What filter works best on Herbig-Haro objects?

Hello

I'm interested in trying to observe some of the brighter Herbig-Haro objects. It seems to me that HH 1 and 2 are tangible targets for an 18", as are possibly HH7, HH11 and HH12. Various sources report that HH32 is the brightest, but it seems to be a bit off-season.

From the looks of it, these are hydrogen emissions. Do they also have a good amount of OIII? What filter should I tend to prefer? Of course, I will try both, so maybe this question is moot, but it would still be interesting to know the physics of good filtration.

Clear Skies

Regards
Akarsh

The nebulae NGC 1333 and NGC 1999 contain several HH objects that are visible in my 20". I used UHC and OIII to observe them all.

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Originally Posted by wvreeven

The nebulae NGC 1333 and NGC 1999 contain several HH objects that are visible in my 20". I used UHC and OIII to observe them all.

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Here is a page with a reasonable labeled photo of the NGC 1999 area... http://www.astroava.org/foro3/viewtopic.php?f=1&t=2594

Here is a great labeled photo for those NGC 1333 objects... http://www2.astro.psu.edu/users/gkos...ptical_big.jpg

Best of luck, ya just never know what you might see!

Quote:

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Originally Posted by wvreeven

The nebulae NGC 1333 and NGC 1999 contain several HH objects that are visible in my 20". I used UHC and OIII to observe them all.

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Wouter, are you able to identify which HH objects you saw in/around NGC 1333?

I've only noted the relatively bright knot on the southwest side of NGC 1333 (midway between HH 12 and BD+30 549), though this object doesn't have an HH designation. SIMBAD calls it LZK 12 (Young Stellar Object).

Steve, my notes only say "the areas around HH 12, 6 and 7-11 are visible." I do seem to remember seeing condensations in those areas but I am afraid my notes don't clarify if I really saw them or not. I am afraid I didn't take very detailed notes back then so I'll have to revisit this nebula to verify.

Dear DSF

I report successful observation of HH1 and HH2 near NGC 1999 unfiltered on 18" at 205x.

Unfortunately, I couldn't accurately check response to filter owing to high humidity and frost formation on the filters. I didn't bother to heat them and put them in. The sky was clear, but the other conditions were difficult with frost forming very easily on everything including (metaphorically) my toes.

My notes read as follows:

Once it was determined exactly where to look and what the field looked like in the eyepiece, it was [sic] distinct but still very faint. Neither HH could be held 100% of time and popped in and out averted.

HH1: diffuse irregular and brighter.
HH2: more stellar and more faint.

HH2 had about 10% holding.
HH1 had about 50% holding, appeared much bigger, and felt irregular and somewhat elongated in shape, axis of elongation roughly E-W.

I did not get the opportunity to try for HH7-12

BTW, Reiner Vogel has an atlas on Young Stellar Objects where he reports observation of HH 7, 11 and 12. It's on his "Observing Guide" pages.

Clear Skies
Regards
Akarsh

Hi all,

@Akrash
I had very similar observation experience with HH1 and HH2 nearby NGC 1999, except the brightness and estimated difficulty of HH 1 and HH 2. The sketch was made with 16-inch, with 257x and UHC filter, which for me gave the best view.
I noted: HH 1: fainter that HH 2, stellar, steadily holding with averted vision; HH 2: brighter, nonstellar, 3:2 N-S elongated, direct vision"
Attachment 1960
A labeled sketch you can find here

@Steve
I observed NGC 1333 + surrounding HH objects several years ago with the 16-inch under very transparent mag 7+ skies. I noted "HH 7-11 easiest HH object but still very tough, could hold it steadily with averted vision with difficulties, 3:1 NW-SE elongated, started from 15mag star GSC 2342122; HH 12 much more difficult, nonstellar, pops in and out of view, could not hold it"

Akarsh, my notes are quite similar to yours with my 17.5" and 18" scope (3 observations) except each time I recorded HH 2 as easier than HH 1 (HH 1 seemed smaller to me and was only intermittently glimpsed).

I've also viewed HH 1/2 from the Mauna Kea visitor center, along with Howard, and through Jimi's scope and logged HH 2 as brighter.

My notes on HH1 and HH2 with my 20" also are not very detailed, except that with my 7 mm William Optics UWAN eye piece (366x) HH1 and HH2 both were visible about 50% of the time in between a few faint stars.

This is odd and interesting, and indicates that I should repeat observation.

The POSS image certainly indicates that HH2 is brighter than HH1, but for some reason I had trouble viewing HH2 (maybe because of its stellar nature?). Also, Steve and Uwe, is HH2 brighter than HH1 with filtration, or also without filtration? Also, Uwe indicates N-S elongation of HH1, whereas I felt it was E-W elongated. Is this a filter effect, or just poor observation on my part?

