.2' SSE of center. It was slightly fainter than #627, round, 15" diameter. Next in line is #522, a faint round knot of 10" situated 1.8' SE of center. East of the core by 1.5' is #406, a very faint, round 10" knot situated 36" S of a superimposed mag 14.5 star. Just 30" W of this star and 1.2' NE of center is #292, a fairly faint, very small knot, ~8" diameter. Continuing inward along this arm, the next knot is #196, a very faint hazy knot 1.6' N of center. Finally, less than 1' NW of center is another very faint patch with Hodge numbers #260-268.

There were no notable knots on the inner southern portion of the northern arm, but a noticeable clump of knots is on the NW portion of this arm. First was #167, a faint 10" knot 1.6' NW of center. Continuing outward 2.0' NNW of center is a faint, elongated patch, ~25" diameter, consisting of #91-95 and #49 at the north end of the glow. I didn't search the outer region of the halo for additional HII knots, except noted #330, a 10" knot situated between two mag 12-13 stars at the eastern edge of halo, 8' from center.
------------

NGC 660
01 43 01.7 +13 38 35
V = 11.2; Size 8.3'x3.2'; Surf Br = 14.6; PA = 170d

This large, striking galaxy contains a very bright, elongated bar oriented SW-NE, ~2'x1'. The northeastern half of the bar is noticeably brighter with a very high surface brightness. The galaxy is fainter and wider on the SW portion of the bar. The central region in mottled and dusty, but I didn't notice the X-shaped dust lanes visible on photos. At the SW end, a broad low surface brightness spiral arm emerges and sweeps south, curving slightly east for a length of 2'. A second faint arm begins at the NE end of the bar and extends north a similar distance, bending gradually to the west. The arms give the galaxy a stretched "S" appearance and significantly increase the overall size to ~6.5'x2.5', roughly N-S.
------------

NGC 891
02 22 33.4 +42 21 03
V = 9.9; Size 13.5'x2.5'; Surf Br = 13.6; PA = 22d

This edge-on galaxy at 375x was one of the top highlights of the observing week with the 48". The galaxy nearly filled the 16' field, stretching nearly 12' by 2' SSW-NNE. A 17th magnitude star superimposed close to the NNE tip and an mag 16.5 star is near the SSW end. The brighter, bulging central region extends 2.5' with a mag 12 star just north of the core on the west side. A similar star is superimposed on the southern extension along with a few fainter stars. A very high contrast dust lane slices through most of the galaxy excepts at the tips, where the galaxy fades out. I was surprised how broad the dust lane appeared, particularly through the central section. Although the dust lane perfectly bisects the galaxy into two symmetric halves, the edge of the lane was ragged and uneven. MAC 0222+4222 = ZOAG G140.39-17.38 was just visible off the east edge, a bit north of the central region. It appeared as an extremely faint, elongated glow, ~15"x8".
------------

NGC 1023
02 40 23.8 +39 03 48
V = 9.4; Size 8.7'x3.0'; Surf Br = 12.8; PA = 87d

This stunner appeared extremely bright, very elongated 4:1 E-W, ~7'x1.8', with a large, brighter central core that increases to an intensely bright inner core punctuated by a bright stellar nucleus. The outer halo gradually fades at the ends of the extensions. Several stars are superimposed on both sides of the core.

NGC 1023A, a low surface brightness dwarf companion, is superimposed on the east side (2.4' ESE of center). It appeared as a faint, fairly large, low surface brightness patch oriented SSW-NNE, roughly 1.2'x0.8', and it blends into the main galaxy. Although most of the companion is within the halo of NGC 1023, part of it juts out the southeast edge of the galaxy. The halo of NGC 1023 extends beyond (east) of the dwarf.
------------

NGC 1032
02 39 23.6 +01 05 37
V = 11.6; Size 3.3'x1.1'; Surf Br = 12.9; PA = 68d

At 385x and 488x appears very bright, large, very elongated 4:1 WSW-ENE, 3.0'x0.8'. Well concentrated with a prominent, bulging oval core that brightens towards the center and long, thin, fainter tapering extensions that dim at the tips. A mag 13 star is at the tip of the ENE extension. The visual treat, though, is a razor thin dust lane that clearly bisects the large central buge. As the much fainter extensions start to taper down, the dust lane loses contrast and disappears towards the ends.
------------

