Object of the Week March 24, 2013 – Leo I Dwarf

Leo I Dwarf Galaxy (Regulus Dwarf) UGC 5470, CGCG 64-73, MCG+2-26-27, DDO74, PGC 29488

Leo

RA: 10 08 28

Dec: +12 18 27

Size: 9.8 x 7.4’

Mag: 11.2b

SB: 15.2

Class: E3

Urano: 93L

Leo I is a local group dwarf spheroidal galaxy located about 900k light-years distant. It is thought to be one of the most distant satellites of the Milky Way galaxy. 1950 by Albert George Wilson discovered Leo I in 1950, by peeling through the POSS-I plates taken with the 48-inch Schmidt camera at Palomar Observatory. Leo I was one of the four local group dwarf galaxies that he discovered by looking over the POSS-I plates.

To date, no globular clusters have been found to be associated to Leo I.

Leo I is located 20’ north of Regulus, thus sometimes called the Regulus Dwarf.
This object was detected visually with telescopes as small as 4”. From Cloudy Nights, Bill Ferris seen it twice with his 6” reflector. Noted that the key is not higher magnification and Regulus need to be off the field. Dan from CN saw it in a 132mm William Optics refractor. Don Pensack saw it in a 6” f/5 telescope. Sue French observed it ay 87x with her 4” refractor.

Personally, I have not looked for it in anything smaller than my old 6” f/6.5 achromat. With that telescope at 76x using the 13mm Ethos, it was a 3:2 elongated large very low surface brightness glow with very ill-defined edges. I’ve seen it many times with my 22” reflector at 96x with a 24mm Panoptic, but with no detail, just a large low SB glow with ill-defined edges. Nothing else. Once Regulus pops in the field, Leo I is not visible.

I think I would like to give this galaxy a shot with my 4” f/11 refractor.

On a side note, I've uploaded a major updated Local Group Observer's guide available for free download on my website. Leo I is on Page 55

DSS image showing its proximity to Regulus
Attachment 527

Sloan Digital Sky Survey image
Attachment 528

So…
“GIVE IT A GO AND LET US KNOW”
GOOD LUCK AND GREAT VIEWING!

Ah... Leo I...

Actually observed this through Ursa during the 2012 Texas Star Party.

This will make an excellent target for the April window just to test the improved contrast after the refigure. Should be an interesting exercise. But will be needing some dark skies to pull it off.

Thanks for the reminder...

Lou,
You are correct about needing truly dark skies. Reviewing my notes, an attempt from the Poconos at Walters Dam (Blakeslee, PA) back in 2002 indicated the center was an averted vision object with a 20" f5. Getting away from the East coast is a must for a better view.

Al

Yeah...

Am hoping to be doing another 3-day Pettigrew run sometime during April.

So the test will be twofold. Mirror and dark site performance.

Alvin,

cool object near the lighthouse Regulus.

I tried the object several times with my small 4" f/4 Newton. With 18x (AP 6mm) under good sky conditions (NELM 6m5) I noticed:
"very tough object with 4", the halo around Regulus is clearly larger and better defined to the N - seems like a big knot in the halo, no elongation or clear separation out the halo"

With my old 16" the galaxy was always an easy target when the sky was transparent enough. My best AP was always around 5mm AP, perhaps because of the near Regulus. With 16" and 75x I wrote:
"easy to detect, can hold galaxy steadily also when Regulus is in the field, elongated 2:1 E-W, structureless, at the E and W end faint 14,5mag stars, no stars within the dwarf"

16", 75x, NELM 6m5+ (S up)
Attachment 535
inverted (Java on)

Regulus is a key issue with this one for sure. To see it in a 4" seems extremely difficult to me but I have not tried so that was interesting.

Sue French (also here from time to time on DSF, 'Hi Sue!') has reported use of a trick, I think for Abell 12, where an eyepiece if fitted at it's focal point with a mask that may be as simple as black tape or cut-out black thin construction paper or foil. This trick allows you to get the star you want to blank out out of the way while still having the object you want to see fairly close to center. This trick may be a good one for Leo I which I have seen a few times in the 18" by placing Regulus off field but sure would be nice to try other contrast improvement techniques like this. This mask is placed at the point that reticles are often used so the plane of the mask is at a focus point for your eye. I have in the past inserted my own custom grids at that point and my experience is that for several eyepieces that point is where the plastic may meet the metal internally. (Some experimentation required) It is also at the point of the field stop I should think.

I saw Leo I with my 14" at low magnifications in April 2011 in Val Visdende.
It was a very humid night sky with a 21.7 sqm, it appeared as a "puff of light ", quite large, it seems a ghost vision and nearby I saw more clearly the IC-591 (mag 14,3) which appeared as a speck of light.