Object of the Week March 15, 2020 – NGC 4559, H II Regions and the LBV
NGC 4559 UGC 07766 CGCG 159-024 CGCG 1233.4+2814 MCG +05-30-030
Constellation: Coma Berenices
Class: Mixed Spiral
Type: SAB(rs)cd
RA: 12h 36m 00.0s
DEC: +27° 58' 00"
Magnitude: 10.0v
Surface Brightness: 13.9
Size: 11.3’ x 5.0’
IC 3550 NGC4559C
Class: Emission Region
RA: 12h 35m 51.8s
DEC: +27° 55' 57"
Size: 0.45’ x 0.25’
IC 3551
Class: HII Emission Region
RA: 12h 35m 53.8s
DEC: +27° 57' 50"
Size: 18.0”
IC 3552
Class: HII Emission Region
RA: 12h 35m 54.0s
DEC: +27° 59' 36"
Size: 6.0”
IC 3553
Class: Star
RA: 12h 35m 55.9s
DEC: +26° 11' 42"
Mag: 16
IC 3554
Class: Star
RA: 12h 35m 55.2s
DEC: +27° 55' 39"
Mag: 16
IC 3555
Class: Emission Region
RA: 12h 35m 56.0s
DEC: +27° 59' 24"
Size: 18.0”
IC 3563
Class: Emission Region
RA: 12h 36m 07.1s
DEC: +27° 55' 36"
Size: 12.0”
IC 3564
Class: Star Cloud
RA: 12h 36m 08.0s
DEC: +27° 55' 40"
AT2016blu Gaia16ada PSN J12355230+2755559
Class: Supernova Imposter
Type: Luminous Blue Variable
RA: 12h 35m 52.3s
DEC: +27° 55' 55.9”
This week’s Object of the Week is located in the constellation of Coma Berenices. Although not an exceptionally large constellation it is the home of a number of well-known a deep sky objects, among them the Black Eye Galaxy (M64), M98, M99, M100, the globular cluster M53, the Needle Galaxy (NGC 4565) and the Coma Cluster of galaxies. It also contains the northern part of the Virgo cluster of galaxies.
Lost among this plethora of galaxies is the galaxy NGC 4559, this week’s Object of the Week. It is a remarkable example of a spiral galaxy system in an intermediate morphological class, mixed SAB(rs)cd1. This means that in shape NGC 4559 lies somewhere between a barred spiral and an un-barred one (SAB), whose inner arms form a ring that surrounds the needle-sharp nucleus (rs) while farther out the arms fly freely open (cd). Beyond these remarkable features, the keen-eyed observer with a large telescope will be able to see several H II emission regions, a star cloud, and an LBV all within NGC 4559.
NGC4559-1.jpeg
Before you give it a go, here are some observing tidbits and teasers, including one rare object.
- NGC 4559 was discovered by William Herschel on April 11, 1785 during sweep 396. He recorded it as: “Very bright, very large, much extended from north preceding south following from northwest to southeast 10’ or 12’ long, 4 stars in it.” In the New General Catalog the galaxy is described as: “Very bright, very large, much extended toward position angle 150°, gradually brighter in the middle, 3 stars following [to the east of the object].”
- NGC 4559 is easily located being 2° due north of NGC 4565 and 2° east-southeast of magnitude 4.3 Gamma Comae Berenices.
- Stephen O’Meara (Deep-Sky Companions: The Caldwell Objects) reports “that at 23x in a 4-inch refractor the galaxy looks obviously oval-shaped, with three 12.5 to 13.5 magnitude stars forming an arc on the galaxy’s southeastern edge. Another conspicuous star lies just beyond the galaxy’s northeastern flank. Increasing the magnification to 72x reveals NGC 4559’s oval core, which gradually brightens to a star-like center.”
- Sue French (Deep-Sky Wonders) writes: “NGC 4559 is very pretty through my 10-inch reflector at 192x and spans 6.5’ x 2.5’. Hazy wisps reach out toward the middle and easternmost of the three stars arcing across the galaxy. A fainter strand starting north of the galaxy’s center trends north-northwest. An elusive, star-like nucleus rests at the heart of NGC 4559, and brighter spots ornament the galaxy’s face.”
- Those “brighter spots that ornament the galaxy’s face” are H II emission regions (IC 3550, IC 3551, IC 3552, IC 3555), a star cloud (IC 3564), and stars (IC 3553, IC 3554).
ngc4559ic.jpg- Christian Luginbuhl and Brian Skiff (Observing Handbook and Catalogue of Deep-Sky Objects) call the galaxy "“impressive” even in a 6-inch telescope, which reveals two stars nearby to the east and south. A 12-inch telescope shows the galaxy 9’ x 2’ in pa 140°. There is little brightening to a very irregular core elongated in pa 130°. The core fades more abruptly on the southeastern end, and the halo is not as extensive to the southeast. Three stars are attending on the southeastern side: a magnitude 12 star on the northeastern flank directly east of center; a magnitude 13 star right on the major axis to the southeast; a magnitude 12.5 star on the southwestern flank. All three lie between 1.5’ and 2.0’ from the center.”
- With a 14” telescope at 125x George Kepple and Glen Sanner (The Night Sky Observers Guide Volume 2 Spring & Summer) call “NGC 4559, a pleasing sight, has a highly irregular 10’ x 4’ NNW-SSE halo with subtle dark streaks and a moderately brighter, highly extended core. The core seems off center to the SE, and the halo is not as extensive in that direction. With averted vision a dark patch can be seen just SE of the core. Three stars surround the SE tip: a 13th magnitude star at its end, and magnitude 12 and 12.5 stars east and south of the galaxy’s center.”
- From Steve Gottlieb’s NGC Notes he shares this fascinating observing report with a 48-inch telescope. “Very bright, very large, very elongated 3:1 NW-SE, 9'x3', large bright core that gradually increases to the center. The core is irregular, mottled and dusty. The inner portion of the disc shows weak spiral structure. At 488x, the outer halo is 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 fades 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 fades 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 a 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. All of the IC numbers were found by Max Wolf on a Heidelberg plate in 1903.”
- NGC 4559 is home to a transient object designated AT2016blu that spatially coincides with IC 3550 (NGC 4559C). This object is a luminous blue variable (LBV). Initially identified as a possible supernova, hence the PSN identifier, it is not a supernova. First discovered in 2012, this is a very massive star that shows recurring outbursts about once per year. The most recent outburst was discovered on January 28, 2020 at magnitude 17.62; prior outbursts have reached magnitude 16.7. Luminous blue variables are extremely rare (there are just a few hundred in the entire Milky Way galaxy). They are among the most massive and brightest stars known. Famous for their unpredictable outbursts, these stars are sometimes mistaken for supernovae. It is possible that some LBV lead to supernova explosions. Eta Carinae is the most well-known example of an LBV.
Now it is your turn. Give it a go and let us know!
1Revised Morphological Galaxy Classification System
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