OR: April observing with a 48-inch in Texas (Part III)
by Steve Gottlieb
|
This is the last installment of my observing notes made
in April using Jimi Lowrey's 48-inch super-sized dob, along with Howard
Banich. I've included a wide mix of objects -- a protoplanetary, a gravitationally
lensed quasar, interacting galaxies, a compact quartet of compact galaxies
and a couple of spiral galaxies. We alternated our observing between
dim and challenging objects and bright showpieces. They're all awesome
through this scope! -- Steve Gottlieb |
 Frosty Leo Nebula = IRAS 09371+1212 09 39 54.0 +11 58 53 Size: 15"x10" In 1987, Forveille and collegues dubbed IRAS 09371+1212 as the "Frosty Leo Nebula" as since water is largely depleted in its gaseous state by ice condensation into grains (ice crystals). The discovery story is at http://adsabs.harvard.edu/abs/1987A%26A...176L..13F At 375x, 697x and 813x (unfiltered); two very small
knots (roughly 6" each) were easily resolved oriented NNW-SSE
with a small gap between and a length of ~15". The south-southeast
knot was slightly brighter as well as slightly irregular and elongated
90° with respect to the orientation of the knots (i.e. WSW-ENE).
The north-northwest knot was also somewhat oval or irregular in shape.
A thin halo connected the two lobes. A roughly oval appendage extended
north-northwest from the north-northwest knot and an extremely faint
stellar brightening was at its tip. I didn't notice a similar extension
on the SSE end, though on images it brings the total length to ~25". French astronomer Stephane Javelle discovered IC 803 visually on 25 Apr 1893 using the 30-inch f/23 refractor at the Nice Observatory in southern France. Halton Arp catalogued it as the first member in the Arp category "Galaxies with Jets". Clearly this is a distorted interacting system on the Sloan Digital Sky Survey. At 488x and 697x; the core of the eastern component appeared fairly faint, small, round. A very faint, thin spike (tidal plume or jet) extends ~15" SE. Occasionally a second, very faint stubby tidal tail extends ~10" north-northwest . The entire length of this chaotic galaxy is ~30". The nucleus of the western component is just 25"
W. It was moderately bright but appeared stellar. At 697x, A very
low surface brightness, very small halo was visible, but the tidal
plume or jet extending southwest was not seen.
M100 is one of the largest and brightest spirals in the Virgo cluster. It was the fist Virgo cluster galaxy in which the HST observed Cepheid variables (1993) and derived a distance of 55 million light years (since revised to ~50 million light years). Spiral structure was first seen by Lord Rosse using his 72" Leviathan in 1850. We had a stunning view of this gorgeous spiral at 375x and 488x. M100 is sharply concentrated with an intensely bright circular nucleus. Two prominent, high contrast arms (fairly narrow) each rotate ~270° and can be clearly traced to within 1' of the center. The south and north outer tips of the arms are between 5.5'-6' apart with the overall size ~6'x5'. One arm begins off the WNW side of the core with a bright mottled section angling nearly north-south for ~25". This section contains multiple HII sites NGC 4321:[HK83]220/223/229/230 from Hodge and Kennicutt's 1983 "An Atlas of H II regions in 125 galaxies". The arm curls clockwise around the south side. A small (~8" dia.) HII knot (#160/171/172) is within this arm, 1.0' S of center. Just to the east [1.5' SE of center] is a brighter, mottled section that contains a close pair [18" separation] of compact HII knots (#110 and #69/87). The surface brightness of the arm abruptly drops as it shoots due north on the east side of the halo for ~3'. The arm dims further as it curves west on the northeast side of the outer halo and ends just southeast of mag 15 star situated 2.9' NNW of center. The second arms begins ~1' SE of center with a thicker, much brighter region. The Hodge-Kennicutt Atlas catalogues numerous HII designations in this region, but none stood out individually. The arm sharply abruptly narrows and rotates clockwise around the north side of the core towards the west. It passes just south of two mag 15.5 stars, where there is a slightly brighter mottled section containing HII regions #252/253. The arm dims significantly as it heads south on the west side of the halo. Finally, it weakens further and spreads out at the end on the southwest side of the galaxy [2.6' from center].
I made another short observation of this remarkable asymmetric edge-on at 375x and 488x before observing the Twin Quasars, which lie 14' NNW. The brightest portions of this 6:1 edge-on NNW-SSE is warped and bowed out in the very bright central section towards the east. An intense nucleus is within this central section, though offset to the east of center. The west side of the central section is irregular in surface brightness due to dust. The northern extention thins and has a slight bend on the north end, beyond a mag 14 star. On the southwest side is a bright streak, but to the east of this streak and further south the galaxy is dusty and sections of the galaxy appear to be highly obscured. Two mag 14 stars are off the west side of the galaxy and mag 9.6 HD 237858 is 3.5' SE of center. Twin Quasars Both mag 16.7/16.9 components easily visible nearly continuously at 697x. The southern component was clearly slightly brighter, although the delta mag is only 0.2. At 6" separation, the pair is relatively widely split at this magnification.
This member of HCG 44 was missed by both Herschels and
discovered at Birr Castle in 1850, along with NGC 3187. At 610x it
appeared very bright, fairly large, oval halo 5:3 NW-SE, ~1.8'x1.1'.
Strongly concentrated with a very bright roundish core which increases
to a slightly brighter stellar nucleus. The halo has a brighter arcs
at the ends of the major axis (northwest and southeast ends) and is
slightly weaker inside, creating a weak ring. A very weak bar is highly
suspected connecting the ends of the major axis and the core, creating
a very subtle barred ring. A mag 14.5 star is just off the west side
[42" from center].
At 488x this late spiral (type SABcd) appeared very
bright, very large, elongated 3:1 WSW-ENE, 5'x1.5'. Well concentrated
with a large bright oval core that gradually increases to a small
bright nucleus and stellar pip. The region surrounding the core is
mottled, due to slightly brighter regions and dust patches. An ill
defined broad spiral arm is on the west side of galaxy, curving from
north to south. A mag 14 star, 2.0' SW of center, is barely off the
southwest end of this arm. A bright patch is 1' SW of center (not
part of the arm), and just to its north is a relatively large darker
(dust) region. A second broad arm arc is visible at the east end of
the galaxy making a sharp curve clockwise, and passing just inside
a mag 13 star at the eastern tip. NGC 3513, which was described in
Part II, lies 11' SE.
This quartet is squeezed into less than 2' of sky! The group is located 36' south of NGC 4124 and has a light travel time of ~920 million years. The Rose letter designations (given in NED) are from the 1996 paper "Morphology of early-type galaxies in compact groups. IV. Rose groups" in A&AS, 118, 429. MCG +02-31-032 = Rose 9b is the first in this very compact quartet and appeared moderately bright, small, round, very small bright core, 12" diameter. MCG +02-31-033 = Rose 9a, the southern component of a double system (UGC 7114), is also moderately bright, small, slightly elongated NW-SE, ~18"x14", very small bright nucleus. MCG +02-31-034 = Rose 9c, just 28" N, is fairly faint, small, round, low even surface brightness, 12" diameter. Two mag 16.6/16/7 stars 1.5' and 1.9' N are exactly collinear with the UGC 7114 pair. MCG +02-31-035 = Rose 9d, the northeast component, is fairly faint, small, round, 12" diameter, low surface brightness. A mag 16.8 star is 27" NW. |
