Steve Gottlieb
March 22nd, 2018, 01:23 AM
I reobserved this unusual galaxy last month (8 Feb 2018) with my 24-inch and thought I'd post this observation. I'm not sure whether its been on OOTW (it should be!) or discussed here in the past. I'm curious if others have observed this starburst before?
2944
He 2-10 = ESO 495-021 = AM 0834-261 = MCG -04-21-005 = PK 248+8.1 = PGC 24171 = PGC 24175
08 36 15.2 -26 24 35
V = 11.6; Size 1.7'x1.3'; Surf Br = 12.4
He 2-10 is a dwarf starburst galaxy in Pyxis. Wikipedia (https://en.wikipedia.org/wiki/Hen_2-10) covers some of information on the galaxy, but its black hole weighs in at a couple of million solar masses. That’s only half the Milky Way’s, but the dwarf itself weighs only a few percent of the mass of the Milky Way. A 2015 study by Cresci et al (https://arxiv.org/pdf/1704.08367.pdf), titled "The MUSE view of He 2-10: No AGN ionization but a sparkling starburst" studied "the physical and dynamical properties of the ionized gas in the prototypical HII galaxy Henize 2-10 using MUSE integral field spectroscopy. The large-scale dynamics are dominated by extended outflowing bubbles that are probably the result of massive gas ejection from the central star forming regions."
This galaxy is listed in several galaxy catalogues including ESO and the Arp-Madore catalogue of Southern Peculiar Galaxies, but it was misclassified as a planetary nebula by Karl Henize in 1967 (http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1967ApJS...14..125H&data_type=PDF_H IGH&whole_paper=YES&type=PRINTER&filetype=.pdf) and was included in the Perek-Kohoutek planetary catalogue as PK 248+8.1. Looking at Henize's table, I notice that Rudolph Minkowski apparently reported it earlier as a planetary (unpublished), due to emission lines.
Interestingly, this object was discovered visually 78 years earlier by E.E. Barnard on 4 Feb 1889 using a 12-inch refractor at Lick Observatory. He recorded in his logbook "Sweeping [for comets] east of Sirius, I find a very small, bright round nebula not in NGC. It is preceding a 7th mag star, which I will use to compare it with." The comparison star he used was mag 6.8 HD 73335 and his notebook sketch at 150x matches the sky. The sketch shows shows a bright star at the east edge of his field, a star close west of He 2-10, a very faint star at its east edge, and two star close northwest and northeast. For whatever reason, Barnard never published the discovery or passed along the discovery to Dreyer, otherwise it would have an IC designation!
24" @200x and 375x; fairly bright, fairly small, slightly elongated NW-SE. Contains an unusually bright core for a small galaxy, perhaps 20" diameter, surrounded by a moderate-sized halo, ~35"-40" diameter. A mag 14.5 star is at the east edge of the halo and a mag 11.5 star is 1.5' W. He 2-10 is located 11' W of mag 6.8 HD 73335 and 24' SW of mag 5.25 Eta Pyxis.
2944
He 2-10 = ESO 495-021 = AM 0834-261 = MCG -04-21-005 = PK 248+8.1 = PGC 24171 = PGC 24175
08 36 15.2 -26 24 35
V = 11.6; Size 1.7'x1.3'; Surf Br = 12.4
He 2-10 is a dwarf starburst galaxy in Pyxis. Wikipedia (https://en.wikipedia.org/wiki/Hen_2-10) covers some of information on the galaxy, but its black hole weighs in at a couple of million solar masses. That’s only half the Milky Way’s, but the dwarf itself weighs only a few percent of the mass of the Milky Way. A 2015 study by Cresci et al (https://arxiv.org/pdf/1704.08367.pdf), titled "The MUSE view of He 2-10: No AGN ionization but a sparkling starburst" studied "the physical and dynamical properties of the ionized gas in the prototypical HII galaxy Henize 2-10 using MUSE integral field spectroscopy. The large-scale dynamics are dominated by extended outflowing bubbles that are probably the result of massive gas ejection from the central star forming regions."
This galaxy is listed in several galaxy catalogues including ESO and the Arp-Madore catalogue of Southern Peculiar Galaxies, but it was misclassified as a planetary nebula by Karl Henize in 1967 (http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1967ApJS...14..125H&data_type=PDF_H IGH&whole_paper=YES&type=PRINTER&filetype=.pdf) and was included in the Perek-Kohoutek planetary catalogue as PK 248+8.1. Looking at Henize's table, I notice that Rudolph Minkowski apparently reported it earlier as a planetary (unpublished), due to emission lines.
Interestingly, this object was discovered visually 78 years earlier by E.E. Barnard on 4 Feb 1889 using a 12-inch refractor at Lick Observatory. He recorded in his logbook "Sweeping [for comets] east of Sirius, I find a very small, bright round nebula not in NGC. It is preceding a 7th mag star, which I will use to compare it with." The comparison star he used was mag 6.8 HD 73335 and his notebook sketch at 150x matches the sky. The sketch shows shows a bright star at the east edge of his field, a star close west of He 2-10, a very faint star at its east edge, and two star close northwest and northeast. For whatever reason, Barnard never published the discovery or passed along the discovery to Dreyer, otherwise it would have an IC designation!
24" @200x and 375x; fairly bright, fairly small, slightly elongated NW-SE. Contains an unusually bright core for a small galaxy, perhaps 20" diameter, surrounded by a moderate-sized halo, ~35"-40" diameter. A mag 14.5 star is at the east edge of the halo and a mag 11.5 star is 1.5' W. He 2-10 is located 11' W of mag 6.8 HD 73335 and 24' SW of mag 5.25 Eta Pyxis.