Object of the Week, February 2nd 2025 - Haro 3-75

[obrazell]

Haro 3-75

PN G193.6-09.5

Orion

R.A.: 05h40m45.0s

Dec.: +12°21'23" (2000)

Magnitude: 13.90

Size: 24"

There are many objects of interest in Orion and the main focus for observers is naturally
the star forming regions around M42 and M78. Orion does however contain a number
objects at the other end of the stellar evolutionary scale with a number of challenging
planetary nebulae. The well-known ones include the popular ones such as NGC 2022
and J320 and there are a number of the more challenging Abell planetary nebulae in
Orion as well such as Abell 10 and Abell 12. There is however a slightly brighter target
than the Abell nebulae in the overlooked planetary nebula Haro 3-75 at the top of Orion.

h375pan.jpg

PanStarss image

First discovered on plates aimed at discovering H-Alpha emission line objects in the star
forming regions of Orion and Taurus by Guillermo Haro in 1953 it was not initially recognised
as a planetary nebula and it took until 1964 before Mayall identified it as such. Interestingly
despite the survey being setup to discover H-Alpha strong YSO’s, undertaken using an
objective prism on the Schmidt telescope at the Tonantzintla observatory in Mexico. The
spectra of H 3-75 is very weak at H-Alpha and much stronger in the OIII lines.
Haro 3-75 lies in the outer regions of our galaxy opposite to the galactic centre at a
distance of perhaps 3700 kpc from us, although there seems to be quite a large range in
distances quoted from 4.3 kpc down to perhaps 2.8 kpc. The central star is also of
interest as it is probably a binary system. The spectral type of the central star is also
odd in that it is very cool for a planetary nebula with a spectral type given as G-K
and there are suggestions that this maybe a born again red giant nucleus
similar to Sakurai’s Object (V4334 Sgr). H 3-75 is classified as a compact high excitation
nebula with a ring structure according to HASH

H3-75.jpg

- Image courtesy of Ian Smith

Lying at the top of Orion near the Taurus border Haro 3-75 sports a 25” disc and although
it is faint it has been reported in telescopes as small as 8” (20cm) from high altitude sites.
There are UK observations with a 16” telescope and it may well be visible in smaller
telescopes on a very clear night. Reports suggest that it responds well to both UHC and OIII
filters. Due to its small size I would suggest using a medium to high power eyepiece when
trying to find this object. It is not clear if the central star is visible or if the apparent spot is
just the brighter core of the nebula. My own observations with a 22” from a low lying site in
the UK say that it was not that difficult and showed a small disk when using an OIII filter.
There is an interesting amateur image at https://www.imagingdeepspace.com/h-3-75.html
showing a lot of structure in the disk and an extended non symmetrical outer halo

[Clear Skies]

First of all, a thank you to Owen for this object that has been in my guides + observing log for years under the incorrect designation of Henize 3-75, where it is in fact Haro 3-75..!

I have a single observation for this planetary, under not-too-dark skies in the northern part of the French Ardennes, but in a night when the transparency was truly good. This is what I observed in my 14" @ 168x / 29' & 259x / 19':

17mm Nagler T4: Brighter than Kohoutek 1-7 (PK 197-14.1) that I observed earlier, a round glow, gradually brighter in the middle. Using AV the central star is visible.

17mm Nagler T4, Lumicon OIII: Using this filter the nebula is even in brightness, both with and without AV and the central star is not visible.

17mm Nagler T4, Lumicon UHC: Using this filter with AV the nebula is a large as it appears unfiltered and is even in brightness. Using AV the nebula is gradually brighter in the middle. The central star is not visible when using this filter.

11mm Nagler T6: Using this magnification the nebula is a small, round glow, even in brightness. Using AV the central star is visible.

DSF OotW 2025-5 - Haro 3-75 Ori_1.jpeg DSF OotW 2025-5 - Haro 3-75 Ori_2.jpeg

Here's the guide.

[Raul Leon]

Hi, here's my observation from 7/26/2011: Haro 3-75 is a planetary nebula in Orion ; magnitude:13.8 ; size: 24" ; small but fairly bright, there is a brightening towards the central area, but not sure this is the central star. I used a 6mm Ethos at 304x with my 14.5 StarStructure f/4.3
haro 3-75.jpg

[Steve Gottlieb]

I observed this planetary back in 1985 with my 17.5-inch and for a long time assumed it was perhaps the first visual observation, but not quite...

17.5" (9/14/85: Slightly non-stellar unfiltered at 105x. Using an OIII filter, H 3-75 appeared as a moderately bright, small disk. At 220x (again unfiltered), a small halo surrounds the 14th mag central star. The planetary was prominently seen using a Daystar 300 filter [similar to a UHC], fairly small, and probably slightly elongated. A string of stars begins about 4' E and extends to the NE. These include the 9th mag stars SAO 94762 10' NE, SAO 94766 14' NE and SAO 94775 18' NE.

I took another look 19 years later (this time with tracking) ...

18" (3/19/04): easily picked up unfiltered at 160x as a small disc with a faint, but obvious central star. Good contrast gain with a UHC filter; it appeared fairly bright with a sharp halo. Beautiful view unfiltered at 323x with a 20"-25" disc surrounding a mag 14 central star which shines steadily The surface brightness is high enough to easily take 435x which also provided a nice view.

More recently, I was researching the observations of Stephane Javelle, who was the main visual contributor to the IC I and II catalogues (1469 objects, nearly all galaxies). These were all discovered between 1891 and 1907 with the 30-inch f/23 refractor of the Nice Observatory in southern France.

In addition, Javelle continued observing visually with this large refractor and discovered another 400 objects that were never published. When I analyzed his unpublished list, I was surprised to find that Javelle's 1,525th discovery, which was found on Feb 16, 1909, is a perfect match in position (and description) with Haro 3-75! So, as it turns out, I missed out on the first observation by over 75 years

Steve

[Uwe Glahn]

Funny thing one - I made the same fault as Victor, funny thing two - I tried the halo independently of the current OOTW last new moon period. The halo was visible at the limit of perception. What made the observation positive for me was, that the brightest visible part congruent with the brightest [OIII] part at the image.

sketch: 27", 586x, no filter, Seeing III, NELM 7m0+ (north down)
H3-75.jpg

--------

sketch: 27", 234x, UHC/[OIII], Seeing IV, NELM 7m0+
H3-75_27.jpg

[timokarhula]

Hallo. I could not remember that I had seen Haro 3-75, but in fact I had! On February 14, 2017, I observed it with my 12-inch Dob and 188x magnification (unfiltered). Haro 3-75 was quite bright and considerably large, I guesstimated the diameter as 0.5'. A faint central star was seen. I suspected some internal structure so it is little bit strange that the nebula was not included in the NGC. The seeing was very good but an 84% illuminated gibbous moon had risen.

/Timo Karhula