I will try and repeat the observations the next time I get a chance (Looking at a showpiece like NGC 1999 is good motivation to go to that field!) with and without filters, hopefully on a less frosty night.

Thanks for your inputs.

Clear Skies

Regards
Akarsh

I viewed HH 1/2 unfiltered. I don't recall if I tried filters, but these are primary reflection nebula, so I'd be surprised if there was a good OIII response.

Steve, this is intriguing, because I thought HH objects were essentially excited interstellar medium emitting light... what exactly are "primary reflection nebulae" and does it emit H-beta/H-alpha but not emit OIII? What mechanisms lead to an object emitting Hydrogen lines but not OIII? Any links to an explanation would be helpful.

Regards
Akarsh

As H-H objects are coalescing proto-stars, I assume they are not hot enough to produce OIII ionization, but perhaps this varies from object to object.

This paper on Herbig-Haro flows characterizes H-H objects as having emission-line spectra of Hydrogen, [OI], [NII] and [SII], with at most a very weak continuum spectra. Besides the very dusty environment, that explains why they're such tough visual objects!

Dear Steve

Thank you for the explanation and for the paper. The paper's introductory section on emissions was quite informative. It says that HH1 is a "high-ionization" object with (relatively) significant OIII, whereas HH7 is a "low-ionization" object with no detection of OIII at all. Even in HH1, OIII is claimed to be only 60% the intensity of H-Beta. This looks like a good case for using UHC or H-Beta.

Why do all the low-ionization-state lines have to be in red!? (well, I guess the answer is because red photons have lower energy, after all).

Clear Skies

Regards
Akarsh

The relatively "high-ionization" ratio of OIII/H-Beta = 0.6 for a HH 1 would be considered low-ionization for a planetary. So, a UHC or H-beta definitely looks like the way to go. For HH objects with a much lower ratio, either a H-Beta or no filter makes sense.

NGC 40 has an OIII/H-beta ratio of just 0.4 and it appears to dim with an OIII filter but responds (weakly) to a UHC or H-beta. An extreme case is Campbell's Hydrogen Star. The OIII/H-beta ratio is less than 0.1! It's one of the few planetaries that has a good response to an H-beta filter (aperture helps in this case).

On the other hand, the OIII/H-beta ratio for M57 is 10:1, NGC 1514 is 12:1 and Jones-Emberson 1 is 22:1 (that's 55x higher than HH 1!). The M57 ratio is pretty typical for planetaries, though obviously there's a wide range.

The emission-line intensities for planetaries are available in the Strausberg-ESO Catalogue of Galactic Planetary Nebula. I have the book but the electronic version is available through Vizier. The relevant page is V/84/intens. The line intensities are given with respect to H-beta = 100.

Thank you Steve. This has been a very interesting discussion. Thanks for the VizieR reference in particular. (It seems like some intensities are given with respect to H-alpha = 100, but those are the exception.)

Unfortunately, I haven't studied enough atomic optics to know, but what controls the ratios of these lines? It seems to me that H-beta vs. H-alpha would be entirely controlled by temperature (which determines the population of the levels) and the ratio of transition probabilities (which is some fixed number calculated from quantum mechanics). So variations in H-beta : H-alpha would entirely be based on temperature? What about OIII : H-Beta?

Regards
Akarsh

The explanation on this NED page is beyond my understanding, but the conclusion is the [OIII] λ5007 / H-beta ratio is proportional to T* (effective temperature of the ionizing star). Other physical/chemical processes that may also be factors are not discussed.

As OIII emission is primarily from collisionally excited material the density of the material will also have an impact as if it is too high then the emission will be quenched by the atoms getting hit before they have time to emit. So unfortunately the strength of the OIII emission is not just down to the temperature of the exciting star but also the density of the nebula. Nothing is ever simple :-)

Owen

Steve, yes, that thing is over my head too; it looks like it might be a good idea to look at Lyman Spitzer's book on the Physical processes in the insterstellar medium (which is what the article references as a good introduction) if one wishes to understand the details.

I wish there were a basic introduction of these topics (a process-oriented one rather than a formulaic development oriented one) for amateur astronomers.

Owen, is it simple to understand why OIII is mostly collisionally excited as opposed to optically excited? Is it because it's a forbidden transition? (This graph from Wikipedia seems to suggest so: https://en.wikipedia.org/wiki/Doubly...iii-linesp.svg)

Regards
Akarsh

Thanks, Owen, I thought the density or chemical mixing was also a factor.

Yes pretty much. It is difficult to get to those levels from a recombination cascade which is the other way it could happen. None of this is easy as that si why it took until 1927 to understand the physics of metastable states in atoms. I think when it comes to Quantum mechanics you just have to except that some things are not easy to understand.

Owen