M77
02 42 40.3 -00 00 48
V = 8.9; Size 7.1'x6.0'; Surf Br = 12.8; PA = 70d

This was by far the best view I've had of M77. Spiral arm structure was easily visible with two main outer arms and a bright inner arm. The bright inner arm attaches at the east side of the intense core and wraps tightly clockwise around the north side of the core and heads south on the west side of the core. There are two main arms in the halo forming an elongated "S" pattern. A long spiral arm is attached near the east side of the core and wraps outside the inner arm described above. It continues around to the west side and heads south, ending near an compact HII knot (listed in NED as [H66] 6 from Paul Hodge's 1996 "Atlas and Catalog of HII Regions in Galaxies"). A second long spiral arm is attached on the southwest side of the core and wraps clockwise to the east side of the core and extends to the northern edge of the halo. Besides these main arms, several fainter pieces of arms are tightly wrapped in the halo.
------------

NGC 1253
03 14 09.1 -02 49 22
V = 11.7; Size 5.2'x2.3'; Surf Br = 14.3; PA = 82d

Very bright, very large, elongated ~5:2 WSW-ENE, ~4'x1.6'. Contains a large, very bright elongated core that gradually increases to the center. A mag 12.5 star is superimposed just SW of the central region. A spiral arm emerges from the galaxy on the ENE end and curls sharply clockwise towards the SW and quickly dimming. The arm appears patchy with a couple of small knots near the outer edge (~1.6' from center). The arm on the west end is harder to make out as it emerges from the central region near the superimposed star and is not as well defined, appearing more as a hazy, mottled region with some brighter patches. A mag 12 star lies 3' ENE and just beyond the star is N1253, a low surface brightness dwarf. N1253A appeared fairly faint, large, irregular, roughly oval 3:2 E-W, 1.2'x0.8', small brighter core, very patchy appearance (contains HII knots). The nearby mag 12 star is just off the SW side.
------------

NGC 1300
03 19 41.0 -19 24 40
V = 10.4; Size 6.2'x4.1'; Surf Br = 13.8; PA = 106d

This prototype barred spiral was mesmerizing at 375x. Running roughly E-W through the center is a long bright bar, ~3' in length. The center is sharply concentrated with an intensely bright 1' core that continues to increase to a stellar nucleus. At the west end of the bar a fairly bright arm emerges and hooks back dramatically to the east (counterclockwise) to the north of the bar and continues to the NE end of the galaxy. The arm is brightest in the thick arc, oriented SW-NE, where is attaches to the bar. The central section of the bar to the north of the core is slightly fainter and then brightens slightly on the NE end of the galaxy. A mag 15.5-16 star is superimposed in the gap between this arm and the core, 45" NE of center. The second arm emerges at the east end of the bar and is brightest initially in a fairly thick arc extending counterclockwise to the SW. This arm is slightly more separated from the core as it gracefully curves to the southwest side of the galaxy. The arms extend the overall size of the galaxy to 5'x3' WNW-ESE.

Steve Gottlieb
Reply With Quote
  #2  
Old 22-11-2011, 09:12 PM
Paddy's Avatar
Paddy (Patrick)
Canis Minor

Paddy is offline
 
Join Date: Jun 2007
Location: Strangways, Vic
Posts: 2,207
Oh, Steve, what a report, what those galaxies must have looked like through a 48" scope. Your descriptions are so vivid! I can't get my head around the level of detail especially in naming the HII regions of M74. Off to read part 2 now!
Reply With Quote
  #3  
Old 24-11-2011, 04:21 AM
SteveG (Steve)
Registered User

SteveG is offline
 
Join Date: Jan 2010
Location: Berkeley, CA, USA
Posts: 39
Thanks, Paddy. I ran across all of the HII designations when I searched in NED for NGC 628 (using extended names) and pulled up nearly 740 HII regions! Using the original journal paper I was able to match up the ones that I logged with the 48-inch.
Reply With Quote
  #4  
Old 24-11-2011, 05:35 AM
SkyViking's Avatar
SkyViking (Rolf)
Registered User

SkyViking is offline
 
Join Date: Aug 2009
Location: Waitakere Ranges, New Zealand
Posts: 2,260
Wow, what an experience it must be to look through such a scope! I really liked your detailed descriptions, thanks for sharing this.
Reply With Quote
Reply

Bookmarks

Thread Tools
Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT +10. The time is now 07:54 PM.

Powered by vBulletin Version 3.8.7 | Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.
Advertisement
OzScopes Authorised Dealer
Advertisement
Lunatico Astronomical
Advertisement
Meade Australia
Advertisement
Celestron Australia
Advertisement
SkyWatcher Australia
Advertisement
NexDome Observatories
Advertisement
Bintel
Advertisement
Astronomy and Electronics Centre
Advertisement