Catalogue of Molecular Hydrogen Emission-Line Objects (MHOs) in Outflows from Young Stars

Go straight to Tables of MHOs

NEWS: New MHOs have recently been added to Aur and Cas (Froebrich & Makin 2016); Aur, Cas, Cep, Cyg, Gem, Mon, Tau and Vul (Wolf-Chase et al. 2017) New objects have also been pencilled in for Gemini (Lehtinen et al.), Cyg (Makin & Froebrich 2017).


For a number of years, astronomers have been imaging Herbig-Haro (HH) objects, jets and outflows in star forming regions in the near-infrared. The molecular hydrogen v=1-0S(1) line at 2.122 micron is a particularly powerful tracer of shock-excited features in molecular outflows. Although excited in a similar way to HH objects, these molecular hydrogen emission-line features are often too deeply embedded to be seen at optical wavelengths. They are thus not classified as HH objects, and are instead labeled in a rather hap-hazard way, often with the authors' initials. In large databases like Simbad this can lead to some ambiguity.

Our goal with this catalogue is therefore to develop a self-consistent list of Molecular Hydrogen emission-line Objects (MHOs). With guidance from the IAU Working Group on Designations we have adopted a scheme that simply lists objects sequentially, although objects are grouped by region (see below). The acronym "MHO" has been approved by the IAU registry, and has been entered into the on-line Reference Dictionary of Nomenclature of Celestial Objects. We use this acronym for all objects in the catalogue (and please note the space between the acronym and the number, e.g. MHO 1, MHO 99, etc.).

What Constitutes an MHO?

Only objects associated with outflows from young stars (Young Stellar Objects and protostars) are included in this catalogue. We do not list outflows from evolved stars (AGB stars or Proto-Planetary Nebulae) or extra-galactic sources. Also, objects should be spatially resolved; unresolved emission-line regions associated with an accretion disk or the base of an outflow (that were observed spectroscopically) are not listed. ... more.

Newly-discovered MHOs

So how do I add new molecular hydrogen emission-line objects to the catalogue? Our aim is to keep the catalogue of MHOs as up-to-date as possible. Also, obviously we want to avoid duplication of catalogue numbers (people using the same numbers for different objects). Therefore, we ask that those with new discoveries please contact Dirk Froebrich ( ) before papers are written, and certainly before figures and tables of MHOs are finalized, so that new numbers can be assigned.

Tables of MHOs

Click on the links below to access tables of MHOs, grouped by region. Coordinates and images of individual objects are presented, together with references to discovery and other imaging papers, designations or names used in the literature, and the numbers of associated HH objects. Please note that the tables do not contain a complete list of all papers written on a given object; only near-IR imaging papers are included. However, amendments and additions are certainly welcome; please contact Dirk Froebrich at .

Region Map Approx. RA Range Approx. Dec Range MHO # .txt
Perseus M2 03h 00m → 04h 00m +25o → +35o 500-699 Per.txt
Auriga (excl. Per/Gem) M2 03h 30m → 06h 30m +30o → +56o 1000-1099,
Taurus (excl. Ori/Per) M2 03h 00m → 05h 50m +10o → +30o 700-799 Tau.txt
Camelopardalis M1 04h 00m → 08h 00m +56o → +90o 1100-1199 Cam.txt
Orion A M3 04h 45m → 06h 00m -15o → -04o 1-299 OriA.txt
Orion B (excl. Tau) M3 04h 45m → 06h 00m -04o → +16o 300-499 OriB.txt
Gemini M3 05h 50m → 08h 00m +14o → + 34o 1200-1299 Gem.txt
Monoceros M3 06h 00m → 08h 30m -13o → +14o 1300-1399,
Puppis (excl. Vela) M4 06h 30m → 09h 00m -52o → -13o 1400-1499 Pup.txt
Vela M4 07h 30m → 11h 00m -55o → -38o 1500-1599 Vel.txt
Carina M5 08h 00m → 12h 00m -75o → -55o 1600-1699 Car.txt
Chameleon (excl. Car) M5 08h 00m → 14h 00m -85o → -70o 3000-3099 Cha.txt
Centaurus M5 12h 00m → 15h 00m -70o → -30o 1700-1799 Cen.txt
Circinus/Lupus M6 15h 00m → 16h 00m -70o → -30o 1800-1899 CirLup.txt
Scorpius M6 16h 00m → 18h 00m -60o → -30o 1900-1999 Sco.txt
Corona Australis M6 18h 00m → 19h 30m -45o → -35o 2000-2099 CrA.txt
Ophiuchus (excl. Ser) M6 16h 00m → 18h 00m -30o → +05o 2100-2199 Oph.txt
Serpens M7 17h 30m → 18h 40m -15o → +05o 2200-2299,
Sagittarius (excl. Ser) M7 18h 00m → 20h 30m -35o → -12o 2300-2399 Sgr.txt
Aquila (excl. Lyr) M7 18h 40m → 20h 30m -12o → +15o 2400-2499 Aqu.txt
Lyra M8 18h 20m → 19h 00m +5o → +45o 2500-2599 Lyr.txt
Vulpecula M8 19h 00m → 21h 30m +15o → +30o 2600-2699 Vul.txt
Cygnus M9 19h 00m → 22h 00m +30o → +55o 800-999,
Cepheus (excl. Cas) M9 19h 00m → 23h 30m +55o → +90o 2700-2799 Cep.txt
Andromeda M9 22h 00m → 00h 00m +30o → +55o 2800-2899 And.txt
Cassiopeia (excl. Cep) M1 23h 00m → 04h 00m +50o → +90o 2900-2999,

Currently there are 2077 entries in the MHO catalogue
(Last update: 04 June 2017)

Links in the first column (and on the side-bar) are to html tables; in the final column we present the same tables (abbreviated) in ascii format. Please note - some of the larger html tables (Perseus, Orion A, etc.) may be slow to load; if you are having difficulty, please try one of the smaller tables (Carina or Sagittarius) first.


Since there are no official names for, or boundaries to, the star-forming molecular clouds in our galaxy, the regions listed above are loosely based on the 88 constellations (which have strict boundaries defined by the IAU) and large-scale molecular line surveys. Moreover, in the heavily-populated area of Orion, we have split the region up into two sub-regions, Orion A and Orion B, again using low-resolution maps of the associated molecular clouds as a guide.

The boundaries of each region are marked on low-resolution CO J=1-0 maps, M1-M9, in the second column in the above table (or see this PDF file of all regions); the approximate RA and Dec ranges of the regions are listed in the third and fourth columns. Note that not all constellations are listed above, since some do not contain star forming regions and/or known outflows with MHOs.

The Entire Catalogue

A simple ascii text table listing MHO#, Right Ascension, Declination, associated HH object, and region, for all MHOs (from all regions) can be found here: masterText.txt

MHO Catalogue Publication

If you wish to acknowledge this web-site, please note that the "MHO catalogue is hosted by the University of Kent". A PAPER describing the catalogue and presenting the first ~1000 objects has also been published in A&A (Davis et al. 2010, A&A, 511, A24). However, note that the tables in the appendix of this paper will become progressively more incomplete as new objects are added to the on-line catalogue.


We thank the "Clearing House" of the Commission 5 Working Group on Designations, particularly the chair, Marion Schmitz, for their guidance, and the star formation community, especially Bo Reipurth, for their valuable input. This project would not have been possible without support from the Joint Astronomy Centre, Liverpool John Moores University (since late 2012), and the University of Kent (since mid 2015).

Website created by Ryan Gell and Chris Davis, maintained by Dirk Froebrich ( )