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Object of the Week January 20, 2019 - ARP 217 The Bow and Arrow Galaxy
Object of the Week January 20, 2019 - ARP 217 The Bow and Arrow Galaxy
ARP 217, NGC 3310, UGC 5786, PGC 31650, VV 356, VV 406, MCG+09-18-008
Constellation: Ursa Major
Type: SAB(r)bc pec
Orientation: face-on
RA: 0h 39m 56.5s
Dec: +53° 24’ 03”
Magnitude: 11.2
Size: 2.2’ x 2.1’
NGC 3310 was discovered by William Herschel on April 12, 1789 during sweep #919. Cataloged as H IV-60 and h731, William Herschel recorded his observation as: “vB, R, planetary, but very ill defined. About 1’ of its diameter is equally bright, and 1/4 of a minute hazy or ill-defined round the margin.” John Herschel recorded his observation as “B; R; vsmbM, so as to for almost a disc 15” diameter. Surrounded by a very feeble atmosphere.”
On March 5, 1848, Lord Rosse and William Rambaut observed NGC 3310 (the earliest observation of Lord Rosse’s 1861 monograph) and reported: “See minute points in it at intervals, also spiral arrangement.” A week later on March 11 they noted: “Nebula well resolved into little stellar points. Saw a broad band across the bottom distinctly and two at the top.”
When compiling his 1966 Atlas of Peculiar Galaxies, Halton Arp identified NGC 3310 as a galactic merger candidate and described it briefly like this: “Much Ha emission including Half arc outside galaxy.” The galaxy was catalogued as Arp 217 and placed it in the Adjacent Loops category. Examples of other galaxies in this class are NGC 2782 (Arp 215), NGC 7679 and NGC 7682 (Apr 216), and IC 4553 (Arp 220).
Arp 217 lies 55 million light years away and is a starburst galaxy, similar to M82. It is commonly called the Bow and Arrow galaxy because of the odd stream of young blue stars piercing a diffuse arc of stars that possibly traces the path of the merging galaxy. Another name associated with this galaxy but less frequently used is the Bowstring Galaxy.
Arp 217 is located in Ursa Major, SW of the southwest corner of the Big Dipper and 10’ SSW of a beautiful reddish-orange magnitude 5.5 star. The galaxy is fairly bright, slightly elongated, and uniformly illuminated. In small to medium aperture scopes the core of the galaxy appears broadly concentrated but the surrounding halo is marginally visible.
Christian Luginbuhl and Brian Skiff in the Observing Handbook and Catalogue of Deep-Sky Objects share their observations of Arp 217 with a wide range of apertures. “Lying 10’ SSW of a reddish mag 5.5 star, 6 cm will show this galaxy easily. At 50x it is a small, evenly bright spot about 1’ diameter that looks much like a planetary nebula. A faint star is visible 3’ N. In 25cm it grows to about 2’ diameter and occasionally seems a bit elongated E-W. The core is a fairly large and broadly concentrated region, but no nucleus stands out. With 30 cm the 1’.5 core forms most of the object; the halo is only a very faint irregular extension to the ESE and WNW sides to an overall length of about 2’. Within the core is a somewhat brighter region about 40” across that has an uneven texture but no distinct central concentration.”
Though Arp 217 is readily visible in smaller apertures, it will benefit immensely from larger apertures and higher powers. Your challenge areas are the knots N of the nucleus, arcs NW and SW, and a jet piercing the NW arc. So…
Give it a go and let us know!
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